cosmetic dermatology - prins and pract. 2nd ed - l. baumann, et al., (mcgraw - hill, 2009)

Cosmetic Dermatology PRINCIPLES AND PRACTICE SECOND EDITION LESLIE BAUMANN, MD Author and Editor Director, University of Miami Cosmetic Medicine and Research Institute Professor of Derma

Cosmetic Dermatology

PRINCIPLES AND PRACTICE

SECOND EDITION

Medicine is an ever-changing science As new research and clinical experience broaden our edge, changes in treatment and drug therapy are required The authors and the publisher of thiswork have checked with sources believed to be reliable in their efforts to provide information that

knowl-is complete and generally in accord with the standards accepted at the time of publication.However, in view of the possibility of human error or changes in medical sciences, neither theauthors nor the publisher nor any other party who has been involved in the preparation or publi-cation of this work warrants that the information contained herein is in every respect accurate orcomplete, and they disclaim all responsibility for any errors or omissions or for the resultsobtained from use of the information contained in this work Readers are encouraged to confirmthe information contained herein with other sources For example and in particular, readers areadvised to check the product information sheet included in the package of each drug they plan toadminister to be certain that the information contained in this work is accurate and that changeshave not been made in the recommended dose or in the contraindications for administration Thisrecommendation is of particular importance in connection with new or infrequently used drugs

Cosmetic Dermatology

PRINCIPLES AND PRACTICE

SECOND EDITION

LESLIE BAUMANN, MD Author and Editor Director, University of Miami Cosmetic Medicine and Research Institute

Professor of Dermatology University of Miami Miami Beach, FL SOGOL SAGHARI, MD Associate Editor Department of Dermatology University of Miami Miami, FL Private Practice Los Angeles, CA EDMUND WEISBERG, MS

Managing Editor Center for Clinical Epidemiology and Biostatistics University of Pennsylvania School of Medicine

Philadelphia, PA

New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto

Copyright © 2009 by The McGraw-Hill Companies, Inc All rights reserved Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.

ISBN: 978-0-07-164128-9

MHID: 0-07-164128-9

The material in this eBook also appears in the print version of this title: ISBN: 978-0-07-149062-7, MHID: 0-07-149062-0

All trademarks are trademarks of their respective owners Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark owner, with no intention of infringement of the trademark Where such designations appear in this book, theyhave been printed with initial caps

McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs To contact a representative please e-mail us at bulksales@mcgraw-hill.com

TERMS OF USE

This is a copyrighted work and The McGraw-Hill Companies, Inc (“McGraw-Hill”) and its licensors reserve all rights in and to the work Use of this work is subject tothese terms Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverseengineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part of it without McGraw-Hill’s prior consent You may use the work for your own noncommercial and personal use; any other use of the work is strictly prohibited Your right to use thework may be terminated if you fail to comply with these terms

THE WORK IS PROVIDED “AS IS.” McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BEACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUD-ING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE McGraw-Hill and its licensors

do not warrant or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resultingtherefrom McGraw-Hill has no responsibility for the content of any information accessed through the work Under no circumstances shall McGraw-Hill and/or its licen-sors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of themhas been advised of the possibility of such damages This limitation of liability shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise

Dedication This book is dedicated to the three men in my life:

Roger Alexander Baumann

Thank you for encouraging me and being there to help

me with all the technology and business aspects of my life Your never- ending support has kept me sane over the years Most of all, my thanks for dragging me out of the mud when times were tough like a good cutting horse does! You are an ideal husband, father, and friend.

Here’s to another 20 years together!

Robert Edward Baumann

I am so proud of what a good person you are growing up

to be You are kind, have a great sense of humor, and have a love for others that is truly refreshing You have many talents, one of which is making me feel very special

and proud to have you as a son.

Keep up the good work!

Maximilian Carl Baumann

When this book comes out, you will be 7 years old It is hard to believe that you are growing up so fast; however, you will always be my baby I am very proud of what a great student and person you are I am so happy to have someone in the family who is so much like me and loves

to read as much as I do.

Never stop snuggling!

Roger, Robert and Max, You all brighten my life, remind me of what is important,

and make it all worthwhile.

Thank you for loving me!

This page intentionally left blank

Section 1 Basic Concepts of Skin Science

1 Basic Science of the Epidermis 3

Leslie Baumann and Sogol Saghari

2 Basic Science of the Dermis 8

Leslie Baumann and Sogol Saghari

3 Fat and the Subcutaneous Layer 14

Voraphol Vejjabhinanta, Leslie Baumann, Suzan

Obagi, and Anita Singh

4 Immunology of the Skin 22

H Ray Jalian and Jenny Kim

5 Hormones and Aging Skin 29

Larissa Zaulyanov-Scanlan

6 Photoaging 34

Leslie Baumann and Sogol Saghari

7 Cigarettes and Aging Skin 42

Leslie Baumann and Sogol Saghari

8 Nutrition and the Skin 45

Leslie Baumann

Section 2 Skin Types

9 The Baumann Skin Typing System 69

Leslie Baumann and Edmund Weisberg

Section 3 Specific Skin Problems

15 Acne (Type 1 Sensitive Skin) 121

Leslie Baumann and Jonette Keri

16 Rosacea (Type 2 Sensitive Skin) 128

Sogol Saghari, Jonette Keri, Stuart Shanler and Leslie Baumann

17 Burning and Stinging Skin (Type 3 Sensitive Skin) 133

Leslie Baumann and Sogol Saghari

21 Prevention and Treatment of Bruising 163

Susan Schaffer, Sogol Saghari and Leslie Baumann

Section 4 Cosmetic Procedures

22 Botulinum Toxin 169

Leslie Baumann, Mohamed L Elsaie and Lisa Grunebaum

23 Dermal Fillers 191

Leslie Baumann, Marianna Blyumin and Sogol Saghari

24 Lasers and Light Devices 212

Joely Kaufman

25 Sclerotherapy 221

Larissa Zaulyanov-Scanlan

26 Facial Scar Revision 227

Suzan Obagi and Angela S Casey

Section 5 Skin Care

27 Starting a Skin Care Product Line 237

Leslie Baumann

28 Cosmetic and Drug Regulation 241

Edmund Weisberg and Leslie Baumann

29 Sunscreens 245

Leslie Baumann, Nidhi Avashia and

Mari Paz Castanedo-Tardan

38 Bioengineering of the Skin 335

Leslie Baumann and Mari Paz Castanedo-Tardan

39 Scales Used to Classify Skin 342

Mari Paz Castanedo-Tardan and Leslie Baumann

40 The Psychosocial Aspects of Cosmetic Dermatology 347

Edmund Weisberg

Index 357

Inja Bogdan Allemann, MD

Cosmetic Dermatology Fellow,

Department of Dermatology and

Cutaneous Surgery, Miller School

of Medicine, University of Miami,

Miami, Florida; Dermatologic

Clinic, University Hospital of

Miller School of Medicine, University

of Miami, Miami, Florida

Chapter 29

Marianna L Blyumin, MD

Dermatology Resident, Department of

Dermatology and Cutaneous

Surgery, Miller School of Medicine,

University of Miami, Miami,

Florida

Chapter 23

Angela S Casey, MD

Assistant Professor, Dermatology and

Mohs Surgery, University of Vermont

College of Medicine, Fletcher Allen

Health Care, Burlington, Vermont

Chapter 26

Maria Paz Castanedo-Tardan, MD

Department of Dermatology and

Cutaneous Surgery, Miller School of

Medicine, University of Miami

Miami, Florida

Chapters 29, 35, 38, and 39

Mohamed L Elsaie, MD, MBA

Cosmetic Dermatology Fellow,Department of Dermatology andCutaneous Surgery, Miller School ofMedicine, University of Miami, Miami,Florida; Department of Dermatologyand Venereology, National ResearchCenter, Cairo, Egypt

Chapters 10 and 22

Lisa Danielle Grunebaum, MD

Assistant Professor, Division of FacialPlastic and Reconstructive Surgery,Department of Otolaryngology andHead and Neck Surgery, University

of Miami, Miami, FloridaChapter 22

Sharon E Jacob, MD

Assistant Professor, Divisions ofMedicine and Pediatrics(Dermatology), University ofCalifornia, San Diego, San Diego,California

Chapter 18

H Ray Jalian, MD

Resident Physician, Department ofMedicine, Division of Dermatology,David Geffen School of Medicine atUCLA, Los Angeles, CaliforniaChapter 4

Joely Kaufman, MD

Assistant Professor, Department ofDermatology and Cutaneous Surgeryand Director of Laser and LightTherapy, University of MiamiaCosmetic Medicine and ResearchInstitute, Miami, Florida

Chapter 24

Jonette Keri, MD, PhD

Assistant Professor, Miller School ofMedicine, University of Miami,Miami, Florida;

Chief, Dermatology Service, Miami VAHospital, Miami, Florida

Chapters 15 and 16

Jenny Kim, MD, PhD

Associate Professor, Department ofMedicine and Division ofDermatology, David Geffen School

of Medicine at UCLA, Los Angeles,California

Chapter 4

Suzan Obagi, MD

Assistant Professor of Dermatology,Director, The Cosmetic Surgery andSkin Health Center, University ofPittsburgh Medical Center,Pittsburgh, PennsylvaniaChapters 3 and 26

Sogol Saghari, MD

Department of Dermatology,University of Miami, Miami, Florida;

Private Practice, Los Angeles,California

Chapters 1, 2, 7, 13, 16, 19, 20, 21, 23,and 30

Susan Schaffer, RN

University of Miami, CosmeticMedicine and Research Institute,Miami Beach, Florida

Chapter 21

Stuart Daniel Shanler, MD, FACMS

Private Practice, New York, New YorkChapter 16

C O N T R I B U T O R S

Anita Singh, MS

Miller School of Medicine, University

of Miami, Miami, Florida

Chapter 3

Kumar Subramanyan, PhD

Senior Manager, Consumer and Clinical

Evaluation, Unilever Global Skin

Research & Development

Shanghai, China

Chapter 31

Voraphol Vejjabhinanta, MD

Postdoctoral Fellow, Mohs, Laser and,

Dermatologic Surgery, Department of

Dermatology and Cutaneous Surgery,

Miller School of Medicine,University

of Miami, Miami, Florida; Clinical

Heather Woolery-Lloyd, MD

Assistant Professor, Department ofDermatology and Cutaneous Surgery,Director of Ethnic Skin Care

University of Miami CosmeticMedicine and Research Institute,Miami, Florida

Chapter 14

Larissa Zaulyanov-Scanlan, MD

Voluntary Faculty, University of MiamiCosmetic Medicine and ResearchInstitute, Miami Beach, Florida;Private Practice, Delray Beach, FloridaChapters 5 and 25

Cosmetic dermatology is a rapidly

grow-ing field that can attribute its popularity

to aging baby boomers Although many

dermatologists perform cosmetic

proce-dures and millions of dollars are spent

each year on cosmetic products, there is a

paucity of published research in this field

I was stimulated to write this text

because I have found it challenging to

conduct thorough research in preparation

for my lectures and articles on cosmetic

science as there exists no undisputed

ref-erence at the moment Of the research

performed by cosmetic scientists, much

of it, unfortunately, is proprietary

infor-mation owned by corporations and is not

published or shared in any way for the

immediate benefit of the medical

com-munity and other cosmetic professionals

This results in each company or cosmetic

scientist having to “reinvent the wheel.”

My goal, with this book, is to create a

link, featuring a better streaming flow of

information, between the fields of

der-matology and cosmetic science This text

is designed to help cosmetic

dermatolo-gists understand the available

informa-tion on various cosmetic products and

procedures It should also help cosmetic

chemists to understand the issues that

cosmetic dermatologists deal with on a

frequent basis In addition, this text

should fill the gap in knowledge among

professionals such as aestheticians who

need to know what to apply to patients’

or clients’ skin and about the products

that people purchase over-the-counter

and apply to their skin This text should

help these professionals answer the

ques-tions that their clients/patients ask about

skin care products and their scientific

validity It is my hope that this text will

encourage cosmetic dermatologists,

cos-metic scientists and aestheticians to insist

upon well researched cosmetic products

and procedures By working together inthis way we can preserve the integrity of

an exciting and rapidly developing field

of study

Research in the field of cosmetic matology should be encouraged formany reasons Obviously, it is vital tomaintain the hard earned integrity of thefield of dermatology In addition, the dis-coveries made though cosmetic derma-tology research will likely benefit otherfields of dermatology For example,research into the anti-aging effects ofantioxidants may lead to enhancedknowledge of chemopreventive tech-niques to be used to prevent skin cancer

der-Advances in acne therapy, vitiligo andother disorders of pigmentation are alsopossible In fact, it is interesting to notethat the development of Vaniqa™, acream designed to slow hair growth inwomen with facial hair, has led to theavailability of an intravenous treatmentfor African Sleeping Sickness, a majorcause of death in Africa Without thefinancial incentive to develop Vaniqa,which is used for purely aesthetic pur-poses, this life-saving drug would not beavailable For many reasons, all pharma-ceutical, medical device, and cosmeticcompanies should be encouraged toresearch their products

Although there is much research formed by cosmetic companies on theeffects of cosmetics on the skin, much ofthis data is proprietary and is not pub-lished nor shared with the rest of the sci-entific community The reasons for thisare numerous, but competition betweencompanies and the desire to be the first

per-to come out with a new “miracle uct” are prominent among them

prod-However, the issue is even more plex The FDA has different definitionsfor drugs and cosmetics Cosmetic prod-

com-ucts do not have to be researched in anystandard way because FDA approval isnot required Instead, cosmetic productsare voluntarily registered by the compa-nies that develop them However, drugsmust undergo years of expensive trialsestablishing both safety and efficacybefore receiving FDA approval (see

Ch 28) This disparity means that a pany is more reluctant to publish datathat could cause their product to belabeled as a drug

com-The dearth of published data on metic products has forced physicians,aestheticians, and lay people to rely onsales people and marketing departments

cos-to obtain information about cosmeticformulations This has led to much mis-information that has diminished thecredibility of cosmetic products and thecosmetic field in general Because anever-increasing number of dermatolo-gists and other physicians are practicing

“cosmetic dermatology,” it is imperativethat the cosmetic dermatologist practiceevidence-based medicine in order to dis-tinguish efficacious treatments frommere marketing hype This text siftsthrough the knowledge of the effectscosmetic products and procedures have

on the skin and its appearance Theamount of research that should still beperformed is daunting; however, thefield is young and the rewards are great

I encourage everyone to join me in theexciting endeavor to find scientificallyproven methods of improving theappearance of the skin

This page intentionally left blank

A C K N O W L E D G M E N T S

The first edition of this book was

printed in 4 languages and was the

best-selling textbook on cosmetic

dermatol-ogy worldwide (or so I have been told)

There are many people to thank for this

and the many wonderful things that

have occurred in the last 6 years First I

would like to thank Dr Stephen Mandy

who took me in as a newly graduated

resident in 1997, and let me and my

hus-band live with him for two weeks while

he taught me about the newly emerging

field of cosmetic dermatology (I learned

to inject collagen on his secretary!) That

was the beginning of what has now

been an 11-year friendship Dr Francisco

Kerdel negotiated my first job and office

space and he and Dr William Eaglstein

mentor me to this day They were

thanked in the first edition but I will

never be able to thank them enough for

what they have done for me

This year, the University of Miami

Miller School of Medicine decided to

create the Cosmetic Medicine and

Research Institute (CMRI), which

con-sists of cosmetic dermatology,

oculo-plastic surgery, facial oculo-plastic surgery and

nutrition The role of this

multi-spe-cialty institute is to provide cutting edge

dermatologic and surgical procedures to

enhance appearance By combining

accomplished physicians from the

vari-ous cosmetic specialties, the Institute

can offer patients the expertise of many

different types of physicians in order to

achieve the best outcome The mission

of the Institute is to perform research in

the area of cosmetic medicine, and many

genetic initiatives to look for the genetic

influences on appearance have begun

In addition, the CMRI will provide

training to physicians on cosmetic

der-matology and cosmetic procedures (See

www.derm.net for more information.)

I am very proud to announce that Ihave been selected to be the Director ofthe University of Miami CosmeticMedicine and Research Institute Forthis honor I would like to thank severalpeople for believing in me and giving methis opportunity:

Pascal Goldschmidt, MD (the Dean ofthe University of Miami MedicalSchool) – Dr Goldschmidt is a truevisionary and a leader in the field ofthe genetic influences in atherosclero-sis He opened the doors to basic sci-ence research for me and shared hisgenetic research team with me until Icould find funding In addition, he didthe great honor of introducing me toBart Chernow, MD and WilliamO’Neil, MD (both of whom are ViceDeans at the University of Miami)

The three of them appointed meDirector of the University of MiamiCosmetic Medicine and ResearchInstitute and gave me one of the mostwonderful opportunities of my life

Dr Chernow is a brilliant man and atrue magician because he can pull allkinds of opportunities and ideas andinnovations “out of his hat.” I con-sider Bart and his wife Peggy goodfriends and I thank them both fortheir support

I would like to thank David Seo, MD,

my partner on the genetic trials, forhis patience in getting me up to speed

on genetic research My fingers arecrossed that we will discover greatthings together in the next 2 years

Thanks to the doctors who are a part

of the CMRI and have chapters in thistext They have all taught me somuch and are great to work with:

Drs Lisa Grunebaum, Joely Kaufman,Wendy Lee, Heather Woolery-Lloyd,

and Larissa Zaulyanov-Scanlan

Thanks to Neal Shapiro for handlingthe financial aspect of the Institute sothat I can concentrate on my trueloves…seeing patients and perform-ing research Huge hugs and thanks toSusan Schaffer-RN who is my greatfriend, confidant, and Head ofNursing for the CMRI She travelsaround the world with me, lecturing

on cosmetic issues and helping tokeep me sane Edmund Weisberg-you are hilarious and fun to workwith I would never have written thefirst edition of this book without you!

Stephanie and Fransheley- you haveworked with me for many years and Ihave loved it and I look forward toMANY more

I would like to thank CatherineDrayton and Richard Pine, my bookagents for my NY Times bestsellingbook called “The Skin Type Solution”

(Bantam 2005) tions.com) They negotiated anunprecedented book deal for me andare the best in the field I first unveiledthe Baumann Skin Typing System inthis book Catherine- Thanks for allthe attention that you give to me inspite of the fact that we live on oppo-site sides of the world (and thanks fortaking me sailing with you in Australiawhen I was there for the book launch-that was SO COOL!) I will never for-get the support that Irwin Applebaumand his amazing team at Bantam Dell(a division of Random House) gaveThe Skin Type Solution when itlaunched Phillip Rappaport is a greateditor and friend

(www.skintypesolu-I would like to thank my family, towhom this book is dedicated Myhusband Roger and my sons Robert

and Max are a constant source of joy

and strength for me I love cooking

with them! I am fortunate to be very

close with both my mother, Lynn

McClendon, and my mother-in-law,

Josie Kenin They are great role

mod-els and friends and I am very lucky to

have them Thanks to my friends Jill

Cooper, Melina Goldstein, Sofie

Matz and Debbie Kramer for listening

to me and keeping me calm

Dr Sogol Saghari, who was my

fel-low for one year and now has a

der-matology practice in Los Angeles,

made huge contributions to this

book She helped on the first draft of

many of the chapters She is a brilliantdermatologist and an incredibly niceperson I was so lucky to have her as afellow Thanks to all the doctors whocontributed to the chapters in thisbook Special thanks to MohammedLotfy, MD, who was available 24hours a day helping me with litera-ture searches and drawing the illustra-tions He is one of the most dedicateddermatologists I have ever met InjaBogdan, MD and Maria PazCastanedo-Tardan, MD were also fel-lows that contributed chapters andhave great careers ahead of them

And last but certainly not

least-I would like to thank Anne Sydor forconvincing me to write the secondedition of this book I never wouldhave been able to get up at 5am andget this done if you had not encour-aged me Thanks for being my cheer-leader and for lighting a fire in me toget this done FINALLY! I am soproud of this book and poured mysoul into it I hope that all of youenjoy reading it as much as I enjoyedwriting it

Affectionately,

Leslie Baumann, MD

xiv

S E C T I O N

Basic Concepts of Skin

Science

This page intentionally left blank

at the base of the epidermis at the mal–epidermal junction (DEJ) They areproduced by stem cells, which are alsocalled basal cells because they reside atthe base, basal layer, of the epidermis.

der-When the stem cells divide, they create

“daughter cells,” which slowly migrate

to the top of the epidermis This process

of daughter cells maturing and moving

to the top is called keratinization

As these cells progress through theepidermis and mature, they develop dif-ferent characteristics The layers of theepidermis are named for these character-istic traits For example, as mentioned,the first layer is the basal layer because it

is located at the base of the epidermis

Basal cells are cuboidal in shape Thenext layer is referred to as the spinouslayer because the cells in this layer haveprominent, spiny attachments calleddesmosomes Desmosomes are complexstructures composed of adhesion mole-cules and other proteins and are integral

in cell adhesion and cell transport Thenext layer is the granular layer, named sobecause these cells contain visible kera-tohyaline granules The last, outermostlayer is the stratum corneum (SC), a con-densed mass of cells that have lost theirnuclei and granules (Figs 1-1 and Fig

1-2) The SC is covered by a proteinmaterial called the cell envelope, whichaids in providing a barrier to water lossand absorption of unwanted materials

As keratinocytes migrate through thelayers of the epidermis, their contentsand functions change according to, ordepending on, the specific epidermallayer in which they are moving Althoughthe functions of the keratinocyte havenot been completely elucidated, many

of them are understood It is known

that keratinocyte activity, such as therelease of cytokines, can be affected bytopical products administered to theskin Keratinocytes and their compo-nents at each level of the epidermisstarting at the basal layer and proceed-ing to the superficial layers of the epi-dermis are described below

Keratinocyte Function

THE BASAL LAYER (STRATUM BASALE)

Basal cells join with other basal and theoverlying spinous cells via desmosomes,thus forming the basement membrane

These basal keratinocytes contain atins 5 and 14, mutations in which result

ker-in an ker-inherited disease called sis bullosa simplex Keratins 5 and 14 arepresumed to establish a cytoskeleton thatpermits flexibility of the cells This flexi-bility allows cells to proceed out of thebasal layer and migrate superficially, thusundergoing the keratinization process

epidermoly-Basal cells are responsible for ing the epidermis by continually renewingthe cell population Of the basal layer,10% of cells are stem cells, 50% areamplifying cells, and 40% are postmitoticcells Normally, stem cells are slowlydividing cells, but under certain conditionssuch as wound healing or exposure togrowth factors, they divide faster Theygive rise to transient amplifying cells

maintain-Transient amplifying cells are responsiblefor most of the cell division in the basallayer and produce postmitotic cells, whichundergo terminal differentiation andmove superficially to become suprabasalcells that continue their upward migration

to become granular cells and ultimatelypart of the SC (Fig 1-3)

THE SPINOUS LAYER (STRATUM SPINOSUM)

Keratins 1 and 10 are first seen in thislayer of suprabasal keratinocytes Thesekeratins form a more rigid cytoskeleton

The skin is composed of three primary

layers: epidermis, dermis, and

subcuta-neous tissue Each layer possesses

specific characteristics and functions

Although research regarding skin layers

continues, much is already known about

the structure of each component New

discoveries about these components

have already led to prenatal diagnoses

of many inherited diseases and to

improved therapies In the future, study

of these components will likely lead to

an enhanced understanding of skin

aging and the effects of topical products

on the biologic function of the skin

The epidermis is the most superficial

layer of the skin It is very important

from a cosmetic standpoint, because it is

this layer that gives the skin its texture

and moisture, and contributes to skin

color If the surface of the epidermis is

dry or rough, the skin appears aged

Knowledge of the basic structure of the

epidermis best enables a practitioner to

improve the appearance of patients’ skin

THE KERATINOCYTE

Keratinocytes, also known as

corneo-cytes, are the cells that comprise the

majority of the epidermis Keratin

fila-ments are major components of the

keratinocytes, and provide structural

support There are two types of keratin

filaments: acidic (type I, K10–20) and

basic (type II, K 1–10) They both must

be expressed for a keratin filament to

쑿 FIGURE 1-1 The layers of the epidermis

쑿 FIGURE 1-2 Histopathology of the epidermis

demonstrating the four layers (Image courtesy of George Ioannides, MD.)

Keratohyaline granules

Desmosomes

Stratum corneum Granular layer Spinous layer

Basal layer Dermis

that confers greater mechanical strength

to the cell It is worth mentioning that

under hyperproliferative conditions such

as actinic keratosis, wound healing, and

psoriasis, keratins 6 and 16 are

upregu-lated in the suprabasal keratinocytes

Lamellar granules, which are

consid-ered the first sign of keratinization, first

appear in this layer They contain lipids

such as ceramides, cholesterol, and fatty

acids as well as enzymes such as

pro-teases, acid phosphatase, lipases, and

glycosidases It has been recently shown

that cathelicidin, an antimicrobial

peptide, is also stored in the lamellar

granules.2These granules migrate to the

surface and expel their contents by

exo-cytosis The released lipids coat the

sur-face, imparting barrier-like properties

Desmosomes are very prominent in this

layer, thus accounting for the name

“spinous layer.”

The advanced stage of differentiation

of suprabasal keratinocytes is conducive

to staining for products not found on

basal cells (i.e., sugar complexes and

blood group antigens) The cytoplasm

contains proteins not found in the lower

layers such as involucrin, keratolinin,

and loricrin These proteins become

cross-linked in the SC to confer strength

to the layer

THE GRANULAR LAYER (STRATUM

GRANULO-SUM) Granular layer keratinocytes reside

in the uppermost viable layer of the

epi-dermis The “granules” represent hyaline granules, which contain profilag-grin, the precursor to filaggrin The pro-tein filaggrin cross-links keratin filamentsproviding strength and structure The pro-teins of the cornified cell envelope(involucrin, keratolinin, pancornulins, andloricrin) are cross-linked in this layer bythe calcium-requiring enzyme transgluta-minase (TGase) to form the cell envelope

kerato-There are four types of transglutaminasespresent in the epidermis: TGase 1 or ker-atinocyte TGase, TGase 2 or tissueTGase, TGase 3 or epidermal TGase, andTGase 5 Only TGases 1, 3, and 5 partici-pate in the development of the corneo-cyte envelope (CE) formation TGase 2has other functions including a role inapoptosis (programmed cell death) It isknown that TGase activity increases with

the elevation of Ca levels in themedium of cultured keratinocytes.3This

in turn results in the formation of thecornified cell envelope and differentia-tion of keratinocytes.4,5 The activemetabolite of vitamin D, known as 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], also plays a role in keratinocyte differenti-ation (Box 1-1) It enhances the

Ca2+ effect on the keratinocytes, and increases transglutaminase activity aswell as involucrin levels,6the combinedeffects of which induce CE formation.7,8Calcium is known to be an inducer ofdifferentiation and a suppressor of prolif-eration in epidermal keratinocytes.9,10Ithas been shown that in the state of low

Ca2+levels (0.05 mM), keratinocytes are in

a proliferative stage, while increases in

Ca2+levels (0.10–0.16 mM) lead to sion of differentiation markers such as ker-atins 1 and 10, TGase, and filaggrin.9Granular cells exhibit anabolic proper-ties such as synthesis of filaggrin, corni-fied cell envelope proteins, and highmolecular weight keratins In addition,they show catabolic events such as dis-solution of the nucleus and organelles

expres-THE HORNY LAYER (SC)The most cial layer of the epidermis is the SC orhorny layer, which is, on average,approximately 15-cell layers thick.13,14The keratinocytes that reside in thislayer are the most mature and have com-pleted the keratinization process Thesekeratinocytes contain no organelles andtheir arrangement resembles a brickwall The SC is composed of protein-richcorneocytes embedded in a bilayer lipidmatrix assembled in a “brick and mortar”fashion The “bricks” are composed ofkeratinocytes and the “mortar” is made

superfi-up of the contents extruded from thelamellar granules including lipids andproteins (Fig 1-4) Cells of the midcorni-fied layer have the most amino acid con-tent and therefore have the highest capa-bility for binding to water, while the

in proliferation and early differentiation while the SRC/p160 complex is engaged in advanced ferentiation.11The vitamin D receptors of undifferentiated keratinocytes bind to the DRIP com-plex, inducing early differentiation markers of K1 and K10.12The DRIP complex on the vitamin Dreceptor is then replaced by the SRC complex The SRC complex induces gene transcription foradvanced differentiation, which occurs with filaggrin and loricrin.12The replacement of the DRIPcomplex with the SRC complex on the vitamin D receptor is believed to be necessary for ker-atinocyte differentiation It is important to realize that vitamin D levels are lower in older peopleand that this reduction may play a role in the slower wound healing characteristic in the elderly

dif-쑿 FIGURE 1-3 The stem cells divide and produce amplifying cells that greatly increase the number of

keratinocytes These in turn become the mature, terminal, and differentiated cells The numbers indicate

the cell generation

3

32

amplifying

Terminallydifferentiated

deeper layers have less water-binding

capacity.15 The SC is described as the

“dead layer” of cells because these cells

do not exhibit protein synthesis and are

unresponsive to cellular signaling.16

The horny layer functions as a

protec-tive barrier One of its protecprotec-tive

func-tions is to prevent transepidermal water

loss (TEWL) Amino acids and their

metabolites, which are by-products

formed from the breakdown of filaggrin,

comprise a substance known as the

natural moisturizing factor (NMF)

Intracellularly-located NMF and lipids

released by the lamellar granules,

located extracellularly, play an

impor-tant role in skin hydration, suppleness,

and flexibility (see Chapter 11)

The Cell Cycle

The above keratinization process is also

referred to as the “cell cycle.” The normal

cell cycle of the epidermis is from 26 to 42

days.17This series of events, known also

as desquamation, normally occurs

invisi-bly with shedding of individual cells or

small clumps of cells Disturbances of this

process may result in the accumulation of

partially detached keratinocytes, which

cause the clinical findings of dry skin

Disease states may also alter the cell

cycle For example, psoriasis causes a

dra-matic shortening of the cell cycle,

result-ing in the formation of crusty cutaneous

eruptions The cell cycle lengthens in time

as humans age.18 This means that the

cells at the superficial layer of the SC are

older and their function may be impaired

Results from such compromised

function-ing include slower wound healfunction-ing and a

skin appearance that is dull and lifeless

Many cosmetic products such as retinol

and alpha hydroxy acids are believed to

quicken the pace of the cell cycle, yieldingyounger keratinocytes at the superficiallayers of the SC, thus imparting a moreyouthful appearance to the skin

GROWTH FACTORS

Growth factors can be classified intotwo groups: proliferative and differen-tiative factors Proliferative factorsengender more DNA synthesis andresult in proliferation of the cells

Differentiative factors inhibit the duction of DNA and suppress growth,thereby resulting in differentiation ofthe keratinocytes Epidermal growthfactor (EGF) is one of the integralchemokines in the regulation of growth

pro-in human cells It bpro-inds to the epidermalgrowth factor receptor (EGFR) located

on the basal and suprabasal cells in theepidermis and activates tyrosine kinaseactivity, which ultimately results in pro-liferation of the cells.19 Keratinocytegrowth factor (KGF), a member of thefibroblast growth factor family, also has

a proliferative effect via the tyrosinekinase receptor on epidermal cells.20 Ithas been shown that KGF contributes toand enhances wound healing.21In addi-tion, KGF has been demonstrated

to enhance hyaluronan synthesis in the keratinocytes.22 Other importantgrowth factors include the polypeptidetransforming growth factors, whichconsist of two types: Transforminggrowth factor alpha (TGF-␣) and trans-forming growth factor beta (TGF-␤)

They differ in both configuration andfunction TGF-␣ is a proliferative factor,similar to EGF, and works by stimulating

a tyrosine kinase response TGF-␤,which includes three subtypes (1–3), is

a differentiative factor with a serine/

threonine kinase receptor TGF-␤1 and TGF-␤2 are present in small amounts inthe keratinocytes The presence ofcalcium, phorbol esters, as well as TGF-␤ itself increases the epidermalTGF-␤ level and promotes differentia-tion.23 TGF-␤ has also been proven tohave a role in scarring, and antibodies tothis factor have been shown to decreasethe inflammatory response in woundsand reduce scarring.24, 25

ANTIMICROBIAL PEPTIDES

Antimicrobial peptides (AMPs) haverecently become an area of interestbecause of their involvement in the innateimmune system of human skin AMPsexhibit broad-spectrum activity againstbacteria, viruses, and fungi.26,27 Thecationic peptide of the AMPs attracts thenegatively charged bacteria, becomingpervasive in the bacterial membrane inthe process, and ultimately eliminates thebacteria Cathelicidin and defensin are thetwo major groups of AMPs believed tohave an influence in the antimicrobialdefense of the skin Cathelicidin has beenidentified in the keratinocytes of humanskin at the area of inflammation, as well

as in eccrine and salivary glands.28–30Inaddition to antimicrobial activity, catheli-cidin LL-37 demonstrates a stimulatoryeffect on keratinocyte proliferation in theprocess of wound healing.31 Pig catheli-cidin PR-39 has been shown to induceproteoglycans production (specifically,syndecan-1 and -4) in the extracellularmatrix in wound repair.32Defensin is alsoexpressed in the human keratinocytes33and mucous membranes.34,35␤-Defensin

1 seems to promote differentiation in thekeratinocytes by increasing expression ofkeratin 10.36Interestingly, UVB radiationhas been shown to increase the levels ofhuman ␤-defensin mRNA in the ker-atinocytes.37

AMPs have been demonstrated to beinvolved in several dermatologic condi-tions including atopic dermatitis, psoria-sis, and leprosy,27as well as wound heal-ing, all of which are beyond the scope ofour discussion The role of AMPs in theepidermal barrier will be discussed inChapter 11

MOISTURIZATION OF THE SC

The main function of the SC is toprevent TEWL and regulate the waterbalance in the skin The two major com-ponents that allow the SC to performthis role are lipids and the NMF

Intercellular

lipids(fats)

쑿 FIGURE 1-4 The desmosomes form attachments between the keratinocytes The keratinocytes are

surrounded by lipids These structures form the skin barrier

Natural Moisturizing Factor

Released by the lamellar granules, NMF

is composed of amino acids and their

metabolites, which are by-products

formed from the breakdown of filaggrin

(Box 1-2) NMF is found exclusively

inside the cells of the SC and gives the

SC its humectant (water-binding)

quali-ties (Fig 1-5) NMF is composed of very

water-soluble chemicals; therefore, it

can absorb large amounts of water, even

when humidity levels are low This

allows the SC to retain a high water

con-tent even in a dry environment The

NMF also provides an important

aque-ous environment for enzymes that

require such conditions to function Theimportance of NMF is clear when onenotes that ichthyosis vulgaris patients,who have been shown to lack NMF,manifest severe dryness, and scaling ofthe skin.38It has been demonstrated thatnormal skin exposed to normal soapwashing has significantly lower levels ofNMF when compared to normal skinnot washed with surfactants.39NMF lev-els have also been reported to declinewith age, which may contribute to theincreased incidence of dry skin in theelderly population (see Chapter 11)

Lipids

In order of abundance, the composition

of skin surface lipids includes erides, fatty acids, squalene, wax esters,diglycerides, cholesterol esters, and cho-lesterol.41These lipids are an integral part

triglyc-of the epidermis and are involved in venting TEWL and the entry of harmfulbacteria They also help prevent the skinfrom absorbing water-soluble agents Fordecades it has been known that theabsence of lipids in the diet leads tounhealthy skin (see Chapter 11) Morerecently, it has been shown that inheriteddefects in lipid metabolism, such as thedeficiency of steroid sulfatase seen in X-linked ichthyosis, will lead to abnormalskin keratinization and hydration.42It isnow known that SC lipids are affected byage, genetics, seasonal variation, and diet

pre-Deficiency of these lipids predisposes theindividual to dry skin This has been

demonstrated in mice with essential fattyacid deficiency (EFAD); when fed a dietdeficient in linoleic acid these mice devel-oped increased TEWL.43 Interestingly,administration of hypocholesterolemicdrugs has also been associated with dryskin changes.44

Skin lipids are produced in andextruded from lamellar granules asdescribed above or are synthesized inthe sebaceous glands and then excreted

to the skin’s surface through the hairfollicle The excretion of sebum by seba-ceous glands is hormonally controlled(see Chapter 10) Lipids help keep theNMF inside the cells where it is needed

to keep cells hydrated and aqueousenzymes functioning Although this isless well characterized, lipids can them-selves influence enzyme function

ROLE OF LIPIDS IN TEWL

The major lipids found in the SC that tribute to the water permeability barrierare ceramides, cholesterol, and fatty acids.Since the 1940s, when the SC wasfirst identified as the primary barrier towater loss, many hypotheses have beenentertained as to exactly which lipidsare important in the SC The researchwith the EFAD mice described above led

con-to a focus on phospholipids becausethey contain linoleic acid However, itwas later found that phospholipids arealmost completely absent from the SC.40

In 1982, ceramide 1 was discovered.This lipid compound is rich in linoleicacid and is believed to play a major role

in structuring SC lipids essential for rier function.45Later, five more distincttypes of ceramides were discovered andnamed according to the polarity of themolecule Ceramide 1 is the most non-polar and ceramide 6 is the most polar.Although the ceramides were oncethought to be the key to skin moisturiza-tion, studies now suggest that no particu-lar lipid is more important than the oth-ers It appears that the proportion of fattyacids, ceramides, and cholesterol is themost important parameter This wasdemonstrated in a study in which afteraltering the water barrier with acetone,the application of a combination ofceramides, fatty acids, and cholesterolresulted in normal barrier recovery.46Application of each of the separate enti-ties alone resulted in delayed barrierrecovery Manufacturers now includeceramides or a mixture of ceramides, cho-lesterol, and fatty acids in several avail-able products as a result of these findings.However, the use of these mixtures to

Filaggrin, named for filament aggregating

protein, derived its name from the fact that it

binds keratin filaments to form a structural

matrix in the SC Genetic defects in the

filag-grin gene are known to play a role in a

sub-set of ichthyosis vulgaris cases.38

Interestingly, filaggrin is not present in the

superficial layers of the SC Studies have

shown that it is completely degraded into

amino acids within 2 to 3 days of profilaggrin

formation and its constituents are further

metabolized to form the NMF.40This is

nature’s way of keeping its water-binding

capabilities in the top layer of the SC where

they are needed while preventing the lower

layers of the SC from being disrupted by

having too much water present In addition,

the level of NMF is regulated by the water

activity present in the SC

쑿 FIGURE 1-5 The keratinocytes are embedded in a lipid matrix that resembles bricks and mortar

Natural moisturizing factor (NMF) is present within the keratinocytes NMF and the lipid bilayer prevent

dehydration of the epidermis

DEEP SUPERFICIAL

NMF Brick

Mortar

Brick

Hydrophilic

Hydrophilic Hydrophobic

Corneocytes (bricks)

Intercellular lipids (mortar)

tured human keratinocytes FEBS Lett.

1989;254:25

11 Oda Y, Sihlbom C, Chalkley RJ, et al

Two distinct coactivators, tor and SRC/p160, are differentiallyinvolved in VDR transactivation during

DRIP/media-keratinocyte differentiation J Steroid Biochem Mol Biol 2004;273:89-90.

12 Bikle D, Teichert A, Hawker N, et al

Sequential regulation of keratinocyte ferentiation by 1,25(OH)2D3, VDR, and

dif-its coregulators J Steroid Biochem Mol Biol.

2007;103:396

13 Christophers E, Kligman AM Visualization

of the cell layers of the stratum corneum J Invest Dermatol 1964;42:407.

14 Blair C Morphology and thickness of the

human stratum corneum Br J Dermatol.

1968;80:430

15 Proksch E, Jensen J Skin as an organ ofprotection In: Wolff K, Goldsmith L,Katz S, Gilchest B, Paller A, Leffell D, eds

Fitzpatrick’s Dermatology in General Medicine 7th ed New York, NY:

McGraw-Hill; 2008:383-395

16 Egelrud T Desquamation In: Loden M,

Maibach H, eds Dry Skin and Moisturizers.

1st ed Boca Raton, FL: CRC Press;

2000:110

17 Proksch E, Jensen J Skin as an organ ofprotection In: Wolff K, Goldsmith L,Katz S, Gilchest B, Paller A, Leffell D, eds

Fitzpatrick’s Dermatology in General Medicine 7th ed New York, NY:

McGraw-Hill; 2008:87

18 Yaar M, Gilchrest B Aging of skin In:

Freedberg IM, Eisen A, Wolff K, Austen

K, Goldmsith L, Katz S, Fitzpatrick T,

eds Fitzpatrick’s Dermatology in General Medicine 5th ed New York, NY:

20 Miki T, Bottaro DP, Fleming TP, et al

Determination of ligand-binding ficity by alternative splicing: two distinctgrowth factor receptors encoded by a

speci-single gene Proc Natl Acad Sci U.S.A.

1992;89:246

21 Brauchle M, Fässler R, Werner S

Suppression of keratinocyte growth tor expression by glucocorticoids in vitro

fac-and during wound healing J Invest Dermatol 1995;105:579.

22 Karvinen S, Pasonen-Seppänen S,Hyttinen JM, et al Keratinocyte growthfactor stimulates migration and hyaluro-nan synthesis in the epidermis by activa-tion of keratinocyte hyaluronan synthases

2 and 3 J Biol Chem 2003;278:49495.

23 William I, Rich B, Kupper T Cytokines

In: Wolff K, Goldsmith L, Katz S, Gilchest

B, Paller A, Leffell D, eds Fitzpatrick’s Dermatology in General Medicine 7th ed.

New York, NY: McGraw-Hill; 2008:116

24 Shah M, Foreman DM, Ferguson MW

Neutralisation of beta 1 and beta 2 or exogenous addition of TGF-beta 3 to cutaneous rat wounds reduces

TGF-scarring J Cell Sci 1995;108:985.

25 Shah M, Foreman DM, Ferguson MW

Control of scarring in adult wounds byneutralising antibody to transforming

growth factor beta Lancet 1992;

339:213

26 Ganz T, Lehrer RI Defensins Curr Opin Immunol 1994;6:584.

27 Izadpanah A, Gallo RL Antimicrobial

pep-tides J Am Acad Dermatol 2005; 52:381.

28 Frohm M, Agerberth B, Ahangari G, et al

The expression of the gene coding for theantibacterial peptide LL-37 is induced inhuman keratinocytes during inflammatory

disorders J Biol Chem 1997;272: 15258.

29 Murakami M, Ohtake T, Dorschner RA,

et al Cathelicidin anti-microbial peptideexpression in sweat, an innate defense

system for the skin J Invest Dermatol.

2002;119:1090

30 Murakami M, Ohtake T, Dorschner RA,

et al Cathelicidin antimicrobial peptidesare expressed in salivary glands and

saliva J Dent Res.2002;81:845.

31 Heilborn JD, Nilsson MF, Kratz G, et al

The cathelicidin anti-microbial peptideLL-37 is involved in re-epithelialization

of human skin wounds and is lacking in

chronic ulcer epithelium J Invest Dermatol.

2003;120:379

32 Gallo RL, Ono M, Povsic T, et al

Syndecans, cell surface heparan sulfateproteoglycans, are induced by a proline-rich antimicrobial peptide from wounds

Proc Natl Acad Sci U S A 1994;91:11035.

33 Ali RS, Falconer A, Ikram M, et al

Expression of the peptide antibioticshuman beta defensin-1 and human beta

defensin-2 in normal human skin J Invest Dermatol 2001;117:106.

34 Mathews M, Jia HP, Guthmiller JM, et al

Production of beta-defensin bial peptides by the oral mucosa and sali-

antimicro-vary glands Infect Immun 1999;67:2740.

35 Dunsche A, Acil Y, Dommisch H, et al

The novel human beta-defensin-3 is

widely expressed in oral tissues Eur J Oral Sci 2002;1110:121.

36 Frye M, Bargon J, Gropp R Expression ofhuman beta-defensin-1 promotes differ-

entiation of keratinocytes J Mol Med.

2001;79:275

37 Seo SJ, Ahn SW, Hong CK, et al Expressions

of beta-defensins in human keratinocyte cell

lines J Dermatol Sci 2001;27:183.

38 Sybert VP, Dale BA, Holbrook KA

Ichthyosis vulgaris: identification of adefect in synthesis of filaggrin correlatedwith an absence of keratohyaline gran-

ules J Invest Dermatol 1985;84:191.

39 Scott IR, Harding CR Physiologicaleffects of occlusion-filaggrin retention

(abstr) Dermatology 1993;2000:773.

40 Rawlings AV, Scott IR, Harding CR, et al

Stratum corneum moisturization at the

molecular level J Invest Dermatol 1994;

103:731

41 Downing DT, Strauss JS, Pochi PE

Variability in the chemical composition

of human skin surface lipids J Invest Dermatol 1969;53:322.

42 Webster D, France JT, Shapiro LJ, et al linked ichthyosis due to steroid-sul-

X-phatase deficiency Lancet 1978;1:70.

43 Prottey C Essential fatty acids and the

skin Br J Dermatol 1976;94:579.

44 Elias PM Epidermal lipids, barrier

func-tion, and desquamation J Invest Dermatol.

1983;80:44s

45 Swartzendruber DC, Wertz PW, Kitko DJ,

et al Molecular models of the intercellularlipid lamellae in mammalian stratum

corneum J Invest Dermatol 1989;92:251.

46 Man MQ, Feingold KR, Elias PM

Exogenous lipids influence permeabilitybarrier recovery in acetone-treated

murine skin Arch Dermatol 1993;129:728.

treat atopic dermatitis and other

ichthy-otic disorders has been disappointing

SUMMARY

The epidermis is implicated in many of

the skin complaints of cosmetic patients

It is the state of the epidermis that

causes the skin to feel rough and appear

dull A flexible, well-hydrated epidermis

is more supple and radiant than a

dehy-drated epidermis The popularity of buff

puffs, exfoliating scrubs, masks,

mois-turizers, chemical peels, and

microder-mabrasion attest to the obsession that

cosmetic patients have with the

condi-tion of their epidermis It is important to

understand the properties of the

epider-mis in order to understand which

cos-metic products and procedures can truly

benefit patients as opposed to those that

are based on myths or hype

REFERENCES

1 Chu D Overview of biology,

develop-ment, and structure of skin In: Wolff K,

Goldsmith L, Katz S, Gilchest B, Paller A,

Leffell D, eds Fitzpatrick’s Dermatology in

General Medicine 7th ed New York, NY:

Mcgraw-Hill; 2008:60

2 Braff MH, Di Nardo A, Gallo RL

Keratinocytes store the antimicrobial

peptide cathelicidin in lamellar bodies

J Invest Dermatol 2005;124:394.

3 Li L, Tucker RW, Hennings H, et al

Inhibitors of the intracellular Ca(2+

)-ATPase in cultured mouse keratinocytes

reveal components of terminal

differenti-ation that are regulated by distinct

intra-cellular Ca2+compartments Cell Growth

Differ 1995;6:1171.

4 Green H The keratinocyte as

differenti-ated cell type Harvey Lect 1980;74:101.

5 Eckert RL, Crish JF, Robinson NA The

epi-dermal keratinocyte as a model for the

study of gene regulation and cell

differentiation Physiol Rev 1997;77:397-424.

6 Su MJ, Bikle DD, Mancianti ML, et al

1,25-Dihydroxyvitamin D3potentiates

the keratinocyte response to calcium

J Biol Chem 1994;269:14723.

7 Hosomi J, Hosoi J, Abe E, et al

Regulation of terminal differentiation of

cultured mouse epidermal cells by

1 alpha, 25-dihydroxyvitamin D3

Endo-crinology 1983;113:1950.

8 Smith EL, Walworth NC, Holick MF

Effect of 1 alpha,25-dihydroxyvitamin

D3on the morphologic and biochemical

differentiation of cultured human

epider-mal keratinocytes grown in serum-free

conditions J Invest Dermatol 1986;86:709.

9 Yuspa SH, Kilkenny AE, Steinert PM,

et al Expression of murine epidermal

dif-ferentiation markers is tightly regulated

by restricted extracellular calcium

concen-trations in vitro J Cell Biol 1989;109:1207.

10 Sharpe GR, Gillespie JI, Greenwell JR An

increase in intracellular free calcium is an

early event during differentiation of

COLLAGEN

Collagen, one of the strongest naturalproteins and the most abundant one inhumans as well as in skin, imparts dura-bility and resilience to the skin It hasbeen the focus of much antiagingresearch and the target of several skinproducts and procedures The impor-tance of collagen is emphasized in theliterature regarding many of the topicalagents that are touted to increase colla-gen synthesis such as glycolic and ascor-bic acids Resurfacing techniques such asthe CO2 laser and dermabrasion areintended to change collagen structure,thereby improving skin texture Variousforms of collagen are injected into thedermis to replace damaged collagen and

to reverse the signs of aging Finally, ical retinoids have been shown toreduce the collagen damage that occursbecause of sun exposure These sundry

top-aspects of collagen health or ment will be discussed separately inupcoming chapters; however, it is neces-sary first to gain an understanding of thestructure and function of collagen

replace-“Collagen” is actually a complexfamily of 18 proteins, 11 of which arepresent in the dermis Collagen fibersare always seen in the dermis in thefinal, mature state of assembly asopposed to elastin, the immature fibers

of which are seen in the superficial mis with the more mature fibers found

der-in the deeper layer of the dermis Eachtype of collagen is composed of threechains (Fig 2-2) Collagen is synthe-sized in the fibroblasts in a precursorform called procollagen Proline residues

on the procollagen chain are converted

to hydroxyproline by the enzyme lyl hydroxylase This reaction requiresthe presence of Fe++, ascorbic acid (vit-amin C), and ␣-ketoglutarate Lysineresidues on the procollagen chain arealso converted to hydroxylysine; inthis case, by the enzyme lysyl hydrox-ylase This reaction also requires thepresence of Fe++, ascorbic acid, and

pro-␣-ketoglutarate It is interesting to notethat a deficiency of vitamin C, which is

an essential mediating component inthese reactions, leads to scurvy, a dis-ease characterized by decreased colla-gen production

Collagen GlycationGlycation of extracellular matrix (ECM)collagen and proteins plays an impor-tant role in the aging process This isnot to be confused with glycosylation

of collagen, which is an ated process in the intracellular step ofcollagen biosynthesis Glycation is anonenzymatic series of biologic eventsthat involves adding a reducing sugarmolecule (such as glucose or fructose)

enzyme-medi-to ECM collagen and proteins Thisreaction is also known as the Maillard reaction The sugar molecule mainlyreacts with the amino group side chains

The dermis lies between the epidermis

and the subcutaneous fat It is responsible

for the thickness of the skin, and as a

result plays a key role in the cosmetic

appearance of the skin The thickness of

the dermis varies over different parts of

the body and the size doubles between

the ages of 3 and 7 years and again at

puberty With aging, this basic layer

decreases in thickness and moisture The

dermis, which is laden with nerves, blood

vessels, and sweat glands, consists mostly

of collagen The uppermost portion of

this layer, which lies beneath the

epider-mis, is known as the papillary dermis and

the lower portion is known as the

reticu-lar dermis Smaller collagen bundles,

greater cellularity, and a higher density in

its vascular elements characterize the

papillary dermis as compared to the

retic-ular dermis Fibroblasts are the primary

cell type in the dermis They produce

collagen, elastin, other matrix proteins,

and enzymes such as collagenase and

stromelysin These structural

compo-nents will be discussed individually

because each exhibits significant

charac-teristics that influence the function of the

skin Immune cells such as mast cells,

polymorphonuclear leukocytes,

lympho-cytes, and macrophages are also present

in the dermis

The junction between the epidermis

and dermis is known as the dermal–

epidermal junction (DEJ) (Fig 2-1) Much

쑿 FIGURE 2-1 Histopathology of the dermal-epidermal junction The basement membrane separates

the epidermis and the dermis (Image courtesy of George Loannides, MD.)

Basement membrane

Blood vesselEpidermis

of lysine and arginine of collagen and

ECM proteins Subsequently, the

prod-uct of this process undergoes oxidative

reactions resulting in the formation of

advanced glycation end products

(AGEs) (Fig 2-3) AGEs have been

implicated in the aging process and

age-related diseases such as diabetes

melli-tus,1–3 chronic renal failure,4,5 and

Alzheimer’s disease.6–8 It is believed

that with time, AGEs increase,9

accu-mulate on human collagen10and elastin

fibers,11and contribute to aging of the

skin As a result of glycation, collagen

networks lose their ability to contract,

and they become stiffer and resistant to

remodeling Fibroblasts are key

ele-ments for collagen contracture, as they

apply contracture force on the collagen

lattice via their actin cytoskeleton.12

Glycated collagen modifies the actin

cytoskeleton of the fibroblasts thereby

diminishing their collagen contraction

capacity.13 Fibroblasts also secrete

col-lagenase (MMP-1), which is essential

for collagen turnover Glycated collagen

has been proven to decrease levels

of collagenase I (MMP-1), leading to

less tissue remodeling.14 Studies have

shown that UV exposure may also

con-tribute to the production and function

of AGEs Ne⑀-(carboxymethyl) lysine

(CML) is one of the AGEs in which theamino side chain of lysine is reduced

This product was shown to accumulate

on elastin tissue of photoaged skin andproven to be higher in sun-exposedskin as compared to sun-protectedskin.11In addition, it has been proposedthat AGE-modified proteins act asendogenous photosensitizers in humanskin via oxidative stress mechanismsinduced by UVA light.15

The Key Types of Collagen Found in the Dermis (Table 2-1)

Type I collagen comprises 80% to 85%

of the dermal matrix and is responsiblefor the tensile strength of the dermis

The amount of collagen I has beenshown to be lower in photoaged skin,and to be increased after dermabrasionprocedures.16Therefore, it is likely thatcollagen I is the most important colla-gen type in regard to skin aging Type III

is the second most important form ofcollagen in the dermis, making up any-where from 10% to 15% of thematrix.17 This collagen type has asmaller diameter than type I and formssmaller bundles allowing for skin plia-bility Type III, also known as “fetal col-lagen” because it predominates in

embryonic life, is seen in higheramounts around the blood vessels andbeneath the epidermis

The other types of collagen that arenoteworthy for a cosmetic dermatolo-gist are type IV collagen, which forms astructure lattice that is found in the base-ment membrane zone and type V colla-gen, which is diffusely distributedthroughout the dermis and comprisesroughly 4% to 5% of the matrix TypeVII collagen makes up the anchoring fib-rils in the DEJ Type XVII collagen islocated in the hemidesmosome andplays an important structural role aswell The importance of these collagensand other structural proteins is evident

in genetic diseases characterized by alack of these structures and in acquireddiseases characterized by antibody for-mation to these important structures

For example, patients with an inheritedblistering disease known as dominantdystrophic epidermolysis have beenshown to have a scarcity of type VII col-lagen with resulting abnormalities intheir anchoring fibrils An acquired bul-lous disease, epidermolysis bullosaacquisita (EBA), is caused by antibodies

to this same collagen type VII Althoughthe discussion of these diseases isbeyond the scope of this text, it is inter-esting that patients with chronic sunexposure have also been found to havealterations in collagen type VII Thismay contribute to the skin fragility seen

in elderly patients Some investigatorshave postulated that a weakened bondbetween the dermis and epidermiscaused by loss of the anchoring fibrils(collagen VII) may lead to wrinkle for-mation.18 The importance of collagenand changes seen in aged skin will bediscussed further in Chapter 6

ELASTIN

Elastic fibers represent one of the essentialcomponents of the ECM of connectivetissue (Fig 2-4) They confer resilience

쑿 FIGURE 2-3 Glycation of proteins is thought to play a role in the aging process

Ketosamines

OxidationAmadori re-arrangement

Advanced Glycation End Products (AGEs)

TABLE 2-1

Major Collagen Types Found in the Dermis

COLLAGENTYPE OTHERNAME LOCATION FUNCTION % OFDERMIS ASSOCIATEDDISEASES

III Fetal collagen Dermis, GI, vessels Gives compliance 15

bullous pemphigoid (BP),herpes gestationis

and elasticity to skin as well as other

organs such as the lungs and blood

ves-sels Elastogenesis starts during fetal life

and reaches its maximum near birth and

the early neonatal period It then

decreases significantly and is virtually

nonexistent by adult life Elastic fibers

have two components Their main

com-ponent is elastin, an amorphous,

insolu-ble connective tissue protein Elastin is

surrounded by microfibrils, the second

component Elastin constitutes 2% to

3% of the dry weight of skin, 3% to 7%

of lung, 28% to 32% of major blood

vessels, and 50% of elastic ligaments.19

Elastin is produced from its precursor

tropoelastin in the fibroblasts as well as

endothelial cells and vascular smooth

muscle cells In contrast to collagen

fibers, elastin fibers are present in the

dermis in various levels of maturity The

least mature fibers are called oxytalan

They course perpendicularly from the

DEJ to the top of the reticular dermis

More mature elastin fibers, called

elaunin, then attach to a horizontal

plexus of fibers found in the reticular

dermis Elaunin is more mature because

it has more elastin deposited on the

fib-rillin mesh The most mature elastin

fibers are unnamed and are found

deeper in the reticular dermis (Fig 2-5)

Microfibrils play a very important

role in elastogenesis and act as a scaffold

for tropoelastin deposition and

assem-bly.20 Microfibrils are primarily

com-posed of glycoproteins from the fibrillin

family and microfibril-associated

glyco-protein (MAGP)-1 and -2 Fibrillin-1 has

been shown to be important in elastic

fiber development21and wound repair.22

Microfibrils are adjacent to

tropoelastin-producing cells and parallel to the

devel-oping elastin fiber.23 The microfibrils

form a template on which tropoelastin is

deposited The tropoelastin

polypep-tides are then covalently cross-linked to

form elastin Tropoelastin polypeptides

contain alternating hydrophilic and

hydrophobic regions The hydrophobic

domains, which are rich in proline,valine, and glycine, are believed to beresponsible for the elasticity of theelastin tissue.24 The hydrophilicdomains on the other hand are rich inalanine and lysine, and interact with theenzyme lysyl oxidase in the process ofcross-linking.25 The cross-linking ofelastin is a complex process necessaryfor its proper function and stability Thisprocess is mediated via the copper-requiring enzyme lysyl oxidase,26 andthe subsequent formation of desmosineand isodesmosine cross-links, whichresult in an insoluble elastin network.27Elastin is fascinating and althoughmuch is known about it, its relevance incosmetic dermatology is unclear Itseems certain that collagen, hyaluronicacid (HA), and elastin bind each othercovalently and make up a three-dimen-sional structure that is impaired in agedskin There is a commonly held beliefthat these three components must beincreased in order to give skin a youngerappearance However, the trick is that

de novo elastin production does notoccur in adulthood Trying to increaseproduction of elastin in adults willsurely be a focus of cosmetic dermatol-ogy research in the future

The elastic fiber’s structure providesclues about its ability to interact with

HA and collagen Mature elastic fiberscontain an array of proteoglycans.Versican is one of the most widely stud-ied proteoglycans28and is a member ofthe hyaluronan binding family that alsoincludes aggrecan and neurocan.Versican contributes to cell adhesion,proliferation, and migration and caninteract with multiple ECM proteins tomediate assembly Mature elastic fibersare found at the periphery of collagenbundles, offering a clue that elastin hasimportant interactions with collagen aswell as with HA

Elastic fibers are degraded by the tolytic enzymes such as human leukocyteelastase (HLE) With significant levels ofsun exposure, elastin degrades and is seen

elas-as an amorphous substance in the dermiswhen viewed by light microscopy Thisresultant “elastosis” is a hallmark of pho-toaged skin Interestingly, there are protec-tive mechanisms in the skin preventingelastin degradation Lysozymes arebelieved to play a protective role in thismatter They have been shown to increaseand deposit on the elastin fibers of UV-exposed skin.29By binding to the elastin,the lysozymes prevent the proper interac-tion between elastase and elastin,30therebyinhibiting the proteolytic activity of theelastolytic enzymes.30,31It is also believedthat damage to the elastin fibers leads tothe decreased skin elasticity seen in agedskin.32Defects or damage to elastin maylead to wrinkles even in the absence ofsun exposure and aging Indeed, in onecase, a child with “wrinkled skin syn-drome” was shown to have a deficiency

of elastin fibers,33 which demonstratesthe importance of elastin in skin integrity.Defective elastic fibers can give rise tomultiple dermatologic diseases includingcutis laxa, pseudoxanthoma elasticum

쑿 FIGURE 2-5 The elastic fiber network in the dermis consists of immature oxytalan fibers in thesuperficial dermis and the more mature elaunin fibers in the middle dermis The most mature elasticfibers are unnamed and are found in the deep reticular dermis

쑿 FIGURE 2-4 A and B Scanning electron micrographs of the elastic fibers in human skin Adapted from

Fitzpatrick’s Dermatology in General Medicine, seventh edition (McGraw Hill), page 532, with permission

Deep reticular dermis

Reticular dermisElaunin fibers

Papillary dermisOxytalan fibers

EPIDERMIS

DE Junction

B A

(PXE), elastosis perforans serpiginosa

(also known as Lutz-Miescher’s

syn-drome), and dermatofibrosis

lenticu-laris (also known as Buschke-Ollendorf

syndrome)

Studies have demonstrated a

reduc-tion in the elastin content in protected

areas of the skin with aging In a study

performed on Egyptian subjects, the

rela-tive amount of elastin in the

non-UV-exposed abdominal skin significantly

decreased from 49.2%⫾0.6% in the first

decade to 30.4%⫾ 0.8% in the ninth

decade.34Another study on elastin

con-tent in the nonexposed buttock skin of

91 Caucasians between 20 and 80 years

of age showed a reduction of 51% in

elastin tissue.31 Although UV exposure

may result in elastosis and a higher

con-tent of elastin tissue, the elastic fibers are

rendered structurally abnormal,34which

is microscopically seen as thickened and

twisted granular deposits of elastin in the

dermis

Replacing the elastin component of

the ECM has always posed a challenge

in skin rejuvenation approaches

Researchers have investigated the

pro-duction of recombinant and cross-linked

tropoelastin in great detail.35 However,

since it is very difficult to have elastin

pass through human skin, stimulating

the dermis to produce elastin may be an

alternative option Recently, zinc has

become a subject of interest as an elastin

tissue stimulator in the skin Zinc has

been shown to increase the epidermal

growth factor (EGF) receptor signaling

pathway.36It increases protein tyrosine

phosphorylation by inhibiting protein

tyrosine phosphatase (PTPase),37 and

activates mitogen-activated protein

(MAP) kinases,38 which are important

for cosignaling in ECM production

Clinical studies have suggested

improvement in the elasticity of

perioc-ular skin following use of a patented

zinc complex topical preparation.39In a

4-week study of 27 female subjects with

a zinc complex-containing eye product,

overall improvement of the eye area

was noted by 78%, reduction of fine

lines by 74%, and firmer skin by 70% of

the patients.39 These studies, although

promising, need to be conducted in a

larger patient population

GLYCOPROTEINS

Glycoproteins (GP) influence cell

migration, adhesion, and orientation

Fibronectin and tenascin are the GPs

most relevant in the dermis although

vitronectin, thrombospondin, and

epi-bolin are also present in the dermis

Fibronectin is a filamentous GP thatmediates platelet binding to collagen,development of granulation tissue, andreepithelialization Chemotactic formonocytes, fibronectin contains sixbinding sites including one for colla-gen, two for heparin, and a region thatbinds fibrin Tenascin is abundant indeveloping skin but found only in thepapillary dermis in adult skin Thesematrix components play a significantrole in tissue remodeling and areimportant in wound healing followingcosmetic procedures

GLYCOSAMINOGLYCANS

Glycosaminoglycans (GAGs) are saccharide chains composed of repeatingdisaccharide units linked to a core pro-tein Together the GAGs and attachedcore protein form proteoglycans AllGAGs except for HA are synthesized inGolgi apparatus HA is the only GAGthat is not produced on a core protein;

poly-rather, it is synthesized by an enzymecomplex of the plasma membrane.40Although all the functions of GAGsare not understood, it is known thatthese compounds avidly bind water andmay contribute to the maintenance ofsalt and water balance GAGs are found

in areas with a fibrous matrix where cellsare closely associated but have littlespace for free movement Most studies

on human skin show an age-relateddecline in GAG content The most abun-dant GAGs in the dermis are HA, which

is the only nonsulfated GAG, and matan sulfate The other GAGs includeheparin sulfate, heparin, keratan sulfate,chondroitin-4, and chondroitin-6-sulfate

der-HA is a very important component ofthe dermis that is responsible for attract-ing water and giving the dermis its vol-ume The name reflects its glassy appear-

ance (the Greek word for glass is hyalos)

and the presence of a sugar known asuronic acid HA is known to be impor-tant in cell growth, membrane receptor

function, and adhesion Its structure isidentical, whether it is derived frombacterial cultures, animals, or humans

(Fig 2-6).HA appears freely in the mis and is more concentrated in areaswhere cells are less densely packed Inyoung skin, HA is found at the periphery

der-of collagen and elastin fibers and at theinterface of these types of fibers Theseconnections with HA are absent in agedskin.41HA is a popular ingredient in cos-metic products because it acts as ahumectant Several types are also avail-able in an injectable version for the treat-ment of wrinkles (see Chapter 23) HAappears to also play a role in ker-atinocyte differentiation and formation

of lamellar bodies via its interaction withCD44,42 a cell surface glycoproteinreceptor with HA binding sites.43–45Decorin is a member of the smallleucine-rich proteoglycans (SLRPs)found in the extracelluar matrix protein

Its name is derived from its apparent

“decorating” of collagen fibers Decorincontains a core protein with a highcontent of leucine repeats and GAGchains of dermatan or chondroitin sul-fate It is shaped in a “horseshoe” pat-tern and binds to collagen fibrils, result-ing in their proper organization.46Decorin-deficient mice have shown clin-ical skin fragility and irregular collagenfibrils with increased interfibrillar space

on histology.47 In addition to collagenfibrillogenesis, decorin interacts withfibronectin48 and fibrinogen,49 therebyplaying a role in wound healing andhemostasis Another interesting function

of decorin is that it reduces the tion of cells in neoplasms by stoppingtheir growth in the G1 phase of the cell cycle.50Carrino et al.51studied the catabolic fragment of decorin in adultskin They noted a higher content of thealtered decorin in adult dermis asopposed to nonmeasurable amounts infetal skin and named it “decorunt.”

prolifera-Decorunt was shown to have a loweraffinity for collagen fibrils This findingmay explain some of the changes related

to collagen disorganization in aging skin

H

H

HOH

HO

OC

OH

HHO

CO2–

OHO

쑿 FIGURE 2-6 HA is made of repeating dimers of glucuronic acid and N-acetyl glucosamine bled into long chains

The ECM architecture of human skin is

based on its continuous remodeling

This process requires ECM-degrading

enzymes followed by synthesis and

deposition of new molecules The

matrix metalloproteinases (MMPs),

which include a large family of

zinc-dependent endopeptidases, are crucial

to the turnover of ECM components

Interstitial collagenase, or MMP-1, was

the first enzyme discovered in this

group MMP-1 is secreted from the

fibroblasts and is mainly involved in the

degradation of collagen types I, II, and

III, but has been shown to also cleave

the anchoring fibrils of collagen VII.52

Human neutrophil collagenase

(MMP-8), another type of collagenase, is

engaged in cleaving collagen types I and

III Collagenase 3 (MMP-13) is the third

member of this group of enzymes, and it

is known to fragment fibrillar collagens

It is also believed to have a role in

scar-less wound healing53 by enhancing

fibroblast proliferation and survival.54

Gelatinases are another class of MMPs

and consist of two types of enzymes,

gelatinase A (MMP-2) and gelatinase B

(MMP-9), that are responsible for

attack-ing gelatin and collagen IV in the

base-ment membrane Other groups of

MMPs include stromelysins, which are

mainly involved in degradation of

pro-teoglycans, laminins, collagen IV, and

matrilysin, which is expressed on

stro-mal tissue, fetal skin, and in the setting

of carcinomas.55

The activity of MMPs is regulated by

an endogenous tissue inhibitor of

metal-loproteinases (TIMPs) TIMPs are

natu-rally produced proteins that specifically

inhibit the MMPs The balance between

MMPs and their inhibition by TIMPs

leads to proper tissue remodeling

TIMPs are regulated via expression of

cytokines (such as IL-1), growth factors,

and even retinoids.56,57 Retinoids have

been shown to provoke a two- to

three-fold increase in the biosynthesis of

human fibroblast-derived TIMP in

vitro.58 Increased production of MMPs

and decreased production of TIMPs

have a role in the metastatic behavior of

tumors Synthetic inhibitors of MMPs

are of interest to researchers especially

in the area of cancer research These

inhibitors, such as hydroxamates,

con-tain a zinc-chelating group that binds to

the active site of MMPs leading to its

inhibition Currently, their use is mostly

limited to research studies because of

their side-effect profile Certain

medica-tions such as doxycycline are also

known for their inhibitory effect onMMPs and have been studied in myriadMMP-related conditions such as perio-dontal and atherosclerotic diseases

The adipocytes secrete a hormonecalled leptin, a product of the obesity

(ob) gene Leptin exhibits a regulatory

effect on human metabolism andappetite and therefore affects adiposetissue mass Leptin has been shown to

be higher in the serum of obese patients,with commensurate levels found inbody fat percentage.59It is believed that

a higher percentage of body fat results inelevated leptin levels and the turning off

of signals to the brain for appetite tion Recombinant leptin injections inmice have been associated with reduc-tion of weight and body fat percent-age.60However, more research is needed

reduc-to ascertain the therapeutic potential ofleptin in humans

SUMMARY

Although the epidermis is the target ofmost topical cosmetic products becausemost do not penetrate to the dermis, thedermis is the target for many of theinjectable treatments for aging The der-mis is an extremely important compo-nent in skin appearance because it isresponsible for imparting thickness andsuppleness to the skin A thinner dermisand an altered DEJ are hallmarks of agedskin Loss of collagen, elastin, and GAGslocated primarily in the dermis contributesignificantly to cutaneous aging Variousmeasures intended to prevent or retardaging target these key constituents ofthe dermis

REFERENCES

1 Monnier VM, Kohn RR, Cerami A

Accelerated age-related browning of

human collagen in diabetes mellitus Proc Natl Acad Sci U S A 1984;81:583.

2 Schnider SL, Kohn RR Glucosylation ofhuman collagen in aging and diabetes

mellitus J Clin Invest 1980;66:1179.

3 Schnider SL, Kohn RR Effects of age anddiabetes mellitus on the solubility andnonenzymatic glucosylation of human

skin collagen J Clin Invest 1981;67:1630.

4 Yamada K, Miyahara Y, Hamaguchi K,

et al Immunohistochemical study ofhuman advanced glycosylation end-products (AGE) in chronic renal failure

Clin Nephrol 1994;42:354.

5 Thornalley PJ Advanced glycation end

products in renal failure J Ren Nutr.

2006;16:178

6 Vitek MP, Bhattacharya K, Glendening

JM, et al Advanced glycation end ucts contribute to amyloidosis in

prod-Alzheimer disease Proc Natl Acad Sci

U S A 1994;91:4766.

7 Yan SD, Chen X, Schmidt AM, et al.Glycated tau protein in Alzheimerdisease: a mechanism for induction of

oxidant stress Proc Natl Acad Sci U S A.

1994;91:7787

8 Takeuchi M, Kikuchi S, Sasaki N, et al.Involvement of advanced glycation end-products (AGEs) in Alzheimer’s disease

Curr Alzheimer Res 2004;1:39.

9 Dyer DG, Dunn JA, Thorpe SR, et al.Accumulation of Maillard reaction prod-ucts in skin collagen in diabetes and

aging J Clin Invest 1993;91:2463.

10 Verzijl N, DeGroot J, Odehinkel E, et al.Age-related accumulation of Maillardreaction products in human articular car-

tilage collagen Biochem J 2000;350: 381.

11 Mizutari K, Ono T, Ikeda K, et al enhanced modification of human skinelastin in actinic elastosis by N(epsilon)-(carboxymethyl)lysine, one of the gly-coxidation products of the Maillard reac-

Photo-tion J Invest Dermatol 1997;108:797.

12 Tomasek JJ, Haaksma CJ, Eddy RJ, et al.Fibroblast contraction occurs on release

of tension in attached collagen lattices:dependency on an organized actin

cytoskeleton and serum Anat Rec 1992;

232:359

13 Howard EW, Benton R, Ahern-Moore J,

et al Cellular contraction of collagen tices is inhibited by nonenzymatic glyca-

lat-tion Exp Cell Res 1996;228:132.

14 Rittie L, Berton A, Monboisse JC, et al.Decreased contraction of glycated collagenlattices coincides with impaired matrix

metalloproteinase production Biochem Biophys Res Commun 1999;264:488.

15 Wondrak GT, Roberts MJ, Jacobson MK,

et al Photosensitized growth inhibition ofcultured human skin cells: mechanismand suppression of oxidative stress from

solar irradiation of glycated proteins J Invest Dermatol 2002;119:489.

16 Nelson B, Majmudar G, Griffiths C,

et al Clinical improvement followingdermabrasion of photoaged skin corre-

lates with synthesis of collagen I Arch Derm 1994;130:1136.

17 Oikarinen A The aging of skin:

chronoaging versus photoaging dermatol Photomed 1990;7:3.

Photo-18 Craven NM, Watson RE, Jones CJ, et al.Clinical features of photodamagedhuman skin are associated with a reduc-

tion in collagen VII Br J Derm 1997;137:

344

19 Vrhovski B, Weiss AS Biochemistry of

tropoelastin Eur J Biochem 1998;258:1.

20 Robb BW, Wachi H, Schaub T, et al.

Characterization of an in vitro model of

elastic fiber assembly Mol Biol Cell 1999;

10:3595

21 Kielty CM, Sherratt MJ, Shuttleworth

CA Elastic fibres J Cell Sci 2002;115:

2817

22 Amadeu TP, Braune AS, Porto LC, et al

Fibrillin-1 and elastin are differentially

expressed in hypertrophic scars and

keloids Wound Repair Regen 2004;12:

169

23 Mithieux SM, Weiss AS Elastin Adv

Protein Chem 2005;70:437.

24 Li B, Daggett V Molecular basis for the

extensibility of elastin J Muscle Res Cell

Motil 2002;23:561.

25 Rosenbloom J, Abrams WR, Mecham R

Extracellular matrix 4: the elastic fiber

FASEB J 1993;7:1208.

26 Smith-Mungo LI, Kagan HM Lysyl

oxi-dase: properties, regulation and multiple

functions in biology Matrix Biol.

1998;16:387

27 Starcher BC Determination of the elastin

content of tissues by measuring

desmo-sine and isodesmodesmo-sine Anal Biochem.

1977;79:11

28 Wight TN Versican: a versatile

extracel-lular matrix proteoglycan in cell biology

Curr Opin Cell Biol 2002;14:617.

29 Suwabe HA, Serizawa H, Kajiwara M, et

al Degenerative processes of elastic

fibers in sun-protected and sun-exposed

skin: immunoelectron microscopic

observation of elastin, fibrillin-1,

amy-loid P component, lysozyme and

alpha1-antitrypsin Pathol Int 1999;49: 391.

30 Park PW, Biedermann K, Mecham L,

et al Lysozyme binds to elastin and

pro-tects elastin from elastase-mediated

degra-dation J Invest Dermatol 1996;106:1075.

31 Seite S, Zucchi H, Septier D, et al Elastin

changes during chronological and

photo-ageing: the important role of lysozyme J

Eur Acad Dermatol Venereol 2006;20:980.

32 Escoffier C, de Rigal J, Rochefort A,

et al Age-related mechanical properties

of human skin: an in vivo study J Invest

Dermatol 1989;93:353.

33 Boente MC, Winik BC, Asial RA

Wrinkly skin syndrome: ultrastructural

alterations of the elastic fibers Pediatr

Dermatol 1999;16:113.

34 El-Domyati M, Attia S, Saleh F, et al

Intrinsic aging vs photoaging: a

compar-ative histopathological,

immunohisto-chemical, and ultrastructural study of

skin Exp Dermatol 2002;11:398.

35 Mithieux SM, Wise SG, Raftery MJ, et al Amodel two-component system for study-ing the architecture of elastin assembly in

vitro J Struct Biol 2005;149:282.

36 Wu W, Graves LM, Jaspers I, et al

Activation of the EGF receptor signalingpathway in human airway epithelial cells

exposed to metals Am J Physiol 1999;

277:L924

37 Samet JM, Silbajoris R, Wu W, et al

Tyrosine phosphatases as targets inmetal-induced signaling in human air-

way epithelial cells Am J Respir Cell Mol Biol 1999;21:357.

38 Samet JM, Graves LM, Quay J, et al

Activation of MAPKs in humanbronchial epithelial cells exposed to met-

als Am J Physiol 1998;275:L551.

39 Baumann L, Weinkle S Improving

elas-ticity: the science of aging skin Cosm Dermatol 2007;20:168.

40 Uitto J, Chu M, Gallo R, Eisen A

Collagen, elastic fibers, and extracellularmatrix of the dermis In: Wolff K,Goldsmith L, Katz S, Gilchrest B, Paller

A, Leffell D, eds Fitzpatrick’s Dermatology

in General Medicine 7th ed New York,

NY: McGraw-Hill; 2008:539

41 Ghersetich I, Lotti T, Campanile G, et al

Hyaluronic acid in cutaneous intrinsic

aging Int J Dermatol 1994;33:119.

42 Bourguignon LY, Ramez M, Gilad E, et al

Hyaluronan-CD44 interaction stimulateskeratinocyte differentiation, lamellarbody formation/secretion, and perme-

ability barrier homeostasis J Invest Dermatol 2006;126:1356.

43 Aruffo A, Stamenkovic I, Melnick M, et al

CD44 is the principal cell surface receptor

for hyaluronate Cell 1990;61:1303.

44 Culty M, Miyake K, Kincade PW, et al

The hyaluronate receptor is a member ofthe CD44 (H-CAM) family of cell surface

glycoproteins J Cell Biol 1990;111:2765.

45 Underhill C CD44: the hyaluronan

receptor J Cell Sci 1992;103:293.

46 Scott JE Proteodermatan and atan sulfate (decorin, lumican/

proteoker-fibromodulin) proteins are horseshoeshaped Implications for their interac-

tions with collagen Biochemistry 1996;35:

8795

47 Danielson KG, Baribault H, Holmes DF,

et al Targeted disruption of decorin leads

to abnormal collagen fibril morphology

and skin fragility J Cell Biol 1997; 136:

729

48 Schmidt G, Robenek H, Harrach B, et al

Interaction of small dermatan sulfate

proteoglycan from fibroblasts with

fibronectin J Cell Biol 1987;104:1683.

49 Dugan TA, Yang VW, McQuillan DJ, et

al Decorin binds fibrinogen in a

Zn2+-dependent interaction J Biol Chem 2003;

278:13655

50 De Luca A, Santra M, Baldi A, et al

Decorin-induced growth suppression isassociated with up-regulation of p21, aninhibitor of cyclin-dependent kinases

J Biol Chem 1996;271:18961.

51 Carrino DA, Onnerfjord P, Sandy JD,

et al Age-related changes in the cans of human skin Specific cleavage ofdecorin to yield a major catabolic fragment

proteogly-in adult skproteogly-in J Biol Chem 2003; 278:17566.

52 Seltzer JL, Eisen AZ, Bauer EA, et al

Cleavage of type VII collagen by tial collagenase and type IV collagenase

intersti-(gelatinase) derived from human skin J Biol Chem 1989;264:3822.

53 Ravanti L, Hakkinen L, Larjava H, et al

Transforming growth factor-beta inducescollagenase-3 expression by human gin-gival fibroblasts via p38 mitogen-acti-

vated protein kinase J Biol Chem 1999;

274:37292

54 Toriseva MJ, Ala-aho R, Karvinen J, et al

Collagenase-3 (MMP-13) enhances eling of three-dimensional collagen andpromotes survival of human skin fibrob-

remod-lasts J Invest Dermatol 2006; 127:49.

55 Karelina TV, Goldberg GI, Eisen AZ

Matrilysin (PUMP) correlates with mal invasion during appendageal develop-

der-ment and cutaneous neoplasia J Invest Dermatol 1994;103:482.

56 Reynolds JJ, Hembry RM, Meikle MC

Connective tissue degradation in healthand periodontal disease and the roles ofmatrix metalloproteinases and their nat-

ural inhibitors Adv Dent Res 1994; 8:312.

57 Wojtowicz-Praga SM, Dickson RB,Hawkins MJ Matrix metalloproteinase

inhibitors Invest New Drugs 1997;15:61.

58 Clark SD, Kobayashi DK, Welgus HG

Regulation of the expression of tissueinhibitor of metalloproteinases and colla-genase by retinoids and glucocorticoids

in human fibroblasts J Clin Invest 1987;

80:1280

59 Considine RV, Sinha MK, Heiman ML, et

al Serum immunoreactive-leptin trations in normal-weight and obese

concen-humans N Engl J Med 1996; 334:292.

60 Pelleymounter MA, Cullen MJ, Baker

MB, et al Effects of the obese gene uct on body weight regulation in ob/ob

prod-mice Science 1995;269:540.

Subcutaneous tissue, or the

hypoder-mis, is one of the largest tissues in the

human body The major components of

this layer are adipocytes, fibrous tissue,

and blood vessels It is estimated that

this layer represents 9% to 18% of

body weight in normal-weight men

and 14% to 20% in women of normal

weight.1 Fat mass can increase up to

four fold in severe obesity, which may

represent 60% to 70% of total body

weight.2 Although gaining fat in the

body is undesirable for many, losing fat

in the face has cosmetic implications as

well Adipose tissue gain and loss and

volume changes contribute to the aged

appearance of the face and body This

chapter will review the importance of

the subcutaneous tissue and its various

functions

The subcutaneous tissue is usually not

given as much attention as the dermis

and epidermis because pathology at

superficial layers is easier to detect or

diagnose by a shave or small punch

biopsy Subcutaneous tissue usually

must have an extensive defect before it is

noticed, and in order to biopsy this area,

an incision or large punch biopsy (e.g., 6mm) is required During histologic tissueprocessing of biopsy tissue, the triglyc-eride component, which is the majorcomponent of adipocytes, is removed byalcohol and xylol For this reason, subcu-taneous tissue has long been ignored

However, with advances in diagnosticmethods and new treatments, muchmore has been learned about the subcu-taneous layer (Box 3-1) It is importantfor dermatologists and cosmetically ori-ented physicians to pay close attention

to this tissue because it has many roles

in cosmetic dermatology and generalappearance

ADIPOCYTES

In the past, adipocytes in adults wereconsidered stable, nondividing cells,like other mature cells However, recentdata reveal that adipocytes in adultshave the potential to increase in num-ber or revert back into stem cells Thesestem calls can differentiate to other tis-sue, such as fibroblasts, collagen, elasticfibers, and hematopoietic stromalcells.4Fat cells are derived from undif-ferentiated fibroblast-like mesenchy-mal cells Under certain conditions,these mesenchymal cells give rise toadipose cells Adipose tissue is classi-fied into two morphologic types: whiteand brown adipose tissue White adi-pose tissue normally appears yellowbecause of the accumulation of

␤-carotene, while brown adipose tissuewas named by its appearance derivedfrom its rich vascular supply Maturewhite adipocytes are called roundunilocular fat cells They have a copi-ous supply of cytoplasm, which con-tains a single, large lipid droplet thatpushes the nucleus to the border of thecell Brown adipocytes, called polygo-nal multilocular fat cells, have multiplesmall lipid droplets

When observed with an electronmicroscope, brown adipocytes demon-strably contain much more mitochon-dria and smooth endoplasmic reticulumthan white adipocytes In humans,brown adipocytes play a major role innonshivering thermogenesis Brownadipose tissue can be found during thefetal and early neonatal phases, whilethe majority of adipocytes in adults arewhite adipocytes Some scientists havetried to elucidate the mechanism of

how brown adipocytes convert fat toenergy, in order to find a way to get rid

of body fat by stimulating brown fat toreturn.5

In the past, it was believed that thenumber of adipocytes, which develop dur-ing the 30th week of gestation, does notincrease after birth However, newerevidence has shown that adipocytes canincrease in number and size in certainsituations or environments In general,adipocytes are thought to have two peri-ods of growth The first period occurs fromthe embryonic stage to 18 months afterbirth, and the second period occurs duringpuberty Changes in adipose tissue massare determined by both size and number

of adipocytes.6An increase in size trophy)7usually precedes an increase in thenumber of cells (hyperplasia).8

(hyper-ANATOMY

Subcutaneous tissue, also known as thesuperficial fascia, is divided into threelayers: apical, mantle, and the deeperlayer The apical layer is located beneaththe reticular dermis surrounding sweatglands and hair follicles It containsblood vessels, lymphatic vessels, andnerves It is also rich in carotenoids andtends to be yellow in gross appearance.Damage to this layer can lead tohematoma, seroma, paresthesia, and fullthickness skin necrosis The mantlelayer is composed of columnar-shapedadipocytes and is absent from eyelids,nail beds, bridge of the nose, and penis

It contributes to the ability to resisttrauma by distributing pressure across alarge field The deeper layer is locatedunder the mantle layer and its shapedepends on gender, genetics, anatomicarea, and diet Adipocytes in this layerare arranged in lobules between septa aswell as between fibrous planes Thislayer is suitable for liposuction Verticalextrusion and/or expansion of this layercan cause cellulite (Fig 3-1)

Subcutaneous tissue is found out the body except for the eyelids, prox-imal nail fold, penis, scrotum, and theentire auricle of the external ear exceptthe lobule In particular, subcutaneous tis-sue is prominent at the temples, cheeks,chin, nose, abdomen, buttocks, andthighs, as well as infraorbital areas andvery thick at the palms and soles Age,gender, and lifestyle choices determinethe distribution and density of adiposedeposits For example, in newborns

through-BOX 3-1 Functions of the

Subcutaneous Tissue

• The largest repository of energy in the body

• Stores fat-soluble vitamins (A, D, E, K),

including their derivatives such as retinoic

acids

• Helps to shape the surface of the body, and

form fat pads that act as shock absorbers

• Helps distribute force or stress to mitigate

damage to underlying organs

• Protects against physical injury from

exces-sive heat, cold, or mechanical factors

• Fills up spaces between other tissues and

helps to keep organs in place

• Involved in thermoregulation by insulating

the body from heat loss

• Functions as a secretory organ that

releases many cytokines

• Plays a role in regulating androgen and

estrogen levels.3

adipose tissue has a uniform thickness

throughout the body, while in adults the

tissue tends to disappear from some areas

of the body and increase in other areas

under the influence of hormones

Adipose tissue is distributed

differ-ently in men and women Men tend to

accumulate fat in an android or upper

abdominal body distribution (apple

shape) In contrast, women tend to

accu-mulate fat in a gynoid or lower body

dis-tribution that predominantly involves

the lower abdomen, hips, and thighs

(pear shape) (Fig 3-2)

In the elderly, hyper- or

hypoaccumu-lation of fat occurs in various areas For

example, infraorbital eye bags, buccal

fat pad accumulation (chipmunk

fea-ture), wattle of the anterior neck, loose

skin and fat accumulation in the

pos-terior arm, increase in breast size of

males, and an increase in abdomen,

but-tock and thigh fat are common

Subcutaneous fat can also be lost in the

malar fat pad during the aging process

This can lead to prominent flattening ofthe cheek/buccal area, sagging of theskin of the face, and prominent deepwrinkles, such as nasolabial folds andmarionette lines or jowls

Role of Lipids in the Human BodyLipids can be found in different areas

of the skin, not only in subcutaneoustissue Lipids are constituents of phos-pholipids in the myelin sheaths of nervetissue and cell membranes (lipid bilay-ers), play an important role in the skinbarrier of the epidermis, and are essen-tial for the production of steroids Theyare water-insoluble organic moleculesbecause they are nonpolar However,after esterification (a condensation reac-tion between acid and alcohol), they aremore water-soluble than their parentforms

The most common lipids in the dietare triglycerides (triacylglycerol), whichare composed of a glycerol subunitattached to three fatty acids (Fig 3-3).Lipids can be saturated or unsaturated

Generally, an unsaturated fatty acid tains at least one double bond while sat-urated fatty acids do not Unsaturatedfatty acids provide slightly less energyduring metabolism than saturated fattyacids with the same number of carbonatoms In addition, saturated fatty acidsare usually solids at room temperature

con-Apical layer Dermis

Mantle layer

Deeper layer Muscle

Epidermis

쑿 FIGURE 3-1 The three layers of the subcutaneous tissue

쑿 FIGURE 3-2 Android (apple) and gynoid (pear) fat distribution patterns in men and women

Above waist

Belowwaist

During digestion, fats in the food are

broken down in the duodenum by

pan-creatic lipase into free fatty acids and

glycerol The intestinal epithelium

absorbs these substances and reesterifies

them in the smooth endoplasmic

reticu-lum into triglycerides These

triglyc-erides are then absorbed into the

circula-tion and lymphatic system When they

arrive in the circulation they are

com-bined with apoprotein to form a

lipoprotein, which is called a

chylomi-cron Chylomicrons are exposed to

lipoprotein lipase, which is synthesized

by adipocytes and stored at the surface

of endothelial cells Lipoprotein lipase

cleaves the chylomicron into free fatty

acids and glycerol again These free fatty

acids pass into adipocytes and combine

with intracellular glycerol phosphate to

form triglycerides and are stored for

energy

Adipose tissue can also convert

exces-sive glucose and amino acids into fatty

acids when stimulated by insulin This

explains why people who consume a

low-fat diet or fat-free diet still gain

weight if they do not reduce the total

amount of calories they consume or have

a high-carbohydrate diet High blood

glu-cose can stimulate insulin synthesis and

insulin can increase synthesis of

lipopro-tein lipase from adipocytes to help

absorb triglycerides into the cells People

who want to control their weight should

avoid any foods that have the ability to

stimulate insulin production Individuals

with type II diabetes have high levels of

insulin; therefore, they have a higher risk

of becoming overweight or obese than

nondiabetic individuals

Lipoproteins

There are many different types of

lipoproteins Low-density lipoprotein

(LDL) brings fat to the cells, while density lipoprotein (HDL) brings fatfrom the circulation to the liver forexcretion in bile High levels of LDL areassociated with a high incidence of coro-nary artery disease and atherosclerosis

high-HDL, or the “good lipoprotein,” can beelevated with exercise

Lipid SynthesisTriglycerides are derived from foods orsynthesized from excessive glucose oramino acids In humans, triglyceridesare stored mainly in adipose tissue,which constitutes the body’s reserveenergy source However, excessive con-sumption of calories can lead to the syn-thesis and accumulation of more fat insubcutaneous tissues Unfortunately, fatstorage is unlimited in the subcutaneoustissue, unlike glycogen storage in theliver and muscle Therefore, excessivefat accumulation will not only change aperson’s cosmetic appearance but alsoincrease their risk for osteoarthritis, dia-betes, hypertension, as well as otherdiseases

VOLUME EXCESS Obesity

Obesity is defined as unhealthy, sive fat mass There are many regimens,products, and exercise programs avail-able; however, there is still a rising pan-demic in the United States9 when compared to the past.10 Obesity andhyperlipidemia are major risk factorsand can lead to significant morbidityand mortality

exces-PATHOPHYSIOLOGY Obesity results fromboth environmental and genetic factors

Two genes that are known to havedirect effects on obesity are the leptin

(ob gene)11,12 and proopiomelanocortin(POMC) genes.13 These genes can con-trol eating behavior and satiety Defects

in these genes can cause severe obesity

However, almost all people gain weightwhen they get older because of dimin-ished physical activity and aging-induced changes in the chemical activity

A normal BMI does not necessarilymean that a person has a “perfect”shape Many people with a BMI lessthan 25 have fat accumulation in somearea, such as the abdomen or buttocks

IMPACT OF OBESITY ON THE SKIN Obesity

is responsible for changes in skin barrierfunction by significantly increasingtransepidermal water loss, which canlead to dry skin and impaired barrierfunction.14Hyperfunction of sebaceousglands due to high levels of androgen-like hormone or insulin-like growth fac-tor hormone can aggravate severity ofacne and hirsutism;15,16 delay woundhealing and collagen deposits in thewound healing process;17 and disturbboth blood and lymphatic circulation,which can cause angiopathy18 andlymphedema, potentially precipitatingchronic leg ulcers.19 Rapid weight gaincan cause striae distensae (stretch marks),which are challenging to treat.20–23 Inaddition, in intertriginous areas such asthe underarms, breasts, and groin, mois-ture accumulation can lead to candidainfection (intertrigo)

It is widely known that obesityincreases the risk of coronary heart dis-ease, hypertension, hyperlipidemia,osteoarthritis, and diabetes It is alsoknown to be directly related to increasedrisk of sleep apnea; breast, endometrial,and colon cancer; gallbladder disease;musculoskeletal disorders; severe pan-creatitis and diverticulitis; infertility;

쑿 FIGURE 3-3 Triglyceride chemical structure

Body Mass Index (BMI) Categories

Less than 18.5 Underweight

25.0–29.9 Overweight30.0 and greater Obese

urinary incontinence; and idiopathic

intracranial hypertension Additionally,

obesity has indirectly been related to

anxiety, impaired social interaction, and

depression

Obesity is implicated in a wide

spec-trum of dermatologic diseases, including

acanthosis nigricans, acrochordons,

keratosis pilaris, hyperandrogenism and

hirsutism, striae distensae, adiposis

dolorosa, fat redistribution, lymphedema,

chronic venous insufficiency, plantar

hyperkeratosis, cellulitis, skin infections,

hidradenitis suppurativa, psoriasis,

in-sulin resistance syndrome, and

topha-ceous gout.24

To determine the severity of a

per-son’s obesity, BMI can be used In fact,

the more overweight a person is the

higher the mortality rate (Table 3-2)

TREATMENT Dietary control is very

important in the treatment of obesity

Patients must understand the principle of

energy intake and expenditure Weight

reduction is usually not accomplished

without exercise However, exercise

alone will usually produce little long-term

benefit The combination of exercise with

dietary therapy can prevent weight being

regained In addition, regular exercise (30

min daily) will improve general health

The best results are obtained with

educa-tion in well-motivated patients Constant

supervision by healthcare professionals

and by family or friends can help to

encourage compliance

PREVENTION Prevention of obesity is key

because once fat is gained and

main-tained over time, it is more difficult to

lose A high-fat diet can induce an

increase in the number of adipocytes.25,26

A low-fat and complex carbohydrate

diet is recommended to reduce body

weight There is an important difference

between preventing weight gain and

producing weight loss To prevent

weight gain, portion size and

composi-tion of food are controlled For weight

loss, restriction of calorie intake is the

most effective treatment

LiposuctionOverweight patients frequently consultplastic surgeons and dermatologists forliposuction.27–29 Liposuction is one ofthe most commonly performed cos-metic surgery procedures in the UnitedStates.30 Physicians must inform theirpatients that liposuction is a modalityfor improving body contour and not fortreatment of generalized obesity Inaddition, excess fatty tissue will return ifregular exercise and diet control are notmaintained

Large-volume liposuction may decreaseweight and fat mass; however, there iscontroversy regarding whether or not itsignificantly improves insulin resistanceand other obesity-associated metabolicabnormalities.31–33 The most commonareas treated are the neck, jowls, arms,abdomen, thighs, knees, and ankles

Other conditions that can be improved byliposuction include lipoma, gynecomastia,buffalo hump, and axillary hyperhidrosis

There are strict guidelines from boththe American Society of DermatologicSurgery (ASDS) and the AmericanAcademy of Cosmetic Surgery (AACS)

on the volume restrictions during tion Tumescent liposuction is consideredthe safest method for performing the pro-

liposuc-cedure This technique relies on the tration of dilute anesthesia based onbody weight, and the removal of limitedamounts of adipose tissue during eachoperation Tumescent anesthesia consists

infil-of very dilute lidocaine and epinephrinesolutions ranging from 0.05% to 0.1% oflidocaine with 1:1,000,000 epinephrineand sodium bicarbonate The total safeconcentration of lidocaine that can beused in this formula is 35 to 55 mg/kgbased on patient weight and any coexist-ing medical conditions Table 3-3is a syn-opsis of the 2006 ASDS guidelines of carefor tumescent liposuction.28

LIPOSUCTION COMPLICATIONS While therehave been reports of mortality with gen-eral anesthesia, there have been noreports of death with tumescent anes-thesia alone When practitioners adhere

to the AACS and ASDS guidelines,tumescent liposuction is a safe outpa-tient procedure Common complicationsare bruising, swelling, localized pares-thesia, and irritated incision sites afterliposuction Other complications includehematomas, seromas, and infection

There are serious complications that thesurgeon must be aware of, however,such as the development of a fat embolus,

heal-Explanation: procedure, risk and benefits, expected outcomes, needing a touch-up procedurePhysical examination: assessment of both general physical health and specific sites amenable toliposuction

Laboratory studies: may or may not be necessary for a given patient depending on the type andextent of anticipated liposuction procedure

Some surgeons may wish to obtain CBC, PT, PTT, LFT, UA, pregnancy test, screening for HIV,hepatitis B, and hepatitis C

30.0–35.0 Moderate obesity (Class I)

35.0–40.0 Severe obesity (Class II)

ⱖ40.0 Morbid obesity (Class III)

visceral perforation, pneumothorax,

deep vein thrombosis, congestive heart

failure, and lidocaine toxicity

Fortu-nately, these complications are very rare

during tumescent liposuction The

rela-tive skills and experience level of the

operating physician represent important

contributing factors to the incidence of

adverse events from liposuction

Careful patient selection is the key to

a successful outcome Younger patients,

those with good skin tone, and those

close to their ideal weight tend to be the

best candidates Poor patient selection

may lead to the development of rippling

or poor skin contraction

VOLUME LOSS

Normal Aging

The aging face shows characteristic

changes, many of which were once

solely attributed to the effects of gravity

on skin, muscle, and fat It is for this

rea-son that the main approach to the aging

face was to lift and reposition “ptotic”

tissue However, we now recognize that

there are complex changes occurring in

which volume loss is a significant

con-tributor These changes include muscle

atrophy, bone resorption, and fat

atro-phy There are some well-designed

stud-ies that look at the bony changes of the

face and the change in the malar fat pad

with time The results of these studies

show that the lower midfacial skeleton

becomes retrusive with age relative to

the upper face.34Study authors speculate

that the skeletal remodeling of the

ante-rior maxillary wall allows soft tissues to

be repositioned downward thereby

accentuating the nasojugal fold and malar

mound In a different study, some of the

same authors describe the increasing

incidence of a “negative vector face” as

one ages.35A “negative-vector” patient is

one in whom the bulk of the malar fat

pads lies posterior to a line drawn straight

down from the cornea to the orbital rim

With this change, the lower eyelid fat

pads appear more prominent but are not

truly hypertrophied

In a magnetic resonance imaging

(MRI) study by Gosain et al the

deep-ening appearance of the nasolabial fold

with age seems to be a combination of

ptosis and fat/skin hypertrophy.36

They found a difference in the

redistri-bution of fat within the malar fat pad

by age, with older women exhibiting a

relatively increased thickness of the

midportion of the malar fat pad and

overlying skin compared to younger

females More interestingly, they did

not find an increase in the length orprojection of the levator labii superi-oris muscle between young and oldsubjects

A more recent cadaveric study sidered the fat distribution of the face.37The authors found distinct facial fatcompartments and subdivisions withinthese areas The malar fat pad is com-posed of three separate compartments:

con-medial, middle, and lateral temporal–

cheek fat The nasolabial fold was formly a discrete unit with distinctanatomic boundaries and little variation

uni-in size from one cadaver to the next

The forehead also consisted of threeanatomic units: central, middle, and lat-eral temporal–cheek fat Orbital fat isnoted in three compartments deter-mined by septal borders However, thesuperior orbital fat did not connect tothe inferior orbital fat The jowl fat is themost inferior of the subcutaneous fatcompartments and was found to beclosely associated with the depressoranguli oris muscle

One of the easiest ways for a metic surgeon to begin to understandthese changes in patients is by evaluat-ing photographs of the patient both inyouth and at the time of presentation for

cos-a consultcos-ation This ccos-an be seen in theworks of surgeons that have performed

a great deal of volume restoration eries over the years.38,39

surg-Autologous Fat TransplantationFat transplantation is the reinjection ofaspirated adipocytes into an area that haslost volume as a result of aging, trauma,

or after an inflammatory process

Autologous fat transplantation offers tain advantages over other fillers, mostnotably that it is an autograft with thesame human leukocyte antigen thereforethere is no allergic reaction or rejection viaimmune processes Indications for fattransfer are volume loss anywhere in theface such as the nasolabial folds, lips,under eye hollow and tear trough defor-mity, submalar depressions, zygomaenhancement, chin augmentation, malaraugmentation, congenital and traumaticdefects, surgical defects, wide-based acnescarring, idiopathic lipodystrophy, facialhemiatrophy, rejuvenation of hands, bodycontour defects, depressions caused byliposuction or trauma, etc.35,40,41This tech-nique can be divided into two processes:

cer-harvesting fat from the donor site, andreinjecting it into the recipient sites Themedical literature is replete with differenttechniques by which fat is harvested, pre-pared, and infiltrated into the tissue The

variation in these techniques probablyaccounts for why some surgeons find suc-cess with this modality and others do notachieve long-lasting results.42

Factors that influence survival of fatafter injection include the anatomicsites of harvesting and placement, thedegree of mobility in the recipient area,the vascularity of the recipient tissue,and the overall health and age of thepatient.43

We found that fat aspirated from thelateral thigh lasts longer than fat takenfrom the abdomen Even during har-vesting, one will find a noticeable differ-ence in the quality of the fat betweenthe two areas The fat of the upperarms, inner thighs, and abdomen tends

to be softer and contain less connectivetissue Fat from the lateral thigh tends to

be more dense and fibrous more, placement of the fat into the tis-sues is critical to ensure viability.Adipocytes require a healthy and vascu-lar bed in which to engraft For this rea-son, fat must be placed in small parcelsand in multiple layers, including in andunder muscles The less movement inthe recipient site, the more that fat sur-vives Therefore, the malar and infraor-bital areas do well while the nasolabialfolds and lips require touch-ups toachieve the desired effect

Further-ComplicationsComplications are rare but includeswelling, ecchymosis, hematoma, andinfection Known cases of blindness andcerebral strokes resulting after fat trans-plantation at the glabella44–46 andparanasal areas47 have been noted Inthese cases, a sharp needle or largesyringe were used to inject the fat Byusing only blunt cannulas and 1 mLsyringes, this complication has not beenreported in the literature

Fat Cells as a Source for Stem Cells and Collagen Stimulation

There is evidence that supports the ity of adipocytes for a potential stem cellrole as well as collagen stimulation First,

util-it is known that even after puberty thehuman body can increase the numberand size of fat cells Second, subcuta-neous tissue contains not only adipocytesbut also fibrous tissue and blood vessels.These tissues are active cells and can pro-liferate when there is an increase in thesize of subcutaneous tissue.48 In addi-tion, there is evidence demonstratingthat aspirated fluid from liposuctioncontains cells that can differentiate into

In contrast to harvesting stem cells

from the bone marrow, harvesting

adipocytes from subcutaneous tissue is

much easier and complications at the

donor site can easily be visualized In

addition, adipocytes can be harvested

from many areas and multiple times

Harvesting stem cells from fat will be an

interesting topic in the future for tissue

reengineering

One intriguing observation noted

both by the senior author (Suzan Obagi)

and in her communications with other

surgeons that frequently perform fat

transfers is that the skin of patients

con-tinues to improve and show a reduction

in rhytides and aging symptoms over

time after autologous fat augmentation

This improvement is not seen in patients

receiving synthetic fillers This leads one

to question whether the stems cells play

a beneficial role in the skin

MISCELLANEOUS ADIPOSE

CONDITIONS

Cellulite

Cellulite occurs mainly in postadolescent

women at the buttocks, abdomen, and

thighs Risk factors include lack of

exer-cise; being female, overweight/obese,

elderly, and having excess hormones and

poor lymphatic drainage It is

character-ized by dimpling and nodularity of the

skin, where the skin looks and feels

irreg-ular, almost like an orange peel (Box 3-2)

Cellulite largely results from changes in

the dermis rather than changes in

subcu-taneous tissue Although cellulite is

fre-quently found in healthy, nonobese

patients, it is aggravated by obesity.53–55

PATHOGENESIS The pathophysiology of

cellulite is not completely understood,

but many theories for the pathogenesis

of cellulite have been postulated One

of the most important factors is theanatomy of this condition There aremorphologic differences of the fat lobesbetween males and females, whichmay explain the large frequency of cel-lulite in females and rare occurrence inmales Cellulite is thought to be formedfrom the breakdown of collagen in thereticular dermis, which leads to weak-ness in the dermis and herniation ofsubcutaneous fat into the dermis, aswell as compression of the microcircu-lation of the dermis Congestion offluid and protein in the dermis isbelieved to lead to formation of fibroticbands between the subcutaneous tissueand dermis resulting in retraction, dim-pling, or nodularity

TREATMENT This condition is considerednormal in postadolescent women and isinnocuous Many people feel that it iscosmetically unappealing both visuallyand tactilely This condition may notimprove by weight reduction; however,weight control may improve the appear-ance of cellulite in some patients

There are many modalities that pose to treat this condition by stimula-tion of collagen production in the der-mis, such as infrared, diode laser, andradiofrequency.56 These methods arenew and the efficacy is unknown at thispoint The most effective method totreat cellulite is to improve blood andlymphatic circulation and drainage ofwaste products with massage; however,the effects are temporary Efforts toincrease exercise can stimulate lymphflow and decrease fluid accumulation Adecrease in fat mass can also occur bylipolysis, such as with exercise and diet,liposuction, ultrasound-assisted lipolysisand mesotherapy In severe dimplinglesions, minimally invasive proceduressuch as subcision can lead to improve-ment.57Many topical products claim totreat cellulite The most effective ofthese contain caffeine and theophylline,which dehydrate the fat cells, temporar-ily shrinking them Despite the manycellulite treatments on the market, nonehave been shown to be convincinglyeffective for more than 24 hours

pro-LipodystrophyLipodystrophy is a term describingabnormality with increasing subcuta-neous fat (lipohypertrophy) or decreas-ing subcutaneous fat (lipoatrophy) Itcan be congenital or acquired, and gen-eralized, partial, or localized The twomost common forms of lipodystrophyinclude lipodystrophy due to the aging

process and HIV-associated phy Aging skin is characterized by aloss of subcutaneous tissue and laxity ofthe anterior supporting dermis Adecrease in supporting bone mass andloss of muscle tone can cause patients tolook older In HIV-associated lipodystro-phy, most patients are treated withhighly active antiretroviral therapy(HAART) This combination therapycontains nonnucleoside reverse tran-scriptase inhibitors that can hinder DNApolymerase leading to adipocyte apop-tosis

lipodystro-Common areas affected by trophy are the cheeks, forehead, tempo-ral, infraorbital, and jowl fat compart-ments Losing fat in some areas canaffect the general appearance in otherareas For example, decreasing subcuta-neous fat in the malar cheeks can cause aprominent nasolabial fold, or decreasingjowl fat can cause prominent marionettelines and jowls Treatment can be per-formed by using synthetic filler agents

lipodys-or autologous fat transplantation

However, many HIV patients lack quate fat for aspiration and transplanta-tion or their fat is very fibrous, whichmakes harvesting difficult Polylacticacid (Sculptra™, Dermik Laboratories,Berwyn, Pennsylvania), FDA-approvedfor the treatment of facial lipoatrophy inHIV patients, is a very useful productthat works by stimulating collagen syn-thesis The more recent use of higherdilutions and longer reconstitution timeshas led to a decrease in the formation ofgranulomas after injection of this agent(see Chapter 25)

ade-FUTURE DIRECTIONS

Understanding the biology of adipocytes

is important to the progress of lipolysistechniques and the possible usage ofadipocytes as stem cells In addition,various methods for fat removal arebeing investigated, including drugs

or chemicals that can stimulate sis (e.g., phosphatedylcholine, isopro-terenal, theophylline, aminophylline,caffeine, carnitine, carbon dioxide, andherbal extracts) and device-assistedliposuction such as ultrasound (to burstfat cells) or 1064 nm Nd:YAG laser (tomelt the fat cell) These new methodsneed to be evaluated for safety andefficacy

• At Stage 0, the skin’s surface is not altered

• At Stage I, skin is smooth when the

indi-vidual is standing or lying down, but some

cellulite appears if the skin is pinched

• At Stage II, skin appears dimpled without

any pinching or manipulation

• At Stage III, skin appears both dimpled

and raised in some areas

aPersonal communication with Doris Hexsel,

Porto Allegre, Brazil

cosmetic dermatologist should pay

attention There are cosmetic concerns

related to both excess and loss of fat

for which the patient will seek

cos-metic intervention Advances in this

field will be centered on more directed

therapies of fat removal or disruption

in heavy patients and on stem cell

purification and injection in thinner

patients It is the role of the cosmetic

dermatologist to remain abreast of

these changes Furthermore, cosmetic

dermatologists and surgeons should

take an active role in counseling

patients on proper nutrition and

weight management from both

extremes (too thin or too heavy)

REFERENCES

1 Hausman DB, DiGirolamo M, Bartness

TJ, et al The biology of white adipocyte

proliferation Obes Rev 2001;2:239.

2 Avram MM, Avram AS, James WD

Subcutaneous fat in normal and diseased

states: 1 Introduction J Am Acad Dermatol.

2005;53:663

3 Bélanger C, Hould FS, Lebel S, et al

Omental and subcutaneous adipose

tis-sue steroid levels in obese men Steroids.

2006;71:674

4 Wang B, Han J, Gao Y, et al The

differen-tiation of rat adipose-derived stem cells

into OEC-like cells on collagen scaffolds

by co-culturing with OECs Neurosci Lett.

2007;421:191

5 Avram MM, Avram AS, James WD

Subcutaneous fat in normal and diseased

states 3 Adipogenesis: from stem cell to

fat cell J Am Acad Dermatol 2007;56:

472

6 Prins JB, O’Rahilly S Regulation of

adi-pose cell number in man Clin Sci.

1997;92:3

7 Faust IM, Miller HM Jr Hyperplastic

growth of adipose tissue in obesity In:

Angel A, Hollenberg CH, Roncari DAK,

eds The Adipocyte and Obesity: Cellular

and Molecular Mechanisms New York,

NY: Raven Press; 1983:41-51

8 Spiegelman BM, Flier JS Adipogenesis

and obesity: rounding out the big picture

Cell 1996;87:377

9 Manson JE, Bassuk SS Obesity in the

United States: a fresh look at its high toll

JAMA 2003;289:229.

10 Kuczmarski RJ, Flegal KM, Campbell

SM, et al Increasing prevalence of

over-weight among US adults The National

Health and Nutrition Examination

Surveys, 1960–1991 JAMA 1994;272:

205

11 Friedman JM, Halaas JL Leptin and the

regulation of body weight in mammals

Nature 1998;395:763.

12 Montague CT, Farooqi IS, Whitehead JP,

et al Congenital leptin deficiency is

asso-ciated with severe early-onset obesity in

humans Nature 1997;387:903.

13 Krude H, Biebermann H, Schnabel D,

et al Obesity due to

proopiomelano-cortin deficiency: three new cases and

treatment trials with thyroid hormone

and ACTH4–10 J Clin Endocrinol Metab.

2003;88:4633

14 Löffler H, Aramaki JU, Effendy I Theinfluence of body mass index on skinsusceptibility to sodium lauryl sulphate

Skin Res Technol 2002;8:19.

15 Deplewski D, Rosenfield RL Growthhormone and insulin-like growth factorshave different effects on sebaceous cell

growth and differentiation Endocrinology.

1999;140:4089

16 Cappel M, Mauger D, Thiboutot D

Correlation between serum levels ofinsulin-like growth factor 1, dehy-droepiandrosterone sulfate, and dihy-drotestosterone and acne lesion counts in

adult women Arch Dermatol 2005;141:

333

17 Goodson WH III, Hunt TK Wound gen accumulation in obese hyper-

colla-glycemic mice Diabetes 1986;35:491.

18 de Jongh RT, Serné EH, IJzerman RG,

et al Impaired microvascular function

in obesity: implications for associated microangiopathy, hyperten-

obesity-sion, and insulin resistance Circulation.

2004;109:2529

19 Garcia-Hidalgo L Dermatological

com-plications of obesity Am J Clin Dermatol.

2002;3:497

20 Pribanich S, Simpson FG, Held B, et al

Low-dose tretinoin does not improvestriae distensae: a double-blind, placebo-

controlled study Cutis 1994;54:121.

21 Hernández-Pérez E, Colombo-Charrier

E, Valencia-Ibiett E Intense pulsed light

in the treatment of striae distensae

Dermatol Surg 2002;28:1124.

22 Jiménez GP, Flores F, Berman B, et al

Treatment of striae rubra and striae albawith the 585-nm pulsed-dye laser

Dermatol Surg 2003;29:362.

23 Goldberg DJ, Sarradet D, Hussain M

308-nm Excimer laser treatment of

mature hypopigmented striae Dermatol Surg 2003;29:596.

24 Yosipovitch G, DeVore A, Dawn A

Obesity and the skin: skin physiology

and skin manifestations of obesity J Am Acad Dermatol 2007;56:901.

25 Lemonnier D Effect of age, sex, and sites

on the cellularity of the adipose tissue inmice and rats rendered obese by a high-

fat diet J Clin Invest 1972;51:2907.

26 Faust IM, Johnson PR, Stern JS, et al

Diet-induced adipocyte number increase

in adult rats: a new model of obesity Am

J Physiol 235:E279, 1978.

27 Coleman WP IV, Hendry SL II Principles

of liposuction Semin Cutan Med Surg.

29 Coleman WP III, Glogau RG, Klein JA,

et al Guidelines of care for liposuction

J Am Acad Dermatol 2001;45:438.

30 Dolsky RL State of the art in liposuction

Dermatol Surg 1997;23:1192.

31 Giese SY, Bulan EJ, Commons GW, et al

Improvements in cardiovascular risk file with large volume liposuction: a pilot

pro-study Plast Reconstr Surg 2001;108:

510

32 Klein S, Fontana L, Young VL, et al

Absence of an effect of liposuction oninsulin action and risk factors for coro-

nary heart disease N Engl J Med.

2004;350:2549

33 Giugliano G, Nicoletti G, Grella E, et al.Effect of liposuction on insulin resistanceand vascular inflammatory markers in

obese women Br J Plast Surg 2004;57:

190

34 Pessa JE, Zadoo VP, Mutimer KL, et al.Relative maxillary retrusion as a naturalconsequence of aging: combining skele-tal and soft-tissue changes into an inte-

grated model of midfacial aging Plast Reconstr Surg 1998;102:205.

35 Obagi S Autologous fat augmentation: aperfect fit in new and emerging technolo-

gies Facial Plast Surg Clin North Am.

2007;15:221

36 Gosain AK, Amarante MT, Hyde JS, et

al A dynamic analysis of changes in thenasolabial fold using magnetic reso-nance imaging: implications for facialrejuvenation and facial animation

surgery Plast Reconstr Surg 1996;98:

38 Donofrio LM Fat distribution: a

mor-phologic study of the aging face Dermatol Surg 2000;26:1107.

39 Coleman SR Concepts of aging: ing the obvious In: Structural FatGrafting St Louis, MO: Quality MedicalPublishing; 2004:xvii-xxiv

rethink-40 Kranendonk S, Obagi S Autologous fattransfer for periorbital rejuvenation: indi-cations, technique, and complications

Dermatol Surg 2007;33:572.

41 Narins RS Fat transfer with fresh andfrozen fat, microlipoinjection, andlipocytic dermal augmentation In: Klein

AW, ed Tissue Augmentation in ClinicalPractice 2nd ed New York, NY: Taylorand Francis; 2006:1-19

42 Eremia S, Newman N Long-term

follow-up after autologous fat grafting: analysis

of results from 116 patients followed atleast 12 months after receiving the last of

a minimum of two treatments Dermatol Surg 2000;26:1150.

43 Sommer B, Sattler G Current concepts offat graft survival: histology of aspiratedadipose tissue and review of the litera-

ture Dermatol Surg 2000;26:1159.

44 Egido JA, Arroyo R, Marcos A, et al.Middle cerebral artery embolism andunilateral visual loss after autologous fat

injection into the glabellar area Stroke.

1993;24:615

45 Teimourian B Blindness following fat

injections Plast Reconstr Surg 1988;82:361.

46 Dreizen NG, Framm L Sudden visualloss after autologous fat injection into the

glabellar area Am J Ophthalmol 1989;107:

85

47 Danesh-Meyer HV, Savino PJ, Sergott

RC Case reports and small case series:ocular and cerebral ischemia following

facial injection of autologous fat Arch Ophthalmol 2001;119:777.

48 Pinski KS, Coleman WP III lipoinjection and autologous collagen

50 Mizuno H, Zuk PA, Zhu M, et al.

Myogenic differentiation by human

processed lipoaspirate cells Plast Reconstr

Surg 2002;109:199.

51 De Ugarte DA, Morizono K, Elbarbary A,

et al Comparison of multi-lineage cells

from human adipose tissue and bone

mar-row Cells Tissues Organs 2003;174:

101

52 Kokai LE, Rubin JP, Marra KG Thepotential of adipose-derived adult stemcells as a source of neuronal progenitor

cells Plast Reconstr Surg 2005;116:1453.

53 Draelos ZD, Marenus KD Cellulite

Etiology and purported treatment

56 Alexiades-Armenakas M Laser and

light-based treatment of cellulite J Drugs Dermatol 2007;6:83.

57 Hexsel DM, Mazzuco R Subcision: a

treatment for cellulite Int J Dermatol.

2000;39:539

Furthermore, the adaptive immune tem is also responsible for immunememory, which confers long-term pro-tection to the host Although the twosystems appear distinct, they are notseparate, and in fact can act synergisti-cally, insofar as the innate immune sys-tem instructs the adaptive immuneresponse and the adaptive immune sys-tem influences the innate system.

sys-In the epidermis, the two main innatecells are the keratinocytes and Langerhanscells In addition, neutrophils, macro-phages, and dendritic cells present withinthe dermis also play a role in innateimmunity When a foreign substance isencountered, activation of innate cellsoccurs through PRRs, including the Toll-like receptors (TLRs), which are reviewedbelow Upon activation, the innate cellsbecome capable of inducing a directantimicrobial response by producing fac-tors that can help protect the host fromexternal insults These factors includereactive oxygen and nitrogen intermedi-ates (also known as “free radicals”) andantimicrobial peptides In addition, acti-

vated innate cells produce cytokines andother inflammatory mediators that caninstruct adaptive immunity Paradoxically,the same innate immune response caninduce proinflammatory cytokine pro-duction that can lead to inflammationand tissue injury, thereby facilitating dis-ease pathology

Cytokines and Growth FactorsCytokines are soluble mediators of theimmune system secreted by particularcell types in response to a variety ofstimuli They differ in molecular weight,structure, and mechanism of action Ingeneral, secreted cytokines act locally ineither an autocrine (effect on the pro-ducing cell itself) or paracrine (effect onadjacent cells) fashion While there havebeen numerous cytokines identified todate, this section will focus on the com-mon cytokines present in the skin andthe changes that occur in expressionprofiles with aging

In the epidermis, cytokines are marily produced by keratinocytes,melanocytes, and Langerhans cells,while fibroblasts, endothelial cells, mastcells, macrophages, dendritic cells, lym-phocytes, and other inflammatory cellsare responsible for cytokine productionwithin the dermis (Table 4-1for a sum-mary of cytokines present in the skinand the cells that produce them)

pri-Little is known about the relationship

between immunology and skin

appear-ance; however, it is certain that the

immune system plays an important role

in the health of the skin Work is ongoing

to help elucidate how this vital system

interacts with the largest organ of the

body It is very likely that this segment of

research, as it pertains to the cosmetic

dermatology arena, will offer significant

potential for discovery of new

therapeu-tics and procedures in the next several

years This chapter will serve as a brief

introduction to the skin as an immune

organ and how the immune response

plays a role in cosmetic dermatology

In the past, the skin was viewed

pri-marily as a barrier mechanism to

prevent invading pathogens and other

environmental toxins, including UV

radiation, from penetrating into internal

organs However, we now know that

the skin essentially acts as an immense

and integral immune organ and first

point of contact with the environment,

capable of initiating an intricate series of

events leading to host defense A basic

review of skin immunology, including

the role of cytokines and growth factors,

will be provided as an important part of

this discussion Mechanisms of various

immune responses found in skin

dis-ease, the interplay between innate

immunity and extracellular matrix

syn-thesis, as well as emerging

immune-based treatments will also be

high-lighted Finally, the relevance of the local

immune system and its relationship to

skin aging, particularly photoaging, will

be briefly reviewed

SKIN—AN INNATE IMMUNE

ORGAN

The immune response can be divided

into innate and adaptive immunity

Innate immune response occurs rapidly

and the cells of the innate immune

system use pattern recognition receptors

(PRRs) to secrete soluble factors that

can lead to both inflammation and

host defense The adaptive immune

IL-1 (␣, ␤) Keratinocytes (IL-1␣), Langerhans cells, melanocytes, fibroblasts,

T cells, B cells, macrophages, neutrophilsTNF-␣ Keratinocytes, Langerhans cells, melanocytes, fibroblasts, T cells,

B cells, macrophages, neutrophils, eosinophils, basophils

PROINFLAMMATORY CYTOKINES Activation

of the immune system is an important

step in protecting the skin from

pathogens and other environmental

tox-ins; however, paradoxically, activation of

the immune mechanism can also lead to

inflammation, thus promoting disease

and aging Interleukin (IL)-1, a cytokine

capable of being expressed by virtually

any nucleated cells, including

ker-atinocytes, exhibits a broad spectrum of

biologic activity Whereas IL-1␤ is

pre-dominantly expressed in most cells, IL-1␣

is expressed by keratinocytes.1 IL-1

induces keratinocyte proliferation,

pro-motes differentiation of B cells, activates

neutrophils and macrophages, and

initi-ates the expression of other

proinflamma-tory cytokines In addition, IL-1 is capable

of enhancing the activation of T cells, and

is involved in aspects of both humoral

(B cells) and cellular immunity (T cells)

IL-1 is continuously expressed at low

lev-els in normal epidermis but is markedly

enhanced when the skin barrier is

dis-rupted Furthermore, upon UV radiation,

keratinocytes can secrete IL-1, which then

initiates a cytokine cascade and the

bio-logic sequelae may accelerate changes

seen in photoaging

Tumor necrosis factor (TNF)-␣,

although structurally unrelated to IL-1,

shares similar biologic spectra TNF-␣ is

a potent inducer of inflammation and

also induces prostaglandin synthesis in

macrophages, further contributing to its

proinflammatory nature Within the

skin, both IL-1 and TNF-␣ are expressed

by keratinocytes and Langerhans cells

IL-6, produced by keratinocytes,

Lan-gerhans cells, and resident immune cells

within the skin, synergizes with other

cytokines, mainly potentiating the

effects of TNF-␣ and IL-1

Other members of the interleukin

family are expressed by various cells

within the skin and contribute to local

innate and adaptive immunity IL-2 is

secreted by activated T cells within the

skin and promotes clonal T cell

prolifer-ation as well as cytokine production,

and is critical for activation of the

adap-tive immune response IL-4, expressed

by activated T cells, mast cells, and

eosinophils, is important in allergic

disease processes and has been shown

to promote IgE production and the

maturation of mast cells and

eosin-ophils IL-5, expressed by monocytes

and eosinophils, serves mainly as an

eosinophil growth and differentiation

factor IL-8, produced by keratinocytes

and resident immune cells within the

skin, is a potent chemotractant for

neutrophils IL-12, produced by antigen

presenting cells, is a critical regulator

of innate and adaptive immunity, andserves to potentiate cell-mediated im-munity It is also expressed by ker-atinocytes and Langerhans cells

ANTI-INFLAMMATORY CYTOKINES Not allmembers of the interleukin family areproinflammatory IL-10 inhibits theinflammatory immune response throughvarious mechanisms Specifically, it hin-ders antigen presenting cell function bydownregulating major histocompatibilitycomplex (MHC) class II expression

Along with T cells, macrophages, and Bcells, keratinocytes express IL-10

Moreover, IL-10 disrupts cytokine duction by immune effector cells andinhibits the generation of reactive oxygenspecies (via oxidative burst) and nitricoxide production UV radiation enhancesIL-10 production in keratinocytes, whichcan lead to immune dysregulation.2Inaddition, the production of IL-10 by non-melanoma skin cancer can inhibit thefunction of tumor infiltrating lympho-cytes and promote tumor growth.3Interestingly, the immune cells of olderindividuals have been shown to producehigh levels of IL-10 in comparison toyounger adults, suggesting that IL-10 is inpart responsible for the immunosuppres-sion observed in the elderly.4

pro-GROWTH FACTORS Growth factors areproteins that have an effect on cellularproliferation and differentiation While

some cytokines can also be classified asgrowth factors, not all cytokines areconsidered growth factors (seeTable 4-2

for a summary of the functions ofcytokines and growth factors) Thereare numerous families of growth fac-tors The epidermal growth factor (EGF)family and the transforming growth fac-tor (TGF)-␤ superfamilies will be dis-cussed further

TGF-␣ is a member of the EGF family

of growth factors, which also consists ofEGF, amphiregulin (AR), epiregulin, andneuregulin 1, 2, and 3 These growth fac-tors are secreted by keratinocytes andbind to the EGF receptor in an autocrinemanner to induce keratinocyte prolifera-tion.5In addition to increasing epider-mal thickness and contributing in a com-plex chain of events to the regulation ofkeratinocyte differentiation, EGF isimportant in wound healing.6Notably,EGF and TGF-␣ enhance migration ofnormal keratinocytes.7EGF accelerateswound healing in mice and enhanceslateral migration of keratinocytes,wound closure, and subsequent reep-ithelialization.8Moreover, EGF stimu-lates fibroblast migration and prolifera-tion and is critical for wound repair anddermal regeneration.9,10

Decreased responsiveness of EGFreceptors is seen with increasing age,possibly because of a lower number anddensity of receptors, as well as to reducedligand binding, receptor autophosphory-lation, and internalization.11In addition,

IL-4 IgE production, mast cell and eosinophil maturationIL-5 Eosinophil growth and differentiation

IL-6 Potentiates effects of TNF-␣ and IL-1IL-8 Neutrophil chemoattractantIL-12 Potentiates cell-mediated immunity

Anti-inflammatory

IL-10 Downregulates MHC class II, disrupts cytokine production, inhibits

production of reactive oxygen species and NO

Growth Factors

TGF-␣ Enhances keratinocyte migration and keratinocyte differentiationTGF-␤ Recruits monocytes, neutrophils, and fibroblasts, decreases matrix

degradationEGF Enhances keratinocyte migration and keratinocyte differentiation,

accelerates wound healing, stimulates fibroblast migration and proliferation

amphiregulin expression is

downregu-lated in aged epidermis.12 Diminished

EGF activity and amphiregulin

expres-sion lead to a subsequent decrease in

fibroblast migration and proliferation at

the site of wound healing These events

result in the impaired wound healing that

is observed in aged skin Moreover, aged

fibroblasts produce fewer matrix

compo-nents,13yielding less dermal tissue and a

thinner, weaker scar

Many cosmeceuticals now contain

var-ious growth factors including EGF,

insulin-like growth factor, platelet growth

factor, and keratinocyte growth factor

Although these growth factors can

theo-retically induce keratinocyte

differentia-tion and dermal remodeling, whether any

of the products available to consumers

demonstrate significant clinical

effective-ness in preventing or reversing

photoag-ing has not yet been established Since

cosmeceuticals are not subject to the

same FDA regulatory requirements as

drugs, well-controlled clinical studies that

support the efficacy of cosmeceuticals are

generally not available

The TGF-␤ superfamily has a broad

spectrum of functions dependent on the

dosage and the target cell type In the

wound healing process, TGF-␤ is

responsible for recruiting monocytes,

neutrophils, and fibroblasts to the

wound site Higher concentrations of

TGF-␤ activate monocytes to release

numerous growth factors and stimulate

fibroblasts to increase matrix synthesis

and decrease matrix degradation.14The

effects of TGF-␤ on keratinocytes are

inconclusive with some studies showing

an inhibitory role in growth, while

oth-ers favoring keratinocyte

chemoattrac-tion and activachemoattrac-tion This apparent

dis-crepancy is perhaps linked to the

temporal kinetics, dose of TGF-␤

admin-istered, and also the dual activity TGF-␤

exerts on keratinocytes

TGF-␤ is best known in cosmetic

der-matology for its ability to promote the

production of the extracellular matrix,

notably the synthesis of procollagen.15

TGF-␤ also serves as a growth factor for

fibroblasts, the cells that produce collagen

and play an important role in wound

healing.14The subcutaneous injection of

TGF-␤ into unwounded skin results in

increased collagen deposition at the

injec-tion site.16Moreover, collagen synthesis is

enhanced in animal models when TGF-␤

is administered locally or systemically.17,18

Despite the encouraging results of TGF-␤

on collagen synthesis, its effects on

reep-ithelialization are less predictable In vivo

studies have shown both accelerated and

impaired reepithelialization in animal

wound models, echoing the tory effects of TGF-␤ on keratinocytes

contradic-Loss of TGF-␤ function may be significant in photoaging UV radiationimpairs the TGF-␤ pathway via down-regulation of TGF-␤ type II receptor(TGF-␤ RII) Loss of TGF-␤ RII occurswithin 8 hours after irradiation and pre-cedes the downregulation of type I pro-collagen expression,21 which leads toreduced collagen production Moreover,

UV exposure decreases the expression ofTGF-␤, and upregulates Smad7, a nega-tive regulator of TGF.22For this reason,TGF-␤ is included in skin care products

Whether the TGF-␤ and other growthfactors contained in cosmeceuticals arestable, can be absorbed adequately, orexert a functionally significant outcome

to induce dermal remodeling and reversephotoaging is unclear since well-con-trolled clinical studies are lacking

Cytokines and AgingAlthough the molecular mechanisms ofphotoaging and actinic damage have notbeen fully elucidated, skin-derived cyto-kines are likely involved in this process

UV radiation exposure, which is thought

to be responsible for photoaging, results

in inflammation, known as sunburn, andincreased proinflammatory cytokines byresident skin cells, including IL-1, IL-6,and IL-8 These cytokines cause inflam-mation, but also initiate activation of ker-atinocytes, macrophages, and otherimmune cells that generate reactive oxy-gen species, resulting in cellular damage

In addition, these reactive oxygen speciesinitiate the production of activator protein(AP)-1 and the formation of destructiveenzymes such as collagenases that con-tribute to skin aging (see Chapter 6).23

UV exposure also increases the duction of TGF-␣ from keratinocytes.24

pro-In addition, UVB irradiation of hairlessmice has been shown to elevate levels ofIL-1␣, and TNF-␣ mRNA in skin.25Interestingly, UV-produced cytokines dis-play opposing functions with regard tokeratinocyte proliferation UV exposureincreases levels of IL-1, IL-6, and TGF-␣,which are known to augment ker-atinocyte proliferation, while TNF-␣ isknown to suppress keratinocyte growth

Keratinocyte- and dermal-derivedcytokines that result from UV exposuremay also partially account for the dys-pigmentation seen with photoaging

An experimental model has strated that UVA-induced granulocytemonocyte colony stimulating factorfrom keratinocytes may play a role inmelanocyte proliferation and thus result

demon-in UVA-demon-induced pigmentation demon-in the dermis.26Further studies are needed toclarify the role of UV-induced cytokines

epi-on melanocyte growth and functiepi-on.Toll-like Receptors

The discovery of TLRs has created anew paradigm for how we view theinnate immune system Moreover, TLRsappear to play important roles in acneand other inflammatory skin diseases.Considering the partial proinflamma-tory nature of UV-induced photoaging,

it is possible that TLRs factor into theaging process Because TLRs are oftenactivated early in the innate immuneresponse resulting in cytokine produc-tion, part of the age-related cytokineaberration may be linked to changes inTLR expression and function The back-ground of TLRs and their known roles inskin disease and photoaging will be dis-cussed in this section In addition, theeffect of retinoids on TLR expressionand function will be explored

The importance of innate immunitybecame clear with the discovery of TLRs

a decade ago The toll receptor, initiallydescribed in relation to drosophila, wasshown to be crucial in preventing fungalinfection in flies Subsequently, it wasdemonstrated that TLRs play a role inhuman host defense.27 To date, 10human TLRs have been described andtheir role in innate immunity has greatlyinfluenced our view on the immune sys-tem TLRs are PRRs capable of recogniz-ing a variety of conserved microbialmotifs collectively referred to aspathogen-associated molecular patterns.Each TLR recognizes a unique microbialmotif, such as bacterial cell wall compo-nents, fungal elements, viral RNA, andbacterial DNA Moreover, individualTLRs can form dimers in order toincrease specificity A summary of TLRsand their respective ligands can be found

in Fig 4-1 Although their extracellulardomains vary in specificity for theirrespective microbial ligands, the intra-cellular domains of TLRs are conservedand converge onto a common pathway.TLR signaling is thought to occur pri-marily in a MyD88-dependent pathwaythat ultimately leads to nuclear translo-cation of the transcription factor NF-␬B.This in turn results in the transcription

of immunomodulatory genes, includingthose that encode for various cytokinesand chemokines.28 In addition to aMyD88-dependent pathway, certainTLR activation can lead to MyD88-inde-pendent signaling resulting in animmune response.29

TLRs are expressed by various cells

of the innate immune system such as

keratinocytes, neutrophils, monocytes,

macrophages, dendritic cells, and mast

cells Moreover, as TLRs are key players

in the innate response to pathogens, the

expression and function of TLRs at sites

of host-pathogen interaction are critical

for host defense It is therefore of little

surprise that the skin, which is the first

point of contact with cutaneous

patho-gens, exhibits functionally significant

TLR expression It is now known that

keratinocytes express TLRs 1, 2, and 5,

with TLR2 and 5 showing preferential

staining in the basal keratinocytes.30 In

addition, other studies have identified

expression of TLR4 in cultured human

keratinocytes.31TLR9 has been shown to

be preferentially expressed in

ker-atinocytes found in the granular layer.32A

more recent study has found that

cul-tured keratinocytes constitutively

express TLR1, 2, 3, 4, 5, 6, 9, and 10

mRNA, but not TLR7 or 8.33,34It has also

been suggested that keratinocyte

expres-sion of TLR can be influenced by

cytokines and growth factors, such as

TGF-␣.32 Furthermore, TLR expression

within the epidermis may correlate with

keratinocyte maturation; as cells progress

from the basal layer to the surface of the

skin, patterns of TLR expression may

change TLRs are also expressed on

fibroblasts TLR1–9 are expressed and

functionally active on cultured gingival

fibroblasts.35 TLR2 and 4 are also

expressed in synovial fibroblasts.36

Expression of TLRs on dermal fibroblasts

has not been fully investigated, however

Significantly, TLR expression andfunction have been demonstrated tochange with aging Studies evaluatingthe levels of TLR expression in murinemacrophages in aged mice have shownsignificantly lower levels of expression

of TLR Moreover, when stimulatedwith known ligands to TLR2/1, 2/6, 3,

4, 5, and 9, significantly lower levels ofIL-6 and TNF-␣ were produced, indicat-ing a decline in function.37 This sup-ports the observation that increasedsusceptibility to pathogens and pooradaptive immunity in elderly individu-als may be caused by a decline in TLRexpression and function A more recentstudy characterized TLR2/1 function inhumans TNF-␣ and IL-6 productionfrom peripheral blood-derived mono-cytes were significantly reduced inthose older than 65 years when com-pared to the cohort aged 21 to 30 years

Moreover, surface expression of TLR1was decreased but TLR2 wasunchanged as a function of aging.38While these studies have showndecreased TLR expression in mono-cytes, the effects of aging on ker-atinocyte TLR expression have not yetbeen described

What role, if any, TLR expression andfunction have in photoaging and accu-mulation of actinic damage is uncertain

However, the importance of TLRs inskin has been gleaned through the study

of various inflammatory skin diseases

For example, TLR2 has been implicated

in the pathogenesis of acne vulgaris

Propionibacterium acnes, a gram-positive anaerobe that plays a sine qua non role in

the pathogenesis of acne, induces the production of proinflammatorycytokines, such as IL-6 and IL-12, bybinding TLR2.39 Furthermore, TLR2plays an important role in the produc-tion of key host defense components,such as antimicrobial peptides, whichhave been demonstrated to increase inculture systems when keratinocytes are

stimulated with P acnes.40 Subtle ability in the expression of TLR1, 2, 5,and 9 has been described in psoriaticlesions when compared to normal skin,although these variances in TLR expres-sion have not been linked to the etiology

vari-or pathogenesis of the disease.30,41Nevertheless, TLR2 is thought to be

a key factor in host response to

Mycobacteria leprae, the organism

impli-cated in leprosy The expression of TLR2and TLR1 is markedly increased intuberculoid leprosy (resistant form ofleprosy) when compared to leproma-tous leprosy (susceptible form of lep-rosy), suggesting that TLR2/1 is impor-tant for activating cell-mediatedimmunity.42 Since TLR expression andfunction appear to play a role in thepathogenesis of various inflammatoryand infectious skin conditions, modula-tion of the expression and function ofthese PRRs with pharmacologic agentsappears to be a potential novel way inwhich certain dermatologic conditionscan be treated

Matrix Metalloproteinases Recently, TLRs have been directly linked

to collagen synthesis or breakdown by

Triacylated

lipoprotein

Diacylated lipoprotein Flagellin CpG DNA

Imidazoquinolones

ssRNA LPS dsRNA unknown

N N

N H3C

NH2 H2C

쑿 FIGURE 4-1 Toll-like receptors and their respective ligands