Part 2 book “Mitochondrial dysfunction caused by drugs and environmental toxicants” has contents: Acylcarnitines as translational biomarkers of mitochondrial dysfunction, imaging of mitochondrial toxicity in the kidney, imaging mitochondrial membrane potential and inner membrane permeability,… and other contents.
373 23 Biomarkers of Mitochondrial Injury After Acetaminophen Overdose: Glutamate Dehydrogenase and Beyond Benjamin L Woolbright and Hartmut Jaeschke Department of Pharmacology, Toxicology & Therapeutics, University of Kansas Medical Center, Kansas City, KS, USA CHAPTER MENU 23.1 Introduction, 373 23.2 Acetaminophen Overdose as a Model for Biomarker Discovery, 373 23.3 Acetaminophen Overdose: Mechanisms of Toxicity in Mice and Man, 374 23.4 Biomarkers of Mitochondrial Injury, 375 23.5 Conclusions, 379 References, 379 23.1 Introduction In the drug discovery process, drug‐induced liver injury is one of the most common reasons for failure in preclini cal development and in clinical trials In addition, idio syncratic hepatotoxicity leads to black box warnings or even withdrawal of approved drugs from the market Whereas currently used biomarkers for liver injury (ala nine (ALT) and aspartate aminotransferases (AST)) and dysfunction (bilirubin) are sufficiently sensitive to detect dose‐dependent hepatotoxins, there are no biomarkers available that could alert to a potential idiosyncratic tox icity Clinically, acetaminophen (APAP) overdose remains the most common source of both drug‐induced liver injury and acute liver failure (ALF) (Lee, 2013) Patients that develop ALF have a very poor outcome, with mortal ity up to 50% (Lee, 2013) Early identification of which patients will proceed to ALF is critical, as these patients can be treated more aggressively or listed for transplanta tion earlier As such, biomarkers of patient outcome are of considerable clinical value for determining early during the patient’s hospitalization which patients will proceed to ALF and will die or need a liver transplant and which patients will recover spontaneously The best biomarkers are those that are also informative of the mechanisms at play in the pathophysiology or valuable clinically due to prognostic capacity Biomarkers present in the serum or urine of patients are of the most interest and the greatest use Many of these serum and urine biomarkers have a single point of origin in tissue and thus accurately reflect what is happening in these tissues, in a mechanistic fashion, without the need for biopsy A number of these “mechanistic biomarkers” have recently been a source of focus in the literature, and con siderable research has gone into fully investigating these compounds (Antoine et al., 2012; McGill et al., 2012; Luo et al., 2014; McGill and Jaeschke, 2014; Beger et al., 2015) Release of many of these mechanistic biomarkers can be traced back to damage of the mitochondria, and thus considerable progress has recently been made in the field of biomarkers of mitochondrial damage The purpose of this chapter will be to define these markers and discuss their clinical viability and basic science relevance with regard to the murine APAP hepatotoxicity model and human patients with APAP overdose 23.2 Acetaminophen Overdose as a Model for Biomarker Discovery A number of mitochondrial biomarkers have been estab lished for liver disease Many of these were originally defined in the murine APAP overdose model (reviewed in McGill and Jaeschke, 2014) This model is convenient Mitochondrial Dysfunction Caused by Drugs and Environmental Toxicants, Volume I, First Edition Edited by Yvonne Will and James A. Dykens © 2018 John Wiley & Sons, Inc Published 2018 by John Wiley & Sons, Inc 374 Mitochondrial Dysfunction by Drug and Environmental Toxicants for biomarker discovery for a number of reasons: (i) it is technically simple and highly repeatable, (ii) the mecha nisms associated with the model are largely well deline ated, and (iii) it is a clinically relevant murine model with high fidelity to the human condition (McGill et al., 2012; Jaeschke et al., 2014, Jaeschke, 2015) We will briefly discuss the APAP overdose model as it relates to mito chondrial dysfunction and subsequent cell death This is not a complete overview of the understood mechanisms of APAP (for a more complete, updated overview: Ramachandran and Jaeschke, 2017; Woolbright and Jaeschke, 2017), but rather a version focused on the pathology associated with the mitochondria 23.3 Acetaminophen Overdose: Mechanisms of Toxicity in Mice and Man 23.3.1 Drug Metabolism and Protein Adducts APAP is an over‐the‐counter analgesic and antipyretic Normally, greater than 85% of an APAP dose is conju gated to either UDP‐glucuronide or sulfate and excreted via phase II metabolism (McGill and Jaeschke, 2013) Therapeutic doses are safe; however, an overdose of APAP partially overwhelms phase II metabolism and results in substantial oxidation of APAP to the reactive metabolite N‐acetyl‐p‐benzoquinone imine (NAPQI) (Dahlin et al., 1984), which is a reactive electrophile that covalently adducts cellular proteins causing oxidative stress in the cell (Dahlin et al., 1984) and is largely detoxi fied through a spontaneous reaction with the endoge nous antioxidant glutathione (GSH) (Mitchell et al., 1973) This results in the depletion of cellular GSH levels in the liver GSH depletion is currently used as a hall mark for measuring APAP metabolic activation experi mentally (McGill and Jaeschke, 2013) The interaction between NAPQI and GSH is also the basis for the cur rent gold‐standard therapeutic, N‐acetylcysteine (NAC), which is a precursor for GSH synthesis The newly formed GSH can scavenge NAPQI (Corcoran and Wong, 1986) and later detoxify reactive oxygen and peroxyni trite (Knight et al., 2002) During this metabolism and GSH depletion, NAPQI begins to adduct sulfhydryl groups on proteins forming acetaminophen–cysteine (APAP–CYS) adducts (Pumford et al., 1989), which have been proposed as a diagnostic indicator of APAP overdose in patients (Roberts et al., 2017) Levels above 1 μM of APAP–CYS in serum are associated with liver toxicity, although recent data indicate APAP–CYS adducts may be released even at therapeutic doses when patients not have any liver toxicity (Heard et al., 2011; McGill et al., 2013) In addition, while adduct formation and release into the blood occur very early in mice (