Purified herba leonuri and leonurine protect middle cerebral artery occluded rats from brain injury through antioxidative mechanism and mitochondrial protection 1

Chapter 2: Introduction Chapter Introduction: Ischemic Stroke, CNS mitochondria and Therapeutic Potential of Traditional Chinese Medicine Department of Pharmacology, YLL School of Medicine 11 Chapter 2: Introduction 2.1 Pathophysiology of stroke Acute stroke can be divided into categories: hemorrhagic stroke and ischemic stroke. Hemorrhagic stroke (Figure 2-1a) describes sudden rupture of the blood vessels within the brain that causes the leakage of the blood into brain cavity, and therefore brain damage results (Zemke et al, 2004). For ischemic stroke (Figure 2-1b), which accounts for 80% of all stroke cases, the brain damage is caused by a reduction or complete blockage of blood flow, resulting in the deficiency of glucose and oxygen supply to the territory of the affected region (Zemke et al, 2004). Neurons are the most vulnerable cells to hypoxia due to their strong dependence on the oxidative metabolism of glucose for energy. Since ischemia is the major problem among all the stroke patients, many researches have been targeting on the treatment of ischemia. This project focused also ischemic stroke as a model to test on the therapeutic potential of studied drugs (see below). a) b) Figure 2-1: a) Ischemic stroke; and b) hemorrhagic stroke (arrow) Department of Pharmacology, YLL School of Medicine 12 Chapter 2: Introduction 2.1.1 Ischemic stroke As mentioned, ischemic stroke results from a transient or permanent reduction in cerebral blood flow (CBF) by an embolus or a thrombus, leading to brain injury. A critical reduction of CBF causes failure of cellular transport mechanisms and massive release of potentially toxic neurotransmitters, subsequently the formation of free radicals, inflammation, induction of immediate early genes and later, cell death by necrosis or apoptosis (Barber, 2008). Therefore, the extent of brain injury is dependent on level of CBF reduction, duration of ischemic insult, tissue temperature, blood glucose concentration and many other physiological variables. The two principle models of human stroke are global ischemia and focal ischemia, either permanent or transient. Global ischemia occurs when CBF is reduced throughout most or all parts of the brain as a result of cardiac arrest or other causes of collapse of system circulation, and subsequently failure of brain perfusion. The tissue injury is dominated by neurons, occurring especially in the most vulnerable region (CA1 region of hippocampus) of the brain first and then proceeding to the less vulnerable region such as thalamus or caudate putamen (Miller, 1999; Canese et al, 1997). Neuronal death in global ischemia is always detected in the hippocampus, striatum, neocortex with most susceptible population lies within CA1 and CA4 area of hippocampus and layer and of the cerebral cortex (Taoufik and Probert, 2008). Department of Pharmacology, YLL School of Medicine 13 Chapter 2: Introduction As for focal ischemia, it is represented by a reduction of blood flow to a specific brain region, such as the occlusion of middle cerebral artery. Although occlusion of vessel occurs during focal ischemia, there is rarely complete blockade of CBF to the area supplied by the occluded vessel because plethora of collateral vessels provides some flow to the area (Horst and Korf, 1997). During focal ischemia, there will be a core infarct area which does not receive sufficient perfusion to sustain any of the neurons, glia, or even the vasculature. The volume of core infarct is correlated to the severity of neurological deficit. On multi-tracer O Positron emission tomography (PET), ischemic core exhibits very low CBF, cerebral blood volume (CBV), and metabolic rates of oxygen and glucose (Marchal et al, 1999). In this region, a CBF of [...]... blood flow (CBF) in MCAO The figure illustrate the CBF reduction following middle cerebral artery (MCA) occlusion in the baboon brain, demonstrating a gradient from ischemic core (red) through to penumbra and oligaemia (blue) to normally perfused cortex (grey) Values indicate approximate CBF in ml100g-1min -1 (adapted from Moustafa and Baron, 2008) Department of Pharmacology, YLL School of Medicine 33 Chapter... participates in neuronal ischemic injury comes from the use of antioxidants and free radical scavengers that prevent the infarct expansion and restore the neurological deficit function after ischemia (Braughler and Hall, 19 89; Tagami et al, 19 99) Cerebral protection was observed with mice with overproduction of free radical scavenging enzymes (WeisbrotLeftkowitz et al, 19 98) Furthermore, the extent of... O2˙¯ and H2O2 (Parks and Granger, 19 86; Warner et al, 2004) It was shown that xanthine oxidase was increased significantly from 8% to 44% after 30 mins of global ischemia (Kinuta et al, 19 89) Allopurinol, a competitive Department of Pharmacology, YLL School of Medicine 26 Chapter 2: Introduction inhibitor of xanthine oxidase, provides protection against ischemic injury in intestine, heart, kidney and brain. .. approach in rats Rats are currently the best species to perform MCAO, because it is relatively inexpensive, its cerebrovascular anatomy and physiology resemble that of higher species, and physiologic parameters can be easily monitored The transcranial approach requires a careful removal of a section of the skull and the underlying dura in order to occlude the middle cerebral artery Tamura et al (19 81) developed... cortex and the caudate putamen The original technique, however, was very invasive and the rats survived only for a few hours Subsequent modifications including preserving the zygoma and the masseter muscle improved the postoperative survival and eventually the subtemporal approach becomes a standard technique of permanent focal ischemia in rats (Duverger et al, 19 88; Nakayama et al, 19 88; Menzies et al 19 92)... therapy 2 .1. 4 Rodent ischemic stroke models Currently, there are two types of animal models of cerebral ischemia used in brain ischemia studies: global ischemia and focal ischemia (Zemke et al, 2004) Global ischemia affects the entire brain, which results most commonly from cardiac arrest or other causes of collapse of system circulation, and subsequently failure of brain perfusion The tissue injury is... relatively simplified and less informative to stroke in humans (Taoufik and Probert, 2008) In contrast, focal ischemia causes the damage only to a portion of brain The size and part of affected area depends on which vessel is occluded (Zemke et al, 2004) In addition, collateral flow contributes another major difference between global and focal ischemia (Horst and Korf, 19 97) Regions of the brain with most... left middle cerebral artery occlusion (MCAO) was chosen as a model for studies in this research Most experiment and clinical research have focused much on MCAO as the infarct formed by MCAO is similar to the brain damage of ischemic stroke in humans (Miller, 19 99) MCA can be occluded close to its branching from internal carotid so that caudate putamen, most neocortical regions, the somatosensory and. .. mitochondrial dysfunction, and it subsequently leads to cell death, as mitochondria involve in energy metabolism, calcium homeostasis and intrinsic pathway of apoptosis (Christophe and Nicolas, 2006) The mitochondria-mediated apoptosis seems to be dominant after cerebral ischemia as mitochondrial dysfunction has been demonstrated in ischemic stroke, and mitochondrial dysfunction will lead to cell injury. .. fusion protein with Bcl-xL protects against ischemic brain injury and neuronal apoptosis (Cao et al, 2002) Indeed, mitochondria are involved in both necrosis and apoptotic pathways, depending on the severity of the damage and nature of the signaling pathways, for instance, PCD requires ATP and a sudden reduction in ATP due to severe ischemic insult leads mitochondrial damage and it can alternatively . core exhibits very low CBF, cerebral blood volume (CBV), and metabolic rates of oxygen and glucose (Marchal et al, 19 99). In this region, a CBF of < ;10 ml /10 0g of brain tissue per minute severely. preferred ligand is (Fas ligand) FasL (Ashe and Berry, 2003). There were reports on Fas/FasL system that it is also involved in neuronal apoptosis following traumatic brain injury and cerebral. Medicine 27 inhibitor of xanthine oxidase, provides protection against ischemic injury in intestine, heart, kidney and brain (Parks and Granger, 19 86; Isik et al, 2005) In addition, NADPH oxidase