Mitochondrial failures in Alzheimer's disease

Mitochondrial dysfunction and free radical-induced oxidative damage have been implicated in the pathogenesis of several different neurodegenerative diseases such as Parkinson disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and Alzheimer's disease (AD). The defective adenosine triphosphate (ATP) production and increased oxygen radicals may induce mitochondria-dependent cell death because damaged mitochondria are unable to maintain the energy demands of the cell. The role of vascular hypoperfusion-induced mitochondria failure in the pathogenesis of AD now has been widely accepted. However, the exact cellular mechanisms behind vascular lesions and their relation to oxidative stress markers identified by RNA oxidation, lipid peroxidation, or mitochondrial DNA (mtDNA) deletion remain unknown. Future studies comparing the spectrum of mitochondrial damage and the relationship to oxidative stress-induced damage during the aging process or, more importantly, during the maturation of AD pathology are warranted.     

Mitochondria and vascular lesions as a central target for the development of Alzheimer's disease and Alzheimer disease-like pathology in transgenic mice

Accumulating evidence strongly suggests that the AD brain is characterized by impairments in energy metabolism, and vascular hypoperfusion, whereby oxidative stress appears to be an especially important contributor to neuronal death and development of AD pathology. We hypothesized that mitochondria play a key role in the generation of reactive oxygen species, resulting in oxidative damage to neuronal cell bodies, as well as other cellular compartments in the AD brain. All of these changes have been found to accompany AD pathology. In this review we have outlined recent evidence from the literature and our own original studies concerning the role of mitochondrial abnormalities and vascular damage in the pathogenesis of AD and AD-like pathology in transgenic mice (as a model for human AD). We examined ultrastructural features of vascular lesions and mitochondria from vascular wall cells in human AD brain biopsies, in human short post-mortem brain tissues and in yeast artificial chromosome (YAC) and C57B6/SJL transgenic positive (Tg+) mice overexpressing amyloid beta precursor protein (A beta PP). In situ hybridization using mitochondrial DNA (mtDNA) probes for human wild type, 5kb deleted and mouse mtDNA was performed along with immunocytochemistry using antibodies against amyloid beta precursor protein (A beta PP), 8-hydroxy-2'-guanosine (8OHG) and cytochrome C oxidase (COX) were studied at the electron microscopic levels. There was a higher degree of amyloid deposition in the vascular walls of the human AD, YAC and C57B6/SJL Tg(+) mice compared to aged-matched controls. In addition, vessels with more severe lesions showed immunopositive staining for APP and possessed large, lipid-laden vacuoles in the cytoplasm of endothelial cells (EC). Significantly more mitochondrial abnormalities were seen in human AD, YAC and C57B6/SJL Tg(+) mouse microvessels where lesions occurred. In situ hybridization using wild and chimera (5 kB) mtDNA probes revealed positive signals in damaged mitochondria from the vascular endothelium and in perivascular cells of lesioned microvessels close to regions of large amyloid deposition. These features were absent in undamaged regions of human AD tissues, YAC and C57B6/SJL Tg(+) mouse tissues and in aged-matched control subjects. In addition, vessels with atherosclerotic lesions revealed endothelium and perivascular cells possessing clusters of wild and deleted mtDNA positive probes. These mtDNA deletions were accompanied by increased amounts of immunoreactive APP, 8OHG and COX in the same cellular compartment. Our observations first time demonstrate that vascular wall cells, especially their mitochondria, appear to be a central target for oxidative stress induced damage.     

Cerebral hypoperfusion, capillary degeneration, and development of Alzheimer disease

Considerable clinical and experimental data have shown that cerebral perfusion is progressively decreased during increased aging and that this decrease in brain blood flow is significantly greater in Alzheimer disease (AD). The authors propose that advanced aging with a comorbid condition, such as a vascular risk factor, which further decreases cerebral perfusion, promotes a critically attained threshold of cerebral hypoperfusion (CATCH). With time, CATCH induces brain capillary degeneration and suboptimal delivery of energy substrates to neuronal tissue. Because glucose is the main fuel of brain cells, its impaired delivery, with the deficient delivery of oxygen, compromises neuronal stability because the supply for aerobic glycolysis fails to meet brain tissue demand. The outcome of CATCH is a metabolic cascade that involves, among other things, mitochondrial dysfunction, oxidative stress, decreased adenosine triphosphate production, abnormal protein synthesis, cell ionic pump deficiency, signal transduction defects, and neurotransmission failure. These events contribute to the progressive cognitive decline characteristic of patients with AD, as well as regional anatomic pathology, consisting of synaptic loss, senile plaques, neurofibrillary tangles, tissue atrophy, and neurodegeneration. CATCH identifies the clinical heterogeneic pattern that characterizes AD because it provides compelling evidence that any of a multitude of different etiopathophysiologic vascular risk factors, in the presence of advanced aging, can lead to AD. The evidence in support of CATCH as the pathogenic trigger of AD is crystallized in this review.     

Expression of 8-oxoguanine DNA glycosylase is reduced and associated with neurofibrillary tangles in Alzheimer's disease brain

Recent studies have confirmed the role of reactive oxygen species in the pathogenesis of Alzheimer's disease (AD). 8-Oxo-2'-deoxyguanosine accumulation in AD brain has been discussed, but few studies of DNA repair enzymes in AD brain have been done. Further, a relationship between mitochondrial function and oxidative stress has been noticed. In this study, to evaluate the repair mechanism for oxidative DNA damage in AD brain, we investigated brain tissues from autopsy cases of AD and control cases using an antibody against the mitochondrial form of 8-oxoguanine DNA glycosylase (hOGG1-2a), an enzyme that repairs 8-oxo-2'-deoxyguanosine. hOGGI-2a is expressed mainly in the neuronal cytoplasm in both AD and control cases in regionally different manners. Expression of hOGG1-2a is decreased in the orbitofrontal gyrus and entorhinal cortex in AD compared to that in control cases. Immunoreactivity to hOGG1-2a is associated with neurofibrillary tangles, dystrophic neurites and reactive astrocytes in AD. Our results indicate that the repair enzyme for oxidative damage in mitochondrial DNA may not function appropriately in AD, and thus oxidative DNA damage in mitochondria may be involved in the pathomechanism of AD.     

Effects of the superoxide dismutase/catalase mimetic EUK-207 in a mouse model of Alzheimer's disease: protection against and interruption of progression of amyloid and tau pathology and cognitive decline

Alzheimer's disease (AD) is characterized by progressive cognitive deficits, accumulation of amyloid-β (Aβ) and intracellular neurofibrillary tangles, and neuronal death. Additionally, mitochondrial dysfunction and free radical damage are hallmarks of AD brain. Here we set out to define the role of oxidative stress in AD pathogenesis and progression by chronically treating 3xTg-AD mice with the superoxide dismutase (SOD)/catalase mimetic, EUK-207. Treatment started at 4 months before onset of pathology and cognitive deficits, and continued until 9 months, when the AD phenotype was established. Cognitive performance was assessed using fear conditioning, and brain oxidative stress, Aβ, and tau pathology were analyzed. At 9 months, 3xTg-AD mice exhibited a decline in performance in both contextual and cued fear conditioning, as compared to wild-type mice. EUK-207-treated 3xTg-AD mice did not display any deficit in fear conditioning and exhibited reduced Aβ, tau, and phosphorylated tau accumulation in amygdala and hippocampus, as well as brain levels of Aβ42, oxidized nucleic acids, and lipid peroxidation. The effects of a 3-month treatment after pathology onset at 9 months on cognitive performance, brain oxidative stress, Aβ, and tau pathology were also evaluated. EUK-207-treated 3xTg-AD mice did not display any deficit in fear conditioning and were protected against increases in brain levels of oxidized nucleic acids and lipid peroxidation; they also had reduced Aβ, tau, and hyperphosphorylated tau accumulation in amygdala and hippocampus. Our results confirm a critical role for oxidative stress in AD pathogenesis and progression and suggest the potential usefulness of EUK-207 in AD treatment.     

Vicious cycles within the neuropathophysiologic mechanisms of Alzheimer's disease

Rigorous scientific research has identified multiple interactive mechanisms that parallel and are likely causative of the development of Alzheimer's disease (AD). Causative mechanisms include genomics, the creation of amyloid beta (Abeta), factors inhibiting the Abeta removal process, the transformation of Abeta to its toxic forms (various forms of Abeta aggregation), and lastly the oxidative, inflammatory, and other effects of toxic Abeta. Fibrillar beta-amyloid peptide, a major component of senile plaques in AD brain, is known to induce microglial-mediated neurotoxicity under certain conditions, but some recent studies support the notion that Abeta oligomers are the primary neurotoxins. Abeta-42 oligomers that are soluble and highly neurotoxic, referred to as Abeta-derived diffusible ligands (ADDLs), assemble under conditions that block fibril formation. These oligomers bind to dendrite surfaces in small clusters with ligand-like specificity and are capable of destroying hippocampal neurons at nanomolar concentrations. Evidence is presented that AD is triggered by these soluble, neurotoxic assemblies of Abeta rather than the late stage pathology landmarks of amyloid plaques and tangles. The premise is that AD symptoms stem from aberrant nerve cell signaling and synaptic failure rather than nerve cell death, which nevertheless follows and exacerbates the initial pathologies of AD. The defective clearance of amyloid leads to amyloid angiopathy that in turn perpetuates hypoperfusion that affects formation as well as absorption of CSF thereby altering clearance of amyloid and promoting vascular and parenchymal deposition[1]. Hypoperfusion, the defective clearance of amyloid, and resultant increase in amyloid deposition thus represent a vicious cycle. Chronic vascular hypoperfusion-induced mitochondrial failure results in oxidative damage, which drives caspase 3-mediated Abeta peptide secretion and enhances amyloidogenic APP processing. Intracellular Abeta accumulation in turn promotes a significant oxidative and inflammatory mechanism that generates a vicious cycle of Abeta generation and oxidation, each accelerating the other. Abeta activates astrocytes that add to the oxidative imbalance, upregulate the expression of APP via TGF-beta, and are capable of expressing BACE1. Each of these 3 actions accelerates the larger cycle of cholinergic neuron destruction. As oxidative stress induces lesions of cholinergic nuclei producing a reduction in cholinergic neurotransmission, a subsequent increase in cortical APP involving PKCepsilon leads to accelerated amyloidogenic APP metabolism. The linkage of cholinergic activation and APP metabolism completes an additional feedback loop wherein the damage wrought by Abeta accelerates further Abeta production. A comprehensive vision of the neuropathophysiologic mechanisms that result in AD reveals several vicious cycles within a larger vicious cycle, that is to say, a number of interactive systems that each, once set in motion, amplify their own processes, thus accelerating the development of AD.     

Mitochondrial alterations in Alzheimer's disease

Morphological alterations of mitochondria may be related to metabolic and energy deficiency in neurons in Alzheimer's disease and other neurodegenerative disorders. Mitochondrial dysfunction is also a hallmark of beta peptide induced neuronal toxicity in Alzheimer's disease. A general change in glucose utilization, increased oxidative stress, and Ca;{2+} deregulation are additional metabolic defects in the AD brain that may also be associated with defective mitochondrial function the result is a cycle of increased mitochondrial dysfunction causing increased oxidative damage until the cellular energy supply falls below the threshold for cellular survival. In a series of studies on the morphological and morphometric estimation of mitochondria in Alzheimer's disease, by electron microscopy we noticed substantial morphological and morphometric changes in the neurons of the hippocampus, the acoustic cortex, the frontal cortex, the cerebellar cortex, the climbing fibers, the thalamus, the globus pallidus, the red nucleus and the locus coeruleus. The morphological alterations consisted of considerable changes of the mitochondrial cristae, accumulation of osmiophilic material, and decrease of their size, in comparison with the normal controls. Mitochondrial alterations were particularly prominent in neurons, which showed loss of dendritic spines and abbreviation of the dendritic arborization. The ultrastructural study of large number of neurons in the thalamus and the red nucleus revealed that the mitochondrial alterations did not coexist with cytoskeletal pathology and accumulation of amyloid deposits, though they were prominent in neurons, which demonstrated fragmentation of the cisternae of the Golgi apparatus. Morphometric analysis showed that mitochondria are significantly reduced in Alzheimer's disease. The relationship between the site and extent of mitochondrial abnormalities and the synaptic alterations suggests an intimate and early association between these features in Alzheimer's disease.     

Oxidative damage, protein synthesis, and protein degradation in Alzheimer's disease

A large number of studies has firmly established that increases in oxidative damage occurs in Alzheimer's disease (AD). Such studies have demonstrated that increased in oxidative damage selectively occurs within the brain regions involved in regulating cognitive performance. Studies from our laboratory and others have provided experimental evidence that increased levels of oxidative damage occur in subjects with Mild Cognitive Impairment (MCI), which is believed to be one of the earliest stages of AD, and is a condition which is devoid of dementia or the extensive neurofibrillary pathology and neuritic plaque deposition observed in AD. Together, these data support a role for the accrual of oxidative damage potentially serving as an early event that then initiates the development of cognitive disturbances and pathological features observed in AD. Recent studies from our laboratory have demonstrated that a decline in protein synthesis capabilities occurs in the same brain regions which exhibit increased levels of oxidative damage in MCI and AD subjects. The focus of this review is to describe the large number of studies which suggest protein synthesis may be one of the earliest cellular processes disrupted by oxidative damage in AD. Taken together, these findings have important implications for understanding the molecular and cellular basis of AD, understanding the basis for oxidative stress in AD, and may have important implications for studies involving proteomics and proteolysis in AD.     

Cerebral hypoperfusion and cognitive impairment: the pathogenic role of vascular oxidative stress

Alzheimer's disease (AD) and vascular dementia (VaD) are the most frequent causes of cognitive impairment in the elderly. In the pathogenesis of cognitive impairment, the association of neurodegenerative and vascular factors indicates a major role of hemodynamic abnormalities including cerebral hypoperfusion. There is also ample evidence that oxidative stress of vascular origin leads to profound alterations in cerebrovascular regulation and is crucial to cerebrovascular dysfunction in a variety of conditions that result in chronic hypoperfusion of the brain. In rodents, experimental chronic cerebral hypoperfusion (CCH) can be initiated by occlusion of the major arterial supply. This way CCH brings about mitochondrial dysfunction and protein synthesis inhibition. These effects may destroy the balance of antioxidases and reactive oxygen species (ROS) and produce oxidative damage. At the same time, oxidative injury to vascular endothelial cell, glia, and neuron impairs vascular function and neurovascular coupling, which may result in a vicious cycle of further reduction of cerebral perfusion. In clinical cases of severe cognitive dysfunction, vascular risk factors are commonly present, while cerebral hypoperfusion is often associated with vascular oxidative damage. Thus we hypothesize that cerebral hypoperfusion is one of the key factors in the development of cognitive impairment, in which vascular oxidative stress plays a major role. The approaches against cerebrovascular dysfunction, combined with antioxidants and others, might make a promising contribution to the treatment of cognitive impairment.     

Gamma-glutamylcysteine ethyl ester-induced up-regulation of glutathione protects neurons against Abeta(1-42)-mediated oxidative stress and neurotoxicity: implications for Alzheimer's disease

Glutathione (GSH) is an important endogenous antioxidant found in millimolar concentrations in the brain. GSH levels have been shown to decrease with aging. Alzheimer's disease (AD) is a neurodegenerative disorder associated with aging and oxidative stress. Abeta(1-42) has been shown to induce oxidative stress and has been proposed to play a central role in the oxidative damage detected in AD brain. It has been shown that administration of gamma-glutamylcysteine ethyl ester (GCEE) increases cellular levels of GSH, circumventing the regulation of GSH biosynthesis by providing the limiting substrate. In this study, we evaluated the protective role of up-regulation of GSH by GCEE against the oxidative and neurotoxic effects of Abeta(1-42) in primary neuronal culture. Addition of GCEE to neurons led to an elevated mean cellular GSH level compared with untreated control. Inhibition of gamma-glutamylcysteine synthetase by buthionine sulfoximine (BSO) led to a 98% decrease in total cellular GSH compared with control, which was returned to control levels by addition of GCEE. Taken together, these results suggest that GCEE up-regulates cellular GSH levels which, in turn, protects neurons against protein oxidation, loss of mitochondrial function, and DNA fragmentation induced by Abeta(1-42). These results are consistent with the notion that up-regulation of GSH by GCEE may play a viable protective role in the oxidative and neurotoxicity induced by Abeta(1-42) in AD brain.     

Overexpression of GRK2 in alzheimer disease and in a chronic hypoperfusion rat model is an early marker of brain mitochondrial lesions

Heterotrimeric guanine nucleotide-binding (G) protein-coupled receptor kinases (GRKs) are cytosolic proteins that are known to contribute to the adaptation of the heptahelical G protein-coupled receptors (GPCRs) and to regulate downstream signals through these receptors. GPCRs mediate the action of messengers that are key modulators of cardiac and vascular cell function, such as growth and differentiation. GRKs are members of a multigene family, which are classified into three subfamilies and are found in cardiac, vascular and cerebral tissues. Increasing evidence strongly supports the hypothesis that vascular damage is an early contributor to the development of Alzheimer disease (AD) and/or other pathology that can mimic human AD. Based on this hypothesis, and since kinases of this family are known to regulate numerous receptor functions both in the brain, myocardium and elsewhere, we explored cellular and subcellular localization by immunoreactivity of G protein-coupled receptor kinase 2 (GRK2), also known as beta-adrenergic receptor kinase-1(betaARK1), in the early pathogenesis of AD and in ischemia reperfusion injury models of brain hypoperfusion. In the present study, we used the two-vessel carotid artery occlusion model, namely the 2-VO system that results in chronic brain hypoperfusion (CBH) and mimics mild cognitive impairment (MCI) and vascular changes in AD pathology. Our findings demonstrate the early overexpression of GRK2 member kinase in the cerebrovasculature, especially endothelial cells (EC) following CBH, as well as in select cells from human AD tissue. We found a significant increase in GRK2 immunoreactivity in the EC of AD patients and after CBH, which preceded any amyloid deposition. Since GRK2 activity is associated with certain compensatory changes in brain cellular compartments and in ischemic cardiac tissue, our findings suggest that chronic hypoperfusion initiates oxidative stress in these conditions and appears to be the main initiating injury stimulus for disruption of brain and cerebrovascular homeostasis and metabolism.     

Vitamin E as an antioxidant/free radical scavenger against amyloid beta-peptide-induced oxidative stress in neocortical synaptosomal membranes and hippocampal neurons in culture: insights into Alzheimer's disease

Amyloid beta-peptide (Abeta), the major constituent in senile plaques in Alzheimer's disease (AD) brain, is thought by many researchers to be central to neurotoxicity in AD brain. Increasing evidence from many laboratories indicates that AD brain is under oxidative stress, with strong evidence of protein oxidation, lipid peroxidation, and peroxynitrite damage. A link between the central role of Abeta and oxidative stress in AD brain may be Abeta-associated free radical oxidative stress. If so, antioxidants such as vitamin E should modulate Abeta-induced oxidative damage and neurotoxicity in brain cells. This review summarizes studies of Abeta-associated free radical oxidative stress and its inhibition by vitamin E in cortical synaptosomal membranes and hippocampal neuronal cells in culture. Taken together with the recent report that vitamin E slows the progression of AD, this review strongly supports a central role of Abeta-associated free radical oxidative stress in neurotoxicity in AD brain.     

Human serum transthyretin levels correlate inversely with Alzheimer's disease

Alzheimer's disease (AD) is histopathologically characterized by the presence of senile plaques, neurofibrillary tangles, and synapse loss. The main component of senile plaques is amyloid β-peptide (Aβ), which has been shown to induce oxidative stress in in vitro and in vivo studies. AD is associated with elevated levels of oxidative damage in brain and peripheral lymphocytes. Further Aβ has been found to be accumulated in mitochondria, which might contribute to the reported alterations in the mitochondrial morphology, and impaired mitochondrial energy metabolism in AD brain. Biomarkers are desperately needed for earlier diagnosis of AD and to monitor efficacy of new therapies. Hence, in the present study we show that markers of oxidative damage are elevated in mitochondria isolated from AD lymphocytes suggesting that these oxidative stress indices potentially could serve as a viable biomarker for AD.     

Pathophysiology of neuronal energy crisis in Alzheimer's disease

A large body of evidence indicates that sporadic Alzheimer's disease (AD) is a vascular disorder with neurodegenerative consequences and needs to be treated and managed as such. Epidemiologic studies of vascular risk factors, together with preclinical detection tools for AD are proof of concept that cerebral hypoperfusion is one of the earliest pathological signs in the development of cognitive failure. Vascular risk factors involving heart disease and stroke in the elderly individual who already possesses a dwindling cerebrovascular reserve due to advancing age contribute to further decline in cerebral blood flow (CBF) resulting in unrelenting brain hypoperfusion. Brain hypoperfusion, in turn, can reach a critically attained threshold of cerebral hypoperfusion (CATCH) giving rise to a neuronal energy crisis via reduced ATP synthesis. The ensuing metabolic energy crisis initially carves up ischemic-sensitive neurons in the hippocampus and posterior parietal cortex setting up cognitive meltdown and progressive neurodegenerative and atrophic changes in the brain. Neuronal energy compromise accelerates oxidative stress, excess production of reactive oxygen species, aberrant protein synthesis, ionic membrane pump dysfunction, signal transduction impairment, neurotransmitter failure, abnormal processing of amyloid precursor protein resulting in beta-amyloid deposition and axonal microtubule disruption from tau hyperphosphorylation. The high energy metabolic changes leading to oxidative stress and cellular hypometabolism precede clinical expression of AD. Regional CBF measurements using neuroimaging techniques can predict AD preclinically at the mild cognitive impairment stage or even before any clinical manifestation of dementia is expressed. Clinical diagnostic assessment of elderly persons who could develop or already present with memory complaints can prevent, reverse or slow down AD development. Although pathologic aging is the subject of thousands of studies, the question of why the elderly (and not younger people) succumb to AD has not been adequately addressed. The explanation(s) as to why vascular risk factors, for example, can trigger AD or vascular dementia usually in the elderly and not the young should provide vital clues in the search for a strategically effective dementia treatment. This review offers inductive hypothetical darts relative to that critical question.     

Zinc and its effects on oxidative stress in Alzheimer’s disease

Alzheimer’s disease (AD) is a progressive age-related neurodegenerative disorder. The patho-physiological characteristic of AD is abnormal deposition of fibrillar amyloid β protein, intracellular neurofibrillary tangles, oxidative damage and neuronal death in the brain. Zinc is an important trace element in human body regulating many physiological processes. Increasing evidence suggests that the etiology of AD may involve disruptions of zinc homeostasis, and oxidative stress facilitating reactive oxygen species production is an early and sustained event in AD disease progression. Both Zn deficiency and Zn overload may affect cellular Zn distribution and be linked to neurodegeneration in AD. Meanwhile, Zn may play paradoxical roles in initiating and inhibiting oxidative stress and neurotoxicity. This review will focus on aspects of the role of zinc in AD, which includes a large body of research regarding zinc dyshomeostasis and its relation with oxidative stress.     

Mitochondrion-specific antioxidants as drug treatments for Alzheimer disease

Age-related dementias such as Alzheimer disease (AD) have been linked to vascular disorders like hypertension, diabetes and atherosclerosis. These risk factors cause ischemia, inflammation, oxidative damage and consequently reperfusion, which is largely due to reactive oxygen species (ROS) that are believed to induce mitochondrial damage. At higher concentrations, ROS can cause cell injury and death which occurs during the aging process, where oxidative stress is incremented due to an accelerated generation of ROS and a gradual decline in cellular antioxidant defense mechanisms. Neuronal mitochondria are especially vulnerable to oxidative stress due to their role in energy supply and use, causing a cascade of debilitating factors such as the production of giant and/or vulnerable young mitochondrion who's DNA has been compromised. Therefore, mitochondria specific antioxidants such as acetyl-L-carnitine and R-alphalipoic acid seem to be potential treatments for AD. They target the factors that damage mitochondria and reverse its effect, thus eliminating the imbalance seen in energy production and amyloid beta oxidation and making these antioxidants very powerful alternate strategies for the treatment of AD.     

Bcl-2 facilitates recovery from DNA damage after oxidative stress.

Oxidative stress is a major factor affecting the brain during aging and neurodegenerative diseases such as Alzheimer's disease (AD). Understanding the mechanisms by which neurons can be protected from oxidative stress, therefore, is critical for the prevention and treatment of such degeneration. Previous studies have shown that bcl-2 expression is increased in neurons with DNA damage in AD and bcl-2 has an antioxidant effect. The goal of this study is to document the effects of oxidative insults on mitochondrial and nuclear DNA in PC12 cells and determine the extent to which bcl-2 prevents damage or facilitates repair. Using extralong PCR to amplify nuclear and mitochondrial DNA, the time course of DNA damage and repair was determined. Within minutes after exposure of cells to low concentrations of hydrogen peroxide and peroxynitrite, significant mitochondrial and nuclear DNA damage was evident. Mitochondrial DNA was damaged to a greater degree than nuclear DNA. Expression of bcl-2 in PC12 cells inhibited nitric oxide donor (sodium nitroprusside)- and peroxynitrite-induced cell death. Although oxidative insults caused both genomic and mitochondrial DNA damage in cells expressing bcl-2, recovery from DNA damage was accelerated in these cells. These results suggest that neuronal up-regulation of bcl-2 may facilitate DNA repair after oxidative stress.     

Acetyl-L-carnitine-induced up-regulation of heat shock proteins protects cortical neurons against amyloid-beta peptide 1-42-mediated oxidative stress and neurotoxicity: implications for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and cognition and by senile plaques and neurofibrillary tangles in brain. Amyloid-beta peptide, particularly the 42-amino-acid peptide (Abeta(1-42)), is a principal component of senile plaques and is thought to be central to the pathogenesis of the disease. The AD brain is under significant oxidative stress, and Abeta(1-42) peptide is known to cause oxidative stress in vitro and in vivo. Acetyl-L-carnitine (ALCAR) is an endogenous mitochondrial membrane compound that helps to maintain mitochondrial bioenergetics and lowers the increased oxidative stress associated with aging. Glutathione (GSH) is an important endogenous antioxidant, and its levels have been shown to decrease with aging. Administration of ALCAR increases cellular levels of GSH in rat astrocytes. In the current study, we investigated whether ALCAR plays a protective role in cortical neuronal cells against Abeta(1-42)-mediated oxidative stress and neurotoxicity. Decreased cell survival in neuronal cultures treated with Abeta(1-42) correlated with an increase in protein oxidation (protein carbonyl, 3-nitrotyrosine) and lipid peroxidation (4-hydroxy-2-nonenal) formation. Pretreatment of primary cortical neuronal cultures with ALCAR significantly attenuated Abeta(1-42)-induced cytotoxicity, protein oxidation, lipid peroxidation, and apoptosis in a dose-dependent manner. Addition of ALCAR to neurons also led to an elevated cellular GSH and heat shock proteins (HSPs) levels compared with untreated control cells. Our results suggest that ALCAR exerts protective effects against Abeta(1-42) toxicity and oxidative stress in part by up-regulating the levels of GSH and HSPs. This evidence supports the pharmacological potential of acetyl carnitine in the management of Abeta(1-42)-induced oxidative stress and neurotoxicity. Therefore, ALCAR may be useful as a possible therapeutic strategy for patients with AD.     

Ginsenoside Rg1 attenuates oligomeric Aβ(1-42)-induced mitochondrial dysfunction

Mitochondrial dysfunction is one of the major pathological changes seen in Alzheimer's disease (AD). Amyloid beta-peptide (Aβ), a neurotoxic peptide, accumulates in the brain of AD subjects and mediates mitochondrial and neuronal stress. Therefore, protecting mitochondrion from Aβ-induced toxicity holds potential benefits for halting and treating and perhaps preventing AD. Here, we report that administration of ginsenoside Rg1, a known neuroprotective drug, to primary cultured cortical neurons, rescues Aβ-mediated mitochondrial dysfunction as shown by increases in mitochondrial membrane potential, ATP levels, activity of cytochrome c oxidase (a key enzyme associated with mitochondrial respiratory function), and decreases in cytochrome c release. The protective effects of Rg1 on mitochondrial dysfunction correlate to neuronal injury in the presence of Aβ. This finding suggests that ginsenoside Rg1 may attenuate Aβ-induced neuronal death through the suppression of intracellular mitochondrial oxidative stress and may rescue neurons in AD.