Role Of Mitochondrial Oxidative Stress Research Articles

Mitochondrial oxidative stress and permeability transition in Isoniazid and Rifampicin induced liver injury in mice

To evaluate the role of mitochondrial oxidative stress and permeability transition (MPT) in isoniazid (INH) and rifampicin (RMP) induced hepatotoxicity in mice. Liver damage was induced by co-treatment of INH (50 mg/kg) and RMP (100 mg/kg). Pre-treatment with either methionine or phorone was done to modulate hepatic GSH level. Liver cell injury was assessed biochemically and histologically. Evidence of apoptosis was sought by TUNEL test, caspase assay and histology. INH and RMP co-treatment caused steatosis and increased apoptosis of the hepatocytes, hepatic oxidative stress, particularly in the mitochondrial fraction with increased mitochondrial permeability transition (MPT). Mitochondrial oxidative stress as well as liver cell injury was increased by prior treatment with phorone. This was attenuated by pretreatment with methionine suggesting a glutathione (GSH) dependent phenomenon. Oxidative stress in the mitochondria and inappropriate MPT are important in the pathogenesis of apoptotic liver cell injury in INH-RMP hepatotoxicity. The phenomenon is GSH dependent and methionine supplementation might have a protective role.

Role of mitochondrial oxidative stress to explain the different longevity between genders. Protective effect of estrogens

Females live longer than males. Work from our laboratory has shown that this may be due to the up-regulation of longevity-associated genes by estrogens. Estrogens bind to the estrogen receptors and subsequently activate the mitogen activated protein kinase and nuclear factor kappa B signalling pathways, resulting in an up-regulation of antioxidant enzymes.Estrogen administration, however, has serious undesirable effects and of course, cannot be administered to males because of its powerful feminizing effects. Thus, we tested the effect of genistein, a phytoestrogen of high nutritional importance whose structure is similar to estradiol, on the regulation of the expression of antioxidant, longevity-related genes and consequently on oxidant levels in mammary gland tumour cells in culture. Phytoestrogens mimic the protective effect of oestradiol using the same signalling pathway.The critical importance of up-regulating antioxidant genes, by hormonal and dietary manipulations, to increase longevity is discussed.

Oxidative Stress and Aging: Catalase Is a Longevity Determinant Enzyme

Schriner and colleagues have reported an important advance in our understanding of the mechanisms controlling lifespan in mammalian species. A transgenic mouse strain was constructed (MCAT) with a C57BL/6J background that has about a 50-fold increase in expression in cardiac mitochondria and skeletal muscle of catalase enzyme activity. The MCAT strain was found to have reduced severity of age-dependent arteriosclerosis and increased genomic stability, as indicated by a decrease in oxidative stress and mitochondrial deletions in heart and muscle tissues. Most exciting, however, is that both median and maximum lifespan were increased about 17-21% compared to wild-type controls. It was disappointing that the Gompertz plot of the MCAT strain ran parallel to the wild-type control, indicating a delay in the onset of aging rather than a decrease in aging rate. Nevertheless, these results support the notion of a role for mitochondrial oxidative stress as a determinant of both healthspan and lifespan. In addition, the relatively large increase in lifespan resulting from upregulation of a single gene suggests the possibility that similar upregulation of relatively few key longevity determinant genes may result in dramatic increases in lifespan.

The role of mitochondrial oxidative stress in aging

Mitochondria are both a major source of oxidants and a target for their damaging effects, and, therefore, mitochondrial oxidative stress appears to be a cause, rather than a consequence, of cell aging. Oxidative damage in aging is particularly high in specific molecular targets, such as mitochondrial DNA and aconitase, and mitochondrial oxidative stress may drive tissue aging through intrinsic apoptosis. Mitochondrial function and morphology are impaired upon aging, as judged by a decline in membrane potential as well as by an increase in peroxide production and size of the organelles. In view of the age-related decreases in mitochondrial protein synthesis, mitochondrial transcripts, and expression of genes involved in mitochondrial turnover, the rate of this turnover might determine its susceptibility of mitochondria to oxidative damage and mutation, thus controlling the rate of cell aging. In fact, aging is a feature of differentiated somatic cells, especially postmitotic cells such as neurons or muscle cells. The age-associated mitochondrial DNA deletions focally accumulate in brain and skeletal muscle, thus contributing significantly to aging of these postmitotic tissues. Expansion of mitochondrial DNA mutations may occur through mitochondrial complementation. The use of mutants of the mitochondrial electron transport system, as well as knockouts or transgenics of mitochondrial antioxidants or repair enzymes, may provide clear-cut evidence of the precise mitochondrial mechanisms that control the rate of cell aging.

Selective Targeting of a Redox-active Ubiquinone to Mitochondria within Cells: ANTIOXIDANT AND ANTIAPOPTOTIC PROPERTIES

With the recognition of the central role of mitochondria in apoptosis, there is a need to develop specific tools to manipulate mitochondrial function within cells. Here we report on the development of a novel antioxidant that selectively blocks mitochondrial oxidative damage, enabling the roles of mitochondrial oxidative stress in different types of cell death to be inferred. This antioxidant, named mitoQ, is a ubiquinone derivative targeted to mitochondria by covalent attachment to a lipophilic triphenylphosphonium cation through an aliphatic carbon chain. Due to the large mitochondrial membrane potential, the cation was accumulated within mitochondria inside cells, where the ubiquinone moiety inserted into the lipid bilayer and was reduced by the respiratory chain. The ubiquinol derivative thus formed was an effective antioxidant that prevented lipid peroxidation and protected mitochondria from oxidative damage. After detoxifying a reactive oxygen species, the ubiquinol moiety was regenerated by the respiratory chain enabling its antioxidant activity to be recycled. In cell culture studies, the mitochondrially localized antioxidant protected mammalian cells from hydrogen peroxide-induced apoptosis but not from apoptosis induced by staurosporine or tumor necrosis factor-alpha. This was compared with untargeted ubiquinone analogs, which were ineffective in preventing apoptosis. These results suggest that mitochondrial oxidative stress may be a critical step in apoptosis induced by hydrogen peroxide but not for apoptosis induced by staurosporine or tumor necrosis factor-alpha. We have shown that selectively manipulating mitochondrial antioxidant status with targeted and recyclable antioxidants is a feasible approach to investigate the role of mitochondrial oxidative damage in apoptotic cell death. This approach will have further applications in investigating mitochondrial dysfunction in a range of experimental models.

Oxidative damage to mitochondrial DNA and glutathione oxidation in apoptosis: studies in vivo and in vitro.

Free radicals may be involved in apoptosis although this is the subject of some controversy. Furthermore, the source of free radicals in apoptotic cells is not certain. The aim of this study was to elucidate the role of oxidative stress in the induction of apoptosis in serum-deprived fibroblast cultures and in weaned lactating mammary glands as in vitro and in vivo experimental models, respectively. Oxidative damage to mtDNA is higher in apoptotic cells than in controls. Oxidized glutathione (GSSG) levels in mitochondria from lactating mammary gland are also higher in apoptosis. There is a direct relationship between mtDNA damage and the GSSG/reduced glutathione (GSH) ratio. Furthermore, whole cell GSH is decreased and GSSG is increased in both models of apoptosis. Glutathione oxidation precedes nuclear DNA fragmentation. These signs of oxidative stress are caused, at least in part, by an increase in peroxide production by mitochondria from apoptotic cells. We report a direct relationship between glutathione oxidation and mtDNA damage in apoptosis. Our results support the role of mitochondrial oxidative stress in the induction of apoptosis.

Manganese Superoxide Dismutase Mediates the Early Release of Mitochondrial Cytochrome C and Subsequent DNA Fragmentation after Permanent Focal Cerebral Ischemia in Mice

Recent studies have shown that release of mitochondrial cytochrome c is a critical step in the apoptosis process. We have reported that cytosolic redistribution of cytochrome c in vivo occurred after transient focal cerebral ischemia (FCI) in rats and preceded the peak of DNA fragmentation. Although the involvement of reactive oxygen species in the cytosolic redistribution of cytochrome c in vitro has been suggested, the detailed mechanism by which cytochrome c release is mediated in vivo has not yet been established. Also, the role of mitochondrial oxidative stress in cytochrome c release is unknown. These issues can be addressed using knock-out mutants that are deficient in the level of the mitochondrial antioxidant manganese superoxide dismutase (Mn-SOD). In this study we examined the subcellular distribution of the cytochrome c protein in both wild-type mice and heterozygous knock-outs of the Mn-SOD gene (Sod2 -/+) after permanent FCI, in which apoptosis is assumed to participate. Cytosolic cytochrome c was detected as early as 1 hr after ischemia, and correspondingly, mitochondrial cytochrome c showed a significant reduction 2 hr after ischemia (p < 0.01). Cytosolic accumulation of cytochrome c was significantly higher in Sod2 -/+ mice compared with wild-type animals (p < 0.05). N-benzyloxycarbonyl-val-ala-asp-fluoromethyl ketone (z-VAD.FMK), a nonselective caspase inhibitor, did not affect cytochrome c release after ischemia. A significant amount of DNA laddering was detected 24 hr after ischemia and increased in Sod2 -/+ mice. These data suggest that Mn-SOD blocks cytosolic release of cytochrome c and could thereby reduce apoptosis after permanent FCI.