Oxidative damage to DNA can be caused by excited oxygen species, which are produced by radiation or are by-products of aerobic metabolism. The oxidized base, 8-hydroxydeoxyguanosine (oh8dG), 1 of =20 known radiation damage products, has been assayed in the DNA of rat liver. oh'dG is present at a level of 1 per 130,000 bases in nuclear DNA and 1 per 8000 bases in mtDNA. Mitochondria treated with various prooxidants have an increased level of oh8dG. The high level of oh8dG in mtDNA may be caused by the immense oxygen metabolism, relatively inefficient DNA repair, and the absence of histones in mitochondria. It may be responsible for the observed high mutation rate of mtDNA.

Oxidative damage to DNA is shown to be extensive and could be a major cause of the physiological changes associated with aging and the degenerative diseases related to aging such as cancer. The oxidized nucleoside, 8-hydroxy-2'-deoxyguanosine (oh8dG), one of the -20 known oxidative DNA damage products, has been measured in DNA isolated from various organs of Fischer 344 rats of different ages. oh8dG was present in the DNA isolated from all the organs studied: liver, brain, kidney, intestine, and testes. Steady-state levels of oh8dG ranged from 8 to 73 residues per 10' deoxyguanosine residues or 0.2-2.0 x 105 residues per cell. Levels of oh8dG in DNA increased with age in liver, kidney, and intestine but remained unchanged in brain and testes. The urinary excretion of oh8dG, which presumably reflects its repair from DNA by nuclease activity, decreased with age from 481 to 165 pmol per kg of body weight per day for urine obtained from 2-month-and 25-month-old rats, respectively. 8-Hydroxyguanine, the proposed repair product of a glycosylase activity, was also assayed in the urine. We estimate -9 x 104 oxidative hits to DNA per cell per day in the rat. The results suggest that the age-dependent accumulation of oh8dG residues observed in DNA from liver, kidney, and intestine is principally due to the slow loss of DNA nuclease activity; however, an increase in the rate of oxidative DNA damage cannot be ruled out.The biochemical mechanisms of aging are under extensive investigation but remain poorly understood. Endogenous metabolic processes are implicated as important factors in aging by the impressive inverse correlation between life-span and species-specific metabolic rate (1).The damage produced by endogenously produced oxygen radicals has been proposed to be a major contributor to aging and the degenerative diseases associated with it, such as cancer and heart disease (2-7). In vivo, oxygen radicals are mainly produced as by-products of normal metabolism (8) from phagocytic cells (9) and from lipid peroxidation (10). Numerous defense systems protect cellular macromolecules against oxidation; nevertheless, there is a high rate of damage to DNA (11), proteins (12), and lipids (10, 13). The steadystate level of oxidatively modified nucleosides in genomic and mitochondrial DNA in rats (11) and the release of these damage products in human and rodent urine (14-16) have been determined. Oxidative damage to DNA has been estimated as 104 hits per cell per day in humans and 1 order of magnitude higher in rodents (7,14,15).Some evidence suggests that an increased production of reactive oxygen species and/or a decreased efficiency of antioxidant defense systems is associated with aging (17,18). Endogenous oxidative damage to lipids (19) and proteins (12) has been reported to increase with age. Damage to DNA has been reported to increase with age in rats fed diets deficient in vitamin E, but not in rats fed vitamin E-sufficient diets (20).The purpose of this study was to evaluate endogenous oxidative damage to DNA as...

Mitochondria are the major organelles that produce reactive oxygen species (ROS) and the main target of ROS-induced damage as observed in various pathological states including aging. Production of NADPH required for the regeneration of glutathione in the mitochondria is critical for scavenging mitochondrial ROS through glutathione reductase and peroxidase systems. We investigated the role of mitochondrial NADP ؉ -dependent isocitrate dehydrogenase (IDPm) in controlling the mitochondrial redox balance and subsequent cellular defense against oxidative damage. We demonstrate in this report that IDPm is induced by ROS and that decreased expression of IDPm markedly elevates the ROS generation, DNA fragmentation, lipid peroxidation, and concurrent mitochondrial damage with a significant reduction in ATP level. Conversely, overproduction of IDPm protein efficiently protected the cells from ROS-induced damage. The protective role of IDPm against oxidative damage may be attributed to increased levels of a reducing equivalent, NADPH, needed for regeneration of glutathione in the mitochondria. Our results strongly indicate that IDPm is a major NADPH producer in the mitochondria and thus plays a key role in cellular defense against oxidative stress-induced damage.Cell damage induced by oxidative stress and reactive oxygen species (ROS) 1 has been implicated in several human diseases including aging, alcohol-mediated organ damage, neurodegenerative diseases, many types of cancers, cardiovascular diseases, and UV-mediated skin disorders (1). As one of the major sources of ROS (2), mitochondria are highly susceptible to oxidative damage. ROS can damage mitochondrial enzymes directly (3), and they can cause mutation in mitochondrial DNAs (4). At the same time, ROS can change the mitochondrial transmembrane potential (⌬m), which is indicative of mitochondrial membrane integrity (5) and precedes cell death induced by various toxic compounds and cytokines (6). Recent reports indicate that mitochondrial ROS cause apoptosis (7, 8) by activating various apoptotic effectors such as cytochrome c release, procaspase-2, procaspase-9, procaspase-3, and latent apoptosis-inducing factor, which is released from the mitochondria during apoptosis (9 -11). Another report also suggested that mitochondrial ROS directly caused apoptosis of T cells (12). It was also reported that tumor necrosis factor ␣ causes a rapid production of mitochondrial ROS (13) and that ceramide, an apoptotic stimulus, also plays a crucial role in tumor necrosis factor ␣-induced mitochondrial ROS generation (14). Furthermore, several other investigators demonstrated that ROS are involved in the signaling pathway of certain growth factors (15) and cytokines (16). In addition, mitochondrial ROS, under hypoxic conditions, activate the transcription of the genes for glycolytic enzymes as well as erythropoietin and vascular endothelial growth factor by upregulating a transcriptional factor, hypoxia-inducible factor 1 (17), suggesting that mitochondrial ROS mediate cross-talk b...

No abstract

No abstract

NADPH is an essential cofactor for many enzymatic reactions including glutathione metabolism and fat and cholesterol biosynthesis. We have reported recently an important role for mitochondrial NADP ؉ -dependent isocitrate dehydrogenase in cellular defense against oxidative damage by providing NADPH needed for the regeneration of reduced glutathione. However, the role of cytosolic NADP ؉ -dependent isocitrate dehydrogenase (IDPc) is still unclear. We report here for the first time that IDPc plays a critical role in fat and cholesterol biosynthesis. During differentiation of 3T3-L1 adipocytes, both IDPc enzyme activity and its protein content were increased in parallel in a time-dependent manner. Increased expression of IDPc by stable transfection of IDPc cDNA positively correlated with adipogenesis of 3T3-L1 cells, whereas decreased IDPc expression by an antisense IDPc vector retarded adipogenesis. Furthermore, transgenic mice with overexpressed IDPc exhibited fatty liver, hyperlipidemia, and obesity. In the epididymal fat pads of the transgenic mice, the expressions of adipocyte-specific genes including peroxisome proliferator-activated receptor ␥ were markedly elevated. The hepatic and epididymal fat pad contents of acetylCoA and malonyl-CoA in the transgenic mice were significantly lower, whereas the total triglyceride and cholesterol contents were markedly higher in the liver and serum of transgenic mice compared with those measured in wild type mice, suggesting that the consumption rate of those lipogenic precursors needed for fat biosynthesis must be increased by elevated IDPc activity. Taken together, our findings strongly indicate that IDPc would be a major NADPH producer required for fat and cholesterol synthesis.Abnormal lipid metabolism is frequently associated with obesity and hyperlipidemia. In fat and cholesterol biosynthesis, NADPH is an essential cofactor for numerous enzymes. For instance, 3-L-hydroxylacyl-coenzyme A dehydrogenase and enoyl-coenzyme A reductase in fatty acid synthesis and hydroxymethylglutaryl-coenzyme A reductase, the rate-limiting enzyme in cholesterol biosynthesis, require NADPH for their enzyme activities. It has been demonstrated that glucose-6-phosphate dehydrogenase (G6PDH), 1 6-phosphogluconate dehydrogenase, and malic enzyme are considered as the major enzymes producing cytosolic NADPH (1). Nevertheless, the activities of these enzymes were markedly lower than that of cytosolic NADP ϩ -dependent isocitrate dehydrogenase (IDPc) in the rat liver (1, 2). Consistent with this observation, McLean and co-workers (3) reported that certain adaptive changes in the pentose phosphate pathway dehydrogenases did not take place in parallel with fat synthesis in adipose tissue and suggested that a major source of NADPH for fat synthesis could be IDPc. It is worthy of note that IDPc is expressed mainly in lipogenic tissues such as liver and adipocytes, whereas G6PDH and 6-phosphogluconate dehydrogenase are expressed ubiquitously (4, 5). These data indicate that NADPH-producing IDPc may ...

Males are much more susceptible to ischemia/reperfusion (I/R)-induced kidney injury when compared with females. Recently we reported that the presence of testosterone, rather than the absence of estrogen, plays a critical role in gender differences in kidney susceptibility to I/R injury in mice. Although reactive oxygen species and antioxidant defenses have been implicated in I/R injury, their roles remain to be defined. Here we report that the orchiectomized animal had significantly less lipid peroxidation and lower hydrogen peroxide levels in the kidney 4 and 24 h after 30 min of bilateral renal ischemia when compared with intact or dihydrotestosterone-treated orchiectomized males. The post-ischemic kidney expression and activity of manganese superoxide dismutase (MnSOD) in orchiectomized mice was much greater than in intact or dihydrotestosterone-administered orchiectomized mice. Four hours after 30 min of bilateral ischemia, superoxide formation was significantly lower in orchiectomized mice than in intact mice. In Madin-Darby canine kidney cells, a kidney epithelial cell line, 1 mM H 2 O 2 decreased MnSOD activity, an effect that was potentiated by pretreatment with dihydrotestosterone. Orchiectomy prevented the post-ischemic decrease of catalase activity. Treatment of male mice with manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP), a SOD mimetic, reduced the post-ischemic increase of plasma creatinine, lipid peroxidation, and tissue hydrogen peroxide. These results suggest that orchiectomy accelerates the post-ischemic activation of MnSOD and reduces reactive oxygen species and lipid peroxidation, resulting in reduced kidney susceptibility to I/R injury.Gender differences in disease susceptibility have been well characterized in many cardiovascular diseases (1-3). The increased risk for cardiovascular diseases in men and postmenopausal women (4) has been attributed primarily to lack of estrogen-mediated protection (5-7). Recently we demonstrated that male mice are much more susceptible to kidney ischemia/reperfusion (I/R) 5 injury when compared with female mice (8), and that orchiectomy decreases kidney susceptibility to I/R injury (9), whereas ovariectomy has no effect on kidney susceptibility to I/R injury (8). Testosterone administration to orchiectomized male or female mice reverses the protective phenotype, increasing susceptibility to kidney I/R injury. We concluded that the presence of testosterone, rather than the absence of estrogen, plays a critical role in the gender differences in kidney susceptibility to I/R injury. The detailed molecular mechanisms responsible for this testosterone effect remain to be defined.Ischemia/reperfusion markedly increases the production of reactive oxygen species (ROS) including superoxide anions, hydroxyl radicals, hypochlorous acid, hydrogen peroxide, and peroxynitrite (10). The abnormal excessive production of ROS results in lipid peroxidation, leukocyte activation, endothelial cell damage, and cytokine production, all of which contribute to tissue ...

The transduction of dopaminergic (DA) neurons with human ras homolog enriched in brain, which has a S16H mutation [hRheb(S16H)] protects the nigrostriatal DA projection in the 6-hydroxydopamine (6-OHDA)-treated animal model of Parkinson's disease (PD). However, it is still unclear whether the expression of active hRheb induces the production of neurotrophic factors such as glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF), which are involved in neuroprotection, in mature neurons. Here, we show that transduction of nigral DA neurons with hRheb(S16H) significantly increases the levels of phospho-cyclic adenosine monophosphate (cAMP) response element-binding protein (p-CREB), GDNF, and BDNF in neurons, which are attenuated by rapamycin, a specific inhibitor of mammalian target of rapamycin complex 1 (mTORC1). Moreover, treatment with specific neutralizing antibodies for GDNF and BDNF reduced the protective effects of hRheb(S16H) against 1-methyl-4-phenylpyridinium (MPP(+))-induced neurotoxicity. These results show that activation of hRheb/mTORC1 signaling pathway could impart to DA neurons the important ability to continuously produce GDNF and BDNF as therapeutic agents against PD.