Alterations of antioxidant enzymes and oxidative damage to macromolecules in different organs of rats during aging

The effect of 1,2,4-thiotriazolyl 5-mercaptoacetic acid new derivatives on lipid peroxidation in the heart from adult and old rats during stress

The effect of 3-(4-pyridyl)-1,2,4-thiotriazolyl 5-mercaptoacetic acid kalium salt (Rumosol) and 3-(4-pyridyl)-1,2,4-thiotriazolyl 5-mercaptoacetic acid morpholinium salt (drug 2) on the concentration of Schiff base in myocardium of adult (10-12 months) and old (22-25 months) Wistar rats during immobilized stress were investigated. Here we show that the accumulation of Schiff base in the heart from both age groups was inhibited after injection of derivatives of 1,2,4-thiotriazolyl 5-mercaptoacetic acid prior to immobilization. Drug 2 possessed a two-fold higher pronounced capacity against Rumosol to inhibit the accumulation of Schiff base in the heart during stress. In myocardium from old rats, drug 2 decreased more effectively the stress-induced stimulation of lipid peroxidation as compared to dimethyl sulfoxide.

Age-related changes in the distribution of nitrotyrosine in the cerebral cortex and hippocampus of rats

A wealth of indirect evidence implicates oxidative damage of cellular constituents in aging, as well as in the pathogenesis of the neurodegenerative diseases of later years. In the present study, we have determined age-related changes in the distribution of 3-nitrotyrosine (3-NT) in the cerebral cortex and hippocampus of rats. In adult rats, no 3-NT-immunoreactive cells were found in the cerebral cortex and hippocampus, whereas 3-NT immunoreactivity was significantly increased in aged rats. Some pyramidal cells of CA3 area and granule cells of the dentate gyrus highly expressed 3-NT in aged rats. Many interneurons located within stratum pyramidale and stratum oriens of CA1 were strongly immunoreactive for 3-NT. Our first demonstrations of increased 3-NT in the cerebral cortex and hippocampus during aging implicate these areas as sites for functionally significant oxidative damage. The mechanisms underlying the increased immunoreactivity for 3-NT, and the functional implications of this increase, require elucidation.

Enhanced maze performance and reduced oxidative stress by combined extracts of zingiber officinale and ginkgo biloba in the aged rat

Here we assessed the effects of i.g. administration of Zingicomb (ZC), a mixture of zingiber officinale and ginkgo biloba extracts, on learning and memory, and on indicators of oxidative stress in aged rats. Effects of ZC (1 and 10 mg/kg) were investigated in 22-24 months old Wistar rats using the Morris water maze, in which they show deficient performance as compared to 3 months old rats in the undrugged state (days 1 and 2). Treatment was administered on days 3 and 4 of training, then over 7 days with training discontinued, and again on days 5 and 6 when training was resumed. Thereafter chronic treatment was maintained over 5 months. 1 mg/kg ZC improved escape learning in the water maze. The two capital indicators of oxidative stress in brain homogenates, the amount of oxidized proteins (assessed as carbonyl group containing proteins) and lipid peroxidation, were significantly reduced in ZC treated animals. Thus, ZC, which had previously been shown to improve inhibitory avoidance learning and to have anxiolytic properties in adult animals, might also facilitate spatial learning in aged animals, and reduces indices of oxidative stress in brain tissue after chronic treatment.

Age-related changes in protein oxidation and proteolysis in mammalian cells

Reactive oxygen species generated as by-products of oxidative metabolism, or from environmental sources, frequently damage cellular macromolecules. Proteins are recognized as major targets of oxidative modification, and the accumulation of oxidized proteins is a characteristic feature of aging cells. An increase in the amount of oxidized proteins has been reported in many experimental aging models, as measured by the level of intracellular protein carbonyls or dityrosine, or by the accumulation of protein-containing pigments such as lipofuscin and ceroid bodies. In younger individuals, moderately oxidized soluble cell proteins appear to be selectively recognized and rapidly degraded by the proteasome. An age-related accumulation of oxidized proteins could, therefore, be a result of declining activity of the proteasome. Previous research to investigate the notion of an age-related decline in the content and/or activity of the proteasome has generated contradictory results. The latest evidence, including our own recent findings, indicates that proteasome activity does, indeed, decline during aging as the enzyme complex is progressively inhibited by oxidized and cross-linked protein aggregates. We propose that cellular aging involves both an increase in (mitochondrial) oxidant production and a progressive decline in proteasome activity. Eventually so much proteasome is inactivated that oxidized proteins begin to accumulate rapidly and contribute to cellular dysfunction and senescence.

Measurements of protein carbonyls, ortho- and meta-tyrosine and oxidative phosphorylation complex activity in mitochondria from young and old rats

Mitochondrial bioenergetic function is often reported to decline with age and the accumulation of oxidative damage is thought to contribute. However, there are considerable uncertainties about the amount and significance of mitochondrial oxidative damage in aging. We hypothesized that, as radical production in mitochondria is greater than the rest of the cell, protein oxidative damage should accumulate more in mitochondria than the cytoplasm, and that this relative accumulation should increase with age. To test these hypotheses we measured the accumulation of three markers of protein oxidative damage in liver, brain, and heart from young and old rats. Ortho- and meta-tyrosine levels in protein hydrolysates were measured by a gas chromatography/mass spectrometry assay, and protein carbonyl content was determined by ELISA. Using these assays we found no evidence for increased protein oxidative damage in mitochondria relative to the cytosol. Most increases found in protein oxidative damage on aging were modest for all three tissues and there was no consistent pattern of increased oxidative damage in mitochondrial proteins on aging. Mitochondrial oxidative phosphorylation complex activities were also assessed revealing 39-42% decreases in F0F1--ATP synthase activity in liver and heart on aging, but not in other oxidative phosphorylation complexes. These findings have implications for the contribution of mitochondrial oxidative damage and dysfunction to aging.

Mitochondrial cytochrome oxidase immunolabeling in aged human temporal bones

Presbycusis, an age-related hearing loss, is accompanied by histopathological cochlear changes including variable amounts of degeneration of the auditory receptors, neurons and the stria vascularis. The causes of degeneration are unknown, although acoustic trauma and exposure to ototoxic agents are certainly contributors to the cellular degeneration. Acquired mitochondrial DNA defects are postulated as important determinants of aging in neuromuscular tissues. The cochlear neurons are highly metabolic and are, therefore, likely to be affected by mitochondrial DNA defects. Sequence analysis has demonstrated a significant number of acquired mutations in the cytochrome oxidase gene in the neurons from aged human cochleas. The current study used immunohistochemical labeling of cytochrome oxidase in the neuronal cell bodies in archival celloidin sections to evaluate relationships among label density, hearing loss, number of neurons and mitochondrial DNA changes within individual cochleas. Label density was less in many aged temporal bones, but not all. There was no relationship among any other variables. It is concluded that while there may be a decrease in the amount of cytochrome oxidase expression in aged spiral ganglion cell bodies, there are many other factors that contribute to hearing loss and cellular degeneration.

Hypothyroidism in the developing rat brain is associated with marked oxidative stress and aberrant intraneuronal accumulation of neurofilaments

The effects of hypothyroidism on parameters of oxidative stress and on intraneuronal distribution of neurofilaments have been investigated in the developing rat brain. Progressive hypothyroidism during the first 4 weeks of postnatal development led to an increase in superoxide dismutase and catalase activity, decline in the level of glutathione and mitochondrial cytochrome c oxidase activity and increase in the level of .OH radical along with enhanced protein carbonylation and lipid peroxidation. Immunocytochemical staining of cryostat sections of normal and hypothyroid cerebella from 25 day postnatal rats with anti neurofilament (NF) light chain (L) antibody showed aberrant accumulation of neurofilaments in the perikaryon of the hypothyroid Purkinje neurons in contrast to relatively uniform distribution in the controls. The morphological and biochemical alterations in the neurons of the developing hypothyroid brain are comparable to those seen in several neurodegenerative diseases.

Antioxidant imbalance in the lungs of cystic fibrosis transmembrane conductance regulator protein mutant mice

Recent studies suggest that the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein modulates epithelial reduced glutathione (GSH) transport and when defective creates an antioxidant imbalance. To test whether the CFTR protein modulates lung antioxidant defenses in vivo, epithelial lining fluid (ELF) and lung tissue from CFTR knockout (CFTR-KO) and wild-type (WT) mice were compared for GSH content and the activities of glutathione reductase, glutathione peroxidase, and gamma-glutamyltransferase. In the CFTR-KO mice, the ELF concentration of GSH was decreased (51%) compared with that in WT mice. The concentration of GSH in the lung tissue of CFTR-KO mice, however, was not significantly different from that in WT mice. The activities of glutathione reductase and glutathione peroxidase in the lung tissue of CFTR-KO mice were significantly increased compared with those in WT mice (48 and 28%, respectively). Tissue lipid and DNA oxidation were evaluated by measurement of thiobarbituric acid-reactive substances and 8-hydroxy-2'-deoxyguanosine, respectively. The levels of thiobarbituric acid-reactive substances and 8-hydroxy-2'-deoxyguanosine in the lung tissue of CFTR-KO mice were significantly increased compared with those in WT mice. These data support our hypothesis that a mutation in the CFTR gene can affect the antioxidant defenses in the lung and may contribute to the exaggerated inflammatory response observed in CF.

Coenzymes Q9 and Q10, vitamin E and peroxidation in rat synaptic and non-synaptic occipital cerebral cortex mitochondria during ageing

Great attention has been devoted both to ageing phenomena at the mitochondrial level and to the antioxidant status of membrane structures. These kinds of investigations are difficult to perform in the brain because of its heterogeneity. It is known that synaptic heavy mitochondria (HM) may represent an aged mitochondrial population characterized by a partial impairment of their typical mitochondrial function. We arranged a novel system requiring no extraction procedure, very limited handling of the samples and their direct injection into the HPLC apparatus, to carry out, for the first time, a systematic and concomitant determination of vitamin E, Coenzyme Q9 (CoQ9) and Coenzyme Q10 (CoQ10) contents in rat brain mitochondria. The trends found for CoQ9 and CoQ10 levels in synaptic and non-synaptic occipital cerebral cortex mitochondria during rat ageing are consistent with previous data. Hydroperoxides (HP) differed with age and it was confirmed that in the HM fraction the summation of contributions results in an oxidatively jeopardized subpopulation. We found that vitamin E seems to increase with age, at least in non-synaptic free (FM) and synaptic light (LM) mitochondria, while it was inclined to remain substantially constant in HM.

Therapeutic potential of dietary phase 2 enzyme inducers in ameliorating diseases that have an underlying inflammatory component

Many diseases associated with ageing have an underlying oxidative stress and accompanying inflammatory component, for example, Alzheimer's disease or atherosclerosis. Reviewed in this manuscript are: the role of oxidative stress in activating the transcription factor nuclear factor kappa B (NFκB), the role of NFκB in activating pro-inflammatory gene transcription, strong oxidants produced by cells, anti-oxidant defense systems, the central role of phase 2 enzymes in the anti-oxidant defense, dietary phase 2 enzyme inducers and evidence that dietary phase 2 enzymes decrease oxidative stress. It is likely that a diet containing phase 2 enzyme inducers may ameliorate or even prevent diseases that have a prominent inflammatory component to them. Research should be directed into the potential therapeutic effects of dietary phase 2 enzyme inducers in ameliorating diseases with an underlying oxidative stress and inflammatory component to them.Key words: Alzheimer's disease, atherosclerosis, diet, glutathione, inflammation, stroke.

Oxidative-stress-dependent up-regulation of Bcl-2 expression in the central nervous system of aged Fisher-344 rats

Oxidative stress has been shown to play a role in aging and in neurodegenerative disorders. Some of the consequences of oxidative stress are DNA base modifications, lipid peroxidation, and protein modifications such as formation of carbonyls and nitrotyrosine. These events may play a role in apoptosis, another factor in aging and neurodegeneration, in response to uncompensated oxidative stress. Bcl-2 is a mitochondrial protein that protects neurons from apoptotic stimuli including oxidative stress. Using immunohistochemistry and western blot analysis, here we show that Bcl-2 is up-regulated in the hippocampus and cerebellum of aged (24 months) Fisher 344 rats. Treatment with the free radical spin trap N-tert-butyl-alpha-phenylnitrone (PBN) effectively reverses this age-dependent Bcl-2 up-regulation indicating that this response is redox sensitive. This conclusion was further supported by inducing the same regional Bcl-2 up-regulation in young (3 months) Fisher 344 rats exposed to 100% normobaric O(2) for 48 h. Our results indicate that Bcl-2 expression is increased in the aged brain, possibly as a consequence of oxidative stress challenges. These results also illustrate the effectiveness of antioxidants in reversing age-related changes in the CNS and support further research to investigate their use in aging and in age-related neurodegenerative disorders.

Resistance of isolated pulmonary mitochondria during in vitro anoxia/reoxygenation

The aim of the study was to investigate the effect of in vitro anoxia/reoxygenation on the oxidative phosphorylation of isolated lung mitochondria. Mitochondria were isolated after harvesting from fresh pig lungs flushed with Euro-Collins solution. Mitochondrial respiratory parameters were determined in isolated mitochondria before anoxia (control), after 5-45 min anoxia followed by 5 min reoxygenation, and after 25 or 40 min of in vitro incubation in order to follow the in vitro aging of mitochondria during respiratory assays. Respiratory parameters measured after anoxia/reoxygenation did not show any oxidative phosphorylation dysfunction, indicating a high resistance of pulmonary mitochondria to in vitro anoxia/reoxygenation (up to 45 min anoxia). These results indicate that mitochondria are not directly responsible of their oxidative phosphorylation damage observed after in vivo ischemia (K. Willet et al., Transplantation 69 (2000) 582) but are a target of others cellular injuries leading to mitochondrial dysfunction in vivo.

NO synthase and NO-dependent signal pathways in brain aging and neurodegenerative disorders: the role of oxidant/antioxidant balance

Nitric oxide and other reactive nitrogen species appear to play several crucial roles in the brain. These include physiological processes such as neuromodulation, neurotransmission and synaptic plasticity, and pathological processes such as neurodegeneration and neuroinflammation. There is increasing evidence that glial cells in the central nervous system can produce nitric oxide in vivo in response to stimulation by cytokines and that this production is mediated by the inducible isoform of nitric oxide synthase. Although the etiology and pathogenesis of the major neurodegenerative and neuroinflammatory disorders (Alzheimer's disease, amyothrophic lateral sclerosis, Parkinson's disease, Huntington's disease and multiple sclerosis) are unknown, numerous recent studies strongly suggest that reactive nitrogen species play an important role. Furthermore, these species are probably involved in brain damage following ischemia and reperfusion, Down's syndrome and mitochondrial encephalopathies. Recent evidence also indicates the importance of cytoprotective proteins such as heat shock proteins (HSPs) which appear to be critically involved in protection from nitrosative and oxidative stress. In this review, evidence for the involvement of nitrosative stress in the pathogenesis of the major neurodegenerative/ neuroinflammatory diseases and the mechanisms operating in brain as a response to imbalance in the oxidant/antioxidant status are discussed.

The effects of aliphatic (n-nonane), naphtenic (1,2, 4-trimethylcyclohexane), and aromatic (1,2,4-trimethylbenzene) hydrocarbons on respiratory burst in human neutrophil granulocytes

This study investigates the effects of aliphatic (n-heptane, n-nonane), naphtenic (methylcyclohexane, 1,2,4-trimethylcyclohexane (TMCH)), and aromatic (methylbenzene, 1,2,4-trimethylbenzene (TMB)) hydrocarbons on respiratory burst in human granulocytes. The free radical formation was measured as 2,7-dichlorofluorescein diacetate-amplified (DCF) fluorescence, by electron paramagnetic resonance (EPR) spectroscopy and by hydroxylation of 4-hydroxybenzoate. The chemotactic peptide N-formyl-met-leu-phe (fMLP) and phorbol 12-myristate 13-acetate (PMA), a diacylglycerol analogue, were included as positive controls. DCF fluorescence was elevated in a concentration-dependent manner by C9 hydrocarbons. The C7 hydrocarbons did not stimulate respiratory burst in the concentration range examined. The naphtenic hydrocarbon TMCH showed the strongest effect on respiratory burst and was therefore selected for mechanistic studies of this free radical formation. In the absence of extracellular Ca(2+), fluorescence in response to TMCH and fMLP was reduced by 77 and 90%, respectively. Preincubation of the granulocytes with the protein kinase C inhibitor bisindolylmaleimide reduced the DCF fluorescence stimulated with TMCH, fMLP, and PMA by 82, 56, and 90%, respectively. The phospholipase C inhibitor U73122 lowered the TMCH- and fMLP-activated DCF fluorescence by 87 and 76%. In addition, the TMCH- and fMLP-induced DCF fluorescence, after the preincubation with the phospholipase D modulator n-butanol, was lowered by 83 and 52%, respectively. The importance of protein kinase C, phospholipase C, and phospholipase D for elevation of respiratory burst was also demonstrated by the EPR experiments using the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO). Preincubation with the NADPH oxidase inhibitor diphenyleneiodonium and diethyldithiocarbamate, which inhibits superoxide dismutase, led to an almost complete reduction of DCF fluorescence in response to TMCH, fMLP, and PMA. Preincubation with diethyldithiocarbamate led to the elevation of superoxide adducts of DEPMPO. The hydrocarbons stimulated formation of mainly the superoxide (O(*-)(2)) adduct of DEPMPO (DEPMPO-OOH) but also small amounts of the hydroxyl adduct ((*)OH) (DEPMPO-OH). Using 4-hydroxybenzoate as a hydroxyl radical trap confirmed formation of (*)OH after stimulation with the hydrocarbons. In conclusion, our findings indicate that TMCH-activated respiratory burst is dependent on the Ca(2+)-dependent phospholipase C, phospholipase D, and protein kinase C prior to activation of the NADPH oxidase.

Catalase expression in delayed and premature aging mouse models

The physiological decline that occurs with aging is thought to result, in part, from accumulation of oxidative damage produced by reactive oxygen species (ROS) generated during normal metabolism. Two genetic mouse models of aging, the Ames dwarf and growth hormone (GH) transgenic, suggest that hormone levels may play a role in antioxidative defense and aging. To explore this possibility, catalase (CAT), an enzyme involved in elimination of ROS, was evaluated in long-lived dwarf and short-lived transgenic mice. Catalase activity and/or protein was significantly elevated in livers from dwarf mice at 3, 6, 13-15, and 24 months of age when compared to age-matched wild type mice. In contrast, a 50 and 38% reduction (P<0.05) in CAT protein was observed in 3 and 10 to 12 month old GH transgenics respectively, when compared to wild type mice. Kidneys from old dwarf mice exhibited significantly increased CAT activity (22%), protein (16%) and mRNA expression (59%) compared to wild type mice. Conversely, kidneys from GH transgenic mice showed reductions in CAT activity. The results of this study suggest that hormonal status modulates antioxidative mechanisms and that CAT is important in overall defense capacity with respect to lifespan in both decelerated (dwarf) and accelerated (transgenic) mammalian models of aging.

A microtiter plate assay for superoxide dismutase using a water-soluble tetrazolium salt (WST-1)

A simple and reproducible microtiter plate assay for measuring superoxide dismutase (SOD) activity is described. Water-soluble tetrazolium, the sodium salt of 4-[3-(4iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-be nzene disulfonate, was used as a detector of superoxide radical generated by xanthine oxidase and hypoxanthine, in the presence of a range of concentrations of superoxide dismutase. A major advantage of the assay is that one reaction mixture is prepared and aliquotted into wells, avoiding pipetting errors and variable xanthine oxidase activity between samples. Inclusion of standardized SOD solution in each run enables inter-assay comparability without requiring a constant superoxide generation rate under all occasions. The assay is applicable for chloroform-ethanol red cell extracts as well as tissue homogenates without high-speed centrifugation. Fifty percent inhibition of formazan formation was achieved at 2.4+/-0.1 ng of Cu, ZnSOD per well with the coefficient of variation 4.2%.

Age-related changes in reactive oxygen species production in rat brain homogenates

The generation of reactive oxygen species (ROS) and resultant oxidative stress have been implicated in the mechanism of brain dysfunction due to age-related neurodegenerative diseases or exposure to environmental chemicals. We have investigated intrinsic age-related differences in the ability of the various brain regions to generate ROS in the absence and presence of Fe(2)+. ROS production in crude brain homogenates from adult rats was linear with respect to time and tissue concentration, and was stimulated to a greater extent by Fe(2)+ than was TBARS production. ROS production was then determined in homogenates from cerebral cortex, striatum, hippocampus, and cerebellum of 7-day-old, 14-day-old, 21-day-old, adult (3-6-month old), and aged (24-month-old) rats using the fluorescent probe 2',7'-dichlorodihydrofluorescin (DCFH). Basal levels of ROS production were similar in 7-, 14-, and 21-day olds, increased in adults, and highest in aged rats, and did not differ between brain regions. ROS production was stimulated by Fe(2)+ (0. 3-30 microM) in a concentration-dependent manner in all brain regions. However, the stimulation of ROS production by Fe(2)+ varied with age. ROS production was greater in 14- and 21-day-old rats compared with adult and aged animals. ROS production in 7-day-old rats was decreased at low Fe(2)+ concentrations and increased at high Fe(2)+ concentrations compared to adult and aged rats. These data show that brain homogenates from neonatal rats respond differently to Fe(2)+, and suggest that developing animals may be more sensitive to oxidative stress in the brain after exposure to toxicants. Published by Elsevier Science Inc.

Hydrogen peroxide-mediated protein oxidation in young and old human MRC-5 fibroblasts

It is suggested that the aging process is dependent on the action of free radicals. One of the highlights of age-related changes of cellular metabolism is the accumulation of oxidized proteins. The present investigation was undertaken to reveal the proliferation-related changes in the protein oxidation and proteasome activity during and after an acute oxidative stress. It could be demonstrated that the activity of the cytosolic proteasomal system declines during proliferative senescence of human MRC-5 fibroblasts and is not able to remove oxidized proteins in old cells efficiently. Whereas in young cells removal of oxidized proteins was accompanied by an increase in the overall protein turnover, this increase in protein turnover could not be seen in old MRC-5 fibroblasts. Therefore, our studies demonstrate that old fibroblasts are much more vulnerable to the accumulation of oxidized proteins after oxidative stress and are not able to remove these oxidized proteins as efficiently as young fibroblasts.

Mitochondrial oxidative stress in mice lacking the glutathione peroxidase-1 gene

Oxidative stress resulting from mitochondrially derived reactive oxygen species (ROS) has been hypothesized to damage mitochondrial oxidative phosphorylation (OXPHOS) and to be a factor in aging and degenerative disease. If this hypothesis is correct, then genetically inactivating potential mitochondrial antioxidant enzymes such as glutathione peroxidase-1 (Gpx1; EC 1.11.1.9) should increase mitochondrial ROS production and decrease OXPHOS function. To determine the expression pattern of Gpx1, isoform-specific antibodies were generated and mutant mice were prepared in which the Gpx1 protein was substituted for by beta-galactosidase, driven by the Gpx1 promoter. These experiments revealed that Gpx1 is highly expressed in both the mitochondria and the cytosol of the liver and kidney, but poorly expressed in heart and muscle. To determine the physiological importance of Gpx1, mice lacking Gpx1 were generated by targeted mutagenesis in mouse ES cells. Homozygous mutant Gpx1(tm1Mgr) mice have 20% less body weight than normal animals and increased levels of lipid peroxides in the liver. Moreover, the liver mitochondria were found to release markedly increased hydrogen peroxide, a Gpx1 substrate, and have decreased mitochondrial respiratory control ratio and power output index. Hence, genetic inactivation of Gpx1 resulted in growth retardation, presumably due in part to reduced mitochondrial energy production as a product of increased oxidative stress.

Oxidative damage and protection of the RPE

This review provides a model for the role of oxidative stress in the etiology of age-related macular degeneration (AMD). Epidemiological studies of diet, environmental and behavioral risk factors suggest that oxidative stress is a contributing factor of AMD. Pathological studies indicate that damage to the retinal pigment epithelium (RPE) is an early event in AMD. In vitro studies show that oxidant treated RPE cells undergo apoptosis, a possible mechanism by which RPE cells are lost during early phase of AMD. The main target of oxidative injury seems to be mitochondria, an organelle known to accumulate genomic damages in other postmitotic tissues during aging. The thiol antioxidant GSH and its amino acid precursors protect RPE cells from oxidant-induced apoptosis. Similar protection occurs with dietary enzyme inducers which increase GSH synthesis. These results indicate that therapeutic or nutritional intervention to enhance the GSH antioxidant capacity of RPE may provide an effective way to prevent or treat AMD.

Age-associated decline in gamma-glutamylcysteine synthetase gene expression in rats

Although glutathione (GSH) concentration has been reported to diminish with age, the mechanism underlying such age-associated decline in the GSH content is not well understood. In this study, we compared the gene expression of both subunits of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo GSH synthesis, in young, adult, and old Fisher 344 rats. It was found that GCS activity was significantly decreased with increased age in liver, kidney, lung, and red blood cells (RBC). Parallel with the decreased enzyme activity, the protein and mRNA contents of both GCS subunits also changed inversely with age in liver, kidney, and lung, implying a decreased GCS gene expression during aging. Such a reduced GCS gene expression was accompanied by a decline in total GSH content without any change in cysteine concentration. Furthermore, the decreased GCS gene expression in old rats was not associated with a decline in the plasma insulin or cortisol level. This study showed, for the first time, that the expression of both GCS subunit genes was decreased in some organs of old rats, which would result in a reduced rate of GSH biosynthesis. Such decline in GSH synthetic capacity may underlie the observed decrease in GSH content during aging.

Age and organ dependent spontaneous generation of nuclear 8-hydroxydeoxyguanosine in male Fischer 344 rats

8-Hydroxydeoxyguanosine (8-OHdG) is a major oxidative DNA adduct playing roles in senescence, carcinogenesis and various disease processes. High-performance liquid chromatography with an electrochemical detection (HPLC-ECD) method has been widely used to assess organ levels of 8-OHdG, and a recently introduced immunohistochemical approach has made it possible to clarify intra-organ localization. In the present study, these methods were employed to reveal age-dependent changes in nuclear 8-OHdG within various tissues of male Fischer 344 rats between 18 fetal days and 104 weeks of age. 8-OHdG was detected in the nuclei of cerebellar small granule and small cortical cells, cerebral nerve cells, and choroid plexus epithelia of the brain and ependymal cells of the spinal cord; parenchymal cells in the anterior lobe of the pituitary and adrenal glands (mainly cortex); bronchial epithelium of the lung; intra-hepatic bile duct, pancreatic duct, glandular gastric and intestinal epithelial cells; renal tubular epithelial cells (mainly medulla); and spermatogonia and spermatocytes of the testis and seminal vesicle epithelia. The nuclear 8-OHdG levels were high (more than two lesions per 10(6) deoxyguanosines) from 7 days to 104 weeks of age in the brain, 3 to 6 weeks in the adrenal gland, 6 to 104 weeks in the lung, and 3 to 52 weeks in the testis. In the other organs, the nuclear 8-OHdG levels remained low throughout. These findings provide a basis for research dealing with oxidative stress by indicating organ-specific and age- but not aging-dependent changes in the localization of spontaneously generated nuclear 8-OHdG in intact rats. The immunohistochemical approach has advantages for assessing variation of 8-OHdG formation at the cellular level not accessible to the HPLC-ECD method.

Aging exacerbates hydrogen peroxide-induced alteration of vascular reactivity in rats

Reactive oxygen species (ROS) such as superoxide anion (O2-*) and hydrogen peroxide (H2O2) can be produced by vascular endothelium and smooth muscle cells under diverse physiological and pathophysiological situations. These species are known to exert various deleterious effects by which they might induce changes in vascular reactivity. The aim of the present study was to evaluate the evolution of vascular susceptibility to H2O2 during aging in rats. Catalase activity was assessed in aortas from young adult (4 months) and aged (24 months) Wistar rats. In parallel experiments, isolated rings from both age groups were exposed to increasing doses of H2O2 (0, 0.1, 1, 5, or 10 mM) for 20 min and the residual vascular response to phenylephrine (PE = 10(-6) M) and acetylcholine (ACh = 10(-6) M) was evaluated. Our results indicate that aging increases aortic catalase activity (4 months: 0.20 +/- 0.02 IU/mg prot versus 24 months: 0.46 +/- 0.06 IU/mg prot, p < 0.001) while it exacerbates vascular sensitivity to H2O2. These results suggest that the observed increased H2O2-induced alterations of vascular reactivity during aging in rats might be due to increased sensitivity of the vasculature to ROS rather than to a decrease in the defense systems against these species.