Attenuation of age-dependent oxidative damage to DNA and protein in brainstem of Tg Cu/Zn SOD mice

Interactive Effects of Swimming High-Intensity Interval Training and Resveratrol Supplementation Improve Mitochondrial Protein Levels in the Hippocampus of Aged Rats

Mitochondrial dysfunction and increased oxidative stress cause damage to cells which can lead to the aging process and age-related diseases. Antioxidants such as resveratrol and high-intensity exercise can benefit oxidative damage prevention. This study is aimed at evaluating the effects of swimming high-intensity interval training and resveratrol on mitochondrial metabolism key proteins, SIRT5, SOD1, and PDH-E1α, and the level of NAD+ as a cofactor in the deacetylation process in aged rat hippocampus. Forty-five male Wistar rats, aged 20 months, were randomly divided into five groups: control (C), Swimming High-Intensity Interval Training (HIIT) (S-HIIT), Swimming HIIT with resveratrol supplementation (S-HIIT-R), resveratrol supplementation (R), and solvent of resveratrol supplementation (SR). S-HIIT and resveratrol groups performed the exercise and received resveratrol (10 mg/kg/day, gavage) for six weeks. Western blot analysis was performed to determine the protein level in the hippocampus. The amount of SIRT5 and SOD1 proteins in the hippocampus increased. S-HIIT with resveratrol or resveratrol alone increased the PDH-E1α level significantly. The amount of NAD+ was analyzed by assay kit that was reduced in S-HIIT, S-HIIT-R, and SR groups compared to controls. The results showed that resveratrol and S-HIIT attenuated the age-related brain changes by increasing the expression of SOD1 and SIRT5 and reducing the level of NAD+ in the hippocampus. Considering these findings, S-HIIT and resveratrol supplementation could be proposed as strategies to attenuate age-related brain changes. Resveratrol alone and exercise through the regulation of crucial proteins and cofactors can influence mitochondrial metabolism and oxidative stress in the hippocampus of aged rats.

Prevention of age-related changes in hippocampal levels of 5-methylcytidine by caloric restriction

Aberrant DNA methylation patterns have been linked to molecular and cellular alterations in the aging brain. Caloric restriction (CR) and upregulation of antioxidants have been proposed as interventions to prevent or delay age-related brain pathology. Previously, we have shown in large cohorts of aging mice, that age-related increases in DNA methyltransferase 3a (Dnmt3a) immunoreactivity in the mouse hippocampus were attenuated by CR, but not by overexpression of superoxide dismutase 1 (SOD1). Here, we investigated age-related alterations of 5-methylcytidine (5-mC), a marker of DNA methylation levels, in a hippocampal subregion-specific manner. Examination of 5-mC immunoreactivity in 12- and 24-month-old wild type (WT) mice on control diet, mice overexpressing SOD1 on control diet, wild type mice on CR, and SOD1 mice on CR, indicated an age-related increase in 5-mC immunoreactivity in the hippocampal dentate gyrus, CA3, and CA1-2 regions, which was prevented by CR but not by SOD1 overexpression. Moreover, positive correlations between 5-mC and Dnmt3a immunoreactivity were observed in the CA3 and CA1-2. These findings suggest a crucial role for DNA methylation in hippocampal aging and in the mediation of the beneficial effects of CR on aging.

Caloric restriction attenuates age-related changes of DNA methyltransferase 3a in mouse hippocampus

Recent studies have suggested that DNA methylation is implicated in age-related changes in gene expression as well as in cognition. DNA methyltransferase 3a (Dnmt3a), which catalyzes DNA methylation, is essential for memory formation and underlying changes in neuronal and synaptic plasticity. Because caloric restriction (CR) and upregulation of antioxidants have been suggested as strategies to attenuate age-related alterations in the brain, we hypothesized that both a diet restricted in calories and transgenic overexpression of normal human Cu/Zn superoxide dismutase 1 (SOD) attenuate age-related changes in Dnmt3a in the aging mouse hippocampus. For this purpose, we performed qualitative and quantitative analyses of Dnmt3a-immunoreactivity (IR) for the hippocampal dentate gyrus (DG), CA3 and CA1-2 regions in 12- and 24-month-old mice from 4 groups, i.e. (1) wild-type (WT) mice on a control diet (WT-CD), (2) SOD-CD mice, (3) WT mice on CR (WT-CR), and (4) SOD-CR. Qualitative analyses revealed two types of Dnmt3a immunoreactive cells: type I cells--present throughout all hippocampal cell layers showing moderate levels of nuclear Dnmt3a-IR, and type II cells--a subpopulation of hippocampal cells showing very intense nuclear Dnmt3a-IR, and colocalization with Bromodeoxyuridine. Quantitative analyses indicated that the age-related increase in Dnmt3a-IR within the CA3 and CA1-2 in type I cells was attenuated by CR, but not by SOD overexpression. In contrast, the density of type II Dnmt3a immunoreactive cells showed an age-related reduction, without significant effects of both CR and SOD. These changes in Dnmt3a levels in the mouse hippocampus may have a significant impact on gene expression and associated cognitive functioning.

Folate deficiency induces neurodegeneration and brain dysfunction in mice lacking uracil DNA glycosylase

Folate deficiency and resultant increased homocysteine levels have been linked experimentally and epidemiologically with neurodegenerative conditions like stroke and dementia. Moreover, folate deficiency has been implicated in the pathogenesis of psychiatric disorders, most notably depression. We hypothesized that the pathogenic mechanisms include uracil misincorporation and, therefore, analyzed the effects of folate deficiency in mice lacking uracil DNA glycosylase (Ung-/-) versus wild-type controls. Folate depletion increased nuclear mutation rates in Ung-/- embryonic fibroblasts, and conferred death of cultured Ung-/- hippocampal neurons. Feeding animals a folate-deficient diet (FD) for 3 months induced degeneration of CA3 pyramidal neurons in Ung-/- but not Ung+/+ mice along with decreased hippocampal expression of brain-derived neurotrophic factor protein and decreased brain levels of antioxidant glutathione. Furthermore, FD induced cognitive deficits and mood alterations such as anxious and despair-like behaviors that were aggravated in Ung-/- mice. Independent of Ung genotype, FD increased plasma homocysteine levels, altered brain monoamine metabolism, and inhibited adult hippocampal neurogenesis. These results indicate that impaired uracil repair is involved in neurodegeneration and neuropsychiatric dysfunction induced by experimental folate deficiency.

Exposure to lead and the developmental origin of oxidative DNA damage in the aging brain

Oxidative damage to DNA has been associated with neurodegenerative diseases. Developmental exposure to lead (Pb) has been shown to elevate the Alzheimer's disease (AD) related beta-amyloid peptide (Abeta), which is known to generate reactive oxygen species in the aging brain. This study measures the lifetime cerebral 8-hydroxy-2'-deoxyguanosine (oxo8dG) levels and the activity of the DNA repair enzyme 8-oxoguanine DNA glycosylase (Ogg1) in rats developmentally exposed to Pb. Oxo8dG was transiently modulated early in life (Postnatal day 5), but was later elevated 20 months after exposure to Pb had ceased, while Ogg1 activity was not altered. Furthermore, an age-dependent loss in the inverse correlation between Ogg1 activity and oxo8dG accumulation was observed. The effect of Pb on oxo8dG levels did not occur if animals were exposed to Pb in old age. These increases in DNA damage occurred in the absence of any Pb-induced changes in copper/zinc-superoxide dismutase (SOD1), manganese-SOD (SOD2), and reduced-form glutathion (GSH). These data suggest that oxidative damage and neurodegeneration in the aging brain could be impacted by the developmental disturbances.

Correlation between copper/zinc superoxide dismutase and the proliferation of neural stem cells in aging and following focal cerebral ischemia

Object

Neural stem cells (NSCs) have been demonstrated in the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone of the hippocampal dentate gyrus (DG). Although aging rats manifest a decrease in NSCs, rats exposed to stress (for example, ischemia, epilepsy, radiation, and trauma) show an increase in these cells. In transgenic mice, the overexpression of human copper/zinc superoxide dismutase (SOD1), an endogenous antioxidant, has been reported to be a protective enzyme against transient focal cerebral ischemia. The authors investigated the correlation between SOD1 and the proliferation of NSCs in aging as chronic oxidative stress (Experiment 1) and acute oxidative stress induced by transient focal cerebral ischemia (Experiment 2) in mice.

Methods

Bromodeoxyuridine (BrdU) was used in the evaluation of NSCs. In Experiment 1, NSCs in the SVZ significantly increased in 16-month-old transgenic mice compared with wild-type mice (p = 0.0001). In Experiment 2, mice were subjected to 30-minute occlusions of the middle cerebral artery. The increase in NSCs in the DG in transgenic mice was significantly greater than that in wild-type mice (p < 0.05).

Conclusions

Results in this study suggest that chronic and acute oxidative stress may inhibit the proliferation of NSCs and that SOD1 may play a key role in NSC proliferation.

Isolation and characterization of neurogenic mesenchymal stem cells in human scalp tissue

Recent studies have shown that adult tissues contain stem/ progenitor cells capable of not only generating mature cells of their tissue of origin but also transdifferentiating themselves into other tissue cells. Murine skin-derived precursor cells, for example, have been described as unique, nonmesenchymal-like stem cells capable of mesodermal and ectodermal neurogenic differentiation. Human-derived skin precursors are less well characterized. In this study, the isolation and characterization of adherent, mesenchymal stem cell-like cells from human scalp tissue (hSCPs) are described. hSCPs initially isolated by both medium-selection (ms-hSCPs) and single-cell (c-hSCPs) methods were cultured in medium containing epidermal growth factor and fibroblast growth factor-beta. Cultured ms-hSCPs and c-hSCPs demonstrated a consistent growth rate, continuously replicated in cell culture, and displayed a stable phenotype indistinguishable from each other. Both hSCPs expressed surface antigen profile (CDw90, SH2, SH4, CD105, CD166, CD44, CD49d-e, and HLA class I) similar to that of bone marrow mesenchymal stem cells (BM-MSCs). The growth kinetics, surface epitopes, and differentiation potential of c-hSCP cells were characterized and compared with BM-MSCs. In addition to differentiation along the osteogenic, chondrogenic, and adipogenic lineages, hSCPs can effectively differentiate into neuronal precursors evident by neurogenic gene expression of glial fibrillary acid protein, NCAM, neuron filament-M, and microtubule-associated protein 2 transcripts. Therefore, hSCPs may potentially be a better alternative of BM-MSCs for neural repairing, in addition to their other mesenchymal regenerative capacity. Our study suggests that hSCPs may provide an alternative adult stem cell resource that may be useful for regenerative tissue repair and autotransplantations.

Lack of the DNA repair enzyme OGG1 sensitizes dopamine neurons to manganese toxicity during development

Onset of Parkinson's disease (PD) and Parkinson-like syndromes has been associated with exposure to diverse environmental stimuli. Epidemiological studies have demonstrated that exposure to elevated levels of manganese produces neuropathological changes localized to the basal ganglia, including neuronal loss and depletions in striatal dopamine content. However, understanding the mechanisms associated with manganese neurotoxicity has been hampered by the lack of a good rodent model. Elevated levels of 8-hydroxy-2'-deoxyguanosine (oxo8dG) have been found in brain areas affected in PD. Whether increased DNA damage is responsible for neuronal degeneration or is a mere epiphenomena of neuronal loss remains to be elucidated. Thus, by using mice deficient in the ability to remove oxo8dG we aimed to determine if dysregulation of DNA repair coupled to manganese exposure would be detrimental to dopaminergic neurons. Wild-type and OGG1 knockout mice were exposed to manganese from conception to postnatal day 30; in both groups, exposure to manganese led to alterations in the neurochemistry of the nigrostriatal system. After exposure, dopamine levels were elevated in the caudate of wild-type mice. Dopamine was reduced in the caudate of OGG1 knockout mice, a loss that was paralleled by an increase in the dopamine index of turnover. In addition, the reduction of dopamine in caudate putamen correlated with the accumulation of oxo8dG in midbrain. We conclude that OGG1 function is essential in maintaining neuronal stability during development and identify DNA damage as a common pathway in neuronal loss after a toxicological challenge.

Cell cycle activation linked to neuronal cell death initiated by DNA damage

Increasing evidence indicates that neurodegeneration involves the activation of the cell cycle machinery in postmitotic neurons. However, the purpose of these cell cycle-associated events in neuronal apoptosis remains unknown. Here we tested the hypothesis that cell cycle activation is a critical component of the DNA damage response in postmitotic neurons. Different genotoxic compounds (etoposide, methotrexate, and homocysteine) induced apoptosis accompanied by cell cycle reentry of terminally differentiated cortical neurons. In contrast, apoptosis initiated by stimuli that do not target DNA (staurosporine and colchicine) did not initiate cell cycle activation. Suppression of the function of ataxia telangiectasia mutated (ATM), a proximal component of DNA damage-induced cell cycle checkpoint pathways, attenuated both apoptosis and cell cycle reentry triggered by DNA damage but did not change the fate of neurons exposed to staurosporine and colchicine. Our data suggest that cell cycle activation is a critical element of the DNA damage response of postmitotic neurons leading to apoptosis.

Hyperoxia, reactive oxygen species, and hyperventilation: oxygen sensitivity of brain stem neurons

Hyperoxia is a popular model of oxidative stress. However, hyperoxic gas mixtures are routinely used for chemical denervation of peripheral O2 receptors in in vivo studies of respiratory control. The underlying assumption whenever using hyperoxia is that there are no direct effects of molecular O2 and reactive O2 species (ROS) on brain stem function. In addition, control superfusates used routinely for in vitro studies of neurons in brain slices are, in fact, hyperoxic. Again, the assumption is that there are no direct effects of O2 and ROS on neuronal activity. Research contradicts this assumption by demonstrating that O2 has central effects on the brain stem respiratory centers and several effects on neurons in respiratory control areas; these need to be considered whenever hyperoxia is used. This mini-review summarizes the long-recognized, but seldom acknowledged, paradox of respiratory control known as hyperoxic hyperventilation. Several proposed mechanisms are discussed, including the recent hypothesis that hyperoxic hyperventilation is initiated by increased production of ROS during hyperoxia, which directly stimulates central CO2 chemoreceptors in the solitary complex. Hyperoxic hyperventilation may provide clues into the fundamental role of redox signaling and ROS in central control of breathing; moreover, oxidative stress may play a role in respiratory control dysfunction. The practical implications of brain stem O2 and ROS sensitivity are also considered relative to the present uses of hyperoxia in respiratory control research in humans, animals, and brain stem tissues. Recommendations for future research are also proposed.

The role of somatic and germline mutations in aging and a mutation interaction model of aging

Mutations with a deleterious effect that is expressed after the average reproductive period are not effectively selected against and can accumulate in the germline. A conservative estimate is that at least 1-2% of new deleterious mutations affect some aspect of DNA replication, repair, or chromosome segregation. Since deleterious mutations can have an effect even as heterozygotes, this mutation accumulation can create an inherited background of late-acting mutations that themselves enhance mutation rate. This can have an interactive effect, in that it may increase the rate of somatic mutation during an individual's lifetime. The aging individual therefore becomes increasingly mosaic for somatic mutations, which in turn could potentially contribute to the gradual deterioration of biological processes and influence what we experience as senescence. Interventions that reduce somatic and germ cell mutations should, therefore, reduce the aging process in present and future generations.

Strain-specific differences in the expression and activity of Ogg1 in the CNS

The expression and activity of 8-oxoguanosine DNA-glycosylase (Ogg1), a key enzyme responsible forthe clearance of the oxidized DNA base 8-hydroxy-2'-deoxyguanosine (oxo8dG), was determined in the cerebellum (CB) and the caudate and the putamen (CP) of male Balb/c, ICR, and C57BL/J mice. There was no significant difference in the protein expression of Ogg1 in the CB or CP. The activity of Ogg1 was not significantly different in the CB; however, in the CP of ICR mice, the activity of Ogg1 was 34% and 31% lower than Balb/c and C57BL/J, respectively. In contrast, the levels of oxo8dG in the CB and CP of C57BL/J mice were nearly twice as high as the values in both regions of Balb/c and ICR mice. The activity of superoxide dismutases (SOD) appeared to account for the differences in the levels of oxo8dG in the C57BL/J strain. Total SOD in the C57BL/J strain was two- and fourfold higher in the CB and CP, respectively, versus the other strains. These results suggest that the enhanced vulnerability of the C57BL/J strain to neurotoxicants may not be due to a decreased capacity for DNA repair, but rather, the significantly higher activity of SODs, which may cause these pathways to become more readily saturated.

Oxidative stress and aging: beyond correlation

The oxidative stress theory of aging has become increasingly accepted as playing a role in the aging process, based primarily on a substantial accumulation of circumstantial evidence. In recent years, the hypothesis that mitochondrially generated reactive oxygen species play a role in organismal aging has been directly tested in both invertebrate and mammalian model systems. Initial results imply that oxidative damage, specifically the level of superoxide, does play a role in limiting the lifespans of invertebrates such as Drosophila melanogaster and Caenorhabditis elegans. In mammalian model systems, the effect of oxidative stress on lifespan is less clear, but there is evidence that antioxidant treatment protects against age-related dysfunction, including cognitive decline.

Antioxidants and Alzheimer's disease: from bench to bedside (and back again)

PURPOSE OF REVIEW

Accumulating evidence from both animal and human studies indicates a major role for oxidative damage in the pathogenesis of Alzheimer's disease, occurring even before symptoms arise and both beta-amyloid-containing plaques and neurofibrillary tangles are formed. This raises the possibility of preventing, or at least slowing down, the progression of Alzheimer's disease by the use of antioxidants. In this review, we present recent studies on the association between oxidative stress and Alzheimer's disease pathology, and on the efficacy of dietary, exogenous antioxidants to prevent or attenuate the progression of Alzheimer's disease.

RECENT FINDINGS

Recent prospective studies have indicated that dietary intake of several exogenous antioxidants is associated with a lower risk for Alzheimer's disease. This suggests that people at risk for developing Alzheimer's disease or being in the early phases of this disease may benefit from intervention with exogenous antioxidants. The clinical studies carried out so far, however, do not provide the final answer to whether antioxidants are truly protective against Alzheimer's disease.

SUMMARY

There is compelling evidence that oxidative stress is involved in Alzheimer's disease pathogenesis, and several lines of evidence indicate that administration of antioxidants may be useful in prevention and treatment of Alzheimer's disease. Further clinical studies, based on larger cohorts studied over a longer period of time, are needed, however, to test this hypothesis. Furthermore, for the future one might expect balanced upregulation of both exogenous and endogenous antioxidants as one of the best treatment strategies for preventing or at least slowing down the progression of Alzheimer's disease.

Effect of DL-alpha-lipoic acid on the status of lipid peroxidation and protein oxidation in various brain regions of aged rats

Free radicals have been implicated in the development of many acute and chronic diseases and in conditions involving brain or neurological tissue. The primary genetic material is subjected to damage by endogenous and exogenous agents, which may lead to instability and transcriptional infidelity. In the present study, we evaluated the protective effect of DL-alpha-lipoic acid, a metabolic antioxidant on lipid peroxidation, protein carbonyl content in various brain regions of aged rats when compared to brain regions of young rats. DL-alpha-lipoic acid was administered intraperitoneally (100mg/kg body weight/day) to experimental rats. Nucleic acid and protein content were low whereas thiobarbituric acid reactive substances and protein carbonyl content (markers of free radical damage) were high in cortex, striatum, hippocampus and hypothalamus followed by cerebellum of aged rat brain. Lipoate administration for 14 days in aged rats increased the levels of nucleic acid and protein and reduced lipid peroxidation and protein oxidation. These results demonstrate that lipoic acid is a potent antioxidant for neuronal cells against age associated oxidative damage.

Effects of diethylmaleate on DNA damage and repair in the mouse brain

The enzyme 8-oxoguanine DNA glycosylase 1 participates in the repair of damaged DNA by excising the oxidized base 8-hydroxy-2'-deoxyguanosine. We have previously demonstrated that enzymatic activity of this enzyme is inversely related to the levels of the damaged base in specific brain regions. We now report that the activity of 8-oxoguanine DNA glycosylase 1 is increased in a region-specific manner following treatment with diethylmaleate, a compound that reduces glutathione levels in the cell. A single treatment with diethylmaleate elicited a significant increase ( approximately 2-fold) in the activity of 8-oxoguanine DNA glycosylase 1 in three brain regions with low basal levels of activity (cerebellum, cortex, and pons/medulla). There was no change in the activity of 8-oxoguanine DNA glycosylase 1 in those regions with high basal levels of activity (hippocampus, caudate/putamen, and midbrain). This is the first report to demonstrate that DNA repair capacity can be upregulated in the CNS, and the increased repair activity correlates with a reduction in the levels of DNA damage. The brain region-specific capacity to deal with increased oxidative damage to DNA may be responsible, in part, for the vulnerability of specific neuronal populations with aging, sources of oxidative stress, and neurodegenerative diseases.

Comparison of base-excision repair capacity in proliferating and differentiated PC 12 cells following acute challenge with dieldrin

Dieldrin, an organochlorine pesticide and known neurotoxicant, is ubiquitously distributed in the environment. Dieldrin depletes brain monoamines in some animal species and is toxic for dopaminergic neurons in vitro. Dieldrin interferes with mitochondrial electron transport and increases generation of superoxide anion. Reactive oxygen species have been shown to produce oxidative lesions to DNA bases, i.e., 8-hydroxy-2'-deoxyguanosine (8-oxodGuo). Accumulation of 8-oxodGuo has been shown to be promutagenic in proliferating cells, and can lead to degeneration in fully differentiated cells. The objective of this study was to determine the effects of dieldrin exposure on the activity of the enzyme responsible for removing 8-oxodGuo, OGG1, from undifferentiated (untreated with NGF) and differentiated (NGF-treated) PC 12 cells. Proliferating PC 12 cells exhibited a mild upregulation of glycosylase activity, reaching a maximum by 1 h and returning to baseline by 6 h. Differentiated (+) NGF cells showed a time-dependent decline in activity reaching a nadir at 3 h with a return towards baseline by 6 h. Levels of the damaged base, 8-oxodGuo, in the differentiated PC12 cells appeared to be regulated by the activity of OGG1. In contrast, levels of the damaged base in actively proliferating cells were independent of the OGG1 activity. This difference between actively dividing and differentiated cells in the regulation of base-excision repair and DNA damage accumulation explains, in part, the vulnerability of postmitotic neurons to oxidative stresses and neurotoxins.

Reduction in DNA damage in brain and peripheral blood lymphocytes of elderly dogs after treatment with dehydroepiandrosterone (DHEA)

Steady state levels of DNA damage are substantial in vertebrate animals as a consequence of exposure to endogenous and environmental mutagens. DNA damage may contribute to organismal senescence and an increased risk for specific age-related diseases. In this study, we determined if treatment with the neuroactive adrenal steroid, dehydroepiandrosterone (DHEA), which exhibits antioxidant and anticarcinogenic properties in rodents, would reduce DNA damage in the brain and peripheral blood lymphocytes (PBLs) of elderly dogs. Elderly male dogs, physiologically equivalent to 59-69-year-old men, were randomly assigned to receive no treatment (n=9 dogs) or DHEA at 100mg/kg PO daily (n=8 dogs). Extent of DNA damage in brain cells and PBLs was measured using alkaline comet assay. The effect of DHEA treatment on the susceptibility of PBLs to H(2)O(2)-induced DNA damage was also measured. We found that elderly male dogs receiving daily DHEA treatment for 7 months had significantly less DNA damage detectable in their brain compared to age-matched control dogs. After 7 months treatment, DHEA-treated dogs also had a significant reduction in DNA damage in PBLs compared to pre-treatment levels. We also found that PBLs of dogs treated with DHEA were more resistant to H(2)O(2)-induced DNA damage than PBLs of untreated dogs. Our results did not show that basal DNA damage in PBLs was strongly correlated with DNA damage within the brain. The results of this study suggest that DHEA supplementation can significantly reduce steady state levels of DNA damage in the mammalian brain. Further evaluation of DHEA as a neuroactive agent and its effects on DNA damage and gene expression in other tissues and species is warranted.

Mutant and genetically modified mice as models for studying the relationship between aging and carcinogenesis

Increased interest is emerging in using mouse models to assess the genetics of aging and age-related diseases, including cancer. However, only limited information is available regarding the relationship between aging and spontaneous tumor development in genetically modified mice. Analysis of various transgenic and knockout rodent models with either a shortened or an extended life span, provides a unique opportunity to evaluate interactions of genes involved in the aging process and carcinogenesis. There are only a few models which show life span extension. Ames dwarf mutant mice, p66(-/-) knockout mice, alpha MUPA and MGMT transgenic mice live longer than wild-type strains. The incidence of spontaneous tumors in these mutant mice was usually similar to those in controls, whereas the latent period of tumor development was increased. Practically all models of accelerated aging showed increased incidence and shorter latency of tumors. This phenomenon has been observed in animals which display a phenotype that more closely resembles natural aging, and in animals which manifest only some features of the normal aging process. These observations are in agreement with an earlier established positive correlation between tumor incidence and the rate of tumor incidence increase associated with aging and the aging rate in a population. Thus, genetically modified animals are a valuable tool in unravelling mechanisms underlying aging and cancer. Systemic evaluation of newly generated models should include onco-gerontological studies.

Zinc and copper in the pathogenesis of amyotrophic lateral sclerosis

1. Missense mutations in the gene encoding Cu,Zn superoxide dismutase (SOD1) are responsible for causing one form of familial amyotrophic lateral sclerosis (FALS) linked to chromosome 21q. 2. Mutant SOD1-induced disease is clearly related to a toxic gain of function for the abnormal enzyme, and recent work has begun to investigate the mechanisms underlying this toxicity. In addition to its well known and likely beneficial dismutase activity, wild type SOD1 also possesses the ability to participate in other enzymatic reactions that may be injurious to cells including peroxidation or nitration. 3. Many of the SOD1 mutations associated with FALS appear to increase the likelihood that the enzyme will perform either one of these potentially harmful functions resulting in increased hydroxyl radical formation or the addition of nitro groups to tyrosine residues within cellular proteins.

Mitochondrial oxidant generation and oxidative damage in Ames dwarf and GH transgenic mice

Aging is associated with an accumulation of oxidative damage to proteins, lipids and DNA. Cellular mechanisms designed to prevent oxidative damage decline with aging and in diseases associated with aging. A long-lived mouse, the Ames dwarf, exhibits growth hormone deficiency and heightened antioxidative defenses. In contrast, animals that over express GH have suppressed antioxidative capacity and live half as long as wild type mice. In this study, we examined the generation of H2O2 from liver mitochondria of Ames dwarf and wild type mice and determined the level of oxidative damage to proteins, lipids and DNA in various tissues of these animals. Dwarf liver mitochondria (24 months) produced less H2O2 than normal liver in the presence of succinate (p<0.03) and ADP (p<0.003). Levels of oxidative DNA damage (8ÕHdG) were variable and dependent on tissue and age in dwarf and normal mice. Forty-seven percent fewer protein carbonyls were detected in 24-month old dwarf liver tissue compared to controls (p<0.04). Forty percent more (p<0.04) protein carbonyls were detected in liver tissue (3-month old) of GH transgenic mice compared to wild types while 12 month old brain tissue had 53% more protein carbonyls compared to controls (p<0.005). Levels of liver malonaldehyde (lipid peroxidation) were not different at 3 and 12 months of age but were greater in Ames dwarf mice at 24 months compared to normal mice. Previous studies indicate a strong negative correlation between plasma GH levels and antioxidative defense. Taken together, these studies show that altered GH-signaling may contribute to differences in the generation of reactive oxygen species, the ability to counter oxidative stress and life span.

Free radical defenses in the liver and kidney of human growth hormone transgenic mice: possible mechanisms of early mortality

The long-term effects of growth hormone (GH) administration are unknown. Although limited data on its short-term effects purport health benefits, numerous detrimental effects are the consequence of chronically elevated GH. We used spectrophotometric assay and Western blot to determine the effects of chronic GH excess on hepatic and renal antioxidant enzymes (AOEs) in young and middle-aged PEPCK (phosphoenolpyruvate carboxykinase) hGH (human GH) transgenic mice. In the liver, glutathione peroxidase (GPx) was reduced in transgenics of both age groups, catalase was reduced only in young transgenics, and Cu-Zn superoxide dismutase (SOD) was similar to normal mice, but declined with age. In all groups, hepatic AOE activity correlated significantly with AOE level. In the kidney, AOEs in young transgenics were similar to those of normal mice. However, middle-aged transgenics showed reduced renal SOD and GPx activities when compared with young transgenic or middle-aged normal mice. Similarly, renal SOD and GPx levels in middle-aged transgenics were reduced when compared with those of middle-aged normal mice. AOE activity in the kidney correlated significantly with AOE protein level among middle-aged animals only. These data suggest the following: ((1)) GH excess is associated with early declines in SOD and GPx in the kidney and reductions of hepatic GPx at all ages examined, perhaps increasing the risk of free radical-induced damage to these tissues; ((2)) in the liver of young animals and in the liver and kidney of middle-aged animals, AOE activity reflects the amount of enzyme protein; and ((3)) age-related reductions in GPx in transgenics may be related to the increased incidence of liver tumors and renal failure in these animals.

DNA damage, repair, and antioxidant systems in brain regions: a correlative study

8-Hydroxy-2'-deoxyguanosine (oxo(8)dG) has been used as a marker of free radical damage to DNA and has been shown to accumulate during aging. Oxidative stress affects some brain regions more than others as demonstrated by regional differences in steady state oxo(8)dG levels in mouse brain. In our study, we have shown that regions such as the midbrain, caudate putamen, and hippocampus show high levels of oxo(8)dG in total DNA, although regions such as the cerebellum, cortex, and pons and medulla have lower levels. These regional differences in basal levels of DNA damage inversely correlate with the regional capacity to remove oxo(8)dG from DNA. Additionally, the activities of antioxidant enzymes (Cu/Zn superoxide dismutase, mitochondrial superoxide dismutase, and glutathione peroxidase) and the levels of the endogenous antioxidant glutathione are not predictors of the degree of free radical induced damage to DNA in different brain regions. Although each brain region has significant differences in antioxidant defenses, the capacity to excise the oxidized base from DNA seems to be the major determinant of the steady state levels of oxo(8)dG in each brain region.

Age-related increases of 8-hydroxy-2'-deoxyguanosine and DNA-protein crosslinks in mouse organs

Experimental data suggest a possible role of DNA damage in aging, mainly related to oxidative lesions. With the objective of evaluating DNA lesions as molecular biomarkers of aging, we measured 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and DNA-protein crosslinks (DPXL) levels in different organs of mice aged 12 and 24 months. 8-OH-dG was detected by 32P postlabelling after removing unmodified dG by trifluoracetic acid, which prevented the artificial formation of 8-OH-dG during 32P labelling procedures. Appreciable 8-OH-dG amounts were detected in 12-month-old mice in liver (1.8 +/- 0.7 8-OH-dG/10(5) normal nucleotides), brain (1.6 +/- 0.5) and heart (2.3 +/- 0.5). In 24-month-old mice these values were higher in all examined organs (liver, 2.7 +/- 0.4; brain, 3.6 +/- 1.1; heart, 6.8 +/- 2.2 8-OH-dG/10(5) normal nucleotides). This accounted for a 1.5-fold increase in liver (not significant), 2.3-fold increase in brain (P < 0.01), and 3.0-fold increase in heart (P < 0.001). A similar trend was observed for DPXL levels, which were the 1.8 +/- 0.3%, 1.2 +/- 0.2%, and 2.2 +/- 0.3% of total DNA in liver, brain, and heart of 12-month-old mice and 1.9 +/- 0.4%, 2.0 +/- 0.4%, and 3.4 +/- 0.5% in 24-month-old mice, with ratios of 1.0, 1.7 (P < 0.01), and 1.5 (P < 0.001), respectively. Highly significant correlations between 8-OH-dG and DPXL levels were recorded in brain (r = 0.619, P < 0.001) and heart (r = 0.800, P < 0.0001), but not in liver (r = 0.201, not significant). These data suggest that brain and heart are more severely affected by the monitored age-related DNA lesions than liver, which can be ascribed to certain characteristics of these postmitotic organs, including the low detoxifying capacities, the high oxygen consumption, and the impossibility to replace damaged cells by mitosis. The strong correlation between 8-OH-dG and DPXL supports a possible contribution of oxidative mechanisms to formation of DPXL in those organs, such as brain and heart, which play a primary role in the aging of the whole organism.

Oxidative DNA damage in the aging mouse brain

The brain exhibits regional vulnerabilities to many insults, and age itself has differential effects on neuronal populations as exemplified by the age-dependent loss of dopaminergic neurons in the nigrostriatal system. We hypothesized that oxidative damage to DNA was more likely to occur in the nigrostriatal system which undergoes significant neurochemical and functional changes with age. To test this hypothesis, oxidative damage to DNA, indicated by levels of 8-hydroxy2'-deoxyguanosine (oxo8dG), was measured in pons-medulla (PM), midbrain (MB), caudate-putamen (CP), hippocampus (HP), cerebellum (CB), and cerebral cortex (CX) at 3, 18, and 34 months of age in C57/b1 mice. Steady-state levels of oxo8dG increased significantly with age in MB, CP, and CB, but not in PM, HP, or CX. Manganese superoxide dismutase (MnSOD) activity decreased with age in MB, CP, and HP, but not in PM, CB, or CX. Regional activities of Cu/Zn superoxide dismutase (Cu/Zn SOD) and glutathione peroxidase (Glut Px) did not change significantly with age. Concomitant with the regional alterations in DNA damage, there was a significant age-dependent decline in locomotor activity, motor coordination, and striatal dopamine content especially during the interval between 18 and 34 months. In conclusion, oxyradical-associated damage to DNA did not accumulate uniformly across brain regions with age and was highest in brain regions that subserve spontaneous locomotor activity and motor coordination.