Age-related DNA Damage Research Articles

Calorie restriction and resveratrol supplementation prevent age-related DNA and RNA oxidative damage in a non-human primate

Oxidative stress is a key factor in the aging process and in the development of age-related diseases. Because nutritional interventions such as caloric restriction (CR) delay the onset of age-related diseases and increase the lifespan of many species, the impact of a moderate CR was tested on male grey mouse lemur (Microcebus murinus), which have a median survival time of 5.7years in captivity. The effects of CR on these lemurs were compared with a potential mimetic, resveratrol (RSV), a polyphenol naturally found in grapes. We hypothesized that both CR and RSV impact oxidative DNA and RNA damage compared to standard-fed control (CTL) animals. Adult (3–4years old) male mouse lemurs were assigned to three dietary groups: a CTL group, a CR group receiving 30% fewer calories than the CTL and a RSV group receiving the CTL diet supplemented with RSV (200mg·day−1·kg−1). Oxidative stress was estimated after 3, 9, 15 and 21months of treatment using the measurement of oxidized nucleosides in urine samples by mass spectrometry. The resting metabolic rate, adjusted for changes in body composition, was also measured to assess the potential relationship between oxygen consumption and oxidative damage markers. This study provides evidence for oxidative stress accumulation with age in grey mouse lemur. Dietary interventions resulted in a short-term increase in oxidative stress levels followed by reduced levels with increasing age. Moreover, in this photoperiod-dependent heterotherm primate, seasonal variations in oxidative stress were observed, which was likely due to a season-dependent, cost–benefit trade-off between torpor use and oxidative stress.

Accumulation of DNA Damage-Induced Chromatin Alterations in Tissue-Specific Stem Cells: The Driving Force of Aging?

Accumulation of DNA damage leading to stem cell exhaustion has been proposed to be a principal mechanism of aging. Using 53BP1-foci as a marker for DNA double-strand breaks (DSBs), hair follicle stem cells (HFSCs) in mouse epidermis were analyzed for age-related DNA damage response (DDR). We observed increasing amounts of 53BP1-foci during the natural aging process independent of telomere shortening and after protracted low-dose radiation, suggesting substantial accumulation of DSBs in HFSCs. Electron microscopy combined with immunogold-labeling showed multiple small 53BP1 clusters diffusely distributed throughout the highly compacted heterochromatin of aged HFSCs, but single large 53BP1 clusters in irradiated HFSCs. These remaining 53BP1 clusters did not colocalize with core components of non-homologous end-joining, but with heterochromatic histone modifications. Based on these results we hypothesize that these lesions were not persistently unrepaired DSBs, but may reflect chromatin rearrangements caused by the repair or misrepair of DSBs. Flow cytometry showed increased activation of repair proteins and damage-induced chromatin modifications, triggering apoptosis and cellular senescence in irradiated, but not in aged HFSCs. These results suggest that accumulation of DNA damage-induced chromatin alterations, whose structural dimensions reflect the complexity of the initial genotoxic insult, may lead to different DDR events, ultimately determining the biological outcome of HFSCs. Collectively, our findings support the hypothesis that aging might be largely the remit of structural changes to chromatin potentially leading to epigenetically induced transcriptional deregulation.

Cep-1/p53-dependent dysplastic pathology of the aging C. elegans gonad

The C. elegans germline and somatic gonad are actively developing until the animal reaches adulthood, and then continue to undergo striking changes as the animal ages. Reported changes include a depletion of available sperm, a decrease in oocyte quality up till mid-life, a reduction in germline nuclei, a decrease in fertility, and an accumulation of DNA in the midbody of aging C. elegans. Here, we have focused on the aging gonad in old animals, and show in detail that the aging gonad undergoes a massive uterine growth composed of endoreduplicating oocytes, yolk, and expanses of chromatin. We use a novel series of imaging techniques in combination with histological methodology for reconstructing aged worms in 3-dimensions, and show in old animals growing masses swelling inside the uterus to occupy most of the diameter of the worm. We link this accelerated growth to the cep-1/p53 tumor suppressor. Because cep-1 is required for DNA damage induced apoptosis, and daf-2 limits longevity, these results suggest a role for age-related DNA damage in dysplastic uterine growths, which in some respects resemble premalignant changes that can occur in aging mammals.

Age- and oxidative stress-induced DNA damage in Drosophila intestinal stem cells as marked by Gamma-H2AX

A decline in stem cell function is considered as a major cause of tissue atrophy, organ-system failure, cancer development and aging process. For a better understanding of the mechanism underlying age-related decline of stem cell function, characterization of aged stem cells is required. DNA damage induces epigenetic modifications that are associated with cell dysfunction. In mammals, γH2AX has been shown as DNA damage marker and an adaptor for recruiting chromatin modifying factors. In current study, utilizing a well-accepted Drosophila midgut model for stem-cell biology, we demonstrated aging- and oxidative stress-related accumulation of γH2AvD foci, analogous to mammal γH2AX, in Drosophila intestinal stem cells (ISCs), and obtained evidence that the changes in γH2AvD is closely associated with γ-ray-induced DNA damage in ISCs and age-related accumulation of 8-oxo-2′-deoxyguanosine. The significance of our study is to document the first direct evidence for the accumulation of age-related DNA-damage in ISCs, and to show γH2AvD as a useful biomarker in exploring the molecular mechanisms underlying stem cell aging in the Drosophila midgut.

Accumulation of DNA Damage in Hematopoietic Stem and Progenitor Cells during Human Aging

BackgroundAccumulation of DNA damage leading to adult stem cell exhaustion has been proposed to be a principal mechanism of aging. Here we tested this hypothesis in healthy individuals of different ages by examining unrepaired DNA double-strand breaks (DSBs) in hematopoietic stem/progenitor cells matured in their physiological microenvironment.Methodology/Principal FindingsTo asses DNA damage accumulation and repair capacities, γH2AX-foci were examined before and after exposure to ionizing irradiation. Analyzing CD34+ and CD34− stem/progenitor cells we observed an increase of endogenous γH2AX-foci levels with advancing donor age, associated with an age-related decline in telomere length. Using combined immunofluorescence and telomere-fluorescence in-situ hybridization we show that γH2AX-foci co-localize consistently with other repair factors such as pATM, MDC1 and 53BP1, but not significantly with telomeres, strongly supporting the telomere-independent origin for the majority of foci. The highest inter-individual variations for non-telomeric DNA damage were observed in middle-aged donors, whereas the individual DSB repair capacity appears to determine the extent of DNA damage accrual. However, analyzing different stem/progenitor subpopulations obtained from healthy elderly (>70 years), we observed an only modest increase in DNA damage accrual, most pronounced in the primitive CD34+CD38−-enriched subfraction, but sustained DNA repair efficiencies, suggesting that healthy lifestyle may slow down the natural aging process.Conclusions/SignificanceBased on these findings we conclude that age-related non-telomeric DNA damage accrual accompanies physiological stem cell aging in humans. Moreover, aging may alter the functional capacity of human stem cells to repair DSBs, thereby deteriorating an important genome protection mechanism leading to exceeding DNA damage accumulation. However, the great inter-individual variations in middle-aged individuals suggest that additional cell-intrinsic mechanisms and/or extrinsic factors contribute to the age-associated DNA damage accumulation.

Origins of Age-Related DNA Damage and Dietary Strategies for Its Reduction

The polyunsaturated fatty acids in biological membranes serve as both the target and source of oxidative damage and can be regarded as the most unstable class of biomolecules in the body. Lipid peroxides arising from both spontaneous and enzymatic oxidation of polyunsaturated fatty acids are the major source of endogenous DNA damage linked to various age-related pathologies and initiating carcinogenesis. Here we describe the major types of lipid peroxide-derived DNA adducts and propose a simple dietary strategy to reduce their formation. This may be particularly beneficial to the aging organism, which has progressively impaired natural protective systems.

Influence of aerobic fitness on age-related lymphocyte DNA damage in humans: relationship with mitochondria respiratory chain and hydrogen peroxide production

The aim of this study was to analyze the influence of aerobic fitness (AF) on age-related lymphocyte DNA damage in humans, giving special attention to the role of the mitochondrial respiratory chain and hydrogen peroxide production. Considering age and AF (as assessed by VO(2)max), 66 males (19-59 years old) were classified as high fitness (HF) or low fitness (LF) and distributed into one of the following groups: young adults (19-29 years old), adults (30-39 years old), and middle-aged adults (over 40 years old). Peripheral lymphocytes obtained at rest were used to assess DNA damage (strand breaks and formamidopyrimidine DNA glycosylase (FPG) sites through the comet assay), activity of mitochondrial complexes I and II (polarographically measured), and the hydrogen peroxide production rate (assayed by fluorescence). Results revealed a significant interaction between age groups and AF for DNA strand breaks (F = 8.415, p = .000), FPG sites (F = 11.766, p = .000), mitochondrial complex I activity (F = 7.555, p = .000), and H(2)O(2) production (F = 7.500, p = .000). Except for mitochondrial complex II activity, the age variation of the remaining parameters was significantly attenuated by HF. Considering each AF level, an increase in DNA strand breaks and FPG sites with age (r = 0.655, p = 0.000, and r = 0.738, p = 0.000, respectively) was only observed in LF. Moreover, decreased mitochondrial complex I activity with age (r = -.470, p = .009) was reported in LF. These results allow the conclusion that high AF seems to play a key role in attenuating the biological aging process.

Modulatory role of grape seed extract on age-related oxidative DNA damage in central nervous system of rats

Aging is the accumulation of diverse deleterious changes in the cells and tissues leading to increased risk of diseases. Oxidative stress is considered as a major risk factor and contributes to age related increase in DNA oxidation and DNA protein cross-links in central nervous system during aging. In the present study, we have evaluated the salubrious role of grape seed extract on accumulation of oxidative DNA damage products such as 8-OHdG and DNA protein cross-links in aged rats. Male albino rats of Wistar strain were divided into four groups: Group I, young control rats; Group II, young rats treated with grape seed extract (100 mg/kg b.wt.) for 30 days; Group III, aged control rats; Group IV, aged rats supplemented with grape seed extract (100 mg/kg b.wt.) for 30 days. Our results, thus, revealed that grape seed extract has inhibiting effect on the accumulation of age-related oxidative DNA damages in spinal cord and in various brain regions such as cerebral cortex, striatum and hippocampus.

Peripheral lymphocyte 8-OHdG levels correlate with age-associated increase of tissue oxidative DNA damage in Sprague–Dawley rats. Protective effects of caloric restriction

8-Hydroxy-deoxyguanosine adducts (8-OHdG), indices of oxidative DNA damage, were measured by immunohystochemistry with diaminobenzidine detection in the brain, skeletal muscle, heart, liver, tenuum mucosa and lymphocytes from young (4 months) and aged (24 months) Sprague–Dawley rats fed ad libitum or held on two different caloric restriction diets (alternate day ad libitum feeding or daily feeding with 40% reduced calories). In the absence of caloric restriction the levels of oxidative DNA damage increased as a function of age in all tissues examined, with a maximum ∼3-fold increase being detected in the peripheral lymphocytes and the heart and a minimum ∼2-fold increase being detected in the liver and brain tissues. Caloric restriction regimens effectively reduced age-dependent increase of oxidative DNA damage in all tissues examined; in particular, the brain and small intestine did not exhibit any age-related increase of oxidative DNA damage. We propose that the levels of 8-OHdG in peripheral lymphocytes may serve a biochemical index of age-related whole organism oxidative DNA damage. Immunohistochemistry might be exploited as a rapid and simple techniques for measuring lymphocytes oxidative DNA damage in large scale studies.

Modulation of age-associated oxidative DNA damage in rat brain cerebral cortex, striatum and hippocampus by l-carnitine

The free radical theory of cell aging may have significant relevance in the pathogenesis of a number of age-related neurological disorders. A large body of experimental evidence supports the existence of a relationship between genomic instability, DNA damage and aging. The age-associated accumulation of oxidative DNA damage is well documented in central nervous system. The decline of mitochondrial respiratory function and loss of normal cellular homeostasis as consequences of excessive accumulation of endogenous oxidative damages to DNA have long been indicated in the aging process. In the present study, age-associated alterations in the content of DNA and accumulation of oxidative DNA damage products such as 8-OHdG and DNA protein cross-links are mainly focused. In parallel, we have also investigated the salubrious effect of l-carnitine against oxidative DNA damage as it possesses energy and antioxidant improving properties. Our results thus reveal that l-carnitine has inhibiting effect on the accumulation of age-related oxidative DNA damage in various brain regions, viz. cerebral cortex, striatum and hippocampus.

Soy Consumption and Phytoestrogens: Effect on Serum Prostate Specific Antigen When Blood Lipids and Oxidized Low-Density Lipoprotein are Reduced in Hyperlipidemic Men

Soy Consumption and Phytoestrogens: Effect on Serum Prostate Specific Antigen When Blood Lipids and Oxidized Low-Density Lipoprotein are Reduced in Hyperlipidemic Men

Contributions of mitochondrial alterations, resulting from bad genes and a hostile environment, to the pathogenesis of Alzheimer's disease

This chapter discusses different genetic and environmental factors that either cause, or increase the risk of, Alzheimer's Disease (AD). Each genetic causal or predisposition factor promotes increased oxidative stress and disrupts cellular calcium homeostasis in neurons. Mitochondrial function is compromised by oxyradicals and calcium overload resulting in further oxyradical production, impaired calcium homeostasis, and activation of apoptotic caspases. Age-related DNA damage (nuclear and mitochondrial) may endanger neurons and render them vulnerable to excitotoxicity and apoptosis. Environmental factors that may predispose to AD include excessive caloric intake, folic-acid insufficiency, and disuse of neural circuits involved in learning and memory. Novel preventative approaches for AD based upon the mechanisms include dietary restriction, mental aerobics, and dietary supplementation with folic acid and certain anti-oxidants . Therapeutic strategies may include antioxidants, anti-inflammatory agents, and drugs that stabilize mitochondrial function.

Oxidative stress in the aging rat heart is reversed by dietary supplementation with (R)-(alpha)-lipoic acid.

Oxidative stress has been implicated as a causal factor in the aging process of the heart and other tissues. To determine the extent of age-related myocardial oxidative stress, oxidant production, antioxidant status, and oxidative DNA damage were measured in hearts of young (2 months) and old (28 months) male Fischer 344 rats. Cardiac myocytes isolated from old rats showed a nearly threefold increase in the rate of oxidant production compared to young rats, as measured by the rates of 2,7-dichlorofluorescin diacetate oxidation. Determination of myocardial antioxidant status revealed a significant twofold decline in the levels of ascorbic acid (P = 0.03), but not alpha-tocopherol. A significant age-related increase (P = 0.05) in steady-state levels of oxidative DNA damage was observed, as monitored by 8-oxo-2'-deoxyguanosine levels. To investigate whether dietary supplementation with (R)-alpha-lipoic acid (LA) was effective at reducing oxidative stress, young and old rats were fed an AIN-93M diet with or without 0.2% (w/w) LA for 2 wk before death. Cardiac myocytes from old, LA-supplemented rats exhibited a markedly lower rate of oxidant production that was no longer significantly different from that in cells from unsupplemented, young rats. Lipoic acid supplementation also restored myocardial ascorbic acid levels and reduced oxidative DNA damage. Our data indicate that the aging rat heart is under increased mitochondrial-induced oxidative stress, which is significantly attenuated by lipoic acid supplementation.

Polymorphisms in the DNA repair genes XRCC1 and ERCC2 and biomarkers of DNA damage in human blood mononuclear cells.

Polymorphisms in several DNA repair genes have recently been identified, but little is known about their phenotypic significance. To determine whether variation in DNA repair genes is related to host DNA damage, we studied the association between polymorphisms in XRCC1 (codon 399) and ERCC2 (codon 751) and two markers of DNA damage, sister chromatid exchange (SCE) frequencies (n = 76) and polyphenol DNA adducts (n = 61). SCE frequencies were determined using a modified fluorescence-Giemsa method and polyphenol DNA adducts were determined using a P1-enhanced (32)P-post-labeling procedure. XRCC1 and ERCC2 genotypes were identified using PCR-RFLP. Mean SCE frequencies among current smokers who were homozygous carriers of the 399Gln allele in XRCC1 were greater than those in 399Arg/Arg current smokers. We also observed a possible gene-dosage effect for XRCC1 399Gln and detectable DNA adducts, and significantly more adducts among older subjects who were carriers of the 399Gln allele than in younger subjects with the 399Arg/Arg genotype. The polymorphism in ERCC2 was unrelated to SCE frequency or DNA adduct level. Our results suggest that carriers of the polymorphic XRCC1 399Gln allele may be at greater risk for tobacco- and age-related DNA damage.

Melatonin protects against age-related DNA damage in the brains of female senescence-accelerated mice.

We investigated whether melatonin reduces the age-related susceptibility of brain to oxidative DNA damage. Brain tissues and blood samples were obtained in the middle of dark period of the daily light:dark cycle from female senescence-accelerated mice (SAM-P/6) at ages 4, 8, and 12 months. Serum melatonin concentrations and the contents of deoxyguanosine (dG) and 8-hydroxydeoxyguanosine (8-OHdG) in DNA extracted from these brain homogenates were measured by high-performance liquid chromatography. Contents of 8-OHdG showed a significant age-related increase (P < 0.001) while that of dG did not. The 8-OHdG:dG ratio also exhibited a significant age-related increase (P < 0.001). Serum melatonin concentration decreased markedly between 8 (159.7 +/- 4.5 pg/mL) and 12 (46.8 + 4.5 pg/mL) months of age (P < 0.0001). Oral melatonin administration (2 microg/mL in water) starting at 8 months of age, which produced a significant increase in serum melatonin concentration at 12 months (187.6 +/- 18.3 pg/mL) compared with untreated animals (P < 0.0001) also resulted in significant decreases in brain 8-OHdG contents and 8-OHdG:dG ratios. These results indicate that administration of a physiologic dose of melatonin to SAM-P 6 mice may prevent the age-related oxidative DNA damage in the brain.

Age-dependent, seasonal and daily variations of the DNA damaging capacity of the hepatocarcinogen ZAMI 1305 in female rat liver

A single injection of the sex-dependent hepatocarcinogen dl-1-(2-nitro-3-methyl-phenoxy)-3- tert-butylamino-propan-2-ol (ZAMI 1305) caused age-related DNA damage, as evaluated by alkaline sucrose gradient analysis, in the liver of female Wistar rats. DNA damage reached a maximum at 4–6 weeks of age, about the onset of sexual maturity, and decreased there-after. In young rats (5–8 weeks of age), the amount of ZAMI 1305-induced DNA damage showed seasonal and daily differences, being higher when the molecule was administered in winter in respect to summer and in the evening in respect to the morning. In older rats (15–22 weeks of age), no seasonal and daily variations were observed.