Role Of Oxidative DNA Damage Research Articles

Role of Oxidative DNA Damage and Antioxidative Enzymatic Defence Systems in Human Aging~!2008-08-08~!2008-10-29~!2008-12-05~!

Role of Oxidative DNA Damage and Antioxidative Enzymatic Defence Systems in Human Aging~!2008-08-08~!2008-10-29~!2008-12-05~!

Urinary level of nickel and acute leukaemia in Chinese children

The 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidized nucleoside of DNA, not only is a widely used biomarker for the measurement of endogenous oxidative DNA damage but might also be a risk factor for many diseases including cancer. Metal exposure may play an important role in oxidative DNA damage among children. However, few studies on urinary 8-OHdG and metals have been conducted in children with acute leukemia. In the present study, urinary Ni and 8-OHdG were examined in 116 children with acute leukaemia (94 acute lymphoid leukaemia [ALL] and 22 acute myeloid leukaemia [AML]) and 51 healthy child controls. Our result showed that urinary Ni in acute leukaemia patients (ALL: 68.40 +/- 133.98, AML: 41.48 +/- 76.31 ng/mg creatinine) was significantly higher than that in controls (62.47 +/- 124.90 vs 17.63 +/- 46.17 ng/mg creatinine, P < 0.05). Similarly, the pretherapy level of urinary 8-OHdG in patients (ALL: 11.83 +/- 16.23, AML: 12.36 +/- 11.36 ng/mg creatinine) was significantly elevated compared with controls (11.92 +/- 15.42 vs 4.03 +/- 4.70 ng/mg creatinine, P < 0.05). Moreover, urinary 8-OHdG and urinary Ni showed a weak but significant association with increased risk of childhood leukaemia. The present study suggests that Ni may be an etiologic factor for childhood acute leukaemia by oxidative DNA damage.

Accumulation of M 1dG DNA adducts after chronic exposure to PCBs, but not from acute exposure to polychlorinated aromatic hydrocarbons

Oxidative DNA damage is one of the key events thought to be involved in mutation and cancer. The present study examined the accumulation of M 1dG, 3-(2′-deoxy-β-D- erythro-pentofuranosyl)-pyrimido[1,2- a]-purin-10(3 H)-one, DNA adducts after single dose or 1-year exposure to polyhalogenated aromatic hydrocarbons (PHAH) in order to evaluate the potential role of oxidative DNA damage in PHAH toxicity and carcinogenicity. The effect of PHAH exposure on the number of M 1dG adducts was explored initially in female mice exposed to a single dose of either 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) or a PHAH mixture. This study demonstrated that a single exposure to PHAH had no significant effect on the number of M 1dG adducts compared to the corn oil control group. The role of M 1dG adducts in polychlorinated biphenyl (PCB)-induced toxicity and carcinogenicity was further investigated in rats exposed for a year to PCB 153, PCB 126, or a mixture of the two. PCB 153, at doses up to 3000 μg/kg/day, had no significant effect on the number of M 1dG adducts in liver and brain tissues from the exposed rats compared to controls. However, 1000 ng/kg/day of PCB 126 resulted in M 1dG adduct accumulation in the liver. More importantly, coadministration of equal proportions of PCB 153 and PCB 126 resulted in dose-dependent increases in M 1dG adduct accumulation in the liver from 300 to 1000 ng/kg/day of PCB 126 with 300–1000 μg/kg/day of PCB 153. Interestingly, the coadministration of different amounts of PCB 153 with fixed amounts of PCB 126 demonstrated more M 1dG adduct accumulation with higher doses of PCB 153. These results are consistent with the results from cancer bioassays that demonstrated a synergistic effect between PCB 126 and PCB 153 on toxicity and tumor development. In summary, the results from the present study support the hypothesis that oxidative DNA damage plays a key role in toxicity and carcinogenicity following long-term PCB exposure.

Mechanism of Oxidative DNA Damage Induced by Environmental Carcinogens and Antioxidants

Modification of DNA is believed to be a key step in mutagenesis and carcinogenesis. Reactive oxygen species (ROS) generated by environmental factors can cause oxidative DNA damage. This review focused on the role of oxidative DNA damage in mutagenesis and carcinogenesis mediated by environmental factors. This research investigated the mechanism of DNA damage induced by environmental chemicals and dietary factors using 32P-labeled DNA fragments obtained from the c-Ha-RAS-1 protooncogene and the p16 and p53 tumor suppressor genes. In addition, the content of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) was measured by using a high performance liquid chromatograph equipped with an electrochemical detector. 8-oxodG is probably one of the most abundant DNA lesion formed during oxidative stress. Antioxidants are considered as the most promising chemopreventive agents against various human cancers. However, some antioxidants play paradoxical roles acting as “double-edged sword”. The present research also investigated the mechanism of DNA damage induced by antioxidants using human cultured cell lines and 32P-labeled DNA fragments. This review shows recent experimental results and discusses the mechanisms of oxidative DNA damage in relation to carcinogenesis.

Oxidative DNA damage in mild cognitive impairment and late-stage Alzheimer's disease

Increasing evidence supports a role for oxidative DNA damage in aging and several neurodegenerative diseases including Alzheimer's disease (AD). Attack of DNA by reactive oxygen species (ROS), particularly hydroxyl radicals, can lead to strand breaks, DNA–DNA and DNA–protein cross-linking, and formation of at least 20 modified bases adducts. In addition, α,β-unsaturated aldehydic by-products of lipid peroxidation including 4-hydroxynonenal and acrolein can interact with DNA bases leading to the formation of bulky exocyclic adducts. Modification of DNA bases by direct interaction with ROS or aldehydes can lead to mutations and altered protein synthesis. Several studies of DNA base adducts in late-stage AD (LAD) brain show elevations of 8-hydroxyguanine (8-OHG), 8-hydroxyadenine (8-OHA), 5-hydroxycytosine (5-OHC), and 5-hydroxyuracil, a chemical degradation product of cytosine, in both nuclear and mitochondrial DNA (mtDNA) isolated from vulnerable regions of LAD brain compared to age-matched normal control subjects. Previous studies also show elevations of acrolein/guanine adducts in the hippocampus of LAD subjects compared to age-matched controls. In addition, studies of base excision repair show a decline in repair of 8-OHG in vulnerable regions of LAD brain. Our recent studies show elevated 8-OHG, 8-OHA, and 5,6-diamino-5-formamidopyrimidine in both nuclear and mtDNA isolated from vulnerable brain regions in amnestic mild cognitive impairment, the earliest clinical manifestation of AD, suggesting that oxidative DNA damage is an early event in AD and is not merely a secondary phenomenon.

Ebselen attenuates oxidative DNA damage and enhances its repair activity in the thalamus after focal cortical infarction in hypertensive rats

Oxidative DNA damage has been proposed to be a major contributor to focal cerebral ischemic injury. However, little is known about the role of oxidative DNA damage in remote damage secondary to the primary infarction. In the present study, we investigated oxidative damage within the ventroposterior nucleus (VPN) after distal middle cerebral artery occlusion (MCAO) in hypertensive rats. We also examined the possible protective effect of ebselen, one glutathione peroxidase mimic, on delayed degeneration in the VPN after distal MCAO. Neuronal damage in the ipsilateral VPN was examined by Nissl staining. Oxidative DNA damage and base repair enzyme activity were assessed by analyzing immunoreactivity of 8-hydroxy-2'-deoxyguanosine (8-ohdG) and 8-oxoguanine DNA glycosylase (OGG1), respectively. The number of intact neurons in the ipsilateral VPN decreased by 52% compared to the contralateral side in ischemia group 2 weeks after distal cerebral cortical infarction. The immunoreactivity of 8-ohdG significantly increased while OGG1 immunoreactivity significantly decreased in the ipsilateral VPN 2 weeks after distal cortical infarction (all p<0.01). Compared with vehicle treatment, ebselen significantly attenuated the neuron loss, ameliorated ischemia-induced increase in 8-ohdG level as well as decrease in OGG1 level within the ipsilateral VPN (all p<0.01). OGG1 was further demonstrated to mainly express in neurons. These findings strongly suggest that oxidative DNA damage may be involved in the delayed neuronal death in the VPN region following distal MCAO. Furthermore, ebselen protects against the delayed damage in the VPN when given at 24 h following distal MCAO.

Increased urinary level of oxidized nucleosides in patients with mild-to-moderate Alzheimer's disease

Objective: Oxidative stress may play an important role in the pathogenesis of Alzheimer's disease (AD). Design and methods: To investigate the possible role of oxidative DNA damage in the pathogenesis of AD, we measured the metabolite concentrations of oxidized nucleosides (pseudouridine, 1-methyladenosine, 5-methylcytidine, 5-methyl-2′-deoxycytidine, 3-methyluridine, N 2, N 2-dimethylguanosine, 8-hydroxy-2′-deoxyguanosine, 5-deoxyadenosine and 2-deoxyguanosine) in urine between AD ( n = 36) and control subjects ( n = 34) using liquid chromatography-mass spectrometry (LC-MS) without urine preparation. Results: In AD, the 3-methyluridine, 1-methyladenosine, 8-hydroxy-2′-deoxyguanosine ( p < 0.05, respectively), 2-deoxyguanosine ( p < 0.01) and pseudouridine, N 2, N 2-dimethylguanosine ( p < 0.001, respectively) were significantly increased when compared with the control subjects. Conclusion: The results indicate that oxidized urinary nucleosides may be useful as biomarkers for AD in early stages.

Higher Leukocyte 8-Oxo-7,8-Dihydro-2'-Deoxyguanosine and Lower Plasma Ascorbate in Aging Humans?

Is oxidative damage of DNA responsible for physiological changes associated with aging? The authors note a positive correlation between the age of human subjects with the level of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in leukocyte DNA. The levels of urinary 8-oxo-7,8-dihydroguanine and 8-oxodG followed the same pattern of correlation. Age-dependent decline in the concentration of plasma vitamin C was also evident. These interesting observations in humans point towards the need to scrutinize in detail the role of oxidative DNA damage and compromised antioxidant defense systems in age-related physiological disorders.

Oxidative DNA Damage and Human Cancer: Need for Cohort Studies

Research of the role of oxidative DNA damage is well established in experimental carcinogenesis. A large number of human studies on biomarkers of oxidative DNA damage, in particular related to guanine oxidation, have been published. The level of oxidative DNA damage and repair activity can be quite different between tumor and normal tissues; case-control studies have shown increased levels of oxidative DNA damage and decreased repair capacity in leukocytes from cases. Similarly, the urinary biomarkers of oxidative DNA damage may be elevated in patients with cancer. However, such studies are likely to be associated with reverse causality. Case-control studies of genetic polymorphisms in DNA repair enzymes suggest that the common variant Ser326Cys in OGG1 may be a risk factor for lung cancer, whereas a rare variant in OGG1 and germ line mutations in the corresponding mismatch repair gene MYH are risk factors for hereditary colon cancer. Cohort studies are required to provide evidence that a high level of oxidative DNA damage implies a high risk of cancer. However, this represents a real challenge considering the large number of subjects and long followup time required with likely spurious oxidation of DNA during collection, assay and/or storage of samples.

Role of Oxidative DNA Damage in Dietary Carcinogenesis

Dietary factors are implicated in approximately 35% of cancers attributed to environmental factors. Although an extremely wide variety of dietary factors are considered to contribute to carcinogenesis, its precise mechanism remains to be clarified. We focused on the role of oxidative DNA damage in carcinogenesis mediated by various dietary factors. We investigated the mechanism of oxidative DNA damage induced by a) amino acid metabolites, in relation to carcinogenesis caused by protein intake and amino acid imbalance, b) heterocyclic amines formed during cooking meat and fish, c) sugar and hyperglycemia-related aldehydes, d) carcinogens contained in fermented foods, such as urethane, e) phytoestrogens including soy isoflavones, f) carcinogens in edible plants, such as caffeic acid and isothiocyanate, g) food additives, such as potassium bromate and benzoyl peroxide. These dietary factors and their metabolites induced metal-mediated oxidative damage to DNA in human cultured cells and 32P-labeled DNA fragments obtained from human cancer-relevant genes. On the basis of our results, it is concluded that polycyclic compounds, such as heterocyclic amines, can cause oxidative DNA damage, although they appear to mainly form DNA adduct. On the other hand, monocyclic and aliphatic compounds, such as amino acid metabolites and urethane, may mainly cause oxidative DNA damage whereas they do not appear to form DNA adduct. Soy isoflavones may cause carcinogenesis through initiation via oxidative DNA damage caused by their metabolites and promotion via cell proliferation induced by themselves. In this review, we discuss the role of oxidative DNA damage as the common mechanism of dietary carcinogenesis.

Regulation of reactive oxygen species, DNA damage and c-Myc function by peroxiredoxin 1

Overexpression of c-Myc results in transformation and multiple other phenotypes, and is accompanied by the deregulation of a large number of target genes. We previously demonstrated that peroxiredoxin 1 (Prdx1), a scavenger of reactive oxygen species (ROS), interacts with a region of the c-Myc transcriptional regulatory domain that is essential for transformation. This results either in the suppression or enhancement of some c-Myc functions and in the altered expression of select target genes. Most notably, c-Myc-mediated transformation is inhibited, implying a tumor suppressor role for Prdx1. Consistent with this, prdx1-/- mice develop age-dependent hemolytic anemias and/or malignancies. We now show that erythrocytes and embryonic fibroblasts from these animals contain higher levels of ROS, and that the latter cells show evidence of c-Myc activation, including the ability to be transformed by a ras oncogene alone. In contrast, other primary cells from prdx1-/- mice do not have elevated ROS, but nonetheless show increased oxidative DNA damage. This apparent paradox can be explained by the fact that ROS localize primarily to the cytoplasm of prdx1+/+ cells, whereas in prdx1-/- cells, much higher levels of nuclear ROS are seen. We suggest that increased DNA damage and tumor susceptibility in prdx1-/- animals results from this shift in intracellular ROS. prdx1-/- mice should be useful in studying the role of oxidative DNA damage in the causation of cancer and its prevention by antioxidants. They should also help in studying the relationship between oncogenes such as c-Myc and DNA damage.

UVA radiation is highly mutagenic in cells that are unable to repair 7,8-dihydro-8-oxoguanine in Saccharomyces cerevisiae

UVA (320-400 nm) radiation constitutes >90% of the environmentally relevant solar UV radiation, and it has been proposed to have a role in skin cancer and aging. Because of the popularity of UVA tanning beds and prolonged periods of sunbathing, the potential deleterious effect of UVA has emerged as a source of concern for public health. Although generally accepted, the impact of DNA damage on the cytotoxic, mutagenic, and carcinogenic effect of UVA radiation remains unclear. In the present study, we investigated the sensitivity of a panel of yeast mutants affected in the processing of DNA damage to the lethal and mutagenic effect of UVA radiation. The data show that none of the major DNA repair pathways, such as base excision repair, nucleotide excision repair, homologous recombination, and postreplication repair, efficiently protect yeast from the lethal action of UVA radiation. In contrast, the results show that the Ogg1 DNA glycosylase efficiently prevents UVA-induced mutagenesis, suggesting the formation of oxidized guanine residues. Furthermore, sequence analysis of UVA-induced canavanine-resistant mutations reveals a bias in favor of GC-->TA events when compared with spontaneous or H(2)O(2)-, UVC-, and gamma-ray- induced canavanine-resistant mutations in the WT strain. Taken together, our data point out a major role of oxidative DNA damage, mostly 7,8-dihydro-8-oxoguanine, in the genotoxicity of UVA radiation in the yeast Saccharomyces cerevisiae. Therefore, the capacity of skin cells to repair 7,8-dihydro-8-oxoguanine may be a key parameter in the mutagenic and carcinogenic effect of UVA radiation in humans.

Increased Levels of 8-Hydroxy-2′-Deoxyguanosine Attributable to Carcinogenic Metal Exposure among Schoolchildren

Arsenic, chromium, and nickel are reported in several epidemiologic studies to be associated with lung cancer. However, the health effects of arsenic, chromium, and nickel exposures are equivocal for children. Therefore, we performed a cross-sectional study to investigate possible associations between the internal concentrations of arsenic, chromium, and nickel and the level of oxidative stress to DNA in children. We measured urinary levels of arsenic, chromium, and nickel for 142 nonsmoking children using atomic absorption spectrometry. As a biomarker for oxidative stress, urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) levels were analyzed with an enzyme-linked immunosorbent assay kit. The median urinary 8-OHdG level for our subjects was 11.7 ng/mg creatinine. No obvious relationship between the levels of urinary nickel and 8-OHdG was found. Multiple linear regression analysis showed that children with higher urinary chromium had greater urinary 8-OHdG than did those with lower urinary chromium. Similarly, subjects with higher urinary arsenic had greater urinary 8-OHdG than did those with lower urinary arsenic. Furthermore, children with both high urinary arsenic and high urinary chromium had the highest 8-OHdG levels (mean ± SE, 16.0 ± 1.3; vs. low arsenic/low chromium, p < 0.01) in urine, followed by those with low arsenic/high chromium (13.7 ± 1.6; vs. low arsenic/low chromium, p = 0.25), high arsenic/low chromium (12.9 ± 1.6 vs. low arsenic/low chromium, p = 0.52), and low arsenic/low chromium (11.5 ± 1.3); the trend was significant (p < 0.001). Thus, environmental carcinogenic metal exposure to chromium and arsenic may play an important role in oxidative DNA damage to children.

Modified comet assay as a biomarker of sodium dichromate-induced oxidative DNA damage: Optimization and reproducibility

Hexavalent chromium (Cr[VI]) is a genotoxic carcinogen that has been associated with an increased risk of nasal and respiratory tract cancers following occupational exposure. Although the precise mechanism(s) remain to be elucidated, there is evidence for a role of oxidative DNA damage in the genotoxicity of Cr(VI). In the current study, human white blood cells were treated in vitro with non-cytotoxic concentrations of sodium dichromate (1–100 μM) for 1 h. Analysis by immunocytochemistry indicated the presence of elevated levels of 8-oxo-7,8-dihydro-2′-deoxyguanosine at concentrations of sodium dichromate greater than 10 μM. In contrast, the lowest concentration of dichromate that resulted in a statistically significant increase in levels of formamidopyrimidine DNA glycosylase (FPG)-dependent DNA strand breaks was 100 nM (p<0.05). In addition, levels of both control and dichromate-induced FPG-dependent strand breaks from blood samples taken from the same individuals over 10 months proved remarkably reproducible in the individuals studied. The coefficients of variation over three different times of the year in control and dichromate-induced oxidative DNA damage for the four individuals were 54, 1, 37 and 4, and 45, 6, 21 and 18%, respectively. In summary, these results indicate that physiologically relevant, nanomolar concentrations of sodium dichromate cause DNA base oxidation in human white blood cells in vitro as assessed by the FPG-modified comet assay. Furthermore, comet assay data from an individual are reproducible over an extended period. This consistency is sufficient to suggest that the modified comet assay might prove to be a useful and sensitive biomonitoring tool for individuals occupationally exposed to hexavalent chromium.

Inducible repair of oxidative DNA lesions in the rat brain after transient focal ischemia and reperfusion.

To determine the role of oxidative DNA damage and repair in brain injury after focal ischemia and reperfusion, the authors investigated DNA base damage and DNA base excision repair (BER) capacity, the predominant repair mechanism for oxidative DNA lesions, in the rat model of temporary middle cerebral artery occlusion. Contents of 8-hydroxyl-2'-deoxyguanosine (8-oxodG) and apurinic/apyrimidinic abasic site (AP site), hallmarks of oxidative DNA damage, were quantitatively measured in nuclear DNA extracts from brains 0.25 to 72 hours after 1 hour of middle cerebral artery occlusion. In parallel to the detection of DNA lesions, the capacity for 8-oxodG- or AP site-dependent DNA repair synthesis was measured in nuclear protein extracts using specific in vitro DNA repair assays. After postischemic reperfusion, the levels of 8-oxodG and AP sites were markedly increased in ischemic tissues. In frontal/parietal cortex, regions that survived ischemia, 8-oxodG and AP sites were efficiently repaired during reperfusion. However, in the caudate, a region that was destined to infarct, the DNA lesions were poorly repaired. In consistent with the patterns of endogenous lesion repair, a markedly induced and long-lasting (at least 72 hours) BER activity was detected in the cortex but not in the caudate after ischemia. The induced BER activity in ischemic cortex was attributed to the upregulation of gene expression and activation of selective BER enzymes, particularly DNA polymerase-beta and OGG1. These results strongly suggest that inducible DNA BER constitutes an important endogenous mechanism that protects brain against ischemia-induced oxidative neuronal injury.

Methodology for Evaluating Oxidative DNA Damage and Metabolic Genotypes in Human Trabecular Meshwork

In vitro studies have suggested the possible role of oxidative DNA damage in degenerative eye diseases such as glaucoma. We propose a method aimed at evaluating the oxidative molecular damage directly in the human trabecular meshwork (HTM) collected during surgery from patients affected by glaucoma. In the same DNA samples, we evaluated two genes involved in the cellular defense against oxidative stress, the glutathione S -transferase-encoding genes GSTM1 and GSTT1. DNA was extracted, using a high-performance phenol/chloroform procedure, from the HTM collected during surgery from nine glaucoma patients and five controls. Oxidative DNA damage was evaluated by determining the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) by means of 32 P postlabeling, thin-layer chromatography, and electronic autoradiography. GSTM1 and GSTT1 polymorphisms were determined by polymerase chain reaction (PCR) and agarose electrophoresis. Sufficient DNA amounts were obtained from all examined specimens. 8-OHdG was detected in all samples, with a level of 4.0 ± 6.5 (mean ± SD) 8-OHdG molecules/10 5 normal nucleotides in the glaucoma patients and a level of 2.6 ± 2.2 in the controls. These results were obtained by using DNA amounts as low as 0.11 μg. The genotype status of GSTM1 and GSTT1 was successfully determined in all patients by analyzing an aliquot of the same DNA used for the 8-OHdG evaluation. This method allows for the use of samples collected from living subjects during ocular surgery in order to study the role of oxidative DNA damage in the pathogenesis of degenerative eye diseases such as glaucoma.

Elevated levels of oxidative DNA damage in patients with coronary artery disease.

Somatic DNA damage has been suggested to contribute to the pathogenesis of atherosclerosis. However, little is known about the role of oxidative DNA damage in patients with coronary artery disease (CAD). In this study, we used the comet assay to measure oxidative DNA damage (DNA strand breaks and enzyme-sensitive sites) in peripheral blood lymphocytes from 13 patients with angiographically documented CAD and 11 age- and sex-matched control participants. Mean values of DNA strand breaks, oxidized pyrimidines and altered purines were significantly higher in CAD patients than in the control group (11.9 +/- 1.4, 18.0 +/- 2.7 and 18.1 +/- 3.1 compared with 3.3 +/- 0.2, 2.7 +/- 0.5 and 4.5 +/- 1.1; P < 0.0001, P < 0.0001 and P = 0.0009, respectively). Moreover, oxidized purines (for example, 8-oxo-guanine) increased with the number of affected vessels and positively correlated with the extent of CAD measured by means of the number of the coronary lesions (P = 0.76, P = 0.003) and the Duke scoring system (P = 0.66, P = 0.01). Diabetic patients showed higher levels of oxidized pyrimidines (31.3 +/- 5.5 compared with 14.1 +/- 2.7; P = 0.013), while patients with dyslipidemia had elevated altered purines compared with normal patients (20.4 +/- 2.6 compared with 4.9 +/- 3.1; P = 0.03). These data indicate an overall elevation of oxidative DNA damage in CAD patients correlated with the severity of the disease and some atherogenic risk factors, suggesting a possible role of oxidative genetic damage in the pathogenesis of atherosclerosis.

Role of dietary antioxidants in the prevention of in vivo oxidative DNA damage

Epidemiological evidence consistently shows that diets high in fresh fruit and vegetables significantly lower cancer risk. Given the postulated role of oxidative DNA damage in carcinogenesis, the assumption has been made that it is the antioxidant properties of food constituents, such as vitamin C, E and carotenoids, which confer protection. However, epidemiological studies with specific antioxidants, either singly or in combination, have not, on the whole, supported this hypothesis. In contrast, studies examining the in vitro effect of antioxidants upon oxidative DNA damage have generally been supportive, in terms of preventing damage induction. The same, however, cannot be said for the in vivo intervention studies where overall the results have been equivocal. Nevertheless, recent work has suggested that some dietary antioxidants may confer protective properties through a novel mechanism, unrelated to their conventional free-radical scavenging abilities. Upregulation of antioxidant defence, xenobiotic metabolism, or DNA-repair genes may all limit cellular damage and hence promote maintenance of cell integrity. However, until further work has clarified whether dietary supplementation with antioxidants confers a reduced risk of cancer and the mechanism by which this effect is exerted, the recommendation for a diet rich in fruit and vegetables remains valid empirically.

DNA Damage and Aging

A popular theory postulates that aging is triggered by cellular accumulation of oxidative damage. The causal role of oxidative DNA damage in aging is strongly supported in a study by de Boer et al. (see the Perspective by Hasty and Vijg) of mice carrying a mutant version of the DNA helicase gene XPD. This gene causes the rare human disorder trichothiodystrophy (TTD). The XPD mutant mice, which are severely impaired in transcription-coupled repair and mildly impaired in nucleotide-excision repair, exhibited many symptoms of premature aging, including osteoporosis, infertility, early graying, and reduced life-span. Mice doubly mutant for XPD and a second gene required for nucleotide-excision repair, XPA, showed greatly accelerated aging that correlated with an increased cellular sensitivity to oxidative DNA damage. The authors propose that the aging phenotype in the TTD mice is caused by unrepaired DNA damage that compromises transcription, which in turn leads to functional inactivation of critical genes and cell death. J. de Boer, J. O. Andressoo, J. de Wit, J. Huijmans, R. B. Beems, H. van Steeg, G. Weeda, G. T. J. van der Horst, W. van Leeuwen, A. P. N. Themmen, M. Meradji, J. H. J. Hoeijmakers, Premature aging in mice deficient in DNA repair and transcription. Science 296 , 1276-1279 (2002). [Abstract] [Full Text] P. Hasty, J. Vijg, Genomic priorities in aging. Science 296 , 1250-1251 (2002). [Summary] [Full Text]

Xanthine oxidase-derived oxygen radicals play significant roles in the development of chronic pancreatitis in WBN/Kob rats.

Although oxygen-derived free radicals are known to play a role in cell injury and DNA alterations, the role of active oxidants in chronic pancreatitis has not been fully elucidated. Using WBN/Kob rats, which spontaneously develop chronic pancreatitis-like lesions, we investigated whether xanthine oxidase (XOD)-derived oxygen radicals are involved in pancreatic tissue injury. WBN/Kob rats were fed a control or a tungsten diet. The latter depletes XOD activity. Histologic al changes, glutathione (GSH) content and XOD and superoxide dismutase (SOD) activities were determined in pancreatic tissue. Pancreatic 8-hydroxy-deoxyguanosine (8-OH-dG) levels and lithostathine mRNA were also examined. In WBN/Kob rats, parenchymal destruction and fibrosis developed at approximately 12 weeks of age and progressed with each month. The activity of XOD was significantly higher in the early period (8-12 weeks), whereas the levels of GSH and SOD decreased after 16 weeks. Levels of 8-OH-dG in WBN/Kob rats were significantly elevated at 16 weeks. Lithostathine mRNA levels started to increase at 8 weeks, but were suppressed at 16 weeks. The tungsten diet significantly attenuated the histological changes in WBN/Kob rats. The increase in pancreatic XOD activity and 8-OH-dG content in WBN/Kob rats was significantly inhibited by the tungsten diet and lithostathine mRNA levels remained high at 16 weeks. These results suggest that oxygen radicals generated by XOD play an important role in oxidative DNA damage and the development of chronic pancreatic injury.