8-OHdG Levels In DNA Research Articles

Possible contribution of 8-hydroxydeoxyguanosine to gene mutations in the kidney DNA of gpt delta rats following potassium bromate treatment

8-Hydroxydeoxyguanosine (8-OHdG) is well known not only as an effective biomarker of oxidative stress but also as a mutagenic DNA modification. Incorporation of dAMP at the opposite site of 8-OHdG induces G>T or A>C transversions. However, in vivo analyses of gene mutations caused by potassium bromate (KBrO3), which can induce 8-OHdG at carcinogenic target sites, showed that G>T was prominent in the small intestines of mice, but not in the kidneys of rats. Because KBrO3 was a much clearer carcinogen in the kidneys of rats, detailed analyses of gene mutations in the kidney DNA of rats treated with KBrO3 could improve our understanding of oxidative stress-mediated carcinogenesis. In the current study, site-specific reporter gene mutation assays were performed in the kidneys of gpt delta rats treated with KBrO3. Groups of 5 gpt delta rats were treated with KBrO3 at concentrations of 0, 125, 250, or 500 ppm in the drinking water for 9 weeks. At necropsy, the kidneys were macroscopically divided into the cortex and medulla. 8-OHdG levels in DNA extracted from the cortex were dramatically elevated at concentrations of 250 ppm and higher compared with those from the medulla. Cortex-specific increases in mutant frequencies in gpt and red/gam genes were found at 500 ppm. Mutation spectrum and sequence analyses of their mutants demonstrated significant elevations in A>T transversions in the gpt gene and single base deletions at guanine or adenine in the gpt or red/gam genes. While A>T transversions and single base deletions of adenine may result from the oxidized modification of adenine, the contribution of 8-OHdG to gene mutations was limited despite possible participation of the 8-OHdG repair process in guanine deletion.

Abstract 614: Increased oxidative DNA damage in human prostate cancer and its relationship to GSTP1 expression

Abstract The pi-class glutathione S-transferase (GSTP1) has been described as a ‘caretaker’ gene, as it actively protects the cell from oxidative genome damage mediated by carcinogens and electrophilic compounds. Loss of GSTP1 expression via promoter hypermethylation is one of the most common epigenetic alterations observed in human prostate cancer. Silencing of GSTP1 can increase prostate epithelial cells more vulnerable to both oxidant and electrophile carcinogens and causes genetic aberrations leading to increased risk of tumor progression. Observations suggest that increased reactive oxygen species (ROS) causes DNA damage in cells, as measured by 8-hydroxy-2′-deoxyguanosine (8-OHdG), contribute to increased incidence of prostate cancer. However there are no studies which demonstrate correlation between GSTP1 protein/activity and DNA damage in prostate cancer. We took a panel of 24 human prostate specimens obtained after surgery which comprised of matched primary tumor and adjacent nontumorous (benign) prostate tissues. Oxidative DNA damage, GSTP1 protein expression and its activity, and GSTP1 promoter methylation was assessed. The 8-OHdG levels in DNA of prostate cancer tissues ranged from 0.307 to 0.609ng/μg DNA, whereas the levels in benign tissue range from 0.156 to 0.322ng/μg DNA, respectively. 8-OHdG and GSTP1 promoter methylation levels were higher in adenocarcinoma compared to their benign counterparts, which positively correlated with the loss of GSTP1 activity. The GSTP1 protein activity of prostate cancer tissues ranged from 738.2 to 1754.4ng/mg protein, whereas the levels in benign tissue range from 1728.6 to 2580.4ng/mg protein. The loss of GSTP1 expression in cells might increase their vulnerability to cytotoxicity and reactive oxygen species (ROS)-mediated DNA damage. In further experiments, human prostate carcinoma LNCaP cells, which contains a silenced GSTP1 gene, was genetically modified to constitutively express high levels of GSTP1. Introduction of GSTP1 lowered endogenous ROS levels in LNCaP cells; treatment with H2O2 significantly reduced ROS and 8-OHdG in LNCaP-GSTP1 cells, compared to parental cell line. Furthermore, treatment with green tea polyphenols to LNCaP cells caused re-expression of GSTP1 which protected the cells from H2O2-mediated DNA damage compared to pretreated cells. These results suggest that oxidative stress-induced DNA damage may be an important measure for primary prevention of prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 614. doi:1538-7445.AM2012-614

1307 RELATIONSHIP BETWEEN GLUTATHIONE-S-TRANSFERASE PI EXPRESSION AND OXIDATIVE DNA DAMAGE IN HUMAN PROSTATE CANCER

You have accessJournal of UrologyProstate Cancer: Basic Research II1 Apr 20121307 RELATIONSHIP BETWEEN GLUTATHIONE-S-TRANSFERASE PI EXPRESSION AND OXIDATIVE DNA DAMAGE IN HUMAN PROSTATE CANCER Rajnee Kanwal, Pingfu Fu, Lee Ponsky, and Sanjay Gupta Rajnee KanwalRajnee Kanwal Cleveland, OH More articles by this author , Pingfu FuPingfu Fu Cleveland, OH More articles by this author , Lee PonskyLee Ponsky Cleveland, OH More articles by this author , and Sanjay GuptaSanjay Gupta Cleveland, OH More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.1654AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The pi-class glutathione S-transferase (GSTP1) has been described as a ‘caretaker' gene, as it actively protects the cell from oxidative genome damage mediated by carcinogens and electrophilic compounds. Loss of GSTP1 expression via promoter hypermethylation is one of the most common epigenetic alterations observed in human prostate cancer. Silencing of GSTP1 can increase prostate epithelial cells more vulnerable to both oxidant and electrophile carcinogens and causes genetic aberrations leading to increased risk of tumor progression. Observations suggest that increased reactive oxygen species (ROS) causes DNA damage in cells, as measured by 8-hydroxy-2'-deoxyguanosine (8-OHdG), contribute to increased incidence of prostate cancer. However there are no studies which demonstrate correlation between GSTP1 protein/activity and DNA damage in prostate cancer. METHODS We used a panel of 24 human prostate specimens, pair-matched primary tumor and adjacent nontumorous (benign) tissue. Oxidative DNA damage, GSTP1 protein expression/activity, and GSTP1 promoter methylation was assessed. GSTP1 over-expression technique was used to assess H2O2-mediated DNA damage in prostate cancer cells. RESULTS The 8-OHdG levels in DNA of prostate cancer tissues ranged from 0.307 to 0.609ng/μg DNA, whereas the levels in benign tissue range from 0.156 to 0.322ng/μg DNA, respectively. 8-OHdG and GSTP1 promoter methylation levels were higher in adenocarcinoma compared to their benign counterparts, which positively correlated (P=0.533) with the loss of GSTP1 activity. The GSTP1 protein activity of prostate cancer tissues ranged from 738.2 to 1754.4ng/mg protein, whereas the levels in benign tissue range from 1728.6 to 2580.4ng/mg protein. The loss of GSTP1 expression in cells might increase their vulnerability to cytotoxicity and reactive oxygen species (ROS)-mediated DNA damage. In further experiments, human prostate carcinoma LNCaP cells, which contains a silenced GSTP1 gene, was genetically modified to constitutively express high levels of GSTP1. Introduction of GSTP1 lowered endogenous ROS levels in LNCaP cells; treatment with H2O2 significantly reduced ROS and 8-OHdG in LNCaP-GSTP1 cells, compared to parental cell line. Furthermore, treatment with green tea polyphenols to LNCaP cells caused re-expression of GSTP1 which protected the cells from H2O2-mediated DNA damage compared to pretreated cells. CONCLUSIONS These results suggest that oxidative stress-induced DNA damage may be an important measure for primary prevention of prostate cancer. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e530 Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Rajnee Kanwal Cleveland, OH More articles by this author Pingfu Fu Cleveland, OH More articles by this author Lee Ponsky Cleveland, OH More articles by this author Sanjay Gupta Cleveland, OH More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Abstract 4903: Oxidative DNA damage and its relationship with GSTP1 methylation in prostate cancer

Abstract Prostate cancer is the most common cancer diagnosed in men and is the second leading cause of cancer-related death in the United States. The risk factor for prostate cancer includes both genetic and epigenetic modifications. Growing evidence suggests that epigenetic mechanisms such as DNA methylation affect gene expression in tissue-specific manner. The most frequent epigenetic alteration observed in human prostate cancer is hypermethylation of gluthathione-S-transferase-pi class (GSTP1) in the promoter region which causes loss or its decrease expression. Inactivation of GSTP1 renders prostate epithelial cells vulnerable to oxidative DNA damage from both oxidants and electrophile carcinogens to acquire relevant genetic alteration and neoplastic transformation. Extensive observations suggest that reactive oxygen species may cause accumulated DNA damage which might contribute to increased incidence of prostate cancer. However, the role of GSTP1 and its correlation with DNA damage has not been studied. Based on the assumption that DNA damage is prevalent in cancer cells compared to nontumorous tissue, we took a panel of 24 human prostate specimens obtained after surgery which comprised of matched primary tumor and adjacent nontumorous (benign) prostate tissues. Oxidative DNA damage was measured by 8-hydroxy-2′-deoxyguanosine (8-OHdG) levels through highly sensitive and quantitative ELISA assay. GSTP1 methylation was determined by methyl-specific PCR and 5-methylcytosine estimation was performed by HPLC analysis. The 8-OHdG levels were higher in cancer specimen compared to their benign counterparts. The 8-OHdG levels in DNA of prostate cancer tissues ranged from 0.151 to 0.616ng/μg DNA, whereas the levels in benign tissue range from 0.149 to 0.318ng/μg DNA, respectively. The increase in 8-OHdG levels correlate with GSTP1 methylation which was higher in cancer specimens compared to the benign counterparts. Furthermore, levels of 5-methylcytosine were higher in tumor specimens compared to benign tissue. Taken together, our studies suggest that there is a link between GSTP1 methylation and DNA damage which correlates to epigenetic modification in prostate cancer. Our results are in agreement with the prediction that positive relationship occur between GSTP1 inactivation and DNA damage in prostate cancer. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4903.

Evaluation of Oxidative Damage Induced by Natural Sunlight in Drosophila

The sunlight that reaches the surface of the earth is composed of polychromatic light with wavelengths ranging from 290 nm to 2500 nm. Ultraviolet (UV) light is a component of sunlight that is harmful to organisms. Although it is known that sunlight induces photoproducts and harmful effects such as major DNA damage caused by UV light in the tissues of many species including human skin, it is not clear whether sunlight induces oxidative damage in organisms. In this study, we investigated whether sunlight causes oxidative damage in exposed organisms using Drosophila. Third instar larvae were exposed to sunlight for an evaluation of viability and 8-hydroxydeoxyguanosine (8-OHdG) content. Urate-null Drosophila mutant larvae (ry506), which are sensitive to active oxygen-producing agents, were more sensitive to sunlight lethality than the wild-type strain under limited conditions. This sunlight-induced toxicity in ry506 larvae was partially prevented by pretreatment of larvae with 400 mM uric acid. The level of 8-OHdG in DNA showed no significant increase in both strains. In contrast, sunlight was significantly mutagenic for all seasons as reported previously. These results suggest that sunlight is partly responsible for oxidative damage in Drosophila and that 8-OHdG-formation plays little or no role in sunlight-induced mutation and toxicity.

Increased oxidative DNA damage, 8-hydroxydeoxy- guanosine, in human pterygium

Chronic exposure to ultraviolet (UV) light is a widely accepted aetiological factor in the development of pterygium. UV radiation may induce production of reactive oxygen species via photosensitized oxidation, thus causing oxidative damage. This study was conducted to test the hypothesis that oxidative damage to DNA is increased in pterygium. Immunohistochemical analysis employing a monoclonal antibody specific for 8-hydroxy-2'-deoxyguanosine (8-OHdG), a ubiquitous maker of oxidative stress, was performed in three patients with primary pterygium. The levels of 8-OHdG in DNA isolated from the other 29 pterygium specimens and their adjacent normal conjunctival tissues were determined using enzyme-linked immunosorbent assay (ELISA). Immunohistochemistry of 8-OHdG showed a distinct pattern of more extensive and intense staining in the nuclei of pterygium tissue compared with that in their adjacent normal conjunctiva. ELISA also revealed that the average level of 8-OHdG in the pterygium tissues was 4.7-fold higher than that of the corresponding normal conjunctiva (P<0.001). The increased levels of 8-OHdG in the pterygium tissues indicate that oxidative stress could play a role in the development of pterygium. These findings provide new information to better understand the pathogenesis of pterygium and are useful in the prevention and treatment of this disease.

Oxidative DNA damage in rats exposed to extremely low frequency electro magnetic fields

Extremely low frequency (ELF) electromagnetic field (EMF) is thought to prolong the life of free radicals and can act as a promoter or co-promoter of cancer. 8-hydroxy-2′-deoxyguanosine (8OHdG) is one of the predominant forms of radical-induced lesions to DNA and is a potential tool to asses the cancer risk. We examined the effects of extremely low frequency electro magnetic field (ELF-EMF) (50 Hz, 0.97 mT) on 8OHdG levels in DNA and thiobarbituric acid reactive substances (TBARS) in plasma. To examine the possible time-dependent changes resulting from magnetic field, 8OHdG and TBARS were quantitated at 50 and 100 days. Our results showed that the exposure to ELF-EMF induced oxidative DNA damage and lipid peroxidation (LPO). The 8OHdG levels of exposed group (4.39±0.88 and 5.29±1.16 8OHdG/dG.105, respectively) were significantly higher than sham group at 50 and 100 days (3.02±0.63 and 3.46±0.38 8OHdG/dG.105) (p<0.001, p<0.001). The higher TBARS levels were also detected in the exposure group both on 50 and 100 days (p<0.001, p<0.001). In addition, the extent of DNA damage and LPO would depend on the exposure time (p<0.05 and p<0.05). Our data may have important implications for the long-term exposure to ELF-EMF which may cause oxidative DNA damage.

Increased Formation of 8-Hydroxy-2’-Deoxyguanosine in Peripheral Blood Leukocytes in Bladder Cancer

Introduction: Reactive oxygen species-induced damage to DNA plays a major role in carcinogenesis. Methods: In order to estimate the level of oxidative damage in bladder cancer, 8-hydroxy-2′-deoxyguanosine (8-OHdG) was determined in DNA isolated from peripheral blood leukocytes of healthy adults and patients with superficial transitional cell carcinoma. Patients with transitional cell carcinoma of the bladder and control individuals were similar in age. In this study, the level of 8-OHdG in DNA in male subjects was measured by the high-performance liquid chromatography-electrochemical detector method. Results: The 8-OHdG levels in DNA from leukocytes of bladder cancer patients were significantly higher than those in controls. Conclusion: Reduction of oxidative stress is thought to be a very important measure for primary prevention of bladder cancer.

8-Hydroxydeoxyguanosine in leukocyte DNA and urine of quartz-exposed workers and patients with silicosis.

To examine radical-induced DNA damage and its elimination in workers exposed to quartz and in patients with silicosis, and to assess the relationship of these effects to lung function. Blood and spontaneous urine samples were obtained from active, quartz-exposed workers without silicosis (n = 63), and from retired workers with silicosis (n = 42). Levels of 8-hydroxydeoxyguanosine (8-OHdG) were determined in peripheral blood leukocyte DNA and urine, by the use of high-performance liquid chromatography coupled with ultra violet- (UV) and electrochemical detection. No significant differences in the mean levels of 8-OHdG in leukocyte DNA and of urinary excretion of 8-OHdG were found between silicosis patients and quartz-exposed healthy workers. However, in the group of silicosis patients with increased oxidative DNA damage the urinary excretion of 8-OHdG was lower than in the corresponding group of active workers without silicosis. In the case of silicosis, urinary 8-OHdG correlated positively, and 8-OHdG in DNA correlated negatively, with forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). Healthy workers with a personally estimated high dust exposure in the workplace showed higher levels of 8-OHdG in DNA than did workers with moderate dust exposure. No association of 8-OHdG formation and/or elimination with duration of employment, field of activity, smoking or age was found. Our findings suggest that a less effective repair of 8-OHdG is associated with a higher degree of pulmonary airway obstruction in patients with silicosis.

Increased formation of oxidative DNA damage, 8-hydroxy-2′-deoxyguanosine, in human breast cancer tissue and its relationship to GSTP1 and COMT genotypes

Reactive oxygen species (ROS) induced damage to DNA plays a major role in carcinogenesis. In order to estimate the level of oxidative damage and its role in breast cancer, 8-hydroxy-2′-deoxyguanosine (8-OHdG) was determined in DNA isolated from human breast tissue. Furthermore, we investigated whether polymorphisms in genes for enzymes involved in generation and elimination of ROS had any association with the level of 8-OHdG in breast tissue. In this study, the level of 8-OHdG in DNA was measured by the high performance liquid chromatography-electrochemical detector (HPLC-ECD) method. Genotypes of cytochrome P450 (CYP)1A1, glutathione S-transferase (GST)M1, GSTP1 and catechol O-methyltransferase (COMT) were determined by PCR-based restriction fragment length polymorphism analysis. A total of 61 Japanese patients were included in the study. The mean level of 8-OHdG in DNA of breast cancer tissues was 2.07±0.95 per 10 5 dG residues, while the mean level of 8-OHdG in DNA of non-cancerous breast tissues was 1.34±0.46 per 10 5 dG residues. The 8-OHdG levels in DNA of breast cancer tissues were significantly higher than those of their corresponding non-cancerous breast tissues ( P<0.0001). There was negative correlation between the clinical stage and the mean level of 8-OHdG in DNA of breast cancer tissues. Furthermore, patients with genotype of high GSTP1 activity had lower level of 8-OHdG in DNA of breast cancer tissues than others. On the contrary, the mean level of 8-OHdG in DNA of breast cancer tissues was higher among patients with genotype of high COMT activity. Our findings support the assumption that cancer cells are more exposed to oxidative stress than adjacent non-cancerous tissue. Genetic polymorphisms in enzymes involved in ROS metabolism may have a role in individual susceptibility to oxidant-related breast disease. At the same time, reduction of oxidative stress is thought to be a very important measure for primary prevention of breast cancer.

Effect of increased vegetable and fruit consumption on markers of oxidative cellular damage.

The goal of this study was to test the hypothesis that increased consumption of vegetables and fruit would reduce markers of oxidative cellular damage that can be assessed in blood or urine. Twenty-eight women participated in a 14 day dietary intervention. The primary end-points assessed were: 8-hydroxydeoxyguanosine (8-OHdG) in DNA isolated from peripheral lymphocytes, determined by HPLC with electrochemical detection; 8-OHdG excreted in urine, measured by ELISA; malondialdehyde (MDA) in urine, measured by fluorimetric detection following derivatization with thiobarituric acid and separation via HPLC; urinary 8-isoprostane F-2alpha (8-EPG) detected by ELISA. Pre- and post-intervention plasma levels of selected carotenoids were determined by HPLC. Subjects were free living and consumed a completely defined recipe-based diet that increased their average daily consumption of vegetables and fruit from 5.8 servings at baseline to 12.0 servings throughout the intervention. Overall, the level of 8-OHdG in DNA isolated from lymphocytes and in urine and the level of 8-EPG in urine were reduced by the intervention, whereas urine concentrations of MDA were minimally affected. The reduction in lymphocyte 8-OHdG was greater in magnitude (32 versus 5%) in individuals with lower average pre-intervention levels of plasma alpha-carotene (56 ng/ml) than in individuals with higher average pre-intervention plasma levels of alpha-carotene (148 ng/ml). The results of this study indicate that consumption of a diet that significantly increased vegetable and fruit intake from a diverse number of botanical families resulted in significant reductions in markers of oxidative cellular damage to DNA and lipids.

8-Hydroxydeoxyguanosine in DNA from leukocytes of healthy adults: relationship with cigarette smoking, environmental tobacco smoke, alcohol and coffee consumption

8-Hydroxydeoxyguanosine (8-OHdG) has been widely used as a biomarker of oxidative DNA damage in both animal and human studies. However, controversial data exist on the relationship between 8-OHdG formation and age, sex and tobacco smoking in humans, while few or no data are available on other exposures such as environmental tobacco smoke, alcohol, coffee and tea consumption. We investigated the level of 8-OHdG in DNA from peripheral leukocytes among 102 healthy adults living in Brescia province, North Italy, aged 25–45 (mean: 35.2 years), of which 51 were males. 8-OHdG levels expressed as a ratio to total deoxyguanosine (8-OHdG/106 dG) in DNA showed wide interindividual variation, the highest value (63.8) being 6.2-fold greater than the lowest (10.3). Current smokers showed lower mean 8-OHdG values than subjects who never smoked (29.3 and 34.0, respectively, p<0.05), and an inverse relationship was found between 8-OHdG and lifetime smoking, which was independent of age, sex and body mass index. An inverse relationship was also found with coffee drinking while no association was observed with alcohol and tea consumption, exposure to environmental tobacco smoke and use of vitamins in all subjects, and with use of oral contraceptives in females. The inverse relationship between smoking status and 8-OHdG levels could be explained by the presence of efficient repair processes for the oxidative damage induced by smoking. In this study, the smokers were relatively young (77% were less than 40 years) and only 7% smoked 30 or more cigarettes a day. In conclusion, it would appear that 8-OHdG levels in leukocytes may not provide a sensitive marker of exposure to tobacco smoking.

8-Hydroxy-2'-Deoxyguanosine Is Increased in Epidermal Cells of Hairless Mice after Chronic Ultraviolet B Exposure

8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a mutation-prone (G:C to T:A transversion) DNA base-modified product generated by reactive oxygen species or photodynamic action. G:C to T:A transversions are observed in the p53 and ras genes of UVB-induced skin cancers of mice and in squamous and basal cell carcinomas of human skin exposed to sunlight. In the current study, 8-OHdG formation was evaluated in the epidermis of hairless mice after repeated exposure to UVB, and possible mechanisms involved were studied. Exposure of hairless mice to either 3.4 [2 minimal erythema dose (MED)] or 16.8 (10 MED) kJ/m2 of UVB three times a week for 2 wk induced a 2.5- or 6.1-fold increase, respectively, in the levels of 8-OHdG in DNA, compared to the unexposed controls. An immunohistochemical method using a monoclonal antibody specific for 8-OHdG showed stronger and more extensive staining in the nuclei of UV-irradiated epidermal cells than in those of nonirradiated cells. Western blots probed with antibodies against 4-hydroxy-2-nonenal-modified proteins confirmed the involvement of reactive oxygen species in the epidermal damage induced by chronic UVB exposure. 3-Nitro-L-tyrosine was detected in western blots in a concentration-dependent manner, suggesting that peroxynitrite derived from the reaction of nitric oxide and superoxide, both of which were probably released from inflammatory cells, was involved in modifying the DNA bases. Therefore, the formation of 8-OHdG after UVB exposure appears to be regulated by at least three pathways: photodynamic action, lipid peroxidation, and inflammation and may play a role in sunlight-induced skin carcinogenesis.

Elevated 8-hydroxydeoxyguanosine in hepatic DNA of rats following exposure to peroxisome proliferators: relationship to carcinogenesis and nuclear localization.

Increased oxidative DNA damage due to increased peroxisomal generation of H2O2 is a potential mechanism in the carcinogenicity of chemical peroxisome proliferators (PP) in rodent liver. In order to determine the relationship between carcinogenicity and peroxisome-dependent DNA damage, levels of DNA base oxidation were examined by comparing 8-hydroxydeoxyguanosine (8-OHdG) in DNA from unfractionated liver of male F344 rats following dietary exposure to PP [WY-14,643, 0.1% or 0.005%; di(2-ethylhexyl)phthalate (DEHP), 1.2%; clofibric acid, 0.5%] or phenobarbital (0.05%). Exposure-related increases in 8-OHdG were not observed at 3 or 11 weeks for any of the compounds fed. At 22 weeks, 8-OHdG was similarly elevated (2-3x) by WY-14,643 (0.1% and 0.005%) and clofibric acid (0.5%). These equivalent increases in 8-OHdG in DNA from unfractionated liver did not parallel the divergent carcinogenicity of these different dietary exposures in the present or previous studies. The potential oxidation of nuclear DNA was examined by comparing levels of 8-OHdG in DNA isolated from purified liver nuclei and unfractionated liver. Elevated levels of 8-OHdG were not detected in DNA isolated from nuclear fractions of livers from rats fed clofibric acid for 22 weeks, indicating the dependence of PP-induced oxidative DNA damage on extranuclear components of samples for DNA isolation. The absence of a quantitative relationship between PP-induced carcinogenicity and oxidative DNA base damage (as 8-OHdG), and the failure to localize this oxidative damage to nuclear DNA, suggest two possible conclusions: (1) quantitation of 8-OHdG, a specific and sensitive indicator of oxidative DNA damage, does not accurately reflect the potential peroxisomal H2O2-dependent DNA damage and carcinogenicity of PP exposure in rodents; (2) other hepatic responses may be more critical features of the mechanism of PP carcinogenicity.

Influence of dietary vitamin E on the 8-hydroxydeoxyguanosine levels in rat liver DNA.

Rats were fed either a low vitamin E (VE) diet (-VE), a basal VE diet (+VE, 4.5 mg%), or a high VE diet (+VE, 45 mg%) for 7 weeks. VE content, oxidative DNA damage and lipid peroxide levels in their livers were measured. When purified lard was used as a dietary fat, VE content decreased in the low VE group to one-thirtieth of that in the basal VE group; in the high VE group it increased to 4.5-fold that in the basal VE group. Corresponding to the VE levels, lipid peroxide levels increased to 2.7-fold in the low VE group and decreased to two-thirds in the high VE group. The level of 8-hydroxydeoxyguanosine (8-OHdG) in DNA, a marker of oxidative DNA damage, was about 0.6 per 10(5) deoxyguanosine in the basal VE group and comparable values were found in the low VE and the high VE groups. When either soybean oil or safflower oil was used as a dietary fat, VE content and lipid peroxide levels in the liver were also markedly changed in both the low VE group and the high VE group. 8-OHdG levels in DNA of the low VE with safflower oil group tended to be higher than that of the basal and high VE groups. However, no significant difference was observed among them. These results suggest that the change in VE has little influence on the level of oxidative DNA damage in the liver.