Oxidative DNA Damage In Rats Research Articles

Genotoxicity and Gene Expression in the Rat Lung Tissue following Instillation and Inhalation of Different Variants of Amorphous Silica Nanomaterials (aSiO2 NM).

Several reports on amorphous silica nanomaterial (aSiO2 NM) toxicity have been questioning their safety. Herein, we investigated the in vivo pulmonary toxicity of four variants of aSiO2 NM: SiO2_15_Unmod, SiO2_15_Amino, SiO2_7 and SiO2_40. We focused on alterations in lung DNA and protein integrity, and gene expression following single intratracheal instillation in rats. Additionally, a short-term inhalation study (STIS) was carried out for SiO2_7, using TiO2_NM105 as a benchmark NM. In the instillation study, a significant but slight increase in oxidative DNA damage in rats exposed to the highest instilled dose (0.36 mg/rat) of SiO2_15_Amino was observed in the recovery (R) group. Exposure to SiO2_7 or SiO2_40 markedly increased oxidative DNA lesions in rat lung cells of the exposure (E) group at every tested dose. This damage seems to be repaired, since no changes compared to controls were observed in the R groups. In STIS, a significant increase in DNA strand breaks of the lung cells exposed to 0.5 mg/m3 of SiO2_7 or 50 mg/m3 of TiO2_NM105 was observed in both groups. The detected gene expression changes suggest that oxidative stress and/or inflammation pathways are likely implicated in the induction of (oxidative) DNA damage. Overall, all tested aSiO2 NM were not associated with marked in vivo toxicity following instillation or STIS. The genotoxicity findings for SiO2_7 from instillation and STIS are concordant; however, changes in STIS animals were more permanent/difficult to revert.

Protective effect of Trigonella foenum-graecum and Cinnamomum zeylanicum against diabetes induced oxidative DNA damage in rats

Diabetes mellitus has become a global epidemic as its prevalence is steadily increasing everywhere at an alarming rate, most markedly in the India. Traditional Indian system of medicine based on herbal therapies is being practiced since ancient times and has been proved very effective against number of diseases. Trigonella foenum-graecum (Tfg) and Cinnamomum zeylanicum (Cz), the two spices, possess multiple medicinal properties. Hence present study is aimed to evaluate the protective effects of these plants on the oxidative DNA damage in diabetic rats. The presence of DNA base oxidation was investigated by modified comet assay which uses bacterial repair enzymes, formamidopyrimidine glycosylase and Endonuclease III which can measure oxidatively damaged purines and pyrimidines, respectively. Diabetes induced alteration in total antioxidant capacity (TAC), generation of superoxide anion and the levels of GSH, GSSG, NADH, NAD+, NADPH and NADP+ were monitored. Diabetes was induced by intravenous injection of alloxan, followed by oral administration of aqueous suspension of Tfg seeds and bark of Cz. Treatment of Tfg and Cz significantly restored the altered level of superoxide anion, TAC, ratios of GSH/GSSG, NAD(P)H/NAD(P)+ and NADH/NAD+ in the diabetic group. Furthermore, both the treatment effectively decreased the level of oxidatively damaged purine and pyrimidine bases.

Effects of Zinc Supplementation on DNA Damage in Rats with Experimental Kidney Deficiency.

This study was carried out to determine the effect of zinc on oxidative DNA damage in rats with experimental acute and chronic kidney deficiency. Six groups of five Wistar-Albino rats each were assigned as controls (C), acute kidney deficiency (AKD), zinc-supplemented (+Zn), acute kidney deficiency, zinc-supplemented (AKD+Zn), chronic kidney deficiency (CKD) and zinc-supplemented chronic kidney deficiency (CKD+Zn). The levels of 8-Oxo-2'-deoxyguanosine (8-OHdG) were determined, being the lowest in the CKD group (p<0.05), higher in the C group than those of rats with CKD but lower than that of all the other groups (p<0.05). There were no significant differences between the controls and the CKD+Zn group, or between the AKD and the +Zn groups. Among all groups, the highest 8-OHdG level was found in the AKD+Zn group (p<0.05). DNA damage was greater in acute renal failure than in rats with chronic renal failure. The DNA damage in the zinc group was significantly higher than in the controls.

Alleviation of Aflatoxin B1-Induced Genomic Damage by Proanthocyanidins via Modulation of DNA Repair.

In order to study the mechanisms underlying the alleviation of aflatoxin B1-induced genomic damage by proanthocyanidins (PAs), we examined the modulation of oxidative DNA damage induced by aflatoxin B1 in PAs-pretreated animals. The effects of PAs on changes in the expression of DNA damage and repair genes induced by aflatoxin B1 were also evaluated in rat marrow cells. Administration of PAs before aflatoxin B1 significantly mitigated aflatoxin B1-induced oxidative DNA damage in a dose-dependent manner. Aflatoxin B1 treatment induced significant alterations in the expression of specific DNA repair genes, and the pre-treatment of rats with PAs ameliorated the altered expression of these genes. Conclusively, PAs protect against aflatoxin B1-induced oxidative DNA damage in rats. These protective effects are attributed to the antioxidant effects of PA and enhanced DNA repair through modulation of DNA repair gene expression. Therefore, PAs are a promising chemoprotective agent for averting genotoxic risks associated with aflatoxin B1 exposure.

Roles of oxidative DNA damage of bone marrow hematopoietic cells in steroid-induced avascular necrosis of femoral head

An animal model of steroid-induced avascular necrosis of femoral head (SANFH) was established to investigate the role of oxidative DNA damage of bone marrow hematopoietic cells in SANFH. Forty-five-month-old Japanese white rabbits (male or female, 2.5 ± 0.5 kg) were randomly divided into groups A (methylprednisolone + Escherichia coli endotoxin), B (methylprednisolone alone), C (E. coli endotoxin alone), and D (blank control). The animals were sacrificed two and four weeks after administration of the last dose (N = 5 each group and each time). Left and right femoral heads were fixed and decalcified. Empty lacunae were counted by hematoxylin and eosin staining and oxidative DNA damage of bone marrow hematopoietic cells was detected by immunohistochemistry. At week 2, the rate of oxidative DNA damage in bone marrow hematopoietic cells was significantly higher in group A than in groups B, C, and D (P < 0.01), while there was no significant difference between groups B, C, and D. At week 4, the rate of oxidative DNA damage in bone marrow hematopoietic cells was significantly higher in group A than in groups B, C, and D (P < 0.01), while there was no significant difference among groups B, C, and D. Thus, oxidative DNA damage of bone marrow hematopoietic cells appears to play an important role in SANFH.

Decrease in Hepatic TNF‐alpha and increase in DNA yield defines hepatoprotection of stem‐bark aqueous extract of Sclerocarya Birrea in ethanol‐induced liver injury in Wistar rats

Modulation of the toxicity of tumor necrosis factor‐alpha (TNF‐α) is important in treatment of alcoholic liver damage as it depletes oxygen in hepatocytes leading to damage of biomolecules (DNA) and apoptosis. Sclerocarya birrea (SB) has shown hepatoprotection in ethanol‐induced liver damage. This study investigates whether the stem‐bark aqueous extract of SB will modulate the expression of hepatic TNF‐α thereby preventing oxidative DNA damage in rats exposed to ethanol. Male Wistar rats were exposed to 40% (v/v) ethanol and/or two doses of SB (15 mg/kg or 30 mg/kg) or distilled water for four weeks by gastric gavage. Liver homogenates and tissue were analyzed for TNF‐α, DNA yield and histopathology. Serum was analyzed for antioxidants (superoxide dismutase and reduced glutathione) and liver function enzymes (alanine and aspartate aminotransferases). Ethanol induced hepatotoxicity with marked increase in hepatic TNF‐α and liver function enzymes while antioxidants and DNA yield decreased. Treatment with SB modulated hepatic damage by decreasing levels of TNF‐α, liver function enzymes and increasing antioxidants. Histopathological examination showed that SB attenuated degenerative changes in hepatocytes and liver parenchyma. Results demonstrate that SB modulates TNF‐α expression and induces antioxidant activity thereby preventing oxidative DNA damage and liver injury.Grant Funding Source: Ahmadu Bello University Research Grant

Alkaline, Endo III and FPG modified comet assay as biomarkers for the detection of oxidative DNA damage in rats with experimentally induced diabetes

Increased production of reactive oxygen species under diabetic condition underlines the higher oxidatively damaged DNA in different tissues. However, it is practically difficult to assess the oxidatively damaged DNA in different internal organs. Therefore, the present study was aimed to evaluate the extent of oxidative stress-induced DNA damage in different organs with the progression of diabetes. Diabetic and control Sprague Dawley rats were sacrificed in time-dependent manner and the lung, liver, heart, aorta, kidney, pancreas and peripheral blood lymphocytes (PBL) were analyzed for both alkaline and modified comet assay with endonuclease-III (Endo III) and formamidopyrimidine-DNA glycosylase (FPG) (hereafter called modified comet assay) for the detection of oxidative DNA damage. The statistically significant increase in olive tail moment (OTM) was found in all the tested tissues. The extent of DNA damage was increased with the progression of diabetes as revealed by the parameter of OTM in alkaline and modified comet assay. Further, the positive correlations were observed between OTM of the lung, liver, heart, aorta, kidney and pancreas with PBL of diabetic rat in the alkaline and modified comet assay. Moreover, significant increase in the 8-oxodG positive nuclei in the lung, liver, heart, aorta, kidney and pancreas was observed in 4th and 8th week diabetic rat as compared to control. Results of the present study clearly indicated the suitability of alkaline and modified comet assay for the detection of multi-organ oxidative DNA damage in streptozotocin (STZ)-induced diabetic rat and showed that damaged DNA of PBL can be used as a suitable biomarker to assess the internal organs response to DNA damage in diabetes.

Comparing the Relative Oxidative DNA Damage Caused by Various Arsenic Species by Quantifying Urinary Levels of 8-Hydroxy-2′-Deoxyguanosine with Isotope-Dilution Liquid Chromatography/Mass Spectrometry

To investigate the association between various arsenicals and the potential oxidative stress caused, we examined the urinary levels of 8-hydroxy-2'-deoxyguanosine (8-OH-dGuo), a biomarker of oxidative DNA damage in rats after daily oral administration of arsenic trioxide/arsenite (As(2)O(3)), realgar (alpha-As(4)S(4)) and orpiment (As(2)S(3)) over 14 days and compared the levels with control rats. 8-OH-dGuo in urine was quantified with isotope-dilution liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) after sample cleaning with solid phase extraction (SPE). Urinary arsenic concentrations were measured by graphite furnace atomic absorption spectrometry (GFAAS). All arsenicals caused elevated urinary 8-OH-dGuo excretion in rats from day 1 after oral administration (p < 0.01 respectively). There were significant correlations between urinary 8-OH-dGuo and urinary arsenic levels (slope = 0.8164, 0.5801, 0.6582; r (2) = 0.5946, 0.7883, 0.8426 for arsenite, realgar and orpiment-treated group respectively, p < 0.001). This illustrates that urinary 8-OH-dGuo level could be a valid biomarker for detecting the extent of arsenic exposure. Arsenite was found to cause significantly higher urinary 8-OH-dGuo levels than both realgar and orpiment (p < 0.01) even after creatinine and dose adjustments. Arsenite could cause more oxidative DNA damage than both realgar and orpiment and may be more genotoxic.

Estrogen Receptor α Enhances the Rate of Oxidative DNA Damage by Targeting an Equine Estrogen Catechol Metabolite to the Nucleus

Exposure to estrogens increases the risk of breast and endometrial cancer. It is proposed that the estrogen receptor (ER) may contribute to estrogen carcinogenesis by transduction of the hormonal signal and as a "Trojan horse" concentrating genotoxic estrogen metabolites in the nucleus to complex with DNA, enhancing DNA damage. 4-Hydroxyequilenin (4-OHEN), the major catechol metabolite of equine estrogens present in estrogen replacement formulations, autoxidizes to a redox-cycling quinone that has been shown to cause DNA damage. 4-OHEN was found to be an estrogen of nanomolar potency in cell culture using a luciferase reporter assay and, using a chromatin immunoprecipitation assay, was found to activate ERalpha binding to estrogen-responsive genes in MCF-7 cells. DNA damage was measured in cells by comparing ERalpha(+) versus ERalpha(-) cells and 4-OHEN versus menadione, a reactive oxygen species (ROS)-generating, but non-estrogenic, quinone. 4-OHEN selectively induced DNA damage in ERalpha(+) cells, whereas menadione-induced damage was not dependent on cellular ER status. The rate of 4-OHEN-induced DNA damage was significantly enhanced in ERalpha(+) cells, whereas ER status had no effect on the rate of menadione-induced damage. Imaging of ROS induced by 4-OHEN showed accumulation selective for the nucleus of ERalpha(+) cells within 5 min, whereas in ERalpha(-) or menadione-treated cells, no selectivity was observed. These data support ERalpha acting as a Trojan horse concentrating 4-OHEN in the nucleus to accelerate the rate of ROS generation and thereby amplify DNA damage. The Trojan horse mechanism may be of general importance beyond estrogen genotoxins.

Dietary fats modulate methylmercury-mediated systemic oxidative stress and oxidative DNA damage in rats

We examined the effects of dietary fats on methylmercury (MeHg)-induced systemic oxidative stress and oxidative DNA damage in liver and kidney of male Sprague-Dawley rats. Rats were treated with a casein-based purified isocaloric diet containing 15% by weight soy oil, docosahexaenoic acid (DHA), seal oil, fish oil, or lard for 28 days, and then gavaged with 0, 1, or 3mg MeHg/kg BW/day for 14 days. Urine was analyzed for 8-hydroxydeoxyguanosine (8-OHdG) and isoprostane, and serum for total antioxidant capacity (TAC). Liver and kidney were analyzed immunohistochemically for 8-OHdG. Both diet and MeHg showed significant main effects on some of these markers. As compared with the vehicle control, 3mg MeHg/kg BW significantly increased urinary 8-OHdG in the lard group, urinary isoprostane in the DHA, seal oil, and fish oil groups, while significantly decreasing serum TAC in the lard and fish oil groups. In all dietary groups, 8-OHdG positive staining was located mainly in the nuclei of various cell types in liver and kidney. MeHg expressed a significant main increasing effect on 8-OHdG-positive cells in kidney. These results suggest that both dietary fats and MeHg are important mediators of systemic oxidative stress and oxidative DNA damage.

Extremely low frequency magnetic fields cause oxidative DNA damage in rats

Purpose: To detect the genotoxic effects of extremely low frequency (ELF) -magnetic fields (MF) on oxidative DNA base modifications [8-hydroxyguanine (8-OH-Gua), 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) and 4,6-diamino-5-formamidopyrimidine (FapyAde)] in rat leucocytes, measured following exposure to ELF-MF.Materials and methods: After exposure to ELF-MF (50 Hz, 100 and 500 μT, for 2 hours/day during 10 months), DNA was extracted, and measurement of DNA lesions was achieved by gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS).Results: Levels of FapyAde, FapyGua and 8OHdG in DNA were increased by both 100 μT and 500 μT ELF-MF as compared to a cage-control and a sham group; however, statistical significance was observed only in the group exposed to 100 μT.Conclusion: This is the first study to report that ELF-MF exposure generates oxidatively induced DNA base modifications which are mutagenic in mammalian cells, such as FapyGua, FapyAde and 8-OH-Gua, in vivo. This may explain previous studies showing DNA damage and genomic instability. These findings support the hypothesis that chronic exposure to 50-Hz MF may be potentially genotoxic. However, the intensity of ELF-MF has an important influence on the extent of DNA damage.

Comparison of the potential for developmental toxicity of prenatal exposure to two dietary chromium supplements, chromium picolinate and [Cr3O(O2CCH2CH3)6(H2O)3]+, in mice

Chromium(III) is generally thought to be an essential trace element that allows for proper glucose metabolism. However, chromium(III) picolinate, Cr(pic)3, a popular dietary supplement form of chromium, has been shown to be capable of generating hydroxyl radicals and oxidative DNA damage in rats. The cation [Cr3O(O2CCH2CH3)(6(H2O)3]+, Cr3, has been studied as an alternative supplemental source of chromium. It has been shown to increase insulin sensitivity and lower glycated hemoglobin levels in rats, making it attractive as a potential therapeutic treatment for gestational diabetes. To date, no studies have been published regarding the safety of Cr3 supplementation to a developing fetus. From gestation days (GD) 6-17, mated CD-1 female mice were fed diets delivering either 25 mg Cr/kg/day as Cr(pic)(3), 3.3 or 26 mg Cr/kg/day as Cr3, or the diet only to determine if Cr3 could cause developmental toxicity. Dams were sacrificed on GD 17, and their litters were examined for adverse effects. No signs of maternal toxicity were observed. No decrease in fetal weight or significantly increased incidence of skeletal defects was observed in the Cr3 or Cr(pic)3 exposed fetuses compared to the controls. Maternal exposure to either Cr(pic)3 or Cr3 at the dosages employed did not appear to cause deleterious effects to the developing offspring in mice.

Effect of dietary fat-soluble vitamins A and E and proanthocyanidin-rich extract from grape seeds on oxidative DNA damage in rats

This study reports the effect of the fat-soluble vitamin A or vitamin E and grape seed proanthocyanidin extract (GSPE) on oxidative DNA damage estimated by 8-oxo-7, 8-dihydro-2′-deoxyguanosine (8-oxodG) contents in urine and leukocyte of rats. Little is known about the antioxidant potency of dietary anthocyanidins and consequently, the aim of this study was to establish whether anthocyanidins could act as putative antioxidant micronutrients. Seven groups of male Sprague-Dawley rats were fed during 47 days with the following diets: a basic diet, two deficient vitamin A or E diets, two supplemented vitamin A or E diets and two supplemented diets enriched with two doses of grape seed proanthocyanidin extract. At the end of the diet intervention period, 24 h, urine and blood were collected. The levels of 8-oxodG in leukocytes rats were significantly lower in the supplemented vitamin A, E and GSPE diet groups with respect to the control group. However, consumption of α-tocopherol, vitamin A or GSPE had no effect on the excretion of the oxidised nucleoside 8-oxodG. These results suggest that a vitamin E and A and GSPE enriched-diets have a protective effect on oxidative DNA damage limited to rat leukocytes.

Tomato-oleoresin supplement prevents doxorubicin-induced cardiac myocyte oxidative DNA damage in rats

Doxorubicin (DOX) is an efficient chemotherapeutic agent used against several types of tumors; however, its use is limited due to severe cardiotoxicity. Since it is accepted that reactive oxygen species are involved in DOX-induced cardiotoxicity, antioxidant agents have been used to attenuate its side effects. To determine tomato-oleoresin protection against cardiac oxidative DNA damage induced by DOX, we distributed Wistar male rats in control (C), lycopene (L), DOX (D) and DOX + lycopene (DL) groups. They received corn oil (C, D) or tomato-oleoresin (5 mg/kg body wt. day) (L, DL) by gavage for a 7-week period. They also received saline (C, L) or DOX (4 mg/kg body wt.) (D, DL) intraperitoneally at the 3rd, 4th, 5th, and at 6th week. Lycopene absorption was checked by HPLC. Cardiac oxidative DNA damage was evaluated by the alkaline Comet assay using formamidopyrimidine-DNA glycosylase (FPG) and endonuclease III (endo III). Cardiomyocyte levels of SBs, SBs FPG and SBs Endo III were higher in rats from D when compared to other groups. DNA damage levels in cardiomyocytes from DL were not different when compared to C and L groups. The viability of cardiomyocytes from D or DL was lower than C or L groups ( p < 0.01). Lycopene levels (mean ± S.D. nmol/kg) in saponified hearts were similar between L (47.43 ± 11.78) and DL (49.85 ± 16.24) groups. Our results showed: (1) lycopene absorption was confirmed by its cardiac levels; (2) DOX-induced oxidative DNA damage in cardiomyocyte; (3) tomato-oleoresin supplementation protected against cardiomyocyte oxidative DNA damage.

Antioxidative effects of daikon sprout ( Raphanus sativus L.) and ginger ( Zingiber officinale Roscoe) in rats

The antioxidative effects of vegetables are expected to prevent carcinogenesis. The intake of daikon sprout (Japanese name “kaiware-daikon”, Raphanus sativus L.) or ginger ( Zingiber officinale Roscoe) significantly decreased the concentration of urinary thiobarbituric acid-reactive substances (TBARS) in rats as compared with those before the intake. Moreover, the intake of these vegetables reduced urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) levels in lipopolysaccharide (LPS)-treated rats as compared with those fed a basal diet only. These results show that these vegetables suppress lipid peroxidation and the formation of malonaldehyde, and protect DNA from LPS-induced oxidative damage in rats. The suppression of lipid peroxidation and oxidative DNA damage in rats by the intake of daikon sprout or ginger indicates that these vegetables have an antioxidative effect in vivo which could be related to the prevention of carcinogenesis.

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.

A mechanism by which nitric oxide accelerates the rate of oxidative DNA damage in Escherichia coli.

The presence of nitric oxide (NO) greatly accelerates the rate at which hydrogen peroxide (H2O2) kills Escherichia coli. Workers have suggested that this effect may be important in the process of bacteriocide by phagocytes. The goal of this study was to determine the mechanism of this synergism. The filamentation of the dead cells, and their protection by cell-permeable iron chelators, indicated that NO/H2O2 killed cells by damaging their DNA through the Fenton reaction. Indeed, the number of DNA lesions was far greater when NO was present during H2O2 exposure. In the Fenton reaction, free intracellular iron transfers electrons from adventitious donors to H2O2, producing hydroxyl radicals. Although NO damaged the [Fe-S] clusters of dehydratases, this did not increase the amount of free iron and was therefore not the reason for acceleration of Fenton chemistry. However, NO also blocked respiration, an event that previous studies have shown can stimulate oxidative DNA damage. The resultant accumulation of NADH accelerates the reduction of free flavins by flavin reductase, and these reduced flavins drive Fenton chemistry by transferring electrons to free iron. Indeed, mutants lacking the respiratory quinol oxidases were sensitive to H2O2, and NO did not have any further effect. Further, mutants that lack flavin reductase were resistant to NO/H2O2, and overproducing strains were hypersensitive. We discuss the possibility that H2O2 and NO synergize when macrophages attack captive bacteria.

Reduced Flavins Promote Oxidative DNA Damage in Non-respiringEscherichia coli by Delivering Electrons to Intracellular Free Iron

When cells are exposed to external H(2)O(2), the H(2)O(2) rapidly diffuses inside and oxidizes ferrous iron, thereby forming hydroxyl radicals that damage DNA. Thus the process of oxidative DNA damage requires only H(2)O(2), free iron, and an as-yet unidentified electron donor that reduces ferric iron to the ferrous state. Previous work showed that H(2)O(2) kills Escherichia coli especially rapidly when respiration is inhibited either by cyanide or by genetic defects in respiratory enzymes. In this study we established that these respiratory blocks accelerate the rate of DNA damage. The respiratory blocks did not substantially affect the amounts of intracellular free iron or H(2)O(2), indicating that that they accelerated damage because they increased the availability of the electron donor. The goal of this work was to identify that donor. As expected, the respiratory inhibitors caused a large increase in the amount of intracellular NADH. However, NADH itself was a poor reductant of free iron in vitro. This suggests that in non-respiring cells electrons are transferred from NADH to another carrier that directly reduces the iron. Genetic manipulations of the amounts of intracellular glutathione, NADPH, alpha-ketoacids, ferredoxin, and thioredoxin indicated that none of these was the direct electron donor. However, cells were protected from cyanide-stimulated DNA damage if they lacked flavin reductase, an enzyme that transfers electrons from NADH to free FAD. The K(m) value of this enzyme for NADH is much higher than the usual intracellular NADH concentration, which explains why its flux increased when NADH levels rose during respiratory inhibition. Flavins that were reduced by purified flavin reductase rapidly transferred electrons to free iron and drove a DNA-damaging Fenton system in vitro. Thus the rate of oxidative DNA damage can be limited by the rate at which electron donors reduce free iron, and reduced flavins become the predominant donors in E. coli when respiration is blocked. It remains unclear whether flavins or other reductants drive Fenton chemistry in respiring cells.

Effect of vitamin C supplementation against cisplatin-induced toxicity and oxidative DNA damage in rats

Antitumor agents are used as a common therapy against some kinds of cancer. However, as with many agents that have mammalian cell toxicity as a target, physiological adverse effects can occur such as nephrotoxicity and genotoxicity that can be induced in non-tumor cells by generating activated oxygen species, which attack the DNA frequently resulting in oxidative DNA damage. To diminish the undesirable side-effects of therapy and to reduce the levels of oxidative DNA damage, it is recommended for patients to ingest food supplements and vitamins combinations containing substantial amounts of antioxidants. In the present study, we investigated the effects of cisplatin and vitamin C on the renal toxicity and on the oxidative DNA damage. Rats were co-treated with the chemotherapeutic agent cisplatin (5 mg kg−1body weight) and dietary doses of vitamin C (50 and 100 mg kg−1body weight). Results demonstrated that depending on the treatment protocol, we observed alterations in parameters such as body weight, urinary volume and urinary creatinine, indicating some kidney toxicity. We also observed changes in the urinary levels of 8-OHdG, suggesting possible oxidative DNA damage.

Effect of Varying Dietary Fat Levels on Rat Growth and Oxidative DNA Damage

Dietary fat has previously been shown to have somewhat complicated relationships to levels of oxidative stress in rats. In this study, we examined the effects of five different dietary fat intakes on levels of oxidative DNA damage in rats. Animals fed diets containing 3%, 5%, 10%, or 15% corn oil had body weights that were similar after 20 weeks. Animals fed a 20% fat diet, however, had significantly higher mean body weight than any other group. Levels of 5-hydroxymethyl-2′-deoxyuridine, one marker of oxidative DNA damage, had different relationships to dietary fat in blood and mammary gland. In blood, levels increased with dietary fat levels, and the highest levels were observed with the 20% fat diet (65% higher levels than with the 3% fat diet). In mammary gland, a plateau-type effect was observed, with maximal levels of oxidative DNA damage being obtained using 10% fat (representing a 68% increase relative to the 3% fat diet). This could be a result of induction of compensatory mechanisms in response to a high-fat diet in mammary gland but not in the short-lived nucleated blood cells. Oxidative DNA damage levels in blood thus appear to be a marker of dietary fat intake. In mammary gland, however, levels of DNA damage are consistent with previously observed promotional effects of dietary fat on mammary gland tumorigenesis at lower levels of fat intake with little or no incremental promoting effects at higher levels of fat intake.