Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00568 (ascorbate)
 23,072 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Isolated rat-liver nuclei were incubated with a series of membrane-permeable metal-ion-complexing agents and examined for DNA damage. Of the reagents tested, only 1,10-phenanthroline (OP) and neocuproine (NC) were found to induce DNA fragmentation. Agarose-gel electrophoresis of the DNA fragments generated in the presence of OP revealed internucleosomal cleavage, which is widely considered to be a hallmark for the enzymic DNA digestion that occurs during apoptosis. Ascorbate, particularly in the presence of hydrogen peroxide, increased the levels of fragmentation induced by OP. As well as undergoing fragmentation, the DNA from nuclei was also found to contain 8-hydroxydeoxyguanosine, which indicates attack (oxidation) by the hydroxyl radical. Complementary experiments in vitro involving ESR determinations of hydroxyl radical formation and measurements of DNA oxidation under biomimetic conditions demonstrated that Cu2+, but not Fe3+, forms a complex with either OP or NC (but not the other complexing agents tested) that stimulates hydroxyl radical formation and DNA damage in the presence of hydrogen peroxide and ascorbate. It is therefore proposed that OP in the nuclei incubations binds to Cu2+, which exists naturally in chromosomes, forming a complex that promotes hydroxyl-radical-dependent DNA fragmentation. These findings demonstrate the promotion of hydroxyl-radical-mediated DNA damage by endogenous Cu2+ and, perhaps more significantly, demonstrate that the internucleosomal DNA 'laddering' that is often used as an indicator of apoptosis may also result from DNA fragmentation by non-enzymic processes.
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PMID:1,10-Phenanthroline stimulates internucleosomal DNA fragmentation in isolated rat-liver nuclei by promoting the redox activity of endogenous copper ions. 854 78

The capability of Cr(III) to induce DNA lesions generated by oxidative damage was investigated in this study by examining the formation of 8-hydroxydeoxyguanosine (8-OHdG) in calf thymus DNA by CrCl3 and/or H2O2 in 10 mM phosphate buffer. In the presence of 0.5 mM H2O2, the formation of 8-OHdG markedly increased with increasing CrCl3 concentration. In contrast, H2O2 or CrCl3 alone did not cause any increase in 8-OHdG level above background. The amount of 8-OHdG induced by CrCl3 plus H2O2 was time dependent; its generation increased linearly over an incubation period of 90 min. The formation of 8-OHdG was unfavorable in an acidic solution (pH < 6); the highest level of 8-OHdG was observed at pH 7-8. Scavengers of reactive oxygen species markedly inhibited the formation of 8-OHdG by CrCl3 plus H2O2; the inhibition effect was sodium azide > D-mannitol > Tris-HCl at an equal concentration. The induction of 8-OHdG by CrCl3 plus H2O2 remained unchanged in D2O. Moreover, an addition of catalase (2.2 U/ml) to the reaction mixture completely inhibited the formation of 8-OHdG by CrCl3/H2O2, whereas only 22% of that formation was inhibited by superoxide dismutase (11 U/ml). A large amount of bovine serum albumin (1.1 mg/ml) could reduce the formation of 8-OHdG by CrCl3 plus H2O2, thereby implying that Cr(III)-mediated DNA-protein crosslinks are unfavorable for 8-OHdG formation. Furthermore, ascorbate could prevent the formation of 8-OHdG by CrCl3 plus H2O2; the extent of prevention increased with increasing ascorbate concentration (10 microM-3 mM). Thus, ascorbate acts as a free radical scavenger in the CrCl3/H2O2 system. The above findings suggest that Cr(III)/H2O2 could generate oxidative damage to DNA, possibly through a Fenton-like reaction, i.e. Cr(III)+H2O2-->Cr(IV)+.OH+OH-. This study also indicates that Cr(III), previously considered as the ultimate kinetically stable species of Cr(VI) metabolites, is capable of inducing carcinogenic lesions through interaction with a cellular oxygen species.
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PMID:Induction of 8-hydroxydeoxyguanosine in DNA by chromium(III) plus hydrogen peroxide and its prevention by scavengers. 856 17

Ultraviolet B radiation (UVB) induces oxidative damage in DNA, resulting in the formation of the adduct 8-hydroxydeoxyguanosine. Previous studies from this laboratory have demonstrated a decrease in antioxidant enzyme defenses after UVB radiation in Skh: HR-1 hairless mice, implicating antioxidant status in protection against oxidative damage. The present study was undertaken to examine mechanisms of UVB damage to DNA and modulation by vitamin C, selenite, or Trolox, a water-soluble vitamin E analog. BALB/c MK-2 mouse keratinocytes were exposed to a dose range of UVB from 4 to 750 mJ/cm2. DNA damage in the form of 80 HdG was measured using high-pressure liquid chromatography coupled with electrochemical and UV absorbance detection. Preincubation of the cells for 2 days with 0.4 or 0.8 microgram/ml ascorbic acid, 10 or 20 micrograms/ml Trolox, and 5 or 12.5 microM selenite resulted in a significant decrease in the number of 8-hydroxydeoxyguanosine adducts per 10(5) deoxyguanines induced by 500 mJ/cm2 UVB. The results indicate a potential role for antioxidant nutrients in protection against UVB damage to skin cells.
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PMID:Antioxidant nutrients protect against UVB-induced oxidative damage to DNA of mouse keratinocytes in culture. 861 44

Oxidative DNA damage is involved in diverse biological phenomena and consists of several kinds of lesions, mainly, strand breaks, base modifications, and DNA-protein crosslinking. However, little is known about the existence of a chemical relationship among them or the ratio by which these different types of lesions are produced. In the present study we investigated whether a relationship exists between DNA strand breakage and base modification. We selected cupric [Cu(II)] and ferric [Fe(III)] ions for this study because these transition metals are active catalysts of DNA damage in vivo. Supercoiled plasmid DNA pZ189 was treated with Cu(II) or Fe(III) in the presence of different reducing agents. We measured in each sample both the number of DNA single-strand breaks (SSB) by quantitative electrophoresis and the amount of a modified DNA base, 8-hydroxy-2'-deoxyguanosine (8-OHdG) by HPLC with simultaneous electrochemical (EC) and spectrophotometric detection. The number of DNA SSBs produced was linearly related to the number of 8-OHdG present. The regression of the number of SSBs as a function of the number of 8-OHdG is expressed by the equation [SSBs] = b x [8-OHdG], where b = 1.7, 2.0, 2.7, 1.7, and 9.4, for Cu(II) in the presence of H2O2, L-cysteine and L-ascorbate, and for Fe(III) in the presence of H2O2 and L-ascorbate, respectively. The linear correlation we observed between the production of SSB and 8-OHdG mediated by Fe(III) and by Cu(II) suggests that these products may arise via a common chemical mechanism and could allow an easier and more precise estimation of DNA breakage.
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PMID:Association between 8-hydroxy-2'-deoxyguanosine formation and DNA strand breaks mediated by copper and iron. 872 35

The DNA adduct 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been widely used as a biomarker for oxidative stress. Bulky DNA adducts, which are detectable by the 32P-postlabelling method, provide evidence for exposure to and metabolic activation of large, mainly apolar compounds, e.g. polycyclic aromatic hydrocarbons. We determined both types of adducts in placental tissues of 30 term pregnancies and related the adduct levels to the exposure to tobacco smoke and the plasma antioxidant status. Urine and plasma continine concentrations were used to select 10 nonsmokers, 9 nonsmokers exposed to environmental tobacco smoke (ETS) and 11 smoking women. Placental levels of 8-OHdG were 0.84 +/- 0.11, 0.90 +/- 0.21 and 0.83 +/- 0.20/10(5) deoxyguanosine bases (dG) for nonsmokers, nonsmokers exposed to ETS and smokers, respectively. The differences between the groups were not significant. Smoking women had significantly lower plasma vitamin C and beta-carotene concentrations than nonsmoking women or nonsmoking women exposed to environmental tobacco smoke. The 8-OHdG adduct level in placental DNA was inversely correlated with the plasma vitamin E concentration (r = -0.47, P < 0.05). There was no association between placental 8-OHdG adducts and vitamin A, C and beta-carotene in plasma. In total, 15 different adducts could be identified in the 30 placenta samples by the 32P-postlabelling method. There was a strong inter-individual variation in both the number of adducts and adduct intensities. No smoking-related or vitamin-related effects on adduct patterns or intensities were found. Our findings suggests that, within the limits of the methods used, tobacco smoke exposure during pregnancy does not lead to a measurable increase in placental DNA adduct levels and that vitamin E appears to have a protective effect on placental 8-OHdG formation.
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PMID:DNA adducts in human placenta in relation to tobacco smoke exposure and plasma antioxidant status. 911 79

The 'spontaneous' frequency of genetic damage (normal background) and the possible relationship of this damage to nutritional variables in humans were investigated in 22 subjects using several indices of genetic damage. The subjects were chosen, out of 122 initially analyzed, for being at the extremes of the highest and lowest values of one index of genetic damage, the frequency of micronucleated erythrocytes in peripheral blood. This index reflects chromosomal damage and loss in bone marrow erythropoietic cells. The assay for micronuclei is convenient but is restricted to splenectomized individuals because the human spleen removes micronucleated cells. The initial 122 subjects were splenectomized, but all were normal and healthy at the time of this study and none had a previous history of neoplastic disease. Factors investigated were stability of micronucleus frequency as a function of time, correlations among multiple markers of genetic damage, and influence on damage indices of nutritional variables, including blood levels of folate, B12 and antioxidant vitamins. Among different individuals, the range of values was 10-fold or more in the erythrocyte micronucleus, glycophorin A, plasma ascorbate and urinary 8-hydroxydeoxyguanosine (oxo8dG) assays, was approximately 6-fold in the lymphocyte micronucleus assay, and was 2-fold in the lymphocyte sister chromatid exchange (SCE) assay. Red blood cell folate and plasma folate, B12 and alpha-tocopherol values varied by up to 10-fold among individuals. Micronucleus frequencies in erythrocytes and peripheral blood lymphocytes ranged from < 0.3 to 16.9/1000 in mature red blood cells, < 1 to 33/1000 in reticulocytes, and 2.5 to 15/1000 in binucleate lymphocytes. Frequencies of glycophorin A variant erythrocytes ranged from 5.6 to 77.3 x 10(6) N/0 cells and 3.2 to 16.2 x 10(6) N/N cells, and oxo8dG excretion varied from 32 to 397 pmol/kg/day. Although a wide range of values was observed in each genetic endpoint, the extreme values for various endpoints of genetic damage were not observed in the same individuals. The frequency of micronucleated erythrocytes varied over time within individuals and indicated that individuals with the highest levels of damage exhibit greater variability than those with lower levels. In some subjects, frequencies of micronucleated erythrocytes changed dramatically over an interval of 2-3 years: four subjects with initial micronucleated reticulocyte frequencies of 20.4, 5.9, 6.4 and 33/1000 changed to 2.5, 20.5, 18.5 and 12/1000, respectively. Among more than 150 individuals we have studied, including the 64 individuals studied by Everson et al. [(1988) J. Natl. Cancer Inst., 80, 525-529] and Smith et al. [(1990) Cancer Res., 50, 5049-5054], the seven individuals with the highest observed frequencies of micronucleated erythrocytes all had exceptionally low values of plasma folate, red cell folate, or plasma B12, suggesting that folate and B12 status are the major determinants of the types of damage that lead to spontaneous micronucleus formation in erythrocytic cells.
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PMID:'Spontaneous' genetic damage in man: evaluation of interindividual variability, relationship among markers of damage, and influence of nutritional status. 921 87

To assess whether Helicobacter pylori-related inflammation increases oxidative DNA damage, we evaluated the association between H. pylori infection and urinary excretion of an adduct of oxidative DNA damage, 8-hydroxy-2-deoxyguanosine (8ohdG). Subjects included 555 healthy persons, ages 20-39, within the Kaiser Permanente Medical Care Program in Northern California. We tested sera for antibodies to H. pylori by ELISA; collected demographic, dietary, smoking, and alcohol data by questionnaire; and assayed 24-h urine samples for 8ohdG with a newly developed ELISA kit. Two hundred eighty-one subjects provided adequate 24-h urine samples for 8ohdG and creatinine assays and had detectable levels of 8ohdG. After adjusting for 24-h urinary creatinine (Ucr) and demographic factors, persons without H. pylori infection had significantly higher amounts of 24-h urinary 8ohdG than infected persons (geometric mean, 18.04 microg 8ohdG/Ucr g versus 14.36 microg 8ohdG/Ucr g, respectively; P = 0.008). Excretion of 8ohdG was higher in whites and Hispanics (17.44 and 18.09 microl/Ucr g) than in blacks (13.21 microg/Ucr g; P < 0.001). Gender was not significantly associated with 8ohdG excretion (16.18 microg/Ucr g for males versus 16.01 microg/Ucr g for females; P = 0.883). Of the dietary factors evaluated, vitamin C negatively correlated (P < 0.001) and carbohydrate intake positively correlated with 8ohdG excretion (P = 0.003). Infection with H. pylori was strongly associated with decreased 8ohdG excretion in the urine. This unexpected finding suggests either that DNA repair is deficient in infected subjects, that inflammation destroys the adduct, or that urinary 8ohdG is not an accurate measure of gastric damage.
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PMID:Helicobacter pylori infection and urinary excretion of 8-hydroxy-2-deoxyguanosine, an oxidative DNA adduct. 948 81

Studies of the interaction between oxidative stress and mitochondrial dysfunction are complicated by analytical limitations, especially the need to assess multiple parameters in relatively small samples. We have addressed this problem by developing a methodology for the simultaneous analysis of the majority of low-molecular-weight, redox-active compounds from mitochondria using HPLC separations followed by coulometric array detection. The method described should also be applicable for the study of redox-active compounds in other subcellular organelles as well as in intact cells and tissues. The protocol described enables simultaneous measurement of antioxidants (e.g., tocopherols, ascorbate, lipoates, uric acid, and glutathione), markers of oxidative stress (e.g., o-tyrosine, m-tyrosine, nitrotyrosine, dityrosine, glutathione disulfide, and 8-hydroxydeoxyguanosine) as well as other metabolites (e.g., purines and indoles). In all, ca. 600 redox active compounds can be detected, most with a limit of detection of approximately 5 pg on column. Results, including analytical parameters, from a study of liver mitochondria from control and diabetic rats are presented to demonstrate utility of this methodology.
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PMID:Simultaneous analysis of the majority of low-molecular-weight, redox-active compounds from mitochondria. 975 Jan 37

Environmental tobacco smoke (ETS) is a pervasive contaminant in the workplace. Previous studies by this laboratory have shown that exposure to workplace ETS results in increased oxidative stress and damage, as measured by increased levels of the antioxidant enzymes superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidase. 8-Hydroxy-2-deoxyguanosine, a marker of oxidative DNA damage, was also 63% greater in the exposed group compared with controls. Subjects in the previous study who reported workplace exposure to ETS were given a 60-day supply of an over-the-counter antioxidant formulation consisting of 3000 microg of beta-carotene, 60 mg of vitamin C, 30 I.U. of alpha-tocopherol, 40 mg of zinc, 40 microg of selenium, and 2 mg of copper. After the 60-day supplementation period, blood samples were again drawn, and the results were compared with the presupplementation values. A 62% decrease in 8-hydroxy-2-deoxyguanosine was observed after supplementation. Lipid peroxidation levels were also decreased, as were the antioxidant enzyme activities. The biochemical evidence suggests that exposure to ETS in the workplace increases oxidative stress and that antioxidant supplementation may provide some protection.
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PMID:Oxidative stress induced by environmental tobacco smoke in the workplace is mitigated by antioxidant supplementation. 982 5

Damage to DNA by oxygen radicals and other reactive oxygen/nitrogen/chlorine species occurs in vivo despite the presence of multiple antioxidant defence and repair systems. Such damage is thought to make a significant contribution to the age-related development of cancer. Modulation of oxidative DNA damage by diet thus constitutes a "biomarker" putatively predictive of the effect of diet on cancer incidence, provided that DNA damage can be accurately quantitated by validated methods. Current issues addressed in this article include the problems of artifactual DNA oxidation during isolation and analysis, the relative merits of different analytical methods, the advantages and disadvantages of relying on measurement of 8-hydroxydeoxyguanosine (8OHdG, 8-oxodG) as an index of oxidative DNA damage, and the limited data that are so far available on how diet can affect "steady-state" levels of oxidative DNA damage in humans. It appears that such damage can be modulated by vegetable intake, although the effects of vegetables may be mediated by components different from the "classical" antioxidants vitamin C, alpha-tocopherol and beta-carotene.
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PMID:Can oxidative DNA damage be used as a biomarker of cancer risk in humans? Problems, resolutions and preliminary results from nutritional supplementation studies. 1009 53


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