(1/1399) Exposure to indoor background radiation and urinary concentrations of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage.
We investigated whether exposure to indoor [gamma]-radiation and radon might be associated with enough free radical formation to increase urinary concentrations of 8-hydroxydeoxyguanosine (8-OHdG), a sensitive marker of DNA damage, due to a hydroxyl radical attack at the C8 of guanine. Indoor radon and [gamma]-radiation levels were measured in 32 dwellings for 6 months by solid-state nuclear track detectors and thermoluminescent dosimeters, respectively. Urine samples for 8-OHdG determinations were obtained from 63 healthy adult subjects living in the measured dwellings. An overall tendency toward increasing levels of 8-OHdG with increasing levels of radon and [gamma]-radiation was seen in the females, presumably due to their estimated longer occupancy in the dwellings measured. Different models were considered for females, with the steepest slopes obtained for [gamma]-radiation with a coefficient of 0.500 (log nmol/l of 8-OHdG for each unit increase of [gamma]-radiation on a log scale) (p<0.01), and increasing to 0.632 (p = 0.035), but with larger variance, when radon was included in the model. In conclusion, there seems to be an effect of indoor radioactivity on the urinary excretion of 8-OHdG for females, who are estimated to have a higher occupancy in the dwellings measured than for males, for whom occupational and other agents may also influence 8-OHdG excretion. ree radicals; [gamma]-radiation; radon. (+info)
(2/1399) RNA oxidation is a prominent feature of vulnerable neurons in Alzheimer's disease.
In this study we used an in situ approach to identify the oxidized nucleosides 8-hydroxydeoxyguanosine (8OHdG) and 8-hydroxyguanosine (8OHG), markers of oxidative damage to DNA and RNA, respectively, in cases of Alzheimer's disease (AD). The goal was to determine whether nuclear and mitochondrial DNA as well as RNA is damaged in AD. Immunoreactivity with monoclonal antibodies 1F7 or 15A3 recognizing both 8OHdG and 8OHG was prominent in the cytoplasm and to a lesser extent in the nucleolus and nuclear envelope in neurons within the hippocampus, subiculum, and entorhinal cortex as well as frontal, temporal, and occipital neocortex in cases of AD, whereas similar structures were immunolabeled only faintly in controls. Relative density measurement showed that there was a significant increase (p < 0.0001) in 8OHdG and 8OHG immunoreactivity with 1F7 in cases of AD (n = 22) as compared with senile (n = 13), presenile (n = 10), or young controls (n = 4). Surprisingly, the oxidized nucleoside was associated predominantly with RNA because immunoreaction was diminished greatly by preincubation in RNase but only slightly by DNase. This is the first evidence of increased RNA oxidation restricted to vulnerable neurons in AD. The subcellular localization of damaged RNA showing cytoplasmic predominance is consistent with the hypothesis that mitochondria may be a major source of reactive oxygen species that cause oxidative damage in AD. (+info)
(3/1399) In vitro reactions of butadiene monoxide with single- and double-stranded DNA: characterization and quantitation of several purine and pyrimidine adducts.
We have previously shown that butadiene monoxide (BM), the primary metabolite of 1,3-butadiene, reacted with nucleosides to form alkylation products that exhibited different rates of formation and different stabilities under in vitro physiological conditions. In the present study, BM was reacted with single-stranded (ss) and double-stranded (ds) calf thymus DNA and the alkylation products were characterized after enzymatic hydrolysis of the DNA. The primary products were regioisomeric N-7-guanine adducts. N-3-(2-hydroxy-3-buten-1-yl)adenine and N-3-(1-hydroxy-3-buten-2-yl)adenine, which were depurinated from the DNA more rapidly than the N-7-guanine adducts, were also formed. In addition, N6-(2-hydroxy-3-buten-1-yl)deoxyadenosine and N6-(1-hydroxy-3-buten-2-yl)deoxyadenosine were detected and evidence was obtained that these adducts were formed by Dimroth rearrangement of the corresponding N-1-deoxyadenosine adducts, not while in the DNA, but following the release of the N-1-alkylated nucleosides by enzymatic hydrolysis. N-3-(2-hydroxy-3-buten-1-yl)deoxyuridine adducts, which were apparently formed subsequent to deamination reactions of the corresponding deoxycytidine adducts, were also detected and were stable in the DNA. Adduct formation was linearly dependent upon BM concentration (10-1000 mM), with adduct ratios being similar at the various BM concentrations. At a high BM concentration (750 mM), the adducts were formed in a linear fashion for up to 8 h in both ssDNA and dsDNA. However, the rates of formation of the N-3-deoxyuridine and N6-deoxyadenosine adducts increased 10- to 20-fold in ssDNA versus dsDNA, whereas the N-7-guanine adducts increased only slightly, presumably due to differences in hydrogen bonding in ssDNA versus dsDNA. These results may contribute to a better understanding of the molecular mechanisms of mutagenesis and carcinogenesis of both BM and its parent compound, 1,3-butadiene. (+info)
(4/1399) Cytotoxic effect of paraquat on rat C6 glioma cells: evidence for the possibility of non-oxidative damage to the cells.
Although paraquat has been shown to cause oxidative damage to neuronal cells, little is known about its effect on glial cells. Thus the effect of paraquat on glial cells was examined using rat C6 glioma cells as a model system. Paraquat reduced cell viability in a concentration- and time-dependent manner, and this toxic effect was not significantly attenuated by various kinds of antioxidants. Furthermore, paraquat failed to increase 8-hydroxy-deoxyguanosine formation in the cells. These results indicate that paraquat can be toxic to glial cells and suggest that this cytotoxic effect may not be associated with the oxidative damage to the cells. (+info)
(5/1399) Age-associated increase in 8-oxo-deoxyguanosine glycosylase/AP lyase activity in rat mitochondria.
The mitochondrial theory of aging postulates that organisms age due to the accumulation of DNA damage and mutations in the multiple mitochondrial genomes, leading to mitochondrial dysfunction. Among the wide variety of DNA damage, 8-oxo-deoxyguanosine (8-oxo-dG) has received the most attention due to its mutagenicity and because of the possible correlation between its accumulation and pathological processes like cancer, degenerative diseases and aging. Although still controversial, many studies show that 8-oxo-dG accumulates with age in the mitochondrial (mt) DNA. However, little is known about the processing of this lesion and no study has yet examined whether mtDNA repair changes with age. Here, we report the first study on age-related changes in mtDNA repair, accomplished by assessing the cleavage activity of mitochondrial extracts towards an 8-oxo-dG-containing substrate. In this study, mitochondria obtained from rat heart and liver were used. We find that this enzymatic activity is higher in 12 and 23 month-old rats than in 6 month-old rats, in both liver and heart extracts. These mitochondrial extracts also cleave oligonucleotides containing a U:A mismatch, at the uracil position, reflecting the combined action of mitochondrial uracil DNA glycosylase (mtUDG) and mitochondrial apurinic/apyrimidinic (AP) endonucleases. The mtUDG activity did not change with age in liver mitochondria, but there was a small increase in activity from 6 to 23 months in rat heart extracts, after normalization to citrate synthase activity. Endonuclease G activity, measured by a plasmid relaxation assay, did not show any age-associated change in liver, but there was a significant decrease from 6 to 23 months in heart mitochondria. Our results suggest that the mitochondrial capacity to repair 8-oxo-dG, the main oxidative base damage suggested to accumulate with age in mtDNA, does not decrease, but rather increases with age. The specific increase in 8-oxo-dG endonuclease activity, rather than a general up-regulation of DNA repair in mitochondria, suggests an induction of the 8-oxo-dG-specific repair pathway with age. (+info)
(6/1399) Hyperglycemia causes oxidative stress in pancreatic beta-cells of GK rats, a model of type 2 diabetes.
Reactive oxygen species are involved in a diversity of biological phenomena such as inflammation, carcinogenesis, aging, and atherosclerosis. We and other investigators have shown that the level of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker for oxidative stress, is increased in either the urine or the mononuclear cells of the blood of type 2 diabetic patients. However, the association between type 2 diabetes and oxidative stress in the pancreatic beta-cells has not been previously described. We measured the levels of 8-OHdG and 4-hydroxy-2-nonenal (HNE)-modified proteins in the pancreatic beta-cells of GK rats, a model of nonobese type 2 diabetes. Quantitative immunohistochemical analyses with specific antibodies revealed higher levels of 8-OHdG and HNE-modified proteins in the pancreatic beta-cells of GK rats than in the control Wistar rats, with the levels increasing proportionally with age and fibrosis of the pancreatic islets. We further investigated whether the levels of 8-OHdG and HNE-modified proteins would be modified in the pancreatic beta-cells of GK rats fed with 30% sucrose solution or 50 ppm of voglibose (alpha-glucosidase inhibitor). In the GK rats, the levels of 8-OHdG and HNE-modified proteins, as well as islet fibrosis, were increased by sucrose treatment but reduced by voglibose treatment. These results indicate that the pancreatic beta-cells of GK rats are oxidatively stressed, and that chronic hyperglycemia might be responsible for the oxidative stress observed in the pancreatic beta-cells. (+info)
(7/1399) Glutathione and ascorbate are negatively correlated with oxidative DNA damage in human lymphocytes.
Intracellular antioxidants, glutathione and ascorbate, and two molecular markers of oxidative DNA damage, 5-hydroxy-2'-deoxycytidine (5-OH-dCyd) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo), were measured in lymphocytes from 105 healthy volunteers. The analysis of 5-OH-dCyd and 8-oxo-dGuo was carried out by HPLC with electrochemical detection such that both compounds were detected on the same chromatography run. There was no significant difference in oxidative DNA damage when the extraction of DNA from cells using phenol was carried out under anaerobic conditions or in the presence of metal ion chelators. This indicates that auto-oxidation of DNA during sample preparation was minimal. Using the above methods, the average level of oxidative DNA damage in lymphocytes was 2.9 +/- 1.4 for 5-OH-dCyd and 4.5 +/- 1.8 for 8-oxo-dGuo lesions per 10(6) dGuo (n = 105). It is unlikely that artifactual oxidation contributed to the observed damage because the level of 5-OH-dCyd was comparable with that of 8-oxo-dGuo in lymphocyte DNA, whereas 8-oxo-dGuo outnumbers 5-OH-dCyd by a ratio of >5:1 when DNA is exposed to various oxidants, including ionizing radiation or Fenton reagents. Rather, the nearly equal levels of 5-OH-dCyd and 8-oxo-dGuo in cellular DNA implies that 8-oxo-dGuo may be more efficiently removed by DNA repair. Finally, and most importantly, the correlation of our endpoints revealed that the naturally occurring level of intracellular antioxidants was negatively correlated to the level of oxidative DNA damage with the strongest correlation observed for glutathione and 8-oxo-dGuo (r = -0.36; P < 0.001). These results strongly suggest that intracellular glutathione and ascorbate protect human lymphocytes against oxidative DNA damage. (+info)
(8/1399) Mutagenic properties of the 8-amino-2'-deoxyguanosine DNA adduct in mammalian cells.
The DNA adduct 8-amino-2'-deoxyguanosine (8-amino-dG) is found in liver DNA of rats treated with the hepatocarcinogen 2-nitropropane. Site-specifically modified oligodeoxynucleotides were used to explore the mutagenic potential of 8-amino-dG in simian kidney (COS-7) cells. Oligodeoxynucleotides (5'-TCCTCCTX1G2CCTCTC and 5'-TCCTCCTG1X2CCTCTC, X = dG or 8-amino-dG) with the lesion positioned at codon 60 or 61 of the non-coding strand of the human c-Ha- ras1 gene were inserted into single-stranded phagemid vectors and transfected into COS-7 cells. The progeny plasmid obtained was used to transform Escherichia coli DH10B. Transformants were analyzed by oligodeoxynucleotide hybridization and DNA sequencing to establish the mutation frequency and spectrum produced by the modified base. The correct base, dCMP, was incorporated preferentially opposite 8-amino-dG at X1and X2. When 8-amino-dG was at X1, targeted GNH2-->T transversions were detected, along with smaller numbers of GNH2-->A transitions and GNH2-->C transversions. When the adduct was at X2, only GNH2-->T transversions were observed. The frequencies of targeted mutation at X1and X2were 2.7 and 1.7%, respectively. Mutation frequency and mutagenic spectrum were sequence context dependent. In addition, non-targeted G-->T transversions, accompanied by some G-->A transitions, were detected 5' to 8-amino-dG when the lesion was at X2. We conclude that 8-amino-dG is a mutagenic lesion, generating G-->T and G-->C transversions and G-->A transitions in mammalian cells. (+info)