Oxidative DNA damage induced by equine estrogen metabolites: role of estrogen receptor alpha.
ABSTRACT Excessive exposure to synthetic and endogenous estrogens has been associated with the development of cancer in several tissues. 4-Hydroxyequilenin (4-OHEN), a major metabolite of equine estrogens present in estrogen replacement formulations, has been shown to induce cytotoxic/carcinogenic effects. In the present study, we have found that 4-OHEN caused DNA damage in breast cancer cells, and cells that contain estrogen receptor alpha (S30) are more sensitive to 4-OHEN-mediated DNA damage as compared to estrogen receptor negative cells (MDA-MB-231). For example, concentration-dependent increases in 8-oxo-deoxyguanosine (8-oxo-dG), as measured by LC-MS-MS or by the Fpg comet assay, were only detected in the S30 cells, and the amount of this lesion could be enhanced by agents, which catalyze redox cycling (NADH) or deplete GSH (diethyl maleate). The role of the estrogen receptor in modulating DNA damage was further established in incubations with the ER antagonist tamoxifen, where decreases in 8-oxo-deoxyguanosine were observed. Another equine estrogen metabolite, 4,17 beta-hydroxyequilenin (4,17 beta-OHEN), was found to have the same cytotoxicity and a similar ability to induce reactive oxygen species (ROS), and caused the same oxidative DNA damage in S30 cells as compared to 4-OHEN. However, 4,17 beta-OHEN induced twice as much single strand DNA breaks in S30 cells compared to 4-OHEN. Also 4,17 beta-OHEN was more estrogenic than 4-OHEN as demonstrated by a higher binding affinity for ER alpha and an enhanced induction in activity of estrogen-dependent alkaline phosphatase in Ishikawa cells. These data suggest that the mechanism of DNA damage induced by equine estrogen metabolites could involve oxidative stress and that the estrogen receptor may play a role in this process.
- SourceAvailable from: Samah R. Khalil[Show abstract] [Hide abstract]
ABSTRACT: The genotoxic parameters are currently among the most valuable fish biomarkers for environmental risk assessment. So, the present study was directed to explore the toxic impacts of Aluminum chloride (AlCl 3) on DNA damage, apoptosis, antioxidant status and ultrastructural investigations of Nile catfish. The experiment was carried out on 48 fish that randomly divided into four equal groups with two replicates; the first group exposed to 1/20 LC 50 of AlCl 3 , the second group exposed to the combined doses of AlCl 3 (1/20 LC 50) and vitamin C (Vit. C) at dose of 5 ppm, the third group exposed to Vit C at the dose previously mentioned and the fourth group was kept as negative control. The experiment was terminated after six months where the fish were sacrificed and specimens from liver and gills of all groups were obtained and kept at -20°C till applying the required measurements and another specimen from the same organs were fixed in 10% neutral –buffered formalin and 3% glutaraldehyde solution for histopathological examination. The results indicated pronounced significant increase in malondialdehyde (MDA) concentration and significant decrease in both reduced glutathione (GSH) concentration and superoxide dismutase (SOD) and catalase (CAT) enzyme activity. AlCl 3 elicited an obvious increase in oxidative DNA damage and frequency of apoptotic cells, these manifestation were markedly ameliorated in the group exposed to the combined doses of AlCl 3 and Vit C. The ultrastructural histopathological findings proved the aforementioned results. It could be concluded that AlCl 3 elucidated a marked ruinous effects on the oxidative and genotoxic impacts as well as the histopathological alterations which were alleviated by Vitamin C.Life Science Journal 11/2012; 9. · 0.17 Impact Factor
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ABSTRACT: Peroxynitrite formed by the reaction of superoxide and nitric oxide is a highly reactive species with a role in various pathological processes such as cancer, chronic inflammation, and cardiovascular and neurological diseases. In the present study, the effect of the carotenoids, lycopene and beta-carotene, on peroxynitrite-mediated modifications in plasmid DNA as well as cellular DNA and proteins were investigated. In pUC18 plasmid DNA, these carotenoids strongly inhibited DNA strand breaks caused by peroxynitrite generated from 3-morpholinosydnonimine (SIN-1). SIN-1 was also used to determine effects on DNA damage and protein tyrosine nitration in Chinese hamster lung fibroblasts. SIN-1 dose-dependently increased nitration of proteins in cells above basal levels as determined by Western blotting. This nitration was inhibited in the presence of the uric acid as well as lycopene. Physiological concentrations (0.31-10 microM) of lycopene and beta-carotene also had protective effects on DNA damage, as measured by the comet assay. Lycopene significantly reduced DNA damage particularly, in the median range of concentrations (2.5 microM). The protective effects of lycopene and beta-carotene could be due to their scavenging of reactive oxygen (ROS) and/or nitrogen species (RNS) as they reduce the amount of intracellular ROS/RNS produced following treatment with SIN-1 by as much as 47.5% and 42.4%, respectively. The results obtained in this study suggest that carotenoids may alleviate some of the deleterious effects of peroxynitrite and possibly other reactive nitrogen species as well in vivo.Toxicology and Applied Pharmacology 10/2006; 215(3):330-40. DOI:10.1016/j.taap.2006.03.006 · 3.63 Impact Factor
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ABSTRACT: Glutathione S-transferases (GSTs) are a family of detoxification isozymes that protect cells by conjugating GSH to a variety of toxic compounds, and they may also play a role in the regulation of both cellular proliferation and apoptosis. We have previously shown that human GST P1-1, which is the most widely distributed extrahepatic isozyme, could be inactivated by the catechol estrogen metabolite 4-hydroxyequilenin (4-OHEN) in vitro [Chang, M., Shin, Y. G., van Breemen, R. B., Blond, S. Y., and Bolton, J. L. (2001) Biochemistry 40, 4811-4820]. In the present study, we found that 4-OHEN and another catechol estrogen, 4,17beta-hydroxyequilenin (4,17beta-OHEN), significantly decreased GSH levels and the activity of GST within minutes in both estrogen receptor (ER) negative (MDA-MB-231) and ER positive (S30) human breast cancer cells. In addition, 4-OHEN caused significant decreases in GST activity in nontransformed human breast epithelial cells (MCF-10A) but not in the human hepatoma HepG2 cells, which lack GST P1-1. We also showed that GSH partially protected the inactivation of GST P1-1 by 4-OHEN in vitro, and depletion of cellular GSH enhanced the 4-OHEN-induced inhibition of GST activity. In addition, 4-OHEN GSH conjugates contributed about 27% of the inactivation of GST P1-1 by 4-OEHN in vitro. Our in vitro kinetic inhibition experiments with 4-OHEN showed that GST P1-1 had a lower K(i) value (20.8 microM) compared to glyceraldehyde-3-phosphate dehydrogenase (GAPDH, 52.4 microM), P450 reductase (PR, 77.4 microM), pyruvate kinase (PK, 159 microM), glutathione reductase (GR, 230 microM), superoxide dismutase (SOD, 448 microM), catalase (562 microM), GST M1-1 (620 microM), thioredoxin reductase (TR, 694 microM), and glutathione peroxidase (GPX, 1410 microM). In contrast to the significant inhibition of total GST activity in these human breast cancer cells, 4-OHEN only slightly inhibited the cellular GAPDH activity, and other cellular enzymes including PR, PK, GR, SOD, catalase, TR, and GPX were resistant to 4-OHEN-induced inhibition. These data suggest that GST P1-1 may be a preferred protein target for equine catechol estrogens in vivo.Chemical Research in Toxicology 08/2002; 15(7):935-42. DOI:10.1021/tx020018i · 4.19 Impact Factor