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
Advances in Molecular Toxicology 01/2006; 1:1-23. DOI:10.1016/S1872-0854(06)01001-0