Induction of DNA strand breaks, DNA-protein crosslinks and sister chromatid exchanges by arsenite in a human lung cell line

Based on in vitro studies, several modes of action for arsenic have been suggested, although the mechanisms responsible for arsenic carcinogenesis have not been well established. In our previous study a dose-dependent increment in DNA migration was detected at low doses of sodium arsenite, but at higher dose levels a reduction in the migration was observed, suggesting the induction of DNA adducts. In order to confirm this hypothesis we performed the experiments considering other parameters and modifications of the standard alkaline comet assay. Additionally, the induction of sister chromatid exchanges was evaluated. The present study showed the induction by sodium arsenite of single strand breaks and DNA-protein adducts assessed by comet assay as well as of sister chromatid exchanges in the human lung fibroblast cell line MRC-5. The standard alkaline comet assay also revealed, at the highest arsenic concentration tested, a reduction in all the considered parameters in relation to untreated cells and the other doses. On the other hand, the incubation with proteinase K induced a dose-dependent increment in DNA migration as a consequence of the release of proteins joined to the DNA. Thus, sodium arsenite was able to induce both DNA-strand breaks and protein-DNA adducts in arsenic exposed MRC-5 cells, depending on the concentrations of arsenic salts tested.