Oxidative DNA damage after acute exposure to arsenite and monomethylarsonous acid in biomethylation-deficient human cells

Abstract

The carcinogen inorganic arsenic (iAs) undergoes biomethylation (BMT) in some cells. The methylated metabolite, monomethylarsonous (MMA³⁺), may cause oxidative DNA damage (ODD). With chronic iAs exposure, BMT-competent cells show ODD while BMT-deficient do not. To further define these events, we studied ODD produced by acute iAs or MMA³⁺ in the BMT-deficient human prostate cell line, RWPE-1. ODD, measured by the immuno-spin trapping method, was assessed after exposure to iAs or MMA³⁺ alone, with the arsenic BMT inhibitor selenite or after glutathione (GSH) depletion. The expression of oxidative stress-related genes (HO-1, SOD-1, SOD-2, Nrf2 and Keap-1) was also assessed. Exposure to iAs at 24 h (0–20 µM), stimulated ODD only at levels above the LC₅₀ of a 48 h exposure (17 µM). If iAs induced ODD, it also activated oxidative stress-related genes. Selenium did not alter iAs-induced ODD. MMA³⁺ at 24 h (0–0.5 µM) caused ODD at levels below the LC₅₀ of a 48 h exposure (1.5 µM), which were greatly increased by GSH depletion but not selenite. MMA³⁺ induced ODD at levels not activating oxidant stress response genes. Overall, iAs induced ODD in BMT-deficient cells only at toxic levels. MMA³⁺ caused ODD at non-toxic levels, independently of cellular BMT capacity and in a fashion not requiring further BMT.

• Arsenic
• immuno-spin trapping
• reactive oxygen species

Acknowledgements

The authors thank Drs Nigel Walker, John Bucher, Chris McPherson and Mathilde Triquigneaux for critical review of this manuscript. The authors also thank Matthew W. Bell for aid with the graphics.