Calcium chelator Quin 2 prevents hydrogen‐peroxide‐induced DNA breakage and cytotoxicity

Abstract

Exposure of cultured Chinese hamster ovary (CHO) cells to hydrogen peroxide results in the production of extensive DNA breakage which can be prevented by the intracellular calcium chelator Quin 2. This effect occurs at Quin 2 AM concentrations as low as 0.1 μM and is maximal at 1 μM. Addition of the extracellular calcium chelator, EGTA, does not affect the level of DNA breakage generated by H₂O₂. Quin 2 also significantly reduces cellular toxicity caused by the oxidant. Experiments with spin-trapping techniques demonstrate that Quin 2 does not affect the formation of hydroxyl radicals generated by the action of Fe²⁺ on H₂O₂. Quin 2 at high concentrations, similar to those reached within the cell, actually enhanced generation of hydroxyl radical in the absence of other iron chelators under our experimental conditions. These results suggest that H₂O₂ or H₂O₂-derived radicals do not directly induce DNA strand breakage in intact mammalian cells; rather, these radicals may disturb intracellular Ca²⁺ homeostasis which results in secondary reactions ultimately leading to DNA strand breakage. In addition to strand breakage, membrane and protein oxidation probably contribute to the cytotoxic effect of H₂O₂.