Toxicity, single-strand breaks, and 5-hydroxymethyl-2'-deoxyuridine formation in human breast epithelial cells treated with hydrogen peroxide.

DNA damage induced by oxidants includes formation of DNA strand breaks as well as oxidative damage to DNA bases. We quantified both forms of DNA damage concurrently in two model human breast epithelial cell lines treated with hydrogen peroxide to compare the dose-dependent induction of each form of DNA damage with growth inhibition. Antioxidant defenses also were quantified. MCF-7 breast cancer cells had relatively higher levels of non-protein thiols, oxidized glutathione (GSSG) reductase, catalase, and superoxide dismutase than did the MCF-10A line of immortalized, but not transformed, human breast epithelial cells. The levels of antioxidant defenses were not predictive of endogenous oxidative DNA damage levels nor of toxicity and DNA damage induced by hydrogen peroxide. The endogenous levels of 5-hydroxymethyl-2'-deoxyuridine were higher in MCF-7 than MCF-10A cells. The cells were treated with 10-200 microM hydrogen peroxide for 15 min at 37 degrees C in complete media. Low concentrations of hydrogen peroxide were growth stimulatory to both cell lines. At higher concentrations, growth inhibition by hydrogen peroxide was greater in MCF-7 than in MCF-10A cells. Accordingly, induction of both single-strand DNA breaks and 5-hydroxymethyl-2'-deoxyuridine in DNA was greater in MCF-7 than MCF-10A cells. In both cell lines, the dose-dependent induction of single-strand breaks paralleled growth inhibition more closely than did formation of 5-hydroxymethyl-2'-deoxyuridine.