Single-strand DNA breaks in rodent and human cells produced by superoxide anion or its reduction products

Chinese hamster ovary cells and human P3 teratocarcinoma cells were exposed to superoxide anion (O₂⁻) generated by the addition of potassium superoxide (KO₂). DNA from the cells was examined by alkaline elution techniques for the production of single-strand breaks, as well as for the production of double-strand breaks and DNA-protein cross-links. It was demonstrated that KO₂ produced only single-strand breaks in DNA in both cell lines, in a dose-dependent manner. The number of breaks was reduced by the prior addition of a metal chelator, indicating that some of the breaks may have been caused by the metal-catalyzed (Fenton reaction) reduction products, hydrogen peroxide or hydroxyl radical. Catalase almost completely inhibited break induction by O₂⁻, evidence for a role of hydrogen peroxide. The results of this study indicate that O₂⁻ and its reduction products can damage intracellular mammalian DNA.