Genetic damage in CHO cells exposed to enzymically generated active oxygen species

The genetic toxicity of active oxygen species produced during the enzymic oxidation of xanthine has been investigated using Chinese hamster ovary (CHO) cells. Incubation of cells with xanthine plus xanthine oxidase resulted in extensive chromosome breakage and sister-chromatid exchange and gave a small increase in frequency of thioguanine-resistant cells (HGPRT test). Inclusion of superoxide dismutase or catalase in the xanthine/xanthine oxidase system inhibited chromosome breakage, whereas only catalase prevented SCE and mutant induction. It is concluded that hydrogen peroxide is responsible for most of the genetic effects observed in CHO cells exposed to xanthine/xanthine oxidase but that superoxide plays a key role in chromosome breakage.