Induction of 6-thioguanine-resistant mutants by hyperoxia and γ-irradiation: effect of compromising cellular antioxidant systems

Abstract

Hyperoxia and γ-irradiation were found to be mutagenic in a transformed Syrian hamster cell line in a dose-dependent manner. The frequency of resistance to 6-thioguanine increased from 10 per 10 6 survivors after 48 h of growth in 70% O 2 to 32.6 (highly significant) after 75 h. Increasing the oxygen tension to 95% resulted in a significant mutagenic response in only 44 h. At equitoxic doses, γ-irradiation was 4 times more mutagenic than 70% O 2. After growth in hyperoxia, the cells showed an enhancement of catalase activity, glutathione peroxidase activity and glutathione levels but there was little effect on superoxide dismutase activity. Diethyldithiocarbamate (3 mM, 1.5 h) was mutagenic in normoxia and potentiated the mutagenic activity of both γ-irradiation and hyperoxia. Cells thus treated showed an 85% reduction in superoxide dismutase activity. When diethyldithiocarbamate was used in conjunction with a direct-acting alkylating agent, the mutagenic response was only additive. Depletion of cellular glutathione with buthionine sulfoximine (0.2 mM) or inhibition of catalase activity with aminotriazole (100 mM) was also effective in potentiating the mutagenic response of γ-irradiation and hyperoxia. The data demonstrates that endogenously produced activated oxygen species are mutagenic to hamster cells in culture and suggest that aerobic organisms are subject to an unavoidable background risk due to living in an oxygen atmosphore.