Induction of a sister-chromatid exchange by nitrogen oxides and its prevention by SOD

Observations were made on the increase in the frequency of sister-chromatid exchanges (SCEs) induced by a nitric oxide (NO) releaser (NOR4) and NaNO2 in Chinese hamster lung cells (CHL/IU). During these observations, NaNO3 did not have any effect on SCE induction. NOR4- and NaNO2- induced SCE frequencies decreased due to treatment with bovine serum (10%), bovine serum albumin (BSA, 0.1%, 1.0%), oxyhemoglobin (Hb, 10 microM), and superoxide dismutase (SOD, 250 U/ml), but not with glutathione (oxidized and reduced forms), cysteine, cystine and catalase. NO2- concentrations decreased with Hb, but not with any other agent, indicating that NO and/or NO2- have a strong binding reaction with Hb. The mechanism for a decrease in genotoxicity due to SOD is still unclear. However, it would appear that S-nitrosothiols in the cells can be stabilized by SOD in consideration of the S-nitrosothiols stabilizing effect of SOD reported by Kowaluk et al. (1990). In the presence of NO and superoxide anions, genotoxicity seemed to be decreased by catalase and SOD, since the former decreases the superoxide anion-induced SCE frequency, and the latter, the NO-induced frequency.