Effect of hydrogen peroxide on nitric oxide (NO)-induced mutagenicity in Salmonella typhimurium

Nitric oxide (NO) has been reported to impart, alone or in combination with reactive oxygen species (ROS), the cytotoxicity and putative genotoxicity associated with the immunological response. The present study examined the change in the mutagenic activity profile of the NO-donor spermine NONOate ( SperNO) as a result of introduction of hydrogen peroxide (H2O2) to the Ames assay. The aim was to determine whether the assay could detect H2O2-induce d co- or anti-mutagenic effects on NO-induced mutagenesis, and the Salmonel la typhimurium base-pair substitution tester strain TA1535 provided an appr opriate tool. While TA1535 was shown by the authors and others to be strong ly sensitive to NO-induced mutagenesis, it has also been shown to be insens itive to H2O2-induced mutagenicity [1,2]. When H2O2 (0.25-4.0 mu mol/pl) wa s added directly to cells treated with SperNO (0.01-1.0 mu mol/pl), comutag enicity was not detected, but a drop in reversion count and detectable toxi city was observed, especially at doses > 0.1 mu mol/pl. When glucose/glucos e oxidase (GOX) or reduced glutathione (GSH) were used as H2O2-generation s ystems the results varied. Reversion induced by SperNO (1 mu mol/pl) was mo derately enhanced by GOX (10-20 mUnits/pl), but the increase albeit reprodu cible did not reach a doubling (comutagenicity). GOX (40 mu mol/pl) induced a reduction in reversion count, but no visible toxicity. On the other hand , GSH (20- 80 mu mol/pl) gave a strong co-mutagenic effect. Co-mutagenicity was highest (> 5x) at 80 mu mol/pl GSH and 0.1 mu mol/ pl SperNO. Based on these findings, it could be concluded that a) H2O2, when steadily generate d in the cell, has a modulatory effect on NO-mutagenicity, and such a concl usion is not inconsistent with the wide range of responses reported for the two chemicals, and/or b) the observed co-mutagenic effects of GSH may not be attributable solely to H2O2 generation. Teratogenesis Carcinog. Mutagen. 21:349-359, 2001. (C) 2001 Wiley-Liss, Inc.