Gaseous nitric oxide-induced 8-nitroguanine formation in human lung fibroblast cells and cell-free DNA

A time- and dose-dependent increase in 8-nitroguanine (8-NO2-G) was observe d in human lung fibroblast cells (MRC-5) after treatment with gaseous NO-sa turated buffer. It was also found that treatment with the inhibitor of indu cible nitric oxide synthase (iNOS), N-G-nitro-L-arginine methyl ester, sign ificantly reduced the 8-NO2-G level in the gaseous NO-saturated buffer-trea ted MRC-5 cells. These results provide evidence indicating that NO gas caus es DNA damage in mammalian cells, which involves the activation of iNOS and the subsequent generation of endogenous NO. On the other hand, a time- and dose-dependent increase in 8-NO2-G was also observed while DNA (isolated f rom MRC-5 cells) was incubated with gaseous NO-saturated buffer. These resu lts suggest that part of the 8-NO2-G formation was due to direct modificati on of gaseous NO on DNA, Furthermore, an increase in nitrite concentration was found in both cell-free and MRC-5 cell-conditioned medium treated with gaseous NO-saturated buffer. Collectively, gaseous NO induced DNA damage by forming 8-NO2-G, a modification performed directly by the treated gaseous NO and indirectly by the following induction of endogenous NO. This effect might be an important pathway in genotoxicity of nitric oxides, and 8-NO2-G could act as a specific marker for DNA damage induced by gaseous NO, a com mon contaminatant in air pollution and cigarette smoke. (C) 2001 Academic P ress.