Mutagenicity of the mononitrobenzo[a]pyrenes in Chinese hamster ovary cells mediated by rat hepatocytes or liver S9.

Previous studies have shown that 1- and 3-nitrobenzo[a]pyrene (NBaP) were mutagenic in the Salmonella reversion assay without exogenous activation and that 1-, 3- and 6-NBaP were mutagenic in the presence of hepatocytes or liver homogenate (S9). In the present study, 1-, 3- and 6-NBaP were tested for mutagenicity in Chinese hamster ovary (CHO) cells under activation conditions similar to those used in the bacterial studies. None of the NBaPs was mutagenic without exogenous activation and none was mutagenically activated by hepatocytes from unpretreated rats or rats pretreated with Aroclor 1254 or 3-methylcholanthrene. Benzo-[a]pyrene (BaP), the parent compound, induced a strong mutagenic response under all hepatocyte mediation conditions. The NBaPs did produce positive mutagenic responses with S9 activation (3- = 1- greater than 6-NBaP), but these moderate responses were less than those of BaP. The difference between the bacterial and CHO results under the variety of activation conditions suggests the importance of the endogenous metabolism of the target cell as well as the source and the type of exogenous metabolic activation.