Characterization of DNA adducts in Chinese hamster ovary cells treated with mutagenic doses of 1- and 3-nitrosobenzo[a]pyrene and the trans-7,8-diol-anti-9,10-epoxides of 1- and 3-nitrobenzo[a]pyrene

Abstract The environmental contaminants 1- and 3-nitrobenzo[ a ]pyrene (1- and 3-nitro-BaP) are mutagens in Chinese hamster ovary (CHO) cells with exogenous metabolic activation. Previous studies demonstrated the potent direct-acting mutagenicity of the oxidized metabolites, trans -7,8-dihydroxy- anti -9,10-epoxy-7,8,9,10-tetrahydro-1-nitrobenzo[ a ]pyrene (1-NBaPDE) and trans -7,8-dihydroxy- anti -9,10-epoxy-7,8,9,10-tetrahydro-3-nitrobenzo[ a ]pyrene (3-NBaPDE), and the partially nitroreduced metabolites, 1- and 3-nitrosobenzo[ a ]pyrene (1- and 3-NO-BaP). In this study, we have identified the major adduct formed by incubation of calf thymus DNA with 1-NBaPDE and used this standard in conjunction with other adduct standards to characterize the 32 P-postlabeled DNA adducts produced by 1- and 3-nitro-BaP metabolites in CHO cultures. The major adduct from 1-NBaPDE exposure was 10-(deoxyguanosin- N 2 -yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-1-nitrobenzo[ a ]pyrene; from 3-NBaPDE, 10-(deoxyguanosin- N 2 -yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-3-nitrobenzo[ a ]pyrene; from 1-NO-BaP, 6-(deoxyguanosin- N 2 -yl)-1-aminobenzo[ a ]pyrene; and from 3-NO-BaP, 6-(deoxyguanosin- N 2 -yl)-3-aminobenzo[ a ]pyrene. For comparison, the adducts formed by trans -7,8-dihydroxy- anti -9,10-epoxy-7,8,9,10-tetrahydrobenzo[ a ]pyrene and the related nitroreduced derivative 6-nitrosobenzo[ a ]pyrene were also examined. The nitrobenzo[ a ]pyrene DNA adducts described in this study are proposed to be involved in the mutagenicity of 1- and 3-nitro-BaP upon either oxidative or reductive metabolism.