INVOLVEMENT OF P450 1A1 IN BENZO(A)PYRENE BUT NOT IN BENZO(A)PYRENE-7,8-DIHYDRODIOL ACTIVATION BY 3-METHYLCHOLANTHRENE-INDUCED MOUSE-LIVER MICROSOMES

Synchronous fluorescence spetrophotometry for benzo(a)pyrene-7,8-diol- 9,10-epoxide (BPDE)-DNA adducts was used to study the activation pathw ay of benzo(a)pyrene in C57BL/6 mice. Benzo(a)pyrene but not benzo(a)p yrene-7, 8-diol activation by 3-methylcholanthrene-induced mouse liver microsomes was inhibited by a monoclonal antibody (Mab 1-7-1) against CYP1A1/2 suggesting that 1A1 probably takes part in the first P450 re action. However, aryl hydrocarbon hydroxylase activity, a classical me asure of benzo(a)pyrene metabolism, was not inhibited by the same conc entration of Mab 1-7-1. None of the other antibodies used, detecting 2 A, 2B, 2C or 2E subfamilies, inhibited the adduct formation. Troleando mycin and gestodene, chemical inhibitors of human 3A4, inhibited benzo (a)pyrene-7,8-diol activation by 3-methylcholanthrene-induced microsom es to some extent only in high concentrations. Although liver microsom es from 3-methylcholanthrene-induced mice catalyzed the formation of B PDE-DNA in vitro clearly more than uninduced microsomes, 3-methylchola nthrene pretreatment in vivo decreased the adduct formation in benzo(a )pyrene-treated mice. These results emphasize the significance of deto xicating and DNA-repairing pathways in vivo. Finally, synchronous fluo rescence spectrophotometry for BPDE-DNA measures the end-point of the three-step activation pathway while aryl hydrocarbon hydroxylase measu res a one-step hydroxylation. Thus, these methods should be used rathe r as corroborative than mutually exclusive assays.