N-Benzylimidazole for preparation of S9 fraction with multi-induction of metabolizing enzymes in short-term genotoxicity assays

To evaluate the usefulness of N-benzylimidazole (BI) as an inducer with wid e spectrum detection of precarcinogens in short-term bioassays, hepatic lev els of cytochrome P-450 (CYP) and mutagenic activation of various carcinoge ns in Wistar and Sprague-Dawley rats orally treated with BI and BI plus eth anol or acetone were compared with those in the same strains of rats treate d with 3-methylcholanthrene (MC), phenobarbital (PB) and polychlorobiphenyl s (PCB). Immunoblot analyses for microsomal CYP proteins revealed a marked induction by BI in the levels of CYP1A1, CYP2B1 and constitutive CYP1A2 (si milar to 11-fold), 2B2 (similar to 21-fold), 2E1 (1.5-fold) and 3A2 (4-fold ) in rats of both strains. These levels were comparable with those induced by MC and PB, but were less than the CYP1A1/2 and 2B1 levels induced by PCB , while CYP2B2 was at the same level. In contrast, the level of CYP2E1 was clearly higher in BI-treated rats. The combinations of BI and acetone or et hanol specifically induced CYP2E1 (4-fold) and 2B1 (1.7-fold) levels when c ompared with BI alone in Wistar rats. The combined treatments also elevated mutagenic activities of eight heterocyclic amines (HCAs), aflatoxin B-1 (A FB(1)), benzo[a]pyrene and 2-aminofluorene in strain TA98 up to 14.3-, 5.1- , 2.8- and 2.1-fold above the untreated group, respectively, and those of f ive N-nitrosamines in strain TA100 up to 19.1-fold. Induction of specific C YP species responsible for activation of HCAs, AFB(1) and N-nitrosamines wa s confirmed by application of several CYP inhibitors. In addition, BI induc ed activities of both MC- and PB-inducible UDP-glucuronyltransferases towar ds 4-nitrophenol and testosterone. These results demonstrate that BI has a bifunctional action, with wide spectrum induction of phase I and II enzymes , and combined treatment with ethanol or acetone would be a pertinent induc er for metabolic enzymes in in vitro bioassays, the potential being compara ble with or superior to other typical ones.