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 wide spectrum detection of precarcinogens in short-term bioassays, hepatic levels of cytochrome P-450 (CYP) and mutagenic activation of various carcinogens in Wistar and Sprague-Dawley rats orally treated with BI and BI plus ethanol or acetone were compared with those in the same strains of rats treated with 3-methylcholanthrene (MC), phenobarbital (PB) and polychlorobiphenyls (PCB). Immunoblot analyses for microsomal CYP proteins revealed a marked induction by BI in the levels of CYP1A1, CYP2B1 and constitutive CYP1A2 (approximately 11-fold), 2B2 (approximately 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 ethanol specifically induced CYP2E1 (4-fold) and 2B1 (1.7-fold) levels when compared with BI alone in Wistar rats. The combined treatments also elevated mutagenic activities of eight heterocyclic amines (HCAs), aflatoxin B(1) (AFB(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 five N-nitrosamines in strain TA100 up to 19.1-fold. Induction of specific CYP species responsible for activation of HCAs, AFB(1) and N-nitrosamines was confirmed by application of several CYP inhibitors. In addition, BI induced activities of both MC- and PB-inducible UDP-glucuronyltransferases towards 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 inducer for metabolic enzymes in in vitro bioassays, the potential being comparable with or superior to other typical ones.
Mori
Y
Y
Laboratory of Radiochemistry, Gifu Pharmaceutical University, 6-1 Mitahora-higashi 5-chome, Gifu 502-8585, Japan. ymori@gifu-pu.ac.jp
Koide
A
A
Fuwa
K
K
Kobayashi
Y
Y
D000284:Administration, Oral; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects; D007093:Imidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D007527:Isoenzymes / Q000096:biosynthesis; D008110:Liver Extracts / Q000737:chemistry* / Q000302:isolation & purification; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009152:Mutagenicity Tests / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar
D007093:Imidazoles; D007527:Isoenzymes; D008110:Liver Extracts; C017062:1-benzylimidazole; D003577:Cytochrome P-450 Enzyme System