Structural Requirements for the Induction of Hepatic Microsomal Cytochrome P450 by Imidazole- and Pyridine-Containing Compounds in Rats

We investigated the structural requirements for the induction of hepatic microsomal cytochrome P450 2B1/2 (P450 2B1/2) and cytochrome P450 1A1/2 (P450 1A1/2) by imidazole- and pyridine-containing compounds in rats. Clotrimazole, an azole antifungal drug, and 1-diphenylmethylimidazole preferentially induced P450 2B1/2 in a dose-dependent manner, and slightly induced P450 1A1/2.1-Benzylimidazole preferentially induced P450 1A1/2. 1-Phenylimidazole, which lacks the methylene bridge of 1-benzylimidazole, only induced P450 1A1/2. In turn, loss of aromaticity of the N-substituted moiety of imidazole, as in 1-cyclohexylmethylimidazole and 1-tert-butylimidazole, resulted in a preferential induction of P450 2B1/2. Likewise, various pyridine-containing compounds showed structure-dependent induction of P450 species. Namely, 4-diphenylmethylpyridine induced P450 2B1/2.4-Benzylpyridine induced both P450 2B1/2 and P4501A1/2. 4-Cyclohexylmethylpyridine and 4-tert-butylpyridine predominantly induced P450 2B1/ 2. 4-Phenylpyridine preferentially induced P450 1A1/2 rather than P450 2B1/2. Oxygenation products at the methylene bridge, 4-benzoylpyridine and phenyl-4-pyridylmethanol, could not induce P450 1A1/2. In turn, 2, 4-dipyridyl induced both P450 2B1/2 and P450 1A1/2, but not 2, 2'-dipyridyl. 4, 4'-Trimethylenedipyridine preferentially induced P450 1A1/2 at very low doses. These findings indicate that imidazole- and pyridine-containing compounds having lipophilic groups are inducers of hepatic P450, and that such compounds having aromatic groups and taking coplanar conformational structures are potent inducers of P450 1A1/2.