Structural and mechanistic aspects of transcriptional induction of cytochrome P450 1A1 by benzimidazole derivatives in rat hepatoma H4IIE cells

The effect of several structurally different benzimidazole compounds on CYP 1A1 expression at the transcriptional, mRNA and protein levels was investig ated in the rat hepatoma H4IIE cell line. Omeprazole, thiabendazole, carben dazim, 2-mercaptobenzimidazole and 2-mercapto-5-methoxybenzimidazole caused a dose-dependent increase in CYP1A1 protein levels that reached maximum ef fect at 250 mu M as measured by Western blot. In addition, hydroxyomeprazol e, 2-aminobenzimidazole and 2-mercapto-5-nitro-benzimidazole caused a notab le increase in CYP1A1 protein expression, whereas 5-O-desmethylomeprazole, 2-hydroxybenzimidazole, 2-benzimidazole propionic acid and 5-benzimidazole carboxylic acid were ineffective. Thus, benzimidazole substituted with a th iol or an amino group in the 2-position were active inducers. Northern blot analysis confirmed an extensive increase of CYP1A1 mRNA induced by omepraz ole and 2-mercapto-5-methoxybenzimidazole which was 32% and 49% of maximal induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) respectively, where as thiabendazole and carbendazim showed approximate to 15% increase as comp ared to TCDD. Transient transfection of H4IIE cells, with a XRE-pGL3 report er gene construct revealed a 2.3-4.3-fold induction by carbendazim, thiaben dazole, and 2-mercapto-5-methoxybenzimidazole as compared to a 3.3- and 23- fold induction by omeprazole and TCDD, respectively. Thus, these data indic ate that the benzimidazoles utilize the aryl hydrocarbon receptor-arnt-XRE- mediated signal-transduction pathway for induction of the CYP1A1 gene.