Isozyme-specific induction of cytochrome P450 in rat hepatocyte cultures
The aim of this study was to investigate the induction of CYP1A by DMSO, to determine whether DMSO induced other P450 isozymes (CYP2B) and to compare the effects of DMSO and another differentiating agent, sodium butyrate. Induction of CYP1A-dependent ethoxyresorufin-O-deethylase (EROD) was observed in the presence of increasing concentrations of DMSO. All concentration investigated (1%, 1.5% and 2%) caused induction (2-3 fold), and enhanced BA-induction of EROD. Enhancement of BA-induction was greater with 1% and 1.5% DMSO (2.5-3 fold over BA alone) than with 2% (1.8-fold). DMSO alone did not increase CYP1A1 RNA levels. Hepatocytes treated with BA and DMSO together exhibited a 1.3-fold greater increase in RNA levels than with BA alone. Western blotting indicated that CYP1A1 protein was increased by inducers (BA, DMSO and isosafrole), but that CYP1A2 was not. This indicates that the CYP1A1 isozyme is responsible for EROD activity in these cultures, and that the CYP1A2-induction mechanism is lost in rat hepatocytes cultured under the conditions of these experiments. This observation was confirmed by the lack of CYP1A2-dependent phenacetin-O-deethylase (POD) activity in culture. The substituted benzimidazole omeprazole has been shown to induce CYP1A isozymes in human hepatocyte cultures. In this study omeprazole was not effective in inducing EROD activity in rat hepatocytes or in vivo in the rat. This confirms that rat hepatocytes are not a good model for CYP1A induction in man. DMSO appears to be isozyme specific, since CYP2B-dependent pentoxyresorufin-O-dealkylase (PROD) activity was not increased by DMSO, and phenobarbitone (PB) induction of PROD was enhanced only slightly by DMSO on day 3 of culture (4-fold over control; 1.5-fold over PB alone). Sodium butyrate and DMSO were both shown to induce differentiation of rat hepatocyte, with maintenance of low level of γ-glutamyl transferase activity, and maintenance of a more rounded morphology.