EFFECTS OF PHENOBARBITAL AND VALPROATE ON THE EXPRESSION OF CYTOCHROMES P-450 IN COCULTURED RAT HEPATOCYTES

We have investigated, in hepatocytes co-cultured with epithelial cells, the effects of phenobarbital and sodium valproate treatment on members of the cytochrome P-450 superfamily. The expression of the P450IIB and P450IV families was examined, using Western blotting, at 4, 7 and 14 days of co-culture either in the presence or absence of drug treatment. The amount of P450IIB was increased after exposure of the co-cultured cells to either phenobarbital or sodium valproate. In contrast, P450IV amounts were increased only by sodium valproate treatment. The maximal induction of P450IIB (17-fold) was observed at 7 and 14 days of co-culture, whereas P450IV was induced to the same extent in cells co-cultured for 4, 7 and 14 days. We also examined the expression of these two cytochrome P-450 subfamilies in hepatocytes cultured for 4 days in the absence of epithelial cells. The amounts of both P450IIB and P450IV were low or undetectable in these cells, and the induction of these proteins by either phenobarbital or valproate was less than that observed in co-cultured hepatocytes. Our results demonstrate that the co-culture system is a suitable in vitro system for examining the effects of various foreign compounds on the expression of phase I drug metabolizing enzymes.