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 membe rs 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 treatm ent. The amount of P450IIB was increased after exposure of the co-cult ured cells to either phenobarbital or sodium valproate. In contrast, P 450IV amounts were increased only by sodium valproate treatment. The m aximal 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 the se two cytochrome P-450 subfamilies in hepatocytes cultured for 4 days in the absence of epithelial cells. The amounts of both P450IIB and P 450IV were low or undetectable in these cells, and the induction of th ese proteins by either phenobarbital or valproate was less than that o bserved in co-cultured hepatocytes. Our results demonstrate that the c o-culture system is a suitable in vitro system for examining the effec ts of various foreign compounds on the expression of phase I drug meta bolizing enzymes.