Induction and activity of several isoenzymes of cytochrome P-450 in primary cultures of rat hepatocytes, in comparison with in vivo data.

Abstract

Changes in cytochrome P-450 isoenzymes were studied in rat liver and in primary cultures of rat hepatocytes after treatment with compounds belonging to various classes of inducers, including phenobarbital (PB), beta-naphthoflavone (BNF), and clofibrate/clofibric acid (CLOF/CLOFA). The enzyme activity toward specific substrates was measured, and the presence of apoprotein of several P-450 isoenzymes was determined semiquantitatively by Western blotting. In untreated cultures the P-450 content and activities of 7-ethoxyresorufin O-deethylation (EROD) and aniline 4-hydroxylation (AH) declined with time at different rates. In cultures treated with BNF, the protein levels of isoenzyme P-450IA1 and P-450IA2 were elevated, as in vivo. This induction was reflected in a markedly increased EROD activity. CLOFA enhanced the AH and EROD activity in primary cultures at the same level as in vivo. The monooxygenase activity pentoxyresorufin O-depentylation (PROD) was stimulated by PB and CLOF in vivo, which correlated with the enhanced protein level of P-450IIB1/2. In contrast, the PROD activity was not induced when cultures were treated with PB or CLOFA, although we could detect apoprotein of P-450IIB1/2 by immunoblotting.