Regulation of phenobarbital-inducible cytochrome P450 2B1/2 mRNA by lovastatin and oxysterols in primary cultures of adult rat hepatocytes.

Lovastatin (LOVA) is a potent inhibitor of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase widely used in clinical practice. We treated primary cultures of adult rat hepatocytes, maintained in a minimal, serum-free medium on Matrigel, a reconstituted basement membrane, with this drug, and found that the amounts of P450 2B2 mRNA detected on Northern blots were increased at the same doses (10(-5) to 3 x 10(-5) M) required for induction of HMG-CoA reductase mRNA, a gene known to be under oxysterol regulatory control. LOVA treatment produced selective effects increasing also the mRNA levels for P450s 2C6, 2C7, 3A1, and 4A1 but not for 1A1, 2A1/2, or NADPH-cytochrome P450 oxidoreductase. LOVA treatment increased the induction of 2B1/2 mRNA in cells cotreated with either phenobarbital (PB; 10(-4) M) or clotrimazole (CTZ; 10(-5) M), or of 3A1 mRNA in cells cotreated with PB (2 x 10(-3) M), but not dexamethasone (10(-5) M. LOVA treatment did not potentiate the induction of 1A1 or 4A1 mRNA in cells cotreated with beta-naphthoflavone (10(-5) M) or ciprofibrate (10(-4) M), respectively. In contrast to the potentiation of 2B1/2 mRNA induction produced by treatments with LOVA in combination with PB or CTZ, cotreatment of hepatocytes with PB and CTZ did not result in increased induction relative to that seen in cells treated with either agent alone. Treatment of hepatocyte cultures with either mevalonate (3 x 10(-4) to 3 x 10(-3) M), the immediate product of HMG-CoA reductase, or 25-hydroxycholesterol (10(-6) to 10(-5) M), a model oxysterol, resulted in dose-dependent suppression of 2B1/2 mRNA induction in cells treated with PB-like inducers. Taken together, our results demonstrate that LOVA is a unique inducer of P450 mRNA in cultured rat hepatocytes and implicate oxysterols as potential intracellular modulators of 2B1/2 induction. We conclude that endogenous metabolic factors including those related to cholesterol biosynthesis are critical in induction of liver cytochromes P450 2B1 and 2B2 by PB and "PB-like" agents.