Influence of P-4502E1 induction on benzene metabolism in rat hepatocytes and on biliary metabolite excretion.

The influence of P-4502E1 induction on the metabolite pattern of benzene was studied in hepatocytes in vitro and in bile in vivo, and compared with that obtained with phenol (the major benzene metabolite). Eight metabolites from benzene and four from phenol (including conjugates) represented over 90% of total metabolites. Benzene metabolism (0.1 mM) in hepatocytes from isopropanol-treated rats (2.5 ml/kg, orally) was 3-fold higher than in corresponding cells from control rats, primarily because of increased formation of hydroquinone and phenylglutathione. Immunoblotting of microsomes revealed a parallel induction of P-4502E1 in hepatocytes from isopropanol-treated rats. In contrast, treatment with 3-methylcholanthrene or phenobarbital caused a decrease of P-4502E1, together with reduced benzene metabolism at 0.01 mM benzene. Addition of isoniazid (5 mM) resulted in a strong inhibition of benzene and phenol metabolism. Benzene metabolites were determined in bile following intraperitoneal administration of benzene (2.5 and 150 mg/kg). Biliary benzene metabolites were increased 2- to 3-fold after isopropanol treatment. Hydroquinone sulfate was identified as a major biliary metabolite of phenol. The results suggest that treatment with inducers of P-4502E1 leads, even at low benzene exposure, to an increased release of potentially myelotoxic metabolites from liver into the systemic circulation.