Induction of cytochrome P 1450 RNA and benzo[ a]pyrene metabolism in primary human hepatocyte cultures with benzanthranene

Abstract

Exposure of cells to microsomal enzyme inducers can modify the potency of many carcinogens. We have examined the steady-state level of RNA from the P 1450 gene and the metabolism of benzo[ a]pyrene (BP) in primary cultures of human hepatocytes exposed for up to 4 days to 12.5 μ m benzanthracene (BA), and in uninduced control cultures. While the steady-state levels of RNA from the P 1450 gene were nondetectable in uninduced (DMSO only) human hepatocytes, 12.5 μ m BA-induced AHH activity, BP metabolism, and/or P 1450-specific RNA in hepatocytes from seven human cases were investigated. RNA levels specific for the P 1450 gene appeared maximal at 24 hr following exposure to BA, whereas, the protein, as determined by AHH enzyme activity from BA-induced hepatocytes, continued to increase up to the last time point examined, 72 hr. BA induction for 96 hr increased metabolism of BP (initial concentration of BP, 10 μ m) over a time course of 3, 6, 12, and 24 hr of incubation with BP compared with that of controls. The major metabolites of BP produced by human hepatocytes in culture were the unidentified polar BP metabolite(s), possibly polyhydroxylated. BA induction caused approximately a twofold increase in these metabolites. BA-induced cultures showed an increase in glutathione conjugation compared to that in controls. The percentage of glucuronide and sulfate conjugates remains similar in all cultures. Total binding of tritium label BP to DNA was 1.3-fold to fivefold greater in induced cultures, and related more to total metabolism than to production of a specific metabolite. Exposure of human hepatocytes in vitro to BA leads to a large increase in the steady-state level of the RNA specific for the P 1450 gene and an increase metabolism of BP.