CYTOCHROME-P450 ACTIVITIES IN PURE AND COCULTURED RAT HEPATOCYTES - EFFECTS OF MODEL INDUCERS

The stability and inducibility of several P450 activities (namely, P45 0 1A1, 2A1, 2B1/2, 2C11, and 3A1) were studied in rat hepatocytes co-c ultured with the MS epithelial cell line derived from monkey kidney. T he results revealed that these monooxygenase activities were systemati cally higher in co-cultures than in conventional hepatocyte cultures. Pure cultures showed a rapid loss of monooxygenase activities, which w ere undetectable after 5 days. In contrast, all isozymes assayed were measurable in co-cultured hepatocytes on Day 7 (about 15 to 40% of the initial activities of Day 0 of culture). The beneficial effects of th e co-culture system seemed to be more selective for certain cytochrome P450 isoforms, with P450 1A1 and 3k1 being the best stabilized isozym es after 1 wk. A clear response to inducers was observed in co-culture s, each isozyme showing a different induction pattern. 3-Methylcholant hrene produced a strong increase in P450 1A1 (7-ethoxyresorufin 0-deet hylase) activity and a low increase in P450 2A1 (testosterone 7 alpha- hydroxylation), whereas no changes were observed in the other activiti es. Phenobarbital treatment resulted in increases in P450 2B1/2(7-pent oxyresorufin O-depentylase and 16 alpha- and 16 beta-hydroxylation of testosterone) activities, while minor effects were observed on P450 3A 1 (testosterone 6 beta-hydroxylation) activity. Dexamethasone markedly increased P450 3A1 (testosterone 6 beta- and 15 beta-hydroxylation) a ctivity and, to a lesser extent, P450 2B1/2 (16 beta-hydroxylation).