PIG HEPATOCYTES AS AN IN-VITRO MODEL TO STUDY THE REGULATION OF HUMANCYP3A4 - PREDICTION OF DRUG-DRUG INTERACTIONS WITH 17-ALPHA-ETHYNYLESTRADIOL

The objective of this study was to provide evidence of the validity of pig hepatocytes as a model to study the regulation of human CYP3A4 wi th special emphasis on drug-drug interactions. Thirteen different drug s were incubated with primary monolayer cultures of pig hepatocytes (n = 4). The study included both drugs reported to cause drug interactio ns in the clinic with 17 alpha-ethynylestradiol (EE2), other drugs met abolized by CYP3A4, and drugs not reported to cause any problems. Effe ct of the drug exposure to pig hepatocytes was determined by immunodet ection using a monoclonal human CYP3A4 antibody and measurement of 6 b eta-hydroxylation of testosterone and 2-hydroxylation of 17 alpha-ethy nylestradioI (EE2), both reactions known to be catalyzed by CYP3A4 in humans. Data were compared to data from human hepatocytes and to repor ted observations of drug-drug interactions in the clinic. The drugs kn own to be inducers of CYP3A4 in humans significantly increased a CYP i soform in pigs catalyzing 6 beta-hydroxylation of testosterone and 2-h ydroxylation of EE2, whereas drugs not reported to have clinical inter actions with EE2 had no or only marginal effect. Induction by the drug s known to be inducers of CYP3A4 increased with drug exposure time and the CYP3A4 activity, represented by testosterone 6 beta-hydroxylation , was highest at 72 h for the investigated induction periods (24, 48 a nd 72 h), except for dexamethasone where the effect peaked after 24 h. Induction of the 2-hydroxyIation of EE2 correlated well with the incr ease in 6 beta-hydroxylation of testosterone (except for sulphinpyranz one) and the increase in the protein level of CYP3A detected by a mono clonal human CYP3A4 antibody, thus confirming the 2-hydroxylation of E E2 in pigs as being biotransformed by a CTP isoform presumably belongi ng to the CYP3A subfamily as in humans. In conclusion, these results i ndicate that pig hepatocytes may be a valuable model to mimic the regu lation of human CYP3A4. (C) 1997 Elsevier Science Ireland Ltd.