QUANTITATIVE PREDICTION OF PHENOBARBITAL INDUCTION OF CYP2B IN VIVO FROM CULTURED HEPATOCYTES STUDIES

In vitro-in vivo scaling works well for metabolic enzyme inhibition, but is less successful with enzyme induction. In this paper, we are attempt to establish the prediction method for enzyme induction in vivo from cultured hepatocytes studies. Phenobarbital (PB) was used as a model inducer for CYP2B and the enzyme activities were assessed by pentoxyresorufin O-depentylation (PROD). In vivo induction was determined in liver microsomes isolated from rats after administration of PB. In vitro induction was assessed in cultured rat hepatocytes treated with PB. To compare in vitro induction with in vivo induction, plasma unbound concentration of PB has been used as a method of approximating unbound hepatocellular PB concentration in rats. Maximum induction (6 fold) and EC50 values (15-20 μM) after single administration of PB were well agreed between in vitro and in vivo studies. Similar results were obtained in repeated administration of PB. In conclusion, although there still remain some problems for quantitative prediction of the enzyme induction, we showed the possibility and effectiveness of the prediction of inducibility in vivo from cultured hepatocytes.