THE EFFECTS OF INDUCING AGENTS ON CYTOCHROME-P450 AND UDP-GLUCURONOSYLTRANSFERASE ACTIVITIES IN HUMAN HEPG2 HEPATOMA-CELLS

Selective induction in vitro of cytochrome P450-dependent mixed-functi on oxidase (MFO) and UDP-glucuronyltransferase (GT) activities was obs erved in the human HepG2 hepatoma cell line. 1,2-Benzanthracene (BA) i nduced MFO O-dealkylation activities for ethoxyresorufin, methoxyresor ufin and benzyloxyresorufin, whereas phenobarbitone (PB) selectively i nduced pentoxyresorufin O-dealkylation and rifampicin (RIF) selectivel y induced benzyloxyresorufin O-dealkylation. Antibody inhibition exper iments indicated that ethoxyresorufin and methoxyreSorufin O-dealkylat ions were catalysed mainly by the P450 1A subfamily in untreated and B A-induced HepG2 cells, that additional unidentified P450 forms were co nsiderably involved in methoxyresorufin and benzyloxyresorufin O-dealk ylations and that the P450 2B subfamily was partially responsible for pentoxyresorufin O-dealkylation in PB-induced cells. Bilirubin GT acti vity was induced by PB, BA, RIF and dexamethasone, but 1-naphthol, mor phine and testosterone GT activities were not induced by any of these treatments.