Mixed function oxidase and UDP-glucuronyltransferase activities in the human Hep G2 hepatoma cell line.

In cultured human hepatoma cells phenolphthalein glucuronidation was increased 3-fold by 2 mM phenobarbitone (PB) in the culture medium but not by 25 microM benz(a)anthracene (BA), while 1-naphthol glucuronidation was not increased by either PB or BA. Ethoxyresorufin O-deethylation (EROD) was increased 15-fold by BA but not by PB, while the O-dealkylations of pentoxyresorufin (PROD) and benzyloxyresorufin (BROD) were increased by either PB or BA. The BROD activity increased by BA was sensitive to inhibition by alpha-naphthoflavone whereas that induced by PB was not. This suggests induction of different cytochrome P-450 isoenzymes. Control Hep G2 cells had similar glucuronide conjugation and cytochrome reductase activities to freshly isolated human adult hepatocytes, but had lower O-dealkylation and elevated microsomal epoxide hydrolase activities.