OBJECTIVETo investigate phase I and phase II enzyme activities in drug metabolism with tissue-like cultures of rat hepatocytes.

METHODSThe gel entrapment and spheroid culture of hepatocytes were used as tissue-like cultures and the monolayer culture was used as a control. The metabolism of phenacetin and 7-hydroxycoumarin (7-HC) was evaluated as the activities of phase I and phase II enzymes after incubated in medium for a period of time. The metabolites were assayed by HPLC. The hepatocytes were exposed to beta-naphthoflavone (BNF, 50 micromol x L(-1)) before the phase I and phase II enzyme activities were analyzed.

RESULTIn monolayer culture, phase I parameters decreased quickly and did not detected at d 5, and the phase II enzyme activities were not detected at d 7. In other two models of tissue-like cultures, the activities of phase I and phase II enzyme maintained at 32%-50% of the initial value at d 7. Paracetamol formation rates in spheroid culture maintained at 96% of that at d 1. The phase I enzyme activities of the spheroid culture were maintained from d 1 to d 3 at a level of 2.7-3.9-fold higher than the monolayer culture. After exposure to BNF the activities on phase I enzyme increased by about 2.5-fold (P <0.05) in all three culture models, while the increase in phase II enzyme was not significant.

CONCLUSIONThe gel entrapment culture and spheroid culture are superior to the monolayer culture in maintenance of drug metabolic enzyme activities.