RAT HEPATOCYTES CULTURED ON A MONKEY KIDNEY-CELL LINE - EXPRESSION OF BIOTRANSFORMATION AND HEPATIC METABOLIC-ACTIVITIES

The present study deals with the expression of cytochrome P-450 and two monooxygenase activities (aryl hydrocarbon hydroxylation and 7-ethoxycoumarin O-deethylation) by hepatocytes cultured on feeder layers of MS cells, in an attempt to investigate the influence of culture medium composition on phase I activities of hepatocytes. When compared with culture medium I (serum-free, hormone-supplemented Ham's F12), 4-day MS hepatocyte cultures supplemented with nicotinamide (medium II) allowed better retention by hepatocytes of cytochrome P-450 and phase I activities (aryl hydrocarbon hydroxylation and 7-ethoxycoumarin O-deethylation). A moderate additive effect was found after increasing branched-chain amino acid composition (medium III). Increasing the concentration of all amino acids, galactose and pyruvate (medium IV) resulted in higher levels of cytochrome P-450, aryl hydrocarbon hydroxylation and 7-ethoxycoumarin O-deethylation which, after 8 days in culture, were at 33, 49 and 43% of day 0 values, respectively. A further increase of branched-chain amino acid concentration produced only a moderate effect (medium V). Under these culture conditions, hepatocytes also expressed basic metabolic functions. After 10 days, MS hepatocyte cultures retained 43, 71 and 65% of ureogenesis, triglyceride secretion and albumin production measured at day 0. In contrast, pure hepatocytes cultured under the same conditions expressed these three hepatic functions only until the fifth or sixth day of culture.