Oxidative biotransformation in primary cultures of chick embryo hepatocytes: induction of cytochrome P-450 and the metabolism of benzo(a)pyrene.

Primary cultures of chick embryo hepatocytes are known to maintain their initial level of cytochrome P-450 for a number of days. To explore the possibilities of chick embryo hepatocyte cultures as a tool in drug metabolism, induction profiles of cytochrome P-450 were determined and the metabolism of benzo(a)pyrene as a model substrate was studied. Maximum induction by phenobarbitone and Aroclor 1254 is reached after 21 h and 18 h, respectively, both in the presence and absence of serum. For beta-naphthoflavone induction is maximal after 31 h in the presence and 43 h in the absence of serum. The levels of P-450 after induction are comparable to those found in vivo in rats: increases of 200% for phenobarbitone, 200% for beta-naphthoflavone and 210% for Aroclor 1254. Ethoxyresorufin-O-deethylase activities are induced by beta-naphthoflavone and Aroclor 1254, but as expected only slightly by phenobarbitone. In the absence of serum in the culture medium, for the control as well as the induced cells a plateau of activity is maintained for at least 24 h. In the presence of serum a decline in P-450 levels is observed. Especially in the case of Aroclor, an increase in porphyrin content of 320% of control values is seen at the same time. A number of representative metabolites of benzo(a)pyrene were quantitated during a 4-h incubation. Relative amounts are comparable to those observed with rat liver microsomes. As expected, beta-naphthoflavone and Aroclor induce the rate of metabolism (by 500% and 400%, respectively, in the absence of serum), but phenobarbitone has no or very little effect.(ABSTRACT TRUNCATED AT 250 WORDS)