The induction of cytochrome P-450 and monooxygenase activities in the chick embryo by 2-acetylaminofluorene

Vitamin K1 amplification of benzo(a)pyrene metabolism in chick embryos

Seventeen-day-old chick embryos were used as a test system to assess the effect of vitamin K1(K1) on benzo(a)pyrene (BP) metabolism as measured by the induction of arylhydrocarbon hydroxylase (AHH) and cytochrome P-450 and the levels of glutathione (GSH) and glutathione S-transferase (GST) in liver. Twenty-four hours after injection of BP into the air sac there was a sharp rise in AHH and P-450 and a drop in GSH. When K1 was injected 24 hr prior to BP there was a decrease in GST activity as compared with the control plus an augmented increase in AHH induction. This augmentation in BP metabolism (Phase I) together with a concomitant decrease in at least one mechanism of Phase II conjugation is in keeping with other evidence that K1 can play an adjuvant role in BP induced mutagenicity and carcinogenicity. Ubiquinone has a much lesser effect on BP metabolism than does K1 in equimolar concentration.

Testosterone metabolite profiles reveal differences in the spectrum of cytochrome P-450 isozymes induced by phenobarbitone, 2-acetylaminofluorene and 3-methylcholanthrene in the chick embryo liver

The regiospecificity and stereoselectivity of testosterone hydroxylation by hepatic microsomes prepared from control, PB, 3MC and 2AAF treated chick embryos has been analysed. Microsomes prepared from control animals hydroxylate testosterone at the 16 alpha and 6 beta positions exclusively: 3MC treatment only causes comparatively minor alterations in the rates of these conversions. PB and 2AAF treatment induced 16 beta-hydroxylation, whilst only 2AAF caused a substantial induction of 6 beta hydroxylation. This data suggests that in the chick, 2AAF not only induces P-450 subforms which are also induced by PB but additional subforms which are not markedly induced by either PB or 3MC.

A study into the effects of 2-acetylaminofluorene on hepatic monooxygenase activities in the chick embryo

2AAF is a potent inducer of cytochrome P-450 in the chick embryo liver. The induction has been characterized with respect to a range of monooxygenase activities and the regiospecificity of 2AAF hydroxylation. Similarities to the response elicited by both PB and 3MC were noted. 2AAF was rapidly deacetylated by hepatic microsomes prepared from control animals to 2AF, an inhibitor of monooxygenase activity. Metabolites generated in vivo and carried over in vitro might have therefore interfered with the subsequent kinetic analysis. In general terms induction of a unique cytochrome P-450 subform(s) could not be attributed to 2AAF in the chick embryo. The data is discussed with respect to the reported resistance of avian species to the hepatocarcinogenic effects of 2AAF. Two possibilities are highlighted, a diversion of 2AAF to ring hydroxylated metabolites and/or deacetylation of 2AAF. Both effects could reduce carcinogenicity by decreasing the concentration of proximate carcinogen and/or promoter(s).