Coumarin-induced changes in δ-aminolaevulinic acid synthase and cytochrome P-450 in chick embryo liver

Coumarin occurs naturally in the diet and inhibits several cytochrome P-450 enzymes in laboratory animals. The effect of coumarin was examined on haem biosynthesis and cytochrome P-450 activities in the 18-day-old chick embryo liver in ovo. At 40 and 50 μmol/embryo coumarin increased δ-aminolaevulinic acid synthase, porphyrins, cytochrome P-450, benzphetamine N-demethylase and benzo[a]pyrene hydroxylase. At 10 μmol/embryo coumarin decreased aniline 4-hydroxylase, and at both 10 and 50 μmol/embryo it decreased 7-ethoxyresorufin O-deethylase, coumarin 7-hydroxylase and nitrosodimethylamine N-demethylase. 7-Hydroxycoumarin and 5, 7-methoxycoumarin at 40 μmol/embryo had none of these effects. Coumarin (5-500 μm) added to liver microsomes inhibited aniline hydroxylase by 45%, but not nitrosodimethylamine N-demethylase, and inhibited 7-ethoxyresorufin O-deethylase in microsomes from 3-methylcholanthrene-treated embryos by 15 and 100% at coumarin concentrations of 250 and 500 μm, respectively. Coumarin 7-hydroxylase activity in chick embryo liver was comparable with that reported for human liver and greater than in the rat. The data indicate that coumarin can both increase and decrease cytochrome P-450 activities in chick embryo liver and can induce haem biosynthesis. Because the chick embryo liver hydroxylates coumarin at position 7 in a manner similar to humans, it may be a more suitable model than the rat for studying some of the metabolic effects of coumarin.