Metabolism of coumarin by rat,gerbil and human liver microsomes

1. o-Hydroxyphenylacetaldehyde was the major metabolite of coumarin (1 mM) in rat, gerbil and human liver microsomes.

2. Treatment of rats with phenobarbitone (PB) or β-naphthoflavone increased the o-hydroxyphenylacetaldehyde formed. 3-Hydroxycoumarin was the other main metabolite produced by rat liver microsomes.

3. Liver microsomal metabolism of coumarin in gerbil was extensive with 3-, 5-, 6-, 7-and 8-hydroxycoumarins, and 3,7- and 6,7-dihydroxycoumarins produced, in addition to o-hydroxyphenylacetaldehyde. The profile of the hydroxy metabolites was altered by in vivo treatment of gerbils with cytochrome P-450 inducers, but there was no increase of coumarin metabolism.

4. Coumarin was metabolized by human liver microsomes to o-hydroxyphenylacetaldehyde, 7-hydroxycoumarin, 3-hydroxycoumarin, and trace amounts of 5-, 6-and 8-hydroxycoumarins.

5. At low substrate concentrations (0-10 μM) hepatic microsomal metabolism of coumarin in gerbil resembled that in man, with 7-hydroxycoumarin being a major metabolite. However, the production of o-hydroxyphenylacetaldehyde was greater in gerbil than human liver microsomes.

6. At higher substrate concentrations (1 mM) metabolism of coumarin by liver microsomes from PB-treated gerbils most closely resembled that by human liver microsomes.

7. The gerbil would appear to be a more appropriate animal model than rat for studies to assess the toxicological hazard of coumarin for man.