Roles of human cytochrome P450 1A2 in coumarin 3,4-epoxidation mediated by untreated hepatocytes and by those metabolically inactivated with furafylline in previously transplanted chimeric mice

Coumarin is a naturally occurring component of food products but is of clinical interest for its potential hepatotoxicity in humans. In the current study, the pharmacokinetics of coumarin in humanized-liver mice after oral and intravenous administrations (30 mg/ kg) were investigated for its transformations to metabolically active coumarin 3,4-epoxide (as estimated by the levels of o-hydroxyphenylacetic acid) and to excretable 7-hydroxycoumarin. After oral administration, control mice metabolized coumarin to o-hydroxyphenylacetic acid at roughly the same rate as that to 7-hydroxycoumarin (total of unconjugated and conjugated forms). In contrast, the in vivo biotransformation of coumarin to o-hydroxyphenylacetic acid by humanized-liver mice was around two orders of magnitude less than that to conjugated and unconjugated 7-hydroxycoumarin. After intravenous administrations of coumarin, differences were observed in the plasma concentrations of o-hydroxyphenylacetic acid between humanized-liver mice treated with furafylline (daily oral doses of 13 mg/kg for 3 days) and untreated humanized-liver mice. The mean values of the areas under the plasma concentration versus time curves and the maximum concentrations for o-hydroxyphenylacetic acid were significantly lower in the group treated with furafylline (45% and 57% of the untreated values, respectively). These results suggested that the metabolic activation of coumarin in humans was mediated mainly by P450 1A2, which was suppressed by furafylline, and that humanized-liver mice orally treated with furafylline might constitute an in vivo model for metabolically inactivated P450 1A2 in human hepatocytes transplanted into chimeric mice.