Involvement of cytochrome P450 in the metabolism of rebamipide by the human liver

1. The metabolism of rebamipide, a gastroprotective agent, was investigated using human liver microsomes and cDNA-expressed human cytochrome P450 systems. 2. 6-Hydroxy and 8-hydroxyrebamipide were produced by human cytochrome P450 enzyme(s), and 8-hydroxylation was the major metabolic pathway. K(m) and V(max) for 8-hydroxylation were 1.35 +/- 0.20 mM and 0.32 +/- 0.34 nmol min(-1) mg protein(-1), respectively (mean SD, n = 6). Kinetic analysis showed that the 8-hydroxylation reaction consisted of a single component. 3. 8-Hydroxylation was inhibited by the addition of CYP3A4 antibodies as well as troleandomycin, a specific inhibitor of CYP3A4. Furthermore, the metabolism of rebamipide in human liver microsomes was compatible with that in a human cDNA-expressed CYP3A4 system, but not for other human P450 expression systems. It is therefore suggested that the hydroxylation of rebamipide only involves CYP3A4. 4. Rebampide showed no inhibitory effect on CYP1A2-, 2C9-, 2C19-, 2D6-, 2E1- and 3A4-catalysed metabolism. In addition, the metabolic contribution by CYP3A4 was considered to be slight for the overall elimination of rebamipide in man. It is therefore considered that drug interactions with cytochrome P450 enzymes are not involved in either the metabolism of rebamipide or the metabolism of other drugs concomitantly administered with rebamipide.