Abstract

(–)-Verbenone, a monoterpene bicyclic ketone, is a component of the essential oil from rosemary species such as Rosmarinus officinalis L., Verbena triphylla, and Eucalyptus globulus and is used for an herb tea, a spice, and a perfume. In this study, (–)-verbenone was found to be converted to 10-hydroxyverbenone by rat and human liver microsomal cytochrome P450 (P450) enzymes. The product formation was determined by high-performance liquid chromatography with UV detection at 251 nm. There was a good correlation between activities of coumarin 7-hydroxylation and (–)-verbenone 10-hydroxylation catalyzed by liver microsomes of 16 human samples, indicating that CYP2A6 is a principal enzyme in (–)-verbenone 10-hydroxylation in humans. Human recombinant CYP2A6 and CYP2B6 catalyzed (-)verbenone 10-hydroxylation at V_max values of 15 and 21 nmol/min/nmol P450 with apparent K_m values of 16 and 91 μM, respectively. In contrast, rat CYP2A1 and 2A2 did not catalyze (–)-verbenone 10-hydroxylation at all, suggesting that there were species-related differences in the catalytic properties of human and rat CYP2A enzymes in the metabolism of (–)-verbenone. In the rat, recombinant CYP2C11, CYP2B1, and CYP3A2 catalyzed (–)-verbenone 10-hydroxylation with V_max and K_m ratios (ml/min/nmol P450) of 0.73, 0.20, and 0.03, respectively. Male-specific CYP2C11 was a major enzyme in (–)-verbenone 10-hydroxylation by untreated rat livers, and CYP2B1 catalyzed this reaction in liver microsomes of phenobarbital-treated rats. Rat CYP2C12, a female-specific enzyme, did not catalyze (-)verbenone 10-hydroxylation. These results suggest that human CYP2A6 and rat CYP2C11 are the major catalysts in the metabolism of (–)-verbenone by liver microsomes and that there are species-related differences in human and rat CYP2A enzymes and sex-related differences in male and female rats in the metabolism of (–)-verbenone.