title: Inhibition on human liver cytochrome P450 3A4 by constituents of fennel (Foeniculum vulgare): identification and characterization of a mechanism-based inactivator.
abstract: Fennel, a seed of Foeniculum vulgare, is used as a culinary spice and traditional medicine. The methanolic extract of fennel showed a characteristic of mechanism-based inactivation on erythromycin N-demethylation mediated by human liver microsomal cytochrome P450 3A4 (CYP3A4). The present study was conducted to identify the fennel constituent having the inhibition. Thirteen compounds have been isolated from a methanol extract of fennel and tested for their inhibition on CYP3A4. Among them, 5-methoxypsoralen (5-MOP) showed the strongest inhibition with an IC50 value of 18.3 microM and a mixed type of inhibition. In addition, with the preincubation time of 20 min only 5-MOP showed preincubation time dependency; the IC50 value decreased from 18.3 microM with a preincubation time of 0 min to 4.6 microM with a preincubation time of 20 min. Further investigation on 5-MOP showed the characteristics of time-dependent inhibition, requirement of NADPH, lack of protecting effect of nucleophiles, and recovery of CYP3A4 activity by the competitive inhibitor. This result suggests that the inhibitory activity of CYP3A4 by 5-MOP was a mechanism-based inactivation. The kinetic parameter for mechanism-based inactivation was characterized by a KI value of 15.0 microM and a kinact value of 0.098 min(-1).
authors.affiliation: Institute of Natural Medicine, University of Toyama, 2630-Sugitani, Toyama 930-0194, Japan.
authors.lastname: Subehan
authors.forename: Syed F H
authors.initials: SF
authors.lastname: Zaidi
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Kadota
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tezuka
mesh_terms: D000078223:5-Methoxypsoralen; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D030001:Foeniculum / Q000201:enzymology*; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008730:Methoxsalen / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D012639:Seeds / Q000201:enzymology*
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D000078223:5-Methoxypsoralen; D009249:NADP; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D008730:Methoxsalen