title: In vitro modulation of naturally occurring flavonoids on cytochrome P450 2A6 (CYP2A6) activity.
abstract: 1. The effect of flavonoids on coumarin 7-hydroxylation, an activity marker of an important human liver cytochrome P450 isoform, cytochrome P450 2A6 (CYP2A6), was investigated in this study. 2. Coumarin 7-hydroxylase activity was measured fluorometrically in reaction mixtures containing cDNA-expressed CYP2A6, nicotinamide adenine dinucleotide phosphate generating system and 10 uM coumarin, at various concentrations of flavonoids. 3. Among the 23 compounds tested, most of the active members were from flavonol group of hydroxylated flavonoids, with myricetin being the most potent inhibitor followed by quercetin, galangin, and kaempferol. 4. Further exploration of the inhibition mechanism of these compounds revealed that myricetin, galangin, and kaempferol exhibited mixed-type of inhibition pattern while quercetin was observed to exhibit competitive mode of inhibition. 5. Structure-function analyses revealed that degree of inhibition was closely related to the number and location of hydroxyl groups, glycosylation of the free hydroxyl groups, degree of saturation of the flavane nucleus as well as the presence of the alkoxylated function.
authors.affiliation: School of Pharmacy and Health Sciences, International Medical University 126, Jalan 19/155B, Bukit Jalil, Kuala Lumpur, Malaysia.
authors.forename: K H
authors.initials: KH
authors.lastname: Tiong
authors.forename: B C
authors.initials: BC
authors.lastname: Yiap
authors.forename: E L
authors.initials: EL
authors.lastname: Tan
authors.forename: R
authors.initials: R
authors.lastname: Ismail
authors.forename: C E
authors.initials: CE
authors.lastname: Ong
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D003374:Coumarins / Q000378:metabolism; D065637:Cytochrome P-450 CYP2A6; D004791:Enzyme Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D005419:Flavonoids / Q000378:metabolism* / Q000494:pharmacology; D005470:Fluorometry; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D006801:Humans; D006900:Hydroxylation; D007093:Imidazoles / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D003374:Coumarins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; C517283:coumarin 7; D009249:NADP; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6