title: Stereoselective glucuronidation of 5-(4'-hydroxyphenyl)-5-phenylhydantoin by human UDP-glucuronosyltransferase (UGT) 1A1, UGT1A9, and UGT2B15: effects of UGT-UGT interactions.
abstract: 5-(4'-Hydroxyphenyl)-5-phenylhydantoin (4'-HPPH), a major metabolite of phenytoin in human, is exclusively metabolized to a glucuronide. 4'-HPPH has a chiral center. (S)-4'-HPPH is a predominant form produced from phenytoin in humans, and (R)-4'-HPPH is an extremely toxic form with respect to gingival hyperplasia. In the present study, we investigated stereoselective 4'-HPPH O-glucuronide formation in human liver microsomes. Human liver microsomes predominantly formed (S)-4'-HPPH O-glucuronide rather than (R)-4'-HPPH O-glucuronide from racemic 4'-HPPH. Among human UDP-glucuronosyltransferase (UGT) enzymes, UGT1A1, UGT1A9, and UGT2B15 showed 4'-HPPH O-glucuronide formation. Interestingly, UGT1A1 stereoselectively formed (R)-4'-HPPH O-glucuronide, whereas UGT1A9 and UGT2B15 stereoselectively formed (S)-4'-HPPH O-glucuronide from racemic 4'-HPPH. By using UGT1A double-expression systems in HEK293 cells that we previously established, the effects of UGT-UGT interactions on 4'-HPPH O-glucuronide formation were investigated. It was demonstrated that coexpression of UGT1A4 increased the V(max) values of (S)- and (R)-4'-HPPH O-glucuronide formation catalyzed by UGT1A1 but decreased the V(max) values of (S)- and (R)-4'-HPPH O-glucuronide formation catalyzed by UGT1A9. Coexpression of UGT1A6 increased the S(50) values and decreased the V(max) values of (S)- and (R)-4'-HPPH glucuronide formation catalyzed by UGT1A1 and UGT1A9. However, the interaction did not alter the stereoselectivity. In conclusion, we found that 4'-HPPH O-glucuronide formation in human liver microsomes is catalyzed by UGT1A1, UGT1A9, and UGT2B15 in a stereoselective manner, being modulated by interaction with other UGT1A isoforms.
authors.affiliation: Drug Metabolism and Toxicology, Division of Pharmaceutical Sciences, Graduate School of Medical Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Nakajima
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Fujiwara
authors.forename: Miki
authors.initials: M
authors.lastname: Katoh
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Yokoi
mesh_terms: D000465:Algorithms; D000818:Animals; D015153:Blotting, Western; D020719:Glucuronides; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008862:Microsomes, Liver / Q000378:metabolism; D010672:Phenytoin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D018411:Spodoptera; D013237:Stereoisomerism; D000090264:UDP-Glucuronosyltransferase 1A9; D000099148:UGT1A1 Enzyme
chemical_list: D020719:Glucuronides; D014453:Glucuronosyltransferase; D010672:Phenytoin; D000090264:UDP-Glucuronosyltransferase 1A9; D000099148:UGT1A1 Enzyme; C000715591:UGT1A9 protein, human; C038540:5-(3,4-dihydroxyphenyl)-5-phenylhydantoin; C472000:UDP-glucuronosyltransferase 2B15, human