title: Bioactivation of diclofenac via benzoquinone imine intermediates-identification of urinary mercapturic acid derivatives in rats and humans.
abstract: The metabolism of diclofenac has been reported to produce reactive benzoquinone imine intermediates. We describe the identification of mercapturic acid derivatives of diclofenac in rats and humans. Three male Sprague-Dawley rats were administered diclofenac in aqueous solution (pH 7) at 50 mg/kg by intraperitoneal injection, and urine was collected for 24 h. Human urine specimens were obtained, and samples were pooled from 50 individuals. Urine samples were analyzed by liquid chromatography-tandem mass spectrometry (LC/MS/MS). Two metabolites with MH(+) ions at m/z 473 were detected in rat urine and identified tentatively as N-acetylcysteine conjugates of monohydroxydiclofenac. Based upon collision-induced fragmentation of the MH(+) ions, accurate mass measurements of product ions, and comparison of LC/MS/MS properties of the metabolites with those of synthetic reference compounds, one metabolite was assigned as 5-hydroxy-4-(N-acetylcystein-S-yl)diclofenac and the other as 4'-hydroxy-3'-(N-acetylcystein-S-yl)diclofenac. The former conjugate also was detected in the pooled human urine sample by multiple reaction-monitoring LC/MS/MS analysis. It is likely that these mercapturic acid derivatives represent degradation products of the corresponding glutathione adducts derived from diclofenac-2,5-quinone imine and 1',4'-quinone imine, respectively. Our data are consistent with previous findings, which suggest that oxidative bioactivation of diclofenac in humans proceeds via benzoquinone imine intermediates.
authors.affiliation: Department of Drug Metabolism, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
authors.forename: G K
authors.initials: GK
authors.lastname: Poon
authors.forename: Q
authors.initials: Q
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Teffera
authors.forename: J S
authors.initials: JS
authors.lastname: Ngui
authors.forename: P R
authors.initials: PR
authors.lastname: Griffin
authors.forename: M P
authors.initials: MP
authors.lastname: Braun
authors.forename: G A
authors.initials: GA
authors.lastname: Doss
authors.forename: C
authors.initials: C
authors.lastname: Freeden
authors.forename: R A
authors.initials: RA
authors.lastname: Stearns
authors.forename: D C
authors.initials: DC
authors.lastname: Evans
authors.forename: T A
authors.initials: TA
authors.lastname: Baillie
authors.forename: W
authors.initials: W
authors.lastname: Tang
mesh_terms: D000111:Acetylcysteine / Q000652:urine*; D000818:Animals; D016227:Benzoquinones / Q000378:metabolism*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D004008:Diclofenac / Q000493:pharmacokinetics*; D006801:Humans; D007097:Imines / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D016227:Benzoquinones; D007097:Imines; D004008:Diclofenac; D000111:Acetylcysteine