RT Journal Article SR Electronic T1 STUDIES ON THE CHEMICAL REACTIVITY OF DICLOFENAC ACYL GLUCURONIDE WITH GLUTATHIONE: IDENTIFICATION OF DICLOFENAC-S-ACYL-GLUTATHIONE IN RAT BILE JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1327 OP 1336 DO 10.1124/dmd.31.11.1327 VO 31 IS 11 A1 Mark P. Grillo A1 Charles G. Knutson A1 Phillip E. Sanders A1 Daniel J. Waldon A1 Fengmei Hua A1 Joseph A. Ware YR 2003 UL http://dmd.aspetjournals.org/content/31/11/1327.abstract AB Diclofenac, a nonsteroidal anti-inflammatory drug, is metabolized to a reactive acyl glucuronide that has been proposed to mediate toxic adverse drug reactions associated with its use. In the present study, we examined the ability of diclofenac acyl glucuronide (D-1-O-G) to transacylate glutathione (GSH) in vitro in buffer and in vivo in rats. Thus, in vitro reactions of D-1-O-G (100 μM) with GSH (10 mM) at pH 7.4 and 37°C showed a linear time-dependent formation of diclofenac-S-acyl-glutathione (D-SG, 3 μM/h) through 60 min of incubation, reaching a maximum of 3.7 μM after 2 h of incubation. The major reaction that occurred was acyl migration of D-1-O-G (t1/2, 54 min) to less reactive isomers. The D-SG thioester product was shown to be unstable by degrading primarily to 1-(2,6-dichlorophenyl)indolin-2-one and by hydrolysis to diclofenac. After administration of diclofenac to rats (200 mg/kg), bile was collected and analyzed for D-SG by liquid chromatography-tandem mass spectrometry. Results indicated the presence of D-SG, which was confirmed by coelution with synthetic standard and by its tandem mass spectrum. When the reactivity of D-SG (100 μM) was compared with D-1-O-G (100 μM) in vitro in reactions with N-acetylcysteine (NAC, 10 mM), results showed the quantitative reaction of D-SG with NAC after 30 min of incubation, whereas only ∼1% of D-1-O-G reacted to form diclofenac-S-acyl-NAC at the same time point. Results from these studies indicate that GSH reacts with D-1-O-G in vitro, and presumably in vivo, to form D-SG, and that the product D-SG thioester is chemically more reactive in transacylation-type reactions than the D-1-O-G metabolite. The American Society for Pharmacology and Experimental Therapeutics