PT  - JOURNAL ARTICLE
AU  - Mark P. Grillo
AU  - Charles G. Knutson
AU  - Phillip E. Sanders
AU  - Daniel J. Waldon
AU  - Fengmei Hua
AU  - Joseph A. Ware
TI  - STUDIES ON THE CHEMICAL REACTIVITY OF DICLOFENAC ACYL GLUCURONIDE WITH GLUTATHIONE: IDENTIFICATION OF DICLOFENAC-<em>S</em>-ACYL-GLUTATHIONE IN RAT BILE
AID  - 10.1124/dmd.31.11.1327
DP  - 2003 Nov 01
TA  - Drug Metabolism and Disposition
PG  - 1327--1336
VI  - 31
IP  - 11
4099  - http://dmd.aspetjournals.org/content/31/11/1327.short
4100  - http://dmd.aspetjournals.org/content/31/11/1327.full
SO  - Drug Metab Dispos2003 Nov 01; 31
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