Studies on the chemical reactivity of diclofenac acyl glucuronide with glutathione: identification of diclofenac-S-acyl-glutathione in rat bile.
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 microM) with GSH (10 mM) at pH 7.4 and 37 degrees C showed a linear time-dependent formation of diclofenac-S-acyl-glutathione (D-SG, 3 microM/h) through 60 min of incubation, reaching a maximum of 3.7 microM 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 microM) was compared with D-1-O-G (100 microM) 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 approximately 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.
Grillo
Mark P
MP
Pharmacokinetics, Dynamics, and Metabolism, Pfizer, Inc., Kalamazoo, Michigan, USA. markgrillo@chartermi.net
Knutson
Charles G
CG
Sanders
Phillip E
PE
Waldon
Daniel J
DJ
Hua
Fengmei
F
Ware
Joseph A
JA
D000818:Animals; D001646:Bile / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004008:Diclofenac / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D020719:Glucuronides / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D005978:Glutathione / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
D020719:Glucuronides; D004008:Diclofenac; D005978:Glutathione