IDENTIFICATION IN RAT BILE OF GLUTATHIONE CONJUGATES OF FLUOROMETHYL 2,2-DIFLUORO-1-(TRIFLUOROMETHYL)VINYL ETHER, A NEPHROTOXIC DEGRADATE OF THE ANESTHETIC AGENT SEVOFLURANE

Recent studies have indicated that the nephrotoxicity of fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether (''Compound A''), a breakd own product of the inhaled anesthetic sevoflurane, may be mediated by a reactive intermediate(s) generated via the cysteine conjugate beta-l yase pathway. In order to gain a better understanding of glutathione ( GSH)-dependent metabolism of Compound A, the present study was carried out with the primary goal of detecting and characterizing Compound A- GSH conjugates. By means of ionspray LC-MSI MS and NMR spectroscopy, a total of four GSH conjugates (''A1-A4'') were identified from the bil e of rats dosed intraperitoneally with Compound A. A1 and A2 were iden tified as two diastereomers of uoromethoxy)-2-(trifluoromethyl)ethyl]g lutathione, while A3 and A4 were identified as (E)- and oromethoxy)-2- (trifluoromethyl)-vinyl]glutathione, respectively. Quantitative analys es indicated that approximately 29% of the administered dose of Compou nd A was excreted into the bile in the form of the above GSH conjugate s over a period of 6 h. Studies conducted in vitro demonstrated that t he reaction of Compound A with GSH was catalyzed by both rat liver cyt osolic and microsomal glutathione S-transferases (GST), with the two e nzyme systems exhibiting different product selectivities. Formation of these GSH conjugates also occurred nonenzymatically at an appreciable rate. These results indicate that spontaneous and enzyme-mediated con jugation with GSH represents a major pathway of metabolism of Compound A in rats. Conjugation of Compound A with GSH in, vivo appeared to be catalyzed preferentially by microsomal rather than cytosolic GST, bas ed on comparison of biliary, microsomal, and cytosolic metabolic profi les. By analogy with other haloalkenes, further metabolism of the corr esponding cysteine conjugates of Compound A by renal cysteine conjugat e beta-lyase may lead to the formation of reactive acylating agents, w hich would be expected to bind covalently to cellular macromolecules a nd cause organ-selective nephrotoxicity.