Evidence for Metabolism of Fluoromethyl 2,2-Difluoro-1-(trifluoromethyl)vinyl Ether (Compound A), a Sevoflurane Degradation Product, by Cysteine Conjugate β-Lyase

The volatile anesthetic sevoflurane is degraded to fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether (FDVE), a potent rat nephrotoxin. In rats in vivo, FDVE undergoes glutathione conjugation and metabolism to cysteine conjugates, whose bioactivation by renal cysteine conjugate beta-lyase has been implicated by the protective effects of (aminooxy)acetic acid, an inhibitor of cysteine conjugate beta-lyase. We specifically tested the hypothesis that FDVE is metabolized via the beta-lyase pathway to yield 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid. Urine of rats administered FDVE (0.3 mmol/kg) was extracted and derivatized with diazomethane. Headspace GC/MS analysis demonstrated a peak whose retention time and mass spectrum were identical to those of synthetic methyl 3,3,3-trifluoro-2-(fluoromethoxy)-propanoate. Pretreatment of rats with (aminooxy)acetic acid significantly decreased the amount of 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid detected in the urine of FDVE-treated animals. The 19F NMR spectrum of urine from rats administered FDVE was consistent with the formation of 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid, but could not be differentiated from that of FDVE mercapturates, which are also excreted in urine. These results suggest that FDVE undergoes biotransformation via the beta-lyase pathway and beta-lyase-catalyzed metabolism may mediate the nephrotoxicity of this compound.