Kharasch E D, Jubert C, Spracklin D K, Hoffman G M
Department of Anesthesiology, University of Washington, Seattle, Washington 98195, USA.
Toxicol Appl Pharmacol. 1999 Oct 1;160(1):49-59. doi: 10.1006/taap.1999.8751.
The volatile anesthetic sevoflurane is degraded in anesthesia machines to fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (FDVE), to which humans are exposed. FDVE is metabolized in rats and humans to two alkane and two alkene glutathione S-conjugates that are hydrolyzed to the corresponding cysteine S-conjugates. The latter are N-acetylated to mercapturic acids, or bioactivated by renal cysteine conjugate beta-lyase to metabolites which may react with cellular macromolecules or hydrolyze to 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid. FDVE causes nephrotoxicity in rats, which evidence suggests is mediated by renal uptake of FDVE S-conjugates and metabolism by beta-lyase. Although pathways of FDVE metabolism have been described qualitatively, the purpose of this investigation was to quantify FDVE metabolism via mercapturic acid and beta-lyase pathways. Fischer 344 rats underwent 3-h nose-only exposure to FDVE (0 +/- 0, 46 +/- 19, 98 +/- 7, 150 +/- 29, and 220 +/- 40 ppm), and urine was collected for 24 h. Urine concentrations of the mercapturates, N-acetyl-S-(1,1,3,3, 3-pentafluoro-2-fluoromethoxypropyl)-L-cysteine and N-acetyl-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl)vinyl)-L- cysteine, the beta-lyase-dependent metabolite 3,3, 3-trifluoro-2-(fluoromethoxy)propanoic acid, and its degradation product trifluorolactic acid, were determined by GC/MS. There was dose-dependent urinary excretion of the alkane mercapturate N-acetyl-S-(1,1,3,3,3-pentafluoro-2-fluoromethoxypropyl)-L- cysteine and 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid, while excretion of the alkene mercapturate N-acetyl-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl)vinyl)-L- cysteine plateaued at higher FDVE exposures. The alkane:alkene mercapturic acid excretion ratio was between 2:1 and 4:1. Trifluorolactic acid was only rarely observed. Urine excretion of the beta-lyase-dependent metabolite 3,3, 3-trifluoro-2-(fluoromethoxy)propanoic acid was 10-fold greater than that of the combined mercapturates. Results show that FDVE cysteine S-conjugates undergo facile metabolism via renal beta-lyase, particularly in comparison with detoxication by mercapturic acid formation. The quantitative assay developed herein may provide a biomarker for FDVE exposure and relative metabolism via toxification and detoxifying pathways, applicable to animal and human investigations.
挥发性麻醉剂七氟醚在麻醉机中会降解为氟甲基 - 2,2 - 二氟 - 1 -（三氟甲基）乙烯基醚（FDVE），人类会接触到这种物质。FDVE在大鼠和人类体内会代谢为两种烷烃和两种烯烃谷胱甘肽S - 共轭物，这些共轭物会水解为相应的半胱氨酸S - 共轭物。后者会N - 乙酰化生成硫醚氨酸，或者通过肾半胱氨酸共轭物β - 裂解酶生物活化生成可能与细胞大分子反应或水解为3,3,3 - 三氟 - 2 -（氟甲氧基）丙酸的代谢物。FDVE会导致大鼠肾毒性，有证据表明这是由肾摄取FDVE S - 共轭物以及β - 裂解酶的代谢介导的。尽管已经定性描述了FDVE的代谢途径，但本研究的目的是通过硫醚氨酸和β - 裂解酶途径对FDVE的代谢进行定量。将Fischer 344大鼠仅经鼻暴露于FDVE 3小时（0±0、46±19、98±7、150±29和220±40 ppm），并收集24小时尿液。通过气相色谱/质谱法测定尿液中硫醚氨酸、N - 乙酰 - S -（1,1,3,3,3 - 五氟 - 2 - 氟甲氧基丙基）- L - 半胱氨酸和N - 乙酰 - S -（1 - 氟 - 2 - 氟甲氧基 - 2 -（三氟甲基）乙烯基）- L - 半胱氨酸的浓度，β - 裂解酶依赖性代谢物3,3,3 - 三氟 - 2 -（氟甲氧基）丙酸及其降解产物三氟乳酸的浓度。烷烃硫醚氨酸N - 乙酰 - S -（1,1,3,3,3 - 五氟 - 2 - 氟甲氧基丙基）- L - 半胱氨酸和3,3,3 - 三氟 - 2 -（氟甲氧基）丙酸的尿排泄呈剂量依赖性，而烯烃硫醚氨酸N - 乙酰 - S -（1 - 氟 - 2 - 氟甲氧基 - 2 -（三氟甲基）乙烯基）- L - 半胱氨酸的排泄在较高的FDVE暴露水平时趋于平稳。烷烃：烯烃硫醚氨酸排泄率在2:1至4:1之间。仅很少观察到三氟乳酸。β - 裂解酶依赖性代谢物3,3,3 - 三氟 - 2 -（氟甲氧基）丙酸的尿排泄量比硫醚氨酸总量大10倍。结果表明，FDVE半胱氨酸S - 共轭物通过肾β - 裂解酶易于代谢，特别是与通过形成硫醚氨酸进行解毒相比。本文开发的定量测定方法可能为FDVE暴露以及通过毒性和解毒途径的相对代谢提供一种生物标志物，适用于动物和人类研究。
