Characterization of thioether compounds formed from alkaline degradation products of enflurane

Background: Renal toxicity has occasionally been observed after enflurane a nesthesia. Although originally attributed to its oxidative metabolism to in organic fluoride, serum levels of inorganic fluoride appear to be small to explain these renal effects. Formation of potentially nephrotoxic halogenat ed alkenes during alkaline degradation in carbon dioxide absorbers and subs equent bioactivation via the glutathione conjugation pathway may be conside red as an alternative mechanism for renal toxicity. The aim of this study w as to characterize the thioethers formed chemically and biosynthetically. Methods: Alkaline degradation of enflurane was achieved by stirring with pu lverized potassium hydroxide. Volatile degradation products were analyzed b y F-19 nuclear magnetic resonance (NMR) analysis of head space gasses trapp ed in dimethyl sulfoxide (DMSO). Thioethers were generated chemically by tr apping head space gasses in DMSO containing N-acetyl-L-cysteine or 2-mercap toacetic acid as model thiol compounds. Glutathione conjugates were generat ed biosynthetically by passing head space through rat liver fractions in pr esence of glutathione. Products formed were analyzed by gas chromatography- mass spectroscopy and F-19-NMR. Results: Direct analysis of head space gasses showed formation of 1-chloro- 1,2-difluorovinyl difluoromethyl ether and two unidentified fluorine-contai ning products as alkaline degradation products of enflurane. When trapped i n DMSO-N-acetyl-L-cysteine-triethylamine, N-acetyl-S-(2-chloro-1,2-difluoro -1-(difluoromethoxy)ethyl)-L-cysteine was identified as the major product. Another N-acetyl-L-cysteine S-conjugate formed was N-acetyl-S-(2-chloro-1,1 ,2-trifluoroethyl;a potent nephrotoxin in rats. F-19-NMR analysis of glutat hione conjugates formed after incubation with rat liver fractions resulted in formation of corresponding S-conjugates. Conclusions: The current study demonstrates that alkaline degradation produ cts of enflurane can be conjugated to thiol compounds, forming S-conjugates that could theoretically contribute to adverse renal effects observed occa sionally with enflurane anesthesia. The N-acetyl-L-cysteine S-conjugates id entified may be biomarkers to assess exposure of humans to alkaline degrada tion products of enflurane.