Cysteine conjugate beta-lyase-dependent biotransformation of the cysteine S-conjugates of the sevoflurane degradation product 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A).
2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (1, Compound A) is a fluoroalkene formed by the base-catalyzed degradation of sevoflurane that is nephrotoxic in rats. Fluoroalkene 1 is a structural analog of other nephrotoxic haloalkenes that undergo glutathione S-conjugate formation and cysteine S-conjugate beta-lyase-dependent bioactivation to reactive intermediates. The present experiments were designed to study the beta-lyase-dependent biotransformation of S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-L-cysteine (4) and S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-L-cysteine (5) by 19F NMR and UV spectroscopy and GC/MS. Incubation of cysteine S-conjugate 4 with rat kidney cytosol or a pyridoxal model system showed the formation of inorganic fluoride, pyruvate, and 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid (9), the expected products of a beta-lyase-catalyzed reaction. The ratio of fluoride to pyruvate ranged from 2.3 to 2.5. The amount of acid 9 formed in the rat kidney cytosol and the pyridoxal model system was, however, less than 5% of the amount of pyruvate formed. Incubation of conjugate 4 with rat kidney cytosol and analysis by 19F NMR spectroscopy showed resonances that were assigned to 3,3,3-trifluorolactic acid (10); the formation of acid 10 was observed in the pyridoxal model only after prolonged incubation (> 18 h). Lactic acid 10 was identified as a degradation product of acid 9. Cysteine S-conjugate 5 was not stable in pH 7.4 buffer and underwent a rapid cyclisation reaction (t1/2 approximately 5 min) to form 2-[1-(fluoromethoxy)-2,2,2-trifluoroethyl]-4,5-dihydro-1,3-thiazol e-4 -carboxylic acid (14). These data show that fluoroalkene 1-derived cysteine S-conjugates are substrates for renal beta-lyase and that acid 9 is formed as a terminal product. Acid 9 is, however, unstable and affords lactic acid 10 as a degradation product.
Iyer
R A
RA
Department of Pharmacology and Physiology, University of Rochester, New York 14642, USA.
Anders
M W
MW
D018685:Anesthetics, Inhalation / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001711:Biotransformation; D013437:Carbon-Sulfur Lyases; D003545:Cysteine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D004987:Ethers / Q000737:chemistry* / Q000378:metabolism; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry* / Q000378:metabolism; D066298:In Vitro Techniques; D007668:Kidney / Q000201:enzymology / Q000378:metabolism; D008190:Lyases / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008738:Methyl Ethers; D051381:Rats; D011916:Rats, Inbred F344; D000077149:Sevoflurane; D013056:Spectrophotometry, Ultraviolet
D018685:Anesthetics, Inhalation; D004987:Ethers; D006845:Hydrocarbons, Fluorinated; D008738:Methyl Ethers; D000077149:Sevoflurane; C078742:fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase; D003545:Cysteine