Bioactivation mechanism of L-thiomorpholine-3-carboxylic acid.
L-Thiomorpholine-3-carboxylic acid (L-TMC) is a cyclized analog of S-(2-chloroethyl)-L-cysteine, which is cytotoxic in vitro and nephrotoxic in vivo. To determine whether L-TMC may play a role in S-(2-chloroethyl)-L-cysteine-induced toxicity, the cytotoxicity of L-TMC was studied in isolated rat kidney cells. L-TMC produced time- and concentration-dependent cytotoxicity. Probenecid, an inhibitor of the renal anion transport system, and L-alpha-hydroxyisocaproic acid, a substrate for L-amino acid oxidase, inhibited L-TMC-induced cytotoxicity. Rat kidney cytosol catalyzed the metabolism of L-TMC to a product absorbing at 300 nm. The increase in absorbance at 300 nm was accompanied by an increase in oxygen consumption and was inhibited by L-alpha-hydroxyisocaproic acid; moreover, the absorbance of the metabolite was quenched by addition of potassium cyanide or sodium borohydride, which indicated the formation of an imine. When L-TMC was incubated with rat kidney cytosol and sodium borodeuteride was added at the end of the incubation period, analysis by gas chromatography/mass spectrometry of the tert-butyldimethylsilyl ester of L-TMC showed the formation of [2H]TMC, indicating the intermediate formation of the imine 5,6-dihydro-2H-1,4-thiazine-3-carboxylic acid; chemically synthesized TMC imine showed similar behavior. The enzyme responsible for the metabolism of L-TMC was purified from rat kidney and was identified as L-amino acid oxidase. These observations indicate a role for L-amino acid oxidase in the bioactivation and cytotoxicity of L-TMC.
Department of Pharmacology, University of Rochester, School of Medicine and Dentistry, New York 14642.
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D000594:Amino Acid Oxidoreductases / Q000378:metabolism; D000818:Animals; D002208:Caproates / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects*; D055598:Chemical Phenomena; D002621:Chemistry; D002853:Chromatography, Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D007098:Imino Acids / Q000378:metabolism / Q000633:toxicity*; D007668:Kidney / Q000378:metabolism; D050830:L-Amino Acid Oxidase; D008297:Male; D013058:Mass Spectrometry; D009025:Morpholines / Q000378:metabolism / Q000633:toxicity*; D011339:Probenecid / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344
D002208:Caproates; D007098:Imino Acids; D009025:Morpholines; C060165:1,4-thiomorpholine-3-carboxylic acid; C019419:alpha-hydroxyisocaproic acid; D000594:Amino Acid Oxidoreductases; D050830:L-Amino Acid Oxidase; D011339:Probenecid