title: Formation of three N-acetyl-L-cysteine monoadducts and one diadduct by the reaction of S-(1,2-dichlorovinyl)-L-cysteine sulfoxide with N-acetyl-L-cysteine at physiological conditions: chemical mechanisms and toxicological implications.
abstract: Previously, our laboratory has shown that S-(1,2-dichlorovinyl)-L-cysteine sulfoxide (DCVCS), a Michael acceptor produced by a flavin-containing monooxygenase 3 (FMO3)-mediated oxidation of S-(1,2-dichlorovinyl)-L-cysteine (DCVC), is a more potent nephrotoxicant than DCVC. In the present study, we characterized reactions of DCVCS with nucleophilic amino acids. DCVCS incubations with N-acetyl-L-cysteine (NAC) at pH 7.4 and 37 degrees C for 1 h resulted in the formation of three monoadducts and one diadduct characterized by LC/MS, 1H NMR, and 1H-detected heteronuclear single quantum correlation. The formation of all adducts (with relative ratios of 29, 31, 24, and 12%, respectively) was rapid and time-dependent; the half-lives of the two DCVCS diastereomers in the presence of NAC were 13.8 (diastereomer I) and 9.4 min (diastereomer II). Adducts 1 and 2 were determined to be diastereomers of S-[1-chloro-2-(N-acetyl-L-cystein- S-yl)vinyl]-L-cysteine sulfoxide formed by Michael addition of NAC to the terminal vinylic carbon of DCVCS followed by loss of HCl. Adduct 4 was determined to be S-[2-chloro-2-(N-acetyl-L-cystein- S-yl)vinyl]-L-cysteine sulfoxide formed from the initial Michael addition product followed by a less favorable loss of HCl and/or by a rearrangement of adduct 2 through the formation of a cyclic chloronium ion. The addition of another molecule of NAC to monoadducts 1, 2, or 4 resulted in the formation of the novel diadduct, S-[2,2-( N-acetyl-L-cystein-S-yl)vinyl]-L-cysteine sulfoxide (adduct 3), whose detection in relatively large amount suggests that DCVCS could act as a cross-linking agent. DCVCS was not reactive with N-acetyl-L-lysine or L-valinamide at similar incubation conditions. Collectively, the results suggest selective reactivity of DCVCS toward protein sulfhydryl groups. Furthermore, the cross-linking properties of DCVCS may in part explain its high nephrotoxic potency.
authors: Department of Comparative Biosciences, University of Wisconsin, Madison 53706, USA.
authors: Nella
authors: N
authors: Barshteyn
authors: Adnan A
authors: AA
authors: Elfarra
mesh_terms: D000111:Acetylcysteine / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D003545:Cysteine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D016166:Free Radical Scavengers / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D007668:Kidney / Q000187:drug effects; D007674:Kidney Diseases / Q000139:chemically induced / Q000378:metabolism; D013454:Sulfoxides / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity
chemical_list: D003432:Cross-Linking Reagents; D016166:Free Radical Scavengers; D013454:Sulfoxides; C039961:S-(1,2-dichlorovinyl)cysteine; D003545:Cysteine; D000111:Acetylcysteine