title: Medium-chain acyl-CoA dehydrogenase- and enoyl-CoA hydratase-dependent bioactivation of 5,6-dichloro-4-thia-5-hexenoyl-CoA.
abstract: 5,6-Dichloro-4-thia-5-hexenoic acid (DCTH) is a potent hepato- and nephrotoxin that induces mitochondrial dysfunction in rat liver and kidney. Previous studies indicate that DCTH undergoes fatty acid beta-oxidation-dependent bioactivation. The objectives of the present experiments were to elaborate the bioactivation mechanism of DCTH and to examine the interaction of the coenzyme A thioester of DCTH (DCTH-CoA) with the medium-chain acyl-CoA dehydrogenase. In the presence of the terminal electron acceptor ferricenium hexafluorophosphate (FcPF6), DCTH-CoA was oxidized by the medium-chain actyl-CoA dehydrogenase to give 5,6-dichloro-4-thia-trans-2,5-hexadienoyl-CoA. Enoyl-CoA hydratase catalyzed the conversion of 5,6-dichloro-4-thia-trans-2,5-hexadienoyl-CoA to 5,6-dichloro-4-thia-3-hydroxy-5-hexenoyl-CoA, which eliminated 1,2-dichloroethenethiol and gave malonyl-CoA semialdehyde as a product. Chloroacetic acid was detected as a terminal product derived from 1,2-dichloroethenethiol. Incubation of DCTH-CoA with the medium-chain acyl-CoA dehydrogenase in the absence of FcPF6 gave 3-hydroxypropionyl-CoA as the major product and resulted in the irreversible inactivation of the enzyme. Under these conditions, DCTH-CoA apparently undergoes a beta-elimination reaction to give 1,2-dichloroethenethiol and acryloyl-CoA, which is hydrated to give 3-hydroxypropionyl-CoA as the terminal product. The beta-elimination product 1,2-dichloroethenethiol may yield reactive intermediates that inactivate the dehydrogenase. Enzyme inactivation was rapid, DCTH-CoA concentration-dependent, and blocked by octanoyl-CoA, but not by glutathione. The medium-chain acyl-CoA dehydrogenase was not inactivated by acryloyl-CoA, and little inactivation was observed in the presence of FcPF6. These results show that DCTH-CoA is bioactivated by the mitochondrial fatty acid beta-oxidation system to reactive intermediates. This bioactivation mechanism may account for the observed toxicity of DCTH in vivo and in vitro.
authors.affiliation: Department of Pharmacology, School of Medicine and Dentistry, University of Rochester, New York 14642, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Fitzsimmons
authors.forename: C
authors.initials: C
authors.lastname: Thorpe
authors.forename: M W
authors.initials: MW
authors.lastname: Anders
mesh_terms: D000085:Acetates / Q000378:metabolism; D000214:Acyl Coenzyme A / Q000378:metabolism / Q000493:pharmacokinetics*; D042964:Acyl-CoA Dehydrogenase; D044944:Acyl-CoA Dehydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D004746:Enoyl-CoA Hydratase / Q000378:metabolism*; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007668:Kidney / Q000201:enzymology; D009682:Magnetic Resonance Spectroscopy; D008316:Malonyl Coenzyme A / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013552:Swine
chemical_list: C092887:5,6-dichloro-4-thia-5-hexenoyl-coenzyme A; D000085:Acetates; D000214:Acyl Coenzyme A; D005182:Flavin-Adenine Dinucleotide; D008316:Malonyl Coenzyme A; C006972:chloroacetic acid; C017123:8-chloro-FAD; D044944:Acyl-CoA Dehydrogenases; D042964:Acyl-CoA Dehydrogenase; D004746:Enoyl-CoA Hydratase