title: Oxidative metabolites of 5-S-cysteinyldopamine inhibit the alpha-ketoglutarate dehydrogenase complex: possible relevance to the pathogenesis of Parkinson's disease.
abstract: A characteristic change in the substantia nigra of Parkinson's disease patients is an apparent accelerated rate of dopamine oxidation as evidenced by an increased 5-S-cysteinyldopamine (5-S-CyS-DA) to dopamine ratio. However, 5-S-CyS-DA is more easily oxidized than dopamine to give 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxylic acid (DHBT-1). Previous studies have demonstrated that DHBT-1 can be accumulated by intact rat brain mitochondria and inhibits complex I but not complex II respiration. In this study, it is shown that DHBT-1 also inhibits the alpha-ketoglutarate dehydrogenase complex (alpha-KGDH) but not cytochrome c oxidase (complex IV). The inhibition of alpha-KGDH is dependent on the oxidation of DHBT-1, catalyzed by an unknown constituent of the inner mitochondrial membrane, to an electrophilic o-quinone imine that covalently modifies active site sulfhydryl residues. The latter conclusion is based on the ability of > or = equimolar glutathione to block the inhibition of alpha-KGDH by DHBT-1, without altering its rate of mitochondrial membrane-catalyzed oxidation, by scavenging the electrophilic o-quinone intermediate forming glutathionyl conjugates which have been isolated and spectroscopically characterized. Activities of mitochondrial alpha-KGDH and complex I, but not other respiratory complexes, are decreased in the parkinsonian substantia nigra. Such changes together with evidence for accelerated dopamine oxidation, increased formation of 5-S-CyS-DA and the ease of oxidation of this conjugate to DHBT-1 which inhibits alpha-KGDH and complex I, without affecting other respiratory enzyme complexes, suggests that the latter putative metabolite might be an endotoxin that contributes to the alpha-KGDH and complex I defects in Parkinson's disease.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, Norman 73019, USA.
authors.forename: X M
authors.initials: XM
authors.lastname: Shen
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: G
authors.initials: G
authors.lastname: Dryhurst
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001921:Brain / Q000201:enzymology*; D002374:Catalase / Q000378:metabolism; D004298:Dopamine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007425:Intracellular Membranes / Q000201:enzymology; D007655:Ketoglutarate Dehydrogenase Complex / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D010084:Oxidation-Reduction; D010300:Parkinson Disease / Q000209:etiology* / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013482:Superoxide Dismutase / Q000378:metabolism; D013843:Thiazines / Q000378:metabolism / Q000494:pharmacology
chemical_list: C108502:7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxylic acid; D000975:Antioxidants; D004791:Enzyme Inhibitors; D013843:Thiazines; C047408:5-S-cysteinyldopamine; D002374:Catalase; D011451:Prostaglandin-Endoperoxide Synthases; D013482:Superoxide Dismutase; D007655:Ketoglutarate Dehydrogenase Complex; D003576:Electron Transport Complex IV; D004298:Dopamine