title: Evaluation of the mechanisms involved in leucine-induced oxidative damage in cerebral cortex of young rats.
abstract: Maple syrup urine disease (MSUD) is a metabolic disorder caused by the deficiency of the activity of the mitochondrial enzyme complex branched-chain L-2-keto acid dehydrogenase. The metabolic block results in tissue and body fluid accumulation of the branched-chain amino acids leucine (Leu), isoleucine and valine, as well as of their respective alpha-keto acids. Neurological sequelae are usually present in MSUD, but the pathophysiologic mechanisms of neurotoxicity are still poorly known. It was previously demonstrated that Leu elicits oxidative stress in rat brain. In the present study we investigated the possible mechanisms involved in Leu-induced oxidative damage. We observed a significant attenuation of Leu-elicited increase of thiobarbituric acid-reactive substances (TBA-RS) measurement when cortical homogenates were incubated in the presence of the free radical scavengers ascorbic acid plus trolox, dithiothreitol, glutathione, and superoxide dismutase, suggesting a probable involvement of superoxide and hydroxyl radicals in this effect. In contrast, the use of Nomega-nitro-L-arginine methyl ester or catalase (CAT) did not affect TBA-RS values. We also demonstrated an inhibitory effect of Leu on the activities of the antioxidant enzymes CAT and gluthathione peroxidase, as well as a significant reduction in the membrane-protein thiol content from mitochondrial enriched preparations. Furthermore, dichlorofluorescein levels were increased although not significantly by Leu. Taken together, our present data indicate that an unbalance between free radical formation and inhibition of critical enzyme activities may explain the mechanisms involved in the Leu-induced oxidative damage.
authors.affiliation: Departamento de Bioquimica, Instituto de Ciências Báisicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2600 Anexo, CEP 90035-003, Porto, Alegre RS, Brazil.
authors.forename: Raquel
authors.initials: R
authors.lastname: Bridi
authors.forename: Alexandra
authors.initials: A
authors.lastname: Latini
authors.forename: Cesar A
authors.initials: CA
authors.lastname: Braum
authors.forename: Giovanni K
authors.initials: GK
authors.lastname: Zorzi
authors.forename: Wajner
authors.initials: W
authors.lastname: Moacir
authors.forename: Eduardo
authors.initials: E
authors.lastname: Lissi
authors.forename: Carlos Severo
authors.initials: CS
authors.lastname: Dutra-Filho
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002374:Catalase / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism* / Q000473:pathology*; D002839:Chromans / Q000494:pharmacology; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005452:Fluoresceins / Q000494:pharmacology; D005609:Free Radicals; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007532:Isoleucine / Q000737:chemistry; D007930:Leucine / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D008375:Maple Syrup Urine Disease / Q000652:urine; D008928:Mitochondria / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species; D013482:Superoxide Dismutase / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances; D014633:Valine / Q000737:chemistry
chemical_list: D000975:Antioxidants; D002839:Chromans; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D005609:Free Radicals; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; D007532:Isoleucine; C037631:2',7'-dichlorofluorescein; D002374:Catalase; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D005978:Glutathione; D007930:Leucine; D014633:Valine; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D010100:Oxygen; D019331:NG-Nitroarginine Methyl Ester