title: Tyrosine promotes oxidative stress in cerebral cortex of young rats.
abstract: Tyrosine accumulates in inborn errors of tyrosine catabolism, especially in tyrosinemia type II, where tyrosine levels are highly elevated in tissues and physiological fluids of affected patients. In tyrosinemia type II, high levels of tyrosine are correlated with eyes, skin and central nervous system disturbances. Considering that the mechanisms of brain damage in these disorders are poorly known, in the present study, we investigated whether oxidative stress is elicited by l-tyrosine in cerebral cortex homogenates of 14-day-old Wistar rats. The in vitro effect of 0.1-4.0mM l-tyrosine was studied on the following oxidative stress parameters: total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR), ascorbic acid content, reduced glutathione (GSH) content, spontaneous chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), thiol-disulfide redox state (SH/SS ratio), protein carbonyl content, formation of DNA-protein cross-links, and the activities of the enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glucose-6-phosphate dehydrogenase (G6PDH). TRAP, TAR, ascorbic acid content, SH/SS ratio and CAT activity were significantly diminished, while formation of DNA-protein cross-link was significantly enhanced by l-tyrosine in vitro. In contrast, l-tyrosine did not affect the other parameters of oxidative stress evaluated. These results indicate that l-tyrosine decreases enzymatic and non-enzymatic antioxidant defenses, changes the redox state and stimulates DNA damage in cerebral cortex of young rats in vitro. This suggests that oxidative stress may represent a pathophysiological mechanism in tyrosinemic patients, in which this amino acid accumulates.
authors.affiliation: Programa de Pós-Graduação em Ciências Biológicas: Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil.
authors.forename: Angela M
authors.initials: AM
authors.lastname: Sgaravatti
authors.forename: Bethânia A
authors.initials: BA
authors.lastname: Vargas
authors.forename: Bernardo R
authors.initials: BR
authors.lastname: Zandoná
authors.forename: Kátia B
authors.initials: KB
authors.lastname: Deckmann
authors.forename: Francieli J
authors.initials: FJ
authors.lastname: Rockenbach
authors.forename: Tarsila B
authors.initials: TB
authors.lastname: Moraes
authors.forename: José M
authors.initials: JM
authors.lastname: Monserrat
authors.forename: Mirian B
authors.initials: MB
authors.lastname: Sgarbi
authors.forename: Carolina D
authors.initials: CD
authors.lastname: Pederzolli
authors.forename: Angela T S
authors.initials: AT
authors.lastname: Wyse
authors.forename: Clóvis M D
authors.initials: CM
authors.lastname: Wannmacher
authors.forename: Moacir
authors.initials: M
authors.lastname: Wajner
authors.forename: Carlos Severo
authors.initials: CS
authors.lastname: Dutra-Filho
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D000975:Antioxidants / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism; D002374:Catalase; D002540:Cerebral Cortex / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances; D014443:Tyrosine / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D013438:Sulfhydryl Compounds; D017392:Thiobarbituric Acid Reactive Substances; D014443:Tyrosine; D005954:Glucosephosphate Dehydrogenase; D002374:Catalase; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D005978:Glutathione; D001205:Ascorbic Acid