title: Inhibition of creatine kinase activity from rat cerebral cortex by 3-hydroxykynurenine.
abstract: 3-hydroxykynurenine, a tryptophan metabolite, is known to be potential neurotoxic in some neurodegenerative disorders. However, the molecular mechanisms of toxicity are not well understood. Creatine kinase plays a key role in energy metabolism of tissues with intermittently high and fluctuating energy requirements, such as nervous tissue. This study investigated the in vitro effect of 3-hydroxykynurenine on creatine kinase activity in the brain cortex of rats. The results indicated that low micromolar 3-hydroxykynurenine concentrations inhibit uncompetitively mitochondrial and cytosolic creatine kinase activities in a time and dose-dependent way. Inhibition was prevented, but not reversed by incubation with reduced glutathione, dithiothreitol and ascorbic acid plus trolox, suggesting adduct formation. The assay under nitrogen atmosphere suggested that the inhibition was caused by products of 3-hydroxykynurenine autoxidation. Determination of thiol groups suggested that adducts between the enzyme and autoxidation products of 3-hydroxykynurenine were not formed with sulfhydryl groups. The interaction plot between tryptophan and 3-hydroxykynurenine suggested different sites of action on creatine kinase with cross-inhibition. Considering the importance of creatine kinase for the maintenance of energy homeostasis in the brain, it is conceivable that an alteration of this enzyme activity may be one of the mechanisms by which 3-hydroxykynurenine might be neurotoxic.
authors.affiliation: Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, UFRGS, Rua Ramiro Barcelos 2600, CEP 90.035-003, Porto Alegre, RS, Brazil.
authors.forename: Andrea Renata
authors.initials: AR
authors.lastname: Cornelio
authors.forename: Valnês da Silva
authors.initials: Vda S
authors.lastname: Rodrigues-Junior
authors.forename: Virginia Cielo
authors.initials: VC
authors.lastname: Rech
authors.forename: Angela Terezinha
authors.initials: AT
authors.lastname: de Souza Wyse
authors.forename: Carlos Severo
authors.initials: CS
authors.lastname: Dutra-Filho
authors.forename: Moacir
authors.initials: M
authors.lastname: Wajner
authors.forename: Clovis Milton Duval
authors.initials: CM
authors.lastname: Wannmacher
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D002540:Cerebral Cortex / Q000187:drug effects* / Q000648:ultrastructure; D003402:Creatine Kinase / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D066298:In Vitro Techniques; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism
chemical_list: D013438:Sulfhydryl Compounds; C005045:3-hydroxykynurenine; D007737:Kynurenine; D014364:Tryptophan; D003402:Creatine Kinase