Inhibition of creatine kinase activity from rat cerebral cortex by 3-hydroxykynurenine.
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.
Cornelio
Andrea Renata
AR
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, UFRGS, Rua Ramiro Barcelos 2600, CEP 90.035-003, Porto Alegre, RS, Brazil.
Rodrigues-Junior
Valnês da Silva
Vda S
Rech
Virginia Cielo
VC
de Souza Wyse
Angela Terezinha
AT
Dutra-Filho
Carlos Severo
CS
Wajner
Moacir
M
Wannmacher
Clovis Milton Duval
CM
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
D013438:Sulfhydryl Compounds; C005045:3-hydroxykynurenine; D007737:Kynurenine; D014364:Tryptophan; D003402:Creatine Kinase