title: On the antioxidant properties of kynurenic acid: free radical scavenging activity and inhibition of oxidative stress.
abstract: Kynurenic acid (KYNA) is an endogenous metabolite of the kynurenine pathway for tryptophan degradation and an antagonist of both N-methyl-D-aspartate (NMDA) and alpha-7 nicotinic acetylcholine (α7nACh) receptors. KYNA has also been shown to scavenge hydroxyl radicals (OH) under controlled conditions of free radical production. In this work we evaluated the ability of KYNA to scavenge superoxide anion (O(2)(-)) and peroxynitrite (ONOO(-)). The scavenging ability of KYNA (expressed as IC(50) values) was as follows: OH=O(2)(-)>ONOO(-). In parallel, the antiperoxidative and scavenging capacities of KYNA (0-150 μM) were tested in cerebellum and forebrain homogenates exposed to 5 μM FeSO(4) and 2.5 mM 3-nitropropionic acid (3-NPA). Both FeSO(4) and 3-NPA increased lipid peroxidation (LP) and ROS formation in a significant manner in these preparations, whereas KYNA significantly reduced these markers. Reactive oxygen species (ROS) formation were determined in the presence of FeSO(4) and/or KYNA (0-100 μM), both at intra and extracellular levels. An increase in ROS formation was induced by FeSO(4) in forebrain and cerebellum in a time-dependent manner, and KYNA reduced this effect in a concentration-dependent manner. To further know whether the effect of KYNA on oxidative stress is independent of NMDA and nicotinic receptors, we also tested KYNA (0-100 μM) in a biological preparation free of these receptors - defolliculated Xenopus laevis oocytes - incubated with FeSO(4) for 1 h. A 3-fold increase in LP and a 2-fold increase in ROS formation were seen after exposure to FeSO(4), whereas KYNA attenuated these effects in a concentration-dependent manner. In addition, the in vivo formation of OH evoked by an acute infusion of FeSO(4) (100 μM) in the rat striatum was estimated by microdialysis and challenged by a topic infusion of KYNA (1 μM). FeSO(4) increased the striatal OH production, while KYNA mitigated this effect. Altogether, these data strongly suggest that KYNA, in addition to be a well-known antagonist acting on nicotinic and NMDA receptors, can be considered as a potential endogenous antioxidant.
authors.affiliation: Laboratorio de Aminoácidos Excitadores, Instituto Nacional de Neurología y Neurocirugía Manuel Velasco Suárez, S.S.A., Mexico D.F. 14269, Mexico.
authors.forename: R
authors.initials: R
authors.lastname: Lugo-Huitrón
authors.forename: T
authors.initials: T
authors.lastname: Blanco-Ayala
authors.forename: P
authors.initials: P
authors.lastname: Ugalde-Muñiz
authors.forename: P
authors.initials: P
authors.lastname: Carrillo-Mora
authors.forename: J
authors.initials: J
authors.lastname: Pedraza-Chaverrí
authors.forename: D
authors.initials: D
authors.lastname: Silva-Adaya
authors.forename: P D
authors.initials: PD
authors.lastname: Maldonado
authors.forename: I
authors.initials: I
authors.lastname: Torres
authors.forename: E
authors.initials: E
authors.lastname: Pinzón
authors.forename: E
authors.initials: E
authors.lastname: Ortiz-Islas
authors.forename: T
authors.initials: T
authors.lastname: López
authors.forename: E
authors.initials: E
authors.lastname: García
authors.forename: B
authors.initials: B
authors.lastname: Pineda
authors.forename: M
authors.initials: M
authors.lastname: Torres-Ramos
authors.forename: A
authors.initials: A
authors.lastname: Santamaría
authors.forename: V Pérez-De
authors.initials: VP
authors.lastname: La Cruz
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage / Q000494:pharmacology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005296:Ferrous Compounds / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology*; D006878:Hydroxides / Q000378:metabolism; D007736:Kynurenic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008845:Microinjections; D009574:Nitro Compounds / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D011422:Propionates / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016548:Prosencephalon / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D000975:Antioxidants; D005296:Ferrous Compounds; D016166:Free Radical Scavengers; D006878:Hydroxides; D009574:Nitro Compounds; D011422:Propionates; D017382:Reactive Oxygen Species; C020748:ferrous sulfate; D007736:Kynurenic Acid; C015392:3-nitropropionic acid