title: Controversial alkoxyl and peroxyl radical scavenging activity of the tryptophan metabolite 3-hydroxy-anthranilic acid.
abstract: 3-Hydroxy-anthranilic acid (3-OHAA), a tryptophan metabolite produced in the kynurenine pathway, is an efficient antioxidant towards peroxyl radicals (ROO) derived from the AAPH (2,2'-azobis(2-amidinopropane) dihydrochloride) thermolysis. However, self-reactions of ROO can give rise to alkoxyl radicals (RO), which could strongly affect the fate of scavenging reactions. In the present work, we studied the influence of RO in the scavenging activity of 3-OHAA in three different systems: i) Monitoring of the direct reaction between 3-OHAA and AAPH-derived free radicals (kinetic studies); ii) Evaluation of the protective effect of 3-OHAA on the AAPH-induced consumption of fluorescein; and, iii) Inhibition, given by 3-OHAA, of the AAPH-initiated lipid peroxidation of both, rat brain synaptosomes and homogenate preparations (assessed by chemiluminescence). For such purposes, the fraction of free radicals (f) trapped per 3-OHAA molecule was determined in each system. Kinetic results show that the oxidation of 3-OHAA follows a process dominated by ROO with a zero order kinetic limit in 3-OHAA, and a fraction (fri) equal to 0.88. From the induction times, elicited by 3-OHAA in the kinetic profiles of fluorescein consumption, a fraction (fT) of 0.28 was determined. 3-OHAA also generated induction times in the kinetic profiles of light emission during the AAPH-initiated lipid peroxidation of rat brain synaptosomes and homogenates. From such induction times, fractions of 0.61 and 0.63 were determined for rat brain synaptosomes (fsyn) and homogenates (fhom), respectively. These results show that during the incubation of 3-OHAA and AAPH, a low fraction of ROO self-reacts to generate RO. Nevertheless, when 3-OHAA is employed to protect particular targets, such as fluorescein, rat brain synaptosomes and homogenates, reactions of ROO and/or RO should be considered.
authors.affiliation: Departamento de Química Física, Pontificia Universidad Católica de Chile, C.P. 782 0436, Santiago, Chile.
authors.forename: E
authors.initials: E
authors.lastname: Dorta
authors.affiliation: Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Correo 33, Santiago, Chile.
authors.forename: A
authors.initials: A
authors.lastname: Aspée
authors.affiliation: Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Correo 33, Santiago, Chile.
authors.forename: E
authors.initials: E
authors.lastname: Pino
authors.affiliation: Departamento de Farmacología, Instituto de Neurociencias, Facultad de Medicina, Universidad de Granada, Avenida de la Investigación 11, E-18016 Granada, Spain.
authors.forename: L
authors.initials: L
authors.lastname: González
authors.affiliation: Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Correo 33, Santiago, Chile.
authors.forename: E
authors.initials: E
authors.lastname: Lissi
authors.affiliation: Departamento de Química Física, Pontificia Universidad Católica de Chile, C.P. 782 0436, Santiago, Chile. Electronic address: clopezr@uc.cl.
authors.forename: C
authors.initials: C
authors.lastname: López-Alarcón
mesh_terms: D000438:Alcohols / Q000378:metabolism; D000578:Amidines / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology*; D005609:Free Radicals / Q000378:metabolism*; D007700:Kinetics; D015227:Lipid Peroxidation / Q000187:drug effects; D051379:Mice; D010084:Oxidation-Reduction / Q000187:drug effects; D010545:Peroxides / Q000378:metabolism*; D051381:Rats; D014364:Tryptophan / Q000494:pharmacology*; D062367:ortho-Aminobenzoates / Q000494:pharmacology*
chemical_list: D000438:Alcohols; D000578:Amidines; D000975:Antioxidants; D016166:Free Radical Scavengers; D005609:Free Radicals; D010545:Peroxides; C059688:alkoxyl radical; D062367:ortho-Aminobenzoates; C031385:anthranilic acid; C049375:perhydroxyl radical; C046728:2,2'-azobis(2-amidinopropane); D014364:Tryptophan
keywords: 3-Hydroxy-anthranilic acid; Alkoxyl radicals; ORAC; Peroxyl radicals; Rat brain homogenates; Rat brain synaptosomes