title: Inhibition of neuronal nitric oxide synthase activity by N1-acetyl-5-methoxykynuramine, a brain metabolite of melatonin.
abstract: We assessed the effects of melatonin, N(1)-acetyl-N (2)-formyl-5-methoxykynuramine (AFMK) and N(1)-acetyl-5-methoxykynuramine (AMK) on neuronal nitric oxide synthase (nNOS) activity in vitro and in rat striatum in vivo. Melatonin and AMK (10(-11)-10(-3) m), but not AFMK, inhibited nNOS activity in vitro in a dose-response manner. The IC(50) value for AMK (70 microm) was significantly lower than for melatonin (>1 mm). A 20% nNOS inhibition was reached with either 10(-9) m melatonin or 10(-11) m AMK. AMK inhibits nNOS by a non-competitive mechanism through its binding to Ca(2+)-calmodulin (CaCaM). The inhibition of nNOS elicited by melatonin, but not by AMK, was blocked with 0.05 mm norharmane, an indoleamine-2,3-dioxygenase inhibitor. In vivo, the potency of AMK to inhibit nNOS activity was higher than that of melatonin, as a 25% reduction in rat striatal nNOS activity was found after the administration of either 10 mg/kg of AMK or 20 mg/kg of melatonin. Also, in vivo, the administration of norharmane blocked the inhibition of nNOS produced by melatonin administration, but not the inhibition produced by AMK. These data reveal that AMK rather than melatonin is the active metabolite against nNOS, which may be inhibited by physiological levels of AMK in the rat striatum.
authors.affiliation: Departamento de Fisiología, Instituto de Biotecnología, Universidad de Granada, Granada, Spain.
authors.forename: Josefa
authors.initials: J
authors.lastname: León
authors.forename: Germaine
authors.initials: G
authors.lastname: Escames
authors.forename: María I
authors.initials: MI
authors.lastname: Rodríguez
authors.forename: Luis C
authors.initials: LC
authors.lastname: López
authors.forename: Víctor
authors.initials: V
authors.lastname: Tapias
authors.forename: Antonio
authors.initials: A
authors.lastname: Entrena
authors.forename: Encarnación
authors.initials: E
authors.lastname: Camacho
authors.forename: María D
authors.initials: MD
authors.lastname: Carrión
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Gallo
authors.forename: Antonio
authors.initials: A
authors.lastname: Espinosa
authors.forename: Dun-Xian
authors.initials: DX
authors.lastname: Tan
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
authors.forename: Darío
authors.initials: D
authors.lastname: Acuña-Castroviejo
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002243:Carbolines; D003342:Corpus Striatum / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006247:Harmine / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D007735:Kynuramine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002243:Carbolines; D004791:Enzyme Inhibitors; D007735:Kynuramine; D006247:Harmine; C041550:N-acetyl-N-formyl-5-methoxykynurenamine; C032131:N-acetyl-5-methoxy kynurenamine; C010262:norharman; D052248:Nitric Oxide Synthase Type I; D008550:Melatonin