Inhibition of neuronal nitric oxide synthase activity by N1-acetyl-5-methoxykynuramine, a brain metabolite of melatonin.
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.
León
Josefa
J
Departamento de Fisiología, Instituto de Biotecnología, Universidad de Granada, Granada, Spain.
Escames
Germaine
G
Rodríguez
María I
MI
López
Luis C
LC
Tapias
Víctor
V
Entrena
Antonio
A
Camacho
Encarnación
E
Carrión
María D
MD
Gallo
Miguel A
MA
Espinosa
Antonio
A
Tan
Dun-Xian
DX
Reiter
Russel J
RJ
Acuña-Castroviejo
Darío
D
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
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