N(G)-nitro-L-arginine and its methyl ester inhibit brain synthesis of kynurenic acid possibly via nitric oxide-independent mechanism.
The effect of nitric oxide synthase (NOS) inhibitors on the brain production of endogenous glutamate receptor antagonist, kynurenic acid, was estimated in vitro. Under standard incubation conditions N(G)-nitro-L-arginine, but not N(G)-nitro-L-arginine methyl ester, up to 5 mM, or 7-nitroindazole, up to 100 microM, inhibited de novo synthesis of kynurenic acid in cortical slices. However, during prolonged incubation, N(G)-nitro-L-arginine methyl ester also reduced the production of kynurenic acid. The substrate for NOS, L-arginine (up to 5 mM), did not influence kynurenic acid synthesis and did not reverse the N(G)-nitro-L-arginine-evoked changes, suggesting that the observed effects are not related to disturbed generation of NO. Enzymatic studies revealed that N(G)-nitro-L-arginine and its methyl ester blocked the activity of brain kynurenine aminotransferase (KAT) I. The activity of KAT II was diminished only by N(G)-nitro-L-arginine. Kinetic analyses have shown that N(G)-nitro-L-arginine and its methyl ester reduce Vmax and increase Km of KAT I, whereas N(G)-nitro-L-arginine diminishes Vmax of KAT II. In conclusion, we report that N(G)-nitro-L-arginine and its methyl ester impair brain synthesis of kynurenic acid, probably via NO-independent mechanism, what could contribute, at least partially, to the enhancement of neurotoxicity or seizures observed in some experimental designs based on their use.
Luchowski
P
P
Department of Pharmacology and Toxicology, Medical University, Lublin, Poland.
Kocki
T
T
Urbańska
E M
EM
D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000201:enzymology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000378:metabolism*; D066298:In Vitro Techniques; D007191:Indazoles / Q000494:pharmacology; D007700:Kinetics; D007736:Kynurenic Acid / Q000378:metabolism*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D019335:Nitroarginine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity; D000637:Transaminases / Q000037:antagonists & inhibitors
D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D007191:Indazoles; D019335:Nitroarginine; D001120:Arginine; D019001:Nitric Oxide Synthase; D000637:Transaminases; C021481:kynurenine-oxoglutarate transaminase; D007736:Kynurenic Acid; C080122:7-nitroindazole; D019331:NG-Nitroarginine Methyl Ester