Nω-Nitro-L-Arginine, a Nitric Oxide Synthase Inhibitor, Antagonizes Quinolinic Acid-Induced Neurotoxicity and Oxidative Stress in Rat Striatal Slices

Nitric oxide (NO) is a potential contributor to neurotoxicity following overactivation of N-methyl-D-aspartate (NMDA) receptors. In this work we investigated the effect of Nω-nitro-L-arginine (L-NARG 25, 50, or 100 μM), a selective inhibitor of nitric oxide synthase (NOS) -the synthetic enzyme of NO- on quinolinic acid (QUIN 100 μM)-induced neurotoxicity (measured as lactate dehydrogenase (LDH) leakage) in rat striatal slices. Oxidative stress was also measured both as lipid peroxidation and as the levels of reduced (GSH) and oxidized (GSSG) glutathione, in an effort to elucidate a possible participation of NO in the toxic mechanisms involved in NMDA receptor-mediated neuronal injury. The action of L-arginine (L-ARG 100 or 200 μM), a well-known NO precursor, was also tested on QUIN-induced neurotoxicity and oxidative stress. Results showed that QUIN produced significant changes in both cell damage (177%) and oxidative injury (203% in lipid peroxidation, 68% in GSH, and 123% in GSSG) as compared to control values. All these effects were antagonized by adding L-NARG to the incubation media, whereas L-ARG alone, or in combination with QUIN, significantly enhanced both lipid peroxidation and LDH leakage. Moreover, the protective effects of L-NARG on QUIN-induced lipid peroxidation were reversed by addition of an excess of L-ARG to the media. These findings indicate that NO is probably mediating the mechanism of neurotoxicity produced by QUIN, which may be of potential value to explain the molecular basis of neurodegenerative processes linked to QUIN-mediated NMDA receptor overactivation.