Abstract 12185: Complete Disruption of All Nitric Oxide Synthases Markedly Reduces Cerebral Infarct Size After Middle Cerebral Artery Occlusion in Mice

Abstract

Background: The role of each nitric oxide synthase (NOS) isoform in cerebral infarction has been studied in individual NOS isoform-deficient mice. It has been reported that, in a model of middle cerebral artery occlusion (MCAO), neuronal and inducible NOSs exacerbate cerebral infarction, whereas endothelial NOS conversely alleviates it. Although the role of the whole NOSs system in cerebral infarction has been examined in pharmacological studies with non-selective NOS inhibitors, the results are quit inconsistent, possibly because of non-specificity of the agents. In this study, we addressed this point in mice in which all three NOS genes are completely disrupted. Method and Results: We newly generated triple NOSs -/- mice and wild-type littermates by crossbreeding single NOS -/- mice. Transient (1 hour) or permanent MCAO was performed in male triple NOSs -/- and wild-type mice at 8-12 weeks of age (n=8-11). There was no anatomical difference in the structure of cerebral arteries between the triple NOSs -/- and the wild-type mice. Reductions in cerebral blood flow during MCAO were also comparable between the two genotypes. However, cerebral infarct size at 24 hours after transient MCAO was markedly reduced in the triple NOSs -/- genotype as compared with the wild-type genotype ( P <0.05). Cerebral infarct size at 24 hours after permanent MCAO was also markedly smaller in the triple NOSs -/- than in the wild-type genotype ( P <0.05). In addition, neurological deficit was significantly less and the survival rate was significantly better in the triple NOSs -/- genotype compared with the wild-type genotype (each P <0.05). Importantly, 3-nitrotyrosine protein levels (a marker of peroxynitrite production) in the cerebral infarct region were significantly decreased in the triple NOSs -/- genotype as compared with the wild-type genotype ( P <0.05), suggesting an involvement of decreased oxidative stress. Conclusions: These results provide the first evidence that complete disruption of all NOS genes markedly reduces cerebral infarct size after MCAO in mice, demonstrating a novel injurious role of the entire NOSs system in the pathogenesis of cerebral infarction. Inhibition of the NOSs system may be a new therapeutic option in the treatment of cerebral infarction.