Nitric oxide synthase inhibitors in experimental ischemic stroke and their effects on infarct size and cerebral blood flow: a systematic review

Inhibition of NF-kappaB activation by 5-lipoxygenase inhibitors protects brain against injury in a rat model of focal cerebral ischemia

Background

Stroke is one of the leading causes of death worldwide and a major cause of morbidity and mortality in the United States of America. Brain ischemia-reperfusion (IR) triggers a complex series of biochemical events including inflammation. Leukotrienes derived from 5-lipoxygenase (5-LOX) cause inflammation and are thus involved in the pathobiology of stroke injury.

Methods

To test the neuroprotective efficacy of 5-LOX inhibition in a rat model of focal cerebral IR, ischemic animals were either pre- or post-treated with a potent selective 5-LOX inhibitor, (N- [3-[3-(-fluorophenoxy) phenyl]-1-methyl-2-propenyl]-N-hydroxyurea (BW-B 70C). They were evaluated at 24 h after reperfusion for brain infarction, neurological deficit score, and the expression of 5-LOX. Furthermore, the mechanism and the anti-inflammatory potential of BW-B 70C in the regulation of nuclear factor kappa B (NF-κB) and inflammatory inducible nitric oxide synthase (iNOS) were investigated both in vivo and in vitro.

Results and discussion

Both pre- and post-treatment with BW-B 70C reduced infarctions and improved neurological deficit scores. Immunohistochemical study of brain sections showed IR-mediated increased expression of 5-LOX in the neurons and microglia. BW-B 70C down-regulated 5-LOX and inhibited iNOS expression by preventing NF-κB activation. Two other structurally different 5-LOX inhibitors were also administered post IR: caffeic acid and 2, 3, 5-trimethyl-6- [12-hydroxy-5, 10-dodecadiynyl]-1, 4-benzoquinone (AA-861). As with BW-B 70C, they provided remarkable neuroprotection. Furthermore, in vitro, BW-B 70C inhibited lipopolysaccharide (LPS) mediated nitric oxide production, iNOS induction and NF-κB activation in the BV2 microglial cell line. Treating rat primary microglia with BW-B70C confirmed blockage of LPS-mediated translocation of the p65 subunit of NF-κB from cytosol to nucleus.

Conclusion

The study demonstrates the neuroprotective potential of 5-LOX inhibition through down-regulation of NF-κB in a rat model of experimental stroke.

Analysis of the Endothelial Nitric Oxide Synthase Gene as a Modifier of the Cerebral Response to Ischemia

We studied the endothelial nitric oxide synthase (eNOS or NOS-3) gene as a potential modifier of the cerebral response to ischemia by investigating the association of two common polymorphisms with ischemic stroke volume. We genotyped an intronic variable number tandem repeat and a single nucleotide polymorphism, G894T, in 132 patients with nonlacunar ischemic strokes in whom clinical data and stroke lesion volume were recorded. Our results show that all genotypes are in Hardy-Weinberg equilibrium. After adjustment of covariates, neither of the NOS-3 polymorphisms showed significant differences comparing the genotypes and mean stroke volume (analysis of variance). Our results do not suggest a major gene effect of the NOS-3 gene as a modifier of the cerebral response to ischemia.

Arginine metabolic pathways determine its therapeutic benefit in experimental heatstroke: role of Th1/Th2 cytokine balance

We have demonstrated that therapeutic administration of L-arginine (L-arg) (120 mg/kg) at +2 h of whole body hyperthermia (WBH) could rescue the mice from heatstroke-induced death. Studies were undertaken to elucidate the role of L-arg in the immunomodulation of the heat-stressed mice. Administration of L-arginine (L-arg), (120 mg/kg, i.p.), at +2 h of WBH, rescued the mice from heat-induced death and reduced the hypothermia. At +4 and +24 h of WBH, levels of IL-1beta, IFN-gamma, nitrite, TNF-alpha, IL-4, TGF-beta1, inducible form of nitric oxide synthase (iNOS), and corticosterone significantly increased compared to the sham group. The elevated levels of Th(1) cytokines, namely TNF-alpha, IL-1beta, IFN-gamma, nitrite, and iNOS, decreased significantly both at +4 and +24 h of WBH, following L-arg administration. However, L-arg administration did not reduce the increased levels of Th(2) cytokines, namely IL-4 and TGF-beta1, in WBH mice at +4 h of WBH. L-arg administration significantly increased the levels of Th(2) cytokines at +24 h of WBH, compared to the saline-treated WBH mice. L-arg administration significantly increased both the splenic and hepatic arginase activity at +4 and +24 h of WBH compared to the saline-treated WBH mice. L-NAME treatment at +2 h of WBH and anti-TGF-beta antibody treatment at 0 h of WBH significantly increased the mortality compared to the saline-treated WBH mice. Altered liver histopathology was attenuated following the administration of L-arg at +2 h of WBH. These results suggest that therapeutic administration of L-arg at appropriate concentration and time attenuates the acute inflammatory response, leading to the rescue of mice from heatstroke.