SummaryInfarction in adult rat brain was induced by middle cerebral arterial occlusion (MCAO) followed by reperfusion to examine whether taxifolin could reduce cerebral ischemic reperfusion (CI/R) injury. Taxifolin administration (0.1 and 1.0 lg/kg, i.v.) 60 min after MCAO ameliorated infarction (by 42%±7% and 62%±6%, respectively), which was accompanied by a dramatic reduction in malondialdehyde and nitrotyrosine adduct formation, two markers for oxidative tissue damage. Overproduction of reactive oxygen species (ROS) and nitric oxide (NO) via oxidative enzymes (e.g., COX-2 and iNOS) was responsible for this oxidative damage. Taxifolin inhibited leukocyte infiltration, and COX-2 and iNOS expressions in CI/R-injured brain. Taxifolin also prevented Mac-1 and ICAM-1 expression, two key counter-receptors involved in firm adhesion/transmigration of leukocytes to the endothelium, which partially accounted for the limited leukocyte infiltration. ROS, generated by leukocytes and microglial cells, activated nuclear factor-kappa B (NF-jB) that in turn signaled up-regulation of inflammatory proteins. NF-jB activity in CI/R was enhanced 2.5-fold over that of sham group and was inhibited by taxifolin. Production of both ROS and NO by leukocytes and microglial cells was significantly antagonized by taxifolin. These data suggest that amelioration of CI/R injury by taxifolin may be attributed to its antioxidative effect, which in turn modulates NF-jB activation that mediates CI/R injury.

No abstract

phosphate buffer; RMCA, right middle cerebral artery; RNS, reactive nitrogen species; ROS, reactive oxygen species; STAT-1, signal transducer and activator of transcription-1; TNF, tumor necrosis factor. AbstractDimemorfan, an antitussive and a sigma-1 (r 1 ) receptor agonist, has been reported to display neuroprotective properties. We set up an animal model of ischemic stroke injury by inducing cerebral ischemia (for 1 h) followed by reperfusion (for 24 h) (CI/R) in rats to examine the protective effects and action mechanisms of dimemorfan against stroke-induced damage. Treatment with dimemorfan (1.0 lg/kg and 10 lg/ kg, i.v.) either 15 min before ischemia or at the time of reperfusion, like the putative r 1 receptor agonist, PRE084 (10 lg/kg, i.v.), ameliorated the size of the infarct zone by 67-72% or 51-52%, respectively, which was reversed by pretreatment with the selective r 1 receptor antagonist, BD1047 (20 lg/kg, i.v.). Major pathological mechanisms leading to CI/ R injury including excitotoxicity, oxidative/nitrosative stress, inflammation, and apoptosis are all downstream events initiated by excessive accumulation of extracellular glutamate. Dimemorfan treatment (10 lg/kg, i.v., at the time of reperfusion) inhibited the expressions of monocyte chemoattractant protein-1 and interleukin-1b, which occurred in parallel with decreases in neutrophil infiltration, activation of inflammationrelated signals (p38 mitogen-activated protein kinase, nuclear factor-jB, and signal transducer and activator of transcription-1), expression of neuronal and inducible nitric oxide synthase, oxidative/nitrosative tissue damage (lipid peroxidation, protein nitrosylation, and 8-hydroxy-guanine formation), and apoptosis in the ipsilateral cortex after CI/R injury. Dimemorfan treatment at the time of reperfusion, although did not prevent an early rise of glutamate level, significantly prevented subsequent glutamate accumulation after reperfusion. This inhibitory effect was lasted for more than 4 h and was reversed by pre-treatment with BD1047. These results suggest that dimemorfan activates the r 1 receptor to reduce glutamate accumulation and then suppresses initiation of inflammation-related events and signals as well as induction of oxidative and nitrosative stresses, leading to reductions in tissue damage and cell death. In conclusion, our results demonstrate for the first time that dimemorfan exhibits protective effects against ischemic stroke in CI/R rats probably through modulation of r 1 receptor-dependent signals to prevent subsequent glutamate accumulation and its downstream pathologic events.