Dabrafenib,an inhibitor of RIP3 kinase-dependent necroptosis,reduces ischemic brain injury

Ischemic brain injury triggers neuronal cell death by apoptosis via caspase activation and by necroptosis through activation of the receptor-interacting protein kinases （RIPK） associated with the tumor necrosis factor-alpha （TNF-a）/death receptor. Recent evidence shows RIPK inhibitors are neuroprotective and al- leviate ischemic brain injury in a number of animal models, however, most have not yet undergone clinical trials and safety in humans remains in question. Dabrafenib, originally identified as a B-raf inhibitor that is currently used to treat melanoma, was later revealed to be a potent RIPK3 inhibitor at micromolar con- centrations. Here, we investigated whether Dabrafenib would show a similar neuroprotective effect in mice subjected to ischemic brain injury by photothrombosis. Dabrafenib administered intraperitoneally at 10 mg/ kg one hour after photothrombosis-induced focal ischemic injury significantly reduced infarct lesion size in C57BL6 mice the following day, accompanied by a markedly attenuated upregulation of TNF-u. However, subsequent lower doses （5 mg/kg/day） failed to sustain this neuroprotective effect after 4 days. Dabrafenib bl ocked lipopolysaccharides-induced activation of TNF-ct in bone marrow-derived macrophages, suggesting that Dabrafenib may attenuate TNF-ct-induced necroptotic pathway after ischemic brain injury. Since Dab- rafenib is already in clinical use for the treatment of melanoma, it might be repurposed for stroke therapy.

Early expressions of hypoxia-inducible factor 1alpha and vascular endothelial growth factor increase the neuronal plasticity of activated endogenous neural stem cells after focal cerebral ischemia

Endogenous neural stem cells become ＂activated＂ after neuronal injury, but the activation sequence and fate of endogenous neural stem cells in focal cerebral ischemia model are little known. We evaluated the relationships between neural stem cells and hypoxia-inducible factor-1α and vascular endothelial growth factor expression in a photothromobotic rat stroke model using immunohistochemistry and western blot analysis. We also evaluated the chronological changes of neural stem cells by 5-bromo-2′-deoxyuridine（BrdU） incorporation. Hypoxia-inducible factor-1α expression was initially increased from 1 hour after ischemic injury, followed by vascular endothelial growth factor expression. Hypoxia-inducible factor-1α immunoreactivity was detected in the ipsilateral cortical neurons of the infarct core and peri-infarct area. Vascular endothelial growth factor immunoreactivity was detected in bilateral cortex, but ipsilateral cortex staining intensity and numbers were greater than the contralateral cortex. Vascular endothelial growth factor immunoreactive cells were easily found along the peri-infarct area 12 hours after focal cerebral ischemia. The expression of nestin increased throughout the microvasculature in the ischemic core and the peri-infarct area in all experimental rats after 24 hours of ischemic injury. Nestin immunoreactivity increased in the subventricular zone during 12 hours to 3 days, and prominently increased in the ipsilateral cortex between 3–7 days. Nestin-labeled cells showed dual differentiation with microvessels near the infarct core and reactive astrocytes in the peri-infarct area. BrdU-labeled cells were increased gradually from day 1 in the ipsilateral subventricular zone and cortex, and numerous BrdU-labeled cells were observed in the peri-infarct area and non-lesioned cortex at 3 days. BrdU-labeled cells rather than neurons, were mainly co-labeled with nestin and GFAP. Early expressions of hypoxia-inducible factor-1α and vascular endothelial growth factor after ischemia made up the microenvironment to increase the neuronal plasticity of activated endogenous neural stem cells. Moreover, neural precursor cells after large-scale cortical injury could be recruited from the cortex nearby infarct core and subventricular zone.

Establishing an experimental rat model of photo-dynamically-induced retinal vein occlusion using erythrosin B

AIM:To develop a reliable,reproducible rat model of retinal vein occlusion(RVO)with a novel photosensitizer(erythrosin B)and study the cellular responses in the retina.METHODS:Central and branch RVOs were created in adult male rats via photochemically-induced ischemia.Retinal changes were monitored via color fundus photography and fluorescein angiography at 1 and 3h,and 1,4,7,14,and 21d after irradiation.Tissue slices were evaluated histopathologically.Retinal ganglion cell survival at different times after RVO induction was quantified by nuclear density count.Retinal thickness was also observed.RESULTS:For all rats in both the central and branch RVO groups,blood flow ceased immediately after laser irradiation and retinal edema was evident at one hour.The retinal detachment rate was 100%at 3h and developed into bullous retinal detachment within 24h.Retinal hemorrhages were not observed until 24h.Clearance of the occluded veins at 7d was observed by fluorescein angiography.Disease manifestation in the central RVO eyes was more severe than in the branch RVO group.A remarkable reduction in the ganglion cell count and retinal thickness was observed in the central RVO group by 21d,whereas moderate changes occurred in the branch RVO group.CONCLUSION:Rat RVO created by photochemicallyinduced ischemia using erythrosin B is a reproducible and reliable animal model for mimicking the key features of human RVO.However,considering the 100%rate ofretinal detachment,this animal model is more suitable for studying RVO with chronic retinal detachment.

Activation of dopamine 2 receptors modulates glutamate decarboxylases 65 and 67 during stroke recovery in mice

Backgrounds:Treatment with levodopa enhances recovery of lost neurological functions in preclinical stroke models and patients.Here,we studied whether dopamine signaling modulates GABAergic neurotransmission in parvalbumin-positive interneurons after experimental stroke.Methods:Following block randomization,mice were subjected to experimental stroke induced by photothrombosis(PT).Two days after the insult,mice were treated either with the D1 receptor antagonist by R(+)-SCH-23390(0.1 mg/kg),the selective D1 receptor agonist(R)-(+)-SKF-38393 hydrochloride(1 mg/kg),the D2 receptor agonist R(−)-2,10,11-trihydroxy-Npropyl-noraporphine hydrobromide hydrate(TNPA)(1 mg/kg),the D2 receptor antagonist S-(−)-eticlopride hydrochloride(0.3 mg/kg),or vehicle(saline)by daily intraperitoneal injection for five consecutive days,respectively.Recovery of function was assessed by paw placement and foot fault test before and on Days 2 and 7 after surgery.Results:Mice treated with TNPA showed a statistically significant improvement of recovery compared to all other treatment conditions.Synthesis of gamma-aminobutyric acid(GABA)was quantified by levels of full-length and cleaved glutamate acid decarboxylase 67 and 65(GAD65 and GAD67)in the peri-infarct area and homotypic regions of the contralateral cortex.Compared to the other treatments,TNPA significantly reduced the level of the GAD67 isoform both in the ischemic and contralateral hemispheres.Levels of GAD65 were found significantly higher in the contralateral hemisphere in TNPA-treated mice after PT accompanied by an increase in the 58 kDa-truncated form.Conclusion:Our results point toward reduced GABA synthesis in a D2 receptor-mediated mechanism possibly contributing to counteract functional inhibition after stroke.