Experimental Study Of Neuroprotective Effects Of Intra-arterial Dexamethasone Infusion On Cerebral Ischemia/reperfusion Models Of Rats

Stroke is one of the leading causes of disability and mortality worldwide. The latest statistics suggest that stroke is the first cause of death in our country. The 80% of stroke is ischemic cerebrovascular disease. The mechanisms contributing to the brain damage after cerebrovascular disease may be related with ischemic cascade reaction, including lactic acid accumulation, calcium overload, inflammatory injury, free radical injury and cell apoptosis. Inflammation plays an important role in the pathogenesis of ischemic stroke. The brain responds to ischemic injury with an acute inflammatory process, characterized by rapid production of inflammatory mediators in the ischemic brain tissue which collaboratively contribute to ischemic brain injury.The glucocorticoid has fast and powerful anti-inflammatory effect. Experimentally and clinically, the glucocorticoid could reduce brain damage resulting from cerebral ischemia. However, several trials in patients with ischemic stroke have failed to show a reduction in mortality and a significant improvement in functional outcome. Clinical studies of corticosteroids in stroke have conflicting results, which may reflect differences in dosage regimens, the time to onset of treatment, or the specific clinical condition.We summarize these trials and some conclusions are obtained: 1.High dose, but not low dose, glucocorticoid possess neuroprotective role following cerebral ischemia. 2. In most experiments getting positive results, treatment is started in the early stage of cerebral infarction. We suspect that early treatment with high dose glucocorticoid has remarkable neuroprotective effects in animal models of cerebral ischemia. This study explores the time dependence of high dose dexamethasone in treating cerebral ischemia.The risk of side effects increase as the dose of glucocorticoid rose, and short therapeutic time window limits the application of glucocorticoid for cerebral ischemia therapy. By delivering drug intraarterially to the ischemic tissue, “first pass” loss in the liver is reduced and drug effects are more concentrated in the ischemic zone. Moreover, when delivered intra-arterially, drugs directly enter the target tissues. Drug can reach therapeutic concentrations much faster than systemic infusion, so as not to miss the therapeutic window. A follow-up study probes the neuroprotective effects of intra-arterial dexamethasone infusion on cerebral ischemia/reperfusion models of rats.Experiment 1:A New Middle Cerebral Artery Occlusion Model for Intra-arterial Drug Infusion in RatsObjective: to develop a novel stroke model for intra-arterial drug deliveryMethod: Middle Cerebral Artery Occlusion(MCAO) was induced in Sprague–Dawley rats with the microcatheter device(c MCAO group) or a monofilament nylon suture(s MCAO group). After 48-h occlusion, neurologic deficit and infarct volume were compared between the groups. Drug-delivery models used in stroke studies were compared with our model to verify the drug-delivery ability of our device. MCAO was induced using our device in 21 Sprague–Dawley rats. At 2h after occlusion, 4% Evans blue dye was infused using different methods, and 4h later, the dye was extracted from each hemisphere and spectrophotometrically quantified.Result: Neurologic deficits and infarct volumes were similar in the c MCAO and s MCAO groups. Significantly more dye leakage occurred in the ischemic hemispheres of the rats who received the dye via the microcatheter device.Conclusion: The effectiveness of the microcatheter device in inducing stroke rivaled that of the widely recognized monofilament nylon suture method. Compared to other intra-arterial drug-delivery models used in stroke studies, our model enabled highly efficient drug delivery. What is more, in the novel model, drugs could be delivered into the ischemic brain at any time(with or without reperfusion). It is suitable not only for investigating the effect of intra-arterial drug delivery on reperfusion injury in ischemic stroke but also for assessing intra-arterial neuroprotection in case of missing reperfusion therapy.Experiment 2 : Experimental Study of Neuroprotective Effects of High Dose Dexamethasone Infusion on Cerebral Ischemia/Reperfusion Models of RatsObjective: to explore the mechanism and the time dependence of high dose dexamethasone in treating cerebral ischemia.Method: adult Sprague–Dawley rats subjected to transient middle cerebral artery occlusion(MCAO)/reperfusion. At different time points(30min、60min、120min)after MCAO, rats were treated with high dose dexamethasone(10mg/kg), After 2 h MCAO and 48 h reperfusion, neurological deficit, infarct sizes were measured. The activation of NF-κB Signaling pathway was observed after 2h of ischemia by western blot analysis and immunohistochemistry. The expression of NF-κB target genes, including inducible nitric oxide synthase(i NOS), cyclooxygenase(COX-2), tumor necrosis factor-α(T NF-α) and interleukin-1β(IL-1β), were determined by western blot analysis and ELISA.Result: Dexamethasone delivered at 30 min after MCAO markedly decreased the infarct size, improved neurological deficits. Dexamethasone infused at other time points(60min, 120min) showed no neuroprotective effects. Dexamethasone delivered at 30 min significantly inhibited NF-κB p65 expression and phosphorylation. The expression of NF-κB target genes, including inducible nitric oxide synthase(i NOS), cyclooxygenase(COX-2), tumor necrosis factor-α(TNF-α) and interleukin-1β(IL-1β), were also suppressed by Dexamethasone delivered at 30 min after MCAO.Conclusion: Dexamethasone protected the brain against ischemic damage caused by MCAO, and this effect may be through downregulation of NF-κB-mediated inflammatory responses.Experiment 3:Experimental Study of Neuroprotective Effects of Intra-arterial Dexamethasone Infusion on Cerebral Ischemia/Reperfusion Models of RatsObjective: to explore the neuroprotective effects of intra-arterial dexamethasone infusion on cerebral ischemia/reperfusion models of ratsMethod: Middle Cerebral Artery Occlusion(MCAO) was induced in Sprague–Dawley rats with the microcatheter device. 2mg/kg or 10mg/kg dexamethasone was infusion at different time points(30min, 6omin) Intra-arterially or intravenously. After 2 h MCAO and 48 h reperfusion, neurological deficit, motor behavior(foot-fault placing test, parallel-bar crossing test, and rope climbing test) and infarct sizes were measured.Result: Low dose dexamethasone delivered at 60 min after MCAO markedly decreased the infarct size, improved neurological deficits and motor behavior.Conclusion: Intra-arterial dexamethasone infusion prolonged the therapeutic window and decreased the total drug dose needed.