ROLE OF OXYGEN RADICALS AND XANTHINE OXIDASE IN STROKE

卒中后24小时内死亡的常见结果 由于脑水肿，目前还没有有效的治疗方法 可用。井中氧自由基对内皮细胞的损伤 肺和其他器官浮肿形成的公认原因 但它在脑缺血中的作用尚不清楚。我们证明了 酶促氧自由基清除剂可缩小心肌梗死体积 大鼠局灶性卒中模型的建立及黄嘌呤氧化酶的假说 (XO)是这些氧自由基的重要来源。证据是 提出了脑缺血诱导的转换 一种正常的良性酶，黄嘌呤脱氢酶(XDH)，到一个 产生自由基的氧化酶，将分子氧还原到 有毒的中间体，超氧化物和过氧化氢。大脑的大部分 XdH和XO定位于内皮细胞，使 血脑屏障存在氧自由基损伤的风险。在这 建议，细胞毒性氧自由基的作用将是 脑缺血后早期脑血变化的研究 局灶性血流、水肿形成、中性粒细胞涌入和脑梗塞 建立大鼠卒中模型。中风是由闭塞动脉引起的 右侧大脑中动脉(MCA)和短暂阻断双侧大脑中动脉 颈动脉长达90分钟，这产生了可重复的， 可量化的梗死局限于右侧皮质，适用于 检查药理作用。治疗的效果 用特定的酶类自由基清除剂研究开发 细胞毒性和血管源性水肿，脑血流量改变 大脑中动脉-颈动脉闭塞后的组织学损伤 已评估。优化向自由基部位的传递 生产，氧自由基清除酶，超氧化物 歧化酶和过氧化氢酶，将要么与聚乙烯偶联 乙二醇或包裹在脂质体中，这会增加它们的循环 半衰期和细胞进入。缺血诱导的作用 XDHXO向损伤的转化将通过耗尽来检查 三种独立方法测定大鼠XDH/XO活性及 测量对脑梗塞体积、水肿形成的影响， 大脑中动脉-颈动脉损伤后的脑血流量和组织学损伤 程序。体内氧自由基的产生速度将是 用自由基清除剂治疗后测量 黄嘌呤氧化酶抑制剂。这些研究将有助于定义 氧自由基在脑缺血中的作用及可能导致新的 中风的治疗方法。

Mortality within the first 24 hours after stroke frequently results from cerebral edema for which no effective treatment is available. Injury to endothelium by oxygen radicals in a well- recognized cause of edema formation in the lung and other organs but its role in cerebral ischemia is poorly defined. We show that enzymatic oxygen radical scavengers can reduce infarct volume in a rat focal stroke model and hypothesize that xanthine oxidase (XO) is an important source of these oxygen radicals. Evidence is presented to show that cerebral ischemia induces the conversion of a normally benign enzyme, xanthine dehydrogenase (XDH), to a free radical-producing oxidase which reduces molecular oxygen to the toxic intermediates, superoxide and H2O2. Most of the brain XDH and XO is localized within the endothelium, putting the blood-brain barrier at risk of oxygen radical injury. In this proposal, the role of cytotoxic oxygen free radicals will be investigated in early post-ischemic changes in cerebral blood flow, edema formation, neutrophil influx and infarction in a focal stroke model in the rat. The stroke is induced by occluding the right middle cerebral artery (MCA) and transiently clamping both carotid arteries for up to 90 minutes, which yields a reproducible, quantifiable infarct restricted to the right cortex and ideal for examining pharmacological efficacy. The effects of treatment with specific enzymatic radical scavengers on the development of cytotoxic and vasogenic edema, changes in cerebral blood flow and histologic injury after the MCA-carotid occlusion will be evaluated. To optimize delivery to sites of free radical production, the oxygen radical scavenging enzymes, superoxide dismutase and catalase, will be either conjugated to polyethylene glycol or entrapped in liposomes, which increases their circulatory half-life and cell entry. The contribution of ischemia-induced XDH conversion of XO to injury will be examined by depleting XDH/XO activity in rats by three independent methods and measuring the effects on infarct volume, edema formation, cerebral blood flow and histologic injury after the MCA-carotid procedure. Rates of oxygen radical production in vivo will be measured after treatment with free radical scavengers and xanthine oxidase inhibitors. These studies will help define the role of oxygen radicals in cerebral ischemia and may lead to new therapeutic approaches in the treatment of stroke.