Effect of tissue pO2 on free-radical damage in stroke

描述（由申请人提供）：我们提出的研究将描述组织氧合（pO2）和特异性自由基在脑缺血再灌注病理生理中的作用。我们已经开发了一种技术来测量体内组织pO2和自由基的产生，作为大脑特定病灶区域的时间函数，使用电子顺磁共振（EPR）光谱。利用大鼠脑中动脉闭塞（MCAO）缺血性卒中模型，我们已经获得了初步的结果，表明MCAO后pO2的降低导致自由基生成的急剧和意想不到的增加。与普遍预期相反，MCAO术后立即进行常压高氧治疗不仅增加了组织pO2，而且减少了自由基的产生。此外，缺血期间的高氧治疗可减少梗死体积并改善动物的神经功能。这些结果表明，研究组织pO2对自由基生成的影响，以及由此产生的分子反应，对于了解自由基诱导脑损伤的分子事件，以及制定有效的缺血性脑卒中氧基治疗策略至关重要。我们假设局灶性脑缺血期间，低水平的局部组织pO2会导致自由基的产生增加，进而激活有害的分子事件，包括基质金属蛋白酶（MMP）和半胱天蛋白酶级联反应的激活，导致微血管损伤和细胞死亡。为了验证这一假设，我们将：1)测定高氧处理对大鼠缺血性卒中MCAO模型中缺血核心区、半暗区和控制区组织pO2和自由基生成的影响。2)测定高氧处理对脑缺血再灌注后MMP-2、3、9和caspase-3、8、9表达和活化的影响，同时测定组织pO2和自由基生成。3)确定高氧治疗增加组织pO2对血脑屏障开放、神经学评分、梗死体积和水肿的影响。本研究将为缺血性脑卒中脑损伤机制的研究提供新的视角，并有助于设计更有效的神经保护策略。

DESCRIPTION (provided by applicant): Our proposed study will delineate the roles of tissue oxygenation (pO2) and specific free radicals in the pathophysiology of cerebral ischemia and reperfusion. We have developed techniques to measure tissue pO2 and generation of free radicals in vivo, as a function of time in specific focal regions of the brain, using Electron Paramagnetic Resonance (EPR) spectroscopy. Using a middle cerebral artery occlusion (MCAO) model of ischemic stroke in the rat, we have obtained preliminary results showing that decreased pO2 after MCAO leads to a dramatic and unexpected increase in generation of free radicals. Normobaric hyperoxia treatment immediately after an MCAO not only increased tissue pO2, but also decreased free radical generation, contrary to common expectation. Furthermore, hyperoxia treatment during ischemia reduces infarction volume and improves the neurological function of the animal. These results demonstrate that studying the effects of tissue pO2 on free radical generation, and the resulting molecular responses, will be critically important in understanding the molecular events in free radical-induced brain injury, and in developing effective oxygen-based treatment strategies for ischemic stroke. We hypothesize that low levels of localized tissue pO2 during focal cerebral ischemia result in an increased generation of free radicals, which in turn activates deleterious molecular events, including the activation of matrix metalloproteinase (MMP) and the caspase cascade, leading to microvascular damage and cell death. To test this hypothesis, we will: 1) Determine the effect of hyperoxia treatment on tissue pO2 and free radical generation in the ischemic core, penumbra, and control areas in the MCAO model of ischemic stroke in the rat. 2) Determine the effect of hyperoxia treatment on the expression and activation of MMP-2, 3 and 9, and caspase-3, 8, and 9 following cerebral ischemia and reperfusion at the same locations where tissue pO2 and free radical generation are measured. 3) Determine the effects of increasing tissue pO2 with hyperoxia treatment on blood-brain barrier opening, neurological score, infarction volume, and edema. The proposed research will provide new insight into the mechanism of cerebral injury during ischemic stroke, and aid in the design of more effective neuroprotective strategies.