Effect of tissue pO2 on free-radical damage in stroke

描述(申请人提供)：我们建议的研究将描述组织氧合(PO2)和特定的自由基在脑缺血和再灌流的病理生理学中的作用。我们已经开发了使用电子顺磁共振(EPR)光谱来测量体内组织PO2和自由基生成的技术，作为大脑特定焦点区域随时间的函数。采用大鼠大脑中动脉闭塞(MCAO)缺血性卒中模型，初步结果显示MCAO后血氧分压(PO2)下降导致自由基生成显著增加。大脑中动脉阻塞后立即进行常压高氧治疗，不仅增加了组织的PO2，而且还减少了自由基的产生，这与通常的预期相反。此外，缺血期间的高氧治疗可减少脑梗塞体积，改善动物的神经功能。这些结果表明，研究组织PO2对自由基产生的影响以及由此产生的分子反应，对于了解自由基诱导的脑损伤的分子事件，以及开发有效的基于氧的缺血性卒中治疗策略具有重要意义。我们假设，局灶性脑缺血时局部组织中低水平的PO2会导致自由基的生成增加，进而激活有害的分子事件，包括基质金属蛋白酶(MMPs)的激活和caspase级联反应，导致微血管损伤和细胞死亡。为了验证这一假说，我们将：1)在大鼠脑缺血模型中，确定高氧治疗对缺血核心、半影区和对照区域组织PO2和自由基产生的影响。2)观察高氧治疗对大鼠脑缺血再灌流后脑组织氧分压和自由基生成的影响，以及高氧对脑缺血再灌注后基质金属蛋白酶-2、3、9和半胱氨酸蛋白酶-3、8、9表达和活化的影响。3)确定高氧治疗增加组织PO2对血脑屏障开放、神经功能评分、脑梗塞体积和脑水肿的影响。这项研究将对缺血性卒中的脑损伤机制提供新的见解，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.