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（pO 2）和特定自由基在脑缺血和再灌注病理生理学中的作用。我们已经开发了技术来测量组织pO 2和体内自由基的产生，作为时间的函数在特定的脑聚焦区域，使用电子顺磁共振（EPR）光谱。使用大脑中动脉闭塞（MCAO）模型的缺血性中风大鼠，我们已经获得了初步的结果表明，降低pO 2后，MCAO导致一个戏剧性的和意想不到的增加产生的自由基。常压高氧治疗后立即MCAO不仅增加了组织pO 2，但也减少了自由基的产生，与常见的预期。此外，缺血期间的高氧治疗减少了梗死体积并改善了动物的神经功能。这些结果表明，研究组织pO 2对自由基产生的影响，以及由此产生的分子反应，将是至关重要的了解自由基诱导的脑损伤的分子事件，并在开发有效的氧为基础的治疗策略缺血性中风。我们推测，局部脑缺血期间局部组织pO 2水平低导致产生的自由基增加，这反过来又激活有害的分子事件，包括激活基质金属蛋白酶（MMP）和半胱天冬酶级联反应，导致微血管损伤和细胞死亡。为了验证这一假设，我们将：1）确定高氧治疗对大鼠缺血性卒中MCAO模型中缺血核心区、半暗带区和对照区组织pO 2和自由基生成的影响。2)在测量组织pO 2和自由基产生的相同位置，确定脑缺血和再灌注后高氧治疗对MMP-2、3和9以及半胱天冬酶-3、8和9的表达和活化的影响。3)确定高氧治疗增加组织pO 2对血脑屏障开放、神经评分、梗死体积和水肿的影响。这项研究将为缺血性脑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.