EXCITOTOXICITY IN CIRCULATORY ARREST--BRAIN INJURY

描述(逐字摘自申请者摘要)：项目的目标是 明确低温致兴奋性中毒性神经元损伤的机制 循环骤停(HCA)，并开发预防方法。在我们的犬类中 心内直视手术中复制临床经验的HCA生存模型 手术，狗在18摄氏度下停循环2小时 维持一致的神经功能缺陷和选择性脑出血的组织学模式 神经元死亡。我们最初的研究表明，服用选择性谷氨酸 受体拮抗剂在HCA损伤前后使神经元减少 坏死。我们现在已经证明，神经元死亡可以通过细胞凋亡或 坏死性机制。我们发现HCA后谷氨酸的释放会导致 一氧化氮(NO)的积聚，它介导了神经元的死亡 抑制神经元型一氧化氮合酶(NOS)减少NO的产生 保护大脑，防止细胞凋亡。 我们假设线粒体功能障碍决定了 HCA后迟发性兴奋性神经元损伤的细胞凋亡或坏死 缺血预适应(IPC)可防止神经细胞凋亡 通过在细胞内开放依赖于ATP的钾通道来发挥药理作用 线粒体膜。我们进一步假设，NO可以充当调解人 IPC对神经元的损伤和保护作用。在预赛中 实验表明，二氮嗪，一种依赖于ATP的钾通道 能产生药理上的IPC，并能防止这种药物 作用于线粒体内膜的心肌细胞的凋亡。在我们的 犬模型，二氮嗪显示神经功能障碍几乎完全消除 在HCA后，精选神经元群体中的细胞凋亡减少。我们 低氧可通过诱导型一氧化氮合酶激活缺氧诱导因子-1 NO的产生，这是IPC晚期的一种可能的分子途径。 我们建议：(1)测量线粒体功能障碍的代谢指标。 在我们的犬HCA模型中应用‘H和’P磁共振成像的特定脑区 和(2)与神经元存活、凋亡和坏死相关；(3) 用二氮嗪作为神经保护手段检查药理IPC和(4) 确定开放线粒体中的钾通道如何改变其 实现IPC的功能；(5)确定NO如何充当两者的调解人 大脑中的损伤和保护。这项研究将加速临床 在兴奋性毒性级联反应中使用抑制剂，促进IPC的开发 通过药物手段提供脑保护，从而更好地 心血管手术中HCA术后的患者结局。

DESCRIPTION (Verbatim from Applicant's Abstract): The goal of the project is to define the mechanisms of excitotoxic neuronal injury caused by hypothermic circulatory arrest (HCA) and to develop the means to prevent it. In our canine survival model of HCA, replicating clinical experience during cardiac operations, dogs subjected to 2 hours of circulatory arrest at 18degreesC sustain a consistent neurologic deficit and histologic pattern of selective neuronal death. We originally showed that administration of selective glutamate receptor antagonists before and after HCA-induced injury reduced the neuronal necrosis. We have now shown that neuronal death can occur by apoptotic or necrotic mechanisms. We showed that glutamate release after HCA results in accumulation of nitric oxide (NO), which mediates neuronal death and that inhibition of neuronal nitric oxide synthase (NOS) reduces production of NO in the brain and prevents apoptosis. We hypothesize that mitochondrial dysfunction determines the mechanism of delayed excitotoxic neuronal injury after HCA by apoptosis or necrosis and that neuronal apoptosis can be prevented by ischemic preconditioning (IPC), achieved pharmacologically by opening ATP-dependent potassium channels on the inner mitochondrial membrane. We further hypothesize that NO may act as a mediator both of neuronal injury and neuronal protection by IPC. In preliminary experiments we have shown that diazoxide, an ATP-dependent potassium channel opener can produce pharmacologic IPC and that that this agent can prevent apoptosis in cardiomyocytes acting on the inner mitochondrial membrane. In our canine model, diazoxide has shown near total elimination of neurologic deficit following HCA, with reduction in apoptosis in select neuronal populations. We also showed that hypoxia can activate HIF-1 with induction of iNOS and production of NO, a putative molecular pathway of the late form of IPC. We propose to: (1) measure metabolic indicators of mitchondrial dysfunction in specific brain regions using 'H and 'P MRSI following HCA in our canine model and (2) correlate these with neuronal survival, apoptosis and necrosis; (3) to examine pharmacologic IPC with diazoxide as means of neuroprotection and (4) determine how opening the potassium channels in the mitochondrion alters its function to effect IPC; (5) to establish how NO can act as mediator of both injury and protection in the brain. This research will expedite the clinical use of inhibitors in the excitotoxic cascade and facilitate exploitation of IPC by pharmacologic means to provide cerebral protection resulting in better patient outcomes after HCA in cardiovascular operations.