Ischemic Edge Dynamics in Ischemic Stroke: Potassium and the Blood-Brain Barrier

描述（由申请方提供）：该提案解决了局灶性缺血性卒中治疗研究的核心问题：血脑屏障（BBB）通过血管源性水肿破坏，限制了tPA给药窗口。我们将使用K+动力学和Gd-DTPA增强研究初始BBB破坏后tPA诱导的出血性转化的风险增加。我们的初步研究指出，在中风后3-4小时，在缺血区域边缘的事件组合表明，与中央缺血核心相比，该区域正在经历加速的病理变化：1）Na+增加的速率在该边缘最大; 2）脑[K+]，[K+]br，低于中央缺血区域;[K+]br福尔斯在发病后3-4 h下降，4）Gd-DTPA在发病后3- 4 h在蛛网膜下腔直接在该边缘出现短暂性增强。三个具体目标地址：1）Gd增强区域是否包含CSF而非脑实质; 2）细胞外[K+]、[K+]ex下降的时间和位置;以及3）[K+]ex下降是否先于Gd增强。本文用K ~+敏感电极观察大鼠实验性脑卒中时[K ~+]的变化。将使用1.5T MRI Gd-DTPA增强将这种[K+]ex突然下降的时间与BBB击穿进行比较。我们认为，这种短暂的Gd增强，标志着最初的血脑屏障破坏的时间，这可以很容易地在临床上成像，以下的K+下降。还将使用创新的K/Rb替代MRI在7 T下在体内监测脑K+的变化，并通过K+定量组织化学染色和火焰光度法进行验证。虽然BBB渗透性的初始变化有许多微妙的指标，但K+的下降是一个突然且容易识别的事件。我们认为，K+下降发生在细胞毒性和血管源性水肿之间的过渡的开始，因为缺血区域的高[K+]ex通过BBB泄漏，并被剩余的滴流或CSF流带走。如果我们表明K+下降先于蛛网膜下CSF空间中指示BBB破裂的初始Gd增强，那么所提出的研究将是我们对限制溶栓有用性的因素的基础知识和理解的重大进步。这些发现可以通过直接评估每个个体的组织状态来提高我们对限制tPA有效性的病理过程的理解，而不是卒中发作时间。公共卫生相关性：当血脑屏障出现渗漏后，治疗急性缺血性中风或脑梗死的可能性就越来越小。虽然这种击穿首先发生在2至5小时之间，但确切的时间尚不清楚，而且确切的击穿方式也不清楚。我们怀疑，在一个精确的时间钾泄漏通过屏障发生，然后是一个更广泛的分解，允许血液及其成分泄漏到大脑，加速损伤和限制可能的治疗。我们计划确定这一确切时间，并将其与进一步的泄漏联系起来。通过在实验环境中了解这些事件，我们将提高我们对大脑发作后立即发生在患者身上的事情的理解，并希望提供更好的治疗方案。

DESCRIPTION (provided by applicant): This proposal addresses a problem central to the study of focal ischemic stroke therapy: the blood- brain barrier (BBB) breakdown via vasogenic edema that restricts the window of tPA administration. We will study the initial BBB disruption after which the risk of tPA-induced hemorrhagic transformation increases, using K+ dynamics and Gd-DTPA enhancement. Our preliminary studies point to the combination of events at 3-4 h after stroke at the edge of the ischemic region indicating that this area is undergoing accelerated pathological changes in comparison to the central ischemic core: 1) the rate of Na+ increase is maximal at this edge; 2) brain [K+], [K+]br, is lower than in the central ischemic region; 3) [K+]br falls at 3-4 h after onset; and 4) transient Gd-DTPA enhancement occurs in the subarachnoid space directly over this edge at 3- 4 h after onset. Three Specific Aims address: 1) whether the region of Gd enhancement contains CSF and not brain parenchyma; 2) the timing and position of the fall in extracellular [K+], [K+]ex; and 3) whether the [K+]ex fall precedes the Gd enhancement. We propose to observe the [K+]ex fall with K+-sensitive electrodes in experimental stroke in rats. The time of this abrupt [K+]ex drop will be compared to BBB breakdown using 1.5T MRI Gd-DTPA enhancement. We contend that this transient Gd enhancement that marks the time of initial BBB disruption, which can be easily imaged in the clinical setting, follows the fall in K+. Changes in brain K+ will also be monitored in vivo using innovative K/Rb substitution MRI at 7T and verified by K+ quantitative histochemical staining and flame photometry. Although there are many subtle indicators of the initial changes of BBB permeability, the fall in K+ is an abrupt and easily recognized event. We propose that the K+ drop occurs at the beginning of the transition between cytotoxic and vasogenic edema because high [K+]ex in the ischemic region leaks through the BBB and is carried away by the remaining trickle flow or by CSF flow. If we show that the K+ drop precedes the initial Gd enhancement in the subarachnoid CSF space indicative of BBB breakdown, then the proposed studies will be a significant advance in our basic knowledge and understanding of factors that limit the usefulness of thrombolysis. These findings could improve our understanding of the pathological processes that limit tPA's effectiveness other than time of stroke onset by assessing tissue status directly in each individual. PUBLIC HEALTH RELEVANCE: After the blood-brain barrier becomes leaky, possible therapies for acute ischemic stroke, or a brain attack, become less and less likely to succeed. Although this breakdown first occurs between 2 and 5 hours, the exact time is not known and exactly how it breaks is unclear. We suspect that at a precise time potassium leakage across the barrier occurs, and then is followed by a more generalized breakdown that permits blood and its components to leak into brain, accelerating damage and limiting possible therapies. We plan to determine this exact time and relate it to further leakage. By understanding these events in an experimental setting, we will improve our understanding of what happens to a patient immediately after a brain attack, and hopefully provide better treatment options.