White Matter Protection in Acute Ischemic Stroke

描述（申请人提供）：白色物质（WM）占人脑总体积的50%，代谢率与灰质相似。然而，WM的血液供应量少，侧支循环少，使其极易受到缺氧缺血性损伤。然而，由于常规MRI或CT方法难以检测，WM损伤尚未成为急性缺血性卒中临床评估的组成部分。同样，在过去的中风临床前研究中，对WM保护策略的研究也不是最前沿的。因此，目前尚不确定是否溶栓治疗是足够的，或需要额外的细胞保护剂，以挽救急性缺血性卒中的WM。本项目是基于我们最近的研究结果表明，扩散张量成像（DTI）可以用来检测不同的组织病理学WM损伤的啮齿动物模型血栓性中风。具体而言，我们发现，径向/横向扩散率的快速降低与少突胶质细胞肿胀和轴浆压缩相关，而迟发性，分数各向异性（FA）的大幅度降低意味着严重的轴突结构破坏。此外，WM损伤与少突胶质细胞中的反应性氧化应激有关，这可能起因果作用。总之，这些结果不仅重新证明了卒中患者DTI改变的特征模式（即径向扩散率快速降低和分数各向异性的初始变化很小），而且还提供了一个实验系统来研究急性缺血性卒中中的白色物质保护策略。基于这些初步的结果，我们将在本项目中测试两种WM保护策略。在目标1中，我们将检验以下假设，即tPA和依达拉奉（一种抗氧化剂）的组合对于脑卒中中WM的最大保护是必需的。这是因为脑缺氧缺血后再灌注可矛盾地增加WM中的氧化应激。依达罗酮是一种有效的血脑屏障渗透性自由基清除剂，在日本已被批准用于治疗急性缺血性卒中，但其对WM保护的作用尚待研究。在目标2中，我们将测试抗氧化剂补充剂对缺血性卒中WM保护的靶点。我们假设，提高铜/锌超氧化物歧化酶（SOD 1）和细胞膜相关的磷脂过氧化氢酶（GPx 4）可以减少缺血性中风中少突胶质细胞和WM的损伤。这是因为需要SOD 1和GPx的连续作用来解毒超氧化物和羟基自由基。此外，GPx 4在限制膜结合脂质过氧化方面特别有效。在这个项目中，总共八组成年小鼠将接受各种遗传和药理学治疗的血栓性中风模型，并通过组织学，生物化学和DTI评估进行检查。通过定量分析和不同治疗组间的结果比较，这些实验将为急性缺血性脑卒中的WM保护策略和WM损伤机制提供新的见解。 公共卫生相关性：中风是西方世界的第二大死亡原因，排在心脏病之后，但在所有类型的癌症之前。过去对中风的研究主要集中在挽救灰质，但最近的研究表明，对连接和整合神经系统不同部分的白色物质（WM）的损伤是中风功能障碍的关键，如果不是更重要的原因的话。然而，目前还没有敏感和有效的成像方法来检测急性卒中中的WM损伤，并且很少有专门设计用于在急性缺血性卒中动物模型中开发WM保护的研究。本计画应用扩散张量成像（DTI）、生化及组织学方法于血栓性中风模型，探讨缺血性脑白质损伤的原因及治疗。该项目的积极成果将验证使用DTI评估急性缺血性卒中的WM损伤，并提出WM保护的新策略。

DESCRIPTION (provided by applicant): White matter (WM) occupies 50% of the total brain volume in human and has a metabolic rate similar to that of gray matter. Yet, WM has a disproportionally small blood supply and less collateral circulation, making it highly susceptible to hypoxic-ischemic insults. However, due to the difficulty in detection by conventional MRI or CT methods, WM injury has not been an integral part of clinical assessment in acute ischemic stroke. Similarly, the search for strategies of WM protection was not at the forefront of pre- clinical studies of stroke in the past. Thus, it remains uncertain whether thrombolytic therapy is sufficient, or additional cytoprotective agents are needed, to salvage WM in acute ischemic stroke. The present project is based on our recent results showing that diffusion tensor imaging (DTI) can be used to detect distinct histopathologies of WM injury in a rodent model of thrombotic stroke. Specifically, we found that rapid reduction of radial/transverse diffusivity correlates with oligodendrocyte swelling and compression of the axoplasma, while the late-onset, large reduction of fractional anisotropy (FA) signifies severe structural breakdown of the axons. Moreover, WM injury was associated with reactive oxidative stress in oligodendrocytes, which may play a causal role. Together, these results not only re-capitulate the signature pattern of DTI alterations in stroke patients (i.e. rapid reduction of radial diffusivity and little initial change of fractional anisotropy), but also provide an experimental system to study the strategies of WHITE MATTER PROTECTION IN ACUTE ISHCMEIC STROKE. Based on these preliminary results, we will test two strategies of WM protection in the present project. In Aim 1, we will test the hypothesis that the combination of tPA and Edaravone, an anti-oxidant, is needed for the maximal protection of WM in stroke. This is because reperfusion following cerebral hypoxia-ischemia may paradoxically increase the oxidative stress in WM. Edarovone is a potent blood- brain-barrier-permeable free radical scavenger already approved for treating acute ischemic stroke in Japan, but its effects on WM protection are yet to be examined. In Aim 2, we will test the targets of anti-oxidant supplement for WM protection in ischemic stroke. We hypothesize that boosting Cu/Zn superoxide dismutase (SOD1) and the cell membrane-associated phospholipids hydroperoxidase (GPx4) can reduce oligodendrocyte and WM injury in ischemic stroke. This is because sequential actions of SOD1 and GPx are needed to detoxify superoxide and hydroxyl radicals. Further, GPx4 is particularly potent in limiting the membrane-bound lipid peroxidation. In this project, a total of eight groups of adult mice will be subjected to a thrombotic model of stroke with various genetic and pharmacological therapies, and examined by a panel of histological, biochemical, and DTI evaluations. By quantitative analysis and outcome comparison among various treatment-groups, these experiments will suggest strategies of WM protection and shed new insights into the mechanisms of WM injury in acute ischemic stroke. PUBLIC HEALTH RELEVANCE: Stroke is the second leading cause of death in the Western world, ranking after heart disease but before all types of cancer combined. Past research of stroke focuses on salvaging the grey matter, but recent studies suggest that damage to the white matter (WM), which connects and integrates different parts of the nervous system, is a critical, if not more important cause of functional disability in stroke. However, there are no sensitive and validated imaging methods to detect WM injury in acute stroke, and very few studies specifically designed to develop WM protection in animal models of acute ischemic stroke. This project applies diffusion tensor imaging (DTI), biochemical, and histological assays in a thrombotic model of stroke to investigate the causes and therapies of ischemic WM injury. Positive outcomes of this project will validate the use of DTI to assess WM injury in acute ischemic stroke and suggest novel strategies of WM protection.