White Matter Protection in Acute Ischemic Stroke

描述(申请人提供)：白质(WM)占人类大脑总体积的50%，代谢率与灰质相似。然而，西医的血液供应不成比例地少，侧支循环也更少，这使得它非常容易受到缺氧缺血的侮辱。然而，由于常规MRI或CT方法难以发现，WM损伤尚未成为急性缺血性卒中临床评估的一个组成部分。同样，过去对西医保护策略的探索并不是中风临床前研究的前沿。因此，尚不确定急性缺血性卒中溶栓治疗是否足够，或者是否需要额外的细胞保护剂来挽救西医。本项目基于我们最近的研究结果，即扩散张量成像(DTI)可用于检测血栓性卒中啮齿动物模型中WM损伤的不同组织病理学。具体地说，我们发现径向/横向扩散系数的迅速降低与少突胶质细胞的肿胀和轴浆的压缩有关，而起病较晚的部分各向异性(FA)的大幅降低意味着轴突的严重结构破坏。此外，WM损伤与少突胶质细胞的反应性氧化应激有关，这可能起到因果作用。综上所述，这些结果不仅再现了卒中患者DTI改变的特征模式(即径向弥散系数迅速降低，分数各向异性初始变化很小)，而且为研究急性缺血性卒中的白质保护策略提供了一个实验系统。基于这些初步结果，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tPA和抗氧化剂依达拉奉联合使用才能最大限度地保护中风西药的假设。这是因为脑缺氧缺血后的再灌流可能会矛盾地增加西医的氧化应激。依达洛酮是一种有效的血脑屏障透过性自由基清除剂，已在日本被批准用于治疗急性缺血性中风，但其对WM的保护作用尚未得到检验。在目标2中，我们将检测抗氧化剂补充对缺血性中风西药保护的指标。我们推测，提高铜/锌超氧化物歧化酶(SOD_1)和细胞膜相关磷脂过氧化氢酶(Gpx_4)可减轻缺血性卒中少突胶质细胞和WM的损伤。这是因为SOD1和GPX的连续作用是清除超氧阴离子和羟基自由基所必需的。此外，Gpx4在限制膜结合的脂质过氧化方面特别有效。在这个项目中，共有八组成年小鼠将受到不同遗传和药物治疗的中风血栓模型的影响，并接受组织学、生化和DTI评估小组的检查。通过不同治疗组之间的定量分析和结果比较，这些实验将为急性缺血性卒中的WM保护策略提供建议，并为WM损伤的机制提供新的见解。

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.