Ultrasound-Assisted Thrombolysis for Stroke Therapy

描述(申请人提供)：超声和组织型纤溶酶原激活剂(rt-PA)联合治疗，或超声溶栓，已被证明能改善急性缺血性中风患者的再通。为了减少溶栓剂的用量和降低出血事件的风险，已经研究了加强溶栓的有效方法。我们利用体外猪和人全血凝块模型研究了rt-PA和120 kHz超声在溶栓中的协同作用。在我们正在进行的研究中，我们已经证明了显著的溶栓增强与存在稳定的空化相关，这种类型的温和气泡活动可以通过间歇注入造影剂来维持。此外，我们还发现，引起宽带声发射的惯性空化对强化溶栓有反作用。相反，最有效的气泡活动形式是稳定的空化，这会导致超声次谐波的产生。重要的是，我们已经展示了rt-PA在一种专门针对血栓的造影剂中的包裹。这些初步数据有力地支持了我们建议的中心假设，即超声主要通过机械机制促进血栓溶解。为了验证这一假设，我们建议研究三个具体目标：在目标1中，我们将开发一种双元件环形阵列换能器，以促进120 kHz脉冲超声照射和体内和体外被动空化检测。在第二个目标中，我们将通过使用荧光标记的RT-PA脂质体或气体造影剂以及神经病理学检查在猪脑出血性中风模型中的活体研究来证明120 kHz超声增强溶栓的有效性。作为AIM#3中的一种新方法，我们将在体外猪颈动脉模型中研究回声脂质体将rt-PA和一氧化氮(一种生物活性气体)输送到血管内血栓附近的可能性。将评估血管反应性和rt-PA通过血管内皮细胞的渗漏程度，以澄清在存在气体造影剂的情况下进行超声溶栓的潜在风险。这些研究的成功完成将对我们的长期目标做出重大贡献，即开发一种能够在脑血管系统中提供和加强溶栓治疗并在缺血性中风后迅速恢复灌注的超声溶栓系统。公共卫生相关性：我们的长期目标是开发一种经颅超声增强的溶栓系统，将颅内出血的风险降至最低，增加中风幸存者的数量，改善长期预后，并降低医疗成本。这项提案中列出的试剂和技术的发展将对改善中风的定向治疗产生深远的影响。

DESCRIPTION (provided by applicant): Combined ultrasound and tissue plasminogen activator (rt-PA) therapy, or sonothrombolysis, has been shown to improve recanalization in patients with acute ischemic stroke. Effective methods of enhancing thrombolysis have been examined in an attempt to reduce the dosage of the thrombolytic agent and reduce the risk of hemorrhagic events. We have investigated the synergistic effect of rt-PA and 120-KHz ultrasound on thrombolysis using in vitro porcine and human whole blood clot models. In our ongoing studies, we have demonstrated that significant enhancement of thrombolysis correlates with the presence of stable cavitation and this type of gentle bubble activity can be sustained using an intermittent infusion of a contrast agent. In addition, we have shown that inertial cavitation, which elicits broadband acoustic emissions, is counter-productive for enhanced thrombolysis. Rather, the most effective form of bubble activity is stable cavitation, which elicits ultrasonic subharmonic generation. Importantly, we have shown encapsulation of rt-PA in a contrast agent specifically targeted to clot. These preliminary data strongly support the central hypothesis of our proposal that ultrasound enhances thrombolysis primarily via mechanical mechanisms. To test this hypothesis we propose to investigate three Specific Aims: In Aim #1, we will develop a dual-element annular array transducer to facilitate simultaneous 120-kHz pulsed ultrasound exposure and passive cavitation detection in vitro and in vivo. In Aim #2, we will demonstrate the efficacy of 120-kHz ultrasound-enhanced thrombolysis through in vivo studies in a porcine intracerebral hemorrhagic stroke model using fluorescently labeled rt-PA-loaded liposomes or gas contrast agents and neuropathologic examination. As a novel approach in Aim #3, we will investigate the potential of echogenic liposomes to deliver rt-PA and nitric oxide, a bioactive gas, near an intravascular clot in an ex vivo porcine carotid model. Vascular reactivity and the degree of rt-PA leakage across the vascular endothelium will be assessed to clarify the potential risks for sonothrombolysis in the presence of gas contrast agents. Successful completion of these studies will contribute significantly to our long-term goal to develop a sonothrombolysis system that delivers and enhances thrombolytic therapy in the cerebral vasculature and rapidly restores perfusion after ischemic stroke. PUBLIC HEALTH RELEVANCE: Our long-term objective is to develop a transcranial, ultrasound-enhanced thrombolysis system that minimizes the risk of intracranial hemorrhage, increases the number of stroke survivors, improves long-term prognosis, and reduces health care costs. The development of the agents and techniques listed in this proposal would have far reaching implications in improving directed therapeutic treatment of stroke.