Preconditioning improves coronary patency

描述(由申请人提供)：预适应(PC)是一种被充分描述的现象，在这种现象中，短暂的心肌缺血发作使心肌细胞对后来持续的缺血损伤具有抵抗力。然而，来自我们小组的证据表明，在模拟急性缺血综合征的临床病例的反复血栓形成模型中，PC在维持血管通畅方面具有辅助的、有利的作用。在我们以前的应用中，我们假设：(1)PC缺血所见的增强的通畅性是由于PC诱导的一个或多个血小板激活-聚集分子指数的减弱；以及(2)PC刺激期间释放的腺苷，以及由此产生的对血小板表面腺苷A2A受体的刺激，是改善通畅性的触发因素。第一个概念得到了PC诱导的显著下调血小板P-选择素表达、血小板-纤维蛋白原结合和中性粒细胞-血小板聚集体(NPA)形成的新证据的支持。然而，这种有利的血小板反应性分子指标的减弱并不是仅仅由血小板-A2a受体的刺激来解释的。因此，我们在这次竞争性更新中的目的是扩展血小板-A2a受体的范例，并研究PC缺血引起的血管通畅性的改善是多个位置(中性粒细胞和血小板上的受体)的多个触发器(即腺苷和缓激肽)复杂相互作用的结果。我们将在多种反复血栓形成的活体模型(从大鼠到转基因小鼠再到狗)中，使用生理学和分子细胞终点的综合分析来询问两个主要假设：(I)中性粒细胞(即NPA的形成和中性粒细胞L-选择素的激活)在反复血栓形成的病理生理学中起作用。此外，PC缺血时腺苷的释放有助于通过A2A介导的中性粒细胞L-选择素活化下调来改善血管通畅性的维持。(Ii)PC缺血时缓激肽的释放及其快速分解和产生稳定的缓激肽代谢物，有助于PC通过刺激血小板PAR4受体而增加动脉通畅性。此外，我们认为，先期PC缺血的有利影响并不局限于预处理策略；相反：(Iii)在复发血栓形成发生后应用基于PC的治疗，改善我们的急性冠脉综合征模型的动脉通畅性。我们建议的最终目标是获得新的机械性见解，这些见解可能在未来被用于为有发生血栓事件风险的患者设计新的治疗方法。公共卫生相关性：在急性缺血综合征患者中，未能维持冠状动脉通畅性可引发多种有害后果，包括延长住院时间，增加对介入手术的需求，最值得注意的是，死亡率增加~2倍。现有的旨在降低血栓事件发生概率的疗法(最值得注意的是预防性使用阿司匹林和氯吡格雷)对大约5%-40%的患者无效。因此，从拟议的实验中获得的见解--即确定短暂的预适应缺血和腺苷A2a受体刺激改善血管通畅性的机制--可能在未来用于设计新的抗血小板策略。

DESCRIPTION (provided by applicant): Preconditioning (PC) is the well-described phenomenon whereby brief episodes of myocardial ischemia render cardiomyocytes resistant to a later, sustained ischemic insult. However, evidence from our group has shown that PC has an ancillary, favorable effect on the maintenance of vessel patency in models of recurrent thrombosis mimicking clinical instances of acute ischemic syndromes. We hypothesized, in our previous application, that: (1) the enhanced patency seen with PC ischemia is due to a PC-induced attenuation in one or more molecular indices of platelet activation-aggregation; and (2) adenosine liberated during the PC stimulus, and resultant stimulation of adenosine A2A receptors on the platelets' surface, serves as the trigger for the improved patency. The first concept was supported by novel evidence of a significant, PC-induced down-regulation of platelet P-selectin expression, platelet-fibrinogen binding, and formation of neutrophil-platelet aggregates (NPAs). However, this favorable attenuation in molecular indices of platelet reactivity was not explained solely by platelet-A2A receptor stimulation. Accordingly, our aim in this competitive renewal is to expand on the platelet-A2A receptor paradigm and investigate the concept that the improved vessel patency initiated by PC ischemia is a consequence of a complex interplay among multiple triggers (i.e., adenosine and bradykinin) acting at multiple sites (receptors on neutrophils as well as platelets). We will use an integrated analysis of physiologic and molecular-cellular endpoints, in multiple in vivo models of recurrent thrombosis (ranging from rats to genetically modified mice to dogs), to interrogate two primary hypotheses: (I) Neutrophils (i.e., formation of NPAs and activation of neutrophil L- selectin) contribute to the pathophysiology of recurrent thrombosis. Moreover, release of adenosine during PC ischemia contributes to the improved maintenance of vessel patency by an A2A-mediated down- regulation of neutrophil L-selectin activation. (II) Release of bradykinin during PC ischemia, and its rapid breakdown and production of stable bradykinin metabolites, contribute to the PC-induced augmentation of arterial patency via stimulation of platelet PAR4 receptors. Furthermore, we propose that the favorable effects of antecedent PC ischemia are not confined to a pretreatment strategy; rather: (III) 'PC'-based therapies, applied after the onset of recurrent thrombosis, improve arterial patency in our models of acute coronary syndromes. The ultimate goal of our proposal is to obtain novel mechanistic insights that may, in future, be exploited for the design of new treatments for patients at risk of developing thrombotic events. PUBLIC HEALTH RELEVANCE: In patients with acute ischemic syndromes, failure to maintain coronary patency can precipitate multiple deleterious consequences, including prolonged hospitalization, an increased need for interventional procedures, and, most notably, a ~2-fold increase in mortality. Existing therapies aimed at reducing the probability of thrombotic events (most notably, prophylactic administration of aspirin and clopidogrel) are ineffective in an estimated 5-40% of patients. Thus, insights gained from the proposed experiments - i.e., identification of the mechanisms by which brief episodes of preconditioning ischemia and adenosine A2A receptor stimulation improve vessel patency - may, in future, be exploited in the design of novel anti-platelet strategies.