PLATELET-HEPARIN INTERACTIONS IN CARDIOVASCULAR SURGERY

血栓形成和出血是两个主要的问题， 心血管手术，血小板是两者的核心。 的行动 肝素导致出血，包括肝素作用， 超越了对经典血浆凝固途径的抑制。 特别是，虽然肝素可能会通过损害血管内皮细胞而引起病理性出血， 关键的血小板止血功能，肝素也有有限的疗效， 预防动脉循环中的血栓形成，这是一个介导的过程， 部分通过血小板与血管性血友病因子（vWF）之间的相互作用 在血管壁损伤的部位。 因此，显然需要 开发具有更高特异性和选择性的抗血栓药物 血小板效应，适合心血管疾病的独特要求 手术、动脉损伤和血液与人造表面接触。 我们实验室的数据表明，某些肝素 血小板，我们已经确定了血小板糖蛋白IIb和IIIa， 结合位点（除其他外）。 血小板结合肝素可直接调节 血小板功能通过其对钙的影响。 相反，肝素 间接抑制血小板止血功能，通过干扰vWF- 血小板结合 肝素对vWF功能的抑制不依赖于 其常规抗凝活性。 我们已经确定， 其特征在于结合肝素的vWF的23个氨基酸结构域， 这已经分离出具有增强的抑制vWF能力的肝素级分， 依赖血小板功能。 我们现在建议确定肝素直接 通过血小板结合位点的生化分析改变血小板功能 肝素介导的血小板生理学研究 activation. 我们将绘制vWF的肝素结合结构域， 肝素结合诱导的构象变化，并分离和 表征具有强效抗vWF活性的肝素的结构。 这些调查路线直接导致我们的长期目标： 开发具有独特的、集中的 适合特定血栓形成和出血问题的生物活性 与心血管手术和体外循环相关。

Thrombosis and hemorrhage are two of the dominant problems associated with cardiovascular surgery, and platelets are central to both. The actions of heparin contribute to bleeding, including heparin's effects which lay beyond the inhibition of the classic plasma coagulation pathways. Paradoxically, while heparin may cause pathologic bleeding by impairment of critical platelet hemostatic function, heparin also has limited efficacy in preventing thrombosis in the arterial circulation, a process mediated in part by the interactions between platelets and von Willebrand Factor (vWF) at sites of vessel wall injury. Thus, there is a clear need for the development of antithrombotic agents with more specific and selective platelet effects, suited to the unique requirements of cardiovascular surgery, arterial injury, and blood contact with artificial surfaces. Data from our laboratories suggest that certain heparins bind more avidly to platelets, and we have identified platelet glycoproteins IIb and IIIa as binding sites (among others). Platelet-bound heparin may directly modulate platelet function via its effects on calcium. In contrast, heparin indirectly inhibits platelet hemostatic function, by interfering with vWF- platelet binding. Heparin's inhibition of vWF function is independent of its conventional anticoagulant activity. We have identified and characterized a 23 amino acid domain of vWF which binds heparin, and with this have isolated a heparin fraction with enhanced ability to inhibit vWF- dependent platelet function. We now propose to identify the mechanism(s) by which heparin directly alters platelet function by biochemical analysis of platelet binding sites and heparin structure, and physiologic studies of heparin-mediated platelet activation. We will map the heparin-binding domain(s) of vWF, determine the conformational changes induced by heparin binding, and isolate and characterize the structure of heparins with potent anti-vWF activity. These lines of investigation lead directly to our long term goals: the development of new antithrombotic glycosaminoglycans with unique, focussed biologic activity suited to the specific thrombotic and hemorrhage problems associated with cardiovascular surgery and extracorporeal circulation.