PLATELET-HEPARIN INTERACTIONS IN CARDIOVASCULAR SURGERY

血栓和出血是与以下疾病相关的两个主要问题 心血管手术和血小板是两者的中心。的行为 肝素导致出血，包括肝素的作用 超越了经典的血浆凝固途径的抑制。 自相矛盾的是，肝素可能通过损害 关键的血小板止血功能，肝素也有有限的疗效 防止动脉循环中的血栓形成，这一过程介导了 部分是由于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 更具特异性和选择性的抗血栓药物的研究进展 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工表面接触。 来自我们实验室的数据表明，某些肝素更容易结合。 我们已经鉴定了血小板膜糖蛋白IIb和IIIa是 结合位点(以及其他)。与血小板结合的肝素可能直接调节 血小板的功能是通过它对钙的作用来实现的。相比之下，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功能的抑制作用不依赖于 它的常规抗凝血活性。我们已经确定并 鉴定了vWF与肝素结合的23个氨基酸结构域，并与 这分离出一种肝素组分，其抑制vWF的能力增强- 依赖的血小板功能。 我们现在建议确定肝素直接作用的机制(S) 通过对血小板结合部位的生化分析改变血小板功能 和肝素结构，肝素介导的血小板的生理研究 激活。我们将定位vWF的肝素结合结构域(S)，确定 肝素结合引起的构象变化，并分离和 表征具有强大的抗vWF活性的肝素的结构。 这些调查工作直接通向我们的长期目标： 具有独特靶向性的新型抗血栓糖胺聚糖的研究进展 适用于特定血栓和出血问题的生物活性 与心血管手术和体外循环有关。

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.