Multimeric Structural Degradation of vWF in Turbulent Flows

摘要 获得性血管性血友病综合征(AvWS)，其特征是大分子多聚体丢失 血管性血友病因子(VWF)的高相对分子质量常与非生理性血流有关。AvWS是 发现于有严重主动脉狭窄(AS)或持续血流左心室辅助装置(cf-LVADs)的患者。 有趣的是，这种与严重AS相关的止血异常在第二天就完全纠正了 做手术。对于与cf-Lvad关联的AvWS，它在移除设备后迅速消失，强烈 这表明设备本身就是导致这种综合症的原因。人们普遍认为，超生理学 重度AS和cf-LVADs的剪应力和/或长暴露时间是导致HMWM丢失的原因。 尽管HMWM的破坏被认为是机械和酶切割的组合，但 完整的机制仍不清楚。同样值得注意的是，在搏动性血流中很少观察到AvWS。 设备。有必要了解vWF的退化机制和曝光时间，特别是当 预计会有非生理性的血流。这项提案的目的是描述 完全控制层流通过湍流条件下的HMWM功率密度 (单位质量的能量耗散率)和临床相关的暴露时间。中心假设是 VWF的HMWM降解是一个时间敏感的机械酶事件，主要发生在 通过将ADAMTS13暴露在vWF上的解理位置来实现湍流条件。基于我们之前的 以及文献中的证据，我们认为大多数vWF多聚体的降解是 ADAMTS13介导。然而，我们认识到vwf还有其他潜在的汇和源。 包括对设备表面的吸附，与血小板的结合，以及从⍺颗粒释放vWF 激活的血小板。我们将在这些实验中测试并说明这些汇和源。成功 拟议研究的完成将使我们能够：1)确定非生理性血液之间的关系 流动和曝光时间与cf-lvad中HMWM损耗的关系，ii)评价降解机理 以及iii)从机械酶、机械学和酶的角度来表征该机理 通过全面的vWF生物学提高敏感性。最终，预期模型将成为一种工具 优化设备设计，为患者带来下一代血泵和更好的临床结果 使用AvWS。

ABSTRACT Acquired von Willebrand Syndrome (AvWS) characterized by the loss of high molecular weight multimers (HMWMs) of von Willebrand factor (vWF) is often associated with nonphysiologic blood flows. AvWS is found in patients with severe aortic stenosis (AS) or continuous-flow left ventricular assist devices (cf-LVADs). Interestingly, this hemostatic abnormality associated with severe AS is fully corrected on the first day after surgery. For AvWS associated with cf-LVADs, it disappears quickly after removal of the device, strongly suggesting that the device itself is responsible for the syndrome. It is widely believed that the supraphysiologic shear stress and/or long exposure time in severe AS and cf-LVADs are responsible for the loss of HMWM. Although the destruction of HMWM is believed to be a combination of mechanical and enzymatic cleavage, the complete mechanism still remains unclear. Also notable is that AvWS is rarely observed in pulsatile blood flow devices. There is a need to understand the degradation mechanism of vWF and exposure time especially when nonphysiologic blood flows are expected. The objective of this proposal is to characterize the degradation of HMWM under fully controlled laminar through turbulent blood flow conditions in terms of power density (energy dissipation rate per unit mass) and clinically relevant exposure times. The central hypothesis is that the degradation of HMWM of vWF is a time-sensitive mechanoenzymatic event that occurs primarily under turbulent flow conditions by exposing the ADAMTS13 to cleavage sites on vWF. Based on our previous publications as well as evidence in the literature, we believe that the majority of vWF multimer degradation is ADAMTS13 mediated. However, we recognize that there are other potential sinks and sources of vWF including adsorption to the surfaces of a device, binding to platelets, and release of vWF from ⍺-granules of activated platelets. We will test and account for these sinks and sources in these experiments. Successful completion of the proposed study will allow us to i) determine the relationship between nonphysiologic blood flow and exposure time involved in the loss of HMWM in cf-LVADs, ii) evaluate the degradation mechanism of HMWM, and iii) characterize the mechanism in terms of mechanoenzymatic, mechanistic, and enzymatic sensitivity through comprehensive vWF biology. Ultimately, the prospective model is expected to be a tool for device design optimization leading to a next-generation blood pump and better clinical outcomes for patients with AvWS.