Singh Pradeep K, Chen Zu-Lin, Horn Katharina, Norris Erin H
Patricia and John Rosenwald Laboratory of Neurobiology and Genetics The Rockefeller University New York New York USA.
Res Pract Thromb Haemost. 2022 Oct 13;6(7):e12815. doi: 10.1002/rth2.12815. eCollection 2022 Oct.
The contact system is initiated by factor (F) XII activation and the assembly of high molecular weight kininogen (HK) with either FXI or prekallikrein (PK) on a negatively charged surface. Overactivation of this system contributes to thrombosis and inflammation in numerous diseases. To develop effective therapeutics for contact system disorders, a detailed understanding of this pathway is needed.
We performed coagulation assays in normal human plasma and various factor-deficient plasmas. To evaluate how HK-mediated PK and FXI activation contributes to coagulation, we used an anti-HK antibody to block access to domain 6 of HK, the region required for efficient activation of PK and FXI.
FXI's binding to HK and its subsequent activation by activated FXII contributes to coagulation. We found that the 3E8 anti-HK antibody can inhibit the binding of FXI or PK to HK, delaying clot formation in human plasma. Our data show that in the absence of FXI, however, PK can substitute for FXI in this process. Addition of activated FXI (FXIa) or activated PK (PKa) abolished the inhibitory effect of 3E8. Moreover, the requirement of HK in intrinsic coagulation can be largely bypassed by adding FXIa. Like FXIa, exogenous PKa shortened the clotting time in HK-deficient plasma, which was not due to feedback activation of FXII.
This study improves our understanding of HK-mediated coagulation and provides an explanation for the absence of bleeding in HK-deficient individuals. 3E8 specifically prevented HK-mediated FXI activation; therefore, it could be used to prevent contact activation-mediated thrombosis without altering hemostasis.
接触系统由因子（F）XII激活以及高分子量激肽原（HK）与因子XI或前激肽释放酶（PK）在带负电荷的表面组装启动。该系统的过度激活在多种疾病中导致血栓形成和炎症。为了开发针对接触系统紊乱的有效疗法，需要对该途径有详细的了解。
我们在正常人血浆和各种因子缺乏的血浆中进行了凝血试验。为了评估HK介导的PK和因子XI激活如何促进凝血，我们使用抗HK抗体来阻断对HK结构域6的 access，该区域是有效激活PK和因子XI所必需的。
因子XI与HK的结合及其随后被激活的因子XII激活有助于凝血。我们发现3E8抗HK抗体可以抑制因子XI或PK与HK的结合，延迟人血浆中的凝块形成。然而，我们的数据表明，在没有因子XI的情况下，PK可以在这个过程中替代因子XI。添加激活的因子XI（因子XIa）或激活的PK（PKa）消除了3E8的抑制作用。此外，通过添加因子XIa可以很大程度上绕过内源性凝血中对HK的需求。与因子XIa一样，外源性PKa缩短了HK缺乏血浆中的凝血时间，这不是由于因子XII的反馈激活。
本研究增进了我们对HK介导的凝血的理解，并为HK缺乏个体无出血现象提供了解释。3E8特异性地阻止了HK介导的因子XI激活；因此，它可用于预防接触激活介导的血栓形成而不改变止血功能。
