Procoagulant microparticles promote coagulation in a factor XI‐dependent manner in human endotoxemia

Abstract

Summary Background Human endotoxemia is characterized by acute inflammation and activation of coagulation, as well as increased numbers of circulating microparticles (MPs). Whether these MPs directly promote coagulation and through which pathway their actions are mediated, however, has not been fully explored. Objectives In this study, we aimed to further characterize endotoxin-induced MPs and their procoagulant properties using several approaches. Methods Enumeration and characterization of MPs were performed using a new generation flow cytometer. Relative contributions of the extrinsic and intrinsic pathways in MP-mediated procoagulant activity were assessed using plasmas deficient in FVII or FXI or with blocking antibodies to tissue factor (TF) or FXIa. Results Total MPs and platelet MPs were significantly elevated in plasma at 6 hours after infusion of endotoxin in healthy human subjects. MPs isolated from plasma following endotoxin infusion also demonstrated increased TF activity in a re-constituted buffer system. When added to re-calcified platelet poor plasma, these MPs also promoted coagulation, as judged by a decreased clotting time with shortening of the lag time and time to peak thrombin using calibrated automated thrombography (CAT). However, the use of FVII deficient plasma or blocking antibody to TF did not inhibit these procoagulant effects. In contrast, plasma clotting time was prolonged in FXI deficient plasma, and a blocking antibody to FXIa inhibited all MP-mediated parameters in the CAT assay. Conclusions The initiation of coagulation by cellular TF in endotoxemia is in contrast to (and presumably complemented by) the intrinsic pathway-mediated procoagulant effects of circulating MPs.

Transfusion of autologous extracellular vesicles from stored red blood cells does not affect coagulation in a model of human endotoxemia

“…). During endotoxemia, the increase in EV‐induced thrombin generation was more pronounced compared to TF‐initiated thrombin generation, which is in accordance with previously published studies . We found no evidence that transfusion of fresh or stored blood containing high levels of EVs further increased thrombin generation (Figs.…”

“…In our study, infusion of LPS increased the levels of WBC and platelet EVs and induced EV‐dependent hypercoagulability. This is in accordance with earlier studies . However, infusion of high numbers of RBC EVs from stored RBC products did not augment thrombin generation.…”

“…They are released by RBCs, platelets, white blood cells (WBCs), or endothelial cells and are involved in a broad spectrum of biological activities. The hemostatic functions of EVs are thought to be mediated by the presence of tissue factor (TF) and phosphatidylserine (PS) on the surface of the microvesicles …”

Application of Extracellular Vesicles Proteomics to Cardiovascular Disease: Guidelines, Data Analysis, and Future Perspectives

“…There are many similarities between the complement and coagulation systems, both being characterized by sequential activation of a series of proteins . In this context, recent studies have described that EVs have multiple roles in promoting the coagulation cascade and the immune modulation . Complement cascade proteins are well known to predict the risk of future cardiovascular events.…”

Sepsis-Associated Coagulopathy

“…The relative contributions of the intrinsic and extrinsic pathways to MP-initiated thrombin generation were assessed using FVII-deficient plasma or antibodies to block TF effects, revealing the important role for FXI and the intrinsic pathway in the MP-induced pro-coagulant activity [28].…”