Highly procoagulant extracellular vesicles in amniotic fluid

J. Thaler1, L. Hell1, L. Wisgrill1, C. Ay1, A. Spittler1, M. Schwameis1, B. Jilma1, P. Altevogt2, I. Pabinger1 (1Vienna, Austria, 2Heidelberg, Germany)

Women issues in thrombosis and hemostasis
Date: 17.02.2017,
Time: 17:15 - 18:15

Objective: The pathomechanisms underlying disseminated intravascular coagulation (DIC) following amniotic fluid (AF) embolism remain to be fully elucidated. Highly procoagulant phosphatidylserine (PS)- and tissue factor (TF) exposing extracellular vesicles (EVs) might play a central role. It was the objective of the study to perform analyses of the procoagulant properties of AF with a panel of functional coagulation assays and flow cytometry to investigate the pathogenesis of AF induced DIC.

Methods: A prothrombinase assay, an EV-TF dependent factor Xa (FXa) generation assay, a modified thrombin- and fibrin-generation assay, a whole blood clotting model and flow cytometry were applied in AF and control plasma.

Results: Phosphatidylserine expression was 21-fold increased in AF compared to plasma. Factor Xa generation was extremely high when TF-exposing EVs from AF were co-incubated with recombinant FVIIa. In the thrombin- and fibrin generation assay AF-derived EVs strongly activated the blood coagulation cascade via PS and TF. In a whole blood clotting model AF-derived TF-exposing EVs significantly shortened the clotting time from 734 ± 139 seconds in the presence- to 232 ± 139 seconds in the absence of an anti-TF antibody. The contact activation pathway via factor FXII was not affected. Applying flow cytometry, a sub-population of PS- and TF co-exposing EVs was clearly identified in AF.

Conclusion: We investigated the effect of AF on blood coagulation and found that PS+ and TF+ EVs determine its procoagulant potential. Taken together our data further delineate the pathomechanisms underlying AF-induced coagulopathy, which could improve diagnostic- and treatment modalities.