Highly Procoagulant Extracellular Vesicles in Amniotic Fluid

Background: 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) expressing extracellular vesicles (EVs) might play a central role.

Objective: To perform extensive 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-expressing 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-expressing 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-expressing EVs was clearly identified in AF.

Conclusions: We thoroughly 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.