Procoagulant extracellular vesicles in amniotic fluid.

Embolization of amniotic fluid (AF) into the blood circulation leads to disseminated intravascular coagulation (DIC). Procoagulant phosphatidylserine (PS)- and tissue factor (TF)-exposing extracellular vesicles (EVs) might play an important role in AF embolism-induced DIC. It was the aim of the present study to perform analyses of the procoagulant properties of AF with a panel of functional coagulation assays and flow cytometry. We applied a prothrombinase assay (that quantifies PS exposure on EVs), an EV-associated TF activity assay, a fibrin generation assay, a thrombin generation assay, a whole blood clotting model, and flow cytometry in AF and control plasma. We found that PS exposure on EVs was 21-fold increased in AF compared with plasma. Also, EV-associated TF activity was highly increased in AF compared with plasma. AF-derived EVs activated the blood coagulation cascade via PS and TF in the fibrin and thrombin generation assays. In a whole blood clotting model, AF-derived 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 XII (FXII) was not affected. Applying flow cytometry, a subpopulation of PS and TF EVs was identified in AF but not in control plasma. In conclusion, we investigated the effect of AF on blood coagulation and found that PS and TF EVs determine their procoagulant potential. Taken together, our data further delineate the pathomechanisms underlying AF-induced coagulopathy.