PB0543 - Extracellular vesicles from human body fluids trigger coagulation directly by exposing functional tissue factor/factor VIIa complexes

Monday, July 11, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Yong Hu, MA

Graduate student
Amsterdam University Medical Center, University of Amsterdam
Amsterdam, Noord-Holland, Netherlands

Co-Author(s)

CH

Chi Hau

Support Staff
Department of Experimental Clinical Chemistry, Amsterdam UMC, The Netherlands
Amsterdam, Noord-Holland, Netherlands
Cihan Ay, MD

Professor, Head of the Thrombosis and Haemostasis Research Group
Clinical Division of Haematology and Haemostaseology, Department of Medicine I, Medical University of Vienna, Vienna, Austria
Vienna, Wien, Austria
AR

Andreas Repa

Doctor
Clinical Division of Neonatology, Paediatric Intensive Care & Neuropaediatrics, Department of Paediatrics and Adolescent Medicine, Medical University of Vienna, Vienna, Austria
Vienna, Wien, Austria
Ingrid Pabinger, MD

Co-Head of the Thrombosis and Haemostasis Research Group
Clinical Division of Hematology and Hemostaseology, Department of Medicine I, Medical University of Vienna, Vienna, Austria
Vienna, Wien, Austria
RN

Rienk Nieuwland

Research Associate
University of Amsterdam
Amsterdam, Noord-Holland, Netherlands
Johannes Thaler, MD, PhD

Specialist Hematology
Clinical Division of Hematology and Hemostaseology, Department of Medicine I, Medical University of Vienna, Austria
Vianna, Wien, Austria

Background: Tissue factor (TF) is the transmembrane receptor of (activated) coagulation factor (F)VII(a). Together membrane-bound TF and FVIIa form the so-called “extrinsic tenase” complex, which directly triggers coagulation by activating FX to FXa. Surprisingly, TF occurs not only in the vessel wall, but is also present on extracellular vesicles (EVs) in body fluids such as amniotic fluid, milk, saliva, and urine. In amniotic fluid also FVII(a) has been encountered.

Aims: To investigate whether TF-exposing EVs and FVII(a) form functional extrinsic tenase complexes in physiological body fluids.

Methods: Milk, saliva, and urine were collected from healthy breastfeeding women (n=6), and amniotic fluid was collected from healthy women undergoing routine amniocentesis (n=7). EVs were isolated by size exclusion chromatography (SEC) and coagulation (clotting) experiments were performed in the presence and absence of antibodies against TF and FVIIa in normal plasma and in FVII-deficient plasma.

Results: All body fluids (5% vol/vol) triggered clotting of normal plasma (mean clotting time after addition of milk: 89 ± 27s, amniotic fluid 375 ± 148s, saliva 514 ± 110s, urine 1672 ± 1081s, all p-values [compared to buffer] < 0.01) and of FVII-deficient plasma (milk: 123 ± 74 s, followed by amniotic fluid 530 ± 139s, saliva 902 ± 602s, urine 2678 ± 642s, all p-values < 0.05), which was almost completely inhibited by anti-FVII and to a lesser extend by anti-TF. Fractionation of body fluids by SEC showed that only the fractions containing EVs triggered clotting and generated FXa in normal plasma and FVII-deficient plasma, which again was almost completely inhibited by anti-FVII and partially by anti-TF.

Conclusion(s): We demonstrate that normal human body fluids contain functional extrinsic tenase complexes in the form of TF/FVIIa-complex exposing EVs. These EVs activate FX directly, thereby bypassing a major part of the coagulation cascade and may provide direct hemostatic protection.