Thromb Haemost 2016; 115(03): 580-590
DOI: 10.1160/th15-04-0354
Coagulation and Fibrinolysis
Schattauer GmbH

Role of exosite binding modulators in the inhibition of Fxa by TFPI

Sameera Peraramelli*
1   Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, the Netherlands
,
Stella Thomassen*
1   Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, the Netherlands
,
Alexandra Heinzmann
1   Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, the Netherlands
,
Tilman M. Hackeng
1   Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, the Netherlands
,
Rudolf Hartmann
2   Baxalta Innovations GmbH, Vienna, Austria
,
Friedrich Scheiflinger
2   Baxalta Innovations GmbH, Vienna, Austria
,
Michael Dockal
2   Baxalta Innovations GmbH, Vienna, Austria
,
Jan Rosing
1   Department of Biochemistry, Cardiovascular Research Institute Maastricht, University Maastricht, the Netherlands
› Institutsangaben
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Publikationsverlauf

Received: 29. April 2015

Accepted after major revision: 21. Oktober 2015

Publikationsdatum:
20. März 2018 (online)

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Summary

Tissue factor pathway inhibitor (TFPI) down-regulates the extrinsic coagulation pathway by inhibiting FXa and FVIIa. Both TFPI and FXa interact with several plasma proteins (e. g. prothrombin, FV/FVa, protein S) and non-proteinaceous compounds (e. g. phospholipids, heparin). It was our aim to investigate effects of ligands that bind to FXa and TFPI on FXa inhibition by full-length TFPI (designated TFPI) and truncated TFPI (TFPI1-150). Inhibition of FXa by TFPI and TFPI1-150 and effects of phospholipids, heparin, prothrombin, FV, FVa, and protein S thereon was quantified from progress curves of conversion of the FXa-specific chromogenic substrate CS11-(65). Low concentrations negatively charged phospholipids (~10 μM) already maximally stimulated (up to 5- to 6-fold) FXa inhibition by TFPI. Unfractionated heparin at concentrations (0.2–1 U/ml) enhanced FXa inhibition by TFPI ~8-fold, but impaired inhibition at concentrations > 1 U/ml. Physiological protein S and FV concentrations both enhanced FXa inhibition by TFPI 2- to 3-fold. In contrast, thrombin-activated FV (FVa) impaired the ability of TFPI to inhibit FXa. FXa inhibition by TFPI1–150 was not affected by FV, FVa, protein S, phospholipids and heparin. TFPI potently inhibited FXa-catalysed prothrombin activation in the absence of FVa, but hardly inhibited prothrombin activation in the presence of thrombin-activated FVa. In conclusion, physiological concentrations TFPI (0.25–0.5 nM TFPI) inhibit FXa with a t1/2 between 3–15 minutes. Direct FXa inhibition by TFPI is modulated by physiological concentrations prothrombin, FV, FVa, protein S, phospholipids and heparin indicating the importance of these modulators for the in vivo anticoagulant activity of TFPI.

* These authors contributed equally.