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

Sameera Peraramelli, Stella Thomassen*, Alexandra Heinzmann, Tilman M. Hackeng, Rudolf Hartmann, Friedrich Scheiflinger, Michael Dockal, Jan Rosing

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

24 Citations (Web of Science)

Abstract

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 (similar to 10 mu M) 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 similar to 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 t(1/2) 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.
Original languageEnglish
Pages (from-to)580-590
JournalThrombosis and Haemostasis
Volume115
Issue number3
DOIs
Publication statusPublished - Mar 2016

Keywords

  • Exosites
  • prothrombin
  • factor V/Va
  • factor Xa
  • TFPI

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