TY - JOUR
T1 - Role of exosite binding modulators in the inhibition of Fxa by TFPI
AU - Peraramelli, Sameera
AU - Thomassen, Stella
AU - Heinzmann, Alexandra
AU - Hackeng, Tilman M.
AU - Hartmann, Rudolf
AU - Scheiflinger, Friedrich
AU - Dockal, Michael
AU - Rosing, Jan
PY - 2016/3
Y1 - 2016/3
N2 - 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.
AB - 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.
KW - Exosites
KW - prothrombin
KW - factor V/Va
KW - factor Xa
KW - TFPI
U2 - 10.1160/TH15-04-0354
DO - 10.1160/TH15-04-0354
M3 - Article
C2 - 26607136
SN - 0340-6245
VL - 115
SP - 580
EP - 590
JO - Thrombosis and Haemostasis
JF - Thrombosis and Haemostasis
IS - 3
ER -