Inhibitory effects of TFPI on thrombin and factor Xa generation in vitro--modulatory action of glycosaminoglycans.
The effect of tissue factor pathway inhibitor (TFPI) on thrombin and factor Xa generation was studied in an in vitro system using a prothrombin complex concentrate. It was found that TFPI, via the direct inhibition of factor Xa and the tissue factor/factor VIIa complex, inhibited both the further generation of factor Xa and the generation of thrombin in a concentration-dependent manner. The generation of thrombin (IC50 255 ng/ml) was more pronounced than that of factor Xa (IC50 684 ng/ml). The inhibitory activity of TFPI was significantly enhanced when unfractionated heparin was present in the assay system at a concentration of 10 micrograms/ml which did not show any inhibitory effects on protease generation in the same system. Furthermore, the influence of TFPI at subthreshold concentrations (100 ng/ml and 200 ng/ml, resp.) on the inhibitory action of unfractionated heparin (UFH), a low molecular weight heparin (LMWH), heparan sulfate (HS) and the synthetic heparin pentasaccharide (PS) was investigated. Whereas in the concentration range used (0.3-40 micrograms/ml) these glycosaminoglycans did not inhibit thrombin and factor Xa generation, after supplementation of the system with TFPI a concentration-dependent inhibition of the generation of the proteases up to 40-50% was seen for UFH, LMWH and HS. TFPI did not increase the activity of PS.
Loyola University Medical Center, Department of Pathology, Maywood, IL.
B
B
Kaiser
D A
DA
Hoppensteadt
W
W
Jeske
T C
TC
Wun
J
J
Fareed
D000818:Animals; D015942:Factor VIIa / Q000037:antagonists & inhibitors; D015951:Factor Xa / Q000096:biosynthesis; D065427:Factor Xa Inhibitors; D006493:Heparin / Q000494:pharmacology*; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology*; D006497:Heparan Sulfate / Q000494:pharmacology*; D008074:Lipoproteins / Q000494:pharmacology*; D009844:Oligosaccharides / Q000494:pharmacology*; D013552:Swine; D013917:Thrombin / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D013925:Thromboplastin / Q000037:antagonists & inhibitors
D015942:Factor VIIa; D015951:Factor Xa; D065427:Factor Xa Inhibitors; D006493:Heparin; D006495:Heparin, Low-Molecular-Weight; D006497:Heparan Sulfate; D008074:Lipoproteins; D009844:Oligosaccharides; D013917:Thrombin; D013925:Thromboplastin; C051928:lipoprotein-associated coagulation inhibitor; C049714:IC 831423