Endogenous Tissue Factor Pathway Inhibitor Modulates Thrombus Formation in an In Vivo Model of Rabbit Carotid Artery Stenosis and Endothelial Injury

Abstract

Background —Tissue factor pathway inhibitor (TFPI) is the sole known inhibitor of the extrinsic coagulation pathway of physiological importance; however, its role in modulating thrombosis in vivo is still unclear. Methods and Results —Intravascular thrombosis was initiated by placing an external constrictor around endothelially injured rabbit carotid arteries (n=10). Carotid blood flow velocity was measured by a Doppler flow probe. After placement of the constrictor, cyclic flow reductions (CFRs), due to recurrent thrombosis, developed at the site of stenosis. Transstenotic TFPI plasma activity was measured in blood samples before induction of CFRs and after 30, 60, and 180 minutes of CFRs. TFPI plasma activity distal to the site of thrombosis was significantly lower than the corresponding proximal values at 30, 60, and 180 minutes of CFRs. In addition, a progressive decrease in TFPI plasma activity was observed in both the proximal and the distal samples, indicating consumption of TFPI during thrombus formation. In 10 additional rabbits, CFRs were abolished by administration of aspirin (10 mg/kg). In the animals in which aspirin abolished CFRs, endogenous TFPI was depleted by a bolus of a polyclonal antibody against rabbit TFPI, and the effects on restoration of CFRs were monitored. In 5 of 6 animals in which aspirin abolished CFRs, depletion of endogenous TFPI activity caused full restoration of CFRs. Conclusions —The data of the present study support the involvement of endogenous TFPI in the process of thrombus formation in vivo and its active role in modulating arterial thrombosis .

Early Atherosclerosis Exhibits an Enhanced Procoagulant State

“…Furthermore, it has been shown that TFPI modulates thrombus formation in experimental models in vivo, 16 primarily by attenuating the procoagulant activity and overexpression of TF. 17,18 Therefore, we tested the levels of TFPI by utilizing a homemade enzyme-linked immunosorbent assay.…”

Deficiency of Tissue Factor Pathway Inhibitor Promotes Atherosclerosis and Thrombosis in Mice

“…5 In addition, human atherosclerotic arterial segments exposed to flowing blood are less thrombogenic when treated with recombinant TFPI or a polyclonal antibody against tissue factor. 16 Conversely, inhibition of endogenous TFPI with a polyclonal antibody leads to more thrombus formation in a rabbit carotid artery injury model, 6 and a mutation in the TFPI gene, resulting in the replacement of proline at position 151 by leucine, was recently shown to be a risk factor for vascular thrombosis in humans. 17 Mice homozygous for an inactive TFPI allele generated by gene targeting exhibit an embryonic lethal phenotype that seems to be due to disseminated thrombosis.…”

“…Overexpression of TFPI has been shown to reduce thrombus formation after vascular injury in animal models, 4,5 whereas reduced endogenous TFPI activity may enhance thrombus formation. 6 Mice genetically engineered to be completely deficient in functional TFPI demonstrate embryonic lethality, whereas mice heterozygous for TFPI deficiency appear normal, although plasma TFPI activity is reduced. 7 To test the hypothesis that modest reductions in TFPI levels will promote atherosclerosis and thrombosis, mice with a combined apolipoprotein E (apoE) and TFPI deficiency were generated and analyzed for the development of atherosclerosis throughout the vascular tree and for thrombosis after plaque injury.…”

Lethal Perinatal Thrombosis in Mice Resulting From the Interaction of Tissue Factor Pathway Inhibitor Deficiency and Factor V Leiden

“…Animal studies have demonstrated an important in vivo regulatory role of TFPI in vascular thrombosis. 10,11 Variations in TFPI expression may be particularly important in the setting of other prothrombotic risk factors. In a synthetic in vitro assay of thrombin generation, reduction of TFPI concentration by 50% resulted in a slight increase in thrombin generation.…”