Adenovirus-mediated local expression of human tissue factor pathway inhibitor eliminates shear stress-induced recurrent thrombosis in the injured carotid artery of the rabbit

The main cause of acute coronary syndrome may be recurrent thrombosis, which is initiated by the activation of the extrinsic coagulation pathway. Tissue factor (TF) pathway inhibitor (TFPI) efficiently inhibits an early step in this pathway by the formation of a complex with factor VIIa, TF, and factor Xa. We determined whether local TFPI gene transfer can inhibit thrombosis in an injured artery without inducing systemic side effects. Balloon-injured rabbit carotid arteries were infected with an adenoviral vector that expressed either human TFPI (AdCATFPI) or bacterial beta-galactosidase (AdCALacZ). Two to 6 days after gene transfer, thrombosis was induced by the production of constant stenosis of the artery, and blood flow was measured continuously with an electromagnetic flow probe. A cyclic flow variation, which is thought to reflect the recurrent formation and dislodgment of mural thrombi, was observed in all AdCALacZ-infected arteries as well as in saline-infused arteries. In contrast, no cyclic flow variation was detectable in AdCATFPI-transfected arteries, even in the presence of epinephrine (1 microg. kg-1. min-1 infusion). Prothrombin time, activated partial thromboplastin time, and the ex vivo platelet aggregation induced by either adenosine diphosphate or collagen were unaltered in AdCATFPI-infected rabbits. We found that in vivo TFPI gene transfer into an injured artery completely inhibits the recurrent thrombosis induced by shear stress even in the presence of catecholamine, without affecting systemic coagulation status. Adenovirus-mediated local expression of TFPI may have the potential for the treatment of human thrombosis.

Effects of recombinant human tissue factor pathway inhibitor on thrombus formation and its in vivo distribution in a rat DIC model

Tissue factor pathway inhibitor (TFPI) plays a key role in modulating tissue factor-dependent blood coagulation. This study was done to determine not only the inhibitory effects of recombinant human TFPI (rTFPI) on thrombus formation in rat models with disseminated intravascular coagulation (DIC), but also to identify the distribution of exogenous TFPI in vivo. Disseminated intravascular coagulation was induced by administering a priming dose of carrageenan 10 mg/kg body weight and was followed 24 hours later by a provocative dose of lipopolysaccharide (LPS) 500 mg/kg body weight. The rTFPI was administered intravenously at a dose of either 1 or 4 mg/kg body weight immediately after LPS treatment. Exogenous rTFPI at a dose of 4 mg/kg significantly inhibited the consumption of fibrinogen, platelets and factor VIIa (P < .05) and also reduced the number of fibrin thrombi formed in the liver, lungs, kidneys, and spleen (P < .05), whereas rTFPI at a dose of 1 mg/kg had no significant inhibitory effect on these DIC parameters. Recombinant human rTFPI activity was rapidly cleared from the plasma; however, a significant amount of the inhibitor was still present in tissues even 3 to 6 hours after intravenous administration. Exogenous TFPI was mainly identified in Kupffer cells, macrophages, and on the microvascular endothelial lining of different organs. In the kidney, rTFPI was identified on both the abluminal surface of the renal tubules and the luminal surface of the proximal convoluted tubules. No rTFPI, however, was detected in the hepatocytes. Tissue factor was mainly expressed by monocytes/macrophages. These findings suggest that TFPI plays an important role in modulating TF-dependent thrombogenesis. The elucidation of the rTFPI distribution and interactions in vivo might thus provide valuable insight into its inhibitory mechanisms as well as its therapeutic implications in DIC.