Dissociation of Antithrombotic Effect and Bleeding Time Prolongation in Rabbits by Inhibiting Tissue Factor Function

Abstract

SummaryInhibition of the tissue factor/factor Vila (TF/F. Vila) complex attenuates thrombosis in different animal models of arterial thrombosis. However, it remains unclear to what extent the antithrombotic effects are associated with changes in hemostatic functions and how this compares with inhibition of thrombin, an enzyme acting at a later stage in the coagulation cascade. The antithrombotic and the antihemostatic effects of a monoclonal anti-TF antibody (AP-1) were compared in a model of arterial thrombosis to those of a direct thrombin inhibitor (napsagatran) and heparin. In anesthetized rabbits transient arterial thrombi were induced by mechanical damage to the subendothelium of a moderately stenosed carotid artery. Recurrent formation and dis lodgement of thrombi resulted in cyclic flow variations (CFVs) which were monitored over 2 hours. Rabbits received intravenously either a placebo (control), a monoclonal anti-rabbit TF antibody (AP-1, 05 mg/kg as an i.v. bolus repeated every 15 min, a specific low molecular weight thrombin inhibitor (napsagatran, 3 fxg/kg/min) or heparin (3 and 13 fig/kg/min). The effect of the inhibitors on the hemostatic system was studied in a separate set of rabbits by measuring template bleeding times (BT) in the ear arterioles, marginal ear vein and the nail cuticle of the foreleg. AP-1 and napsagatran showed a similar antithrombotic activity (78% and 80% abolition of the CFVs, respectively), whereas either low or high dose heparin was poorly effective (43 % and 40% inhibition of CFVs, respectively). At these antithrombotic doses and even at 4-fold higher dosage, AP-1 did not significantly alter the BT, whereas napsagatran and heparin prolonged the ear vessels and cuticle BT in a dose-dependent manner. These results suggest that in contrast to direct thrombin inhibition, the blockade of the TF/F. Vila function did not result in a concomitant prolongation of the bleeding time. Thus, dissociation of antithrombotic and antihemostatic effects indicates that inhibition of the coagulation system at its initial stage represents a promising approach for the development of new anticoagulants.

Pharmacological Interruption of Acute Thrombus Formation with Minimal Hemorrhagic Complications by a Small Molecule Tissue Factor/Factor VIIa Inhibitor: Comparison to Factor Xa and Thrombin Inhibition in a Nonhuman Primate Thrombosis Model

“…Previous reports (Harker et al, 1996;Himber et al, 1997;Zoldhelyi et al, 2000), using various approaches to inactivate the TF/VIIa axis, corroborate the current findings. Taken together, these studies indicate that pharmacological interruption of coagulation at this very early point in the cascade (TF/VIIa inhibition), results in desirable antithrombotic efficacy that is accompanied by little or no change in bleeding diatheses.…”

“…Pharmacological attempts have been made at various points of potential intervention in the coagulation cascade, ranging from nonspecific inhibitors such as warfarin, unfractionated heparin, and low-molecular weight heparins, to specific inhibitors of factor Xa or direct acting thrombin inhibitors (Hara et al, 1995;Sanderson et al, 1998;Hauptmann and Sturzebecher, 1999;Pinto et al, 2001). Previous reports suggest that inhibitors of the TF/VIIa complex may prevent thrombosis with a lower bleeding risk than other types of coagulation inhibitors (Harker et al, 1996;Himber et al, 1997;Zoldhelyi et al, 2000).…”

Structural Requirements for TFPI-Mediated Inhibition of Neointimal Thickening After Balloon Injury in the Rat

“…Recent studies have suggested that agents targeting factor VIIa/TF (eg, VIIai, anti-TF antibodies) may induce less bleeding than agents that target coagulation at latter stages. [31][32][33] Consistent with this notion, in preliminary studies, plasma levels of XK 1 Ͼ100-fold its IC 50 in the rat thromboplastin-induced coagulation assay did not produce hemorrhagic manifestations during the surgical manipulations required for the balloon angioplasty procedure.…”

Nonpeptide Factor Xa Inhibitors III: Effects of DPC423, an Orally-Active Pyrazole Antithrombotic Agent, on Arterial Thrombosis in Rabbits

“…The rabbit cuticle bleeding time model, described previously by Himber et al (1997), was used in this study with some modifications. Briefly, rabbits were anesthetized as described above, and their hind paws were shaved.…”

“…Since the efficacy of DPC423 for the prevention of arterial thrombosis and its bleeding risk have not been evaluated, the objective of this study was to compare effects of DPC423 with those of the currently used anticoagulants enoxaparin (a low-molecular-weight heparin; Noble and Spencer, 1998) and argatroban (a direct thrombin inhibitor; McKeage and Plosker, 2001) on arterial thrombosis and hemostasis in rabbit models of the electrically induced carotid artery thrombosis (ECAT; Wong et al, 2000a) and cuticle bleeding (Himber et al, 1997), respectively. We also examined the oral antithrombotic activity of DPC423 in the rabbit ECAT model.…”