Long-lasting antithrombotic effects of a single dose of human recombinant, active site-blocked factor VII: insights into possible mechanism(s) of action

Summary.  Tissue factor (TF) is important in initiating intravascular thrombosis. We demonstrated that active-site blocked factor VII (FVIIai) inhibits intravascular thrombosis for at least 6 h following a single injection, despite FVIIai plasma half-life was ∼45 min. The aims of the present study were: (a) to determine the duration of the antithrombotic effects of a single injection of FVIIai; and (b) to assess whether FVIIai prolonged effects can be explained by a slow dissociation rate from TF in the arterial wall. Cyclic flow variations (CFVs), obtained in stenotic rabbit carotid arteries with endothelial injury, were abolished by either FVIIai (100 µg kg⁻¹ min⁻¹ for 10 min) or hirudin (1 mg kg⁻¹). After CFVs were abolished, carotid blood flow velocity was recorded continuously for 24 h. CFVs restored in all hirudin-treated animals after 2.1 ± 0.3 h, while they restored in only four of nine FVIIai-treated rabbits in 10.1 ± 2.2 h. Five animals in this group did not show restoration of CFVs up to 24 h. Immunohistochemistry revealed that FVIIai was still bound to the arterial wall 24 h following its administration, despite at this time FVIIai plasma levels were undetectable. Prothrombin time and partial thromboplastin time did not change significantly. FVIIai exerts potent, long-lasting antithrombotic effects without affecting systemic hemostatic parameters; a possible mechanism is a slow dissociation rate of FVIIai from TF. These proprieties make FVIIai particularly attractive as an antithrombotic intervention.