Preferential localization of recombinant factor VIIa to platelets activated with a combination of thrombin and a glycoprotein VI receptor agonist

Abstract

To cite this article: Kjalke M, Kjellev S, Rojkjaer R. Preferential localization of recombinant factor VIIa to platelets activated with a combination of thrombin and a glycoprotein VI receptor agonist. J Thromb Haemost 2007; 5: 774-80.Summary. Background: Activation of platelets with a combination of collagen and thrombin generates a subpopulation of highly procoagulant ÔcoatedÕ platelets characterized by high surface expression of fibrinogen and other procoagulant proteins. Objectives: To analyze the interaction of recombinant factor VIIa (rFVIIa) with coated platelets. Methods and results: rFVIIa localized to the coated platelets in flow cytometry experiments, while minimal rFVIIa was found on platelets activated with adenosine diphosphate, thrombin or via glycoprotein VI individually, and essentially no rFVIIa was found on non-stimulated platelets. Removal of the c-carboxyglutamic acid (Gla) domain of rFVIIa, and addition of EDTA, annexin V or excess prothrombin inhibited rFVIIa localization to the coated platelets, indicating that the interaction was mediated by the calcium-dependent conformation of the Gla domain and platelet exposure of negatively charged phospholipids. A reduced level of platelet fibrinogen exposure was observed at hemophilia A-like conditions in a model system of cell-based coagulation, indicating that coated platelet formation in hemophilia may be diminished. Addition of rFVIIa dosedependently enhanced thrombin generation and partly restored platelet fibrinogen exposure. Conclusions: The data suggest that rFVIIa localized preferentially on platelets activated with dual agonists, thereby ensuring enhanced thrombin generation localized at the site of injury where both collagen and tissue factor are exposed, the latter ensuring the formation of thrombin necessary for coated platelet formation.

Decreased generation of procoagulant platelets detected by flow cytometric analysis in patients with bleeding diathesis

“…Finally, in vitro studies have shown that recombinant FVIIa preferentially binds to procoagulant platelets (34,35), and similar preferential binding to COAT platelets has been described for vatreptacog alfa, a novel recombinant FVIIa variant (36). Taking these data into account, the individual level of COAT platelets might be an important component for explaining the difference in hemostatic response to these drugs.…”

Hemostatic and neuroprotective effects of human recombinant activated factor VII therapy after traumatic brain injury in pigs

“…Thus, it is possible that rFVIIa enters the brain parenchyma as a result of the pathological BBB disruption secondary to trauma and directly exerts its neuroprotective effects via this mechanism. Alternatively, rFVIIa controls bleeding pharmacologically by enhancing thrombin generation on the surface of platelets adherent to the site of vascular injury (Kjalke et al, 2007). Thrombin has been demonstrated to be neurotoxic at high concentrations and neuroprotective at low concentrations (Figueroa et al, 1998;Gorbacheva et al, 2006;Gingrich and Traynelis, 2000).…”

The endothelial protein C receptor enhances hemostasis of FVIIa administration in hemophilic mice in vivo

“…6,7 Alternatively, rhFVIIa administration is hemostatic through an activated platelet-dependent but TF-independent mode of action. Specifically, the poor affinity of FVII for anionic phospholipid membranes 8 necessitates large doses of rhFVIIa for treatment to generate hemostatic amounts of FXa. 9,10 This mode of action is supported by the greater clinical efficacy of an analog of rhFVIIa with enhanced TF-independent activity and platelet-binding sites.…”