Tissue factor-independent effects of recombinant factor VIIa on hemostasis

Human platelets express endothelial protein C receptor, which can be utilized to enhance localization of factor VIIa activity

Essentials Factor VIIa binds activated platelets to promote hemostasis in hemophilia patients with inhibitors. The interactions and sites responsible for platelet-FVIIa binding are not fully understood. Endothelial cell protein C receptor (EPCR) is expressed on activated human platelets. EPCR binding enhances the efficacy of a FVIIa variant and could impact design of new therapeutics.

SUMMARY

Background High-dose factor VIIa (FVIIa) is routinely used as an effective bypassing agent to treat hemophilia patients with inhibitory antibodies that compromise factor replacement. However, the mechanism by which FVIIa binds activated platelets to promote hemostasis is not fully understood. FVIIa-DVQ is an analog of FVIIa with enhanced tissue factor (TF)-independent activity and hemostatic efficacy relative to FVIIa. Our previous studies have shown that FVIIa-DVQ exhibits greater platelet binding, thereby suggesting that features in addition to lipid composition contribute to platelet-FVIIa interactions. Objectives Endothelial cell protein C receptor (EPCR) also functions as a receptor for FVIIa on endothelial cells. We therefore hypothesized that an interaction with EPCR might play a role in platelet-FVIIa binding. Methods/results In the present study, we used flow cytometric analyses to show that platelet binding of both FVIIa and FVIIa-DVQ is partially inhibited in the presence of excess protein C or an anti-EPCR antibody. This decreased binding results in a corresponding decrease in the activity of both molecules in FXa and thrombin generation assays. Enhanced binding to EPCR was sufficient to account for the increased platelet binding of FVIIa-DVQ compared with wild-type FVIIa. As EPCR protein expression has not previously been shown in platelets, we confirmed the presence of EPCR in platelets using immunofluorescence, flow cytometry, immunoprecipitation, and mass spectrometry. Conclusions This work represents the first demonstration that human platelets express EPCR and suggests that modulation of EPCR binding could be utilized to enhance the hemostatic efficacy of rationally designed FVIIa analogs.

Inherited, congenital and acquired disorders by hemostasis (vascular, platelet & plasmatic phases) with repercussions in the therapeutic oral sphere

The hemostasis alterations, either congenital or hereditary origin, and acquired, are circumstances that hinder oral care to patients who suffer them and also generates in the professional who has to attend, high stress. Bleeding control once established and dental treatment planning, both in the aspect of preparation, as the realization of the odonto-stomatological therapeutic, has suffered updates that do need to remember certain aspects of the care of these patients. But we must not forget that the hematologist or internist who controls the patient's medical condition, is a cornerstone for the planning and implementation of treatment plans. We must also remember that, in certain circumstances, treatment should be performed in a hospital setting. In this review, we aim to provide the odonto-stomatologist guidance on how to address the problem and provide simple and updated guidelines to apply in the treatment of these people.

A zymogen-like factor Xa variant corrects the coagulation defect in hemophilia

Effective therapies are needed to control excessive bleeding in a range of clinical conditions. We describe a surprisingly useful approach to improve hemostasis in vivo using a variant of coagulation factor Xa (FXa^I16L). This conformationally pliant derivative is partially inactive due to a defect in transitioning from zymogen to protease ^1,2. Using mouse models of hemophilia, we show that FXa^I16L has a prolonged half-life, relative to wild-type FXa and does not cause excessive activation of coagulation. Once clotting mechanisms are activated to produce its cofactor FVa, FXa^I16L is driven to the protease state and restores hemostasis in hemophilic animals upon vascular injury. Moreover, using human or murine analogs, we show that FXa^I16L is more efficacious than FVIIa which is used to treat bleeding in hemophilia inhibitor patients³. Because of its underlying mechanism of action, FXa^I16L may provide an effective strategy to enhance blood clot formation and act as a rapid pan-hemostatic agent for the treatment of bleeding conditions.

Platelet binding and activity of a factor VIIa variant with enhanced tissue factor independent activity

BACKGROUND AND OBJECTIVES

Platelet binding and activity play important roles in the efficacy of factor VIIa (FVIIa) as a bypassing agent for hemophilia treatment. An analog of FVIIa with increased tissue factor (TF)-independent activity, NN1731, has been produced by introducing three amino acid changes in the protease domain. NN1731 has a conformation similar to TF-bound FVIIa, even in the absence of TF. This results in much greater intrinsic proteolytic activity, but similar activity in the presence of TF.

OBJECTIVES

We hypothesized that these changes would not alter binding to platelets or phospholipid, a characteristic thought to be localized to the Gla domain. The goal of the current work was to compare platelet binding and activity of NN1731 and wild-type FVIIa.

METHODS/RESULTS

FVIIa and NN1731 bound identically to phospholipid vesicles as assessed by both activity assays and electrophoretic quasielastic light scattering techniques. However, NN1731 bound to a greater number of sites on activated platelets than FVIIa, as assessed by flow cytometry. Removal of the Gla domain abolished binding of both FVIIa and NN1731. Inhibition of the active site did not reduce NN1731 binding to the level of FVIIa. When corrected for the amount of protein bound, NN1731 had greater activity than FVIIa on platelet surfaces.

CONCLUSIONS

While the Gla domain is essential for FVIIa binding to platelets, changes in the protease domain in NN1731 enhanced platelet binding as well as proteolytic activity. Features in addition to lipid composition appear to contribute to binding of rFVIIa and, especially, NN1731 to platelets.

[Efficacy of recombinant activated factor VII in diffuse alveolar haemorrhage]

INTRODUCTION

Alveolar haemorrhage is a serious complication of a range of different pathologies. Published recent literature has reported only cases unresponsive to the usual treatment (steroids, transfusions, immunosuppressors and mechanical ventilation) as well as multiple secondary complications of these kinds of therapies. Recombinant activated factor VII (rF VIIa) is a new class of agent, which appears to be a successful adjunct therapy in the case of failure of conventional treatments.

OBSERVATIONS

We describe two cases of alveolar haemorrhage treated with rF VIIa. The first patient had leukaemia and the second had ANCA-associated granulomatous vasculitis. Both were admitted to the intensive care unit for mechanical ventilation with persistent diffuse alveolar haemorrhage that responded only to a single dose of rF VIIa (90 μg/kg).

DISCUSSION AND CONCLUSION

rF VIIa is a promising treatment for diffuse, persistent alveolar haemorrhage, with only a small dose required to be effective. Future studies are needed in order to establish a clear protocol for the administration of this novel agent.

Hemophilic synovitis: factor VII and the potential role of extravascular factor VIIa

The initiation of coagulation via tissue factor/factor VIIa is relatively weak in normal synovium and joint tissues, so that hemophilic patients with additional deficiency of the intrinsic pathway of coagulation are especially at risk for joint bleeding and the development of hemophilic synovitis. The inflamed joint that results from recurrent bleeding-induced injury, however, may be an environment in which pharmacologic doses of factor VIIa have potentially greater procoagulant action than in the uninjured joint. There is accumulating evidence suggesting that coagulation factors in the extravascular space, and not only circulating plasma factors, have the potential to contribute to hemostatic protection of joints. The potential role of extravascular factor VIIa is considered.