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Recombinant human factor VIIa (rFVIIa) can activate factor FIX on activated platelets
D A Gabriel1, X Li, D M Monroe
1Division of Hematology/Oncology, The Bone Marrow Transplant Program and The University of North Carolina School of Medicine, Carolina Center for Cardiovascular Biology, Chapel Hill, NC 27599, USA. laser@med.unc.edu
Journal of Thrombosis and Haemostasis : JTH
|October 1, 2004
Summary
Recombinant factor VIIa (rFVIIa) activates factor IX (FIX) on activated platelets without tissue factor, enhancing thrombin generation. This finding explains rFVIIa
Area of Science:
- Biochemistry
- Hematology
- Pharmacology
Background:
- Factor VIIa (FVIIa) is a key enzyme in the coagulation cascade.
- Tissue factor (TF) typically initiates FVIIa activity.
- The role of FVIIa in TF-independent pathways is under investigation.
Purpose of the Study:
- To investigate the ability of recombinant FVIIa (rFVIIa) to activate factor IX (FIX) on activated platelets.
- To determine the binding kinetics of FIX and FVIIa to activated platelets.
- To elucidate the mechanism of TF-independent thrombin generation by rFVIIa.
Main Methods:
- Electrophoretic light scattering to detect protein binding to platelets.
- Functional assays to measure FIX activation.
- Kinetic analysis (K(d)) of FIX and FVIIa binding to activated platelets with and without FVIIIa.
Main Results:
- rFVIIa activates FIX on activated platelets in the absence of TF.
- FIX and FIXa exhibit high affinity binding to activated platelets.
- rFVIIa binding to platelets is enhanced in the presence of FIX and FVIIIa, facilitating FIX activation.
- This activation leads to the formation of tenase complexes and increased thrombin generation.
Conclusions:
- Pharmacological doses of rFVIIa can directly activate FIX on activated platelets, independent of TF.
- This TF-independent pathway contributes to enhanced thrombin generation.
- The findings provide mechanistic insights into rFVIIa's efficacy in treating acquired coagulopathies.