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Factor VIIa-mediated tenase function on activated platelets under flow.

M S Goel1, S L Diamond

  • 1Institute for Medicine and Engineering, Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA, USA.

Journal of Thrombosis and Haemostasis : JTH
|August 12, 2004
PubMed
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Activated platelets can generate thrombin without added tissue factor, suggesting they expose active factor VIIa (FVIIa) and cofactors. This finding is crucial for understanding platelet-mediated coagulation pathways.

Area of Science:

  • Hematology
  • Biochemistry
  • Coagulation Cascade

Background:

  • Resting platelets may store tissue factor (TF) and/or active factor (F)VIIa.
  • Platelet activation is critical for hemostasis and thrombosis.

Purpose of the Study:

  • To investigate if GPVI-activated platelets support tenase and prothrombinase activity independently of exogenous tissue factor.
  • To elucidate the mechanisms of thrombin generation on activated platelets.

Main Methods:

  • Utilized gel-filtered platelets, platelet-free plasma (PFP), and platelet-rich plasma (PRP) assays.
  • Studied thrombin (IIa) formation using fluorogenic substrates and fibrin visualization under flow conditions.
  • Employed specific inhibitors including anti-TF, anti-FVII/VIIa, PPACK, and EGR-CK.

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Main Results:

  • Activated platelets, even without added TF, demonstrated significant thrombin generation.
  • Inhibition of TF or FVII/VIIa delayed or abolished thrombin burst.
  • Anionic phospholipid alone was insufficient for tenase activity; activated platelets exposed FVIIa or cofactors.

Conclusions:

  • Activated platelets possess intrinsic mechanisms to support tenase and prothrombinase activity.
  • This activity is mediated by elevated FVIIa function and exposure of FVIIa-cofactors, potentially distinct from TF.
  • Platelets play a direct role in initiating coagulation beyond providing a surface for TF-initiated pathways.