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Factor VIII-induced superaggregation of human platelets.

E P Kirby, D C Mills, H Holmsen

    Blood
    |December 1, 1982
    PubMed
    Summary
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    High concentrations of bovine factor VIII cause platelet superaggregation, a unique clumping response distinct from typical aggregation. This process involves factor VIII binding to multiple platelet receptors and can be reversed by dextran sulfate.

    Area of Science:

    • Hematology
    • Biochemistry
    • Platelet Biology

    Background:

    • Platelet aggregation is crucial for hemostasis.
    • Factor VIII is a key protein in the coagulation cascade.
    • The precise mechanisms of factor VIII-mediated platelet interactions are not fully understood.

    Purpose of the Study:

    • To investigate the phenomenon of platelet superaggregation induced by bovine factor VIII.
    • To differentiate superaggregation from other forms of platelet aggregation.
    • To elucidate the molecular mechanisms underlying factor VIII-induced superaggregation.

    Main Methods:

    • Utilized washed platelets and bovine factor VIII.
    • Tested various known platelet agonists and inhibitors.
    • Employed radiolabeled factor VIII to assess binding.

    Related Experiment Videos

  • Used crosslinking agents (formaldehyde, glutaraldehyde) and dextran sulfate for mechanistic studies.

    • Main Results:

    • High concentrations of bovine factor VIII induce platelet superaggregation, a response distinct from agglutination and independent of calcium or energy metabolism.
    • Superaggregation is not triggered by common agonists like thrombin or ADP, nor inhibited by typical anti-aggregation drugs.
    • Formaldehyde and glutaraldehyde block superaggregation without preventing factor VIII binding; superaggregated platelets remain separated by ~50 nm.
    • Superaggregation is reversible by dextran sulfate, with platelets retaining responsiveness to ADP.

    Conclusions:

    • Platelet superaggregation is mediated by the binding of high molecular weight factor VIII multimers to multiple platelet receptors.
    • This process involves receptor recruitment and is distinct from shape change or degranulation seen in other aggregation types.
    • Protein crosslinking agents interfere with the receptor recruitment mechanism of superaggregation.