Abstract
Circulating cell-derived microparticles (MPs) exhibit procoagulant activity and have
been investigated for a possible role in some human pathologies. However, their potential
role in hemostasis has been neglected and often denied. This review brings to attention
a specific body of direct clinical evidence supporting an important but distinctive
role of MPs in hemostasis. Evidence for a role of MPs in hemostasis includes: (1)
two congenital bleeding disorders attributed to impaired release of MPs; (2) two recent
studies of trauma patients relating naturally elevated endogenous MPs at admission
to reduced transfusion requirements and better outcomes; (3) a study of coronary surgery
patients showing that elevated MP before surgery reduces transfusion requirements
during surgery; and (4) a clinical study of patients with immune thrombocytopenia
demonstrating that those with high circulating MP have reduced bleeding compared to
patients with similar platelet counts but lower MP levels. Mechanisms involving potentiating
the contact factor pathway are thought to play a key role and are probably synergistic
with polyphosphate released from activated platelets at sites of endothelial injury.
Hemostatic defect of patients with deficient MP-mediated coagulation resembles deficiency
of FXI (hemophilia C), distinct from hemophilia A or B, so can be termed type C hemostasis.
A better understanding of this proposed hemostatic pathway may lead to improved methods
for controlling excessive bleeding in surgery, trauma, and other clinical settings.
Keywords
cell-derived microparticles - extracellular vesicles - hemostasis - contact pathway
- coagulation
