Research Information System
5th International Conference on Thrombosis and Hemostasis Issues in Cancer, Stresa, Italy, 23 - 25 April 2010, vol.125
Platelet derived microparticles induce factor XII mediated thrombin
generation
H.M. Spronk1 *, E. Kilinc1, R. van Oerle1, K. Hamulyak1, T. Renne2, H. ten
Cate1. 1Laboratory for Clinical Thrombosis and Haemostasis, Department of
Internal Medicine, Cardiovascular Research Institue Maastricht, Maastricht
University, The Netherlands, 2Department of Molecular Medicine and Surgery,
Karolinska Institutet, Karolinska University Hospital Solna, Stockholm, Sweden
Introduction: Microparticles are small (<1 mm) cell derived vesicles
expressing antigens from the ancestor cell at their outer surface. Due to
the presence of a procoagulant phospholipid bilayer as well as tissue factor,
the main physiological activator of coagulation, microparticles have been
linked to the hypercoagulable state in cancer patients. Given the recently
described activation of factor XII by platelet derived polyphosphates
(polyP), we hypothesized that platelet derived microparicles induce
thrombin generation through activation of factor XII.
Methods: Isolated human platelets were stimulated by ADP and ionophore
or ionophore alone, whereas monocytes were activated by ionophore with
and without lipopolysacharide (LPS) activation. Generated microparticles
were isolated and characterised for expression of antigens through FACS
analysis, tissue factor activity, and quantified using a newly developed
ELISA-based method.
Results: Platelet derived microparticles expressed mainly antigens also
present on platelets and had low tissue factor activity of <1 pM.
Microparticles from LPS stimulated monocytes, however, displayed a
higher tissue factor activity (>500 pM) as expected. Using a GP1b-specific
antibody and detection through an antibody against GPIIb (CD41) alowed
for quantification of platelet derived microparticles. Addition of plateletderived microparticles to human normal pooled plasma induced thrombin
generation characterised by a lag time of >10 min and a peak height of
100 nM thrombin. Inhibition of the tissue factor pathway, using active site
inhibited seven (ASIS), had no effect on thrombin generation. In contrast,
platelet derived microparticles failed to induce thrombin generation
in factor XII-deficient plasma. Monocyte derived microparticle induced
thrombin generation, however, was comparable between normal and fXIIdeficient plasma and almost completely abolished in the presence of ASIS.
Conclusions: Monocyte derived microparticles mainly induced thrombin
generation through tissue factor, whereas microparticles from platelets
activated factor XII mediated coagulation.