Phosphatidylserine expression on the platelet membrane of patients with myeloproliferative disorders and its effect on platelet-dependent thrombin formation

Recently, the asymmetric distribution of phospholipids in eukaryotic cell membranes has been appreciated and been found to be dependent on the activity of a number of enzymes. The expression of phosphatidylserine (PS), a negatively charged phospholipid, on the platelets of patients with polycythemia vera (P vera) and essential thrombocythemia (ET) was compared to that in normal individuals. The effect of platelet aggregation on PS expression was determined. Exposure of PS on platelets obtained from patients with P vera and ET and from age and sex-matched healthy volunteers was measured by fluorescein-labeled Annexin V binding to platelets and by the platelets' thrombin-generating capacity determined by the prothrombinase assay. Platelet prothrombinase activity (mean standard deviation [SD]), as measured by thrombin generation, was 2.32 +2.2 /u/mL in the P vera group and 1.55 ±1. 0 /mL in the control group (p=0.3). PS expression as measured by Annexin V binding (mean ±SD) was 2.6 ±2.4% in the P vera group ...