Platelet Density Distribution in Essential Thrombocythemia

Abstract

Essential thrombocythemia (ET) is characterized by high platelet counts and a slightly increased bleeding risk. Why severe hemorrhage does not occur more frequently is not known. Variations of platelet density (kg/l) depend mainly on cell organelle content in that high-density platelets contain more α and dense granules. This study compares ET patients (n = 2) and healthy volunteers (n = 2) with respect to platelet density subpopulations. A linear Percoll™ gradient containing prostaglandin E₁ was employed to separate platelets according to density. The platelet population was subsequently divided by density into 16 or 17 subpopulations. Determination of platelet counts was carried out. In each density fraction, platelet in vivo activity, i.e. platelet-bound fibrinogen, was measured using a flow cytometer. To further characterize platelet subpopulations, we determined intracellular concentrations of CD40 ligand (CD40L) and P-selectin in all fractions. Patients and controls demonstrated similar density distributions, i.e. 1 density peak. High-density platelets had more surface-bound fibrinogen in conjunction with signs of platelet release reactions, i.e. with few exceptions they contained less CD40L and P-selectin. Peak density platelets showed less surface-bound fibrinogen. These platelets contained less CD40L and P-selectin than nearby denser populations. The light platelets had more surface-bound fibrinogen than peak platelets together with elevated concentrations of CD40L. In ET, the malignant platelet production could exist together with platelets originating from normal megakaryocytes. It is also possible that clonal megakaryocytes produce platelets covering the entire density span. The ‘normal’ density distribution offers a tenable explanation as to why serious bleedings do not occur more frequently.

Automated assessment of the neutrophil and platelet activation status in patients with essential thrombocythemia

“…These findings are in agreement with those from early studies using platelet morphology in blood smears or other Hematology analyzers [21][22][23][24]. The increase in platelet volume and the decrease in platelet buoyant density that we observed could be explained by proliferation or dilation of the dense tubular and open canalicular system and reduction of the mitochondria, dense granules, and -granules, as found in ultrastructural studies of platelets from ET patients [25][26][27][28]. Presumably, the origin of the above morphologic findings may be an aberrant proplatelet formation and abnormalities in ploidy, growth rates, and demarcation during the clonal megakaryocytopoiesis of ET, although enhanced platelet activation in the circulation would also be a possibility [2,3,[26][27][28][29][30].…”

“…The reduced MPC and the elevated PCDW found in ET patients are consistent with the degranulation and shape changes that occur during the process of platelet activation [9,25,27,28]. It must be noted that, in agreement with other experimental and clinical data [4,8,9,25, 27, 28, 31, 32], we observed a negative correlation with moderate intensity of concordance between the percentage of baseline P-selectin expression and the MPC.…”

“…The increase in platelet volume and the decrease in platelet buoyant density that we observed could be explained by proliferation or dilation of the dense tubular and open canalicular system and reduction of the mitochondria, dense granules, and -granules, as found in ultrastructural studies of platelets from ET patients [25][26][27][28]. Presumably, the origin of the above morphologic findings may be an aberrant proplatelet formation and abnormalities in ploidy, growth rates, and demarcation during the clonal megakaryocytopoiesis of ET, although enhanced platelet activation in the circulation would also be a possibility [2,3,[26][27][28][29][30]. Finally, the high values of MPV and PDW and their correlation with the platelet P-selectin expression suggest that the increased heterogeneity in platelet volume would be related, at least in part, to platelet activation of ET, although no association was observed between the automated platelet parameters and thrombosis.…”

High In vivo Platelet Activity in Female Fibromyalgia Patients

“…Venous blood (7.5 mL) was anticoagulated with 2.5 mL 0.129 M disodium citrate. In order to separate platelets according to density a linear Percoll™ (GE Healthcare Bio-Sciences AB, Sweden) gradient was used [29,30]. The following substances were mixed in order to provide the two Percoll™ solutions (1.09 and 1.04 kg/L) for the gradient ( Table 2).…”

“…The tube was thereafter centrifuged at 2767 g for 1½ hours. After centrifugation, the underside of the test tube was punctured and the contents was separated by gravity into 17 different density fractions [30]. By this setting every fraction holds about 2 mL of the test tube content.…”