Differential procoagulant activity of microparticles derived from monocytes, granulocytes, platelets and endothelial cells: impact of active tissue factor.

: Microparticles released by activated/apoptotic cells exhibit coagulation activity as they express phosphatidylserine and some of them - tissue factor. We compared procoagulant properties of microparticles from monocytes, granulocytes, platelets and endothelial cells and assessed the impact of tissue factor in observed differences. Microparticles were sedimented (20 000g, 30 min) from the supernatants of activated monocytes, monocytic THP-1 cells, granulocytes, platelets and endothelial cells. Coagulation activity of microparticles was examined using plasma recalcification assay. The size of microparticles was evaluated by dynamic light scattering. Tissue factor activity was measured by its ability to activate factor X. All microparticles significantly accelerated plasma coagulation with the shortest lag times for microparticles derived from monocytes, intermediate - for microparticles from THP-1 cells and endothelial cells, and the longest - for microparticles from granulocytes and platelets. Average diameters of microparticles ranged within 400-600 nm. The largest microparticles were produced by endothelial cells and granulocytes, smaller - by monocytes, and the smallest - by THP-1 cells and platelets. The highest tissue factor activity was detected in microparticles from monocytes, lower activity - in microparticles from endothelial cells and THP-1 cells, and no activity - in microparticles from platelets and granulocytes. Anti-tissue factor antibodies extended coagulation lag times for microparticles from monocytes, endothelial cells and THP-1 cells and equalized them with those for microparticles from platelets and granulocytes. Higher coagulation activity of microparticles from monocytes, THP-1 cells and endothelial cells in comparison with microparticles from platelets and granulocytes is determined mainly by the presence of active tissue factor.

Relationships of glycoproteins IIb-IIIa and Ib content with mean platelet volume and their genetic polymorphisms.

Quantity of platelet adhesion molecules significantly varies in normal donors and cardiovascular patients and might be affected by platelet size and genetic variations. In this study, we assessed relationships of the content of glycoprotein (GP) IIb-IIIa and GPIb with mean platelet volume (MPV) and their genetic polymorphisms. MPV and GPIIb-IIIa and GPIb numbers were measured in 116 patients with acute coronary syndrome (ACS) at days 1, 3-5 and 8-12 after disease onset and in 32 healthy volunteers. GPIIb-IIIa and GPIb allelic variants were determined in ACS patients. Strong interactions of GPIIb-IIIa and GPIb numbers and MPV were observed in ACS patients and healthy volunteers. In patients, coefficients of correlation (r) were 0.642 and 0.510 (analysis of individual mean values) and in volunteers - 0.594 and 0.508 for GPIIb-IIIa and GPIb, respectively (everywhere P < 0.005). In ACS patients, correlations were highly significant at each tested time point. GPIIb-IIIa and GPIb genetic polymorphisms [GPIIIa Leu33Pro, GPIbα Thr145Met and GPIbα (-5)T/C (Kozak)] determined in ACS patients had no significant impact on their expression. Modest correlation was revealed between MPV and plasma thrombopoietin (TPO) measured at the first day of ACS (r = 0.279, P = 0.005). The data obtained indicated that GPIIb-IIIa and GPIb levels are mainly affected by platelet size (MPV) but not by their genetic variations. In some ACS patients, production of large platelets with high GPIIb-IIIa and GPIb contents might be stimulated by elevated TPO.

The composition, structural properties and binding of very-low-density and low-density lipoproteins to the LDL receptor in normo- and hypertriglyceridemia: relation to the apolipoprotein E phenotype.

The composition, apolipoprotein structure and lipoprotein binding to the LDL receptor were studied for very-low-density (VLDL) and low-density lipoprotein (LDL) particles isolated from subjects with apoE phenotype E3/3 (E3), E2/2 or E2/3 (E2+) and E3/4 or E4/4 (E4+) and a wide range of plasma triglyceride (TG) contents. The data combined for all three phenotype groups can be summarized as follows. (i) A decrease in accessibility of VLDL tryptophan residues to I- anions with a decrease in tryptophan surface density, concomitant with an increase in VLDL dimensions, reflects the increased efficiency of protein-protein interactions. (ii) A gradual increase in the quenching constant for LDL apoB fluorescence with an increase in TG/cholesterol (Chol) ratio reflects the 'freezing' effect of Chol molecules on apoB dynamics. (iii) Different mechanisms specific for a particular lipoprotein from E3/3 or E2/3 subjects are responsible for apoE-mediated VLDL binding and apoB-mediated LDL binding to the LDL receptor in a solid-phase binding assay. (iv) The 'spacing' effect of apoC-III molecules on apoE-mediated VLDL binding results in a decrease in the number of binding sites. (v) The maximum of the dependence of the LDL binding affinity constant on relative tryptophan density corresponds to LDL intermediate size. VLDL particles from hypertriglyceridemic E2/3 heterozygotic individuals had remnant-like properties (increased cholesterol, apoE and decreased apoC-III content) while their binding efficiency was unchanged. Based on the affinity constant value and LDL-Chol content, increased competition between VLDL and LDL for the binding to the LDL receptor upon increase in plasma TG is suggested, and LDL from hypertriglyceridemic E3/3 homozygotic individuals is the most efficient competitor.