[Coagulation activity of circulating membrane microparticles in patients with cardiovascular diseases]. / Koaguliatsionnaia aktivnost' tsirkuliruiushchikh membrannykh mikrochastits u patsientov s serdechno-sosudistymi zabolevaniiami.

Membrane microparticles (MP) are released by activated or damaged cells and are able to accelerate blood clotting (coagulation). MP possess coagulation activity since all of them contain on their surface phosphatidylserine (PS), a substrate for the assembly of coagulation complexes, and some of them tissue factor (TF), the primary initiator of coagulation cascade reactions. We compared the coagulation activity and amount of MP in the blood of healthy donors (n=34) and patients with myocardial infarction (MI) (n=32), advanced atherosclerosis (AA) (n=32) and idiopathic pulmonary arterial hypertension (IPAH) (n=19). Total MP fraction was obtained from blood plasma by sedimentation at 20000 g, 30 min. The coagulation activity of PM isolated from 100 µl of donor and patient plasma was determined using a modified recalcification test. MP were added to substrate plasma devoid of endogenous MF, plasma was recalcified, and clotting was recorded by changes in optical density (A450), determining lag phase (min) and maximum rate (Vmax, %A450/min). MP were counted by flow cytometry as PS+ particles (lactadgerin-FITC staining) smaller than 1 µm and their concentration was expressed as 105 MP/µl plasma. MP in all patient groups accelerated plasma clotting more effectively than donor MP. Lag phase compared with donors (11.8 [11.0-13.1] median and interquartile range) was shorter in patients with AA (8.8 [7.0-10.3], p.

Platelet subpopulation bearing leukocyte specific antigen and tissue factor.

Platelets bearing leukocyte antigen CD45 were identified in the blood of patients with myocardial infarction (MI) and healthy donors by flow cytofluorimetry. Part of these platelets contained tissue factor (TF)-primary initiator of blood clotting. The number of CD45+ and CD45+/TF+ platelets in MI patients at the first day was comparable with their level in healthy donors, but was increased at 8-12 days after MI onset. At that time in some patients the amount of CD45+ and CD45+/TF+ platelets reached 5-6 and 2-3% of their total number. It is assumed that CD45+/TF+ platelets could be formed as a result of platelet interaction with leukocytes or leukocyte produced membrane microparticles.

Spontaneous platelet aggregation in patients with acute coronary syndrome.

Spontaneous platelet aggregation was evaluated in patients with acute coronary syndrome on days 1, 3-5, and 8-12 of the disease. On day 1, aggregation was analyzed after aspirin, but before clopidogrel administration; during other periods after both antiaggregants. The mean levels of spontaneous aggregation after antithrombotic therapy did not change during different periods after the onset of acute coronary syndrome, in contrast to ADP-induced aggregation that decreased after the development of clopidogrel effects (days 3-5 and 8-12). Spontaneous aggregation during different periods directly correlated (r>0.4, p<0.01) with spontaneous and ADP-induced aggregation during different periods (r=0.372, r=0.447, and r=0.543 on days 1, 3-5, and 8-12, respectively; p<0.01). No relationship between spontaneous aggregation and plasma concentration of von Willebrand's factor was detected. Spontaneous aggregation was completely suppressed after in vitro addition of prostaglandin E1 (platelet activation inhibitor), slightly (by ≈20%) decreased in the presence of antibodies to glycoprotein Ib, blocking its reactions with von Willebrand's factor, and did not change in the presence of aptamer inhibiting thrombin activity.

Glycoprotein IIb-IIIa content and platelet aggregation in healthy volunteers and patients with acute coronary syndrome.

Glycoprotein (GP) IIb-IIIa (αIIbß3-integrin) is the central receptor of platelet aggregation. Activated GP IIb-IIIa binds fibrinogen or von Willebrand factor, which forms molecular bridges between aggregating platelets. This review summarizes data on the relationship between GP IIb-IIIa expression on the platelet surface and platelet aggregating activity. GP IIb-IIIa number, measured as maximal binding of complex-specific monoclonal antibody, varied by approximately two fold in both healthy volunteers (n = 35) and patients with acute coronary syndrome (ACS) (n = 65). In healthy volunteers positive associations were observed between GP IIb-IIIa number and the level of ADP-induced aggregation when this relationship was analysed in untreated platelet-rich plasma (PRP) as well as upon in vitro addition of aspirin or non-saturating concentrations of GP IIb-IIIa blockers. In the same group of volunteers almost no differences in aggregating activity were detected between donors carrying the GP IIIa Pro33 allele (n = 15) and those with the GP IIIa Leu33Leu33 genotype (n = 20). No significant relationships were revealed between platelet aggregability and variations of plasma fibrinogen concentration. Positive correlation of the level of ADP-induced aggregation and GP IIb-IIIa content was detected in patients with ACS within the first hour upon admission to the hospital when they had already received aspirin, but not clopidogrel. However, there were no correlations between these parameters at days 3-5 and days 8-12 (before discharge). At these time points patients were treated not only with aspirin but were saturated with clopidogrel as well. In ACS patients we also evaluated the expression of another platelet adhesive receptor, GP Ib, and found a significant positive correlation between GP IIb-IIIa and GP Ib content. A strong association was also revealed between the number of both receptors and mean platelet volume. The latter observation indicated that individual variations of the number of glycoprotein molecules are mainly affected by platelet size but not the density of their expression on the platelet membrane. Possible usefulness of measuring GP IIb-IIIa content as a marker of increased platelet reactivity is discussed.