Release Of Platelet-derived Microparticles Research Articles

An Investigation of Size Distribution and Calcium Signaling in Human Platelets.

Background Platelets are thin disc-shaped blood cells that play a major role in hemostasis, maintenance of vascular integrity, and blood coagulation. Large platelets are more reactive and seen in patients with cardiovascular disease. This study aims to analyze the changes in platelet size of ex vivo activated platelets which phenotypically simulates that of a patient at risk of cardiovascular disease and elucidate the calcium signaling pathway responsible for this change. Methodology Platelets were isolated from adult human blood by differential centrifugation. Calcium was mobilized into platelets by treatment with calcium ionophore A23187 in the presence of Ca2+. Platelet size distribution was analyzed using Coulter Counter Multisizer 4. The following signaling parameters were studied: intracellular Ca2+ measurement (using Fura-2/AM by fluorescence spectrophotometry), Ca2+-dependent thiol protease calpain assay (using fluorogenic substrate t-butoxycarbonyl-Leu-metchloromethylcoumarin in fluorescence microplate reader), platelet-derived microparticles (using FACS Calibur flow cytometry), and cytoskeletal protein talin expression (by western immunoblotting). Results When adult platelets were treated with A23187 and Ca2+, two subcellular populations (<2 µm and between 2-4 µm) were noted. The mean size of the second cell population was significantly higher than that of resting platelets (2.94 ± 0.13 µm vs. 2.82 ± 0.15 µm, t = 4.605, p = 0.00). A23187 treatment led to elevated intracellular Ca2+, release of platelet-derived microparticles, increase in calpain activity, and cytoskeletal talin degradation. These events were inhibited by calpeptin (a specific calpain inhibitor). Conclusions Elevated calcium caused talin degradation by calpain activity. Breakdown of this cytoskeletal protein leads to relative swelling of cells reflected by the increase in platelet size.

Platelets activated by the anti-\u03b22GPI/\u03b22GPI complex release microRNAs to inhibit migration and tube formation of human umbilical vein endothelial cells

BackgroundPatients with anti-β2GPI antibodies display significantly higher platelet activation/aggregation and vascular endothelial cell damage. The mechanism underlying the correlation between platelet activation, vascular endothelial cell dysfunctions and anti-β2GPI antibodies remains unknown.MethodsIn this study, we derived miR-96 and -26a from platelets activated by the anti-β2GPI/β2GPI complex and explored their role in modulating human umbilical vein endothelial cell (HUVEC) migration and tube formation.ResultsAnti-β2GPI/β2GPI complex induces the release of platelet-derived microparticles (p-MPs). The amounts of miR-96 and -26a in these p-MPs were also higher than for the control group. Co-incubation of HUVECs with p-MPs resulted in the transfer of miR-96 and -26a into HUVECs, where they inhibited migration and tube formation. The targeting role of these miRNAs was further validated by directly downregulating targeted selectin-P (SELP) and platelet-derived growth factor receptor alpha (PDGFRA) via luciferase activity assay.ConclusionOur study suggests that miR-96 and -26a in p-MPs can inhibit HUVEC behavior by targeting SELP and PDGFRA.

Platelet Glycoprotein VI Haplotypes and The Generation Of Microparticles In Health and Disease

Platelets are well known for their role in hemostasis, thrombosis, and wound repair. However, there is growing evidence for established platelet paradigms being relevant to other biological processes, such as inflammation and cancer. As one example, the platelet-specific collagen receptor, glycoprotein (GP) VI, has been shown to exacerbate rheumatoid arthritis in mouse models of the disease and also support experimental metastasis. GPVI exists as a membrane surface receptor that once engaged is capable of eliciting activation-dependent intraplatelet signals. An outcome of GPVI engagement is the release of platelet-derived microparticles (arbitrarily defined as less than 1 μm) and, in the case of rheumatoid arthritis, the microparticle further augments the inflammatory cascade. Beyond this example, platelet-derived microparticles are being recognized as relevant in a wide range of proinflammatory and prothrombotic pathophysiologic states. Characterization of the human GPVI gene has revealed genetic haplotypes corresponding to altered in vitro platelet response. A growing body of evidence has also linked these haplotypes to pathologic responses in the acute setting, such as myocardial infarction and stroke. The GPVI haplotypes, referred to as GP6a and GP6b, differ in 5 codons resulting in 3 polymorphic amino acids in the extracellular portion of the GPVI (S219P, K237E, and T249A) and 2 polymorphic amino acids in the cytoplasmic tail (Q317L and H322N). While GPVI haplotypes have been linked to cardiovascular disease outcome, a gap exists in determining whether the same polymorphisms influence platelet microparticle production and whether microparticle levels might vary in disease states. We have performed a detailed flow cytometry analysis of GPVI-dependent platelet-derived microparticles both in vivo and following agonist stimulation in vitro using blood from normal donors. A correlation exists between GPVI haplotypes and circulating levels of platelet-specific (αIIb) microparticles. Comparing homozygous GP6a (n=34) and heterozygous GP6a/b (n=17) individuals reveals an approximate 2-fold difference in the number of platelet microparticles that is statistically significant (p= 0.005). The GPVI dependent in vitro release is also haplotype specific following addition of type I fibrillar collagen. However, in a human condition of chronic inflammation, such as rheumatoid arthritis, haplotype-dependent changes in platelet-derived microparticle are not observed and reveal a maximum level of microparticle release occurring in the chronic inflammatory state. The results demonstrate that common polymorphisms within the human GPVI gene impact the level of circulating platelet-specific microparticles in normal individuals and in a state of chronic inflammation. The physiologic contribution of GPVI in disease states must consider the representative haplotype and levels of GPVI-dependent microparticles. Disclosures:No relevant conflicts of interest to declare.

Elevated Circulating Platelet-Derived Microparticles in Ph1 Negative Chronic Myeloproliferative Disorders.

Abstract 1906Poster Board I-929Microparticles (MP) are plasma membrane vesicles bearing potent procoagulant proteins and released into the circulation by various blood and endothelial cells during cellular activation and apoptosis. Their concentration has been shown markedly increased in vascular and thromboembolic diseases and in several types of cancer. Essential Thrombocythemia (ET), Polycythemia Vera (PV) and Primary Myelofibrosis (PM) are Bcr-Abl-negative chronic myeloproliferative disorders (MPD) with common biological and clinical features, especially thrombocytosis and more or less effective megakaryocytic proliferation. ET, PV and PMF are also characterized by an increased risk of thrombotic complications. Given the involvement of megacaryocytopoiesis in this group of diseases, we chose to focus on circulating platelet-derived microparticles (PMP) whose count can be established by flow cytometry. Our goals were to look for an increased release of PMP in MPD and if so, try to establish a correlation between thrombotic events recorded retrospectively and PMP level. Patients and methods:Plasma samples were collected from 85 patients with MPD (40 ET, 28 PV, 17 PMF) at any time of the disease course except blastic phase and 31 healthy age-paired controls ; the quantity of PMP (positive for the platelet marker CD41 and the microparticle marker AnnexinV) was measured by flow cytometric analysis using the FC500 cytometer from Beckmann-Coulter™. Pre-analytic and testing procedures complied with the recommendations of the ISTH Standardization Subcommittee and besides, our laboratory participates in a multicenter program to standardize the enumeration of cellular microparticles. Results:The number of PMP is significantly higher in ET, PV and MFP patients (median: 4862 MPP/mL, 3289 MPP/mL and 6114 MPP/mL respectively) than in controls (median 1310 MPP/mL) [p=0.000018, p=0.0013, p=0.0009]. Neither in MPD patients nor in control group PMP correlates with platelet count and appears thus as an independent parameter. ROC method allows to fix a cut-off at 3121 MPP/mL to discriminate MPD from controls. This value has a sensibility of 75 % and a specificity of 94%. Interestingly, the total number of PMP is not different between untreated patients (mean=7246 MPP/mL) and those who received myelosuppressive therapy (mean=6320 MPP/mL). Regarding thrombotic events, we failed to demonstrate any significant difference between patients with previous thrombosis and those without; however, the small size of the series and the retrospective assessment are possible bias. Conclusion:Patients with Phi negative MPDs have a high number of circulating PMP, irrelevant to platelet count or treatment by Hydroxy-urea or aspirin. A role for microparticles in the development of these diseases and in the occurrence of thrombotic complications can be hypothesized but requires further studies -;preferably prospective- on larger cohorts of patients. Disclosures:Charpentier:Schering-Plough: Research Funding.

A new method for the detection of platelet derived microparticles by cytometric bead array and its evaluation

To establish a new method for the detection of platelet derived microparticles (PMPs) by cytometric bead array and to evaluate the characteristic of this method. Using detection beads coated with monoclonal antibody against platelet glycoprotein IIIa to capture PMPs, then using CD41 PE to react with PMPs captured by detection beads, finally using flow cytometer detect beads-PMPs-CD41 PE complex. Anticoagulant, reaction time and other condition were optimized. Then reproducibility and linear range of this method were evaluated. PMPs of 45 health adults were determined by this method. Detection beads were stable in 4 degrees C for over 90 days (coefficient of variance was 0.65%) which matched the basic request of clinical detection. CTAD could restrain the in vitro release of PMPs efficiently; The reaction could reach maximum combination at room temperature after 4 hour; Non-specific absorbance of detection beads could be eliminated by washing of PBS. This method had preferable reproducibility (CV in batch was 6.8%; CV between batch was 10.4%) and a wide linear range from 0 to 200 microl of platelet activation suspension (r = 0.9962). PMP level of 45 health adults was 1.031-1.766. PMPs can be detected exactly by cytometric bead array, and it's important for PMPs detection to be an assistant for diagnosis of haemorrhagic and thrombotic diseases.

A new method to evaluate spontaneous platelet aggregation in type 2 diabetes by Cellfacts

Background: The alterations in the functional activities of platelets in diabetes produce an increase of spontaneous platelet aggregation (SPA) and release of platelet-derived microparticles. Platelet-derived microparticles are shed from platelets during activation by high shear stress, collagen and certain agonists. Although the physiologic role of microparticles has been difficult to assess, the characterization of their biological activity is of interest in view of a possible role in hemostasis and coagulation and their reported involvement in thrombotic disease. Methods: We propose a new, simple method to evaluate spontaneous platelet aggregation and release of platelet-derived microparticles by the Cellfacts analyser (Microbial System Limited (MSL), Coventry, England) that uses electrical sensing flow impedance determination to detect the size particles and the cells in a conductive fluid. Platelet-rich plasma (PRP) from type 2 diabetes was employed for this study. The importance of platelet-activating factor (PAF) on spontaneous platelet aggregation was evaluated and the effect of vitamin E and WEB 2086-BS, an antagonist of platelet-activating factor, was measured. Results and conclusions: Data presented show that Cellfacts could be an easy and fast instrument to check the state of platelets in patients with alterations in the functionality of platelets, and to follow the effect of pharmacological therapy on spontaneous platelet aggregation and the release of platelet-derived microparticles.

Circulating platelet-derived microparticles with procoagulant activity may be a potential cause of thrombosis in uremic patients

Clinical experience indicates that bleeding and thrombotic tendencies co-exist in uremic patients. Numerous studies have shown that platelet functional defects contribute to the bleeding tendency in uremic patients. In contrast, there are no solid studies clarifying the pathogenesis of the prothrombotic state in uremic patients. Platelet-derived microparticles (PMPs), which are small vesicles with procoagulant activity released from activated platelets, are thought to be involved in clinical thrombogenesis. This study addressed the question of why uremic patients are thrombophilic even though they have a bleeding tendency, focusing on the clinical significance of PMPs. The subjects were pre-dialyzed patients, patients under hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) therapy, and age-matched healthy controls. Analyses of PMPs were performed using a flow cytometer. Annexin V was used to probe procoagulant activity of PMPs. The impacts of the HD procedure, arteriovenous (AV) fistula, and recombinant human erythropoietin (rHuEPO) treatment on the release of PMPs were additionally assessed. Major results are: (1) PMP counts were significantly greater in each uremic group than in controls. The PMP counts were not different among three types of uremic groups; (2) PMP counts were significantly higher in uremic patients with thrombotic events than in those without thrombotic events; and (3) the HD procedure and existence of AV fistula did not affect PMP counts, but rHuEPO treatment possibly enhanced the PMP release in these patients. Elevated PMP counts may trigger thrombosis in uremic patients. The primary cause of PMP elevation in uremia was not clarified in this study.

Effect of Cilostazol on Soluble Adhesion Molecules and Platelet-derived Microparticles in Patients with Diabetes

We evaluated the plasma concentrations of soluble adhesion molecules and platelet-derived microparticles (PMP) in patients with non-insulin dependent diabetes mellitus (NIDDM) and studied the effect of cilostazol on PMP generation. There were differences in the levels of soluble adhesion molecules between NIDDM patients (N = 43) and the control subjects (N = 30) (soluble thrombomodulin: 11.5+/-5.3 vs. 7.0+/-1.2 TU/ml, p<0.0001; soluble vascular cell adhesion molecule-1: 708+/-203 vs. 492+/-113 ng/dl, p<0.0001; soluble intercellular cell adhesion molecules- 1: 274+/-65 vs. 206+/-48 ng/dl, p<0.0001; soluble P-selectin: 194+/-85 vs. 125+/-43 ng/dl, p<0.0001). There were also differences in the levels of PMP and platelet activation markers between NIDDM patients and the controls (PMP: 943+/-504 vs. 488+/-219/10(4) plt, p<0.0001; platelet CD62P: 9.2+/-4.6 vs. 4.4+/-4.3%, p<0.001; platelet CD63: 10.2+/-4.5 vs. 4.5+/-3.3%, p<0.0001; platelet annexin V: 9.1+/-3.9 vs. 5.3+/-3.8%, p<0.001). To study the release of PMP into plasma, a modified cone-and-plate viscometer was used. Increased release of PMP from platelets was observed in diabetic plasma compared to normal plasma under high shear stress conditions (2,672+/-645 vs. 1,498+/-386/10(4) plt, p<0.05). Therefore, one cause of PMP elevation in NIDDM may be high shear stress. The levels of PMP, activated platelets, and soluble adhesion molecules all decreased significantly after treatment with cilostazol. These results suggest that cilostazol may be useful for the inhibition of both PMP-dependent and -independent vascular damage in NIDDM.