Megakaryocyte- and Platelet-Derived Microparticles as Novel Diagnostic and Prognostic Biomarkers for Immune Thrombocytopenia

Altered cell-derived microparticles (MPs) have been reported in multiple autoimmune diseases. However, the roles of megakaryocyte- and platelet-derived MPs (MKMPs and PMPs) in immune thrombocytopenia (ITP) have not been investigated. In this study, we examined plasma MKMP and PMP levels in patients with ITP and evaluated their potential diagnostic values. Plasma MKMP and PMP levels were analyzed by flow cytometry in a discovery set of ITP patients (n = 78), non-immune thrombocytopenia (TP) patients (n = 69), and age- and gender-matched healthy controls (n = 88). Samples from a therapy set of ITP patients (n = 21) were used to assess the response to thrombopoietin receptor agonist (TPO-RA) treatment. Spearman correlation analysis was performed between MP levels and disease parameters. Receiver operator characteristic (ROC) curves were generated to evaluate the diagnostic values of the MPs. We found that plasma MKMP and PMP levels were significantly lower in ITP patients than those in healthy controls (p values < 0.0001) but higher than in those in TP patients (p < 0.002 and p < 0.0002, respectively). After normalization to platelet counts, PMP/Platelet ratios in ITP patients were higher than those in TP patients and healthy controls (p values < 0.001). PMP/Platelet ratios had a diagnostic value for ITP (area under the curve = 0.808, p < 0.0001) with 73.1% sensitivity and 77.3% specificity. MKMP levels can be used to discriminate ITP from TP with a cut-off value of 112.5 MPs/μL and a sensitivity of 74.4%. Moreover, both MKMP and PMP levels were elevated in ITP patients who responded to TPO-RA treatment. Plasma PMP levels positively correlated with platelet counts in the responders (r = 0.558, p < 0.01). Our results indicate that plasma MKMP and PMP levels are decreased in ITP patients and that plasma MKMP and PMP levels may serve as biomarkers for ITP diagnosis and prediction of TPO-RA treatment response.

Platelets in ITP: Victims in Charge of Their Own Fate?

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder. The pathophysiological mechanisms leading to low platelet levels in ITP have not been resolved, but at least involve autoantibody-dependent and/or cytotoxic T cell mediated platelet clearance and impaired megakaryopoiesis. In addition, T cell imbalances involving T regulatory cells (Tregs) also appear to play an important role. Intriguingly, over the past years it has become evident that platelets not only mediate hemostasis, but are able to modulate inflammatory and immunological processes upon activation. Platelets, therefore, might play an immuno-modulatory role in the pathogenesis and pathophysiology of ITP. In this respect, we propose several possible pathways in which platelets themselves may participate in the immune response in ITP. First, we will elaborate on how platelets might directly promote inflammation or stimulate immune responses in ITP. Second, we will discuss two ways in which platelet microparticles (PMPs) might contribute to the disrupted immune balance and impaired thrombopoiesis by megakaryocytes in ITP. Importantly, from these insights, new starting points for further research and for the design of potential future therapies for ITP can be envisioned.

Positive Association between Endothelium-Platelet Microparticles and Urinary Concentration of Lead and Cadmium in Adolescents and Young Adults

(1) Background: In previous research, higher levels of urine heavy metals, especially lead and cadmium, have been associated with increased cardiovascular risk. However, there is no information linking exposure to heavy metal to endothelial and platelet microparticles (EMPs and PMPs), particularly in the younger population, which are novel biomarkers of endothelial dysfunction. (2) Methods: From a nationwide database, which was incepted in 1992–2000, screening for renal health among Taiwanese school children, a total of 789 subjects were recruited. Cross-sectional analysis was performed to evaluate the association between serum EMPs/PMPs and urine iron, nickel, copper, cadmium, lead, chromium, manganese, and zinc levels in the adolescent and young adult population. (3) Results: After we adjusted the conventional cardiovascular risk factors, CD31+/CD42a− and CD31+/CD42a+ counts, in subjects’ serum, respective markers of EMP and PMP displayed a significant positive dose-response relationship with urinary lead and cadmium levels. Higher quartiles of urine lead and cadmium levels were associated with an increased risk of higher EMPs/PMPs (≥75th percentile) in a multivariate logistic regression model. (4) Conclusion: Higher urinary lead and cadmium concentrations are strongly associated with endothelium–platelet microparticles in this adolescent and young adult population, which could help explain, in part, the mechanism through which heavy metal exposure results in cardiotoxicity.

Enrichment of plasma in platelets and extracellular vesicles by the counterflow to erythrocyte settling

In order to prepare optimal platelet and extracellular vesicle (EV)-rich plasma for the treatment of chronic temporal bone inflammation, we studied effects of centrifugation parameters on redistribution of blood constituents in blood samples of 23 patients and 20 volunteers with no record of disease. Concentrations of blood cells and EVs were measured by flow cytometry. Sample content was inspected by scanning electron microscopy. A mathematical model was constructed to interpret the experimental results. The observed enrichment of plasma in platelets and EVs after a single spin of blood depended on the erythrocyte sedimentation rate, thereby indicating the presence of a flow of plasma that carried platelets and EVs in the direction opposite to settling of erythrocytes. Prolonged handling time correlated with the decrease of concentration of platelets and larger EVs in platelet and EV-rich plasma (PVRP), R = -0.538, p = 0.003, indicating cell fragmentation during the processing of samples. In further centrifugation of the obtained plasma, platelet and EV enrichment depended on the average distance of the sample from the centrifuge rotor axis. Based on the agreement of the model predictions with observations, we propose the centrifugation protocol optimal for platelet and EV enrichment and recovery in an individual sample, adjusted to the dimensions of the centrifuge rotor, volume of blood and erythrocyte sedimentation rate.[Figure: see text].

The Effects of the Combined Argatroban/Nitric Oxide-Releasing Polymer on Platelet Microparticle-Induced Thrombogenicity in Coated Extracorporeal Circuits

Clotting, anticoagulation, platelet consumption, and poor platelet function are major factors in clinical extracorporeal circulation (ECC). We have shown that nitric oxide-releasing (NOReL) coatings prevent thrombosis in a rabbit model of ECC without systemic anticoagulation. Nitric oxide-releasing prevents platelet adhesion and activation, resulting in preserved platelet count and function. Previous work has shown that activated platelets form platelet-derived microparticles (PMPs). These experiments were designed to determine if PMPs can identify platelet function during ECC. The objective of this study is to investigate the effects of NOReL on platelet activation and PMP formation during ECC. Uncoated ECCs, including with and without systemic heparin, and NOReL-coated ECCs, including DBHD/N2O2 and argatroban (AG)/DBHD/N2O2-coated ECCs without systemic heparin, were tested in a 4-hour rabbit thrombogenicity model. Before and after ECC exposure, platelets were stimulated with collagen, and PMPs were measured using flow cytometry. The uncoated ECCs clotted within the first hour, while the NOReL-coated ECCs circulated for 4 hours. During pre-ECC blood exposure, platelets stimulated with collagen produced PMPs. With post-ECC exposure, platelets from uncoated circuits generated less PMPs than baseline (mean ± SDs: 23246 ± 3611 baseline vs. 1300 ± 523 uncoated post circuit, p = 0.018) when stimulated with collagen. However, platelets from the AG/DBHD/N2O2-coated ECCs generated a greater number of PMPs as baseline values (23246 ± 3611 baseline vs. 37040 ± 3263 AG/DBHD/N2O2 post 4 hours circuit, p = 0.023). Blood exposure during ECC results in platelet activation and clotting in uncoated ECCs. The remaining circulating platelets have lost function, as demonstrated by the low PMP formation in response to collagen. AG/DBHD/N2O2-coated ECCs prevented significant platelet activation and clotting, while DBHD/N2O2 trended towards prevention of platelet activation. In addition, function of the circulating platelets was preserved, as demonstrated by PMP formation in response to collagen. These results indicate that PMPs may be an important measure of platelet activation during ECC. Platelet-derived microparticles may provide a simplified way to measure platelet function during clinical ECC.

Platelet microparticles load a repertory of miRNAs programmed to drive osteogenic phenotype

Autologous platelet-rich plasma accelerates bone healing by releasing biomolecules during their degranulation process, which are transported by vesicle-like structures called platelet microparticles (PMPs). However, the underlying mechanisms regulating the osteogenic differentiation by PMP-released miRs remain poorly understood and this prompted us to better address this issue. Thus, miRNAseq expression profiles (E-GEOD-76789) were downloaded from ArrayExpress database. GEO2R was performed to evaluate the differential expression, and mirnatap R package was used to find targets for differentially expressed miRNAs. An extend protein-protein (ePPI) network for osteogenic marker proteins was generated using String, and DAVID tools were used to perform gene ontology and KEGG pathway analysis from ePPI and miRNAs targets. Our data show that ePPI network was composed by 232 nodes and 2,175 edges, with a clustering coefficient of 0.546. MCODE was able to identify seven clusters contained in the ePPI network, and the two that presented a score above 10 were used in further analysis. Conversely, 15,944 different targets were found as down-expressed while 5,715 different targets were up-expressed. Among the downregulated 75 miRNAs, 70 have predicted targets present in the ePPI network, while the 21 upregulated miRNAs have 19 predicted targets in the ePPI network. Our study provides a registry of miRNAs that play a central role in regulating osteogenic phenotype, which might have potential therapeutic applications in bone regeneration and bone tissue engineering.

Platelet microparticles-derived miR-25-3p promotes the hepatocyte proliferation and cell autophagy via reducing B-cell translocation gene 2

Platelets are critical regulators of liver regeneration, but the mechanisms are still not fully understood. Platelets have been shown to contain a wide variety of microRNAs (miRNAs) and play an important role in many diseases. However, the mechanism that how the platelet microparticles (PMPs)-derived miRNA regulate the hepatocyte proliferation is not very clear. In this study, we have successfully isolated and identified PMPs. We also found that PMPs, which could be well integrated into the HHL-5 cells, could upregulate the level of miR-25-3p in HHL-5 cells. Meanwhile, we found that PMPs-derived miR-25-3p promoted HHL-5 cells proliferation by accelerating cells into the S phase, and enhanced the autophagy by increasing the LC3II expression and reducing the P62 expression. Then, we proved that the miR-25-3p could target the B-cell translocation gene 2 (BTG2) and downregulate the expression levels of the BTG2 gene in HHL-5 cells. In addition, the overexpression of BTG2 significantly inhibited the proliferation and autophagy abilities of HHL-5 cells, while cotransfected miR-25-3p mimics or PMPs could partially rescue HHL-5 cells proliferation and autophagy. Furthermore, we proved that PMPs accelerated hepatocyte proliferation by regulating autophagy pathways. Therefore, PMPs-derived miR-25-3p promoted HHL-5 cell proliferation and autophagy by targeting BTG2, which may be a new therapeutic method for liver regeneration.

Platelet-Derived Microparticles Bearing PF4 and Anti-GAGS Immunoglobulins in Patients with Sepsis

PF4 is a megakaryocyte-derived cationic chemokine that plays a part in innate immunity through its activity on the macrophages. In bacterial sepsis, PF4 binds to glycosaminoglycans (GAGs) on the surface of aerobic bacteria, giving rise to an antigenic complex that induces the early formation of anti-PF4 IgG-IgA-IgM. This triggers the immune response in patients receiving heparin therapy who develop heparin-induced thrombocytopenia (HIT). These antibodies have also been identified in patients with chronic Gram-negative infections. Given the complexity of this innate immune response network, our study on 45 patients with sepsis focused on the immune response mediated by platelet PF4. We analyzed the role of IgG-IgA-IgM against PF4-GAGs, and the presence of specific PF4-bearing platelet microparticles (PMPs). Anti-GAGs/PF4 IgG-IgA-IgM levels were significantly higher in septic patients than in control groups (healthy controls or acute patients without sepsis, p < 0.001). PF4-bearing PMP levels were only significantly higher in septic patients (p < 0.001). The occurrence of IgG-IgA-IgM against PF4-GAGs and PF4+ PMPs correlated with an improvement in patients’ sepsis. In conclusion, we demonstrated that, in the course of bacterial sepsis, platelet activation leads to the formation of specific PF4-bearing PMPs. These specific microparticles bind to polyanionic sequences on the surface of aerobic bacteria, giving rise to an antigenic complex that induces the early formation of IgG-IgA-IgM against PF4-GAGs as an innate immune response to infection.

Black Sorghum Phenolic Extract Modulates Platelet Activation and Platelet Microparticle Release

Platelet hyper-activation and platelet microparticles (PMPs) play a key role in the pathogenesis of cardiovascular diseases. Dietary polyphenols are believed to mimic antiplatelet agents by blunting platelet activation receptors via its antioxidant phenomenon. However, there is limited information on the anti-platelet activity of grain-derived polyphenols. The aim of the study is to evaluate the effects of sorghum extract (Shawaya short black 1 variety), an extract previously characterised for its high antioxidant activity and reduction of oxidative stress-related endothelial dysfunction, on platelet aggregation, platelet activation and PMP release. Whole blood samples collected from 18 healthy volunteers were treated with varying non-cytotoxic concentrations of polyphenol-rich black sorghum extract (BSE). Platelet aggregation study utilised 5 µg/mL collagen to target the GPVI pathway of thrombus formation whereas adenine phosphate (ADP) was used to stimulate the P2Y1/P2Y12 pathway of platelet activation assessed by flow cytometry. Procaspase-activating compound 1 (PAC-1) and P-selectin/CD62P were used to evaluate platelet activation- related conformational changes and degranulation respectively. PMPs were isolated from unstimulated platelets and quantified by size distribution and binding to CD42b. BSE treatment significantly reduced both collagen-induced platelet aggregation and circulatory PMP release at 40 µg/mL (p < 0.001) when compared to control. However, there was no significant impact of BSE on ADP-induced activation-dependent conformational change and degranulation of platelets. Results of this study suggest that phenolic rich BSE may confer cardio-protection by modulating specific signalling pathways involved in platelet activation and PMP release.

Polyphenols: Modulators of Platelet Function and Platelet Microparticle Generation?

Platelets and platelet microparticles (PMPs) play a key role in the pathophysiology of vascular disorders such as coronary artery disease and stroke. In atherosclerosis, for example, the disruption of the plaque exposes endogenous agonists such as collagen, which activates platelets. Platelet hyper-activation and the high levels of PMPs generated in such situations pose a thrombotic risk that can lead to strokes or myocardial infarctions. Interestingly, dietary polyphenols are gaining much attention due to their potential to mimic the antiplatelet activity of treatment drugs such as aspirin and clopidogrel that target the glycoprotein VI (GPVI)-collagen and cyclooxygenease-1 (COX-1)-thromboxane platelet activation pathways respectively. Platelet function tests such as aggregometry and flow cytometry used to monitor the efficacy of antiplatelet drugs can also be used to assess the antiplatelet potential of dietary polyphenols. Despite the low bioavailability of polyphenols, several in vitro and dietary intervention studies have reported antiplatelet effects of polyphenols. This review presents a summary of platelet function in terms of aggregation, secretion, activation marker expression, and PMP release. Furthermore, the review will critically evaluate studies demonstrating the impact of polyphenols on aggregation and PMP release.

Extracellular Vesicles in the Blood of Dogs with Cancer-A Preliminary Study

Extracellular vesicles (EVs) are a heterogeneous population of submicron-sized structures released during the activation, proliferation, or apoptosis of various types of cells. Due to their size, their role in cell-to-cell communication in cancer is currently being discussed. In blood, the most abundant population of EVs is platelet-derived EVs (PEVs). The aim of this study was to estimate the absolute number and the origin of EVs in the blood of healthy dogs and of dogs with various types of cancer. The EV absolute number and cellular origin were examined by flow cytometry technique. EVs were classified on the basis of surface annexin V expression (phosphatidylserine PS+) and co-expression of specific cellular markers (CD61, CD45, CD3, CD21). The number of PEVs was significantly higher in dogs with cancer (median: 409/µL, range: 42-2748/µL vs. median: 170/µL, range: 101-449/µL in controls). The numbers of EVs derived from leukocytes (control median: 86/µL, range: 40-240/µL; cancer median: 443/µL, range: 44-3 352/µL) and T cells (control median: 5/µL, range: 2-66/µL; cancer median: 108/µL, range: 3-1735/µL) were higher in dogs with neoplasia compared to healthy controls. The estimation of PEV and leukocyte-derived EV counts may provide a useful biological marker in dogs with cancer.

Platelet Microparticles: A Tool to Predict Infarction Area in Rats

Background: Whether there is a quantitative correlation between platelet microparticles (PMPs)/calpain and infarction area is still unclear. Whether present antiplatelet agents can improve myocardial infarction by influencing PMPs need to be revealed. The object of our study was to answer those questions. Methods: Male Wistar rats were used for all studies. All rats were randomly divided into five groups: sham-operated group, myocardial infarction group (blank control group), aspirin intervention group, aspirin combined with clopidogrel intervention group, and aspirin combined with ticagrelor intervention group. Venous blood and hearts were collected at day 7 following MI. ELISA was applied to detect PMPs level. Infarction size was determined by TTC staining method. The comparisons of multiple means were tested with analysis of variance. And the two-two comparisons among the means were done by Student-Newman-Keuls and LSD method. Results: PMPs level and infarction area did not differ between aspirin combined with clopidogrel intervention group and aspirin combined with ticagrelor intervention group. However, significant differences were detected between any two other groups. PMPs were decreased more in dual antiplatelet intervention group. Pearson correlation analysis showed a strong correlation between PMPs and infarction area (r = 0.90) as well as calpain 10 and infarction area (r = 0.84). We created a regression model: y = 4.61 + 0.28*x (y: infarction area, x: PMPs) to assess myocardial infarction area by PMPs level. Conclusions: Antiplatelet agents may decrease infarction areas by modifying PMPs. There was a strong correlation between PMPs and infarction area. Therefore, PMPs could be used as a tool to assess infarction area.

Platelet microparticles contribute to aortic vascular endothelial injury in diabetes via the mTORC1 pathway

Platelet microparticles (PMPs) are closely associated with diabetic macrovascular complications. The present study aimed to investigate the effects of PMPs in diabetes on aortic vascular endothelial injury and to explore the underlying mechanisms. Peritoneal injection of streptozotocin was used to generate a diabetic rat model in vivo, and human umbilical vein endothelial cells (HUVECs) treated with PMPs were used in vitro. PMP levels in the circulation and aorta tissues were time-dependently increased in streptozotocin-induced diabetic rats at weeks 4, 8, and 12 (P < 0.05). Aspirin significantly inhibited the PMP levels at each time point (P < 0.05). In diabetic rats, the endothelial nitric oxide levels were decreased significantly combined with increased endothelial permeability. PMPs were internalized by HUVECs and primarily accumulated around the nuclei. PMPs inhibited endothelial nitric oxide levels to about 50% and caused approximately twofold increase in reactive oxygen species production. Furthermore, PMPs significantly decreased the endothelial glycocalyx area and expression levels of glypican-1 and occludin (P < 0.05). Interestingly, the PMP-induced endothelial injuries were prevented by raptor siRNA and rapamycin. In conclusion, increased PMPs levels contribute to aortic vascular endothelial injuries in diabetes through activating the mTORC1 pathway.

Circulating microparticles as biomarkers of stroke: A focus on the value of endothelial- and platelet-derived microparticles

Stroke is one of the leading causes of mortality and disability worldwide. Numerous pathophysiological mechanisms involving blood vessels, coagulation and inflammation contribute to the vascular occlusion. Perturbations in these pathways can be detected by numerous methods including changes in endoplasmic membrane remodeling and rearrangement leading to the shedding of microparticles (MPs) from various cellular origins in the blood. MPs are small membrane-derived vesicles that are shed from nearly all cells in the body in resting state or upon stimulation. MPs act as biological messengers to transfer information to adjacent and distant cells thus regulating various biological processes. MPs may be important biomarkers and tools for the identification of the risk and diagnosis of cerebrovascular diseases. Endothelial activation and dysfunction and altered thrombotic responses are two of the main features predisposing to stroke. Endothelial MPs (EMPs) have been recognized as both biomarkers and effectors of endothelial cell activation and injury while platelet-derived MPs (PMPs) carry a strong procoagulant potential and are activated in thrombotic states. Therefore, we reviewed here the role of EMPs and PMPs as biomarkers of stroke. Most studies reported high circulating levels of EMPs and PMPs in addition to other cell origins in stroke patients and have been linked to stroke severity, the size of infarction, and prognosis. The identification and quantification of EMPs and PMPs may thus be useful for the diagnosis and management of stroke.

Rac1 regulates platelet microparticles formation and rheumatoid arthritis deterioration

Platelets play important roles in blood clotting, hemostasis and wound repair, while more and more research show that platelets also have significant contributions in the process of inflammation. Rheumatoid arthritis is a chronic systemic inflammatory autoimmune disease. Platelet microparticles, which are membrane vesicles shed by activated platelets, are reported to amplify inflammation in Rheumatoid arthritis. Here we show that either platelet-specific deletion of Rac1 (Rac1^-/-) or Rac1-specific inhibitor NSC23766 dramatically inhibit platelet-derived microparticles formation. As we all know, collagen-induced arthritis (CIA) mouse model is the most common autoimmune model of rheumatoid arthritis. Interestingly, NSC23766 alleviated the process of collagen-induced arthritis of DBA mice in vivo, including the reduced hind paw thickness and ankle stiffness, the reduction of arthritic scores and incidence of arthritis. Our work also found that NSC23766-treated CIA mouse spleen is less swollen and contains less enlarged white pulp than PBS control. The histological analysis shows that NSC23766-treated but not solvent control improve the cartilage erosion symptom in the joint of CIA mouse. Interestingly, platelet microparticles in the peripheral blood of NSC23766-treated CIA mice were decreased significantly compared with PBS-treated CIA mice. In conclusion, our work demonstrated that Rac1 inhibition alleviates collagen-induced arthritis through the decrease of platelet microparticles' release. In short, Rac1 aggravate the rheumatoid arthritis deterioration through the regulation of platelet microparticles formation.

Role of Platelet Microparticles in Blood Diseases: Future Clinical Perspectives

Platelet microparticles (PMPs) are released from the resting or activated platelet membrane, which includes a variety of proteins, mRNA, miRNA, lipids, and other substances. PMPs are involved in cell communication in vivo and are potential markers for multiple diseases. This narrative review focuses on the extraction, identification, and intercellular role of PMPs, with emphasis on the lesser known aspects of PMPs, namely, PMPs and complement systems, and their role in some diseases and disorders of women such as miscarriage and polycystic ovary syndrome, as well as the application of proteomics. For clinical purposes, we should first consider the importance of PMPs quantification and then what treatment should be given in response to increased quantities of PMPs as observed in many diseases. Currently, methods for quantification of PMPs are still in the experimental stages. Proteomics testing will expand biomarker discovery as well as future PMPs diagnostic and therapeutic applications.

Circulating microparticles and central blood pressure according to antihypertensive strategy

OBJECTIVES

This prospective, randomized, open-label study aimed to compare the effects of antihypertensive treatment based on amlodipine or hydrochlorothiazide on the circulating microparticles and central blood pressure values of hypertensive patients.

METHODS

The effects of treatments on circulating microparticles were assessed during monotherapy and after the consecutive addition of valsartan and rosuvastatin followed by the withdrawal of rosuvastatin. Each treatment period lasted for 30 days. Central blood pressure and pulse wave velocity were measured at the end of each period. Endothelial, monocyte, and platelet circulating microparticles were determined by flow cytometry. Central blood pressure values and pulse wave velocity were recorded at the end of each treatment period.

RESULTS

No differences in brachial blood pressure were observed between the treatment groups throughout the study. Although similar central blood pressure values were observed during monotherapy, lower systolic and diastolic central blood pressure values and early and late blood pressure peaks were observed in the amlodipine arm after the addition of valsartan alone or combined with rosuvastatin. Hydrochlorothiazide-based therapy was associated with a lower number of endothelial microparticles throughout the study, whereas a higher number of platelet microparticles was observed after rosuvastatin withdrawal in the amlodipine arm.

CONCLUSIONS

Despite similar brachial blood pressure values between groups throughout the study, exposure to amlodipine was associated with lower central blood pressure values after combination with valsartan, indicating a beneficial interaction. Differences between circulating microparticles were modest and were mainly influenced by rosuvastatin withdrawal in the amlodipine arm.

[Real-time investigation of dynamic morphology of live platelets and generation of platelet microparticles using hopping probe ion conductance microscopy]

Platelets are rapidly activated by activators and produce a large number of platelet microparticles (PMPs) with high coagulation activity, resulting in coagulation dysfunction. However, the generation mechanism of PMPs is still not clear. Hopping probe ion conductance microscopy (HPICM) has special technical advantages in non-contact, real-time, high-resolution imaging of living cells under physiological conditions. Using HPICM, this study monitored the processes of platelet activation and generation of PMPs in real time in the presence of calcium ionophore A23187 and cytochalasin D (CD), respectively. The results proved that the intracellular calcium concentration and the cytoskeletal proteins played important roles in the platelet activation and the generation of PMPs. Compared with the low density spread shape platelets (LDSS), the high density bubble shape platelets (HDBS) were more sensitive to the calcium ionophore A23187 and cytochalasin D. This research has a guiding significance for the further study on the relationship between platelet activation and coagulation function using HPICM.

Platelet microvesicles in health and disease

Interest in cell-derived extracellular vesicles and their physiological and pathological implications is constantly growing. Microvesicles, also known as microparticles, are small extracellular vesicles released by cells in response to activation or apoptosis. Among the different microvesicles present in the blood of healthy individuals, platelet-derived microvesicles (PMVs) are the most abundant. Their characterization has revealed a heterogeneous cargo that includes a set of adhesion molecules. Similarly to platelets, PMVs are also involved in thrombosis through support of the coagulation cascade. The levels of circulatory PMVs are altered during several disease manifestations such as coagulation disorders, rheumatoid arthritis, systemic lupus erythematosus, cancers, cardiovascular diseases, and infections, pointing to their potential contribution to disease and their development as a biomarker. This review highlights recent findings in the field of PMV research and addresses their contribution to both healthy and diseased states.

The significance of platelet microparticles in patients with chronic hepatitis C and their association with antiviral treatment and smoking

Background

Platelet microparticles (PMPs) are platelet-derived membrane vesicles involved in cardiovascular diseases and atherosclerosis. Chronic hepatitis C (CHC) is associated with increased atherosclerosis, but the effect of therapy on its atherogenic potential has not been adequately studied.

Methods

We evaluated PMP levels before and after treatment with pegylated-interferon-alfa and ribavirin in 28 CHC patients compared with 20 non-alcoholic fatty liver disease (NAFLD) patients and 20 healthy volunteers (HV).

Results

Twenty-four (86%) CHC patients achieved sustained virological response (SVR). PMP levels were determined at baseline in CHC, NAFLD patients, and HV, and at end-of-treatment (EOT) and 24 weeks post-treatment (SVR24) in CHC patients. PMP levels at baseline were higher in CHC than NAFLD patients (P<0.001) and HV (P=0.007). Higher PMPs at baseline were observed in smokers than non-smokers with CHC (P=0.006). Among smokers from all groups, PMPs at baseline were higher in CHC than NAFLD patients (P=0.001) and HV (P=0.024). In CHC patients, PMPs declined from baseline to both EOT (P=0.035) and SVR24 (P=0.006). Only CHC patients with SVR had a significant decline in PMPs from baseline to SVR24 (P=0.018). PMPs at ΕΟΤ and SVR24 in all CHC patients were similar to PMPs in NAFLD patients and HV.

Conclusions

PMP levels are increased in CHC patients, particularly smokers, which further supports the atherosclerotic potential of CHC and suggests a potentially synergistic effect of smoking and CHC on the atherosclerotic process. Since PMP levels in CHC patients with SVR were similar to NAFLD patients and HV, the atherosclerotic potential of CHC seems to be abolished by effective antiviral treatment.

Evaluation of flow cytometric HIT assays in relation to an IgG-Specific immunoassay and clinical outcome

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a severe side effect of heparin treatment caused by platelet activating IgG antibodies generated against the platelet factor 4 (PF4)-heparin complex. Thrombocytopenia and thrombosis are the leading clinical symptoms of HIT.

METHODS

The clinical pretest probability of HIT was evaluated by the 4T score system. Laboratory testing of HIT was performed by immunological detection of antibodies against PF4-heparin complex (EIA) and two functional assays. Heparin-dependent activation of donor platelets by patient plasma was detected by flow cytometry. Increased binding of Annexin-V to platelets and elevated number of platelet-derived microparticles (PMP) were the indicators of platelet activation.

RESULTS

EIA for IgG isotype HIT antibodies was performed in 405 suspected HIT patients. Based on negative EIA results, HIT was excluded in 365 (90%) of cases. In 40 patients with positive EIA test result functional tests were performed. Platelet activating antibodies were detected in 17 cases by Annexin V binding. PMP count analysis provided nearly identical results. The probability of a positive flow cytometric assay result was higher in patients with elevated antibody titer. 71% of patients with positive EIA and functional assay had thrombosis.

CONCLUSIONS

EIA is an important first line laboratory test in the diagnosis of HIT; however, HIT must be confirmed by a functional test. Annexin V binding and PMP assays using flow cytometry are functional HIT tests convenient in a clinical diagnostic laboratory. The positive results of functional assays may predict the onset of thrombosis. © 2016 International Clinical Cytometry Society.

Time course of various cell origin circulating microparticles in ST-segment elevation myocardial infarction patients undergoing percutaneous transluminal coronary intervention

The present study aimed to investigate the time course of changes in microparticles (MPs) in patients with ST-segment elevation myocardial infarction (STEMI) that underwent percutaneous transluminal coronary intervention (PCI). A total of 24 STEMI patients undergoing primary PCI were enrolled, and circulating MPs were detected immediately prior to and after PCI, and at 4, 24 and 48 h post-PCI. Standard Megamix beads, based measurement protocols, were employed to measure MPs of different cell origin, including endothelial MPs (EMPs), platelet MPs (PMPs) and leukocyte-derived MPs (LMPs), which were identified by CD144, CD41 and CD45, respectively. The results indicated that PMP levels were evidently elevated immediately after PCI, and reached a maximum level at 48 h. In addition, LMP and EMP levels were significantly decreased immediately after the PCI, and then increased gradually with time. The total quantity of the three aforementioned MP types increased gradually at 48 h following PCI. Furthermore, coronary angiographic Gensini scores were significantly positively correlated with the level of PMPs (r2=0.42; P=0.0006). Log-normalized high sensitivity-C-reactive-protein was also significantly correlated with LMPs (r2=0.86; P<0.01). In conclusion, the time course of the changes in circulating MPs of different cell origin, provided information on possible functions of different MPs in STEMI.

Staphylococcal SSL5-induced platelet microparticles provoke proinflammatory responses via the CD40/TRAF6/NFκB signalling pathway in monocytes

Pathogens-induced platelet activation contributes to inflammation in cardiovascular diseases, but underlying mechanisms remain elusive. Staphylococcal superantigen-like protein 5 (SSL5) is a known activator of platelets. Here we examined whether SSL5 is implicated in Staphylococcus aureus (S. aureus)-induced inflammation and potential mechanisms involved. As expected, we show that SSL5 activates human platelets and induces generation of platelet microparticles (PMPs). Flow cytometry and scanning electron microscopy studies demonstrate that SSL5-induced PMPs (SSL5-PMPs) bind to monocytes, causing aggregate formation. In addition, SSL5-PMPs provoke monocyte expression and release of inflammatory mediators, including interleukin-1β (IL-1β), tumour necrosis factor-α (TNFα), monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-9 (MMP-9) in a dose- and time-dependent manner. SSL5-PMPs also enhance MCP-1-induced monocyte migration. Blockade of CD40 and CD40 ligand (CD40L) interactions with neutralising antibodies significantly reduce monocyte release of inflammatory mediators and migration induced by SSL5-PMPs. SiRNA-mediated silencing of CD40 or TNF receptor (TNFR)-associated factor 6 (TRAF6) gene largely abrogates phosphorylation and nuclear translocation of NFκB (p65). In conclusion, SSL5 provokes the release of inflammatory mediators in monocytes, at least in part, via PMPs-mediated activation of the CD40/TRAF6/NFκB signalling pathway, though it normally inhibits leukocyte function. Our findings thus reveal a novel mechanism by which S. aureus induces inflammation.

Effects of anti-TNF-α agents on circulating endothelial-derived and platelet-derived microparticles in psoriasis

Psoriasis involves TNF-α secretion leading to release of microparticles into the bloodstream. We investigated the effect of TNF blockers on microparticles levels before and after treatment in patients (twenty treated by anti-TNF-α agents and 6 by methotrexate) with severe psoriasis. Plasmatic microparticles were labelled using fluorescent monoclonal antibodies and were analysed using cytometry. Three months later, 70% of patients treated with anti-TNF-α agents achieved a reduction in PASI score of at least 75%. The clinical improvement in patients treated with anti-TNF-α agents was associated with a significant reduction of the mean number of platelet microparticles (2837/μl vs 1849/μl, P = 0.02) and of endothelial microparticles (64/μl vs 22/μl, P = 0.001). Microparticles are significantly decreased in psoriatic patients successfully treated by anti-TNF-α. Microparticles levels as circulating endothelial cells represent signs of endothelial dysfunction and are elevated in psoriasis. Then, TNF blockade may be effective to reduce cardiovascular risk through the reduction of circulating microparticles.

Platelets are relevant mediators of renal injury induced by primary endothelial lesions

Several studies have suggested a prominent (pro)inflammatory and harmful role of platelets in renal disease, and newer work has also demonstrated platelet release of proangiogenic factors. In the present study, we investigated the role of platelets in a mouse model of selective endothelial cell injury using either platelet depletion or the pharmacological P2Y12 receptor blocker clopidogrel as an interventional strategy. The concanavalin A/anti-concanavalin A model was induced in left kidneys of C57bl/6J wild-type mice after initial platelet depletion or platelet-inhibiting therapy using clopidogrel. FACS analysis of glycoprotein IIb/IIIa/P-selectin double-positive platelets and platelet-derived microparticles demonstrated relevant platelet activation after the induction of selective endothelial injury in mice. Enhanced platelet activation persisted for 5 days after disease induction and was accompanied by increased amounts of circulating platelet-derived microparticles as potential mediators of a prolonged procoagulant state. By immunohistochemistry, we detected significantly reduced glomerular injury in platelet-depleted mice compared with control mice. In parallel, we also saw reduced endothelial loss and a consequently reduced repair response as indicated by diminished proliferative activity. The P2Y12 receptor blocker clopidogrel demonstrated efficacy in limiting platelet activation and subsequent endothelial injury in this mouse model of renal microvascular injury. In conclusion, platelets are relevant mediators of renal injury induced by primary endothelial lesions early on, as demonstrated by platelet depletion as well as platelet inhibition via the P2Y12 receptor. While strategies to prevent platelet-endothelial interactions have shown protective effects, the contribution of platelets during renal regeneration remains unknown.

Elevated platelet microparticle levels after acute ischemic stroke with concurrent idiopathic thrombocytopenic purpura

We report a 60-year-old woman with idiopathic thrombocytopenic purpura who experienced acute infarction of the middle cerebral artery. She was treated with an antiplatelet agent and prednisolone to limit platelet activation and destruction. In parallel with clinical amelioration, levels of plasma platelet microparticles (PMPs), a procoagulant factor in platelet activation, decreased after treatment but increased after reduction of the prednisolone dose, resulting in progression of vascular stenosis. Immunosuppressive therapy with cyclosporine normalized plasma PMP levels, and no additional vascular events occurred during the 3-month follow-up period. Immunosuppressive therapy to decrease plasma PMP levels is warranted after acute ischemic stroke in the context of idiopathic thrombocytopenic purpura.