Factors influencing the level of circulating procoagulant microparticles in acute pulmonary embolism

Proteomic analysis of extracellular vesicle cargoes mirror the cardioprotective effects of rivaroxaban in patients with venous thromboembolism

BACKGROUND

Venous thromboembolism (VTE) remains a significant cause of morbidity and mortality worldwide. Rivaroxaban, a direct oral factor Xa inhibitor, mediates anti-inflammatory and cardiovascular-protective effects besides its well-established anticoagulant properties; yet, these remain poorly characterized. Extracellular vesicles (EVs) are considered proinflammatory messengers regulating a myriad of (patho)physiological processes and may be highly relevant to the pathophysiology of VTE. The effects of Rivaroxaban on circulating EVs in VTE patients remain unknown. We have established that differential EV biosignatures are found in patients with non-valvular atrial fibrillation anticoagulated with Rivaroxaban versus warfarin. Here, we investigated whether differential proteomic profiles of circulating EVs could also be found in patients with VTE.

METHODS AND RESULTS

We performed comparative label-free quantitative proteomic profiling of enriched plasma EVs from VTE patients anticoagulated with either Rivaroxaban or warfarin using a tandem mass spectrometry approach. Of the 182 quantified proteins, six were found to be either exclusive to, or enriched in, Rivaroxaban-treated patients. Intriguingly, these proteins are involved in negative feedback regulation of inflammatory and coagulation pathways, suggesting that EV proteomic signatures may reflect both Rivaroxaban's anti-coagulatory and anti-inflammatory potential.

CONCLUSIONS

These differences suggest Rivaroxaban may have pleiotropic effects, supporting the reports of its emerging anti-inflammatory and cardiovascular-protective characteristics relative to warfarin.

Extracellular vesicles from activated platelets possess a phospholipid-rich biomolecular profile and enhance prothrombinase activity

BACKGROUND

Extracellular vesicles (EVs), in particular those derived from activated platelets, are associated with a risk of future venous thromboembolism.

OBJECTIVES

To study the biomolecular profile and function characteristics of EVs from control (unstimulated) and activated platelets.

METHODS

Biomolecular profiling of single or very few (1-4) platelet-EVs (control/stimulated) was performed by Raman tweezers microspectroscopy. The effects of such EVs on the coagulation system were comprehensively studied.

RESULTS

Raman tweezers microspectroscopy of platelet-EVs followed by biomolecular component analysis revealed for the first time 3 subsets of EVs: (i) protein rich, (ii) protein/lipid rich, and (iii) lipid rich. EVs from control platelets presented a heterogeneous biomolecular profile, with protein-rich EVs being the main subset (58.7% ± 3.5%). Notably, the protein-rich subset may contain a minor contribution from other extracellular particles, including protein aggregates. In contrast, EVs from activated platelets were more homogeneous, dominated by the protein/lipid-rich subset (>85%), and enriched in phospholipids. Functionally, EVs from activated platelets increased thrombin generation by 52.4% and shortened plasma coagulation time by 34.6% ± 10.0% compared with 18.6% ± 13.9% mediated by EVs from control platelets (P = .015). The increased procoagulant activity was predominantly mediated by phosphatidylserine. Detailed investigation showed that EVs from activated platelets increased the activity of the prothrombinase complex (factor Va:FXa:FII) by more than 6-fold.

CONCLUSION

Our study reports a novel quantitative biomolecular characterization of platelet-EVs possessing a homogenous and phospholipid-enriched profile in response to platelet activation. Such characteristics are accompanied with an increased phosphatidylserine-dependent procoagulant activity. Further investigation of a possible role of platelet-EVs in the pathogenesis of venous thromboembolism is warranted.

Extracellular Vesicles (EVs) as Crucial Mediators of Cell-Cell Interaction in Asthma

Asthma is the most common chronic respiratory disorder worldwide and accounts for a huge health and economic burden. Its incidence is rapidly increasing but, in parallel, novel personalized approaches have emerged. Indeed, the improved knowledge of cells and molecules mediating asthma pathogenesis has led to the development of targeted therapies that significantly increased our ability to treat asthma patients, especially in severe stages of disease. In such complex scenarios, extracellular vesicles (EVs i.e., anucleated particles transporting nucleic acids, cytokines, and lipids) have gained the spotlight, being considered key sensors and mediators of the mechanisms controlling cell-to-cell interplay. We will herein first revise the existing evidence, mainly by mechanistic studies in vitro and in animal models, that EV content and release is strongly influenced by the specific triggers of asthma. Current studies indicate that EVs are released by potentially all cell subtypes in the asthmatic airways, particularly by bronchial epithelial cells (with different cargoes in the apical and basolateral side) and inflammatory cells. Such studies largely suggest a pro-inflammatory and pro-remodelling role of EVs, whereas a minority of reports indicate protective effects, particularly by mesenchymal cells. The co-existence of several confounding factors-including technical pitfalls and host and environmental confounders-is still a major challenge in human studies. Technical standardization in isolating EVs from different body fluids and careful selection of patients will provide the basis for obtaining reliable results and extend their application as effective biomarkers in asthma.

Plasma levels of platelet-enriched microRNAs change during antiplatelet therapy in healthy subjects

Platelets are the main effectors of primary hemostasis but also cause thrombosis in pathological conditions. Antiplatelet drugs are the cornerstone for the prevention of adverse cardiovascular events. Monitoring the extent of platelet inhibition is essential. Currently available platelet function tests come with constraints, limiting use in antiplatelet drug development as well as in clinical routine. With this study, we aim to investigate whether plasma miRNAs might be suitable biomarkers for monitoring antiplatelet treatment. Platelet-poor plasma was obtained from a trial including 87 healthy male volunteers that either received ticagrelor (n = 44) or clopidogrel (n = 43). Blood was collected before drug intake and after 2 h, 6 h, and 24 h. We measured a panel of 11 platelet-enriched miRNAs (thrombomiRs) by RT-qPCR and selected four biomarker candidates (i.e., miR-223-3p, miR-150-5p, miR-126-3p, miR-24-3p). To further characterize those miRNAs, we performed correlation analyses with the number of extracellular vesicles and clotting time dependent on procoagulant vesicles (PPL assay). We show that platelet-enriched miRNAs in the circulation are significantly reduced upon P2Y12-mediated platelet inhibition. This effect occurred fast, reaching its peak after 2 h. Additionally, we demonstrate that higher baseline levels of thrombomiRs are linked to a stronger reduction upon antiplatelet therapy. Finally, we show that miRNAs from our panel might be the cargo of platelet-derived and procoagulant vesicles. In conclusion, we provide evidence that thrombomiR levels change within 2 h after pharmacological platelet inhibition and circulate the body within platelet-derived and procoagulant extracellular vesicles, rendering them potential biomarker candidates for the assessment of in vivo platelet function.

Pathophysiology of Coagulation and Emerging Roles for Extracellular Vesicles in Coagulation Cascades and Disorders

The notion of blood coagulation dates back to the ancient Greek civilization. However, the emergence of innovative scientific discoveries that started in the seventeenth century formulated the fundamentals of blood coagulation. Our understanding of key coagulation processes continues to evolve, as novel homeostatic and pathophysiological aspects of hemostasis are revealed. Hemostasis is a dynamic physiological process, which stops bleeding at the site of injury while maintaining normal blood flow within the body. Intrinsic and extrinsic coagulation pathways culminate in the homeostatic cessation of blood loss, through the sequential activation of the coagulation factors. Recently, the cell-based theory, which combines these two pathways, along with newly discovered mechanisms, emerged to holistically describe intricate in vivo coagulation mechanisms. The complexity of these mechanisms becomes evident in coagulation diseases such as hemophilia, Von Willebrand disease, thrombophilia, and vitamin K deficiency, in which excessive bleeding, thrombosis, or unnecessary clotting, drive the development and progression of diseases. Accumulating evidence implicates cell-derived and platelet-derived extracellular vesicles (EVs), which comprise microvesicles (MVs), exosomes, and apoptotic bodies, in the modulation of the coagulation cascade in hemostasis and thrombosis. As these EVs are associated with intercellular communication, molecular recycling, and metastatic niche creation, emerging evidence explores EVs as valuable diagnostic and therapeutic approaches in thrombotic and prothrombotic diseases.

Plasma levels of platelet-derived microvesicles are associated with risk of future venous thromboembolism

BACKGROUND

Microvesicles (MVs) are small double-membrane encapsulated particles shed from cells. Case-control studies have reported elevated plasma levels of platelet-derived MVs (PDMVs) in patients with venous thromboembolism (VTE). However, it is not known whether high PDMV levels is a risk factor or a consequence of the acute VTE event.

OBJECTIVES

To investigate the association between PDMVs in plasma and risk of future incident VTE.

METHODS

We performed a population-based nested case-control study with 314 VTE cases and 705 age- and sex-matched controls (from The Tromsø Study) to investigate the association between the proportion of PDMVs (PDMVs%) in plasma and risk of future incident VTE. MVs isolated from plasma sampled at baseline (i.e., before VTE) were stained for platelet markers and analyzed by flow cytometry. PDMVs% were defined as the number of PDMVs divided by the total number of MVs. Odds ratios (ORs) with 95% confidence intervals (CI) for VTE risk were estimated across quartiles of PDMVs%.

RESULTS

Subjects with PDMVs% in the highest quartile had an OR for VTE of 1.78 (95% CI: 1.21-2.64) and 1.99 (95% CI: 1.24-3.26) for provoked VTE, compared to those in the lowest quartile. The association was moderately affected by multivariable adjustment for age, sex, body mass index, C-reactive protein, platelet count, and cancer. The OR for VTE was higher when the time between blood sampling and event was shorter.

CONCLUSIONS

Our results show that high proportions of PDMVs are associated with future risk of incident VTE and imply a role of platelet activation in the pathogenesis of VTE.

Extracellular Vesicles and Thrombosis: Update on the Clinical and Experimental Evidence

Extracellular vesicles (EVs) compose a heterogenous group of membrane-derived particles, including exosomes, microvesicles and apoptotic bodies, which are released into the extracellular environment in response to proinflammatory or proapoptotic stimuli. From earlier studies suggesting that EV shedding constitutes a cellular clearance mechanism, it has become evident that EV formation, secretion and uptake represent important mechanisms of intercellular communication and exchange of a wide variety of molecules, with relevance in both physiological and pathological situations. The putative role of EVs in hemostasis and thrombosis is supported by clinical and experimental studies unraveling how these cell-derived structures affect clot formation (and resolution). From those studies, it has become clear that the prothrombotic effects of EVs are not restricted to the exposure of tissue factor (TF) and phosphatidylserines (PS), but also involve multiplication of procoagulant surfaces, cross-linking of different cellular players at the site of injury and transfer of activation signals to other cell types. Here, we summarize the existing and novel clinical and experimental evidence on the role and function of EVs during arterial and venous thrombus formation and how they may be used as biomarkers as well as therapeutic vectors.

Individualised Risk Assessments for Recurrent Venous Thromboembolism: New Frontiers in the Era of Direct Oral Anticoagulants

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality and is associated with high recurrence rates. The introduction of direct oral anticoagulants (DOACs) in the 2010s has changed the landscape of VTE management. DOACs have become the preferred anticoagulant therapy for their ease of use, predictable pharmacokinetics, and improved safety profile. Increasingly, guidelines have recommended long term anticoagulation for some indications such as following first unprovoked major VTE, although an objective individualised risk assessment for VTE recurrence remains elusive. The balance of preventing VTE recurrence needs to be weighed against the not insignificant bleeding risk, which is cumulative with prolonged use. Hence, there is a need for an individualised, targeted approach for assessing the risk of VTE recurrence, especially in those patients in whom the balance between benefit and risk of long-term anticoagulation is not clear. Clinical factors alone do not provide the level of discrimination required on an individual level. Laboratory data from global coagulation assays and biomarkers may provide enhanced risk assessment ability and are an active area of research. A review of the prediction models and biomarkers for assessing VTE recurrence risk is provided, with an emphasis on contemporary developments in the era of DOACs and global coagulation assays.

Predicting the Risk of Recurrent Venous Thromboembolism: Current Challenges and Future Opportunities

Acute venous thromboembolism (VTE) is a commonly diagnosed condition and requires treatment with anticoagulation to reduce the risk of embolisation as well as recurrent venous thrombotic events. In many cases, cessation of anticoagulation is associated with an unacceptably high risk of recurrent VTE, precipitating the use of indefinite anticoagulation. In contrast, however, continuing anticoagulation is associated with increased major bleeding events. As a consequence, it is essential to accurately predict the subgroup of patients who have the highest probability of experiencing recurrent VTE, so that treatment can be appropriately tailored to each individual. To this end, the development of clinical prediction models has aided in calculating the risk of recurrent thrombotic events; however, there are several limitations with regards to routine use for all patients with acute VTE. More recently, focus has shifted towards the utility of novel biomarkers in the understanding of disease pathogenesis as well as their application in predicting recurrent VTE. Below, we review the current strategies used to predict the development of recurrent VTE, with emphasis on the application of several promising novel biomarkers in this field.

Promising biomarkers for the prediction of catheter-related venous thromboembolism in hospitalized children: An exploratory study

BACKGROUND

Pediatric venous thromboembolism (VTE) has increased over the past 10 years, with central venous catheters (CVC) being the strongest risk factor. Current tools are not sufficient to predict VTE risk. The utility of biomarkers in predicting CVC-related VTE has been minimally explored. Our objective is to determine the utility of microparticles (MPs), factor VIII (FVIII) activity, and thrombin generation (TG) in prospectively predicting VTE occurrence in hospitalized children with CVCs.

PROCEDURE

In this nested case-control pilot study, consecutive hospitalized children needing CVC placement (1 month to 21 years) were enrolled. Venous samples were collected prior to or within 24 h of CVC placement. MPs were measured using factor Xa initiated clot-based assay. FVIII was measured using a one-stage clot-based assay. TG was measured using calibrated automated thrombogram.

RESULTS

There were three CVC-related VTE events (7%) in our cohort of 42 subjects. Xa clotting time (XaCT) ratio was lower (0.68 ± 0.07 vs 0.95 ± 0.21, P = .4), while FVIII (461 ± 120 vs 267 ± 130, P = .02), peak thrombin (418 ± 89 vs 211 ± 101, P = .001), endogenous thrombin potential (ETP) (1828 ± 485 vs 1282 ± 394, P = .03), and velocity index (VI) (182 ± 28 vs 75 ± 53, P = .001) were higher in subjects with CVC-related VTE compared to those without CVC-related VTE. Sensitivity/specificity analysis revealed optimal cutoff values for XaCT ratio (0.75), FVIII (370), ETP (1680), peak (315), and VI (130), with receiver operating characteristic area under the curve values >0.9.

CONCLUSION

MPs, FVIII, and TG can potentially predict pediatric CVC-related VTE in a prospective fashion. Stratification according to VTE risk may aid in guiding preventative efforts in future studies.

Extracellular vesicles derived from pancreatic cancer cells BXPC3 or breast cancer cells MCF7 induce a permanent procoagulant shift to endothelial cells

The endothelium could be a potential target of cancer cell derived extracellular vesicles (CaCe-dEV). We investigated in vitro the effect of CaCe-dEV on the hemostatic balance of endothelial cells. Extracellular vesicles released from pancreas adenocarcinoma cells (BXPC3) or human breast cancer cells (MCF7) were isolated by differential centrifugation. Human umbilical vein endothelial cells (HUVEC) were cultured for 72 h in the presence or absence of CaCe-dEV. Subsequently, they were washed and re-cultivated over three cycles to get daughter cell generations (DG) which were not exposed to CaCe-dEV. Thrombin generation of normal platelet poor plasma (PPP) added in wells carrying HUVEC was assessed by the Calibrated Automated Thrombogram®. Tissue factor activity (TFa) and procoagulant phospholipid clotting time were assessed. Some traces of TFa were displayed by non-exposed HUVEC (0.18 ± 0.03 pM) and their EVs (1.2 ± 1.0 pM). Non-exposed HUVEC did not induce any detectable thrombin generation. BXPC3-dEV displayed significantly higher TFa as compared to MCF7-dEV (45 ± 5 pM versus 4.6 ± 2.3pM respectively; p < 0.05). HUVEC exposed to CaCe-dEV enhanced thrombin generation. BXPC3-dEV induced significantly higher thrombin generation as compared to those exposed to MCF7-dEV. The procoagulant properties of HUVEC, acquired upon exposure to CaCe-dEV were transferred to DG. In conclusion, CaCe-dEV lead to a procoagulant shift of endothelial cells which, upon exposure, display TFa and enhance thrombin generation which is transferred to DG of HUVEC. The potency of CaCe-dEV to induce procoagulant shift of HUVEC depends on the histological type of the cancer cells. The procoagulant shift of endothelial cells which is transferable to DG could be an additional mechanism - together with cancer-induced blood hypercoagulability - in the pathogenesis of cancer associated thrombosis.

Endothelial Extracellular Vesicles in Pulmonary Function and Disease

The pulmonary vascular endothelium is involved in the pathogenesis of acute and chronic lung diseases. Endothelial cell (EC)-derived products such as extracellular vesicles (EVs) serve as EC messengers that mediate inflammatory as well as cytoprotective effects. EC-EVs are a broad term, which encompasses exosomes and microvesicles of endothelial origin. EVs are comprised of lipids, nucleic acids, and proteins that reflect not only the cellular origin but also the stimulus that triggered their biogenesis and secretion. This chapter presents an overview of the biology of EC-EVs and summarizes key findings regarding their characteristics, components, and functions. The role of EC-EVs is specifically delineated in pulmonary diseases characterized by endothelial dysfunction, including pulmonary hypertension, acute respiratory distress syndrome and associated conditions, chronic obstructive pulmonary disease, and obstructive sleep apnea.

Diagnostic value of platelet-derived microparticles in pulmonary thromboembolism: A population-based study

An early and accurate diagnosis of pulmonary thromboembolism (PTE) remains challenging. The present study aimed to evaluate the diagnostic value of platelet-derived microparticles in PTE based on a population study. A total of 102 patients with PTE, 102 healthy controls and 40 patients suspected with PTE were enrolled in this study. The platelet count, mean platelet volume and platelet distribution width were assessed using an automated hematology analyzer, P-selectin was assessed using an ELISA kit and PMPs were explored using flow cytometry using Megamix beads. Receiver operating characteristic curves were established to evaluate the diagnostic values of PMPs, D-dimer, PMPs combined with D-dimer, and multiple parameters (including PMPs, platelet distribution width, P-selectin and D-dimer in PTE). The PMP levels were significantly higher in the patients with PTE (609.10/µl) compared with those in the healthy controls (230.60/µl) and patients with suspicious PTE (166.70/µl; P<0.01). The accuracy (72.06%) of PMPs in the diagnosis of PTE was similar to those of D-dimer (P>0.05). The combination of D-dimer and PMPs significantly increased the sensitivity (86.27%) of D-dimer and the specificity of PMP for the diagnosis of PTE (P<0.01). The combination of PMPs, platelet distribution width, P-selectin and D-dimer exhibited high sensitivity (88.24%), specificity (91.18%) and accuracy (89.71%) in the diagnosis of PTE. These findings suggest that elevated PMP levels are an effective predictor of PTE. The combination of PMPs, platelet distribution width, P-selectin and D-dimer may be used in the diagnosis of PTE with high sensitivity and specificity.

Endothelial microvesicles in hypoxic hypoxia diseases

Hypoxic hypoxia, including abnormally low partial pressure of inhaled oxygen, external respiratory dysfunction-induced respiratory hypoxia and venous blood flow into the arterial blood, is characterized by decreased arterial oxygen partial pressure, resulting in tissue oxygen deficiency. The specific characteristics include reduced arterial oxygen partial pressure and oxygen content. Hypoxic hypoxia diseases (HHDs) have attracted increased attention due to their high morbidity and mortality and mounting evidence showing that hypoxia-induced oxidative stress, coagulation, inflammation and angiogenesis play extremely important roles in the physiological and pathological processes of HHDs-related vascular endothelial injury. Interestingly, endothelial microvesicles (EMVs), which can be induced by hypoxia, hypoxia-induced oxidative stress, coagulation and inflammation in HHDs, have emerged as key mediators of intercellular communication and cellular functions. EMVs shed from activated or apoptotic endothelial cells (ECs) reflect the degree of ECs damage, and elevated EMVs levels are present in several HHDs, including obstructive sleep apnoea syndrome and chronic obstructive pulmonary disease. Furthermore, EMVs have procoagulant, proinflammatory and angiogenic functions that affect the pathological processes of HHDs. This review summarizes the emerging roles of EMVs in the diagnosis, staging, treatment and clinical prognosis of HHDs.

Initiation and Propagation of Vascular Calcification Is Regulated by a Concert of Platelet- and Smooth Muscle Cell-Derived Extracellular Vesicles

The ageing population continues to suffer from its primary killer, cardiovascular disease (CVD). Despite recent advances in interventional medicinal and surgical therapies towards the end of the 20th century, the epidemic of cardiovascular disease has not been halted. Yet, rather than receding globally, the burden of CVD has risen to become a top cause of morbidity and mortality worldwide. Most CVD arises from thrombotic rupture of an atherosclerotic plaque, the pathologic thickening of coronary and carotid artery segments and subsequent distal ischemia in heart or brain. In fact, one-fifth of deaths are directly attributable to thrombotic rupture of a vulnerable plaque. Atherosclerotic lesion formation is caused by a concert of interactions between circulating leukocytes and platelets, interacting with the endothelial barrier, signalling into the arterial wall by the release of cytokines and extracellular vesicles (EVs). Both platelet- and cell-derived EVs represent a novel mechanism of cellular communication, particularly by the transport and transfer of cargo and by reprogramming of the recipient cell. These interactions result in phenotypic switching of vascular smooth muscle cells (VSMCs) causing migration and proliferation, and subsequent secretion of EVs. Loss of VSMCs attracts perivascular Mesenchymal Stem Cells (MSCs) from the adventitia, which are a source of VSMCs and contribute to repair after vascular injury. However, continuous stress stimuli eventually switch phenotype of cells into osteochondrogenic VSMCs facilitating vascular calcification. Although Virchow’s triad is over 100 years old, it is a reality that is accurate today. It can be briefly summarised as changes in the composition of blood (platelet EVs), alterations in the vessel wall (VSMC phenotypic switching, MSC infiltration and EV release) and disruption of blood flow (atherothrombosis). In this paper, we review the latest relevant advances in the identification of extracellular vesicle pathways as well as VSMCs and pericyte/MSC phenotypic switching, underlying vascular calcification.

Modulating thrombotic diathesis in hereditary thrombophilia and antiphospholipid antibody syndrome: a role for circulating microparticles?

Over the past decades, there have been great advances in the understanding of the pathogenesis of venous thromboembolism (VTE) in patients with inherited and acquired thrombophilia [mainly antiphospholipid antibody syndrome (APS)]. However, a number of questions remain unanswered. Prognostic markers capable of estimating the individual VTE risk would be of great use. Microparticles (MPs) are sub-micron membrane vesicles constitutively released from the surface of cells after cellular activation and apoptosis. The effects of MPs on thrombogenesis include the exposure of phopshatidylserine and the expression of tissue factor and MPs have been described in clinical studies as possible diagnostic and prognostic biomarkers for VTE. This review will provide a novel perspective on the current knowledge and research trends on the possible role of MPs in hereditary thrombophilia and APS. Basically, the published data show that circulating MPs may contribute to the development of VTE in thrombophilic carriers, both in mild and severe states. Moreover, the presence of endothelial-MPs and platelet-MPs has been described in antiphospholipid syndrome and seems to be directly linked to antiphospholipid antibodies and not to other underlying autoimmune disorders or the thrombotic event itself. In conclusion, circulating MPs may constitute an epiphenomenon of thrombophilia itself and could be up-regulated in acute particular conditions, promoting a global prothrombotic state up to the threshold of the clinical relevant thrombotic event.

Extracellular vesicles in renal disease

Extracellular vesicles, such as exosomes and microvesicles, are host cell-derived packages of information that allow cell-cell communication and enable cells to rid themselves of unwanted substances. The release and uptake of extracellular vesicles has important physiological functions and may also contribute to the development and propagation of inflammatory, vascular, malignant, infectious and neurodegenerative diseases. This Review describes the different types of extracellular vesicles, how they are detected and the mechanisms by which they communicate with cells and transfer information. We also describe their physiological functions in cellular interactions, such as in thrombosis, immune modulation, cell proliferation, tissue regeneration and matrix modulation, with an emphasis on renal processes. We discuss how the detection of extracellular vesicles could be utilized as biomarkers of renal disease and how they might contribute to disease processes in the kidney, such as in acute kidney injury, chronic kidney disease, renal transplantation, thrombotic microangiopathies, vasculitides, IgA nephropathy, nephrotic syndrome, urinary tract infection, cystic kidney disease and tubulopathies. Finally, we consider how the release or uptake of extracellular vesicles can be blocked, as well as the associated benefits and risks, and how extracellular vesicles might be used to treat renal diseases by delivering therapeutics to specific cells.

Cell-derived microparticles and the lung

Cell-derived microparticles are small (0.1-1 μm) vesicles shed by most eukaryotic cells upon activation or during apoptosis. Microparticles carry on their surface, and enclose within their cytoplasm, molecules derived from the parental cell, including proteins, DNA, RNA, microRNA and phospholipids. Microparticles are now considered functional units that represent a disseminated storage pool of bioactive effectors and participate both in the maintenance of homeostasis and in the pathogenesis of diseases. The mechanisms involved in microparticle generation include intracellular calcium mobilisation, cytoskeleton rearrangement, kinase phosphorylation and activation of the nuclear factor-κB. The role of microparticles in blood coagulation and inflammation, including airway inflammation, is well established in in vitro and animal models. The role of microparticles in human pulmonary diseases, both as pathogenic determinants and biomarkers, is being actively investigated. Microparticles of endothelial origin, suggestive of apoptosis, have been demonstrated in the peripheral blood of patients with emphysema, lending support to the hypothesis that endothelial dysfunction and apoptosis are involved in the pathogenesis of the disease and represent a link with cardiovascular comorbidities. Microparticles also have potential roles in patients with asthma, diffuse parenchymal lung disease, thromboembolism, lung cancer and pulmonary arterial hypertension.

Microparticles in patients undergoing transcatheter aortic valve implantation (TAVI)

Degenerative aortic stenosis (AS) is the most frequent form of acquired valvular heart disease. AS is known to entail endothelial dysfunction caused by increased mechanical shear stress leading to elevated circulatory levels of microparticles. Endothelial and platelet microparticles (EMP and PMP) are small vesicles that originate from activated cells and thrombocytes. We sought to evaluate whether transcatheter aortic valve implantation (TAVI) procedure would elicit effects on circulating EMP and PMP. 92 patients undergoing TAVI procedure for severe AS were included in this study. Samples were obtained at each visit before TAVI, 1 week post-procedure and at 1, 3 and after 6 months after TAVI and were evaluated using flow cytometry. A 12 month clinical follow-up was also performed. CD62E+ EMP concentration before TAVI was 21.11 % (±6.6 % SD) and declined to 20.99 % (±6.8 % SD) after 1 week, to 16.63 % (±5.4 % SD, p < 0.0001) after 1 month, to 17.08 % (±4.6 % SD, p < 0.0001) after 3 months and to 15.94 % (±5.4 % SD, p < 0.0001) after 6 months. CD31+/CD42b-, CD31+/Annexin+/- EMP remained unchanged. CD31+/CD41b+ PMP evidenced a slight, but statistically significant increase after TAVI and remained elevated during the entire follow-up. Apart from a procedure-related improvement in echocardiographic parameters, TAVI procedure led also to a decline in CD62E+ EMP. The reduction in pressure gradients with less hemodynamic shear stress seems also to have beneficially affected endothelial homeostasis.

Microparticles as biomarkers of venous thromboembolic events

Microparticles (MPs) are small (0.1–1.0 μm) membrane vesicles constitutively released from the surface of cells after activation and apoptosis. The clinical research on MPs is hampered by the limitations of the currently available detection methods. A correlation between MPs and venous thromboembolism (VTE) has been observed. The effects of MPs on thrombogenesis involve the exposure of phosphatidylserine, the vehiculation of tissue factor, and MP-induced intercellular cross-talk between inflammation and coagulation. This review will focus on the potential role of plasma MPs as biomarkers in detecting acute unprovoked VTE, predicting VTE occurrence in high-risk situations (mainly cancer), and ultimately, we will discuss currently available studies on the prognostic role of MPs to guide primary and secondary VTE prevention protocols.

Evaluation of Endothelial and Platelet Derived Microparticles in Patients with Acute Coronary Syndrome

BACKGROUND

Microparticles (MP) are a nuclear fragments of membrane released by the damaged cell during stress. Elevated levels of MP have been found in patients with acute coronary syndrome (ACS) owing to the damage in the endothelium.

AIM

To determine if the levels of endothelial and platelet microparticles (EMP & PMP) in patients with ACS influenced the severity of the disease.

MATERIALS AND METHODS

This was a prospective cohort study performed in 63 ACS patients (ST elevation myocardial infarction- STEMI-28, non ST elevation myocardial infarction -NSTEMI-35). After obtaining consent, blood samples were collected from the patients and processed by flow cytometry.

RESULTS

The NSTEMI group had higher levels of EMP {792.11(327.59-1661.49) vs 300.35 (176.3-550.46), p=0.001} and PMP {218.87(86.65-439.77) vs 114.45(50.34-196.75), p= 0.007} as compared to the STEMI group. However, it was found that the EMP (r=-0.438, p=0.001) and PMP (r= -0.316, p=0.024) negatively correlated with Global Registry of Acute Coronary Events score (GRACE in-hospital score) for the entire cohort.

CONCLUSION

The levels of microparticles are elevated in ACS patients and may reflect a protective effect in patients with acute coronary syndrome.

Proteomics of pulmonary hypertension: could personalized profiles lead to personalized medicine?

Pulmonary hypertension (PH) is a fatal syndrome that arises from a multifactorial and complex background, is characterized by increased pulmonary vascular resistance and right heart afterload, and often leads to cor pulmonale. Over the past decades, remarkable progress has been made in reducing patient symptoms and delaying the progression of the disease. Unfortunately, PH remains a disease with no cure. The substantial heterogeneity of PH continues to be a major limitation to the development of newer and more efficacious therapies. New advances in our understanding of the biological pathways leading to such a complex pathogenesis will require the identification of the important proteins and protein networks that differ between a healthy lung (or right ventricle) and a remodeled lung in an individual with PH. In this article, we present the case for the increased use of proteomics--the study of proteins and protein networks--as a discovery tool for key proteins and protein networks operational in the PH lung. We review recent applications of proteomics in PH, and summarize the biological pathways identified. Finally, we attempt to presage what the future will bring with regard to proteomics in PH and offer our perspectives on the prospects of developing personalized proteomics and custom-tailored therapies.

Microparticles: new light shed on the understanding of venous thromboembolism

Microparticles are small membrane fragments shed primarily from blood and endothelial cells during either activation or apoptosis. There is mounting evidence suggesting that microparticles perform a large array of biological functions and contribute to various diseases. Of these disease processes, a significant link has been established between microparticles and venous thromboembolism. Advances in research on the role of microparticles in thrombosis have yielded crucial insights into possible mechanisms, diagnoses and therapeutic targets of venous thromboembolism. In this review, we discuss the definition and properties of microparticles and venous thromboembolism, provide a synopsis of the evidence detailing the contributions of microparticles to venous thromboembolism, and propose potential mechanisms, by which venous thromboembolism occurs. Moreover, we illustrate a possible role of microparticles in cancer-related venous thromboembolism.

Coagulation and the vessel wall in pulmonary embolism

Venous thromboembolism comprises deep-vein thrombosis, thrombus in transit, acute pulmonary embolism, and chronic thromboembolic pulmonary hypertension (CTEPH). Pulmonary thromboemboli commonly resolve, with restoration of normal pulmonary hemodynamics. When they fail to resorb, permanent occlusion of the deep veins and/or CTEPH are the consequences. Apart from endogenous fibrinolysis, venous thrombi resolve by a process of mechanical fragmentation, through organization of the thromboembolus by invasion of endothelial cells, leukocytes, and fibroblasts leading to recanalization. Recent data utilizing various models have contributed to a better understanding of venous thrombosis and the resolution process that is directed at maintaining vascular patency. This review summarizes the plasmatic and cellular components of venous thrombus formation and resolution.

Climacteric lowers plasma levels of platelet-derived microparticles: a pilot study in pre- versus postmenopausal women

BACKGROUND

Climacteric increases the risk of thrombotic events by alteration of plasmatic coagulation. Up to now, less is known about changes in platelet- (PMP) and endothelial cell-derived microparticles (EMP).

METHODS

In this prospective study, plasma levels of microparticles (MP) were compared in 21 premenopausal and 19 postmenopausal women.

RESULTS

No altered numbers of total MP or EMP were measured within the study groups. However, the plasma values of CD61-exposing MP from platelets/megakaryocytes were higher in premenopausal women (5,364 × 10(6)/l, range 4,384-17,167) as compared to postmenopausal women (3,808 × 10(6)/l, range 2,009-8,850; p = 0.020). This differentiation was also significant for the subgroup of premenopausal women without hormonal contraceptives (5,364 × 10(6)/l, range 4,223-15,916; p = 0.047; n = 15). Furthermore, in premenopausal women, higher plasma levels of PMP exposing CD62P were also present as compared to postmenopausal women (288 × 10(6)/l, range 139-462, vs. 121 × 10(6)/l, range 74-284; p = 0.024). This difference was also true for CD63+ PMP levels (281 × 10(6)/l, range 182-551, vs. 137 × 10(6)/l, range 64-432; p = 0.015).

CONCLUSION

Climacteric lowers the level of PMP but has no impact on the number of EMP in women. These data suggest that PMP and EMP do not play a significant role in enhancing the risk of thrombotic events in healthy, postmenopausal women.

Cellular mechanisms underlying the formation of circulating microparticles

Microparticles (MPs) derived from platelets, monocytes, endothelial cells, red blood cells, and granulocytes may be detected in low concentrations in normal plasma and at increased levels in atherothrombotic cardiovascular diseases. The elucidation of the cellular mechanisms underlying the generation of circulating MPs is crucial for improving our understanding of their pathophysiological role in health and disease. The flopping of phosphatidylserine (PS) to the outer leaflet of the plasma membrane is the key event that will ultimately lead to the shedding of procoagulant MPs from activated or apoptotic cells. Research over the last few years has revealed important roles for calcium-, mitochondrial-, and caspase-dependent mechanisms leading to PS exposure. The study of Scott cells has unraveled different molecular mechanisms that may contribute to fine-tuning of PS exposure and MP release in response to a variety of specific stimuli. The pharmacological modulation of MP release may have a substantial therapeutic impact in the management of atherothrombotic vascular disorders. Because PS exposure is a key feature in pathological processes different from hemostasis and thrombosis, the most important obstacle in the field of MP-modulating drugs seems to be carefully targeting MP release to relevant cell types at an optimal level, so as to achieve a beneficial action and limit possible adverse effects.