Platelet Microvesicles Research Articles

#1591 Analysis of microvesicles and their relationship with oxidative stress as biomarkers of cardiovascular damage in chronic kidney disease

Abstract Background and Aims Chronic kidney disease (CKD) is associated with a higher incidence of cardiovascular diseases. These diseases are preceded by endothelial dysfunction and alterations in coagulation systems. One of the challenges of research in this field is the search for diagnostic and predictive biomarkers of cardiovascular pathology. Our hypothesis is that endothelial dysfunction and cardiovascular risk could be evidenced by the increased release of endothelial microvesicles (EMVs) and platelet microvesicles (PMVs), as well as a greater expression of tissue factor (TF). We also propose a relationship between the release of microvesicles and the oxidative stress observed in these patients. The aim of the study was to analyze the levels of MVEs and MVPs, the expression of FT and its relationship with pro-oxidant and antioxidant parameters as possible early biomarkers of cardiovascular and thrombotic risk in different stages and treatments of CKD. Method It is a cross-sectional study consisted of 116 patients (40 with advanced chronic disease (CKD), 40 undergoing hemodialysis (HD) and 36 undergoing peritoneal dialysis (PD)), as well as 17 healthy subjects (CT). Microvesicle phenotyping was performed by direct immunofluorescence and flow cytometry in plasma isolated by centrifugation from peripheral blood. The analysis of oxidative stress parameters was carried out by spectrophotometry, after isolation of plasma and mononuclear and polymorphonuclear leukocytes by means of a ficoll gradient. Results Patients on PD have higher plasma PMVs levels (p = 0.0005 vs ACKD and p = 0,0002 vs HD), while those on HD and PD have higher levels of EMVs compared to ACKD (p = 0,0001 and p = 0,0125, respectively). FT expression in PMVs is lower in HD (p < 0.0001 vs ACKD) and FT expression in EMVs is lower in HD and PD compared to ACKD (p = 0,0004 and p= 0.0033, respectively) (Fig. 1). Patients with CKD have a higher activity of pro-oxidant enzymes (XO, GPx), as well as high levels of lipid peroxidation by-products (TBARS-MDA) and lower activity of antioxidant enzymes (GSH, CAT, SOD) at the plasma and cellular level. A positive relationship has been observed between pro-oxidant parameters and the release of MVP and MVE, as well as the expression of FT (Table 1). Patients with cardiovascular events during the years of follow-up have higher levels of FT expressed in microvesicles, and long-term survival decreases in patients with elevated FT levels. Conclusion Patients with CKD have higher plasma levels of PMVs and EMVs and higher FT expression, related to a state of oxidative stress. These parameters could be considered as biomarkers for predicting, diagnosing, and prognostic cardiovascular events in CKD.

Dietary omega-3 fatty acids modulate the production of platelet-derived microvesicles in an in vivo inflammatory arthritis model.

The aim of this study was to investigate the effects of different ω-3 polyunsaturated fatty acid (PUFA) enriched diets, including a novel renewable plant source of ω-3 fatty acids (Buglossoides arvensis), on the development and progression of rheumatoid arthritis (RA). RA was induced in mice consuming experimental diets using the K/BxN model. The experimental diets consisted of either a western control diet (control), diets containing B. arvensis oil or fish oil. The effects of the diets on platelets, platelet microvesicles (PMVs), and inflammatory markers such as clinical index, ankle thickness and cytokine/chemokine release were measured. While ω-3 PUFA-enriched diets did not prevent the development of arthritis in the K/BxN model, a significant decrease in ankle swelling was observed compared to the control group. Platelets isolated from mice consuming either low content of B. arvensis oil or fish oil diets exhibited significantly decreased PMVs production compared to mice consuming the control diet. Our study provides insight into the contribution of ω-3 PUFA supplementation in modulating the pro-inflammatory phenotype of platelets in RA pathology. Furthermore, our study suggests that low concentrations of dietary B. arvensis oil may have similar anti-inflammatory potential seen with dietary fish oil supplementation.

ADAMTS13, von Willebrand Factor, Platelet Microparticles, Factor VIII, and Impact of Somatic Mutations in the Pathogenesis of Splanchnic Vein Thrombosis Associated with BCR-ABL-Negative Myeloproliferative Neoplasms.

Myeloproliferative neoplasms (MPNs) are often associated with splanchnic vein thrombosis (SVT). Not all the factors involved in the thrombotic tendency are currently known. This study aims to evaluate a possible association between ADAMTS13, von Willebrand factor (VWF), platelet microvesicles (MV), and factor VIII activity (FVIII:C) with thrombotic events in MPN patients. In total, 36 consecutive MPN patients with SVT were enrolled. The MPNs were diagnosed based on clinical characteristics and one or more gene mutations among JAK-2, CALR, and MPL. As controls, 50 randomly selected patients with MPN without thrombosis, 50 patients with deep vein thrombosis without MPNs, and 50 healthy blood donors were evaluated. Complete blood count, ADAMTS13, VWF, MV, and FVIII:C in plasma were measured in all the subjects. The JAK-2 mutation was found in 94% of the patients with SVT, but none were triple-negative for genetic mutations (JAK2 V617F, CALR, MPL, and exon 12). Compared to the normal subjects, in all the MPN patients (with or without SVT), the levels of ADAMTS13 were found to be significantly lower (p < 0.001) and the MV concentrations were significantly higher (p < 0.001). Among the MPN patients, the VWF and FVIII:C levels were significantly higher in the patients with SVT than those without thrombosis (p = 0.007 and p = 0.04, respectively). Splenomegaly was present in 78% of MPN patients with SVT and in 30% of those without SVT (p < 0.001). The ADAMTS13/VWF ratio was reduced in all the patients, but not in the healthy blood donors (p < 0.001). The significant increase in circulating MV, VWF, and FVIII:C in the MPN patients and in the patients with thrombosis supports the role of endothelium damage in promoting thrombotic events. In particular, a significant increase in VWF and FVIII:C levels was found in the MPN patients with SVT.

Platelet and Monocyte Microvesicles as Potential Biomarkers of COVID-19 Severity: A Cross-Sectional Analysis.

Coronavirus disease (COVID-19) induces inflammation, coagulopathy following platelet and monocyte activation, and fibrinolysis, resulting in elevated D-dimer levels. Activated platelets and monocytes produce microvesicles (MVs). We analyzed the differences in platelet and monocyte MV counts in mild, moderate, and severe COVID-19, as well as their correlation with D-dimer levels. In this cross-sectional study, blood specimens were collected from 90 COVID-19 patients and analyzed for D-dimers using SYSMEX CS-2500. Platelet MVs (PMVs; PMVCD42b+ and PMVCD41a+), monocyte MVs (MMVs; MMVCD14+), and phosphatidylserine-binding annexin V (PS, AnnV+) were analyzed using a BD FACSCalibur instrument. PMV and MMV counts were significantly increased in COVID-19 patients. AnnV+ PMVCD42b+ and AnnV+ PMVCD41a+ cell counts were higher in patients with severe COVID-19 than in those with moderate clinical symptoms. The median (range) of AnnV+ PMVCD42b+ (MV/μL) in mild, moderate, and severe COVID-19 was 1,118.3 (328.1-1,910.5), 937.4 (311.4-2,909.5), and 1,298.8 (458.2-9,703.5), respectively (P =0.009). The median (range) for AnnV+ PMVCD41a+ (MV/μL) in mild, moderate, and severe disease was 885.5 (346.3-1,682.7), 663.5 (233.8-2,081.5), and 1,146.3 (333.3-10,296.6), respectively (P =0.007). D-dimer levels (ng/mL) weak correlated with AnnV+ PMVCD41a+ (P =0.047, r=0.258). PMV PMVCD42b+ and PMVCD41a+ counts were significantly increased in patients with severe clinical symptoms, and PMVCD41a+ counts correlated with D-dimer levels. Therefore, MV counts can be used as a potential biomarker of COVID-19 severity.

Neutrophil extracellular traps mediated by platelet microvesicles promote thrombosis and brain injury in acute ischemic stroke

AimsNeutrophil extracellular traps (NETs) have been implicated in thrombotic diseases. There is no definitive explanation for how NETs form during acute ischemic strokes (AIS). The purpose of our study was to investigate the potential mechanism and role of NETs formation in the AIS process.MethodsAs well as 45 healthy subjects, 45 patients with AIS had ELISA tests performed to detect NET markers. Expression of high-mobility group box 1 (HMGB1) on platelet microvesicles (PMVs) was analyzed by flow cytometry in healthy subjects and AIS patients’ blood samples. We established middle cerebral artery occlusion (MCAO) mice model to elucidate the interaction between PMPs and NETs.ResultsA significant elevation in NET markers was found in patient plasma in AIS patients, and neutrophils generated more NETs from patients’ neutrophils. HMGB1 expression was upregulated on PMVs from AIS patients and induced NET formation. NETs enhanced Procoagulant activity (PCA) through tissue factor and via platelet activation. Targeting lactadherin in genetical and in pharmacology could regulate the formation of NETs in MCAO model.ConclusionsNETs mediated by PMVs derived HMGB1 exacerbate thrombosis and brain injury in AIS.59eUbqf-2Yb-L2dvdE9ZeTVideo

Platelet Microvesicles, Inflammation, and Coagulation Markers: A Pilot Study.

Platelet "Microvesicles" (MVs) are studied for their role in blood coagulation and inflammation. The study aimed to establish if MVs are related to age, plasma levels of inflammation, coagulation, and fibrinolysis markers in healthy individuals. We prospectively enrolled volunteers aged over 18 years. MVs, plasma levels of C-reactive protein (CRP), Interleukin 6 (IL-6), Interleukin 10 (IL-10), Interleukin 17 (IL-17), and transforming growth factor β (TGF-β), fibrinogen, plasminogen activator inhibitor-1 (PAI-1), von Willebrand factor (VWF), homocysteine, factor VII (FVII), thrombin activatable fibrinolysis inhibitor (TAFI), and Protein S were tested. A total of 246 individuals (median age 65 years ("IQR"54-72)) were evaluated. Both univariate analysis and logistic regression models showed that MVs positively correlate with age, CRP, IL-6, IL-10, IL-17, TGF-β, fibrinogen, PAI-1, VWF, FVII, and homocysteine, while inversely correlating with TAFI and Protein S. The ROC curve analysis performed to identify a cut off for MV values (700 kMP) showed a good accuracy with over-range cytokines fibrinolysis factor and coagulation markers. To the best of our knowledge, this study is the first to correlate MVs with an entire panel of cardiovascular risk factors in healthy individuals. A future possible role of MVs in screening exams is suggested.

The study of platelet microparticles and P-selectin expression in patients with the peripheral arterial diseases

BACKGROUND: High platelet reactivity leads to the progression of atherosclerosis and its complications. Activated platelets adhere to the site of endothelium damage on the vessel wall and initiate the formation of an arterial thrombus, followed by acute ischemia of the organ. Biochemical and cellular marker such as platelet microvesicles and P-selectin can be analyzed using flow cytometry, which is based on a specific antigen-antibody interaction. Patients with peripheral arterial disease are at significantly greater risk of cardiovascular and cerebrovascular complications than individuals of the same age and sex. The use of antiplatelet agents is an important part of pathogenetic therapy and prevention of cardiovascular diseases and their complications.&#x0D; AIM: This study was to evaluate the level of platelet microparticles and P-selectin expression in patients with peripheral arterial disease receiving antiplatelet therapy.&#x0D; MATERIALS AND METHODS: The study included 49 people, which included three study groups: patients with obliterating disease of the arteries of the lower extremities (n = 14) on the background of long-term use (more than 14 days) of double (75 mg clopidogrel and 100 mg Acetylsalicylic acid) antiplatelet therapy, patients with COVID-19 (n = 15), who made up the positive control group in the determination of microparticles of platelet origin, and healthy volunteers (n = 20) without signs of acute respiratory disease, without a history of cardiovascular and thromboembolic episodes, not taking antiplatelet drugs. The functional activity of platelets was assessed by two methods: using light aggregometry and analysis of P-selectin expression on platelet surface by flow cytometry. The number of platelets microparticles in blood plasma was also determined using flow cytometry.&#x0D; RESULTS: A significant decrease in platelet aggregation was found in patients with peripheral arterial disease taking antiplatelet agents, compared with controls by used light aggregometry. Similar changes were obtained when analyzing the expression of P-selectin on platelets. A higher percentage of platelets microparticles with the CD9+CD41+ phenotype was found in patients with severe inflammation compared with peripheral arterial disease patients treated with antiplatelet agents and compared with the healthy controls.&#x0D; CONCLUSIONS: Thus, our study reflects the consistency of the results of three different laboratory tests in assessing the platelets reactivity in patients with the peripheral arterial diseases taking antiplatelet drugs.

Transcription factors in megakaryocytes and platelets.

Transcription factors bind promoter or regulatory sequences of a gene to regulate its rate of transcription. However, they are also detected in anucleated platelets. The transcription factors RUNX1, GATA1, STAT3, NFκB, and PPAR have been widely reported to play key roles in the pathophysiology of platelet hyper-reactivity, thrombosis, and atherosclerosis. These non-transcriptional activities are independent of gene transcription or protein synthesis but their underlying mechanisms of action remain poorly defined. Genetic and acquired defects in these transcription factors are associated with the production of platelet microvesicles that are known to initiate and propagate coagulation and to promote thrombosis. In this review, we summarize recent developments in the study of transcription factors in platelet generation, reactivity, and production of microvesicles, with a focus on non-transcriptional activities of selected transcription factors.

Assessment of microvesicles from different cell origins in patients with psoriasis: evidence of thrombogenic, proinflammatory microenvironment in the absence of established cardiovascular disease.

Psoriasis is associated with increased cardiovascular risk. Endothelial, platelet, and erythrocyte microvesicles (MVs) are novel biomarkers of endothelial dysfunction and thromboinflammation. We explored whether MVs of different cell types are elevated in patients with psoriasis, and investigated potential associations with disease severity and macrovascular function. Endothelial, platelet and erythrocyte MVs were measured using a standardized flow cytometry protocol in psoriasis patients and controls free from established cardiovascular disease. Carotid intima-media thickness (IMT) and pulse wave velocity (PWV) were measured as markers of subclinical atherosclerosis and arterial stiffness. Psoriasis severity was assessed with PASI (Psoriasis Area Severity Index). Both platelet (p < 0.001) and erythrocyte MVs (p = 0.046), yet not endothelial MVs, were significantly increased in patients with psoriasis (n = 41) compared with controls (n = 41). Patients with higher PASI (≥10) presented significantly higher levels of ErMVs compared to those with lower PASI (<10) (p = 0.047). Carotid IMT and PWV were comparable between psoriasis patients and controls and did not significantly correlate with MVs. In the multivariate analysis, psoriasis was identified as an independent predictor of both platelet (p < 0.001) and erythrocyte MVs (p = 0.043), while hypertension was independently associated with endothelial MVs (p < 0.001). Increased formation of platelet and erythrocyte MVs may be evident in psoriasis patients and is indicative of prothrombotic, proinflammatory microenvironment, even in the absence of subclinical macrovascular dysfunction and before the clinical onset of overt cardiovascular complications. Potential mechanistic links and prognostic implications of increased MVs in psoriasis warrant further investigation.

MMP-2 inhibition prevents platelet activation in ischemia/reoxygenation conditions.

Platelets play a fundamental role in myocardial infarction and the pathogenesis of ischemia/reoxygenation (I/R) injuries. They contain matrix metalloproteinases (MMPs) that are involved in arterial thrombosis. The MMP inhibitor doxycycline has been shown to exert protective effects in I/R injuries involving various organs and mechanisms. To explore the influence of doxycycline on platelet activation and MMP-2 activity during I/R. Platelets isolated from the blood of healthy human volunteers were subjected to chemical I/R conditions. The study included aerobic controls (AERO), I/R platelets and I/R platelets pretreated with doxycycline (I/R+D). The concentration of doxycycline used was standardized to 10 μM. The analysis of platelet activation markers and platelet microvesicles (PMVs) was performed using flow cytometry. Adenosine diphosphate (ADP)-induced and collagen-induced aggregation, as well as MMP-2 activity and its concentration in platelets were evaluated. Doxycycline decreased the expression of activated glycoprotein IIb/IIIa on platelets (p = 0.043). Additionally, an increased expression of CD63 was observed in buffers containing PMVs after doxycycline administration (p = 0.043). The ADP-dependent aggregation of I/R platelets was significantly lower in comparison to AERO (p = 0.022). Furthermore, there was a stronger tendency of enhanced ADP-dependent aggregation in I/R platelets pretreated with doxycycline compared to platelets that underwent I/R without doxycycline. Higher MMP-2 activity was observed in I/R+D platelets compared to I/R platelets (p < 0.01). The inhibition of platelet MMP-2 by doxycycline attenuated platelet activation and protected platelets by preserving their aggregation ability.

The role of platelet microvesicles in the pathogenesis of preeclampsia

Among the diverse picture of preeclampsia, the hematological component, thrombocytopenia, attracts attention. Platelets are able to form microvesicles by budding the plasma membrane from the cell surface during apoptosis, stimulation, and also in a small amount in normal conditions. The membrane of these particles has a negative charge and contains phospholipids and an integral glycoprotein on the outer monolayer, due to which platelet microvesicles are involved in the process of blood coagulation and angiogenesis. Microvesicles are of platelet origin, they were first discovered in the middle of the last century in England when describing the phenomenon of plasma and serum coagulation in the absence of platelets in them. The number of platelet microvesicles dynamically changes during the formation of preeclampsia in pregnant women and in women with risk factors for the development of preeclampsia, which include obesity, arterial hypertension, diabetes mellitus, antiphospholipid syndrome. Exposure to these risk factors for preeclampsia before pregnancy leads to a change in the concentration of cells that produce microvesicles, which in turn can create conditions favorable for the development of preeclampsia during pregnancy. A special risk group are women with a history of preeclampsia. Taking into account the direct role of microvesicles in the processes of angiogenesis and blood coagulation, the study of these particles will allow a more detailed study of the pathophysiological aspects of the preeclampsia development, which will expand the possibilities for early prediction of this pathology and improvement of perinatal outcomes.

Rosmarinic Acid Inhibits Platelet Aggregation and Neointimal Hyperplasia In Vivo and Vascular Smooth Muscle Cell Dedifferentiation, Proliferation, and Migration In Vitro via Activation of the Keap1-Nrf2-ARE Antioxidant System.

The activation of platelets and proliferation of vascular smooth muscle cells (VSMCs) in the vascular intima play an essential role in the pathological mechanism of vascular restenosis (RS). Rosmarinic acid (RA) is a natural phenolic acid compound. However, its mechanism of action on platelets and VSMCs is still unclear. This study investigated the effects of RA on platelet function, VSMCs phenotypic conversion, proliferation, and migration in vascular remodeling with a specific focus on the Keap1-Nrf2-ARE signaling pathway. RA inhibited platelet aggregation and Ca2+ release and significantly reduced the release of platelet microvesicles. In addition, RA inhibited the phenotypic transition of VSMCs in vitro and in vivo. In vitro experiments showed that RA could effectively inhibit the proliferation and migration of VSMCs induced by the platelet-derived growth factor (PDGF)-BB. PDGF-BB triggered ROS generation and a decrease in mitochondrial membrane potential, which were inhibited by RA. Mechanistically, after artery injury or treatment with PDGF-BB, VSMCs presented with inhibition of the Nrf2/antioxidant response element (ARE) signaling pathway. RA treatment reversed this profile by activating the Nrf2/ARE signaling pathway; stabilizing Keap1 protein; upregulating HO-1, NQO1, GCLM, and GST protein levels; promoting typical Nrf2 nuclear translocation; and preventing VSMCs from oxidative stress damage. On the other hand, RA also inhibited the NF-κB pathway to reduce inflammation. In summary, these results indicate that RA inhibits platelet function and attenuates the proliferation, migration, and phenotypic transition of VSMCs induced by PDGF-BB in vitro and vascular remodeling in vivo. Therefore, RA treatment may be a potential therapy for preventing or treating RS.

Hyperadhesive von Willebrand Factor Promotes Extracellular Vesicle-Induced Angiogenesis: Implication for LVAD-Induced Bleeding

Bleeding associated with left ventricular assist device (LVAD) implantation has been attributed to the loss of large von Willebrand factor (VWF) multimers to excessive cleavage by ADAMTS-13, but this mechanism is not fully supported by the current evidence. We analyzed VWF reactivity in longitudinal samples from LVAD patients and studied normal VWF and platelets exposed to high shear stress to show that VWF became hyperadhesive in LVAD patients to induce platelet microvesiculation. Platelet microvesicles activated endothelial cells, induced vascular permeability, and promoted angiogenesis in a VWF-dependent manner. Our findings suggest that LVAD-driven high shear stress primarily activates VWF, rather than inducing cleavage in the majority of patients.

Platelet microRNAs inhibit primary tumor growth via broad modulation of tumor cell mRNA expression in ectopic pancreatic cancer in mice.

We investigated the contributions of platelet microRNAs (miRNAs) to the rate of growth and regulation of gene expression in primary ectopic tumors using mouse models. We previously identified an inhibitory role for platelets in solid tumor growth, mediated by tumor infiltration of platelet microvesicles (microparticles) which are enriched in platelet-derived miRNAs. To investigate the specific roles of platelet miRNAs in tumor growth models, we implanted pancreatic ductal adenocarcinoma cells as a bolus into mice with megakaryocyte-/platelet-specific depletion of mature miRNAs. We observed an ~50% increase in the rate of growth of ectopic primary tumors in these mice compared to controls including at early stages, associated with reduced apoptosis in the tumors, in particular in tumor cells associated with platelet microvesicles—which were depleted of platelet-enriched miRNAs—demonstrating a specific role for platelet miRNAs in modulation of primary tumor growth. Differential expression RNA sequencing of tumor cells isolated from advanced primary tumors revealed a broad cohort of mRNAs modulated in the tumor cells as a function of host platelet miRNAs. Altered genes comprised 548 up-regulated transcripts and 43 down-regulated transcripts, mostly mRNAs altogether spanning a variety of growth signaling pathways–notably pathways related to epithelial-mesenchymal transition—in tumor cells from platelet miRNA-deleted mice compared with those from control mice. Tumors in platelet miRNA-depleted mice showed more sarcomatoid growth and more advanced tumor grade, indicating roles for host platelet miRNAs in tumor plasticity. We further validated increased protein expression of selected genes associated with increased cognate mRNAs in the tumors due to platelet miRNA depletion in the host animals, providing proof of principle of widespread effects of platelet miRNAs on tumor cell functional gene expression in primary tumors in vivo. Together, these data demonstrate that platelet-derived miRNAs modulate solid tumor growth in vivo by broad-spectrum restructuring of the tumor cell transcriptome.

Patients with autoimmune chronic inflammatory diseases present increased biomarkers of thromboinflammation and endothelial dysfunction in the absence of flares and cardiovascular comorbidities.

Cardiovascular risk is increased in patients with autoimmune rheumatic diseases. Endothelial, erythrocyte and platelet microvesicles (MVs) are elevated in patients with cardiovascular diseases and represent novel markers of endothelial dysfunction and thromboinflammation. We tested whether their levels are increased in patients with autoimmune rheumatic diseases (ARDs) in the absence of disease flare and cardiovascular comorbidities. Well-controlled patients with rheumatoid arthritis or systemic lupus erythematosus were studied, provided they were free from cardiovascular comorbidities and established cardiovascular disease. We additionally studied (a) a control group consisting of healthy volunteers and (b) a reference group including patients with stable coronary artery disease (CAD). MVs were measured using a standardized flow cytometry protocol. In a population of 74 participants, patients with ARDs (n = 17) presented increased levels of both endothelial (283.3 ± 195.0/μL vs 168.5 ± 54.8/μL, p = 0.029) and platelet MVs (374.0 ± 275.3/μL vs 225.7 ± 101.1/μL, p = 0.046) compared to controls (n = 34), whereas erythrocyte MVs did not significantly differ. In addition, patients with ARDs showed similar levels of endothelial MVs compared to CAD patients (n = 23) (283.3 ± 195.0/μL vs 297.0 ± 211.8/μL, p = 0.846). Platelet MVs were significantly associated with disease duration, and erythrocyte MVs with patients' perceived disease activity. In conclusion, increased levels of endothelial and platelet MVs may be evident in patients with ARDs, even in the absence of disease flares and before the establishment of cardiovascular complications. Levels of endothelial MVs resemble those of patients with profound atherothrombotic profile. The prognostic potential of MVs in terms of cardiovascular disease prevention warrants further investigation in patients with ARDs.

Reconstituted cryopreserved platelets synthesize proteins during short-term storage and packaging a defined subset into microvesicles.

Cryopreservation of platelets (PLTs) could allow extension of their shelf-life to years, compared to days for liquid stored platelets. Due to their greater hemostatic effect, reconstituted cryopreserved platelets (cryo-PLTs) would be able to support bleeding emergencies. Since protein synthesis has been linked to PLT functions, such as clot formation and immune responses, the translational capacity of reconstituted cryo-PLTs was assessed upon thawing and short-term storage. Platelets were frozen at -80°C with 5-6% DMSO. Upon thawing, they were reconstituted in plasma and then aliquoted (12 ml) into mini-bags and assessed over 24 h of storage at RT. One series served as control; the second and third series were spiked with either 300 μM puromycin (Pm) or 227 nM biotin-labeled Pm. Samples were tested for in vitro quality and PLT microvesicle enumeration by flow cytometry. Protein synthesis in cryo-PLTs was assessed using a modified method based on puromycin-associated nascent chain proteomics. In vitro parameters of reconstituted and subsequently stored platelets were consistent with previously published results. Mass-spectrometry analyses identified that 22 proteins were synthesized in PLTs and 13 of those were observed in platelet microvesicles (PMVs). Cryo-PLTs can synthesize proteins upon reconstitution and storage. Discovery of a subset of these proteins in the PMV suggests a role in vesicle encapsulation, possibly in a selective manner. This observation provides novel insights into the capacity for protein synthesis in cryo-PLTs and the potential regulation of protein packaging into PMV.

A study of endothelial and platelet microvesicles across different hypertension phenotypes.

Rather than being mere biomarkers reflecting generalized vascular injury, endothelial- (EMVs) and platelet-derived (PMVs) microvesicles have emerged as potent regulators of intercellular communication with significant biologic effects in vascular homeostasis and several pathophysiological responses including inflammation and thrombosis. So far, studies in hypertension are scarce, whereas no studies exist in masked hypertension (MH). We measured EMVs and PMVs in untreated, newly diagnosed hypertensives (HTs) and MHs compared to normotensive controls (NTs), and associated them with various cardiovascular risk factors. Sustained hypertension (SHT) and MH were defined according to standard blood pressure (BP) criteria. All HTs were free of cardiovascular disease and medications. Microvesicles' quantitation and detection were performed by flow cytometry by using cell-specific antibodies and corresponding isotypes (anti-CD105 and anti-CD144 for EMVs, anti-CD42a for PMVs, and Annexin V-fluorescein isothiocyanate for all microvesicles). In this study, we included 59 HTs (44 SHTs and 15 MHs) and 27 NTs. HTs had significantly elevated EMVs (p = 0.004), but not PMVs compared to NTs. MHs had significantly elevated EMVs compared to NTs (p = 0.012) but not compared to SHTs. Furthermore, EMVs significantly correlated with ambulatory (r = 0.214-0.284), central BP (r = 0.247-0.262), and total vascular resistance (r = 0.327-0.361). EMVs are increased not only in SHTs but also in MHs, a hypertension phenotype with a cardiovascular risk close to SHT. EMVs have emerged as active contributors to thromboinflammation and vascular damage and may explain, in part, the adverse cardiovascular profile of SHTs and MHs.

Releasates of riboflavin/UV-treated platelets: Microvesicles suppress cytokine-mediated endothelial cell migration/proliferation.

Accelerated development of the platelet (PLT) storage lesion upon pathogen inactivation (PI) is associated with the release of proteins from granules and platelet microvesicles (PMVs). Whether PI treatments alter the interaction between PLT factors and the vessel endothelium is of interest in understanding the risk profile of these technologies. In a pool-and-split study, one platelet concentrate (PC) was treated with riboflavin/UV (RF/UV) light, while the other one was kept as an untreated control. Releasates and PMV-depleted releasates were prepared by differential centrifugation steps on days 0, 1, 5, and 7 of storage. Cytokine/chemokine release following PI treatment was analyzed by an antibody array, and results were verified by the enzyme-linked immunosorbent assay. PMVs were enumerated by CD41 labeling and flow cytometry. Wound scratch assays were performed using cultured Ea.hy926 cells exposed to the differently prepared releasates. Effects of releasates on the phosphorylation levels of kinases ERK and p38 expressed by endothelial cells were analyzed by immunoblot. Cytokine/chemokine assays identified a 2-fold increase in epidermal growth factor released from PCs treated with RF/UV light compared with control. PMV count increased ~100-fold following PI treatment. Unmodified releasates and PMV-depleted releasates displayed different contributions to the kinetics of endothelial cell wound closure. This observation was associated with an increased ERK versus unaltered p38 activation in the endothelial cells. This study identified an inhibitory impact of PMVs on endothelial cell migration/proliferation upon stimulation by released cytokines and PMVs from PLTs treated with RF/UV light for endothelial cell wound closure.

Analysis of Circulating Microvesicles Levels and Effects of Associated Factors in Elderly Patients With Obstructive Sleep Apnea.

Background: The incidence of obstructive sleep apnea (OSA) in the elderly is high, and the disorder is associated with a variety of chronic diseases. Microvesicles (MVs) are extracellular vesicles secreted by various cells during stimulation or apoptosis that play an important role in the pathogenesis of OSA. However, concentrations of circulating MVs in elderly patients with OSA remain unclear.Methods: Patients aged >60 years old were recruited and underwent polysomnography. Circulating plasma MV concentrations, including annexin V+MVs, endothelial MVs (EMVs), platelet MVs (PMVs), and leukocyte MVs (LMVs) levels, were measured using a flow cytometer with different labeling methods. Potential factors affecting the concentration of circulating MVs in elderly patients with OSA were determined via Spearman's correlation and multiple linear regression analysis.Results: Levels of circulating MVs, including both single- (annexin V+MVs, CD144+EMVs, CD41a+PMVs, and CD45+LMVs) and dual-labeled MVs (annexin V+CD144+EMVs), were elevated in elderly patients with OSA. Circulating MVs were positively correlated with OSA severity (AHI, ODI, and SPO2min). To some extent, obesity affected the MV concentrations in elderly patients with OSA. In addition, age and comorbidities may be associated with MV levels, but the correlations between the MV levels and age or comorbidities were not significant.Conclusion: Concentrations of circulating MVs in elderly patients with OSA are associated with the labeling method used, OSA severity, and obesity. The effects of age and comorbidities on circulating MV levels require further verification using a larger sample size.

Abstract 16824: Circulating Microvesicles in Heart Failure Patients Prior to, and Following LVAD Implantation

Introduction: Elevated levels of circulating endothelial and platelet (EMV and PMV) microvesicles are associated with endothelial dysfunction and thrombosis/inflammation, respectively. EMVs and PMVs are elevated in patients with heart failure with reduced ejection fraction (HFrEF) and are associated with clinical outcomes. We sought to characterize longitudinal changes in EMV and PMV following LVAD implantation in these patients. Methods: Blood samples were obtained from patients with advanced HFrEF (59±9years, N=9 males) during an invasive hemodynamic assessment with Swan-Ganz catheterization 2.7±4.1 and 4.3±1.3 months prior to, and following CF-LVAD implantation, respectively. Circulating concentrations of total MV, EMVs (CD31+) and PMVs (CD42b+) were determined by flow cytometry. Results: Demographics and hemodynamics pre- and post-LVAD implantation are displayed in the table . Prior to LVAD, four patients were on inotropes. Six patients received a Heartware VAD, and four patients received a Heartmate 3 VAD. As demonstrated in the figure , there was a significant reduction in total MV concentration, as well as EMVs and PMVs following LVAD implantation. Conclusion: Circulating concentrations EMVs and PMVs decline significantly in HFrEF patients following LVAD implantation. These findings are indicative of improvements in both endothelial function and thrombotic/inflammatory state associated with the heart-failure syndrome.