Comparison of assays measuring extracellular vesicle tissue factor in plasma samples: communication from the ISTH SSC Subcommittee on Vascular Biology.

BACKGROUND: Scientific and clinical interest in extracellular vesicles (EVs) is growing. EVs that expose tissue factor (TF) bind factor VII/VIIa and can trigger coagulation. Highly procoagulant TF-exposing EVs are detectable in the circulation in various diseases, such as sepsis, COVID-19, or cancer. Many in-house and commercially available assays have been developed to measure EV-TF activity and antigen, but only a few studies have compared some of these assays. OBJECTIVES: The International Society on Thrombosis and Haemostasis Scientific and Standardization Committee Subcommittee on Vascular Biology initiated a multicenter study to compare the sensitivity, specificity, and reproducibility of these assays. METHODS: Platelet-depleted plasma samples were prepared from blood of healthy donors. The plasma samples were spiked either with EVs from human milk or EVs from TF-positive and TF-negative cell lines. Plasma was also prepared from whole human blood with or without lipopolysaccharide stimulation. Twenty-one laboratories measured EV-TF activity and antigen in the prepared samples using their own assays representing 18 functional and 9 antigenic assays. RESULTS: There was a large variability in the absolute values for the different EV-TF activity and antigen assays. Activity assays had higher specificity and sensitivity compared with antigen assays. In addition, there was a large intra-assay and interassay variability. Functional assays that used a blocking anti-TF antibody or immunocapture were the most specific and sensitive. Activity assays that used immunocapture had a lower coefficient of variation compared with assays that isolated EVs by high-speed centrifugation. CONCLUSION: Based on this multicenter study, we recommend measuring EV-TF using a functional assay in the presence of an anti-TF antibody.

Platelet-released extracellular vesicles: the effects of thrombin activation.

Platelets exert fundamental roles in thrombosis, inflammation, and angiogenesis, contributing to different pathologies from cardiovascular diseases to cancer. We previously reported that platelets release extracellular vesicles (pEVs) which contribute to thrombus formation. However, pEV composition remains poorly defined. Indeed, pEV quality and type, rather than quantity, may be relevant in intravascular cross-talk with either circulating or vascular cells. We aimed to define the phenotypic characteristics of pEVs released spontaneously and those induced by thrombin activation to better understand their role in disease dissemination. pEVs obtained from washed platelets from healthy donor blood were characterized by flow cytometry. pEVs from thrombin-activated platelets (T-pEVs) showed higher levels of P-selectin and active form of glycoprotein IIb/IIIa than baseline non-activated platelets (B-pEVs). Following mass spectrometry-based differential proteomic analysis, significant changes in the abundance of proteins secreted in T-pEVs compared to B-pEVs were found. These differential proteins were involved in coagulation, adhesion, cytoskeleton, signal transduction, metabolism, and vesicle-mediated transport. Interestingly, release of proteins relevant for cell adhesion, intrinsic pathway coagulation, and platelet activation signalling was significantly modified by thrombin stimulation. A novel pEV-associated protein (protocadherin-α4) was found to be significantly reduced in T-pEVs showing a shift towards increased expression in the membranes of activated platelets. In summary, platelet activation induced by thrombin triggers the shedding of pEVs with a complex proteomic pattern rich in procoagulant and proadhesive proteins. Crosstalk with other vascular and blood cells in a paracrine regulatory mode could extend the prothrombotic signalling as well as promote proteostasic changes in other cellular types.

High miR-133a levels in the circulation anticipates presentation of clinical events in familial hypercholesterolaemia patients.

AIMS: Presentation of acute events in patients with atherosclerosis remains unpredictable even after controlling for classical risk factors. MicroRNAs (miRNAs) measured in liquid biopsies could be good candidate biomarkers to improve risk prediction. Here, we hypothesized that miRNAs could predict atherosclerotic plaque progression and clinical event presentation in familial hypercholesterolaemia (FH) patients. METHODS AND RESULTS: Circulating miRNAs (plasma, exosomes, and microvesicles) were investigated by TaqMan Array and RT-qPCR assays. Patients with genetic diagnosis of FH and healthy relatives from the SAFEHEART cohort were included. A differential signature of 10 miRNA was obtained by comparing two extreme phenotypes consisting of FH patients suffering a cardiovascular event (CVE) within a 8-year follow-up period (FH-CVE, N = 42) and non-FH hypercholesterolaemic relatives from the same cohort, matched for age and treatment, without CVE during the same period (nFH-nCVE, N = 30). The validation studies included two independent groups of patients with FH background (discovery group, N = 89, validation group N = 196), developing a future CVE (FH-CVE) or not (FH-nCVE) within the same time period of follow-up. Of the 10 miRNAs initially selected, miR-133a was significantly higher in FH-CVE than in FH-nCVE patients. Receiver operating characteristic analysis confirmed miR-133a as the best microRNA for predicting CVE in FH patients (0.76 ± 0.054; P < 0.001). Furthermore, Kaplan-Meier and COX analysis showed that high plasma miR-133a levels associated to the higher risk of presenting a CVE within the next 8 years (hazard ratio 3.89, 95% confidence interval 1.88-8.07; P < 0.001). In silico analysis of curate biological interactions related miR-133a with target genes involved in regulation of the cell-membrane lipid-receptor LRP6 and inflammatory cytokines (CXCL8, IL6, and TNF). These predictions were experimentally proven in human macrophages and endothelial cells transfected with agomiR-133a. CONCLUSION: Elevated levels of miR-133a in the circulation anticipate those FH patients that are going to present a clinical CVE within the next 2 years (average). Mechanistically, miR-133a is directly related with lipid- and inflammatory signalling in key cells for atherosclerosis progression.

Hyperglycemia Induces Myocardial Dysfunction via Epigenetic Regulation of JunD.

RATIONALE: Hyperglycemia -induced reactive oxygen species are key mediators of cardiac dysfunction. JunD (Jund proto-oncogene subunit), a member of the AP-1 (activator protein-1) family of transcription factors, is emerging as a major gatekeeper against oxidative stress. However, its contribution to redox state and inflammation in the diabetic heart remains to be elucidated. OBJECTIVE: The present study investigates the role of JunD in hyperglycemia-induced and reactive oxygen species-driven myocardial dysfunction. METHODS AND RESULTS: JunD mRNA and protein expression were reduced in the myocardium of mice with streptozotocin-induced diabetes mellitus as compared to controls. JunD downregulation was associated with oxidative stress and left ventricular dysfunction assessed by electron spin resonance spectroscopy as well as conventional and 2-dimensional speckle-tracking echocardiography. Furthermore, myocardial expression of free radical scavenger superoxide dismutase 1 and aldehyde dehydrogenase 2 was reduced, whereas the NOX2 (NADPH [nicotinamide adenine dinucleotide phosphatase] oxidase subunit 2) and NOX4 (NADPH [nicotinamide adenine dinucleotide phosphatase] oxidase subunit 4) were upregulated. The redox changes were associated with increased NF-κB (nuclear factor kappa B) binding activity and expression of inflammatory mediators. Interestingly, mice with cardiac-specific overexpression of JunD via the α MHC (α- myosin heavy chain) promoter (α MHC JunDtg) were protected against hyperglycemia-induced cardiac dysfunction. We also showed that JunD was epigenetically regulated by promoter hypermethylation, post-translational modification of histone marks, and translational repression by miRNA (microRNA)-673/menin. Reduced JunD mRNA and protein expression were confirmed in left ventricular specimens obtained from patients with type 2 diabetes mellitus as compared to nondiabetic subjects. CONCLUSIONS: Here, we show that a complex epigenetic machinery involving DNA methylation, histone modifications, and microRNAs mediates hyperglycemia-induced JunD downregulation and myocardial dysfunction in experimental and human diabetes mellitus. Our results pave the way for tissue-specific therapeutic modulation of JunD to prevent diabetic cardiomyopathy.

Liquid Biopsies: Microvesicles in Cardiovascular Disease.

Significance: Circulating microvesicles (cMV) are small (0.1-1 µm) phospholipid-rich blebs released by almost all cell types, and their release increases with cell activation and injury, thus reflecting the state of the cell from which they are originated. Microvesicles (MV) are found in the bloodstream, and they affect the phenotype of recipient cells, after local or systemic circulation, by intercellular transfer of their molecular content. Recent Advances: Several studies suggest the use of cell-specific MV subpopulations as predictive biomarkers for cardiovascular diseases (CVDs) at different stages and degrees of severity. In this review, we describe the state of the art of cMV as noninvasive surrogate biomarkers of vascular injury and dysfunction correlated with poor clinical outcomes in CVD. Critical Issues: Despite the growing body of evidence supporting the importance of cMV as hallmarks of CVD and their utility as biomarkers of CVD, the specific roles of each phenotype of cMV in CVD burden and prognosis still remain to be elucidated and validated in large cohorts. In addition, the development of standardized and reproducible techniques is required to be used as biomarkers for disease progression in the clinical setting. Future Directions: A multipanel approach with specific cMV phenotypes, added to current biomarkers and scores, will undoubtedly provide unique prognostic information to stratify patients for appropriate therapy on the basis of their risk of atherothrombotic disease and will open a new research area as therapeutic targets for CVD. MV will add to the implementation of precision medicine by helping the cellular and molecular characterization of CVD patients.

Liquid Biopsy of Extracellular Microvesicles Predicts Future Major Ischemic Events in Genetically Characterized Familial Hypercholesterolemia Patients.

Objective- Circulating microvesicles (cMVs) exert regulatory roles in atherothrombosis. Patients with familial hypercholesterolemia (FH) that are at high risk for premature cardiovascular events (CVEs) have previously shown high levels of cMVs related to disease severity. However, much remains unknown about their value as markers of CVE. We sought to investigate the prognostic cMV signature for future major CVE presentation in patients with FH. Approach and Results- Liquid biopsies from genetically characterized patients with FH from the SAFEHEART (Spanish Familial Hypercholesterolemia Cohort Study)-cohort without clinical manifestation of disease at entry that were going to suffer a CVE within a mean period of 3.3±2.6 years postsampling (CVE, N=92) and from age/cardiovascular risk factor/treatment-matched patients with FH that did not suffer an event within the same time-period (non-CVE, N=48) were investigated. cMVs were phenotyped by flow cytometry to identify activated parental cells. Patients with CVE had higher number of overall procoagulant annexin V+-cMVs than non-CVE ( P<0.05). Pan-leukocyte-derived and neutrophil-derived cMVs, as well as activated platelet-derived cMVs, were significantly higher in patients with CVE. Baseline number of cMVs derived from lymphocytes, neutrophils, and activated platelets were positively associated with mortality at follow-up ( P<0.05). Patient-risk calculated by classical cardiovascular risk-factor scores did not correlate with cMVs. Inclusion of the cMV signature into the SAFEHEART risk model for patients with FH for the prediction of ischemic events increased the area under the curve from 0.603±0.050 to 0.768±0.042 ( P<0.005). Conclusions- Patients with FH who are going to suffer a CVE within a mean period of 3.3 years, despite being treated according to guidelines, have ongoing innate immune cell and platelet activation. The proposed cMV signature is a prognostic marker for accelerated atherosclerosis and clinical event presentation in patients with FH.

Macrophages of genetically characterized familial hypercholesterolaemia patients show up-regulation of LDL-receptor-related proteins.

Familial hypercholesterolaemia (FH) is a major risk for premature coronary heart disease due to severe long-life exposure to high LDL levels. Accumulation of LDL in the vascular wall triggers atherosclerosis with activation of the innate immunity system. Here, we have investigated (i) gene expression of LDLR and LRPs in peripheral blood cells (PBLs) and in differentiated macrophages of young FH-patients; and (ii) whether macrophage from FH patients have a differential response when exposed to high levels of atherogenic LDL. PBLs in young heterozygous genetically characterized FH patients have higher expression of LRP5 and LRP6 than age-matched healthy controls or patients with secondary hypercholesterolaemia. LRP1 levels were similar among groups. In monocyte-derived macrophages (MACs), LRP5 and LRP1 transcript levels did not differ between FHs and controls in resting conditions, but when exposed to agLDL, FH-MAC showed a highly significant up-regulation of LRP5, while LRP1 was unaffected. PBL and MAC cells from FH patients had significantly lower LDLR expression than control cells, independently of the lipid-lowering therapy. Furthermore, exposure of FH-MAC to agLDL resulted in a reduced expression of CD163, scavenger receptor with anti-inflammatory and atheroprotective properties. In summary, our results show for first time that LRPs, active lipid-internalizing receptors, are up-regulated in innate immunity cells of young FH patients that have functional LDLR mutations. Additionally, their reduced CD163 expression indicates less atheroprotection. Both mechanisms may play a synergic effect on the onset of premature atherosclerosis in FH patients.

CD142+/CD61+, CD146+ and CD45+ microparticles predict cardiovascular events in high risk patients following a Mediterranean diet supplemented with nuts.

Circulating microparticles (cMPs) are small phospholipid-rich microvesicles shed by activated cells that play a pivotal role in cell signalling related to the pathogenesis of atherothrombosis. We aimed to investigate the prognostic value of cMPs released from different vascular cells for cardiovascular event (CVE) presentation in asymptomatic patients at high cardiovascular risk factors under nutritional and pharmacologic treatment. This is a nested case-control study of 50 patients from the five-year follow-up prospective PREDIMED trial enrolled in the nuts arm of the Mediterranean diet (MedDiet-nuts). We randomly selected 25 patients who had suffered a CVE during follow-up and pair-matched them for sex, age, and classical CV risk factors to 25 patients who remained asymptomatic (no-CVE). Total Annexin V-(AV)+ cMPs and cMPs from cells of the vascular compartment were quantified by flow cytometry at baseline and after one year follow-up. MedDiet-nuts and pharmacological treatment neither modified levels nor source of MP shedding in CVE patients. However, no-CVE patients showed 40-86 % decreased total AV+, PAC-1+/AV+, CD61+/AV+, CD142+/CD61+/AV+, CD62P+/AV+, CD146+/AV+, CD63+/AV+ and CD11a+/AV+ cMPs at one year follow-up (p≤0.046, all). CD142+/CD61+/AV+, CD146+/AV+ and CD45+/AV+ cMPs were decreased in no-CVE patients compared to CVE patients. A ROC-curve clustered model for CD142+/CD61+/AV+, CD45+/AV+ and CD146+/AV+ cMPs predicted a future CVE [p<0.0001, AUC=0.805 (0.672 to 0.938)]. In patients at high CV risk profile treated with a controlled MedDiet supplemented with nuts and receiving up-to-date CV drug treatment, reduced cMPs derived from activated platelets, leukocytes and endothelial cells are predictive of protection against CVE within the next four years.

High levels of TSP1+/CD142+ platelet-derived microparticles characterise young patients with high cardiovascular risk and subclinical atherosclerosis.

Circulating microparticles (cMPs) play important roles in cellular crosstalk and are messengers of cell activation. We have previously reported that platelet-released microparticles (pMPs) stimulate thrombosis and that lipid-lowering treatment as per guidelines in patients with familial hypercholesterolaemia (FH) is not sufficiently effective in reducing pro-inflammatory cell activation and, consequently, CD45+/CD3+-lymphocyte-derived cMP shedding. FH patients, due to life-long vascular exposure to high LDL-cholesterol levels, are at high cardiovascular risk (HCVR) and develop premature coronary artery disease. Our objectives were to investigate a) whether patients with HCVR have cMPs with a prothrombotic phenotype, and b) whether patients with magnetic resonance imaging (MRI) evidence of lipid-rich atherosclerotic lesions have a specific cMP profile regarding prothrombotic protein cargos. cMPs were isolated from HCVR-patients and from age/gender/treatment-matched control patients. cMP phenotype was characterised by triple-labelling flow cytometry. HCVR--patients have higher numbers of pMPs derived from activated platelets as well as of tissue factor-rich microparticles (TF+-cMPs) than controls (P< 0.0001). TF+-cMPs showed procoagulant activity, which associate with atherosclerotic plaque burden, indicating that TF in the cMPs is functional. In HCVR-patients, overall TF+-cMPs (monocyte-derived [CD142+/CD14+] and platelet-derived [CD142+/TSP1+]) and activated pMPs directly correlate with MRI-detected lipid-rich atherosclerotic plaques while inversely correlate with MRI-detected calcified plaques. C-statistics analysis showed that prothrombotic cMPs add significant prognostic value to a risk factor model for the prediction of lipid-rich plaques. In conclusion, the activation status of blood cells in HCVR-patients differed markedly from controls as shown by higher circulating levels of prothrombotic and TF+-cMPs. Prothrombotic cMP numbers identify subclinical atherosclerotic plaque burden.

Circulating CD45+/CD3+ lymphocyte-derived microparticles map lipid-rich atherosclerotic plaques in familial hypercholesterolaemia patients.

Circulating microparticles (cMPs) seem to play important roles in vascular function. Beyond markers of activated cells, cMPs may have potential paracrine functions and influence atherosclerosis. Here, our objective was to characterise a) the abundance and phenotype of cMPs in stable statin-treated heterozygous familial hypercholesterolaemia (FH) patients exposed to life-long hypercholesterolaemia and b) the principal phenotype associated to lipid-rich atherosclerotic plaques in hFH-patients with significant atherosclerotic plaque burden. An age/gender/treatment-matched group of adult-onset non-FH hypercholesterolaemic patients (n=37/group) was comparatively analysed. cMPs were characterised by flow cytometry using annexin-V and cell surface-specific antibodies. Our study shows that LLT-FH patients had higher overall cMP-numbers (p<0.005) than LLT-non-FH patients. Endothelial cell-shed cMPs were also significantly higherin FH (p<0.0005). Within the leukocyte-derived cMP-subpopulations, FH-patients had significantly higher lymphocyte- and monocyte-derived cMP-numbers as well as cMPs carrying leukocyte-activation markers. Normalisation of cMPs by LDL levels did not affect cMP number or phenotype, indicating that the proinflammatory effect was derived from chronic vascular damage. Levels of AV+-total, CD45+-pan-leukocyte and CD45+/CD3+-lymphocyte-derived cMPs were significantly higher in FH-patients with subclinical lipid-rich atherosclerotic plaques than fibrous plaques. Levels of CD45+/CD3+-lymphocyte-MPs above 20,000/ml could differentiate between FH-patients with lipidic or non-lipidic plaques (area under the ROC curve of 0.803, 95%CI: 0.641-0.965, p=0.008). In summary, in this snapshot cross-sectional study cMP concentration and phenotype in FH differed markedly from non-FH hypercholesterolaemia. Patients with life-long high LDL exposure have higher endothelial activation and higher proinflammatory profile, even under current state-of-the-art LLT. cMPs carrying lymphocyte-epitopes appear as markers of lipid-rich atherosclerotic plaques in FH.