Flow cytometric detection of endothelial microparticles (EMP): Effects of centrifugation and storage alter with the phenotype studied

Endothelial Microparticles as Potential Biomarkers in the Assessment of Endothelial Dysfunction in Hypercholesterolemia

Background and Objectives: Endothelial microparticles (EMP) particularly CD31+/42−/AV+, CD144+/AV+ and CD62e+/AV+ have been reported as having increased in cardiovascular-related diseases, making them potential biomarkers for endothelial dysfunction. This study aimed to compare these EMPs in patients with hypercholesterolemia and healthy controls and to correlate their levels with endothelium-dependent vasodilation (EDV) assessed via pulse wave analysis (PWA); an established method of assessing endothelial function. Materials and Methods: EMPs from 88 subjects (44 hypercholesterolemia patients and 44 controls) were quantified from whole blood using flow cytometry analysis. Endothelial function was determined using PWA combined with pharmacological challenge. Results: CD31+/42−/AV+ (3.45 ± 4.74 count/µL vs. 1.33 ± 4.40 count/µL; p = 0.03), CD144+/AV+ (7.37 ± 12.66 count/µL vs. 1.42 ± 1.71 count/µL; p = 0.003) and CD62e+/AV+ (57.16 ± 56.22 count/µL vs. 20.78 ± 11.04 count/µL; p < 0.001) were significantly elevated in the hypercholesterolemic group compared with the controls, respectively. There was a significant inverse moderate correlation between all circulating EMPs and EDV: CD31+/42−/AV+ (r = −0.36, p = 0.001), CD144+/AV+ (r = −0.37, p = 0.001) and CD62e+/AV+ (r = −0.35, p = 0.002). Conclusions: All EMPs were raised in the patients with hypercholesterolemia, and these values correlated with the established method of assessing endothelial function.

Impact of Storage Conditions on EV Integrity/Surface Markers and Cargos

Extracellular vesicles (EVs) are small biological particles released into biofluids by every cell. Based on their size, they are classified into small EVs (<100 nm or <200 nm) and medium or large EVs (>200 nm). In recent years, EVs have garnered interest for their potential medical applications, including disease diagnosis, cell-based biotherapies, targeted drug delivery systems, and others. Currently, the long-term and short-term storage temperatures for biofluids and EVs are −80 °C and 4 °C, respectively. The storage capacity of EVs can depend on their number, size, function, temperature, duration, and freeze−thaw cycles. While these parameters are increasingly studied, the effects of preservation and storage conditions of EVs on their integrity remain to be understood. Knowledge gaps in these areas may ultimately impede the widespread applicability of EVs. Therefore, this review summarizes the current knowledge on the effect of storage conditions on EVs and their stability and critically explores prospective ways for improving long-term storage conditions to ensure EV stability.

Protocol for Measuring Concentrations of Extracellular Vesicles in Human Blood Plasma with Flow Cytometry

Extracellular vesicles (EVs) are lipid membrane enclosed particles that are released from cells into body fluids, such as blood. EVs offer potential new biomarkers of diseases, because the cellular origin, composition, concentration, and function of EVs change in health and disease. The concentration of EVs from specific cell types in blood can be determined with flow cytometry. A flow cytometer measures fluorescence and light scattering signals from single EVs, but only if these signals are sufficiently bright to be detected. Measured concentrations of EVs are therefore only reproducible and comparable if the detection ranges are known and reported in standard units, such as molecules of equivalent soluble fluorophore (MESF) for fluorescence signals and the diameter in nm for scatter signals. The goal of this protocol is to discuss all steps needed to derive the concentration of cell-type specific EVs within a known diameter range and fluorescence range. More specifically, this protocol describes how to determine the concentration of CD61+ (Integrin beta-3, platelet marker), CD235a+ (Glycophorin A, erythrocyte marker), and CD45+ (leukocyte common antigen) EVs in human blood plasma with an Apogee A60-Micro flow cytometer using scatter-based triggering. The principles behind this protocol could lay a firm basis for the design of a protocol suitable for other flow cytometers and body fluids.

Epithelial-Cell-Derived Extracellular Vesicles in Pathophysiology of Epithelial Injury and Repair in Chronic Rhinosinusitis: Connecting Immunology in Research Lab to Biomarkers in Clinics

Epithelial barrier disruption and failure of epithelial repair by aberrant epithelial-mesenchymal transition (EMT)-induced basal cells observed in nasal mucosa of chronic rhinosinusitis (CRS) are speculated to play important roles in disease pathophysiology. Microparticles (MPs) are a type of extracellular vesicle (EV) released by budding or shedding from the plasma membrane of activated or apoptotic cells. MPs are detected in nasal lavage fluids (NLFs) and are now receiving attention as potential biomarkers to evaluate the degree of activation of immune cells and injury of structural cells in nasal mucosa of subjects with sinus disease. There are three types of epithelial-cell-derived MPs, which are defined by the expression of different epithelial specific markers on their surface: EpCAM, E-cadherin, and integrin β6 (ITGB6). When these markers are on MPs that are also carrying canonical EMT/mesenchymal markers (Snail (SNAI1); Slug (SNAI2); alpha-smooth muscle actin (αSMA, ACTA2)) or pro- and anti-coagulant molecules (tissue factor (TF); tissue plasminogen activator (tPA); plasminogen activator inhibitor-1 (PAI-1)), they provide insight as to the roles of epithelial activation for EMT or regulation of coagulation in the underlying disease. In this review, we discuss the potential of epithelial MPs as research tools to evaluate status of nasal mucosae of CRS patients in the lab, as well as biomarkers for management and treatment of CRS in the clinic.

Separation of distinct exosome subpopulations: isolation and characterization approaches and their associated challenges

Exosomes are nano-sized extracellular vesicles that serve as a communications system between cells and have shown tremendous promise as liquid biopsy biomarkers in diagnostic, prognostic, and even therapeutic use in different human diseases. Due to the natural heterogeneity of exosomes, there is a need to separate exosomes into distinct biophysical and/or biochemical subpopulations to enable full interrogation of exosome biology and function prior to the possibility of clinical translation. Currently, there exists a multitude of different exosome isolation and characterization approaches which can, in limited capacity, separate exosomes based on biophysical and/or biochemical characteristics. While notable reviews in recent years have reviewed these approaches for bulk exosome sorting, we herein present a comprehensive overview of various conventional technologies and modern microfluidic and nanotechnological advancements towards isolation and characterization of exosome subpopulations. The benefits and limitations of these different technologies to improve their use for distinct exosome subpopulations in clinical practices are also discussed. Furthermore, an overview of the most commonly encountered technical and biological challenges for effective separation of exosome subpopulations is presented.

Extracellular Vesicles and Exosomes: Insights From Exercise Science

The benefits of exercise on health and longevity are well-established, and evidence suggests that these effects are partially driven by a spectrum of bioactive molecules released into circulation during exercise (e.g., exercise factors or 'exerkines'). Recently, extracellular vesicles (EVs), including microvesicles (MVs) and exosomes or exosome-like vesicles (ELVs), were shown to be secreted concomitantly with exerkines. These EVs have therefore been proposed to act as cargo carriers or 'mediators' of intercellular communication. Given these findings, there has been a rapidly growing interest in the role of EVs in the multi-systemic, adaptive response to exercise. This review aims to summarize our current understanding of the effects of exercise on MVs and ELVs, examine their role in the exercise response and long-term adaptations, and highlight the main methodological hurdles related to blood collection, purification, and characterization of ELVs.

Centrifugation Removes a Population of Large Vesicles, or "Macroparticles," Intermediate in Size to RBCs and Microvesicles

Microparticles or microvesicles (MPs/MVs) are sub-cellular vesicles with a growing number of known biological functions. Microvesicles from a variety of parent cells within the vascular system increase in numerous pathological states. Red blood cell-derived MVs (RMVs) are relatively less studied than other types of circulating MVs despite red blood cells (RBCs) being the most abundant intravascular cell. This may be in part due the echoes of past misconceptions that RBCs were merely floating anucleate bags of hemoglobin rather than dynamic and responsive cells. The initial aim of this study was to maximize the concentration of RMVs derived from various blood or blood products by focusing on the optimal isolation conditions without creating more MVs from artificial manipulation. We found that allowing RBCs to sediment overnight resulted in a continuum in size of RBC membrane-containing fragments or vesicles extending beyond the 1 µm size limit suggested by many as the maximal size of an MV. Additionally, dilution and centrifugation factors were studied that altered the resultant MV population concentration. The heterogeneous size of RMVs was confirmed in mice models of hemolytic anemia. This methodological finding establishes a new paradigm in that it blurs the line between RBC, fragment, and RMV as well as suggests that the concentration of circulating RMVs may be widely underestimated given that centrifugation removes the majority of such RBC-derived membrane-containing particles.

Flow Cytometry Analysis of Circulating Extracellular Vesicle Subtypes from Fresh Peripheral Blood Samples

Extracellular vesicles (EVs) are released by shedding during different physiological processes and are increasingly thought to be new potential biomarkers. However, the impact of pre-analytical processing phases on the final measurement is not predictable and for this reason, the translation of basic research into clinical practice has been precluded. Here we have optimized a simple procedure in combination with polychromatic flow cytometry (PFC), to identify, classify, enumerate, and separate circulating EVs from different cell origins. This protocol takes advantage of a lipophilic cationic dye (LCD) able to probe EVs. Moreover, the application of the newly optimized PFC protocol here described allowed the obtainment of repeatable EVs counts. The translation of this PFC protocol to fluorescence-activated cell sorting allowed us to separate EVs from fresh peripheral blood samples. Sorted EVs preparations resulted particularly suitable for proteomic analyses, which we applied to study their protein cargo. Here we show that LCD staining allowed PFC detection and sorting of EVs from fresh body fluids, avoiding pre-analytical steps of enrichment that could impact final results. Therefore, LCD staining is an essential step towards the assessment of EVs clinical significance.

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.

Circulating Cancer Stem Cell-Derived Extracellular Vesicles as a Novel Biomarker for Clinical Outcome Evaluation

The recent introduction of the "precision medicine" concept in oncology pushed cancer research to focus on dynamic measurable biomarkers able to predict responses to novel anticancer therapies in order to improve clinical outcomes. Recently, the involvement of extracellular vesicles (EVs) in cancer pathophysiology has been described, and given their release from all cell types under specific stimuli, EVs have also been proposed as potential biomarkers in cancer. Among the techniques used to study EVs, flow cytometry has a high clinical potential. Here, we have applied a recently developed and simplified flow cytometry method for circulating EV enumeration, subtyping, and isolation from a large cohort of metastatic and locally advanced nonhaematological cancer patients (N = 106); samples from gender- and age-matched healthy volunteers were also analysed. A large spectrum of cancer-related markers was used to analyse differences in terms of peripheral blood circulating EV phenotypes between patients and healthy volunteers, as well as their correlation to clinical outcomes. Finally, EVs from patients and controls were isolated by fluorescence-activated cell sorting, and their protein cargoes were analysed by proteomics. Results demonstrated that EV counts were significantly higher in cancer patients than in healthy volunteers, as previously reported. More interestingly, results also demonstrated that cancer patients presented higher concentrations of circulating CD31+ endothelial-derived and tumour cancer stem cell-derived CD133 + CD326- EVs, when compared to healthy volunteers. Furthermore, higher levels of CD133 + CD326- EVs showed a significant correlation with a poor overall survival. Additionally, proteomics analysis of EV cargoes demonstrated disparities in terms of protein content and function between circulating EVs in cancer patients and healthy controls. Overall, our data strongly suggest that blood circulating cancer stem cell-derived EVs may have a role as a diagnostic and prognostic biomarker in cancer.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Circulating Endothelial Microparticles and Aortic Stiffness in Patients with Type 2 Diabetes Mellitus

Diabetes mellitus represents a metabolic disorder the incidence of which has been on the increase in recent years. The well-known long-term complications of this disease encompass a wide spectrum of renal, neurological and cardiovascular conditions. The aim of the study was to investigate the serum concentration of endothelial microparticles (EMPs) as well as selected noninvasive parameters of the ascending aorta stiffness calculated with echocardiography. In this study, 58 patients were enrolled-38 subjects diagnosed with type 2 diabetes mellitus (T2DM) and 20 healthy controls. The analyzed populations did not differ significantly with respect to age, renal function, systolic and diastolic blood pressure. The patients with diabetes and concomitant hypertension presented higher levels of EMPs in comparison with diabetic normotensive subjects. Among patients with diabetes and hypertension, aortic stiffness assessed with the elasticity index (Ep) was higher and the aortic compliance index (D) lower than in the diabetic normotensive group. No correlation between the amount of EMPs and lipid profile, C-reactive protein (CRP) level and glycemia, was observed in the studied group. There was, however, a statistically significant positive correlation between the creatinine level and amount of EMPs, while the negative relationship was documented for EMPs level and the estimated glomerular filtration rate (eGFR).

Effects of Cryopreservation on Microparticles Concentration, Procoagulant Function, Size Distribution, and Morphology

Background

Research on microparticles is rapidly evolving and has extended to the field of many diseases. It is unclear whether microparticles can be stored frozen. In this study, our goal was to verify whether cryopreservation had an effect on the properties of the microparticles.

Material/Methods

We obtained C57BL/6J mouse-derived microparticles by grinding and gradient centrifugation. The specimens were divided into 2 groups: without dimethyl sulfoxide and with dimethyl sulfoxide. The microparticles were then stored at 25°C, 4°C, −20°C, −80°C, and −196°C for 0.5 days, 1 day, 3 days, 5 days, and 7 days. We tested whether the concentration, coagulation function, diameter distribution, and morphology of the microparticles in the 2 groups changed compared to those of a fresh sample.

Results

We discovered that the concentrations of total microparticles, annexin V-positive microparticles, and brain-derived microparticles changed with freezing. The coagulation function, morphology, and size distribution of the microparticles were also affected by cryopreservation. Finally, there was no difference in the effects of cryopreservation on microparticles between the dimethyl sulfoxide group and the dimethyl sulfoxide-free group.

Conclusions

This study suggests that cryopreservation has diverse effects on microparticles within 1 week and that dimethyl sulfoxide has no protective effect on cryopreserved microparticles. Therefore, microparticles should be used fresh for future studies, and they should not be cryopreserved with or without dimethyl sulfoxide.

Microparticles from vascular endothelial growth factor pathway inhibitor-treated cancer patients mediate endothelial cell injury

Vascular endothelial growth factor pathway inhibitors (VEGFi), used as anti-angiogenic drugs to treat cancer are associated with cardiovascular toxicities through unknown molecular mechanisms. Endothelial cell-derived microparticles (ECMPs) are biomarkers of endothelial injury and are also functionally active since they influence downstream target cell signalling and function. We questioned whether microparticle (MP) status is altered in cancer patients treated with VEGFi and whether they influence endothelial cell function associated with vascular dysfunction. Plasma MPs were isolated from cancer patients before and after treatment with VEGFi (pazopanib, sunitinib, or sorafenib). Human aortic endothelial cells (HAECs) were stimulated with isolated MPs (106 MPs/mL). Microparticle characterization was assessed by flow cytometry. Patients treated with VEGFi had significantly increased levels of plasma ECMP. Endothelial cells exposed to post-VEGFi treatment ECMPs induced an increase in pre-pro-ET-1 mRNA expression, corroborating the increase in endothelin-1 (ET-1) production in HAEC stimulated with vatalanib (VEGFi). Post-VEGFi treatment MPs increased generation of reactive oxygen species in HAEC, effects attenuated by ETA (BQ123) and ETB (BQ788) receptor blockers. VEGFi post-treatment MPs also increased phosphorylation of the inhibitory site of endothelial nitric oxide synthase (eNOS), decreased nitric oxide (NO), and increased ONOO- levels in HAEC, responses inhibited by ETB receptor blockade. Additionally, gene expression of proinflammatory mediators was increased in HAEC exposed to post-treatment MPs, effects inhibited by BQ123 and BQ788. Our findings define novel molecular mechanism involving interplay between microparticles, the ET-1 system and endothelial cell pro-inflammatory and redox signalling, which may be important in cardiovascular toxicity and hypertension associated with VEGFi anti-cancer treatment. New and noteworthy: our novel data identify MPs as biomarkers of VEGFi-induced endothelial injury and important mediators of ET-1-sensitive redox-regulated pro-inflammatory signalling in effector endothelial cells, processes that may contribute to cardiovascular toxicity in VEGFi-treated cancer patients.

Increased circulating microparticles in streptozotocin-induced diabetes propagate inflammation contributing to microvascular dysfunction

KEY POINTS

Circulating microparticles (MPs) are elevated in many cardiovascular diseases and have been considered as biomarkers of disease prognosis; however, current knowledge of MP functions has been mainly derived from in vitro studies and their precise impact on vascular inflammation and disease progression remains obscure. Using a diabetic rat model, we identified a >130-fold increase in MPs in plasma of diabetic rats compared to normal rats, the majority of which circulated as aggregates, expressing multiple cell markers and largely externalized phosphatidylserine; vascular images illustrate MP biogenesis and their manifestations in microvessels of diabetic rats. Using combined single microvessel perfusion and systemic cross-transfusion approaches, we delineated how diabetic MPs propagate inflammation in the vasculature and transform normal microvessels into an inflammatory phenotype observed in the microvessels of diabetic rats. Our observations derived from animal studies resembling conditions in diabetic patients, providing a mechanistic insight into MP-mediated pathogenesis of diabetes-associated multi-organ microvascular dysfunction.

ABSTRACT

In various cardiovascular diseases, microparticles (MPs), the membrane-derived vesicles released during cell activation, are markedly increased in the circulation. These MPs have been recognized to play diverse roles in the regulation of cellular functions. However, current knowledge of MP function has been largely derived from in vitro studies. The precise impact of disease-induced MPs on vascular inflammation and disease progression remains obscure. In this study we investigated the biogenesis, profile and functional roles of circulating MPs using a streptozotocin-induced diabetic rat model with well-characterized microvascular functions. Our study revealed a >130-fold increase in MPs in the plasma of diabetic rats compared to normal rats. The majority of these MPs originate from platelets, leukocytes and endothelial cells (ECs), and circulate as aggregates. Diabetic MPs show greater externalized phosphatidylserine (PS) than normal MPs. When diabetic plasma or isolated diabetic MPs were perfused into normal microvessels or systemically transfused into normal rats, MPs immediately adhered to endothelium and subsequently mediated leukocyte adhesion. These microvessels then exhibited augmented permeability responses to inflammatory mediators, replicating the microvascular manifestations observed in diabetic rats. These effects were abrogated when MPs were removed from diabetic plasma or when diabetic MPs were pre-coated with a lipid-binding protein, annexin V, suggesting externalized PS to be key in mediating MP interactions with endothelium and leukocytes. Our study demonstrated that the elevated MPs in diabetic plasma are actively involved in the propagation of vascular inflammation through their adhesive surfaces, providing mechanistic insight into the pathogenesis of multi-organ vascular dysfunction that commonly occurs in diabetic patients.

Moderate-intensity exercise reduces activated and apoptotic endothelial microparticles in healthy midlife women

Endothelial microparticles (EMPs) are related to cardiovascular disease (CVD) risk. Risk factors for CVD increase with menopause, and greater cardiorespiratory fitness is generally expected to reduce CVD risk. The effects of habitual physical activity on endothelial health may be due in part to the effect of acute exercise on circulating EMPs. This study was performed to evaluate the effect of an acute bout of exercise on CD62E⁺ and CD31⁺/42b^- EMPs in healthy fit midlife women at different menopausal stages. Healthy, active premenopausal (PRE), perimenopausal (PERI), and postmenopausal (POST) women completed a single bout of moderate-intensity treadmill exercise. Activated (CD62E⁺) and apoptotic (CD31⁺/42b^-) EMPs were evaluated before and 30 min after exercise by using fluorescent activated cell sorting. In an exploratory analysis, these results were compared with data from low-fit peri- and postmenopausal women. Differences by group and time point were evaluated with repeated-measure ANOVAs. There was a reduction in the number of total microparticles ( P < 0.001), CD62E⁺ ( P = 0.003), and CD31⁺/42b^- ( P < 0.001) EMPs/μl plasma following acute exercise. The percentage of CD62E⁺ EMPs increased with acute exercise ( P < 0.001), whereas the percentage of CD31⁺/42b^- EMPs did not change ( P = 0.40). There was no effect of menopausal status on CD62E⁺or CD31⁺/42b^- EMPs, or on total microparticles (all P > 0.05). The exploratory analysis revealed that low-fit women had similar changes in EMPs with acute exercise. We concluded that acute moderate-intensity exercise reduces CD62E⁺and CD31⁺/42b^- EMPs, as well as total microparticles, in healthy midlife women. These effects occurred despite differences in menopausal status and fitness. NEW & NOTEWORTHY This study demonstrates that acute moderate-intensity exercise reduces activated and apoptotic endothelial microparticles in healthy midlife women.

Semiautomatic Assessment of the Terminal Ileum and Colon in Patients with Crohn Disease Using MRI (the VIGOR++ Project)

RATIONALE AND OBJECTIVES

The objective of this study was to develop and validate a predictive magnetic resonance imaging (MRI) activity score for ileocolonic Crohn disease activity based on both subjective and semiautomatic MRI features.

MATERIALS AND METHODS

An MRI activity score (the "virtual gastrointestinal tract [VIGOR]" score) was developed from 27 validated magnetic resonance enterography datasets, including subjective radiologist observation of mural T2 signal and semiautomatic measurements of bowel wall thickness, excess volume, and dynamic contrast enhancement (initial slope of increase). A second subjective score was developed based on only radiologist observations. For validation, two observers applied both scores and three existing scores to a prospective dataset of 106 patients (59 women, median age 33) with known Crohn disease, using the endoscopic Crohn's Disease Endoscopic Index of Severity (CDEIS) as a reference standard.

RESULTS

The VIGOR score (17.1 × initial slope of increase + 0.2 × excess volume + 2.3 × mural T2) and other activity scores all had comparable correlation to the CDEIS scores (observer 1: r = 0.58 and 0.59, and observer 2: r = 0.34-0.40 and 0.43-0.51, respectively). The VIGOR score, however, improved interobserver agreement compared to the other activity scores (intraclass correlation coefficient = 0.81 vs 0.44-0.59). A diagnostic accuracy of 80%-81% was seen for the VIGOR score, similar to the other scores.

CONCLUSIONS

The VIGOR score achieves comparable accuracy to conventional MRI activity scores, but with significantly improved reproducibility, favoring its use for disease monitoring and therapy evaluation.

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.

Extracellular Vesicles: A Novel Target for Exercise-Mediated Reductions in Type 2 Diabetes and Cardiovascular Disease Risk

Regular exercise is important for reducing type 2 diabetes (T2D) and/or cardiovascular disease (CVD) risk. However, only about 40-50% of this CVD risk reduction is accounted for by adiposity, hyperglycemia, hypertension, and dyslipidemia. Herein, we present the novel hypothesis that extracellular vesicles (EVs) are candidate biomarkers that may relate to impaired endothelial function and insulin resistance independent of obesity risk factors. EVs are small membrane-bound particles that are generated by cells following stimulation, stress, or activation. They carry markers of their parent cell and are thought to be potent bioactivators and communicators. We discuss the underlying physiology of specific cell type EVs, as well as examine how acute and chronic exercise interventions impact EV count and phenotype. We also propose that current gaps in the field are in part related to use of different detection techniques and the lack of standardized measurements of EV affecting the pre- and postanalytical phase. Ultimately, improving the understanding of how EVs impact cardiometabolic health and their function will lead to improved approaches for enhancing diagnostic options as well as designing exercise interventions that treat and/or prevent T2D and CVD.

Influence of Diabetes on Circulating Apoptotic Microparticles in Patients with Chronic Hepatitis C

BACKGROUND/AIM

Type 2 diabetes mellitus (DM) frequently occurs in patients with chronic hepatitis C (CHC) and is associated with atherosclerosis, in which circulating microparticles (MPs) play an important role. We asked whether the presence of DM affects endothelial-derived (EMPs) and platelet-derived microparticles (PMPs) levels; and whether MPs levels associate with biomarkers of inflammation and oxidative stress in patients with CHC.

MATERIALS AND METHODS

Overall, 136 patients were enrolled in the study, 86 CHC patients (41 with DM with moderate glycemic control), 20 outpatients with DM and 30 controls. Circulating MPs were phenotyped by flow cytometry.

RESULTS

When the MPs levels were analyzed individually in CHC patients, there was a positive association of plasma apoptotic MPs with oxidative stress markers. We report a hitherto undescribed relationship between diabetes prevalence and apoptotic MPs-associated inflammation in patients with CHC.

CONCLUSION

The presence of apoptotic MPs in the plasma of CHC patients, with increased levels being found in patients with DM and moderate glycemic control was herein demonstrated. The simultaneous monitoring of plasma apoptotic MPs, oxidative stress markers and inflammatory biomarkers can be helpful for the cardiovascular disease control in diabetic patients with CHC.

Low cardiorespiratory fitness is associated with higher extracellular vesicle counts in obese adults

Low cardiorespiratory fitness (CRF) is associated with cardiovascular disease (CVD) independent of obesity. Extracellular vesicles (EVs) are a novel target of CVD, however, it remains unknown if obese individuals with very poor fitness (VPF) have elevated EVs versus people with poor fitness (PF). Thus, we tested whether VPF was associated with greater EV subtypes in obese adults. Subjects with VPF (n = 13, VO2 peak: 15.4 ± 0.6 mL/kg/min, BMI: 34.1 ± 1.7 kg/m2 ) and PF (n = 13, VO2 peak: 25.9 ± 3.0 mL/kg/min, BMI: 32.1 ± 1.2 kg/m2 ) were compared in this cross-sectional study. After an overnight fast, AnnexinV (AV) +/- platelet (CD31+ /CD41+ ), leukocyte (CD45+ /CD41- ), and endothelial EVs (CD105+ , CD31+ /CD41- ) were analyzed from fresh platelet poor plasma via imaging flow cytometry. Body fat, blood pressure (BP), and glucose tolerance (OGTT) were also tested. Body weight, BP, and circulating glucose were similar between groups, although VPF subjects were older than PF (64.0 ± 2.1 vs. 49.8 ± 4.2 year; P < 0.05). People with VPF, compared with PF, had higher total AV- EVs (P = 0.04), AV- platelet EVs (CD31+ /CD41+ ; P = 0.006), and AV- endothelial EVs (CD31+ /CD41- ; P = 0.005) independent of age and body fat. Higher AV- platelet and endothelial EVs were associated with lower VO2 peak (r = -0.56, P = 0.006 and r = -0.55, P = 0.005, respectively). Endothelial-derived AV- /CD31+ /CD41- EVs were also related to pulse pressure (r = 0.45, P = 0.03), whereas AV- /CD105 was linked to postprandial glucose (r = 0.41, P = 0.04). VPF is associated with higher AnnexinV- total, endothelial, and platelet EVs in obese adults, suggesting that subtle differences in fitness may reduce type 2 diabetes and CVD risk through an EV-related mechanism.

Strategies for enumeration of circulating microvesicles on a conventional flow cytometer: Counting beads and scatter parameters

Enumeration of circulating microvesicles (MVs) by conventional flow cytometry is accomplished by the addition of a known amount of counting beads and calculated from the formula: MV/μl = (MV count/bead count) × final bead concentration. We sought to optimize each variable in the equation by determining the best parameters for detecting ‘MV count’ and examining the effects of different bead preparations and concentrations on the final calculation. Three commercially available bead preparations (TruCount, Flow-Count and CountBright) were tested, and MV detection on a BD FACSCanto was optimized for gating by either forward scatter (FSC) or side scatter (SSC); the results were compared by calculating different subsets of MV on a series of 74 typical patient plasma samples. The relationship between the number of beads added to each test and the number of beads counted by flow cytometry remained linear over a wide range of bead concentrations (R² ≥ 0.997). However, TruCount beads produced the most consistent (concentration variation = 3.8%) calculated numbers of plasma CD41⁺/Annexin V⁺ MV, which were significantly higher from that calculated using either Flow-Count or CountBright (p < 0.001). The FACSCanto was able to resolve 0.5 μm beads by FSC and 0.16 μm beads by SSC, but there were significantly more background events using SSC compared with FSC (3113 vs. 470; p = 0.008). In general, sample analysis by SSC resulted in significantly higher numbers of MV (p < 0.0001) but was well correlated with enumeration by FSC for all MV subtypes (ρ = 0.62–0.89, p < 0.0001). We conclude that all counting beads provided linear results at concentrations ranging from 6 beads/μl to 100 beads/μl, but TruCount was the most consistent. Using SSC to gate MV events produced high background which negatively affected counting bead enumeration and overall MV calculations. Strategies to reduce SSC background should be employed in order to reliably use this technique.

Biological Functions and Current Advances in Isolation and Detection Strategies for Exosome Nanovesicles

Exosomes are nanoscale (≈30-150 nm) extracellular vesicles of endocytic origin that are shed by most types of cells and circulate in bodily fluids. Exosomes carry a specific composition of proteins, lipids, RNA, and DNA and can work as cargo to transfer this information to recipient cells. Recent studies on exosomes have shown that they play an important role in various biological processes, such as intercellular signaling, coagulation, inflammation, and cellular homeostasis. These functional roles are attributed to their ability to transfer RNA, proteins, enzymes, and lipids, thereby affecting the physiological and pathological conditions in various diseases, including cancer and neurodegenerative, infectious, and autoimmune diseases (e.g., cancer initiation, progression, and metastasis). Due to these unique characteristics, exosomes are considered promising biomarkers for the diagnosis and prognosis of various diseases via noninvasive or minimally invasive procedures. Over the last decade, a plethora of methodologies have been developed for analyzing disease-specific exosomes using optical and nonoptical tools. Here, the major biological functions, significance, and potential role of exosomes as biomarkers and therapeutics are discussed. Furthermore, an overview of the most commonly used techniques for exosome analysis, highlighting the major technical challenges and limitations of existing techniques, is presented.

Cell Derived Microparticles in Gingival Crevicular Fluid from Periodontitis Patients with Type 2 Diabetes

Cell-derived microparticles (MPs) have been described as vital contributors to the inflammatory process. However, its role in the periodontal disease pathogenesis remains unclear. Therefore, we aimed to detect the presence neutrophil (CD66b+) and platelet (CD41b+) derived microparticles in gingival crevicular fluid from individuals having periodontitis aggravated by type 2 diabetes. Twelve patients (56.2 ±7.2 yrs) with severe form of chronic periodontitis aggravated by type 2 diabetes were included. Clinical and metabolic data were gathered. Gingival crevicular fluid was collected using filter strips from deep and shallow sites. MPs were detected by flow cytometry according to their size (< 1 µm) and the expression of surface markers (CD66b for neutrophil-derived MPs and CD41b for platelet-derived MPs). All samples were positive for the antibodies. Median levels of CD66b+ MPs and CD41b+ MPs were, respectively, 3,677.0 (2,553.2 - 9,059.8) MP/µL and 520.7 (432.9 - 766.1) MP/µL in deep sites. In shallow sites, the corresponding values were 2,644.9 (1,451.5 - 3,858.9) MP/µL and 371.2 (287.2 - 692.7) MP/µL. There was no significant difference between deep and shallow sites (p>0.05). In conclusion, this study reported the presence of neutrophil and platelet derived microparticles in gingival crevicular fluid from individuals having severe periodontitis and type 2 diabetes.

Extracellular Vesicles Move Toward Use in Clinical Laboratories

Extracellular vesicles (EVs) are membranous particles found in a variety of biofluids that encapsulate molecular information from the cell, which they originate from. This rich source of information that is easily obtained can then be mined to find diagnostic biomarkers. This article explores the current biological understanding of EVs and specific methods to isolate and analyze them. A case study of a company leading the charge in using EVs in diagnostic assays is provided.

Circulating microparticles: challenges and perspectives of flow cytometric assessment

Circulating blood microparticles are likely to play a significant role as messengers of biological information. Their accurate quantification and characterisation is challenging and needs to be carefully designed with preferable usage of fresh minimally-processed blood samples. Utilisation of flow cytometers specifically designed for analysis of small-size particles is likely to provide considerable methodological advantages and should be the preferable option. This viewpoint manuscript provides a critical summary of the key methodological aspects of microparticle analysis.

Note: The review process for this viewpoint article was fully handled by Christian Weber, Editor in Chief.

Peripheral blood microvesicles secretion is influenced by storage time, temperature, and anticoagulants

Microvesicles (MVs) are small membrane bound vesicles released from various cell types after activation or apoptosis. In the last decades, MVs received an increased interest as biomarkers in inflammation, coagulation and cancer. However, standardized pre-analytical steps are crucial for the minimization of artifacts in the MV analysis. Thus, this study evaluated the MV release in whole blood samples under the influence of different anticoagulants, storage time and various temperature conditions. Samples were collected from healthy probands and processed immediately, after 4, 8, 24 and 48 hours at room temperature (RT) or 4°C. To identify MV subpopulations, platelet free plasma (PFP) was stained with Annexin V, calcein AM, CD15, CD41 and CD235a. Analysis was performend on a CytoFLEX flow cytometer. Procoagulatory function of MVs was measured using a phospholipid dependent activity and a tissue factor MVactivity assay. Without prior storage, sodium citrate showed the lowest MV count compared to heparin and EDTA. Interestingly, EDTA showed a significant release of myeloid-derived MVs (MMVs) compared to sodium citrate. Sodium citrate showed a stable MV count at RT in the first 8 hours after blood collection. Total MV counts increased after 24 hours in sodium citrated or heparinzed blood which was related to all subpopulations. Interestingly, EDTA showed stable platelet-derived MV (PMV) and erythrocyte-derived MV (EryMV) count at RT over a 48 h period. In addition, the procoagulatory potential increased significantly after 8-hour storage. Based on both, this work and literature data, the used anticoagulant, storage time and storage temperature differently influence the analysis of MVs within 8 hours. To date, sodium citrated tubes are recommended for MV enumeration and functional analysis. EDTA tubes might be an option for the clinical routine due to stable PMV and EryMV counts. These new approaches need to be validated in a clinical laboratory setting before being applied to patient studies. © 2016 International Society for Advancement of Cytometry.

Prognostic implications and procoagulant activity of phosphatidylserine exposure of blood cells and microparticles in patients with atrial fibrillation treated with pulmonary vein isolation

The present study aimed to evaluate the procoagulant effects of phosphatidylserine (PS) exposure on blood cells and microparticles (MPs), and examine its role in predicting early recurrence atrial fibrillation (ERAF) in patients with atrial fibrillation (AF) treated with pulmonary vein isolation (PVI). Blood samples were obtained from 40 healthy controls and 56 patients with AF at baseline (prior to PVI), and 0, 1 h, 1 day, 3 days and 7 days following PVI. The exposure of PS (PS⁺) to blood cells (platelets, erythrocytes and leukocytes) and MPs was detected using flow cytometry. The procoagulant activity was evaluated by coagulation time, and the formation of factor Xa (FXa) and thrombin. In addition, independent factors associated with PS⁺ blood cells and MPs, and significant predictors of ERAF following PVI were investigated by statistical analyses. The numbers of PS⁺ blood cells and MPs were significantly increased by PVI (P<0.01). A significant decrease in coagulation time, and increases in FXa and thrombin were exhibited in the PS⁺ blood cells and MPs from patients with AF treated with PVI, whereas these alterations were inhibited by either lactadherin or anti-tissue factor (P<0.01). The maximum power of the PVI was significantly associated with platelet-derived MPs, and high-sensitivity C-reactive protein (hs-CRP) was closely associated with leukocyte-derived MPs and endothelial-derived MPs (EMPs) (P<0.01). In addition, hs-CRP and EMPs >355/µl were identified as independent predictors of ERAF (P<0.05). The increased numbers of PS⁺ platelets, erythrocytes, leukocytes and MPs contributed to the procoagulant state of AF, and hs-CRP and EMPs were able to predict ERAF following PVI.

Endothelial microparticles act as novel diagnostic and therapeutic biomarkers of circulatory hypoxia-related diseases: a literature review

Circulatory hypoxia-related diseases (CHRDs), including acute coronary syndromes, stroke and organ transplantation, attract increased attention due to high morbidity and mortality. Mounting evidence shows that hypoxia-induced oxidative stress, coagulation, inflammation and angiogenesis play extremely important roles in the physiological and pathological processes of CHRD-related vascular endothelial injury. Interestingly, hypoxia, even hypoxia-induced oxidative stress, coagulation and inflammation can all induce release of endothelial microparticles (EMPs). EMPs, shed from activated or apoptotic endothelial cells (ECs), reflect the degree of EC damage, and elevated EMP levels are found in several CHRDs. Furthermore, EMPs, which play an important role in cell-to-cell communication and function, have confirmed pro-coagulant, proinflammatory, angiogenic and other functions, affecting pathological processes. These findings suggest that EMPs and CHRDs have a very close relationship, and EMPs may help to identify CHRD phenotypes and stratify the severity of disease, to improve risk stratification for developing CHRDs, to better define prophylactic strategies and to ameliorate prognostic characterization of patients with CHRDs. This review summarizes the known and potential roles of EMPs in the diagnosis, staging, treatment and clinical prognosis of CHRDs.

Methodological Guidelines to Study Extracellular Vesicles

Owing to the relationship between extracellular vesicles (EVs) and physiological and pathological conditions, the interest in EVs is exponentially growing. EVs hold high hopes for novel diagnostic and translational discoveries. This review provides an expert-based update of recent advances in the methods to study EVs and summarizes currently accepted considerations and recommendations from sample collection to isolation, detection, and characterization of EVs. Common misconceptions and methodological pitfalls are highlighted. Although EVs are found in all body fluids, in this review, we will focus on EVs from human blood, not only our most complex but also the most interesting body fluid for cardiovascular research.

Microparticles during long-term follow-up after acute myocardial infarction. Association to atherosclerotic burden and risk of cardiovascular events

Microparticles (MPs) are formed from platelets (PMPs), endothelial cells (EMPs) and monocytes (MMPs), and in acute myocardial infarction (MI), there is an increase of MPs in the culprit artery. In this study MPs were evaluated in whole blood in 105 patients with MI at five time-points during a two-year follow-up (FU). Patients with non-ST-elevated MI had higher concentrations of CD41+MPs compared to ST-elevated MI patients (p=0.024). The concentrations of PMPs in whole blood increased during the time period (p<0.001), but no significant change over time was found for EMPs and MMPs. CD62P+MP counts were higher in MI patients with diabetes (p=0.020), and patients with hypertension had increased levels of CD14+MPs (p=0.004). The amount of CD62P+TF+MPs increased significantly during FU (p<0.001). Patients with atherosclerosis in three arterial beds, i. e. coronary, carotid and peripheral arteries, had lower concentrations of CD62P+TF+MPs (p=0.035) and CD144+TF+MPs (p=0.004) compared to patients with atherosclerosis in one or two arterial beds. Higher concentrations of CD62P+MPs early after MI were associated with an increased risk of cardiovascular events during FU, hazard ratio 3.32 (95 %CI1.20-9.31). Only small variations in PMP, EMP and MMP concentrations were found during long-term FU after MI and their levels seem to reflect the underlying cardiovascular disease rather than the acute MI. PMPs expressing P-selectin might be a promising biomarker for predicting future cardiovascular events, but further studies are needed to confirm these results.

A transmission electron microscopy study of anticoagulant-induced platelet vesiculation

Highlights

EDTA induces platelet microparticles (PMPs) vesiculation.Sodium citrated tubes are better than EDTA tubes in PMPs analysis.Sodium citrate has a minor impact on platelet structure.

Abstract

Platelet microparticles (PMPs) are small membrane fragments released from activated platelets in response to various stimuli. PMPs serve as biomarkers for several diseases and conditions and are useful tools for prognostic, diagnostic, and therapeutic purposes. The objective of our study was to compare the direct effects of ethylenediaminetetraacetic acid (EDTA) and sodium citrate anticoagulants on platelet structure and PMP vesiculation using transmission electron microscopy to visualize the morphologic changes in platelets. Micrographs revealed that platelets in the EDTA-anticoagulated tube manifested with significant morphologic changes and induced PMP vesiculation. On the other hand, the sodium citrate-anticoagulated tube showed a normal platelet structure and minor modifications in some cases, with poor indication of PMP vesiculation. In conclusion, EDTA induced platelet activation and PMP vesiculation and represents a major source of artifacts during the pre-analysis steps of PMP vesiculation.

Endothelial Microparticles Act as Novel Diagnostic and Therapeutic Biomarkers of Diabetes and Its Complications: A Literature Review

Diabetes mellitus- (DM-) related vascular diseases attract increased attention due to their high morbidity and mortality. The incidence of obesity, atherosclerosis, coronary heart disease, hypertension, and dyslipidemia is significantly higher in DM patients, with an earlier onset and faster progression compared with non-DM patients. DM-related vascular diseases including macrovascular and microvascular complications are characterized by endothelial dysfunction. Therefore, a better understanding of the etiology and mechanisms of endothelial dysfunction is important for the diagnosis and treatment of DM. Endothelial microparticles (EMPs) are new diagnostic and therapeutic targets and biomarkers in DM-related vascular disease. Circulating EMPs containing biologically active substances act as intercellular signals under physiological and pathological conditions. They serve as biological markers of altered vascular endothelium and reflect the pathological progression and diminished endothelial function of blood vessels. Recent evidence suggests that the plasma level of EMPs is significantly higher in DM patients than in healthy population and is significantly correlated with DM-related complications. These observations have prompted speculation that EMPs play a crucial role in the pathophysiology of DM. This review summarizes the known and potential roles of EMPs in the diagnosis, staging, treatment, and clinical prognosis of DM and related vascular diseases.

Endothelial and inflammatory responses to acute exercise in perimenopausal and late postmenopausal women

Endothelial dysfunction and inflammation are characteristics of subclinical atherosclerosis and may increase through progressive menopausal stages. Evaluating endothelial responses to acute exercise can reveal underlying dysfunction not apparent in resting conditions. The purpose of this study was to investigate markers of endothelial function and inflammation before and after acute exercise in healthy low-active perimenopausal (PERI) and late postmenopausal (POST) women. Flow-mediated dilation (FMD), CD31⁺/CD42b^- and CD62E⁺ endothelial microparticles (EMPs), and the circulating inflammatory factors monocyte chemoattractant protein 1 (MCP-1), interleukin 8 (IL-8), and tumor necrosis factor-α (TNF-α) were measured before and 30 min after acute exercise. Before exercise, FMD was not different between groups (PERI: 6.4 ± 0.9% vs. POST: 6.5 ± 0.8%, P = 0.97); however, after acute exercise PERI tended to improve FMD (8.5 ± 0.9%, P = 0.09), whereas POST did not (6.2 ± 0.8%, P = 0.77). Independent of exercise, we observed transient endothelial dysfunction in POST with repeated FMD measures. There was a group × exercise interaction for CD31⁺/CD42b^- EMPs (P = 0.04), where CD31⁺/CD42b^- EMPs were similar before exercise (PERI: 57.0 ± 6.7 EMPs/μl vs. POST: 58.5 ± 5.3 EMPs/μl, P = 0.86) but were higher in POST following exercise (PERI: 48.2 ± 6.7 EMPs/μl vs. POST: 69.4 ± 5.3 EMPs/μl, P = 0.023). CD62E⁺ EMPs were lower in PERI compared with POST before exercise (P < 0.001) and increased in PERI (P = 0.04) but did not change in POST (P = 0.68) in response to acute exercise. After acute exercise, MCP-1 (P = 0.055), TNF-α (P = 0.02), and IL-8 (P < 0.001) were lower in PERI but only IL-8 decreased in POST (P < 0.001). Overall, these data suggest that perimenopausal and late postmenopausal women display different endothelial and inflammatory responses to acute exercise.

From trash to treasure: The untapped potential of endothelial microparticles in neurovascular diseases

Discovered in 1947, microparticles (MP) represent a group of sub-micron cell-derived particles isolated by high speed centrifugation. Once regarded as cellular 'trash', in the past decade MP have gained tremendous attention in both basic sciences and medical research both as biomarkers and mediators of infection, injury and response to therapy. Because MP bear cell surface markers derived from parent cells, accumulate in extracellular fluids (plasma, serum, milk, urine, cerebrospinal fluid) MP based tests are being developed commercially as important components in 'liquid biopsy' approaches, providing valuable readouts in cardiovascular disease and cancer, as well as stroke, Alzheimer's disease and Multiple Sclerosis. Importantly, MP have been reported as mobile transport vectors in the intercellular transfer of mRNAs, microRNAs, lipids and proteins. Here we discuss MP structure, properties and functions with particular relevance to neurological and neurovascular diseases.

Childhood obesity-related endothelial dysfunction: an update on pathophysiological mechanisms and diagnostic advancements

Childhood obesity jeopardizes a healthy future for our society's children as it is associated with increased cardiovascular morbidity and mortality later on in life. Endothelial dysfunction, the first step in the development of atherosclerosis, is already present in obese children and may well represent a targetable risk factor. Technological advancements in recent years have facilitated noninvasive measurements of endothelial homeostasis in children. Thereby this topic ultimately starts to get the attention it deserves. In this paper, we aim to summarize the latest insights on endothelial dysfunction in childhood obesity. We discuss methodological advancements in peripheral endothelial function measurement and newly identified diagnostic markers of vascular homeostasis. Finally, future challenges and perspectives are set forth on how to efficiently tackle the catastrophic rise in cardiovascular morbidity and mortality that will be inflicted on obese children if they are not treated optimally.

Circulating Endothelial Microparticles: A Key Hallmark of Atherosclerosis Progression

The levels of circulating microparticles (MPs) are raised in various cardiovascular diseases. Their increased level in plasma is regarded as a biomarker of alteration in vascular function. The prominent MPs present in blood are endothelial microparticles (EMPs) described as complex submicron (0.1 to 1.0 μm) vesicles like structure, released in response to endothelium cell activation or apoptosis. EMPs possess both physiological and pathological effects and may promote oxidative stress and vascular inflammation. EMPs release is triggered by inducer like angiotensin II, lipopolysaccharide, and hydrogen peroxide leading to the progression of atherosclerosis. However, there are multiple physiological pathways for EMPs generation like NADPH oxidase derived endothelial ROS formation, Rho kinase pathway, and mitogen-activated protein kinases. Endothelial dysfunction is a key initiating event in atherosclerotic plaque formation. Atheroemboli, resulting from ruptured carotid plaques, is a major cause of stroke. Increasing evidence suggests that EMPs play an important role in the pathogenesis of cardiovascular disease, acting as a marker of damage, either exacerbating disease progression or triggering a repair response. In this regard, it has been suggested that EMPs have the potential to act as biomarkers of disease status. This review aims to provide updated information of EMPs in relation to atherosclerosis pathogenesis.

Microparticle-Induced Activation of the Vascular Endothelium Requires Caveolin-1/Caveolae

Microparticles (MPs) are small membrane fragments shed from normal as well as activated, apoptotic or injured cells. Emerging evidence implicates MPs as a causal and/or contributing factor in altering normal vascular cell phenotype through initiation of proinflammatory signal transduction events and paracrine delivery of proteins, mRNA and miRNA. However, little is known regarding the mechanism by which MPs influence these events. Caveolae are important membrane microdomains that function as centers of signal transduction and endocytosis. Here, we tested the concept that the MP-induced pro-inflammatory phenotype shift in endothelial cells (ECs) depends on caveolae. Consistent with previous reports, MP challenge activated ECs as evidenced by upregulation of intracellular adhesion molecule-1 (ICAM-1) expression. ICAM-1 upregulation was mediated by activation of NF-κB, Poly [ADP-ribose] polymerase 1 (PARP-1) and the epidermal growth factor receptor (EGFR). This response was absent in ECs lacking caveolin-1/caveolae. To test whether caveolae-mediated endocytosis, a dynamin-2 dependent process, is a feature of the proinflammatory response, EC’s were pretreated with the dynamin-2 inhibitor dynasore. Similar to observations in cells lacking caveolin-1, inhibition of endocytosis significantly attenuated MPs effects including, EGFR phosphorylation, activation of NF-κB and upregulation of ICAM-1 expression. Thus, our results indicate that caveolae play a role in mediating the pro-inflammatory signaling pathways which lead to EC activation in response to MPs.

Measurement of microvesicle levels in human blood using flow cytometry

Microvesicles are fragments of cells released when the cells are activated, injured, or apoptotic. Analysis of microvesicle levels in blood has the potential to shed new light on the pathophysiology of many diseases. Flow cytometry is currently the only method that can simultaneously separate true lipid microvesicles from other microparticles in blood, determine the cell of origin and other microvesicle characteristics, and handle large numbers of clinical samples with a reasonable effort, but expanded use of flow cytometric measurement of microvesicle levels as a clinical and research tool requires improved, standardized assays. The goal of this review is to aid investigators in applying current best practices to microvesicle measurements. First pre-analytical factors are evaluated and data summarized for anticoagulant effects, sample transport and centrifugation. Next flow cytometer optimization is reviewed including interference from background in buffers and reagents, accurate microvesicle counting, swarm interference, and other types of coincidence errors, size calibration, and detection limits using light scattering, impedance and fluorescence. Finally current progress on method standardization is discussed and a summary of current best practices provided. © 2016 Clinical Cytometry Society.

Analytical challenges of extracellular vesicle detection: A comparison of different techniques

The interest in extracellular vesicles (EVs) has grown exponentially over the last decade. Evolving evidence is demonstrating that these EVs are playing an important role in health and disease. They are involved in intercellular communication and have been shown to transfer proteins, lipids, and nucleic acids. This review focuses on the most commonly used techniques for detection of EVs, to include microparticles, 100-1,000 nm in size, and exosomes, 50-100 nm in size. Conventional flow cytometry is the most prevalent technique, but nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), and resistive pulse sensing have also been used to detect EVs. The accurate measurement of these vesicles is challenged by size heterogeneity, low refractive index, and the lack of dynamic measurement range for most of the available technologies. Sample handling during the preanalytical phase can also affect the accuracy of measurements. Currently, there is not one single method which allows phenotyping, sizing, and enumerating the whole range of EVs and, therefore, providing all the necessary information to truly understand the biology of these particles. A combination of methods is probably needed which might also include electron and atomic force microscopy and full RNA, lipid, and protein profiling.

High correlation between 2 flow cytometry platforms in the microparticles analysis using a new calibrated beads strategy

Microparticles (MPs) are potential noninvasive biomarkers for diagnosis or prognosis in pathologic conditions. However, the lack of standardization of the preanalytical and analytical methods leads to a wide variability in MPs results. The recently developed Megamix-Plus beads, a new bead-based standardization tool optimized to specific types of flow cytometers, could help circumvent this problem. The aim of the present study was to determine whether the number of total MPs and platelet-derived MPs (PMPs) is similar using 2 different cytometer platforms calibrated with the Megamix-Plus beads. Blood samples from 65 patients with deep venous thrombosis were collected and processed to obtain platelet poor plasma (PPP). The number of total MPs and PMPs in each PPP sample was measured using 2 flow cytometers. Megamix-Plus side scatter channel beads were used to calibrate the LSRFortessa flow cytometer from Becton Dickinson, whereas Megamix-Plus forward scatter channel beads were applied to the Navios flow cytometer from Beckman Coulter. High correlation of total MPs and PMPs values between the flow cytometers was found (r = 0.908, P < 0.01 and r = 0.910, P < 0.001, respectively). However, the absolute numbers of total MPs and PMPs were significantly higher measured with the Navios flow cytometer compared with the LSRFortessa cytometer. Therefore, both platforms are valid for MPs determination in general, although a similar platform with the same calibration tool could be a better choice for multicenter studies.

Elevated circulating endothelial cell-derived microparticle levels in patients with liver cirrhosis: a preliminary report

Aim of the study

To determine plausible associations between liver cirrhosis and circulating endothelial cell-derived microparticles (EMPs), vascular endothelial growth factor (VEGF) levels and plasma nitric oxide (NO) metabolites.

Material and methods

Sixty patients with cirrhosis and 20 healthy control subjects were enrolled in the study. Circulating EMPs from platelet-poor plasma samples were examined by flow cytometry. These microparticles were categorized into endothelial cell-derived activated MPs (EMP-ac) (CD31⁺ CD42b^– AN-V^–) and endothelial cell-derived apoptotic MPs (EMP-ap) (CD31⁺ CD42b^– AN-V⁺). Plasma VEGF levels were measured by enzyme-linked immunosorbent assay. Plasma NO metabolites (NO_x^–) levels were determined using a Greiss reaction method.

Results

Compared with the healthy control subjects, the patients with cirrhosis showed a significant increase in plasma levels of both phenotypes of EMPs. When the presence of ascites was considered, the plasma levels of EMP-ap were higher (p < 0.01), as well as NO_x^– (p < 0.05). EMP-ap positively correlated with VEGF level in all cirrhotic patients and this correlation was stronger in decompensated cirrhotic patients. In multivariate logistic regression analysis, the independent factors associated with the presence of ascites were high EMP-ap levels and elevated VEGF levels.

Conclusions

Elevated plasma levels of EMP-ap in addition to high levels of VEGF might be considered as valuable parameters for predicting the occurrence of ascites in cirrhotic patients.

Immuno-analysis of microparticles: probing at the limits of detection

Microparticle (MP) research is clouded by debate regarding the accuracy and validity of flow cytometry (FCM) as an analytical methodology, as it is influenced by many variables including the pre-analytical conditions, instruments physical capabilities and detection parameters. This study utilises a simplistic in vitro system for generating MP, and through comparative analysis with immuno-electron microscopy (Immuno-EM) assesses the strengths and limitations of probe selection and high-sensitivity FCM. Of the markers examined, MP were most specifically labelled with phosphatidylserine ligands, annexin V and lactadherin, although only ~60% MP are PS positive. Whilst these two ligands detect comparable absolute MP numbers, they interact with the same population in distinct manners; annexin V binding is enhanced on TNF induced MP. CD105 and CD54 expression were, as expected, consistent and enhanced following TNF activation respectively. Their labelling however accounted for as few as 30-40% of MP. The greatest discrepancies between FCM and I-EM were observed in the population solely labelled for the surface antigen. These findings demonstrate that despite significant improvements in resolution, high-sensitivity FCM remains limited in detecting small-size MP expressing low antigen levels. This study highlights factors to consider when selecting endothelial MP probes, as well as interpreting and representing data.

Effects of normoxic and hypoxic exercise regimens on monocyte-mediated thrombin generation in sedentary men

Exercise and hypoxia paradoxically modulate vascular thrombotic risks. The shedding of procoagulant-rich microparticles from monocytes may accelerate the pathogenesis of atherothrombosis. The present study explores the manner in which normoxic and hypoxic exercise regimens affect procoagulant monocyte-derived microparticle (MDMP) formation and monocyte-promoted thrombin generation (TG). Forty sedentary healthy males were randomized to perform either normoxic (NET; 21% O2, n=20) or hypoxic (HET; 15% O2, n=20) exercise training (60% VO(2max)) for 30 min/day, 5 days/week for 5 weeks. At rest and immediately after HET (100 W under 12% O2 for 30 min), the MDMP characteristics and dynamic TG were measured by flow cytometry and thrombinography respectively. The results demonstrated that acute 12% O2 exercise (i) increased the release of coagulant factor V (FV)/FVIII-rich, phosphatidylserine (PS)-exposed and tissue factor (TF)-expressed microparticles from monocytes, (ii) enhanced the peak height and rate of TG in monocyte-rich plasma (MRP) and (iii) elevated concentrations of norepinephrine/epinephrine, myeloperoxidase (MPO) and interleukin-6 (IL-6) in plasma. Following the 5-week intervention, HET exhibited higher enhancements of peak work-rate and cardiopulmonary fitness than NET did. Moreover, both NET and HET decreased the FV/FVIII-rich, PS-exposed and TF-expressed MDMP counts and the peak height and rate of TG in MRP following the HET. However, HET elicited more suppression for the HE (hypoxic exercise)-enhanced procoagulant MDMP formation and dynamic TG in MPR and catecholamine/peroxide/pro-inflammatory cytokine levels in plasma than NET. Hence, we conclude that HET is superior to NET for enhancing aerobic capacity. Furthermore, HET effectively suppresses procoagulant MDMP formation and monocyte-mediated TG under severe hypoxic stress, compared with NET.

Microvesicles from platelets: novel drivers of vascular inflammation

Microvesicles are receiving increased attention not only as biomarkers but also as mediators of cell communication and as integral effectors of disease. Platelets present a major source of microvesicles and release these microvesicles either spontaneously or upon activation. Platelet-derived microvesicles retain many features of their parent cells and have been shown to exert modulatory effects on vascular and immune cells. Accordingly, microvesicles from platelets can be measured at increased levels in patients with cardiovascular disease or individuals at risk. In addition, isolated microvesicles from platelets were shown to exert immunomodulatory actions on various cell types. In this review the various aspects of platelet-derived microvesicles including release, clearance, measurement, occurrence during disease and relevance for the pathophysiology of vascular inflammation will be discussed.

Endothelial dysfunction in acute brain injury and the development of cerebral ischemia

Cerebral ischemia (CeI) is a major complicating event after acute brain injury (ABI) in which endothelial dysfunction is a key player. This study evaluates cellular markers of endothelial function and in vivo reactive hyperemia in patients with ABI and their relationship to the development of cerebral ischemia. We studied cellular markers of endothelial dysfunction and the peripheral reactive hyperemia index (RHI) in 26 patients with ABI at admission and after 6 and 12 days, and compared these with those of healthy volunteers (n = 15). CeI was determined clinically or by computer tomography. In patients with ABI, RHI at admission was significantly reduced compared with healthy subjects (P = 0.003), coinciding with a decrease in circulating endothelial progenitor cells (EPC; P = 0.002). The RHI recovered in eight patients without development of CeI, but failed to fully recover by day 12 in three of four patients who developed CeI. Despite recovery of the RHI within 12 days in these patients (P = 0.003), EPC count remained significantly lower after 12 days in patients with ABI (P = 0.022). CD31(+) T cells and endothelial microparticles were not different between controls and patients. No differences were noted in cellular markers of endothelial dysfunction in patients developing CeI and those not. In conclusion, patients with ABI exhibit impaired microvascular endothelial function measured as RHI and a decreased circulating level of EPC.