Comparison of Generic Fluorescent Markers for Detection of Extracellular Vesicles by Flow Cytometry

Fluorescent, phosphorescent, magnetic resonance contrast and radioactive tracer labelling of extracellular vesicles

This review focusses on the significance of fluorescent, phosphorescent labelling and tracking of extracellular vesicles (EVs) for unravelling their biology, pathophysiology, and potential diagnostic and therapeutic uses. Various labeling strategies, such as lipid membrane, surface protein, luminal, nucleic acid, radionuclide, quantum dot labels, and metal complex-based stains, are evaluated for visualizing and characterizing EVs. Direct labelling with fluorescent lipophilic dyes is simple but generally lacks specificity, while surface protein labelling offers selectivity but may affect EV-cell interactions. Luminal and nucleic acid labelling strategies have their own advantages and challenges. Each labelling approach has strengths and weaknesses, which require a suitable probe and technique based on research goals, but new tetranuclear polypyridylruthenium(II) complexes as phosphorescent probes have strong phosphorescence, selective staining, and stability. Future research should prioritize the design of novel fluorescent probes and labelling platforms that can significantly enhance the efficiency, accuracy, and specificity of EV labeling, while preserving their composition and functionality. It is crucial to reduce false positive signals and explore the potential of multimodal imaging techniques to gain comprehensive insights into EVs.

Extracellular vesicles in atherosclerosis: Current and forthcoming impact?

Atherosclerosis is the main pathogenic substrate for cardiovascular diseases (CVDs). Initially categorized as a passive cholesterol storage disease, nowadays, it is considered an active process, identifying inflammation among the key players for its initiation and progression. Despite these advances, patients with CVDs are still at high risk of thrombotic events and death, urging to deepen into the molecular mechanisms underlying atherogenesis, and to identify novel diagnosis and prognosis biomarkers for their stratification. In this context, extracellular vesicles (EVs) have been postulated as an alternative in search of novel biomarkers in atherosclerotic diseases, as well as to investigate the crosstalk between the cells participating in the processes leading to arterial remodelling. EVs are nanosized lipidic particles released by most cell types in physiological and pathological conditions, that enclose lipids, proteins, and nucleic acids from parental cells reflecting their activation status. First considered cellular waste disposal systems, at present, EVs have been recognized as active effectors in a myriad of cellular processes, and as potential diagnosis and prognosis biomarkers also in CVDs. This review summarizes the role of EVs as potential biomarkers of CVDs, and their involvement into the processes leading to atherosclerosis.

Physio-chemical Modifications to Re-engineer Small Extracellular Vesicles for Targeted Anticancer Therapeutics Delivery and Imaging

Cancer theranostics developed through nanoengineering applications are essential for targeted oncologic interventions in the new era of personalized and precision medicine. Recently, small extracellular vesicles (sEVs) have emerged as an attractive nanoengineering platform for tumor-directed anticancer therapeutic delivery and imaging of malignant tumors. These natural nanoparticles have multiple advantages over synthetic nanoparticle-based delivery systems, such as intrinsic targeting ability, less immunogenicity, and a prolonged circulation time. Since the inception of sEVs as a viable replacement for liposomes (synthetic nanoparticles) as a drug delivery vehicle, many studies have attempted to further the therapeutic efficacy of sEVs. This article discusses engineering strategies for sEVs using physical and chemical methods to enhance their anticancer therapeutic delivery performance. We review physio-chemical techniques of effective therapeutic loading into sEV, sEV surface engineering for targeted entry of therapeutics, and its cancer environment sensitive release inside the cells/organ. Next, we also discuss the novel hybrid sEV systems developed by a combination of sEVs with lipid and metal nanoparticles to garner each component's benefits while overcoming their drawbacks. The article extensively analyzes multiple sEV labeling techniques developed and investigated for live tracking or imaging sEVs. Finally, we discuss the theranostic potential of engineered sEVs in future cancer care regimens.

Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches

Extracellular vesicles (EVs), through their complex cargo, can reflect the state of their cell of origin and change the functions and phenotypes of other cells. These features indicate strong biomarker and therapeutic potential and have generated broad interest, as evidenced by the steady year-on-year increase in the numbers of scientific publications about EVs. Important advances have been made in EV metrology and in understanding and applying EV biology. However, hurdles remain to realising the potential of EVs in domains ranging from basic biology to clinical applications due to challenges in EV nomenclature, separation from non-vesicular extracellular particles, characterisation and functional studies. To address the challenges and opportunities in this rapidly evolving field, the International Society for Extracellular Vesicles (ISEV) updates its 'Minimal Information for Studies of Extracellular Vesicles', which was first published in 2014 and then in 2018 as MISEV2014 and MISEV2018, respectively. The goal of the current document, MISEV2023, is to provide researchers with an updated snapshot of available approaches and their advantages and limitations for production, separation and characterisation of EVs from multiple sources, including cell culture, body fluids and solid tissues. In addition to presenting the latest state of the art in basic principles of EV research, this document also covers advanced techniques and approaches that are currently expanding the boundaries of the field. MISEV2023 also includes new sections on EV release and uptake and a brief discussion of in vivo approaches to study EVs. Compiling feedback from ISEV expert task forces and more than 1000 researchers, this document conveys the current state of EV research to facilitate robust scientific discoveries and move the field forward even more rapidly.

Assessing Extracellular Vesicles in Human Biofluids Using Flow-Based Analyzers

Extracellular vesicles (EVs) are increasingly being analyzed by flow cytometry. Yet their minuscule size and low refractive index cause the scatter intensity of most EVs to fall below the detection limit of most flow cytometers. A new class of devices, known as spectral flow analyzers, are becoming standards in cell phenotyping studies, largely due to their unique capacity to detect a vast panel of markers with higher sensitivity for light scatter detection. Another class of devices, known as nano-analyzers, provides high-resolution detection of sub-micron-sized particles. Here, the EV phenotyping performance between the Aurora (Cytek) spectral cell analyzer and the NanoFCM (nFCM) nanoflow analyzer are compared. These two devices are specifically chosen given their lead in becoming gold standards in their respective fields. Immune cell-derived EVs remain poorly characterized despite their clinical potential. Therefore, B- and T-cell line-derived EVs and donor-matched human biofluid-derived EVs from plasma, urine, and saliva are used in combination with a panel of established immune markers for this comparative study. A comparative evaluation of both cytometry platforms is performed, discussing their potential and suitability for different applications. It is found that nFCM can accurately i) analyze small EVs (40-200 nm) matching the size accuracy of electron microscopy; ii) measure the concentration of a single EV particle per volume; iii) identify underrepresented EV marker subsets; and iv) provide co-localization of EV surface markers. It can also be shown that human sample biofluids have unique EV marker signatures that can have future clinical relevance. Finally, nFCM and Aurora have their unique strength, preferred fashion of data acquisition, and visualization to fit different research interests.

Quantitative assessment of lipophilic membrane dye-based labelling of extracellular vesicles by nano-flow cytometry

Although lipophilic membrane dyes (LMDs) or probes (LMPs) are widely used to label extracellular vesicles (EVs) for detection and purification, their labelling performance has not been systematically characterized. Through concurrent side scattering and fluorescence detection of single EVs as small as 40 nm in diameter by a laboratory-built nano-flow cytometer (nFCM), present study identified that (1) PKH67 and PKH26 could maximally label ∼60%-80% of EVs isolated from the conditioned cell culture medium (purity of ∼88%) and ∼40%-70% of PFP-EVs (purity of ∼73%); (2) excessive PKH26 could cause damage to the EV structure; (3) di-8-ANEPPS and high concentration of DiI could achieve efficient and uniform labelling of EVs with nearly 100% labelling efficiency for di-8-ANEPPS and 70%-100% for DiI; (4) all the four tested LMDs can aggregate and form micelles that exhibit comparable side scatter and fluorescence intensity with those of labelled EVs and thus hardly be differentiate from each other; (5) as the LMD concentration went up, the particle number of self-aggregates increased while the fluorescence intensity of aggregates remained constant; (6) PKH67 and PKH26 tend to form more aggregated micelles than di-8-ANEPPS and DiI, and the effect of LMD self-aggregation can be negligible at optimal staining conditions. (7) All the four tested LMDs can label almost all the very-low-density lipoprotein (VLDL) particles, indicating potential confounding factor in plasma-EV labelling. Besides, it was discovered that DSPE-PEG2000 -biotin can only label ∼50% of plasma-EVs. The number of LMP inserted into the membrane of single EVs was measured for the first time and it was confirmed that membrane labelling by lipophilic dyes did not interfere with the immunophenotyping of EVs. nFCM provides a unique perspective for a better understanding of EV labelling by LMD/LMP.

Extracellular Vesicles of the Plant Pathogen Botrytis cinerea

Fungal secretomes are known to contain a multitude of components involved in nutrition, cell growth or biotic interactions. Recently, extra-cellular vesicles have been identified in a few fungal species. Here, we used a multidisciplinary approach to identify and characterize extracellular vesicles produced by the plant necrotroph Botrytis cinerea. Transmission electron microscopy of infectious hyphae and hyphae grown in vitro revealed extracellular vesicles of various sizes and densities. Electron tomography showed the co-existence of ovoid and tubular vesicles and pointed to their release via the fusion of multi-vesicular bodies with the cell plasma membrane. The isolation of these vesicles and exploration of their protein content using mass spectrometry led to the identification of soluble and membrane proteins involved in transport, metabolism, cell wall synthesis and remodeling, proteostasis, oxidoreduction and traffic. Confocal microscopy highlighted the capacity of fluorescently labeled vesicles to target cells of B. cinerea, cells of the fungus Fusarium graminearum, and onion epidermal cells but not yeast cells. In addition, a specific positive effect of these vesicles on the growth of B. cinerea was quantified. Altogether, this study broadens our view on the secretion capacity of B. cinerea and its cell-to-cell communication.

Extracellular Vesicles in Liquid Biopsies as Biomarkers for Solid Tumors

Extracellular vesicles (EVs) are secreted by all living cells and are ubiquitous in every human body fluid. They are quite heterogeneous with regard to biogenesis, size, and composition, yet always reflect their parental cells with their cell-of-origin specific cargo loading. Since numerous studies have demonstrated that EV-associated proteins, nucleic acids, lipids, and metabolites can represent malignant phenotypes in cancer patients, EVs are increasingly being discussed as valuable carriers of cancer biomarkers in liquid biopsy samples. However, the lack of standardized and clinically feasible protocols for EV purification and characterization still limits the applicability of EV-based cancer biomarker analysis. This review first provides an overview of current EV isolation and characterization techniques that can be used to exploit patient-derived body fluids for biomarker quantification assays. Secondly, it outlines promising tumor-specific EV biomarkers relevant for cancer diagnosis, disease monitoring, and the prediction of cancer progression and therapy resistance. Finally, we summarize the advantages and current limitations of using EVs in liquid biopsy with a prospective view on strategies for the ongoing clinical implementation of EV-based biomarker screenings.

A compendium of single extracellular vesicle flow cytometry

Flow cytometry (FCM) offers a multiparametric technology capable of characterizing single extracellular vesicles (EVs). However, most flow cytometers are designed to detect cells, which are larger than EVs. Whereas cells exceed the background noise, signals originating from EVs partly overlap with the background noise, thereby making EVs more difficult to detect than cells. This technical mismatch together with complexity of EV-containing fluids causes limitations and challenges with conducting, interpreting and reproducing EV FCM experiments. To address and overcome these challenges, researchers from the International Society for Extracellular Vesicles (ISEV), International Society for Advancement of Cytometry (ISAC), and the International Society on Thrombosis and Haemostasis (ISTH) joined forces and initiated the EV FCM working group. To improve the interpretation, reporting, and reproducibility of future EV FCM data, the EV FCM working group published an ISEV position manuscript outlining a framework of minimum information that should be reported about an FCM experiment on single EVs (MIFlowCyt-EV). However, the framework contains limited background information. Therefore, the goal of this compendium is to provide the background information necessary to design and conduct reproducible EV FCM experiments. This compendium contains background information on EVs, the interaction between light and EVs, FCM hardware, experimental design and preanalytical procedures, sample preparation, assay controls, instrument data acquisition and calibration, EV characterization, and data reporting. Although this compendium focuses on EVs, many concepts and explanations could also be applied to FCM detection of other particles within the EV size range, such as bacteria, lipoprotein particles, milk fat globules, and viruses.

Water-soluble extracellular vesicle probes based on conjugated oligoelectrolytes

We developed a series of transmembrane conjugated oligoelectrolytes (COEs) with tunable optical emissions from the UV to the near IR to address the false-positive problem when detecting nanometer-sized extracellular vesicles (EVs) by flow cytometry. The amphiphilic molecular framework of COEs is defined by a linear conjugated structure and cationic charged groups at each terminal site. Consequently, COEs have excellent water solubility and the absence of nanoaggregates at concentrations up to 50 μM, and unbound COE dyes can be readily removed through ultrafiltration. These properties enable unambiguous and simple detection of COE-labeled small EVs using flow cytometry with negligible background signals. We also demonstrated the time-lapsed tracking of small EV uptake into mammalian cells and the endogenous small EV labeling using COEs. Briefly, COEs provide a class of membrane-targeting dyes that behave as biomimetics of the lipid bilayer and a general and practical labeling strategy for nanosized EVs.

Removal of platelets from blood plasma to improve the quality of extracellular vesicle research

BACKGROUND

Blood plasma is commonly used for biomarker research of extracellular vesicles (EVs). Removing all cells prior to analysis of EVs is essential.

OBJECTIVES

We therefore studied the efficacy of the most commonly used centrifugation protocol to prepare cell-free plasma.

METHODS

Plasma was prepared according to the double centrifugation protocol of the International Society on Thrombosis and Haemostasis (ISTH) in three independent studies. The concentrations of platelets, platelet-derived EVs, and erythrocyte-derived EVs were measured by calibrated flow cytometry.

RESULTS

The mean platelet concentration ranged from 5.1 × 105 /ml to 2.8 × 107 /ml and differed 55-fold between studies. Thus, the ISTH centrifugation protocol does not remove all platelets and results in variation between studies. As the concentration of platelet-derived EVs and platelets correlates linearly (R2  = .56), and the volume fraction of EVs and platelets in plasma are similar, the presence of platelets affects downstream analysis. To remove platelets a 0.8-μm polycarbonate filter was used to lower the platelet concentration 146-fold (p = .0013), without affecting the concentration of platelet-derived and erythrocyte-derived EVs (p = .982, p = .742).

CONCLUSIONS

To improve the quality of EV research, we recommend (1) measuring and reporting the platelet concentration in plasma used for EV research, or (2) removing platelets by centrifugation followed by filtration.

Tissue chaperoning—the expanded functions of fetuin-A beyond inhibition of systemic calcification

Traditionally, fetuin-A embodies the prototype anti-calcification protein in the blood, preventing cardiovascular calcification. Low serum fetuin-A is generally associated with mineralization dysbalance and enhanced mortality in end stage renal disease. Recent evidence indicates that fetuin-A is a crucial factor moderating tissue inflammation and fibrosis, as well as a systemic indicator of acute inflammatory disease. Here, the expanded function of fetuin-A is discussed in the context of mineralization and inflammation biology. Unbalanced depletion of fetuin-A in this context may be the critical event, triggering a vicious cycle of progressive calcification, inflammation, and tissue injury. Hence, we designate fetuin-A as tissue chaperone and propose the potential use of exogenous fetuin-A as prophylactic agent or emergency treatment in conditions that are associated with acute depletion of endogenous protein.

Lipid-based strategies used to identify extracellular vesicles in flow cytometry can be confounded by lipoproteins: Evaluations of annexin V, lactadherin, and detergent lysis

Flow cytometry (FCM) is a popular method used in characterisation of extracellular vesicles (EVs). Circulating EVs are often identified by FCM by exploiting the lipid nature of EVs by staining with Annexin V (Anx5) or lactadherin against the membrane phospholipid phosphatidylserine (PS) and evaluating the specificity of the labels by detergent lysis of EVs. Here, we investigate whether PS labelling and detergent lysis approaches are confounded by lipoproteins, another family of lipid-based nanoparticles found in blood, in both frozen and fresh blood plasma. We demonstrated that Anx5 and lactadherin in addition to EVs stained ApoB-containing lipoproteins, identified by the use of fluorophore-labelled polyclonal ApoB-antibody, and that Anx5 had a significantly larger tendency for labelling lipoprotein-bound PS than lactadherin. Furthermore, detergent lysis resulted in a decrease in both EV and lipoprotein events and especially lipoproteins positive for either Anx5 or lactadherin. Taken together, our findings pose concerns to the use of lipid-based strategies in identifying EVs by FCM and support the use of transmembrane proteins such as tetraspannins to distinguish EVs from lipoproteins.

Measurement of canine blood microparticles by flow cytometry: effect of anticoagulants and staining reagents

Microparticles (MPs) are released from budding plasma membranes into body fluids. The use of flow cytometry for the measurement of MP in canines has not been standardized. In this fundamental study, we compared the effect of anticoagulant agents, such as acid-citrate-dextrose (ACD) and heparin on the measurement of canine MPs in platelet-free plasma (PFP) using flow cytometry. In addition, we used annexin V, carboxyfluorescein succinimidyl ester (CFSE), or calcein tetraacetoxymethyl ester (calcein-AM), and explored the characteristics of the staining reagents in MP detection using flow cytometry. We were able to measure canine MPs in PFP prepared from ACD-anticoagulated blood using flow cytometry, in which the highest positive rate for fluorescent staining was observed when CFSE was used.

Secreted therapeutics: monitoring durability of microRNA-based gene therapies in the central nervous system

The preclinical development of microRNA-based gene therapies for inherited neurodegenerative diseases is accompanied by translational challenges. Due to the inaccessibility of the brain to periodically evaluate therapy effects, accessible and reliable biomarkers indicative of dosing, durability and therapeutic efficacy in the central nervous system are very much needed. This is particularly important for viral vector-based gene therapies, in which a one-time administration results in long-term expression of active therapeutic molecules in the brain. Recently, extracellular vesicles have been identified as carriers of RNA species, including microRNAs, and proteins in all biological fluids, whilst becoming potential sources of biomarkers for diagnosis. In this study, we investigated the secretion and potential use of circulating miRNAs associated with extracellular vesicles as suitable sources to monitor the expression and durability of gene therapies in the brain. Neuronal cells derived from induced pluripotent stem cells were treated with adeno-associated viral vector serotype 5 carrying an engineered microRNA targeting huntingtin or ataxin3 gene sequences, the diseases-causing genes of Huntington disease and spinocerebellar ataxia type 3, respectively. After treatment, the secretion of mature engineered microRNA molecules was confirmed, with extracellular microRNA levels correlating with viral dose and cellular microRNA expression in neurons. We further investigated the detection of engineered microRNAs over time in the CSF of non-human primates after a single intrastriatal injection of adeno-associated viral vector serotype 5 carrying a huntingtin-targeting engineered microRNA. Quantifiable engineered microRNA levels enriched in extracellular vesicles were detected in the CSF up to two years after brain infusion. Altogether, these results confirm the long-term expression of adeno-associated viral vector serotype 5-delivered microRNAs and support the use of extracellular vesicle-associated microRNAs as novel translational pharmacokinetic markers in ongoing clinical trials of gene therapies for neurodegenerative diseases.

EDTA stabilizes the concentration of platelet-derived extracellular vesicles during blood collection and handling

Citrate is the recommended anticoagulant for studies on plasma extracellular vesicles (EVs). Because citrate incompletely blocks platelet activation and the release of platelet-derived EVs, we compared EDTA and citrate in that regard. Blood from healthy individuals (n = 7) was collected and incubated with thrombin receptor-activating peptide-6 (TRAP-6) to activate platelets, subjected to pneumatic tube transportation (n = 6), a freeze-thaw cycle (n = 10), and stored before plasma preparation (n = 6). Concentrations of EVs from platelets (CD61⁺), activated platelets (P-selectin⁺), erythrocytes (CD235a⁺), and leukocytes (CD45⁺) were measured by flow cytometry. Concentrations of EVs from platelets and activated platelets increased 1.4-fold and 1.9-fold in EDTA blood upon platelet activation, and 4.2-fold and 9.6-fold in citrate blood. Platelet EV concentrations were unaffected by pneumatic tube transport in EDTA blood but increased in citrate blood, and EV concentrations of erythrocytes and leukocytes were comparable. The stability of EVs during a freeze-thaw cycle was comparable for both anticoagulants. Finally, the concentration of platelet EVs was stable during storage of EDTA blood for six hours, whereas this concentration increased 1.5-fold for citrate blood. Thus, EDTA improves the robustness of studies on plasma EVs.

Extracellular Vesicles in Human Milk

Milk supports the growth and development of infants. An increasing number of mostly recent studies have demonstrated that milk contains a hitherto undescribed component called extracellular vesicles (EVs). This presents questions regarding why milk contains EVs and what their function is. Recently, we showed that EVs in human milk expose tissue factor, the protein that triggers coagulation or blood clotting, and that milk-derived EVs promote coagulation. Because bovine milk, which also contains EVs, completely lacks this coagulant activity, important differences are present in the biological functions of human milk-derived EVs between species. In this review, we will summarize the current knowledge regarding the presence and biochemical composition of milk EVs, their function(s) and potential clinical applications such as in probiotics, and the unique problems that milk EVs encounter in vivo, including survival of the gastrointestinal conditions encountered in the newborn. The main focus of this review will be human milk-derived EVs, but when available, we will also include information regarding non-human milk for comparison.

CM-Dil Staining and SEC of Plasma as an Approach to Increase Sensitivity of Extracellular Nanovesicles Quantification by Bead-Assisted Flow Cytometry

The quantification of the specific disease-associated populations of circulating extracellular membrane nanovesicles (ENVs) has opened up new opportunities for liquid biopsy in cancer and other chronic diseases. However, the sensitivity of such methods is mediated by an optimal combination of the isolation and labeling approaches, and is not yet sufficient for routine clinical application. The presented study aimed to develop, characterize, and explore a new approach to non-specific ENV staining, followed by size-exclusive chromatography (SEC), which allows us to increase the sensitivity of bead-assisted flow cytometry. Plasma from healthy donors was purified from large components, stained with lipophilic CM-Dil dye, and fractionated by means of SEC. The obtained fractions were analyzed in terms of particle size and concentration using NTA, as well as vesicular markers and plasma protein content via dot-blotting. We characterized the process of CM-Dil-stained plasma fractionation in detail and indicated the fractions with optimal characteristics. Finally, we explored the sensitivity of on-bead flow cytometry for the analysis of specific populations of plasma ENVs and demonstrated the advantages and limitations of the proposed technique.

Biophotonics for diagnostic detection of extracellular vesicles

Extracellular Vesicles (EVs) are versatile carriers for biomarkers involved in the pathogenesis of multiple human disorders. Despite the increasing scientific and commercial interest in EV application in diagnostics, traditional biomolecular techniques usually require consistent sample amount, rely on operator-dependent and time- consuming procedures and cannot cope with the nano-size range of EVs, limiting both sensitivity and reproducibility of results. The application of biophotonics, i.e. light-based methods, for the diagnostic detection of EVs has brought to the development of innovative platforms with excellent sensitivity. In this review, we propose an overview of the most promising and emerging technologies used in the field of EV-related biomarker discovery. When tested on clinical samples, the reported biophotonic approaches in most cases have managed to discriminate between nanovesicles and contaminants, achieved much higher resolution compared to traditional procedures, and reached moderate to excellent diagnostic accuracy, thus demonstrating great potentialities for their clinical translation.

Urinary Extracellular Vesicles for Diabetic Kidney Disease Diagnosis

Diabetic kidney disease (DKD) is the leading cause of end stage renal disease (ESRD) in developed countries, affecting more than 40% of diabetes mellitus (DM) patients. DKD pathogenesis is multifactorial leading to a clinical presentation characterized by proteinuria, hypertension, and a gradual reduction in kidney function, accompanied by a high incidence of cardiovascular (CV) events and mortality. Unlike other diabetes-related complications, DKD prevalence has failed to decline over the past 30 years, becoming a growing socioeconomic burden. Treatments controlling glucose levels, albuminuria and blood pressure may slow down DKD evolution and reduce CV events, but are not able to completely halt its progression. Moreover, one in five patients with diabetes develop DKD in the absence of albuminuria, and in others nephropathy goes unrecognized at the time of diagnosis, urging to find novel noninvasive and more precise early diagnosis and prognosis biomarkers and therapeutic targets for these patient subgroups. Extracellular vesicles (EVs), especially urinary (u)EVs, have emerged as an alternative for this purpose, as changes in their numbers and composition have been reported in clinical conditions involving DM and renal diseases. In this review, we will summarize the current knowledge on the role of (u)EVs in DKD.

Extracellular Vesicle-Based Therapeutics for Heart Repair

Extracellular vesicles (EVs) are constituted by a group of heterogeneous membrane vesicles secreted by most cell types that play a crucial role in cell–cell communication. In recent years, EVs have been postulated as a relevant novel therapeutic option for cardiovascular diseases, including myocardial infarction (MI), partially outperforming cell therapy. EVs may present several desirable features, such as no tumorigenicity, low immunogenic potential, high stability, and fine cardiac reparative efficacy. Furthermore, the natural origin of EVs makes them exceptional vehicles for drug delivery. EVs may overcome many of the limitations associated with current drug delivery systems (DDS), as they can travel long distances in body fluids, cross biological barriers, and deliver their cargo to recipient cells, among others. Here, we provide an overview of the most recent discoveries regarding the therapeutic potential of EVs for addressing cardiac damage after MI. In addition, we review the use of bioengineered EVs for targeted cardiac delivery and present some recent advances for exploiting EVs as DDS. Finally, we also discuss some of the most crucial aspects that should be addressed before a widespread translation to the clinical arena.

A simple, high-throughput method of protein and label removal from extracellular vesicle samples

Evidence continues to increase of the clinical utility extracellular vesicles (EVs) as translational biomarkers. While a wide variety of EV isolation and purification methods have been implemented, few techniques are high-throughput and scalable for removing excess fluorescent reagents (e.g. dyes, antibodies). EVs are too small to be recovered from routine cell-processing procedures, such as filtration or centrifugation. The lack of suitable methods for removing unbound labels, especially in optical assays, is a major roadblock to accurate EV phenotyping and utilization of EV assays in a translational or clinical setting. Therefore, we developed a method for using a multi-modal resin, referred to as EV-Clean, to remove unbound labels from EV samples, and we demonstrate improvement in flow cytometric EV analysis with the use of this EV-Clean method.

Calciprotein particles: mineral behaving badly?

PURPOSE OF REVIEW

Calciprotein particles (CPP) are formed in supersaturated solutions of calcium, phosphate and the mineral-binding protein fetuin-A. CPP have garnered considerable interest as potential mediators of mineral stress, but little consideration has been given to their origin, clearance and role in metabolism.

RECENT FINDINGS

CPP are made whilst buffering the mineral absorbed from the intestine after a meal or during remodelling of bone matrix. The postprandial rise in circulating CPP rise may be sensed by osteoblasts/osteocytes in bone, stimulating the secretion of the master phosphatonin fibroblast growth factor 23. Amorphous calcium phosphate-containing CPP are rapidly cleared by endothelial cells in the liver whereas crystalline apatite-containing CPP are filtered by phagocytic cells of the reticuloendothelial system. Impaired excretory function in kidney disease may lead to accumulation of CPP and its precursors with possible pathological sequalae. Inability to stabilize CPP in fetuin-A-deficiency states can result in intraluminal precipitation and inflammatory cascades if other mineralisation regulatory networks are compromised.

SUMMARY

CPP allow efficient transport and clearance of bulk calcium phosphate as colloids without risk of precipitation. As circulating factors, CPP may couple dietary mineral exposure with endocrine control of mineral metabolism in bone, signalling the need to dispose of excess phosphate from the body.

Comparison of extracellular vesicle isolation and storage methods using high-sensitivity flow cytometry

Extracellular vesicles (EVs) are of interest for a wide variety of biomedical applications. A major limitation for the clinical use of EVs is the lack of standardized methods for the fast and reproducible separation and subsequent detection of EV subpopulations from biofluids, as well as their storage. To advance this application area, fluorescence-based characterization technologies with single-EV resolution, such as high-sensitivity flow cytometry (HS-FCM), are powerful to allow assessment of EV fractionation methods and storage conditions. Furthermore, the use of HS-FCM and fluorescent labeling of EV subsets is expanding due to the potential of high-throughput, multiplex analysis, but requires further method development to enhance the reproducibility of measurements. In this study, we have applied HS-FCM measurements next to standard EV characterization techniques, including nanoparticle tracking analysis, to compare the yield and purity of EV fractions obtained from lipopolysaccharide-stimulated monocytic THP-1 cells by two EV isolation methods, differential centrifugation followed by ultracentrifugation and the exoEasy membrane affinity spin column purification. We observed differences in EV yield and purity. In addition, we have investigated the influence of EV storage at 4°C or -80°C for up to one month on the EV concentration and the stability of EV-associated fluorescent labels. The concentration of the in vitro cell derived EV fractions was shown to remain stable under the tested storage conditions, however, the fluorescence intensity of labeled EV stored at 4°C started to decline within one day.

Recombinant extracellular vesicles as biological reference material for method development, data normalization and assessment of (pre-)analytical variables

The diagnostic and therapeutic use of extracellular vesicles (EV) is under intense investigation and may lead to societal benefits. Reference materials are an invaluable resource for developing, improving and assessing the performance of regulated EV applications and for quantitative and objective data interpretation. We have engineered recombinant EV (rEV) as a biological reference material. rEV have similar biochemical and biophysical characteristics to sample EV and function as an internal quantitative and qualitative control throughout analysis. Spiking rEV in bodily fluids prior to EV analysis maps technical variability of EV applications and promotes intra- and inter-laboratory studies. This protocol, which is an Extension to our previously published protocol (Tulkens et al., 2020), describes the production, separation and quality assurance of rEV, their dilution and addition to bodily fluids, and the detection steps based on complementary fluorescence, nucleic acid and protein measurements. We demonstrate the use of rEV for method development, data normalization and assessment of pre-analytical variables. The protocol can be adopted by researchers with standard laboratory and basic EV separation/characterization experience and requires ~4-5 d.

Plasma Concentrations of Extracellular Vesicles Are Decreased in Patients with Post-Infarct Cardiac Remodelling

Simple Summary

A heart attack may lead to the remodelling of the cardiac muscle, which negatively affects patient’s prognosis. At present, the mechanisms of cardiac remodelling remain unclear. In patients with heart attack, many body cells become activated and release small particles, called extracellular vesicles, which can either aggravate cardiac injury, or contribute to healing of heart muscle. In our study, we hypothesized that the concentrations of these small particles in plasma allow to determine which patients will experience remodelling of the cardiac muscle after the heart attach. We found that concentrations of extracellular vesicles from endothelial cells, erythrocytes and platelets, measured directly the heart attack, were lower in patients who developed cardiac remodelling 6 months later, compared to patients who had no remodelling. Vesicles from endothelial cells and erythrocytes allowed to determine remodelling independently of other clinical features. Hence, decreased concentrations of these vesicles may on one hand be a sign of inappropriate cardiac repair mechanisms, and on the other hand may allow to identify patients, who will develop cardiac remodelling after the heart attack.

Abstract

Background, the mechanisms underlying left ventricular remodelling (LVR) after acute myocardial infarction (AMI) remain obscure. In the course of AMI, blood cells and endothelial cells release extracellular vesicles (EVs). We hypothesized that changes in EV concentrations after AMI may underlie LVR. Methods, plasma concentrations of EVs from endothelial cells (CD146+), erythrocytes (CD235a+), leukocytes (CD45+), platelets (CD61+), activated platelets (P-selectin+), and EVs exposing phosphatidylserine after AMI were determined by flow cytometry in 55 patients with the first AMI. LVR was defined as an increase in left ventricular end-diastolic volume by 20% at 6 months after AMI, compared to baseline. Results, baseline concentrations of EVs from endothelial cells, erythrocytes and platelets were lower in patients who developed LVR (p ≤ 0.02 for all). Concentrations of EVs from endothelial cells and erythrocytes were independent LVR predictors (OR 8.2, CI 1.3–54.2 and OR 17.8, CI 2.3–138.6, respectively) in multivariate analysis. Combining the three EV subtypes allowed to predict LVR with 83% sensitivity and 87% specificity. Conclusions, decreased plasma concentrations of EVs from endothelial cells, erythrocytes and platelets predict LVR after AMI. Since EV release EVs contributes to cellular homeostasis by waste removal, decreased concentrations of EVs may indicate dysfunctional cardiac homeostasis after AMI, thus promoting LVR.

Conventional, High-Resolution and Imaging Flow Cytometry: Benchmarking Performance in Characterisation of Extracellular Vesicles

Flow cytometry remains a commonly used methodology due to its ability to characterise multiple parameters on single particles in a high-throughput manner. In order to address limitations with lacking sensitivity of conventional flow cytometry to characterise extracellular vesicles (EVs), novel, highly sensitive platforms, such as high-resolution and imaging flow cytometers, have been developed. We provided comparative benchmarks of a conventional FACS Aria III, a high-resolution Apogee A60 Micro-PLUS and the ImageStream X Mk II imaging flow cytometry platform. Nanospheres were used to systematically characterise the abilities of each platform to detect and quantify populations with different sizes, refractive indices and fluorescence properties, and the repeatability in concentration determinations was reported for each population. We evaluated the ability of the three platforms to detect different EV phenotypes in blood plasma and the intra-day, inter-day and global variabilities in determining EV concentrations. By applying this or similar methodology to characterise methods, researchers would be able to make informed decisions on choice of platforms and thereby be able to match suitable flow cytometry platforms with projects based on the needs of each individual project. This would greatly contribute to improving the robustness and reproducibility of EV studies.

Cellular origin and microRNA profiles of circulating extracellular vesicles in different stages of diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes and the main cause of end-stage renal disease. Extracellular vesicles (EVs) are small cell-derived vesicles that can alter disease progression by microRNA (miRNA) transfer.

METHODS

In this study, we aimed to characterize the cellular origin and miRNA content of EVs in plasma samples of type 2 diabetes patients at various stages of DN. Type 2 diabetes patients were classified in three groups: normoalbuminuria, microalbuminuria and macroalbuminuria. The concentration and cellular origin of plasma EVs were measured by flow cytometry. A total of 752 EV miRNAs were profiled in 18 subjects and differentially expressed miRNAs were validated.

RESULTS

Diabetic patients with microalbuminuria and/or macroalbuminuria showed elevated concentrations of total EVs and EVs from endothelial cells, platelets, leucocytes and erythrocytes compared with diabetic controls. miR-99a-5p was upregulated in macroalbuminuric patients compared with normoalbuminuric and microalbuminuric patients. Transfection of miR-99a-5p in cultured human podocytes downregulated mammalian target of rapamycin (mTOR) protein expression and downregulated the podocyte injury marker vimentin.

CONCLUSIONS

Type 2 diabetes patients with microalbuminuria and macroalbuminuria display differential EV profiles. miR-99a-5p expression is elevated in EVs from macroalbuminuria and mTOR is its validated mRNA target.

Considerations for the Analysis of Small Extracellular Vesicles in Physical Exercise

Physical exercise induces acute physiological changes leading to enhanced tissue cross-talk and a liberation of extracellular vesicles (EVs) into the circulation. EVs are cell-derived membranous entities which carry bioactive material, such as proteins and RNA species, and are important mediators of cell-cell-communication. Different types of physical exercise interventions trigger the release of diverse EV subpopulations, which are hypothesized to be involved in physiological adaptation processes leading to health benefits and longevity. Large EVs (“microvesicles” and “microparticles”) are studied frequently in the context of physical exercise using straight forward flow cytometry approaches. However, the analysis of small EVs (sEVs) including exosomes is hampered by the complex composition of blood, confounding the methodology of EV isolation and characterization. This mini review presents a concise overview of the current state of research on sEVs released upon physical exercise (ExerVs), highlighting the technical limits of ExerV analysis. The purity of EV preparations is highly influenced by the co-isolation of non-EV structures in the size range or density of EVs, such as lipoproteins and protein aggregates. Technical constraints associated with EV purification challenge the quantification of distinct ExerV populations, the identification of their cargo, and the investigation of their biological functions. Here, we offer recommendations for the isolation and characterization of ExerVs to minimize the effects of these drawbacks. Technological advances in the ExerV research field will improve understanding of the inter-cellular cross-talk induced by physical exercise leading to health benefits.

Multiple factors are involved in regulation of extracellular membrane vesicle biogenesis in Streptococcus mutans

Streptococcus mutans, a major etiological agent of human dental caries, produces membrane vesicles (MVs) that contain protein and extracellular DNA. In this study, functional genomics, along with in vitro biofilm models, was used to identify factors that regulate MV biogenesis. Our results showed that when added to growth medium, MVs significantly enhanced biofilm formation by S. mutans, especially during growth in sucrose. This effect occurred in the presence and absence of added human saliva. Functional genomics revealed several genes, including sfp, which have a major effect on S. mutans MVs. In Bacillus sp. sfp encodes a 4'-phosphopantetheinyl transferase that contributes to surfactin biosynthesis and impacts vesiculogenesis. In S. mutans, sfp resides within the TnSmu2 Genomic Island that supports pigment production associated with oxidative stress tolerance. Compared to the UA159 parent, the Δsfp mutant, TW406, demonstrated a 1.74-fold (p < .05) higher MV yield as measured by BCA protein assay. This mutant also displayed increased susceptibility to low pH and oxidative stressors, as demonstrated by acid killing and hydrogen peroxide challenge assays. Deficiency of bacA, a putative surfactin synthetase homolog within TnSmu2, and especially dac and pdeA that encode a di-adenylyl cyclase and a phosphodiesterase, respectively, also significantly increased MV yield (p < .05). However, elimination of bacA2, a bacitracin synthetase homolog, resulted in a >1.5-fold (p < .05) reduction of MV yield. These results demonstrate that S. mutans MV properties are regulated by genes within and outside of the TnSmu2 island, and that as a major particulate component of the biofilm matrix, MVs significantly influence biofilm formation.

Exosomes in disease and regeneration: biological functions, diagnostics, and beneficial effects

Exosomes are a subtype of extracellular vesicles. They range from 30 to 150 nm in diameter and originate from intraluminal vesicles. Exosomes were first identified as the mechanism for releasing unnecessary molecules from reticulocytes as they matured to red blood cells. Since then, exosomes have been shown to be secreted by a broad spectrum of cells and play an important role in the cardiovascular system. Different stimuli are associated with increased exosome release and result in different exosome content. The release of harmful DNA and other molecules via exosomes has been proposed as a mechanism to maintain cellular homeostasis. Because exosomes contain parent cell-specific proteins on the membrane and in the cargo that is delivered to recipient cells, exosomes are potential diagnostic biomarkers of various types of diseases, including cardiovascular disease. As exosomes are readily taken up by other cells, stem cell-derived exosomes have been recognized as a potential cell-free regenerative therapy to repair not only the injured heart but other tissues as well. The objective of this review is to provide an overview of the biological functions of exosomes in heart disease and tissue regeneration. Therefore, state-of-the-art methods for exosome isolation and characterization, as well as approaches to assess exosome functional properties, are reviewed. Investigation of exosomes provides a new approach to the study of disease and biological processes. Exosomes provide a potential "liquid biopsy," as they are present in most, if not all, biological fluids that are released by a wide range of cell types.

An Emerging Fluorescence-Based Technique for Quantification and Protein Profiling of Extracellular Vesicles

Robust and well-established techniques for the quantification and characterization of extracellular vesicles (EVs) are a crucial need for the utilization of EVs as potential diagnostic and therapeutic tools. Current bulk analysis techniques such as proteomics and Western blot suffer from low resolution in the detection of small changes in target marker expression levels, exemplified by the heterogeneity of EVs. Microscopy-based techniques can provide valuable information from individual EVs; however, they are time-consuming and statistically less powerful than other techniques. Flow cytometry has been successfully employed for the quantification and characterization of individual EVs within larger populations. However, traditional flow cytometry is not highly suited for the examination of smaller, submicron particles. Here we demonstrate the accurate and precise quantification of nanoparticles such as EVs using the Virus Counter 3100 (VC3100) platform, a fluorescence-based technique that uses the principles of flow cytometry with critical enhancements to enable the effective detection of smaller particles. This approach can detect nanoparticles precisely with no evidence of inaccurate concentration measurement from masking effects associated with traditional nanoparticle tracking analysis (NTA). Fluorescently labeled EVs from different sources were successfully quantified using the VC3100 without a postlabeling washing step. Moreover, protein profiling and characterization of individual EVs were achieved and have been shown to determine the expression level of target protein markers.

Employing Flow Cytometry to Extracellular Vesicles Sample Microvolume Analysis and Quality Control

Extracellular Vesicles (EVs), membrane vesicles released by all cells, are emerging mediators of cell-cell communication. By carrying biomolecules from tissues to biofluids, EVs have attracted attention as non-invasive sources of clinical biomarkers in liquid biopsies. EVs-based liquid biopsies usually require EVs isolation before content analysis, which frequently increases sample volume requirements. We here present a Flow Cytometry (FC) strategy that does not require isolation or concentration of EVs prior to staining. By doing so, it enables population analysis of EVs in samples characterized by challenging small volumes, while reducing overall sample processing time. To illustrate its application, we performed longitudinal non-lethal population analysis of EVs in mouse plasma and in single-animal collections of murine vitreous humor. By quantifying the proportion of vesicular particles in purified and non-purified biological samples, this method also serves as a precious tool to quality control isolates of EVs purified by different protocols. Our FC strategy has an unexplored clinical potential to analyze EVs in biofluids with intrinsically limited volumes and to multiply the number of different analytes in EVs that can be studied from a single collection of biofluid.

Reliable measurements of extracellular vesicles by clinical flow cytometry

Extracellular vesicles (EVs) are cell‐derived particles with a phospholipid membrane present in all body fluids. Because EV properties change in health and disease, EVs have excellent potential to become biomarkers for diagnosis, prognosis, or monitoring of disease. The only technique capable of detecting, sizing, and phenotyping a million of EVs within minutes is (clinical) flow cytometry. A flow cytometer measures light scattering and fluorescence signals of single EVs. Although these signals contain valuable information about the presence and composition of EVs, the signals are expressed in arbitrary units, which make the comparison of measurement results impossible between instruments and laboratories. Additionally, unintended and undocumented variations in the source, preparation, and analysis of the sample lead to orders of magnitude variations in the measured EV concentrations. Here, we will explain the basics, challenges, and common misconceptions of EV flow cytometry. In addition, we provide an overview of recent standardization initiatives, which are a prerequisite for comparison of clinical data and thus for clinical biomarker exploration of EVs.

Fluorescent labeling of extracellular vesicles

Fluorescent labeling of extracellular vesicles (EVs) enables studying their uptake and influence on individual cells, biodistribution as well as facilitates their characterization using high-resolution flow cytometry at a single EV level. Here we describe the importance of fluorescent labeling, the available fluorescent dyes and labeling approaches, the characteristics of an ideal dye, and the available techniques for post-labeling purification. We discuss the importance of preserving the size of EVs for uptake, biodistribution, and characterization studies and focus on the effect of common lipophilic PKH and luminal CFSE dyes on the size of EVs. Lastly, we present an example protocol for luminal labeling of EVs and characterization of the effect of labeling on the size of EVs using nanoparticles tracking analysis (NTA).

Mud in the blood: the role of protein-mineral complexes and extracellular vesicles in biomineralisation and calcification

Protein-mineral interaction is known to regulate biomineral stability and morphology. We hypothesise that fluid phases produce highly dynamic protein-mineral complexes involved in physiology and pathology of biomineralisation. Here, we specifically focus on calciprotein particles, complexes of vertebrate mineral-binding proteins and calcium phosphate present in the systemic circulation and abundant in extracellular fluids - hence the designation of the ensuing protein-mineral complexes as "mud in the blood". These complexes exist amongst other extracellular particles that we collectively refer to as "the particle zoo".

Cancer-ID: Toward Identification of Cancer by Tumor-Derived Extracellular Vesicles in Blood

Extracellular vesicles (EVs) have great potential as biomarkers since their composition and concentration in biofluids are disease state dependent and their cargo can contain disease-related information. Large tumor-derived EVs (tdEVs, >1 μm) in blood from cancer patients are associated with poor outcome, and changes in their number can be used to monitor therapy effectiveness. Whereas, small tumor-derived EVs (<1 μm) are likely to outnumber their larger counterparts, thereby offering better statistical significance, identification and quantification of small tdEVs are more challenging. In the blood of cancer patients, a subpopulation of EVs originate from tumor cells, but these EVs are outnumbered by non-EV particles and EVs from other origin. In the Dutch NWO Perspectief Cancer-ID program, we developed and evaluated detection and characterization techniques to distinguish EVs from non-EV particles and other EVs. Despite low signal amplitudes, we identified characteristics of these small tdEVs that may enable the enumeration of small tdEVs and extract relevant information. The insights obtained from Cancer-ID can help to explore the full potential of tdEVs in the clinic.

Detection of extracellular vesicles in plasma and urine of prostate cancer patients by flow cytometry and surface plasmon resonance imaging

Large (> 1 μm) tumor-derived extracellular vesicles (tdEVs) enriched from the cell fraction of centrifuged whole blood are prognostic in metastatic castration-resistant prostate cancer (mCRPC) patients. However, the highest concentration of tdEVs is expected in the cell-free plasma fraction. In this pilot study, we determine whether mCRPC patients can be discriminated from healthy controls based on detection of tdEVs (< 1μm, EpCAM+) and/or other EVs, in cell-free plasma and/or urine. The presence of marker+ EVs in plasma and urine samples from mCRPC patients (n = 5) and healthy controls (n = 5) was determined by flow cytometry (FCM) and surface plasmon resonance imaging (SPRi) using an antibody panel and lactadherin. For FCM, the concentrations of marker positive (+) particles and EVs (refractive index <1.42) were determined. Only the lactadherin+ particle and EV concentration in plasma measured by FCM differed significantly between patients and controls (p = 0.017). All other markers did not result in signals exceeding the background on both FCM and SPRi, or did not differ significantly between patients and controls. In conclusion, no difference was found between patients and controls based on the detection of tdEVs. For FCM, the measured sample volumes are too small to detect tdEVs. For SPRi, the concentration of tdEVs is probably too low to be detected. Thus, to detect tdEVs in cell-free plasma and/or urine, EV enrichment and/or concentration is required. Furthermore, we recommend testing other markers and/or a combination of markers to discriminate mCRPC patients from healthy controls.

Improved Flow Cytometric Light Scatter Detection of Submicron-Sized Particles by Reduction of Optical Background Signals

Flow cytometry allows multiparameter analysis on a single‐cell basis and is currently the method of choice to rapidly assess heterogeneity of cell populations in suspension. With the research field of extracellular vesicles (EV) rapidly expanding, there is an increased demand to address heterogeneity of EV populations in biological samples. Although flow cytometry would be the ideal technique to do so, the available instruments are in general not equipped to optimally detect the dim light scatter signals generated by submicron‐sized particles like EV. Although sideward scatter light and fluorescence are currently used as a threshold signal to identify EV within samples, the forward scatter light (FSC) parameter is often neglected due to the lack of resolution to distinguish EV‐related signals from noise. However, after optimization of FSC detection by adjusting the size of the obscuration bar, we recently showed that certain EV‐subsets could only be identified based on FSC. This observation made us to further study the possibilities to enhance FSC‐detection of submicron‐sized particles. By testing differently sized obscuration bars and differently sized pinholes in the focal plane behind the FSC detection lens, we generated a matrix that allowed us to determine which combination resulted in the lowest optical background in terms of numbers of events regarding FSC detection of submicron‐sized particles. We found that a combination of an 8‐mm obscuration bar and a 200‐μm pinhole reduced optical background in a reproducible manner to such extent that it allowed a robust separation of 100‐nm polystyrene beads from background signals within the FSC channel, and even allowed thresholding on FSC without the interference of massive background signals when both beads and EV were measured. These technical adaptations thus significantly improved FSC detection of submicron‐sized particles and provide an important lead for the further development and design of flow cytometers that aid in detection of submicron‐sized particles. © 2020 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Purification and Analysis of Caenorhabditis elegans Extracellular Vesicles

The secretion of small membrane-bound vesicles into the external environment is a fundamental physiological process of all cells. These extracellular vesicles (EVs) function outside the cell to regulate global physiological processes by transferring proteins, nucleic acids, metabolites, and lipids between tissues. EVs reflect the physiological state of their cells of origin. EVs are implicated to have fundamental roles in virtually every aspect of human health. Thus, EV protein and genetic cargos are being increasingly analyzed for biomarkers of health and disease. However, the EV field still lacks a tractable invertebrate model system that permits the study of EV cargo composition. C. elegans is well suited for EV research because it actively secretes EVs outside of its body into its external environment, permitting facile isolation. This article provides all the necessary information for generating, purifying, and quantifying these environmentally secreted C. elegans EVs including how to work quantitatively with very large populations of age-synchronized worms, purifying EVs, and a flow cytometry protocol that directly measures the number of intact EVs in the purified sample. Thus, the large library of genetic reagents available for C. elegans research can be tapped into for investigating the impacts of genetic pathways and physiological processes on EV cargo composition.

Ticagrelor attenuates the increase of extracellular vesicle concentrations in plasma after acute myocardial infarction compared to clopidogrel

BACKGROUND

Platelet P2Y12 antagonist ticagrelor reduces mortality after acute myocardial infarction (AMI) compared to clopidogrel, but the underlying mechanism is unknown. Because activated platelets, leukocytes, and endothelial cells release proinflammatory and prothrombotic extracellular vesicles (EVs), we hypothesized that the release of EVs is more efficiently inhibited by ticagrelor compared to clopidogrel.

OBJECTIVES

We compared EV concentrations and EV procoagulant activity in plasma of patients after AMI treated with ticagrelor or clopidogrel.

METHODS

After percutaneous coronary intervention, 60 patients with first AMI were randomized to ticagrelor or clopidogrel. Flow cytometry was used to determine concentrations of EVs from activated platelets (CD61+ , CD62p+ ), fibrinogen+ , phosphatidylserine (PS+ ), leukocytes (CD45+ ), endothelial cells (CD31+ , 146+ ), and erythrocytes (CD235a+ ) in plasma at randomization, after 72 hours and 6 months of treatment. A fibrin generation test was used to determine EV procoagulant activity.

RESULTS

Concentrations of platelet, fibrinogen+ , PS+ , leukocyte, and erythrocyte EVs increased 6 months after AMI compared to the acute phase of AMI (P ≤ .03). Concentrations of platelet EVs were lower on ticagrelor compared to clopidogrel after 6 months (P = .03). Concentrations of fibrinogen+ , PS+ , and leukocyte EVs were lower on ticagrelor compared to clopidogrel both after 72 hours and 6 months (P ≤ .03). Concentrations of endothelial EVs and EV procoagulant activity did not differ between patient groups and over time (P ≥ .17).

CONCLUSIONS

Ticagrelor attenuates the increase of EV concentrations in plasma after acute myocardial infarction compared to clopidogrel. The ongoing release of EVs despite antiplatelet therapy might explain recurrent thrombotic events after AMI and worse clinical outcomes on clopidogrel compared to ticagrelor.

Transcytosis of Bacillus subtilis extracellular vesicles through an in vitro intestinal epithelial cell model

Bacterial EVs have been related to inter-kingdom communication between probiotic/pathogenic bacteria and their hosts. Our aim was to investigate the transcytosis process of B. subtilis EVs using an in vitro intestinal epithelial cell model. In this study, using Confocal Laser Scanning Microscopy, we report that uptake and internalization of CFSE-labeled B. subtilis EVs (115 nm ± 27 nm) by Caco-2 cells are time-dependent. To study the transcytosis process we used a transwell system and EVs were quantified in the lower chamber by Fluorescence and Nanoparticle Tracking Analysis measurements. Intact EVs are transported across a polarized cell monolayer at 60-120 min and increased after 240 min with an estimated average uptake efficiency of 30% and this process is dose-dependent. EVs movement into intestinal epithelial cells was mainly through Z axis and scarcely on X and Y axis. This work demonstrates that EVs could be transported across the gastrointestinal epithelium. We speculate this mechanism could be the first step allowing EVs to reach the bloodstream for further delivery up to extraintestinal tissues and organs. The expression and further encapsulation of bioactive molecules into natural nanoparticles produced by probiotic bacteria could have practical implications in food, nutraceuticals and clinical therapies.

Label-free identification and chemical characterisation of single extracellular vesicles and lipoproteins by synchronous Rayleigh and Raman scattering

Extracellular vesicles (EVs) present in blood originate from cells of different origins such as red blood cells (RBCs), platelets and leukocytes. In patients with cancer, a small portion of EVs originate from tumour cells and their load is associated with poor clinical outcome. Identification of these tumour-derived extracellular vesicles (tdEVs) is difficult as they are outnumbered by EVs of different tissue of origin as well a large number of lipoproteins (LPs) that are in the same size range. In order to detect tdEVs from the abundant presence of other particles, single-particle techniques are necessary. Here, synchronous Rayleigh and Raman scattering is used for that purpose. This combination of light scattering techniques identifies optically trapped single particles based on Rayleigh scattering and distinguishes differences in chemical composition of particle populations based on Raman scattering. Here, we show that tdEVs can be distinguished from RBC EVs and LPs in a label-free manner and directly in suspension.

MIFlowCyt-EV: a framework for standardized reporting of extracellular vesicle flow cytometry experiments

Extracellular vesicles (EVs) are small, heterogeneous and difficult to measure. Flow cytometry (FC) is a key technology for the measurement of individual particles, but its application to the analysis of EVs and other submicron particles has presented many challenges and has produced a number of controversial results, in part due to limitations of instrument detection, lack of robust methods and ambiguities in how data should be interpreted. These complications are exacerbated by the field's lack of a robust reporting framework, and many EV-FC manuscripts include incomplete descriptions of methods and results, contain artefacts stemming from an insufficient instrument sensitivity and inappropriate experimental design and lack appropriate calibration and standardization. To address these issues, a working group (WG) of EV-FC researchers from ISEV, ISAC and ISTH, worked together as an EV-FC WG and developed a consensus framework for the minimum information that should be provided regarding EV-FC. This framework incorporates the existing Minimum Information for Studies of EVs (MISEV) guidelines and Minimum Information about a FC experiment (MIFlowCyt) standard in an EV-FC-specific reporting framework (MIFlowCyt-EV) that supports reporting of critical information related to sample staining, EV detection and measurement and experimental design in manuscripts that report EV-FC data. MIFlowCyt-EV provides a structure for sharing EV-FC results, but it does not prescribe specific protocols, as there will continue to be rapid evolution of instruments and methods for the foreseeable future. MIFlowCyt-EV accommodates this evolution, while providing information needed to evaluate and compare different approaches. Because MIFlowCyt-EV will ensure consistency in the manner of reporting of EV-FC studies, over time we expect that adoption of MIFlowCyt-EV as a standard for reporting EV- FC studies will improve the ability to quantitatively compare results from different laboratories and to support the development of new instruments and assays for improved measurement of EVs.

Tumour-derived extracellular vesicles in blood of metastatic cancer patients associate with overall survival

BACKGROUND

Circulating tumour cells (CTCs) in blood associate with overall survival (OS) of cancer patients, but they are detected in extremely low numbers. Large tumour-derived extracellular vesicles (tdEVs) in castration-resistant prostate cancer (CRPC) patients are present at around 20 times higher frequencies than CTCs and have equivalent prognostic power. In this study, we explored the presence of tdEVs in other cancers and their association with OS.

METHODS

The open-source ACCEPT software was used to automatically enumerate tdEVs in digitally stored CellSearch® images obtained from previously reported CTC studies evaluating OS in 190 CRPC, 450 metastatic colorectal cancer (mCRC), 179 metastatic breast cancer (MBC) and 137 non-small cell lung cancer (NSCLC) patients before the initiation of a new treatment.

RESULTS

Presence of unfavourable CTCs and tdEVs is predictive of OS, with respective hazard ratios (HRs) of 2.4 and 2.2 in CRPC, 2.7 and 2.2 in MBC, 2.3 and 1.9 in mCRC and 2.0 and 2.4 in NSCLC, respectively.

CONCLUSIONS

tdEVs have equivalent prognostic value as CTCs in the investigated metastatic cancers. CRPC, mCRC, and MBC (but not NSCLC) patients with favourable CTC counts can be further prognostically stratified using tdEVs. Our data suggest that tdEVs could be used in clinical decision-making.

Aptasensor-enabled quantitative analysis of nano-sized extracellular vesicles by flow cytometry

Flow cytometry analysis of extracellular vesicles enabled by an aptamer-based biosensor to interact with tetraspanin CD63 proteins.

Detection and Quantification of Extracellular Vesicles via FACS: Membrane Labeling Matters!

The field of extracellular vesicle (EV) research is challenged by the lack of standardized protocols to identify and specifically distinguish between exosomes and ectosomes, which are released via exocytosis or plasma membrane shedding, respectively. Using sequential centrifugation, we separated EV subpopulations from supernatants of COLO 357 pancreas carcinoma cells based on size and mass. After 10,000× g centrifugation, we reconstituted high-speed (hs) EVs from the pellet, directly labeled them with the membrane dye carboxyfluorescein diacetate succinimidyl ester (CFSE), and performed flow cytometry based analysis. The aim was to optimize the conditions for EV labeling and detection and hence to obtain a maximum yield of intact hsEVs. We found that, for sufficient labeling of EVs, minimal temperature variations and short incubation times correlated with EV stability. Furthermore, threshold adjustment significantly improved the sensitivity of the flow cytometer for the detection of CFSE labeled hsEVs. When cells were CFSE labeled, we observed a transition of fluorescence onto EVs that were reconstituted from the pellet but not onto those that remained in the supernatant after hs centrifugation, suggesting the indirect labeling of EVs based on the way of biogenesis as a specific method for the distinction of exosomes and ectosomes. Protocol standardization is of major importance for the use of EVs as diagnostic markers in liquid biopsies.

Extracellular vesicles and coagulation in blood from healthy humans revisited

Background: In 2001, we studied the presence and coagulant properties of “microparticles” in the blood of healthy humans. Since then, multiple improvements in detection, isolation and functional characterization of the now called “extracellular vesicles” (EVs) have been made, and shortcomings were identified. Aim: To revisit the presence and function of EVs in blood from healthy humans. Methods: Blood was collected from 20 healthy donors. EV-containing plasma was prepared according to new guidelines, and plasma was diluted to prevent swarm detection. Single EVs were measured by flow cytometry with known sensitivity of fluorescence and light scatter. The haemostatic properties of EVs were measured by thrombin-, fibrin-, and plasmin generation. Plasma concentrations of thrombin-antithrombin complexes and prothrombin fragment 1 + 2 were measured to assess the coagulation status in vivo. Results: Compared to 2001, the total concentrations of detected EVs increased from 190- to 264-fold. In contrast to 2001, however, EVs are non-coagulant which we show can be attributed to improvements in blood collection and plasma preparation. No relation is present between the plasma concentrations of EVs and either TAT or F1 + 2. Finally, we show that EVs support plasmin generation. Discussion: Improvements in blood collection, plasma preparation and detection of EVs reveal that results from earlier studies have to be interpreted with care. Compared to 2001, higher concentrations of EVs are detected in blood of healthy humans which promote fibrinolysis rather than coagulation.