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

Monitoring and reporting the composition of plasma and serum to improve biobanks and comparability of extracellular vesicle research: communication from the ISTH SSC Subcommittee on Vascular Biology

Transparent reporting is key to improving the reproducibility of scientific research. In 2023, the International Society for Extracellular Vesicles updated the "Minimal information for studies of extracellular vesicles" (MISEV) reporting guidelines and published new recommendations for blood extracellular vesicle (EV) research entitled "MIBlood-EV: Minimal information to enhance the quality and reproducibility of blood extracellular vesicle research." The MIBlood-EV recommendations are part of MISEV 2023 and promote reporting not only the protocols used for blood collection and handling but also the composition of the prepared samples that are used to measure EVs. Plasma and serum are commonly used starting materials for EV research; reporting their composition can help to improve reproducibility, comparison of measurement results, and support evidence-based guideline development. We conducted an online survey among the International Society on Thrombosis and Haemostasis (ISTH) EV researchers. Of the 20 respondents, 95% were familiar with MISEV, but 35% were unaware of the 2023 update, and only 65% applied these guidelines to their reports. With regard to MIBlood-EV, 40% were unaware of this reporting tool, and 20% did not follow its recommendations. This is surprising because most respondents agree that preanalytical variables of blood EV research are not satisfactorily described (75%), confirm that having a standardized reporting tool is beneficial for blood EV research (90%), and consider MIBlood-EV applicable to other fields of ISTH research (80%). In this Scientific and Standardization Committee communication, we summarize the survey results, as well as the background and goals of MISEV and how MIBlood-EV can be useful to improve the reproducibility of blood research within the ISTH community.

Mitochondrial-Mediated Platelet Activation in Polymyalgia Rheumatica

OBJECTIVE

Platelet activation is thought to participate in polymyalgia rheumatica (PMR) pathogenesis. Upon platelet activation, mitochondria are expelled into the extracellular space. However, whether extracellular mitochondria are present in patients with PMR and whether they can induce platelet activation is not known.

METHODS

To investigate this, we measured markers of platelet activation (thrombospondin-1 [TSP-1]), mitochondrial-derived N-formyl methionine peptide (fMET), and autoantibodies directed toward specific mitochondrial antigen mitofusin-1 (MFN1) by enzyme-linked immunosorbent assay in plasma of healthy controls (HCs, n = 30) and patients with PMR without giant cell arteritis (GCA) (n = 45) and patients with PMR with GCA (n = 9) before and after treatment with glucocorticoid therapy. Ultrapure mitochondria were opsonized with plasma from patients with PMR without GCA (n = 45) or HCs (n = 10) and were subsequently incubated with HC platelets. Platelet activation was assessed by P-selectin levels using flow cytometry.

RESULTS

Plasma levels of anti-MFN1 IgG were elevated in patients with PMR with and without GCA before glucocorticoid therapy when compared with HCs (P < 0.01 for both groups). Levels of anti-MFN1 IgG significantly reduced after treatment with glucocorticoids in both groups (P < 0.01). Levels of fMET were also significantly higher in patients with PMR with and without GCA before glucocorticoid therapy in comparison with HCs (P < 0.001 and P < 0.01, respectively). However, the levels of fMET only dropped significantly after therapy in patients with PMR without GCA (P < 0.001). Plasma levels of TSP-1 were elevated in patients with PMR with and without GCA before glucocorticoid therapy when compared to HC (P < 0.001 for both groups). After glucocorticoid therapy, plasma levels of TSP-1 decreased significantly only in patients with PMR without GCA (P = 0.023). Mitochondria opsonized with plasma from patients with PMR without GCA induced higher platelet activation regardless of treatment status as compared with plasma from HCs (P < 0.0001 and P < 0.01 for pretreatment and posttreatment).

CONCLUSION

Our results indicate increased platelet activation and the presence of mitochondrial antigens and antibodies in the circulation of patients with PMR. Blocking mitochondrial-mediated platelet activation may reduce inflammation in patients with PMR, with potential therapeutic implications.

Purified adipose tissue-derived extracellular vesicles facilitate adipose organoid vascularization through coordinating adipogenesis and angiogenesis

One of the major challenges in the way of better fabricating vascularized adipose organoids is the destructive effect of adipogenic differentiation on preformed vasculature, which probably stems from the discrepancy between thein vivophysiological microenvironment and thein vitroculture conditions. As an intrinsic component of adipose tissue (AT), adipose tissue-derived extracellular vesicles (AT-EVs) have demonstrated both adipogenic and angiogenic ability in recent studies. However, whether AT-EVs could be employed to coordinate the angiogenesis and adipogenesis in the vascularization of adipose organoids remains largely unexplored. Herein, we present an efficient method for isolating higher-purity AT-EV preparations from lipoaspirates, and verify the superiority of AT-EV preparations' angiogenic and adipogenic capabilities over those from unpurified lipoaspirates. Next, in the spheroid culture model, it was discovered that the addition of AT-EVs could effectively improve the aggregation through enhancing intercellular adhesion of monoculture spheroids composed of human umbilical vascular endothelial cells (HUVECs), and helped produce vascularized adipose organoids with proper lipolysis and glucose uptake ability in the coculture spheroids comprised of adipose-derived stem cells (ADSCs) and HUVECs. Subsequently, it was observed that AT-EVs could exert a retaining effect on the vasculature of prevascularized coculture spheroids cultured in an adipogenic environment, compared to the reduced vascular networks where AT-EVs were absent. Altogether, these results indicate that AT-EVs, by means of releasing bioactive molecules that emulate thein vivomicroenvironment, can modify non-replicativein vitromicroenvironments, coordinatein vitroadipogenesis and angiogenesis, and facilitate the fabrication of vascularized adipose organoids.

Deciphering Platelets: Are They Cells or an Evolved Form of Extracellular Vesicles?

Platelets are abundant in blood, where they maintain the integrity of the vasculature. Megakaryocytes, the cells responsible for platelet genesis, produce membrane protrusions from which as many as 5000 anucleate platelets can be released into the bloodstream. Platelets lack genomic DNA but contain different molecules, such as RNA, as well as organelles transmitted from the parent megakaryocyte. There is no consensus in the scientific community on whether platelets are cells or not: for example, they are sometimes called cells, small cells, anucleated cells, cell fragments, or megakaryocyte fragments. Extracellular vesicles are particles delimited by a lipid bilayer that are released from cells but cannot replicate on their own. Like platelets, extracellular vesicles lack a nucleus and carry components from their donor cell. Herein, we will explore various viewpoints suggesting that platelets may be cells, albeit not conventional cells, or may be a previously unrecognized type of extracellular vesicle. Beyond a mere debate over terminology, this perspective seeks to help properly define and classify platelets, aiming for better integration into the concept of either cells or extracellular vesicles. This will foster a clearer understanding and drive advances in platelet research.

Stoichiometric constraints for detection of EV-borne biomarkers in blood

Stochiometric issues, encompassing both the quantity and heterogeneity of extracellular vesicles (EVs) derived from tumour or other tissues in blood, pose important challenges across various stages of biomarker discovery and detection, affecting the integrity of data, introducing losses and artifacts during blood processing, EV purification and analysis. These challenges shape the diagnostic utility of EVs especially within the framework of established and emerging methodologies. By addressing these challenges, we aim to delineate crucial parameters and requirements for tumour-specific EV detection, or more precisely, for tumour identification via EV based assays. Our endeavour involves a comprehensive examination of the layers that mask or confound the traceability of EV markers such as nucleic acids and proteins, and focus on 'low prevalence-low concentration' scenario. Finally, we evaluate the advantages versus limitations of single-particle analysers over more conventional bulk assays, suggesting that the combined use of both to capture and interpret the EV signals, in particular the EV surface displayed proteins, may ultimately provide quantitative information on their absolute abundance and distribution.

Leukocyte Extracellular Vesicles Predict Progression of Systolic Dysfunction in Heart Failure with Mildly Reduced Ejection Fraction (LYCHEE) - A Prospective, Multicentre Cohort Study

Risk stratification in heart failure with mildly-reduced ejection fraction (HFmrEF) remains challenging. We evaluated the predictive value of advanced glycation end products (AGEs) and plasma concentrations of extracellular vesicles (EVs) for the systolic and diastolic dysfunction progression in HFmrEF patients. Skin AGE accumulation was measured using AGE Reader. Plasma EV concentrations were measured using flow cytometry. Among 74 patients enrolled, 13 (18%) had systolic dysfunction progression and 5 (7%) had diastolic dysfunction progression during 6.5 months follow-up. Leukocyte EVs concentrations were higher in patients with systolic dysfunction progression (p = 0.002) and predicted the progression with 75.0% sensitivity and 58.3% specificity, independent of other clinical variables (OR 4.72, 95% CI 0.99-22.31). Skin AGE levels and concentrations of other EV subtypes were not associated with systolic or diastolic dysfunction progression. Increased leukocyte EVs concentrations are associated with 4.7-fold higher odds of systolic dysfunction progression in HFmrEF patients.

Comprehensive Phenotyping of Extracellular Vesicles in Plasma of Healthy Humans - Insights Into Cellular Origin and Biological Variation

Despite immense interest in biomarker applications of extracellular vesicles (EVs) from blood, our understanding of circulating EVs under physiological conditions in healthy humans remains limited. Using imaging and multiplex bead-based flow cytometry, we comprehensively quantified circulating EVs with respect to their cellular origin in a large cohort of healthy blood donors. We assessed coefficients of variations to characterize their biological variation and explored demographic, clinical, and lifestyle factors contributing to observed variation. Cell-specific circulating EV subsets show a wide range of concentrations that do not correlate with cell-of-origin concentrations in blood, suggesting steady-state EV subset concentrations are regulated by complex mechanisms, which differ even for EV subsets from the same cell type. Interestingly, tetraspanin+ circulating EVs largely originate from platelets and to a lesser extent from lymphocytes. Principal component analysis (PCA) and association analyses demonstrate high biological inter-individual variation in circulating EVs across healthy humans, which are only partly explained by the influence of sex, menopausal status, age and smoking on specific circulating EV and/or tetraspanin+ circulating EV subsets. No global influence of the explored subject's factors on circulating EVs was detected. Our findings provide the first comprehensive, quantitative data towards the cell-origin atlas of plasma EVs, with important implications in the clinical use of EVs as biomarkers.

Extracellular Vesicles to Predict Outcomes After Transcatheter Aortic Valve Implantation - a Prospective, Multicenter Cohort Study

INTRODUCTION

Transcatheter aortic valve implantation (TAVI) is an established treatment for aortic stenosis (AS) in patients at intermediate and high surgical risk. Circulating extracellular vesicles (EVs) are nanoparticles involved in cardiovascular diseases. We aimed to (i) determine the effect of TAVI on plasma concentrations of five EV subtypes and (ii) evaluate the predictive value of EVs for post-TAVI outcomes.

METHODS

Blood samples were collected 1 day before TAVI and at hospital discharge. Concentrations of EVs were evaluated using flow cytometry.

RESULTS

Concentration of leukocytes EVs decreased after TAVI, compared to the measurement before (p = 0.008). Among 123 patients discharged from the hospital, 19.5% experienced MACCE during the median of 10.3 months. Increased pre-TAVI concentration of phosphatidylserine-exposing EVs was an independent predictor of MACCE in multivariable analysis (OR 5.313, 95% CI 1.164-24.258, p = 0.031).

CONCLUSIONS

Patients with increased pre-TAVI concentration of procoagulant, PS-exposing EVs have over fivefold higher odds of adverse outcomes.

Choice of blood collection methods influences extracellular vesicles counts and miRNA profiling

Circulating RNAs have been investigated systematically for over 20 years, both as constituents of circulating extracellular vesicles (EVs) or, more recently, non-EV RNA carriers, such as exomeres and supermeres. The high level of variability and low reproducibility rate of EV/extracellular RNA (exRNA) results generated even on the same biofluids promoted several efforts to limit pre-analytical variability by standardizing sample collection and sample preparation, along with instrument validation, setup and calibration. Anticoagulants (ACs) are often chosen based on the initial goal of the study and not necessarily for the later EV and/or exRNA analyses. We show the effects of blood collection on EV size, abundance, and antigenic composition, as well on the miRNAs. Our focus of this work was on the effect of ACs on the number and antigenic composition of circulating EVs and on a set of circulating miRNA species, which were shown to be relevant as disease markers in several cancers and Alzheimer's disease. Results show that while the number of plasma EVs, their relative size, and post-fluorescence labeling profile varied with each AC, their overall antigenic composition, with few exceptions, did not change significantly. However, the number of EVs expressing platelet and platelet-activation markers increased in serum samples. For overall miRNA expression levels, EDTA was a better AC, although this may have been associated with stimulation of cells in the blood collection tube. Citrate and serum rendered better results for a set of miRNAs that were described as circulating markers for Alzheimer's disease, colon, and papillary thyroid cancers.

Choice of size-exclusion chromatography column affects recovery, purity, and miRNA cargo analysis of extracellular vesicles from human plasma

Aim

The miRNA cargo of plasma extracellular vesicles (EVs) is commonly studied for its biomarker potential. However, isolation of EVs from human plasma is challenging. Although size-exclusion chromatography (SEC) is commonly used to isolate plasma EVs, SEC does not completely separate EVs from other miRNA carriers such as cells, lipoproteins, and proteins. Recently, new SEC columns were introduced, but hitherto, no systematic study was performed to compare the recovery and purity of plasma EVs using both traditional and new columns. In this study, we investigated the recovery of EVs and separation efficacy from lipoproteins and proteins using different SEC columns, and how recovery and separation affect miRNA cargo analysis.

Methods

EVs were isolated from pooled (n = 5) platelet-depleted plasma using 10 different SEC columns. For each column, three EV-enriched fractions were pooled and concentrations of EVs, lipoproteins, proteins, and miRNAs were measured by flow cytometry, enzyme-linked immunosorbent assay (ELISA), Bradford assay, and qRT-PCR, respectively.

Results

Our results show that the resin pore size affects all measured parameters: a small pore size increases recovery of EVs and quantity of miRNA, but decreases the separation efficacy compared to a large pore size. Regression analysis showed that the investigated miRNAs are more strongly associated with EVs than with lipoproteins or proteins.

Conclusion

The choice of a SEC column markedly affects the recovery, separation efficacy, and miRNA cargo analysis of human plasma-derived EVs. We recommend either using SEC columns with a 70-nm pore size due to their superior EV purity or studying the effect of non-EV particles on the miRNAs of interest.

Effect of the 35 nm and 70 nm Size Exclusion Chromatography (SEC) Column and Plasma Storage Time on Separated Extracellular Vesicles

The technical difficulty of separating extracellular vesicles (EVs) from plasma proteins in human blood presents a significant hurdle in EV research, particularly during nano ultra-high-performance liquid chromatography-tandem mass spectrometric (UHPLC-MS/MS) analysis, where detecting "vesicular" proteins among abundant plasma proteins is challenging. Standardisation is a pressing issue in EV research, prompting collaborative global efforts to address it. While the MISEV guidelines offer valuable recommendations, unanswered questions remain, particularly regarding sample storage. We compared size exclusion chromatography (SEC) columns with pore sizes of 35 nm and 70 nm to identify fractions with minimal contaminating proteins and the highest concentration of small EVs (sEVs). Following column selection, we explored potential differences in the quality and quantity of sEVs isolated from platelet-free plasma (PFP) after long-term storage at -80 °C (>2.5 years) compared to freshly drawn blood. Our methodologically rigorous study indicates that prolonged storage, under correct storage and processing conditions, does not compromise sEV quality. Both columns effectively isolated vesicles, with the 70 nm column exhibiting a higher abundance of "vesicular" proteins. We propose a relatively rapid and moderately efficient protocol for obtaining a comparatively pure sEV fraction from plasma, facilitating sEV processing in clinical trials.

Density-based lipoprotein depletion improves extracellular vesicle isolation and functional analysis

BACKGROUND

Blood plasma is the main source of extracellular vesicles (EVs) in clinical studies aiming to identify biomarkers and to investigate pathophysiological processes, especially regarding EV roles in inflammation and thrombosis. However, EV isolation from plasma has faced the fundamental issue of lipoprotein contamination, representing an important bias since lipoproteins are highly abundant and modulate cell signaling, metabolism, and thromboinflammation.

OBJECTIVES

Here, we aimed to isolate plasma EVs after depleting lipoproteins, thereby improving sample purity and EV thromboinflammatory analysis.

METHODS

Density-based gradient ultracentrifugation (G-UC) was used for lipoprotein depletion before EV isolation from plasma through size-exclusion chromatography (SEC) or serial centrifugation (SC). Recovered EVs were analyzed by size, concentration, cellular source, ultrastructure, and bottom-up proteomics.

RESULTS

G-UC efficiently separated lipoproteins from the plasma, allowing subsequent EV isolation through SEC or SC. Combined analysis from EV proteomics, cholesterol quantification, and apoB-100 detection confirmed the significant reduction in lipoproteins from isolated EVs. Proteomic analysis identified similar gene ontology and cellular components in EVs, regardless of lipoprotein depletion, which was consistent with similar EV cellular sources, size, and ultrastructure by flow cytometry and transmission electron microscopy. Importantly, lipoprotein depletion increased the detection of less abundant proteins in EV proteome and enhanced thromboinflammatory responses of platelets and monocytes stimulated in vitro with EV isolates.

CONCLUSION

Combination of G-UC+SEC significantly reduced EV lipoprotein contamination without interfering in EV cellular source, gene ontology, and ultrastructure, allowing the recovery of highly pure EVs with potential implications for functional assays and proteomic and lipidomic analyses.

High-Throughput Microfluidic Extraction of Platelet-free Plasma for MicroRNA and Extracellular Vesicle Analysis

Cell-free RNAs and extracellular vesicles (EVs) are valuable biomarkers in liquid biopsies, but they are prone to preanalytical variabilities such as nonstandardized centrifugation or ex vivo blood degradation. Herein, we report a high-throughput and label-free inertial microfluidic device (ExoArc) for isolation of platelet-free plasma from blood for RNA and EV analysis. Unlike conventional inertial microfluidic devices widely used for cell sorting, a submicrometer size cutoff (500 nm) was achieved which completely removed all leukocytes, RBCs, platelets, and cellular debris based on differential lateral migration induced by Dean vortices. The single-step operation also reduced platelet-associated miRNAs (∼2-fold) compared to centrifugation. We clinically validated ExoArc for plasma miRNA profiling (39 samples) and identified a 7-miRNA panel that detects non-small cell lung cancer with ∼90% sensitivity. ExoArc was also coupled with size exclusion chromatography (SEC) to isolate EVs within 50 min with ∼10-fold higher yield than ultracentrifugation. As a proof-of-concept for EV-based transcriptomics analysis, we performed miRNA analysis in healthy and type 2 diabetes mellitus (T2DM) subjects (n = 3 per group) by coupling ExoArc and ExoArc+SEC with quantitative polymerase chain reaction (RT-qPCR) assay. Among 293 miRNAs detected, plasmas and EVs showed distinct differentially expressed miRNAs in T2DM subjects. We further demonstrated automated in-line EV sorting from low volume culture media for continuous EV monitoring. Overall, the developed ExoArc offers a convenient centrifugation-free workflow to automate plasma and EV isolation for point-of-care diagnostics and quality control in EV manufacturing.

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.

Towards the Clinical Implementation of Extracellular Vesicle-Based Biomarker Assays for Cancer

BACKGROUND

Substantial research has been devoted to elucidating the role of extracellular vesicles (EVs) in the different hallmarks of cancer. Consequently, EVs are increasingly explored as a source of cancer biomarkers in body fluids. However, the heterogeneity in EVs, the complexity of body fluids, and the diversity in methods available for EV analysis, challenge the development and translation of EV-based biomarker assays.

CONTENT

Essential steps in EV-associated biomarker development are emphasized covering biobanking, biomarker discovery, verification and validation, and clinical implementation. A meticulous study design is essential and ideally results from close interactions between clinicians and EV researchers. A plethora of different EV preparation protocols exists which warrants quality control and transparency to ensure reproducibility and thus enable verification of EV-associated biomarker candidates identified in the discovery phase in subsequent independent cohorts. The development of an EV-associated biomarker assay requires thorough analytical and clinical validation. Finally, regulatory affairs must be considered for clinical implementation of EV-based biomarker assays.

SUMMARY

In this review, the current challenges that prevent us from exploiting the full potential of EV-based biomarker assays are identified. Guidelines and tools to overcome these hurdles are highlighted and are crucial to advance EV-based biomarker assays into clinical use.

A beginner's guide to study extracellular vesicles in human blood plasma and serum

Blood is the most commonly used body fluid for obtaining and studying extracellular vesicles (EVs). While blood is a standard choice for clinical analysis, using blood as a source of EVs introduces multiple layers of complexity. At the Blood Extracellular Vesicle Workshop organized by the International Society for Extracellular Vesicles in Helsinki (2022), it became evident that beginner researchers lack trustworthy information on how to initiate their research and avoid common pitfalls. This educational guide explains the composition and frequently used terminology of blood, provides guidelines for blood collection, and the preparation of plasma and serum. It also introduces the basic principles of isolating and detecting blood EVs while considering blood-related factors. The goal of this guide is to assist beginners by offering a concise and evidence-based introduction to the current knowledge and available resources to study blood EVs.

MIBlood-EV: Minimal information to enhance the quality and reproducibility of blood extracellular vesicle research

Blood is the most commonly used body fluid for extracellular vesicle (EV) research. The composition of a blood sample and its derivatives (i.e., plasma and serum) are not only donor-dependent but also influenced by collection and preparation protocols. Since there are hundreds of pre-analytical protocols and over forty variables, the development of standard operating procedures for EV research is very challenging. To improve the reproducibility of blood EV research, the International Society for Extracellular Vesicles (ISEV) Blood EV Task Force proposes standardized reporting of (i) the applied blood collection and preparation protocol and (ii) the quality of the prepared plasma and serum samples. Gathering detailed information will provide insight into the performance of the protocols and more effectively identify potential confounders in the prepared plasma and serum samples. To collect this information, the ISEV Blood EV Task Force created the Minimal Information for Blood EV research (MIBlood-EV), a tool to record and report information about pre-analytical protocols used for plasma and serum preparation as well as assays used to assess the quality of these preparations. This tool does not require modifications of established local pre-analytical protocols and can be easily implemented to enhance existing databases thereby enabling evidence-based optimization of pre-analytical protocols through meta-analysis. Taken together, insight into the quality of prepared plasma and serum samples will (i) improve the quality of biobanks for EV research, (ii) guide the exchange of plasma and serum samples between biobanks and laboratories, (iii) facilitate inter-laboratory comparative EV studies, and (iv) improve the peer review process.

Clinical applications and challenges in the field of extracellular vesicles

Body fluids contain cell-derived particles called extracellular vesicles (EVs). EVs are released by cells and are present in all body fluids (i. e. liquid biopsies). EVs contribute to physiology and pathology and offer a plethora of potential clinical applications, ranging from biomarkers to therapeutic applications. In this manuscript we provide an overview of this new and rapidly growing research field, along with its challenges and opportunities.

Single vesicle analysis reveals the release of tetraspanin positive extracellular vesicles into circulation with high intensity intermittent exercise

Small extracellular vesicles (sEVs) are released from all cell types and participate in the intercellular exchange of proteins, lipids, metabolites and nucleic acids. Proteomic, flow cytometry and nanoparticle tracking analyses suggest sEVs are released into circulation with exercise. However, interpretation of these data may be influenced by sources of bias introduced by different analytical approaches. Seven healthy participants carried out a high intensity intermittent training (HIIT) cycle protocol consisting of 4 × 30 s at a work-rate corresponding to 200% of individual max power (watts) interspersed by 4.5 min of active recovery. EDTA-treated blood was collected before and immediately after the final effort. Platelet-poor (PPP) and platelet-free (PFP) plasma was derived by one or two centrifugal spins at 2500 g, respectively (15 min, room temperature). Platelets were counted on an automated haemocytometer. Plasma samples were assessed with the Exoview R100 platform, which immobilises sEVs expressing common tetraspanin markers CD9, CD63, CD81 and CD41a on microfluidic chips and with the aid of fluorescence imaging, counts their abundance at a single sEV resolution, importantly, without a pre-isolation step. There was a lower number of platelets in the PFP than PPP, which was associated with a lower number of CD9, CD63 and CD41a positive sEVs. HIIT induced an increase in fluorescence counts in CD9, CD63 and CD81 positive sEVs in both PPP and PFP. These data support the concept that sEVs are released into circulation with exercise. Furthermore, platelet-free plasma is the preferred, representative analyte to study sEV dynamics and phenotype during exercise. KEY POINTS: Small extracellular vesicles (sEV) are nano-sized particles containing protein, metabolites, lipid and RNA that can be transferred from cell to cell. Previous findings implicate that sEVs are released into circulation with exhaustive, aerobic exercise, but since there is no gold standard method to isolate sEVs, these findings may be subject to bias introduced by different approaches. Here, we use a novel method to immobilise and image sEVs, at single-vesicle resolution, to show sEVs are released into circulation with high intensity intermittent exercise. Since platelet depletion of plasma results in a reduction in sEVs, platelet-free plasma is the preferred analyte to examine sEV dynamics and phenotype in the context of exercise.

Optimization of extracellular vesicle isolation and their separation from lipoproteins by size exclusion chromatography

Interest in the use of extracellular vesicles (EVs) as biomarkers of disease is rapidly growing. However, one main unsolved issue in the EV field is finding a technique able to eliminate non-EV contaminants present in biofluid samples in a one-step isolation protocol. Due to the expansion and value of size exclusion chromatography (SEC) as one of the best EV isolation methods, we have tested several agarose resins with different agarose percentages, bead sizes and crosslinking features to optimize EV isolation. For this optimization of SEC, we first employed conditioned media from a melanoma cell culture, a simpler sample in comparison to biological fluids, but which also contains abundant contaminants such as soluble protein and lipoproteins (LPPs). The distinct agaroses and the combinations of resins with different agarose percentages in the same column were tested. Soluble protein, EVs and LPPs levels from the different eluted fractions were quantitated by immunodetection or absorbance measurements. Samples were also analysed by NTA and TEM to verify the yield and the LPP contamination. Different percentages of agarose resins (2%, 4% and 6%) yielded samples with increasing LPP contamination respectively, which was not improved in the columns that combined them. Crosslinking of the agarose did not affect EV isolation yield nor the LPP contamination. In contrast, reducing the bead size greatly improved EV purity. We thus selected 4% Rapid Run Fine agarose beads as the resin that more efficiently isolated EVs with almost no contamination of other particles. Using blood plasma samples, this resin also demonstrated an improved capacity in the isolation of EVs from LPPs in comparison to the agaroses most commonly used in the field and differential ultracentrifugation.

Can the molecules carried by extracellular vesicles help to diagnose pancreatic cancer early?

BACKGROUND

Pancreatic cancer is a deadly malignancy mainly because of its asymptomatic onset which prevents the implementation of the primary tumour's resection surgery, leading to metastatic spread resistant to chemotherapy. Early-detection of this cancer in its initial stage would represent a game changer in the fight against this disease. The few currently available biomarkers detectable in patients' body fluids lack sensitivity and specificity.

SCOPE OF REVIEW

The recent discovery of extracellular vesicles and their role in promoting cancer's advancement, has boosted interest in researching their cargo, to find reliable early detection biological markers. This review examines the most recent discoveries in the analysis of potential extra vesicle-carried biological markers for the early detection of pancreatic cancer.

MAJOR CONCLUSIONS

Despite the advantages of using extracellular vesicles for early diagnosis, and the promising findings of extracellular vesicle-carried molecules possibly functional as biomarkers, until now there are no validated markers derived from extracellular vesicles available to be used in the clinic.

GENERAL SIGNIFICANCE

Further studies in this direction are urgently required to provide what would be a major asset for defeating pancreatic cancer.

Plasma extracellular vesicle test sample to standardize flow cytometry measurements

Background

Extracellular vesicles (EVs) in body fluids are explored as disease biomarkers, but EV concentrations measured by flow cytometers (FCMs) are incomparable.

Objectives

To improve data comparability, new reference materials with physical properties resembling EVs and reference procedures are being developed. The validation of new reference materials and procedures requires biological test samples. We developed a human plasma EV test sample (PEVTES) that i) resembles subcellular particles in plasma, ii) is ready-to-use, iii) is flow cytometry-compatible, and iv) is stable.

Methods

The PEVTES was prepared from human plasma of 3 fasting donors. EVs were immunofluorescently stained with antibodies against platelet-specific (CD61) and erythrocyte-specific (CD235a) antigens or lactadherin. To reduce the concentration of soluble proteins, lipoproteins, and unbound reagents, stained EVs were isolated from plasma by size-exclusion chromatography. After isolation, the PEVTES was filtered to remove remnant platelets. PEVTESs were diluted in cryopreservation agents, dimethyl sulfoxide, glycerol, or trehalose and stored at -80 °C for 12 months. After thawing, stained EV concentrations were measured with a calibrated FCM (Apogee A60-Micro).

Results

We demonstrate that the developed PEVTES resembles subcellular particles in human plasma when measured using FCM and that the concentrations of prestained platelet-derived, erythrocyte-derived, and lactadherin+ EVs in the PEVTES are stable during storage at -80 °C for 12 months when stored in trehalose.

Conclusion

The PEVTES i) resembles subcellular particles in plasma, ii) is ready-to-use, iii) is flow cytometry-compatible, and iv) is stable. Therefore, the developed PEVTES is an ideal candidate to validate newly developed reference materials and procedures.

Standardising the preanalytical reporting of biospecimens to improve reproducibility in extracellular vesicle research - A GEIVEX study

The standardization of clinical studies using extracellular vesicles (EVs) has mainly focused on the procedures employed for their isolation and characterization; however, preanalytical aspects of sample collection, handling and storage also significantly impact the reproducibility of results. We conducted an online survey based on SPREC (Standard PREanalytical Code) among members of GEIVEX (Grupo Español de Investigación en Vesiculas Extracelulares) to explore how different laboratories handled fluid biospecimens destined for EV analyses. We received 70 surveys from forty-three different laboratories: 44% focused on plasma, 9% on serum and 16% on urine. The survey indicated that variability in preanalytical approaches reaches 94%. Moreover, in some cases, researchers had no access to all relevant preanalytical details of samples, with some sample aspects with potential impact on EV isolation/characterisation not coded within the current version of SPREC. Our study highlights the importance of working with common standard operating procedures (SOP) to control preanalytical conditions. The application of SPREC represents a suitable approach to codify and register preanalytical conditions. Integrating SPREC into the SOPs of laboratories/biobanks will provide a valuable source of information and constitute an advance for EV research by improving reproducibility and credibility.

Evaluation of four commercial ELISAs to measure tissue factor in human plasma

Background

Under pathological conditions, tissue factor (TF)-positive extracellular vesicles (EVs) are released into the circulation and activate coagulation. Therefore, it is important to identify methods that accurately quantitate levels of TF in plasma. Enzyme-linked immunosorbent assays (ELISAs) are a fast and simple method to quantitate levels of proteins. However, there are several specific challenges with measuring TF antigen in plasma including its low concentration and the complexity of plasma.

Objectives

We aimed to evaluate the ability of 4 commercial ELISAs to measure TF in human plasma.

Methods

We determined the ability of 4 commercial ELISAs (Imubind, Quantikine, Human SimpleStep, and CD142 Human) to detect recombinant human TF (Innovin) (12.5-100 pg/mL), TF-positive EVs isolated from the culture supernatant from a human pancreatic cancer cell line (57 pg/mL), TF in plasma containing low levels of EV TF activity (1.2-2.6 pg/mL) from lipopolysaccharide-stimulated whole blood, and plasma containing high levels of EV TF activity (151-696 pg/mL) from patients with acute leukemia.

Results

The CD142 Human ELISA could not detect recombinant TF. Imubind and Quantikine but not Human SimpleStep detected recombinant TF spiked into plasma and TF-positive EVs isolated from the culture supernatant of a human pancreatic cancer cell line. Quantikine and Imubind could not detect low levels of TF in plasma from lipopolysaccharide-stimulated whole blood. However, Quantikine but not Imubind detected TF in plasma from acute leukemia patients with high levels of EV TF activity.

Conclusion

Our results indicate that commercial ELISAs have different abilities to detect TF. Quantikine and Imubind could not detect low levels of TF in plasma, but Quantikine detected TF in plasma with high levels of TF.

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.

Platelet removal from human blood plasma improves detection of extracellular vesicle-associated miRNA

Human blood plasma prepared by centrifugation contains not only extracellular vesicles (EVs) but also platelets and erythrocyte ghosts (ery-ghosts). Here we studied whether analysis of miRNA associated with plasma EVs (EV-miRNA) is affected by the presence of platelets and ery-ghosts. EDTA blood was collected from healthy donors (n = 3), and plasma was prepared by the centrifugation protocol recommended by the International Society on Thrombosis and Haemostasis (ISTH), and by a centrifugation protocol from an EV-miRNA expert lab (non-ISTH protocol). EVs were isolated from plasma by size-exclusion chromatography CL-2B (SEC2B), and concentrations of platelets, activated platelets, ery-ghosts and EVs (150-1000 nm) were measured by calibrated flow cytometry. Two EV-associated miRNAs (let7a-5p and miR-21-5p), and one platelet-associated miRNA (miR-223-3p), were measured by qRT-PCR. Measurements were performed with and without filtration using 0.8 μm track-etched filters to remove platelets and ery-ghosts from plasma and EV-enriched SEC fractions. Plasma prepared by both centrifugation protocols contained platelets and ery-ghosts, which co-migrated with EVs into the EV-enriched SEC2B fractions. Filtration removed platelets and ery-ghosts (>97%; p ≤ 0.05) and did not affect the EV concentrations (p > 0.17). The miRNA concentrations were 2-4-fold overestimated due to the presence of platelets but not ery-ghosts. Thus, filtration of human plasma is expected to improve comparability and reproducibility of quantitative EV-miRNA studies. Therefore, we recommend to measure and report the plasma concentration of platelets for EV-miRNA studies, and to filter plasma before downstream analyses or storage in biobanks.

Extracellular vesicles and high-density lipoproteins: Exercise and oestrogen-responsive small RNA carriers

Decreased systemic oestrogen levels (i.e., menopause) affect metabolic health. However, the detailed mechanisms underlying this process remain unclear. Both oestrogens and exercise have been shown to improve metabolic health, which may be partly mediated by circulating microRNA (c-miR) signalling. In recent years, extracellular vesicles (EV) have increased interest in the field of tissue crosstalk. However, in many studies on EV-carried miRs, the co-isolation of high-density lipoprotein (HDL) particles with EVs has not been considered, potentially affecting the results. Here, we demonstrate that EV and HDL particles have distinct small RNA (sRNA) content, including both host and nonhost sRNAs. Exercise caused an acute increase in relative miR abundancy in EVs, whereas in HDL particles, it caused an increase in transfer RNA-derived sRNA. Furthermore, we demonstrate that oestrogen-based hormonal therapy (HT) allows the acute exercise-induced miR-response to occur in both EV and HDL particles in postmenopausal women, while the response was absent in nonusers.

Blood Biomarkers Discriminate Cerebral Amyloid Status and Cognitive Diagnosis when Collected with ACD-A Anticoagulant

BACKGROUND

The development of biomarkers that are easy to collect, process, and store is a major goal of research on current Alzheimer's Disease (AD) and underlies the growing interest in plasma biomarkers. Biomarkers with these qualities will improve diagnosis and allow for better monitoring of therapeutic interventions. However, blood collection strategies have historically differed between studies. We examined the ability of various ultrasensitive plasma biomarkers to predict cerebral amyloid status in cognitively unimpaired individuals when collected using acid citrate dextrose (ACD). We then examined the ability of these biomarkers to predict cognitive impairment independent of amyloid status.

METHODS

Using a cross-sectional study design, we measured amyloid beta 42/40 ratio, pTau-181, neurofilament-light, and glial fibrillary acidic protein using the Quanterix Simoa® HD-X platform. To evaluate the discriminative accuracy of these biomarkers in determining cerebral amyloid status, we used both banked plasma and 18F-AV45 PET cerebral amyloid neuroimaging data from 140 cognitively unimpaired participants. We further examined their ability to discriminate cognitive status by leveraging data from 42 cognitively impaired older adults. This study is the first, as per our knowledge, to examine these specific tests using plasma collected using acid citrate dextrose (ACD), as well as the relationship with amyloid PET status.

RESULTS

Plasma AB42/40 had the highest AUC (0.833, 95% C.I. 0.767-0.899) at a cut-point of 0.0706 for discriminating between the two cerebral amyloid groups (sensitivity 76%, specificity 78.5%). Plasma NFL at a cut-point of 20.58pg/mL had the highest AUC (0.908, 95% CI 0.851- 0.966) for discriminating cognitive impairment (sensitivity 84.8%, specificity 89.9%). The addition of age and apolipoprotein e4 status did not improve the discriminative accuracy of these biomarkers.

CONCLUSION

Our results suggest that the Aβ42/40 ratio is useful in discriminating clinician-rated elevated cerebral amyloid status and that NFL is useful for discriminating cognitive impairment status. These findings reinforce the growing body of evidence regarding the general utility of these biomarkers and extend their utility to plasma collected in a non-traditional anticoagulant.