Use of SYTO 13, a fluorescent dye binding nucleic acids, for the detection of microparticles in in vitro systems

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.

Immature platelets and platelet reactivity in patients with acute ST-segment Elevation Myocardial Infarction using whole blood flow cytometry with SYTO-13 staining

BACKGROUND

Reduced effect of antiplatelet therapy has been reported in patients with ST-segment elevation myocardial infarction (STEMI). Multiple factors may concur to explain this, including increased amount of highly reactive immature platelets.

OBJECTIVES

To investigate the association between immature platelets and reactivity determined with multicolour flow cytometry using the SYTO-13 dye in STEMI patients.

METHODS

We conducted an observational study of 59 patients with acute STEMI. Blood samples were obtained within 24 h after admission and after loading doses of dual antiplatelet therapy. For comparison, samples were obtained from 50 healthy individuals. Immature platelets and platelet reactivity were investigated using multicolour flow cytometry including the SYTO-13 dye that binds to platelet RNA and thus provides a method for subdividing platelets into immature and mature platelets. Additionally, we assessed platelet aggregation, serum-thromboxane B2 levels and standard immature platelet markers.

RESULTS

Immature platelets were more reactive than mature platelets in both STEMI patients and healthy individuals (p-values < 0.05). STEMI patients had lower platelet aggregation and thromboxane B2 levels than healthy individuals. We found a positive association between automatically determined immature platelet markers and CD63 expression on activated platelets (Spearman's rho: 0.27 to 0.58, p-values < 0.05).

CONCLUSIONS

Our study shows that immature platelets identified with a multicolour flow cytometric method using the SYTO-13 dye are more reactive than mature platelets in patients with acute STEMI and in healthy individuals. The presence of immature platelets may be important for the overall platelet reactivity, which may have implications for the effect of antiplatelet therapy.

Time- and cost-effective production of untagged recombinant MVA by flow virometry and direct virus sorting

BACKGROUND

Recombinant MVAs (rMVAs) are widely used both in basic and clinical research. Our previously developed Red-to-Green Gene Swapping Method (RGGSM), a cytometry-based Cell-Sorting protocol, revolves around the transient expression of a green fluorescent cytoplasmic marker, to subsequently obtain purified untagged rMVA upon loss of that marker by site-specific recombination. The standard RGSSM is quite costly in terms of bench work, reagents, and Sorting Facility fees. Although faster than other methods to obtain recombinant MVAs, the standard RGSSM still is time-consuming, taking at least 25 days to yield the final product.

METHODS

The direct sorting of fluorescent virions is made amenable by the marker HAG, a flu hemagglutinin/EGFP fusion protein, integrated into the external envelope of extracellular enveloped virions (EEVs). Fluorescent EEVs-containing supernatants of infected cultures are used instead of purified virus. Direct Virus-Sorting was performed on BD FACSAria Fusion cell sorter equipped with 4 lasers and a 100-mm nozzle, with 20 psi pressure and a minimal flow rate, validated using Megamix beads.

RESULTS

Upon infection of cells with recombinant EEVs, at the first sorting step virions that contain HAG are harvested and cloned, while the second sorting step yields EEVs that have lost HAG, allowing to clone untagged rMVA. Because only virion-containing supernatants are used, no virus purification steps and fewer sortings are necessary. Therefore, the final untagged rMVA product can be obtained in a mere 8 days.

CONCLUSIONS

Altogether, we report that the original RGSSM has been markedly improved in terms of time- and cost efficiency by substituting Cell-Sorting with direct Virus-Sorting from the supernatants of infected cells. The improved virometry-based RGGSM may find wide applicability, considering that rMVAs hold great promise to serve as personalized vaccines for therapeutic intervention against cancer and various types of infectious diseases.

In vivo imaging of EVs in zebrafish: New perspectives from "the waterside"

To harmoniously coordinate the activities of all its different cell types, a multicellular organism critically depends on intercellular communication. One recently discovered mode of intercellular cross-talk is based on the exchange of "extracellular vesicles" (EVs). EVs are nano-sized heterogeneous lipid bilayer vesicles enriched in a variety of biomolecules that mediate short- and long-distance communication between different cells, and between cells and their environment. Numerous studies have demonstrated important aspects pertaining to the dynamics of their release, their uptake, and sub-cellular fate and roles in vitro. However, to demonstrate these and other aspects of EV biology in a relevant, fully physiological context in vivo remains challenging. In this review we analyze the state of the art of EV imaging in vivo, focusing in particular on zebrafish as a promising model to visualize, study, and characterize endogenous EVs in real-time and expand our understanding of EV biology at cellular and systems level.

Exosome: A New Player in Translational Nanomedicine

Summary: Exosomes are extracellular vesicles released by the vast majority of cell types both in vivo and ex vivo, upon the fusion of multivesicular bodies (MVBs) with the cellular plasma membrane. Two main functions have been attributed to exosomes: their capacity to transport proteins, lipids and nucleic acids between cells and organs, as well as their potential to act as natural intercellular communicators in normal biological processes and in pathologies. From a clinical perspective, the majority of applications use exosomes as biomarkers of disease. A new approach uses exosomes as biologically active carriers to provide a platform for the enhanced delivery of cargo in vivo. One of the major limitations in developing exosome-based therapies is the difficulty of producing sufficient amounts of safe and efficient exosomes. The identification of potential proteins involved in exosome biogenesis is expected to directly cause a deliberate increase in exosome production. In this review, we summarize the current state of knowledge regarding exosomes, with particular emphasis on their structural features, biosynthesis pathways, production techniques and potential clinical applications.

Leukocyte-Derived Extracellular Vesicles in Blood with and without EpCAM Enrichment

Large tumor-derived Extracellular Vesicles (tdEVs) detected in blood of metastatic prostate, breast, colorectal, and non-small cell lung cancer patients after enrichment for Epithelial Cell Adhesion Molecule (EpCAM) expression and labeling with 4',6-diamidino-2-phenylindole (DAPI), phycoerythrin-conjugated antibodies against Cytokeratins (CK-PE), and allophycocyanin-conjugated antibody against the cluster of differentiation 45 (CD45-APC), are negatively associated with the overall survival of patients. Here, we investigated whether, similarly to tdEVs, leukocyte-derived EVs (ldEVs) could also be detected in EpCAM-enriched blood. Presence of ldEVs and leukocytes in image data sets of EpCAM-enriched samples of 25 healthy individuals and 75 metastatic cancer patients was evaluated using the ACCEPT software. Large ldEVs could indeed be detected, but in contrast to the 20-fold higher frequency of tdEVs as compared to Circulating Tumor Cells (CTCs), ldEVs were present in a 5-fold lower frequency as compared to leukocytes. To evaluate whether these ldEVs pre-exist in the blood or are formed during the CellSearch procedure, the blood of healthy individuals without EpCAM enrichment was labelled with the nuclear dye Hoechst and fluorescently tagged monoclonal antibodies recognizing the leukocyte-specific CD45, platelet-specific CD61, and red blood cell-specific CD235a. Fluorescence microscopy imaging using a similar setup as the CellSearch was performed and demonstrated the presence of a similar population of ldEVs present at a 3-fold lower frequency as compared to leukocytes.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Role of microparticles derived from monocytes, endothelial cells and platelets in the exacerbation of COPD

Background

Microparticles (MPs) are shedding membrane vesicles released from activated blood and endothelial cells under inflammatory conditions. The role of endothelial MPs (EMPs) in pathophysiology of COPD is relatively well known. However, the release and function of MPs of other cellular origins, eg, platelets, red blood cells and leukocytes, are not clearly evaluated in COPD.

Purpose

The aim of this study was to measure EMPs and other cell-derived circulating MPs in stable and exacerbated COPD patients.

Patients and methods

A total of 50 patients with COPD and 19 healthy volunteers were enrolled in the study. EMPs (CD31+, CD62E+) and platelet-derived (CD61+, CD41+, CD42a+, PAC1+), red blood cell-derived (GlyA+) and leukocyte-derived (CD45+, CD13+, CD14+, CD56+) MPs were measured. Flow cytometry (FC) was performed on Beckman Coulter FC500 analyzer. MP reference gate was set using 0.3–0.5–0.9 µm microbeads with MP size gates of 0.5–1.0 µm.

Results

All the measured MPs were significantly (P<0.001) higher in COPD patients than in the controls. Furthermore, CD62E+, CD41+, CD42a+ and CD14+ MP values were significantly (P<0.001) increased in exacerbated COPD compared to stable COPD. These MPs showed significant (P<0.001) inverse correlation with FEV₁/FVC, as well.

Conclusion

In this study, we describe a reliable flow cytometric assay for MP analysis that was successfully applied in COPD. Besides EMPs, COPD is accompanied by an increased concentration of various MPs in the systemic circulation; particularly, platelet- and monocyte-derived MPs seem to be important in exacerbation.

Towards Therapeutic Delivery of Extracellular Vesicles: Strategies for In Vivo Tracking and Biodistribution Analysis

Extracellular vesicles (EVs), such as microvesicles and exosomes, are membranous structures containing bioactive material released by several cells types, including mesenchymal stem/stromal cells (MSCs). Increasing lines of evidences point to EVs as paracrine mediators of the beneficial effects on tissue remodeling associated with cell therapy. Administration of MSCs-derived EVs has therefore the potential to open new and safer therapeutic avenues, alternative to cell-based approaches, for degenerative diseases. However, an enhanced knowledge about in vivo EVs trafficking upon delivery is required before effective clinical translation. Only a few studies have focused on the biodistribution analysis of exogenously administered MSCs-derived EVs. Nevertheless, current strategies for in vivo tracking in animal models have provided valuable insights on the biodistribution upon systemic delivery of EVs isolated from several cellular sources, indicating in liver, spleen, and lungs the preferential target organs. Different strategies for targeting EVs to specific tissues to enhance their therapeutic efficacy and reduce possible off-target effects have been investigated. Here, in the context of a possible clinical application of MSC-derived EVs for tissue regeneration, we review the existing strategies for in vivo tracking and targeting of EVs isolated from different cellular sources and the studies elucidating the biodistribution of exogenously administered EVs.

Production Conditions Affect the In Vitro Anti-Tumoral Effects of a High Concentration Multi-Strain Probiotic Preparation

A careful selection of the probiotic agent, standardization of the dose and detailed characterization of the beneficial effects are essential when considering use of a probiotic for the dietary management of serious diseases. However, changes in the manufacturing processes, equipment or facilities can result in differences in the product itself due to the live nature of probiotics. The need to reconfirm safety and/or efficacy for any probiotic product made at a different factory is therefore mandatory. Recently, under the brand VSL#3®, a formulation produced by a manufacturer different from the previous one, has been commercialized in some European countries (the UK and Holland). VSL#3 is a high concentration multi-strain preparation which has been recognized by the main Gastroenterology Associations for the dietary management of pouchitis as well as ulcerative colitis. We have compared the “original” VSL#3 produced in USA with the “newfound” VSL#3 produced in Italy. According to our results, the “newfound” VSL#3 has 130–150% more “dead bacteria” compared to the “original” product, raising concerns for the well-known association between dead microbes with adverse effects. The abilities of bacterial lysates from the two formulations to influence in vitro viability and proliferation of different tumor cell lines also resulted different. The repair of previously scratched monolayers of various adherent tumor cell lines (i.e. HT1080, and Caco-2 cells) was inhibited more significantly by the “original” VSL#3 when compared to the “newfound” VSL#3. Tumor cell cycle profile, in particular cell cycle arrest and apoptotic death of the cancer cells, further confirms that the “original” VSL#3 has a better functional profile than the “newfound” VSL#3, at least in in vitro. Our data stress the importance of the production conditions for the “newfound” VSL#3 considering that this product is intended to be used for the dietary management of patients with very serious diseases, such as chronic inflammatory bowel diseases.

The expression of HMGB1 on microparticles from Jurkat and HL-60 cells undergoing apoptosis in vitro

HMGB1 is a highly conserved nuclear protein that displays important biological activities inside as well as outside the cell and serves as a prototypic alarmin to activate innate immunity. The translocation of HMGB1 from inside to outside the cell occurs with cell activation as well as cell death, including apoptosis. Apoptosis is also a setting for the release of cellular microparticles (MPs), which are small membrane-bound vesicles that represent an important source of extracellular nuclear molecules. To investigate whether HMGB1 released from cells during apoptosis is also present on MPs, we determined the presence of HMGB1 on particles released from Jurkat and HL-60 cells induced to undergo apoptosis in vitro by treatment with either etoposide or staurosporine; MPs released from cells undergoing necrosis by freeze-thaw were also characterized. As shown by both Western blot analysis and flow cytometry, MPs from apoptotic cells contain HMGB1, with binding by antibodies indicating an accessible location in the particle structure. These results indicate that HMGB1, like other nuclear molecules, can translocate into MPs during apoptosis and demonstrate another biochemical form of this molecule that may be immunologically active.

The expression of HMGB1 on microparticles released during cell activation and cell death in vitro and in vivo

High mobility group box protein 1 (HMGB1) is a nonhistone nuclear protein that is a prototypic alarmin that can stimulate innate immunity and drive the pathogenesis of a wide range of inflammatory diseases. While HMGB1 can be released from both activated and dying cells, its biochemical and immunological properties differ depending on the release mechanism, resulting from redox changes and posttranslational modifications including acetylation. In addition to release of HMGB1, cell death is associated with the release of microparticles. Microparticles are small membrane-bound vesicles that contain cytoplasmic, nuclear and membrane components. Like HMGB1, microparticles display immunological activity and levels are elevated in diseases characterized by inflammation and vasculopathy. While studies have addressed the immunological effects of HMGB1 and microparticles independently, HMGB1, like other nuclear molecules, is a component of microparticles. Evidence for the physical association of HMGB1 comes from Western blot analysis of microparticles derived from RAW 264.7 macrophage cells stimulated by lipopolysaccharide (LPS) or induced to undergo apoptosis by treatment with etoposide or staurosporine in vitro. Analysis of microparticles in the blood of healthy volunteers receiving LPS shows the presence of HMGB1 as assessed by flow cytometry. Together, these findings indicate that HMGB1 can be a component of microparticles and may contribute to their activities. Furthermore, particle HMGB1 may represent a useful biomarker for in vivo events that may not be reflected by measurement of the total amount of HMGB1 in the blood.

EPC-derived microvesicles protect cardiomyocytes from Ang II-induced hypertrophy and apoptosis

Cell-released microvesicles (MVs) represent a novel way of cell-to-cell communication. Previous evidence indicates that endothelial progenitor cells (EPCs)-derived MVs can modulate endothelial cell survival and proliferation. In this study, we evaluated whether EPC-MVs protect cardiomyocytes (CMs) against angiotensin II (Ang II)-induced hypertrophy and apoptosis. The H9c2 CMs were exposed to Ang II in the presence or absence of EPC-MVs. Cell viability, apoptosis, surface area and β-myosin heavy chain (β-MHC) expression were analyzed. Meanwhile, reactive oxygen species (ROS), serine/threonine kinase (Akt), endothelial nitric oxide synthase (eNOS), and their phosphorylated proteins (p-Akt, p-eNOS) were measured. Phosphatidylinositol-3-kinase (PI3K) and NOS inhibitors were used for pathway verification. The role of MV-carried RNAs in mediating these effects was also explored. Results showed 1) EPC-MVs were able to protect CMs against Ang II-induced changes in cell viability, apoptosis, surface area, β-MHC expression and ROS over-production; 2) The effects were accompanied with the up-regulation of Akt/p-Akt and its downstream eNOS/p-eNOS, and were abolished by PI3K inhibition or partially blocked by NOS inhibition; 3) Depletion of RNAs from EPC-MVs partially or totally eliminated the effects of EPC-MVs. Our data indicate that EPC-MVs protect CMs from hypertrophy and apoptosis through activating the PI3K/Akt/eNOS pathway via the RNAs carried by EPC-MVs.

Multianalyte microphysiometry reveals changes in cellular bioenergetics upon exposure to fluorescent dyes

Fluorescent dyes have been designed for internal cellular component specificity and have been used extensively in the scientific community as a means to monitor cell growth, location, morphology, and viability. However, it is possible that the introduction of these dyes influences the basal function of the cell and, in turn, the results of these studies. Electrochemistry provides a noninvasive method for probing the unintended cellular affects of these dyes. The multianalyte microphysiometer (MAMP) is capable of simultaneous electrochemical measurement of extracellular metabolites in real-time. In this study, analytes central to cellular metabolism, glucose, lactate, oxygen, as well as extracellular acidification were monitored to determine the immediate metabolic effects of nuclear stains, including SYTO, DAPI dilactate, Hoechst 33342, and FITC dyes upon the pheochromocytoma PC-12 cells and RAW 264.7 macrophages. The experimental results revealed that the SYTO dye 13 significantly decreased glucose and oxygen consumption and increased extracellular acidification and lactate production in both cell lines, indicating a shift to anaerobic respiration. No other dyes caused significantly definitive changes in cellular metabolism upon exposure. This study shows that fluorescent dyes can have unintended effects on cellular metabolism and care should be taken when using these probes to investigate cellular function and morphology.

Cell-derived microparticles in atherosclerosis: biomarkers and targets for pharmacological modulation?

Cardiovascular diseases remain an important cause of morbi-mortality. Atherosclerosis, which predisposes to cardiovascular disorders such as myocardial infarction and stroke, develops silently over several decades. Identification of circulating biomarkers to evaluate cardiovascular event risk and pathology prognosis is of particular importance. Microparticles (MPs) are small vesicles released from cells upon apoptosis or activation. Microparticles are present in blood of healthy individuals. Studies showing a modification of their concentrations in patients with cardiovascular risk factors and after cardiovascular events identify MPs as potential biomarkers of disease. Moreover, the pathophysiological properties of MPs may contribute to atherosclerosis development. In addition, pharmacological compounds, used in the treatment of cardiovascular disease, can reduce plasma MP concentrations. Nevertheless, numerous issues remain to be solved before MP measurement can be applied as routine biological tests to improve cardiovascular risk prediction. In particular, prospective studies to identify the predictive values of MPs in pathologies such as cardiovascular diseases are needed to demonstrate whether MPs are useful biomarkers for the early detection of the disease and its progression.

Microparticles as mediators and biomarkers of rheumatic disease

Microparticles (MPs) are small membrane-bound vesicles that arise from activated and dying cells and enter the blood to display pro-inflammatory and pro-thrombotic activities. MPs are 0.1-1.0 μm in size and incorporate nuclear, cytoplasmic and membrane molecules as they detach from cells. This process can occur with cell activation as well as cell death, with particles likely corresponding to blebs that form on the cell surface during apoptosis. To measure particle expression, flow cytometry allows determination of particle numbers based on size as well as surface markers that denote the cell of origin; platelet MPs are usually the most abundant type in blood. As shown in in vitro and in vivo systems, MPs can promote inflammation and thrombosis resulting from their content of cytokines like IL-1 and pro-coagulant molecules like tissue factor. Certain particle types can be anti-inflammatory, however, suggesting a range of immunomodulatory activities depending on the cell of origin. Studies on patients with a wide range of rheumatic disease show increased MP numbers in blood, with platelet and endothelial particles associated with vascular manifestations; increased numbers of particles also occur in the joint fluid where they may drive cytokine production and activate synoviocytes. In autoimmune diseases such as SLE and RA, MPs may also contribute to disease pathogenesis by the formation of immune complexes. MPs thus represent novel subcellular structures that can impact on the pathogenesis of rheumatic disease and serve as biomarkers of underlying cellular disturbances.

The extracellular release of DNA and HMGB1 from Jurkat T cells during in vitro necrotic cell death

In innate immunity, dead and dying cells release internal constituents that can serve as damage-associated molecular patterns (DAMPs) or alarmins. This release occurs more abundantly during necrosis than apoptosis and may account for the differences in the immunologic properties of these death forms. To elucidate DAMP release in necrosis, we compared the levels of two nuclear molecules (DNA and HMGB1, a non-histone protein with alarmin activity) in media following necrosis of Jurkat T cells by freeze-thawing, ethanol, heat or hydrogen peroxide treatment. In our experiments, DNA release was measured by fluorimetry with the dye PicoGreen, while HMGB1 was measured by Western blotting. As the results of our study show, each form of necrosis is associated with a distinct pattern of DNA and HMGB1 release with respect to kinetics and amounts. Of these, freeze-thawing produced the highest and most rapid increase in HMGB1 and DNA levels, although the released DNA was subject to nuclease digestion; in addition, freeze-thawing led to the production of particles measured by flow cytometry. Together, these results indicate that experimental necrosis leads to diverse patterns of nuclear molecule release which could affect their immunologic activity.

HMGB1 and microparticles as mediators of the immune response to cell death

In a wide variety of diseases, cell death represents both an outcome and an important step in pathogenesis. This duality occurs because cell death leads to the extracellular release of molecules and structures that can potently induce the innate immune system. These mediators include the alarmins which are endogenous cellular constituents that exit activated or dying cells to stimulate toll-like receptors (TLRs) as well as non-TLR receptors. Of alarmins, the nonhistone protein HMGB1 is the prototype. Like DNA and RNA, HMGB1 can translocate from cells as they die. The activity of HMGB1 may reflect its interaction with other molecules such as LPS, DNA, and cytokines. In addition to alarmins, dead and dying cells can release subcellular organelles called microparticles that contain cytoplasmic and nuclear constituents, including DNA and RNA. These particles can impact on many cell types to induce inflammation. The release of HMGB1 and microparticles shows important similarities, occurring with cell death as well as stimulation of certain but not all TLRs. Furthermore, nitric oxide can induce the release of both. These observations suggest that the products of dead cells can serve as important mediators to drive immune responses and promote inflammation and autoreactivity.

Microparticles as a source of extracellular DNA

Microparticles are small membrane-bound vesicles that display pro-inflammatory and pro-thrombotic activities important in the pathogenesis of a wide variety of diseases. These particles are released from activated and dying cells and incorporate nuclear and cytoplasmic molecules for extracellular export. Of these molecules, DNA is a central autoantigen in systemic lupus erythematosus (SLE). As studies in our laboratory show, DNA occurs prominently in microparticles, translocating into these structures during apoptotic cell death. This DNA is antigenically active and can bind to lupus anti-DNA autoantibodies. These findings suggest that microparticles are an important source of extracellular DNA to serve as an autoantigen and autoadjuvant in SLE.