Fluorescent labeling of nano-sized vesicles released by cells and subsequent quantitative and qualitative analysis by high-resolution flow cytometry

In Vivo Characterization of Endogenous Cardiovascular Extracellular Vesicles in Larval and Adult Zebrafish

Objective

Extracellular vesicles (EVs) facilitate molecular transport across extracellular space, allowing local and systemic signaling during homeostasis and in disease. Extensive studies have described functional roles for EV populations, including during cardiovascular disease, but the in vivo characterization of endogenously produced EVs is still in its infancy. Because of their genetic tractability and live imaging amenability, zebrafish represent an ideal but under-used model to investigate endogenous EVs. We aimed to establish a transgenic zebrafish model to allow the in vivo identification, tracking, and extraction of endogenous EVs produced by different cell types.

Approach and Results

Using a membrane-tethered fluorophore reporter system, we show that EVs can be fluorescently labeled in larval and adult zebrafish and demonstrate that multiple cell types including endothelial cells and cardiomyocytes actively produce EVs in vivo. Cell-type specific EVs can be tracked by high spatiotemporal resolution light-sheet live imaging and modified flow cytometry methods allow these EVs to be further evaluated. Additionally, cryo electron microscopy reveals the full morphological diversity of larval and adult EVs. Importantly, we demonstrate the utility of this model by showing that different cell types exchange EVs in the adult heart and that ischemic injury models dynamically alter EV production.

Conclusions

We describe a powerful in vivo zebrafish model for the investigation of endogenous EVs in all aspects of cardiovascular biology and pathology. A cell membrane fluorophore labeling approach allows cell-type specific tracing of EV origin without bias toward the expression of individual protein markers and will allow detailed future examination of their function.

Recent advances in Extracellular Vesicles and their involvements in vasculitis

Systemic vasculitis is a heterogeneous group of multisystem autoimmune disorders characterized by inflammation of blood vessels. Although many progresses in diagnosis and immunotherapies have been achieved over the past decades, there are still many unanswered questions about vasculitis from pathological understanding to more advanced therapies. Extracellular vesicles (EVs) are double-layer phospholipid membrane vesicles harboring various cargoes. EVs can be classified into exosomes, microvesicles (MVs), and apoptotic bodies depending on their size and origin of cellular compartment. EVs can be released by almost all cell types and may be involved in physical and pathological processes including inflammation and autoimmune responses. In systemic vasculitis, EVs may have pathogenic involvement in inflammation, autoimmune responses, thrombosis, endothelium injury, angiogenesis and intimal hyperplasia. EV-associated redox reaction may also be involved in vasculitis pathogenesis by inducing inflammation, endothelial injury and thrombosis. Additionally, EVs may serve as specific biomarkers for diagnosis or monitoring of disease activity and therapeutic efficacy, i.e. AAV-associated renal involvement. In this review, we have discussed the recent advances of EVs, especially their roles in pathogenesis and clinical involvements in vasculitis.

Time- and Space-Resolved Flow-Cytometry of Cell Organelles to Quantify Nanoparticle Uptake and Intracellular Trafficking by Cells

The design of targeted nanomedicines requires intracellular space- and time-resolved data of nanoparticle distribution following uptake. Current methods to study intracellular trafficking, such as dynamic colocalization by fluorescence microscopy in live cells, are usually low throughput and require extensive analysis of large datasets to quantify colocalization in several individual cells. Here a method based on flow cytometry to easily detect and characterize the organelles in which nanoparticles are internalized and trafficked over time is proposed. Conventional cell fractionation methods are combined with immunostaining and high-sensitivity organelle flow cytometry to get space-resolved data of nanoparticle intracellular distribution. By extracting the organelles at different times, time-resolved data of nanoparticle intracellular trafficking are obtained. The method is validated by determining how nanoparticle size affects the kinetics of arrival to the lysosomes. The results demonstrate that this method allows high-throughput analysis of nanoparticle uptake and intracellular trafficking by cells, therefore it can be used to determine how nanoparticle design affects their intracellular behavior.

Designed Co-DNA-Locker and Ratiometric SERS Sensing for Accurate Detection of Exosomes Based on Gold Nanorod Arrays

Exosomes, which can transfer and deliver information about the original cell, are considered to be ideal candidates for early cancer diagnosis and evaluation of therapeutic efficacy due to their high abundance and stability. However, the highly expressed proteins on the surface of exosomes are usually associated with a variety of cancers; it is difficult to distinguish them by a single marker. Herein, a controlled self-assembly of gold nanorod (AuNR) arrays was prepared to construct a surface-enhanced Raman spectroscopy (SERS) sensor for the specific detection of exosomes secreted by SK-Br-3 cells based on a designed colocalization-dependent system (Co-DNA-Locker) and ratiometric strategy. After the exosomes are captured in the sensing array by the EpCAM aptamer modified on the surface of AuNRs, the DNA logic process occurs because the other two proteins, CD63 and HER2, are expressed simultaneously on the surface of exosomes secreted by SK-Br-3 cells, and the SERS signal intensity of the Rhodamine 6G (R6G) tagged on the terminal of DNA T_E increased with an increase in the concentration of the exosomes, while the SERS signal intensity of Cy5 linked on the terminal of the EpCAM aptamer, which acts as an internal standard, remains stable. The AuNRs are uniformly arranged in a hexagonal shape, and the dense "hot spots" produce "hot surfaces," which greatly improve the sensitivity and uniformity of detection. In the presence of target exosomes, the DNA colocalization three-signal input switch and the ratiometric strategy realize the specific and accurate detection of exosomes. This sensing strategy achieves a wide detection range (1.0 × 10⁴-5.0 × 10⁶ particles/mL) and a lower detection limit (5.3 × 10³ particles/mL), without using any signal amplification mechanism, demonstrating promising applications in health care monitoring and clinical diagnostics.

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.

Tick extracellular vesicles enable arthropod feeding and promote distinct outcomes of bacterial infection

Extracellular vesicles are thought to facilitate pathogen transmission from arthropods to humans and other animals. Here, we reveal that pathogen spreading from arthropods to the mammalian host is multifaceted. Extracellular vesicles from Ixodes scapularis enable tick feeding and promote infection of the mildly virulent rickettsial agent Anaplasma phagocytophilum through the SNARE proteins Vamp33 and Synaptobrevin 2 and dendritic epidermal T cells. However, extracellular vesicles from the tick Dermacentor andersoni mitigate microbial spreading caused by the lethal pathogen Francisella tularensis. Collectively, we establish that tick extracellular vesicles foster distinct outcomes of bacterial infection and assist in vector feeding by acting on skin immunity. Thus, the biology of arthropods should be taken into consideration when developing strategies to control vector-borne diseases.

Using single-vesicle technologies to unravel the heterogeneity of extracellular vesicles

Extracellular vesicles (EVs) are heterogeneous lipid containers with a complex molecular cargo comprising several populations with unique roles in biological processes. These vesicles are closely associated with specific physiological features, which makes them invaluable in the detection and monitoring of various diseases. EVs play a key role in pathophysiological processes by actively triggering genetic or metabolic responses. However, the heterogeneity of their structure and composition hinders their application in medical diagnosis and therapies. This diversity makes it difficult to establish their exact physiological roles, and the functions and composition of different EV (sub)populations. Ensemble averaging approaches currently employed for EV characterization, such as western blotting or 'omics' technologies, tend to obscure rather than reveal these heterogeneities. Recent developments in single-vesicle analysis have made it possible to overcome these limitations and have facilitated the development of practical clinical applications. In this review, we discuss the benefits and challenges inherent to the current methods for the analysis of single vesicles and review the contribution of these approaches to the understanding of EV biology. We describe the contributions of these recent technological advances to the characterization and phenotyping of EVs, examination of the role of EVs in cell-to-cell communication pathways and the identification and validation of EVs as disease biomarkers. Finally, we discuss the potential of innovative single-vesicle imaging and analysis methodologies using microfluidic devices, which promise to deliver rapid and effective basic and practical applications for minimally invasive prognosis systems.

Critical Review of the Evolution of Extracellular Vesicles' Knowledge: From 1946 to Today

Extracellular vesicles (EVs) are a family of particles/vesicles present in blood and body fluids, composed of phospholipid bilayers that carry a variety of molecules that can mediate cell communication, modulating crucial cell processes such as homeostasis, induction/dampening of inflammation, and promotion of repair. Their existence, initially suspected in 1946 and confirmed in 1967, spurred a sharp increase in the number of scientific publications. Paradoxically, the increasing interest for EV content and function progressively reduced the relevance for a precise nomenclature in classifying EVs, therefore leading to a confusing scientific production. The aim of this review was to analyze the evolution of the progress in the knowledge and definition of EVs over the years, with an overview of the methodologies used for the identification of the vesicles, their cell of origin, and the detection of their cargo. The MISEV 2018 guidelines for the proper recognition nomenclature and ways to study EVs are summarized. The review finishes with a “more questions than answers” chapter, in which some of the problems we still face to fully understand the EV function and potential as a diagnostic and therapeutic tool are analyzed.

Human Mesenchymal Stromal Cell-Derived Exosomes Promote In Vitro Wound Healing by Modulating the Biological Properties of Skin Keratinocytes and Fibroblasts and Stimulating Angiogenesis

Bone marrow-derived mesenchymal stromal cells (MSCs) are major players in regenerative therapies for wound healing via their paracrine activity, mediated partially by exosomes. Our purpose was to test if MSC-derived exosomes could accelerate wound healing by enhancing the biological properties of the main cell types involved in the key phases of this process. Thus, the effects of exosomes on (i) macrophage activation, (ii) angiogenesis, (iii) keratinocytes and dermal fibroblasts proliferation and migration, and (iv) the capacity of myofibroblasts to regulate the turnover of the extracellular matrix were evaluated. The results showed that, although exosomes did not exhibit anti-inflammatory properties, they stimulated angiogenesis. Exposure of keratinocytes and dermal (myo)fibroblasts to exosomes enhanced their proliferation and migratory capacity. Additionally, exosomes prevented the upregulation of gene expression for type I and III collagen, α-smooth muscle actin, and MMP2 and 14, and they increased MMP13 expression during the fibroblast–myofibroblast transition. The regenerative properties of exosomes were validated using a wound healing skin organotypic model, which exhibited full re-epithelialization upon exosomes exposure. In summary, these data indicate that exosomes enhance the biological properties of keratinocytes, fibroblasts, and endothelial cells, thus providing a reliable therapeutic tool for skin regeneration.

Pitfalls and opportunities in quantitative fluorescence-based nanomedicine studies - A commentary

Fluorescence-based techniques are prevalent in studies of nanomedicine-targeting to cells and tissues. However, fluorescence-based studies are rarely quantitative, thus prohibiting direct comparisons of nanomedicine-performance across studies. With this Commentary, we aim to provoke critical thinking about experimental design by treating some often-overlooked pitfalls in 'quantitative' fluorescence-based experimentation. Focusing on fluorescence-labeled nanoparticles, we cover mechanisms like solvent-interactions and fluorophore-dissociation, which disqualify the assumption that 'a higher fluorescence readout' translates directly to 'a better targeting efficacy'. With departure in recent literature, we propose guidelines for circumventing these pitfalls in studies of tissue-accumulation and cell-uptake, thus covering fluorescence-based techniques like bulk solution fluorescence measurements, fluorescence microscopy, flow cytometry, and infrared fluorescence imaging. With this, we hope to lay a foundation for more 'quantitative thinking' during experimental design, enabling (for example) the estimation and reporting of actual numbers of fluorescent nanoparticles accumulated in cells and organs.

Regular Industrial Processing of Bovine Milk Impacts the Integrity and Molecular Composition of Extracellular Vesicles

BACKGROUND

Bovine milk contains extracellular vesicles (EVs), which act as mediators of intercellular communication by regulating the recipients' cellular processes via their selectively incorporated bioactive molecules. Because some of these EV components are evolutionarily conserved, EVs present in commercial milk might have the potential to regulate cellular processes in human consumers.

OBJECTIVES

Because commercial milk is subjected to industrial processing, we investigated its effect on the number and integrity of isolated milk EVs and their bioactive components. For this, we compared EVs isolated from raw bovine milk with EVs isolated from different types of commercial milk, including pasteurized milk, either homogenized or not, and ultra heat treated (UHT) milk.

METHODS

EVs were separated from other milk components by differential centrifugation, followed by density gradient ultracentrifugation. EVs from different milk types were compared by single-particle high-resolution fluorescence-based flow cytometry to determine EV numbers, Cryo-electron microscopy to visualize EV integrity and morphology, western blot analysis to investigate EV-associated protein cargo, and RNA analysis to assess total small RNA concentration and milk-EV-specific microRNA expression.

RESULTS

In UHT milk, we could not detect intact EVs. Interestingly, although pasteurization (irrespective of homogenization) did not affect mean ± SD EV numbers (3.4 × 108 ± 1.2 × 108-2.8 × 108 ± 0.3 × 107 compared with 3.1 × 108 ± 1.2 × 108 in raw milk), it affected EV integrity and appearance, altered their protein signature, and resulted in a loss of milk-EV-associated RNAs (from 40.2 ± 3.4 ng/μL in raw milk to 17.7 ± 5.4-23.3 ± 10.0 mg/μL in processed milk, P < 0.05).

CONCLUSIONS

Commercial milk, that has been heated by either pasteurization or UHT, contains fewer or no intact EVs, respectively. Although most EVs seemed resistant to pasteurization based on particle numbers, their integrity was affected and their molecular composition was altered. Thus, the possible transfer of bioactive components via bovine milk EVs to human consumers is likely diminished or altered in heat-treated commercial milk.

Extracellular vesicles derived from mesenchymal stem cells: A platform that can be engineered

Mesenchymal stem cells play an important role in tissue damage and repair. This role is mainly due to a paracrine mechanism, and extracellular vesicles (EVs) are an important part of the paracrine function. EVs play a vital role in many aspects of cell homeostasis, physiology, and pathology, and EVs can be used as clinical biomarkers, vaccines, or drug delivery vehicles. A large number of studies have shown that EVs derived from mesenchymal stem cells (MSC-EVs) play an important role in the treatment of various diseases. However, the problems of low production, low retention rate, and poor targeting of MSC-EVs are obstacles to current clinical applications. The engineering transformation of MSC-EVs can make up for those shortcomings, thereby improving treatment efficiency. This review summarizes the latest research progress of MSC-EV direct and indirect engineering transformation from the aspects of improving MSC-EV retention rate, yield, targeting, and MSC-EV visualization research, and proposes some feasible MSC-EV engineering methods of transformation.

Exploring interactions between extracellular vesicles and cells for innovative drug delivery system design

Extracellular vesicles (EVs) are submicron cell-secreted structures containing proteins, nucleic acids and lipids. EVs can functionally transfer these cargoes from one cell to another to modulate physiological and pathological processes. Due to their presumed biocompatibility and capacity to circumvent canonical delivery barriers encountered by synthetic drug delivery systems, EVs have attracted considerable interest as drug delivery vehicles. However, it is unclear which mechanisms and molecules orchestrate EV-mediated cargo delivery to recipient cells. Here, we review how EV properties have been exploited to improve the efficacy of small molecule drugs. Furthermore, we explore which EV surface molecules could be directly or indirectly involved in EV-mediated cargo transfer to recipient cells and discuss the cellular reporter systems with which such transfer can be studied. Finally, we elaborate on currently identified cellular processes involved in EV cargo delivery. Through these topics, we provide insights in critical effectors in the EV-cell interface which may be exploited in nature-inspired drug delivery strategies.

Isolation and characterization of exosomes from adipose tissue-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are the subject of intense research as they are a potential therapeutic tool for several clinical applications. The new MSCs action models are focused on the use of MSC-derived secretome which contains several growth factors, cytokines, microRNAs, and extracellular vesicles such as exosomes. Exosomes have recently emerged as a component with great potential involved as mediators in cellular communication. The isolation and identification of exosomes has made it possible for them to be used in cell-free therapies. The purposes of this study are: (i) to detect exosomes released into adipose-derived MSC conditioned cell culture medium, (ii) to identify exosome morphology, and (iii) to carry out a complete characterization of said exosomes. Moreover, it is aimed at determining which method for exosome isolation would be best to use. Precipitation has been identified as a highly useful method of exosome isolation since it provides higher efficiency and purity values than other methods. A broad characterization of the exosomes present in the MSC-conditioned medium was also carried out. This work fills a gap in the existing literature on bioactive molecules which have attracted a great deal of interest due to their potential use in cellular therapies.

Emerging methods in biomarker identification for extracellular vesicle-based liquid biopsy

Extracellular vesicles (EVs) are released by many cell types and distributed within various biofluids. EVs have a lipid membrane-confined structure that allows for carrying unique molecular information originating from their parent cells. The species and quantity of EV cargo molecules, including nucleic acids, proteins, lipids, and metabolites, may vary largely owing to their parent cell types and the pathophysiologic status. Such heterogeneity in EV populations provides immense challenges to researchers, yet allows for the possibility to prognosticate the pathogenesis of a particular tissue from unique molecular signatures of dispersing EVs within biofluids. However, the inherent nature of EV's small size requires advanced methods for EV purification and evaluation from the complex biofluid. Recently, the interdisciplinary significance of EV research has attracted growing interests, and the EV analytical platforms for their diagnostic prospect have markedly progressed. This review summarizes the recent advances in these EV detection techniques and methods with the intention of translating an EV-based liquid biopsy into clinical practice. This article aims to present an overview of current EV assessment techniques, with a focus on their progress and limitations, as well as an outlook on the clinical translation of an EV-based liquid biopsy that may augment current paradigms for the diagnosis, prognosis, and monitoring the response to therapy in a variety of disease settings.

Intriguing Biomedical Applications of Synthetic and Natural Cell-Derived Vesicles: A Comparative Overview

The significant role of a vesicle is well recognized; however, only lately has the advancement in biomedical applications started to uncover their usefulness. Although the concept of vesicles originates from cell biology, it later transferred to chemistry and material science to develop nanoscale artificial vesicles for biomedical applications. Herein, we examine different synthetic and biological vesicles and their applications in the biomedical field in general. As our understanding of biological vesicles increases, more suitable biomimicking synthetic vesicles will be developed. The comparative discussion between synthetic and natural vesicles for biomedical applications is a relevant topic, and we envision this could enable the development of a proper approach to realize the next-generation treatment goals.

Therapeutic and Diagnostic Translation of Extracellular Vesicles in Cardiovascular Diseases: Roadmap to the Clinic

Exosomes are small membrane-bound vesicles of endocytic origin that are actively secreted. The potential of exosomes as effective communicators of biological signaling in myocardial function has previously been investigated, and a recent explosion in exosome research not only underscores their significance in cardiac physiology and pathology, but also draws attention to methodological limitations of studying these extracellular vesicles. In this review, we discuss recent advances and challenges in exosome research with an emphasis on scientific innovations in isolation, identification, and characterization methodologies, and we provide a comprehensive summary of web-based resources available in the field. Importantly, we focus on the biology and function of exosomes, highlighting their fundamental role in cardiovascular pathophysiology to further support potential applications of exosomes as biomarkers and therapeutics for cardiovascular diseases.

Extracellular Vesicles: Novel Opportunities to Understand and Detect Neoplastic Diseases

With a size range from 30 to 1000 nm, extracellular vesicles (EVs) are one of the smallest cell components able to transport biologically active molecules. They mediate intercellular communications and play a fundamental role in the maintenance of tissue homeostasis and pathogenesis in several types of diseases. In particular, EVs actively contribute to cancer initiation and progression, and there is emerging understanding of their role in creation of the metastatic niche. This fact underlies the recent exponential growth in EV research, which has improved our understanding of their specific roles in disease and their potential applications in diagnosis and therapy. EVs and their biomolecular cargo reflect the state of the diseased donor cells, and can be detected in body fluids and exploited as biomarkers in cancer and other diseases. Relatively few studies have been published on EVs in the veterinary field. This review provides an overview of the features and biology of EVs as well as recent developments in EV research including techniques for isolation and analysis, and will address the way in which the EVs released by diseased tissues can be studied and exploited in the field of veterinary pathology. Uniquely, this review emphasizes the important contribution that pathologists can make to the field of EV research: pathologists can help EV scientists in studying and confirming the role of EVs and their molecular cargo in diseased tissues and as biomarkers in liquid biopsies.

On-Chip Optical Detection of Viruses: A Review

The current outbreak of the coronavirus disease-19 (COVID-19) pandemic worldwide has caused millions of fatalities and imposed a severe impact on our daily lives. Thus, the global healthcare system urgently calls for rapid, affordable, and reliable detection toolkits. Although the gold-standard nucleic acid amplification tests have been widely accepted and utilized, they are time-consuming and labor-intensive, which exceedingly hinder the mass detection in low-income populations, especially in developing countries. Recently, due to the blooming development of photonics, various optical chips have been developed to detect single viruses with the advantages of fast, label-free, affordable, and point of care deployment. Herein, optical approaches especially in three perspectives, e.g., flow-free optical methods, optofluidics, and surface-modification-assisted approaches, are summarized. The future development of on-chip optical-detection methods in the wave of emerging new ideas in nanophotonics is also briefly discussed.

Role of Exosomes in Prostate Cancer Metastasis

Prostate cancer remains a life-threatening disease among men worldwide. The majority of PCa-related mortality results from metastatic disease that is characterized by metastasis of prostate tumor cells to various distant organs, such as lung, liver, and bone. Bone metastasis is most common in prostate cancer with osteoblastic and osteolytic lesions. The precise mechanisms underlying PCa metastasis are still being delineated. Intercellular communication is a key feature underlying prostate cancer progression and metastasis. There exists local signaling between prostate cancer cells and cells within the primary tumor microenvironment (TME), in addition to long range signaling wherein tumor cells communicate with sites of future metastases to promote the formation of pre-metastatic niches (PMN) to augment the growth of disseminated tumor cells upon metastasis. Over the last decade, exosomes/ extracellular vesicles have been demonstrated to be involved in such signaling. Exosomes are nanosized extracellular vesicles (EVs), between 30 and 150 nm in thickness, that originate and are released from cells after multivesicular bodies (MVB) fuse with the plasma membrane. These vesicles consist of lipid bilayer membrane enclosing a cargo of biomolecules, including proteins, lipids, RNA, and DNA. Exosomes mediate intercellular communication by transferring their cargo to recipient cells to modulate target cellular functions. In this review, we discuss the contribution of exosomes/extracellular vesicles in prostate cancer progression, in pre-metastatic niche establishment, and in organ-specific metastases. In addition, we briefly discuss the clinical significance of exosomes as biomarkers and therapeutic agents.

Genetic Background and Kinetics Define Wound Bed Extracellular Vesicles in a Mouse Model of Cutaneous Injury

Extracellular vesicles (EVs) have an important role in mediating intercellular signaling in inflammation and affect the kinetics of wound healing, however, an understanding of the mechanisms regulating these responses remains limited. Therefore, we have focused on the use of cutaneous injury models in which to study the biology of EVs on the inflammatory phase of wound healing. For this, the foreign body response using sterile subcutaneous polyvinylalcohol (PVA) sponges is ideally suited for the parallel analysis of immune cells and EVs without the need for tissue dissociation, which would introduce additional variables. We have previously used this model to identify mediators of EV biogenesis, establishing that control of how EVs are made affects their payload and biological activity. These studies in normal mice led us to consider how conditions such as immunodeficiency and obsesity affect the profile of immune cells and EVs in this model using genetically defined mutant mice. Since EVs are intrinsically heterogenous in biological fluids, we have focused our studies on a novel technology, vesicle flow cytometry (vFC) to quantify changes in EVs in mouse models. Here, we show that myeloid-derived immune cells and EVs express proteins relevant in antigen presentation in PVA sponge implants that have distinct profiles in wildtype, immune-deficient (NOD scid) vs. diabetic (Leprdb) mice. Together, these results establish a foundation for the parallel analysis of both immune cells and EVs with technologies that begin to address the heterogeneity of intercellular communication in the wound bed.

Zoom in on Antibody Aggregates: A Potential Pitfall in the Search of Rare EV Populations

High-resolution flow cytometers (hFCM) are used for the detection of extracellular vesicles (EV) in various biological fluids. Due to the increased sensitivity of hFCM, new artifacts with the potential of interfering with data interpretation are introduced, such as detection of antibody aggregates. The aim of this study was to investigate the extent of aggregates in labels commonly used for the characterization of EVs by hFCM. Furthermore, we aimed to compare the efficacy of centrifugation and filtering treatments to remove aggregates, as well as to quantify the effect of the treatments in reducing aggregates. For this purpose, we labeled phosphate buffered saline (PBS) with fluorescently conjugated protein labels and antibodies after submitting them to 5, 10, or 30 min centrifugation, filtering or washed filtering. We investigated samples by hFCM and quantified the amount of aggregates found in PBS labeled with untreated and pre-treated labels. We found a varying amount of aggregates in all labels investigated, and further that filtering is most efficient in removing all but the smallest aggregates. Filtering protein labels can reduce the extent of aggregates; however, how much remains depends on the specific labels and their combination. Therefore, it is still necessary to include appropriate controls in a hFCM study of EVs.

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.

Integrins mediate placental extracellular vesicle trafficking to lung and liver in vivo

Membrane-bound extracellular vesicles (EVs) mediate intercellular communication in all organisms, and those produced by placental mammals have become increasingly recognized as significant mediators of fetal-maternal communication. Here, we aimed to identify maternal cells targeted by placental EVs and elucidate the mechanisms by which they traffic to these cells. Exogenously administered pregnancy-associated EVs traffic specifically to the lung; further, placental EVs associate with lung interstitial macrophages and liver Kupffer cells in an integrin-dependent manner. Localization of EV to maternal lungs was confirmed in unmanipulated pregnancy using a transgenic reporter mouse model, which also provided in situ and in vitro evidence that fetally-derived EVs, rarely, may cause genetic alteration of maternal cells. These results provide for the first time direct in vivo evidence that placental EVs target maternal immune cells, and further, that EVs can alter cellular phenotype.

Influence of Anti-Glaucoma Drugs on Uptake of Extracellular Vesicles by Trabecular Meshwork Cells

Background

Extracellular vesicles (EVs) are capable of manipulating cellular functions for the maintenance of biological homeostasis and disease progression, such as in glaucoma disease. These nano-particles carry a net negative surface charge under physiological conditions that can contribute to EVs:EVs interaction and their uptake by target cells.

Purpose

To investigate the effect of glaucoma drugs on EVs physicochemical characters and the implications for their uptake by trabecular meshwork (TM) cells.

Methods

TM or non-pigmented ciliary epithelium (NPCE) cells derived EVs were incubated with commercial anti-glaucoma formulation, Timolol maleate, Brinzolamide or Benzalkonium Cl and their size and zeta potential (ZP) and physical interactions of EVs derived from NPCE cells and TM cells were evaluated. The contribution of EVs interactions to up-take by TM cells was examined using fluorescence-activated cell sorting.

Results

EVs size and ZP were affected by the ionic strength of the buffer rather than EVs type. Commercial glaucoma eye drops, including β-blocker, α-2-agonist and prostaglandin analogs, reduced NPCE EVs ZP, whereas exposure of EVs to carbonic anhydrase inhibitor caused an increase in the ZP. A correlation was found between increased ZP values and increased NPCE EVs uptake by TM cells. We were able to show that Benzalkonium chloride stands behind this ZP effect and not Timolol or Brinzolamide.

Conclusion

Altogether, our findings demonstrate that EVs size, surface membrane charge, and ionic strength of the surrounding have an impact on EVs:EVs interactions, which affect the uptake of NPCE EVs by TM cells.

Flow cytometry: principles, applications and recent advances

Flow cytometry (FCM) is a sophisticated technique that works on the principle of light scattering and fluorescence emission by the specific fluorescent probe-labeled cells as they pass through a laser beam. It offers several unique advantages as it allows fast, relatively quantitative, multiparametric analysis of cell populations at the single cell level. In addition, it also enables physical sorting of the cells to separate the subpopulations based on different parameters. In this constantly evolving field, innovative technologies such as imaging FCM, mass cytometry and Raman FCM are being developed in order to address limitations of traditional FCM. This review explains the general principles, main applications and recent advances in the field of FCM.

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.

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.

An Immunocapture-Based Assay for Detecting Multiple Antigens in Melanoma-Derived Extracellular Vesicles

Most human cells release extracellular vesicles (EVs) of different sizes and composition, containing biomolecules characteristic from the originating tissue. In consequence, when EVs derive from a cancer cell, they also contain tumor antigens. Therefore, isolating and characterizing tumor-derived EVs has attracted great interest as an invaluable source of biomarkers, both for diagnosis and stratification of cancer. In this chapter, we describe a method for flow cytometry assessment of melanoma-derived EVs which are firstly captured onto antibody-coated beads recognizing either a common EV marker, namely, a tetraspanin, or a tumor antigen like the stress-related molecules MICA or PDL1. Then, after staining with a fluorophore-conjugated antibody directed against a different protein present on the EV surface, the EV-bead complex can be visualized in a conventional flow cytometer. The technique allows detection of proteins present on EVs isolated from tissue culture supernatants of melanoma cell lines and, more importantly, directly from plasma.

Therapeutic application of extracellular vesicles for musculoskeletal repair & regeneration

Traumatic musculoskeletal injuries are common in both the civilian and combat care settings. Significant barriers exist to repairing these injuries including fracture nonunion, muscle fibrosis, re-innervation, and compartment syndrome, as well as infection and inflammation. Recently, extracellular vesicles (EVs), including exosomes and microvesicles, have attracted attention in the field of musculoskeletal regeneration. These vesicles are released by different cell types and play a vital role in cell communication by delivering functional cargoes such as proteins and RNAs. Many of these cargo molecules can be utilized for repair purposes in skeletal disorders such as osteoporosis, osteogenesis imperfecta, sarcopenia, and fracture healing. There are, however, some challenges to overcome in order to advance the successful application of these vesicles in the therapeutic setting. These include large-scale production and isolation of exosomes, long-term storage, in vivo stability, and strategies for tissue-specific targeting and delivery. This paper reviews the general characteristics of exosomes along with their physiological roles and contribution to the pathogenesis of musculoskeletal diseases. We also highlight new findings on the use of synthetic exosomes to overcome the limitations of native exosomes in treating musculoskeletal injuries and disorders.

Exosomes: Their Role in Pathogenesis, Diagnosis and Treatment of Diseases

Simple Summary

The aim of this review is to provide an overview of the current scientific evidence concerning the role played by exosomes in the pathogenesis, diagnosis and treatment of diseases. The potential use of exosomes as delivery vectors for small-molecule therapeutic agents will be discussed. In addition, a special emphasis will be placed on the involvement of exosomes in oncological diseases, as well as to their potential therapeutic application as liquid biopsy tools mainly in cancer diagnosis. A better understanding of exosome biology could improve the results of clinical interventions using exosomes as therapeutic agents.

Abstract

Exosomes are lipid bilayer particles released from cells into their surrounding environment. These vesicles are mediators of near and long-distance intercellular communication and affect various aspects of cell biology. In addition to their biological function, they play an increasingly important role both in diagnosis and as therapeutic agents. In this paper, we review recent literature related to the molecular composition of exosomes, paying special attention to their role in pathogenesis, along with their application as biomarkers and as therapeutic tools. In this context, we analyze the potential use of exosomes in biomedicine, as well as the limitations that preclude their wider application.

Adsorption of extracellular vesicles onto the tube walls during storage in solution

Short term storage of extracellular vesicle (EV) solutions at +4°C is a common practice, but the stability of EVs during this procedure has not been fully understood yet. Using nanoparticle tracking analysis, we have shown that EVs isolated from the conditioned medium of HT-29 cells exhibit a pronounced concentration decrease when stored in PBS in ordinary polypropylene tubes within the range of (0.5–2.1) × 10¹⁰ particles/ml. EV losses reach 51±3% for 0.5 ml of EVs in Eppendorf 2 ml tube at 48 hours of storage at +4°C. Around 2/3 of the observed losses have been attributed to the adsorption of vesicles onto tube walls. This result shows that the lower part (up to at least 2 × 10¹⁰ particles/ml) of the practically relevant concentration range for purified EVs is prone to adsorption losses at +4°C. Total particle losses could be reduced to 18–21% at 48 hours by using either Eppendorf Protein LoBind tubes or ordinary tubes with the surface blocked with bovine serum albumin or EVs. Reduction of losses to 15% has been shown for isolated EVs dissolved in the supernatant after 100 000 g centrifugation as a model of conditioned medium. Also, a previously unknown feature of diffusion-controlled adsorption was revealed for EVs. In addition to the decrease in particle count, this process causes the predominant losses of smaller particles.

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.

Bead-Based Extracellular Vesicle Analysis Using Flow Cytometry

Extracellular vesicles (EVs) represent promising circulating biomarkers for cancers, but their high-throughput analyses in clinical settings prove challenging due to lack of simple, fast, and robust EV assays. Here, a bead-based EV assay detected by flow cytometry is described, which integrates EV capture using microbeads with EV protein analyses by flow cytometry. The assay is fast (<4 h for 48 samples), robust, and compatible with conventional flow cytometry instruments for high-throughput EV analysis. With the method, a panel of pancreatic cancer biomarkers in EVs from plasma samples of pancreatic cancer patients is successfully analyzed. The assay is readily translatable to other biomarkers or cancer types and can be run with standard materials on conventional flow cytometers, making it highly flexible and adaptable to diverse research and clinical needs.

Recent Advances in Experimental Models of Breast Cancer Exosome Secretion, Characterization and Function

Breast cancer (BC) is responsible for 15% of all the cancer deaths among women in the USA. The tumor microenvironment (TME) has the potential to act as a driver of breast cancer progression and metastasis. The TME is composed of stromal cells within an extracellular matrix and soluble cytokines, chemokines and extracellular vesicles and nanoparticles that actively influence cell behavior. Extracellular vesicles include exosomes, microvesicles and large oncosomes that orchestrate fundamental processes during tumor progression through direct interaction with target cells. Long before tumor cell spread to future metastatic sites, tumor-secreted exosomes enter the circulation and establish distant pre-metastatic niches, hospitable and permissive milieus for metastatic colonization. Emerging evidence suggests that breast cancer exosomes promote tumor progression and metastasis by inducing vascular leakiness, angiogenesis, invasion, immunomodulation and chemoresistance. Exosomes are found in almost all physiological fluids including plasma, urine, saliva, and breast milk, providing a valuable resource for the development of non-invasive cancer biomarkers. Here, we review work on the role of exosomes in breast cancer progression and metastasis, and describe the most recent advances in models of exosome secretion, isolation, characterization and functional analysis. We highlight the potential applications of plasma-derived exosomes as predictive biomarkers for breast cancer diagnosis, prognosis and therapy monitoring. We finally describe the therapeutic approaches of exosomes in breast cancer.

Preparation and characterization of extracellular vesicles

Extracellular vesicles (EVs) are heterogeneous membranous vesicles secreted by every cell type and offer significant potential in therapy and diagnostics. Differential ultracentrifugation is the gold standard for EV isolation, although other techniques including, polyethylene glycol (PEG) precipitation, immunoprecipitation, size exclusion chromatography, and immuno-isolation approaches are common. Purified EVs can be characterized based on their physical characteristics, biochemical composition, or cell of origin. For size and concentration measurement, nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), and electron microscopy are commonly employed methods. Biochemical analyses of EVs are typically performed using flow cytometry, immunoblotting, or proteomic investigation. Based on tissue of origin, EVs have specific markers that can be used to isolate and purify specific cell-associated EVs using an affinity selection approach. Despite existence of several methods for isolation and characterization, major limitations associated with each method hinder the progress of the field. Evolving concepts in EV biology possess great promise for better isolation and characterization leading to a better insight of biological function and have immense clinical implications. In this review, we discuss recent advancements in EV isolation and characterization approaches.

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.

Exosomes in Cardiovascular Diseases

Exosomes are nano-sized biovesicles of endocytic origin physiologically released by nearly all cell types into surrounding body fluids. They carry cell-specific cargos of protein, lipids, and genetic materials and can be selectively taken up by neighboring or distant cells. Since the intrinsic properties of exosomes are strictly influenced by the state of the parental cell and by the cellular microenvironment, the analysis of exosome origin and content, and their cell-targeting specificity, make them attractive as possible diagnostic and prognostic biomarkers. While the possible role of exosomes as messengers and a regenerative tool in cardiovascular diseases (CVDs) is actively investigated, the evidence about their usefulness as biomarkers is still limited and incomplete. Further complications are due to the lack of consensus regarding the most appropriate approach for exosome isolation and characterization, both important issues for their effective clinical translation. As a consequence, in this review, we will discuss the few information currently accessible about the diagnostic/prognostic potential of exosomes in CVDs and on the methodologies available for exosome isolation, analysis, and characterization.

Orally Administered 5-aminolevulinic Acid for Isolation and Characterization of Circulating Tumor-Derived Extracellular Vesicles in Glioblastoma Patients

Background: In glioblastoma (GB), tissue is required for accurate diagnosis and subtyping. Tissue can be obtained through resection or (stereotactic) biopsy, but these invasive procedures provide risks for patients. Extracellular vesicles (EVs) are small, cell-derived vesicles that contain miRNAs, proteins, and lipids, and possible candidates for liquid biopsies. GB-derived EVs can be found in the blood of patients, but it is difficult to distinguish them from circulating non-tumor EVs. 5-aminolevulinic acid (5-ALA) is orally administered to GB patients to facilitate tumor visualization and maximal resection, as it is metabolized to fluorescent protoporphyrin IX (PpIX) that accumulates in glioma cells. In this study, we assessed whether PpIX accumulates in GB-derived EVs and whether these EVs could be isolated and characterized to enable a liquid biopsy in GB. Methods: EVs were isolated from the conditioned media of U87 cells treated with 5-ALA by differential ultracentrifugation. Blood samples were collected and processed from healthy controls and patients undergoing 5-ALA guided surgery for GB. High-resolution flow cytometry (hFC) enabled detection and sorting of PpIX-positive EVs, which were subsequently analyzed by digital droplet PCR (ddPCR). Results: PpIX-positive EVs could be detected in conditioned cell culture media as well as in patient samples after administration of 5-ALA. By using hFC, we could sort the PpIX-positive EVs for further analysis with ddPCR, which indicated the presence of EVs and GB-associated miRNAs. Conclusion: GB-derived EVs can be isolated from the plasma of GB patients by using 5-ALA induced fluorescence. Although many challenges remain, our findings show new possibilities for the development of blood-based liquid biopsies in GB patients.

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.

Diameters and Fluorescence Calibration for Extracellular Vesicle Analyses by Flow Cytometry

Extracellular vesicles (EVs) play a crucial role in the intercellular crosstalk. Mesenchymal stem cell-derived EVs (MSC-EVs), displaying promising therapeutic roles, contribute to the strong rationale for developing EVs as an alternative therapeutic option. EV analysis still represents one of the major issues to be solved in order to translate the use of MSC-EV detection in clinical settings. Even if flow cytometry (FC) has been largely applied for EV studies, the lack of consensus on protocols for FC detection of EVs generated controversy. Standard FC procedures, based on scatter measurements, only allows the detection of the “tip of the iceberg” of all EVs. We applied an alternative FC approach based on the use of a trigger threshold on a fluorescence channel. The EV numbers obtained by the application of the fluorescence triggering resulted significantly higher in respect to them obtained from the same samples acquired by placing the threshold on the side scatter (SSC) channel. The analysis of EV concentrations carried out by three different standardized flow cytometers allowed us to achieve a high level of reproducibility (CV < 20%). By applying the here-reported method highly reproducible results in terms of EV analysis and concentration measurements were obtained.

Challenges in the development and establishment of exosome-based drug delivery systems

Exosomes are extracellular vesicles released from cells and are characterized by a lipid bilayer membrane encapsulating a variety of biological molecules such as nucleic acids or proteins within the lumen or the lipid-bilayer. Under physiological environments, exosomes mediate cell-to-cell communication and cargo transport. Therefore, exosomes have been explored as drug delivery vehicles for improving therapeutic outcomes. Although recent studies have demonstrated promising advances with exosome-based drug delivery systems, several challenges severely hinder further development of exosomes for clinical applications. This review summarizes and emphasizes some of the technical challenges related to the isolation, characterization, and stability testing of exosomes. More importantly, challenges related specifically to the application of exosomes for drug delivery such as cell-uptake, drug loading, drug release, and in vivo distribution will be examined in this article.

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).

Improvement, scaling-up, and downstream analysis of exosome production

Exosomes are the most researched extracellular vesicles. In many biological, physiological, and pathological studies, they have been identified as suitable candidates for treatment and diagnosis of diseases by acting as the carriers of both drugs and genes. Considerable success has been achieved regarding the use of exosomes for tissue regeneration, cancer diagnosis, and targeted drug/gene delivery to specific tissues. While major progress has been made in exosome extraction and purification, extraction of large quantities of exosomes is still a major challenge. This issue limits the scope of both exosome-based research and therapeutic development. In this review, we have aimed to summarize experimental studies focused at increasing the number of exosomes. Biotechnological studies aimed at identifying the pathways of exosome biogenesis to manipulate some genes in order to increase the production of exosomes. Generally, two major strategies are employed to increase the production of exosomes. First, oogenesis pathways are genetically manipulated to overexpress activator genes of exosome biogenesis and downregulate the genes involved in exosome recycling pathways. Second, manipulation of the cell culture medium, treatment with specific drugs, and limiting certain conditions can force the cell to produce more exosomes. In this study, we have reviewed and categorized these strategies. It is hoped that the information presented in this review will provide a better understanding for expanding biotechnological approaches in exosome-based therapeutic development.

A flow virometry process proposed for detection of SARS-CoV-2 and large-scale screening of COVID-19 cases

The viral pneumonia COVID-19, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread rapidly over 210 countries and declared as pandemic by WHO. WHO has emphasized on the scale-up of testing capacity, followed by isolation of infected individuals, and contact tracing, as the ‘backbone’ of managing the pandemic. Globally, the detection of SARS-CoV-2 in patients is done by real-time PCR (RT-PCR) and blood antibody-based testing. Here, a flow cytometry-based high-throughput screening system is proposed for testing of COVID-19 cases where the virus particle binds to specific primary antibodies and the resultant virus–antibody complex then binds to fluorescent-tagged secondary antibodies. The fluorescence signal could be measured in a flow channel for qualitative detection of virus in the test sample.

Zeta Potential of Extracellular Vesicles: Toward Understanding the Attributes that Determine Colloidal Stability

Extracellular vesicles (EVs), including exosomes and microvesicles (<200 nm), play a vital role in intercellular communication and carry a net negative surface charge under physiological conditions. Zeta potential (ZP) is a popular method to measure the surface potential of EVs, while used as an indicator of surface charge, and colloidal stability influenced by surface chemistry, bioconjugation, and the theoretical model applied. Here, we investigated the effects of such factors on ZP of well-characterized EVs derived from the human choriocarcinoma JAr cells. The EVs were suspended in phosphate-buffered saline (PBS) of various phosphate ionic concentrations (0.01, 0.1, and 1 mM), with or without detergent (Tween-20), or in the presence (10 mM) of different salts (NaCl, KCl, CaCl₂, and AlCl₃) and at different pH values (4, 7, and 10) while the ZP was measured. The ZP changed inversely with the buffer concentration, while Tween-20 caused a significant (p < 0.05) lowering of the ZP. Moreover, the ZP was significantly (p < 0.05) less negative in the presence of ions with higher valency (Al³⁺/Ca²⁺) than in the presence of monovalent ones (Na⁺/K⁺). Besides, the ZP of EVs became less negative at acidic pH, and vice versa. The integrated data underpins the crucial role of physicochemical attributes that influence the colloidal stability of EVs.

Direct counting of exosomes in a cell culture medium using neither isolation nor preconcentration

Exosomes are expected to be biomarkers of cancer since they contain information about the cells that excrete them. In this study we developed a method to count the exosomes secreted from cancer cells in a culture medium without the need for isolation and/or preconcentration. This detection system consists of a square capillary on which a laser beam is focused in a sheet shape via the use of two cylindrical lenses. A fluorescently labeled anti-CD63 antibody is used to mark the exosomes that are then flowed into the square capillary. In this study, individual exosomes were observed on a trajectory when passing through the laser beam sheet and were counted for 10 min at a constant flow velocity. The total analysis time was less than 1.5 h including the steps required to remove large particles and allow reaction with the antibody. The results for two samples prepared with and without the isolation of exosomes showed a loss of exosomes in the isolation step. We also determined the number of the exosomes secreted by the cells to a culture medium during cultivation. As expected, the total number of exosomes in a culture medium increased with an increase in the cultivation time, and the number of exosomes released every 12 h either remained constant or showed no more than a slight increase for as long as 72 h. It was unclear whether the number exosomes was dependent on the cell population at confluences of 10-60%.