Systematic review of factors influencing extracellular vesicle yield from cell cultures

Process development for the production of mesenchymal stromal cell-derived extracellular vesicles in conventional 2D systems

BACKGROUND

In recent years, the importance of extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) has increased significantly. For their widespread use, a standardized EV manufacturing is needed which often includes conventional, static 2D systems. For these system critical process parameters need to be determined.

METHODS

We studied the impact of process parameters on MSC proliferation, MSC-derived particle production including EVs, EV- and MSC-specific marker expression, and particle functionality in a HaCaT cell migration assay.

RESULTS

We found that cell culture growth surface and media affected MSCs and their secretory behavior. Interestingly, the materials that promoted MSC proliferation did not necessarily result in the most functional MSC-derived particles. In addition, we found that MSCs seeded at 4 × 103 cells cm-2 produced particles with improved functional properties compared to higher seeding densities. MSCs in a highly proliferative state did not produce the most particles, although these particles were significantly more effective in promoting HaCaT cell migration. The same correlation was found when investigating the cultivation temperature. A physiological temperature of 37°C was not optimal for particle yield, although it resulted in the most functional particles. We observed a proliferation-associated particle production and found potential correlations between particle production and glucose consumption, enabling the estimation of final particle yields.

CONCLUSIONS

Our findings suggest that parameters, which must be defined prior to each individual cultivation and do not require complex and expensive equipment, can significantly increase MSC-derived particle production including EVs. Integrating these parameters into a standardized EV process development paves the way for robust and efficient EV manufacturing for early clinical phases.

Immersed in a reservoir of potential: amniotic fluid-derived extracellular vesicles

This review aims to encapsulate the current knowledge in extracellular vesicles extracted from amniotic fluid and amniotic fluid derived stem/stromal cells. Amniotic fluid (AF) bathes the developing fetus, providing nutrients and protection from biological and mechanical dangers. In addition to containing a myriad of proteins, immunoglobulins and growth factors, AF is a rich source of extracellular vesicles (EVs). These vesicles originate from cells in the fetoplacental unit. They are biological messengers carrying an active cargo enveloped within the lipid bilayer. EVs in reproduction are known to play key roles in all stages of pregnancy, starting from fertilisation through to parturition. The intriguing biology of AF-derived EVs (AF-EVs) in pregnancy and their untapped potential as biomarkers is currently gaining attention. EV studies in numerous animal and human disease models have raised expectations of their utility as therapeutics. Amniotic fluid stem cell and mesenchymal stromal cell-derived EVs (AFSC-EVs) provide an established supply of laboratory-made EVs. This cell-free mode of therapy is popular as an alternative to stem cell therapy, revealing similar, if not better therapeutic outcomes. Research has demonstrated the successful application of AF-EVs and AFSC-EVs in therapy, harnessing their anti-inflammatory, angiogenic and regenerative properties. This review provides an overview of such studies and discusses concerns in this emerging field of research.

Characterization of Nanohybridosomes from Lipids and Spruce Homogenate Containing Extracellular Vesicles

Introduction

Lipid nanovesicles associated with bioactive phytochemicals from spruce needle homogenate (here called nano-sized hybridosomes or nanohybridosomes, NSHs) were considered.

Methods

We formed NSHs by mixing appropriate amounts of lecithin, glycerol and supernatant of isolation of extracellular vesicles from spruce needle homogenate. We visualized NSHs by light microscopy and cryogenic transmission electron microscopy and assessed them by flow cytometry, dynamic light scattering, ultraviolet-visual spectroscopy, interferometric light microscopy and liquid chromatography-mass spectrometry.

Results

We found that the particles consisted of a bilayer membrane and a fluid-like interior. Flow cytometry and interferometric light microscopy measurements showed that the majority of the particles were nano-sized. Dynamic light scattering and interferometric light microscopy measurements agreed well on the average hydrodynamic radius of the particles Rh (between 140 and 180 nm), while the concentrations of the particles were in the range between 1013 and 1014/mL indicating that NSHs present a considerable (more than 25%) of the sample which is much more than the yield of natural extracellular vesicles (EVs) from spruce needle homogenate (estimated less than 1%). Spruce specific lipids and proteins were found in hybridosomes.

Discussion

Simple and low-cost preparation method, non-demanding saving process and efficient formation procedure suggest that large-scale production of NSHs from lipids and spruce needle homogenate is feasible.

CRISPR-Cas9 delivery strategies with engineered extracellular vesicles

Therapeutic genome editing has the potential to cure diseases by directly correcting genetic mutations in tissues and cells. Recent progress in the CRISPR-Cas9 systems has led to breakthroughs in gene editing tools because of its high orthogonality, versatility, and efficiency. However, its safe and effective administration to target organs in patients is a major hurdle. Extracellular vesicles (EVs) are endogenous membranous particles secreted spontaneously by all cells. They are key actors in cell-to-cell communication, allowing the exchange of select molecules such as proteins, lipids, and RNAs to induce functional changes in the recipient cells. Recently, EVs have displayed their potential for trafficking the CRISPR-Cas9 system during or after their formation. In this review, we highlight recent developments in EV loading, surface functionalization, and strategies for increasing the efficiency of delivering CRISPR-Cas9 to tissues, organs, and cells for eventual use in gene therapies.

Polyethylene glycol precipitation is an efficient method to obtain extracellular vesicle-depleted fetal bovine serum

Mesenchymal stromal/stem cell derived-extracellular vesicles (MSC-EVs) have gained interest as drug delivery nanoparticles, having immunoregulatory and potentiating tissue repair property. To maintain growth of MSCs and obtain pure MSC-derived EVs, the culture media should contain fetal bovine serum (FBS) devoid of EVs, as the presence of FBS EVs confounds the properties of MSC-EVs. Therefore, we tested three methods: 18h ultracentrifugation (UC) and ultrafiltration (UF), which are common FBS EV depletion methods in current MSC-EV research, and polyethylene glycol (PEG) precipitation to obtain three EV depleted FBS (EVdFBS) batches, and compared them to FBS and commercial (Com) EVdFBS on human adipose stem cell (hADSC) growth, differentiation, enrichment of EVs in hADSC supernatant and their biological function on collagen metabolism. Our comparative study showed UC and UF vary in terms of depletion efficiency and do not completely deplete EVs and affects the growth-promoting quality of FBS. Specifically, FBS EV depletion was comparable between PEG (95.6%) and UF (96.6%) but less by UC (82%), as compared to FBS. FBS protein loss was markedly different among PEG (47%), UF (87%), and UC (51%), implying the ratio of EV depletion over protein loss was PEG (2.03), UF (1.11), and UC (1.61). A significant decrease of TGFβ/Smad signaling, involving in MSC growth and physiology, was observed by UF. After 96 hours of exposure to 5% FBS or 5% four different EVdFBS cell growth media, the osteogenesis ability of hADSCs was not impaired but slightly lower mRNA expression level of Col2a observed in EVdFBS media during chondrogenesis. In consistent with low confluency of hADSCs observed by optical microscope, cell proliferation in response to 5% UF EVdFBS media was inhibited significantly. Importantly, more and purer ADSCs EVs were obtained from ADSCs cultured in 5% PEG EVdFBS media, and they retained bioactive as they upregulated the expression of Col1a1, TIMP1 of human knee synovial fibroblast. Taken together, this study showed that PEG precipitation is the most efficient method to obtain EV depleted FBS for growth of MSCs, and to obtain MSC EVs with minimal FBS EV contamination.

A comprehensive review of quantum bioreactor cell manufacture: Research and clinical applications

The Quantum cell expansion system manufactured by Terumo-BCT is perhaps the most widely reported Good Manufacturing Practice-compliant bioreactor used for the expansion of adherent cell populations, both for research purposes and clinical cell-based therapies/trials. Although the system was originally designed for adherent cell expansion, more recently suspension cultures and extracellular vesicle manufacturing protocols have been published using the Quantum system. Cell therapy research and regenerative medicine in general is a rapidly expanding field and as such it is likely that the use of this system will become even more widespread and perhaps mandatory, for both research and development and in the clinic. The purpose of this review is to describe, compare and discuss the diverse range of research and clinical applications currently using the Quantum system, which to our knowledge has not previously been reviewed. In addition, current and future challenges will also be discussed.

Cell culture-derived extracellular vesicles: Considerations for reporting cell culturing parameters

Cell culture-conditioned medium (CCM) is a valuable source of extracellular vesicles (EVs) for basic scientific, therapeutic and diagnostic applications. Cell culturing parameters affect the biochemical composition, release and possibly the function of CCM-derived EVs (CCM-EV). The CCM-EV task force of the Rigor and Standardization Subcommittee of the International Society for Extracellular Vesicles aims to identify relevant cell culturing parameters, describe their effects based on current knowledge, recommend reporting parameters and identify outstanding questions. While some recommendations are valid for all cell types, cell-specific recommendations may need to be established for non-mammalian sources, such as bacteria, yeast and plant cells. Current progress towards these goals is summarized in this perspective paper, along with a checklist to facilitate transparent reporting of cell culturing parameters to improve the reproducibility of CCM-EV research.

Pharmacokinetic Approach for the Elucidation of Elevated Plasma Small Extracellular Vesicle (sEV) Concentration in Cancer

The abundance of circulating plasma small extracellular vesicles (sEVs) has been reported to be elevated in cancer; however, the underlying mechanism remains unclear. In this study, a pharmacokinetic approach was used to determine the factors contributing to elevated plasma sEV levels during cancer in a tumor-bearing mouse model. Mouse plasma-derived sEVs (MP-sEVs) isolated from tumor-bearing mice showed increased protein concentrations and physicochemical characteristics comparable to MP-sEVs isolated from healthy mice. The steady-state concentration of sEVs is determined by the balance between the MP-sEV production and clearance. Thus, to determine whether tumorigenesis influences sEV clearance, isolated MP-sEVs were intravenously administered to either tumor-bearing or healthy mice. The results showed minimal differences in sEV clearance rates, suggesting that sEV production is the driving force of elevated MP-sEV concentrations. Lastly, CD63-gLuc stably expressing B16BL6-bearing mice were used to estimate the contribution of tumor cell-derived sEVs in the plasma. The gLuc activity of the MP-sEVs isolated was below the limit of detection, and it was estimated that the tumor cell-derived sEVs comprised at most 0.5% of the total MP-sEVs. Taken together, these results suggest that cells other than tumor cells contribute to elevated plasma sEV levels in cancer.

Assessment of anti-inflammatory bioactivity of extracellular vesicles is susceptible to error via media component contamination

Extracellular vesicles (EVs) are widely implicated as novel diagnostic and therapeutic modalities for a wide range of diseases. Thus, optimization of EV biomanufacturing is of high interest. In the course of developing parameters for a human embryonic kidney cells (HEK293T) EV production platform, we examined the combinatorial effects of cell culture conditions (i.e., static versus dynamic) and isolation techniques (i.e., ultracentrifugation versus tangential flow filtration versus size-exclusion chromatography) on functional characteristics of HEK293T EVs, including anti-inflammatory bioactivity using a well-established lipopolysaccharide-stimulated mouse macrophage model. We unexpectedly found that, depending on culture condition and isolation strategy, HEK293T EVs appeared to significantly suppress the secretion of pro-inflammatory cytokines (i.e., interleukin-6, RANTES [regulated upon activation, normal T cell expressed and secreted]) in the stimulated mouse macrophages. Further examination revealed that these results were most likely due to non-EV fetal bovine serum components in HEK293T EV preparations. Thus, future research assessing the anti-inflammatory effects of EVs should be designed to account for this phenomenon.

Magnetic enrichment of immuno-specific extracellular vesicles for mass spectrometry using biofilm-derived iron oxide nanowires

Immuno-specific enrichment of extracellular vesicles (EVs) can provide important information into cellular pathways underpinning various pathologies and for non-invasive diagnostics, including mass spectrometry-based analyses. Herein, we report an optimised protocol for immuno-magnetic enrichment of specific EV subtypes and their subsequent processing with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Specifically, we conjugated placental alkaline phosphatase (PLAP) antibodies to magnetic iron oxide nanowires (NWs) derived from bacterial biofilms and demonstrated the utility of this approach by enriching placenta-specific EVs (containing PLAP) from cell culture media. We demonstrate efficient PLAP+ve EV enrichment for both NW-PLAP and Dynabeads™-PLAP, with high PLAP protein recovery (83.7 ± 8.9% and 83.2 ± 5.9%, respectively), high particle-to-protein ratio (7.5 ± 0.7 × 10⁹ and 7.1 ± 1.2 × 10⁹, respectively), and low non-specific binding of non-target EVs (7 ± 3.2% and 5.4 ± 2.2%, respectively). Furthermore, our optimized EV enrichment and processing approach identified 2518 and 2545 protein groups with LC-MS/MS for NW-PLAP and Dynabead™-PLAP, respectively, with excellent reproducibility (Pearson correlation 0.986 and 0.988). These findings demonstrate that naturally occurring iron oxide NWs have comparable performance to current gold standard immune-magnetic beads. The optimized immuno-specific EV enrichment for LC-MS/MS method provides a low-cost and highly-scalable yet efficient, high-throughput approach for quality EV proteomic studies.

Convenient exosome separation by phosphatidylserine targeting polymer brush materials

We report phosphatidylserine targeting polymer brush materials to selectively separate exosomes. This method provides an efficient separation strategy with ordinary centrifuge force, which improves the integrity and purity of the exosomes. Compared with the common methods, the content of contaminated lipoprotein in the resulting exosomes decreased obviously.

Extracellular Vesicles and Cellular Ageing

Ageing is a complex process characterized by deteriorated performance at multiple levels, starting from cellular dysfunction to organ degeneration. Stem cell-based therapies aim to administrate stem cells that eventually migrate to the injured site to replenish the damaged tissue and recover tissue functionality. Stem cells can be easily obtained and cultured in vitro, and display several qualities such as self-renewal, differentiation, and immunomodulation that make them suitable candidates for stem cell-based therapies. Current animal studies and clinical trials are being performed to assess the safety and beneficial effects of stem cell engraftments for regenerative medicine in ageing and age-related diseases.Since alterations in cell-cell communication have been associated with the development of pathophysiological processes, new research is focusing on the modulation of the microenvironment. Recent research has highlighted the important role of some microenvironment components that modulate cell-cell communication, thus spreading signals from damaged ageing cells to neighbor healthy cells, thereby promoting systemic ageing. Extracellular vesicles (EVs) are small-rounded vesicles released by almost every cell type. EVs cargo includes several bioactive molecules, such as lipids, proteins, and genetic material. Once internalized by target cells, their specific cargo can induce epigenetic modifications and alter the fate of the recipient cells. Also, EV's content is dependent on the releasing cells, thus, EVs can be used as biomarkers for several diseases. Moreover, EVs have been proposed to be used as cell-free therapies that focus on their administration to slow or even reverse some hallmarks of physiological ageing. It is not surprising that EVs are also under study as next-generation therapies for age-related diseases.

A quick pipeline for the isolation of 3D cell culture-derived extracellular vesicles

Recent advances in cell biology research regarding extracellular vesicles have highlighted an increasing demand to obtain 3D cell culture-derived EVs, because they are considered to more accurately represent EVs obtained in vivo. However, there is still a grave need for efficient and tunable methodologies to isolate EVs from 3D cell cultures. Using nanofibrillar cellulose (NFC) scaffold as a 3D cell culture matrix, we developed a pipeline of two different approaches for EV isolation from cancer spheroids. A batch method was created for delivering high EV yield at the end of the culture period, and a harvesting method was created to enable time-dependent collection of EVs to combine EV profiling with spheroid development. Both these methods were easy to set up, quick to perform, and they provided a high EV yield. When compared to scaffold-free 3D spheroid cultures on ultra-low affinity plates, the NFC method resulted in similar EV production/cell, but the NFC method was scalable and easier to perform resulting in high EV yields. In summary, we introduce here an NFC-based, innovative pipeline for acquiring EVs from 3D cancer spheroids, which can be tailored to support the needs of variable EV research objectives.

Methods of the Large-Scale Production of Extracellular Vesicles

To date, extracellular vesicles (EVs) have been extensively investigated as potential substitutes for cell therapy. Research has suggested their ability to overcome serious risks associated with the application of these cells. Although, the translation of EVs into clinical practice is hampered by the lack of a cheap reasonable way to obtain a clinically relevant number of EVs, an available method for the large-scale production of EVs ensures vesicles’ integrity, preserves their biological activity, and ensures they are well reproducible, providing homogeneity of the product from batch to batch. In this review, advances in the development of methods to increase EVs production are discussed. The existing approaches can be divided into the following: (1) those based on increasing the production of natural EVs by creating and using high capacity “cell factories”, (2) those based on the induction of EVs secretion under various cell stressors, and (3) those based on cell fragmentation with the creation of biomimetic vesicles. The aim of this review is to stimulate the introduction of EVs into clinical practice and to draw attention to the development of new methods of EVs production on a large scale.

Magnetic bead-based adsorption strategy for exosome isolation

Exosomes, one type of extracellular vesicle (EV) secreted by cells, participate in intercellular communication and other biological processes as carriers of lipids, functional proteins, mRNAs, miRNAs, lncRNAs, and DNA fragments. Their presence in biofluids makes them attractive candidates as innovative clinical diagnostic tools. However, the conventional isolation and analysis of high-purity exosomes in clinical application is challenging, with traditional methods facing a number of shortcomings, including low yield or purity, long periods of processing, high cost, and difficulties in standardization. In this study, we provide an overview of commonly used exosome isolation approaches with a focus on magnetic bead-based capture, an ideal methodology with high purity and integrality of exosomes. The current challenges on exosome isolation methods are also described to highlight areas for future research and development.

Overcoming the blood-brain barrier: Exosomes as theranostic nanocarriers for precision neuroimaging

Exosomes are cell-derived vesicles with a lipid bilayer membrane that play important roles in intercellular communication. They provide an unprecedented opportunity for the development of drug delivery nanoplatforms due to their low immunogenicity, low toxicity, biocompatibility, stability, and ability to change the functions of recipient cells. In addition, exosomes can penetrate the blood-brain barrier and then target and accumulate in relevant pathological brain regions. However, few studies have focused on the applications of exosomes as nanocarriers for use in precision neuroimaging studies. Thus, this report presents the feasibility of fabricating specific exosome-based diagnostic reagents for the application of personalized/precision radiology in the central nervous system based on important recent fundamental discoveries and technological advances.

Isolation, characterization, and functional study of extracellular vesicles derived from Leishmania tarentolae

Leishmania (L.) species are protozoan parasites with a complex life cycle consisting of a number of developmental forms that alternate between the sand fly vector and their host. The non-pathogenic species L. tarentolae is not able to induce an active infection in a human host. It has been observed that, in pathogenic species, extracellular vesicles (EVs) could exacerbate the infection. However, so far, there is no report on the identification, isolation, and characterization of L. tarentolae EVs. In this study, we have isolated and characterized EVs from L. tarentolaeGFP+ (tEVs) along with L. majorGFP+ as a reference and positive control. The EVs secreted by these two species demonstrated similar particle size distribution (approximately 200 nm) in scanning electron microscopy and nanoparticle tracking analysis. Moreover, the said EVs showed similar protein content, and GFP and GP63 proteins were detected in both using dot blot analysis. Furthermore, we could detect Leishmania-derived GP63 protein in THP-1 cells treated with tEVs. Interestingly, we observed a significant increase in the production of IFN-γ, TNF-α, and IL-1β, while there were no significant differences in IL-6 levels in THP-1 cells treated with tEVs following an infection with L. major compared with another group of macrophages that were treated with L. major EVs prior to the infection. Another exciting observation of this study was a significant decrease in parasite load in tEV-treated Leishmania-infected macrophages. In addition, in comparison with another group of Leishmania-infected macrophages which was not exposed to any EVs, tEV managed to increase IFN-γ and decrease IL-6 and the parasite burden. In conclusion, we report for the first time that L. tarentolae can release EVs and provide evidence that tEVs are able to control the infection in human macrophages, making them a great potential platform for drug delivery, at least for parasitic infections.

Characterization of Extracellular Vesicles Secreted by a Clinical Isolate of Naegleria fowleri and Identification of Immunogenic Components within Their Protein Cargo

Extracellular vesicles (EVs) are small lipid vesicles released by both prokaryotic and eukaryotic cells, involved in intercellular communication, immunomodulation and pathogenesis. In this study, we performed a characterization of the EVs produced by trophozoites of a clinical isolate of the free-living amoeba Naegleria fowleri (N. fowleri). Size distribution, zeta potential, protein profile and protease activity were analyzed. Under our incubation conditions, EVs of different sizes were observed, with a predominant population ranging from 206 to 227 nm. SDS-PAGE revealed protein bands of 25 to 260 KDa. The presence of antigenic proteins was confirmed by Western blot, which evidenced strongest recognition by rat polyclonal antibodies raised against N. fowleri in the region close to 80 KDa and included peptidases, as revealed by zymography. Proteins in selected immunorecognized bands were further identified using nano-ESI-MS/MS. A preliminary proteomic profile of the EVs identified at least 184 proteins as part of the vesicles' cargo. Protease activity assays, in combination with the use of inhibitors, revealed the predominance of serine proteases. The present characterization uncovers the complexity of EVs produced by N. fowleri, suggesting their potential relevance in the release of virulence factors involved in pathogenicity. Owing to their cargo's diversity, further research on EVs could reveal new therapeutic targets or biomarkers for developing rapid and accurate diagnostic tools for lethal infections such as the one caused by this amoeba.

Characterisation of Extracellular Vesicles from Equine Mesenchymal Stem Cells

Extracellular vesicles (EVs) are nanosized lipid bilayer-encapsulated particles secreted by virtually all cell types. EVs play an essential role in cellular crosstalk in health and disease. The cellular origin of EVs determines their composition and potential therapeutic effect. Mesenchymal stem/stromal cell (MSC)-derived EVs have shown a comparable therapeutic potential to their donor cells, making them a promising tool for regenerative medicine. The therapeutic application of EVs circumvents some safety concerns associated with the transplantation of viable, replicating cells and facilitates the quality-controlled production as a ready-to-go, off-the-shelf biological therapy. Recently, the International Society for Extracellular Vesicles (ISEV) suggested a set of minimal biochemical, biophysical and functional standards to define extracellular vesicles and their functions to improve standardisation in EV research. However, nonstandardised EV isolation methods and the limited availability of cross-reacting markers for most animal species restrict the application of these standards in the veterinary field and, therefore, the species comparability and standardisation of animal experiments. In this study, EVs were isolated from equine bone-marrow-derived MSCs using two different isolation methods, stepwise ultracentrifugation and size exclusion chromatography, and minimal experimental requirements for equine EVs were established and validated. Equine EVs were characterised using a nanotracking analysis, fluorescence-triggered flow cytometry, Western blot and transelectron microscopy. Based on the ISEV standards, minimal criteria for defining equine EVs are suggested as a baseline to allow the comparison of EV preparations obtained by different laboratories.

Fatty Acid Fingerprints and Hyaluronic Acid in Extracellular Vesicles from Proliferating Human Fibroblast-like Synoviocytes

Extracellular vesicles (EVs) function as conveyors of fatty acids (FAs) and other bioactive lipids and can modulate the gene expression and behavior of target cells. EV lipid composition influences the fluidity and stability of EV membranes and reflects the availability of lipid mediator precursors. Fibroblast-like synoviocytes (FLSs) secrete EVs that transport hyaluronic acid (HA). FLSs play a central role in inflammation, pannus formation, and cartilage degradation in joint diseases, and EVs have recently emerged as potential mediators of these effects. The aim of the present study was to follow temporal changes in HA and EV secretion by normal FLSs, and to characterize the FA profiles of FLSs and EVs during proliferation. The methods used included nanoparticle tracking analysis, confocal laser scanning microscopy, sandwich-type enzyme-linked sorbent assay, quantitative PCR, and gas chromatography. The expression of hyaluronan synthases 1-3 in FLSs and HA concentrations in conditioned media decreased during cell proliferation. This was associated with elevated proportions of 20:4n-6 and total n-6 polyunsaturated FAs (PUFAs) in high-density cells, reductions in n-3/n-6 PUFA ratios, and up-regulation of cluster of differentiation 44, tumor necrosis factor α, peroxisome proliferator-activated receptor (PPAR)-α, and PPAR-γ. Compared to the parent FLSs, 16:0, 18:0, and 18:1n-9 were enriched in the EV fraction. EV counts decreased during cell growth, and 18:2n-6 in EVs correlated with the cell count. To conclude, FLS proliferation was featured by increased 20:4n-6 proportions and reduced n-3/n-6 PUFA ratios, and FAs with a low degree of unsaturation were selectively transferred from FLSs into EVs. These FA modifications have the potential to affect membrane fluidity, biosynthesis of lipid mediators, and inflammatory processes in joints, and could eventually provide tools for translational studies to counteract cartilage degradation in inflammatory joint diseases.

Extracellular Vesicles from Human Cardiac Fibroblasts Modulate Calcium Cycling in Human Stem Cell-Derived Cardiomyocytes

Cardiac fibroblasts regulate the development of the adult cardiomyocyte phenotype and cardiac remodeling in disease. We investigate the role that cardiac fibroblasts-secreted extracellular vesicles (EVs) have in the modulation of cardiomyocyte Ca²⁺ cycling–a fundamental mechanism in cardiomyocyte function universally altered during disease. EVs collected from cultured human cardiac ventricular fibroblasts were purified by centrifugation, ultrafiltration and size-exclusion chromatography. The presence of EVs and EV markers were identified by dot blot analysis and electron microscopy. Fibroblast-conditioned media contains liposomal particles with a characteristic EV phenotype. EV markers CD9, CD63 and CD81 were highly expressed in chromatography fractions that elute earlier (Fractions 1–15), with most soluble contaminating proteins in the later fractions collected (Fractions 16–30). Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were treated with fibroblast-secreted EVs and intracellular Ca²⁺ transients were analyzed. Fibroblast-secreted EVs abbreviate the Ca²⁺ transient time to peak and time to 50% decay versus serum-free controls. Thus, EVs from human cardiac fibroblasts represent a novel mediator of human fibroblast-cardiomyocyte interaction, increasing the efficiency of hiPSC-CM Ca²⁺ handling.

Identifying the Efficacy of Extracellular Vesicles in Osteogenic Differentiation: An EV-Lution in Regenerative Medicine

Mesenchymal stromal cells (MSCs) have long been the focus for regenerative medicine and the restoration of damaged or aging cells throughout the body. However, the efficacy of MSCs in cell-based therapy still remains unpredictable and carries with it enumerable risks. It is estimated that only 3-10% of MSCs survive transplantation, and there remains undefined and highly variable heterogeneous biological potency within these administered cell populations. The mode of action points to secreted factors produced by MSCs rather than the reliance on engraftment. Hence harnessing such secreted elements as a replacement for live-cell therapies is attractive. Extracellular vesicles (EVs) are heterogenous lipid bounded structures, secreted by cells. They comprise a complex repertoire of molecules including RNA, proteins and other factors that facilitate cell-to-cell communication. Described as protected signaling centers, EVs can modify the cellular activity of recipient cells and are emerging as a credible alternative to cell-based therapies. EV therapeutics demonstrate beneficial roles for wound healing by preventing apoptosis, moderating immune responses, and stimulating angiogenesis, in addition to promoting cell proliferation and differentiation required for tissue matrix synthesis. Significantly, EVs maintain their signaling function following transplantation, circumventing the issues related to cell-based therapies. However, EV research is still in its infancy in terms of their utility as medicinal agents, with many questions still surrounding mechanistic understanding, optimal sourcing, and isolation of EVs for regenerative medicine. This review will consider the efficacy of using cell-derived EVs compared to traditional cell-based therapies for bone repair and regeneration. We discuss the factors to consider in developing productive lines of inquiry and establishment of standardized protocols so that EVs can be harnessed from optimal secretome production, to deliver reproducible and effective therapies.

Adipose Tissue-Derived Mesenchymal Stem/Stromal Cells and Their Contribution to Angiogenic Processes in Tissue Regeneration

Mesenchymal stem/stromal cells (MSCs) are widely described in the context of their regenerative and immunomodulatory activity. MSCs are isolated from various tissues and organs. The most frequently described sources are bone marrow and adipose tissue. As stem cells, MSCs are able to differentiate into other cell lineages, but they are usually reported with respect to their paracrine potential. In this review, we focus on MSCs derived from adipose tissue (AT-MSCs) and their secretome in regeneration processes. Special attention is given to the contribution of AT-MSCs and their derivatives to angiogenic processes described mainly in the context of angiogenic dysfunction. Finally, we present clinical trials registered to date that concern the application of AT-MSCs and their secretome in various medical conditions.

Culture Condition of Bone Marrow Stromal Cells Affects Quantity and Quality of the Extracellular Vesicles

Extracellular vesicles (EVs) released by bone marrow stromal cells (BMSCs) have been shown to act as a transporter of bioactive molecules such as RNAs and proteins in the therapeutic actions of BMSCs in various diseases. Although EV therapy holds great promise to be a safer cell-free therapy overcoming issues related to cell therapy, manufacturing processes that offer scalable and reproducible EV production have not been established. Robust and scalable BMSC manufacturing methods have been shown to enhance EV production; however, the effects on EV quality remain less studied. Here, using human BMSCs isolated from nine healthy donors, we examined the effects of high-performance culture media that can rapidly expand BMSCs on EV production and quality in comparison with the conventional culture medium. We found significantly increased EV production from BMSCs cultured in the high-performance media without altering their multipotency and immunophenotypes. RNA sequencing revealed that RNA contents in EVs from high-performance media were significantly reduced with altered profiles of microRNA enriched in those related to cellular growth and proliferation in the pathway analysis. Given that pre-clinical studies at the laboratory scale often use the conventional medium, these findings could account for the discrepancy in outcomes between pre-clinical and clinical studies. Therefore, this study highlights the importance of selecting proper culture conditions for scalable and reproducible EV manufacturing.

Isolation methods of large and small extracellular vesicles derived from cardiovascular progenitors: A comparative study

Since the discovery of the beneficial therapeutical effects of extracellular vesicles (EVs), these agents have been attracting great interest as next-generation therapies. EVs are nanosized membrane bodies secreted by all types of cells that mediate cell-cell communication. Although the classification of different subpopulations of EVs can be complex, they are broadly divided into microvesicles and exosomes based on their biogenesis and in large and small EVs based on their size. As this is an emerging field, current investigations are focused on basic aspects such as the more convenient method for EV isolation. In the present paper, we used cardiac progenitor cells (CPCs) to study and compare different cell culture conditions for EV isolation as well as two of the most commonly employed purification methods: ultracentrifugation (UC) and size-exclusion chromatography (SEC). Large and small EVs were separately analysed. We found that serum starvation of cells during the EV collecting period led to a dramatic decrease in EV secretion and major cell death. Regarding the isolation method, our findings suggest that UC and SEC gave similar EV recovery rates. Separation of large and small EV-enriched subpopulations was efficiently achieved with both purification protocols although certain difference in sample heterogeneity was observed. Noteworthy, while calnexin was abundant in large EVs, ALIX and CD63 were mainly found in small EVs. Finally, when the functionality of EVs was assessed on primary culture of adult murine cardiac fibroblasts, we found that EVs were taken up by these cells, which resulted in a pronounced reduction in the proliferative and migratory capacity of the cells. Specifically, a tendency towards a larger effect of SEC-related EVs was observed. No differences could be found between large and small EVs. Altogether, these results contribute to establish the basis for the use of EVs as therapeutic platforms, in particular in regenerative fields.

Extracellular vesicles: General features and usefulness in diagnosis and therapeutic management of colorectal cancer

In the world, among all type of cancers, colorectal cancer (CRC) is the third most commonly diagnosed in males and the second in females. In most of cases, (RP1) patients’ prognosis limitation with malignant tumors can be attributed to delayed diagnosis of the disease. Identification of patients with early-stage disease leads to more effective therapeutic interventions. Therefore, new screening methods and further innovative treatment approaches are mandatory as they may lead to an increase in progression-free and overall survival rates. For the last decade, the interest in extracellular vesicles (EVs) research has exponentially increased as EVs generation appears to be a universal feature of every cell that is strongly involved in many mechanisms of cell-cell communication either in physiological or pathological situations. EVs can cargo biomolecules, such as lipids, proteins, nucleic acids and generate transmission signal through the intercellular transfer of their content. By this mechanism, tumor cells can recruit and modify the adjacent and systemic microenvironment to support further invasion and dissemination. This review intends to cover the most recent literature on the role of EVs production in colorectal normal and cancer tissues. Specific attention is paid to the use of EVs for early CRC diagnosis, follow-up, and prognosis as EVs have come into the spotlight of research as a high potential source of ‘liquid biopsies’. The use of EVs as new targets or nanovectors as drug delivery systems for CRC therapy is also summarized.

Bovine extracellular vesicles contaminate human extracellular vesicles produced in cell culture conditioned medium when 'exosome-depleted serum' is utilised

Extracellular vesicles (EVs) are important intercellular communication messengers. Half of the published studies in the field are in vitro cell culture based in which bovine serum in various concentrations and forms is used to facilitate the production of extracellular vesicles. 'Exosome depleted serum' is the type of bovine serum most widely used in the production of human EVs. Herein, we demonstrate that, despite the initial caution raised in 2014 about the persistence of bovine EVs, 'exosome depleted serum' was still used in 46% of publications on human or rodent EVs between 2015 and 2019. Using nanoparticle tracking analysis combined with detergent lysis of vesicles as well as bovine CD9 ELISA, we show that there were approximately 5.33 x 10⁷/mL of bovine EVs remaining in the 'exosome depleted serum'. Importantly, the 'exosome depleted serum' was relatively enriched in small EVs by approximately 2.7-fold relative to the large EVs compared to that in the original serum. Specifically, the percentage of small EVs in total vesicles had increased from the original 48% in the serum before ultracentrifugation to 92% in the 'exosome depleted serum'. Furthermore, the pervasive bovine EVs carried over by the 'exosome depleted serum', even when the lowest concentration (0.5%) was used in cell culture, resulted in a significant contamination of human EVs in cell culture conditioned medium. Our findings indicate that the use 'exosome depleted serum' in cell culture-based studies may introduce artefacts into research examining the function of human and rodent EVs, in particular those involving EV miRNA. Thus, we appeal to the researchers in the EV field to seriously reconsider the practice of using 'exosome depleted serum' in the production of human and other mammalian EVs in vitro.

Importance of stem cell culture conditions for their derived extracellular vesicles therapeutic effect

Stem cell-derived extracellular vesicles (EVs) could be enhanced by modifying specific in vitro parameters when culturing their originating stem cells. Controlling stem cell growth conditions with physical properties, oxygen tension and media preconditioning with soluble factors may influence EVs biogenesis and EVs biological function as well. Unfortunately, many misconceptions and methodological issues have hampered the progress in understanding the biological properties of EVs. In this review we will first discuss the major concerns involved in a suitable EVs production from stem cell culture. Then, we will describe the current techniques for EV isolation, focusing on their advantages and disadvantages, as well as their impact on EVs yield, recovery and functionality. Standardization of the methodology is a prerequisite to compare, to validate and to improve the reliability and credibility of all the different findings reported for the development of EV-based therapeutics.

Therapeutic role of extracellular vesicles derived from stem cells in cutaneous wound models: A systematic review

A growing body of evidence has shown that extracellular vesicles can be efficient as experimental therapeutics in pre-clinical models of skin wounds, but there is a significant unmet need to translate this to clinical utilization. The objectives of the current systematic review were to identify the strength of the therapeutic effects of EVs derived from stem cells in cutaneous wounds and to assess which EV-mediated mechanisms could be involved in the therapeutic response. PubMed, ISI Web of Science, and Scopus databases were systematically searched. We retrieved English-language articles published through June 2020. In vivo studies which applied stem cell-derived EVs were included for further analysis. The Risk of bias was assessed by the SYRCLE tool. We identified thirty-nine pre-clinical studies that evaluated the effects of EVs on the wound healing process. The included studies varied greatly in EVs isolation techniques, route of administration, EVs producing cells, and follow-up time. In vivo application revealed beneficial effects of EVs on accelerating wound closure and re-epithelialization in a dose-dependent manner. Elevated angiogenesis was reported in twelve eligible studies through multiple signaling pathways such as PI3K/Akt, MAPK/ERK, and JAK/STAT. The well-known signaling pathway to inhibit scar formation was TGF-β2/SMAD2. However, all included studies were not blinded enough which may have introduced bias. Therefore, the transition of EV's efficacy into the clinics is deeply rooted in the following important factors: 1) pre-clinical studies with a lower risk of bias and longer follow-up time, and 2) consistent, reproducible, and feasible manufacturing of EVs production in a large-scale commercial program.

Extracellular Vesicle (EV) biohybrid systems for cancer therapy: Recent advances and future perspectives

Extracellular vesicles (EVs) are a class of cell-derived lipid-bilayer membrane vesicles secreted by almost all mammalian cells and involved in intercellular communication by shuttling various biological cargoes. Over the last decade, EVs - namely exosomes and microvesicles - have been extensively explored as next-generation nanoscale drug delivery systems (DDSs). This is in large due to their endogenous origin, which enables EVs to circumvent some of the limitations associated with existing cancer therapy approaches (i.e. by preventing recognition by the immune system and improving selectivity towards tumor tissue). However, successful translation of these cell-derived vesicles into clinical applications has been hindered by several factors, among which the loading of exogenous therapeutic molecules still represents a great challenge. In order to address this issue and to further advance these biologically-derived systems as drug carriers, EV-biohybrid nano-DDSs, obtained through the fusion of EVs with conventional synthetic nano-DDSs, have recently been proposed as a valuable alternative as DDSs. Building on the idea of "combining the best of both worlds", a combination of these two unique entities aims to harness the beneficial properties associated with both EVs and conventional nano-DDSs, while overcoming the flaws of the individual components. These biohybrid systems also provide a unique opportunity for exploitation of new synergisms, often leading to improved therapeutic outcomes, thus paving the way for advancements in cancer therapy. This review aims to describe the recent developments of EV-biohybrid nano-DDSs in cancer therapy, to highlight the most promising results and breakthroughs, as well as to provide a glimpse on the possible intrinsic targeting mechanisms of EVs that can be bequeathed to their hybrid systems. Finally, we also provide some insights in the future perspectives of EV-hybrid DDSs.

A Comprehensive Review on Factors Influences Biogenesis, Functions, Therapeutic and Clinical Implications of Exosomes

Exosomes are nanoscale-sized membrane vesicles secreted by almost all cell types into the extracellular environment upon fusion of multivesicular bodies and plasma membrane. Biogenesis of exosomes is a protein quality control mechanism, and once released, exosomes transmit signals to other cells. The applications of exosomes have increased immensely in biomedical fields owing to their cell-specific cargos that facilitate intercellular communications with neighboring cells through the transfer of biologically active compounds. The diverse constituents of exosomes reflect their cell of origin and their detection in biological fluids represents a diagnostic marker for various diseases. Exosome research is expanding rapidly due to the potential for clinical application to therapeutics and diagnosis. However, several aspects of exosome biology remain elusive. To discover the use of exosomes in the biomedical applications, we must better understand the basic molecular mechanisms underlying their biogenesis and function. In this comprehensive review, we describe factors involved in exosomes biogenesis and the role of exosomes in intercellular signaling and cell-cell communications, immune responses, cellular homeostasis, autophagy, and infectious diseases. In addition, we discuss the role of exosomes as diagnostic markers, and their therapeutic and clinical implications. Furthermore, we addressed the challenges and outstanding developments in exosome research, and discuss future perspectives.

Comparison of separation methods for tissue-derived extracellular vesicles in the liver, heart, and skeletal muscle

Extracellular vesicles (EVs), which are nanosized vesicles released by cells as intracellular messengers, have high potential as biomarkers. EVs are usually collected from in vitro sources, such as cell culture media or biofluids, and not from tissues. Techniques enabling direct collection of EVs from tissues will extend the applications of EVs. We compared methods for separating EVs from solid liver, heart, and skeletal muscle. Compared with a precipitation method, an ultracentrifugation-based method for collection of EVs from solid tissues yielded a higher proportion of EVs positive for EV-related markers, with minimum levels of intracellular organelle-related markers. Some tissue-specific modifications, such as a sucrose cushion step, may improve the yield and purity of the collected EVs.

Platinum Nanoparticles Enhance Exosome Release in Human Lung Epithelial Adenocarcinoma Cancer Cells (A549): Oxidative Stress and the Ceramide Pathway are Key Players

Background

Several studies have demonstrated various molecular mechanisms involved in the biogenesis and release of exosomes. However, how external stimuli, such as platinum nanoparticles (PtNPs), induces the biogenesis and release of exosomes remains unclear. To address this, PtNPs were synthesized using lutein to examine their effect on the biogenesis and release of exosomes in human lung epithelial adenocarcinoma cancer cells (A549).

Methods

The size and concentration of isolated exosomes were characterized by dynamic light scattering (DLS) and nanoparticle tracking analysis system (NTA). Morphology and structure of exosomes were examined using scanning electron microscopy and transmission electron microscopy (TEM), respectively. Quantification of exosomes were analyzed by EXOCET^TM assay and fluorescence polarization (FP). The expression of typical markers of exosomes were analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA).

Results

A549 cells cultured with PtNPs enhance exosome secretion by altering various physiological processes. Interestingly, A549 cells treated with PtNPs increases total protein concentration, biogenesis and release of exosomes associated with PtNPs-induced oxidative stress. GW4869 inhibits PtNPs induced biogenesis and release of exosomes and also acetylcholinesterase (AChE), neutral sphingomyelinase activity (n-SMase), and exosome counts. A549 cells pre-treated with N-acetylcysteine (NAC) significantly inhibited PtNPs induced exosome biogenesis and release. These findings confirmed that PtNPs-induced exosome release was due to the induction of oxidative stress and the ceramide pathway. These factors enhanced exosome biogenesis and release and may be useful in understanding the mechanism of exosome formation, release, and function.

Conclusion

PtNPs provide a promising agent to increase exosome production in A549 cells. These findings offer novel strategies for enhancing exosome release, which can be applied in the treatment and prevention of cancer. Importantly, this is the first study, to our knowledge, showing that PtNPs stimulate exosome biogenesis by inducing oxidative stress and the ceramide pathway.

Fluorescence-Based Nanoparticle Tracking Analysis and Flow Cytometry for Characterization of Endothelial Extracellular Vesicle Release

As extracellular vesicles (EVs) have become a prominent topic in life sciences, a growing number of studies are published on a regular basis addressing their biological relevance and possible applications. Nevertheless, the fundamental question of the true vesicular nature as well as possible influences on the EV secretion behavior have often been not adequately addressed. Furthermore, research regarding endothelial cell-derived EVs (EndoEVs) often focused on the large vesicular fractions comprising of microvesicles (MV) and apoptotic bodies. In this study we aimed to further extend the current knowledge of the influence of pre-isolation conditions, such as cell density and conditioning time, on EndoEV release from human umbilical vein endothelial cells (HUVECs). We combined fluorescence nanoparticle tracking analysis (NTA) and the established fluorescence-triggered flow cytometry (FT-FC) protocol to allow vesicle-specific detection and characterization of size and surface markers. We found significant effects of cell density and conditioning time on both abundance and size distribution of EndoEVs. Additionally, we present detailed information regarding the surface marker display on EVs from different fractions and size ranges. Our data provide crucial relevance for future projects aiming to elucidate EV secretion behavior of endothelial cells. Moreover, we show that the influence of different conditioning parameters on the nature of EndoEVs has to be considered.

Shared extracellular vesicle miRNA profiles of matched ductal pancreatic adenocarcinoma organoids and blood plasma samples show the power of organoid technology

Extracellular vesicles (EV) are considered as a promising diagnostic tool for pancreatic ductal adenocarcinoma (PDAC), a disease with a poor 5-year survival that has not improved in the past years. PDAC patient-derived 3D organoids maintain the intratumoral cellular heterogeneity, characteristic for the tumor in vivo.Thus, they represent an ideal in vitro model system to study human cancers. Here we show that the miRNA cargo of EVs from PDAC organoids largely differs among patients. However, we detected a common set of EV miRNAs that were present in matched organoids and blood plasma samples of individual patients. Importantly, the levels of EV miR-21 and miR-195 were higher in PDAC blood EV preparations than in healthy controls, albeit we found no difference compared to chronic pancreatitis (CP) samples. In addition, here we report that the accumulation of collagen I, a characteristic change in the extracellular matrix (ECM) in both CP and PDAC, largely increases EV release from pancreatic ductal organoids. This provides a possible explanation why both CP and PDAC patient-derived plasma samples have an elevated amount of CD63 + EVs. Collectively, we show that PDAC patient-derived organoids represent a highly relevant model to analyze the cargo of tumor cell-derived EVs. Furthermore, we provide evidence that not only driver mutations, but also changes in the ECM may critically modify EV release from pancreatic ductal cells.

Osteogenically-induced exosomes stimulate osteogenesis of human adipose-derived stem cells

Exosomes exhibit great therapeutic potential in bone tissue engineering. The study aimed to investigate whether the exosomes derived from human adipose-derived stem cells (hADSCs-Exos) during different time-span of osteogenic differentiation could promote osteogenesis. The appropriate concentrations of hADSCs-Exos to enhance the proliferation, migration and osteogenesis of hADSCs-Exos were also examined. PKH67 labelled hADSCs-Exos was used to detect the internalization ability of hADSCs. The osteogenic differentiation abilities of hADSCs after treatment with hADSCs-Exos was evaluated by Alizarin red staining (ARS). The proliferation and migration of hADSCs was examined by cell counting kit-8 and wound healing assay, respectively. The expression of exosomal surface markers and osteoblast-related protein of hADSCs was assessed by Western blot. PKH67-labelled exosomes were internalized by hADSCs after 4 h incubation. ARS showed that the amount of mineralized nodules in Exo^1−14d group was significantly higher than that in Exo^15−28d group. hADSCs-Exos could promote the proliferation and migration capacity of hADSCs. Western blot analysis showed that after hADSCs-Exos treatment, ALP and RUNX2 were significantly enhanced. Specially, the Exo^1−14d group of 15 μg/mL significantly upregulated the expression of RUNX2 than the other exosomes treated groups. Our findings suggest that exosomes secreted by hADSCs during osteogenic induction for 1–14 days could be efficiently internalized by hADSCs and could induce osteogenic differentiation of hADSCs. Moreover, administration of Exo^1−14d at 15 μg/mL promoted the proliferation and migration of hADSCs. In conclusion, our research confirmed that comprised of hADSCs-Exos and hADSCs may provide a new therapeutic paradigm for bone tissue engineering.

Isolation and characterization of exosomes for cancer research

Exosomes are a subset of extracellular vesicles that carry specific combinations of proteins, nucleic acids, metabolites, and lipids. Mounting evidence suggests that exosomes participate in intercellular communication and act as important molecular vehicles in the regulation of numerous physiological and pathological processes, including cancer development. Exosomes are released by various cell types under both normal and pathological conditions, and they can be found in multiple bodily fluids. Moreover, exosomes carrying a wide variety of important macromolecules provide a window into altered cellular or tissue states. Their presence in biological fluids renders them an attractive, minimally invasive approach for liquid biopsies with potential biomarkers for cancer diagnosis, prediction, and surveillance. Due to their biocompatibility and low immunogenicity and cytotoxicity, exosomes have potential clinical applications in the development of innovative therapeutic approaches. Here, we summarize recent advances in various technologies for exosome isolation for cancer research. We outline the functions of exosomes in regulating tumor metastasis, drug resistance, and immune modulation in the context of cancer development. Finally, we discuss prospects and challenges for the clinical development of exosome-based liquid biopsies and therapeutics.

Surface-Enhanced Raman Spectroscopy as a Tool for Distinguishing Extracellular Vesicles under Autophagic Conditions: A Marker for Disease Diagnostics

Extracellular vesicles (EVs) laden with lipids, proteins, DNA, and micro-RNAs play important biological functions in intercellular communication and have pivotal roles in pathophysiological conditions. Characterization of the EVs has always been a multistep process involving large volumes, and they are heterogeneous in size and properties. A multitude of approaches is used to distinguish the EVs. Here, we report simple citrate reduced silver nanoparticles assisted surface-enhanced Raman spectroscopy (SERS) as a tool to distinguish EVs extracted from several cell lines isolated under autophagic conditions (nitrogen starvation). This study is the first report of its kind in characterizing EVs from cells under autophagic conditions using SERS. We used two cancerous cell lines, HeLa, its corresponding autophagy-deficient cell line (Atg5^-/-), and a noncancerous cell line, HEK293, to isolate EVs. Our study helps in the facile detection and differentiation of EVs isolated between two closely related human cell lines that differ by their autophagic ability. The principal component analysis (PCA) of the SERS spectra of these EVs consistently showed the presence of distinct chemical compositions of the EVs. SERS of EVs can help in probing more into the molecular level information from EVs and could become a powerful tool once coupled with improved microscopy techniques for diagnosis and therapy.

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.

Characterization and internalization of small extracellular vesicles released by human primary macrophages derived from circulating monocytes

Extracellular vesicles (EVs) are small membrane-limited structures derived from outward budding of the plasma membrane or endosomal system that participate in cellular communication processes through the transport of bioactive molecules to recipient cells. To date, there are no published methodological works showing step-by-step the isolation, characterization and internalization of small EVs secreted by human primary macrophages derived from circulating monocytes (MDM-derived sEVs). Thus, here we aimed to provide an alternative protocol based on differential ultracentrifugation (dUC) to describe small EVs (sEVs) from these cells. Monocyte-derived macrophages were cultured in EV-free medium during 24, 48 or 72 h and, then, EVs were isolated from culture supernatants by (dUC). Macrophages secreted a large amount of sEVs in the first 24 h, with size ranging from 40-150 nm, peaking at 105 nm, as evaluated by nanoparticle tracking analysis and scanning electron microscopy. The markers Alix, CD63 and CD81 were detected by immunoblotting in EV samples, and the co-localization of CD63 and CD81 after sucrose density gradient ultracentrifugation (S-DGUC) indicated the presence of sEVs from late endosomal origin. Confocal fluorescence revealed that the sEVs were internalized by primary macrophages after three hours of co-culture. The methodology here applied aims to contribute for enhancing reproducibility between the limited number of available protocols for the isolation and characterization of MDM-derived sEVs, thus providing basic knowledge in the area of EV methods that can be useful for those investigators working with sEVs released by human primary macrophages derived from circulating monocytes.

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.

Optimized method for extraction of exosomes from human primary muscle cells

Skeletal muscle is increasingly considered an endocrine organ secreting myokines and extracellular vesicles (exosomes and microvesicles), which can affect physiological changes with an impact on different pathological conditions, including regenerative processes, aging, and myopathies. Primary human myoblasts are an essential tool to study the muscle vesicle secretome. Since their differentiation in conditioned media does not induce any signs of cell death or cell stress, artefactual effects from those processes are unlikely. However, adult human primary myoblasts senesce in long-term tissue culture, so a major technical challenge is posed by the need to avoid artefactual effects resulting from pre-senescent changes. Since these cells should be studied within a strictly controlled pre-senescent division count (<21 divisions), and yields of myoblasts per muscle biopsy are low, it is difficult or impossible to amplify sufficiently large cell numbers (some 250 × 10⁶ myoblasts) to obtain sufficient conditioned medium for the standard ultracentrifugation approach to exosome isolation.

Thus, an optimized strategy to extract and study secretory muscle vesicles is needed. In this study, conditions are optimized for the in vitro cultivation of human myoblasts, and the quality and yield of exosomes extracted using an ultracentrifugation protocol are compared with a modified polymer-based precipitation strategy combined with extra washing steps. Both vesicle extraction methods successfully enriched exosomes, as vesicles were positive for CD63, CD82, CD81, floated at identical density (1.15-1.27 g.ml⁻¹), and exhibited similar size and cup-shape using electron microscopy and NanoSight tracking. However, the modified polymer-based precipitation was a more efficient strategy to extract exosomes, allowing their extraction in sufficient quantities to explore their content or to isolate a specific subpopulation, while requiring >30 times fewer differentiated myoblasts than what is required for the ultracentrifugation method. In addition, exosomes could still be integrated into recipient cells such as human myotubes or iPSC-derived motor neurons.

Modified polymer-based precipitation combined with extra washing steps optimizes exosome yield from a lower number of differentiated myoblasts and less conditioned medium, avoiding senescence and allowing the execution of multiple experiments without exhausting the proliferative capacity of the myoblasts.

The Therapeutic Potential of Extracellular Vesicles Versus Mesenchymal Stem Cells in Liver Damage

BACKGROUND

The extracellular vesicles (EVs) secreted by bone marrow-derived mesenchymal stem cells (MSCs) hold significant potential as a novel alternative to whole-cell therapy. We herein compare the therapeutic potential of BM-MSCs versus their EVs (MSC-EVs) in an experimental Carbon tetrachloride (CCl₄)-induced liver damage rat model.

METHODS

Rats with liver damage received a single IV injection of MSC-EVs, 1 million MSCs, or 3 million MSCs. The therapeutic efficacy of each treatment was assessed using liver histopathology, liver function tests and immunohistochemistry for liver fibrosis and hepatocellular injury.

RESULTS

Animals that received an injection of either MSCs-EVs or 3 million MSCs depicted significant regression of collagen deposition in the liver tissue and marked attenuation of hepatocellular damage, both structurally and functionally.

CONCLUSION

Similar to high doses of MSC-based therapy (3 million MSCs), MSC-EVs mitigated the fibrogenesis and hepatocellular injury in a rat model of CCl₄-induced liver fibrosis. The anti-fibrinogenic effect was induced by attenuating hepatic stellate cell activation. Therefore, the administration of MSC-EVs could be considered as a candidate cell-free therapeutic strategy for liver fibrosis and hepatocellular damage.

Semipermeable Cellulose Beads Allow Selective and Continuous Release of Small Extracellular Vesicles (sEV) From Encapsulated Cells

The clinical benefit of therapies using Mesenchymal Stem Cells (MSCs) is attributable to their pleiotropic effect over cells and tissues, mainly through their secretome. This paracrine effect is mediated by secreted growth factors and extracellular vesicles (EV) including small EV (sEV). sEV are extra-cellular, membrane encompassed vesicles of 40 to 200 nm diameter that can trigger and signal many cellular responses depending on their cargo protein and nucleic acid repertoire. sEV are purified from cell culture conditioned media using several kits and protocols available that can be tedious and time-consuming, involving sequences of ultracentrifugations and density gradient separations, making their production a major challenge under Good Manufacturing Practices (GMP) conditions. We have developed a method to efficiently enrich cell culture media with high concentrations of sEV by encapsulating cells in semipermeable cellulose beads that allows selectively the release of small particles while offering a 3D culture condition. This method is based on the pore size of the capsules, allowing the release of particles of ≤ 200 nm including sEV. As a proof-of-principle, MSCs were encapsulated and their sEV release rate (sEV-Cap) was monitored throughout the culture and compared to sEV isolated from 2D seeded cells (sEV-2D) by repetitive ultracentrifugation cycles or a commercial kit. The isolated sEV expressed CD63, CD9, and CD81 as confirmed by flow cytometry analysis. Under transmission electron microscopy (TEM), they displayed the similar rounded morphology as sEV-2D. Their corresponding diameter size was validated by nanoparticle tracking analysis (NTA). Interestingly, sEV-Cap retained the expected biological activities of MSCs, including a pro-angiogenic effect over endothelial cells, neuritic outgrowth stimulation in hippocampal neurons and immunosuppression of T cells in vitro. Here, we successfully present a novel, cost, and time-saving method to generate sEV from encapsulated MSCs. Future applications include using encapsulated cells as a retrievable delivery device that can interact with the host niche by releasing active agents in vivo, including sEV, growth factors, hormones, and small molecules, while avoiding cell clearance, and the negative side-effect of releasing undesired components including apoptotic bodies. Finally, particles produced following the encapsulation protocol display beneficial features for their use as drug-loaded delivery vehicles.

Mesenchymal stromal/stem cell-derived extracellular vesicles in tissue repair: challenges and opportunities

Mesenchymal stem/stromal cells (MSCs) are important players in tissue homeostasis and regeneration owing to their immunomodulatory potential and release of trophic factors that promote healing. They have been increasingly used in clinical trials to treat multiple conditions associated with inflammation and tissue damage such as graft versus host disease, orthopedic injuries and cardiac and liver diseases. Recent evidence demonstrates that their beneficial effects are derived, at least in part, from their secretome. In particular, data from animal models and first-in-man studies indicate that MSC-derived extracellular vesicles (MSC-EVs) can exert similar therapeutic potential as their cells of origin. MSC-EVs are membranous structures loaded with proteins, lipids, carbohydrates and nucleic acids, which play an important role in cell-cell communication and may represent an attractive alternative for cell-based therapy. In this article we summarize recent advances in the use of MSC-EVs for tissue repair. We highlight several isolation and characterization approaches used to enrich MSC-derived EVs. We discuss our current understanding of the relative contribution of the MSC-EVs to the immunomodulatory and regenerative effects mediated by MSCs and MSC secretome. Finally we highlight the challenges and opportunities, which come with the potential use of MSC-EVs as cell free therapy for conditions that require tissue repair.