Correction: Gurunathan, S. et al. Review of the Isolation, Characterization, Biological Function, and Multifarious Therapeutic Approaches of Exosomes. Cells 2019, 8, 307

MSC Exosomes Containing Valproic Acid Promote Wound Healing by Modulating Inflammation and Angiogenesis

PURPOSE

Chronic wounds that are difficult to heal pose a major challenge for clinicians and researchers. Currently, common treatment methods focus on isolating the wound from the outside world, relying on the tissue at the wound site to grow and heal unaided. Umbilical cord mesenchymal stem cell (MSC) exosomes can promote wound healing by enhancing new blood vessel growth at the wound site. Valproic acid (VPA) reduces the inflammatory response and acts on macrophages to accelerate wound closure. In this study, VPA was loaded into umbilical cord MSC exosomes to form a drug carrier exosome (VPA-EXO) with the aim of investigating the effect of VPA-EXO on wound healing.

METHODS

This study first isolated and obtained umbilical cord MSC exosomes, then added VPA to the exosomes and explored the ability of VPA-EXO to promote the proliferation and migration of human skin fibroblasts (HSFs) and human umbilical vein endothelial cells (HUVECs), as well as the ability to promote the angiogenesis of HUVECs, by using scratch, Transwell, and angiogenesis assays. An in vitro cell model was established and treated with VPA-EXO, and the expression levels of inflammation and pro-angiogenesis-related proteins and genes were examined using Western blot and qRT-PCR. The therapeutic effect of VPA-EXO on promoting wound healing in a whole skin wound model was investigated using image analysis of the wound site, H&E staining, and immunohistochemical staining experiments in a mouse wound model.

RESULTS

The in vitro model showed that VPA-EXO effectively promoted the proliferation and migration of human skin fibroblast cells and human umbilical vein endothelial cells; significantly inhibited the expression of MMP-9, IL-1β, IL-8, TNF-α, and PG-E2; and promoted the expression of vascular endothelial growth factors. In the mouse wound model, VPA-EXO reduced inflammation at the wound site, accelerated wound healing, and significantly increased the collagen content of tissue at the wound site.

CONCLUSIONS

As a complex with dual efficacy in simultaneously promoting tissue regeneration and inhibiting inflammation, VPA-EXO has potential applications in tissue wound healing and vascular regeneration. In future studies, we will further investigate the mechanism of action and application scenarios of drug-loaded exosome complexes in different types of wound healing and vascular regeneration.

Mesenchymal stem cell-derived exosomes ameliorate hypoxic pulmonary hypertension by inhibiting the Hsp90aa1/ERK/pERK pathway

Hypoxic pulmonary hypertension (HPH) is a serious and life-threatening chronic cardiopulmonary disease characterized by progressive elevation of pulmonary artery pressure and pulmonary vascular remodeling. Mesenchymal stem cell- derived exosomes (MSC-Exos) can relieve HPH by reversing pulmonary vascular remodeling. The HPH model was established in healthy male Sprague-Dawley (SD) rats aged 6 to 8 weeks. The rats were placed in a room with oxygen concentration of (10 ± 1) % for 8 hours a day over 28 days, were then injected intravenously with MSC-Exos (100 ug protein/kg) or equal-volume phosphate buffer saline (PBS) once a day over 1 week. Right ventricular systolic pressure (RVSP), right ventricular hypertrophy index (RVHI) and pulmonary vascular remodeling were observed after anesthesia. In addition, platelet-derived growth factor BB (PDGF-BB) was used to stimulate rat pulmonary artery smooth muscle cells (PASMCs) to construct HPH pathological cell models. The results showed that MSC-Exos could not only reduce the elevation of RVSP, right ventricular hypertrophy and the degree of pulmonary vascular remodeling in HPH rats, but also reduce the proliferation, migration and apoptosis resistance of PASMCs. Finally, GSE53408 and GSE113439 datasets were analyzed and showed that the expression of Hsp90aa1 and pERK/ERK were significantly increased in HPH, also could be inhibited by MSC-Exos. Meanwhile, inhibition of Hsp90aa1 also reduced PASMCs migration and pERK/ERK protein level. In conclusion, MSC-Exos alleviated HPH by suppressing PASMCs proliferation, migration and apoptosis resistance through inhibiting the Hsp90aa1/ERK/pERK pathway.

Lipid metabolism of plasma-derived small extracellular vesicles in COVID-19 convalescent patients

The coronavirus disease 2019 (COVID-19), which affects multiple organs, is causing an unprecedented global public health crisis. Most COVID-19 patients recover gradually upon appropriate interventions. Viruses were reported to utilize the small extracellular vesicles (sEVs), containing a cell-specific cargo of proteins, lipids, and nucleic acids, to escape the attack from the host's immune system. This study aimed to examine the sEVs lipid profile of plasma of recovered COVID-19 patients (RCs). Plasma sEVs were separated from 83 RCs 3 months after discharge without underlying diseases, including 18 recovered asymptomatic patients (RAs), 32 recovered moderate patients (RMs), and 33 recovered severe and critical patients (RSs), and 19 healthy controls (HCs) by Total Exosome Isolation Kit. Lipids were extracted from sEVs and then subjected to targeted liquid chromatography-mass spectrometry. The size, concentration, and distribution of sEVs did not differ in RCs and HCs as validated by transmission electron microscopy, nanoparticle tracking analysis, and immunoblot analysis. Fifteen subclasses of 508 lipids were detected in plasma sEVs from HCs, RAs, RMs, and RSs, such as phosphatidylcholines (PCs) and diacylglycerols (DAGs), etc. Total lipid intensity displayed downregulation in RCs compared with HCs. The relative abundance of DAGs gradually dropped, whereas PCs, lysophosphatidylcholines, and sphingomyelins were higher in RCs relative to HCs, especially in RSs. 88 lipids out of 241 in sEVs of RCs were significantly different and a conspicuous increase was revealed with disease status. The sEVs lipids alternations were found to be significantly correlated with the clinical indices in RCs and HCs, suggesting that the impact of COVID-19 on lipid metabolism lingered for a long time. The lipid abnormalities bore an intimate link with glycerophospholipid metabolism and glycosylphosphatidylinositol anchor biosynthesis. Furthermore, the lipidomic analysis showed that RCs were at higher risk of developing diabetes and sustaining hepatic impairment. The abnormality of immunomodulation in RCs might still exist. The study may offer new insights into the mechanism of organ dysfunction and help identify novel therapeutic targets in the RCs.

Exosome-mediated effects and applications in inflammatory diseases of the digestive system

Exosomes are membranous vesicles containing RNA and proteins that are specifically secreted in vivo. Exosomes have many functions, such as material transport and signal transduction between cells. Many studies have proven that exosomes can not only be used as biomarkers for disease diagnosis but also as carriers to transmit information between cells. Exosomes participate in a variety of physiological and pathological processes, including the immune response, antigen presentation, cell migration, cell differentiation, and tumour development. Differences in exosome functions depend on cell type. In recent years, exosome origin, cargo composition, and precise regulatory mechanisms have been the focus of research. Although exosomes have been extensively reported in digestive tumours, few articles have reviewed their roles in inflammatory diseases of the digestive system, especially inflammatory-related diseases (such as reflux oesophagitis, gastritis, inflammatory bowel disease, hepatitis, and pancreatitis). This paper briefly summarizes the roles of exosomes in inflammatory diseases of the digestive system to provide a basis for research on the mechanism of inflammatory diseases of the digestive system targeted by exosomes.

Therapeutic effect of modified zengye decoction on primary Sjogren’s syndrome and its effect on plasma exosomal proteins

Background: Modified Zengye Decoction (MZD), a traditional Chinese medicine, is an effective treatment for patients with primary Sjögren’s syndrome (pSS).

Purpose: To evaluate the efficacy of MZD and investigate its effect on plasma exosomal proteins.

Methods: Eighteen pSS patients were treated with MZD for 2 weeks. The therapeutic effect was evaluated by observing the changes in clinical symptoms, laboratory parameters, and plasma cytokines before and after treatment. Then, the differentially expressed proteins (DEPs) in the plasma exosomes before and after treatment were identified via label-free proteomics, while Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment were used to analyze the possible biological functions and signaling pathways involved in the exosomal DEPs.

Results: MZD can effectively relieve the clinical symptoms of pSS patients, downregulate the plasma IgG and IgM levels, and inhibit plasma cytokine production. Thirteen DEPs were identified via label-free proteomics in the plasma exosomes before and after MZD treatment, of which 12 were downregulated proteins. GO analysis showed that these downregulated proteins were mainly related to the insulin response involved in dryness symptoms and the Gram-negative bacterial defense response and proteoglycan binding involved in infection. KEGG enrichment analysis showed that these downregulated proteins were primarily associated with the porphyrin metabolism involved in oteoarthrosis and the NF-κB and TLR4 pathways involved in infection.

Conclusion: MZD can effectively alleviate SS symptoms, while its mechanism may be associated with the reduced protein expression in insulin response, porphyrin metabolism, and the TLR4/NF-κB pathway.

Red Blood Cell Extracellular Vesicle-Based Drug Delivery: Challenges and Opportunities

Recently, red blood cell-derived extracellular vesicles (RBCEVs) have attracted attention for clinical applications because of their safety and biocompatibility. RBCEVs can escape macrophages through the binding of CD47 to inhibitory receptor signal regulatory protein α. Furthermore, genetic materials such as siRNA, miRNA, mRNA, or single-stranded RNA can be encapsulated within RBCEVs and then released into target cells for precise treatment. However, their side effects, half-lives, target cell specificity, and limited large-scale production under good manufacturing practice remain challenging. In this review, we summarized the biogenesis and composition of RBCEVs, discussed the advantages and disadvantages of RBCEVs for drug delivery compared with synthetic nanovesicles and non-red blood cell-derived EVs, and provided perspectives for overcoming current limitations to the use of RBCEVs for clinical applications.

The emerging role of extracellular vesicles in retinal diseases

As a type of nanosized membranous vesicles secreted by living cells, extracellular vesicles (EVs) mediate intercellular communications with excellent physicochemical stability and biocompatibility. By delivering biologically active molecules including proteins, nucleic acids and lipids, EVs participate in many physiological and pathological processes. Increasing studies have suggested that EVs may be biomarkers for liquid biopsy of retinal diseases due to the ability to transfer through the blood-retinal barrier. EVs also represent a novel cell-free strategy to repair tissue damage in regenerative medicine. Evidence has indicated that EVs can be engineered and modified to enhance their efficacy. In this review, an overview of the characteristics, isolation, and identification of EVs is provided. Moreover, recent advances with EVs in the diagnosis and treatment of retinal diseases and the engineering approaches to elevate their effects are introduced, and opportunities and challenges for clinical application are discussed.

Regulating the production and biological function of small extracellular vesicles: current strategies, applications and prospects

Numerous studies have confirmed the great application potentials of small extracellular vesicles (sEVs) in biological medical field, especially in tissue repair and regeneration. However, the production capability of sEVs by noncancerous cells is very limited, while their dosage requirements in disease treatments are usually very high. Meanwhile, as cell aging, the sEV production capability of cells decreases and the biological function of sEVs changes accordingly. In addition, for special applications, sEVs carrying desired bioactive substances should be designed to perform their expected biological function. Therefore, improving the production of sEVs and precisely regulating their biological function are of great significance for promoting the clinical applications of sEVs. In this review, some of the current classic strategies in affecting the cellular behaviors of donor cells and subsequently regulating the production and biological function of their sEVs are summarized, including gene engineering methods, stress-inducing conditions, chemical regulators, physical methods, and biomaterial stimulations. Through applying these strategies, increased yield of sEVs with required biological function can be obtained for disease treatment and tissue repair, such as bone regeneration, wound healing, nerve function recovery and cancer treatment, which could not only reduce the harvest cost of sEV but promote the practical applications of sEVs in clinic.

MSCs and their exosomes: a rapidly evolving approach in the context of cutaneous wounds therapy

Currently, mesenchymal stem/stromal stem cell (MSC) therapy has become a promising option for accelerating cutaneous wound healing. In vivo reports have outlined the robust competences of MSCs to offer a solid milieu by inhibition of inflammatory reactions, which in turn, enables skin regeneration. Further, due to their great potential to stimulate angiogenesis and also facilitate matrix remodeling, MSCs hold substantial potential as future therapeutic strategies in this context. The MSCs-induced wound healing is thought to mainly rely on the secretion of a myriad of paracrine factors in addition to their direct differentiation to skin-resident cells. Besides, MSCs-derived exosomes as nanoscale and closed membrane vesicles have recently been suggested as an effective and cell-free approach to support skin regeneration, circumventing the concerns respecting direct application of MSCs. The MSCs-derived exosomes comprise molecular components including lipid, proteins, DNA, microRNA, and also mRNA, which target molecular pathways and also biological activities in recipient cells (e.g., endothelial cell, keratinocyte, and fibroblast). The secreted exosome modifies macrophage activation, stimulates angiogenesis, and instigates keratinocytes and dermal fibroblast proliferations as well as migrations concurrently regulate inherent potential of myofibroblast for adjustment of turnover of the ECM. In the present review, we will focus on the recent findings concerning the application of MSCs and their derivative exosome to support wound healing and skin regeneration, with special focus on last decade in vivo reports.

Diagnostic and Therapeutic Role of Extracellular Vesicles in Articular Cartilage Lesions and Degenerative Joint Diseases

Two leading contributors to the global disability are cartilage lesions and degenerative joint diseases, which are characterized by the progressive cartilage destruction. Current clinical treatments often fail due to variable outcomes and an unsatisfactory long-term repair. Cell-based therapies were once considered as an effective solution because of their anti-inflammatory and immunosuppression characteristics as well as their differentiation capacity to regenerate the damaged tissue. However, stem cell-based therapies have inherent limitations, such as a high tumorigenicity risk, a low retention, and an engraftment rate, as well as strict regulatory requirements, which result in an underwhelming therapeutic effect. Therefore, the non-stem cell-based therapy has gained its popularity in recent years. Extracellular vesicles (EVs), in particular, like the paracrine factors secreted by stem cells, have been proven to play a role in mediating the biological functions of target cells, and can achieve the therapeutic effect similar to stem cells in cartilage tissue engineering. Therefore, a comprehensive review of the therapeutic role of EVs in cartilage lesions and degenerative joint diseases can be discussed both in terms of time and favorability. In this review, we summarized the physiological environment of a joint and its pathological alteration after trauma and consequent changes in EVs, which are lacking in the current literature studies. In addition, we covered the potential working mechanism of EVs in the repair of the cartilage and the joint and also discussed the potential therapeutic applications of EVs in future clinical use.

TGF-β loaded exosome enhances ischemic wound healing in vitro and in vivo

Rationale: With over seven million infections and $25 billion treatment cost, chronic ischemic wounds are one of the most serious complications in the United States. The controlled release of bioactive factor enriched exosome from finbrin gel was a promising strategy to promote wound healing. Methods: To address this unsolved problem, we developed clinical-grade platelets exosome product (PEP), which was incorporate with injectable surgical fibrin sealant (TISSEEL), to promote chronic wound healing and complete skin regeneration. The PEP characterization stimulated cellular activities and in vivo rabbit ischemic wound healing capacity of TISSEEL-PEP were performed and analyzed. Results: PEP, enriched with transforming growth factor beta (TGF-β), possessed exosomal characteristics including exosome size, morphology, and typical markers including CD63, CD9, and ALG-2-interacting protein X (Alix). In vitro, PEP significantly promoted cell proliferation, migration, tube formation, as well as skin organoid formation. Topical treatment of ischemic wounds with TISSEEL-PEP promoted full-thickness healing with the reacquisition of hair follicles and sebaceous glands. Superior to untreated and TISSEEL-only treated controls, TISSEEL-PEP drove cutaneous healing associated with collagen synthesis and restoration of dermal architecture. Furthermore, PEP promoted epithelial and vascular cell activity enhancing angiogenesis to restore blood flow and mature skin function. Transcriptome deconvolution of TISSEEL-PEP versus TISSEEL-only treated wounds prioritized regenerative pathways encompassing neovascularization, matrix remodeling and tissue growth. Conclusion: This room-temperature stable, lyophilized exosome product is thus capable of delivering a bioactive transforming growth factor beta to drive regenerative events.

Elucidating Methods for Isolation and Quantification of Exosomes: A Review

Exosomes are the smallest extracellular vesicles present in most of the biological fluids. They are found to play an important role in cell signaling, immune response, tumor metastasis, etc. Studies have shown that these vesicles also have diagnostic and therapeutic roles for which their accurate detection and quantification is essential. Due to the complexity in size and structure of exosomes, even the gold standard methods face challenges. This comprehensive review discusses the various standard methods such as ultracentrifugation, ultrafiltration, size-exclusion chromatography, precipitation, immunoaffinity, and microfluidic technologies for the isolation of exosomes. The principle of isolation of each method is described, as well as their specific advantages and disadvantages. Quantification of exosomes by nanoparticle tracking analysis, flow cytometry, tunable resistive pulse sensing, electron microscopy, dynamic light scattering, and microfluidic devices are also described, along with the applications of exosomes in various biomedical domains.

Function of exosomes in neurological disorders and brain tumors

Exosomes are a subtype of extracellular vesicles released from different cell types including those in the nervous system, and are enriched in a variety of bioactive molecules such as RNAs, proteins and lipids. Numerous studies have indicated that exosomes play a critical role in many physiological and pathological activities by facilitating intercellular communication and modulating cells' responses to external environments. Particularly in the central nervous system, exosomes have been implicated to play a role in many neurological disorders such as abnormal neuronal development, neurodegenerative diseases, epilepsy, mental disorders, stroke, brain injury and brain cancer. Since exosomes recapitulate the characteristics of the parental cells and have the capacity to cross the blood-brain barrier, their cargo can serve as potential biomarkers for early diagnosis and clinical assessment of disease treatment. In this review, we describe the latest findings and current knowledge of the roles exosomes play in various neurological disorders and brain cancer, as well as their application as promising biomarkers. The potential use of exosomes to deliver therapeutic molecules to treat diseases of the central nervous system is also discussed.

Exosome isolation using nanostructures and microfluidic devices

Exosomes contain cargoes of proteins, lipids, micro-ribonucleic acids, and functional messenger RNAs, and they play a key role in cell-to-cell communication and hold valuable information about biological processes such as disease pathology. To harvest their potentials in disease diagnostics, prognostics, and therapeutics, exosome isolation is a crucial first step in providing pure and intact samples for both research and clinical purposes. Unfortunately, conventional methods for exosome separation suffer from low purity, low capture efficiency, long processing time, large sample volume requirement, the need for dedicated equipment and trained personnel, and high cost. In the last decade, microfluidic devices, especially those that incorporate nanostructures, have emerged as superior alternatives for exosome isolation and detection. In this review, we examine microfluidic platforms, dividing them into six categories based on their capture mechanisms: passive-structure-based affinity, immunomagnetic-based affinity, filtration, acoustofluidics, electrokinetics, and optofluidics. Here, we start out exploring the research and clinical needs that translate into important performance parameters for new exosome isolation designs. Then, we briefly introduce the conventional methods and discuss how their failure to meet those performance standards sparks an intense interest in microfluidic device innovations. The essence of this review is to lead an in-depth discussion on not only the technicality of those microfluidic platforms, but also their strengths and weaknesses with regards to the performance parameters set forth. To close the conversation, we call for the inclusion of exosome confirmation and contamination evaluation as part of future device development and performance assessment process, so that collectively, efforts towards microfluidics and nanotechnology for exosome isolation and analysis may soon see the light of real-world applications.

Stem cell secretome derived from human amniotic fluid affords neuroprotection in an ischemic model

Human amniotic fluid stem cells (hAFSCs) are growing in interest; yet, little is understood about their secretome and neuroprotective actions in different diseases, including stroke. When stem cells are grown in vitro, they release an array of cytokines and growth factors that can stimulate neuroprotective processes. Furthermore, administering secretome rather than cells may be a safer route for patients who are at risk for rejection, promoting innate restorative processes. Current literature implicates that the miRNA contents of such secretome, more specifically exosomes, may regulate the effectiveness of secretome administration. In this review, we explore what factors may promote pro-survival and pro-apoptotic pathways after the administration of hAFSCs-derived secretome in ischemic models.