Current Knowledge and Future Perspectives of Exosomes as Nanocarriers in Diagnosis and Treatment of Diseases

Abstract

Exosomes, as natural nanocarriers, characterized with low immunogenicity, non-cytotoxicity and targeted delivery capability, which have advantages over synthetic nanocarriers. Recently, exosomes have shown great potential as diagnostic markers for diseases and are also considered as a promising cell-free therapy. Engineered exosomes have significantly enhanced the efficacy and precision of delivering therapeutic agents, and are currently being extensively employed in targeted therapeutic investigations for various ailments, including oncology, inflammatory disorders, and degenerative conditions. Particularly, engineered exosomes enable therapeutic agent loading, targeted modification, evasion of MPS phagocytosis, intelligent control, and bioimaging, and have been developed as multifunctional nano-delivery platforms in recent years. The utilization of bioactive scaffolds that are loaded with exosome delivery has been shown to substantially augment retention, extend exosome release, and enhance efficacy. This approach has advanced from conventional hydrogels to nanocomposite hydrogels, nanofiber hydrogels, and 3D printing, resulting in superior physical and biological properties that effectively address the limitations of natural scaffolds. Additionally, plant-derived exosomes, which can participate in gut flora remodeling via oral administration, are considered as an ideal delivery platform for the treatment of intestinal diseases. Consequently, there is great interest in exosomes and exosomes as nanocarriers for therapeutic and diagnostic applications. This comprehensive review provides an overview of the biogenesis, composition, and isolation methods of exosomes. Additionally, it examines the pathological and diagnostic mechanisms of exosomes in various diseases, including tumors, degenerative disorders, and inflammatory conditions. Furthermore, this review highlights the significance of gut microbial-derived exosomes. Strategies and specific applications of engineered exosomes and bioactive scaffold-loaded exosome delivery are further summarized, especially some new techniques such as large-scale loading technique, macromolecular loading technique, development of multifunctional nano-delivery platforms and nano-scaffold-loaded exosome delivery. The potential benefits of using plant-derived exosomes for the treatment of gut-related diseases are also discussed. Additionally, the challenges, opportunities, and prospects of exosome-based nanocarriers for disease diagnosis and treatment are summarized from both preclinical and clinical viewpoints.

Keywords: diagnosis; diseases; exosomes; nanocarriers; treatment.

Figure 1

An overview of the main sources and applications of natural exosomes, as well as the main delivery strategies and engineering modification strategies for exosomes.

Figure 2

Mechanisms of exosome biogenesis and uptake, and the main structure and composition of exosomes.

Figure 3

Exosomes mediate communication between intestinal microbes and host cells and together maintain the balance of the intestinal microenvironment. Exosomes from healthy intestinal microbes promote food metabolism, protect intestinal barrier integrity, and promote maturation of intestinal immune cells, whereas exosomes from intestinal host cells regulate the abundance and diversity of intestinal microbes. Conversely, exosomes from dysregulated intestinal microbiota adversely affect food metabolism, disrupt the integrity of the intestinal barrier, and lead to immune dysfunction, while exosomes from intestinal host cells cause dysregulation of the intestinal microbiota. Both intestinal microbial-derived exosomes that enter the circulation through the disrupted intestinal barrier and microbial-derived exosomes in feces can be used for liquid biopsies.

Figure 4

Strategies and applications of exosome loading cargo. (A) Direct loading cargo strategies. (B) Indirect cargo loading strategy via parental cells. (C) Exosomes loaded with curcumin via direct co-incubation for targeted anti-inflammatory therapy. Reprinted from Sun D, Zhuang X, Xiang X, et al. A novel nanoparticle delivery system: enhanced anti-inflammatory activity of curcumin when encapsulated in exosomes. Mol Ther. 2010;18(9):1606–1614. http://creativecommons.org/licenses/by/4.0/. (i) Plasma circulation times of exosome-loaded curcumin and free curcumin, **P < 0.01. (ii) TNF-α and IL-6 levels in supernatants after PBS, exosomes, free curcumin and curcumin-loaded exosomes treatment of LPS-stimulated RAW 264.7 cells, *P < 0.05, **P < 0.01. (D) Exosomes from MSC loaded with Dox by direct co-incubation for osteosarcoma treatment. Reprinted from Wei H, Chen J, Wang S, et al. A Nanodrug Consisting of Doxorubicin and Exosome Derived from Mesenchymal Stem Cells for Osteosarcoma Treatment In Vitro. Int J Nanomedicine. 2019; 14:8603–8610. http://creativecommons.org/licenses/by-nc/3.0/. (i) Fluorescence intensity of exosome-loaded Dox and free Dox co-incubated with osteosarcoma cells for different times, ****P < 0.0001. (ii) Cell viability of osteosarcoma cells treated with the same concentration of free Dox and exosome-loaded Dox for 24 hours and the half-maximal inhibitory concentration (IC50) of free Dox and exosome-loaded Dox. (E) Treatment of CIA mice by transfection of MSC loaded to exosomes with miRNA-150-5p. Reprinted with permission from Chen Z, Wang H, Xia Y, Yan F, Lu Y. Therapeutic Potential of Mesenchymal Cell-Derived miRNA-150-5p-Expressing Exosomes in Rheumatoid Arthritis Mediated by the Modulation of MMP14 and VEGF. J Immunol. 2018;201(8):2472–2482.www.jimmunol.org. Copyright © 2018 by The American Association of Immunologists, Inc. (i) Immunohistochemistry showed the expression levels of VEGF and MMP14 in the synovium after transfection of exosomes with miRNA-150-5p to treat CIA mice. (ii) The DiO-labeled MSC exosomes in the joint cavity of CIA model as shown by immunofluorescence.

Figure 5

Strategies and applications of exosome membrane modification. (A) Direct modification of exosome membrane strategies. (B) Indirect modification of exosome membrane strategies by genetic engineering. (C) Targeting peptide c (RGDyK)-modified exosomes loaded with miR-210 for the treatment of cerebral ischemia models. Reprinted from Zhang H, Wu J, Wu J, et al. Exosome-mediated targeted delivery of miR-210 for angiogenic therapy after cerebral ischemia in mice. J Nanobiotechnology. 2019;17(1):29. http://creativecommons.org/licenses/by/4.0/. (i) Fluorescence intensity of GRD-modified exosomes and unmodified exosomes loaded with miR-210 in a brain ischemia-reperfusion model in the lesioned (intralesional) and matched non-lesioned (contralateral) areas 6 hours after intravenous injection, *P < 0.05, **P < 0.01. (ii) VEGF expression in the lesion area at 7 and 14 days after reperfusion and administration of RGD-exo:NC or RGD-exo:miR-210, *P < 0.05, **P < 0.01. (D) FPC-modified exosome for RA-targeted therapy. Reprinted from Yan F, Zhong Z, Wang Y, et al. Exosome-based biomimetic nanoparticles targeted to inflamed joints for enhanced treatment of rheumatoid arthritis. J Nanobiotechnology. 2020;18(1):115. http://creativecommons.org/licenses/by/4.0/. (i) In vivo imaging of plasma and organs 24 hours after intravenous injection of Dex-loaded liposomes, Dex-loaded exosomes, and Dex-loaded FPC-modified exosomes. (ii) Serum levels of inflammatory cytokines (TNF-α, IL-1β and IL-10) in normal and treated CIA mice, *p < 0.05, **p < 0.01, ***p < 0.001, ^#p < 0.05. (iii) Serum levels of ALT and AST in normal and treated CIA mice. (E). IMTP-Exosomes for Myocardial Ischemia Targeted Therapy. Reprinted from Wang X, Chen Y, Zhao Z, et al. Engineered Exosomes With Ischemic Myocardium-Targeting Peptide for Targeted Therapy in Myocardial Infarction. J Am Heart Assoc. 2018;7(15):e008737. http://creativecommons.org/licenses/by/4.0/. (i) Fluorescence imaging of DiR-labeled blank-Exos and IMTP-Exos in a mouse model of myocardial ischemia after 72h of intravenous injection. (ii) Expression levels of inflammatory factors (TNF-α, IL-1β and IL-6) after IMTP-Exos and blank-Exos treatment, ****p < 0.001.

Figure 6

Summary of hydrogel-loaded exosome delivery strategies.

Figure 7

Strategies for the development of exosome-based multifunctional nano-delivery platforms. The multifunctional nano-delivery platforms mainly include active loading of therapeutic agents, targeted functional modifications, evasion of MPS clearance (CD47-SIRPα axis, PEG membrane coating); controlled release using sensitive chemical bonds or hybridized liposomes (PH-sensitive, light-sensitive, heat-sensitive), inorganic nanoparticles (heat-sensitive, light-sensitive) and in vivo bioimaging; utilization of adjuvant therapies, such as magnetothermal therapy, photothermal therapy to further improve the efficacy.