What are exosomes, and what can they do?
Exosomes were first discovered by Pan and Johnstone in 1983. They are lipid-bilayer extracellular vesicles (EVs) with 30–150 nm diameter.¹,² They are intracellularly produced in organelles (multivesicular bodies) and released from nearly all cell types into the extracellular milieu (Figure 1).³ Exosomes are rich in proteins, nucleic acids, and other bioactive molecules involved in intercellular communication.⁴ They can be obtained from several sources, including peripheral blood, saliva, urine, cerebrospinal fluid, and milk.⁵
Figure 1. Biogenesis of exosomes (Created in https://BioRender.com).
Among their properties are biocompatibility, stability, low toxicity, and efficient exchange of molecular cargo.⁶ Exosomes can deliver their cargo to specific distant targets to regulate cellular division, survival, differentiation, response to stress, and apoptosis.⁷ Evidence has confirmed that exosomes promote wound healing, stimulate bone regeneration, and enable cartilage repair by inducing angiogenesis, collagen fiber deposition, and inhibiting inflammation.⁸⁻¹⁰ However, due to the technical limitations in obtaining sufficient exosome quantities for clinical applications, no commercial products based on exosomes have been approved by medicine agencies.¹¹ In contrast, autologous-derived exosomes obtained from the patient’s tissues, such as platelets, whole blood, or fat, are emerging as a promising avenue for regenerative treatments.
Figure 2. Hallmarks of exosomes (Created in https://BioRender.com).
How can exosomes be characterized, isolated and quantified?
Although emerging detection methods and new analytical techniques exist, there is no purification method to separate exosomes based on their size and no consensus on specific markers that uniquely distinguish the origin of these vesicles once they have left the cell.¹²
Several methods are used to characterize EVs, identify protein composition, and detect nucleic acids and lipids. They include conventional western blotting, mass spectrometry, flow cytometry (bead coupled), microfluidics chips, polymerase chain reaction, and nuclear magnetic resonance (Figure 3). Super-resolving techniques, such as electron microscopy, determine the size, shape, morphology-integrity, inter-particle interaction, and spatial relationship with tissues and cells to complete exosome qualitative information.¹³,¹⁴
Figure 3. Isolation and characterization methods of exosomes (Created in https://BioRender.com).
Regarding other quantification techniques, we can find atomic force microscopy, nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), dynamic light scattering, surface plasmon resonance (SPR), and the single particle interferometric reflectance imaging sensor (SP-IRIS) (Figure 3). Among the isolation techniques are ultracentrifugation, ultrafiltration, size exclusion chromatography, precipitation, and immunoaffinity-based capture. However, each isolation and quantification method have some advantages and disadvantages, particularly regarding the integrity of the exosomes obtained and the specificity of the particles detected.¹⁵,¹⁶
While these issues are solving, treatments with autologous materials, such as platelet-rich plasma or adipose-derived stem cells preconditioned with photothermal biomodulation to stimulate exosome release, have been proven to be efficacious and safe for regenerative medicine.
For more in-depth insights on exosomes, download our free eBook here: https://metacelltech.com/exosomesebook/
References
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12. Yakubovich EI, Polischouk AG, Evtushenko VI. Principles and Problems of Exosome Isolation from Biological Fluids. Biochem (Mosc) Suppl Ser A Membr Cell Biol [Internet]. 2022 Jun 16;16(2):115–26. Available from: https://link.springer.com/10.1134/S1990747822030096
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