[Comparison of four methods for extracting extracellular vesicles from human umbilical cord mesenchymal stem cells]

Objective To compare the efficiency of four methods for extracting extracellular vesicles (EVs) from human umbilical cord mesenchymal stem cells(hUCMSCs). Methods EVs were isolated from the conditioned medium of hUCMSCs by ultracentrifugation (group A), or ultrafiltration combined with ultracentrifugation (group B), or ultrafiltration combined with polyethylene glycol precipitation (group C), or ultrafiltration combined with aqueous two phase system (group D). The total protein concentration of EVs in each group was determined by BCA method. The expression of Alix, CD9, and calnexin were detected by Western blotting. The morphology of EVs was analyzed by transmission electron microscopy. The particle size distribution and particle concentration of EVs were measured by nanoparticle tracking analysis. Results The total protein concentrations of EVs extracted by the above four methods were (1.92±1.77) μg/μL, (18.1±1.07) μg/μL, (6.33±1.02) μg/μL, (36.48±23.13) μg/μL from group A to D respectively. We observed the expression of CD9 and Alix, but not calnexin, in EVs from group A, B and C. However, the expression levels of CD9 and Alix were lowest in group C. In addition, the expression of CD9, Alix and calnexin were undetectable in EVs from group D. The particle concentrations of EVs in group A, B and C were 0.85×10¹¹ particles/mL, 0.63×10¹¹ particles/mL, 1.83×10¹¹ particles/mL, respectively. Meanwhile, the particle distributions were all within the size range of EVs. We also observed the typical saucer-like membrane structure in EVs from group A, B and C. Conclusion The method of ultrafiltration combined with ultracentrifugation could be applied to the experiments demanding large amounts of EVs. The method of ultracentrifugation is recommended for the extraction of little amounts of EVs due to the lower risk of EV fragmentation.