Isolation of small extracellular vesicles from human serum using a combination of ultracentrifugation with polymer-based precipitation

Methods for reproducibly isolating and enriching small extracellular vesicles (EVs) from blood are essential for clinical utilization of small EVs in cancer patients. We combined ultracentrifugation (UC) with polymer-based precipitation (ExoQuick [EQ] or Total Exosome Isolation [TEI] kit) to isolate small EVs (diameter, 30-150 nm) from the serum of breast cancer patients. We compared the performance of four cycles of UC (UC4x) with that of two cycles of UC followed by enrichment using the EQ (UC2x→EQ) or TEI (UC2x→TEI) kits. The mean concentration of small EVs isolated from 1 mL of serum using UC2x→EQ (139.0±29.1 μg) and UC2x→TEI (140.4±5.0 μg) did not differ from that obtained using UC4x (141.8±26.9 μg). The mean number of EV particles obtained using UC4x was 29.2± 9.9×10⁹ per mL of serum, whereas UC2x→EQ and UC2x→TEI yielded higher numbers of EVs (50.7±17.0×10⁹ and 59.3±20.6×10⁹, respectively). Concentrations of EV microRNAs, including miR-21 and miR-155, did not differ between the three methods. In conclusion, performing UC prior to the use of polymer-based precipitation kits could be feasible for isolating small EVs from human serum in large sample-based translational researches.