Comparison of the yield and purity of plasma exosomes extracted by ultracentrifugation, precipitation, and membrane-based approaches

Exosomes were enriched from plasma by ultracentrifugation, precipitation, and membrane-based approaches for yield and purity. Using the four isolation approaches, particles with mode sizes within the expected range (50–200 nm) can be isolated. By protein estimation, polymer precipitation resulted in a maximum yield (5610.59 ± 51.189 µg/mL), followed by membrane affinity (471.57 ± 12.16 µg/mL), ultracentrifugation (440.22 ± 11.71 µg/mL) and filter + ultracentrifugation (235.47 ± 13.27 µg/mL). By total RNA estimation, the yield of polymer precipitation (3.26 ± 0.42 ng/mL) was higher than that of ultracentrifugation (1.52 ± 0.06 ng/mL), filter + ultracentrifugation (1.21 ± 0.25 ng/mL) and membrane affinity (1.44 ± 0.14 ng/mL). The purity of exosomal preparations was determined as the ratio of the particle number to protein and of protein to RNA. According to the ratio of the particle number to protein concentration, the “purity” of the polymer precipitation method was similar to that of the membrane affinity method and higher than that of ultracentrifugation and filter + ultracentrifugation. When the ratio of RNA to protein was used, the “purity” of the polymer precipitation method was lower than that of the membrane affinity method. Differential methods can be employed to enrich specific exosome subpopulations. The steps of the methods affect the particle number, protein content, and even exosomal purity. The best extraction and evaluation methods for exosomes need to be selected in the laboratory according to their experimental needs.