Comparison of an Optimized Ultracentrifugation Method versus Size-Exclusion Chromatography for Isolation of Exosomes from Human Serum

Exosomes are nanosized vesicles that
are abundant in biological
fluids. In recent years, exosomes have attracted increasing attention
as their cargo may provide promising biomarkers for the early diagnosis
of and therapy for many diseases, such as cancer. In addition to ultracentrifugation
(UC), many alternative methods including size-exclusion chromatography
(SEC) have been developed for isolating exosomes. It has been reported
that the SEC method provided improved performance relative to the
UC method in isolating exosomes from plasma, where the former contained
less residual blood protein contamination. We have compared the SEC
method with an optimized UC method in isolating exosomes from human
serum. This was based on dilution of the serum to reduce the viscosity
and a prolonged cycle of UC, followed by another four cycles. We found
that >95% of serum proteins were removed without a significant
loss
of exosome proteins relative to SEC. We also combined one cycle of
UC with SEC and found that this method provided improved results relative
to the SEC method, although the serum protein contamination was several
times higher than that of our optimized UC method. The TEM showed
that the size distribution of exosomes isolated from each of the three
methods was similar.