Circulating extracellular vesicles have emerged as potential new biomarkers in a wide
variety of diseases. Despite the increasing interest, their isolation and purification
from body fluids remains challenging. Here we studied human pre-prandial and 4 hours
postprandial platelet-free blood plasma samples as well as human platelet concentrates.
Using flow cytometry, we found that the majority of circulating particles within the
size range of extracellular vesicles lacked common vesicular markers. We identified
most of these particles as lipoproteins (predominantly low-density lipoprotein, LDL)
which mimicked the characteristics of extracellular vesicles and also co-purified
with them. Based on biophysical properties of LDL this finding was highly unexpected.
Current state-of-the-art extracellular vesicle isolation and purification methods
did not result in lipoprotein-free vesicle preparations from blood plasma or from
platelet concentrates. Furthermore, transmission electron microscopy showed an association
of LDL with isolated vesicles upon in vitro mixing. This is the first study to show
co-purification and in vitro association of LDL with extracellular vesicles and its
interference with vesicle analysis. Our data point to the importance of careful study
design and data interpretation in studies using blood-derived extracellular vesicles
with special focus on potentially co-purified LDL.
