Abstract
Human plasma is a complex fluid, increasingly used for extracellular vesicle (EV) biomarker studies. Our aim was to find a simple EV-enrichment method for reliable quantification of EVs in plasma to be used as biomarker of disease. Plasma of ten healthy subjects was processed using sedimentation rate- (sucrose cushion ultracentrifugation—sUC) and size- (size exclusion chromatography—SEC) based methods. According to nanoparticle tracking analysis (NTA), asymmetrical flow field-flow fractionation coupled to detectors (AF4-UV-MALS), miRNA quantification, transmission electron microscopy and enzyme-linked immunosorbent assay, enrichment of EVs from plasma with sUC method lead to high purity of EVs in the samples. High nanoparticle concentrations after SEC resulted from substantial contamination with lipoproteins and other aggregates of EV-like sizes that importantly affect downstream EV quantification. Additionally, sUC EV-enrichment method linked to quantification with NTA or AF4-UV-MALS is repeatable, as the relative standard deviation of EV size measured in independently processed samples from the same plasma source was 5.4% and 2.1% when analyzed by NTA or AF4-UV-MALS, respectively. In conclusion, the sUC EV-enrichment method is compatible with reliable measurement of concentration and size of EVs from plasma and should in the future be tested on larger cohorts in relation to different diseases. This is one of the first studies using AF4-UV-MALS to quantify EVs in blood plasma, which opens new possible clinical utility for the technique.
Highlights
Human plasma is a complex fluid, increasingly used for extracellular vesicle (EV) biomarker studies
We compared two methods for enrichment of EVs from one mL of blood plasma, separating particles based on their sedimentation rate—sucrose cushion ultracentrifugation (sUC), and size—size exclusion chromatography (SEC)
According to nanoparticle tracking analysis (NTA), AF4-UV-multi-angle light scattering (MALS), miRNA quantification, transmission electron microscopy (TEM) and enzyme-linked immunosorbent assay (ELISA), sUC enrichment method leads to high purity of EVs in the samples
Summary
Human plasma is a complex fluid, increasingly used for extracellular vesicle (EV) biomarker studies. The sUC EV-enrichment method is compatible with reliable measurement of concentration and size of EVs from plasma and should in the future be tested on larger cohorts in relation to different diseases This is one of the first studies using AF4-UV-MALS to quantify EVs in blood plasma, which opens new possible clinical utility for the technique. Research of EVs is currently focused on their function and molecular composition (miRNA, DNA or proteins), whereas studies of changes in size and/or concentration of EVs as biomarkers of disease are rare This is likely due to EVs’ small size and low refractive index, making their detection and analysis technically very difficult[18,19]. EV-enrichment should be coupled to different quantification techniques, to provide sufficient dynamic range for reliable determination of EV size and concentration in biomarker discovery studies
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