U6/miR-211 expression ratio as a purity parameter for HEK293 cell-derived exosomes

Area of Science:

• Biotechnology
• Cell Biology
• Nanomedicine

Background:

• Small extracellular vesicles (sEVs), including exosomes, are released by cells and found in bodily fluids.
• High-purity isolation of exosomes from protein-rich sources is difficult, often leading to co-isolation of contaminants like microvesicles (MVs) and apoptotic bodies.
• Accurate purity assessment is vital for standardizing exosome separation methods, especially for therapeutic uses.

Purpose of the Study:

• To advance the purity assessment of small extracellular vesicle (sEV) preparations.
• To develop a novel, reliable method for quantifying exosome purity in mixed sEV populations.
• To compare different isolation techniques for their effectiveness in yielding pure exosome preparations.

Main Methods:

• sEVs were isolated from HEK293 cell culture supernatants using differential ultracentrifugation, precipitation, and size exclusion chromatography.
• Electron microscopy was used to confirm vesicle size (30-150 nm).
• Flow cytometry assessed protein contamination, and a novel qRT-PCR-based approach utilizing miR-211 enrichment was developed to differentiate exosomes from MVs and apoptotic bodies.

Main Results:

• All isolation methods yielded sEVs within the typical exosome size range.
• The novel qRT-PCR approach enabled estimation of exosome fraction within sEV mixtures.
• Differential ultracentrifugation produced sEVs with the most intact morphology and highest purity, validated by the new qRT-PCR method and other established techniques.

Conclusions:

• A simple, qRT-PCR-based method can significantly improve the characterization and purity assessment of sEV isolates.
• Differential ultracentrifugation is a preferred method for obtaining highly pure exosomes compared to precipitation and SEC.
• Precise characterization of sEVs is essential for their future use as carriers for therapeutic nucleic acids.