Deep dive on the proteome of salivary extracellular vesicles: comparison between ultracentrifugation and polymer-based precipitation isolation

Salivary extracellular vesicles (EVs), as novel functional carriers and potential biomarkers, are usually obtained by ultracentrifugation (UC) and polyethylene glycol (PEG)-based precipitation methods. However, salivary EVs obtained by these two methods have not been systematically compared. Here, we perform an in-depth analysis on EVs isolated by these two methods using proteomics. Both methods obtain EVs ranging from 40 to 210 nm, with the PEG method resulting in a wider size distribution. PEG-separated products were irregularly shaped and aggregated, while UC-separated ones were monodispersed and teacup-shaped. Additionally, the expression of EV-specific markers was higher in UC-separated EVs. Using tandem mass spectrometry proteomics, we identified and quantified 1217 kinds of saliva exosomal proteins and 361 kinds of differential proteins, showing that UC can isolate more EV-related proteins. These results offer some guidance for EV separating and provide potential direction for the use of EVs in non-invasive diagnosis.