Exosomes have been used as a source of biomarkers in diagnostics for many diseases, including cancer, and are now being used as therapeutic delivery systems. To date, the most efficient method for isolating exosomes from serum or plasma samples has been to use a size exclusion, chromatography (SEC) based isolation. The conditions of the SEC separation can be modified to yield extracellular vesicles of different sizes and diagnostic value. Apoptotic bodies, 50-5000nm, microvesicles, 50-1000nm, and exosomes, 30-120nm, all have different diagnostic and targeted applications. Here, we show a routine and robust method for the isolation and monitoring of proteins in exosomes isolated from plasma samples. The methods and conditions used here are focused on rapidly providing a high yield of exosome vesicles in a monodisperse 40nm size range from a plasma sample.
Materials and methods:
K2EDTA plasma samples from donor disease and control groups were collected with IRB approval. All SEC columns and reagents for exosome isolation were obtained as a kit (NX Prenatal, Houston, TX). The 40nm exosome fraction from the column was lysed, the proteins reduced, alkylated and digested with trypsin; the subsequent peptides were analyzed by ultra-high performance liquid chromatography (Vanquish Horizon, ThermoFisher Scientific), tandem mass spectrometry (Q-Exactive, ThermoFisher Scientific), to quantify and identify greater than 500 proteins from exosomes, isolated from a single plasma sample, in a 1 hour method. Subsequent isolations of 40nm exosome fractions were labeled with a sulfo-NHS-biotin linker, followed by lysis and enrichment with streptavidin columns, and an identical LC-MS analysis to obtain quantitative analysis of the surface membrane protein contents on the exosomes.
Raw data was analyzed using the label-free quantitation module in Proteome Discoverer (Thermofisher Scientific). Peptide peak areas from three technical replicate runs were used to ascertain the reproducibility of the method across both normal and disease samples. Membrane protein extracts LC-MS data was further grouped by Protein Center (ThermoFisher Scientific) by cell type and tissue of origin.
The methods shown here provide a robust and efficient platform for 40nm exosome isolation from human plasma samples, and quantitative analysis of the protein content thereof for the purposes of biomarker discovery, quantification and screening purposes.
Citation Format: David A. Sarracino, Xiaolei Xie, Courtney E. Martel, Shen Luan, Kevin Rosenblatt. Exosomes in plasma for protein based cancer biomarkers: A clinical research tool using UHPLC-MS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2225.