Concentration and Composition of Circulating Adipocyte-Derived Extracellular Vesicles in Patients with Colonic Polyps and Colorectal Cancer

Extracellular vesicles (EVs) are a heterogeneous populationof membrane-bound nanoparticles (< 1 µm in size) secreted byvarious cell types. Most of EVs circulating in human blood are derivedfrom platelets, leukocytes, erythrocytes, and endotheliocytes. Thecomposition of circulating adipocyte-derived EVs under various pathologicalconditions has been virtually unknown. Small EVs were isolated byultrafiltration and double ultracentrifugation from blood plasmaof patients with colorectal cancer (CRC) and colonic polyps withobesity or metabolic syndrome. The composition of adipocyte-derived EVswas analyzed by immunoprecipitation combined with Western blottingand flow cytometry. EVs fractions (FABP4- and CD11b-immunoprecipitatedEVs, as well as EVs contained in the supernatant after removal ofCD11b-positive EVs) contained a complex of adipocyte markers (FABP4,PPAR-γ, perilipin 1). In CRC patients without obesity, monocyte/macrophage-derivedEVs precipitated on CD11b-coated particles were characterized bya combined overexpression of FABP4 and perilipin 1, while such anoverexpression was not typical for CRC patients with metabolic syndromeor obesity. The fraction of true adipocyte-derived EVs (supernatantafter removal of CD11b-positive EVs) was characterized by the presenceof a complex of adipocyte markers with a predominant expressionof FABP4 in all patients both with metabolic syndrome/metabolicallyhealthy obesity and without metabolic disorders. To correctly characterizecirculating EVs in patients without obesity, it is necessary firstto remove the fraction of CD11b-positive monocyte/macrophage-derivedEVs from EV preparations by immunoprecipitation or similar methods,and then, after removal/sorption of precipitated EVs, to analyzethe composition of adipocyte-derived EVs in the supernatant usinga set of above-mentioned adipocyte markers. Moreover, in patientswith metabolic disorders, given the insignificant FABP4 expressionin CD11b-immunoprecipitated EVs, the pre-depletion of EV preparationsdoes not appear to be that necessary.