Abstract
Extracellular vesicles (EVs) are a heterogeneous population of membrane particles less than 1 μm in size, secreted by various cell types. Most EVs circulating in human blood are particles of platelet, leukocyte, erythrocyte and endothelial origin. The composition of circulating adipocyte EVs in various pathological conditions has been virtually unknown. Small EVs from the blood plasma of patients with colorectal cancer (CRC) and colon polyps with obesity or metabolic syndrome were isolated by ultrafiltration with double ultracentrifugation. To study the composition of adipocyte EVs, immunoprecipitation in combination with Western blotting and flow cytometry were used. Vesicle fractions (FABP4- and CD11b-immunoprecipitated EVs, as well as EVs contained in the supernatant after removal of CD11b-positive EVs) contained a complex of adipocyte markers (FABP4, PPAR-γ and perilipin 1). EVs of monocyte-macrophage origin precipitated on CD11b-coated particles in CRC patients without obesity were characterized by combined overexpression of FABP4 and perilipin 1, while such overexpression was not typical for CRC patients with metabolic syndrome or obesity. The fraction of truly adipocyte vesicles (supernatant after removal of CD11b-positive EVs) was characterized by the presence in all patients of a complex of adipocyte markers with predominant expression of FABP4 in both patients with metabolic syndrome/metabolically healthy obesity and patients without metabolic disorders. To correctly characterize circulating EVs of patients without obesity, it is first necessary to remove the fraction of CD11b-positive monocyte-macrophage EVs from EV preparations by immunoprecipitation or similar methods, and in the supernatant after removal/sorption of precipitated EVs, the composition of adipocyte vesicles can be studied using a set of markers (FABP4, PPAR-γ, perilipin 1, etc.). Moreover, in patients with metabolic disorders, taking into account the insignificant expression of FABP4 in CD11b-immunoprecipitated EVs, preliminary depletion of vesicle preparations is apparently not so necessary.
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