Exosomes are secreted nanovesicles shed by almost all kinds of cells. Recently, increased interest has been focused on these extracellular vesicles as natural carriers transporting biological contents for intercellular communication. However, current isolation techniques, such as ultracentrifugation, are not convenient and often require specialized equipment. Herein, we describe a polyethylene glycol (PEG)-based approach, which could permit facile, low-cost and effective isolation of exosomes from cell culture supernatant. High-resolution electron microscopes clearly visualized the size and morphology of isolated exosome aggregates, implying the mechanism of PEG-based precipitation. Combined with tandem mass spectrometry analysis, 6299 protein groups encoded by 5120 genes were successfully characterized from HeLa cell culture supernatant, including numerous exosome proteins which could overlap 97% of the Top 100 exosome marker proteins recorded in the ExoCarta database, as well as a series of low-abundance cytokines and biomarkers. Furthermore, we found a higher ratio of neo-cleavage sites in proteins identified from exosomes compared with cellular proteins, revealing the potential roles of exosomes in accumulation and transportation of protein degradation intermediates.

Human epithelial cell culture models of monolayer Caco-2 cells have been widely employed to assess the absorption of drug molecules across intestinal mucosa. However, cautions should be taken when interpreting the conclusions from those models due to their undesirable phenotype and functionality when compared with the native intestinal tissue. In the present study, an improved, more physiologically relevant three-dimensional (3D) culture model of the intestinal mucosa was developed to study drug absorption, in which a coculture of epithelial cells, including Caco-2 cells and HT29-methotrexate cells, was indirectly seeded on a Transwell filter insert with collagen gel and stromal cells (fibroblasts and immunocytes) incorporation. This setting-up provided a compatible environment to improve the phenotype and functionality of the epithelial cells. Compared with the monolayer culture of Caco-2 cells, the reconstructed 3D model displayed more physiologically relevant characteristics evidenced by its decreased TEER value and mucus-like layer formation. A decreased expression of P-gp and an increased expression of BCRP were also observed in the current 3D culture model, leading to a changed secretory permeability of their substrates. More importantly, an improved correlation (R(2)=0.843) was obtained between the absorptive permeability across the 3D coculture model and the human absorption fraction especially for those model compounds with moderate or high permeability. Thus, this engineered 3D coculture model presents a unique, improved opportunity to evaluate drug permeability in vitro.

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