Exosomes (extracellular vesicles/EVs) participate in cell–cell communication and contain bioactive molecules, such as microRNAs. However, the detailed characteristics of secreted EVs produced by cells grown under low pH conditions are still unknown. Here, we report that low pH in the cell culture medium significantly affected the secretion of EVs with increased protein content and zeta potential. The intracellular expression level and location of stably expressed GFP‐fused CD63 (an EV tetraspanin) in HeLa cells were also significantly affected by environmental pH. In addition, increased cellular uptake of EVs was observed. Moreover, the uptake rate was influenced by the presence of serum in the cell culture medium. Our findings contribute to our understanding of the effect of environmental conditions on EV‐based cell–cell communication.
Background/Aim: Extracellular vesicles (exosomes, EVs) (30-200 nm in diameter) are secreted by various cells in the body. Owing to the pharmaceutical advantages of EVs, an EV-based drug delivery system (DDS) for cancer therapy is expected to be the next-generation therapeutic system. However, preservation methods for functional and therapeutic EVs should be developed. Here, we developed the method of lyophilization of arginine-rich cell penetrating peptide (CPP)modified EVs and investigated the effects of lyophilization on the characteristics of EVs. Materials and Methods: Particle size, structure, zeta-potential, and cellular uptake efficacy of the arginine-rich CPP-modified EVs were analyzed. The model protein saporin (SAP), having anti-cancer effects, was encapsulated inside the EVs to assess the cytosolic release of EV content after cellular uptake. Results: Lyophilization of the EVs did not affect their particle size, structure, zeta-potential, and cellular uptake efficacy; however, the biological activity of the encapsulated SAP was inhibited by lyophilization. Conclusion: Lyophilization of EVs may affect SAP structures and/or reduce the cytosolic release efficacy of EV's content after cellular uptake and needs attention in EV-based DDSs.Extracellular vesicles (exosomes, EVs) are cellular membrane vesicles (ca. 30-200 nm diameter) that are secreted from almost all the cells of the body (1-3). EVs are generated in multivesicular endosomes (MVEs) by inward budding of cellular membranes. After fusion of plasma and MVE membranes, EVs are secreted and taken up by other cells via membrane fusion and endocytosis (1-3). Because of encapsulation of biofunctional molecules including microRNAs and enzymes in the MVEs, EVs participate in cell-to-cell communication and regulate cellular/body homeostasis and the progression of diseases such as cancer (1-4). In cancer cells, cell-to-cell communication based on EVs induces angiogenesis, tumor cell migration, metastasis, and immune response modulation (2, 3). EV-based diagnostics have gained increased attention owing to ability EVs to encapsulate disease-related proteins and microRNAs (3, 4). In addition, the development of EV-based drug delivery systems (DDSs) is highly expected to become the next-generation therapeutic system because of the several advantages of EVs, such as immunological control, usage of EV-based cell-to-cell communication routes, low toxicity, controlled and designed expression of protein in/on EVs, infinite secretion, and artificial/natural encapsulation of therapeutic molecular cocktails (3,4). A receptor target system has been developed by expressing on EV membranes, through genetic engineering, a sequence that interacts with a receptor target. Examples include the central nervous system-specific rabies viral glycoprotein (RVG) peptide for targeting acetylcholine receptor (5), anti-epidermal growth factor receptor (EGFR) nanobodies fused with glycosylphosphatidylinositol (GPI) anchor signal peptides derived from decay-accelerating factor (DAF) (6),...
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