Advancing EV Research: Comprehensive Protocols for Characterizing Internalization Dynamics in Cell Lines

  Introduction: Accumulating evidence underscores the pivotal role of extracellular vesicles (EVs) in intercellular communication, positioning them as potential candidates for treating various diseases. Furthermore, EVs hold promise as vehicles for drug delivery. However, the biotechnological exploration of EVs necessitates a concerted effort to harmonize the techniques used for their characterization. Methods: This study presents a comprehensive protocol for validating the internalization of EVs in cell lines and assessing the kinetics of this process. Initially, EVs are labeled with the Vybrant DiO membrane dye, chosen for its efficacy in integrating into the EV membrane without compromising its integrity or functionality. The internalization of EVs is initially evaluated using conventional fluorescence microscopy, a cost-effective and expeditious method that serves as an initial indicator of EV presence in or around the target cells. To overcome the limitation of this technique in precisely determining the location of EVs, confocal microscopy is employed. This step is crucial, as co-staining with a cytoskeleton dye enables accurate determination of the three-dimensional localization of EVs, confirming their internalization. Time-lapse confocal microscopy and flow cytometry are utilized to elucidate the dynamics of this process, including the rate of internalization and potential saturation point. Results: Our findings demonstrate the successful labeling of EVs with the fluorescent dye Vybrant DiO, facilitating the visualization and confirmation of EV internalization within targeted cell lines. Initial examination via conventional fluorescence microscopy provided preliminary evidence of EV presence near or within cells. Subsequent confocal fluorescence microscopy enabled more detailed observation, confirming EV internalization with greater specificity and spatial resolution. Furthermore, the dynamics of EV uptake were elucidated using time-lapse confocal microscopy and flow cytometry techniques. These methodologies not only validated the internalization process but also enabled the capture and quantification of the temporal progression of EV uptake, offering comprehensive insights into the kinetics and efficiency of EV-cell interactions. Conclusions: This study contributes to the standardization of EV uptake assays, providing valuable insights into EV-cell interactions and fostering advancements in research pertaining to therapeutic applications based on EVs.