Extracellular vesicles (EVs) are nanoscale lipid bilayer particles secreted by cells that mediate intercellular communication by transporting biomolecules such as proteins and RNA. Among them, exosomes have attracted significant attention for applications in diagnostics and therapeutics, including cancer and neurodegenerative diseases. However, standardized criteria for evaluating their quality and functionality remain insufficient.
In a comprehensive review published in ACS Nano Medicine, Dr. Naohiro Seo (Project Associate Professor, Graduate School of Engineering, The University of Tokyo) and Professor Takanori Ichiki systematically clarified the relationship between EV surface charge and membrane lipid composition, revealing their fundamental role in determining EV function .
A key physicochemical parameter, surface charge (zeta potential), plays a critical role in nanoparticle behavior in biological environments, influencing stability, circulation, and cellular uptake. Despite its importance, the origin and variability of surface charge among different EV types have not been systematically understood.
The study demonstrates that different EV types exhibit distinct surface charge characteristics. Exosomes tend to show relatively weak negative charge, whereas cell membrane-derived EVs, such as microvesicles, display stronger negative charge. This difference is attributed to membrane lipid asymmetry.
In particular, the distribution of phosphatidylserine (PS), a negatively charged phospholipid, plays a central role. In exosomes, PS is predominantly retained on the inner leaflet of the lipid bilayer, while in membrane-derived EVs it is more frequently exposed on the outer surface. This asymmetry directly influences the zeta potential of EVs and their interactions with biological systems.
Importantly, the study highlights that EV surface charge is not merely a physical property, but also reflects cellular conditions and functional characteristics. This positions zeta potential as a promising indicator for EV classification, separation, and quality evaluation.
As EV-based therapeutics continue to advance toward clinical applications, ensuring consistency, safety, and reproducibility remains a major challenge. The framework presented in this review provides a scientific basis for establishing standardized quality metrics and regulatory approaches.
Furthermore, controlling membrane lipid composition and surface charge may enable the rational design of next-generation nanomedicine. By tuning these parameters, it may be possible to optimize targeting efficiency, biodistribution, and therapeutic performance. For example, strongly negatively charged EVs derived from senescent cells may be associated with age-related diseases, suggesting potential strategies for selective targeting or removal.
This work provides a unified perspective linking membrane structure, physicochemical properties, and biological function of EVs, paving the way for advances in diagnostics, therapeutics, and regulatory science in the rapidly expanding field of extracellular vesicles.
This research was carried out as part of a broader effort to understand and control aging-related biological processes under the JST COI-NEXT Program Kawasaki Hub* . The program is centered at Innovation Center of NanoMedicine (iCONM) in Kawasaki, where Professor Takanori Ichiki, one of the authors, serves as the Research Director, promoting interdisciplinary research at the interface of nanotechnology, medicine, and engineering.
"This work provides a unified framework linking membrane structure to EV function," said Takanori Ichiki, "by identifying surface charge as a key indicator, we expect this to contribute to the standardization and rational design of EV-based therapeutics."
*About COI-NEXT Program Kawasaki Hub (Project CHANGE): https://change.kawasaki-net.ne.jp/en
Homepage for Ichiki Lab of the University of Tokyo: https://bionano.t.u-tokyo.ac.jp/en/
