Impact of Lipid Bilayer Composition and Physicochemical Properties on Constitution of a Transmembrane Helical Peptide into Exosome-Mimetic Vesicles

Exosomes are expected to efficiently deliver drugs, such as microRNAs and proteins, to targeted organs. However, using natural exosomes presents many difficulties in terms of safety, quality control, and manufacturing; therefore, developing exosome-mimetic artificial materials is desirable. In this study, we elucidated how sphingomyelin (SM) and cholesterol (CH), the main constituents of the exosome membrane, in addition to phosphatidylcholine (PC), influence the physicochemical properties of PC vesicles. Then, the relevance of these properties to the secondary structure and insertion efficiency of a helical peptide, the transmembrane domain of integrin α, was investigated. The constitution of this peptide was most successful with exosome-mimetic vesicles (EMV) bearing 15 mol % SM and 40 mol % CH, and the exclusion of SM or CH resulted in low dispersion stability or unsuccessful peptide constitution. Physicochemical analysis of the membrane properties revealed that successful peptide incorporation into the lipid membrane relied on the membrane softness induced by CH and the appearance of a highly mobile boundary phase induced by SM, which together created a favorable environment for the peptide. These results provide important insights that serve as a foundation for developing EMV as drug carriers.