pH-dependent disruption of erythrocyte membrane by amphiphilic poly(amino acid) nanoparticles.

The efficient cytoplasmic delivery of therapeutic agents is especially important for the induction of a maximal therapeutic effect. Previously, we reported that 200-nm-sized nanoparticles composed of hydrophobically-modified poly(gamma-glutamic acid) (gamma-PGA) showed great potential as protein carriers. Moreover, protein-encapsulated hydrophobic gamma-PGA (gamma-hPGA) nanoparticles efficiently delivered loaded proteins from the endosomes to the cytoplasm in dendritic cells, but the mechanism of the nanoparticle translocation into the cytoplasm remains to be elucidated. In this study, we examined how polymer composition, hydrophobic modification, size, conformation and surface properties of the amphiphilic nanoparticles are related to functional membrane-disruptive activities. To evaluate their potential applications as membrane-disruptive nanoparticles, the nanoparticles were characterized with respect to their hemolytic activity against erythrocytes as a function of pH. The pH-dependent conformation changes of the nanoparticles were studied by Fourier transform infrared (FT-IR) spectroscopy. The gamma-hPGA nanoparticles showed hemolytic activity with decreasing pH from 7 to 5.5, and were membrane-inactive at physiological pH. This activity was dependent on the hydrophobicity of gamma-PGA. The mechanism responsible for the pH-dependent hemolysis by the nanoparticles involved a conformational change of gamma-hPGA and corresponding increase in the surface hydrophobicity. We conclude that gamma-hPGA nanoparticles have significant potential as membrane-disruptive carriers. These results have important implications for the design of endosome-disruptive nanoparticles as drug, protein and DNA delivery systems.