PEGylation of Phosphatidylglycerol/Docosahexaenoic Acid Hexosomes with d-α-Tocopheryl Succinate Poly(ethylene glycol)₂₀₀₀ Induces Morphological Transformation into Vesicles with Prolonged Circulation Times

Considering the broad therapeutic potential of omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA), here we study the effect of PEGylation of DHA-incorporated hexosomes on their physicochemical characteristics and biodistribution following intravenous injection into mice. Hexosomes were formed from phosphatidylglycerol and DHA with a weight ratio of 3:2. PEGylation was achieved through the incorporation of either d-α-tocopheryl succinate poly(ethylene glycol)₂₀₀₀ (TPGS-mPEG₂₀₀₀) or 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy-poly(ethylene glycol)₂₀₀₀ (DSPE-mPEG₂₀₀₀) at a concentration of 1.5 wt %. Nanoparticle tracking analysis, synchrotron small-angle scattering, and cryo-transmission electron microscopy were employed to characterize the nanodispersions. The results show that PEGylated lipids induce a structural transition from an inverse hexagonal (H₂) phase inside the nanoparticles (hexosomes) to a lamellar (L_α) phase (vesicles). We also followed the effect of mouse plasma on the nanodispersion size distribution, number, and morphology because changes brought by plasma constituents could regulate the in vivo performance of intravenously injected nanodispersions. For comparative biodistribution studies, fluorescently labeled nanodispersions of equivalent quantum yields were injected intravenously into healthy mice. TPGS-mPEG₂₀₀₀-induced vesicles were most effective in avoiding hepatosplenic clearance at early time points. In an orthotopic xenograft murine model of glioblastoma, TPGS-mPEG₂₀₀₀-induced vesicles also showed improved localization to the brain compared with native hexosomes. We discuss these observations and their implications for the future design of injectable lyotropic nonlamellar liquid crystalline drug delivery nanosystems for therapeutic interventions of brain and liver diseases.