Intracellular trafficking mechanism, from intracellular uptake to extracellular efflux, for phospholipid/cholesterol liposomes

Liposomes are widely used as drug delivery vehicles to transfer chemotherapeutic agents, proteins, and nucleic acids into target cells. To improve therapeutic effects and reduce unexpected toxic side-effects, it is necessary to understand the mechanism of liposomal uptake into cells, and the intracellular fate of internalized liposomes. The intracellular fate of synthesized components used in the construction of liposomes remains unclear. In the work presented here, we investigated the trafficking processes from intracellular uptake to extracellular efflux using conventional liposomes constructed with phospholipids (DOPC) and cholesterols (Chol). Following intracellular transport of liposomes via endocytosis, DOPC was localized in the endoplasmic reticulum (ER) and Golgi apparatus after escape from the endosome/lysosome, whereas Chol was only localized in the ER. Moreover, proteins involved in the intracellular trafficking of liposomal components were identified. Additionally, we showed that DOPC was partly effluxed via ABCG1, while Chol was partly effluxed via ABCA1 or ABCB1; suggesting that each liposomal component examined in this study was effluxed through different transporters. Our findings offer valuable information regarding targeted delivery to specific intracellular organelles, and how to possibly avoid unexpected toxic effects following multiple applications of liposome formulations.