Intracellular fate of octaarginine-modified liposomes in polarized MDCK cells

Octaarginine (R8)-modified liposomes have been used to deliver therapeutic substances into cells owing to the efficient cellular uptake via macropinocytosis. Recent analyses revealed that R8-modified liposomes are mainly taken up via macropinocytosis, and escape from endosomes efficiently to avoid lysosomal degradation in non-polarized NIH-3T3 cells. In the present study, we evaluated the intracellular fate of R8-modfied liposomes in polarized MDCK cells, comparing their trafficking with that of conventional cationic liposomes by confocal laser scanning microscopy (CLSM). In contrast to what occurs in NIH-3T3 cells, R8-modified liposomes are internalized by MDCK cells equally well via clathrin-mediated endocytosis and macropinocytosis. The most salient characteristic in subsequent intracellular trafficking in MDCK cells is that R8-modified liposomes become trapped in the endosomal compartment and subsequently, a portion of them colocalizes with the Golgi apparatus. Similar colocalization with the Golgi apparatus was observed for octalysine (K8)-modified liposomes. In contrast, cationic liposomes were found to colocalize predominantly with lysosomes stained with lysotracker. Collectively, in polarized MDCK cells, cationic peptide-modified liposomes may be subjected to a different sorting pathway from that used for liposomes composed of cationic lipids.