Characterization of endocytosis and exocytosis of cationic nanoparticles in airwayepithelium cells

Abstract

A major challenge of drug delivery using colloids via the airway is to understand themechanism implied in their interactions with epithelial cells. The purpose of thiswork was to characterize the process of endocytosis and exocytosis of cationicnanoparticles (NPs) made of maltodextrin which were developed as a deliverysystem for antigens in vaccine applications. Confocal microscopy demonstrated thatthese NP are rapidly endocytosed after as little as 3 min incubation, and that theendocytosis was also faster than NP binding since most of the NPs were foundin the middle of the cells around the nuclei. A saturation limit was observedafter a 40 min incubation, probably due to an equilibrium becoming establishedbetween endocytosis and exocytosis. Endocytosis was dramatically reduced at4 °C comparedwith 37 °C,or by NaN3 treatment, both results suggesting an energy dependent process. Protamine pretreatment ofthe cells inhibited NPs uptake and we found that clathrin pathway is implied in theirendocytosis. Cholesterol depletion increased NP uptake by 300% and this phenomenon wasexplained by the fact that cholesterol depletion totally blocked NP exocytosis. Theseresults suggest that these cationic NPs interact with anionic sites, are quicklyendocytosed via the clathrin pathway and that their exocytosis is cholesterol dependent,and are similar to those obtained in other studies with viruses such as influenza.