In vitro uptake evaluation in Caco-2 cells and in vivo results in diabetic rats of insulin-loaded PLGA nanoparticles

PLGA nanoparticles (NPs) are largely developed for biological applications but little is known about their uptake. Therefore, we focused our study on the modalities of insulin-loaded PLGA NPs transport across Caco-2 monolayers, and their hypoglycaemic effect on diabetic rats. Insulin-loaded PLGA NPs were formulated by a double emulsion solvent evaporation process. NPs mean diameter was between 130 and 180 nm. NPs were smooth and spherical with an entrapment efficiency above 80%. Fluorescently labeled NPs were incubated with Caco-2 cells to study the process of uptake and the intracellular fate by flow cytometry and confocal laser scanning microscopy. The kinetic of absorption was time-dependent and occurred by clathrin-mediated endocytosis. The intracellular traffic led to a basolateral exocytosis of NPs. In vitro studies and in vivo intraduodenal administration to diabetic rats showed that NPs were resistant in intestinal conditions long enough to allow both the intestinal absorption of NPs and the delivery of functional insulin in bloodstream. The resulting in vivo hypoglycaemic effect was similar to a long-acting insulin one. As no effect on glycaemia occurred after oral administration, further studies need to be conducted to protect NPs from the degradation occurring at the enteric level.