Evaluation of pegylated lipid nanocapsules versus complement system activation and macrophage uptake

This work consisted in defining the in vitro behavior of pegylated lipid nanocapsules (LNC) toward the immune system. LNC were composed of an oily core surrounded by a shell of lecithin and polyethylene glycol (PEG) known to decrease the recognition of nanoparticles by the immune system. The "stealth" properties were evaluated by measuring complement activation (CH50 technique and crossed-immunoelectrophoresis (C3 cleavage)) and macrophage uptake. These experiments were performed on 20-, 50-, and 100-nm LNC before and after dialysis. A high density of PEG at the surface led to very low complement activation by LNC with a slight effect of size. This size effect, associated to a dialysis effect in macrophage uptake, was due to differences in density and flexibility of PEG chains related to LNC curvature radius. Thanks to a high density, 660-Da PEG provided LNC a steric stabilization and a protective effect versus complement protein opsonization, but this protection decreased with the increase of LNC size, especially versus macrophage uptake.