Mechanisms of interaction of biodegradable polyester nanocapsules with non-phagocytic cells

The interaction of polymer nanocapsules (NC) prepared from four biodegradable polyesters with variable polymer hydrophobicity (PCL, PLA, PLGA and PLA-PEG) was investigated in the non-phagocytic Vero, Caco-2 and HepG2 cell lines. The NC, labeled with the highly lipophilic fluorescent indocarbocyanine dye DIL, had very similar sizes (approx. 140 nm) and negative zeta-potentials. Asymmetric flow field-flow fractionation evidenced NC colloidal stability and negligible transfer of the dye to serum proteins in the incubation medium. The cytotoxicity of the NC was evaluated via MTT assay over a large polymer concentration range (1-1000 μg/mL) and time of exposure (2, 24 and 48 h). The NC were safe in vitro up to a concentration of approx. 100 μg/mL or higher, depending on the cell line and nature of the polymer. Vero cells were more sensitive to the NC, in particular NC of the more hydrophobic polymer. The cells were exposed to endocytosis inhibitors, incubated with NC, and the cell-associated fluorescence was quantified by spectrofluorometry. HepG2 cells presented a 1.5-2-fold higher endocytic capacity than Caco-2 and Vero cells. The main mechanism of NC uptake was caveolin-mediated endocytosis in HepG2 and Vero cells, and macropinocytosis in Caco-2 cells. Polymer hydrophobicity had an effect on the level of NC associated to HepG2 cells and to a lesser extent on the endocytosis mechanisms in Vero and Caco-2 cells. The NC uptake levels and endocytosis mechanisms differed significantly between cell lines tested.