Comparative evaluation of nano-CuO crossing Caco-2 cell monolayers and cellular uptake

Different concentrations of CuSO₄, micro-CuO, and nano-CuO were added to Caco-2 cell monolayers to study the absorption and transport characteristics in this epithelial cell model. Nano-CuO nanoparticles had a diameter of 10–20 nm. Inhibitors of endocytosis were used to explore whether nano-CuO could enter the Caco-2 cell in the form of nanoparticles, and to ascertain the endocytotic pathway that is involved in the transport process. The apparent permeability coefficient (P _app) of CuSO₄ and nano-CuO increased with the Cu concentration in the culture medium (p < 0.05). The micro-CuO of different concentrations had no significant impact on the P _app value of Caco-2 cells (p > 0.05). When the Cu concentration in the culture medium was in the range 31.25–500 μM, the P _app value of Caco-2 cells incubated with nano-CuO was significantly higher than that obtained with CuSO₄. The latter was also significantly higher than that when cells were incubated with micro-CuO (p < 0.05). The amount of Cu transport increased with the increase of CuSO₄ concentration in the culture medium. After 90 min, the amount of transport began to saturate, and the transport rate of Cu declined with the increase of CuSO₄ concentration. For the cells incubated with nano-CuO, the amount of Cu transport increased with the increase of nano-CuO concentration, but did not show an obvious saturation with the extension of transport time. Nano-CuO could enter the Caco-2 cell in the form of nanoparticles, and were found in the cytoplasm, vesicles, lysosomes, and cell nuclei. Several inhibitors of endocytosis effectively prevented the entry of nano-CuO into the Caco-2 cells. It was concluded that nano-CuO particles can enter the Caco-2 cells through several cellular endocytotic pathways.