Macrophages and Epithelial Cells Differently Respond to Palladium Nanoparticles

Platinum group metals represent a class of anthropogenic pollutants generated as a byproduct of their use in automobile catalytic converters. We prepared palladium nanoparticles (Pd-NPs, about 6 nm) similar to those emitted in auto exhaust, and examined their behavior in different liquids using dynamic light scattering and transmission electron microscopy (TEM). We found that serum-containing DMEM medium or conditioned DMEM provides good dispersion and stability for Pd-NPs at pH 7.2–7.4. We then incubated primary mouse macrophages and epithelial MDCK cells with Pd-NPs for 10 and 30 min, 3, 5 and 24 h, and sampled for TEM. Pd-NPs penetrated into MDCK cells by crossing the plasma membrane and were located in the cytoplasm, organelles and preferentially in the nucleus. The macrophages actively phagocytosed clusters of Pd-NPs, which were observed inside the membrane-bound structures but were not found in the cytoplasm and nucleus. Macrophage phagocytosis could be efficient in the lungs of living organisms, where they move across the surface of the respiratory epithelium and collect inhaled pollutants. Our study showed harmful effect of Pd-NPs on epithelial cells and the possibility of this effect being ameliorated by macrophages, which are resistant to penetration by Pd-NPs and sequestered them in phagolysosomes.