Comparative effects of metal oxide nanoparticles on human airway epithelial cells and macrophages

Among nanomaterials of industrial rele- vance, metal-based nanoparticles (NPs) are widely used, but their effects on airway cells are relatively poorly characterized. To compare the effects of metal NPs on cells representative of the lung-blood barrier, Calu-3 epithelial cells and Raw264.7 macrophages were incubated with three industrially relevant prep- arations of TiO2 NPs (size range 4-33 nm), two preparations of CeO2 NPs (9-36 nm) and CuO NPs (25 nm). While Raw264.7 were grown on standard plasticware, Calu-3 cells were seeded on permeable filters, where they form a high-resistance monolayer, providing an in vitro model of the airway barrier. Metal NPs, obtained from industrial sources, were character- ized under the conditions adopted for the biological tests. Cytotoxicity was assessed with resazurin method in both epithelial and macrophage cells, while epithe- lial barrier permeability was monitored measuring the trans-epithelial electrical resistance (TEER). In mac- rophages, titania and ceria had no significant effect on viability in the whole range of nominal doses tested (15-240 lg/cm 2 of monolayer), while CuO NPs pro- duced a marked viability loss. Moreover, only CuO NPs, but not the other NPs, lowered TEER of Calu-3 monolayers, pointing to the impairment of the epithe- lial barrier. TEER decreased by 30 % at the dose of 10 lg/cm 2 of CuO NPs, compared to untreated control, and was abolished at doses C80 lg/cm 2 , in strict correlation with changes in cell viability. These results indicate that (1) CuO NPs increase airway epithelium permeability even at relatively low doses and are significantly toxic for macrophages and airway epi- thelial cells, likely through the release of Cu ions in the medium; (2) TiO2 and CeO2 NPs do not affect TEER and exhibit little acute toxicity for airway epithelial cells and macrophages; and (3) TEER measurement can provide a simple method to assess the impairment