Differential reactivity of engineered nanomaterials with human alveolar epithelium and macrophages in vitro: importance of physicochemistry

Abstract

There is a vast range of diverse consumer applications for engineered nanomaterials (ENM). Commercially, titanium dioxide nanoparticles (nano-TiO2) and carbon nanotubes (CNT) are two of the most popular ENMs. Appreciating the overt vulnerability of the lung to ENM occupational and consumer exposure, we studied the biointeraction of these ENMs with cells of the alveolar unit. We hypothesised that the bioreactivity of nano-TiO2 and CNTs with cells of the alveolar unit depends on the physicochemical properties of the ENM. Transformed human alveolar type-I-like epithelial cells (TT1) and primary human alveolar type-II epithelial cells (ATII) and alveolar macrophages (AM), in mono- and co-culture, were exposed to concentrations of ENMs before probing for cytotoxicity, apoptosis, oxidative stress, glutathione activity, inflammatory mediator release, kinase signal transduction and gene transcription. With TT1 cells, we found that ENM crystalline phase is important in cellular reactivity; predominantly rutile and pure rutile nano-TiO2 induced a greater pro-inflammatory response from exposed TT1 cells than their pure and mixed anatase counterparts. The dynamic pro-inflammatory mediator release from TT1 cells, induced by nano-TiO2 exposure, was accompanied by concomitant changes in oxidative stress and modified glutathione activity. Assessing CNTs, we found that shorter CNTs (~0.6 m in length, 15nm in diameter) induced significantly greater pro-inflammatory mediator release from TT1 and ATII cells when compared to longer CNTs. Conversely, AMs showed greater reactivity following exposure to longer CNTs (~20 m in length, 15nm in diameter), releasing greater amounts of pro-inflammatory mediators when compared to shorter CNTs; these responses were associated with kinase signal transduction. Mechanisms of ENM reactivity with TT1 cells were further elucidated using transcriptomics, where a number of common and unique gene transcription responses were identified. In conclusion, we have critically shown that ENM interactions with alveolar cells depend on the physicochemical properties of the particular ENM, and the cell type involved.