Establishing the Impact of Metal Oxide Nanoparticle Size and Solubility on Lung Epithelial Cell Toxicity

Abstract

Metal oxide nanoparticles (MONPs) are one of the most commonly used types of engineered nanomaterials (manufactured substances with at least one dimension in the 1-100 nm range), and they are used in a wide variety of applications in several industries. Many studies have observed cytotoxicity, genotoxicity, oxidative stress, and pulmonary inflammation induced by MONPs in in vitro and in vivo models. The overall objective of this study was to investigate and compare the toxicities of metal oxide nanoparticles (MONPs) of different chemical composition, size, and solubility to provide insight into the importance of physicochemical properties on MONP induced toxicity. FE1 mouse lung epithelial cells were exposed to manganese dioxide (MnO₂) and iron (III) oxide (Fe₂O₃) nanoparticles (NPs), microparticles (MPs), and soluble manganese sulfate (MnSO₄). Cell viability was assessed after 24h and 48h using the trypan blue exclusion assay while DNA damage was assessed using the high throughput CometChip® platform after 2h and 4h of exposure. Chromosomal damage was examined using the microflow assay at 40h. Changes in gene expression after 24h and 48h were examined using microarray to identify perturbations in molecular pathways that are associated with the manifestation of toxicological responses. The NPs in general appeared to be slightly more cytotoxic and genotoxic than the MPs and produced a larger transcriptomic response. MnO₂ NPs were more potent than Fe₂O₃ NPs with respect to genotoxicity and transcriptional perturbations, although they both induced low levels of cytotoxicity. Dissolved manganese ions from MnSO₄ (at concentrations close to what would be released by the MnO₂ NP treatments) did not induce cytotoxicity or genotoxicity but did induce transcriptional alterations. The molecular pathways perturbed by MnO₂ NPs, MnO₂ MPs, and MnSO₄ were primarily related to inflammation, immune response, and DNA damage/cell cycle while Fe₂O₃ NPs and Fe₂O₃ MPs primarily affected pathways involving inflammation, immune response, and cellular/tissue development. These results suggest that size, solubility, and chemical composition influence their potential to induce toxicity. The information produced will address data gaps identified by risk assessors and aid in the development of read-across strategies for the assessment of other MONPs.