9 Understanding how CeO2 Nanoparticles Modulate Bleomycin-Induced Inflammatory and Fibrotic Events in Both in Vivo and in Vitro Models

Abstract Cerium oxide nanoparticles (CeO2NPs) from some diesel fuel additives and other applications have been detected in ambient air. Concerns have been raised over their potential human health impact in situations of inadvertent exposure. Oxidative mechanisms have been suggested as a common feature for pulmonary injury in response to airborne particulate matter, including engineered nanomaterials. To understand in depth how CeO2NPs may influence oxidative stress induced pulmonary inflammation and fibrotic events, we used both in vivo and in vitro bleomycin-induced lung injury models. Male Sprague-Dawley rats were intratracheally instilled with bleomycin or saline (control) followed by nose-only inhalation exposure to nano-sized CeO2NP aerosols (mass concentration 1.8 mg/m3) or water (controls) for 3 hours per day for 4 days per week for one or two weeks. At 3 days post exposure, animals were sacrificed and bronchoalveolar lavage (BAL) fluid, lung histopathology and global mRNA expression analysed. Bleomycin exposure resulted in an increase in total BAL cells, fibrotic staining and significant induction of inflammatory and oxidative stress on mRNA sequencing analysis. Modifications of these responses by one-week exposure to CeO2NPs included attenuation of fibrotic staining and gene expression markers of lung function, inflammation and epithelial-mesenchymal transition (EMT). CeO2NP alone resulted in increased inflammatory responses but did not appear to cause fibrotic changes. Interpretation of these responses at a cellular level was further explored using 3D human small airway epithelium cultures (SmallAirTM) in an aerosol exposure air-liquid-interface system. This also indicated that some bleomycin-induced cellular responses could be attenuated by exposure to CeO2NP aerosols.