Assessing respiratory toxicity of chemicals in two human bronchial in vitro systems
Risk assessment and management relies on approaches that can accurately and efficiently predict the toxicity of chemicals in humans. Inhalation is a major route by which exposure to substances can occur, and is an area where resources have been dedicated to optimize human-relevant in vitro approaches. In this study a two-dimensional (2D) human bronchial epithelial cell line (BEAS-2B) and a three-dimensional (3D) human reconstructed tissue model (MucilAir™, Epithelix) were used to predict the ability of chemicals to cause portal-of-entry effects on the human respiratory tract. The human cell-based systems were exposed to different concentrations of silanes (triethoxysilane (TES) and trimethoxysilane (TMS)) surfactants (Triton X-100 and oleoyl sarcosine) at the air-liquid interface in a VITROCELL® 6/4 exposure module. Nitrogen dioxide (NO2) was included as a positive control and sodium chloride and clean air (CA) or nitrogen gas (N) as negative controls. Endpoints assessed include cell viability (Prestoblue™ assay), cytotoxicity (lactate dehydrogenase assay; LDH), and expression of inflammatory markers (electrochemiluminescence immunoassay, Meso Scale Discovery) and, in addition for the 3D tissues, morphology (hematoxylin and eosin (H&E) staining), barrier integrity (transepithelial electrical resistance, TEER), and cilia beat frequency (SAVA system). Preliminary studies demonstrated a concentration-dependent decrease in cell viability and an increase in cytotoxicity after 1 hour exposure of BEAS-2B cells to TES (0.72 ppm, 25 ppm, and 85 ppm) as compared to CA. A significant increase in expression of inflammatory markers, including interleukin IL-6, IL-8, IL-2, and tumour necrosis factor-alpha (TNF-α), was observed at 25 ppm of TES. Studies are underway to assess the additional test chemicals and endpoints in both systems. The results of this project can be used to better understand the usefulness of different test systems and, therefore, help guide selection. They may also be used to predict the likelihood of a chemical to cause portal-of-entry effects on the human respiratory tract and inform regulatory decision-making.