Exposure of zinc oxide nanoparticles on lung epithelium: A comparison between submerged and air-liquid interface cultures

Zinc oxide nanoparticles (ZnO NPs) are often used in sunscreen and other cosmetic products with sun protection. They are also candidate to be used for various biological applications such as drug delivery, or in material science in for example solar cells. ZnO NPs are produced as liquid suspensions but also as dry powders, which increases the risk of exposure via the air. In this master’s thesis, the effects of aerosolized ZnO NP exposure on lung epithelial cells were examined and compared to the effects of exposure to particles suspended in liquid. Immortalized human alveolar type II-like A549 cells were used as a model for the lung. Cell cultures were cultured on insert membranes in 24- or 6-well plates, either submerged (SUB (24) and SUB (6), respectively) in growth media or at the air-liquid interface (ALI) with air on one side. The cells were exposed to suspended particles in isotonic solution (containing 9 mg/ml sodium chloride) or growth media and to aerosol particles in the NACIVT system (nano aerosol chamber for in vitro toxicity). ALI and SUB (24) cultures showed similar responses for the lower doses used, while SUB (24) cultures seemed more affected than ALI cultures by the higher doses. This was probably due to that larger particles were present in the isotonic solution used to expose ALI cultures. Generally, SUB (6) cultures showed greater responses than both ALI and SUB (24) cultures. Cultures exposed to aerosol particle doses comparable to the two lowest doses in exposures to particles suspended in liquid, had a significantly higher metabolic activity than the untreated negative controls 3 hours after the exposure. They also showed a lower metabolic activity 24 hours after the exposure. This indicates that aerosolized ZnO NPs affect the cellular metabolism in low doses