Establishing an Alveolar in Vitro Model to Test Potential Pathogenic Aerosols

Objectives: Despite the defensive mechanisms of the upper respiratory tract to deter substances from entering the lung, small aerosols can pass almost unhindered to the alveoli, potentially resulting in pathological reactions but also a possibility to deliver therapeutics. To test small particles and liquids for their pathological potential and also determine the molecular mechanism in the diverse cell types, we developed an alveolar in vitro model that can be used in an aerosol chamber. Moreover, protective substances preventing or attenuating the pathological reaction could be screened for with this model and cellular uptake of therapeutics can be tested.

Methods: Human cell lines (lung epithelial, monocyte/macrophage, mast cell and endothelial) were cultured on porous membrane inserts with their apical and basolateral sides simulating the orientation of the alveoli in vivo. The cellular model was investigated for viability, barrier function and presenting a single cell layer. After the basic model was developed, oil-emulsions were tested at different time points for their inflammatory potential and the production of reactive oxygen species.

Results: The model consisted of a single layer of endothelial cells on the basolateral side and of a mixture of lung epithelial cells, macrophages and mast cells on the apical side of the model. The viability was above 95% and membrane integrity was given. After time-dependent exposure to diverse oil-emulsion-aerosols a dose-dependent reduction in viability and an increase in inflammatory mediators was observed for the hydraulic fluid whereas the turbine oil did not reproducibly induce any damage. In addition, the potential for drug delivery has been looked at with GFP-transfection in the aerosol chamber.

Conclusion: The developed in vitro alveolar model was physiologically similar to the alveoli (barrier and single layer of cells). During a short time span of ~24–48 hour it is possible to screen diverse aerosols for their pathological potential and the underlying mechanism as well as cellular uptake of drugs. Currently, a deviation of the model is created as a pathological model where protective substances can be tested on.