Beyond the Barrier: Using Novel In Vitro Organotypic Airway Trans-Epithelial Exposure Models to Study the Depth of Inhaled Chemical Toxicity
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The majority of studies examining the cellular and molecular effects of inhaled chemical exposures have utilized in vitro epithelial cell monoculture models. While easy to use, these models do not incorporate aspects of the airway microenvironment that play key roles in airway structure and function in vivo (e.g., stromal cells and extracellular matrix), nor do they provide insight into the effects of inhaled exposures beyond the epithelial barrier (“trans-epithelial” exposures). To address this limitation, we developed and applied a three-dimensional organotypic model of the bronchial epithelial-stromal interface in the large airway to characterize the cellular and molecular effects of inhaled chemical exposures on the large airway stroma in comparison to the associated epithelial cells. Despite never directly interacting with the exposure material, and thus receiving doses that deviate in both composition and concentration from those experienced by neighboring epithelial cells, airway fibroblasts exhibited changes in redox homeostasis, as well as oxidative stress-responsive and pro-inflammatory gene expression compared to directly-exposed epithelial cells. This in vitro organotypic model of the human airway microenvironment was constructed using widely-available materials, cells lines, low-serum growth medium to facilitate both scalability to support the sample size demands of various assays and general accessibility to researchers across sectors and funding levels. Further, the model is modular to support primary cell-validated, cell line-based screening as well as the assessment of inter-individual variability and susceptible populations via primary cell usage. This ability facilitates characterization of different assay measures for each component of the system and can be used to quantify ADME and key events, thereby supporting dosimetry modeling and adverse outcome pathway (AOP) development.