Applying NAMs in BMD Analysis and CFD Modeling to Advance In Vitro Inhalation Toxicity Testing
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Comprehensive in vitro inhalation toxicity testing is a unique challenge for many chemicals due to difficulties in mimicking the route of exposure, lack of dosimetry, and the lack of high-throughput methodologies. Volatile organic compounds (VOCs) and aerosols are notoriously difficult to generate and deliver in a consistent manner but are preferable as they mimic inhalation exposures. Appropriate choice of cell models and endpoints are equally important because VOC and aerosol exposures are not compatible with high-throughput submerged cell culture assays. Thus, new approach methods (NAMs) for in vitro exposure technology and analysis are necessary to predict chemical hazard and inhalation risks. To address these challenges and screen volatile chemicals for inhalation toxicity, we developed a cell culture exposure system (CCES) that exposes human bronchial cell models to multiple concentrations of VOCs at air-liquid interface (ALI) in a 24-well format. The CCES permits direct pollutant-to-cell interaction at physiological humidity and temperature in a medium-throughput manner. Whole transcriptomics data from VOC exposures were analyzed using benchmark dose (BMD) modeling to determine points of departure (POD). Among the VOCs tested, many of the most sensitive gene pathways correlate with known adverse exposure effects in occupational settings and in vivo data sets, providing early markers for the impact of a chemical exposure. In order to apply the same analysis to nonvolatile and insoluble compounds to support risk assessment, a new aerosol-specific cell culture exposure system (ACCES) is being developed. Computer-aided design (CAD) and computational fluid dynamics (CFD) coupled to the discrete phase method (DPM) were utilized to predict aerosol dilution and delivery in ACCES prototypes. CFD-DPM results revealed that our VOC-optimized CCES was incompatible with particle delivery given the differences in transport physics. Together, CAD and CFD modeling has proved to be an invaluable tool to redesign in vitro inhalation exposure technology that is compatible with aerosols in the respirable range. [Abstract does not reflect views or policies of the U.S. EPA.]