Development of in vitro systems for testing of volatile chemicals
Inhalation is the most relevant route of VOC exposure. However, due to unique challenges posed by properties of VOCs and their poor solubility in aqueous solutions, in vitro chemical safety testing is predominantly performed using direct application dosing or submerged exposures. To address the difficulties in screening toxic effects of VOCs, scientists in the U.S. EPA Office of Research and Development developed a cell culture system that permits cells to be exposed to multiple concentrations at air-liquid interface (ALI) in a 24-well format. A pilot study with eight volatile compounds was conducted to determine whether high-throughput transcriptomics (HTTr) using the TempO-Seq assay would predict toxicity at sub-cytotoxic exposure concentrations delivered to human airway cells at the ALI. The publication describing these results (Speen et al. 2022) was recognized as a “Top 10 Best Paper Demonstrating an Application of Risk Assessment” in March 2023 by the Society of Toxicology Risk Assessment Specialty Section. To expand the applications of the ALI exposure system, computer-aided design and computational fluid dynamics modeling were conducted to optimize operational parameters. Results indicate that a redesign of the system would improve VOC delivery and expand its applications to include aerosols. Planned 2024 activities include the evaluation of a broad array of VOCs and nonvolatile compounds with a focus on direct quantification of deposition and cellular uptake to improve in vitro to in vivo extrapolation (IVIVE). Furthermore, comparisons between ALI and direct liquid application studies are underway to determine best practices for in vitro new approach methodologies (NAMs).