Evaluation of in vitro rat and human airway epithelial models for acute inhalation toxicity testing

In vivo models (mostly rodents) are currently accepted by regulatory authorities for assessing acute inhalation toxicity. Considerable efforts have been made in recent years to evaluate in vitro human airway epithelial models (HAEM) as replacements for in vivo testing. In the current work, an organotypic in vitro rat airway epithelial model (RAEM), rat EpiAirway, was developed and characterized to allow a direct comparison with the available HAEM, human EpiAirway, in order to address potential interspecies variability in responses to harmful agents. The rat and human models were evaluated in 2 independent laboratories with 14 reference chemicals, selected to cover a broad range of chemical structures and reactive groups, as well as known acute animal and human toxicity responses, in 3 replicate rounds of experiments. Toxicity endpoints included changes in tissue viability (MTT assay), epithelial barrier integrity (TEER, transepithelial electrical resistance), and tissue morphology (histopathology). The newly developed rat EpiAirway model produced reproducible results across all replicate experiments in both testing laboratories. Furthermore, a high level of concordance was observed between the RAEM and HAEM toxicity responses (determined by IC25) in both laboratories, with R-2=0.78 and 0.88 when analyzed by TEER; and R-2=0.92 for both when analyzed by MTT. These results indicate that rat and human airway epithelial tissues respond similarly to acute exposures to chemicals. The new in vitro RAEM will help extrapolate to in vivo rat toxicity responses and support screening as part of a 3Rs program.