Bridging in vitro and in vivo inhalation toxicity: Volatile organic compounds elicit similar transcriptomic points of departure in human airway cells and mouse respiratory tract
In vitro differential gene expression analysis has been proposed as a higher throughput alternative to traditional animal toxicity testing for chemical risk assessment, but few studies have compared transcriptomic differences between respiratory in vitro systems and in vivo inhalation exposures. We assessed physiological responses and respiratory tract gene changes in adult mice after a single acute nose-only inhalation exposure to acrolein, dichloromethane, trichloroethylene, or 1,3-butadiene, and compared gene expression responses with those of differentiated primary human bronchial epithelial cells (pHBECs) and immortalized BEAS-2B cells exposed to VOCs at the air-liquid interface. Gene expression in response to VOCs was compared using whole transcriptome analyses of mouse nasal septum and lung samples and human in vitro cell lysates. Gene expression patterns of human and mouse tissues were distinct, with relatively little overlap of differentially expressed genes (DEGs) except for Hmox1 which was commonly upregulated across exposures to VOCs. To enable comparisons across in vitro and in vivo exposures, we calculated VOC cellular uptake and applied a high-throughput, generic physiologically based toxicokinetic (PBTK) model to estimate internal lung concentrations. Although transcriptomic responses varied across species and tissues, in vitro and in vivo points of departure (PODs) derived from benchmark dose modeling with predicted internal concentrations were largely comparable (<2-fold) except for dichloromethane, which exhibits known species-specific differences in metabolic activation. These results highlight the utility of new approach methodologies (NAMs) for evaluating acute inhalation exposures and emphasize the importance of refining internal dose estimates to improve in vitro to in vivo extrapolation (IVIVE).