Marjory Moreau, Jeff Fisher, Melvin E. Andersen, Asayah Barnwell, Sage Corzine, Aarati Ranade, Patrick D. McMullen, Scott D. Slattery
ScitoVation, LLC, 6 Davis Drive, Suite 146, Durham, NC 27709, USA
This case study has implemented a NAM-based chemical risk assessment approach that uses in vitro and in silico methods to account for pharmacodynamic and pharmacokinetic factors of in vivo toxicity. The experiments were performed with the immortalized cell lines A549 and BEAS-2B, of human alveolar and bronchial origin, respectively, to identify a dose range likely to produce a toxic effect in the differentiated cultures. A549 and BEAS-2B cells, grown at the ALI on Transwell permeable supports, were exposed to vapor for 4 h in a Vitrocell 12/12 exposure system, and viability was assessed 24 h after the initiation of exposure.
Time, cost, ethical, and regulatory considerations surrounding in vivo testing methods render them insufficient to meet existing and future chemical safety testing demands. There is a need for the development of in vitro and in silico alternatives to replace traditional in vivo methods for inhalation toxicity assessment. Exposures of differentiated airway epithelial cultures to gases or aerosols at the air–liquid interface (ALI) can assess tissue responses and in vitro to in vivo extrapolation can align in vitro exposure levels with in-life exposures expected to give similar tissue exposures. Because the airway epithelium varies along its length, with various regions composed of different cell types, we have introduced a known toxic vapor to five human-derived, differentiated, in vitro airway epithelial cell culture models—MucilAir of nasal, tracheal, or bronchial origin, SmallAir, and EpiAlveolar—representing five regions of the airway epithelium—nasal, tracheal, bronchial, bronchiolar, and alveolar. We have monitored toxicity in these cultures 24 h after acute exposure using an assay for transepithelial conductance (for epithelial barrier integrity) and the lactate dehydrogenase (LDH) release assay (for cytotoxicity). Our vapor of choice in these experiments was 1,3-dichloropropene (1,3-DCP). Finally, we have developed an airway dosimetry model for 1,3-DCP vapor to predict in vivo external exposure scenarios that would produce toxic local tissue concentrations as determined by in vitro experiments. Measured in vitro points of departure (PoDs) for all tested cell culture models were similar. Calculated rat equivalent inhaled concentrations varied by model according to position of the modeled tissue within the airway, with nasal respiratory tissue being the most proximal and most sensitive tissue, and alveolar epithelium being the most distal and least sensitive tissue. These predictions are qualitatively in accordance with empirically determined in vivo PoDs. The predicted PoD concentrations were close to, but slightly higher than, PoDs determined by in vivo subchronic studies.