Characterizing intra-human variation in common toxicity endpoints in differentiated primary bronchial epithelial cell cultures.
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The use of primary human bronchial epithelial cells (pHBECs) has increased in recent years because they can be differentiated under air-liquid interface (ALI) culture conditions and offer greater in vivo physiological relevance than their cell line counterparts. pHBEC ALI models may also provide insight into the intra-human (i.e., within the human population) variation in response to test agents that cannot be addressed by isogenic cell lines or inbred rodent strains. These models also provide the opportunity to incorporate complex concepts such as individual susceptibility into in vitro testing approaches. One fundamental challenge facing the interpretation of toxicity data from these models is a lack of consensus on the normal range of variation in commonly used endpoints and definition of the magnitude of an exposure-induced change required for an effect to be considered pathologic. We sought to characterize the pre- and post-exposure ranges of variability for mature culture morphology after single- and repeated-acute exposures using trans-epithelial electrical resistance (TEER), ciliary beat frequency (CBF), and oxidative stress-associated gene expression in organotypic in vitro bronchial tissues constructed from donor-matched, co-cultured pHBECs and human lung fibroblasts. Preliminary experiments revealed that co-cultures eliminated the formation of cyst-like structures in the epithelium and promoted functional and molecular divergence that epithelial mono-culture does not recapitulate. pHBECs also exhibit similar cell-type diversity, CBF, and viability characteristics; however, donors exhibit disparate mature TEER values and oxidative stress endpoints, most notably a significant decrease in HMOX1 gene expression after repeated exposure to a household concentration of ambient acrolein, which supports an adaptation response that requires future research. Future work will characterize and identify applications of this model that advance our ability to recapitulate and detect inter-individual variability in vitro, determine the implications for environmental justice research, and assess the potential to replace animal models. Does not reflect EPA policy.