An In Vitro Alveolar Model Allows for the Rapid Assessment of Particles for Respiratory Sensitization Potential

Gene regulation and signaling pathways in immune response to respiratory sensitizers: a database analysis

Introduction

Humans are regularly exposed to environmental substances through inhaled air. Some chemicals or particles are respiratory sensitizers that can cause adverse respiratory health effects by triggering amplified immune responses. Understanding the process of respiratory sensitization and identifying potential sensitizers have been challenging due to the complexity of the underlying mechanisms.

Methods

This study leverages the transcriptomics from a previous in vitro 3D human lung model to investigate the pathways of chemical respiratory sensitization. Differentially expressed genes between two known and two nonsensitizers are cross-referenced against databases on biological processes and disease pathways.

Results

The GO results revealed 43 upregulated genes, and the KEGG revealed 52. However, only 18 upregulated genes were common between GO and KEGG. The GO results revealed 26 downregulated genes, and the KEGG revealed 40. However, only 9 of those downregulated genes were common.

Discussion

These findings support using multiple databases in perturbed gene analyses. The results from this study and data available in the scientific literature contribute toward building a biomarker profile for identifying respiratory sensitizers.

The transcriptomic signature of respiratory sensitizers using an alveolar model

Environmental contaminants are ubiquitous in the air we breathe and can potentially cause adverse immunological outcomes such as respiratory sensitization, a type of immune-driven allergic response in the lungs. Wood dust, latex, pet dander, oils, fragrances, paints, and glues have all been implicated as possible respiratory sensitizers. With the increased incidence of exposure to chemical mixtures and the rapid production of novel materials, it is paramount that testing regimes accounting for sensitization are incorporated into development cycles. However, no validated assay exists that is universally accepted to measure a substance's respiratory sensitizing potential. The lungs comprise various cell types and regions where sensitization can occur, with the gas-exchange interface being especially important due to implications for overall lung function. As such, an assay that can mimic the alveolar compartment and assess sensitization would be an important advance for inhalation toxicology. Some such models are under development, but in-depth transcriptomic analyses have yet to be reported. Understanding the transcriptome after sensitizer exposure would greatly advance hazard assessment and sustainability. We tested two known sensitizers (i.e., isophorone diisocyanate and ethylenediamine) and two known non-sensitizers (i.e., chlorobenzene and dimethylformamide). RNA sequencing was performed in our in vitro alveolar model, consisting of a 3D co-culture of epithelial, macrophage, and dendritic cells. Sensitizers were readily distinguishable from non-sensitizers by principal component analysis. However, few differentially regulated genes were common across all pair-wise comparisons (i.e., upregulation of genes SOX9, UACA, CCDC88A, FOSL1, KIF20B). While the model utilized in this study can differentiate the sensitizers from the non-sensitizers tested, further studies will be required to robustly identify critical pathways inducing respiratory sensitization.