Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants with established carcinogenic potential. The prevailing assumption has been that PAHs induce cancer through a unified mechanism. However, emerging research indicates that PAHs may operate via distinct mechanisms, potentially leading to non-additive cancer outcomes. This study delves into a Comparative Definition of the mechanistic differences between two specific PAHs, benzo[a]pyrene (BAP) and dibenzo[def,p]chrysene (DBC), in contrast to a complex PAH mixture, using a human 3D bronchial epithelial cell (HBEC) model. Our approach leverages short-term biosignatures derived from transcriptional profiling to elucidate these disparities.
In our investigation, differentiated bronchial epithelial cells were exposed to varying concentrations of BAP (100-500 μg/ml), a fixed concentration of DBC (10 μg/ml), and coal tar extract (CTE 500-1500 μg/ml, SRM1597a) for a 48-hour period. Gene expression analysis was subsequently conducted using RNA sequencing and quantitative PCR. A comparative definition of the gene signatures induced by BAP and DBC revealed that approximately 60% of genes exhibited unique regulation patterns dependent on the PAH treatment. Notably, DBC uniquely modulated signaling pathways associated with inflammation and DNA damage, whereas BAP primarily influenced processes related to cell cycle progression, hypoxia, and oxidative stress.
Further comparative definition at the pathway level indicated that BAP upregulated targets of key transcription factors AhR, NRF2, and KLF4. Conversely, DBC downregulated these very same targets. This contrasting regulatory pattern suggests a chemical-specific modulation of transcriptional responses involved in antioxidant defense, potentially explaining observed differences in PAH potency. Despite these divergent pathways, our comparative definition also identified common mechanisms shared across PAH treatments (BAP, DBC, and CTE). Specifically, all PAH exposures resulted in the downregulation of genes crucial for cell adhesion and a corresponding reduction in functional measurements of barrier integrity within the bronchial epithelial cell model.
These findings, derived from a human organotypic 3D model, corroborate previous in vivo studies and underscore the value of profiling short-term biosignatures. This approach offers a powerful tool for a comparative definition of the mechanisms underlying carcinogenic risk associated with diverse PAHs in humans. By highlighting both unique and shared pathways, this research contributes to a more nuanced understanding of PAH toxicity and its implications for human health.
