Comparison of submerged and air liquid interface exposure: limitations and differences in the toxicological effects evaluated in bronchial epithelial cells

Airborne particulate matter (PM) is the primary environmental cause of death worldwide. The understanding of the toxicological mechanism has improved over the last decades, nonetheless now novel exposure systems allow the possibility to mimic the in vivo interaction between particles or particle constituents and lung cells. Here we report the results obtained after exposure to the organic extract of fine PM (PM_2.5-0.3) of the BEAS-2B cells cultured in submerged or at the air liquid interface (ALI) conditions. Deposition efficiency of both PM and its organic extract was followed. Cell viability, inflammatory responses and gene expression were then evaluated. The comparison of submerged vs ALI exposure revealed significant differences in the expression of specific genes such as CYP1A1 and NQO1 6h after exposure and CYP1B1 and NFkB1 24h post exposure. Also, the results demonstrate the importance of evaluating the efficiency of deposition of the treatment to avoid misinterpretation of the results. PM particles determined an extremely low deposition efficiency, making it impossible to use this particle for ALI exposure tests. Although biological results, such as gene expression, may vary between the two exposure approaches (submerged or ALI), the ALI exposure should be preferred as it is more representative of human exposure via the respiratory route.