Differential expression of pro-inflammatory and oxidative stress mediators induced by nitrogen dioxide and ozone in primary human bronchial epithelial cells

Abstract

Context: NO₂ and O₃ are ubiquitous air toxicants capable of inducing lung damage to the respiratory epithelium. Due to their oxidizing capabilities, these pollutants have been proposed to target specific biological pathways, but few publications have compared the pathways activated.

Objective: This work will test the premise that NO₂ and O₃ induce toxicity by activating similar cellular pathways.

Methods: Primary human bronchial epithelial cells (HBECs, n = 3 donors) were exposed for 2 h at an air-liquid interface to 3 ppm NO₂, 0.75 ppm O₃, or filtered air and harvested 1 h post-exposure. To give an overview of pathways that may be influenced by each exposure, gene expression was measured using PCR arrays for toxicity and oxidative stress. Based on the results, genes were selected to quantify whether expression changes were changed in a dose- and time-response manner using NO₂ (1, 2, 3, or 5 ppm), O₃ (0.25, 0.50, 0.75, or 1.00 ppm), or filtered air and harvesting 0, 1, 4 and 24 h post-exposure.

Results: Using the arrays, genes related to oxidative stress were highly induced with NO₂ while expression of pro-inflammatory and vascular function genes was found subsequent to O₃. NO₂ elicited the greatest HMOX1 response, whereas O₃ more greatly induced IL-6, IL-8 and PTGS2 expression. Additionally, O₃ elicited a greater response 1 h post-exposure and NO₂ produced a maximal response after 4 h.

Conclusion: We have demonstrated that these two oxidant gases stimulate differing mechanistic responses in vitro and these responses occur at dissimilar times.

• In vitro
• inflammation
• nitrogen dioxide
• oxidant
• oxidative stress
• ozone

Acknowledgements

The authors thank Dr. Shaun D. McCullough and Mr. David S. Morgan for technical assistance; TRC Environmental Corporation for engineering support; Dr. Andy Ghio, Dr. Martha Sue Carraway, Maryann Bassett, R.N., Tracey Montilla, R.N. and Julie Wood, R.N for clinical support.

Declaration of interest

This work was supported by United States Environmental Protection Agency intramural funding, the EPA Cooperative Agreement with the Center for Environmental Medicine, Asthma, and Lung Biology at the University of North Carolina [CR83346301], and a National Institutes of Environmental Health Sciences T32 grant [T32ES007126]. The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency, nor does the mention of trade names of commercial products constitute endorsement or recommendation for use. The authors report no declaration of interest.