The Impact of NO2 on Epithelial Barrier Integrity of a Primary Cell‐Based Air–Liquid Interface Model of the Nasal Respiratory Epithelium

ABSTRACT Nitrogen dioxide (NO 2 ) is a pervasive gaseous air pollutant with well‐documented hazardous effects on health, necessitating precise toxicological characterization. While prior research has primarily focused on lower airway structures, the upper airways, serving as the first line of defense against airborne substances, remain understudied. This study aimed to investigate the functional effects of NO 2 exposure alone or in combination with hypoxia as a secondary stimulus on nasal epithelium and elucidate its molecular mechanisms because hypoxia is considered a pathophysiological factor in the onset and persistence of chronic rhinosinusitis, a disease of the upper airways. Air–liquid interface cell cultures derived from primary nasal mucosa cells were utilized as an in vitro model, offering a high in vitro–in vivo correlation. Our findings demonstrate that NO 2 exposure induces malfunction of the epithelial barrier, as evidenced by decreased transepithelial electrical resistance and increased fluorescein isothiocyanate (FITC)‐dextran permeability. mRNA expression analysis revealed a significant increase in IL‐6 and IL‐8 expressions following NO 2 . Reduced mRNA expression of the tight junction component occludin was identified as a structural correlate of the damaged epithelial barrier. Notably, hypoxic conditions alone did not alter epithelial barrier integrity. These findings provide information on the harmful effects of NO 2 exposure on the human nasal epithelium, including compromised barrier integrity and induction of inflammatory responses. Overall, this study contributes to our understanding of pathophysiological mechanisms underlying also upper airway respiratory diseases associated with air pollution exposure and emphasizes the importance of mitigating NO 2 emissions to safeguard respiratory health.