From the Cover: ImpairedProliferation and Differentiation of the Conducting Airway Epithelium Associated With Bronchiolitis Obliterans After Sulfur Mustard Inhalation Injury in Rats

Sulfur mustard (SM) is a chemical warfare agent that causes chronic airway remodeling. This study’s objective was to assess for changes to the bronchiolar epithelium after SM exposure to explain its contribution to chronic airway remodeling. Materials and methods: Adult male rats were exposed to a sublethal dose of SM inhalation (1.0–1.2 mg/kg) for 50 min. Histological sections of the bronchiolar epithelium were analyzed for changes using hematoxylin and eosin, trichrome, and immunofluorescent staining for acetylated tubulin (AT) and club cell secretory protein (CCSP). CCSP in bronchoalveolar lavage fluid was assessed using western blot. A bromodeoxyuridine (BRDU) assay was used to assess for epithelial proliferation, and real-time PCR measured changes in Notch mRNA expression. Results: SM caused significant proximal bronchiolar epithelial injury with epithelial denudation, loss of acetylated tubulin and CCSP staining, and reduced bronchoalveolar lavage fluid CCSP levels. bromodeoxyuridine (BRDU) + staining of proximal bronchiolar epithelial cells was not increased, but staining was increased in the distal bronchiolar epithelium. One month after injury, the proximal bronchiolar epithelium was not fully repaired. Significant collagen deposition surrounded proximal bronchioles with luminal obstruction, consistent with bronchiolitis obliterans. These changes corresponded with a downregulation of Notch1, Notch3, and Hes1 mRNA expressions. Conclusions: This study demonstrates that SM exposure resulted in severe proximal airway epithelial injury, persistent morphological changes, impaired epithelial proliferation and, ultimately, bronchiolitis obliterans. These changes occurred at the same time that the Notch signaling genes were downregulated. Thus, the lung epithelium and the Notch signaling pathway may be worthy targets for the prevention of chronic airway remodeling after SM inhalation injury.