Cold exposure is associated with acute exacerbations in patients with chronic obstructive pulmonary disease (COPD) and asthma, accompanied by mucus hypersecretion. Previous studies have shown cold temperature-induced mucus hypersecretion in the upper and lower airway epithelium. However, the effects of drugs used to treat cold-induced mucin production and airway inflammation in epithelium have not been elucidated. We assessed the effects of cold exposure on mucin production and airway inflammation in well-differentiated primary human bronchial epithelial cells and studied the effect of corticosteroids and tiotropium bromide on this process.  

Differentiated normal human bronchial epithelium (NHBE) were cultured at the air-liquid interface (ALI). Quantitative real-time PCR, immunofluorescence staining, ELISA, and western blotting assays were used to assess the effects of cold exposure and drugs, including corticosteroid and tiotropium.

Cold exposure (24°C) increased mucin (MUC5AC) gene expression and protein release. When exploring this in more detail in cold-induced epithelial cells, mucin expression was found to be accompanied by significant increases in the expression of genes proinflammatory (IL-6, and IL-8) and T2-related cytokines (IL-4, IL-13, IL-25, and TSLP). Pre-treatment with tiotropium bromide inhibits cold-induced MUC5AC gene expression and protein release, the degree of which was comparable with dexamethasone. In addition, cold-induced increased IL-4 and IL-13 gene expressions were significantly attenuated with tiotropium. Tiotropium decreased phosphorylation of cold-enhanced ERK 1/2 and Jnk MAPK. 

These data show that tiotropium bromide exerts inhibitory effects on cold-induced epithelial mucin production through ERK 1/2 and Jnk MAPK pathways and accompanying airway inflammation, thus providing insight into the underlying mechanisms of clinical benefit of using tiotropium in the treatment of asthma and COPD.