Abstract
The human airway surface is covered by a mucus layer composed primarily of the mucins MUC5AC and MUC5B. Excessive mucin production and secretion by airway epithelial cells in patients with asthma result in airway obstruction and worsened asthma symptoms. This study investigated the effects of liquiritin, a widely used flavonoid, on intracellular and secreted MUC5AC and MUC5B levels in the NCI-H292 human airway epithelial cell line. Liquiritin treatment suppressed both mucin types in a dose-dependent manner, accompanied by decreased activity of extracellular signal-regulated kinase (ERK) and p38. The effect of liquiritin was further examined in cells stimulated with phorbol 12-myristate 13-acetate (PMA) to induce excessive mucin production and secretion. Liquiritin dose-dependently reduced PMA-induced increases in intracellular and secreted MUC5AC and MUC5B levels as well as PMA-induced ERK and p38 activity. Overall, these results suggest that liquiritin reduces intracellular and secreted MUC5AC and MUC5B levels by suppressing the ERK and/or p38 signaling pathway.