Tiotropium inhibits mucin production stimulated by neutrophil elastase but not by IL-13

Tiotropium, a muscarinic antagonist, is approved for the treatment of chronic obstructive pulmonary disease and poorly controlled asthma. Because mucus hypersecretion is characteristic of both of these diseases, and muscarinic agonists stimulate mucus secretion, we hypothesized that tiotropium would attenuate airway MUC5AC expression. We grew normal human bronchial epithelial (NHBE) cells to a goblet cell phenotype with 1 or 5 ng/mL of IL-13 and exposed these cells to 10 nM tiotropium or excipient for the full 14 days. Normally differentiated NHBE cells (without IL-13) were exposed to neutrophil elastase (NE) 1 × 10^-7 or 5 × 10^-7 M for 1 h. MUC5AC was measured by quantitative PCR and ELISA. Acetylcholine production by the epithelium was evaluated by quantitative PCR and by choline/acetylcholine quantification. Tiotropium had no effect on IL-13-stimulated MUC5AC, but attenuated MUC5AC stimulated by NE (p = 0.007 at 5 × 10^-7 M). IL-13 increased CarAT mRNA (p < 0.001 at 5 ng/mL) and acetylcholine concentration in the medium (p = 0.018 at 5 ng/mL), while NE had no effect. Tiotropium had no direct effect on IL-13 or NE-induced CarAT or acetylcholine concentration. Tiotropium decreased MUC5AC stimulated by NE, but had no effect on MUC5AC stimulated by IL-13. These results may be due to IL-13, but not NE, increasing acetylcholine production.