Nebulized Hypertonic Saline-Triggered Increase in Mucociliary Clearance Rate is Mediated by the Nervous System

Abstract

Inhaled nebulized hypertonic saline (HTS) is a commonly prescribed mutation-agnostic therapy used in the treatment of CF-related lung disease. It is currently well-understood that HTS functions, in part, to increase the volume of airway surface liquid (ASL) by generating an osmotic gradient that draws water into the airway lumen and, thus, increasing mucociliary clearance (MCC). However, recent research has also demonstrated that HTS-triggered increase in ASL height is mediated by the nervous system, whereby HTS stimulates sensory neurons to promote active secretion of ASL via airway epithelia. It has been shown that there is an approximate 50% reduction in the effects of HTS on ASL height in the presence of neural blockers. To study how this relationship translates into potential differences in MCC, this thesis seeks to test whether neurogenic component of HTS influences HTS-triggered increase in MCC ex vivo in excised swine trachea. Using a MCC assay based on tracking the clearance of tantalum microdisks by the ciliated epithelium of the trachea, we were able to observe that the HTS-mediated increase in MCC is mostly eliminated following preincubation with the neural blocker tetrodotoxin (TTX) in wild-type swine. To further demonstrate the utility of the nervous system in promoting MCC, we used sensory agonists capsaicin and menthol in combination with HTS or isotonic saline (ITS), and found them to cause substantial improvements on MCC in wild-type swine. Lastly, our experiments using CFTR-/- piglets demonstrated a surprising trend, whereby preincubation with TTX potentiated the effects of HTS, rather than decreasing them. We conclude that HTS-triggered increase in MCC is heavily dependent on the nervous system in swine. The next step will be to test the effects of neuromodulators in vivo using swine, or possibly even in human CF patients.