Durability of Hypertonic Saline for Enhancing Mucociliary Clearance in Cystic Fibrosis

A reduction in epithelial lining fluid height in cystic fibrosis (CF) as a consequence of decreased function of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) chloride channel and related increased activity of the Epithelial sodium (Na) Channel (ENaC) results in impaired mucociliary clearance (MCC), mucus stasis, inflammation, infection, and ultimately progressive bronchiectasis. Inhalation of hypertonic saline (HS), through a direct osmotic effect on the airways, results in an increase in epithelial lining fluid height in vitro and an increase in MCC in vivo as measured following inhalation of a radiotracer with gamma scintigraphy (Sood, et al 2003). MCC as a biomarker is being validated in the clinic, as administration of inhaled hypertonic saline (HS) to cystic fibrosis patients results in short- and medium-term improvements in MCC (Donaldson, et al 2006), while long-term administration of HS is associated with improvements in the registration endpoints of lung function and pulmonary exacerbations (Elkins, et al 2006). Based in large part on these studies, HS has gained acceptance in the CF community, with estimates of up to 50% of patients being treated with this therapy. MCC/CC is thus an excellent choice as a Proof of Concept endpoint for exploratory clinical studies of ENaC modulators. Prior clinical experience with the ENaC blocker amiloride, which improves MCC acutely in healthy volunteers (Sood, et al 2003) but failed to improve lung function in long-term studies in CF (Pons, et al 2000), suggests that durable ENaC modulation will be required for clinical success. It is believed that modulation of ENaC for a period of at least 4 hours will be required to achieve the necessary durability. This durability should also enable twice daily dosing. For comparison we need to know the effectiveness of HS over this same period. Thus, this study is intended to assess 1) the duration of action out to 4 hours for inhaled hypertonic saline (7%) in adult CF patients and 2) the variability of MCC/CC measurements with and without HS treatment. These assessments at UNC will be compared to similar measures at Johns Hopkins University (JHU) for Novartis to determine the feasibility for future multicenter studies using MCC/CC as a primary endpoint.