Linking increased airway hydration, ciliary beating, and mucociliary clearance through ENaC inhibition

Abstract

Airway dehydration causes mucus stasis and bacterial overgrowth in cystic fibrosis and chronic bronchitis (CB). Rehydration by hypertonic saline is efficacious but suffers from a short duration of action. We tested whether epithelial sodium channel (ENaC) inhibition would rehydrate normal and dehydrated airways to increase mucociliary clearance (MCC) over a significant time frame. For this, we used a tool compound (Compound A), which displays nanomolar ENaC affinity and retention in the airway surface liquid (ASL). Using normal human bronchial epithelial cultures (HBECs) grown at an air-liquid interface, we evaluated in vitro potency and efficacy using short-circuit current (I(sc)) and ASL height measurements where it inhibited I(sc) and increased ASL height by ∼ 50% (0.052 μM at 6 h), respectively. The in vivo efficacy was investigated in a modified guinea pig tracheal potential difference model, where we observed an effective dose (ED50) of 5 μg/kg (i.t.), and by MCC measures in rats and sheep, where we demonstrated max clearance rates at 100 μg/kg (i.t.) and 75 μg/kg (i.t.), respectively. Acute cigarette smoke-induced ASL height depletion in HBECs was used to mimic the situation in patients with CB, and pretreatment prevented both cigarette smoke-induced ASL dehydration and lessened the decrease in ciliary beat frequency. Furthermore, when added after cigarette smoke exposure, Compound A increased the rate of ASL rehydration. In conclusion, Compound A demonstrated significant effects and a link between increased airway hydration, ciliary function, and MCC. These data support the hypothesis that ENaC inhibition may be efficacious in the restoration of mucus hydration and transport in patients with CB.

Automated acquisition and analysis of airway surface liquid height by confocal microscopy

“…ASL height measurements by confocal microscopy have been widely used to study the regulation of ASL height by airway epithelia and have revealed that maintaining hydrated ASL by correctly modulating ENaC and CFTR activity maintains efficient mucus transport (20,26,30). Moreover, this technique has been used to investigate the efficacy of therapeutic agents for CF and COPD (3,30,34). To reduce the time burden of manually acquiring and analyzing ASL images, we have designed a novel automatic image acquisition and analysis method.…”

“…Previously, ASL height measurements have been used to show that PCL transport is dependent on mucus transport (20,21,29). Also, studies on ASL absorption rates using ASL measurements revealed the importance of restoring ASL volume to treat dehydrated airway in CF and chronic obstructive pulmonary disease (COPD) (3,12,15,30). Moreover, the function of ENaC and CFTR and ASL hydration was studied by using ASL measurements (11,15,26,41).…”

Targeting ion channels in cystic fibrosis

“…Besides CFTR modulators, the preclinical development of novel more potent and long-acting ENaC inhibitors has been an active area of preclinical CF research [120][121][122][123][124][125][126]. In addition to direct pharmacological inhibition, several alternative strategies have been explored experimentally that may enable effective inhibition of ENaC in vivo.…”

Autism genes are selectively targeted by environmental pollutants including pesticides, heavy metals, bisphenol A, phthalates and many others in food, cosmetics or household products

“…Long-term exposure to cigarette smoke leads to reduced numbers of ciliated cells in mice [293,294]. A combination of cigarette smoke and alcohol also decreases ciliary beat frequency in bovine primary ciliated bronchial epithelial cells [295].…”