Nonantibiotic macrolides prevent human neutrophil elastase-induced mucus stasis and airway surface liquid volume depletion

Abstract

Mucus clearance is an important component of the lung's innate defense system. A failure of this system brought on by mucus dehydration is common to both cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Mucus clearance rates are regulated by the volume of airway surface liquid (ASL) and by ciliary beat frequency (CBF). Chronic treatment with macrolide antibiotics is known to be beneficial to both CF and COPD patients. However, chronic macrolide usage may induce bacterial resistance. We have developed a novel macrolide, 2'-desoxy-9-(S)-erythromycylamine (GS-459755), that has significantly diminished antibiotic activity against Staphylococcus aureus, Streptococcus pneumonia, Moraxella catarrhalis, and Haemophilus influenzae. Since neutrophilia frequently occurs in chronic lung disease and human neutrophil elastase (HNE) induces mucus stasis by activating the epithelial sodium channel (ENaC), we tested the ability of GS-459755 to protect against HNE-induced mucus stasis. GS-459755 had no effect on HNE activity. However, GS-459755 pretreatment protected against HNE-induced ASL volume depletion in human bronchial epithelial cells (HBECs). The effect of GS-459755 on ASL volume was dose dependent (IC₅₀ ~3.9 μM) and comparable to the antibacterial macrolide azithromycin (IC₅₀ ~2.4 μM). Macrolides had no significant effect on CBF or on transepithelial water permeability. However, the amiloride-sensitive transepithelial voltage, a marker of ENaC activity, was diminished by macrolide pretreatment. We conclude that GS-459755 may limit HNE-induced activation of ENaC and may be useful for the treatment of mucus dehydration in CF and COPD without inducing bacterial resistance.

The Role of Airway Surface Liquid in the Primary Management of Rhinosinusitis

“…Similarly, the sinonasal surface epithelium is maintained optimally hydrated through CFTR anion channel which regulates the amount of Cl -that is secreted, maintaining an adequate salt content and therefore water which impacts directly on the viscosity of the ASL [6,10]. In order for mucus to be cleared optimally, the PCL needs to reach the height of the outspread cilia, this height being approximately 7-10 µm [4]. In this way the PCL keeps the mucus away from the epithelia and allows the cilia to function efficiently ( Figure Figure 1: Photomicrograph of the lining of the maxillary sinus.…”

“…1-Mucus layer; 2-Cilia with periciliary liquid; 3-Ciliated cell; 4-Mucus producing goblet cell (HE section, X1000). 2) [4]. The composition of the PCL was initially thought to be watery but it is now recognized to be a 'grafted polyanionic gel' [10].…”

“…It has been demonstrated that administration of macrolide antibiotics in chronic respiratory diseases such as cystic fibrosis provides significant amelioration of symptoms [4]. Macrolides have the capacity to reduce bacterial virulence and inhibit the formation of bacterial biofilm by altering its structure and function [26].…”

“…In addition to their antimicrobial activity, macrolides are able to moderate the inflammatory response associated with CRS by inhibiting the production of interleukin-8 which is a powerful neutrophil chemotactant cytokine [26,27]. In chronic respiratory conditions, a chronic neutrophilia is also present which increases mucosal human neutrophil elastase levels and disturbs the normal functioning of epithelial sodium channel leading to greater Na + absorption contributing to the dehydration of the ASL [4]. Macrolides seem to limit disturbances to airway epithelial sodium channel function caused by the proteolytic activity of neutrophil elastase, thereby enhancing MCC clearance [4].…”

“…Mucus is an important component of ASL and is positioned over the cilia and PCL serving as an efficient trap for inhaled particles which are transported to the nasopharynx by the synchronised, one-directional movement of the cilia [2]. Adequate mucociliary clearance (MCC) is also dependent on the hydration state of the ASL as well as on ciliary beat frequency [4]. In chronic rhinosinusitis (CR), there is disruption in the Cl -transport which leads to dehydration of ASL and mucus stasis [5].…”