Microstructural alterations of sputum in cystic fibrosis lung disease

Abstract

The stasis of mucus secretions in the lungs of cystic fibrosis (CF) patients leads to recurrent infections and pulmonary exacerbations, resulting in decreased survival. Prior studies have assessed the biochemical and biophysical features of airway mucus in individuals with CF. However, these measurements are unable to probe mucus structure on microscopic length scales relevant to key players in the progression of CF-related lung disease, namely, viruses, bacteria, and neutrophils. In this study, we quantitatively determined sputum microstructure based on the diffusion of muco-inert nanoparticle probes in CF sputum and found that a reduction in sputum mesh pore size is characteristic of CF patients with reduced lung function, as indicated by measured FEV. We also discovered that the effect of ex vivo treatment of CF sputum with rhDNase I (Pulmozyme) on microstructure is dependent upon the time interval between the most recent inhaled rhDNase I treatment and the sample collection. Microstructure of mucus may serve as a marker for the extent of CF lung disease and as a parameter for assessing the effectiveness of mucus-altering agents.

Nanoparticles that do not adhere to mucus provide uniform and long-lasting drug delivery to airways following inhalation

“…Second, if the NP used were muco-inert, the magnetic force may have caused the NP to run into mucus bundles, causing them to potentially deform around and trap the particles or to enter mucus pores smaller than the particle diameter and rendered them sterically trapped. We have previously shown that various mucus samples exhibit highly heterogeneous pore size distributions, with significant percentages of pores smaller than the size of conventional NP ( 25 , 26 , 53 – 56 ). In addition, NP were under a constant unidirectional magnetic force, such that NP that entered into small mucus pockets would be unlikely to escape.…”

The Mucus Barrier to Inhaled Gene Therapy

“…64 Recently, we have confirmed that increased DNA levels in CF mucus correlates with reduced mucus mesh size. 71 Recombinant human DNase (Pulmozyme) is a commonly used mucolytic compound that reduces CF mucus viscoelasticity upon inhalation by cleaving DNA oligomer chains. 70 Increased levels of actin may also enhance mucus barrier properties, as gelsolin treatment, which depolymerizes actin, greatly reduces the viscoelastic properties of CF airway secretions.…”

“…71,74,75 The diffusion of polystyrene (PS) nanoparticles (NP) and antibioticloaded liposomes is greatly hindered within the extracellular matrix of biofilms produced by bacteria commonly found in the lungs of CF patients, including Pseudomonas aeruginosa and Burkhedia cepacia complex. [76][77][78] As such, bacterial biofilms may represent an additional extracellular barrier component unique to CF airway mucus that must be overcome by inhaled gene vectors.…”

“…We have recently shown that increased disulfide cross-linking reduces the mucus pore size. 71 Furthermore, the treatment of CF mucus with a mucolytic that disrupts mucus cross-linking, N-acetyl cysteine, increased mucus mesh pore size (Figure 2b) and increased the diffusion rate of muco-inert PS-PEG NP. 65 Increased DNA content may further tighten the mucus mesh by entangling with mucin fibers (Figure 2c).…”

Disulfide disruption reverses mucus dysfunction in allergic airway disease

“…To evaluate mucus directly on mouse airway surfaces, we employed MPT to quantify MSD of muco-inert nano-particles (MIPs) aerosolized onto mouse tracheas ex vivo [24][25][26] . Tracheas were removed from saline or AOE challenged mice, opened, placed on glass coverslips, and treated with nebulized 100 nm diameter MIPs suspended in saline vehicle or TCEP (Fig 2a).…”