Observations of, and Insights into, Cystic Fibrosis Mucus Heterogeneity in the Pre-Modulator Era: Sputum Characteristics, DNA and Glycoprotein Content, and Solubilization Time

Deborah L. Chance,Thomas P. Mawhinney

doi:10.3390/jor1010002

Deborah L. Chance, Thomas P. Mawhinney

Open Access

https://doi.org/10.3390/jor1010002

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Abstract

Airway obstruction with chronic inflammation and infection are major contributors to the lung damage and mortality of cystic fibrosis (CF). A better understanding of the congested milieu of CF airways will aid in improving therapeutic strategies. This article retrospectively reports our observations, and discusses insights gained in the handling and analysis of CF sputa. CF and non-CF mucus samples were surveyed for morphological features by electron microscopy and analyzed for the macromolecular dry weight (MDW), total protein, lipid, carbohydrate, and DNA. Mucus character was investigated with chemical solubilization time as a comparative tool. CF mucus appeared distinctly thick, viscous, and heterogeneous, with neutrophils as the dominant immune cell. CF sputum DNA content varied markedly for and between individuals (~1–10% MDW), as did solubilization times (~1–20 h). CF Sputum DNA up to 7.1% MDW correlated positively with solubilization time, whereas DNA >7.1% MDW correlated negatively. 3D analysis of CF sputa DNA, GP, and solubilization times revealed a dynamic and predictive relationship. Reflecting on the heterogeneous content and character of CF mucus, and the possible interplay in space and time in the respiratory tract of polymeric DNA and mucous glycoproteins, we highlight it’s potential to affect infection-related airway pathologies and the success of therapeutic interventions.

Highlights

Cystic fibrosis (CF) is an exocrine and genetic disorder hallmarked by thick mucus in the respiratory tract, bronchitis, and frequent and persistent infections [1,2,3,4,5,6]
The presence of disintegrating nuclei was so characteristic of the CF sputa that specimens could be identified as CF
DNA composition of the total sputum macromolecular dry weight (MDW), with the non-purulent classification assigned to sputa with DNA of less than 0.025% MDW, and purulent for all specimens with DNA >0.25% MDW

Summary

Introduction

Cystic fibrosis (CF) is an exocrine and genetic disorder hallmarked by thick mucus in the respiratory tract, bronchitis, and frequent and persistent infections [1,2,3,4,5,6]. Chronic infection, inflammation, and airway obstruction contribute to bronchiectasis, diminished lung function, and shortened life spans [1,2,3,4,5,6]. Loss of function mutations in the DNA for the cystic fibrosis transmembrane conductance regulator (CFTR) lead to imbalances in salts (including bicarbonate) and water transport across the secretory systems throughout the body, and contribute to altered mucus rheology (viscosity and elasticity), diminished mucociliary clearance (MCC), and declining pulmonary function [4,7,8,9,10,11]. Differences in CF and non-CF airways and how they manage infection have been recognized for decades and investigated intensively with functional assays and chemical and microscopic analyses [1,12,13,14,15,16,17,18].

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