Cystic Fibrosis Sputum Reflections from the Pre‐Modulator Age

Toward the understanding and improvement of cystic fibrosis (CF) airway health, our laboratories have studied the tracheobronchial mucous glycoproteins (mGP) of individuals with and without CF. With the increased mucus viscosity and charged character of the mGP oligosaccharide species, obstructions in the CF gastrointestinal and respiratory tracts readily occur and lead to malnutrition, frequent and persistent pulmonary infections with opportunistic pathogens, and COPD. With new medications (“modulators”) targeting the basic defects, we anticipate marked improvements in CF airway health. With respect for the current airway clearance challenges faced by many with CF, we reflect on our experiences in handling sputum specimens over the years as we processed them toward mGP oligosaccharide structural elucidation. These studies provided opportunities for microscopic, chemical and biochemical observations about CF sputum relative to non‐CF sputum and insights about sputa heterogeneity of an individual. Toward improving therapeutic strategies, here we briefly report these observations. Microscopically, dense CF sputum typically depicted a neutrophil inflammatory response with large numbers of clumped neutrophils, many with degenerating nuclei, and much cellular debris, whereas non‐CF purulent sputa commonly displayed abundant mucous material and scattered inflammatory cells. Average chemical compositions of >1000 sputa (213 non‐purulent, NP; 322 purulent, P; and 468 CF), showed for CF less water content per specimen and greater dry weight (NP, P, CF respectively: water mg/mL 959, 939, 862; macromolecular dry weight [MDW] mg/mL 43, 61, 98 respectively). CF sputa possessed a higher % of MDW as lipid and DNA than non‐CF sputa and surprisingly, decreased total carbohydrate (CHO), (NP, P, CF respectively: lipid 25, 31, 34 % MDW; DNA 0.01, 1.4, 2.7 % MDW, with CF DNA ranging 0.1 – 9.1% MDW; CHO 21, 20, 14 % MDW.) Sputa of 4 CF patients collected over 5 days of hospitalization, showed >35% reduction in sputa DNA content regardless of initial DNA % MDW at admission. Sputa solubilization with guanidinium HCl showed no correlation of lipid content to hours to complete solubilization (hS); a trend to longer times with increased glycoprotein content (GP); and a marked impact of DNA content on solubilization. With CF focus, GP, DNA content, and hS were determined for 77 CF sputa. Rather than linear concentration trends, there were scattered relationships of % MDW of DNA and of GP. 3D graphical analysis revealed longer solubilization times (i.e. 10–20 h) when both mucins and DNA were in significant quantity, than specimens of high levels of DNA with little GP (i.e. 4–8h). Compiling these types of observations, we see CF sputa, over the population, and for a given individual, reflect a heterogenous spectrum of DNA‐mucin relative concentrations. As therapeutic strategies continue to evolve for the mobilization of the viscous obstructive materials, these data suggest that approaches which address both the DNA and mucous glycoprotein components will be the most beneficial in the ever‐changing airway dynamic. As COPDs share many features with CF, these CF sputum reflections may also guide airway clearance strategies in general.