The Role of DNA and Actin Polymers on the Polymer Structure and Rheology of Cystic Fibrosis Sputum and Depolymerization by Gelsolin or Thymosin Beta 4

Abstract

Mucus clearance is the first line of pulmonary defense against inhaled irritants, microorganisms, and allergens. In health, the gel-forming mucins are the principal polymeric components of airway mucus but in cystic fibrosis (CF), the necrotic death of inflammatory and epithelial cells releases a network of copolymerized extracellular DNA and filamentous (F-) actin-producing secretions that are similar to pus and difficult to clear by cilia or airflow. The large amounts of F-actin in CF sputum suggested that thymosin beta4 (Tbeta4) or gelsolin could depolymerize the secondary polymer network of CF sputum. Dose-dependent CF sputum rheology and polymer structure were measured before and after the addition of excipient, dornase alfa, Tbeta4, gelsolin, and Tbeta4 or gelsolin with dornase for 30 min. Sputum was also incubated with Tbeta4 30 microg/mL, gelsolin 10 microg/mL or excipient for 0, 5, 10, 15, 20, or 60 min. There was a dose-dependent decrease in cohesivity with Tbeta4 and a time-dependent decrease in cohesivity at 30 microg/mL. With the combination of dornase alfa and Tbeta4 at 1.5 microg/mL, there was a 65% decrease in elasticity (P = 0.013). There was a time-dependent decrease in cohesivity (P = 0.0004) and elasticity (P = 0.047) with gelsolin and a dose-dependent fall in cohesivity (P = 0.0008). An apparent synergy of Tbeta4 or gelsolin on actin and dornase on DNA may be explained by the combined effect of actin depolymerization and DNA filament severing or by virtue of actin depolymerization increasing the effectiveness of dornase alfa.

MUC5B Is the Major Mucin in the Gel Phase of Sputum in Chronic Obstructive Pulmonary Disease

“…However, in hypersecretory disease, other macromolecules also contribute to the physical properties of the gel (12)(13)(14). Previous studies have shown that airways mucus is a heterogeneous mixture of these two glycoproteins, and their relative amounts are different in sputum from healthy and diseased airways (11).…”

A New Era of Pulmonary Delivery of Nano-antimicrobial Therapeutics to Treat Chronic Pulmonary Infections

“…This thickness allows easy diffusion of gas, nutrients, ions, proteins, etc., and the entrapment of particulate matter which is then efficiently removed by the mucociliary clearance process. Chronic lung diseases, such as COPD, chronic bronchitis, asthma and CF are associated with impaired mucociliary clearance and necrotic death of epithelial and inflammatory cells in patients' lungs leading to bronchiectasis and deposition of thick, stationary, tenacious mucus plaques where heavy colonization of bacteria especially by P. aeruginosa is evident, due to the availability of a nutrient rich environment that is optimal for bacterial growth [96][97][98]. This viscoelastic and adhesive mucus secretion acts as a physical barrier and hinders diffusion of antibiotics and acts as an electrostatic barrier.…”

“…This viscoelastic and adhesive mucus secretion acts as a physical barrier and hinders diffusion of antibiotics and acts as an electrostatic barrier. Necrotic cells contribute to excess release of a network of copolymerized polyanionic contents including DNA, mucin glycoproteins and F-actin which physically bind to polycationic antibiotics, such as tobramycin leading to their deactivation [96,98,99]. Antibiotics delivered for treating bacterial infections associated with these diseases needs to penetrate the sputum and distribute evenly.…”

Mucoactive drugs

“…Furthermore, children with CF show improved lung function and outcome following treatment with dornase alfa [70]. Both gelsolin and thymosin b4, conversely, are recognised to specifically depolymerise Factin polymers in CF sputum, therefore reducing its' viscosity [71,72]; however, these agents need to be further evaluated in clinical trials.…”