Dose-dependent in vitro effect of recombinant human DNase on rheological and transport properties of cystic fibrosis respiratory mucus

Abstract

Recombinant human deoxyribonuclease (rhDNase) has been demonstrated to reduce the viscosity of purulent cystic fibrosis (CF) respiratory mucus, to improve exacerbations, but its effect on mucus transportability has not so far been investigated. The dose-dependent effect of rhDNase was analysed in vitro on mucus transport rate (tr) by ciliary activity and by simulated cough (cough transport (ct)), as well as on mucus viscosity and surface properties. Purulent CF sputa (n=15) were incubated for 30 min at 37°C with either rhDNase at three different concentrations (final concentrations 0.2, 2 or 20 μg · ml-1 of mucus) or placebo. No significant dose-dependent effect of rhDNase on the mucociliary transport rate was observed when the samples were statistically analysed together. However, in the larger group of mucus samples (n=11) with a low initial mucociliary transport rate, the latter was improved at each rhDNase concentration (tr0.2=0.69, tr2=0.88 and tr20=0.87) as compared to placebo (tr(p)=0.58). In the smaller group of mucus samples (n=4) with high initial transport rate, a decrease in mucociliary transport rate was observed, particularly at the highest concetration rhDNase assayed, i.e. 20 μg · ml-1 of mucus (tr20=0.58) as compared to placebo (tr(p)=0.86). The mucus cough transport was increased by rhDNase (ct0.2=25 mm, ct2=27.5 mm and ct20=31 mm) as compared to placebo (ct(p)=23.5 mm). The alterations in the mucus transport capacity were associated with a decrease in mucus viscosity and an improvement in mucus surface properties. These results suggest that rhDNase, at concentrations found in respiratory mucus after inhalation of the recommended therapeutic dose, improves both the cough and mucociliary transport of CF mucus samples characterized by a low mucociliary transport rate.