Am J Respir Cell Mol Biol 2020 Oct 23. Epub 2020 Oct 23.
Virginia Commonwealth University, 6889, Department of Pharmaceutics, Richmond, Virginia, United States.
Mucus obstruction is a key feature of many inflammatory airway diseases. Neutrophil extracellular traps (NETs) are released upon neutrophil stimulation and consist of extracellular chromatin networks studded with cytotoxic proteins. When released in the airways, these NETs can become part of the airway mucus. We hypothesized that the extracellular DNA and/or oxidative stress e.g. by the release of reactive oxygen species (ROS) and myeloperoxidase (MPO) during NETs formation in the airways would increase mucus viscoelasticity. We collected human mucus from endotracheal tubes of healthy patients admitted for elective surgery and co-incubated these samples with NETs from PMA- stimulated neutrophils. Unstimulated neutrophils served as controls and blocking experiments were performed with dornase alfa for extracellular DNA and the free radical scavenger dimethylthiourea (DMTU) for oxidation. Compared to controls, the co-incubation of mucus with NETs resulted in 1) a significant increase of the mucus viscoelasticity (macrorheology), 2) significantly decreased mesh pore size of the mucus and decreased movement of muco-inert nanoparticles through the mucus (microrheology) but 3) NETs did not cause visible changes in the microstructure of the mucus by scanning electron microscopy. Incubation with either dornase alfa or DMTU attenuated the observed changes in macro- and microrheology. This suggests that the release of NETs may contribute to airway mucus obstruction by increasing mucus viscoelasticity and that this effect is not solely due to the release of DNA but may in part be due to oxidative stress.