Mucus plugs in patients with asthma linked to eosinophilia and airflow obstruction
Eleanor M. Dunican, … , John V. Fahy, The National Heart Lung and Blood Institute (NHLBI) Severe Asthma Research Program (SARP)
Eleanor M. Dunican, … , John V. Fahy, The National Heart Lung and Blood Institute (NHLBI) Severe Asthma Research Program (SARP)
Published February 5, 2018
Citation Information: J Clin Invest. 2018;128(3):997-1009. https://doi.org/10.1172/JCI95693.
View: Text | PDF
Clinical Research and Public Health Pulmonology

Mucus plugs in patients with asthma linked to eosinophilia and airflow obstruction

Abstract

BACKGROUND. The link between mucus plugs and airflow obstruction has not been established in chronic severe asthma, and the role of eosinophils and their products in mucus plug formation is unknown. METHODS. In clinical studies, we developed and applied a bronchopulmonary segment–based scoring system to quantify mucus plugs on multidetector computed tomography (MDCT) lung scans from 146 subjects with asthma and 22 controls, and analyzed relationships among mucus plug scores, forced expiratory volume in 1 second (FEV1), and airway eosinophils. Additionally, we used airway mucus gel models to explore whether oxidants generated by eosinophil peroxidase (EPO) oxidize cysteine thiol groups to promote mucus plug formation. RESULTS. Mucus plugs occurred in at least 1 of 20 lung segments in 58% of subjects with asthma and in only 4.5% of controls, and the plugs in subjects with asthma persisted in the same segment for years. A high mucus score (plugs in ≥ 4 segments) occurred in 67% of subjects with asthma with FEV1 of less than 60% of predicted volume, 19% with FEV1 of 60%–80%, and 6% with FEV1 greater than 80% (P < 0.001) and was associated with marked increases in sputum eosinophils and EPO. EPO catalyzed oxidation of thiocyanate and bromide by H2O2 to generate oxidants that crosslink cysteine thiol groups and stiffen thiolated hydrogels. CONCLUSION. Mucus plugs are a plausible mechanism of chronic airflow obstruction in severe asthma, and EPO-generated oxidants may mediate mucus plug formation. We propose an approach for quantifying airway mucus plugging using MDCT lung scans and suggest that treating mucus plugs may improve airflow in chronic severe asthma. TRIAL REGISTRATION. Clinicaltrials.gov NCT01718197, NCT01606826, NCT01750411, NCT01761058, NCT01761630, NCT01759186, NCT01716494, and NCT01760915. FUNDING. NIH grants P01 HL107201, R01 HL080414, U10 HL109146, U10 HL109164, U10 HL109172, U10 HL109086, U10 HL109250, U10 HL109168, U10 HL109257, U10 HL109152, and P01 HL107202 and National Center for Advancing Translational Sciences grants UL1TR0000427, UL1TR000448, and KL2TR000428.

Authors

Eleanor M. Dunican, Brett M. Elicker, David S. Gierada, Scott K. Nagle, Mark L. Schiebler, John D. Newell, Wilfred W. Raymond, Marrah E. Lachowicz-Scroggins, Selena Di Maio, Eric A. Hoffman, Mario Castro, Sean B. Fain, Nizar N. Jarjour, Elliot Israel, Bruce D. Levy, Serpil C. Erzurum, Sally E. Wenzel, Deborah A. Meyers, Eugene R. Bleecker, Brenda R. Phillips, David T. Mauger, Erin D. Gordon, Prescott G. Woodruff, Michael C. Peters, John V. Fahy, The National Heart Lung and Blood Institute (NHLBI) Severe Asthma Research Program (SARP)

×

Figure 7

Eosinophil products are associated with mucus plugging.

Options: View larger image (or click on image) Download as PowerPoint
Eosinophil products are associated with mucus plugging. (A) The sputum e...
(A) The sputum eosinophil percentage is positively associated with sputum EPO levels. (B) Sputum EPO is higher in the high mucus group (n = 32) than in the zero mucus group (n = 45) and healthy controls (n = 39). (C) Schematic representation of the cysteine-linking assay: 2 cysteines labeled with BODIPY FL fluoresce green as monomers but quench when oxidized to form a cystine dimer. (D) Effect of EPO and H2O2 on cysteine crosslinking in the presence of chloride, bromide, or thiocyanate. Cysteines do not undergo significant crosslinking with EPO and H2O2 in the presence of chloride, but cysteines exposed to EPO and H2O2 in the presence of bromide, and especially thiocyanate, undergo much more oxidation and crosslinking. RFU, relative fluorescent units. (E) Effect of HOSCN, the product of EPO-catalyzed reaction of H2O2 and thiocyanate, on the viscoelastic properties of a thiolated hydrogel measured by rheology. A large increase in the elastic modulus (G′) of the hydrogel was seen following exposure of the hydrogel to EPO with H2O2 and KSCN. There was no significant increase in G′ in the hydrogel in the absence of EPO. (F) Conceptual model for how type 2 inflammation promotes airway mucus plug formation in asthma. IL-13 increases thiocyanate transfer into the airway lumen. Once in the airway lumen, it is oxidized by H2O2 to form HOSCN, a reaction catalyzed by EPO. HOSCN targets cysteine thiol groups in secreted mucin polymers to generate covalent disulfide mucin crosslinks. Crosslinked mucins have a high elasticity that decreases their clearance by the mucociliary escalator and results in mucus plug formation. The data are presented as mean ± SD of 3 replicates in D and 4 replicates in E. *P < 0.05; **P < 0.01; †P < 0.01; ‡P < 0.001. P value was determined by ANOVA with Bonferroni’s correction.