title: Sialic acid-to-urea ratio as a measure of airway surface hydration.
abstract: Although airway mucus dehydration is key to pathophysiology of cystic fibrosis (CF) and other airways diseases, measuring mucus hydration is challenging. We explored a robust method to estimate mucus hydration using sialic acid as a marker for mucin content. Terminal sialic acid residues from mucins were cleaved by acid hydrolysis from airway samples, and concentrations of sialic acid, urea, and other biomarkers were analyzed by mass spectrometry. In mucins purified from human airway epithelial (HAE), sialic acid concentrations after acid hydrolysis correlated with mucin concentrations (r2= 0.92). Sialic acid-to-urea ratios measured from filters applied to the apical surface of cultured HAE correlated to percent solids and were elevated in samples from CF HAEs relative to controls (2.2 ± 1.1 vs. 0.93 ± 1.8,P< 0.01). Sialic acid-to-urea ratios were elevated in bronchoalveolar lavage fluid (BALF) from β-epithelial sodium channel (ENaC) transgenic mice, known to have reduced mucus hydration, and mice sensitized to house dust mite allergen. In a translational application, elevated sialic acid-to-urea ratios were measured in BALF from young children with CF who had airway infection relative to those who did not (5.5 ± 3.7 vs. 1.9 ± 1.4,P< 0.02) and could be assessed simultaneously with established biomarkers of inflammation. The sialic acid-to-urea ratio performed similarly to percent solids, the gold standard measure of mucus hydration. The method proved robust and has potential to serve as flexible techniques to assess mucin hydration, particularly in samples like BALF in which established methods such as percent solids cannot be utilized.
authors.affiliation: Pediatric Pulmonology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; charles_esther@med.unc.edu.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Esther
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: David B
authors.initials: DB
authors.lastname: Hill
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Brian
authors.initials: B
authors.lastname: Button
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Shuai
authors.initials: S
authors.lastname: Shi
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Corey
authors.initials: C
authors.lastname: Jania
authors.affiliation: Rheumatology, Allergy, and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.|Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Duncan
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.|Pulmonary Diseases and Critical Care Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.|Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Doerschuk
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.affiliation: Murdoch Children's Research Institute, University of Melbourne, Parkville, Australia; and.
authors.forename: Sarath
authors.initials: S
authors.lastname: Ranganathan
authors.affiliation: Murdoch Children's Research Institute, University of Melbourne, Parkville, Australia; and.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Stick
authors.affiliation: Marsico Lung Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Boucher
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000378:metabolism; D003710:Demography; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D006801:Humans; D006868:Hydrolysis; D008168:Lung / Q000378:metabolism*; D008297:Male; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009077:Mucins / Q000378:metabolism; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D014508:Urea / Q000378:metabolism*
chemical_list: D009077:Mucins; D014508:Urea; D019158:N-Acetylneuraminic Acid
keywords: dehydration; mass spectrometry; mucins