title: Exhaled endogenous particles contain lung proteins.
abstract: BACKGROUND
  We recently developed a novel, noninvasive method for sampling nonvolatile material from the distal airways. The method is based on the collection of endogenous particles in exhaled air (PEx). The aim of this study was to characterize the protein composition of PEx and to verify that the origin of PEx is respiratory tract lining fluid (RTLF).
  
  
  METHODS
  Healthy individuals exhaled into the sampling device, which collected PEx onto a silicon plate inside a 3-stage impactor. After their extraction from the plates, PEx proteins were separated by SDS-PAGE and then analyzed by LC-MS. Proteins were identified by searching the International Protein Index human database with the Mascot search engine.
  
  
  RESULTS
  Analysis of the pooled samples identified 124 proteins. A comparison of the identified PEx proteins with published bronchoalveolar lavage (BAL) proteomic data showed a high degree of overlap, with 103 (83%) of the PEx proteins having previously been detected in BAL. The relative abundances of the proteins were estimated according to the Mascot exponentially modified protein abundance index protocol and were in agreement with the expected protein composition of RTLF. No amylase was detected, indicating the absence of saliva protein contamination with our sampling technique.
  
  
  CONCLUSIONS
  Our data strongly support that PEx originate from RTLF and reflect the composition of undiluted RTLF.
authors.affiliation: Occupational and Environmental Medicine, University of Gothenburg, Gothenburg, Sweden. anna.bredberg@amm.gu.se
authors.forename: Anna
authors.initials: A
authors.lastname: Bredberg
authors.forename: Johan
authors.initials: J
authors.lastname: Gobom
authors.forename: Ann-Charlotte
authors.initials: AC
authors.lastname: Almstrand
authors.forename: Per
authors.initials: P
authors.lastname: Larsson
authors.forename: Kaj
authors.initials: K
authors.lastname: Blennow
authors.forename: Anna-Carin
authors.initials: AC
authors.lastname: Olin
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Mirgorodskaya
mesh_terms: D000328:Adult; D001944:Breath Tests / Q000379:methods*; D003593:Cytoplasm / Q000737:chemistry; D045853:Exhalation; D005110:Extracellular Space / Q000737:chemistry; D005260:Female; D006801:Humans; D008168:Lung / Q000737:chemistry*; D008297:Male; D008565:Membrane Proteins / Q000032:analysis; D008875:Middle Aged; D011506:Proteins / Q000032:analysis*; D040901:Proteomics
chemical_list: D008565:Membrane Proteins; D011506:Proteins