title: Surfactant disaturated-phosphatidylcholine kinetics in acute respiratory distress syndrome by stable isotopes and a two compartment model.
abstract: BACKGROUND
  In patients with acute respiratory distress syndrome (ARDS), it is well known that only part of the lungs is aerated and surfactant function is impaired, but the extent of lung damage and changes in surfactant turnover remain unclear. The objective of the study was to evaluate surfactant disaturated-phosphatidylcholine turnover in patients with ARDS using stable isotopes.
  
  
  METHODS
  We studied 12 patients with ARDS and 7 subjects with normal lungs. After the tracheal instillation of a trace dose of 13C-dipalmitoyl-phosphatidylcholine, we measured the 13C enrichment over time of palmitate residues of disaturated-phosphatidylcholine isolated from tracheal aspirates. Data were interpreted using a model with two compartments, alveoli and lung tissue, and kinetic parameters were derived assuming that, in controls, alveolar macrophages may degrade between 5 and 50% of disaturated-phosphatidylcholine, the rest being lost from tissue. In ARDS we assumed that 5-100% of disaturated-phosphatidylcholine is degraded in the alveolar space, due to release of hydrolytic enzymes. Some of the kinetic parameters were uniquely determined, while others were identified as lower and upper bounds.
  
  
  RESULTS
  In ARDS, the alveolar pool of disaturated-phosphatidylcholine was significantly lower than in controls (0.16 +/- 0.04 vs. 1.31 +/- 0.40 mg/kg, p < 0.05). Fluxes between tissue and alveoli and de novo synthesis of disaturated-phosphatidylcholine were also significantly lower, while mean resident time in lung tissue was significantly higher in ARDS than in controls. Recycling was 16.2 +/- 3.5 in ARDS and 31.9 +/- 7.3 in controls (p = 0.08).
  
  
  CONCLUSIONS
  In ARDS the alveolar pool of surfactant is reduced and disaturated-phosphatidylcholine turnover is altered.
authors.affiliation: Department of Pediatrics, University of Padova, Padova, Italy. cogo@pediatria.unipd.it
authors.forename: Paola E
authors.initials: PE
authors.lastname: Cogo
authors.forename: Gianna Maria
authors.initials: GM
authors.lastname: Toffolo
authors.forename: Carlo
authors.initials: C
authors.lastname: Ori
authors.forename: Andrea
authors.initials: A
authors.lastname: Vianello
authors.forename: Marco
authors.initials: M
authors.lastname: Chierici
authors.forename: Antonina
authors.initials: A
authors.lastname: Gucciardi
authors.forename: Claudio
authors.initials: C
authors.lastname: Cobelli
authors.forename: Aldo
authors.initials: A
authors.lastname: Baritussio
authors.forename: Virgilio P
authors.initials: VP
authors.lastname: Carnielli
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000008:administration & dosage / Q000493:pharmacokinetics; D000328:Adult; D000368:Aged; D002247:Carbon Isotopes; D005260:Female; D006801:Humans; D007322:Instillation, Drug; D008168:Lung / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011650:Pulmonary Alveoli / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000378:metabolism*; D012128:Respiratory Distress Syndrome / Q000378:metabolism*; D014132:Trachea
chemical_list: D002247:Carbon Isotopes; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine