title: Synergistic Inhibition of β2-adrenergic Receptor-mediated Alveolar Epithelial Fluid Transport by Interleukin-8 and Transforming Growth Factor-β.
abstract: BACKGROUND
  Patients with acute respiratory distress syndrome who retain maximal alveolar fluid clearance (AFC) have better clinical outcomes. The release of endogenous catecholamines associated with shock or the administration of β2-adrenergic receptor (β2AR) agonists enhances AFC via a 3'-5'-cyclic adenosine monophosphate-dependent mechanism. The authors have previously reported that transforming growth factor-β1 (TGF-β1) and interleukin-8 (IL-8), two major mediators of alveolar inflammation associated with the early phase of acute respiratory distress syndrome, inhibit AFC upregulation by β2AR agonists via a phosphoinositol-3-kinase (PI3K)-dependent mechanism. However, whether TGF-β1 and IL-8 cause an additive or synergistic inhibition of AFC is unclear. Thus, the central hypothesis of the study was to determine whether they synergistically inhibit the β2AR-stimulated AFC by activating two different isoforms of PI3K.
  
  
  METHODS
  The effects of TGF-β1 or IL-8 on β2AR agonist-stimulated net alveolar fluid transport were studied using short-circuit current studies. Molecular pathways of inhibition were confirmed by pharmacologic inhibitors and Western blotting of p-Akt, G-protein-coupled receptor kinase 2, protein kinase C-ζ, and phospho-β2AR. Finally, our observations were confirmed by an in vivo model of AFC.
  
  
  RESULTS
  Combined exposure to TGF-β1 and IL-8/cytokine-induced neutrophil chemoattractant-1 caused synergistic inhibition of β2AR agonist-stimulated vectorial Cl across alveolar epithelial type II cells (n = 12 in each group). This effect was explained by activation of different isoforms of PI3K by TGF-β1 and IL-8/cytokine-induced neutrophil chemoattractant-1 (n = 12 in each group). Furthermore, the inhibitory effect of TGF-β1 on 3'-5'-cyclic adenosine monophosphate-stimulated alveolar epithelial fluid transport required the presence of IL-8/cytokine-induced neutrophil chemoattractant-1 (n = 12 in each group). Inhibition of cytokine-induced neutrophil chemoattractant-1 prevented TGF-β1-mediated heterologous β2AR downregulation and restored physiologic β2AR agonist-stimulated AFC in rats (n = 6 in each group).
  
  
  CONCLUSIONS
  TGF-β1 and IL-8 have a synergistic inhibitory effect on β2AR-mediated stimulation of pulmonary edema removal by the alveolar epithelium. This result may, in part, explain why a large proportion of the patients with acute respiratory distress syndrome have impaired AFC.
authors.affiliation: From the Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, Alabama (B.M.W.); Institute of Research on Cancer and Ageing, University of Nice-Sophia-Antipolis, Nice, France (J.R.); Department of Anesthesiology, University of Nice-Sophia-Antipolis, Nice, France (M.C.); and Departments of Anesthesiology, Surgery and Cell Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama (J.-F.P.).
authors.forename: Brant M
authors.initials: BM
authors.lastname: Wagener
authors.forename: Jérémie
authors.initials: J
authors.lastname: Roux
authors.forename: Michel
authors.initials: M
authors.lastname: Carles
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Pittet
mesh_terms: D058666:Adrenergic beta-2 Receptor Agonists / Q000494:pharmacology; D058672:Adrenergic beta-2 Receptor Antagonists / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D054360:Chemokine CXCL1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D004357:Drug Synergism; D006801:Humans; D016209:Interleukin-8 / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D058672:Adrenergic beta-2 Receptor Antagonists; D018932:Chemokine CCL2; D054360:Chemokine CXCL1; C513297:Cxcl1 protein, rat; D016209:Interleukin-8; D016212:Transforming Growth Factor beta; D019869:Phosphatidylinositol 3-Kinases