title: Etanercept prevents airway hyperresponsiveness by protecting neuronal M2 muscarinic receptors in antigen-challenged guinea pigs.
abstract: OBJECTIVE
  Increased tumour necrosis factor-alpha (TNF-alpha) is associated with airway hyperreactivity in antigen-challenged animals. In human asthmatics, TNF-alpha is increased and blocking it prevents airway hyperreactivity in some asthmatic patients. However, the mechanisms by which TNF-alpha mediates hyperreactivity are unknown. Airway hyperreactivity can be caused by dysfunction of neuronal M(2) muscarinic receptors that normally limit acetylcholine release from parasympathetic nerves. Here we test whether blocking TNF-alpha receptors with etanercept prevents M(2) receptor dysfunction and airway hyperreactivity in antigen-challenged guinea pigs.
  
  
  METHODS
  Ovalbumin-sensitized guinea pigs were challenged by inhalation of antigen. Some animals received etanercept (3 mg kg(-1) i.p.) 3 h before challenge. 24 h after challenge, airway hyperreactivity and M(2) receptor function were tested. Inflammatory cells in bronchoalveolar lavage, blood and lung were counted. TNF-alpha and its receptors were detected by real-time RT-PCR and immunocytochemistry in parasympathetic nerves from humans and guinea pigs and in human neuroblastoma cells.
  
  
  RESULTS
  Antigen-challenged animals were hyperreactive to vagal stimulation and neuronal M(2) receptors were dysfunctional. Both M(2) receptor dysfunction and airway hyperreactivity were prevented by etanercept. Etanercept reduced eosinophils around airway nerves, and in blood, bronchoalveolar lavage and airway smooth muscle. Also, TNF-alpha decreased M(2) receptor mRNA in human and guinea pig parasympathetic neurons.
  
  
  CONCLUSIONS
  Tumour necrosis factor-alpha may contribute to M(2) receptor dysfunction and airway hyperreactivity directly by decreasing receptor expression and indirectly by promoting recruitment of eosinophils, containing major basic protein, an M(2) antagonist. This suggests that etanercept may be beneficial in treatment of allergic asthma.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR 97239, USA.
authors.forename: Zhenying
authors.initials: Z
authors.lastname: Nie
authors.forename: David B
authors.initials: DB
authors.lastname: Jacoby
authors.forename: Allison D
authors.initials: AD
authors.lastname: Fryer
mesh_terms: D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology* / Q000627:therapeutic use; D016535:Bronchial Hyperreactivity / Q000276:immunology / Q000503:physiopathology / Q000517:prevention & control*; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology / Q000276:immunology; D016084:Bronchoconstriction / Q000187:drug effects*; D045744:Cell Line, Tumor; D004804:Eosinophils / Q000276:immunology / Q000473:pathology; D000068800:Etanercept; D006168:Guinea Pigs; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology* / Q000627:therapeutic use; D009130:Muscle, Smooth / Q000276:immunology / Q000503:physiopathology; D009206:Myocardium / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D010047:Ovalbumin / Q000276:immunology; D010275:Parasympathetic Nervous System / Q000378:metabolism / Q000473:pathology; D043585:Receptor, Muscarinic M2 / Q000502:physiology*; D018124:Receptors, Tumor Necrosis Factor / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000627:therapeutic use; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014132:Trachea / Q000294:innervation; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D007074:Immunoglobulin G; D043585:Receptor, Muscarinic M2; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D010047:Ovalbumin; D000068800:Etanercept