title: A positive allosteric modulator of α7 nAChRs augments neuroprotective effects of endogenous nicotinic agonists in cerebral ischaemia.
abstract: OBJECTIVE
  Activation of α7 nicotinic acetylcholine receptors (nAChRs) can be neuroprotective. However, endogenous choline and ACh have not been regarded as potent neuroprotective agents because physiological levels of choline/ACh do not produce neuroprotective levels of α7 activation. This limitation may be overcome by the use of type-II positive allosteric modulators (PAMs-II) of α7 nAChRs, such as 1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)-urea (PNU-120596). This proof-of-concept study presents a novel neuroprotective paradigm that converts endogenous choline/ACh into potent neuroprotective agents in cerebral ischaemia by inhibiting α7 nAChR desensitization using PNU-120596.
  
  
  METHODS
  An electrophysiological ex vivo cell injury assay (to quantify the susceptibility of hippocampal neurons to acute injury by complete oxygen and glucose deprivation; COGD) and an in vivo middle cerebral artery occlusion model of ischaemia were used in rats.
  
  
  RESULTS
  Choline (20-200 μM) in the presence, but not absence of 1 μM PNU-120596 significantly delayed anoxic depolarization/injury of hippocampal CA1 pyramidal neurons, but not CA1 stratum radiatum interneurons, subjected to COGD in acute hippocampal slices and these effects were blocked by 20 nM methyllycaconitine, a selective α7 antagonist, thus, activation of α7 nAChRs was required. PNU-120596 alone was ineffective ex vivo. In in vivo experiments, both pre- and post-ischaemia treatments with PNU-120596 (30 mg·kg(-1) , s.c. and 1 mg·kg(-1) , i.v., respectively) significantly reduced the cortical/subcortical infarct volume caused by transient focal cerebral ischaemia. PNU-120596 (1 mg·kg(-1) , i.v., 30 min post-ischaemia) remained neuroprotective in rats subjected to a choline-deficient diet for 14 days prior to experiments.
  
  
  CONCLUSIONS
  PNU-120596 and possibly other PAMs-II significantly improved neuronal survival in cerebral ischaemia by augmenting neuroprotective effects of endogenous choline/ACh.
authors.affiliation: Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, IL, USA.
authors.forename: Bopanna I
authors.initials: BI
authors.lastname: Kalappa
authors.forename: Fen
authors.initials: F
authors.lastname: Sun
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Johnson
authors.forename: Kunlin
authors.initials: K
authors.lastname: Jin
authors.forename: Victor V
authors.initials: VV
authors.lastname: Uteshev
mesh_terms: D000818:Animals; D002545:Brain Ischemia / Q000188:drug therapy* / Q000378:metabolism*; D002794:Choline / Q000378:metabolism / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D007555:Isoxazoles / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010671:Phenylurea Compounds / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000187:drug effects* / Q000378:metabolism
chemical_list: C508388:1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)urea; D007555:Isoxazoles; D018696:Neuroprotective Agents; D018722:Nicotinic Agonists; D010671:Phenylurea Compounds; D064569:alpha7 Nicotinic Acetylcholine Receptor; D002794:Choline
keywords: PNU-120596; PNU120596; anoxic depolarization; choline; cortex; hippocampus; ischaemia; neuroprotection; α7 nAChR