title: Leptin, the obesity-associated hormone, exhibits direct cardioprotective effects.
abstract: OBJECTIVE
  Protection against ischaemia-reperfusion (I/R) injury involves PI3K-Akt and p44/42 MAPK activation. Leptin which regulates appetite and energy balance also promotes myocyte proliferation via PI3K-Akt and p44/42 MAPK activation. We, therefore, hypothesized that leptin may also exhibit cardioprotective activity.
  
  
  METHODS
  The influence of leptin on I/R injury was examined in perfused hearts from C57Bl/6 J mice that underwent 35 min global ischaemia and 35 min reperfusion, infarct size being assessed by triphenyltetrazolium chloride staining. The concomitant activation of cell-signalling pathways was investigated by Western blotting. The effect of leptin on mitochondrial permeability transition pore (MPTP) opening was studied in rat cardiomyocytes.
  
  
  RESULTS
  Leptin (10 nM) administered during reperfusion reduced infarct size significantly. Protection was blocked by either LY294002 or UO126, inhibitors of Akt and p44/42 MAPK, respectively. Western blotting confirmed that leptin stimulated p44/42 MAPK phosphorylation significantly. Akt phosphorylation was also enhanced but did not achieve statistical significance. Additionally, leptin treatment was associated with a significant increase in p38 phosphorylation. By contrast, leptin caused downregulation of phosphorylated and non-phosphorylated STAT3, and of total AMP-activated kinase. Cardiomyocytes responded to leptin with delayed opening of the MPTP and delayed time until contracture.
  
  
  CONCLUSIONS
  Our data indicate for the first time that the adipocytokine, leptin, has direct cardioprotective properties which may involve the PI3-Akt and p44/42 MAPK pathways.
authors.affiliation: The Hatter Cardiovascular Institute, University College London Hospital and Medical School, London, UK.
authors.forename: C C T
authors.initials: CC
authors.lastname: Smith
authors.forename: M M
authors.initials: MM
authors.lastname: Mocanu
authors.forename: S M
authors.initials: SM
authors.lastname: Davidson
authors.forename: A M
authors.initials: AM
authors.lastname: Wynne
authors.forename: J C
authors.initials: JC
authors.lastname: Simpkin
authors.forename: D M
authors.initials: DM
authors.lastname: Yellon
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002316:Cardiotonic Agents; D066298:In Vitro Techniques; D020738:Leptin / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism; D015428:Myocardial Reperfusion Injury / Q000473:pathology / Q000517:prevention & control*; D009206:Myocardium / Q000473:pathology; D032383:Myocytes, Cardiac / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D002316:Cardiotonic Agents; D020738:Leptin