title: Annexin A5 uptake in ischemic myocardium: demonstration of reversible phosphatidylserine externalization and feasibility of radionuclide imaging.
abstract: Ischemic insult to the myocardium is associated with cardiomyocyte apoptosis. Because apoptotic cell death is characterized by phosphatidylserine externalization on cell membrane and annexin-A5 (AA5) avidly binds to phosphatidylserine, we hypothesized that radiolabeled AA5 should be able to identify the regions of myocardial ischemia.
  
  
  METHODS
  Models of brief myocardial ischemia by the occlusion of the coronary artery for 10 min (I-10) and reperfusion for 180 min (R-180) for the detection of phosphatidylserine exteriorization using (99m)Tc-labeled AA5 and gamma-imaging were produced in rabbits. (99m)Tc-AA5 uptake after brief ischemia was compared with an I-40/R-180 infarct model. Histologic characterization of both myocardial necrosis and apoptosis was performed in ischemia and infarct models. Phosphatidylserine exteriorization was also studied in a mouse model, and the dynamics and kinetics of phosphatidylserine exposure were assessed using unlabeled recombinant AA5 and AA5 labeled with biotin, Oregon Green, or Alexa 568. Appropriate controls were established.
  
  
  RESULTS
  Phosphatidylserine exposure after ischemia in the rabbit heart could be detected by radionuclide imaging with (99m)Tc-AA5. Pathologic characterization of the explanted rabbit hearts did not show apoptosis or necrosis. Homogenization and ultracentrifugation of the ischemic myocardial tissue from rabbit hearts recovered two thirds of the radiolabeled AA5 from the cytoplasmic compartment. Murine experiments demonstrated that the cardiomyocytes expressed phosphatidylserine on their cell surface after an ischemic insult of 5 min. Phosphatidylserine exposure occurred continuously for at least 6 h after solitary ischemic insult. AA5 targeted the exposed phosphatidylserine on cardiomyocytes; AA5 was internalized into cytoplasmic vesicles within 10-30 min. Twenty-four hours after ischemia, cardiomyocytes with internalized AA5 had restored phosphatidylserine asymmetry of the sarcolemma, and no detectable phosphatidylserine remained on the cell surface. The preadministration of a pan-caspase inhibitor, zVAD-fmk, prevented phosphatidylserine exposure after ischemia.
  
  
  CONCLUSIONS
  After a single episode of ischemia, cardiomyocytes express phosphatidylserine, which is amenable to targeting by AA5, for at least 6 h. Phosphatidylserine exposure is transient and internalized in cytoplasmic vesicles after AA5 binding, indicating the reversibility of the apoptotic process.
authors.affiliation: Cardiovascular Research Institute Maastricht, Maastricht, The Netherlands.
authors.forename: Heidi
authors.initials: H
authors.lastname: Kenis
authors.forename: Harmen Reinier
authors.initials: HR
authors.lastname: Zandbergen
authors.forename: Leonard
authors.initials: L
authors.lastname: Hofstra
authors.forename: Artiom D
authors.initials: AD
authors.lastname: Petrov
authors.forename: Ewald A
authors.initials: EA
authors.lastname: Dumont
authors.forename: Francis D
authors.initials: FD
authors.lastname: Blankenberg
authors.forename: Nezam
authors.initials: N
authors.lastname: Haider
authors.forename: Nicole
authors.initials: N
authors.lastname: Bitsch
authors.forename: Marion
authors.initials: M
authors.lastname: Gijbels
authors.forename: Johan W H
authors.initials: JW
authors.lastname: Verjans
authors.forename: Navneet
authors.initials: N
authors.lastname: Narula
authors.forename: Jagat
authors.initials: J
authors.lastname: Narula
authors.forename: Chris P M
authors.initials: CP
authors.lastname: Reutelingsperger
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000235:genetics; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D015609:Organotechnetium Compounds; D010718:Phosphatidylserines / Q000378:metabolism*; D011817:Rabbits; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins / Q000235:genetics
chemical_list: D017304:Annexin A5; D015609:Organotechnetium Compounds; D010718:Phosphatidylserines; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins; D053148:Caspase 3