title: Apoptosis-related mitochondrial dysfunction in the early postoperative neonatal lamb heart.
abstract: BACKGROUND
  In the early postoperative period, the neonatal myocardium undergoes sparse apoptotic cell loss ( approximately 1% of myocytes). Because apoptosis is preceded by events associated with mitochondrial dysfunction, the fraction of myocytes with preapoptotic mitochondrial changes has important clinical implications (eg, postoperative myocardial dysfunction). My colleagues and I therefore hypothesized that postoperative apoptotic myocytes represent a tip of the iceberg, with more myocytes upstream with apoptosis-related mitochondrial dysfunction (ARMD).
  
  
  METHODS
  Neonatal lambs underwent cardiopulmonary bypass, 60 minutes of cardioplegic arrest, and 6 hours of recovery (cardiopulmonary bypass with cardioplegic arrest [CPB+CP]; n = 5) and were compared with nonbypass controls (non-CPB; n = 5). Myocardium (left ventricle [LV] and right ventricle [RV]) was examined by using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining, electron microscopy, immunohistochemistry, Western blot, and isolated mitochondrial oxygen consumption measurement.
  
  
  RESULTS
  TUNEL-positive nuclei and electron microscopy-confirmed mitochondrial structural changes were more common in CPB+CP than non-CPB myocardium and were more common in the LV than RV (p = 0.0016). Bax (a proapoptotic mediator) translocated from the cytosol to the mitochondria (LV > RV; p < 0.05). Immunohistochemistry demonstrated diffuse mitochondrial loss of cytochrome c that was consistent with outer mitochondrial membrane permeabilization (LV > RV > non-CPB). Permeabilization was further demonstrated by augmentation of oxygen consumption in isolated mitochondria after administration of exogenous cytochrome c. The mitochondrial oxygen consumption boost was 57% for CPB+CP:LV; 23% for CPB+CP:RV; and 18% and 17% for non-CPB:LV and non-CPB:RV, respectively (p < 0.01, CPB+CP:LV vs other groups).
  
  
  CONCLUSIONS
  ARMD is much greater than the prevalence of TUNEL-positive myocytes in postoperative neonatal myocardium. Greater LV vulnerability may represent a relationship between increased afterload and ARMD. These changes are consistent with the early postoperative myocardial dysfunction commonly reported after neonatal cardiac operations.
authors.affiliation: Division of Cardiovascular Surgery, University of Iowa College of Medicine, Iowa City, Iowa, USA. christopher.caldarone@sickkids.ca
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Caldarone
authors.forename: Elesa W
authors.initials: EW
authors.lastname: Barner
authors.forename: Lixing
authors.initials: L
authors.lastname: Wang
authors.forename: Mohsen
authors.initials: M
authors.lastname: Karimi
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Mascio
authors.forename: James M
authors.initials: JM
authors.lastname: Hammel
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Segar
authors.forename: Changqing
authors.initials: C
authors.lastname: Du
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Scholz
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D004195:Disease Models, Animal; D007150:Immunohistochemistry; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure*; D028361:Mitochondrial Diseases / Q000473:pathology* / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure*; D010101:Oxygen Consumption; D010539:Permeability; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012756:Sheep; D051028:bcl-2-Associated X Protein
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein