Apoptosis-related mitochondrial dysfunction in the early postoperative neonatal lamb heart.
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.
Caldarone
Christopher A
CA
Division of Cardiovascular Surgery, University of Iowa College of Medicine, Iowa City, Iowa, USA. christopher.caldarone@sickkids.ca
Barner
Elesa W
EW
Wang
Lixing
L
Karimi
Mohsen
M
Mascio
Christopher E
CE
Hammel
James M
JM
Segar
Jeffrey L
JL
Du
Changqing
C
Scholz
Thomas D
TD
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
D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein