Neonatal vulnerability to ischemia and reperfusion: cardioplegic arrest causes greater myocardial apoptosis in neonatal lambs than in mature lambs

AbstractObjectivesApoptosis is a mechanism for deletion of injured or obsolete cells that is distinct from necrosis and mediated by mitochondrial release of cytochrome c caspase activation. Because myocardial apoptosis is a part of normal fetal and postnatal maturation, we hypothesize that neonatal myocardium is more vulnerable to undergo myocardial apoptosis than mature myocardium after cardioplegic arrest.MethodsNewborn and mature lambs (n = 5 in each group) underwent cardiopulmonary bypass, antegrade crystalloid hyperkalemic cardioplegic arrest for 60 minutes, and a 6-hour recovery period. Myocardium was examined by using terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate–digoxigenin nick end labeling (TUNEL), Western blotting, in vitro kinase assays, and fluorometric assays of the activity of caspases 3, 8, and 9. Myocardium from nonoperated control subjects (n = 5 in each age group) was also obtained.ResultsMore TUNEL-positive nuclei were present in the newborn postcardioplegic myocardium (P = .04). Caspase 3, 8, and 9 activities were 1.6-fold, 1.5-fold, and 1.4-fold greater in the newborn postcardioplegic myocardium (P = .04, P = .01, and P = .01, respectively). The Bax/Bcl-2 ratio was higher in the newborn postcardioplegic myocardium (P = .04). Apoptosis signal-regulating kinase 1 activity and cleaved caspase 3 levels were higher in the newborn postcardioplegic myocardium (P = .02 and P = .009). Mitochondrial release of cytochrome c was greater in the newborn postcardioplegic myocardium (P = .009).ConclusionsThe increased Bax/Bcl-2 ratio in the newborn myocardium suggests a proapoptotic state that is manifested by greater TUNEL staining, cytochrome c release, and cleavage of caspase 3. Increased apoptosis signal-regulating kinase 1 activity suggests greater oxidative stress, immature mechanisms to ameliorate oxidative stress, or both in the neonatal myocardium. Mitochondrial release of cytochrome c suggests that apoptosis-related mitochondrial dysfunction might contribute to early postoperative myocardial dysfunction in the neonate