title: Myocardial cytochrome oxidase activity increases with age and hypoxemia in patients with congenital heart disease.
abstract: BACKGROUND
  Myocardial tolerance to ischemia is influenced by age and preoperative cyanosis through unknown mechanisms and significantly affects postoperative outcomes. Cytochrome c oxidase (CcOx), the terminal enzyme of the mitochondrial electron transport chain, may play a role in the susceptibility to ischemic-reperfusion (IR) injury. Our study aimed at investigating changes in human myocardial CcOx activity based on age and preoperative oxygen saturation to understand its role in transition from neonatal to mature myocardium and hypoxic conditions.
  
  
  METHODS
  The right atrial appendage from patients undergoing first time surgical repair/palliation of congenital heart defects was analyzed for steady state CcOx activity by oxidation of ferrocytochrome c via spectrophotometry and steady state CcOx subunit I protein content by protein immunoblotting. Student's t-test compared CcOx activity and protein levels between patients with preoperative hypoxia and normoxia. Multiple linear regression analysis was used to assess the effects of age and preoperative arterial oxygen saturations (SaO2) on CcOx protein activity and protein content.
  
  
  RESULTS
  Thirty-two patients with a median (interquartile range) age of 83 days (8-174) and preoperative oxygen saturation 98% (85-100%) were enrolled. Independent of age, preoperative SaO2⩽90% was associated with significantly greater CcOx steady state activity (p=0.004). Additionally, older age itself was associated with increased CcOx steady state activity (p=0.022); the combination of preoperative SaO2and age account for 33% of the variation in CcOx steady state activity (R2=0.332). There was no increase in the CcOx subunit I protein content with either age or preoperative hypoxia.
  
  
  CONCLUSIONS
  In patients with congenital heart disease, an increase in CcOx steady state activity is seen with increasing age. Hypoxia leads to upregulation of CcOx steady state activity without an increase in the amount of enzyme protein itself. Higher CcOx activity in older and cyanotic patients may indicate CcOx-dependent reactive oxygen species as the mechanism for IR injury.
authors.affiliation: 1 Howard University College of Medicine, Washington, D.C., USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Onwugbufor
authors.affiliation: 2 Division of Anesthesiology & Pain Medicine, Children's National Medical Center, Washington, D.C., USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Levy
authors.affiliation: 3 Departments of Surgery and Anesthesia, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: David
authors.initials: D
authors.lastname: Zurakowski
authors.affiliation: 4 Department of Cardiovascular Surgery, Children's National Medical Center, Washington, D.C., USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Jonas
authors.affiliation: 4 Department of Cardiovascular Surgery, Children's National Medical Center, Washington, D.C., USA.
authors.forename: Pranava
authors.initials: P
authors.lastname: Sinha
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006330:Heart Defects, Congenital / Q000201:enzymology*; D006801:Humans; D000860:Hypoxia / Q000201:enzymology*; D008875:Middle Aged; D055815:Young Adult
chemical_list: D003576:Electron Transport Complex IV
keywords: cyanotic congenital heart disease; cytochrome oxidase; ischemia reperfusion; myocardial protection; neonatal cardiac surgery