How does hypothermia protect cardiomyocytes during cardioplegic ischemia?
OBJECTIVE
Insufficient myocardial protection is still a considerable cause for in-hospital mortality in children. The purpose of our study was to investigate underlying the basic mechanisms of cardioplegic cardioprotection during hypothermic and normothermic ischemia in a cardiomyocyte cell culture model.


METHODS
We cooled cardiomyocytes to 20°C for 20min; during this time, cardiac arrest was simulated by oxidative damage with 2mM H₂O₂ and cardioplegic solution, followed by rewarming to 37°C. Later on, we analyzed cardiomyocyte cell morphology (phase-contrast-microscopy), viability (trypan blue staining), inflammation (cyclooxygenase-2 (Cox-2) and phosphorylated-extracellular signal-regulated kinase (pERK) 1/2 expression in Western blot analysis), and expression of Akt survival protein (Western blot technique).


RESULTS
Hypothermia increases cell survival of cardiomyocytes after cardioplegic ischemia, as demonstrated in significantly higher cell viability and less cell death in these cells compared with normothermic H₂O₂-damaged cardiomyocytes. As a possible underlying cellular mechanism, we found that, during cold cardioplegic ischemia, ERK 1/2 enzyme is less phosphorylated than under conditions of normothermic cardioplegic ischemia. This is in line with significantly diminished Cox-2 expression during cold cardioplegic ischemia. Moreover, hypothermic cardioplegia preserved cell survival by upregulation of Akt transcription factor in cardiomyocytes.


CONCLUSIONS
In the present cell culture study, we clearly demonstrated that hypothermia exerts additional protection for cardiomyocytes during cardioplegic ischemia. The understanding of underlying basic mechanisms is evident to improve current techniques of myocardial protection.
Department of Congenital Heart Disease/Pediatric Cardiology, Deutsches Herzzentrum Berlin, Berlin, Germany.
Cornelia
C
Drescher
Antje
A
Diestel
Sonja
S
Wollersheim
Felix
F
Berger
Katharina R L
KR
Schmitt
D002314:Cardioplegic Solutions / Q000494:pharmacology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D003080:Cold Temperature; D051546:Cyclooxygenase 2 / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D006324:Heart Arrest, Induced; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008858:Microscopy, Phase-Contrast; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D017202:Myocardial Ischemia / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D018384:Oxidative Stress / Q000502:physiology; D010766:Phosphorylation / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism
D002314:Cardioplegic Solutions; D006861:Hydrogen Peroxide; D051546:Cyclooxygenase 2; D051057:Proto-Oncogene Proteins c-akt; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3