Diazoxide amelioration of myocardial injury and mitochondrial damage during cardiac surgery.
BACKGROUND
Recently, we have shown that the selective opening of mitochondrial ATP-sensitive potassium channels with diazoxide significantly decreases myocardial injury. The purpose of this study was to determine the effects of diazoxide on apoptosis and the mechanisms modulating apoptosis and myocardial injury in a blood-perfused model of acute myocardial infarction.


METHODS
Pigs (32 to 42 kg) undergoing total cardiopulmonary bypass underwent left anterior descending coronary artery occlusion for 30 minutes. The aorta was cross-clamped and magnesium-supplemented potassium cold-blood cardioplegia (DSA; n = 6) or magnesium-supplemented potassium cardioplegia containing 50 micromol/L diazoxide (DZX; n = 6) was administered, followed by 30 minutes of global ischemia and 120 minutes of reperfusion. Left ventricular tissue samples from DSA and DZX hearts were obtained after reperfusion. Apoptosis was determined by TUNEL, caspase-3 and PARP cleavage, and caspase-3 activity. Bax and bcl-2 levels were determined and tissue morphology was examined by light and transmission electron microscopy.


RESULTS
Apoptosis, as estimated by TUNEL-positive nuclei/3,000 myocardial cells, was 120.3 +/- 48.8 in DSA hearts and was significantly decreased to 21.4 +/- 5.3 in DZX hearts (p < 0.05 vs control). Caspase-3 and poly-ADP-ribose polymerase cleavage and pro-apoptotic bax protein levels were significantly decreased with diazoxide (p < 0.05 vs DSA). Light and transmission electron microscopy indicated severe disruption of tissue with capillary dilatation, mitochondrial cristae damage, and evidence of increased presence of mitochondrial granules in DSA as compared with DZX hearts.


CONCLUSIONS
The addition of diazoxide (50 micromol/L) to cardioplegia significantly decreases regional myocardial apoptosis and mitochondrial damage, and provides an additional modality for achieving myocardial protection.
McCully
James D
JD
Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, Boston, Massachusetts 02115, USA. james_mccully@hms.harvard.edu
Wakiyama
Hidetaka
H
Cowan
Douglas B
DB
Federman
Micheline
M
Parker
Robert A
RA
Levitsky
Sidney
S
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002315:Cardiopulmonary Bypass; D053148:Caspase 3; D020169:Caspases / Q000032:analysis; D003981:Diazoxide / Q000494:pharmacology*; D005260:Female; D006352:Heart Ventricles / Q000473:pathology; D020287:In Situ Nick-End Labeling; D008297:Male; D008854:Microscopy, Electron; D008929:Mitochondria, Heart / Q000187:drug effects*; D015428:Myocardial Reperfusion Injury / Q000473:pathology*; D011065:Poly(ADP-ribose) Polymerases / Q000032:analysis; D011518:Proto-Oncogene Proteins / Q000032:analysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D013552:Swine; D051028:bcl-2-Associated X Protein
D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3; D020169:Caspases; D003981:Diazoxide