Adenosine but Not Diazoxide or Ischemic Preconditioning Significantly Rescues Myocardial Injury in HIF-1alpha Deficient Heart
H Zhong, K Fox-Talbot, D Zagzag, G Semenza. New York University School of Medicine, New York, NY; Johns Hopkins University School of Medicine, Baltimore, MD
Background: Ischemic preconditioning (IPC) has a profound protective effect against a subsequent prolonged episode of ischemiareperfusion. Many mechanisms have been proposed in the process, including mitochondrial KATP channel or reactive oxygen species (ROS) dependent or independent. As a master transcription factor in responsive to hypoxia, HIF-1 is highly possible to be involved in preconditioning protection against ischemia-reperfusion.
Design: The study is based on Langendorff perfusion system performed with hearts from HIF-1alpha wild-type (WT) mice and mice heterozygous for a null allele at the locus encoding HIF-1alpha (HET). The hearts were subjected to IPC (two cycles of 5 min ischaemia/5 min reperfusion), followed by 30 min ischemia (I30) and reperfusion (45 or 120 minutes). ROS production in isolated cardiac mitochondria was measured by a chemiluminescence assay. Apoptosis and infarct size were assessed by TUNEL assay, cleaved caspase 3 immunohistochemistry, and triphenyltetrazolium chloride staining.
Results: In our previous study, IPC was shown to increase mitochondrial production of hydrogen peroxide and superoxide in WT but not in HET hearts. In current study, the IPC was associated with 14% reduction of hydrogen peroxide and 29% reduction of superoxide in WT hearts with prolonged ischemia followed early (5 minutes) reperfusion (WTIPC+I30/R5 vs. WTI30/R5), whereas in HET hearts it did not reduce but increased mitochondrial production of hydrogen peroxide and superoxide in 140% and 5% respectively (HETIPC+I30/R5 vs. HETI30/R5). In addition, preconditioning by IPC or diazoxide limited myocardial apoptosis and infarct size after prolonged ischemiareperfusion (I30/R45 or R120) in WT hearts, but not in HET hearts. In contrast, Adenosine preconditioning reduced apoptosis and infarct size after prolonged ischemiareperfusion in both WT and HET hearts.
Conclusions: Ischemia preconditioning can prevent myocardial injury in prolonged ischemic events, which likely involves small amount of ROS production to lessen subsequent ROS bursting. However, such a mechanism is disrupted in HIF-1alpha deficient heart. Adenosine but not diazoxide or ischemic preconditioning can significantly rescue myocardial injury in HIF-1alpha deficient heart with prolong ischemic attack.
Tuesday, March 10, 2009 1:00 PM
Poster Session IV # 203, Tuesday Afternoon