Hypoxic postconditioning enhances the survival and inhibits apoptosis of cardiomyocytes following reoxygenation: role of peroxynitrite formation.
OBJECTIVE
Our previous study has shown that slow or "controlled" reperfusion for the ischemic heart reduces cardiomyocyte injury and myocardial infarction, while the mechanisms involved are largely unclear. In this study, we tested the hypothesis that enhancement of survival and prevention of apoptosis in hypoxic/reoxygenated cardiomyocytes by hypoxic postconditioning (HPC) are associated with the reduction in peroxynitrite (ONOO(-)) formation induced by hypoxia/reoxygenation (H/R).


METHODS
Isolated adult rat cardiomyocytes were exposed to 2 h of hypoxia followed by 3 h of reoxygenation. After 2 h of hypoxia the cardiomyocytes were either abruptly reperfused with pre-oxygenized culture medium or postconditioned by two cycles of 5 min of brief reoxygenation and 5 min of re-hypoxia followed by 160 min of abrupt reoxygenation.


RESULTS
H/R resulted in severe injury in cardiomyocytes as evidenced by decreased cell viability, increased LDH leakage in the culture medium, increased apoptotic index (P values all less than 0.01 vs. normoxia control group) and DNA ladder formation, which could be significantly attenuated by HPC treatment applied before the abrupt reoxygenation (P < 0.05 vs. H/R group). In addition, H/R induced a significant increase in ONOO(-) formation as determined by nitrotyrosine content in cardiomyocytes (P < 0.01 vs. normoxia control). Treatment with the potent ONOO(-) scavenger uric acid (UA) at reoxygenation significantly decreased ONOO(-) production and protected myocytes against H/R injury, whereas the same treatment with UA could not further enhance myocyte survival in HPC group (P > 0.05 vs. HPC alone). Statistical analysis showed that cell viability closely correlated inversely with myocyte ONOO(-) formation (P < 0.01).


CONCLUSIONS
These data demonstrate that hypoxic postconditioning protects myocytes against apoptosis following reoxygenation and enhances myocytes survival, which is partly attributable to the reduced ONOO(-) formation following reoxygenation.
Wang
Hai-Chang
HC
Department of Cardiology and Department of Physiology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, China.
Zhang
Hai-Feng
HF
Guo
Wen-Yi
WY
Su
Hui
H
Zhang
Kun-Ru
KR
Li
Qiu-Xia
QX
Yan
Wenli
W
Ma
Xin L
XL
Lopez
Bernard L
BL
Christopher
Theodore A
TA
Gao
Feng
F
D000818:Animals; D017209:Apoptosis; D002470:Cell Survival; D000860:Hypoxia / Q000503:physiopathology*; D019157:Ischemic Preconditioning, Myocardial; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology*; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000502:physiology; D010100:Oxygen / Q000378:metabolism* / Q000494:pharmacology; D030421:Peroxynitrous Acid / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014527:Uric Acid / Q000494:pharmacology
D030421:Peroxynitrous Acid; D014527:Uric Acid; D007770:L-Lactate Dehydrogenase; D010100:Oxygen