title: Hypothermia-induced cardioprotection using extended ischemia and early reperfusion cooling.
abstract: Optimal timing of therapeutic hypothermia for cardiac ischemia is unknown. Our prior work suggests that ischemia with rapid reperfusion (I/R) in cardiomyocytes can be more damaging than prolonged ischemia alone. Also, these cardiomyocytes demonstrate protein kinase C (PKC) activation and nitric oxide (NO) signaling that confer protection against I/R injury. Thus we hypothesized that hypothermia will protect most using extended ischemia and early reperfusion cooling and is mediated via PKC and NO synthase (NOS). Chick cardiomyocytes were exposed to an established model of 1-h ischemia/3-h reperfusion, and the same field of initially contracting cells was monitored for viability and NO generation. Normothermic I/R resulted in 49.7 +/- 3.4% cell death. Hypothermia induction to 25 degrees C was most protective (14.3 +/- 0.6% death, P < 0.001 vs. I/R control) when instituted during extended ischemia and early reperfusion, compared with induction after reperfusion (22.4 +/- 2.9% death). Protection was completely lost if onset of cooling was delayed by 15 min of reperfusion (45.0 +/- 8.2% death). Extended ischemia/early reperfusion cooling was associated with increased and sustained NO generation at reperfusion and decreased caspase-3 activation. The NOS inhibitor N(omega)-nitro-L-arginine methyl ester (200 microM) reversed these changes and abrogated hypothermia protection. In addition, the PKCepsilon inhibitor myr-PKCepsilon v1-2 (5 microM) also reversed NO production and hypothermia protection. In conclusion, therapeutic hypothermia initiated during extended ischemia/early reperfusion optimally protects cardiomyocytes from I/R injury. Such protection appears to be mediated by increased NO generation via activation of protein kinase Cepsilon; nitric oxide synthase.
authors.affiliation: The Emergency Resuscitation Center, Sections of Emergency Medicine, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Zuo-Hui
authors.initials: ZH
authors.lastname: Shao
authors.forename: Wei-Tien
authors.initials: WT
authors.lastname: Chang
authors.forename: Kim Chai
authors.initials: KC
authors.lastname: Chan
authors.forename: Kim R
authors.initials: KR
authors.lastname: Wojcik
authors.forename: Chin-Wang
authors.initials: CW
authors.lastname: Hsu
authors.forename: Chang-Qing
authors.initials: CQ
authors.lastname: Li
authors.forename: Juan
authors.initials: J
authors.lastname: Li
authors.forename: Travis
authors.initials: T
authors.lastname: Anderson
authors.forename: Yimin
authors.initials: Y
authors.lastname: Qin
authors.forename: Lance B
authors.initials: LB
authors.lastname: Becker
authors.forename: Kimm J
authors.initials: KJ
authors.lastname: Hamann
authors.forename: Terry L
authors.initials: TL
authors.lastname: Vanden Hoek
mesh_terms: D000818:Animals; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D003080:Cold Temperature; D007036:Hypothermia, Induced; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000378:metabolism
chemical_list: D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D051744:Protein Kinase C-epsilon; D053148:Caspase 3