Classic ischemic but not pharmacologic preconditioning is abrogated following genetic ablation of the TNFalpha gene.
OBJECTIVE
Tumor necrosis factor alpha (TNFalpha) is known to mimic ischemic preconditioning (IP). However, it is not known whether TNFalpha-preconditioning is mediated by 'established' preconditioning signaling or via novel signaling cascades. Moreover, whether TNFalpha is required to induce the ischemic preconditioning phenotype has not been determined.


METHODS
To evaluate the role of TNFalpha, we determined the infarct-sparing effect of IP comparing TNFalpha null (TNFalpha-/-) and wild-type mice. The IP protocol included 4x5 min ischemia/reperfusion (I/R) prior to the index 35 min of global ischemia followed by 45 min of reperfusion in isolated perfused murine hearts. Infarct size was measured as a percentage of cardiac volume. To evoke particular signaling pathways numerous pharmacologic studies were performed.


RESULTS
Following IP, infarct size was significantly reduced by 43% in wild-type mice. In contrast, infarct size was not attenuated by IP in the TNFalpha-/- group versus I/R controls (Infarct size-36+/-3%). Interestingly, pharmacologic preconditioning with adenosine (100 microM) and diazoxide (30 microM) mimicked IP in both the wild-type (infarct size-11+/-4% and 18+/-2%) and in TNFalpha-/- mice (infarct size-15+/-4% and 23+/-3%) versus respective I/R controls. Recombinant TNFalpha (0.5 ng/ml) administered for 7 min followed by a 10-min washout mimicked IP in wild-type mice but not in the TNFalpha deficient mouse hearts. The cardioprotective effects of IP, adenosine and TNFalpha were abolished by the co-administration of the putative mitochondrial K(ATP) blocker 5-hydroxydecanoate.


CONCLUSIONS
We demonstrate that cardiac TNFalpha production is required for ischemic preconditioning-induced cardioprotection but not necessary in pharmacologic preconditioning with adenosine or diazoxide in TNFalpha-/- mice. Moreover, TNFalpha administration is sufficient to activate preconditioning in wild-type mice. Finally, as 5-hydroxydecanoate abrogates ischemic, adenosine and TNFalpha induced preconditioning, this suggests that diverse signaling pathways converge at the level of mitochondrial K(ATP) channel activation to mediate this cardioprotection.
Smith
Robert M
RM
Hatter Institute for Cardiology Research, MRC Inter-University Cape Heart Group, University of Cape Town Medical School, Observatory 7925, South Africa.
Suleman
Naushaad
N
McCarthy
Joy
J
Sack
Michael N
MN
D000241:Adenosine / Q000627:therapeutic use; D000704:Analysis of Variance; D000818:Animals; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000627:therapeutic use; D006880:Hydroxy Acids / Q000494:pharmacology; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009203:Myocardial Infarction / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D010477:Perfusion; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000502:physiology*
D003652:Decanoic Acids; D006880:Hydroxy Acids; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; C052853:5-hydroxydecanoic acid; D000241:Adenosine; D003981:Diazoxide