Reactive oxygen species function as second messenger during ischemic preconditioning of heart

Ischemic preconditionining has been shown to trigger a signaling pathway by potentiating tyrosine kinase phosphorylation leading to the activation of p38 MAP kinase and MAPKAP kinase 2. Recently, the nuclear transcription fac tor, NF kappa B, was found to play a role in the signaling process. Since N F kappa B is a target of oxygen free radicals, we hypothesized that reactiv e oxygen species might play a role in the signaling process. To test this h ypothesis, isolated rat hearts were perfused in the absence or presence of either dimethyl thiourea (DMTU), a OH . radical scavenger, or SN 50 peptide , a NF kappa B blocker. Hearts were then subjected to ischemic precondition ing by four repeated episodes of 5 min ischemia each followed by 10 min rep erfusion. All hearts were then made globally ischemic for 30 min followed b y 2 h of reperfusion. The results of our study demonstrated enhanced tyrosi ne kinase phosphorylation during ischemic preconditioning which was blocked by DMTU. DMTU also inhibited preconditioning mediated increased phosphoryl ation of p38 MAP kinase and MAPKAP kinase 2 activity. However, DMTU had no effect on the translocation and activation of protein kinase C (PKC) result ing from preconditioning. Preconditioning reduced myocardial infarct size a s expected. This cardioprotective effect of preconditioning was abolished b y both DMTU and SN 50. Preconditioning resulted in the nuclear translocatio n and activation of NF kappa B. Increased NF kappa B binding was blocked by both DMTU and SN 50. The results of this study demonstrate that reactive o xygen species play a crucial role in signal transduction mediated by precon ditioning. This signaling process appears to be potentiated by tyrosine kin ase phosphorylation resulting in the activation of p38 MAP kinase and MAPKA P kinase 2 leading to the activation of NF kappa B suggesting a role of oxy gen free radicals as second messenger. Free radical signaling seems to be i ndependent of PKC although PKC is activated during preconditioning process suggesting the role of two separate signaling pathways in ischemic precondi tioning.