Ischemic preconditioning or p38 MAP kinase inhibition attenuates myocardial TNF α production and mitochondria damage in brief myocardial ischemia

Coronary artery occlusion increased the TNF α level in the membrane fraction of the rat heart, almost maximally at 30 min. TNF α immunofluorescence labeled streak-like reticular structures inside of the cardiomyocyte but not vascular or interstitial cells in myocardial ischemia. Immuno-electron microscopy confirmed the localization of TNF α between myofibrils, mitochondria, or other membrane structures in the ischemic cardiomyocyte. Ischemic preconditioning (IP) is the protection of myocardium conferred by cycles of brief ischemia-reperfusion. The increases in TNF α production, as well as phosphorylation of p38 MAP kinase and S6 kinase after ischemia were inhibited by IP or p38 MAP kinase inhibitors (SB203580, FR167653). TNF α production appeared to be regulated possibly at the post-transcriptional step by ribosomal S6 phosphorylation given that IP did not suppress TNF α mRNA up-regulation and was independent of NFκB activation. Electron microscopy (EM) showed mitochondria damage in ischemic cardiomyocyte, which was inhibited either by IP or SB203580. This is the first demonstration of the TNF α up-regulation in membrane structures of ischemic cardiomyocyte through p38 MAP kinase-mediated post-transcriptional mechanism, in association with mitochondrial damage.