Release of TNF-α during myocardial reperfusion depends on oxidative stress and is prevented by mast cell stabilizers

Objectives: Our study sought to elucidate the role of oxidative stress for shedding of tumor necrosis factor-alpha (TNF-alpha) and for activating TNF-alpha-converting enzyme (TACE). Background: TNF-alpha, a central inflammatory cytokine, is discussed as one of the mediators of reperfusion injury. Shedding of membrane-bound pro-TNF-alpha. is thought to be largely due to TNF-alpha-converting enzyme (TACE). Methods: Release of TNF-alpha and TACE dependency were studied in isolated rat hearts and in the human mast cell line HMC-1. Results: In reperfused hearts, interstitial release of TNF-alpha occurred in two phases (2 - 10 and >45 min). It depended on the presence of oxygen during reperfusion and was attenuated by reduced glutathione. Infusion of the oxidants H2O2 or HOCl elicited release in non-ischemic hearts. TNF-alpha release was inhibited in hearts treated with degranulation inhibitors ketotifen or cromoglycate, suggesting mast cells as major source for myocardial TNF-alpha. This was confirmed by tissue staining. Post-ischemic release of histamine, however, did not parallel that of TNF-alpha. Heart tissue contained mainly mature TACE. HMC-1 expressed abundant pro-TACE and cleaved the pro-TNF-alpha-peptide Ac-SPLAQAVRSSSR-NH2. However, cleavage was nonspecific and only partly inhibited by TACE inhibitor TAPI-2 (10-100 mumol/l), while it was stimulated by H2O2 and HOCI and fully blocked by the nonspecific metalloprotease inhibitor o-phenanthroline. Conclusions: The mechanism underlying TNF-alpha release from post-ischemic myocardium is oxidation-dependent but largely independent of activation of TACE. Mast cell stabilizers may be useful in preventing TNF-alpha release during reperfusion. (C) 2003 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.