TNFα is required to confer protection in an in vivo model of classical ischaemic preconditioning

Although Tumor Necrosis Factor alpha (TNF alpha) is used as a preconditioning mimetic in vitro, its role in ischaemic preconditioning (IPC) has not been clearly defined. Here, we propose to use an in vivo model (that takes into account the activation of leukocytes which may affect levels of TNF alpha to demonstrate that i) TNF alpha acts as a trigger in IPC and ii) the dose-dependent nature of this cardioprotective effect of TNF alpha. Male Wistar rats were subjected to 30 min of left coronary artery occlusion (index ischaemia), followed by 24 h reperfusion. In the presence or absence of a soluble TNF alpha receptor (sTNF alpha-R), preconditioning was induced by 3 cycles of ischaemia (3 min)/reperfusion (5 min) (IPC) or various doses (0.05-4 mu g/kg) of exogenous TNF alpha. Following 24 h reperfusion, infarct size (IS, expressed as % of the area at risk (AAR)) was assessed. Tissue levels of TNF alpha from the AAR, following IPC and TNF alpha stimulus were determined using Western Blot. IPC caused decrease in IS (4.5 +/- 1.3% vs 30.8 +/- 4.3% in ischaemic rats; P < 0.001) and increase of TNF alpha levels following the IPC stimulus. The protective effect of IPC was abrogated in the presence of the sTNF alpha-R. In addition, exogenous TNF alpha dose-dependently reduced IS with maximal protection at a dose of 0.1 mu g/kg (IS=12.6%, P < 0.01 vs ischaemic). In conclusion our data provide strong evidence for a role of TNF alpha during the trigger phase of IPC. In addition, exogenous TNFa mimics IPC by providing a dose-dependent cardioprotective effect against ischaemia-reperfusion injury in vivo. (c) 2007 Elsevier Inc. All rights reserved.