Cardiac protection by metallothionein against ischemia-reperfusion injury and its possible relation to ischemic preconditioning

Abstract

Oxidative stress is believed to play a major role in ischemia-reperfusion injury to the heart. Metallothionein (MT), a potential free radical scavenger, may function in protection against this cardiac injury. Hearts isolated from cardiac MT overexpressing transgenic mice and from the nontransgenic littermates were subjected to 50 min of warm (37°C) zero-flow ischemia followed by 90 min reflow. Compared with the nontransgenic controls, the transgenic hearts with MT concentrations about 10-fold higher than normal, showed significantly improved recovery of contractile force (73% versus 22% at the end of 90 min reperfusion, p < 0.01). Efflux of creatine kinase was reduced by more than 50% and the zone of myocardial infarction as demarcated by triphenyl-tetrazolium at the end of reperfusion was reduced by about 40% in the transgenic hearts compared with the nontransgenic controls. The second part of this study was to determine the role of MT in the ischemic preconditioning (PC). An open-chest mouse model was used to determine the effect of ischemic PC on MT synthesis in the heart, then the effect of MT induction on ischemic injury. Mouse hearts were processed four cycles of 5 min occlusion and 5 min reperfusion via ligation of left anterior descending coronary artery to produce ischemic PC. At different time points, cardiac MT was measured by a cadmium-hemoglobin affinity assay. Compared to sham-operated mice (6.6 ± 1.8 μg/g tissue), MT was significantly (p < 0.01) increased to 15.8 ± 1.8 and 17.9 ± 5.0 μg/g 12 and 24 h, respectively, after ischemic PC. Treatment with cadmium for 24 h increased cardiac MT to the same level as that induced by the ischemic PC and inhibited the subsequent injury induced by ischemia reperfusion. These results indicated that MT functions in cardiac protection against ischemia-reperfusion injury, and it may be an important factor involved in the “second window” of protection induced by ischemic PC.