Role of C‐jun N‐terminal Kinase in the Mitochondria of Ischemia‐Reperfusion Injury of Isolated Heart (LB648)

Abstract

Background: Previous studies indicate that inhibition of JNK activation during heart reperfusion reduces cell death and infarct size. However, the studies could not eliminate off‐target effects due to the use of non‐specific JNK inhibitors. In the present study, we observed whether two mechanistically unrelated, specific JNK inhibitors, SU3327 and SR3306, would reduce damage from ischemia/reperfusion (IR) and improve cardiac function.Methods: Using the Langendorff model of ischemia‐reperfusion, isolated rat hearts underwent 25 min of global ischemia followed by concurrent JNK inhibitor administration (2 and 10 µM for SU3327, 0.5 and 2 µM for SR3306) and 30 or 60 min of reperfusion. Throughout perfusion, we monitored cardiac function based on the percent recovery of left ventricular developed pressure, minimum and maximum rates of pressure change in the ventricle, and the rate pressure product. Myocardial damage was assessed by measuring lactate dehydrogenase activity in heart effluent. At the end of reperfusion, we used isolated mitochondria to determine respiration rates and mitochondria permeability transition pore opening. Proteins from the heart homogenate were analyzed using Western blot.Results: Our results indicate that the specific JNK inhibitors did not improve cardiac function. As expected, mitochondrial respiration control index was correlated to recovery of heart function. We observed marginal reduction of myocardial damage by JNK inhibitor SU3327 at the 10 min time point after reperfusion. Western blot analysis demonstrated inhibition of phospho‐JNK and total‐JNK at high doses (10 uM) of SU3327, but it coincided with activation of p38.Conclusion: JNK inhibition may provide cardioprotection against IR. However, in practice, it may be ineffective due to compensatory activation of p38 by an unknown mechanism.Grant Funding Source: Supported by SC1HL118669 (to S.J.), and in part, G12RR‐03051 NIH grants.