Cardio-protective effects of combined L-arginine and insulin: Mechanism and therapeutic actions in myocardial ischemia-reperfusion injury

Reduced nitric oxide (NO) bioavailability plays a central role in the pathogenesis of myocardial ischemiareperfusion injury (I-R), and reduced 1.-arginine transport via cationic amino acid transporter-1 is a key contributor to the reduced NO levels. Insulin can increase NO levels by increasing the transport of its substrate 1.-arginine but insulin alone exerts minimal cardiac protection in I-R. We hypothesized that combined insulin and t-arginine may provide cardioprotective effects in the setting of myocardial I-R. The effect of supplemental insulin, t-arginine and the combination was examined in cardiomyocytes exposed to hypoxia/reoxygenation and in isolated perfused mouse hearts undergoing ischemia/reperfusion. When compared to controls, cardiomyocytes treated upon reoxygenation with 1 nM insulin+ 1 mM 1.-arginine exhibited significant (all P < 0.05) improvements in NO generation and mitochondrial membrane potential, with a concomitant fall in reactive oxygen species production and LDH release. Insulin also increased t-arginine uptake following hypoxia-reoxygenation (P< 0.05; n=4-6). In langendorff perfused isolated mouse hearts, combined L-arginine-insulin treatment upon reperfusion significantly (all P < 0.05; n = 9-11) improved recovery of left ventricular developed pressure, rate pressure product and end diastolic pressure following ischemia, independent of any changes in postischemic coronary flow, together with significantly lower LDH release. The observed improvements were greater than 1.-arginine or insulin treatment alone. In isolated cardiomyocytes (n=3-5), 1 nM insulin caused cationic amino acid transporter-1 to redistribute to the cellular membrane from the cytosol and the effects of insulin ont-arginine uptake were partially dependent on the PI3K/Akt pathway.i.-arginineinsulin treatment may be a novel strategy to ameliorate I-R injury. (C) 2015 Elsevier BY. All rights reserved.