Abstract 3511: Cardioprotective Effects of Combined L-arginine and Insulin Treatment for Myocardial Ischemia-Reperfusion Injury
Myocardial injury due to ischemia-reperfusion (I-R) damage remains a major clinical challenge. Its pathogenesis is complex including endothelial dysfunction, heightened oxidative stress and reduced nitric oxide (NO) bioavailability although the key driving mechanism remains uncertain. In recent studies we have found reduced L-arginine (L-arg) transport in cardiomyocytes following I-R and that increasing L-arg availability is protective to both isolated cardiomyocytes and the intact heart. In this study we investigated the potential therapeutic role of insulin as a means to further enhance L-arg transport in cardiomyocytes during I-R. In neonatal rat ventricular cardiomyocytes (NVCM), 1nM insulin significantly (p<0.05) increased L-arg uptake (166±13%). These effects were significantly (p<0.001) reduced by pre-treatment with 1μM wortmannin (PI3K inhibitor, 61.2±11%), 1μM SN (Akt inhibitor, 68.9±5%), 10μM gliben-clamide (K+ ATP channel blocker, 86.3±4%) and 15nM PKC inhibitor (68.3±3%). Insulin (1nM) also increased L-arg uptake following hypoxia-reoxygenation (H-R) (77±13% vs 31±4% untreated H-R, p<0.05). When compared to untreated controls, NVCMs treated with 1nM insulin + 1mM L-arg upon reoxygenation exhibited significant (all p<0.01) improvements in NO generation (92±1% vs 74±1%) and mitochondrial membrane potentials (88±1% vs 72±1%), with a concomitant significant fall in ROS production (112±1% vs 129±1%) and lactate dehydrogenase release. These improved responses were also significantly greater than insulin or L-arg treatment alone. Pre-treating NVCMs with 1μM wortmannin significantly reduced the protective effect of insulin + L-arg, whilst the addition of high glucose (25mM) further enhanced the protective effects observed. Co-treating with 1mM L-NAME significantly decreased NO levels (71±1.5%, p<0.001) yet ROS production and mitochondrial membrane potential were still significantly improved. L-NAME alone did not alter L-arg uptake although it reduced the increase in L-arg uptake induced by insulin. Taken together these data suggest that a combination of insulin and L-arg may have therapeutic potential in the setting of myocardial I-R injury.