Abstract 104: Vasonatrin Peptide Inhibits Endoplasmic Reticulum Stress and Attenuates Myocardial Ischemia/reperfusion Injury in Diabetic Rats

Abstract

Aims: Diabetes mellitus (DM) increases morbidity/mortality of ischemic heart disease. Although the ability of the natriuretic peptides to modulate cardiac function and cell proliferation has been recognized, their effects on myocardial ischemia/reperfusion (MI/R) injury is still unclear. This study was to investigate the effects of the artificial synthetic natriuretic peptide — vasonatrin peptide (VNP) on MI/R injury in diabetic rats, and underlying mechanisms.

Method: The high-fat diet-fed streptozotocin induced diabetic rats were subjected to MI/R (30 min/4 h) and VNP treatment (100 μg/kg, i.v., 10 min before R). In vitro study was performed using H9c2 cardiomyocytes subjected to hypoxia/reoxygenation (H/R, 3 h/6 h) and incubated with or without VNP (10^-8 mol/L).

Result: The diabetic state aggravated MI/R injury and showed more severe myocardial functional impairment than normal state. VNP treatment (100 μg/kg, i.v., 10 min before R) significantly improved ± LV dP/dt_max and LVSP, and decreased infarct size, apoptosis index, caspase-3 activity, serum CK and LDH levels (n=8, P<0.05). Moreover, VNP inhibited endoplasmic reticulum (ER) stress by suppressing GRP78 and CHOP, and consequently increased Akt and ERK1/2 expression and phosphorylation levels (n=3, P<0.05). These effects were mimicked by 8-Br-cGMP (1 mg/kg, i.p., 20 min before R), a cGMP analogue, whereas inhibited by KT-5823 (0.5 mg/kg, i.p.), the selective inhibitor of PKG (P<0.05). Pretreated DM rats with TUDCA (50 mg/kg, i.p.), an inhibitor of ER stress, couldn’t further promote the VNP’s cardioprotective effect. Additionally, gene knockdown of PKG1α with siRNA blunted VNP’s inhibition of ER stress and apoptosis, while overexpression of PKG1α resulted in significant decreased ER stress and apoptosis in H/R H9c2 cardiomyocytes (n=6, P<0.05).

Conclusion: We demonstrated that VNP protects diabetic heart against MI/R injury by inhibiting ER stress via cGMP-PKG signaling pathway.