Abstract P132: Diabetes-Induced Cardiac Dysfunction Is Rescued by Endothelial Cationic Amino Acid Transporter 1 Overexpression in Mice

Abstract

Nitric oxide (NO) bioavailability is markedly impaired in diabetes, contributing to endothelial and myocardial dysfunction. Our aim was to determine if endothelial-specific overexpression of Cationic Amino Acid Transporter 1 (CAT-1, to enhance L-arginine uptake and NO generation) prevents diabetes-induced endothelial and cardiac dysfunction in diabetic mice. Male CAT-1 transgenic and non-transgenic (Ntg) 6 week old mice were administered streptozotocin (STZ, 55mg/kg ip daily for 5 days). Sham mice received citrate buffer vehicle. Myocardial function was assessed in anaesthetised mice in vivo 12 weeks later, via echocardiography. Vascular reactivity was then assessed in vitro. Compared to their non-diabetic littermates (n=6), Ntg STZ mice (n=6) exhibited reduced early-to-late blood flow velocity ratios (E/A, 1.7±0.2 vs 2.4±0.1, p<0.01) and prolonged deceleration time (DT, 40±1 vs 31±2msec, p<0.002), indicative of diastolic dysfunction. Decreased E-wave velocity (109±4 vs 76±12msec, p<0.01) and increased A-wave velocity (45±3 vs 55±4msec, p<0.05) were also observed. Systolic dysfunction was observed in Ntg STZ mice compared to shams, on reduced fractional shortening (FS, 30±1 vs 39±1%, p<0.002). In CAT-1 mice, diabetes did not impair E/A ratio (2.1±0.2), FS (40±3%) or DT (33±1msec, n=8). Thoracic aortic responses to the endothelium-dependent vasodilator acetylcholine (ACh) were unchanged by diabetes in Ntg and CAT-1 Tg mice compared to sham Ntg mice (pEC50 7.0±0.1 vs 7.2±0.1 and 7.1±0.1). There was a non-significant trend for sham CAT-1 Tg mice to show greater sensitivity to ACh than sham Ntg mice (pEC50 7.5±0.1 vs 7.1±0.1). Responses to the endothelium-independent vasodilator sodium nitroprusside and the vasoconstrictor noradrenaline were unaffected by diabetes and/or genotype. In conclusion, our results suggest that endothelial-specific CAT-1 overexpression protects against cardiac dysfunction via a mechanism independent of the systemic vasculature. The involvement of the coronary vasculature remains to be determined. Endothelial CAT-1 up-regulation as a potential therapeutic target for diabetic cardiomyopathy is an exciting prospect.