Introduction: Endothelial dysfunction, cardiomyocyte hypertrophy and interstitial fibrosis are pathological hallmarks of diabetes-related complications. Serelaxin (recombinant human relaxin-2) treatment prevents hyperglycaemia-induced endothelial dysfunction in the mouse aorta ex vivo, and limits apoptosis and hypertrophy in neonatal rat cardiomyocytes in vitro. Little is known about the effects of in vivo serelaxin treatment in a Type 1 model of diabetes. This study aimed to test the hypothesis that serelaxin (RLX) treatment reverses diabetes-induced vascular dysfunction and left ventricular remodelling in streptozotocin (STZ)-injected mice.
Methods: Type 1 diabetes was induced in mice by five consecutive daily intraperitoneal injections of STZ (55 mg/kg body weight, in 0.1 M citrate buffer, pH4.5) with overnight fasting. An equivalent volume of citrate buffer was injected into the mice in control group. Eleven weeks after the initial STZ/citrate buffer injections, the mice were further allocated into citrate buffer+placebo (20 mM sodium acetate, pH5.0), STZ+placebo and STZ+RLX (0.5 mg/kg/day) treated groups. Placebo and RLX treatments were administered via sterile subcutaneous osmotic pump for two weeks. Blood glucose levels were monitored fortnightly two weeks after the initial STZ/citrate buffer injections using a glucometer. Mice with blood glucose levels greater than 25 mM were considered diabetic. After 12 weeks of diabetes, the mice were anaesthetized by a cocktail of ketamine (85 mg/kg) and xylazine (8.5 mg/kg) via intraperitoneal injections followed by cardiac puncture. Vascular function and left ventricular morphology were assessed using wire myography in the absence or presence of pharmacological blockers and histology, respectively.
Results: After 12 weeks of diabetes, sensitivity to the endothelium-dependent vasodilator, acetylcholine was reduced in the mesenteric artery (pEC50; CB+placebo 7.57±0.11 vs STZ+placebo 6.76±0.07, n=12-13, P<0.0001). This was accompanied by an increased contribution of vasoconstrictor prostanoids and a decrease in endothelium-derived hyperpolarisation (EDH)-mediated relaxation. Serelaxin restored mesenteric artery endothelial function (pEC50; 7.19±0.12, n=12) by increasing nitric oxide (NO), but not EDH-mediated relaxation. It also normalized the contribution of vasoconstrictor prostanoids and suppressed diabetes-induced hyper-responsiveness to angiotensin II (Ang II). In the left ventricle, diabetes promoted significant hypertrophy (cardiomyocyte cross-sectional area; n=6, P<0.0001) and fibrosis (interstitial collagen area; n=6, P=0.006), whereby serelaxin effectively reversed cardiomyocyte hypertrophy through a reduction in B-type natriuretic peptide gene expression. Interestingly, serelaxin did not induce any significant effects in attenuating diabetes-induced cardiac fibrosis.
Conclusions: In vivo serelaxin treatment for two weeks attenuated diabetes-induced endothelial dysfunction in the mesenteric artery of STZ mice. This was partly attributed to a serelaxin-mediated reduction in the contribution of vasoconstrictor prostanoids and Ang II to vascular function, as well as an up-regulation of NO-mediated relaxation in the mesenteric artery. Favourable effects of serelaxin were also evident in the left ventricle because there was a reduction in diabetes-induced cardiomyocyte hypertrophy. This study suggests a potential role for serelaxin as an adjunctive agent in the treatment of diabetes-related cardiovascular complications.