Irisin improves endothelial function in type 2 diabetes through reducing oxidative/nitrative stresses

Vascular complications are the major causes of death in patients with diabetes, and endothelial dysfunction is the earliest event in vascular complications of diabetes. It has been reported that plasma irisin level is significantly reduced in patients with type 2 diabetic patients. The present study aimed to investigate whether irisin improved endothelial function in type 2 diabetes as well as the underlying mechanisms. The type 2 diabetes model was established by feeding C57BL/6 mice with high-fat diet. The type 2 diabetic mice exhibited reduced serum irisin level and impaired endothelial function. Irisin treatment (0.5 mg/kg/d) for two weeks improved vascular function based on the evaluation of endothelium-dependent vasorelaxation and p-VASP levels. To investigate the direct endothelial protective effects of irisin, diabetic aortic segments were incubated with irisin (1 μg/ml) ex vivo. Exposure to irisin improved endothelium-dependent vasorelaxation of diabetic aortas. Mechanically, the diabetic aortic segments exhibited increased oxidative/nitrative stresses. Irisin reduced the diabetes-induced oxidative/nitrative stresses evidenced by reducing overproduction of superoxide and peroxynitrite, and down-regulation of iNOS and gp91phox. To further investigate the protective effects of irisin on endothelial cells and the underlying mechanisms, human umbilical vein endothelial cells (HUVECs) cultured in high-glucose/high-fat (HG/HF) medium were pre-incubated with irisin. Irisin (1 μg/ml) reduced the oxidative/nitrative stresses and apoptosis induced by HG/HF in HUVECs probably via inhibiting activation of PKC-β/NADPH oxidase and NF-κB/iNOS pathways. Taken together, irisin alleviates endothelial dysfunction in type 2 diabetes partially via reducing oxidative/nitrative stresses through inhibiting signaling pathways implicating PKC-β/NADPH oxidase and NF-κB/iNOS, suggesting that irisin may be a promising molecule for the treatment of vascular complications of diabetes.