Syringin attenuates insulin resistance via adiponectin-mediated suppression of low-grade chronic inflammation and ER stress in high-fat diet-fed mice

In the treatment of type 2 diabetes, improvements in glucose control are often linked to side effects such as weight gain and altered lipid metabolism, increasing the risk of cardiovascular disease. It is therefore important to develop antidiabetic drugs that exert beneficial effects on insulin sensitivity and lipid metabolism at the same time. Here we demonstrate that syringin, a naturally occurring glucoside, improves glucose tolerance without increased weight gain in high-fat diet-induced obese mice. Syringin augmented insulin-stimulated Akt phosphorylation in skeletal muscle, epididymal adipose tissue (EAT), and the liver, showing an insulin-sensitizing activity. Syringin-treated mice also showed markedly elevated adiponectin production in EAT and suppressed expression of pro-inflammatory cytokines in peripheral tissues, indicating a significant reduction in low-grade chronic inflammation. Additionally, syringin enhanced AMP-activated protein kinase activity and decreased the expression of lipogenic genes in skeletal muscle, which was associated with reduced endoplasmic reticulum (ER) stress. Taken together, our data suggest that syringin attenuates HFD-induced insulin resistance through the suppressive effect of adiponectin on low-grade inflammation, lipotoxicity, and ER stress, and show syringin as a potential therapeutic agent for prevention and treatment of type 2 diabetes with low risk of adverse effects such as weight gain and dysregulated lipid metabolism.