Pomegranate peel polyphenols alleviate insulin resistance through the promotion of insulin signaling pathway in skeletal muscle of metabolic syndrome rats

Insulin resistance (IR) has been considered to be an important causative factor of metabolic syndrome (MetS). The present study investigated whether pomegranate peel polyphenols (PPPs) could prevent the development of MetS by improving IR in rats. Male Sprague-Dawley (SD) rats were fed high fat diet (HFD) to induce MetS and supplemented with different dosages of PPPs for 12 weeks. The results showed that HFD-induced insulin resistant rats had disordered metabolism of blood glucose, blood lipid, and terrible muscle fiber morphology when compared with normal diet-fed rats, but PPPs treatment at a dosage of 300 mg/kg·day significantly reversed these negative effects. Moreover, in skeletal muscle tissue of insulin resistant rats, PPPs treatments significantly increased the protein expressions of insulin receptor (InsR) and phosphorylated insulin receptor substrate 1 (IRS-1), stimulated peroxisome proliferator activated receptor gamma (PPARγ) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT/PKB) signaling pathway, and aggrandized the protein levels of phosphorylated glycogen synthase kinase-3β (GSK-3β) and glucose transporter 4 (GLUT4). Our results suggest that PPPs possess of the beneficial effects on alleviating IR by enhancing insulin sensitivity and regulating glucose metabolism.