Pectic Bee Pollen Polysaccharide from Rosa rugosa Alleviates Diet-Induced Hepatic Steatosis and Insulin Resistance via Induction of AMPK/mTOR-Mediated Autophagy

Despite it is used as a nutraceutical against diabetes and obesity, the mechanism of action of bee pollen is still unclear. Pectic bee pollen polysaccharide (RBPP-P) was isolated from Rosa rugosa, and its structure was characterized by (13)C-NMR and Fourier transform-infrared spectroscopy (FT-IR). Using high glucose and fatty acids-treated HepG2 cells and high fat diet (HFD)-induced obesity mice, we detected its effect on insulin function and lipid metabolism based on autophagy. RBPP-P contained arabinogalactan, rhamnogalacturonan I, and homogalacturonan domains. In vivo studies demonstrated that RBPP-P markedly ameliorated insulin resistance, glucose intolerance, and liver steatosis in obese mice. The suppressive effects of RBPP-P on liver steatosis and triglyceride content were mediated by increased autophagy and lipase expression in liver. In AMPK knockdown cells (prkaa 1/2(−/−) MEF) and HFD-fed mice tissues (liver, gonadal white adipose, and inguinal white adipose), RBPP-P enhanced autophagy in AMPK/mTOR-dependent way in liver, but not in adipose tissue. These findings demonstrated that bee pollen polysaccharide alleviated liver steatosis and insulin resistance by promoting autophagy via an AMPK/mTOR-mediated signaling pathway, suggesting that RBPP-P could be a novel therapeutic agent used for the treatment of obesity and diabetes.