Sulfated Polysaccharides from Enteromorpha prolifera Attenuate Lipid Metabolism Disorders in Mice with Obesity Induced by a High-Fat Diet via a Pathway Dependent on AMP-Activated Protein Kinase

Obesity-related metabolic diseases have recently evoked worldwide attention. Studies have demonstrated that Enteromorpha polysaccharide (EP) exerts lipid-lowering effects, but the underlying mechanism remains unclear.We investigated whether EP regulates lipid metabolism disorders in mice with high-fat diet (HFD)-induced obesity via an AMP-activated protein kinase (AMPK)-dependent pathway.Six-week-old male C57BL/6J mice (18 ± 2 g) were fed a normal diet (ND; 10% energy from fats) or an HFD (60% energy from fats) for 6 weeks to induce obesity and treated intragastrically with EP (200 mg/kg body weight) or distilled water (10 mL/kg body weight) for 8 weeks. Biochemical indicators, AMPK-dependent pathways, and lipid metabolism-related genes were evaluated to assess the effects of EP on HFD-induced lipid metabolism disorders. The essential role of AMPK in the EP-mediated regulation of lipid metabolism was confirmed using HFD-fed male Ampka2-knockout mice (aged 6 weeks; 17 ± 2 g) treated or not treated with the above-mentioned dose of EP. The data were analyzed by t-tests, 2-factor and 1-way ANOVAs.Compared to the ND, the HFD resulted in a greater body weight (24.3%), perirenal fat index (2.2-fold), and serum total cholesterol (24.66%) and LDL cholesterol (1.25-fold) concentrations (P < 0.05) and dysregulated the AMPK-dependent pathway and the expression of most lipid metabolism-related genes (P < 0.05). Compared to the HFD, EP treatment resulted in a lower perirenal fat index (31.22%) and LDL cholesterol concentration (23.98%) and partly reversed the dysregulation of the AMPK-dependent pathway and the altered expression of lipid metabolism-related genes (P < 0.05). Ampka2 knockout abolished the above-mentioned effects of EP in obese mice and the EP-mediated effects on the expression of lipid metabolism-related genes (P > 0.05).These findings suggest that EP can ameliorate lipid metabolism disorders in mice with HFD-induced obesity via an AMPK-dependent pathway.