Ganoderma lucidum Extract Reduces Insulin Resistance by Enhancing AMPK Activation in High-Fat Diet-Induced Obese Mice

Ganoderma lucidum is used widely in oriental medicine to treat obesity and metabolic diseases. Bioactive substances extracted from G. lucidum have been shown to ameliorate dyslipidemia, insulin resistance, and type 2 diabetes in mice via multiple 5' AMP-activated protein kinase (AMPK)-mediated mechanisms; however, further studies are required to elucidate the anti-obesity effects of G. lucidum in vivo. In this study, we demonstrated that 3% G. lucidum extract powder (GEP) can be used to prevent obesity and insulin resistance in a mouse model. C57BL/6 mice were provided with a normal diet (ND) or a high-fat diet (HFD) supplemented with 1, 3, or 5% GEP for 12 weeks and the effect of GEP on body weight, liver, adipose tissue, adipokines, insulin and glucose tolerance (ITT and GTT), glucose uptake, glucose-metabolism related proteins, and lipogenesis related genes was examined. GEP administration was found to reduce weight gain in the liver and fat tissues of the mice. In addition, serum parameters were significantly lower in the 3% and 5% GEP mice groups than in those fed a HFD alone, whereas adiponectin levels were significantly higher. We also observed that GEP improved glucose metabolism, reduced lipid accumulation in the liver, and reduced adipocyte size. These effects may have been mediated by enhanced AMPK activation, which attenuated the transcription and translation of lipogenic genes such as fatty acid synthase (FAS), stearoyl-CoA desaturase 1 (SCD1), and sterol regulatory element-binding protein-1c (SREBP1c). Moreover, AMP-activated protein kinase (AMPK) activation increased acetyl-CoA carboxylase (ACC), insulin receptor (IR), IR substrate 1 (IRS1), and Akt protein expression and activation, as well as glucose transporter type 1/4 (GLUT1/4) protein production, thereby improving insulin sensitivity and glucose metabolism. Together, these findings demonstrate that G. lucidum may effectively prevent obesity and suppress obesity-induced insulin resistance via AMPK activation.