ABSTRACT
<b>Objective:</b> The water-soluble extract of <i>Ganoderma lucidum</i> mycelia (WER), which is used as a health food, reduced hyperglycemia and enhanced glucose transporter 4 (GLUT4) translocation to the plasma membrane in skeletal muscle and adipose tissue in KK-<i>A</i><sup>y</sup><i> </i>mice, a type 2 diabetic animal model with obesity.In order to elucidate the reduction of hyperglycemia by WER, we investigated the translocation of glucose transporter 4, glucose uptake and associating signal transduction in rat skeletal muscle (L6) cells. <b>Method:</b> The glucose uptake was analyzed with radioactive 2-deoxy-D-glucose.The localization of GLUT4 in L6 cells treated with various concentrations of WER was analyzed with immunohistochemical staining and Western blot technique.As a positive control, insulin or troglitazone was used in these experiments.Furthermore, the activation of intracellular signaling pathways by Western blot analysis and the influence of glucose uptake using four kinds of inhibitors (LY294002 as potent PI3K inhibitor, rapamycin as mTOR inhibitor, Gö6983 as broad PKC inhibitor, compound C as AMPK inhibitor) was evaluated. <b></b><b>Results: </b>GLUT4 protein content in the plasma membrane was induced in a dose-dependent manner of WER without increasing the gene expression and amount of total protein in the L6 cells and the glucose uptake was augmented with increasing the amount of GLUT4 translocated on the plasma membrane.The phosphorylation of phosphatidylinositol-3 kinase (PI3K), Akt and acetyl CoA carboxylase (ACC) were induced in a concentration dependent manner and inhibited by the above inhibitors except rapamycin. <b>Conclusion: </b>These results indicate that the hypoglycemic effect of some material(s) in WER may be due to the enhancement of glucose uptake through GLUT4 translocation on the plasma membrane by activating the PI3K/Akt pathway through improving insulin resistance.
ABSTRACT
<b>Objective:</b> Recently, we reported that long-term intake of a water-soluble extract from culture medium of <i>Ganoderma lucidum</i> mycelia (WER) reduced hyperglycemia and enhanced glucose transporter-4 (GLUT4) translocation to the plasma membrane in skeletal muscles and adipose tissue in KK-<i>A<sup>y</sup></i> mice, a type 2 diabetic animal model with obesity. In the present study, we investigated the effect of WER on hepatic carbohydrate metabolism.<br> <b>Methods: </b>Female KK-<i>A<sup>y</sup></i> mice were given free access to water and high-fat food containing 0.5% WER for 8 weeks, and blood glucose levels were assessed every week. At the end of the experimental period, the expression and activities of sugar metabolic enzymes in the liver were determined by Real Time RT-PCR and each activity measurement method. Also, the amount of glycogen was measured by anthrone-sulfuric acid method. Furthermore, the expression level of GLUT2 and activation of AMP kinase (AMPK) and glycogen synthase kinase 3β (GSk3β) was also determined by western blot analysis.<br> <b>Results: </b>The mice with the high-fat ingestion showed a gradual increase in the levels of blood glucose and body weight. In the WER-treated mice, the blood glucose level was suppressed after 2 weeks of intake. The gene expression and enzyme activities of both glucose-6-phosphatase and phosphoenolpyruvate carboxykinase were suppressed, whereas those of glucokinase were increased in the mice with WER intake and pioglitazone administration. The accumulation of glycogen was increased. Moreover the expression of GLUT2 and phosphorylation levels of AMPK and GSk3β were also increased in the mice with WER intake.<br> <b>Conclusion: </b>These results indicate that WER affects hepatic carbohydrate metabolism, which may derive from the suppression of gluconeogenesis through the modulation of related enzymes and enhancement of glucose uptake, glycolysis and glycogen synthesis.<br>