Semipurified Fractions from the Submerged-Culture Broth of Agaricus blazei Murill Reduce Blood Glucose Levels in Streptozotocin-Induced Diabetic Rats

摘要

Hypoglycemic action of semipurified fractions from hot-water extracts of the submerged-culture broth of Agaricus blazei Murill was examined in streptozotocin (60 mg/kg, intraperitoneal)-induced diabetic male Sprague-Dawley rats, relative to the diabetes drug metformin. The hot-water extract, treated with ethanol to remove β-glucans and glycoproteins, was freeze-dried, and fractionated into hexane, chloroform, ethyl acetate (EA), and butanol fractions. The EA fraction (EAF; 200 mg/kg body weight) reduced (p < 0.05) the blood glucose level in the oral glucose tolerance test, relative to the other fractions and control. In a 14 day-treatment study, diabetic rats treated with the EAF displayed a suppressed blood glucose level and elevated plasma insulin and glucose transport-4 proteins; the reactions occurred in a dose-dependent manner (200 and 400 mg/kg body weight) compared to those in control animals. The EAF reduced the levels of triglyceride and cholesterol in plasma, the activity of glutamate-oxaloacetate transaminase and glutamate-pyruvate transaminase in blood, and the content of thiobarbituric acid reactive substance in the liver and kidney. The hypoglycemic efficacy of the EAF (400 mg/kg body weight) was similar to that of metformin (500 mg/ kg body weight). The EAF contained substantial amounts of isoflavonoids including genistein, genistin, daidzein, and daidzin, which could have contributed to the fraction's hypoglycemic action. These results indicate that the hot-water extract of the submerged-culture broth of Agaricus blazei contains an EAF having potent hypoglycemic action, which could be useful in the treatment of diabetes mellitus.