Anti-Diabetic Effect of a Flavonoid and Sitosterol - Rich Aqueous Extract ofPleurotus tuberregiumSclerotia in Alloxan-Induced Diabetic Rabbits

Objective: Traditionally prepared infusions and decoctions are commonly used in the management of diabetes mellitus, in southern Nigeria; one of such is the aqueous extract of the sclerotia of Pleurotus tuberregium (“usu” milk). In this study, the effects of the extract on the body weights, tissue/ organ weights, fasting blood glucose, blood/plasma lipid profiles and atherogenic indices were investigated in normal and alloxan-induced diabetic rabbits. Methods: Diabetes mellitus was induced by the injection of alloxan (120 mg/kg body weight) via the marginal ear vein. The extract was administered orally at 100, 200 and 300 mg/kg to normal and diabetic rabbits; while metformin was administered at 50 mg/kg. The crude extract was analyzed by gas chromatography, coupled to flame ionization detector. Results: Thirty-one known flavonoids were detected, consisting mainly of isoquercetin (28.5%), luteolin (24.3%), quercetin (18.8%) and kaempferol (11.3%). Sitosterol (82.0%) and stigmasterol (12.5%) were the most abundant of the seven phytosterols detected. Compared to the diabetic control, the treatment significantly (p<0.05) lowered the weights of the kidney and liver, as well as the levels of blood glucose and triglyceride, plasma VLDL, LDL and non-HDL cholesterol, atherogenic index of plasma, cardiac risk ratio, atherogenic coefficient and Castelli’s risk index II. It, however, significantly (p<0.05) increased plasma HDL cholesterol, without significantly affecting blood total cholesterol levels. Conclusion: This study showed that the extract was hypoglycemic, and improved lipid profile and atherogenic indices, thus highlighting its cardioprotective potential, thereby supporting its use in the management of diabetes mellitus.