α-glucosidase inhibitory in vitro and antidiabetic activity in vivo of Osmanthus fragrans

In this study, EtOAC extract of Osmanthus fragrans were evaluated by a-glucosidaseinhibitory activity in in-vitro, and showed stronger inhibiting activity of a-glucosidase (IC50=12.5 μg/ml) compared with acarbose as positive control (IC50=1081.27 μg/ml). Based on the result, two active compounds of ursolic acid and oleanolic acid were isolated from EtOAC extract of O. fragrans and exhibited great inhibitory activity of a-glucosidase (IC50=3.38 and 3.3 μg/ml, respectively). The antidiabetic effect of EtOAC extract, ursolic acid and oleanolic acid were investigated on diabetic mice induced by tail vein injection with alloxan. Compared with diabetic control group, oral administration of ursolic acid (300 mg/kg) and oleanolic acid (120 and 40 mg/kg) could significantly decrease the fasting blood glucose and postprandial blood glucose, oral administration of EtOAC extract (160 mg/kg), ursolic acid (300 mg/kg) and oleanolic acid (120 and 40 mg/kg) could significantly increase liver glycogen content. Each treatment group could significantly decrease serum TG (triglyceride) level and MDA (malondialdehyde) content in diabetic rats. Oral administration of EtOAC extract (160 mg/kg), ursolic acid (100 mg/kg) and oleanolic acid (120) could significantly decrease serum TC (total cholesterol) level, and oral administration of EtOAC extract (500 mg/kg), ursolic acid (300 mg/kg) could significantly increase SOD (superoxide dismutase) level. Results demonstrate the antidiabetic and antioxidant potential of O. fragrans and suggest that the plant may have therapeutic value in diabetes and related complications.   Key words: Osmanthus fragrans, α-glucosidase, antidiabetic activity.