Therapeutic potential of octyl gallate isolated from fruits of Terminalia bellerica in streptozotocin-induced diabetic rats

Context: Medicinal plants are a potential source of antidiabetic drugs. Terminalia bellerica Roxb. (Combretaceae) is used in Indian traditional systems of medicine to treat diabetes mellitus. Objective: The aim of this study was to isolate and identify antihyperglycemic principle(s) from the fruits of T. bellerica and assess the bioactivity in streptozotocin (STZ)-induced diabetic rats. Materials and methods: Bioassay-guided fractionation was followed to isolate the active compound(s), structure was elucidated using H-1 and C-13 NMR, IR and mass spectrometry and administered intragastrically to diabetic Wistar rats at different doses (5, 10 and 20 mg/kg, body weight) for 28 d. Plasma glucose, insulin, C-peptide and other biochemical parameters were studied. Results: Octyl gallate (OG) isolated first time from the fruit rind of T. bellerica significantly (p < 0.05) reduced plasma glucose to near normal values (108.47 +/- 6.9 mg/dl) after 14 d at the dose of 20 mg/kg. In addition, OG significantly increased plasma insulin, C-peptide, total protein, albumin, tissue glycogen, body weight and markedly decreased serum total cholesterol, triglyceride, LDL-cholesterol, urea, uric acid and creatinine in diabetic rats. Also OG restored the altered regulatory enzymes of carbohydrate metabolism. Discussion and conclusion: OG might have augmented the secretion of insulin by the modulation of cAMP and intracellular calcium levels in the beta cells of the pancreas. Our findings indicate that OG isolated first time from the fruit rind of T. bellerica has potential antidiabetic effect as it augments insulin secretion and normalizes the altered biochemical parameters in experimental diabetic rat models.