Hypoglycemic effect of leafy vegetables from Ankole and Teso sub-regions of Uganda: preclinical evaluation using a high fat diet-streptozotocin model

Abstract

Abstract Background: The hypoglycemic effect of the most frequently eaten leafy vegetables in Ankole and Teso sub-regions of Uganda, Hibiscus sabdariffa L. (Hs), Vigna unguiculata L. Walp (Vu) and Solanum nigrum L. (Sn) was studied in an attempt to explain the remarkable difference in prevalence of hyperglycemia observed in the two sub-regions. Methods: Phytochemical screening was done and the phytochemicals in the Aqueous leaf extracts (ALEs) of Hs, Vu and Sn were quantified by means of UV-visible spectrophotometer using the standard calibration graph. The phytochemical concentration was given as standard equivalent of the vegetable fresh weight. The extracts were then tested for their hypoglycemic activity in high fat diet-streptozotocin (HFD-STZ) induced diabetic Wistar rats. These extracts were administered to diabetic rats at 100- and 200 mg/kg/body weight, orally once a day for 12 days. Glibenclamide (a standard drug used to treat diabetes mellitus) was similarly given to a positive control group to support the results at a dose of 5 mg/kg/body weight. Diabetic and normal control groups received vehicle (distilled water) daily for the same period of time. Results: More phytochemical compounds were found in aqueous than methanol solvent. The highest quantity of total phenolic (TP) compounds was found in Hs 66.11±0.19 Gallic Acid Equivalent (GAE) (µg/mg fresh weight), highest quantity of total flavonoids (TF), total tannins (TT) and total alkaloids (TA) were found in Sn (71.35±0.14 Quercetin equivalent of flavonoids (QEF), 172.17±8.69 GAE and 119.71±3.64 Atropine equivalent (µg/mg, fresh weight) respectively, whereas the total saponins (TS) were highest in Vu 125.78±0.47 Diosgenin equivalent of Saponin per mg of fresh weight of the vegetable. Conclusions: The ALEs of Hs lowered the fasting blood glucose (FBG) levels most significantly (65%) at the dose of 200 mg/kg; Sn lowered the FBG by 57%, while Vu lowered the FBG by 43%, compared to the diabetic control. Vegetable hypoglycemic effects were comparable with glibenclamide (66%). Animal body weights showed insignificant increases by the end of the study. These vegetables can be considered effective in prevention and management of hyperglycemia.