Evaluation of hypoglycemic activity of selected medicinal plants from Central Uganda in alloxan induced diabetic rats
Seble, Shambel Enyew
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Background: In Uganda diabetes mellitus affects 1.7% of the general population. It is a chronic condition that requires prolonged treatment in specialized health facilities, especially the use of oral hypoglycemic agents (OHAs) in type 2 DM. However, these drugs are expensive, associated with side effects, and not easily accessible for the majority of the people. As a result many people in Uganda have turned to medicinal herbs including: fruits of Solanum anguivi, leaves of Chenopodium opulifolium, fruits of Solanum melongena, leaves of Brassica oleracea and seeds of Arachis hypogeae. These medicinal herbs are considered to be safe, easily accessible and relatively cheap and also reported in ethnobotanical surveys for being used in management of type 2 DM. However, their safety and efficacy have not yet been documented and scientifically evaluated. Objective: To evaluate the hypoglycemic activity of selected medicinal plants used to treat signs and symptoms of type 2 diabetes mellitus in Central Uganda. Materials and Methods: This study was undertaken to investigate the hypoglycemic effects of selected medicinal plants in alloxan induced diabetic rats, their safety in mice and the various classes of compounds in each extract. The five selected medicinal plants including fruits of Solanum anguivi, leaves of Chenopodium opulifolium, fruits of Solanum melongena, leaves of Brassica oleracea and seeds of Arachis hypogeae. These plants were collected, identified, processed and extracted using ether and ethanol (75%, v/v) by sequential extraction. Screening of the five selected medicinal plants for hypoglycemic activity was done and the two most active medicinal plants were selected for further study. Type 2 DM was induced in rats fasted for 18 hours using alloxan (120 mg/kg bwt). Glibenclamide and cooking oil + normal saline were used as controls. Extracts of S. anguivi fruits and C. opulifolium leaves were administered at doses of 1000, 500 and 250 mg/kg bwt. Blood glucose levels (BGL) were measured using glucometer at 0, 30, 60, 90, 120 and 180 minutes data were analyzed using Student’s t – test (Stata version 11). Results: Diabetic rats treated with ether extract of S. anguivi fruits exhibited hypoglycemic activity at doses of 250, 500 and 1000 mg/kg bwt respectively with maximum reduction of 50.8% %, 26.7%% and 48.8%% respectively as compared to standard drug glibenclamide (10 mg/kg bwt) with maximum % reduction of 37.52%. Diabetic rats treated with the ethanol extract of S. anguivi fruits at doses of 250, 500 and 1000 mg/kg bwt produced hypoglycemic activity with a maximum reduction of 35.4%, 12.3% and 20.0% respectively compared to standard drug glibenclamide (10 mg/kg) with maximum % reduction of 37.52%. Diabetic rats treated with ether extract of C. opulifolium leaves at doses of 250, 500 and 1000 mg/kg bwt showed dose - dependent hypoglycemic activity with a maximum reduction of 24.8%, 18.4% and 50.6% respectively. However, the reduction by doses of 250 and 500 mg/kg bwt was not statistically significant throughout the experimental period. Diabetic rats treated with ethanol extract of C. opulifolium leaves at doses of 250, 500 and 1000 mg/kg bwt experienced hypoglycemic activity with maximum reduction of 23.5%, 27.6% and 32.2% respectively after 2 hours of extract administration. The hypoglycemic effect of the ether and ethanol extracts of Solanum anguivi fruits and Chenopodium opulifolium leaves could possibly be due to the presence of alkaloids, tannins, steroids and triterpenoids, anthraquinones, flavonoids and saponins present in these extracts. There was no death of the mice at different doses of the ether and ethanol extracts of Solanum anguivi fruits and Chenopodium opulifolium leaves even at the limit dose of 5000 mg/kg bwt according to the OECD (2001) guideline. Absence of death at the highest limit dose 5000 mg/kg bwt indicates that these medicinal plants are considered relatively safe and hence their increased use as medicine in Uganda by TMP and the local communities. Conclusions: S. anguivi fruits and C. opulifolium leaves contain active principles with hypoglycemic activity and the effect was comparable to glibenclamide in most cases. The different extracts of Solanum anguivi fruits and Chenopodium opulifolium leaves considered relatively safe as no death was observed up to 5000 mg/kg bwt limit dose. Therefore, these medicinal plants are considered to be effective and safe hence, can be used as an alternative treatment for management of type 2 DM and their use by traditional medical practitioners (TMP) and the local communities.