EFFECT OF BITTER LEAF (Vernonia amygdalina) SAPONIN-RICH EXTRACT ON STREPTOZOTOCIN-INDUCED DIABETES IN WISTAR RATS

Abstract

Vernonia amygdalina is widely used as a daily green vegetable or herb to treat malaria and diabetes. The aim of the study was to evaluate the antioxidant and antihyperglycemic potentials of saponin-rich extracts of V. amygdalina in streptozotocin (STZ)-induced diabetic rats. Powdered leaf was soaked in 80% methanol for 48 hours, filtered and lyophilized to obtain the crude methanolic extract. The crude methanolic extract was subjected to solvent partitioning to obtain the saponin extract. Qualitative tests (frothing test, emulsifying property, hemolytic effect on red blood cells (RBC) and thin layer chromatography was carried out to confirm the presence of saponin. Diabetes was induced by administering intraperitoneally a freshly prepared solution of STZ (65 mg/kg body weight) in ice-cold 0.1M citrate buffer (pH 4.5) to overnight fasted rats. Normal animals were injected with citrate buffer alone. Seventy-two hours after STZ injection Wistar rats with blood glucose level of ≥250mg/dl and above was considered diabetic. The animals were divided into five groups with six animals in each group. Animals in groups I served as normal animals and receive distilled water and citrate buffer. Animals in groups II were diabetic animals treated with the standard drug glibenclamide (0.5 mg/kg body weight), group IV and V animals were diabetic rats with saponin extract (20 mg/kg & 60 mg/kg body weight respectively) for 14 days while group III animals were diabetic untreated group. The fasting blood glucose was estimated every week of the study using Accu Check glucometer. The animals were sacrificed 24 hours after the last administration. The assessment of the antihyperglycemic activity of the extracts on STZ-induced diabetic rats was determined by estimating the blood glucose level, activities of plasma lactate dehydrogenase and activity of carbohydrate metabolizing enzyme (glucose-6-phosphate dehydrogenase) in the liver. Indices of oxidative stress (glutathione concentration and malondialdehyde level), activities of the major antioxidant enzymes (catalase and glutathione peroxidase) as well as lipid profile (total cholesterol, triglyceride, high density lipoprotein & low density lipoprotein) were evaluated. Histological assessment was also performed. The result revealed crude and saponin-rich extract with percentage yield of 13.9 and 7.2 per gm of extract respectively. The TLC showed presence The TLC showed presence of crude extract with RF 0.37, saponin with RF 0.44, saponin with RF 0.41 and crude extract with RF 0.38. A significant reduction (p<0.05) in fasting blood glucose level was observed from the first to second week of extract treatment while increased liver activity of LDH, G6PDH and catalase was observed in treated diabetic rats. The triglyceride, total cholesterol, low density lipoprotein and very low density lipoprotein cholesterol levels were increased significantly (P<0.05) in untreated diabetic group as compared with reduction in the control group and saponin-extract treated groups. Also, the level of high density lipoprotein cholesterol was reduced significantly (p<0.05) in untreated diabetic group when compared with the groups treated with the extract. Furthermore, STZ-induced increase in liver MDA concentration as well as reduction in GSH and CAT activity observed in the induced group was ameliorated in in diabetic rats treated with saponin extracts. The observed effects of the extract was similar to those observed for the standard drug, glibenclamide. V. amygdalina saponin-rich extracts also ameliorated the severity of degenerative changes in STZ-induced diabetes on pancreatic β-cells. The result suggest that the antidiabetic property of the saponin-rich extracts of V. amygdalina leaf could be due to its ability to enhance production of antioxidants against generation of free radicals and modulating the activities of the carbohydrate metabolizing enzymes investigated.