ANTIDIABETIC POTENTIAL OF FLAVONOID-RICH EXTRACT OF MIRACLE TREE (Synsepalum dulcificum) LEAVES ON STREPTOZOTOCIN-INDUCED DIABETIC WISTAR RATS

Abstract

Diabetes mellitus (Dm) is one of the world's main cause of disability and death. Long-term diabetes is associated with liver dysfunction and other comorbidities. Synsepalum dulcificum (S.d) pulp has been reported to possess antidiabetic property. The main objective of this study was to investigate antidiabetic potentials of a flavonoid-rich extract of S.d leaves on fructose/streptozotocin (STZ)-induced diabetic Wistar rats. The crude extract of the leaves was obtained by extraction in 80% methanol for 72 hours. The flavonoid-rich extract was prepared from the crude methanolic extract. Both extracts were kept in the refridgerator until when required. A total number of seventy-seven (77) Wistar rats were divided into eleven (11) Groups with seven (7) animals apiece. Type 2 diabetes mellitus (T2Dm) was induced intraperitoneally with freshly prepared solution of STZ (40 mg/kg body weight) to overnight fasted Wistar rats after administering 10% fructose solution for two weeks. Animals that had fasting blood glucose concentration above 250 mg/dL were considered diabetic. Animals in groups I and II were negative and positive controls respectively, groups III, IV, V, VI and VII were diabetic Groups that were treated with the extracts. Groups 1 and II received the normal drinking water. Groups III and IV, V and VI were treated with 30 mg/kg body weigh (b.w) crude extract of S.d leaves (CSD), 60 mg/kg b.w CSD, 30 mg/kg b.w flavonoid-rich extract of S.d leaves (FSD) and 60 mg/kg b.w FSD respectively. The treatment lasted for 21 days. Before sacrifice, Oral Glucose Tolerance Test (OGGT) was carried out with animals in the normal control and diabetic animals to determine the clearance rate of glucose after a 2g/kg b.w D-glucose administration. At the end of the experimental period, overnight fasted Wistar rats were euthanized by cervical dislocation. Serum concentrations of glucose(Glu), total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) were estimated in the serum of the Wistar rats. Activities of glucose metabolizing enzyme {glucose-6-phosphate dehydrogenase (G6PDH)}, major liver function enzymes {aspartate transaminase (AST) and alanine transaminase (ALT)} were determined in the serum of experimental animals. Enzyme biomarkers of hepatic oxidative stress (superoxide dismutase, glutathione-s-transferase) and non-enzyme (reduced glutathione) were also quantitated. Hepatic lipid peroxidation level was thereafter determined in the liver homogenates. After result analysis, Serum concentrations of Glu, TC, TG, LDL-C, AST ALT in the diabetic control (DBC) groups were increased significantly. The values observed in the normal control group were reduced significantly and were not statistically different (p0.05) from the flavonoid-treated diabetic groups (FTDGs). Serum G6PDH activity and HDL-C concentrations in the normal and FTDGs were increased significantly and statistically different (p0.05) from the same values in the DBC group. Hepatic biomarkers of oxidative stress in the FTDGs were not statistically different from the normal control group (p0.05) and the results were statistically different from the DBC group (p0.05). The results obtained suggest that particular dietary components present in the plant leaves, such as flavonoids, assist in T2Dm amelioration in ways other than those already followed by the currently available therapeutic approaches.