ANTI-DIABETIC EFFECT OF AQUEOUS EXTRACT OF SPHENOSTYLIS STENOCARPA (AFRICAN YAM BEAN) ON ALLOXAN-INDUCED DIABETIC RATS

Abstract

The study was undertaken to determine the anti-diabetic effect of the aqueous extract of Sphenostylis stenocarpa in alloxan-induced diabetic rats to see if this plant could be used in the management of diabetes mellitus which is a global disease. The phytochemical constituents of the extract showed the presence of flavonoids, soluble carbohydrates (1.916 ± 0.003 mg/100g), alkaloids (3.426 ± 0.003 mg/100g), saponins (2.590 ± 0.003 mg/100g), phenols (5.387 ± 0.002 mg/100g), cyanogenic glycosides (0.0114 ± 0.006) and proteins (12.258 ± 0.002 mg/100g). The acute toxicity study on the extract showed no mortality or adverse reaction by the test mice up to the dose of 5000 mg/kg body weight which indicates it is safe for consumption. The sub-acute toxicity studies showed no significant (p > 0.05) difference in the glucose concentration, total cholesterol, triacylglycerol (TAG), high density lipoprotein (HDL) cholesterol and low density lipoprotein (LDL) cholesterol, aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) of the normal mice after treatment with the extract for 7 days at graded doses (100 and 1000 mg/kg body weight) compared to the control mice. The result of the 14 days treatment with the extract on alloxan-induced diabetic rats at graded doses of 200 mg/kg b.w and 400 mg/kg b.w significantly (p < 0.05) lowered the glucose concentration from 330 ± 45.9 to 126.00 ± 3.05 mg/dl and 413.67 ± 59.76 to 115.00 ± 2.89 mg/dl respectively compared to the diabetic control rats which showed elevation in the glucose concentration from (349.67 ± 77.076 to 429.67 ± 50.51 mg/dl) and the effect was comparable with the standard drug metformin which reduced from (494. 00 ± 0.577 to 97.67 ± 4.51 mg/dl). The extract at 200 mg/kg dose showed significant (p < 0.05) reduction in AST (42.00 ± 0.667 IU/L) and ALP (74.00 ± 2.12 IU/L) activities and no significant difference in ALT (57.50 ± 3.18 IU/L) activity respectively compared to the diabetic untreated rats (45.00 ± 3.48, 94.67 ± 1.20 and 56.00 ± 0.57 IU/L) while 400 mg/kg dose showed significant (p < 0.05) reduction in the activities of the liver function enzyme AST, ALT and ALP (40.00 ± 1.13, 44.00 ± 2.309 and 59.50 ± 10.11 IU/L) respectively when compared to diabetic untreated rats. The diabetic rats treated with standard drug metformin showed significant (p < 0.05) reduction in the ALT and ALP (50. 00 ± 2.12 and 59.60 ± 6.12 IU/L) activities respectively and no significant (p > 0.05) difference in the AST (44.67 ± 0.667 IU/L) activity compared to diabetic rats as seen above. Measurement of the serum lipid profile in diabetic rats treated with 400 mg/kg b.w of the extract showed significant (p < 0.05) reduction in the total cholesterol (3.10 ± 0.28 mmol/l), TAG (1.45 ± 0.05 mmol/l) LDL cholesterol (1.60 ± 0.59 mmol/l) concentrations and a significantly (p < 0.05) higher concentration of high density lipoprotein (HDL)-cholesterol (1.20 ± 0.17 mmol/l) concentration respectively when compared to diabetic untreated rats (4.20 ± 0.350, 1.78 ± 0.03, 2.18 ± 0.06 and 0.67 ± 0.14 mmol/l). On the other hand, treated rats administered 200 mg/kg dose of the extract showed significant (p < 0.05) reduction in the total cholesterol concentration (3.00 ± 0.20 mmol/l) and TAG concentration (1.60 ± 0.06 mmol/l) respectively compared to the diabetic untreated rats. Furthermore there was no significant (p > 0.05) difference in HDL-cholesterol (0.71 ± 0.02 mmol/l) and LDL-cholesterol (1.850 ± 0.04 mmol/l) concentrations respectively compared to the diabetic control rats. The rats treated with the standard drug showed significant (p < 0.05) reduction in the total cholesterol (2.55 ± 0.35 mmol/l), TAG (1.20 ± 0.06 mmol/l), LDL (1.50 ± 0.27 mmol/l) cholesterol and significantly (p < 0.05) higher HDL (1.10 ± 0.08 mmol/l) cholesterol concentrations when compared to diabetic untreated rats. The oral intake of S. stenocarpa at 200 mg/kg dose (341.33 ± 135.85 mg/dl) and 300 mg/kg dose (382 ± 17.32 mg/dl) showed non-significant (p > 0.05) reduction in the postprandial hyperglycaemia in glucose loaded alloxan induced diabetic rats respectively compared to control (493.33 ± 114. 04 mg/dl) after 2 hours. The rats treated with 100 mg/kg dose (578.67 ± 21.33 mg/dl) showed non-significant elevation of the postprandial hyperglycaemia compared to the control as seen above. On the other hand, in rats that received maltose and S. stenocarpa, postprandial hyperglycaemia was not effectively suppressed. The current study suggests first, that the plant has anti-diabetic properties because one of the mechanisms in which S. stenocarpa exerts anti-diabetic activity is by effectively enhancing glucose uptake leading to a lowering effect on postprandial hyperglycaemia. This result generally indicate that the aqueous extract of S. stenocarpa might be adopted for the management and/amelioration of diabetes and its complications. T