ABSTRACT
Extracts of Dialium guineensehave been shown to possesshypoglycemic effect, but little or nothing is known about their toxicity and potential antidiabetic effects.This study investigated the toxicological and antidiabetic properties of the extracts, and isolated saponins and tannins of D. guineensestem barkin streptozotocin-induced diabetic Wistar rats.
The study was conducted in four phases. Phase 1 involved aqueous and ethanol extraction of the plant stem bark, phytochemical, proximate, elemental and vitamin analyses; and the in vitro determination of α-amylase, α-glucosidase, and antioxidant activities of the medicinal plant. Phase 2 involved acute, subchronic and dose response studies. Phase 3 involved the isolation of total saponins and tannins from the stem bark of D. guineense using standard methods. Phase 4 dwelt on the assessment of some biochemical parameters in normal Wistar rats and antidiabetic evaluation of the stem bark extracts/isolated saponins and tannins.
Results of phytochemical analyses revealed the presence of saponins, tannins, alkaloids and other polyphenolics. Xanthoprotein, oxalate and acids were not detected. Tannins and phenols were present in high concentrations, while glycosides and steroids were present in low concentrations. Proximate analysis showed that the stem bark contain more nitrogen-free substances. The concentrations of selenium and manganese were higher in the aqueous extract than ethanol extract, while the concentrations of zinc, chromium, vanadium and calcium were higher in the ethanol extract than aqueous extract. However, the differences were not significant (p > 0.05). Vitamin analysis revealed the presence of high concentrations of the B-group of vitamins in both extracts. Both extracts had high concentrations of methionine and arginine, but there was no trace of tryptophan in the aqueous extract. The extracts and total saponins and tannins exhibited good α-amylase and α-glucosidase inhibitory activities which were comparable with those of acarbose. The ethanol extract showed significantly higher in vitro antioxidant activities, total phenol, flavonoid, flavonol and proanthocyanidin contents, relative to the aqueous extract (p < 0.05). The oral LD50 of both extracts were greater than 5000 mg/kg body weight, bwt. The aqueous and ethanol extracts did not elicit any deleterious effects on the liver, kidney, cardiac and pancreatic functions. The results of histopathological examination showed that the ethanol extract induced greater changes in the vascular walls of the liver, while the aqueous extract activated the immune system the most. After isolation, the yields of total saponins and total tannins were 4.35 and 3.45 %, respectively. Dose response study showed that1000 mg/kg bwt (for both extracts) and 150 mg/kg bwt (for saponins and tannins) were effective in reducing the blood glucose of rats.Induction of diabetes using 50 mg/kg bwt streptozotocin (STZ) resulted in metabolic derangements such as hyperglycemia, hypertriacylglycerolemia, hypercholesterolemia, and significant reductions in enzyme and non-enzyme antioxidants and levels of insulin, testosterone, C-peptide, pancreatic total DNA, RNA and protein. However, after treatment with the extracts, and total saponins and tannins of D. guineense stem bark, the effect of STZ was significantly ameliorated (p < 0.05). These results suggest that the extracts and total saponins and tannins possess some antidiabetic properties.
