Studies of the anti-hyperglycemic and antioxidant activities of the extract of aerial yam (Dioscorea bulbifera)

Abstract

This study investigated the anti-hyperglycemic and antioxidant activities of methanol extract of Dioscorea bulbifera with a view to studying the possibility of utilizing the yam in the management of hyperglycemia. Methanol extracts of the peels (MEPL), fresh (MEFL), and the whole tuber (MEWT) were prepared, phytochemically screened and assayed for α-amylase. Hyperglycemia was induced in rats using intraperitoneal injections of streptozotocin (40 mg/kg bwt) for five days, followed by administration of various doses of extract.  Fasting blood sugar, alpha amylase, total protein, lipid profiles, creatinine, albumin, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured in plasma of test rats. The extracts were found to contain alkaloids, cardiac glycosides, carbohydrate, flavonoids, protein, saponins, tannins, triterpenoids and vitamin C and E. Preliminary assessment revealed that the whole tuber (MEWT) contained the highest levels of these phytochemicals and exhibited highest α-amylase inhibitory potential (47.54%, IC50 169.83 ± 18.64 μg/ml). Also, the extract possessed potent and concentration-dependent radical scavenging activities, comparable to that of the standard (Vitamin C). The extract also inhibited alpha amylase activity and caused significant improvement in elevated lipid profile and creatinine, comparable with that brought about by the standard drug Metformin. Histological examination of pancreatic section showed improved arrangement of islets of Langerhans in exocrine tissues of hyperglycemic groups treated with the extract when compared with hyperglycemic control. These results suggest that methanol extract of whole tubers possesses potent significant anti-hyperglycemic activity and that whole yam (without peeling) is appropriate for use in the management of hyperglycemia disorders. Key words: Dioscorea bulbifera, methanol extract, Streptozotozin, hyperglycemia, diabetes mellitus, antioxidants, lipid profile.