Antihyperglycemic Studies on the Leaf Extract and Active Fractions of Newbouldia laevis (Bignoniaceae)

Optimal control of chronic hyperglycemia prevents both micro and macro vascular complications—a leading cause of morbidity and mortality in diabetic subjects. This study was undertaken to give credence to the traditional use of Newbouldia laevis leaves in the treatment of diabetes mellitus (DM). Dichloromethane-methanol (1:1) extract (DME) of N. laevis leaves was prepared by cold maceration. Separation of DME into column chromatographic fractions yielded the n-hexane fraction (HF), ethylacetate fraction (EF) and methanol fraction (MF). The extract and fractions were evaluated for antihyperglycemic activity in alloxanized diabetic rats. The results showed that the oral administration of extract and fractions (250, 500, 1000 mg/kg) caused a significant (P < 0.5) and dose-dependent reduction in blood glucose level in diabetic rats. The hypoglycemic potency after 24 h was in the order MF (methanol fraction; 56.31%) > DME (dichloromethane/methanol extract; 36.19%) > EF (ethylacetate fraction; 20.70%) > HF (n-hexane fraction; 10.09. The methanol fraction, which showed the highest potency in oral glucose tolerance test (OGTT), was further separated into column chromatographic sub-fractions—F1, F2, F3 and F4 fractions. These sub-fractions were evaluated for antihyperglycemic activity. Sub-fractions F1, F2 and F3 (1000 mg/kg) did produce significant (P > 0.05) reduction in blood glucose level after 24 h. Sub-fraction F4 (50, 100, 200 mg/kg), however caused a significant (P < 0.05) and dose-dependent reduction in blood glucose level. The reduction at 200 mg/kg dose of F4 (74.57%) was significantly (P < 0.05) higher than that of glibenclamide (58.04%). These findings suggest that leaf extract and fractions of Newbouldia laevis possess antihyperglycemic activities and can be the basis for the folk use N. laevis in management of diabetes mellitus.