P 29: Insulinotropic constituents and evaluation of ethnomedical claim of gongronema latifolium root and stem

Abstract

Background and aims The insulinotropic activity of the combined root and stem of Gongronema latifolium was evaluated to justify its African ethnomedicinal use in the management of diabetes. Materials and Methods A methanolic extract of the combined root and stem and its vacuum liquid chromatographic fractions (A1–A6) were tested for glucose reducing and in vitro insulin stimulating abilities, using glucose loaded rats and INS-1 cells, respectively. In vivo insulin releasing activities for the significantly in vivo anti-hyperglycaemic active A5 and A6 were similarly determined, using glucose loaded rats. In vitro insulin stimulating potentials of column chromatographic fraction C1 and its isolated constituents were also determined. Results The extract (100 mg/kg) had higher in vivo anti-hyperglycaemic activity than A1-A6, indicating a synergistic effect of the plant constituents. Higher in vivo insulin release given by A5 (100 mg/kg) than that of A6, agreed with their in vivo anti-hyperglycaemic activities and confirmed insulin as a hitherto unreported mechanism of action of the plant. Extract, A3, A6 and C1 (100.0 μg/ml) elicited significantly high in vitro insulin release similar (p > 0.05) to glibenclamide (1.0 μg/ml). Fraction C1 gave a 1:1 mixture of α-amyrin and β-amyrin cinnamates (1a/1b), lupenyl cinnamate (2), lupenyl acetate (3) as well as two unidentified triterpenoids, Y and Z. The 1a/1b was an addition to the chemistry of the plant. The highest insulinotropic activity of 178.3% given by 1a/1b (100.0 μg/ml) was similar (p > 0.05) to that of glibenclamide (1.0 μg/ml). The 1a/1b, with contributions from 2, 3 and Z were the insulinotropic constituents. Some fractions and isolates demonstrated synergistic activity. Conclusion The results confirmed pancreatic activity as a mechanism of antidiabetic action of G. latifolium and justified this ethnomedical use.