The insulinotropic activity of the combined root and stem of Gongronema latifolium (Asclepiadaceae) was evaluated to justify its African ethnomedicinal use in the management of diabetes.Methods:
A methanolic extract and its 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 (P < 0.05) active antihyperglycemic A5 and A6 and in vitro insulinotropic activity of the C1 fraction and its isolated constituents were also similarly determined.Results:
The extract (100 mg/kg) had higher in vivo antihyperglycemic activity than the individual A1–A6, indicating a synergistic effect of the plant constituents. Higher in vivo insulin release in response to A5 (100 mg/kg) than A6, agreed with their in vivo antihyperglycemic activities and confirmed insulin release as a mechanism of action of the plant. Compared with 5.6 mmol/L glucose (negative control), the extract and the A3, A6, and C1 (all at 100.0 μmg/mL) elicited significantly higher in vitro insulin release that was similar to that of glibenclamide (1.0 μmg/mL; P > 0.05). Fraction C1 yielded a 1:1 mixture of α-amyrin and β-amyrin cinnamates (1a:1b), lupenyl cinnamate (2), lupenyl acetate (3), and two unidentified triterpenoids, Y and Z. The 1a:1b mixture (100.0 μmg/mL) demonstrated the highest insulinotropic activity that was comparable (P > 0.05) to that of glibenclamide (1.0 μmg/mL).Conclusions:
The results confirm pancreatic activity as a mechanism underlying the antidiabetic action of G. latifolium and justify its ethnomedical use.