Glucose uptake-enhancing activity of the ethyl acetate extract of Dennettia tripetala in 3T3-L1 adipocytes.

Glucose uptake-enhancing activity of the ethyl acetate extract of Dennettia tripetala (EDT) was investigated using 3T3-L1 adipocytes. EDT yielded 4.43 percent w/w dry matter, showed the presence of alkaloids and flavonoids, contained calcium, iron, zinc, magnesium, copper and manganese. Out of the five extracts of D. tripetala, EDT gave the highest activity (75 percent) in enhancing glucose uptake in 3T3-L1 adipocytes, which was not significantly (p > 0.05) different from insulin (340 nM), the standard drug. EDT caused concentration-dependent increase in glucose uptake with maximal effect at 5 μg/ml, but further increase beyond 10 μg/ml caused a shut down in glucose uptake. Optimal effect was achieved at 16 h post incubation. There was no synergistic effect with increasing doses (2.5, 5.0, 10 μg/ml) of sub maximal concentrations of insulin, rather there was significant (p < 0.05) decrease compared with insulin (340 nM) alone. Unlike other protein inhibitors used, brefeldin significantly (p < 0.05) inhibited EDT-induced glucose uptake by more than 40 percent. In conclusion, EDT enhanced glucose uptake partly by the mobilization of glucose uptake proteins from the interior of the cell to plasma membrane via the Golgi apparatus. Therefore, this mechanism may be responsible for the antihyperglycaemic effect of EDT reported in our previous study.