Insulin sensitizing effect of 3 Indian medicinal plants: An in vitro study

OBJECTIVE: Measurement of glucose uptake into peripheral tissue is an important mechanism to assess Insulin sensitivity. The present in vitro study was conducted to evaluate the Insulin sensitizing activity of Phyllanthus emblica (Pe), Tinospora cordifolia (Tc) and Curcuma longa (Cl) by assessing glucose uptake activity in a 3T3L1 adipocyte model. MATERIALS AND METHODS: The 3T3 L1 fibroblast cells were differentiated to adipocytes, using a cocktail of insulin, isobutyl-1-methylxanthine and dexamethazone. These adipocytes were initially treated with different concentrations of the selected plants following which 2-deoxy glucose uptake was estimated using a radioactive assay. The effects of plants on glucose uptake both in the presence and absence of insulin was evaluated and compared with pioglitazone, a known insulin sensitizer. RESULTS: Pe and Tc per se significantly stimulated glucose uptake in 3T3-L1 adipocytes in a dose dependent manner with maximal effect at higher concentrations (200μg/ml). The effect of both Pe and Tc at 200μg/ml was comparable to insulin and greater than pioglitazone. Cl per se stimulated glucose uptake with maximal effect at 50μg/ml. However, this effect was lesser as compared to insulin with higher concentrations inhibiting glucose uptake. When combined with insulin, an antagonist effect was observed between Pe, Tc and insulin indicating a possible plant-drug interaction while Cl in combination with insulin showed an increase in the glucose uptake as compared to Cl alone. CONCLUSION: The results suggest that one of the mechanisms for the anti-diabetic effect of Pe, Cl and Tc may be through an insulin sensitizing effect (stimulation of glucose uptake into adipocytes). Further studies using other target sites viz. skeletal muscle and hepatocytes models and in an insulin resistant state would help substantiate this conclusion.