Do plants mediate their anti-diabetic effects through anti-oxidant and anti-apoptotic actions? an in vitro assay of 3 Indian medicinal plants.

BACKGROUND: Both experimental and clinical studies suggest that oxidative stress plays a major role in the pathogenesis of both types of diabetes mellitus. This oxidative stress leads to ß-cell destruction by apoptosis. Hence exploring agents modulating oxidative stress is an effective strategy in the treatment of both Type I and Type II diabetes. Plants are a major source of anti-oxidants and exert protective effects against oxidative stress in biological systems. Phyllanthus emblica, Curcuma longa and Tinospora cordifolia are three such plants widely used in Ayurveda for their anti-hyperglycemic activity. Additionally their anti-oxidant properties have been scientifically validated in various experimental in vitro and in vivo models. Hence the present in vitro study was planned to assess whether the anti-hyperglycemic effects of the hydro-alcoholic extracts of Phyllanthus emblica (Pe) and Curcuma longa (Cl) and aqueous extract of Tinospora cordifolia (Tc) are mediated through their antioxidant and/or anti-apoptotic property in a streptozotocin induced stress model. METHODS: RINm5F cell line was used as a model of pancreatic ß-cells against stress induced by streptozotocin (2 mM). Non-toxic concentrations of the plant extracts were identified using MTT assay. Lipid peroxidation through MDA release, modulation of apoptosis and insulin release were the variables measured to assess streptozotocin induced damage and protection afforded by the plant extracts. RESULTS: All 3 plants extracts significantly inhibited MDA release from RIN cells indicating protective effect against STZ induced oxidative damage. They also exhibited a dose dependent anti-apoptotic effect as seen by a decrease in the sub G0 population in response to STZ. None of the plant extracts affected insulin secretion from the cells to a great extent. CONCLUSION: The present study thus demonstrated that the protective effect of the selected medicinal plants against oxidative stress induced by STZ in vitro, which was exerted through their anti-oxidant and anti-apoptotic actions.

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 (200 µg/ml). The effect of both Pe and Tc at 200 µg/ml was comparable to insulin and greater than pioglitazone. Cl per se stimulated glucose uptake with maximal effect at 50 µg/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.