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 β-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 β-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.