Antioxidant Activities of Stilbenoids from Rheum emodi Wall.

Rheum emodi Wall has been reported to possess protective effect in many inflammatory diseases and oxidative stress-related injuries. This study aims to investigate antioxidant power of stilbenoids from R. emodi and then explore the material basis for its antioxidant potential. The most abundant stilbenoid piceatannol-4'-O-β-D-glucopyranoside (PICG) and its aglycon piceatannol (PICE) were isolated from R. emodi rhizome. Using well-accepted antioxidant chemicals as reference, antioxidant activity of these stilbenoids was examined by measuring DPPH and superoxide anion radical scavenging, ferric reducing power, and inhibition of lipid peroxidation in vitro. Both PICG and PICE displayed promising antioxidant activity in all the four assays. Comparisons among the tested compounds indicated that PICE has the most potent antioxidant activity and the presence of 3'-hydroxyl group may enhance antioxidant activity of stilbenoids. The antioxidative effect of PICE at the cellular level was further demonstrated on the model of hydrogen-peroxide-induced H9c2 rat cardiomyoblasts injury. Taking into account the rapid in vivo metabolic transformation of PICG into PICE it can be inferred that the most abundant stilbenoid PICG may be an important constituent responsible for the antioxidant potential of R. emodi and promising to be developed as an antioxidant agent for supplementary or therapeutic use.