Abstract: Eucalyptus leaves are valued as an enormous resource with various biological activities, but rare information is available concerning systematical evaluation of the antioxidant activity of eucalyptus leaf polyphenol extract. Therefore, the aim of this study was to evaluate the antioxidant activity of purified eucalyptus leaf polyphenol extract (PEPE) in vitro and in vivo. The in vitro antioxidant activity was evaluated?through the determination of free radial scavenging capacity and total reducing power by chemical assays. The in vivo antioxidant activity was assessed using RAW264.7 cells and Caenorhabditis elegans. Results showed that PEPE had potent free radical scavenging capacity and reducing power, which was equivalent to the effect of ascorbic acid at a certain concentration. PEPE treatment significantly dose-dependently increased the activities of the antioxidant enzymes (superoxide dismutase and catalase) and glutathione content in RAW264.7 cells with oxidative injury and reduced malondialdehyde content (P < 0.05). In addition, PEPE suppressed reactive oxygen species accumulation in the nematodes under normal and oxidative damage conditions (P < 0.05), enhanced their antioxidant capacity and prolonged their lifespan. In conclusion, PEPE has a strong antioxidant activity both in vivo and in vitro, and thus possesses the potential to be developed as food antioxidants or an ingredient in functional foods.

Key words: eucalyptus leaf polyphenol extracts; antioxidant activity; RAW264.7 macrophages; Caenorhabditis elegans