Antioxidant actions of Du-zhong (Eucommia ulmoides oliv.) toward oxidative damage in biomolecules

This study aimed to investigate the antioxidant effect of water extracts of Duzhong (WEDZ) on oxidative damage in biomolecules such as deoxyribose, DNA and 2′-deoxyguanosine (2′-dG) as induced by Fenton reaction. The WEDZ used included leaves, raw cortex and roasted cortex. All of the WEDZ inhibited the oxidation of deoxyribose induced by Fe3+-EDTA/H2O2/ascorbic acid in a concentration dependent manner. At a concentration of 1.14 mg/mL, the inhibitory effect of the extracts of leaves, roasted cortex and raw cortex was 85.2%, 68.0% and 49.3%, respectively. The extract of leaves inhibited the strand-breaking of DNA induced by the Fenton reaction at concentrations of 5 and 10 μg/μL. This inhibitory effect was similar to mannitol whereas the extracts of raw cortex and roasted cortex had no inhibitory effect at all. WEDZ also inhibited the oxidation of 2′-dG to 8-OH-2′-dG induced by Fe3+-EDTA/H2O2/ascorbic acid. Gallic acid had a prooxidant effect, but trolox and mannitol had an antioxidant effect. The leaf extract had a marked inhibitory effect on Fenton reaction induced oxidative damage in biomolecules. The extract of roasted cortex exhibited modest inhibition while the extract of raw cortex had the least inhibitory effect on oxidative damage in biomolecules. This is in contrast to gallic acid in the same reaction system, whose higher reducing power and weaker chelating ability may contribute to its prooxidant effect. In the present study, leaf extract of Du-zhong had inhibitory effect on oxidative damage in biomolecules. Therefore, drinking of Du-zhong tea (leaf extract) over a long period of time may have anticancer potential.