Antioxidant Activity of Extracts from Du-zhong (Eucommia ulmoides) toward Various Lipid Peroxidation Models in Vitro

The antioxidant effect of extracts from leaves, raw cortex, and roasted cortex of Du-zhong was evaluated using various lipid peroxidation models. The inhibitory activity of extracts of Du-zhong (200 μg/mL) on the peroxidation of linoleic acid measured by thiocyanate method followed the order leaves (99.9%) > roasted cortex (95.9%) > raw cortex (77.2%) at 60 h of incubation. The IC₂₀ for leaves, roasted cortex, and raw cortex on the peroxidation of liposome, induced by Fe³⁺/H₂O₂/ascorbic acid, was <0.06, 0.24, and 0.81 mg/mL, respectively. The thiobarbituric acid reactive substances values for leaves, roasted cortex, and raw cortex were 0.12, 1.54, and 1.81 μmol of malondialdehyde/ mg of protein in enzyme-mediated microsomal peroxidation and 0.08, 0.69, and 0.88 μmol of malondialdehyde/mg of protein in the nonenzyme-mediated microsomal peroxidation, respectively. The antioxidant activity of extracts of Du-zhong correlates to their polyphenol content. The results presented herein indicate that extracts of Du-zhong leaves may be useful in inhibiting membrane lipid peroxidation and preventing free radical-linked disease.