Inhibitory effect of Eucommia ulmoides Oliv. on oxidative DNA damage in lymphocytes induced by H₂O₂

This study used the alkaline single cell gel electrophoresis assay (comet assay) to investigate the effect of water extracts of roasted cortex and leaves from Du-zhong on DNA damage in lymphocytes induced by H₂O₂. The results showed that the DNA damage in human lymphocytes increased with an increase in the concentration of H₂O₂ (0-200 μM), but that the water extracts from Du-zhong (0-2 g 1^-1) only slightly affected DNA damage. The inhibitory effect of leaf extract on DNA damage induced by H₂O₂ in lymphocytes was more significant (P<0.05) than that of roasted cortex. Leaf extract showed a rather significant inhibitory effect in a concentration-dependent manner. At a concentration of 2 g 1^-1, the leaf extract inhibited 37.9% DNA oxidative damage in human lymphocytes. In order to elucidate the mechanism of the leaf extract suppression effect on DNA damage induced by H₂O₂ in lymphocytes, an experiment was divided with six groups (A-F). Group A was used to evaluate the repair ability of the leaf extract for DNA damage; Group B was employed to determine the scavenging ability on H₂O₂; and Group C was studied to assess the ability of leaf extract to increase the defense capability. Groups D-F were negative controls and blank. The results showed that group B had the best inhibitory effect. Also, leaf extract had significant ability to scavenge H₂O₂ in an in vitro HRP-phenol red test. Thus, it appears that H₂O₂ scavenging potency may be the major mechanism whereby leaf extract inhibits oxidative DNA damage induced by H₂O₂.