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 H(2)O(2). The results showed that the DNA damage in human lymphocytes increased with an increase in the concentration of H(2)O(2) (0-200 micro;M), but that the water extracts from Du-zhong (0-2 g l(-1)) only slightly affected DNA damage. The inhibitory effect of leaf extract on DNA damage induced by H(2)O(2) 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 l(-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 H(2)O(2) 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 H(2)O(2); 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 H(2)O(2) in an in vitro HRP-phenol red test. Thus, it appears that H(2)O(2) scavenging potency may be the major mechanism whereby leaf extract inhibits oxidative DNA damage induced by H(2)O(2).
Copyright 2003 Wiley-Liss, Inc.