Protective effect of methyl gallate from Toona sinensis (Meliaceae) against hydrogen peroxide-induced oxidative stress and DNA damage in MDCK cells

Methyl gallate (MG) has been shown to be an effective antioxidant in a variety of acellular experiments. Accordingly, this study was designed to assess the ability of MG, extracting from Toona sinensis to protect cultured Madin-Darby canine kidney (MDCK) cells against hydrogen peroxide (H2O2)-mediated oxidative stress. Trolox, a cell permeable and water-soluble vitamin E analogue, was included for comparison. First, when MDCK cells were pretreated with MG and trolox for 1 h, followed by exposing to H2O2 (0.8 mM) for an additional hour, we found that the intracellular peroxide productions, as reflected by dichlorofluorescein (DCF) fluorescence, were shown to be decreased in a concentration-dependent manner. Furthermore, using C-11-BODIPY581/591 as a lipid peroxidation probe, we also found that MG, in a concentration of 100 muM, could alleviate lipid peroxidation of the cells exposed to a short-term H2O2 treatment. In addition, MG-treated cells could prevent intracellular glutathione (GSH) from being depleted following an exposure of H2O2 (8.0 mM) for a 3 h period. Next, we also examined the effect of MG on H2O2-mediated oxidative damage to DNA. Using 8-oxoguanine as an indicator for oxidative DNA damage, we demonstrated that the percentage of MDCK cells containing 8-oxoguanine was drastically increased by exposing to H2O2 (40 mM) for 3 h. However, 8-oxoguanine contents were shown to be significantly decreased in the presence of MG prior to H2O2 exposure. Comparatively, MG was shown to be a better protective agent against oxidative damage to DNA as compared to trolox. Taken together, our data suggest that MG is effective in preventing H2O2-induced oxidative stress and DNA damage in MDCK cells. The underlying mechanisms involved scavenging of intracellular reactive oxygen species (ROS), inhibition of lipid peroxidation and prevention of intracellular GSH depletion. (C) 2004 Elsevier Ltd. All rights reserved.