摘要：

The plant-derived phenolic compounds gossypol, quercetin and myricetin are powerful inhibitors of iron-induced lipid peroxidation in rat liver microsomes, under all five experimental conditions tested and at low micromolar concentrations (IC 50 1.5 μM). However, they greatly accelerate the generation of hydroxyl radicals (.OH) from H 2O 2 in the presence of Fe 3+-EDTA at pH 7.4, as measured by the deoxyribose assay. At 100 μm, the three phenolic compounds enhanced · OH formation up to eight-fold. The hydroxyl radical generation was inhibited by catalase and Superoxide dismutase, suggesting a mechanism in which the phenols oxidize to produce Superoxide radical, which then assists · OH generation from H 2O 2 in the presence of Fe 3+-EDTA. At concentrations up to 75 μM, quercetin and myricetin also accelerate bleomycin-dependent DNA damage in the presence of Fe 3+, possibly by reducing the Fe 3+-bleomycin-DNA complex to the Fe 2+ form. Hence these naturally-occurring substances can have pro-oxidant effects under some reaction conditions and cannot be classified simplistically as "antioxidants".

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