The antioxidant and prooxidant effects of tannic, ellagic and gallic acids (1–60 μM) in the presence of hydrogen peroxide (40 and 100 μM) or copper ions (50 μM) on B14 Chinese hamster cells were examined.
The fluorescence probe DCFH-DA (dichlorofluorescein-diacetate) was used to analyse the levels of reactive oxygen species. This method showed the reduction in oxidation of DCF (dichlorofluorescein). It indicates that antioxidant capacity of tested polyhenols is decreased in the presence of hydrogen peroxide or copper ions.
Spectrophotometric assay with Ellman's reagent was used to determine SH-groups. The experimental results revealed the oxidative modification of proteins after exposure to polyphenols at concentrations above 15 μM. Additional incubation with H2O2 or Cu2+ ions showed the prooxidant activity of tested complexes also for polyphenols used at a concentration of 1 μM.
Fluorescence method with Hoechst 33258/propidium iodide dyes was used to study apoptotic and necrotic cell death. The obtained data demonstrated that polyphenols alone, as well as in the presence of hydrogen peroxide or copper ions, can induce DNA fragmentation.