Effects of vitamins E, C and catalase on bromobenzene- and hydrogen peroxide-induced intracellular oxidation and DNA single-strand breakage in Hep G₂ cells

Background/aims: Water-soluble vitamin E (Trolox C), ascorbic acid and catalase were shown in our previous study to protect isolated rat hepatocytes against bromobenzene-induced toxicity. Methods: In order to study the mechanisms of this protection and the pathogenesis of bromobenzene-induced hepatocellular injury, a fluorometric assay for the investigation of intracellular oxidation, indicated by conversion of dichlorofluorescein diacetate to dichlorofluorescein, was used. Single-strand DNA breakage was also evaluated in Hep G₂ cells by a radio-labelling method. Results: Bromobenzene (2.4 and 4.8 mM) induced a significant increase in dichlorofluorescein fluorescence intensity compared to the controls. Trolox C, ascorbic acid or catalase significantly inhibited bromobenzene-induced enhancement of fluorescence intensity (p < 0.05-0.001), as well as reduced auto-intracellular oxidation in untreated Hep G₂ cells. Hydrogen peroxide (H₂O₂) evoked a dose-dependent increase in dichlorofluorescein fluorescence intensity in Hep G₂ cells, and the effect was completely blocked by Trolox C (2.0 mM) and catalase (4800 unit/ml). Bromobenzene caused significant single-strand DNA breakage in Hep G₂ cells during 2 h suspension incubation and 24 h primary incubation. H₂O₂ (400 μM) led to marked single-strand DNA breakage in 20 min, and the effect was attenuated by Trolox C. Conclusions: Metabolism of bromobenzene in Hep G2 cells induces production of H₂O₂, indicated by enhancement of dichlorofluorescein fluorescence intensity, or other free radicals, which leads to single-strand DNA breakage in the cells. Vitamins E and C and catalase display strong intracellular antioxidative effects. Vitamin E could partially inhibit H₂O₂-induced single-strand DNA breakage in the cells.