Zinc Ion Enhances GABA Tea-Mediated Oxidative DNA Damage

GABA tea is a tea product that contains a high level of gamma-aminobutyric acid (GABA). Previous study has demonstrated a synergistic effect of GABA tea and copper ions on DNA breakage. This study further explored whether zinc (Zn), a nonredox metal, modulated DNA cleavage induced by GABA tea extract. In a cell-free system, Zn2+ significantly enhanced GABA tea extract and (-)-epigallocatechin-3-gallate (EGCG)- or H2O2-induced DNA damage at 24 h of incubation. Additionally, low dosages of GABA tea extract (1-10 mu g/mL) possessed pro-oxidant activity to increase H2O2/Zn2+-induced DNA cleavage in a dose-dependent profile. By use of various reactive oxygen scavengers, it was observed that glutathione, catalase, and potassium iodide effectively inhibited DNA degradation caused by the GABA tea extract/H2O2/Zn2+ system. Moreover, the data showed that the GABA tea extract itself (0.5-5 mg/mL) could induce DNA cleavage in a long-term exposure (48 h). EGCG, but not the GABA tea extract, enhanced H2O2-induced DNA cleavage. In contrast, GABA decreased H2O2- and EGCG-induced DNA cleavage, suggesting that GABA might contribute the major effect on the antioxidant activity of GABA tea extract. Furthermore, a comet assay revealed that GABA tea extract (0.25 mg/mL) and GABA had antioxidant activity on H2O2-induced DNA breakage in human peripheral lymphocytes. Taken together, these findings indicate that GABA tea has the potential of both pro-oxidant and antioxidant. It is proposed that a balance between EGCG-induced pro-oxidation and GABA-mediated antioxidation may occur in a complex mixture of GABA tea extract.