Prooxidant action of chebulinic acid and tellimagrandin I: Causing copper-dependent DNA strand breaks

The prooxidant activity of two hydrolysable tannins, chebulinic acid and tellimagrandin I, on plasmid DNA and genomic DNA of cultured MRC-5 human embryo lung fibroblasts was assessed. The results revealed that both hydrolysable tannins in combination with Cu(II) induced DNA strand breaks in pBR322 plasmid DNA in a concentration-dependent manner. Chebulinic acid and tellimagrandin I also induced genomic DNA strand breaks of MRC-5 human embryo lung fibroblasts in the presence of Cu(II). After treatment with chebulinic acid or tellimagrandin I alone, the pBR322 plasmid DNA and genomic DNA in MRC-5 cells kept intact. In addition, addition of Cu(I) reagent bathocuproinedisulfonic acid or catalase markedly inhibited the copper-dependent DNA strand breaks by both tannins. However, three typical hydroxyl radical scavengers, DMSO, ethanol and mannitol, did not inhibit the DNA strand breaks. Both tannins were able to reduce Cu(II) to Cu(I). These results indicated that chebulinic acid and tellimagrandin I induced the copper-dependent strand breaks of pBR322 plasmid DNA and MRC-5 genomic DNA with prooxidant action, in which Cu(II)/Cu(I) redox cycle and H2O2 were involved and hydroxyl radical formation is important in the hypothetical mechanism by which DNA strand breaks are formed.