The repair of the oxidative DNA damage and its relationship to the cytotoxic effect of the oxidants.

H2O2 is a strong oxidant and therefore affects all cell structures. Especially the oxidative damage of DNA is known as being very severe. It is considered to be contributing cause of carcinogenesis, mutagenesis and aging. Our work is focused on the relationship between cytotoxic effect of H2O2 and the repair of oxidative DNA damage caused by H2O2. We also studied the effects of epigallocatechin gallate (EGCG). Several studies have already proven its protective activity on DNA in particular concentrations. In our experiments we used the test of cytotoxicity to demonstrate the colony forming inhibition and the comet assay test which measures the number of single strand breaks (SSB) in 109 daltons of DNA. Generally we used cells of line AA8 and in one experiment also NER deficient cells of line UV-20. We found out that EGCG in concentrations of 12,5 and 25 μg/ml significantly protects the cells against cytotoxic effects of H2O2. When we followed the repair of the oxidative DNA damage, we have found that EGCG did not affect the repair of direct DNA breaks, but the repair of oxidised pyrimidines and purines was accelerated. And this acceleration is probably largely responsible for the protection against cytotoxic effect of H2O2. However, the EGCG function of free radical scavenger and iron ions chelator..