Vitamin C modulates DNA damage induced by hydrogen peroxide in human colorectal adenocarcinoma cell lines (HT29) estimated by comet assay in vitro

INTRODUCTION: Cancer cells, compared to normal cells, are under increased oxidative stress associated with oncogenic transformation, alterations in metabolic activity, and increased generation of reactive oxygen species. MATERIAL AND METHODS: We investigated the ability of vitamin C to reduce the damage induced by hydrogen peroxide, in human colorectal adenocarcinoma cells in vitro by the comet assay. Additionally, we measured the kinetics and efficacy of the repair of DNA damage after incubation with vitamin C in the presence of H(2)O(2). RESULTS: The obtained results showed that 1 h pre-incubation with vitamin C and exposure to H(2)O(2) for the last 10 min of incubation caused a statistically significant (p < 0.05) increase in DNA migration in comet tails in all experimental series. For the 10 µM, 25 µM, 50 µM, 100 µM vitamin C concentrations the levels of DNA damage were as follows: 18.6%, 21.1%, 25.3% and 27.2%, respectively, as compared to the untreated cells (3.26%). However, in comparison with H(2)O(2) alone (29.1%), we observed a statistically significant (p < 0.05) decrease of the genotoxic effect in HT29 cells induced by H(2)O(2) for the two lowest of concentrations of vitamin C: 10 µM and 25 µM. The HT29 cells were able to achieve effective repair of the damaged DNA within 60 and 120 min after incubation with the tested compounds. All the values obtained in the test were statistically significant (p < 0.05). CONCLUSIONS: Vitamin C caused a weaker DNA damaging effect of hydrogen peroxide and positively influences the level of oxidative DNA damage in HT29 cells (decrease ∼ 30%). We noted that DNA damage was effectively repaired during 120 min postincubation in the tested cells and that oxidative damage was the major type of damage.