Vitamin C and quercetin modulate DNA-damaging effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)

The effects of natural compounds, vitamin C and quercetin, present in fruits and vegetables, on the DNA damaging activity of a food carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined using the comet assay. Vitamin C, at a concentration of 50 microM, inhibited MNNG-induced DNA damage in human lymphocytes. Quercetin, up to a concentration of 10 microM, increased the extent of DNA damage, but at concentrations above 10 microM decreased damage below control values. Furthermore, quercetin had a strong antioxidant activity against oxidative damage evoked by H2O2 at 10 microM. The results obtained suggest that vitamin C and quercetin may have anti- or pro-oxidative properties depending on the state of the cell.