*3.4. Cellular Repair of Oxidized Purines*

We next investigated the effect of vitamin C on the kinetics of BER after pre-incubating HeLa cells with different concentrations of vitamin C overnight. We induced oxidized purines, mostly 8-oxoGua, using Ro plus light. The comet assay was performed after different times of incubation of the treated cells up to 6 h. The pre-incubation of cells with 50 or 100 μM vitamin C overnight did not affect the removal of the FPG-sensitive sites induced by Ro plus light (data not shown). We modified the protocol by pre-incubating HeLa cells with 200 μM of vitamin C for 30 min, and adding the same concentration of vitamin C also during the 6 h incubation period after inducing the damage. Figure 5 shows that the repair of oxidized bases is much slower than SB rejoining, and the presence of vitamin C during the incubation period after damaging the cells still did not influence the repair of the FPG-sensitive sites induced by Ro plus light.

**Figure 5.** Effect of incubation of HeLa cells with 200 μM of vitamin C before and during the repair of oxidized bases induced by Ro plus light; residual FPG-sensitive sites were measured at different time points. Bars: SD calculated from the results of 3 independent experiments. No significant effects were seen.
