Handbook of Vitamin C Research

102Ana I. Haza, Almudena García and Paloma MoralesDNA Strand Break and Oxidative DNA Damage Induction by Vitamin CInduction of DNA damage by vitamin C in human HepG2 cells incubated with orwithout Fpg enzyme, is shown in Figure 6. None of the vitamin C concentrations tested (1, 5and 10 M) in presence or absence of Fpg enzyme, caused DNA damage per se. Nocytotoxicity has been previously found at the concentrations of vitamin C tested (Figure 12and 13). This concentration range was therefore used in subsequent studies.Figure 6.Figure 6. Induction of oxidative DNA damage by vitamin C in human HepG2 cells incubated with ( )and without ( ) Fpg enzyme.Oxidative DNA Damage Induction by a Simultaneous Treatment of N-Nitrosamines and Vitamin CIn subsequent combined treatment experiments with N-Nitrosamines and vitamin C, theHepG2 cells were always incubated in presence of Fpg enzyme. Figure 7 shows theprotective effect of vitamin C on NDMA (27 mM) (A), NPYR (5 mM) (B), NPIP (44 mM)(C) or NDBA (3 mM)(D)-induced oxidative DNA damage. Simultaneous treatment of HepG2cells with vitamin C and NDMA, NPYR, NDBA or NPIP reduced the genotoxic effects of theN-Nitrosamines in a dose-dependent manner. At concentrations of 1-5 µM vitamin C, theprotective effect was higher towards NPYR-induced oxidative DNA damage (78-79%) thanagainst NDMA (39-55%), NDBA (12-14%) and NPIP (3-55%), in presence of Fpg enzyme.However, a concentration of 10 µM vitamin C led to a maximum reduction in NDBA (94%),NPYR (81%), NPIP (80%) and NDMA (61%)-induced oxidative DNA damage, in presenceof Fpg enzyme. The protective effect of vitamin C (10 µM) was higher towards NDBAinducedoxidative DNA damage than against NDMA, NPYR and NPIP.