Handbook of Vitamin C Research

Vitamin C Protects from Oxidative DNA Damage… 115vitamin C (1-10 M) exerted a pronounced effect on UDP-glucuronyltransferase activity,increasing almost 1.8-fold (171-178%, respectively) (Figure 11). Moreover, there was a goodcorrelation between induction of human UDP-glucuronyltransferase activity by vitamin Cand its inhibition of oxidative DNA damage induced by N-Nitrosamines.The protective role of vitamin C against oxidative stress induced by environmentalmutagens has been previously demonstrated [91]. Collins et al. [92] showed that 3-weekingestion of 1–3 kiwi fruits, rich in vitamin C, per day, decreased Endo III and Fpg sensitivesites, as well as decreased ex vivo sensitivity toward H 2 O 2 . Thus, vitamin C is includedamong the radical trapping antioxidants and is considered one of the most efficientantioxidants [93]. It has been shown that vitamin C reacts directly with superoxide, hydroxylradicals, and singlet oxygen [94]. Witenberg et al. [95] has also suggested that vitamin C,being an antioxidant, partially neutralizes peroxides and decreases the intracellular oxidativelevel, and thus protects cells from oxidative DNA damage.In our study, vitamin C protected against DNA strand breaks and oxidative DNA damageinduced by H 2 O 2 , although it was more effective against oxidative damage in pyrimidines(35%) than in purines (12%) (Figure 10). These findings suggest that one possiblemechanism for the protective effect of vitamin C towards oxidative DNA damage induced byN-Nitrosamines could be due to the free radical scavenging efficiency of vitamin C. Qi et al.[96], using HPLC, showed a decrease in 8-oxoguanine in H 2 O 2 -treated calf thymus DNA,after administering vitamin C (1-250 M). Cheng et al. [97] demonstrated an inhibitory effectof vitamin C (50–200 M) on ozone-induced 8-oxoguanine in human lung carcinoma cells(A549 cells). Moreover, Lazarová and Slamenová [82] found that pre-treatment of HepG2cells with 0.5 mM of vitamin C efficiently reduced the level of oxidative DNA damageinduced by benzo(a)pyrene, which generates hydroxyl radicals. Overall, the vitamin C is apowerful antioxidant acting both directly via scavenging of ROS and indirectly throughregeneration of other antioxidant systems [98].Apoptosis induced by carcinogens seems to have an important role in cancerdevelopment [99, 100, 101]. Accordingly, the mechanism and cell signaling pathwaysinvolved in food carcinogen-induced cell death or cell survival and proliferation haverecently received much interest [74, 102]. Our results showed that exposure of HepG2 andHL-60 cells to increasing concentrations of NDMA (27-135 mM), NPYR (10-50 mM) NPIP(10-45 mM; 5-20 mM; respectively) and NDBA (1-3.5 mM; 0.5-2.5 mM; respectively)resulted in an elevated percentage of apoptosis via a caspase-dependent pathway [44, 45, 46].NDBA was the most effective N-Nitrosamine to induce apoptosis in HepG2 and HL-60 celllines. At 72 h, 2.5 and 2 mM NDBA induced 51 and 44% of apoptotic HepG2 and HL-60cells, respectively, whereas it was necessary to use doses of 25 and 20 mM NPIP (70 and75%, respectively), 50 mM NPYR (52 and 51%, respectively) and 68 mM NDMA (54 and49%, respectively) to obtain a high percentage of apoptotic cells by TUNEL assay. The factthat the percentage of apoptotic cells varied with the type of N-Nitrosamine suggests that theapoptotic effect depended on the chemical structure of N-Nitrosamine.Recently, much effort has been directed towards the manipulation of the apoptoticprocess for the treatment and prevention of cancer, and the search for compounds thatinfluence apoptosis [103]. In the present chapter, we first evaluated the cytotoxicity ofvitamin C using the MTT and the LDH assay in HepG2 and HL-60 cells. Moreover, in order