Vitamin C in Cultured Human (HeLa) Cells: Lack of Effect on DNA Protection and Repair

Abstract

Aims: Dietary antioxidants, including vitamin C, may be in part responsible for the cancer-preventive effects of fruits and vegetables. Human intervention trials with clinical endpoints have failed to confirm their protective effects, and mechanistic studies have given inconsistent results. Our aim was to investigate antioxidant/ pro-oxidant effects of vitamin C at the cellular level. Experimental approach: We have used the comet assay to investigate effects of vitamin C on DNA damage, antioxidant status, and DNA repair, in HeLa (human tumor) cells, and HPLC to measure uptake of vitamin C into cells. Results: Even at concentrations in the medium as high as 200 μM, vitamin C did not increase the background level of strand breaks or of oxidized purines in nuclear DNA. Vitamin C is taken up by HeLa cells and accumulates to mM levels. Preincubation of cells with vitamin C did not render them resistant to strand breakage induced by H2O2 or to purine oxidation by photosensitizer plus light. Vitamin C had no effect on the rate of repair of strand breaks or oxidized bases by HeLa cells. However, vitamin C at a concentration of less than 1 μM, or extract from cells preincubated for 6 h with vitamin C, was able to induce damage (strand breaks) in lysed, histone-depleted nuclei (nucleoids). Conclusion: In these cultured human cells, vitamin C displays neither antioxidant nor pro-oxidant properties; nor does it affect DNA strand break or base excision repair.

Ascorbic Acid and Thiol Antioxidants Suppress Spontaneous Mutagenesis in a Cu,Zn-superoxide Dismutase-deficient Mutant of Saccharomyces cerevisiae

“…Therefore, the role of AsA in protecting against oxidative DNA damage in living cells is controversial (26)(27)(28). Our result provides evidence that AsA has a protective eŠect against oxidative damage-induced mutagenesis in vivo.…”

Genotoxic effect of ethacrynic acid and impact of antioxidants

“…In particular, ascorbic acid and vitamin E attenuated the oxidative DNA damage that was caused by either X-ray radiation or hydrogen peroxide , benzo(a)pyrene [Gajecka et al, 1999], and N-nitrosomorpholine [Robichová and Slamenová, 2002]. On the other hand, ascorbic acid and vitamin E did not attenuate oxidative DNA damage that was caused by the anticancer drug known as Q-85 HCl [Azqueta et al, 2007] and by either hydrogen peroxide or the photosensitizer called Ro-19-8022 [Azqueta et al, 2013]. Taken…”

Dietary Antioxidant and Oxidative Stress: Interaction between Vitamins and Genetics

“…The ascorbic acid content in fruits and vegetables varies with the conditions under which they grow, and the degree of maturation [17]. Vitamin C consumed is absorbed in the small intestine by active transportation performed by the Vitamin C transporter type 1, which is encoded by the SLC23A1 gene (vitamin C transporter gene 1).…”

“…In addition to neutralizing free radicals, vitamin C also acts in the regeneration of α-tocopherol, a component of the vitamin E family, which also has antioxidant action [17].…”