Inhibition of Pro-oxidative Activity of β-Carotene in Human Cells by Intracellular Ascorbic Acid

Inconsistent results exist in the literature regarding whether ascorbic acid (AA) interacts with β-carotene (BC) directly and decreases BC autooxidation and pro-oxidative activity. We previously reported that BC enhances oxidative damage in human foreskin fibroblasts (Hs68) induced by 2, 2′-azobis (2, 4-dimethyl-valeronitrile) (AMVN). Herein, we investigated whether intercellular AA reduces the pro-oxidative activity of BC induced by AMVN in Hs68 cells and human embryo intestine cells (Int407) and whether such an effect is direct or indirect. Both types of cells were pre-incubated with AA or dehydroascorbate (DHA) with or without subsequent incubation with 20 μM BC, followed by 50 mM AMVN treatment. Lipid peroxidation, comet assay and the consumption of intercellular AA and BC were determined. The results showed that incubation of both cell types with 20 μM AA or DHA significantly decreased AMVN-induced DNA damage, but the effect of such a treatment on lipid peroxidation was significant only in Int407 cells. By contrast, lipid peroxidation induced by AMVN was significantly decreased in both cell lines pre-incubated with either AA or DHA with subsequent incubation with BC. However, intracellular AA only slightly decreased the consumption of BC by AMVN and this effect of AA was not concentration-dependent, indicating the impossibility of direct recycling of BC by AA. The results suggest that protection against the pro-oxidative activity of BC by AA in cells is indirect, possibly through blocking the chain reaction of BC oxidative products.