Antioxidant ability of Vitamin C for scavenging radiation induced long-lived radicals

Abstract

Chemical properties of vitamin C have been well studied by G. R. Buettner and his colleagues. Because pK_a of two OH group on the furan ring of L-ascorbic acid (AscH₂ ^-) are 4.1 and 11.8, ascorbate anions (AscH^-) are major chemical structure in biological system of weak alkaline. Although vitamin E (α-tocopherol) as antioxidants of oxidized lipid can reduce lipid radicals, vitamin E turn into α-tocopherol radicals those are in weakly oxidative. AscH^- can reduce α-tocopherol radicals by H atom (or H⁺ and e^-) transfer to be back in, α-tocopherol, and AscH^--- are oxidized to be Asc⋅^-. Because an unpaired electron in an Asc⋅^- are stabilized on π-conjugated system of furan ring with two ketons, Asc⋅^- are not reductive enough to produce super oxides by reduction of oxygen molecules. Two Asc⋅^- turned to an AscH^- and a DHA as dehydro-form by dismutation reaction, so that one Asc⋅^- can be recover as an AscH^-. DHA molecules can be reduced by GSH with enzymes to be AscH^- in biological system. We have been measured mutagenic long-lived radicals (LLRs) generated in irradiated hamster cells or non-irradiated recipient cells having irradiated medium with irradiated cells. LLRs in irradiated cells removed by the addition of vitamin C and/or N-acetylcysteine (NAC), however, NAC could not reduce LLRs in the recipient cells. Both vitamin C and NAC can be incorporated into cytsol of the cells, so that LLRs in irradiated cells may be distributed in the cytsol of the cells. On the other hand LLRs on the bystander effects could be produced in organelles having some proteins incorporating vitamin C such as GLUT-1 which can incorporate DHA from mitochondria intermembrane space to matrix. The difference in the reactivity of vitamin C and NAC with LLRs produced by bystander effects must be very important results for elucidating the mechanisms of inducing mutation from the LLRs.