EFFECT OF ANTIOXIDANT VITAMIN SUPPLEMENTATION ON DNA-DAMAGE AND REPAIR IN HUMAN LYMPHOBLASTOID-CELLS

In this study the possible protective effects of ascorbic acid and alp ha-tocopherol (singly and in combination) on Raji lymphoblastoid cells exposed to various doses of X-rays or hydrogen peroxide (H2O2) are in vestigated. DNA strand breaks and alkali-labile sites were measured us ing the alkaline comet assay. Survival and hypoxanthine guanine phosph oribosyl transferase mutant frequency were measured using the colony-f orming assay. Ascorbic acid (60 mu M) and alpha-tocapherol (30 mu M) w ere added singly or together to cell culture medium 24 hours before tr eatment and were present during treatment. After the 24-hour supplemen tation period with ascorbic acid atone, alpha-tocopherol alone, and as corbic acid + alpha-tocopherol, the level of endogenous DNA damage was significantly lower (p < 0.05) than in the nonsupplemented culture, a s assessed by the comet assay. By use of the comet assay, it was obser ved that ascorbic acid exhibited an overall protective effect against DNA damage induced after X-ray treatment, whereas alpha-tocopherol exh ibited an overall protective effect against DNA damage induced after H 2O2 treatment. Significant increases were observed in the percent surv ival after 1-Gy X-rays and 5 and 20 mu M H2O2 in those cultures supple mented with ascorbic acid alone and alpha-tocopherol alone relative to the nonsupplemented cultures. The endogenous level of mutant frequenc y was also significantly decreased in the presence of ascorbic acid re lative to the nonsupplemented culture. These findings are consistent w ith the concept that ascorbic acid and alpha-tocopherol can, under cer tain conditions, protect against oxidatively induced DNA damage.