EFFECT OF DIET AND VITAMIN-C ON DNA STRAND BREAKAGE IN FRESHLY-ISOLATED HUMAN WHITE BLOOD-CELLS

We have measured DNA strand breaks induced by ionising radiation in nu cleated cells from freshly isolated whole blood from normal human subj ects. Samples were taken after subjects had fasted overnight and again 1 h after they had eaten breakfast in combination with approximately 35 mg/kg vitamin C. Damage was measured by single cell gel electrophor esis (the 'comet' assay), in which DNA single strand breaks generate a comet tail streaming from the nucleus. In repeat experiments on 6 sub jects a reduction in DNA damage, as indicated by a highly significant decrease in overall comet length, was observed following vitamin C ing estion, both in the unirradiated control blood samples and in the dose response to ionising radiation damage. In addition, consistent differ ences in dose response between individual subjects were found. The pea k effect was 4 h after intake of food and vitamin C. An effect was als o seen with vitamin C alone and after breakfast without additional vit amin C. Protection against strand breakage was also seen in Ficoll-sep arated mononuclear cells but evidence was not obtained for protection of separated, mitogen stimulated T-lymphocytes either against ionising radiation cell killing in a clonal assay, or against clastogenicity a ssessed by micronucleus formation following one cell division. Exposur e of separated lymphocytes in vitro to vitamin C, at doses greater tha n 200 mu M, did not offer protection but induced strand breakage. Our results raise the possibility that variation in normal diet may not on ly affect susceptibility to endogenous oxidative damage, but may affec t some responses of the individual to radiation.