Uracil misincorporation into DNA of leukocytes of young women with positive folate balance depends on plasma vitamin B12 concentrations and methylenetetrahydrofolate reductase polymorphisms. A pilot study.J Nutr Biochem 2005; 16(8):467-78JN
Changes in the folate and vitamin B12 status in the body influence the extent of uracil misincorporation (UrMis) into DNA, which is one of the biomarkers of genomic stability and, thus, portends a risk of cancer. In our study, the level of UrMis into DNA was evaluated by the comet assay (using the specific DNA repair enzyme, uracil DNA glycosylase) in leukocytes from blood donated by healthy young women with positive folate balance achieved by 4 weeks of folic acid supplementation (400 microg/day). The nutritional status was evaluated on the basis of nine food diaries recorded by the subjects during two winter months. The data were computerized, and the intake of nutrients and micronutrients was estimated using the DIETA 2 program (Food and Nutrition Institute, Warsaw, Poland) linked to recently updated Polish food tables. The plasma folate and vitamin B12 concentration, as well as methylenetetrahydrofolate reductase (MTHFR) polymorphisms, were evaluated to determine their influence on the level of UrMis into DNA. The mean value of B12 intake for all subjects reached 100% of the Polish recommended dietary allowances (RDA), whereas the mean value of folate intake, before folate supplementation, was 50%, suggesting moderate deficiency. Folic acid supplementation brought the folate intake way above the RDA, and plasma folate concentration in each individual was above the deficient range (mean value 14.67 ng/ml). The UrMis did not correlate with the plasma folate concentration, but the level of UrMis was significantly lower in subjects with plasma vitamin B12 concentration above 400 pg/ml (P=.02) only after folic acid supplementation. The concentration of folate in plasma correlated (P<or=.05) with the wild-type MTHFR homozygote 1298 AA but not with the MTHFR 677 genotype. When subjects were grouped according to genotype, the mean concentration of folate in plasma was significantly lower in subjects with the MTHFR 677 (CT+TT) polymorphism, which was accompanied by a lower UrMis, compared to individuals with the CC genotype. The significantly higher concentrations of folate in serum, accompanied by increased UrMis, were seen in subjects with the combined MTHFR 1298 (AC+CC) genotype, as compared to the 1298 AA wild type. Our results suggest that more than 400 pg/ml of vitamin B12 in plasma in subjects with a positive folate balance is critical for genomic stability and indicate that the amount of UrMis into DNA is related to the MTHFR genotype.