Folate, vitamin B12, homocysteine status and DNA damage in young Australian adults

Abstract

We performed a cross-sectional study (n = 49 males, 57 females) and a randomized double-blind placebo-controlled dietary intervention study (n = 31/32 per group) to determine the effect of folate and vitamin B12 (B12) on DNA damage (micronucleus formation and DNA methylation) and plasma homocysteine (HC) in young Australian adults aged 18-32 years. None of the volunteers were folate deficient (i.e. red blood cell folate <136 nmol/l) and only 4.4% (all females) were vitamin B12 deficient (i.e. serum vitamin B12 <150 pmol/l). The cross-sectional study showed that (i) the frequency of micronucleated cells (MNCs) was positively correlated with plasma HC in males (R = 0.293, P < 0.05) and (ii) in females MNC frequency was negatively correlated with serum vitamin B12 (R = -0.359, P < 0.01) but (iii) there was no significant correlation between micronucleus index and folate status. The results also showed that the level of unmethylated CpG (DNA) was not significantly related to vitamin B12 or folate status. The dietary intervention involved supplementation with 3.5x the recommended dietary intake (RDI) of folate and vitamin B12 in wheat bran cereal for three months followed by ten times the RDI of these vitamins via tablets for a further three months. In the supplemented group, MNC frequency was significantly reduced during the intervention by 25.4% in those subjects with initial MNC frequency in the high 50th percentile but there was no change in those subjects in the low 50th percentile for initial MNC frequency. The reduction in MNC frequency was significantly correlated with serum vitamin B12 (R = -0.49, P < 0.0005) and plasma HC (R = 0.39, P < 0.006), but was not significantly related to red blood cell folate. DNA methylation status was not altered in the supplemented group. The greatest decrease in plasma HC (by 37%) during the intervention was observed in those subjects in the supplemented group with initial plasma HC in the high 50th percentile, and correlated significantly with increases in red blood cell folate (R = -0.64, P < 0.0001) but not with serum vitamin B12. The results from this study suggest that (i) MNC frequency is minimized when plasma HC is below 7.5 micromol/l and serum vitamin B12 is above 300 pmol/l and (ii) dietary supplement intake of 700 microg folic acid and 7 microg vitamin B12 is sufficient to minimize MNC frequency and plasma HC. Thus, it appears that elevated plasma HC, a risk factor for cardiovascular disease, may also be a risk factor for chromosome damage.

Oxidative damage to cellular and isolated DNA by homocysteine: implications for carcinogenesis

“…However, recent studies have indicated that elevated homocysteine level is correlated with an elevated chromosome damage rate even when folate deficiency was not observed (Fenech et al, 1997(Fenech et al, , 1998. This result cannot be explained by deficient methylation of uracil to thymine.…”

“…In addition, over the age of 85, mortality in men with mutation of methylenetetrahydrofolate reductase gene (MTHFR), which is associated with an elevated level of plasma homocysteine, appeared to be primarily attributable to cancer rather than cardiovascular disease (Heijmans et al, 1999). Interestingly, recent investigations have demonstrated a link between elevated homocysteine status and the rate of chromosomal damage in the absence of folate and vitamin B 12 deficiencies (Fenech et al, 1997(Fenech et al, , 1998. This chromosome damage could contribute to the increased risk of cancer.…”

Methylenetetrahydrofolate reductase (MTHFR) polymorphisms and risk of molecularly defined subtypes of childhood acute leukemia

“…The role of folate in cancer probably is due to defects in different but related branches of folate metabolism including defective cell division caused by a shortage of thymidine for DNA synthesis and a shortage of methyl groups for DNA methylation. These pathways have been linked to chromosome instability in both in vitro and human studies of both cancerous and normal tissues (29)(30)(31)(32).…”

Cancer prevention and diet: Help from single nucleotide polymorphisms

“…Both high DNA uracil levels and chromosome breaks in humans are reversed by folate administration (4). Folate supplementation also minimized chromosome breakage in a different study (6). The potential role in human carcinogenesis of uracil misincorporation is supported by two studies that show a 2-to 4-fold lower risk of colon cancer for individuals who are homozygous for the variant 677 (CϾT) allele of methylene-THF reductase compared with controls (8,9).…”

“…There is accumulating evidence for this (R. T. Ingersoll, S. N. Wickramasinghe, and B.N.A., unpublished work; ref. 44) as well as chromosome breaks (6,7). The two deficiencies may act synergistically.…”