Global DNA and p53 region-specific hypomethylation in human colonic cells is induced by folate depletion and reversed by folate supplementation.

There is increasing evidence to suggest that reduced folate status may be a causative factor in carcinogenesis, particularly colorectal carcinogenesis. Folate is essential for the synthesis of S-adenosylmethionine, the methyl donor required for all methylation reactions in the cell, including the methylation of DNA. Global DNA hypomethylation appears to be an early, and consistent, molecular event in carcinogenesis. We have examined the effects of folate depletion on human-derived cultured colon carcinoma cells using 2 novel modifications to the Comet (single cell gel electrophoresis) assay to detect global DNA hypomethylation and gene region–specific DNA hypomethylation. Colon cells cultured in folate-free medium for 14 d showed a significant increase in global DNA hypomethylation compared with cells grown in medium containing 3µmol/L folic acid. This was also true at a gene level, with folate-deprived cells showing significantly more DNA hypomethylation in the region of the p53 gene. In both cases, the effects of folate depletion were completely reversed by the reintroduction of folic acid to the cells. These results confirm that decreased folate levels are capable of inducing DNA hypomethylation in colon cells and particularly in the region of the p53 gene, suggesting that a more optimal folate status in vivo may normalize any DNA hypomethylation, offering potential protective effects against carcinogenesis. This study also introduces 2 novel functional biomarkers of DNA hypomethylation and demonstrates their suitability to detect folate depletion–induced molecular changes.

The effect of folic acid supplementation on dna biomarkers of colorectal cancer risk (uracil misincorporation, global and gene-specific dna hypomethylation) : a randomised intervention study

Background - Alterations in folate status are associated with colorectal carcinogenesis. Folate’s role has been postulated to be either via prevention of changes in DNA methylation or uracil misincorporation.
Objective - To investigate the effect of folic acid supplementation on colonocyte folate status and DNA biomarkers.
Design - Twenty individuals harbouring colonic adenomas were randomised to receive folic acid (600 g daily) or placebo for 6 months post polypectomy. Systemic and colonocyte folate status was determined at baseline and following the intervention. Modified Comet assays were used to determine uracil misincorporation and global DNA hypomethylation at the site adjacent to the polyp and a site distal to the polyp.
Outcomes - Supplementation resulted in increased colonocyte folate, which approached significance, at the site adjacent to the polyp (P= 0.06) but not distal to the polyp (P= 0.36); correspondingly there was a reduction in uracil misincorporation at the site adjacent to the polyp (P = 0.02) and the distal site showed no such trend (P= 0.39). There were no significant changes in global DNA hypomethylation at either site post-intervention.
Conclusions - Folic acid supplementation resulted in increased colonocyte folate and decreased uracil misincorporation at the site of the adenoma but not distal to the adenoma. This supports the hypothesis that localised areas of folate deficiency may exist in human colonic mucosa which respond to folic acid supplementation through increasing colonocyte folate and improving folate-related DNA biomarkers of cancer risk.

Evolution of a contagious cancer: epigenetic variation in devil facial tumour disease

The emergence of Devil Facial Tumour Disease (DFTD), a highly contagious cancer, is driving Tasmanian devils (Sarcophilus harrisii) to extinction. The cancer is a genetically and chromosomally stable clonal cell line which is transmitted by biting during social interactions. In the present study, we explore the Devil Facial Tumour (DFT) epigenome and the genes involved in DNA methylation homeostasis. We show that tumour cells have similar levels of methylation to peripheral nerves, the tissue from which DFTD originated. We did not observe any strain or region-specific epimutations. However, we revealed a significant increase in hypomethylation in DFT samples over time (p < 0.0001). We propose that loss of methylation is not because of a maintenance deficiency, as an upregulation of DNA methyltransferase 1 gene was observed in tumours compared with nerves (p < 0.005). Instead, we believe that loss of methylation is owing to active demethylation, supported by the temporal increase in MBD2 and MBD4 (p < 0.001). The implications of these changes on disease phenotypes need to be explored. Our work shows that DFTD should not be treated as a static entity, but rather as an evolving parasite with epigenetic plasticity. Understanding the role of epimutations in the evolution of this parasitic cancer will provide unique insights into the role of epigenetic plasticity in cancer evolution and progression in traditional cancers that arise and die with their hosts.

Folic acid supplementation in postpolypectomy patients in a randomized controlled trial increases tissue folate concentrations and reduces aberrant DNA biomarkers in colonic tissues adjacent to the former polyp site

BACKGROUND: Low folate status is associated with an increased risk of colorectal carcinogenesis. Optimal folate status may be genoprotective by preventing uracil misincorporation into DNA and DNA hypomethylation. Adenomatous polyps have low folate status compared with normal colonic mucosa, and they are surrounded by histologically normal mucosa that also is of low folate status. OBJECTIVE: In a randomized controlled trial conducted at a single Dublin hospital between April 2002 and March 2004, we assessed the effect of folic acid supplementation on tissue folate, uracil misincorporation into DNA, and global DNA hypomethylation in colonocytes isolated from sites of adenomatous polyps and from histologically normal tissue adjacent and 10-15 cm distal to them. METHODS: Twenty patients with adenomatous polyps on initial colonoscopy and polypectomy were randomly assigned to receive either 600 μg folic acid/d [n = 12, 38% men, mean age 64.3 y, and body mass index (BMI, in kg/m(2)) 26.6] or placebo (n = 8, 50% men, mean age 68.4 y, and BMI 27.2) for 6 mo, and then repeat the colonoscopy. Blood and colonocyte tissue folate concentrations were measured with the use of a microbiological assay. Uracil misincorporation and global DNA hypomethylation were measured in colonocytes with the use of modified comet assays. RESULTS: Over time, folic acid supplementation, compared with placebo, increased tissue folate (mean ± SEM) from 15.6 ± 2.62 pg/10(5) cells to 18.1 ± 2.12 pg/10(5) cells (P < 0.001) and decreased the global DNA hypomethylation ratio from 1.7 ± 0.1 to 1.0 ± 0.1 (P < 0.001). The uracil misincorporation ratio decreased by 0.5 ± 0.1 for the site adjacent to the polyp over time (P = 0.05). CONCLUSION: A response to folic acid supplementation, which increased colonocyte folate and improved folate-related DNA biomarkers of cancer risk, was seen in the participants studied. Exploratory analysis points toward the area formerly adjacent to polyps as possibly driving the response. That these areas persist after polypectomy in the absence of folate supplementation is consistent with a potentially carcinogenic field's causing the appearance of the polyp.