N05028: Folic acid and colon health

Study Duration: January 2001 to February 2004

Contractor: University of Ulster

Reduced folate status is associated with a higher risk of colorectal cancer; conversely, optimal status may confer some protective effect. Several molecular mechanisms have been proposed by which reduced folate status could increase the risk of carcinogenesis in the colon by perturbing DNA metabolism. The aim of this project is to investigate the relationship between folate status and replicative capacity, in colon biopsies and thus tests for carcinogenic mechanisms dependent on reduced folate status. This project uses novel techniques, based on the Comet assay (single-cell gel electrophoresis), to establish functional markers of relevance to neoplastic transformation which relate to folate status.

Objectives:

• To establish a protocol for the collection and preparation of colonic biopsy specimens for subsequent analysis of colon cells for DNA replication biomarkers through modified Comet assays.
• To confirm the inter-intra-sample reproducibility of the assays for DNA replication biomarkers likely to cause an increased risk of carcinogenesis.
• To investigate the variation in DNA replication biomarkers in colon cells (a) within and between individuals without polyps of the colonic mucosa and (b) within and between samples of normal mucosa in subjects found to have polyps of the colonic mucosa.
• To investigate the association between folate status and the DNA replication biomarkers.
• To investigate the role of low dose folic acid supplementation in reversing any DNA abnormalities: validation of DNA replication biomarkers which putatively relate to carcinogenesis, as functional markers of folate status.

Colonic mucosal biopsies will be collected and the colon epithelial cell folate and plasma and red blood cell folate status determined. Plasma homocysteine and MTHFR C677T genotype will also be determined. Dietary folate status will be determined by the diet history method and food frequency questionnaire. Comet assay will be performed on single cells from the biopsies; modified comet assays will also be performed to assay misincorporation of deoxyuridine into DNA and hypomethylation.

In a double-blind placebo controlled trial, subjects with colonic mucosal polyps (a minimum of n=24) will be assigned to one of three goups to receive either placebo, 200μg/d or 400μg/d for 6 months. On completion of the intervention, pre and post systemic folate status, local folate status, biomarkers of misincorporation of deoxyuridine and methylation status will be compared. Validation of these biomarkers will be based on the demonstration of modulation in their measurement in response to the achievement of optimal folate status defined as homocysteine lowering.