DNA stability and genomic methylation status in colonocytes isolated from methyl-donor-deficient rats.

Abstract

Epidemiological studies report an inverse relationship between intake of the B vitamin folic acid and colon cancer. Folate is important for DNA synthesis and repair. Moreover, the production of S-adenosylmethionine (SAM), essential for normal DNA methylation and gene expression, is dependent on folic acid. Folate deficiency may increase the risk of malignant transformation by perturbing these pathways. The principal aim of this study was to determine the effects of folate deficiency on DNA stability and DNA methylation in rat colonocytes in vivo. As the metabolic pathways of folate and other dietary methyl donors are closely linked, the effects of methionine and choline deficiency were also evaluated. Male Hooded-Lister rats were fed a diet deficient in folic acid, or in methionine and choline, or in folate, methionine and choline for 10 weeks. DNA strand breakage and misincorporated uracil were determined in isolated colonocytes using alkaline single cell gel electrophoresis. Global DNA methylation was measured in colonic scrapings. Folate was measured in plasma, erythrocyte and liver samples. Methyl donor deficiency induced DNA strand breakage in colonocytes isolated from all experimental groups. Uracil levels in colonocyte DNA remained unchanged compared with controls. DNA methylation was unaffected either by folate and/or methionine and choline depletion. Rats fed a folate-deficient diet had less folate in plasma, red blood cells and liver than controls. Folate and methyl deficiency in vivo primarily affects DNA stability in isolated colonocytes of rats, without affecting overall DNA methylation.