1a. Objectives (from AD-416)
1. Determine the impact of mandatory food folic acid fortification in the United States. 2. Determine the interrelationships between B vitamin status, methionine intake, genetic polymorphism and plasma homocysteine. 3. Determine the hereditary association of plasma homocysteine and vitamin status. 4. Determine the biochemical, pathological and functional impact of nutritional and genetic disruptions of one-carbon metabolism, in animal models of age-related vascular and neurological dysfunction, with emphasis on the roles of B vitamins, homocysteine and methionine in tissue-specific susceptibility to disease.
1b. Approach (from AD-416)
In this project, we will use multiple approaches to study the biochemistry and molecular biology of the interaction of B vitamins with each other and their role in modulating the risk for age-related pathologies, and the genetic factors that influence these interactions. We will determine the interaction between vitamin B12 status, unmetabolized folic acid, methyl tetrahydrofolate and folic acid intake in relation to cognitive impairment, bone mineral density, cardiovascular disease risk, diabetes and cancer. For this purpose, we will measure the unmetabolized folic acid and methyl folate in the plasma of participants in National Health and Nutrition Examination Survey 1999-2002 and Framingham Heart Study (FHS) Offspring cohorts, measure plasma concentration of methylmalonic acid (MMA) in FHS Offspring cycle 7 examinations and use plasma MMA as a marker of vitamin B12 status. We will also use an animal model of vitamin B12 deficiency to characterize the biochemical and hematological effect of high folate status under vitamin B12 deficiency. The gene-nutrient interaction between folate and the 677C>T polymorphism of the methylene tetrahydrofolate reductase (MTHFR) gene will be studied by determining the changes in DNA methylation and gene expression using microarray analysis after a 3-month dietary supplementation of 400µg/day folic acid in individuals homozygous for the C and T alleles of the MTHFR polymorphism. The heritability of plasma homocysteine concentration in FHS cohort will be determined by comparing data on plasma homocysteine from 3 generations of FHS participants in the context of their plasma folate and vitamin B12 status, and by determining the association between polymorphisms in genes that influence methylation of homocysteine including those involved in uptake of vitamin B12, and plasma homocysteine concentration.
3. Progress Report
Developed a more efficient and accurate method to measure distribution of various forms of folate in tissue samples and unmetabolized folic acid in blood samples. Continued our research on assessing risks and benefits of folic acid fortification of food and supplement use. In a collaborative project, we showed that excess folic acid supplementation during pregnancy negatively influences embryonic development in mice. Developed immunoassays for the following micronutrients or their biomarkers. Folate, zinc, iron (ferritin), vitamin A (retinol binding protein), and iodine (thyroglobulin). This was done as a part of the project for developing a multiplex assay for micronutrients in plasma for population studies. We are in the process of optimizing the assays for plasma samples. Measured plasma concentration of MMA from exam 7 of Framingham heart Study cohort. These data have been reported to the Framingham subcontractors, who have assembled the analytic data sets and begun the statistical analyses upon which the conclusions of our study will be based. Determined the change in genomic DNA methylation in white blood cells of individuals who were supplemented with folic acid or placebo to study the effect of the polymorphism of methylene tetrahydrofolate reductase (MTHFR) gene and folate status on DNA methylation. After supplementation with folic acid for a 3 month period we did not detect any change in DNA methylation in the white blood cells when compared to those who did not receive folic acid supplementation.
1. High intake of folic acid disrupts embryonic development in mice. Folic acid fortification and supplementation has increased folate intake and blood folate concentrations and successfully reduced the incidence of neural tube defects. However, the developmental consequences of high folate intake are unknown. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, in collaboration with researchers from McGill University and Montreal Children's Hospital Research Institute, investigated the impact of high folate intake on embryonic and placental development in mice in the presence or absence of a defect in the enzyme methylene tetrahydrofolate reductase (MTHFR) that has been shown to be associated with developmental abnormalities. Pregnant mice on a control diet (recommended intake of folic acid for rodents) or folic acid-supplemented diet (20-fold higher than the recommended intake) were examined for embryonic loss, delay, and defects. The folic acid supplemented diet was associated with embryonic delay and growth retardation, and may confer susceptibility to embryonic defects. Our study suggests that high folate intake may have adverse effects on fetal mouse development and that maternal MTHFR deficiency may improve or rescue some of the adverse outcomes. These findings underscore the need for additional studies on the potential negative impact of high folate intake during pregnancy.
2. Plasma vitamin B6 may be protective against colorectal adenoma in a multiethnic population. Plasma concentration of vitamin B6 has been inversely associated with colorectal cancer (CRC) risk but few studies have examined the relationship of vitamin B6 to colorectal adenoma, the precursor lesion to most CRCs. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, in collaboration with researchers from University of Hawaii Cancer Center, measured plasma levels of folate, vitamin B6, and vitamin B12 in patients with pathologically confirmed first occurrence of colorectal adenoma and controls among Caucasians, Japanese Americans, and Native Hawaiians undergoing flexible sigmoidoscopy screening in Hawaii. High plasma level of vitamin B6 was independently inversely associated with risk of colorectal adenoma. This study suggests that vitamin B6 may be protective against the early stages of colorectal carcinogenesis.