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
Low vitamin B6 status, based on plasma concentrations of pyridoxal-5’-phosphate (PLP), has been identified in inflammatory diseases including cardiovascular disease (CVD), rheumatoid arthritis, inflammatory bowel disease and diabetes. We examined the association between plasma PLP and multiple markers of inflammation in a community-based cohort (n=2605 participants (55% women, mean age 61±9)). We created an overall inflammation score (IS) as the sum of standardized values of 13 individual inflammatory markers. Multivariable-adjusted regression analysis was used to assess associations between the IS and plasma PLP. Mean plasma PLP concentrations were lower with higher tertile categories of IS. This relationship persisted after accounting for vitamin B6 intake. In addition, similar relations were seen between plasma PLP and four inflammation scores based on functionally related markers including acute phase reactants, cytokines, adhesion molecules and oxidative stress. Secondary analyses adjusting for CRP revealed an inverse association between plasma PLP and tertile categories of individual inflammatory biomarkers. This study in combination with past findings further supports our hypothesis that inflammation is associated with a functional deficiency of vitamin B6. We continued our research on assessing risks and benefits of folic acid fortification of food and supplement use. We tested a rat model to study the interaction between high folate status and B12 deficiency. This rat model did not exhibit clinical symptoms of B12 deficiency during the long duration of the study (43 weeks). Hence we are exploring other models including mice made B12 deficient in utero and cell cultures to study the deleterious effects of folate /B12 interaction. We developed an immunoassay for measuring plasma zinc. This was done as a part of the project for developing a multiplex assay for micronutrients in plasma for population studies.
1. High folic acid levels are related to anemia and poor cognitive test results in seniors. Folic acid from diet and supplements has to be converted into a biologically active form. High folic acid intake may result in presence of biologically inactive unutilized folic acid in the body. ARS-funded researchers from Tufts University in Boston, MA have found that presence of unutilized folic acid in blood is related to anemia and poor cognitive test performance in American seniors. Presence of unutilized folic acid in blood was related to increased occurrence of anemia in alcohol users. In seniors with a low vitamin B12 nutritional status, the presence of unutilized folic acid in blood was related to lower cognition. When vitamin B12 nutritional status is low, higher level of biologically active folate in the blood was related to increased odds of anemia. The results of this study show that nutritional imbalance due to high intake of folic acid can have negative health consequences especially when there is deficiency of vitamin B12.
2. Higher Intake of Vitamin B-6 May Protect Against Inflammation Low blood levels of the active form of vitamin B6 (PLP) have been linked to inflammation and the occurrence of inflammatory diseases like cardiovascular disease, rheumatoid arthritis and diabetes. However, the implications of these findings are unclear. ARS-funded researchers from Tufts University in Boston, MA have found that vitamin B-6 intake from diet and vitamin supplements is inversely related to inflammation status. We investigated the relationship between PLP and a marker of inflammation C-reactive protein (CRP) in participants of National Health and Nutrition Examination Survey which samples the general U.S. population. The results showed that higher vitamin B-6 intakes were linked to protection against inflammation. The results identify low B6 intake as a possible risk factor for inflammatory disease.