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:
For our studies on the association between B vitamins and health outcomes in Framingham Heart Study cohorts, we completed measurement of plasma concentration of methylmalonic acid (MMA, biomarker of vitamin B-12 nutritional status) in the Offspring cohort and Gen3 cohort. We have begun analysis of the association between plasma concentrations of MMA, vitamin B-12 and folate, and cognitive function in this cohort. Among Framingham Offspring Cohort members aged >/= 65 years, those with low plasma vitamin B-12 and high plasma MMA concentrations showed poor performance and accelerated decline in performance on cognitive tests. Accelerated decline in performance on cognitive tests was also observed in individuals whose average folate intake was 917 microgram/day – more than twice the current recommendation. These results reinforce the notion that high folic acid intakes adversely affect cognitive function. We are currently in the process of writing the manuscript reporting on the results of these analyses. The data on MMA concentration from Gen3 cohort was sent to Framingham subcontractors to assemble the analytical data set for our study on B vitamins and bone mineral density. To identify populations at risk for micronutrient deficiency, it is critical to have analytical methods for nutrient assessment in biospecimens. Similarly, laboratory assessment of absorption and bioavailability of micronutrients are essential to confirm efficacy of the any nutrient intervention. The purpose of this project was to develop a proof of concept for a unique, new technology that allows, for the first time, measurement of multiple micronutrients simultaneously in biospecimens, rather than one at a time. We developed a multiplex assay for measuring 5 nutrients (or their biomarkers) in plasma samples simultaneously. The nutrients that can be measured using this assay include folate, zinc, iron (ferritin), vitamin A (retinol binding protein) and iodine (thyroglobulin).
1. Plasma pyridoxal-5-phosphate is inversely associated with systemic markers of inflammation in a population of US Adults. Low pyridoxal 5’phosphate (functional form of vitamin B-6) concentration in blood has been associated with various inflammatory diseases, including cardiovascular disease, rheumatoid arthritis, inflammatory bowel disease, and diabetes. Presence of inflammation even in the absence of a disease can be determined using markers of inflammation in blood. To determine the association between concentration of pyridoxal phosphate in blood and inflammation ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, Massachusetts created an overall inflammation score using 13 individual markers of inflammation. We examined the association between pyridoxal phosphate concentration in plasma and inflammation score among 2229 participants of Framingham Heart Study. Blood concentrations of pyridoxal phosphate were lower among individuals with a high inflammation score when compared with those who have low inflammation score. These relationships persisted after accounting for vitamin B-6 ingestion showing that these results are not due to differences in vitamin B-6 in the diet. These results suggest that during inflammation there is a higher demand for vitamin B-6 and it may be used for the processes of inflammation.
2. Risk of retinoblastoma is associated with a maternal polymorphism in dihydrofolate reductase (DHFR) and prenatal folic acid intake. Maternal intake of naturally occurring folate from vegetables during pregnancy is associated with lower risk of retinoblastoma (cancer of the eye) in offspring. ARS-funded researchers at JM USDA HNRCA at Tufts University in Boston, Massachusetts in collaboration with researchers at Columbia University, New York, Hospital Infantil de Mexico (HIM), Mexico, National Institute of Public Health, Mexico and Mexican Institute of Social Security, Mexico examined the association between retinoblastoma risk and maternal genetic variations in genes for 2 enzymes that carry out reactions involving folate, methylene tetrahydrofolate reductase and dihydrofolate reductase. One hundred three mothers of children with newly diagnosed retinoblastoma and 97 mothers who had healthy children from central Mexico were enrolled in the study. The risk of having a child with retinoblastoma was associated with maternal genetic variation in dihydrofolate reductase and the risk was elevated significantly among those who reported taking folic acid supplements during pregnancy. Dihydrofolate reductase is necessary for converting synthetic folic acid into biological folate. The genetic variation in dihydrofolate reductase decreases the ability of the body to convert folic acid. Prenatal ingestion of synthetic folic acid supplements may be associated with increased risk for early childhood cancer in a genetically susceptible subset of the population.