Research Project: One Carbon Nutrients and Metabolism

Location: Jean Mayer Human Nutrition Research Center On Aging

2016 Annual Report

Objectives
LAB NAME: Vitamin Metabolism & Aging 1. Develop new and efficient methods for assessing nutritional status in individuals for B vitamins and their functional markers with internal standards obtained from plants grown on D2O or yeast grown on C-13 glucose. 2. Determine the biochemical, pathological and functional impact of nutritional status and genetic variations in B complex vitamin metabolism with special emphasis on the effect of age, in human, animal and cell culture models. Consider the nutritional status of other B vitamins while studying the effect of each B vitamin. 3. Determine the impact of mandatory folic acid fortification of cereals including effects of improved nutritional status as well as excess intake of folic acid on outcomes including disease risk, cognitive function, inflammation and immune response, with emphasis on understanding the mechanism behind the side-effects.

Approach
LAB NAME: Vitamin Metabolism & Aging We will use biochemical, molecular biological and epidemiological approaches to study the role of B vitamins and the genes involved in their metabolism, in modulating processes associated with aging, disease development and increased risk for diseases. We will explore the association between pyridoxal 5’-phosphate, the active form of vitamin B6 and inflammation by measuring the immunomodulatory compounds in plasma that are produced from pyridoxal 5’-phosphate-dependent reactions in a cohort of elders. Decrease in vitamin B12 status can potentially result in decrease in muscle strength. We will explore the association between vitamin B12 and muscle strength and power, to determine the feasibility of an intervention trial to improve muscle strength. Fortification of cereals with folic acid was adopted by the US and many other countries to reduce neural tube defects. While natural folate from plants and meat can enter the metabolic pathway directly, folic acid, the synthetic form of the vitamin in supplements and fortified foods, has to be reduced by dihydrofolate reductase prior to entering the metabolic pathway. A 19bp deletion polymorphism in intron 1 of dihydrofolate reductase has been associated with increased risk for cancer in supplement users. We will determine the effect of this 19bp deletion on gene expression and enzyme activity of dihydrofolate reductase and the reactions of folate pathway. Intake of folic acid in excess of the ability of the body to metabolize it has been associated with negative health outcomes. Using a mouse model we will determine the effect of excess intake of folic acid on immune function and response to infections. We will explore the association between the polymorphism in dihydrofolate reductase gene and folic acid intake in modulating the risk for breast cancer using the samples and data from the PLCO cohort.

Progress Report
LAB NAME: Vitamin Metabolism & Aging: While adequate folate nutrition is necessary for optimal immune function, high folate intake is associated with reduced natural killer cytotoxicity, which is the first line of defense against cancer and infections. We have successfully established a causal relationship between high folic acid intake and lower natural killer cytotoxicity in aged mice. In this project period we found that aged mice fed a high folic acid diet were more susceptible to influenza infection. Mice fed a high folic acid diet had higher viral titer in lung tissues after 2 days post-infection compared to control mice, although there were no differences after 5 days post-infection. Mice fed a high folic acid diet also had significantly lower expression of the inflammatory cytokines 5 days post-infection compared to mice fed a control diet. Inflammatory response after infection is important for viral load clearance and recovery from infection. However, too much inflammation can also result in lung pathology and tissue damage. Additional research is necessary to determine if the difference in inflammation response in the mice fed a high folic acid and control diets affects lung pathology or clearance of influenza virus. Folic acid, the synthetic form of folate used in supplements and fortified foods, has to be reduced by dihydrofolate reductase (DHFR) before it can enter the metabolic pathway. A 19bp deletion polymorphism (19bpdel) in intron 1 of DHFR is associated with increased risk for cancer. We had previously determined that individuals with the polymorphism have more DHFR transcript when compared to those without the polymorphism. In unstimulated cells, there was no difference between the genotypes in the amount of DHFR protein. Using a cell culture model we determined that the homozygosity for the polymorphism results in lower levels of DHFR protein and impaired folate pathway reactions. This could be a mechanism by which the polymorphism increases the risk for cancer.

Accomplishments
1. LAB NAME: Vitamin Metabolism & Aging: High folic acid diet results in lower natural killer cell activity in aged mice. Consumption of folic acid, the synthetic form of the B vitamin folate beyond the ability of the body to convert it to biological folate, is associated with lower activity of natural killer (NK) cell in post-menopausal women. NK cells are specialized immune cells that are critical for surveillance and defense against virus-infected and cancer cells. Tufts University researchers at USDA in Boston, Massachusetts, determined if a high folic acid diet can result in reduced NK cell activity in aged mice fed a diet with the recommended dietary allowance (1x RDA, control) or 20x RDA (high) folic acid for 3 months. Mice fed a high folic acid diet had lower NK cell activity when compared to mice on control diet. Mice fed high folic acid had a high proportion of naive and less effective NK cells compared to mature, active NK cells, suggesting that their development process had been impaired. These results show that high folic acid intake can reduce NK cell activity which may increase the susceptibility to cancer and viral infections especially in the elderly who are already at increased risk for these diseases.

2. LAB NAME: Vitamin Metabolism & Aging: Exposure to supplemental folic acid at recommended levels during pregnancy does not lead to increased unmetabolized folic acid concentrations in maternal or cord blood. Folic acid (FA) from fortified foods and supplements, although largely considered beneficial, is associated with unmetabolized FA in the circulation, which has raised some health concerns. Tufts University researchers at USDA in Boston, Massachusetts, in collaboration with scientists at University of Ulster, Causeway Hospital, Royal-Jubilee Maternity Service, Frontier Science from U.K. and University College Dublin, Dublin City University and Trinity College from Ireland determined the effect of supplemental FA at a dose of 400 µg/d during pregnancy on unmetabolized FA concentrations in maternal plasma and newborn cord blood plasma. A higher proportion of women in the FA compared with the placebo group had detectable FA in plasma, but the concentrations were not significantly different between the 2 groups. FA treatment throughout pregnancy resulted in higher cord blood plasma total folate concentrations, but the proportion of samples with detectable FA concentrations was similar in FA-treated and placebo groups. The benefits for mothers and offspring of continuing FA supplementation beyond the first trimester of pregnancy can be achieved without posing any risk of increasing unmetabolized circulating FA, even in those already exposed to FA from fortified food.

3. LAB NAME: Vitamin Metabolism & Aging: Unmetabolized folic acid in pre-diagnostic plasma and the risk of colorectal cancer. Higher folate has been associated with a reduced colorectal cancer (CRC) risk, but excessive folate may promote tumor progression. Tufts University researchers at USDA in Boston, Massachusetts, in collaboration with scientists at Harvard Medical School and Harvard School of Public Health evaluated pre-diagnostic plasma levels of unmetabolized folic acid (FA) in relation to CRC risk using blood samples collected prior to FA fortification from 618 CRC cases and 1207 cancer free individuals. FA levels increased CRC risk 1.57 fold among men and 2.2 fold among those with a common genetic variation in folate metabolizing gene methylene-tetrahydrofolate reductase. Unmetabolized FA in plasma indicative of folic acid intake beyond the metabolic capacity of the body may increase CRC risk in a subset of population.

4. LAB NAME: Vitamin Metabolism & Aging: Genetic variations in maternal folate pathway genes interact with arsenic in drinking water to influence risk of neural tube defects. Arsenic induces neural tube defects and reduces the protective effect of folic acid supplementation on neural tube defects. Tufts University researchers at USDA in Boston, Massachusetts, school of Public Health and Dhaka Community Hospital in Bangladesh determined whether genetic variations in folate metabolism affects the risk for neural tube defect associated with drinking water contaminated with inorganic arsenic. Arsenic concentration in drinking water was associated with increased risk of neural tube defects in children if the mothers had genetic variation in genes involved in folate metabolism or enzymes that use chemical groups generated by folate metabolism to modify DNA and arsenic. Environmental arsenic exposure increases the risk of neural tube defects by means of interaction with folate metabolic pathways.

LAB NAME: Vitamin Metabolism & Aging None.