Location: Houston, Texas2010 Annual Report
1a. Objectives (from AD-416)
Objective 1: Determine the absorption of dietary calcium, magnesium, iron and zinc in children and the influence of other nutrients and dietary factors on the absorption. Sub-objective 1.A: Evaluate the effects of supplemental vitamin D in enhancing calcium absorption in healthy children 4 to 8 yrs of age. Sub-objective 1.B: Assess the absorption of magnesium and zinc in healthy children 4 to 8 yrs of age. Sub-objective 1.C: Determine the effects of a diet lacking in meat (lacto-ovo vegetarian diet) on iron status in small children using a highly precise stable isotope method to measure iron status as determined by absorption of iron (reference dose). Objective 2: Determine the effect of dietary components on the upregulation of intestinal iron transporter genes in human models. Sub-objective 2.A: Test the quantity of a food component that must be provided and the duration of exposure to the Caco-2 cells that is needed to obtain a change in expression of the divalent metal transporter (DMT1) and the brush border ferrireductase (Dcytb) genes involved in iron absorption. Sub-objective 2.B: Apply micro-array technology, once the appropriate conditions have been determined, to identify other intestinal genes that are affected by dietary components. Sub-objective 2.C. Evaluate foods that contain the food component(s) in question to assess if the food component is able to alter gene expression in a food matrix. This would indicate that the digestion procedure is able to release the food component(s). Objective 3: Evaluate multiple roles of Vitamin C and ocido-reductases in molecular regulation. Sub-Objective 3.A: Characterize dynamic indices of bone formation by quantitative histomorphometry and micro computed tomography in 7 mouse models developed in our laboratory. Sub-Objective 3.B: Quantitate specific gene expression by qRT-PCR in calvarial osteoblasts derived from appropriate models to clarify the specific roles of each knockout gene. Sub-Objective 3.C: Determine the effects of castration, iron loading, ASC feeding and plant derived antioxidants on bone parameters in vivo.
1b. Approach (from AD-416)
The goal of our research is to provide data to enhance the development of nutritional guidelines, especially as related to mineral nutrition, in children. Using both human experimentation and cell culture models, we are studying methods of delivering the key minerals of calcium, zinc, and iron in the diet so as to optimize health outcomes. This is done by evaluating enhancers of mineral absorption, such as ascorbic acid, prebiotic fibers, and vitamin D and by considering nutrient:nutrient interactions that may limit mineral absorption such as an excess in the zinc:copper intake ratio. We will conduct a controlled trial of vitamin D supplementation to assess the effects of vitamin D status on calcium absorption in small children. We will evaluate different types of whole diets (lacto-ovo vegetarian) on iron status and the effects of differing intakes of zinc on zinc and copper absorption. We will determine if benefits previously seen for prebiotic fibers in enhancing calcium absorption also occur for iron absorption. These studies will utilize stable isotope techniques so as to provide accurate, practically applicable information that may be obtained from the study populations in a safe manner. In vitro studies will seek to identify genetic basis for mineral absorption and to develop appropriate models for evaluation of mineral absorption. Taken together, this project will provide novel information directly useful to government, industry, and the consumer related to dietary requirements. These data will have global application and provide a strong basis for evidence-based nutritional recommendations to be developed.
3. Progress Report
During this year we conducted clinical studies of vitamin D supplementation according to protocol in approximately 30 children who were 4 to 8 years of age. This consisted of screening the subjects, obtaining dietary histories and consent from the children and their parents, and then conducting the study. The initial studies for each child consisted of a measurement of biochemical markers of mineral and vitamin D status and measuring the absorption of calcium, magnesium, and zinc in each subject. This was followed by beginning the children on either 1000 international units of vitamin D3 daily or a placebo. Each child returned after 6 weeks for a follow-up measurement of vitamin D and a calcium absorption test. Studies are in the process of being analyzed, and we have no data results available yet. Results from the blinded controlled trial will be available 2 years from now as per our plan. There have been no problems with the study. We have prepared the human use documents for submission related to an additional group of children 4 to 8 years of age who are vegetarians. Iron absorption will be studied using stable isotopes in this group of children. We are interested in testing how certain food components (such as beta-carotene, insulin, and the so-called meat factor) affect the physiologic mechanism(s) involved in intestinal iron absorption. More specifically, we want to determine how these food components affect the expression level of two genes involved in intestinal iron uptake, namely DMT1 and Dcytb. DMT1 is a divalent metal transporter that transports ferrous iron into cells. Dcytb is an enzyme that reduces ferric iron into ferrous iron. As a prelude to testing how the food components might affect these two genes of interest, we first needed to characterize the gene expression level of DMT1 and Dcytb under different iron concentrations. These experiments are being conducted with a human intestinal cell line (Caco-2). We have finished determining that component of our project and currently are working on other aspects, such as testing gene expression with different durations of iron exposure to the Caco-2 cells. Additionally, in preparation for our animal studies, we have submitted a renewal application to the IACUC for approval of our animal protocols for the next 3 years. The ADODR monitors activities for the project by routine site visits. The ADODR reviews and approves major purchases of supplies and equipment, use of SCA funds for foreign travel, and submission of grant applications by investigators funded through the SCA.