Location: Obesity and Metabolism Research2014 Annual Report
The goal of the research is to identify novel functions and biomarkers of vitamins and minerals. OBJECTIVE 1: Determine by using metabolomic approaches in animal and cell models, as appropriate, novel functions of zinc related to energy metabolism, insulin resistance in skeletal muscle, and adipose tissue and immune function. Sub-Objective 1A: Determine the mechanism of insulin resistance induced by marginal zinc deficiency in Znt7 KO mice. Sub-Objective 1B: Investigate the mechanisms underlying insulin resistance in the skeletal muscle of Znt7 KO mice. Sub-Objective 1C: Investigate the impact of mild zinc deficiency induced by the Znt7-null mutation on CD40-mediated signaling pathway activation and gene expression. OBJECTIVE 2: Discover novel functions of vitamin B12 related to energy, carbohydrate and 1-C metabolism by measuring metabolomic responses to vitamin B12 supplementation of B12 deficient humans. OBJECTIVE 3. Measure and validate novel functional biomarkers of Zn and vitamin B12 status in response to supplementation of deficient human subjects. OBJECTIVE 4. Evaluate in human intervention trials the impact of dairy consumption on measures of bone, endocrine and immune function.
OBJECTIVE 1: Hypothesis: Altered lipid metabolism induced by zinc insufficiency in muscle and adipose tissues contributes to glucose intolerance and insulin resistance. Advanced metabolomic, molecular and cellular technologies will be employed to determine blood and tissue signatures reflective of Zn status and pathways affected by Zn that lead to insulin resistance in muscle and mechanisms underlying Zn effects on adiposity and immune function. Tissue culture and animal models will be used, e.g., marginally Zn deficient mouse model Znt7 knockout. OBJECTIVE 2: Hypothesis: B12 supplementation of those with compromised status will alter pathways of TCA cycle, mitochondrial function, fatty acids, 1-C, amino acid and CHO metabolism. To investigate these pathways, samples from a randomized B12 supplementation trial in deficient Chilean elders will be analyzed using two metabolomic platforms. Relationships among B12 markers, metabolites and physiological functions will be evaluated before and after B12 supplementation. OBJECTIVE 3. Hypothesis: Znt7-null associated metabolite profiles of fatty acid metabolism will be used as biomarkers of zinc status. Serum collected from a Zn depletion/repletion/supplementation study will be measured for target metabolite abundance changes related to oxidative stress from zinc deficiency. Hypothesis: A combined B12 biomarker will be a better predictor of functional B12 status than single or paired biomarkers. Samples used from deficient women and their infants in Bangladesh in a randomized trial of B12 supplementation during pregnancy and lactation plus samples from Chilean elders supplemented for 18 months with B12. Responses in markers of immune function, bone turnover, and breast milk B12 will be measured, and compared to new marker of B12 status with plasma B12, homocysteine, methylmalonic acid and holotranscobalamin in Bangladeshi women. Chilean elders outcomes are neurological function, markers of inflammation, and metabolomics. The combined B12 biomarker will be evaluated in response to supplementation and associated with functional outcomes. OBJECTIVE 4. Evaluate in human intervention trials the impact of dairy consumption on measures of bone, endocrine and immune function. Hypothesis: Inclusion of 4 servings of dairy foods per day will improve bone profile, reduce fractures, improve muscle density and endocrine and inflammation profiles in elderly adults. Serum samples from a dairy interventionl in 600 ambulatory elders will be used to examine the interrelationships among bone, endocrine, immune systems and the responsiveness to dairy intake when diets with insufficient vs. adequate calcium are consumed.
This report documents progress for this new project which began in January of 2014 and continues research from 5306-51000-003-00D, "Mineral and Vitamin Interventions for At-risk Populations". Although this is a new project, substantial work has already been accomplished. For Objective 1A, a new group of mice including 6 wild-type (WT) and 6 ZnT7 knock-out (KO) have been added to the metabolomic study. Intraperitoneal insulin tolerance test (IPITT) and intraperitoneal glucose tolerance test (IPGTT) have been completed in these mice. For Objective 1B, zinc deficient and supplemental conditions for cultured mouse adipocyte differentiation have been optimized. The activity of the insulin signaling pathway has been examined in adipocytes that were differentiated in normal, zinc deficient or zinc supplemental condition. An adipocyte cell line that expresses less ZnT7 protein has been established using siRNA knockdown technology. Work on objective 2 has begun and a number of the biomarkers have been analyzed at this time. It is expected that the remainder of the samples will be completed within the year. Objective 3A, serum lipid profiles for triglycerides, free fatty acids, and cholesterol in 64 blood samples collected from a zinc depletion/repletion/supplementation study conducted by a researcher at the UCSF Benioff Children's Hosptial Oakland have been received. Objective 3B has progressed with the recent submission of a manuscript describing and validating the mathematical approach used to develop the novel combined indicator of vitamin B12 status. The method is now being applied to data from a vitamin B12 supplementation study in the Chilean elderly in order to improve our ability to detect effects of B12 status on neurological function. Two manuscripts on this topic will be submitted by the end of this calendar year. Objective 4 is well underway with subjects enrolled from half of the study sites and assigned to control or intervention groups. It is expected that all study sites will be enrolled by the end of the calendar year with baseline measurements in early 2015.
1. Insulin is required for maintaining glucose levels in the body. Insulin-secreting beta-cells in the pancreas contain high levels of zinc. Zinc has been shown to co-localize with insulin in secretory granules in pancreatic beta-cells with ZNT8 being the major transporter of Zinc in beta-cells for insulin crystallization and storage. A recent genome-wide association study has suggested that individuals with ZNT8-null mutations are protected from development of type 2 diabetes (T2D). ARS scientists at the Western Human Nutrition Research Center (WHNRC) in Davis, California, have studied the expression and cellular localization of all members of the ZNT family in normal and T2D human pancreases as well as in a human beta-cell subline (established in the WHNRC) to investigate the potential roles of other ZNT proteins in insulin processing, maturation, and secretion. The findings suggest that ZNT2, ZNT7, and ZNT9 may be up-regulated in the beta-cell bearing a ZNT8-null mutation and this compensation mechanism probably protects individuals from development of T2D.
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