Location: Obesity and Metabolism Research2010 Annual Report
1a. Objectives (from AD-416)
Objective 1: Evaluate mediators of behavior change critical for adopting a healthy diet by investigating interrelationships between psychosocial stress, nutritional behavior and metabolism in humans and animal models. Objective 2: Determine how diet patterns, whole foods, and food components influence physiology and metabolic health by impacting eating- and neuro-behaviors, energy balance and substrate utilization, fitness, body weight and body composition in humans. Objective 3: Determine mechanisms underlying the regulation of body weight and disorders associated with obesity, by examining hormonal, neuronal, and metabolite pathways linking adipose and non-adipose tissues, and characterizing tissue-specific inflammation in humans, cells, and animal models. Objective 4: Determine the impact of dietary lipids on body weight, adiposity, and/or metabolic health indices by assessing their influence on lipoprotein-dependent trafficking of bioactive lipids to adipose and peripheral tissues, their effects on the regulation of metabolic homeostasis, and their interactions with distinct fatty acid desaturase/elongase activity phenotypes. Objective 5: Characterize the roles of cellular zinc in regulation of lipid metabolism, body fat mass, and fat distribution during postnatal development in genetically-modified animal models. Objective 6. Develop and validate phenotyping tools that classify and predict metabolic and body weight responses to dietary and physical activity interventions in individuals and populations.
1b. Approach (from AD-416)
We will use a multidisciplinary approach to test molecular, physiological, and metabolic responses to diets composed of whole foods or enriched with select macro- and micronutrients, determine how physical activity, stress, and genetic factors modify metabolism and responses to foods, identify important behavioral and psychosocial factors related to adopting the U.S. Dietary Guidelines, and determine basic physiological mechanisms underlying links between nutrition, physical activity, and metabolic health. Our work will use classical investigations of metabolism and energetics, along with metabolomic analyses, real-time determinations of brain activity in response to foods, and gene/protein expression determinations to investigate these questions, linking findings from these approaches to whole-organism phenotypes and human behavioral traits. Randomized controlled trials and analyses of samples from longitudinal observational studies will also be conducted. Important studies in animal and cell culture models will complement this work to gain a deeper understanding of underlying mechanisms and/or to obtain proof-of-concept information before designing and conducting human trials. Replacing: 5306-51530-016-00D (Laugero, Keim, Adams, Newman) and 5603-51530-014-00D (Huang). (2/09)
3. Progress Report
Psychosocial Stress: 35 out of targeted 40 human subjects have enrolled in the study, & data collection is in progress. Stress-reactivity & Brain Imaging: Methodology was developed & successfully piloted. Recruitment & enrollment are in progress; 15 subjects have enrolled, & brain imaging tasks have been completed for 6 subjects. Titi monkey model: Completed study, samples assayed, & data were statistically analyzed. A manuscript describing the results has been submitted to Psychoneuroendocrinology. Whole Grains: Intervention study examining consumer behavior & health benefits associated with whole grain products was initiated; enrollment of subjects is ongoing. Breakfast & Metabolism: Extramural funding was obtained to study the effect of breakfast eating on dietary choices & mitigation of the stress response. 22 volunteers have enrolled; data collection is in progress. Added Sugars & Metabolism: Subjects (n=20) have completed 24-h energy expenditure, satiety, & stress protocols in the WHNRC calorimeter as part of the sugar dose response study. Unique Neural-Adipocyte Genes: Tusc5 & SNCG are expressed in fat cells & peripheral neurons that sense temperature, pain, & other signals. It was found that the genes for these factors are targets of molecules that activate a metabolic pathway (PPARg) important to metabolic regulation. Adipose Tissue Inflammation: A new factor, CD11d, was found to have the highest relative increase in expression in the fat tissue of obese vs. lean animals. Dairy food, but not high calcium alone, markedly reduced inflammation in the fat, suggesting bioactives in dairy attenuate inflammation associated with metabolic disease. Intermediary Metabolism of Sugar & Fats: Increased blood levels of certain amino acids & novel molecules in type 2 diabetics were correlated with poor blood sugar control & poor fat combustion, highlighting the close link between dysfunction & metabolism of multiple nutrients in diabetes. Dietary Fats: Techniques were developed to isolate, separate, & quantify lipid metabolites within lipoprotein particles, providing the ability to investigate the functional impact of perturbed lipid metabolism as occurs in obesity & diabetes. Znt7: Male Znt7 knockout (KO) mice fed a high fat diet developed hyperinsulinemia & impaired glucose clearance; Znt7 KO mice fed a low fat diet had reduced glucose clearance, indicating that defects in insulin production/secretion and/or peripheral tissue insulin sensitivity are due to the defect of Znt7. These preliminary data were included in an innovation award application to American Diabetes Association. Pancreatic beta-cells: Over expression of Znt7 in beta-cells increased total cellular insulin levels leading to high basal insulin secretion. Manuscript describing this work has been accepted for publication in Experimental Cell Research. Body weight gain in Znt7 knockout mice: A preliminary QTL mapping study was completed and 8 QTLs were identified that were associated with epididymal fat mass & body weight. Additional SNP markers & animals will be added to increase the power in this QTL mapping study.
1. Middle-aged, perimenopausal obese and normal weight women present a good model for assessing behavioral and physiological mechanisms of stress. Life transition periods, such as perimenopause and middle age, are commonly associated with vulnerability to psychological stress, and women can gain significant weight in mid-life. The roles of stress or stress hormones and their relationship to food choices and body weight or composition during this transition period are unknown. ARS researchers at Davis, CA established a test paradigm to examine an individual’s vulnerability to the effects of stress on food selection, dietary patterns and body weight changes. We discovered that differences cortisol responsiveness to a social stress test predict self-selected palatable food intake from a snack buffet and body fat composition in perimenopausal women. These findings demonstrate that stress reactivity interacts with body fat to influence food choice and food intake.
2. Compared to women, men who consume large quantities of beverages sweetened with fructose, are prone to metabolic dysfunction following ingestion of meals. The use of fructose-containing sweeteners has increased in parallel as obesity has become more prevalent in our society. Little is known about how consumption of large quantities of fructose affect metabolism of sugars and fats in humans. In collaboration with University of California-Davis scientists, ARS researchers at Davis, CA found that regular consumption of fructose-sweetened beverages over 10 weeks led to a preference for burning sugar to produce energy, but not fat—an effect that was particularly pronounced among men. Further, as the ability to burn fat was reduced, body fat accumulated in the abdominal region. These findings demonstrate, for the first time, that regular consumption of sweeteners containing fructose can cause an accumulation of body fat in individuals that have limited capacity to burn fat for energy.
3. Inflammation in adipose tissue: the roles of specific nutrients and foods, such as calcium and dairy products, on this phenomenon. ARS researchers at Davis, CA studied mice fed high-fat diets with different sources of calcium. Inclusion of dairy as the primary protein source led to significantly lower body fat, reduced weight gain, more limited inflammation, and improved blood sugar control without lowering food intake. In contrast, mice fed the high fat diet with high calcium and no dairy actually gained more weight, were fatter, and displayed increased inflammation. Dairy foods and calcium are considered components of a healthy diet, and have been implicated in healthy body weight control. It has not been clear if the latter is due to mineral calcium or factors specifically associated with dairy foods. This study established that dairy protein factors and/or dairy carbohydrates are key to the positive metabolic effects of dairy foods, which calcium alone cannot mimic.
4. Alterations in intermediary metabolism of sugars and fats in obesity and diabetes. Metabolism of sugars, fats, and proteins are perturbed in obesity and diabetes. ARS scientists at Davis, CA, in collaboration with scientists at the University of Alabama at Birmingham and UC, Davis conducted a comprehensive comparison of small molecules (metabolites) in the blood plasma of non-diabetic vs. type 2 diabetic (T2D) obese African-American women. In T2D women there is abnormal metabolism of the building blocks of proteins (amino acids; likely due to perturbation in amino acid breakdown), and that a unique metabolite signature tracks blood sugar control. New methods were developed that allowed metabolite profiling in sub cellular structures called mitochondria (sites of nutrient conversion to energy). Disruptions in normal fat metabolism in these structures is believed to underlie some of the poor outcomes of T2D by influencing export of important molecules that support sugar, amino acid, and fat utilization. The newly-identified metabolites that tracked blood sugar markers may have utility as new biomarkers for predicting diabetes risk clinically and could be used to track efficacy of strategies designed to thwart the disease. The new insights from mitochondrial studies enabled a formulation of a testable metabolic model in which T2D tissues are believed to have compromised mitochondria in part due to dysfunctional loss and poor replenishment of key metabolites that support normal metabolism.
5. The unique peripheral neuron-adipocyte gene, Tusc5—biological roles are associated with adiposity and gene regulation by nutritional and environmental cues. A gene-regulating protein termed peroxisome proliferator activated receptorgamma (PPARg) is a master controller of fat metabolism and fat cell (adipocyte) growth and function. Previous studies conducted by ARS researchers at Davis, CA suggested that the newly-characterized adipocyte factor Tusc5 is regulated by PPARg, raising the possibility that Tusc5 is involved in the physiological changes in metabolism pathways and new fat cell differentiation that is triggered by stimulators of PPARg such as certain lipids or diabetes drugs. Recent studies using mouse cells have now firmly established that regions of the Tusc5 gene physically interact with PPARg, proving it to be a bona fide target gene. However, in diabetic humans treated with PPARg agonist drugs, fat tissue Tusc5 expression was not stimulated. While not discounting the potential importance of Tusc5 for normal fat tissue function, its lack of apparent involvement in PPARg-related changes in humans indicate that future studies by researchers to explore function in people should focus away from PPARg associations.
6. Obesity is associated with mild inflammatory conditions. A mild inflammation state may be involved in some of the obesity related adverse health effects, but our ability to measure mild inflammation is limited. Researchers at ARS, Davis, CA in collaboration with international collaborators in the Netherlands, studied obese men who were treated with diclofenac, an over-the-counter pain medication, to identify obesity-associated changes in inflammatory mediators and genes. A number of potential markers of chronic inflammation in obese men were identified that may be prognostic of risk of the development of obesity-related chronic disease states, which if translated into clinical practice would enable earlier and more targeted nutritional or pharmacologic intervention to thwart metabolic disease.
7. Does consumption of omega-3 fatty acids have anti-inflammatory effects, reducing pro-inflammatory metabolite levels? More scientific evidence is needed to determine if consumption of omega-3 fatty acids significantly reduces inflammation in humans. ARS Researchers at WHNRC, Davis, CA, fed overweight and obese men fatty acid supplements, and measured levels of pro- and anti-inflammatory lipid metabolites. Individuals with the highest levels of pro-inflammatory metabolites at baseline showed the greatest reduction in these metabolites, while those with the lowest levels of these compounds showed no changes with supplementation. Measurements of these compounds in blood serum can provide an indication of a therapeutic need for omega-3 fatty acid supplements, and, if consumed regularly, these supplements will effectively reduce inflammatory metabolites.
8. Biological roles of different sub-classes of polyunsaturated fatty acids. The USDA Dietary Guidelines make recommendations on saturated, monounsaturated, and polyunsaturated fatty acids to promote health in the general population. However, sufficient evidence to support recommendations on specific polyunsaturated fatty acids, such as omega-6 (n6) and omega-3 (n3) forms of PUFA does not exist. By altering the relative amounts of these fats in a rodent-based feeding study, ARS researchers at Davis, CA found that regardless of n6/n3 ratios, moderately high fat diets (40% caloric fat) with controlled saturated and mono-unsaturated fatty acid do not produce significant weight gain or changes in clinical lipid chemistry panels when fed to healthy hamsters. Moreover, low fat diets (12% caloric fat) showed distinct differences in circulating monounsaturated fatty acids, and dietary lipids produced subtle, but distinct impacts on liver gene expression. The impact of this result is currently being more fully investigated.
9. Zinc is important in glucose metabolism. Overweight and obesity are major health concerns in the developed countries as these conditions are associated with a number of serious and costly chronic medical conditions, including type 2 diabetes, cardiovascular disease, hypertension, osteoarthritis, and certain cancers. Connections between zinc nutrition and homeostasis with metabolic diseases remain largely unknown. Using a zinc transporter (Znt7) knockout mouse model and cell cultures overexpressing Znt7, ARS researchers in Davis, CA discovered that loss of Znt7 leads to poor blood sugar control due to abnormal blood levels of the glucose-regulating hormone insulin, and increased Znt7 in pancreatic beta-cells (cells that produce insulin) increased insulin expression and basal insulin secretion. It was demonstrated, for the first time, that the insulin genes (Ins1 and Ins2) in rodents are targets of the metal-responsive transcription factor Mtf1 that is activated by zinc. These studies establish the importance of cellular zinc in regulation of insulin synthesis and secretion and thus control of blood sugar level, and highlight that proper zinc nutrition and beta-cell zinc handling could be important for maintenance of metabolic health.
10. Identification of quantitative trait loci (QTLs) that influence body weight gain in Znt7 knockout mice. A direct link between body weight regulation/adiposity and zinc homeostasis is lacking, but ARS researchers in Davis, CA recently discovered that mice lacking the zinc transporter protein Znt7 are leaner even when fed a high fat diet. The mechanisms for this phenomenon may involve factors including oxidative and inflammatory stress, endocrine secretion/signaling, energy partitioning, glucose homeostasis, carbohydrate and lipid metabolism, and adipocyte differentiation/proliferation. Quantitative trait loci (QTLs: chromosomal regions statistically associated with a particular characteristic such as body fat) are a valuable resource to identify candidate genes responsible for the lean characteristics of Znt7 knockout mice, and a QTL mapping approach in the knockout mice revealed QTLs associated with body weight as well as fat pad weight on chromosomes 10, 16, and 19. This study is the first to identify genetic regions that associate zinc metabolism to body weight and adiposity (body fatness), in support of a role for proper zinc nutrition and cellular zinc handling in maintaining body weight and metabolic health, and provides a set of candidate genes that will form the basis for future experiments to identify those most prominently involved in the zinc-body weight association.
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