1a. Objectives (from AD-416):
1. Determine the extent to which dietary antioxidants alter obesity-induced and/or exercise-induced changes in mitochondrial function and insulin sensitivity. Sub-objective 1A. Determine the influence of anti-oxidant supplementation on changes in insulin sensitivity induced in the rat by high dietary fat and exercise. Sub-objective 1B. Determine the degree to which anti-oxidant supplementation alters exercise-induced changes in insulin sensitivity and mitochondrial function responses of overweight/obese individuals. 2. Identify sites and causes of obesity-induced and exercise-induced oxidative stress. Sub-objective 2A. Determine the effects of obesity and exercise on the temporal and cellular activation of the nuclear factor (erythroid-derived 2)-like 2 (Nrf-2)/Anti-oxidant Response Element pathway. Sub-objective 2B. Identify and characterize obesity-induced and exercise-induced oxidative changes to insulin signaling pathway proteins. 3. Identify, characterize and compare sites of obesity-induced versus exercise-induced mitochondrial respiratory changes. Sub-objective 3A. Determine the degree to which anti-oxidant supplementation blunts exercised-induced and obesity-induced changes in mitochondria.
1b. Approach (from AD-416):
In order to complete the objectives of this proposal, we will utilize a combination of studies in humans, rodents that examine physiologic, metabolomic, genetic, and proteomic endpoints. In Objective 1, we will perform studies in humans and rodents to determine how antioxidant (vitamin E and vitamin C) supplementation affects insulin responses to exercise and obesity. The study in humans will involve analysis of exercise adaptation and insulin responses in previously untrained individuals and if antioxidant supplementation either enhances or negates these adaptations. Rodent studies will further examine molecular mechanisms underlying these adaptations. In Objective 2, we will determine the extent to which obesity, exercise, and anti-oxidant supplementation alter redox balance in animals and specific cells and to identify specific proteins whose thiol redox status is altered in obesity, exercise, and anti-oxidant supplementation. These studies will utilize transgenic mouse models and proteomic approaches. In Objective 3, we will determine the extent to which obesity, exercise, and anti-oxidant supplementation alter mitochondrial function. These studies will utilize rat models of exercise and obesity. Whole tissue and isolated mitochondria will be studied for changes in total mitochondrial content, mitochondrial gene expression, and respiration, and mitochondrial enzyme activities.
3. Progress Report:
Objective 1A. During FY 2013 we completed two studies testing the hypotheses that supplementation with the antioxidants alpha-tocopherol and vitamin C exacerbated insulin resistance under (1) sedentary and (2) exercising conditions. For experiment 1, obese-prone rats were fed a eucaloric diet (10% fat energy), or a hypercaloric (45% fat energy) diet for 12 weeks, or a hypercaloric diet supplemented with d-alpha-tocopherol acetate and vitamin C. Our data demonstrated that the hypercaloric diet induced glucose intolerance and that extent of glucose intolerance was not modified by supplementation with the anti-oxidants. Data also indicated that supplementation did not alter levels of adipose inflammation and macrophage infiltration. These data indicate that antioxidant supplementation does not modify obesity-induced hyperglycemia. This work is being prepared for publication. For experiment 2, obese-prone rats were made obese by feeding a hypercaloric diet for 12 weeks. Obese animals were then exercised for a further 12 weeks with and without supplementation with d-alpha-tocopherol acetate and vitamin C. Our data demonstrated that glucose tolerance, once established, was not ameliorated by the 12 week exercise regimen even though the body composition of the exercise rats returned to that of the control, eucaloric-fed rats. Anti-oxidant supplementation did not modify the glucose response to exercise. These data indicate that exercise alone is not able to reduce pre-existing hyperglycemia and that antioxidant supplementation has no positive or negative effects. Samples from this study are currently being processed. Objective 2B. Previously, we demonstrated that obesity reduces protein modification by glutathione, a process termed glutathionylation, in visceral adipose tissue obtained from obese rats. In order to fully explore this finding, we developed more quantitative ways of measuring glutathionylation using liquid chromatography coupled to mass spectrometry. We are currently preparing these results for publication.
1. Antioxidants and high-blood sugar. Obesity-induced hyperglycemia (high blood sugar) is a problem facing over 75 million Americans. Although many Americans take antioxidant supplements, some reports suggest that antioxidant supplements may make hyperglycemia worse. ARS scientists at Grand Forks, ND, determined that supplementation with the antioxidants vitamin E and vitamin C did not worsen or prevent hyperglycemia in rats fed a high-calorie, high fat diet. These results suggest that supplementation with vitamin C and vitamin E has no effect on the development of high blood sugar.
Raatz, S.K., Rosenberger, T.A., Johnson, L., Wolters, W.R., Burr, G.S., Picklo, M.J. 2013. Dose-dependent consumption of farmed Atlantic salmon (salmo salar) increases plasma phospholipid n-3 fatty acids differentially. Journal of the Academy of Nutrition and Dietetics. 113(2):282-287.