Anthocyanins, Macronutrient Utilization and Insulin Sens

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Insulin resistance is a key pathophysiologic feature of the "metabolic syndrome" and is strongly associated with co-existing cardiovascular risk factors and accelerated atherosclerosis. Strategies to improve insulin resistance by pharmacological means have represented the traditional approach for clinical medicine. However, because of the widespread use of dietary supplements by the general public, nutritional supplementation with the use of botanicals that increase insulin sensitivity represent an attractive and novel approach for intervention of the development of metabolic syndrome. Results of our hypothesis generating studies in mice suggest that anthocyanin supplementation may increase insulin sensitivity and decrease ectopic fat. Genes involved in carbohydrate and fatty acid metabolism were altered in the liver, consistent with increased insulin sensitivity. In the heart, genes involved in fatty acid uptake and oxidation were increased, consistent with increased peripheral fatty acid utilization. Furthermore, the pattern of gene expression observed in our preliminary studies suggests involvement of specific transcription factors including, but not limited to sterol regulatory element binding protein-1c, PPAR-gamma coactivatory-1alpha and -1beta. Finally, tissue culture studies (3T3-L1) demonstrated that anthocyanins reverse the fatty acid mediated suppression of insulin signaling, glycogen accumulation and adiponectin secretion. We hypothesize that anthocyanins, through modulation of the activities of specific transcription factors such as liver x-receptor, peroxisome proliferators activated receptors (PPARalpha, PPARdelta, PPARgamma), sterol regulatory element binding protein (SREBP)-1c, PPARgamma coactivator-1alpha and -1beta, increase the peripheral oxidation of fatty acids and thereby decrease ectopic fat accumulation in muscle and liver, affect insulin signaling, and improve overall insulin sensitivity. We propose to conduct a series of animal and cell culture studies designed to critically evaluate this overall hypothesis and its corollaries. Our specific aims are as follows: 1) To examine the in vivo effects of a semipurified grape anthocyanin preparation on insulin sensitivity, energy expenditure, fatty acid and carbohydrate oxidation and disposal, and tissue lipid accumulation in a mouse model of insulin resistance; 2) To evaluate the effects of a semipurified grape anthocyanin preparation on transcription factors, gene expression levels, protein abundance, intracellular pathways of insulin receptor signaling, and substrate metabolism in relevant cell culture models. 3) To identify the active component(s) within the anthocyanin preparation responsible for the observed changes in gene expression and substrate metabolism. Thus, our research plan is designed to comprehensively evaluate the effect of anthocyanins on pathogenic mechanisms leading to the development of insulin resistance and metabolic syndrome, and evaluates the cellular mechanisms of action for their effects.