The goal of this proposal is to establish an experimental model that can be used to comprehensively investigate the role of nutrients in the development of insulin resistance. The model involves the measurement and integration of diet-induced changes in insulin action at three levels of biologic organization: whole-body, tissue, and molecular. This proposal focuses on sucrose because a). preliminary data clearly establishes the ability of physiologic quantities of sucrose to induce hepatic and skeletal muscle insulin resistance, and b) consumption of dietary sweeteners, such as sucrose and fructose, represent a significant portion of the daily per capita caloric intake in the U.S. The first specific aim is to identify environmental or biologic variables that can modify sucrose-induced insulin resistance. To address this aim the following variables will be studied: 1) amount of sucrose in the diet, 2) duration of exposure to sucrose, 3) the interaction of dose and exposure, and 4) developmental stage. The preliminary data also demonstrate that chronic sucrose exposure increases basal phosphoenolpyruvate carboxykinase (PEPCK) mRNA and activity in the liver and reduces the ability of insulin to suppress PEPCK. Therefore, the second specific aim is to determine whether there is a relationship between sucrose-induced hepatic insulin resistance, gluconeogenic capacity, and PEPCK gene expression. These studies will be accomplished by combining in vivo measures of glucose production and gluconeogenesis with measurements of PEPCK transcription. The third specific aim is to investigate nutrient (fructose, glucose) - hormone (insulin, dexamethasone) regulation of the PEPCK gene. These studies will utilize in vitro techniques to determine whether sucrose absorption products can induce PEPCK or whether sucrose exposure impairs hormonal regulation of PEPCK. The studies in this proposal will a) demonstrate how environmental and biologic factors modify the ability of sucrose to induce insulin resistance, b) define the role of sucrose as a modifier of insulin action, and c) determine the mechanisms by which sucrose exposure affects PEPCK. They will also provide a model which can be used in the future to study the role of nutrients and other environmental variables in the development of insulin resistance.
