Location: Immunity and Disease Prevention Research
Project Number: 2032-51530-017-00-D
Project Type: In-House Appropriated
Start Date: Jan 22, 2009
End Date: Jan 21, 2014
The overall goal of the proposed studies is to determine whether enhanced inflammation promotes development of insulin resistance, and the mechanisms by which dietary fatty acids and certain plant phytochemicals alleviate insulin resistance. Objective 1: Determine the effect of citrus limonoid glucoside (LG) on risk factors for cardiovascular disease including blood lipids and markers of inflammation in hypercholesterolemic humans. Objective 2: Evaluate the impact of dietary docosahexaenoic acid (DHA) on the development and reversal of fatty liver and insulin resistance induced by conjugated linoleic acid (t10,c12 CLA) in animal (mouse) models. Roles of inflammation, adipokines, and insulin signaling will be investigated to understand the changes in lipid and glucose metabolism, and the mechanisms involved. Objective 3: Prepare transgenic mice in which Toll-like receptor 4 (TLR4) is over-expressed in adipose tissue. Then, determine whether enhanced inflammation in adipose tissue induced by over-expression of TLR4 promotes the development of insulin resistance, and whether dietary n-3 PUFAs ameliorate these processes.
APPROACH: Proposed experiments will involve studies in human volunteers, and in animal and cell culture models. For specific objective 1, we will determine the safety and metabolism of LG and its effects of on serum concentrations of lipids, lipoproteins and their sub-fractions, markers of inflammation and oxidative stress in hypercholesterolemic human subjects. We will determine the responsiveness of monocytes and T lymphocytes by testing various immunological parameters, such as production of inflammatory cytokines, lymphocyte activation, proliferation, and phenotypic analysis for subtypes before and after limonoid ingestion. We will also determine the pharmacokinetics of the metabolism of limonoids by examining the blood and urine concentrations of different LG metabolites. Experiments for specific objective 2 will be conducted in the mouse model to determine the prevention and reversal of CLA induced insulin resistance and non-alcoholic fatty liver disease. To understand the mechanisms involved we will investigate the effects of these fatty acids on the expression of genes involved in fatty acid and lipid metabolism. Further, we will determine the effects of these fatty acids on insulin secretion and insulin signaling pathways. For specific objective 3, we will determine whether enhanced sterile inflammation promotes development of insulin resistance, and the mechanism by which n-3 fatty acids alleviate insulin resistance using transgenic mice in which inflammation is enhanced in adipose tissue. The first study is to prepare and characterize phenotypes of the transgenic mice that over-express a constitutively active form of TLR4 in adipose tissue, in an organ specific manner. The second study is to determine whether dietary n-3 PUFA diet alleviates insulin resistance in these transgenic mice. The third study is to elucidate the mechanism by which n-3 fatty acids alleviate insulin resistance. The fourth study is to determine the efficacy and mechanism by which plant polyphenols alleviate insulin resistance using the transgenic mice described above. The fourth study will be performed only if extramural funding becomes available.