The goal of this research is to understand the mechanistic relationship between dietary lipid absorption and overall metabolism. The drug ezetimibe lowers plasma cholesterol by blocking its absorption in the intestine, apparently by disrupting the pathway associated with NPC1L1 (Nieman-Pick disease, type C1-protein -like protein 1). Preliminary studies into other physiological effects of ezetimibe have revealed that postprandial intestinal lipoproteins from ezetimibe-treated mice are different in size and composition than those from control mice. Our results also show that loss of NPC1L1 function, through ezetimibe treatment or gene deletion, protects mice from diet-induced obesity and insulin resistance. Reduced fat absorption may account for part of the difference in weight gain, but additional mechanisms, including increased energy expenditure, may also confer protection against diabetes and obesity. The focus of this proposal is to determine the mechanism(s) responsible for these different phenotypes.
In Specific Aim 1, ezetimibe-treated, Npc1l1-/-, and control mice will be fed high fat diets that are either well absorbed by each group (safflower oil based) or poorly absorbed by Npc1l1-/- and ezetimibe-treated mice (cocoa butter based). Weight gain, plasma glucose, and energy expenditure will be monitored to test the hypothesis that mechanisms in addition to reduced fat absorption contribute resistance to obesity and diabetes of drug-treated and knockout mice. Other experiments will examine the partitioning of dietary fat among high energy tissues such as adipose, muscle, heart and liver in these three groups of mice to test the hypothesis that NPC1L1 inactivation alters postprandial lipid delivery to and utilization by these tissues.
Aim 1 will also determine if metabolic changes derive from increased activation of specific receptors in hepatocytes due to chronic cholesterol loss.
Specific Aim 2 will use in vivo methods to determine if the difference in dietary triglyceride utilization by muscle, liver and adipose is caused by disruption of NPC1L1-dependent pathways in those tissues or if it is caused by altered chylomicron composition from decreased cholesterol and fatty acid absorption. The effect of NPC1L1 and ezetimibe on glucose metabolism by these tissues will also be specifically tested.
Specific Aim 3 will identify the mechanism by which inhibiting cholesterol absorption reduces saturated fatty acid absorption without affecting absorption of unsaturated fatty acids. In vitro, cell culture, and in vivo experiments will test the hypothesis that unabsorbed cholesterol inhibits solubilization of saturated fatty acids by bile salt micelles causing their precipitation and excretion. Together, these studies will provide novel insights about underlying causes of obesity and diabetes, especially the relationship of fat absorption and metabolism with glucose metabolism and overall energy balance. These studies will also provide valuable information about mechanisms of action for existing drugs, with potential for the design and development of new therapeutic entities for treatment of the closely related diseases of hyperlipidemia, obesity and diabetes.
This research project will provide important new information about underlying causes of obesity and diabetes, especially the relationship of fat absorption and metabolism with glucose metabolism and overall energy balance. These studies will also provide valuable information about mechanisms of action for existing drugs, and will identify potential new targets for the design and development of new therapeutic entities for treatment of the closely related diseases of hyperlipidemia, obesity and diabetes.
| Howles, Philip N (2016) Cholesterol Absorption and Metabolism. Methods Mol Biol 1438:177-97 |
| Shen, Ling; Xiong, Ye; Wang, David Q-H et al. (2013) Ginsenoside Rb1 reduces fatty liver by activating AMP-activated protein kinase in obese rats. J Lipid Res 54:1430-8 |
| Kohan, Alison B; Howles, Philip N; Tso, Patrick (2012) Methods for studying rodent intestinal lipoprotein production and metabolism. Curr Protoc Mouse Biol 2:219-230 |
| Yang, Li; Li, Xiaoming; Ji, Yong et al. (2010) Effect of ezetimibe on incretin secretion in response to the intestinal absorption of a mixed meal. Am J Physiol Gastrointest Liver Physiol 299:G1003-11 |
