The central hypothesis of this proposal is that reverse cholesterol transport is related to coronary heart disease (CHD) risk. It is complementary to the concept that reduction of cholesterol biosynthesis with statin drugs prevents CHD, but it focuses on whole body cholesterol metabolism and kinetic cholesterol transport rather than on static levels of circulating lipoproteins. Although this is an old idea, it has not been adequately tested in humans because of lack of suitable methods. In this proposal we will apply innovative stable isotope and mass spectroscopic technology to study reverse cholesterol transport in human subjects. The first specific aim is to improve the preparation of intravenous deuterated cholesterol tracer, a critical limiting element in the study of whole body cholesterol metabolism.
The second aim i s to use that intravenous tracer, along with a different oral tracer, to partition fecal cholesterol into excreted endogenous cholesterol, unabsorbed dietary cholesterol and newly-synthesized cholesterol derived from the liver and intestine. Measurements will be made during consumption of a controlled diet provided by the metabolic kitchen. The pool size of the rapidly-mixing body cholesterol pool will be measured along with the fractional rate of cholesterol catabolism. These direct measures of reverse cholesterol transport will be correlated with plasma biomarkers and with metabolic covariates. The relation of reverse cholesterol transport to carotid intima-media thickness will be determined. The third specific aim will use similar methods to study the mechanism of action for the widely-used drug ezetimibe. Changes in fractional endogenous cholesterol excretion and related measures will be determined after ezetimibe or placebo treatment in a clinical trial. This work represents a new direction for cholesterol research with the potential to develop new and complementary methods of reducing CHD risk that can be added to diet and statin drug treatment.
Cholesterol is an important cause of heart disease. Most cholesterol-related projects focus only on circulating blood cholesterol. Here we will study whole body cholesterol, including the largest portion, which is tissue cholesterol outside the bloodstream. Understanding how much cholesterol individuals possess and how efficiently they excrete it is the underlying purpose of this application. This knowledge will allow consideration of new treatments that can work alongside reduction of blood cholesterol to lower heart disease risk.