DIET, HDL, AND REVERSE CHOLESTEROL TRANSPORT

大多数肝外组织获得的胆固醇必须返回肝脏排泄，这一过程被称为胆固醇逆向转运。 胆固醇逆向转运的概念主要基于对被认为参与胆固醇逆向转运的单个酶的生物化学研究和对培养细胞中胆固醇流出的研究。最近，被认为参与胆固醇逆向转运的蛋白质在小鼠中被敲除或过表达。 然而，没有直接证据表明胆固醇逆向转运在这些模型中发生了改变。迄今为止，尚未在整个动物中获得明确的胆固醇反向转运途径的证明。在初步研究中，我们证明了胆固醇从个体肝外组织到体内重建的新生前β-迁移HDL的净（质量）运动，并表明胆固醇反向转运的这一初始步骤可以大大加速。 在这里，我们提出的主要步骤，在体内的胆固醇逆向转运的特点，并证明顺序，在胆固醇逆向转运途径中的每一步可以加速导致净（质量）运动的胆固醇从肝外组织到肝脏排泄到胆汁。 最后，我们将证明，通过整个胆固醇逆向转运途径的胆固醇流量可以在体内加速，导致胆固醇从单个肝外组织净运动到粪便中。这些目标现在是可行的，因为方法的进步，使我们能够量化，第一次，在体内的所有组织中的固醇流量的主要途径。 具体目标是：（1）从胆固醇外流增强对肝外组织获取胆固醇途径的影响、受体颗粒组成对胆固醇外流的影响以及饮食对胆固醇外流的影响等方面来表征体内胆固醇反向转运途径的初始步骤，（2）表征过表达卵磷脂胆固醇酰基转移酶（LCAT）对体内胆固醇逆向转运的影响，（3）确定增加HDL胆固醇酯或LDL胆固醇向肝脏的流量的代谢后果，以及（4）为了证明通过整个胆固醇反向转运途径的胆固醇流量可以在体内加速，导致胆固醇从肝外组织净移动到粪便中，以及在具有胆固醇酯转移蛋白（CETP）的动物中。

Cholesterol that is acquired by most extrahepatic tissues must be returned to the liver for excretion in a process that has been termed reverse cholesterol transport. The concept of reverse cholesterol transport is based mainly on biochemical studies of individual enzymes thought to be involved in reverse cholesterol transport and studies of cholesterol efflux from cultured cells. More recently, proteins thought to be involved in reverse cholesterol transport have been knocked out or overexpressed in mice. However, there is no direct evidence that reverse cholesterol transport has been altered in any of these models. To date, an unambiguous demonstration of the reverse cholesterol transport pathway has not been obtained in whole animals. In preliminary studies we demonstrated the net (mass) movement of cholesterol from individual extrahepatic tissues into reconstituted nascent prebeta-migrating HDL in vivo and showed that this initial step in reverse cholesterol transport can be greatly accelerated. Here we propose to characterize the major steps in reverse cholesterol transport in vivo and to demonstrate sequentially that each step in the reverse cholesterol transport pathway can be accelerated resulting in the net (mass) movement of cholesterol from extrahepatic tissues to the liver for excretion into bile. Finally, we will demonstrate that cholesterol flux through the entire reverse cholesterol transport pathway can be accelerated in vivo resulting in the net movement of cholesterol from individual extrahepatic tissues into feces. These goals are now feasible because of methodological advances that allow us to quantify, for the first time, the major pathways of sterol flux in all tissues of the body in vivo. The specific aims are: (1) to characterize the initial step in the reverse cholesterol transport pathway in vivo in terms of the effect of enhanced cholesterol efflux on pathways of cholesterol acquisition by extrahepatic tissues, the effect of acceptor particle composition on cholesterol efflux and the effect of diet on cholesterol efflux, (2) to characterize the effects of overexpressing lecithin cholesterol acyl transferase (LCAT) on reverse cholesterol transport in vivo, (3) To determine the metabolic consequences of increasing the flux of HDL cholesteryl ester or LDL cholesterol to the liver and (4) to demonstrate that cholesterol flux through the entire reverse cholesterol transport pathway can be accelerated in vivo resulting in the net movement of cholesterol from extrahepatic tissues into feces both in animals that lack and in animals that possess cholesteryl ester transfer protein (CETP).