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Alterations in plasma lipoproteins are major risk factors for coronary heart disease caused by atherosclerosis. The purpose of this chapter is to provide the reader with an overview of lipids, lipoprotein composition, lipoprotein metabolism, and lipoprotein disorders, with particular relevance to coronary heart disease risk (CHD). This chapter will then provide a framework for the reader to understand...
In humans, the apolipoprotein A-I (apoA-I) gene is expressed abundantly in liver and intestine, and to a lesser extent in other tissues. Following synthesis, apoA-I is secreted in plasma and proceeds to participate in the formation of high density lipoprotein (HDL). In the absence of apoA-I, HDL is not formed. In this chapter, we review in detail how the transcription of the human apoA-I gene...
Low levels of high density lipoprotein (HDL) cholesterol have been associated with an increased risk of coronary heart disease. In this chapter, we discuss the compositional and functional heterogeneity of HDL particles. We briefly describe different approaches to HDL particle characterization (by size, by apolipoprotein content, by protein content) and concentrate specifically on characterization...
Low levels of high density lipoprotein (HDL) cholesterol have been associated with an increased risk of coronary heart disease. In the previous chapter, we have described the presence of distinct apolipoprotein A-I containing HDL particles beginning with small discoidal precursor HDL particles known as preβ-1 HDL and ending with large mature spherical HDL known as alpha 1 HDL. In this chapter, we...
The high density lipoproteins (HDL) in human plasma are structurally and functionally diverse. They consist of numerous subpopulations of particles that are continually being interconverted from one to another. There is compelling evidence from epidemiological and animal studies that HDL protect against cardiovascular disease. The cardioprotective properties of HDL have largely been attributed to...
Our purpose is to review the characteristics of probands described with familial apolipoprotein (apo) A-I deficiency. Decreased plasma high density lipoprotein (HDL) cholesterol levels (<40 mg/dl in men and <50 mg/dl in women) have been associated with an increased risk of coronary heart disease (CHD) [1]. Marked HDL deficiency states (HDL cholesterol <5 mg/dl) and undetectable plasma apolipoprotein...
Forty-six mutations in the human APOA1 gene are listed in the Human Gene Mutation Database. Eighteen mutations cause a Low-HDL phenotype associated with an extremely variable atherosclerosis burden and coronary risk, illustrating that the plasma HDL level per se does not necessarily reflect the atheroprotective potential of these lipoproteins, and highlighting the need for novel tools for cardiovascular...
The ATP binding cassette A1 (ABCA1) transporter facilitates the efflux of free cholesterol and phospholipid onto high density lipoprotein (HDL) particles, mainly very small discoidal precursor HDL particles, known as prebeta 1 HDL. Once these particles pick up these lipids, they are converted to small discoidal alpha 4 migrating HDL and with cholesterol esterification mature into larger spherical...
The ability of HDL to promote the efflux of cholesterol from macrophage foam cells is thought to be central to its antiatherogenic properties. The active transport of cholesterol from macrophage foam cells to plasma HDL or apoA-1 is mediated by ABCG1 or ABCA1, respectively. In most reports, transplantation of ABCG1−/− bone marrow in atherosclerosis-susceptible recipient mice results in unchanged or...
Reverse cholesterol transport (RCT) is a complex process. Several steps, utilizing enzymes and transfer proteins, occur within the plasma compartment before the cholesterol molecules are delivered from peripheral cells to hepatocytes (Atherosclerosis 88:99-107, 1991; Arterioscler Thromb Vasc Biol 21:13-27, 2001). Both intracellular and extracellular factors affect the direction of cholesterol flux...
Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for the synthesis of most of the plasma cholesteryl esters, and plays a central role in intravascular HDL metabolism, in the determination of plasma HDL levels, and in macrophage cholesterol efflux and reverse cholesterol transport. Mutations in the human LCAT gene cause two LCAT deficiency syndromes, classical familial LCAT deficiency...
Plasma cholesteryl ester transfer protein (CETP) facilitates neutral lipid exchange among lipoproteins. As naturally CETP-deficient animals such as mice, rat and dogs, the deficiency of CETP in human results in increased HDL levels due to decreased catabolism of HDL apoA-I and decreased LDL levels due to increased catabolism of LDL apoB. Genetic polymorphisms of the CETP gene promoter slightly decrease...
Scavenger receptor class B type I (SR-BI) was the first molecularly well-defined and functionally active cell surface HDL receptor to be described. SR-BI mediates the transfer of cholesterol from HDL to cells via a mechanism called selective lipid uptake. In vitro and in vivo studies have established that SR-BI is a physiologically relevant lipoprotein receptor. It plays an important role in HDL metabolism...
The majority of variation in HDL cholesterol observed at the population level is of polygenic origin and is the result of the complex interaction between genetic and environmental factors. For many years, genotype-phenotype associations were explored by evaluating a single common variant in a candidate gene. Although important genetic determinants of HDL cholesterol variation have been identified...
The purpose of this chapter is to review our knowledge of the effects of nutritional and lifestyle factors on high-density lipoprotein (HDL) metabolism. Alcohol intake increases HDL apolipoprotein (apo) A-I by increasing its production, and is the topic of a chapter by Dr. Brinton. Dietary cholesterol increases HDL apolipoprotein (apo) A-I by increasing its secretion, probably due to a greater need...
Moderate ethanol intake consistently has been associated with a decreased risk of cardiovascular disease (CVD) in observational studies [1-3], although the decrease is most pronounced and consistent for coronary heart disease [1] and less so for stroke [1]. Although a few studies have shown increases [4] or no changes [5] in carotid atherosclerosis by ultrasound (carotid intima-media thickness, CIMT)...
Coronary heart disease (CHD) is the leading cause of morbidity and mortality in postmenopausal women. While observational studies have shown a reduction in CHD risk in postmenopausal women on hormone therapy (HT), randomized clinical trials have found no protection or increased risk of CHD with HT, despite HT-associated favorable changes in plasma lipid levels. The different findings of observational...
Nicotinic acid, a vitamin of the B complex (B3), is the most potent high-density lipoprotein cholesterol (HDL-C) raising agent currently available, when used at pharmacological doses. In randomized intervention trials, nicotinic acid has been shown to lower the risk of coronary heart disease and to slow the progression of coronary artery lesions. Niacin lowers plasma triglyceride (TG) and low-density...
Statins, inhibitors of the key enzyme in the endogenous synthesis of cholesterol (3-hydroxy-3-methylglutaryl coenzyme A reductase, or HMG-CoA reductase) have been proven to be very effective in lowering plasma LDL-C levels and significantly reduce the risk of coronary heart disease. Statins also modestly increase plasma levels of HDL-C. The mechanism of the effect of statins on apo A-I metabolism...
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