Properties of Plasma Lipoproteins

In 1951 Kellner et al. reported that administration of the nonionic detergents Triton A-20 or Tween 80 to rabbits and guinea pigs was followed by a sustained hyperlipemia. This observation was later extended to other animal species mice (Hirsch and Kellner, 1956a, b), rats (Friedman and Byers, 1953), and dogs (Scanu et al., 1961). Studies by Friedman and Byers (1953, 1957) and Hirsch and Kellner (1956a, b) led to the hypothesis that the hyperlipemia was secondary to the action of the detergent on the physical and chemical properties of plasma lipoproteins. Experimental support for this hypothesis was provided by the... 

Cholesterol is a principal component of animal cell plasma membranes, and much smaller amounts of cholesterol are found in the membranes of intracellular organelles. The relatively rigid fused ring system of cholesterol and the weakly polar alcohol group at the C-3 position have important consequences for the properties of plasma membranes. Cholesterol is also a component of lipoprotein complexes in the blood, and it is one of the constituents oiplaques that form on arterial walls in atherosclerosis. 

Chromatographic procedures have been applied increasingly in the fractionation and purification of plasma lipoproteins (Bll, L3, W2). Agarose media have proved to be particularly valuable because of their sieving properties for particles in the size range of plasma lipoproteins, including the low- and very low-density classes (SI). 

Table 5.6 some properties of plasma lipids and lipoproteins... 

LeBoeuf, R.C., Puppione, Dl,., Schumaker, VJ4., and Lusis, A J. (1983) Genetic Control of Lipid Transport in Mice. I. Structural Properties and Polymorphisms of Plasma Lipoproteins, J. Biol. Chem. 258,5063-5070. 

Ciassification and properties of the lipoproteins of human blood plasma. (F.T. Lindgren etal. in G. J. Nelson (ed.) Blood Lipids and Lipoproteins Quantitation, Composition and Metabolism (Wiley-ln-terscience, New York, 1972) pp. 181-274]... 

Oncley, J.L., Gurd, F.R.N. and Melin, M. (1950). Preparation and properties of serum and plasma proteins XXV. Composition and properties on human serum d-lipoprotein. J. Am. Chem. Soc. 72, 458-464. 

An important characteristic of mammalian 15-LOX is its capacity to oxidize the esters of unsaturated acid in biological membranes and plasma lipoproteins without their hydrolysis to free acids. Jung et al. [19] found that human leukocyte 15-LOX oxidized phosphatidylcholine at carbon-15 of the AA moiety. Soybean and rabbit reticulocyte 15-LOXs were also active while human leukocyte 5-LOX, rat basophilic leukemia cell 5-LOX, and rabbit platelet 12-LOX were inactive. It was suggested that the oxygenation of phospholipid is a unique property of 15-LOX. However, Murray and Brash [20] showed that rabbit reticulocyte... 

Vitamin E may be indicated in some rare forms of anemia such as macrocytic, megaloblastic anemia observed in children with severe malnutrition and the hemolytic anemia seen in premature infants on a diet rich in polyunsaturated fatty acids. Also anemia s in malabsorption syndromes have shown to be responsive to vitamin E treatment. Finally, hemolysis in patients with the acanthocytosis syndrome, a rare genetic disorder where there is a lack of plasma jS-lipoprotein and consequently no circulating alpha tocopherol, responds to vitamin E treatment. In neonates requiring oxygen therapy vitamin E has been used for its antioxidant properties to prevent the development retrolental fibroplasia. It should be noted that high dose vitamin E supplements are associated with an increased risk in allcause mortality. 

Raloxifene (Evista) is a new SERM approved for use in the treatment and prevention of osteoporosis because it has estrogenic activity in bone. Raloxifene is an estrogen antagonist in both breast and endometrial tissues. The estrogenhke properties of raloxifene result in the maintenance of a favorable serum Upid profile (decreased low-density lipoprotein levels with no change in either high-density lipoproteins or triglycerides). Raloxifene is 95% bound to plasma proteins. Absorption of raloxifene is impaired by cholestyramine. 

The role of the antioxidant properties of vitamins C, E, and p-carotene in the prevention of cardiovascular disease has been the focus of several recent studies. Antioxidants reduce the oxidation of low-density lipoproteins, which may play a role in the prevention of atherosclerosis. However, an inverse relationship between the intake or plasma levels of these vitamins and the incidence of coronary heart disease has been found in only a few epidemiological studies. One study showed that antioxidants lowered the level of high-density lipoprotein 2 and interfered with the effects of lipid-altering therapies given at the same time. While many groups recommend a varied diet rich in fruits and vegetables for the prevention of coronary artery disease, empirical data do not exist to recommend antioxidant supplementation for the prevention of coronary disease. 

Relevant heparin-binding enzymes not involved in the coagulation cascade are, for example, elastase, cathepsin G, superoxide dismutase, lipoprotein lipase and other lipases. The plasma clearing properties of heparin are associated with its binding to lipoprotein lipase and hepatic lipase when the enzymes are released from the surface of endothelial cells [11] and have been studied in view of a potential impact on the regulation of atherosclerosis. 

TABLE 21-2 Major Classes of Human Plasma Lipoproteins Some Properties... 

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