Lipoprotein classification

Lipoprotein characteristics depends on the varying proportions of protein and lipid present. Lipids are of lower density (<0.9 g/ml) than proteins (>1.28 g/ml), giving a range of lipoprotein densities from 0.9 to 1.21 g/ml. Lipoprotein classification is made according to the respective densities as determined by ultracentrifugation or according to their electrophoretic migration. 

The National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) recommends that a fasting lipoprotein profile and risk factor assessment be used in the initial classification of adults. 

LDL, low-density lipoproteins CHD, coronary heart disease. Classification <130 mg/dL is the desirable LI3L cholesterol level 130-159 mg/dl is borderline-high-risk >160 mg/dl is high-risk. 

Plasma lipoproteins are generally classified by their density and separation achieved with ultracentrifugation. According to this density-based classification system, the major lipoprotein classes are chylomicrons (CH), very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). 

These lipids are insoluble in water and are classified on the basis of their ultracentrifugal properties into chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in order of ascending density. Table 2.4 gives the classification and roles of lipoproteins. 

Antilipemics lower lipid levels (Table 19.4). Lipids are composed of cholesterol, triglycerides, and phospholipids, which are bound to lipoproteins (Table 19.5) that transport lipids throughout the body. There are three classifications of lipoproteins ... 

Lipoproteins transport lipids in blood an early classification system was established using centrifugation methods, which are based on their different densities. Lipoproteins are classified as chylomicrons, largest and lowest in density... 

TABLE 26-18 NCEP Classification of Total and Low-Density Lipoprotein (LDL) Cholesterol in Children and Adolescents ... 

TABLE 72—14. Classification of Lipid and Lipoprotein Levels in Adults... 

Cholesterol, which is largely insoluble in aqueous m a, travels through the blood circulation in the form of Upoprotein complexes. The plasma lipoproteins are a family of globular particles that share common structural features. A core of hydrophobic lipid, principally triacylglycerols (triglycerides) and cholesterol esters, is surrounded by a hydrophilic monolayer of phospholipid and protein (the apolipoproteins) [1-3]. Lipid-apolipoprotein interactions, facihtated byi amphi-pathic protein helices that segregate polar from nonpolar surfaces [2,3], provide the mechanism by which cholesterol can circulate in a soluble form. In addition, the apolipoproteins modulate the activities of certain enzymes involved in Upoprotein metabolism and interact with specific cell surface receptors which take up Upopro-teins by receptor-mediated endocytosis. Differences in the Upid and apoUpoprotein compositions of plasma Upoproteins determine their target sites and classification based on buoyant density. 

Although the assembly, structure, metabolism, and receptor interactions of lipoproteins are determined by their apolipoprotein components, the most common classifications of lipoproteins are based on their hydrated density or mobility on agarose gel electrophoresis. 

The classification into chylomicrons (CM), very low density (VLDL), low density (LDL), and high density (HDL) lipoproteins is based on their relative contents of protein and lipid that determine the densities of these lipoprotein classes. CM have only 1-2% protein while HDL have about 50% protein by weight. The diameters of lipoproteins are inversely correlated with their densities and range from about 6000 A for CM to 70 A for the smallest HDL (Fig. 1). 

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