Classification of Serum Lipoproteins According to Their Electrophoretic Mobilities

With the development of techniques to separate proteins according to their electrophoretic behavior, it could be demonstrated that most of the lipid present in serum was associated with proteins migrating with a1- and ^-globulin mobilities. This resulted in the first classification of lipoproteins as a1- and ^-lipoproteins. The ratio of lipid to protein on the ^-lipoproteins was approximately 1:1, whereas the ^-lipoproteins had a greater relative content of lipids. Application of more advanced electrophoretic techniques resulted in further discrimination among the lipoprotein classes and for many years lipopro-teins were classified as 3-, pre-3-, and «-lipoproteins. Careful observation of the electrophoretic lipoprotein profiles in normals and subjects with familial lipoprotein disorders gave rise to the first classification of lipoprotein disorders by Fredrickson and colleagues. The equivalence between electro-phoretic and ultracentrifugal separation is presented in Table 1.

Several electrophoretic supports have been used to separate plasma lipoproteins. These include paper, cellulose acetate, agarose, and polyacrylamide. Agarose gel electrophoresis remains the most commonly used for easy and rapid assessment of lipo-protein patterns in the clinical laboratory. This technique is especially useful for identifying the presence of a broad 3 band in the diagnosis of type III hyperlipidemia. Gradient agarose-polyacrylamide gel electrophoresis under nondenaturing conditions has been an essential tool to analyze low-density lipoprotein (LDL) and high-density lipoprotein (HDL) subclasses, providing a greater resolution than ultracentrifugation. LDL subfractions have been resolved by nondenaturing polyacrylamide gradient gel electrophoresis (2-16%) in up to seven LDL subclasses with densities ranging from 1.020 to 1.063 gml-1 and diameters ranging from 22.0 to 28.5 nm. Usually a major subpopulation and several (one to four) minor LDL subpopulations are found in most subjects examined. A predominance of smaller, more dense LDL, versus larger, more buoyant LDL particles in plasma has been associated with increased coronary heart disease (CHD) risk. There is evidence supporting the genetic origin of the

Table 1 Classification of plasma lipoproteins

Lipoprotein

Diameter (nm)

Density (gml 1)

Electrophoretic mobility

Major lipids

Major apolipoproteins

Chylomicrons

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