Rapid, simple laser-light-scattering method for HDL particle sizing in whole plasma.

Abstract

HDL particles are composed of an outer layer of phospholipids and free cholesterol surrounding a hydrophobic core that consists primarily of cholesterol esters and small amounts of triglycerides (1). Apolipoprotein A-I (apo A-I) accounts for ∼60% of the protein content of HDL. Other apolipoprotein species found in HDL particles include apo A-II, apo A-IV, apo CI, apo CIII, and apo E. Several subfractions of HDL have been identified on the basis of density, electrophoretic mobility, particle size, and apolipoprotein composition (2). Differences in particle size are ascribed mainly to the number of apolipoprotein molecules on the particle surface and the amounts of cholesterol esters in the core (1)(2). Furthermore, there is growing evidence suggesting that most of the cardioprotective properties of HDL are associated with the HDL2 fraction (larger particles) rather than the HDL3 fraction (smaller particles) in patients with coronary artery disease (3)(4), in postmenopause women (5), in diabetes (6), and in patients with familial hypercholesterolemia (9). Several methods, such as sequential ultracentrifugation, chemical precipitation, immunoaffinity chromatography, and nondenaturing polyacrylamide gradient gel electrophoresis, have been used to separate HDL subfractions (8). The sizes of the subfractions have been estimated by nondenaturing polyacrylamide gradient gel electrophoresis (9) and, more recently, by nuclear magnetic resonance spectroscopy (10). In general, these procedures are either laborious or expensive. Laser-light scattering (LLS) has been used in the measurement of LDL particle sizes after isolation of this fraction by ultracentrifugation (11). There is great similarity between the data obtained with this approach and those obtained with the nondenaturing polyacrylamide gradient gel electrophoresis method ( P <0.0001; r = 0.78). To date, however, LLS has not been used to perform HDL sizing. HDL sizing by LLS can be performed after chemical precipitation of the apo B-containing lipoprotein (8). This approach …