Effect of different neutral phospholipids on apolipoprotein binding by artificial lipid particles in vivo

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Abstract
Soybean triacylglycerol particles, stabilized with egg yolk sphingomyelin (SPH), phosphatidylcholine (PC), phosphatidylethanolamine (PE), or PC–PE mixtures, with diameters ranging from 170 to 550 nm were prepared by sonication and isolated by ultracentrifugation. Binding of apoproteins to the lipid particles was studied in vivo using the strategy of Connelly and Kuksis. The recoveries of the injected particles, which had decreased in size and undergone minimal changes in lipid composition, ranged from 70% and 57% for SPH- and PC-stabilized particles to 14% for particles stabilized with egg yolk PC–PE mixtures. The apoprotein (apo) composition of the recovered particles showed qualitative and quantitative differences, which were affected by the number of washes during isolation. After four washes, the SPH and PC particles contained apoE, apoC-II, and apoC-III as major components and apoA-IV as minor components. In addition, all particles, except those stabilized with egg yolk PC, contained large amounts of albumin. In contrast to egg yolk PC, the dipalmitoyl PC particles bound albumin as a major component. The recovered PC-PE and PE particles were characterized by a relative decrease of apoC and greatly increased binding of albumin. The higher rate of clearance of the PE-containing particles was attributed to a relative absence of apoC-III, which is known to delay hepatic uptake of lipid particles containing it, and to a more rapid hydrolysis of PE by lipoprotein lipases. Since PE occurs as a minor and variable component of chylomicrons and plasma lipoproteins, the present observations are of physiological interest.