Effect of Structure and Composition of Reconstituted High Density Lipoproteins on Phosphatidylcholine Transfer by Human Plasma Phospholipid Transfer Protein

183 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Discoidal-reconstructed high density lipoproteins (rHDL) were used to study the effect of HDL substrates on phosphatidylcholine (PC) transfer by human plasma phospholipid transfer protein (PLTP) by changing the composition and size of rHDL. Sonicated egg-PC:cholesterol vesicles containing radiolabelled dipalmitoyl-PC ($\sp $C-DPPC) were used as donors and varied rHDL, consisting of apolipoprotein, phospholipid and cholesterol, were used as acceptors. PLTP, purified about 3,400-fold, was used in the experiments. Activity was measured by the percent $\sp $C-DPPC transferred from vesicles into rHDL.There was no selectivity in facilitated $\sp $C-DPPC transfer at 5:1, PC molar ratio of vesicles/rHDL for the three major apolipoproteins of HDL; however, apolipoprotein (apo) AI-containing rHDL was more stable than apo AII and apo C-containing rHDL in the incubation system. Therefore, apo AI was used in subsequent experiments. When DPPC, egg-PC, palmitoyloleoyl-PC (POPC), dioleoyl-PC (DOPC), and dilinoleoyl-PC (DLPC) were incorporated into rHDL, the particle sizes and transfer activity decreased as follows: DPPC $>$ egg-PC $>$ POPC $>$ DOPC $\approx$ DLPC. The inclusion of varied amounts of cholesterol (0-30%)and sphingomyelin (0-100%) resulted in decreased transfer as these structural lipids increased. The effect of charge was studied by incorporating the anionic phospholipid, dipalmitoyl-phosphatidylserine (DPPS), 0-20%, and the cationic detergent, stearylamine, 0-20%. At low DPPS levels (0-5%), transfer was inhibited, whereas, at higher levels (10-20%), the transfer was higher than that seen at lower DPPS levels. Opposite effects were observed for stearylamine. From these results it is concluded that PC transfer appears to be sensitive to the morphology and changes in the interfacial properties of the acceptor particles--indicating that PLTP interacts with the rHDL acceptor. Fluidity is probably not a major factor.PLTP accelerates PC mass transfer from rHDL into native human LDL, leading to the formation of rHDL particles with a limiting diameter of 7.8 nm. Both the spontaneous and facilitated transfer rates increased with increasing concentrations of rHDL and LDL--suggesting participation of both particles in the transfer mechanism. The E$\sb{\rm a}$ values were similar for both the vesicle-rHDL and the rHDL-LDL systems.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD