Abstract
Remodelling of plasma high density lipoproteins (HDL) promotes the dissociation of lipid-free apolipoprotein (apo)A-I from the particles. In the present study, we have investigated the formation of new HDL particles from lipid-free apoA-I in a process dependent on the presence of nonesterified fatty acids (NEFA) and other lipoprotein fractions (as donors of lipid). Incubations were carried out that included lipid-free apoA-I, VLDL, and lipoprotein lipase (LPL) or lipid-free apoA-I, either VLDL or LDL, and sodium oleate. Any new HDL particles that were formed were separated from lipid-free apoA-I in the ultracentrifuge. When any one of the ingredients in the incubation was absent, the apoA-I remained lipid-free; however, when all the ingredients were present, a significant proportion of the apoA-I was recovered in the HDL density fraction. This coincided with the formation of at least three HDL-sized subpopulations; one of the subpopulations was considerably smaller than HDL3c and had pre-beta 1 mobility while two were in the size range of human HDL2b and HDL3c and had pre-beta 2 electrophoretic mobility. The new HDL were predominantly discoidal in shape and their major constituents were apoA-I, phospholipid, and unesterified cholesterol. In conclusion, these results show that lipid-free apoA-I can form new HDL particles in the presence of NEFA and other lipoprotein fractions. The formation of pre-beta 1 HDL from lipid-free apoA-I indicates that this process is potentially of great importance in terms of generating plasma acceptors of cell cholesterol in reverse cholesterol transport.
Highlights
Remodelling of plasma high density lipoproteins (HDL)promotes the dissociation of lipid-free apolipoproteinA-I from the particles
We confirm that lipid-free apoA-I does form complexes with phospholipids and unesterified cholesterol released from very low density lipoprotein(s) (VLDL) or low density lipoprotein(s) (LDL) in the presence of either lipolysis products or exogenous nonesterified fatty acids (NEFA).We showthat the apoA-I-lipidcomplexesthat are formed are a heterogeneous group of discoidalparticles with pre-flelectrophoretic mobility; one of these populations appears to be comparable to the pre-01 HDL reported to be the initial acceptors of cell cholesterol in the reverse cholesterol transport pathway ( 1)
The VLDL were removed by ultracentrifugation and the incorporation of lipid-freeapoA-I into new lipid-associatedparticles was assessed as the appearance
Summary
Remodelling of plasma high density lipoproteins (HDL)promotes the dissociation of lipid-free apolipoprotein (apo)A-I from the particles. Evidence for the participation of lipolysis-generated non-esterified fatty acids (NEFA) in the formation of these particles has been provided by a recent study showing that sodium oleate can facilitate reassembly of lipid-free apoA-I with egg yolk phosphatidylcholineto form smalllipid-poor particles [11].Small apoA-Icontaining particles have been reported after in vitro incubations of delipidated HDL with LDL in the presence of NEFA [9]. These particles are yet to be clearly defined. We confirm that lipid-free apoA-I does form complexes with phospholipids and unesterified cholesterol released from VLDL or LDL in the presence of either lipolysis products or exogenous NEFA.We showthat the apoA-I-lipidcomplexesthat are formed are a heterogeneous group of discoidalparticles with pre-flelectrophoretic mobility; one of these populations appears to be comparable to the pre-01 HDL reported to be the initial acceptors of cell cholesterol in the reverse cholesterol transport pathway ( 1)
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