Structural and functional properties of human plasma high density-sized lipoprotein containing only apoE particles.
To investigate the metabolism of HDL-apolipoprotein E (apoE) particles in human plasma, we isolated a fraction of plasma HDL-apoEs that lack apoA-I (HDL-LpE) from subjects with apoE3/3 phenotype by immunoaffinity. Plasma HDL-LpE had a particle size ranging from 9 nm to 18.5 nm in diameter and was characterized by two-dimensional nondenaturing gradient gel electrophoresis as having either gamma-, prebeta1-, prebeta2-, or alpha-electrophoretic mobility. HDL-LpE was also present in the medium of cultured human hepatoma cell lines and monocyte-derived macrophages. The majority of apoE3 was found as a monomeric form in HDL-LpE and floated at density d > 1.21 g/ml. Plasma levels of HDL-LpE in normolipidemic, CETP-deficient, and ABCA1-deficient subjects were 0.72 +/- 0.15 mg/dl (n = 12), 1.77 +/- 0.75 mg/dl (n = 3), and 0.55 +/- 0.11 mg/dl (n = 3), respectively. The ratio of HDL-apoE containing apoA-I to HDL-LpE was significantly higher 4 h after a fat load, representing a 35 +/- 9% increase (n = 3). Isolated plasma HDL-LpE3 was as effective as apoE3, reconstituted HDL particles, or apoA-I in promoting cellular cholesterol efflux. These results demonstrate that 1) plasma HDL-LpE may have hepatogenous and macrophagic origins; 2) HDL-LpE was preserved even with large reductions in apoA-I-containing lipoproteins; 3) HDL-LpE was active in the transfer of apoE to triglyceride-rich lipoproteins, and 4) HDL-LpEs efficiently take up cell-derived cholesterol.
Krimbou
Larbi
L
Cardiovascular Genetics Laboratory, McGill University Health Center/Royal Victoria Hospital, Montréal, Québec H3A 1A1, Canada.
Marcil
Michel
M
Chiba
Hitoshi
H
Genest
Jacques
J
D016632:Apolipoprotein A-I / Q000097:blood / Q000302:isolation & purification; D001057:Apolipoproteins E / Q000097:blood* / Q000302:isolation & purification; D001692:Biological Transport / Q000502:physiology; D045744:Cell Line, Tumor; D002784:Cholesterol / Q000097:blood / Q000302:isolation & purification; D002846:Chromatography, Affinity; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D006801:Humans; D008055:Lipids / Q000097:blood / Q000302:isolation & purification; D008075:Lipoproteins, HDL / Q000097:blood* / Q000302:isolation & purification / Q000502:physiology; D008297:Male; D013997:Time Factors
D016632:Apolipoprotein A-I; D001057:Apolipoproteins E; D008055:Lipids; D008075:Lipoproteins, HDL; D002784:Cholesterol