title: Isolation and partial characterization of lipoprotein A-II (LP-A-II) particles of human plasma.
abstract: High density lipoproteins (HDL) consist of a mixture of chemically and functionally distinct families of particles defined by their characteristic apolipoprotein (Apo) composition. The two major lipoprotein families are lipoprotein A-I (LP-A-I) and lipoprotein A-I:A-II (LP-A-I:A-II). This study describes the isolation of a third minor HDL family of particles referred to as lipoprotein A-II (LP-A-II) because it lacks ApoA-I and contains ApoA-II as its main or sole apolipoprotein constituent. Because ApoA-II is an integral protein constituent of three distinct lipoprotein families (LP-A-I:A-II, LP-A-II: B:C:D:E and LP-A-II), LP-A-II particles were isolated from whole plasma by sequential immunoaffinity chromatography on immunosorbers with antisera to ApoA-II, ApoB and ApoA-I, respectively. In normolipidemic subjects, the concentration of LP-A-II particles, based on ApoA-II content, is 4-18 mg/dl accounting for 5-20% of the total ApoA-II not associated with ApoB-containing lipoproteins. The lipid composition of LP-A-II particles is characterized by low percentage of triglycerides and cholesterol esters and a high percentage of phospholipids in comparison with lipid composition of LP-A-I and LP-A-II: A-II. The major part of LP-A-II particles contain ApoA-II as the sole apolipoprotein constituent; however, small subsets of LP-A-II particles may also contain ApoD and other minor apolipoproteins. The lipid/protein ratio of LP-A-II is higher than those of LP-A-I and LP-A-I:A-II. In homozygous ApoA-I and ApoA-I/ApoC-III deficiencies, LP-A-II particles are the only ApoA-containing high density lipoprotein with levels found to be within the same range (7-13 mg/dl) as those of normolipidemic subjects. However, in contrast to normal LP-A-II, their lipid composition is characterized by higher percentages of triglycerides and cholesterol esters and a lower percentage of phospholipids and their apolipoprotein composition by the presence of ApoC-peptides and ApoE in addition to ApoA-II and ApoD. These results show that LP-A-II particles are a minor HDL family and suggest that, in the absence of ApoA-I-containing lipoproteins, they become an efficient acceptor/donor of ApoC-peptides and ApoE required for a normal metabolism of triglyceride-rich lipoproteins. Their other possible functional roles in lipid transport remain to be established in future experiments.
authors.affiliation: Lipoprotein and Atherosclerosis Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104.
authors.forename: E D
authors.initials: ED
authors.lastname: Bekaert
authors.forename: P
authors.initials: P
authors.lastname: Alaupovic
authors.forename: C
authors.initials: C
authors.lastname: Knight-Gibson
authors.forename: R A
authors.initials: RA
authors.lastname: Norum
authors.forename: M J
authors.initials: MJ
authors.lastname: Laux
authors.forename: M
authors.initials: M
authors.lastname: Ayrault-Jarrier
mesh_terms: D016632:Apolipoprotein A-I / Q000172:deficiency*; D016633:Apolipoprotein A-II / Q000737:chemistry / Q000302:isolation & purification* / Q000502:physiology; D001053:Apolipoproteins / Q000032:analysis; D006801:Humans; D008055:Lipids / Q000032:analysis
chemical_list: D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001053:Apolipoproteins; D008055:Lipids