title: Evidence for the presence of lipid-free monomolecular apolipoprotein A-1 in plasma.
abstract: The first step in reverse cholesterol transport is a process by which lipid-free or lipid-poor apoA-1 removes cholesterol from cells through the action of ATP binding cassette transporter A1 at the plasma membrane. However the structure and composition of lipid-free or -poor apoA-1 in plasma remains obscure. We previously obtained a monoclonal antibody (MAb) that specifically recognizes apoA-1 in preβ1-HDL, the smallest apoA-1-containing particle in plasma, which we used to establish a preβ1-HDL ELISA. Here, we purified preβ1-HDL from fresh normal plasma using said antibody, and analyzed the composition and structure. ApoA-1 was detected, but neither phospholipid nor cholesterol were detected in the purified preβ1-HDL. Only globular, not discoidal, particles were observed by electron microscopy. In nondenaturing PAGE, no difference in the mobility was observed between the purified preβ1-HDL and original plasma preβ1-HDL, or between the preβ1-HDL and lipid-free apoA-1 prepared by delipidating HDL. In sandwich ELISA using two anti-preβ1-HDL MAbs, reactivity with intact plasma preβ1-HDL was observed in ELISA using two MAbs with distinct epitopes but no reactivity was observed in ELISA using a single MAb, and the same phenomenon was observed with monomolecular lipid-free apoA-1. These results suggest that plasma preβ1-HDL is lipid-free monomolecular apoA-1.
authors.affiliation: Tsukuba Research Institute, Research and Development Division, Sekisui Medical Co., Ltd., Ibaraki 301-0852, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Miyazaki
authors.forename: Jun
authors.initials: J
authors.lastname: Ogihara
authors.forename: Isamu
authors.initials: I
authors.lastname: Fukamachi
authors.forename: Takafumi
authors.initials: T
authors.lastname: Kasumi
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D016632:Apolipoprotein A-I / Q000097:blood* / Q000737:chemistry* / Q000276:immunology; D000939:Epitopes / Q000276:immunology; D053442:High-Density Lipoproteins, Pre-beta / Q000737:chemistry / Q000302:isolation & purification; D006801:Humans; D008969:Molecular Sequence Data
chemical_list: D000911:Antibodies, Monoclonal; D016632:Apolipoprotein A-I; D000939:Epitopes; D053442:High-Density Lipoproteins, Pre-beta
keywords: lipid-free apolipoprotein A-1; pre-beta-high density lipoprotein; reverse cholesterol transport