Human Apolipoprotein AI ELISA

Introduction
Human apolipoprotein A-I (ApoA-I) comprises about 70% of the high-density lipoproteins (HDL) protein mass and ApoA-II another 15 – 20%. ApoA-I, a 243-amino acid molecule that contains a series of highly homologous amphipathic alpha-helices, is a 28-kDa single polypeptide that lacks glycosylation or disulfide linkages (1). About 5 – 10% of human plasma ApoA-I exists in a lipoprotein-unassociated state. ApoA-I appears to have effects on the atherosclerosis inhibition, reverse cholesterol transport, and anti-inflammation (2). Oxidation of specific amino acid residues in ApoA-I may contribute to atherogenesis by impairing cholesterol efflux from macrophages (3). A majority of HDL functionality is derived from the ability of ApoA-I to sequester phospholipid and cholesterol and interact with plasma enzymes and cellular receptors (4). During reverse cholesterol transport, HDL interacts with lecithin:cholesteryl acyltransferase (LCAT) and cellular receptors, including ATP-binding cassette transporter protein A-1 (ABCA1) and the scavenger receptor class B type I in an ordered fashion that is reflected by HDL particle lipid composition. A high-affinity HDL receptor for ApoA-I is beta-chain of ATP synthase on the surface of hepatocytes (5). The plasma concentration of ApoA-I is one of the best indicators of susceptibility to cardiovascular disease (6).

Principle of the Assay
The AssayMax Human Apolipoprotein A-I ELISA (Enzyme-Linked Immunosorbent Assay) kit is designed for detection of human ApoA-I in urine, saliva, milk, and cell culture supernatant samples. This assay employs a quantitative sandwich enzyme immunoassay technique that measures human ApoA-I in less than 4 hours. A polyclonal antibody specific for human ApoA-1 has been pre-coated onto a 96-well microplate with removable strips. ApoA-1 in standards and samples is sandwiched by the immobilized antibody and the biotinylated polyclonal antibody specific for ApoA-1, which is recognized by a streptavidin-peroxidase conjugate. All unbound material is then washed away and a peroxidase enzyme substrate is added. The color development is stopped and the intensity of the color is measured.