Human Apolipoprotein AI ELISA

Introduction
Human Apolipoprotein A-I (ApoA-I) comprises about 70% of the high-density lipoprotein’s (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 phospholipids and cholesterol as well as 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-I (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 plasma and serum. This assay employs a quantitative competitive enzyme immunoassay technique that measures human apoA-I in less than 3 hours. A polyclonal antibody specific for human apoA-I has been pre-coated onto a 96-well microplate with removable strips. ApoA-I in standards and samples is competed with a biotinylated apoA-I sandwiched by the immobilized antibody and 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.