Apolipoprotein E assay

Description

Intended Use

For the quantitative in vitro determination of Apo E in serum or plasma. This product is suitable for automated, semi-automated and manual use.

Clinical Significance

Lipoproteins are large complexes of molecules that transport lipids (primarily triglycerides and cholesterols) through the blood. Apolipoproteins are proteins on the surface of the lipoprotein complex that bind to specific enzymes or transport proteins on the cell membranes. This directs the lipoprotein to the proper site of metabolism. Apolipoprotein E is a 299 amino acid protein synthesised mainly in the liver and to a lesser extent in the brain, spleen, lungs adrenals, ovaries, kidneys, muscle cells and in macrophages. Apo E has many functions including transport of triglycerides to the liver tissue (as part of VLDL) and distribution of cholesterol between cells (as part of HDL). Apo E is a ligand for LDL and mediates the receptor binding of Apo E lipoproteins to the LDL receptor protein.

Apo E is a polymorphic protein and there are three isoforms of Apo E including Apo E2, Apo E3 and Apo E4. Apo E3 is the most common form with a prevalence in Caucasian populations of 77%, Apo E4 is the second most common isoform (15%) and E2 is the rarest (8%). Apo E polymorphism influences physiological and pathological processes. It influences the serum levels of total cholesterol, LDL-cholesterol and the concentration of Apo B. The polymorphism has been implicated in several diseases including cardiovascular disease, neurodegenerative diseases such as Alzheimer?s and many others. Apo E2 is associated with Type III hyperproteinemia (excess protein in the blood) and does not bind the lipid receptor. Apo E deficiency causes high serum cholesterol and triglyceride levels and leads to premature atherosclerosis. Apo E has also been shown to affect the formation of atherosclerotic lesions by inhibition of platelet aggregation.

The polymorphism also influences the Apo E concentration, which directly affects the metabolic processes. Biological factors that affect Apo E concentration include the genetic polymorphism, oral contraceptive intake, puberty, BMI and age1. Reference range values are generally used for the most common isoform and if levels fall outside this range then the genotype should be determined.