Apolipoprotein B

Apolipoprotein B (ApoB) is a protein that in humans is encoded by the gene. It is commonly used to detect risk of atherosclerotic cardiovascular disease. Apolipoprotein B is the primary apolipoprotein of chylomicrons, VLDL, Lp(a), IDL, and LDL particles (LDL—commonly known as "bad cholesterol" when in reference to both heart disease and vascular disease in general), which is responsible for carrying fat molecules (lipids), including cholesterol, around the body to all cells within all tissues. While all the functional roles of ApoB within the LDL (and all larger) particles remain somewhat unclear, it is the primary organizing protein (of the entire complex shell enclosing/carrying fat molecules within) component of the particles and is absolutely required for the formation of these particles. What is also clear is that the ApoB on the LDL particle acts as a ligand for LDL receptors in various cells throughout the body (i.e., less formally, ApoB indicates fat-carrying particles are ready to enter any cells with ApoB receptors and deliver fats carried within into the cells). Through mechanisms only partially understood, high levels of ApoB, especially associated with the higher LDL particle concentrations, are the primary driver of plaques that cause vascular disease (atherosclerosis), commonly first becoming obviously symptomatic as heart disease, stroke and many other body wide complications after decades of progression. There is considerable evidence that concentrations of ApoB and especially the NMR assay (specific for LDL-particle concentrations) are superior indicators of vascular/heart disease driving physiology than either total cholesterol or LDL-cholesterol (as long promoted by the NIH starting in the early 1970s). However, primarily for historic cost/complexity reasons, cholesterol, and estimated LDL-cholesterol by calculation, remains the most commonly promoted lipid test for the risk factor of atherosclerosis. ApoB is routinely measured using immunoassays such as ELISA or nephelometry.