Our apolipoprotein products

Learn about apolipoproteins and how they are used as biomarkers in cardiovascular and neurodegenerative diseases. Find out which antibodies and ELISA kits we offer for quantifying apolipoproteins.

Introduction to apolipoproteins

Apolipoprotein functions

Apolipoproteins are proteins that bind to and help solubilize hydrophobic lipids in the blood. Together with phospholipids, apolipoproteins form lipoprotein particles into which different lipids can be packed. Apolipoproteins have pivotal functions as structural components in lipoprotein particles, as ligands for receptors, and as co-factors for enzymes. Lipoprotein particles are necessary for transportation of lipids used for energy and for synthesis of hormones, vitamins, and bile acids. The apolipoproteins apoB and apoE are important in the transport of dietary and endogenous lipids to the peripheral tissues where these lipids are used as an energy source, whereas apoA1 is crucial for returning excess cholesterol from peripheral tissues to the liver. Apolipoproteins also have an essential role in neurological processes; for example, apoE and apoJ are involved in the transportation of lipids in the brain. Other apolipoproteins, such as apoH, apoD, and apoM, have not been thoroughly investigated and their functions remain to be elucidated.

Apolipoprotein distribution

Apolipoproteins are components of different lipoproteins and can be defined as non-exchangeable or exchangeable. ApoB is non-exchangeable and anchored in the lipoprotein article whereas apoA1, apoE, apoD, apoJ, apoH, and apoM are exchangeable and can be transferred between different lipoprotein particles. ApoA1 and apoB represent the main protein components of HDL and LDL, respectively. There are two forms of apoB: apoB-100 and apoB-48. ApoB-100 is produced in the liver and is incorporated into LDL, whereas apoB-48 is produced in the intestine as a component of chylomicrons. ApoB-100 mediates ligand–receptor uptake of LDL, and approximately 98% of plasma apoB is in this form. ApoE is mainly present in VLDL and HDL. The high-density HDL particle contains large amounts of proteins as well as apoD, apoM, apoH, and apoJ; however, these apolipoproteins can also be associated with other lipoproteins and ApoH can circulate in its free form.

Apolipoproteins comparison

Apolipoprotein	Plasma concentration	Lipoprotein	Characteristics	Clinical significance
ApoA1 (28 kDa)	Men: 0.8-1.8 g/l Women: 0.8-2.2 g/l	HDL, chylomicrons	ApoA1 is the major structural and functional protein in HDL. It is produced in the liver and the small intestine. ApoA1 activates LCAT and is essential for reverse cholesterol transport and for the atheroprotective functions of HDL.	Low plasma levels of apoA1 are associated with risk for cardiovascular disease.
ApoB-100 (512 kDa)	0.4-1.3 g/l Men > Women	LDL, VLDL	ApoB-100 is the main protein component of LDL. It is produced in the liver and mediates ligand–receptor uptake of LDL. Approximately 98% of plasma apoB is in the form of apoB-100.	The apoB-100/apoA1 ratio is a predictor of myocardial infarction. As each LDL particle carries one apoB-100 molecule, the plasma level of apoB-100 reflects the number of LDL particles in plasma.
ApoD (29 kDa)	0.05-0.15 g/l	HDL, LDL, VLDL	ApoD is a lipocalin that binds lipids and steroid hormones. The apoD gene is expressed in many tissues, e.g., brain, testis, adrenal gland, kidney, placenta, spleen, lung, and pancreas. ApoD likely functions as a transporter of lipids or lipid hormones, and is involved in the interaction between HDL and LDL.	ApoD gene polymorphisms are associated with obesity, hyperinsulinemia, and type 2 diabetes.
ApoE (34 kDa)	0.02-0.08 g/l	Chylomicrons, VLDL, HDL	ApoE is produced by many cell types, including hepatocytes, macrophages, and endothelial cells. It is a polymorphic, heparin-binding glycoprotein and the primary carrier of lipids in the brain.	ApoE is considered to be anti-atherogenic and is associated with cardiovascular and neurological diseases.
ApoH (β2-glycoprotein I) (50 kDa)	0.05–0.6 g/l	HLD, chylomicrons, VLDL, LDL	ApoH, also known as beta 2-glycoprotein I, binds several molecules including phospholipids, cardiolipin, and heparin. In plasma, apoH binds lipoproteins but can also circulate in its free form. It is believed to have an effect on coagulation and may activate lipoprotein lipase, but its functions have not been fully elucidated.	ApoH is involved in autoimmune diseases such as antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). It is also thought to have anti-atherogenic properties.
ApoJ (clusterin) (70 kDa)	0.035-0.3 g/l	HLD, VLDL, LDL	ApoJ, also known as clusterin, is expressed in almost all mammalian cells and is also found in most biological fluids including blood, milk, urine, cerebrospinal fluid, and semen. It is a multifunctional protein with chaperone capabilities.	Increased plasma levels of apoJ are associated with age, atherosclerosis, myocardial infarction, diabetes, inflammation, cancer, and Alzheimer’s disease.
ApoM (25 kDa)	6–60 mg/l	HDL, LDL, VLDL	ApoM is a lipocalin mainly produced by the liver. It binds sphingosine-1-phosphate (S1P), and HDL containing apoM is the major transporter of S1P. ApoM–S1P is involved in several signaling pathways implicated in the atheroprotective functions of HDL.	ApoM has a role in lipoprotein metabolism, atherosclerosis, diabetes, and renal diseases.

Apolipoprotein research

Apolipoproteins play a key role in many physiological processes, especially in the lipid metabolism. This explains their involvement in various disorders, and they have therefore become an increasingly popular target for research. Apolipoproteins are utilized as biomarkers in studies on cardiovascular diseases, inflammation, autoimmunity, and neurodegenerative diseases.

Apolipoprotein analysis

A prerequisite for apolipoprotein research and diagnostics is an accurate method for measuring apolipoprotein concentrations in different samples. In this setting, the use of highly specific monoclonal antibodies facilitates the sensitive measurement of different apolipoproteins in serum, plasma, or cell culture supernatants. While techniques to measure turbidity (immunoturbidimetry and nephelometry) have been used for this purpose, methods such as ELISA are increasing in popularity due to superior sensitivity.