Lipoproteïne

Lipoproteins are molecular complexes that transport lipids through the aqueous environment of blood and lymph. They consist of a hydrophobic core made up of triglycerides and cholesteryl esters and a surrounding surface layer rich in phospholipids, free cholesterol, and apolipoproteins. The particles vary in size, density, and composition and are typically grouped into chylomicrons, very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).

Structurally, lipoproteins share a common architecture: a core of neutral lipids enveloped by a monolayer of amphipathic lipids and surface proteins. Apolipoproteins serve as structural elements and as ligands for cellular receptors or cofactors for enzymes. Major apolipoproteins include apoB-48 and apoB-100, apoA-I, apoC-II, and apoE, with different lipoprotein classes carrying distinct complements.

Metabolism begins with intestinal absorption of dietary fats, forming chylomicrons that acquire apoC-II and apoE from HDL. Lipoprotein lipase hydrolyzes triglycerides in the chylomicron core, releasing fatty acids to tissues; remnants are cleared by the liver via apoE receptors. In the liver, VLDL is secreted and remodels to IDL and LDL, which deliver cholesterol to peripheral cells through LDL receptors. HDL participates in reverse cholesterol transport, collecting cholesterol from tissues and delivering it to the liver, aided by LCAT and SR-BI.

Clinically, abnormal lipoprotein levels are associated with atherosclerotic cardiovascular disease. LDL particles are a major atherogenic factor, whereas HDL has a complex, not fully understood protective role. Lipid measurements, including LDL-C, HDL-C, and triglycerides, are used for risk assessment; apolipoprotein B and apolipoprotein A-I are sometimes used as alternative markers. Treatments target LDL levels and lipoprotein metabolism.