Lipoproteine

Lipoproteins are complex particles that enable the transport of lipids through the aqueous environment of blood. They consist of a surface monolayer of phospholipids, free cholesterol, and amphipathic apolipoproteins, surrounding a hydrophobic core of triglycerides and cholesterol esters. The apolipoproteins provide structural stability, serve as enzyme cofactors, and act as ligands for receptors that mediate lipid uptake and metabolism.

Lipoproteins are traditionally classified by density, from least to most dense: chylomicrons, VLDL, IDL, LDL, and HDL. Chylomicrons are large and TG-rich, formed in the intestinal mucosa to transport dietary lipids; they contain apolipoproteins such as ApoB-48, ApoC-II, and ApoE. VLDL is produced by the liver to carry endogenous triglycerides and contains ApoB-100, ApoC-II, and ApoE. As triglycerides are removed, VLDL becomes IDL and then LDL, with LDL being rich in cholesterol esters and carrying ApoB-100. HDL, the smallest and most dense, participates in reverse cholesterol transport and contains ApoA-I and ApoA-II, among others.

Physiological and clinical relevance centers on lipid transport and cholesterol homeostasis. Lipoprotein levels are assessed as part of lipid panels (LDL-C, HDL-C, triglycerides). Elevated LDL-C and triglycerides or low HDL-C are linked to atherosclerosis. Genetic disorders such as familial hypercholesterolemia affect LDL receptor function. Management includes lifestyle measures and pharmacotherapy (statins, PCSK9 inhibitors, fibrates). Emerging approaches consider apolipoprotein levels and particle number (for example, ApoB as a surrogate for atherogenic particles) to refine risk assessment and treatment.