lipoproteinene

Lipoproteins are macromolecular complexes that enable the transport of hydrophobic lipids through the aqueous environment of blood. They are composed of a core of triglycerides and cholesterol esters surrounded by a surface layer of phospholipids, free cholesterol, and apolipoproteins. The apolipoproteins serve as receptor ligands and enzyme cofactors, determining each particle’s metabolic fate and interactions.

Lipoproteins are traditionally classified by density into chylomicrons, very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL). Chylomicrons form in intestinal mucosa after a fat-containing meal and transport dietary triglycerides; they are the least dense particles. Lipoprotein lipase on capillary endothelium hydrolyzes their triglycerides, forming chylomicron remnants that are cleared by the liver via receptors recognizing apolipoprotein E. In the liver, VLDL is secreted and remodeled by lipoprotein lipase into IDL and then LDL, which delivers cholesterol to peripheral tissues through LDL receptors that recognize apolipoprotein B-100. HDL participates in reverse cholesterol transport, acquiring surplus cholesterol from cells and delivering it to the liver; ApoA-I and ApoE are important apolipoproteins in HDL, and the process interacts with cholesteryl ester transfer protein (CETP) activity.

Clinical relevance includes dyslipidemias and cardiovascular risk. Lipid panels measure total cholesterol, triglycerides, HDL cholesterol, and calculated LDL cholesterol. Genetic disorders affecting lipoprotein metabolism, such as familial hypercholesterolemia, highlight the importance of receptor- and apolipoprotein-mediated pathways in health and disease.