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Lipoproteins are particle complexes that transport lipids through the aqueous bloodstream. They consist of a core of triglycerides and cholesteryl esters surrounded by a surface monolayer of phospholipids, free cholesterol, and apolipoproteins, which confer structural integrity and serve as ligands for receptors.

Based on density and size, the main classes are chylomicrons, VLDL, IDL, LDL, and HDL. Chylomicrons deliver dietary triglycerides to tissues; VLDL and remnants transport endogenous triglycerides and cholesterol; LDL primarily carries cholesterol to cells; HDL participates in reverse cholesterol transport, collecting excess cholesterol from tissues and bringing it to the liver.

Lipoprotein(a) Lp(a) is a particle similar to LDL with an additional apolipoprotein(a) attached, linked to increased cardiovascular risk.

Metabolism involves lipoprotein lipase hydrolyzing triglycerides in triglyceride-rich lipoproteins; hepatic lipase; CETP mediates lipid exchange; hepatic uptake occurs via the LDL receptor pathway; apoB-100 is required for uptake of LDL and VLDL; apoA-I is the main protein of HDL and supports cholesterol efflux from tissues.

Clinical significance: Dyslipidemias are common and influence atherosclerosis and cardiovascular risk. Lipid panels measure total cholesterol, LDL-C, HDL-C, and triglycerides; non-HDL cholesterol is an additional marker. Treatments include lifestyle modification and drugs such as statins; newer therapies target PCSK9, CETP, or triglyceride-rich lipoproteins.

Genetic disorders such as familial hypercholesterolemia (LDLR, ApoB, PCSK9 mutations) illustrate the biological importance of lipoproteins and their pathways in health and disease.