High-density lipoprotein

High-density lipoprotein (HDL) is a particle made of lipids and proteins that transports cholesterol from peripheral tissues toward the liver and other sites of disposal.

Reverse cholesterol transport: The movement of cholesterol from peripheral tissues toward the liver, largely mediated by HDL. HDL is the principal carrier in this multistep route, though the pathway also uses other lipoproteins.
Lipoprotein: A particle of lipids and proteins that transports water-insoluble fats through blood and other body fluids. HDL is one class in this broader family of lipid-transport particles.
HDL cholesterol: The amount of cholesterol carried in HDL particles per volume of blood. This routine laboratory measure quantifies cargo, not HDL particle function or number.
Low-density lipoprotein: A cholesterol-rich lipoprotein that transports cholesterol through blood to peripheral tissues and is associated with atherosclerosis. LDL carries cholesterol outward, contrasting with HDL’s net transport toward the liver.
Apolipoprotein A-I: The main structural protein of HDL and an activator of the enzyme LCAT. It helps nascent HDL acquire cholesterol and supports its maturation.
Apolipoprotein: A protein component of lipoproteins that helps organize particles and regulate their metabolism. HDL’s proteins provide its structure and interact with enzymes and receptors.
Lipid panel: A blood test that reports cholesterol and triglyceride measures used to assess cardiovascular risk. HDL cholesterol is routinely reported alongside LDL cholesterol and triglycerides.
Very-low-density lipoprotein: A liver-produced lipoprotein that transports triglycerides to peripheral tissues and is remodeled into smaller particles. VLDL primarily distributes triglycerides, unlike HDL’s role in cholesterol collection and exchange.
ABCA1: A membrane transporter that transfers cellular cholesterol and phospholipids to lipid-poor apolipoproteins. Its transfer of lipids to apolipoprotein A-I begins HDL particle formation.
Phospholipid: A lipid with a water-attracting head and water-repelling tails that forms biological membranes and lipoprotein surfaces. Phospholipids form the water-compatible outer surface of HDL.

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