HDL3

HDL3, or high-density lipoprotein 3, is a subclass of high-density lipoprotein particles. HDL particles in plasma exist in several size and density ranges; HDL3 particles are smaller and denser than the larger HDL2 particles. Typical HDL3 diameter is about 7 to 9 nanometers, with a density around 1.125 to 1.21 g/mL.

Composition and structure: HDL3 particles are relatively protein-rich and carry apolipoproteins such as ApoA-I and ApoA-II, along with cholesterol esters and phospholipids. They form through maturation of nascent discoidal HDL by lecithin–cholesterol acyltransferase (LCAT) and are remodeled by enzymes such as hepatic lipase and phospholipid transfer protein.

Biogenesis and metabolism: HDL3 is formed in the liver and intestine and participates in the reverse cholesterol transport pathway. Cholesterol is taken up from peripheral tissues into HDL particles, where LCAT esterifies the cholesterol to form cholesteryl esters. Through remodeling by hepatic lipase and interactions with other lipoproteins via CETP, HDL3 can be converted to the larger HDL2 or exchange lipids with other particles.

Function and clinical relevance: HDL3 participates in reverse cholesterol transport by accepting cholesterol from cells and delivering it to the liver, directly or via transfer to larger HDL particles. It also exhibits anti-inflammatory and anti-oxidant properties in some contexts. Clinically, HDL-C measures cholesterol within all HDL subclasses, but some panels can quantify HDL3-C separately. The interpretation of HDL3-C in cardiovascular risk is complex and research-focused, and perspectives on HDL particle functionality are increasingly considered alongside total HDL-C.