Cholesterinester

Cholesterinester, or cholesterol ester, is the esterified form of cholesterol with a fatty acid. In chemical terms, a free cholesterol molecule is linked to a fatty acyl chain via an ester bond, producing a hydrophobic molecule that is less polar than free cholesterol. The most common cholesteryl esters in the human body are cholesteryl palmitate and cholesteryl oleate.

Formation and sources of cholesteryl esters occur through two main enzymatic pathways. In cells, acetyl-CoA:cholesterol acyltransferase (ACAT) catalyzes the formation of cholesteryl esters for intracellular storage. There are two main ACAT isoforms: ACAT1 and ACAT2, with ACAT1 broadly expressed and ACAT2 enriched in enterocytes and hepatocytes, contributing to the esterification of dietary and endogenous cholesterol. In plasma, lecithin:cholesterol acyltransferase (LCAT) catalyzes the esterification of free cholesterol on nascent HDL particles, using phosphatidylcholine as the acyl donor, which moves cholesteryl esters into the HDL core. This process aids cholesterol transport and HDL maturation.

Functionally, cholesteryl esters serve as the storage form of cholesterol in cells and as core lipids within circulating lipoproteins. They are packed in lipid droplets in cells and form the dense interior of LDL and HDL particles, facilitating transport of cholesterol through the bloodstream. Cholesteryl esters are liberated by cholesteryl ester hydrolases and various lipases when free cholesterol is needed by tissues.

Clinical relevance includes their role in atherosclerosis, where excess cholesteryl ester accumulation in macrophages forms foam cells and contributes to plaque development. Abnormal ACAT or LCAT activity can disturb cholesterol storage and transport, with implications for cardiovascular risk and lipid disorders.