Esteroles

Esteroles, also known as sterol esters, are esters formed when a fatty acid is linked to a sterol molecule through an ester bond. The most common example is cholesteryl ester, where cholesterol is esterified with a fatty acid. Other sterols, such as sitosterol, campesterol, and ergosterol, can also form sterol esters in plants, fungi, and animals.

In biological systems, sterol esters serve as storage and transport forms for sterols. In animals, cholesteryl esters are the main lipid form of cholesterol found in lipid droplets within adipose tissue and inside circulating lipoproteins (such as LDL and HDL). They are more hydrophobic and less soluble than free cholesterol, facilitating safe transport and storage. In plants and fungi, sterol esters contribute to membrane lipid pools and energy storage, particularly in seeds and spores.

Biosynthesis and metabolism occur through specific enzymes. In mammals, acyl-CoA cholesterol acyltransferases (ACAT1 and ACAT2) catalyze the formation of cholesteryl esters, while lecithin-cholesterol acyltransferase (LCAT) esterifies cholesterol on HDL particles. Hydrolysis of sterol esters to release cholesterol and fatty acids is performed by cholesteryl ester hydrolases. The balance between esterification and hydrolysis regulates cellular cholesterol homeostasis and lipoprotein metabolism.

Physicochemical properties and analytical methods: sterol esters are highly hydrophobic and are typically extracted from biological samples after saponification. They are analyzed by chromatography and mass spectrometry to determine composition and concentration in nutritional, clinical, and research contexts. See also cholesterol, cholesteryl esters, sterols, and lipoproteins.