CE(22:0) is a cholesterol fatty acid ester or simply a cholesterol ester (CE). Cholesterol esters are cholesterol molecules with long-chain fatty acids linked to the hydroxyl group. They are much less polar than free cholesterol and appear to be the preferred form for transport in plasma and for storage. Cholesterol esters do not contribute to membranes but are packed into intracellular lipid particles or lipoprotein particles. Because of the mechanism of synthesis, plasma cholesterol esters tend to contain relatively high proportions of C18 fatty acids. Cholesterol esters are major constituents of the adrenal glands and they also accumulate in the fatty lesions of atherosclerotic plaques. Cholesterol esters are also major constituents of the lipoprotein particles carried in blood (HDL, LDL, VLDL). The cholesterol esters in high-density lipoproteins (HDL) are synthesized largely by transfer of fatty acids to cholesterol from position sn-2 (or C-2) of phosphatidylcholine catalyzed by the enzyme lecithin cholesterol acyl transferase (LCAT). The enzyme also promotes the transfer of cholesterol from cells to HDL. As cholesterol esters accumulate in the lipoprotein core, cholesterol is removed from its surface thus promoting the flow of cholesterol from cell membranes into HDL. This in turn leads to morphological changes in HDL, which grow and become spherical. Subsequently, cholesterol esters are transferred to the other lipoprotein fractions LDL and VLDL, a reaction catalyzed by cholesteryl ester transfer protein. Another enzyme, acyl-CoA:cholesterol acyltransferase (ACAT) synthesizes cholesterol esters from CoA esters of fatty acids and cholesterol. Cholesterol ester hydrolases liberate cholesterol and free fatty acids when required for membrane and lipoprotein formation, and they also provide cholesterol for hormone synthesis in adrenal cells.
