Cholesteryl oleate is a sterol ester classified among complex lipids, formed by esterification of cholesterol's hydroxyl group at C3 with oleic acid (C18:1 cis-Δ9). This structural feature distinguishes it from simple wax esters through its rigid tetracyclic sterol backbone. Abundant in atherosclerotic plaques and adipocyte lipid droplets, this cholesterol storage form exemplifies sterol-lipid conjugates bridging membrane components and energy reserves.
Chemical Structure
Cholesteryl oleate features the molecular formula C45H78O2 and a molecular weight of 651.12 g/mol. Its structure integrates cholest-5-en-3β-ol esterified via an (Z)-octadec-9-enoate chain, yielding 28 rotatable bonds in the acyl tail, LogP ~18.3, and TPSA 26.3 Ų. The planar sterol ring, with Δ5 unsaturation, methyl groups at C10/C13, and an isooctyl substituent at C17, enforces conical packing unlike linear wax esters.
Physical Properties
Cholesteryl oleate is a white to off-white solid with a melting point of 44–47°C, density of approximately 0.93 g/cm³, and refractive index measured at −20°C in THF. It is insoluble in water but highly soluble in chloroform (up to 100 mg/mL as a clear solution) and ethanol. For stability, it is typically stored at −20°C, with a flash point above 110°C. Liquid crystalline phases, including cholesteric and smectic forms, may emerge above its melting temperature due to sterol rigidity.
Biosynthesis and Metabolism
ACAT1 and ACAT2 enzymes catalyze cholesterol esterification in the endoplasmic reticulum, enabling storage of excess sterol within lipid droplets. Cholesteryl oleate can be hydrolyzed by hormone-sensitive lipase (HSL) or CES1 during lipolysis, releasing free cholesterol for membrane synthesis or reverse transport via HDL-mediated pathways.
