Anatomy & Organs

Cholesterol Esters – Function & Diseases

Cholesterol Esters

Cholesterol esters are cholesterol molecules esterified with fatty acids. They represent a transport form of cholesterol , which is found up to 75 percent in the blood . Esterified cholesterol is more easily broken down in the liver than unesterified cholesterol.

What is cholesterol ester?

Cholesterol ester represents a cholesterol molecule esterified with fatty acids. Cholesterol is a polycyclic alcohol whose hydroxyl group is attached to a fatty acid molecule with the help of an enzyme , with the elimination of water . The cholesterol ester is a transport form of cholesterol, which as an ester can also be broken down more easily in the liver.

In the body, 75 percent of cholesterol occurs as cholesterol esters. It serves as an intermediate product and storage material in the metabolism of the organism. It is therefore also an immanent part of human nutrition. The cholesterol esters are mainly found in animal food products. The most common fatty acids found in the cholesterol ester are oleic acid, palmic acid, and linoleic acid . The enzyme lecithin-cholesterol acyltransferase is responsible for the esterification of cholesterol. This enzyme is located in the HDL particles and also controls the esterification of the cholesterol there.

The HDL particles consist of cholesterol, triglycerides and lipoproteins. Bound to the lipoproteins, the water-insoluble cholesterol esters are made transportable and transported from the organs to the liver via the HDL particles. Esterification increases the density of these particles, so they are considered high-density lipoproteins (closely packed lipoproteins).

Function, effect & tasks

Cholesterol esters are just one transport form of cholesterol. They are bound to the lipoproteins in HDL, LDL or VLDL. Cholesterol occurs both free and esterified with fatty acids. However, esterified cholesterol is more easily broken down by the liver. It can be transported very well with the help of lipoproteins in the blood . 

Its formation takes place in the high density lipoproteins . These are highly concentrated lipoproteins. The HDLs transport cholesterol from the extrahepatic organs (organs located outside of the liver) to the liver, where it is then broken down into bile acids . The bile acids are excreted via the bile into the intestines and at the same time emulsify the fats, cholesterol and cholesterol esters ingested from food. Over 90 percent of the cholesterol converted into bile acid is converted back into the circulatory system. Cholesterol and cholesterol esters are precursors for the formation of hormones such as sex hormones, mineral corticoids and glucocorticoids (cortisone). They are also used to form bile acids and vitamin D.

Formation, Occurrence, Properties & Optimal Values

Cholesterol esters are formed in the HDL by the enzyme lecithin-cholesterol acyltransferase. HDL or high-density lipoproteins are responsible for transporting cholesterol from the body’s tissues to the liver. This transport is also known as reverse cholesterol transport. Esterified cholesterol can be easily broken down in the liver. However, the cholesterol esters can also be transferred from the HDL to the LDL or VLDL by exchanging with triglycerides. Therefore, there are also cholesterol esters in the LDL and VLDL.

HDL is commonly referred to as good cholesterol because it transports cholesterol found in tissues to the liver for breakdown. It was found that the risk of developing arteriosclerosis and cardiovascular disorders is lower with a high HDL concentration. In some cases, even a slight regression of arteriosclerotic changes could be observed. In order to break down cholesterol in the liver, it is first necessary to break the ester bond between cholesterol and fatty acid. This requires a hormone-sensitive lipase. The cholesterol esters ingested with food are broken down into their individual components by a bile salt-activated lipase. This releases both fatty acids and cholesterol.

Within a cell, free cholesterol is also esterified by the so-called sterol-O-acyltransferase and converted into its storage form as cholesterol ester. In this way, undesired effects of free cholesterol in the cytosol are avoided. However, accumulations of cholesterol esters in the macrophages or in the smooth muscles indicate the onset of arteriosclerosis.

Diseases & Disorders

A balance is established in the cells between cholesterol synthesis and the release of cholesterol from cholesterol esters. Cholesterol esters are broken down by what is known as acid lipase. There are two very rare conditions associated with loss of function or reduced activity of acid lipase. 

A genetic defect on chromosome 10 affects a gene that codes for acid lipase. If this enzyme fails completely, cholesterol ester can no longer be broken down in the lysosomes. There is a reduced concentration of cholesterol in the cytoplasm of the cell. This interrupts the control loop and leads to uncontrolled production of cholesterol. This also increases the LDL receptor activity. The cell is now overloaded with cholesterol, which ultimately leads to cell death. This disease is usually fatal in the earliest childhood (at the age of three to six months). Cholesterol ester storage disease (CEST) is a much milder form of the disease .

The same gene is also affected here. However, the acidic lipase still has a residual function here, so that the disease only affects the liver. This residual function means that cholesterol ester degradation can still take place in most cells . Due to the high metabolic activity in the liver, however, the slower degradation has an effect there. Increased concentrations of cholesterol esters are stored in the liver. The disease usually only becomes apparent after the age of 18 with an enlarged liver and an increased risk of developing arteriosclerosis.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.