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Squalene

Squalene is an aliphatic hydrocarbon having six unconjugated double bonds, has an iodine number of about 310, a molecular weight of 423, and is found in shark liver oil. Squalene is an intermediate in the biosynthesis of sterols, such as, cholesterol. The biosynthesis of cholesterol is a complex process which will be considered here as three principal stages, including: the conversion of acetic acid to mevalonic acid, the conversion of mevalonic acid to squalene, and the conversion of squalene to cholesterol. In the last stage, squalene is first converted into 2,3-oxido-squalene and then to lanosterol. Lanosterol is then converted to cholesterol through a number of enzymatic steps. In humans, squalene serves a as precursor in the synthesis of cholesterol and all of the steroid hormones. Both squalene and cholesterol are transported in the blood on very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Squalene and cholesterol are also synthesized in the liver and in the epidermis of the skin where squalene comprises a large amount of the oil secreted by sebaceous glands. Squalene (SQE) is a triterpenoid hydrocarbon oil. The terpenoids constitute the largest family of natural products and play diverse functional roles in plants as hormones, photosynthetic pigments, electron carriers, mediators of polysccharide assembly, and structural components of membranes. Farnesyl pyrophosphate is converted to squalene in the first dedicated step towards sterol biosynthesis. Squalene is then converted to squalene-2,3-epoxide which, in photosynthetic organisms, is converted cycloarterenol. In plants, squalene is converted to squalene epoxide, which is then cyclized to form cycloartenol. Cycloartenol is formed in an early stage in the biosynthetic pathway of sterol production in higher plants. Cycloartenol is formed from squalene epoxide, which is formed from squalene, a derivative of mevalonic acid (mevalonate). Squalene epoxide can alternatively be converted into pentacyclic sterols, containing five instead of four rings. Exemplary pentacyclic sterols include the phytoalexins and saponins. Carotenes, tocols and squalene have been known for long to exhibit antioxidant properties and they are widely used in pharmaceuticals as supplements, nutraceuticals as well as fine chemicals. Squalene, which is widely found in shark liver oil is also present in palm oil and it is a valuable constituent in cosmetics as well as food supplements. Sterols can be used as steroid derivatives in pharmaceuticals. The major sterol present in palm oil, beta-sitosterol has been shown to possess hypocholesterolemic effect.

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