Squalene

Squalene is a natural unsaturated hydrocarbon that plays an important role in human health. It is an isoprenoid: an oligomer that consists of six isoprene units.

Squalene is an intermediate in the biosynthesis of all animal and plant biochemicals that have steroidal structures, including cholesterol and numerous human hormones. Its first isolation from fish liver oils is often attributed to Scottish chemist Isidor (later Ian) Morris Heilbron and coauthors in 1926; but Heilbron cites a 1906 article by Japanese chemist Mitsumaru Tsujimoto¹ as the first report of the isolation of squalene.

Heilbron and colleagues worked out the structure of squalene in 1929. But perhaps the most important scientific work on squalene was the discovery of its biochemical pathway to cholesterol. In 1953, Robert G. Langdon and Konrad Bloch* at the University of Chicago used carbon-14 labeling to follow the route from acetate to squalene and then on to cholesterol. For their pioneering work on cholesterol and fatty acid metabolism, Bloch and Feodor Lynen at the Max Planck Institute for Cellular Chemistry (Munich) received the 1964 Nobel Prize in Physiology or Medicine.

Squalene is found in plant sources such as olive, wheat germ, and rice bran oils; but it is most abundant in fish liver oils, especially those harvested from sharks. Squalene is valuable as an adjuvant in vaccine formulations and (along with its hydrogenation product squalane) as an emollient in cosmetics. Its desirability has, almost predictably, resulted in widespread overfishing of sharks worldwide.

Efforts are under way to find other commercially feasible sources of squalene. Amyris (Emeryville, CA) makes it from products of sugar fermentation; and it can be extracted from olive oil–refining byproducts. The lip cosmetics company Axiology published an impassioned plea to save sharks by developing additional squalene sources.

1. According to Yojiro Tsuzuki at the Science University of Tokyo, Tsujimoto was the “father of lipid chemistry in Japan”; and his report “appears to be the first discovery of any hydrocarbon in the animal kingdom.”