Lipid of the Month

Each month we highlight a lipid of scientific interest. The LIPID MAPS® Lipid of the Month Archive lists lipids highlighted from 2015 - present.

September 2021

Lipid of the month 18-methyl-eicosanoic acid

The most abundant fatty acid in the hair of most mammals, including humans, is 18-methyl-eicosanoic acid (18-MEA). It makes up as much as half of all the fatty acids in hair  and is found exclusively on the surface of the cuticle1. It is covalently linked to the exterior surface of the hair protein via thioester bonds where it functions to maintain a waterproof barrier to the hair surface. It has also been ascribed roles in keeping hair untangled2.

Why this particular fatty acid, unusual for its anteiso methyl branch, is found on the hair surface is unclear, but studies have shown that the methyl group affects the way fatty acids are packed on a surface3 . The branched part of 18-MEA is formed from the amino acid isoleucine. Patients with maple syrup urine disease are unable to metabolise isoleucine and consequently their hair lacks 18-MEA4.

The thioester bond linking 18-MEA to the hair is broken by alkaline conditions, often found in hair colourants and perms, which means the surface lipid layer is damaged by these treatments. There are hair products on the market which contain 18-MEA, but as the linkage is created enzymatically as the hair grows from its follicle, it is hard to see how these would replace 18-MEA to the natural state.


References

Lipid of the Month Archive

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2019
2018
2017
2016
2015