Hydroxyacid derivatives in human epidermis

The principal objective of this investigation was to examine the omega-hydroxyacid derivatives in the cornified layer of human skin. Toward this end, sunburn peelings were collected, and the lipids were extracted with chloroform/methanol. Comparison with authentic standards by thin layer chromatography (TLC) indicated the presence of both N-(omega-acyloxy)acylsphingosine (acylceramide) and omega-acyloxy fatty acid (acyl acid), which accounted for 1.7% and 2.0% of the total lipid, respectively, as estimated by photodensitometry of the charred chromatograms. Each of these lipids was isolated by preparative TLC, hydrolyzed, and the resulting fragments were further analyzed by TLC and by gas liquid chromatography (GLC) of appropriate derivatives. In both of these lipids, the predominant omega-hydroxyacid proved to be the 30-carbon saturated species (56-59% of the total), while linoleate was the major ester-linked fatty acid. Linoleate was more abundant in the acyl acid (38.0%) than in acylceramide (21.4%). These findings represent the first demonstration of acyl acid in human skin and support the proposition that acyl acid, like the other linoleate-rich omega-hydroxyacid derivatives, functions as a molecular rivet in maintaining epidermal structure and function.