Skin ceramides

Abstract

An early investigation by Kooyman using human foot callus demonstrated that as epidermal differentiation progresses to produce the stratum corneum, there is a loss of phospholipids and accumulation of a different polar lipid. In 1965, Nicolaides identified this neutral polar stratum skin lipid class as ceramide. This finding was based on infrared spectral data and was added as a footnote to the proof of the manuscript (personal communication). Long confirmed the earlier findings using cow snout, but was not aware of the report by Nicolaides. Further progress on the chemistry of the skin ceramides was not made until the studies in the mid- to late-1970s by G. Maurice Gray and Harold Yardley and their associates. This series of studies established that ceramide content of human, pig, and rat epidermal cells increases with increasing differentiation, and ceramides are major lipids in the stratum corneum. Overall, the lipid composition of the human and pig epidermis were very close, while that of the rat was somewhat similar. The main building blocks of the epidermal ceramides in pig and human were shown to include sphingosine and dihydrosphingosine and phytosphingosine as the base components, and normal fatty acids, and α-hydroxyacids as the amide-linked fatty acids. In addition, the major glucosylceramides found in the viable portion of the epidermis were isolated, and the amide-linked fatty acid was shown to be an unusual, very long hydroxyacid.