Ceramides of pig epidermis: structure determination.

Seven distinguishable groups of ceramides have been isolated from pig epidermis and identified. In order of increasing polarity there are: 1, N-(omega-acyloxy)acylsphingosines (7.7%); 2, N-acylsphingosines (42.4%); 3, N-acylphytosphingosines (10.2%); 4, N-(alpha-hydroxy)acylsphingosines (12,1%); 5, N-(alpha-hydroxy)acylsphingosines (10.5%); 6a, N-[omega-(alpha-hydroxy)acyloxy]acylsphingosines (1.7%); 6b, N-(alpha-hydroxy)-acylphytosphingosines (15.5%). In ceramide 5, the alpha-hydroxyacid moieties are predominantly C16, whereas in ceramides 4, 6a, and 6b, the alpha-hydroxyacids are mainly C24-C28. The omega-hydroxyacids in ceramides 1 and 6a are mainly C30-C32. In ceramide 1, the fatty acids esterified to the omega-hydroxyl group contain a high proportion of linoleic acid (74.5%). These ceramides apparently form a large proportion of the intercellular lipid lamellae in the epidermal stratum corneum, which are thought to constitute the barrier to water loss.