Glycosphingolipids and Ceramides in Human and Pig Epidermis

Total glycosphingolipids (glucosylceramides) were isolated from both pig (ear) and human (leg) epidermis and each separated into 4 distinct fractions of increasing polarity by silicic acid chromatography. Similarly, 4 separate ceramide fractions were obtained from each of the total free ceramides isolated from pig and human stratum corneum. All ceramide fractions contained large proportions (50% to 80% of total fatty acids) of C24 to C30 acids. The chromatographically more polar ceramides contained C24 to C30 2-hydroxy fatty acids and in the most polar pig ceramide these accounted for 49% of the total fatty acids. Major bases in the pig ceramides were sphingenine, sphinganine, hexadeca-, heptadeca- and eicosa-sphingenine and the 2 most polar fractions also contained hydroxysphinganine. Human ceramide fractions were of similar base composition with nonadecasphin-genine an additional major component. The least polar glucosylceramide fractions from both pig and human epidermis was a 1-(3'-O-acyl)-β-glucosylceramide. Linoleic acid was the major acid esterified to the glucose. The other glucosylceramide fractions contained fatty acids and bases whose compositions and distributions were similar to those in the ceramide fractions from stratum corneum. The glycosphingolipids and ceramides in the stratum corneum which contain high proportions of long chain (>C20) saturated and 2-hydroxy fatty acids with high melting points (>75°) appear well-suited to withstand wide changes in temperature, ultraviolet radiation and atmospheric oxidation that may occur within the environment of the skin surface and, in the absence of phospholipids, are also sufficiently amphipathic to stabilize the lipid phase in the plasma membranes of the stratum corneum cell.