Epidermal barrier lipids in human vernix caseosa: corresponding ceramide pattern in vernix and fetal skin.

Abstract

Vernix caseosa is a protective biofilm covering the fetus during the last trimester. Vernix and epidermal barrier lipids (i.e. cholesterol, free fatty acids and ceramides) appear to share protective functions for fetal and neonatal skin. To analyse vernix samples for epidermal barrier lipid content, and to compare lipid profiles of vernix with those of fetal and postnatal epidermis. Vernix samples were collected from 21 healthy term neonates. Skin samples were collected from 10 fetuses aborted between gestational week (GW) 16 and 25, nine infants and 11 older children. Lipids were extracted according to standard protocols and analysed by high-performance thin-layer chromatography. Vernix contained 196.5 +/- 70.1 microg barrier lipids mg-1 protein (mean +/- SD). Cholesterol formed the major barrier lipid fraction (52.8%), followed by free fatty acids (27.7%) and ceramides (20.1%). The ceramide composition of vernix resembled that of mid-gestational (GW 23-25) fetal epidermis both qualitatively and quantitatively, while there were major differences from postnatal epidermis. The total epidermal ceramide concentration increased significantly between prenatal and postnatal samples. The composition pattern of ceramides mirrors that of mid-gestational fetal epidermis. Vernix thus represents a 'homologous' substitute for the immature epidermal barrier in fetal skin. The differential role of individual ceramides in this process remains to be established.