Aberrant lipid organization in stratum corneum of patients with atopic dermatitis and lamellar ichthyosis

There are several skin diseases in which the lipid composition in the inter cellular matrix of the stratum corneum is different from that of healthy hu man skin. It has been shown that patients suffering from atopic dermatitis have a reduced ceramide content in the stratum corneum, whereas in the stra tum corneum of lamellar ichthyosis patients, the amount of free fatty acids is decreased and the ceramide profile is altered. Both patient groups also show elevated levels of transepidermal water loss indicative of an impaire d barrier function. As ceramides and free fatty acids are essential for a p roper barrier function, we hypothesized that changes in the composition of these lipids would be reflected in the lipid organization in stratum corneu m of atopic dermatitis and lamellar ichthyosis patients. We investigated th e lateral lipid packing using electron diffraction and the lamellar organiz ation using freeze fracture electron microscopy. In atopic dermatitis strat um corneum, we found that, in comparison with healthy stratum corneum, the presence of the hexagonal lattice (gel phase) is increased with respect to the orthorhombic packing (crystalline phase). In lamellar ichthyosis stratu m corneum, the hexagonal packing was predominantly present, whereas the ort horhombic packing was observed only occasionally. This is in good agreement with studies on stratum corneum lipid models that show that the presence o f long-chain free fatty acids is involved in the formation of the orthorhom bic packing. The results of this study also suggest that the ceramide compo sition is important for the lateral lipid packing. Finally, using freeze fr acture electron microscopy, changes in the lamellar organization in stratum corneum of both patient groups could be observed.