Electron diffraction provides new information on human stratum corneum lipid organization studied in relation to depth and temperature

The outermost layer of mammalian skin, the stratum corneum, provides the bo dy with a barrier against transepidermal water loss and penetration of agen ts from outside. The lipid-rich extracellular matrix surrounding the corneo cytes in the stratum corneum is mainly responsible for this barrier functio n. In this study (cryo-) electron diffraction was applied to obtain informa tion about the local lateral lipid organization in the extracellular matrix in relation to depth in human stratum corneum. For this purpose, stratum c orneum grid-strips were prepared from native skin in vivo and ex vivo. It w as found that the lipid packing in samples prepared at room temperature is predominantly orthorhombic. In samples prepared at 32 degrees C the presenc e of a hexagonal packing is more pronounced in the outer layers of the stra tum corneum. Gradually increasing the specimen temperature from 30 to 40 de grees C induced a further transition from an orthorhombic to a hexagonal su blattice, At 90 degrees C all lipids were present in a fluid phase. These r esults are in good agreement with previously reported wide angle X-ray diff raction and Fourier transformed infrared spectroscopy studies. We conclude that the lipids in human stratum corneum are highly ordered throughout the stratum corneum and that electron diffraction allows monitoring of the loca l lipid organization, which contributes to the understanding of stratum cor neum barrier function.