Evaluation of the molecular lipid organization in millimeter-sized stratum corneum by synchrotron X-ray diffraction

Background: The aim of this study was to investigate whether the lamellar and lateral structure of intercellular lipid of stratum corneum (SC) can be evaluated from millimeter-sized SC (MSC) by X-ray diffraction. Materials and Methods: A 12 mm x 12 mm SC sheet from hairless mouse was divided into 16 pieces measuring 3 mm x 3 mm square. From another sheet, 4 pieces of ultramillimeter-sized SC (USC:1.5 mm x 1.5 mm square) were prepared. Small and wide-angle X-ray diffraction (SAXD and WAXD) measurements were performed on each piece. For MSC and USC, changes in the lamellar and lateral structure after the application of d-limonene were measured. Results: The intensity of SAXD peaks due to the lamellar phase of long periodicity phase (LPP) and WAXD peaks due to the lateral hydrocarbon chain-packing structures varied in MSC and USC pieces, although over the 12 mm x 12 mm SC sheet. These results indicated that the intercellular lipid components and their proportion appeared nearly uniform. Application of d-limonene on MSC and USC piece with strong peaks in SAXD and the WAXD resulted in the disappearance of peaks due to the lamellar phase of LPP and decrease in peak intensity for the lateral hydrocarbon chain-packing structures. These changes are consistent with normal-sized sample results. Conclusion: We found that the selection of a sample piece with strong diffraction peaks due to the lamellar and lateral structure enabled evaluation of the SC structure in small-sized samples by X-ray diffraction.