The barrier properties of the skin membrane depend on the molecular organization of the SC components. Considering this, we employed SAXD and WAXD to investigate the effect of glycerol and urea on both the organization of the SC extracellular lipid lamellae and on the soft keratin
structures. The results from the SAXD and WAXD measurements at 32 °C are presented in Fig. 2A and B, respectively. We start by concluding that the results obtained for the SC sample without glycerol or urea are in good agreement with previous SAXD and WAXD studies on hydrated pig SC (Bouwstra et al., 1995). Further, it is shown that the JAK activation SC pretreated in glycerol or urea formulations give rise to similar diffraction curves as the SC pretreated in neat PBS solution. All SAXD curves in Fig. 2A have one broad peak centered around Q = 1.0 nm−1 (6.3 nm in d-spacing). The strong diffraction at low Q is attributed to protein structures of the SC ( Bouwstra et al., 1995 and Garson et al., 1991), which obscures the diffraction pattern of any lipid structures in this region. However, centered around Q = 0.5 nm−1 (12.6 nm in d-spacing) a shoulder is present in the descending diffraction curves, which implies that the peak around 6.3 nm in d-spacing is a learn more 2nd order peak of
a lamellar phase with approx. 12.6 nm in d-spacing. When the SC sample has been pretreated in the formulation that contain urea (bottom curve), the shoulder around Q = 0.5 nm−1 is nearly absent, and the intensity of the peak around Q = 1.0 nm−1 is weaker compared to the other samples. A weak shoulder centered around Q = 1.4 nm−1 (4.5 nm in d-spacing) is present in all diffraction curves in Fig. 2A. In the literature, the same peak at 4.5 nm has been interpreted as the 2nd order of a 9 nm periodicity lamellar phase ( Bouwstra et al., 1995). However, no signs of a 1st
order peak of this 9 nm lamellar phase was observed here. Considering that all reflections are diffuse and broad it cannot be ruled out that all of the above peaks/shoulders belong to the same lamellar found phase with repeat distance of approx. 12.6 nm. Finally, a peak centered around roughly Q = 1.8 nm−1 (3.4 nm in d-spacing) is observed in all diffraction curves, which is attributed to phase separated crystalline cholesterol ( Bouwstra et al., 1995). Fig. 2B shows WAXD data for the corresponding conditions as in Fig. 2A. A distinct peak at approx. Q = 15.2 nm−1 (0.41 nm in d-spacing) is present in all diffraction curves, irrespective of pretreatment formulation. This peak corresponds to hexagonal packed lipid carbon chains. No signs of orthorhombic packing was observed under any conditions (i.e., no peak was present at approx. Q = 17 nm−1 or 0.37 nm in d-spacing), which is in agreement with previous studies on pig SC ( Bouwstra et al., 1995 and Caussin et al., 2008).