Oriented Structure in Human Stratum Corneum Revealed by X-Ray Diffraction

Abstract

Various types of human stratum corneum (sheets or callus) were exposed, in parallel and perpendicular geometry, to the high flux of X rays produced by a synchrotron radiation source. Under these conditions, very clear and rich diffraction patterns, corresponding to the supramolecular organization of stratum corneum proteins and lipids, were obtained. The comparative study of normal or delipidized stratum corneum sheets and membrane couplets allows one to attribute certain diffraction features to lipids. Our results in the 3-7-nm range show two different distances for lipid bilayers. Concerning the protein nature of normal stratum corneum, the results show that keratin would occur in the beta form, whereas for callus it is in the alpha form. Indeed, normal stratum corneum sheets never display the 0.514-nm characteristic of alpha keratin. This result means that the supramolecular organization of keratin could depend on the keratinization process. Finally, our studies also confirm the presence of a still-unknown protein component existing in the beta form that would be located either inside the corneocytes or in some dilatated zones of the intercellular spaces.

Micron-scale assessment of molecular lipid organization in human stratum corneum using microprobe X-ray diffraction

“…The former ring is insensitive to lipid extraction and is therefore attributed to protein component of SC, in particular, the soft keratin ( 4,16 ). This repeat distance is likely related to the molecular arrangement of keratin in the fi lament structure; for example, to the inter-chain distance ( 4,(16)(17)(18). The scattering signal corresponding to the 0.95 nm spacing is noticeably polarized, the intensity in the meridional plane being about 12 nm because of its relatively low intensity (note that the delipidized profi le in Fig.…”

“…The anisotropy can be explained by relative preference of the keratin fi laments to be oriented closer to the plain of corneocytes; i.e., parallel to the SC surface ( 19 ). The second diffuse ring around 0.46 nm is a superposition of the scattering signal from the secondary structure elements of keratin ( 4,16,18 ) and the diffuse contribution from the fl uid-phase lipids characterized by an average inter-chain distance of 0.46 nm.…”

“…Ultrastructural studies, using electron microscopy and diffraction techniques, have revealed that these lipids are organized in stacked bilayers that are predominantly parallel to the skin surface (3)(4)(5). Part of the lipids is covalently bound to the corneocytes whereas another part represents the "free lipids" removable by solvent extraction.…”

“…Most of the SAXS studies of human SC fi nd refl ections corresponding to ‫ف‬ 4.5 nm and ‫ف‬ 6.5 nm inter-bilayer spacings ( 4,6,7 ). Some studies have also detected a refl ection corresponding to a spacing of 11-13.5 nm ( 6,8 ), referred to as the "long periodicity phase" ( 6 ).…”

Nanoscale infrared (IR) spectroscopy and imaging of structural lipids in human stratum corneum using an atomic force microscope to directly detect absorbed light from a tunable IR laser source

“…For experimental design, see Data S1, Supporting Information (18). Figure 1 shows AFM topography images (a, c) and IR spectra (b, d) collected from the locations indicated on the image for the delipidized SC sample (a, b) and the normal SC sample that has not been delipidized (c, d).…”