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

Anne Potter,Carine Baltenneck,Yegor A. Domanov,Jean Doucet

doi:10.1194/jlr.m053389

Abstract

Lipid and protein components of the stratum corneum (SC) are organized in complex supramolecular arrangements. Exploring spatial relations between various possible substructures is important for understanding the barrier function of this uppermost layer of epidermis. Here, we report the first study where micro-focus X-ray scattering was used for assessing fine structural variations of the human skin barrier with micrometer resolution. We found that the scattering profiles were unchanged when scanning in the direction parallel to the SC surface. Furthermore, small-angle scattering profiles did not change as a function of depth in the SC, confirming that the lipid lamellar spacings remained the same throughout the SC. However, the wide-angle scattering data showed that the orthorhombic phase was more abundant in the middle layers of the SC, whereas the hexagonal phase dominated in the surface layers both at the external and the lowest part of the SC; i.e., the lipids were most tightly packed in the middle region of the SC. Taken together, our results demonstrate that microprobe X-ray diffraction provides abundant information about spatial variations of the SC lipid structure and thus may be a promising tool for assessing the effects of topical formulations on the barrier function of skin.

Highlights

Lipid and protein components of the stratum corneum (SC) are organized in complex supramolecular arrangements
Lipid structural variations across the SC The SC comprises 15–30 alternating layers of flat corneocytes and intercellular lipid lamellae [21], the number of cell layers depending on anatomical site, subject, etc
The overall small-angle X-ray scattering (SAXS) profile observed here at different depths in the SC is similar to those previously reported for bulk human SC [4, 6, 8] and does not correspond to a single well-defined lamellar spacing

Summary

Introduction

Lipid and protein components of the stratum corneum (SC) are organized in complex supramolecular arrangements. X-ray diffraction is an excellent technique for studying the spatial organization of the intercellular matrix because the lipid molecules are highly ordered and oriented in a crystalline structure. This technique has provided a number of important results with regard to the SC structure. Some studies have detected a reflection corresponding to a spacing of 11–13.5 nm [6, 8], referred to as the “long periodicity phase” [6] These data indicate that the SC lipid matrix has a complex organization into multiple sublayers or even phase-separated domains with different lamellar repeat distances. A fraction of lipids might exist in a fluid or amorphous state, which would contribute to the broad band corresponding to an average distance of 0.46 nm

Methods

Results

Conclusion