Keratin-water-NMF interaction as a three layer model in the human stratum corneum using in vivo confocal Raman microscopy

Abstract

The secondary and tertiary structure of keratin and natural moisturizing factor (NMF) are of great importance regarding the water regulating functions in the stratum corneum (SC). In this in vivo study, the depth-dependent keratin conformation and its relationship to the hydrogen bonding states of water and its content in the SC, are investigated using confocal Raman microscopy. Based on the obtained depth-profiles for the β-sheet/α-helix ratio, the stability of disulphide bonds, the amount of cysteine forming disulphide bonds, the buried/exposed tyrosine and the folding/unfolding states of keratin, a “three layer model” of the SC, regarding the keratin-water-NMF interaction is proposed. At the uppermost layers (30–0% SC depth), the keratin filaments are highly folded, entailing limited water binding sites, and NMF is mostly responsible for binding water. At the intermediate layers (70–30% SC depth), the keratin filaments are unfolded, have the most water binding sites and are prone to swelling. At the bottom layers (100–80% SC depth), the water binding sites are already occupied with water and cannot swell substantially. The hydrogen bonding states of water molecules can only be explained by considering both, the molecular structure of keratin and the contribution of NMF as a holistic system.

Conformation changes in human hair keratin observed using confocal Raman spectroscopy after active ingredient application

“…The stability of S‐S disulfide bonds in keratin can be assessed by calculating the conformational order of disulfide bonds in the 474–578 cm −1 spectral range which decomposed into three Raman bands: the gauche–gauche–gauche conformation at 493 cm −1 , the gauche‐gauche‐trans conformation at 515 cm −1 and trans‐gauche‐trans conformation at 538 cm −1 . The ratio of the gauche‐gauche‐gauche conformation to the total disulfide bonds is considered a criterion for the stability of disulfide bonds in keratin .…”

Hydrogen bound water profiles in the skin influenced by optical clearing molecular agents—Quantitative analysis using confocal Raman microscopy

“…RS and CRM have been widely used in skin research for clinical and cosmetic purposes within the last decade. RS and CRM are fully automated and easy‐to‐perform techniques allowing to distinguish structural and molecular changes of the tissue with high sensitivity and spatial resolution, for example, to determine the penetration depth of topically applied substances .…”

Human skin in vivo has a higher skin barrier function than porcine skin ex vivo—comprehensive Raman microscopic study of the stratum corneum

“…An area of interest using CRM in dermatology is the analysis of the penetration into the skin , the skin barrier function provided by the SC , and collagen of the dermis . Our group recently introduced methods to determine the molecular properties of skin barrier function‐related parameters, such as water bonding states , ICL ordering and secondary and tertiary structures of keratin in the SC in vivo. Until now, the difference in skin barrier functions between human SC in vivo and porcine SC ex vivo has not been widely investigated regarding depth‐dependent molecular properties, to the extent of the authors' knowledge.…”