Stratum corneum occlusion induces water transformation towards lower bonding state: a molecular level in vivo study by confocal Raman microspectroscopy

Effect of Penetration Enhancer on the Structure of Stratum Corneum: On-Site Study by Confocal Polarized Raman Imaging

Keratin and lipid structures in the stratum corneum (SC) are closely related to the SC barrier function. The application of penetration enhancers (PEs) disrupts the structure of SC, thereby promoting infiltration. To quantify these PE-induced structural changes in SC, we used confocal Raman imaging (CRI) and polarized Raman imaging (PRI) to explore the integrity and continuity of keratin and lipid structures in SC. The results showed that water is the safest PE and that oleic acid (OA), sodium dodecyl sulfate (SDS), and low molecular weight protamine (LMWP) disrupted the ordered structure of keratin, while azone and liposomes had less of an effect on keratin. Azone, OA, and SDS also led to significant changes in lipid structure, while LMWP and liposomes had less of an effect. Establishing this non-invasive and efficient strategy will provide new insights into transdermal drug delivery and skin health management.

Evaluation of Scalp Hydration and pH Values in Hijab-Wearing and Non-Hijab-Wearing Women

Introduction

Indonesia is the most populous Muslim-majority country, where some women wear hijab covering their scalp and neck. Some hijab-wearing women complain of scalp problems eg, itch, dandruff, and hair loss, which might be related to severe and chronic skin barrier impairment due to occlusion. Excessive water accumulation in the occluded stratum corneum might result in increased permeability, followed by increased skin pH values. This study aimed to evaluate scalp hydration and pH values in hijab-wearing and non-hijab-wearing women.

Material and Methods

This was a cross-sectional comparative analytical study using stratified random sampling methods conducted on 63 subjects, who were divided into two groups, consisting of 33 hijab-wearing and 30 non-hijab-wearing women. Both groups underwent physical examination and their medical history recorded. Scalp hydration was measured using a Corneometer (Courage + Khazaka, Koln, Germany), and scalp pH value was measured using a Skin & Scalp pH Tester (Hanna Instruments® HI981037, Rumania). This study was conducted at the Dermatology and Venereology Clinic of Hasan Sadikin General Hospital Bandung.

Results

The mean scalp hydration and pH values were 18.34 ± 2.91 AU and 4.93 ± 0.17, respectively, in hijab-wearing women. Meanwhile, the mean scalp hydration and pH values were 17.71 ± 3.35 AU and 4.91 ± 0.16, respectively, in non-hijab-wearing women. The difference of scalp hydration and pH values between the groups was not statistically significant based on the independent t-test, with p-values of 0.430 and 0.597, respectively.

Conclusion

Scalp hydration and pH values in hijab-wearing and non-hijab-wearing women did not differ significantly. Hijab-wearing women should not worry about scalp barrier impairment as long as they do not have any history of underlying scalp and skin disorders, and do not wear hijab in wet condition.

Altered structure indicating reduced barrier function of lesional compared to non-lesional psoriatic skin-A non-invasive in vivo study of the human stratum corneum with confocal Raman micro-spectroscopy

Psoriasis, one of the most common skin diseases affecting roughly 2%-3% of the world population, is associated with a reduced skin barrier function (SBF) that might play an important role in its pathophysiology. The SBF is provided primarily by the stratum corneum (SC) of the skin. Previous studies have revealed a higher trans-epidermal water loss, lower hydration, abnormal concentration and composition of intercellular lipids, as well as alterations in secondary keratin structure in the psoriatic SC. We compared on molecular level lesional psoriatic skin (LPS) with non-lesional psoriatic skin (nLPS) from 19 patients non-invasively in vivo, using confocal Raman micro-spectroscopy. By analysing the corresponding Raman spectra, we determined SBF-defining parameters of the SC depth-dependently. Our results revealed a lower total lipid concentration, a shift of lamellar lipid organisation towards more gauche-conformers and an increase of the less dense hexagonal lateral packing of the intercellular lipids in LPS. Furthermore, we observed lower natural moisturising factor concentration, lower total water as well as a strong tendency towards less strongly bound and more weakly bound water molecules in LPS. Finally, we detected a less stable secondary keratin structure with increased β-sheets, in contrast to the tertiary structure, showing a higher degree of folded keratin in LPS. These findings clearly suggest structural differences indicating a reduced SBF in LPS, and are discussed in juxtaposition to preceding outcomes for psoriatic and healthy skin. Understanding the alterations of the psoriatic SC provides insights into the exact pathophysiology of psoriasis and paves the way for optimal future treatments.

Optical Methods for Non-Invasive Determination of Skin Penetration: Current Trends, Advances, Possibilities, Prospects, and Translation into In Vivo Human Studies

Information on the penetration depth, pathways, metabolization, storage of vehicles, active pharmaceutical ingredients (APIs), and functional cosmetic ingredients (FCIs) of topically applied formulations or contaminants (substances) in skin is of great importance for understanding their interaction with skin targets, treatment efficacy, and risk assessment-a challenging task in dermatology, cosmetology, and pharmacy. Non-invasive methods for the qualitative and quantitative visualization of substances in skin in vivo are favored and limited to optical imaging and spectroscopic methods such as fluorescence/reflectance confocal laser scanning microscopy (CLSM); two-photon tomography (2PT) combined with autofluorescence (2PT-AF), fluorescence lifetime imaging (2PT-FLIM), second-harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and reflectance confocal microscopy (2PT-RCM); three-photon tomography (3PT); confocal Raman micro-spectroscopy (CRM); surface-enhanced Raman scattering (SERS) micro-spectroscopy; stimulated Raman scattering (SRS) microscopy; and optical coherence tomography (OCT). This review summarizes the state of the art in the use of the CLSM, 2PT, 3PT, CRM, SERS, SRS, and OCT optical methods to study skin penetration in vivo non-invasively (302 references). The advantages, limitations, possibilities, and prospects of the reviewed optical methods are comprehensively discussed. The ex vivo studies discussed are potentially translatable into in vivo measurements. The requirements for the optical properties of substances to determine their penetration into skin by certain methods are highlighted.

Topical dexpanthenol effects on physiological parameters of the stratum corneum by Confocal Raman Microspectroscopy

BACKGROUND

Topical use of dexpanthenol presents well-established moisturizing properties and maintenance and repair of the skin barrier function, however, its exact action mechanisms are not completely elucidated. In this context, Confocal Raman Microspectroscopy is an optical method that enables non-invasive and non-destructive in vivo analysis with the sensitive acquisition of molecular changes in different skin layers. Herein, the aim was to evaluate the effects of topical dexpanthenol on the components and physiological parameters of the stratum corneum (SC).

MATERIALS AND METHODS

Ten healthy female subjects underwent skin evaluation by means of a Confocal Raman Spectrometer Skin Analyzer 3510. Spectral data were obtained from the skin of the anterior forearm region, before and 2 h after applying a cosmetic formulation containing or not containing 5% dexpanthenol.

RESULTS

Semiquantitative analysis of the natural moisturizing factor showed a significant decrease in content after 2 h of topical dexpanthenol application, while the analysis of the lamellar organization of intercellular lipids and the secondary structure of keratin showed a significant increase in hexagonal organization of lipids at the first half of the SC and a significant increase in β-pleated sheet conformation of keratin.

CONCLUSION

Effects of topical dexpanthenol on SC suggest a contribution in increasing fluidity of both lipidic and protein components of the SC and are compatible with dexpanthenol activity in maintaining adequate physiological conditions and preventing transepidermal water loss. This study also contributes to the elucidation of action mechanisms and other concurrent biochemical processes.

Cosmetic Formulations with Melaleuca alternifolia Essential Oil for the Improvement of Photoaged Skin: A Double-Blind, Randomized, Placebo-Controlled Clinical Study

This aim of this study was to evaluate the penetration depth, antioxidant capacity and the clinical efficacy of Melaleuca alternifolia pure essential oil and in a nanoemulsion to prevent skin photoaging. For this, 2% of pure essential oil or 2% of this essential oil in a nanoemulsion were vehiculated in a formulation. The skin penetration was evaluated using confocal Raman microspectroscopy. The radical protection factor was evaluated using electron paramagnetic resonance spectroscopy. For a clinical study, 40 male participants, aged 18-28 years, were enrolled, being divided into three groups: vehicle formulation, M. alternifolia pure essential oil and M. alternifolia Nanoemulsion. All the participants also received a sunscreen SPF 50 to use during the day. Before and after 90 days of study, skin hydrolipidics and morphological characteristics were performed by skin imaging and biophysical techniques. The nanoemulsion presented a lower antioxidant capacity and a higher penetration through the stratum corneum, reaching the viable epidermis, improving the stratum granulosum morphology. The groups presented an increase in the papillary depth, improving in the dermis echogenicity and the collagen fibers. Melaleuca alternifolia essential provides the potential to improve photoaged skin, being the application of nanoemulsion able to reach deeper skin layers.

Glycerol and natural sugar-derived complex modulate differentially stratum corneum water-binding properties and structural parameters in an in vitro Raman-desorption model

The epidermal protective functions are closely associated with skin hydration homeostasis. The understanding of different states of water binding is a rising concept in assessing topically applied formulations and their interaction within the stratum corneum (SC). In addition to global water content, primary bound water, partially bound water, and unbound water and barrier-related lipid lateral packing and protein secondary structure can be measured by Raman spectroscopy. This study aimed to establish an in vitro SC model to evaluate differences in the efficacy of a natural sugar-derived complex in combination with glycerol and a botanical extract in modulating SC water binding and structural proteins and barrier lipids. These compounds were selected due to their water-binding and soothing properties. The SC water profiles were assessed at the surface and in 8 μm SC depth. After a 12-hour hyperhydration and subsequent product incubation the measurements were performed during a 6 hours desiccation phase. The maximal water caption and the time until reaching a steady state are measured as well as water retention and resistance against water loss. Global water content, partially bound, and unbound water, as well as lipid and protein structures were assessed with confocal Raman microspectroscopy. Both the natural sugar-derived mixture and more pronounced, the same mixture with additional glycerol increased all three water-binding parameters at the surface and in 8 μm SC depth at the beginning and during the desiccation phase. Further addition of botanical extract did not result in an additional increase of the water-binding. All three formulations showed an increase in the lipid lateral packing values prevented the protein alteration as measured by β-sheets signal compared to blank. The present model is suited for screening studies comparing the specific effects of different compounds on hydration states. The natural sugar-derived mixture Aquaxyl showed evidence for an improvement of all SC hydration states, lipid and protein structure which was further enhanced by the addition of glycerol 5%. This improvement was evidenced at the surface and within the SC for all hydration-related parameters, and the lipid as well the protein structures. The addition of botanical extract phytoessence blue daisy did not show further improvement.

Confocal Raman Micro-Spectroscopy for Discrimination of Glycerol Diffusivity in Ex Vivo Porcine Dura Mater

Dura mater (DM) is a connective tissue with dense collagen, which is a protective membrane surrounding the human brain. The optical clearing (OC) method was used to make DM more transparent, thereby allowing to increase in-depth investigation by confocal Raman micro-spectroscopy and estimate the diffusivity of 50% glycerol and water migration. Glycerol concentration was obtained, and the diffusion coefficient was calculated, which ranged from 9.6 × 10^-6 to 3.0 × 10^-5 cm²/s. Collagen-related Raman band intensities were significantly increased for all depths from 50 to 200 µm after treatment. In addition, the changes in water content during OC showed that 50% glycerol induces tissue dehydration. Weakly and strongly bound water types were found to be most concentrated, playing a major role in the glycerol-induced water flux and OC. Results show that OC is an efficient method for controlling the DM optical properties, thereby enhancing the in-depth probing for laser therapy and diagnostics of the brain. DM is a comparable to various collagen-containing tissues and organs, such as sclera of eyes and skin dermis.

Penetration Depth of Propylene Glycol, Sodium Fluorescein and Nile Red into the Skin Using Non-Invasive Two-Photon Excited FLIM

The stratum corneum (SC) forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the SC is important for the efficiency of drug delivery and cosmetic safety. In this study, TPT-FLIM (two-photon tomography combined with fluorescence lifetime imaging) was applied as a non-invasive optical method for the visualization of skin structure and components to study penetration depths of exemplary substances, like hydrophilic propylene glycol (PG), sodium fluorescein (NaFl) and lipophilic Nile red (NR) into porcine ear skin ex vivo. Non-fluorescent PG was detected indirectly based on the pH-dependent increase in the fluorescence lifetime of SC components. The pH similarity between PG and viable epidermis limited the detection of PG. NaFl reached the viable epidermis, which was also proved by laser scanning microscopy. Tape stripping and confocal Raman micro-spectroscopy were performed additionally to study NaFl, which revealed penetration depths of ≈5 and ≈8 μm, respectively. Lastly, NR did not permeate the SC. We concluded that the amplitude-weighted mean fluorescence lifetime is the most appropriate FLIM parameter to build up penetration profiles. This work is anticipated to provide a non-invasive TPT-FLIM method for studying the penetration of topically applied drugs and cosmetics into the skin.

Current views on non-invasive in vivo determination of physiological parameters of the stratum corneum using confocal Raman microspectroscopy

Confocal Raman microspectroscopy is widely used in dermatology and cosmetology for analysis of the concentration of skin components (lipids, natural moisturizing factor molecules, water) and the penetration depth of cosmetic/medical formulations in the human stratum corneum (SC) in vivo. In recent years, it was shown that confocal Raman microspectroscopy can also be used for non-invasive in vivo depth-dependent determination of the physiological parameters of the SC, such as lamellar and lateral organization of intercellular lipids, folding properties of keratin, water mobility and hydrogen bonding states. The results showed that the strongest skin barrier function, which is primarily manifested by the orthorhombic organization of intercellular lipids, is provided at ≈20-40% SC depth, which is related to the maximal bonding state of water with surrounding components in the SC. The secondary and tertiary structures of keratin determine water binding in the SC, which is depth-dependent. This paper shows the technical possibility and advantage of confocal Raman microspectroscopy in non-invasive investigation of the skin and summarizes recent results on in vivo investigation of the human SC.

Blind source separation of molecular components of the human skin in vivo: non-negative matrix factorization of Raman microspectroscopy data

Determination of the molecular composition of the skin is crucial for numerous tasks in medicine, pharmacology, dermatology and cosmetology. Confocal Raman microspectroscopy is a sensitive method for the evaluation of molecular depth profiles in the skin in vivo. Since the Raman spectra of most of the skin constituents significantly superimpose, a spectral decomposition by a set of predefined library components is usually performed to disentangle their contributions. However, the incorrect choice of the number and type of components or differences between the spectra of the basic components measured in vitro and in vivo can lead to incorrect results of the decomposition procedure. Here, we investigate an alternative data-driven approach based on a non-negative matrix factorization (NNMF) algorithm of depth-resolved Raman spectra of skin that does not require a priori information of spectral data for the analysis. Using the model and experimentally measured depth-resolved Raman spectra of the upper epidermis in vivo, we show that NNMF provides depth profiles of endogenous molecular components and exogenous agents penetrating through the upper epidermis for the spectra and concentration. Moreover, we demonstrate that this approach is capable of providing new information on the molecular profiles of the skin.

Retaining Skin Barrier Function Properties of the Stratum Corneum with Components of the Natural Moisturizing Factor-A Randomized, Placebo-Controlled Double-Blind In Vivo Study

The influence of a topically applied formulation containing components of natural moisturizing factor (NMF) on barrier-related parameters of the stratum corneum (SC) was investigated in vivo using confocal Raman microspectroscopy in a randomized, placebo-controlled double-blind study on 12 volunteers for 14 days. This method allowed for the elucidation of subtle differences between the verum and the placebo even though the components of the verum naturally occur in the SC. This differentiation is not possible non-invasively by conventional methods. In this study, we found that the applied verum and placebo formulations disrupted the equilibrium of water, NMF and lipids in the SC. The adverse effects of the formulation could be mitigated by incorporating it into a simplified supplementation of NMF molecules. As a long-term effect, the amount of strongly bound water increases at 30–40% SC depth (p < 0.05) and the amount of weakly bound water decreases at 30–40% SC depth (p < 0.05) for the verum. This supplement was also unexpectedly able to prevent intercellular lipids (ICL) disorganization in selected depths. In the long term, the verum treatment limited the lateral disorganization of the ICL to the upper 20% SC depth. Further research is required to elucidate the interplay of these factors in the SC, to better understand their contribution to the equilibrium and barrier function of the skin. This understanding of the interaction of these naturally occurring components could help in the future to develop and optimize topical treatments for diseases like psoriasis, atopic dermatitis, ichthyosis where the skin barrier is disrupted.