Depth profiling of stratum corneum biophysical and molecular properties

Rational Design of Topical Semi-Solid Dosage Forms-How Far Are We?

Specific aspects of semi-solid dosage forms for topical application include the nature of the barrier to be overcome, aspects of susceptibility to physical and chemical instability, and a greater influence of sensory perception. Advances in understanding the driving forces of skin penetration as well as the design principles and inner structure of formulations, provide a good basis for the more rational design of such dosage forms, which still often follow more traditional design approaches. This review analyses the opportunities and constraints of rational formulation design approaches in the industrial development of new topical drugs. As the selection of drug candidates with favorable physicochemical properties increases the speed and probability of success, models for drug selection based on theoretical and experimental approaches are discussed. This paper reviews how progress in the scientific understanding of mechanisms and vehicle-influence of skin penetration can be used for rational formulation design. The characterization of semi-solid formulations is discussed with a special focus on modern rheological approaches and analytical methods for investigating and optimizing the chemical stability of active ingredients in consideration of applicable guidelines. In conclusion, the combination of a good understanding of scientific principles combined with early consideration of regulatory requirements for product quality are enablers for the successful development of innovative and robust semi-solid formulations for topical application.

Continuous Removal of Single Cell Layers by Tape Stripping the Stratum Corneum - a Histological Study

Studies on the penetration of toxicologically or pharmaceutically relevant substances through the skin and, more specifically, through the stratum corneum (s.c.) often rely on the well-established method of tape stripping. Tape stripping involves the removal of skin layers by means of adhesive tape, which is usually followed by quantification of dermally applied substances in these layers. However, the amount of s.c. removed by each individual tape strip is still a matter of scientific debate. While some studies imply that the amount of s.c. adhering to each tape strip decreases with increasing depth into the s.c., others observed a constant removal rate. All these studies rely on the quantification of the amount of s.c. captured on individual or pooled tape strips. Here, we present an approach whereby we measured the amount of s.c. remaining on excised porcine skin in the process of tape stripping. Staining and bloating of the s.c. allowed to measure its thickness and to count individual s.c. layers, respectively. Histologically, we show that the s.c. remaining on the skin decreased linearly as a function of strips taken. We found that each tape strip removes about 0.4µm of s.c., which corresponds to approximately one cellular layer. With a high coefficient of determination (r²>0.95), we were able to linearly correlate the thickness of the remaining s.c., the number of remaining cell layers and the number of tape strips applied. Furthermore, we elaborate on possible reasons for the discrepancies reported in the scientific literature regarding the amount of s.c. removed by each tape strip.

Dermal Delivery of Diclofenac Sodium-In Vitro and In Vivo Studies

Previously, we reported the use of confocal Raman spectroscopy (CRS) as a novel non-invasive approach to determine drug disposition in the skin in vivo. Results obtained by CRS were found to correlate with data from the well-established in vitro permeation test (IVPT) model using human epidermis. However, these studies used simple vehicles comprising single solvents and binary or ternary solvent mixtures; to date, the utility of CRS for monitoring dermal absorption following application of complex marketed formulations has not been examined. In the present work, skin delivery of diclofenac sodium (DFNa) from two topical dermatological drug products, namely Diclac® Lipogel 10 mg/g and Primofenac® Emulsion gel 1%, was determined by IVPT and in vivo by both CRS and tape stripping (TS) methodologies under similar experimental conditions. The in vivo data were evaluated against the in vitro findings, and a direct comparison between CRS and TS was performed. Results from all methodologies showed that Diclac promoted significantly greater DFNa delivery to the skin (p < 0.05). The cumulative amounts of DFNa which permeated at 24 h in vitro for Diclac (86.5 ± 9.4 µg/cm2) were 3.6-fold greater than the corresponding amounts found for Primofenac (24.4 ± 2.7 µg/cm2). Additionally, total skin uptake of DFNa in vivo, estimated by the area under the depth profiles curves (AUC), or the signal intensity of the drug detected in the upper stratum corneum (SC) (4 µm) ranged from 3.5 to 3.6-fold greater for Diclac than for Primofenac. The shape of the distribution profiles and the depth of DFNa penetration to the SC estimated by CRS and TS were similar for the two methods. However, TS data indicated a 4.7-fold greater efficacy of Diclac relative to Primofenac, with corresponding total amounts of drug penetrated, 94.1 ± 22.6 µg and 20.2 ± 7.0 µg. The findings demonstrate that CRS is a methodology that is capable of distinguishing skin delivery of DFNa from different formulations. The results support the use of this approach for non-invasive evaluation of topical products in vivo. Future studies will examine additional formulations with more complex compositions and will use a wider range of drugs with different physicochemical properties. The non-invasive nature of CRS coupled with the ability to monitor drug permeation in real time offer significant advantages for testing and development of topical dermatological products.

Virgin coconut oil as prophylactic therapy against alcohol damage on skin in COVID times

Background

Increased frequency of using alcohol‐based hand sanitizers (ABHS) by consumers during COVID times have resulted in increased incidences of skin issues on palms.

Objective

(1) To quantify skin damage with increased usage frequency of ABHS by consumers and (2) To evaluate Virgin Coconut Oil (VCO) as natural prophylactic agent to counter the adverse effects.

Methods

In‐home usage study was carried out with 60 volunteers for a 15‐day intervention—Control Group: 6 applications per day of ABHS and Test Group: Overnight VCO use (6–8 drops) followed by 6× usage per day of ABHS. This leg included dermatological evaluation and WHO Self‐Assessment Scale for skin health. Another leg of measurement included non‐invasive instrumental study (Moisture & TEWL Probes, Tape Strip for protein content and IR spectroscopy for protein & lipid content) on forearm of 12 subjects (25–60 years age) with and without VCO application and repeated alcohol exposure.

Results

In‐home usage study established consumer experiencing skin protective effect of VCO in the context of ABHS onslaught. 25% increase in perceived moisture content was recorded for VCO users, using WHO Self‐Assessment Scale. Instrumental studies confirmed an increase in TEWL and decrease in lipids & protein content. Overnight VCO application resists the extraction which builds up with repeated application.

Conclusions

Current work provides evidence of compromised hand skin barrier with ABHS daily usage. Overnight VCO application helps prepare the skin for next day alcohol use. Based on the findings, a regimen of overnight VCO application on hands as a natural prophylactic is recommended.

Mass spectrometry-based proteomic analysis of the effect of storage temperature on non-invasively collected samples of human stratum corneum

PURPOSE

The collection of human stratum corneum (SC) samples by tape-stripping promises to deliver a non-invasive method for biomarker analysis of skin diseases. The current study examines the effect of storage temperature and SC layer depth on the proteome profile of SC samples.

EXPERIMENTAL DESIGN

The samples were collected from healthy volunteers (n = 5) using 10 sequential adhesive discs. Discs were pooled by five (discs 1-5, 6-10) and stored at various temperatures for 10 days before their analysis by mass spectrometry.

RESULTS

No statistically significant difference was seen in the protein yield between discs 1-5 (14.8 mg) and 6-10 (14.4 mg), or between discs stored at -80°C (14.7 mg), -20°C (15.8 mg), 4°C (14.9 mg) or room temperature (13.2 mg). Mass spectrometry analysis revealed that the storage of SC samples at higher temperatures does not affect their proteome profile considerably (< 4.7% peptide precursor loss at lower temperatures vs. -80°C). On the other hand, while 95.3% of the identified peptide precursors were shared between discs 1-5 and 6-10, the level of 17 proteins was significantly changed between these conditions.

CONCLUSIONS

The findings of this study will likely have major implications on the conduct of proteomic studies involving SC sample collection, storage, and transportation.

Corneocytes: Relationship between Structural and Biomechanical Properties

BACKGROUND

Skin is the interface between an organism and the external environment, and hence the stratum corneum (SC) is the first to withstand mechanical insults that, in certain conditions, may lead to integrity loss and the development of pressure ulcers. The SC comprises corneocytes, which are vital elements to its barrier function. These cells are differentiated dead keratinocytes, without organelles, composed of a cornified envelope and a keratin-filled interior, and connected by corneodesmosomes (CDs).

SUMMARY

The current review focusses on the relationship between the morphological, structural, and topographical features of corneocytes and their mechanical properties, to understand how they assist the SC in maintaining skin integrity and in responding to mechanical insults. Key Messages: Corneocytes create distinct regions in the SC: the inner SC is characterized by immature cells with a fragile cornified envelope and a uniform distribution of CDs; the upper SC has resilient cornified envelopes and a honeycomb distribution of CDs, with a greater surface area and a smaller thickness than cells from the inner layer. The literature indicates that this upward maturation process is one of the most important steps in the mechanical resistance and barrier function of the SC. The morphology of these cells is dependent on the body site: the surface area in non-exposed skin is about 1,000-1,200 μm2, while for exposed skin, for example, the cheek and forehead, is about 700-800 μm2. Corneocytes are stiff cells compared to other cellular types, for example, the Young's modulus of muscle and fibroblast cells is typically a few kPa, while that of corneocytes is reported to be about hundreds of MPa. Moreover, these skin cells have 2 distinct mechanical regions: the cornified envelope (100-250 MPa) and the keratin matrix (250-500 MPa).

Topical niacinamide enhances hydrophobicity and resilience of corneocyte envelopes on different facial locations

Age-related differences in maturation parameters of corneocyte envelopes (size, hydrophobicity and rigidity) were examined at several facial test sites in young and old female Caucasians. In addition, the effect of topically applied niacinamide on these parameters was evaluated in a 4-week placebo-controlled study.

A proof-of-principle study comparing barrier function and cell morphology in face and body skin

OBJECTIVE

The purpose of this pilot in vivo study was to investigate corneocyte size and transepidermal water loss (TEWL) in facial cheek and volar forearm skin as a function of consecutive tape stripping. Changes in corneocyte size and transepidermal water loss (TEWL) were measured as a function of stratum corneum (SC) depth at both anatomical sites. To our knowledge, this is the first published quantitative comparison based on these parameters. This work complements our previously published studies on face skin barrier recovery at 24 h and 4 weeks post-tape stripping [Gorcea et al., Skin Res. Technol., 19, 2013, e375-e382; Gorcea et al., Int. J. Cosmet. Sci. 35, 2013, 250].

METHODS

Transepidermal water loss in vivo measurements of forearm and facial skin sites were taken before tape stripping commenced (baseline) and after each tape was collected. Optical microscopy and image analysis techniques were employed to characterize corneocyte size as a function of skin depth (tape strip number) for both anatomical sites.

RESULTS

Transepidermal water loss increased significantly from baseline with sequential tape stripping at both anatomical skin sites. Volar forearm skin required approximately three times as many tapes to 'damage' the SC barrier (arbitrarily defined as twice baseline TEWL) compared to facial cheek skin demonstrating significant differences in barrier properties between cheeks and forearms (P < 0.05). Corneocyte size decreased significantly with depth for both sites (P < 0.001). Corneocytes from face skin were significantly smaller than corneocytes from volar forearm skin.

CONCLUSION

Statistically significant differences between facial and body skin stratum corneum cell morphology and transepidermal water loss were demonstrated and quantitatively measured as a function of tape stripping.

12R-lipoxygenase activity is reduced in photodamaged facial stratum corneum. A novel activity assay indicates a key function in corneocyte maturation

Background

During the late stage of keratinocyte differentiation, corneocytes gain a strong protein–lipid structure: the corneocyte envelopes (CE), composed of the inner corneocyte protein envelope (CPE) and the outer corneocyte lipid envelope (CLE). The hydrophobicity of CEs depends on the covalent attachment of linoleoyl‐acyl‐ceramides by transglutaminases (TG). These ceramides are processed by a range of other enzymes, including 12R‐lipoxygenase (12R‐LOX), before the covalent attachment of the free ω‐hydroxyceramides to the CPE surface to form the CLE. The mechanical strength of CE is obtained with the formation of isodipeptide bonds by TG. The increase in hydrophobicity and rigidity leads to CE maturation which supports the integrity and mechanical resistance of the stratum corneum (SC).

Objectives

The aim of this work was to develop and validate a novel enzyme activity assay for 12R‐LOX in tape strippings of photo‐exposed (PE) cheek and photo‐protected (PP) post‐auricular SC of healthy Chinese volunteers (n = 12; age 25 ± 3 years).

Results

A fluorescence‐based assay was developed with ethyl linoleic acid as the substrate and a polyclonal antibody against 12R‐LOX as an inhibitor. The specificity was shown by the lack of effect by a LOX inhibitor (ML351) and an epidermal‐type lipoxygenase 3 (eLOX3) antibody on the acquired 12R‐LOX activity. Reduced 12R‐LOX activity was observed in the outer compared to the inner SC layers. Moreover, dramatically lower activity was shown in the PE vs. PP samples. Furthermore, the enzyme activity has a positive correlation (r = 0.94 ± 0.03) with CE maturity, in particular hydrophobicity, and a negative correlation (r = −0.96 ± 0.01) with transepidermal water loss (TEWL).

Conclusion

This novel enzyme assay revealed a lower 12R‐LOX activity in tape strippings from PE cheek for the first time. This finding is in line with less mature CEs and higher TEWL compared to PP post‐auricular samples. This study indicates a strong link between 12R‐LOX activity and CE maturation and SC integrity.

Transient receptor potential ankyrin 1 (TRPA1) positively regulates imiquimod-induced, psoriasiform dermal inflammation in mice

Transient receptor potential ankyrin 1 (TRPA1), a membrane protein ion channel, is known to mediate itch and pain in skin. The function of TRPA1, however, in psoriasiform dermatitis (PsD) is uncertain. Herein, we found that expression of TRPA1 is highly up-regulated in human psoriatic lesional skin. To study the role of TRPA1 in PsD, we assessed Psoriasis Severity Index (PSI) scores, transepidermal water loss (TEWL), skin thickness and pathology, and examined dermal inflammatory infiltrates, Th17-related genes and itch-related genes in c57BL/6 as wild-type (WT) and TRPA1 gene knockout (KO) mice following daily application of topical IMQ cream for 5 days. Compared with WT mice, clinical scores, skin thickness change and TEWL scores were similar on day 3, but were significantly decreased on day 5 in IMQ-treated TRPA1 KO mice (vs WT mice), suggesting reduced inflammation and skin barrier defects. Additionally, the relative area of epidermal Munro's microabscesses and mRNA levels of neutrophil inducible chemokines (S100A8, S100A9 and CXCL1) were decreased in the treated skin of TRPA1 KO mice, suggesting that neutrophil recruitment was impaired in the KO mice. Furthermore, mast cells, CD31⁺ blood vascular cells, CD45⁺ leukocytes and CD3⁺ T cells were all reduced in the treated skin of TRPA1 KO mice. Lastly, mRNA expression levels of IL-1β, IL-6, IL-23, IL-17A, IL-17F and IL-22 were decreased in TRPA1 KO mice. In summary, these results suggest a key role for TRPA1 in psoriasiform inflammation and raising its potential as a target for therapeutic intervention.

TRPV1 mediates inflammation and hyperplasia in imiquimod (IMQ)-induced psoriasiform dermatitis (PsD) in mice

BACKGROUND

Transient Receptor Potential Vanilloid 1 (TRPV1) is known to mediate itch and neurogenic inflammation, but the role of TRPV1 in psoriasiform dermal inflammation is poorly understood.

OBJECTIVE

To investigate the function of TRPV1 in imiquimod (IMQ)-induced psoriasiform dermatitis (PsD) in mice.

METHODS

Following daily treatment of topical IMQ cream for consecutive 5 days in C57BL/6 wide-type (WT) and TRPV1 gene knockout (KO) mice, we assessed the psoriasis severity index (PSI) scores, transepidermal water loss (TEWL), dermal inflammatory infiltrates, as well as gene expression levels for psoriasis related genes in mouse skin lesions.

RESULTS

Compared with WT mice, the clinical and TEWL scores, the extent of skin hyperplasia, the area of Munro microabscesses (MM) and angiogenesis of psoriasis were all significantly decreased in TRPV1 KO mice triggered with IMQ, suggesting a reduction in skin inflammation and barrier defects. In addition, the infiltration of CD45⁺ leukocytes, mast cells as well as CD3⁺ T cells was all reduced in the IMQ-treated skin of TRPV1 KO mice. Quantitative Real-time PCR (RT-qPCR) revealed that expression levels of IL-1β, IL-6, IL-23, S100A8 were decreased while IL-10 was increased in TRPV1 KO mice.

CONCLUSIONS

In summary, key markers of psoriatic inflammation and epidermal hyperplasia are reduced in TRPV1 KO mice, indicating the involvement of TRPV1 in the psoriasiform inflammation and suggesting its potential as a therapeutic target.

Early-life regional and temporal variation in filaggrin-derived natural moisturizing factor, filaggrin-processing enzyme activity, corneocyte phenotypes and plasmin activity: implications for atopic dermatitis

Background

Filaggrin is central to the pathogenesis of atopic dermatitis (AD). The cheeks are a common initiation site of infantile AD. Regional and temporal expression of levels of filaggrin degradation products [natural moisturizing factors (NMFs)], activities of filaggrin‐processing enzymes [bleomycin hydrolase (BH) and calpain‐1 (C‐1)] and plasmin, and corneocyte envelope (CE) maturity in early life are largely unknown.

Objectives

We conducted a cross‐sectional, observational study investigating regional and age‐dependent variations in NMF levels, activity of proteases and CE maturity in stratum corneum (SC) from infants to determine whether these factors could explain the observed predilection sites for AD in early life.

Methods

We measured NMF using a tape‐stripping method at seven sites in the SC of 129 children (aged < 12 months to 72 months) and in three sites in 56 neonates and infants (< 48 h to 3 months). In 37 of these neonates and infants, corneocyte size, maturity, BH, C‐1 and plasmin activities were determined.

Results

NMF levels are low at birth and increase with age. Cheek SC, compared with elbow flexure and nasal tip, has the lowest NMF in the first year of life and is the slowest to reach stable levels. Cheek corneocytes remain immature. Plasmin, BH and C‐1 activities are all elevated by 1 month of age in exposed cheek skin, but not in elbow skin.

Conclusions

Regional and temporal differences in NMF levels, CE maturity and protease activities may explain the predilection for AD to affect the cheeks initially and are supportive of this site as key for allergen priming in early childhood. These observations will help design early intervention and treatment strategies for AD.

What's already known about this topic?

Atopic dermatitis (AD) frequently starts in early infancy, and the first eczematous lesions emerge on the cheeks.

Filaggrin is a major structural protein in the stratum corneum (SC).

Filaggrin deficiency is associated with the development of AD and, in the context of AD, food allergies and asthma.

Filaggrin is metabolized into natural moisturizing factors (NMFs), which can be measured in the SC.

What does this study add?

Regional differences in NMF levels, corneocyte envelope immaturity and protease activities may help explain why infantile AD most often initially affects the cheeks.

Filaggrin processing, corneocyte maturity, and protease activities show regional and temporal differences in infant skin.

These findings may explain disease patterns in early‐life AD.

What is the translational message?

Cheek skin may be highly relevant for allergen priming.

Emollient therapy at the vulnerable cheek site might help to prevent AD and/or food sensitization.

Linked Editorial: https://doi.org/10.1111/bjd.16806.

https://doi.org/10.1111/bjd.16959 available online

https://goo.gl/Uqv3dl

A new approach to assess the effect of photodamage on corneocyte envelope maturity using combined hydrophobicity and mechanical fragility assays

BACKGROUND

The maturity of the corneocyte envelope (CE) provides information about the barrier functionality of the stratum corneum (SC). Corneocytes are enclosed by the CE, a protein-lipid matrix, contributing to mechanical resistance and hydrophobicity of the SC.

OBJECTIVES

The aim of the work was to develop a novel and robust approach to characterize CE maturity based on rigidity, hydrophobicity and surface area. This offers an alternative approach to the Nile red staining and antigenicity of involucrin to characterize the CE. The photoexposed (PE) cheek and photoprotected (PP) post-auricular sites were selected for investigation.

METHODS

Nine tape strips were obtained from the cheek and post-auricular sites of healthy Caucasians. CEs on the first and last tape strip were subjected to sonication to assess rigidity, and Nile red staining to determine hydrophobicity per unit surface area. In addition, the presence of involucrin and lipids was assessed to determine CE maturity by examination of the red/green pixel ratio, percentage of involucrin expressing CEs and alternatively the ratio of fluorescence density.

RESULTS

The CE rigidity was lower in the deeper SC layers of the cheek, whereas post-auricular CEs were mechanically more resistant. Post-auricular CEs from the superficial SC had a larger surface area with a stronger fluorescence signal than those from the cheek. Interestingly, those CEs from the deeper SC layers had similar surface areas in both anatomical sites but were significantly different in hydrophobicity. These three parameters can be summarized as a relative CE maturity index that expresses CE maturity more precisely with a higher sensitivity than the conventional involucrin and Nile red staining approach. CEs of the cheek surface are more mature than CEs in the deeper SC layer, whereas CEs obtained from the post-auricular surface are more mature than those from the cheek surface.

CONCLUSION

The combined method developed allows characterization of CE maturity based on hydrophobicity per unit surface area and rigidity rather than a simple ratio of lipid to involucrin. A more robust and sensitive measurement has therefore been developed addressing the limitations of earlier protocols.

A novel non-invasive diagnostic sampling technique for cutaneous leishmaniasis

Accurate diagnosis of cutaneous leishmaniasis (CL) is important for chemotherapy and epidemiological studies. Common approaches for Leishmania detection involve the invasive collection of specimens for direct identification of amastigotes by microscopy and the culturing of promastigotes from infected tissues. Although these techniques are highly specific, they require highly skilled health workers and have the inherent risks of all invasive procedures, such as pain and risk of bacterial and fungal super-infection. Therefore, it is essential to reduce discomfort, potential infection and scarring caused by invasive diagnostic approaches especially for children. In this report, we present a novel non-invasive method, that is painless, rapid and user-friendly, using sequential tape strips for sampling and isolation of DNA from the surface of active and healed skin lesions of CL patients. A total of 119 patients suspected of suffering from cutaneous leishmaniasis with different clinical manifestations were recruited and samples were collected both from their lesions and from uninfected areas. In addition, 15 fungal-infected lesions and 54 areas of healthy skin were examined. The duration of sampling is short (less than one minute) and species identification by PCR is highly specific and sensitive. The sequential tape stripping sampling method is a sensitive, non-invasive and cost-effective alternative to traditional diagnostic assays and it is suitable for field studies as well as for use in health care centers.

Chemical ultraviolet absorbers topically applied in a skin barrier mimetic formulation remain in the outer stratum corneum of porcine skin

The objective of the present study was to evaluate the fate of three chemical sunscreens, isoamyl p-methoxycinnamate (IPMC), diethylamino hydroxybenzoyl hexyl benzoate (DHHB), and bis-ethylhexylphenol methoxyphenyl triazine (BEMT), topically applied to mammalian skin from a skin barrier mimetic oil-in-water formulation. High Performance Liquid Chromatography (HPLC) methods were developed for the analysis of each molecule and validated. Franz cell permeation studies were conducted following application of finite doses of the formulations to excised porcine skin. A vehicle formulation containing no sunscreens was evaluated as a control. Permeation studies were conducted for 12h after which full mass balance studies were carried out. Analysis of individual UV sunscreens was achieved with HPLC following application of the formulation to the skin with no interference from the vehicle components. No skin permeation of any of the chemical sunscreens was evident after 12h. While sunscreens were detected in up to 12 tape strips taken from the SC, 87% or more of the applied doses recovered in the first 5 tape strips. When corrected for the amount of protein removed per tape strip this corresponded to a penetration depth in porcine stratum corneum of ∼1.7μm. Mass balance studies indicated total recovery values were within accepted guidelines for cosmetic formulations. Overall, only superficial penetration into the SC was observed for each compound. These findings are consistent with the physicochemical properties of the selected UV absorbing molecules and their formulation into an ordered biomimetic barrier formulation thus support their intended use in topical consumer formulations designed to protect from UV exposure. To our knowledge this is the first report of depth profiling of chemical sunscreens in the SC that combines tape stripping and protein determination following in vitro Franz cell studies.

A fundamental investigation into aspects of the physiology and biochemistry of the stratum corneum in subjects with sensitive skin

BACKGROUND

Sensitive skin is a poorly understood skin condition. Defects in stratum corneum (SC) barrier function and/or extrasensory neuronal networks in the epidermis are believed to be involved in the problem.

OBJECTIVES

This study aimed to unravel the relationships between bleomycin hydrolase (BH) and calpain-1 (C-1), pyrrolidone carboxylic acid (PCA) levels, corneocyte maturation, transglutaminase (TG) and plasmin activities on the cheeks of subjects with sensitive skin.

METHODS

Forty-eight female Caucasian subjects, Fitzpatrick skin phototypes II-III, with self-perceived sensitive facial skin, were assessed and underwent a capsaicin reactivity test. Expert grading of skin condition was conducted as well as the measurement of transepidermal water loss (TEWL), skin capacitance, SC cohesion and SC integrity. BH, C-1 and plasmin activities were measured as well as PCA levels, plasmin and TG activity. Differential Nile red and involucrin immunostaining was performed to assess corneocyte maturation and size.

RESULTS

About 52% of the subjects reacted to capsaicin. There were no significant differences between the capsaicin-sensitive and non-capsaicin-sensitive subjects with reference to skin grading, TEWL, skin capacitance and SC cohesion. PCA levels and BH activity were lowest in the capsaicin-sensitive panel (P < 0.05) and were correlated in non-capsaicin-sensitive subjects (r = 0.72). The activity of TG was significantly lower (48%) in the capsaicin-sensitive subjects (P < 0.001) and their corneocytes were less mature and smaller (P ≤ 0.05). SC was estimated to be thinner (6.87 ± 0.28 vs. 8.68 ± 0.26 μm; P = 0.001) in the capsaicin-sensitive subjects with a corresponding shorter SC path length (83.2 ± 4.4 μm and 113.1 ± 4.5 μm; P = 0.001).

CONCLUSIONS

Despite the physiological similarities between the two groups of sensitive skin subjects, differences in their biochemistry were clearly evident. Lower levels of PCA, BH and TG activities together with a greater number of smaller and immature corneocytes indicate inferior SC maturation in the capsaicin-sensitive subjects. The reduced maturation of corneocytes and thinner SC likely contributes to a greater penetration of capsaicin and the associated increased skin sensitivity.

Variation in the activities of late stage filaggrin processing enzymes, calpain-1 and bleomycin hydrolase, together with pyrrolidone carboxylic acid levels, corneocyte phenotypes and plasmin activities in non-sun-exposed and sun-exposed facial stratum corneum of different ethnicities

BACKGROUND

Knowledge of the ethnic differences and effects of photodamage on the relative amounts of natural moisturizing factor (NMF) together with filaggrin processing enzymes in facial stratum corneum is limited. Our aim was to characterize the activities of calpain-1 (C-1), bleomycin hydrolase (BH) and the levels of pyrrolidone carboxylic acid (PCA) as a marker for total NMF levels and to relate them to plasmin activities and corneocyte maturation.

METHODS

Enzyme activities, PCA levels and corneocyte maturation were determined from facial tape strippings of photoexposed cheek and photoprotected post-auricular areas (PA) of healthy Caucasian (C), Black African (BA) and albino African (AA) female subjects living in South Africa.

RESULTS

PCA concentration levels were of the order AA > BA > C subjects, and the highest activities of BH were present in the AA subjects. BH activities were greater on the photoexposed sites for the BA and C subjects, but they were only numerically elevated in the AA subjects. Photoprotected sites had an increase in C-1 activity in pigmented groups (C and BA), whereas in the AA subjects, the opposite was measured. Plasmin activities were greater on the cheek compared with the PA site for the AA and C subjects, but the activity was low in the BA subjects. In both test sites, the AA, but not the BA and C subjects, had smaller, parakeratotic and less mature corneocytes.

CONCLUSION

Variation in PCA levels has been found for different ethnic groups in this study (AA > BA > C subjects). The values in the AA subjects are surprising as one might expect that the lack of pigmentation, and thereby increased photodamage, might lead to lower levels. Increased BH, but not C-1 activity, was observed in the AA subjects indicating that BH is associated with PCA production to a greater extent. Surprisingly, corneocyte maturation is still impaired with elevated PCA levels in AA subjects. The higher levels of plasmin and BH activities on the cheeks, especially for AA and C subjects, suggest that they can be used as markers for epidermal photodamage.

Lipid to protein ratio plays an important role in the skin barrier function in patients with atopic eczema

BACKGROUND

The barrier function of the skin is primarily provided by the stratum corneum (SC), the outermost layer of the skin. Skin barrier impairment is thought to be a primary factor in the pathogenesis of atopic eczema (AE). Filaggrin is an epidermal barrier protein and common mutations in the filaggrin gene strongly predispose for AE. However, the role of filaggrin mutations in the decreased skin barrier in AE is not fully understood. It was recently shown that changes in SC lipid composition and organization play a role in the reduced skin barrier in AE.

OBJECTIVES

To determine whether the lipid/protein ratio and the total dry SC mass per surface area are related to the skin barrier function of controls and patients with AE.

METHODS

A case-control study was performed to compare nonlesional and lesional skin of AE with skin of controls. The dry SC mass was determined by tape-stripping and Squamescan(™) . The ratio between lipid and protein bands in the Raman spectrum was used to determine the lipid/protein ratio. Skin barrier function was assessed by transepidermal water loss.

RESULTS

The results show that the dry SC mass per skin area is altered only in lesional SC of patients with AE compared with control subjects. The observed reduction in the lipid/protein ratio in SC of patients with AE was more pronounced, both in lesional and nonlesional SC and correlated strongly with the skin barrier function and disease severity.

CONCLUSIONS

The lipid/protein ratio plays a role in the reduced skin barrier function in AE.

Resistance to water diffusion in the stratum corneum is depth-dependent

The stratum corneum (SC) provides a permeability barrier that limits the inflow and outflow of water. The permeability barrier is continuously and dynamically formed, maintained, and degraded along the depth, from the bottom to the top, of the SC. Naturally, its functioning and structure also change dynamically in a depth-dependent manner. While transepidermal water loss is typically used to assess the function of the SC barrier, it fails to provide any information about the dynamic mechanisms that are responsible for the depth-dependent characteristics of the permeability barrier. This paper aims to quantitatively characterize the depth-dependency of the permeability barrier using in vivo non-invasive measurement data for understanding the underlying mechanisms for barrier formation, maintenance, and degradation. As a framework to combine existing experimental data, we propose a mathematical model of the SC, consisting of multiple compartments, to explicitly address and investigate the depth-dependency of the SC permeability barrier. Using this mathematical model, we derive a measure of the water permeability barrier, i.e. resistance to water diffusion in the SC, from the measurement data on transepidermal water loss and water concentration profiles measured non-invasively by Raman spectroscopy. The derived resistance profiles effectively characterize the depth-dependency of the permeability barrier, with three distinct regions corresponding to formation, maintenance, and degradation of the barrier. Quantitative characterization of the obtained resistance profiles allows us to compare and evaluate the permeability barrier of skin with different morphology and physiology (infants vs adults, different skin sites, before and after application of oils) and elucidates differences in underlying mechanisms of processing barriers. The resistance profiles were further used to predict the spatial-temporal effects of skin treatments by in silico experiments, in terms of spatial-temporal dynamics of percutaneous water penetration.

The effects of heat on skin barrier function and in vivo dermal absorption

Enhanced delivery of ingredients across the stratum corneum (SC) is of great interest for improving the efficacy of topically applied formulations. Various methods for improving dermal penetration have been reported including galvanic devices and micro-needles. From a safety perspective it is important that such approaches do not compromise SC barrier function. This study investigates the influence of topically applied heat in vivo on the dermal uptake and penetration of a model active, allantoin from gel and lotion formulations. A custom designed device was used to deliver 42°C for 30s daily to human subjects after application of two formulations containing allantoin. The results were compared with sites treated with formulations containing no active and no heat, and a control site. In addition to penetration of allantoin, the integrity of the SC was monitored using trans-epidermal water loss (TEWL) measurements. The results showed that just 30s of 42°C topically applied heat was enough to cause significantly more penetration of allantoin from the lotion formulation compared with no application of heat. TEWL data indicated that the integrity of the skin was not compromised by the treatment. However, the application of heat did not promote enhanced penetration of the active from the gel formulation. Vehicle composition is therefore an important factor when considering thermal enhancement strategies for targeting actives to the skin.

Aberrant distribution patterns of corneodesmosomal components of tape-stripped corneocytes in atopic dermatitis and related skin conditions (ichthyosis vulgaris, Netherton syndrome and peeling skin syndrome type B)

BACKGROUND

Atopic dermatitis (AD), Netherton syndrome (NS) and peeling skin syndrome type B (PSS) may show some clinical phenotypic overlap. Corneodesmosomes are crucial for maintaining stratum corneum integrity and the components' localization can be visualized by immunostaining tape-stripped corneocytes. In normal skin, they are detected at the cell periphery.

OBJECTIVE

To determine whether AD, NS, PSS and ichthyosis vulgaris (IV) have differences in the corneodesmosomal components' distribution and corneocytes surface areas.

METHODS

Corneocytes were tape-stripped from a control group (n=12) and a disease group (37 AD cases, 3 IV cases, 4 NS cases, and 3 PSS cases), and analyzed with immunofluorescent microscopy. The distribution patterns of corneodesmosomal components: desmoglein 1, corneodesmosin, and desmocollin 1 were classified into four types: peripheral, sparse diffuse, dense diffuse and partial diffuse. Corneocyte surface areas were also measured.

RESULTS

The corneodesmosome staining patterns were abnormal in the disease group. Other than in the 3 PSS cases, all three components showed similar patterns in each category. In lesional AD skin, the dense diffuse pattern was prominent. A high rate of the partial diffuse pattern, loss of linear cell-cell contacts, and irregular stripping manners were unique to NS. Only in PSS was corneodesmosin staining virtually absent. The corneocyte surface areas correlated significantly with the rate of combined sparse and dense diffuse patterns of desmoglein 1.

CONCLUSION

This method may be used to assess abnormally differentiated corneocytes in AD and other diseases tested. In PSS samples, tape stripping analysis may serve as a non-invasive diagnostic test.

Influence of niacinamide containing formulations on the molecular and biophysical properties of the stratum corneum

Niacinamide-containing moisturisers are known be efficacious in alleviating dry skin conditions and improving stratum corneum (SC) barrier function. However, the mechanisms of action of niacinamide at the molecular level in the SC are still not well understood. Previously, we have reported the development of novel methods to probe SC barrier properties in vivo. The aim of the present study was to characterise changes in Trans Epidermal Water Loss (TEWL), corneocyte surface area and maturity, selected protease activities and SC thickness after repeated application of a simple vehicle containing niacinamide. A commercial formulation was also included as a reference. The left and right mid-volar forearms of 20 healthy volunteers were used as study sites, to which topical formulations were applied twice daily for 28 days. After successive tape-stripping, corneocyte maturity and surface area were assessed. In addition, activity of the desquamatory kallikrein (KLK) protease enzymes KLK5 and KLK7, and tryptase and plasmin (implicated in inflammatory process) were measured using a fluorogenic probe assay. The amount of protein removed and TEWL were also recorded. SC thickness before and after treatment was determined using Confocal Raman Spectroscopy (CRS). Overall (i) corneocyte maturity and surface area decreased with increasing number of tape strips, (ii) activity of both the desquamatory and inflammatory enzymes was highest in the outer layers of the SC and decreased with depth (iii) TEWL increased as more SC layers were removed. Furthermore, areas treated with formulations containing niacinamide were significantly different to pre-treatment baseline and untreated/vehicle-control treated sites, with larger and more mature corneocytes, decreased inflammatory activity, decreased TEWL and increased SC thickness. These data (a) confirm the utility of measures and metrics developed previously for the non-invasive assay of SC barrier function, (b) present an holistic picture of a SC compartment managing barrier function through dynamic optimisation of pathlength and quality of building materials used, and (c) shed new light on niacinamide as a topical formulation adjunct with unique SC barrier-augmentation properties.

Variation of stratum corneum biophysical and molecular properties with anatomic site

Several serine protease enzymes are known to be involved in both normal desquamation and the inflammatory processes of the skin. Alteration in the activity of these proteases should also affect corneocyte maturity and size as well as stratum corneum thickness. The aim of the present work was to characterise the baseline changes in corneocyte size, corneocyte maturity, selected protease activity (specifically, Kallikreins-5 and 7, tryptase), protein content and trans-epidermal water loss (TEWL) as a function of anatomic site. The anatomic sites investigated were: cheek, abdomen, wrist and mid-ventral forearm. TEWL values were highest for the cheek (p < 0.05). The TEWL values were also significantly higher (p < 0.05) for cheek and wrist compared with other sites. Protein content was significantly lower for wrist (p < 0.05) compared with other sites. Corneocyte maturity and surface area were significantly (p < 0.05) lower for cheek and wrist compared with other sites. An excellent correlation (r (2) = 0.99) was obtained for maturity and surface area measurements. Kallikrein-5 and tryptase activity were significantly higher for the cheek compared with other sites but Kallikrein-7 values were uniform across sites. The findings have significant implications for skin permeability to drugs and other substances such as environmental toxins depending on the anatomic site of delivery or exposure.

Influence of Aqueous Cream BP on corneocyte size, maturity, skin protease activity, protein content and transepidermal water loss

BACKGROUND

Aqueous Cream BP is frequently prescribed for patients with eczema and is known to induce sensitivity in certain patients and also to decrease the thickness of the stratum corneum (SC). We have previously reported methodology to quantify corneocyte maturity and size, protease activity and protein content within different levels of the SC.

OBJECTIVES

The aim of the present study was to investigate changes in corneocyte size, corneocyte maturity, selected protease activities, protein content and transepidermal water loss (TEWL) in normal skin after a 28-day application of Aqueous Cream BP.

METHODS

The left and right mid volar forearms of six healthy female volunteers were selected as the study sites. Aqueous Cream BP was applied twice daily to treated sites for 28 days. At the end of this period, the site was tape-stripped and corneocyte maturity, corneocyte size and protease activity of the desquamatory kallikrein proteases, KLK5 and KLK7, and the inflammatory proteases tryptase and plasmin were measured. Protein content and TEWL measurements were also recorded.

RESULTS

Corneocyte maturity and size decreased with increasing number of tape strips, and were significantly lower in treated sites compared with untreated sites. Protease activity and TEWL values were higher (P < 0·05) for the treated sites compared with untreated sites. The amount of protein removed from deeper layers of treated sites was significantly lower than from untreated sites.

CONCLUSIONS

We report rapid minimally invasive measures of the effects of Aqueous Cream BP at the cellular and molecular level of the skin. Treatment with this formulation is associated with increased desquamatory and inflammatory protease activity. Changes in corneocyte maturity and size are also indicative of accelerated skin turnover induced by chronic application of this emollient. These findings question firmly the routine prescription of this preparation as a moisturizer in patients with atopic dermatitis.

Transcriptional gene silencing of kallikrein 5 and kallikrein 7 using siRNA prevents epithelial cell detachment induced by alkaline shock in an in vitro model of eczema

Eczema is widely considered to be an exacerbation of alkaline stress to the skin. Epidermal barrier dysfunction is a feature of eczema pathology, which predisposes affected individuals to distressing morbid symptoms. At least two serine proteases, stratum corneum chymotryptic enzyme (kallikrein 7 [KLK7]) and stratum corneum tryptic enzyme (kallikrien 5 [KLK5]), have increased activity levels in eczematous lesions and both have been implicated in the destruction of corneodesomosomes, which are crucial to epidermal integrity. The present in vitro study investigated whether transcriptional gene silencing after siRNA transfection could influence the activity of these signature enzymes in an in vitro model of eczema induced by alkaline shock. HaCaT epithelial cells were subjected to alkaline stress by the addition of 1,1,3,3-tetramethyl guanidine "superbase" (TMG) to the culture media. The culture media were subsequently tested for chymotryspin, trypsin, plasmin, and urokinase activity using colorimetric peptide assays and for reactive oxygen species using WST1 cell viability reagent. Cells that had been transfected with small interfering ribonucleic acid (siRNA) against KLK5 and KLK7 for 24 h before alkaline shock did not exhibit the increase in serine protease levels observed in untreated controls. Moreover, an endpoint MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) confirmed that detachment of cells from the culture substrate observed in alkaline-stressed cells did not occur in siRNA-treated cells. This in vitro study has established the proof-of-principle that siRNA therapy appears to mitigate the consequences of alkaline shock to the serine protease-associated fragility of epithelial cells that is characteristic of eczema.