Recent advances in skin ‘barrier’ research

Development of a Mass Spectrometry Imaging Method to Evaluate the Penetration of Moisturizing Components Coated on Surgical Gloves into Artificial Membranes

Skin dryness and irritant contact dermatitis induced by the prolonged use of surgical gloves are issues faced by physicians. To address these concerns, manufacturers have introduced surgical gloves that incorporate a moisturizing component on their inner surface, resulting in documented results showing a reduction in hand dermatitis. However, the spatial distribution of moisturizers applied to surgical gloves within the integument remains unclear. Using matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI), we investigated the spatial distribution of moisturizers in surgical gloves within artificial membranes. Recently, dermal permeation assessments using three-dimensional models, silicone membranes, and Strat-M have gained attention as alternative approaches to animal testing. Therefore, in this study, we established an in vitro dermal permeation assessment of commercially available moisturizers in surgical gloves using artificial membranes. In this study, we offer a methodology to visualize the infiltration of moisturizers applied to surgical gloves into an artificial membrane using MALDI-MSI, while evaluating commercially available moisturizer-coated surgical gloves. Using our penetration evaluation method, we confirmed the infiltration of the moisturizers into the polyethersulfone 2 and polyolefin layers, which correspond to the epidermis and dermis of the skin, after the use of surgical gloves. The MSI-based method presented herein demonstrated the efficacy of evaluating the permeation of samples containing active ingredients.

Effects of dietary camelina, flaxseed, and canola oil supplementation on inflammatory and oxidative markers, transepidermal water loss, and coat quality in healthy adult dogs

Introduction

Camelina oil contains a greater concentration of omega-3 (n-3) a-linolenic acid (C18:3n-3; ALA) than omega-6 (n-6) linoleic acid (C18:2n-6; LA), in comparison to alternative fat sources commonly used to formulate canine diets. Omega-3 FAs are frequently used to support canine skin and coat health claims and reduce inflammation and oxidative stress; however, there is a lack of research investigating camelina oil supplementation and its effects on these applications in dogs. The objective of this study was to evaluate the effects of camelina oil supplementation on coat quality, skin barrier function, and circulating inflammatory and oxidative marker concentrations.

Methods

Thirty healthy [17 females; 13 males; 7.2 ± 3.1 years old; 27.4 ± 14.0 kg body weight (BW)] privately-owned dogs of various breeds were used. After a 4-week wash-in period consuming sunflower oil (n6:n3 = 1:0) and a commercial kibble, dogs were blocked by age, breed, and size, and randomly assigned to one of three treatment oils: camelina (n6:n3 = 1:1.18), canola (n6:n3 = 1:0.59), flaxseed (n6:n3 = 1:4.19) (inclusion level: 8.2 g oil/100 g of total food intake) in a randomized complete block design. Transepidermal water loss (TEWL) was measured using a VapoMeter on the pinna, paw pad, and inner leg. Fasted blood samples were collected to measure serum inflammatory and oxidative marker concentrations using enzyme-linked immunosorbent assay (ELISA) kits and spectrophotometric assays. A 5-point-Likert scale was used to assess coat characteristics. All data were collected on weeks 0, 2, 4, 10, and 16 and analyzed using PROC GLIMMIX in SAS.

Results

No significant changes occurred in TEWL, or inflammatory and oxidative marker concentrations among treatments, across weeks, or for treatment by week interactions. Softness, shine, softness uniformity, color intensity, and follicle density of the coat increased from baseline in all treatment groups (P < 0.05).

Discussion

Outcomes did not differ (P > 0.05) among treatment groups over 16-weeks, indicating that camelina oil is comparable to existing plant-based canine oil supplements, flaxseed, and canola, at supporting skin and coat health and inflammation in dogs. Future research employing an immune or exercise challenge is warranted, as the dogs in this study were not subjected to either.

Prevention and management of moisture-associated skin damage

Disruption to the integrity of the skin can reduce patient wellbeing and quality of life. A major cause of skin breakdown is prolonged exposure to moisture, but this is often overlooked. When skin is wet, it becomes more susceptible to damage from friction and shearing forces, and skin flora can penetrate the disrupted barrier, causing further irritation and inflammation. If untreated, moisture-associated skin damage (MASD) can rapidly lead to excoriation and skin breakdown. MASD includes incontinence-associated dermatitis (IAD), which is caused by prolonged skin exposure to urine and stool, particularly liquid stool. For patients at a high risk of developing IAD, preventive measures should be instituted as soon as possible. The main one is to prevent excessive contact of the skin with moisture. Optimal skin care should be provided to patients with any form of MASD. It should be based on a structured regimen and include the use of a gentle skin cleanser, a barrier product and moisturiser. Derma Protective Plus is a liquid barrier that gives long-lasting protection against chafing or ingress of urine and stool into the skin. This product is less greasy than others, and provides a barrier and a healing environment, with resistance to further maceration from IAD or persistent loose stools.

The Role of Environmental Exposures in Atopic Dermatitis

PURPOSE OF REVIEW

Although genetic factors clearly play a role in the development of atopic dermatitis (AD), the recent dramatic increase in the prevalence of AD in low- and middle-income countries is not consistent with only a role of genetic factors. These findings strongly suggest that environmental factors may play an important role in the pathogenesis of AD.

RECENT FINDINGS

We reviewed the role of gene-environment studies; in utero exposures including tobacco smoke, alcohol, maternal stress, various digestive supplements, and gestational diabetes; early-life exposures including diet, gut microbiota, antibiotics, and breastfeeding; climate including temperature, ultraviolet radiation exposure, and air pollution; and household products, indoor allergens, water hardness, pH, and skin microbiota and their effects on AD. Environmental factors definitely play a role in the pathogenesis of AD. However, identifying definitive factors continues to be difficult in the setting of conflicting evidence and the complex interactions between genotypes and the environment resulting in a multitude of AD phenotypes. All of the different environmental interactions discussed highlight the importance of intervening on multiple levels in a patient's environment to improve or even prevent AD symptoms. Further, the importance of modifying environmental factors early on in a person's life is demonstrated. When possible, all of these environmental factors should be considered in treating a patient with AD and the appropriate modifications should be made at population and individual levels.

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

OBJECTIVE

It is conventionally understood that occlusive effects are the retention of excessive water in the stratum corneum (SC), the increase of SC thickness (swelling) and a decrease of the transepidermal water loss. However, the influence of occlusion on water binding properties in the SC is unknown.

METHODS

The action of plant-derived jojoba and almond oils, as well as mineral-derived paraffin oil and petrolatum topically applied on human skin, is investigated in vivo using confocal Raman microspectroscopy. To understand the oils' influence on the SC on the molecular level, the depth-dependent hydrogen bonding states of water in the SC and their relationship to the conformation of keratin, concentration of natural moisturizing factor (NMF) molecules and lipid organization were investigated.

RESULTS

A significant SC swelling was observed only in petrolatum-treated skin. The water concentration was increased in oil-treated skin in the intermediate SC region (40-70% SC depth). Meanwhile, the amount of free, weakly and tightly bound water increased, and strongly bound water decreased in the uppermost SC region (0-30% SC depth). The NMF concentration of oil-treated skin was significantly lower at 50-70% SC depth. The lateral organization of lipids in oil-treated skin was lower at 0-30% SC depth. The secondary structure of keratin was changed towards an increase of β-sheet content in mineral-derived oil-treated skin and changed towards an increase of α-helix content in plant-derived oil-treated skin.

CONCLUSION

The occlusive properties can be summarized as the increase of free water and the transformation of water from a more strongly to a more weakly hydrogen bonding state in the uppermost SC, although some oils cause insignificant changes of the SC thickness. The accompanied changes in the keratin conformation at the intermediate swelling region of the SC also emphasize the role of keratin in the SC's water-transporting system, that is the water in the SC transports intercellularly and intracellularly in the intermediate swelling region and only intercellularly in the uppermost non-swelling region. Bearing this in mind, almond, jojoba and paraffin oils, which are not occlusive from the conventional viewpoint, have an occlusion effect similar to petrolatum on the SC.

Prevention and management of moisture-associated skin damage

The harmful effects of excessive moisture on a patient's skin are well known. While traditionally considered an issue only encountered in continence care and older people, it is now recognised that the harmful effects of excessive moisture can occur across the lifespan and in various patient groups. The term 'moisture-associated skin damage' describes the spectrum of inflammatory damage that occurs in response to the prolonged exposure of a patient's skin to perspiration, urine, faeces or wound exudate. It is generally accepted that moisture-associated skin damage consists of four conditions: incontinence-associated dermatitis, intertrigo, peristomal moisture-associated dermatitis, and periwound moisture-associated dermatitis. This article describes the aetiologies of each of the different types of moisture-associated skin damage, and outlines the nursing interventions required for their prevention and management.

A modification for the calculation of water depth profiles in oil-treated skin by in vivo confocal Raman microscopy

In this study, an extended calculation method for the determination of the water profiles in oil-treated skin is proposed, which is based on the calculation of the ratio between the Raman band intensities of water (3350-3550 cm^-1 ) and keratin Amide I at 1650 cm^-1 . The proposed method is compared with the conventional method based on the ratio of the Raman band intensities of water (3350-3550 cm^-1 ) and keratin at 2930 cm^-1 . The conventional method creates artifacts in the depth profiles of the water concentration in oil-treated skin, showing a lower amount of water in the upper and intermediate layers of the stratum corneum, which is due to the superposition of oil- and keratin-related Raman bands at 2930 cm^-1 . The proposed extended method shows no artifacts and has the potential to determine the water depth profiles after topical application of formulations on the skin.

Challenging a paradigm: skin sensitivity to sodium lauryl sulfate is independent of atopic diathesis

BACKGROUND

Sodium lauryl sulfate (SLS) is the best-studied detergent in irritant contact dermatitis. In atopic dermatitis, the two major pathophysiological abnormalities concern skin barrier function and regulation of cutaneous immune responses. The probability of atopic skin diathesis can be assessed by comprehensive analysis of patient history, as well as clinical and laboratory findings, resulting in the Erlangen Atopy Score (EAS).

OBJECTIVES

To investigate the impacts of (i) atopic skin diathesis according to the EAS and (ii) the physician-assessed diagnoses 'atopic dermatitis', 'allergic rhinitis' and 'allergic asthma' on SLS skin reactions.

METHODS

This is a retrospective analysis of data from 2030 consecutive patients patch tested with SLS (0·25% aqueous) from two tertiary referral centres in Germany, from 2008 to 2014.

RESULTS

Patients with a high probability of atopic skin diathesis showed no significant increase in positive SLS reactions compared with patients without atopic skin diathesis (14·2% vs. 16·8%). The grading of positive SLS skin reactions (1-4) revealed no differences in patients with or without atopic skin diathesis. Furthermore, diagnoses of atopic dermatitis, allergic rhinitis or allergic asthma had no impact on positive SLS skin reactions in multivariate logistic regression analysis.

CONCLUSIONS

We found no association of increased skin irritability to SLS with atopic skin diathesis, atopic dermatitis, allergic rhinitis or allergic asthma in a large patient cohort. It therefore seems that the test of skin irritability with SLS, which is currently common practice in many centres, does not allow prediction of susceptibility to irritant eczematous inflammation in atopic vs. nonatopic individuals. What's already known about this topic? Irritant contact dermatitis and atopic skin diathesis share impaired skin barrier function as a pathophysiological pattern. Sodium lauryl sulfate (SLS) is tested at 0·25% aqueous as an irritant control in patch testing, and hence the results might be affected by atopic skin diathesis. What does this study add? Challenging a long-standing paradigm, we found no association of increased reactivity to SLS patch tests in individuals with atopic skin diathesis, atopic dermatitis, allergic rhinitis or allergic asthma in a large patient cohort. Thus, irritant control testing with SLS, which is useful in interpreting doubtful allergen patch test results, does not depend on individual atopy status.

Biomarker Mapping on Skin Tape Strips Using MALDI Mass Spectrometry Imaging

Keratinocyte organization and biochemistry are important in forming the skin's protective barrier. Intrinsic and extrinsic factors can affect skin barrier function at the cellular and molecular levels. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometric imaging, a technique which combines both molecular aspects and histological details, has proven to be a valuable method in various disciplines including pharmacology, dermatology and cosmetology. It typically requires ex vivo samples, prepared following frozen tissue sectioning. This paper demonstrates the feasibility of performing MALDI analysis on tape strips collected non-invasively on skin. The aim is to obtain molecular imaging of corneocytes on tapes towards novel biological insights. Tapes were collected from two skin sites (volar forearm and cheek) of human volunteers. Ten molecules relating to skin barrier function were detected with a single mode of acquisition at high spatial resolution with a 7 T MALDI-Fourier transform ion cyclotron resonance (FTICR) instrument. The method sensitivity was adequate to create molecular maps which could be overlaid on transmission microscopy images of the same area of the tape. Analysis of the molecular distributions from tapes at the two skin sites was consistent with the known skin properties of the two sites, confirming the validity of the observations. Hierarchical clustering analysis was used to differentiate corneocyte populations based on their molecular profiles. Furthermore, morphological analysis provided a new way of considering statistical populations of corneocytes on the same tape, rather than measuring a single averaged value, providing additional useful information relating to their structure-function relationship.

A 3D self-organizing multicellular epidermis model of barrier formation and hydration with realistic cell morphology based on EPISIM

The epidermis and the stratum corneum (SC) as its outermost layer have evolved to protect the body from evaporative water loss to the environment. To morphologically represent the extremely flattened cells of the SC - and thereby the epidermal barrier - in a multicellular computational model, we developed a 3D biomechanical model (BM) based on ellipsoid cell shapes. We integrated the BM in the multicellular modelling and simulation platform EPISIM. We created a cell behavioural model (CBM) with EPISIM encompassing regulatory feedback loops between the epidermal barrier, water loss to the environment, and water and calcium flow within the tissue. This CBM allows a small number of stem cells to initiate self-organizing epidermal stratification, yielding the spontaneous emergence of water and calcium gradients comparable to experimental data. We find that the 3D in silico epidermis attains homeostasis most quickly at high ambient humidity, and once in homeostasis the epidermal barrier robustly buffers changes in humidity. Our model yields an in silico epidermis with a previously unattained realistic morphology, whose cell neighbour topology is validated with experimental data obtained from in vivo images. This work paves the way to computationally investigate how an impaired SC barrier precipitates disease.

Developmental Changes in Skin Barrier and Structure during the First 5 Years of Life

The structure of the stratum corneum (SC) and the corresponding skin barrier develops from before birth up to about 4 years of age. Large subject-to-subject variability within an age group requires a large population to observe trends in skin barrier properties over time. Barrier function, quantified by transepidermal water loss (TEWL) and SC thickness, was measured on the upper inner arm and dorsal forearm in subjects aged 3 months to 4 years (n = 171) and a subset of mothers (n = 44). The rate of skin surface area expansion as a function of age peaked before birth (∼90 cm2/week) and declined to a steady plateau (∼10 cm2/week) by 1 year of age. SC thickness increased and TEWL decreased, but did not reach adult values until 3-4 years of age. A better understanding of how skin hydration changes after birth suggests that barrier function may be related mechanistically to skin surface area expansion.

Molecular basis for stratum corneum maturation and moisturization

This themed edition of BJD is dedicated to the work of Professor Ronald Marks for his untiring work on the understanding of stratum corneum (SC) structure and function. He and his coworkers, in my opinion, had the right focus for cosmetic dermatology issues. Namely, consumers experience the wonderful properties of the SC through sight, touch and the somatosensory system. They do not experience, for example, transepidermal water loss and skin conductance or capacitance! Marks understood this and set about developing the methodologies to examine the changes in SC architecture and function when desquamation goes haywire. More importantly, he understood that moisturizers do far more than simply hydrate the SC, as exemplified in the paper by Tree and Marks, 'An explanation for the placebo effect of bland ointment bases.' Moisturizing ingredients influence the properties of the SC in many ways with the sole purpose of overcoming the signs and symptoms of dry skin. Marks demonstrated the decrease in SC cohesion following use of hydrating agents, which led to the mechanistic work on the effects of a simple molecule like glycerol on the desquamatory process. In further exploiting forced desquamation and use of abrasion, he showed that improvements in exfoliation contribute to the mitigation of the signs of photodamaged skin, which can explain part of the antiageing effect of simple moisturizers. It is here that I should point out that at least this particular author in 1988 was 'standing on the shoulders of' a great corneologist whose work influenced his research directions. So this paper will provide an update on the latest developments for the molecular basis of SC maturation and moisturization, while highlighting the contributions of Professor Marks in the different areas.

TRP channels in the skin

Emerging evidence suggests that transient receptor potential (TRP) ion channels not only act as 'polymodal cellular sensors' on sensory neurons but are also functionally expressed by a multitude of non-neuronal cell types. This is especially true in the skin, one of the largest organs of the body, where they appear to be critically involved in regulating various cutaneous functions both under physiological and pathophysiological conditions. In this review, we focus on introducing the roles of several cutaneous TRP channels in the regulation of the skin barrier, skin cell proliferation and differentiation, and immune functions. Moreover, we also describe the putative involvement of several TRP channels in the development of certain skin diseases and identify future TRP channel-targeted therapeutic opportunities.

Numerical modelling of transdermal delivery from matrix systems: parametric study and experimental validation with silicone matrices

A model is presented for transdermal drug delivery from single-layered silicone matrix systems. The work is based on our previous results that, in particular, extend the well-known Higuchi model. Recently, we have introduced a numerical transient model describing matrix systems where the drug dissolution can be non-instantaneous. Furthermore, our model can describe complex interactions within a multi-layered matrix and the matrix to skin boundary. The power of the modelling approach presented here is further illustrated by allowing the possibility of a donor solution. The model is validated by a comparison with experimental data, as well as validating the parameter values against each other, using various configurations with donor solution, silicone matrix and skin. Our results show that the model is a good approximation to real multi-layered delivery systems. The model offers the ability of comparing drug release for ibuprofen and diclofenac, which cannot be analysed by the Higuchi model because the dissolution in the latter case turns out to be limited. The experiments and numerical model outlined in this study could also be adjusted to more general formulations, which enhances the utility of the numerical model as a design tool for the development of drug-loaded matrices for trans-membrane and transdermal delivery.

Non-invasive assessment of tryptophan fluorescence and confocal microscopy provide information on skin barrier repair dynamics beyond TEWL

The stratum corneum (SC) serves a primary function of skin barrier and understanding the kinetics of SC formation may provide great insight for skin diagnosis and evaluation of therapies. Besides trans-epidermal water loss (TEWL), few methods have been characterized to assess skin barrier non-invasively in vivo, particularly for dynamic measurements on the same specimen over time. The objective of this study was to characterize alternative non-invasive methods to evaluate the dynamic processes involved in the recovery of normal human SC after total removal. TEWL, tryptophan fluorescence and reflectance confocal microscopy (RCM) were used to determine skin barrier function, cell turnover and epidermal morphology over a period of 10 days after total removal of the SC by tape stripping. The results show a biphasic recovery of TEWL over time, which contrasted with a linear increase of 2.3 μm/day in SC thickness. Tryptophan assessment of cell turnover also demonstrated a biphasic pattern attaining a maximum three to four times the levels of the control site 3 days after injury that slowly returned to baseline and displayed great correlation (R(2)  > 0.95) to viable epidermis thickness that also achieved a maximum about 3 days after injury with an approximate increase of 55%. When plotting the change of TEWL versus SC thickness, a single exponential function is observed [Δ-TEWL = 55 exp (-0.157×)] which contrasts with other proposed models. These methods were able to present rates for SC recovery processes beyond skin barrier (TEWL) that may provide new insights on kinetics of barrier formation for evaluation of skin conditions and treatments.

Recent advances in predicting skin permeability of hydrophilic solutes

Understanding the permeation of hydrophilic molecules is of relevance to many applications including transdermal drug delivery, skin care as well as risk assessment of occupational, environmental, or consumer exposure. This paper reviews recent advances in modeling skin permeability of hydrophilic solutes, including quantitative structure-permeability relationships (QSPR) and mechanistic models. A dataset of measured human skin permeability of hydrophilic and low hydrophobic solutes has been compiled. Generally statistically derived QSPR models under-estimate skin permeability of hydrophilic solutes. On the other hand, including additional aqueous pathway is necessary for mechanistic models to improve the prediction of skin permeability of hydrophilic solutes, especially for highly hydrophilic solutes. A consensus yet has to be reached as to how the aqueous pathway should be modeled. Nevertheless it is shown that the contribution of aqueous pathway can constitute to more than 95% of the overall skin permeability. Finally, future prospects and needs in improving the prediction of skin permeability of hydrophilic solutes are discussed.

Cellular changes that accompany shedding of human corneocytes

Corneocyte desquamation has been ascribed to either: 1) proteolytic degradation of corneodesmosomes (CD); 2) disorganization of extracellular lamellar bilayers; and/or 3) ‘swell-shrinkage-slough’ (SSS) from hydration/dehydration. To address the cellular basis for normal exfoliation, we compared changes in lamellar bilayer architecture and CD structure in DSquame® strips from the 1st vs. 5th stripping (‘outer’ vs. ‘mid’-stratum corneum [SC], respectively) from 9 normal adult forearms. Strippings were either processed for standard EM or for ruthenium (Ru-V)- or osmium-tetroxide (Os-V) vapor fixation, followed by immediate epoxy embedment, an artifact-free protocol that to our knowledge is previously unreported. CDs are largely intact in the mid-SC, but replaced by electron-dense (hydrophilic) clefts (lacunae) that expand laterally, splitting lamellar arrays in the outer SC. Some undegraded DSG1/DSC1 redistribute uniformly into corneocyte envelopes (CEs) in the outer SC (shown by proteomics, Z-stack confocal imaging and immunoEM). CEs then thicken, likely facilitating exfoliation by increasing corneocyte rigidity. In vapor-fixed images, hydration only altered the volume of the extracellular compartment, expanding lacunae further separating membrane arrays. During dehydration, air replaced water, maintaining the expanded extracellular compartment. Hydration also provoked degradation of membranes by activating contiguous acidic ceramidase activity. Together, these studies identify several parallel mechanisms that orchestrate exfoliation from the surface of normal human skin.

The channel physiology of the skin

During embryonic development, the skin, the largest organ of the human body, and nervous system are both derived from the neuroectoderm. Consequently, several key factors and mechanisms that influence and control central or peripheral nervous system activities are also present and hence involved in various regulatory mechanisms of the skin. Apparently, this is the case for the ion and non-ion selective channels as well. Therefore, in this review, we shall focus on delineating the regulatory roles of the channels in skin physiology and pathophysiology. First, we introduce key cutaneous functions and major characteristics of the channels in question. Then, we systematically detail the involvement of a multitude of channels in such skin processes (e.g. skin barrier formation, maintenance, and repair, immune mechanisms, exocrine secretion) which are mostly defined by cutaneous non-neuronal cell populations. Finally, we close by summarizing data suggesting that selected channels are also involved in skin diseases such as e.g. atopic dermatitis, psoriasis, non-melanoma cancers and malignant melanoma, genetic and autoimmune diseases, etc., as well as in skin ageing.