Barrier recovery is impeded at neutral pH, independent of ionic effects: implications for extracellular lipid processing

Fluctuations in equine cutaneous pH and transepidermal water loss with time of day and ambient conditions

Cutaneous pH and transepidermal water loss (TEWL) are commonly utilized measures in dermatological research as they provide information concerning barrier function. The importance of dermal health has become more evident in recent years. Accordingly, the aim of this work was to identify natural fluctuations in the biophysical parameters of healthy equine skin. Cutaneous pH and TEWL was collected on nine mares at 6:00 AM, 12:00 PM, and 6:00 PM daily for five days on the nose, withers, girth area, mid-back, and base of tail. Ambient temperature and humidity were measured at each collection. Statistical analysis was completed using SAS On Demand. Tests included repeated measures, ANOVA, and regression analysis. Mean cutaneous pH significantly differed by day (P = 0.0052) and time (P = 0.0073) but was unaffected by anatomical location (P = 0.2841). Interestingly, cutaneous pH had a significant interaction of day and location (P = 0.0004). Mean TEWL measures significantly differed by day (P < 0.0001), time (P < 0.0001), and anatomical location (P = 0.0231). Interaction of day and time had a significant effect on TEWL (P < 0.0001) and also resulted in a three-way interaction of day, time, and location (P = 0.0167). There were no significant associations of pH with temperature and humidity. All measures of TEWL across all locations were significantly correlated with temperature and humidity (P < 0.0001). Cutaneous pH and TEWL measures are affected by environmental conditions which should be considered in future models and work using dermal characteristics of horses.

Changes in skin barrier over the first four days of life: a cross-sectional study

BACKGROUND

We aimed to evaluate the trajectory of skin barrier properties in full-term newborns during the first four days after birth.

METHODS

Based on the MKNFOAD cohort (NCT02889081), transepidermal water loss (TEWL), stratum corneum hydration (SCH), skin pH, and sebum content at five anatomical sites (cheek, forehead, volar forearm, abdomen, and dorsal lower leg) were examined once within 96 h after birth in 384 full-term infants. Multivariable linear regression analysis was performed to assess variations in these skin barrier parameters with age adjusted for gestational age, neonate's sex, parents' allergy history, delivery mode, amniotic fluid characteristics, and birth weight. The regression coefficient (ß) and 95% confidence interval were reported.

RESULTS

We analyzed a total of 384 neonates including 198 (51.6%) boys. TEWL values remained stable and showed no significant association with age (days). pH values exhibited a declining trend with age (p for trend <0.001). Both SCH values and sebum content grew with age (p for trend <0.001).

CONCLUSION

During the first four days after birth, the skin TEWL remained stable, pH decreased, and the SCH and sebum content increased over time. These findings provide insights into the neonatal skin physiological development at the beginning of life.

IMPACT

From birth to 96 h, TEWL was stable, pH showed a steep decline, SCH and sebum content increased. This study provides the first evidence of skin adaptation in the newborn due to changes in utero to after birth in the first 4 days of life in an Asian population. These findings will provide a new theoretical basis for neonatal skin physiology and clinical strategies for guiding newborn skin care.

Utilizing Silk Sericin as a Biomaterial for Drug Encapsulation in a Hydrogel Matrix with Polycaprolactone: Formulation and Evaluation of Antibacterial Activity

Hydrogels have emerged as a potential tool for enhancing bioavailability and regulating the controlled release of therapeutic agents. Owing to its excellent biocompatibility, silk sericin-based hydrogels have garnered interest in biomedical applications. This study focuses on synthesizing a soft hydrogel by blending silk sericin (SS) and polycaprolactone (PCL) at room temperature. The physicochemical characteristics of the hydrogels have been estimated by different analytical techniques such as UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The rheological studies demonstrate the non-Newtonian behavior of the hydrogels. Further, the porosity analysis indicates a commendable absorption capacity of the hydrogels. The swelling degree of the hydrogels has been checked in both distilled water and buffer solutions of different pHs (2-10). Moreover, the drug release profile of the hydrogels, using diclofenac sodium (DS) as a model drug, has revealed a substantial release of approximately 67% within the first 130 min with a drug encapsulation efficiency of 60.32%. Moreover, both the empty and the drug-loaded hydrogels have shown antibacterial properties against Gram-positive and Gram-negative bacteria, with the drug-loaded hydrogels displaying enhanced effectiveness. Additionally, the prepared hydrogels are biodegradable, demonstrating their future prospects in biomedical applications.

Skin electroporation for transdermal drug delivery: Electrical measurements, numerical model and molecule delivery

Skin electroporation for drug delivery involves the application of Pulsed Electric Fields (PEFs) on the skin to disrupt its barrier function in a temporary and non-invasive manner, increasing the uptake of drugs. It represents a potential alternative to delivery methods that are invasive (e.g. injections) or limited. We have developed a drug delivery system comprising nanocomposite hydrogels which act as a reservoir for the drug and an electrode for applying electric pulses on the skin. In this study, we employed a multi-scale approach to investigate the drug delivery system on a mouse skin model, through electrical measurements, numerical modeling and fluorescence microscopy. The Electrical properties indicated a highly non-linear skin conductivity behavior and were used to fine-tune the simulations and study skin recovery after electroporation. Simulation of electric field distribution in the skin showed amplitudes in the range of reversible tissue electroporation (400-1200 V/cm), for 300 V PEF. Fluorescence microscopy revealed increased uptake of fluorescent molecules compared to the non-pulsed control. We reported two reversible electroporation domains for our configuration: (1) at 100 V PEF the first local transport regions appear in the extracellular lipids of the stratum corneum, demonstrated by a rapid increase in the skin's conductivity and an increased uptake of lucifer yellow, a small hydrophilic fluorophore and (2) at 300 V PEF, the first permeabilization of nucleated cells occurred, evidenced by the increased fluorescence of propidium iodide, a membrane-impermeable, DNA intercalating agent.

A review of sebum in mammals in relation to skin diseases, skin function, and the skin microbiome

Diseases vary among and within species but the causes of this variation can be unclear. Immune responses are an important driver of disease variation, but mechanisms on how the body resists pathogen establishment before activation of immune responses are understudied. Skin surfaces of mammals are the first line of defense against abiotic stressors and pathogens, and skin attributes such as pH, microbiomes, and lipids influence disease outcomes. Sebaceous glands produce sebum composed of multiple types of lipids with species-specific compositions. Sebum affects skin barrier function by contributing to minimizing water loss, supporting thermoregulation, protecting against pathogens, and preventing UV-induced damage. Sebum also affects skin microbiome composition both via its antimicrobial properties, and by providing potential nutrient sources. Intra- and interspecific variation in sebum composition influences skin disease outcomes in humans and domestic mammal species but is not well-characterized in wildlife. We synthesized knowledge on sebum function in mammals in relation to skin diseases and the skin microbiome. We found that sebum composition was described for only 29 live, wild mammalian species. Sebum is important in dermatophilosis, various forms of dermatitis, demodicosis, and potentially white-nose syndrome. Sebum composition likely affects disease susceptibility, as lipid components can have antimicrobial functions against specific pathogens. It is unclear why sebum composition is species-specific, but both phylogeny and environmental effects may drive differences. Our review illustrates the role of mammal sebum function and influence on skin microbes in the context of skin diseases, providing a baseline for future studies to elucidate mechanisms of disease resistance beyond immune responses.

Improvement in Cutaneous Conditions Can Benefit Some Health Conditions in the Elderly

As we are aging, a number of cutaneous and extracutaneous disorders will be developed. Although the pathogenesis of these aging-associated disorders is not clear yet, abnormalities in the skin are linked to some aging-associated disorders at least to some extent. Inflammatory dermatoses such as psoriasis and atopic dermatitis predispose to the development of cardiovascular diseases, obesity and type 2 diabetes. In addition, both chronologically aged skin and individuals with some aging-associated systemic conditions display altered epidermal function, such as reduced stratum corneum hydration levels, which can provoke cutaneous inflammation. Because aged skin exhibits higher expression levels of inflammatory cytokines, which play a pathogenic role in a variety of aging-associated health condition, the association of the skin with some aging-associated disorders is likely mediated by inflammation. This postulation is supported by the evidence that improvement in either epidermal function or inflammatory dermatoses can mitigate some aging-associated disorders such as mild cognitive impairment and insulin sensitivity. This perspective discusses the association of the skin with aging-associated disorders and highlights the potential of improvement in cutaneous conditions in the management of some health conditions in the elderly.

Carbon dioxide foam bubbles enhance skin penetration through the stratum corneum layer with mechanical mechanism

Topical skin formulations often include penetration enhancers that interact with the outer stratum corneum (SC) layer to chemically enhance diffusion. Alternatively, penetration can be mechanically enhanced with simple rubbing in the presence of solid particles sometimes included to exfoliate the top layers of the SC. Our goal was to evaluate micron-sized carbon dioxide bubbles included in a foamed moisturizing formulation as a mechanical penetration enhancement strategy. We show that moisturizing foam bubbles cause an increase in SC formulation penetration using both mechanical and spectroscopic characterization. Our results suggest viscous liquid film drainage between coalescing gaseous bubbles creates local regions of increased hydrodynamic pressure in the foam liquid layer adjacent to the SC surface that enhances treatment penetration. An SC molecular diffusion model is used to rationalize the observed behavior. The findings indicate marked increased levels of treatment concentration in the SC at 2 h and that persists to 18 h after exposure, far exceeding non-foamed treatments. The study suggests an alternate strategy for increasing formulation penetration with a non-chemical mechanism.

Five dimensions of cleansing: A holistic view on the facets and importance of skin cleansing

Cleansing is an important human ritual practised for hygiene, well-being and relaxation over centuries. As part of body care it is often taken for granted, yet its relevance cannot be underestimated. Although cleansing the skin may seem trivial to some, it is accepted, that this fundamental function of skin cleansing products is highly complex, diverse and crucial for a variety of reasons in the personal, public, healthcare and dermatological settings. Employing a comprehensive and strategic approach in viewing cleansing and its rituals, supports innovation, understanding and development. Apart from being a fundamental function, as far as we know, there is no comprehensive presentation of skin cleansing with all its effects besides 'removing dirt'. To our knowledge, comprehensive analyses on the multi-dimensional facets of skin cleansing are either rare or not published. Against this background, we examine the importance of cleansing in terms of function, relevance and concepts. First, the key functions and efficacies of skin cleansing were investigated by literature research. Based on this survey, the functions were analysed, sorted and merged and a novel approach to skin cleansing 'dimensions' was developed. Herewith, we took into consideration the evolution of skin cleansing in terms of concept evolution, complexity and testing methods for cleansing products and their claims. Several multi-dimensional functions of skin cleansing were identified and then established into five skin cleansing dimensions, namely: hygienic and medical importance; socio-cultural and interpersonal relevance; mood, emotion and well-being; cosmetic and aesthetic function; corneobiological interactions. It became obvious, that these five dimensions with their corresponding 11 sub-dimensions, are influenced by each other throughout history by culture and society, technical progress, scientific knowledge and consumer trends. This article presents the enormous complexity of skin cleansing. Skin cleansing has evolved from basic care up to a highly complex and diverse cosmetic product category in terms of technology, efficacy and usage routine(s). In view of future challenges, such as the effects of climate and associated lifestyle changes, the development of skin cleansing will remain an exciting and important topic and thus will finally, again, further increase the complexity of skin cleansing itself.

How do the skin barrier and microbiome adapt to the extra-uterine environment after birth? Implications for the clinical practice

The multiple protective functions of the skin derive from the interactions between epithelial skin and immune cells as well as the commensal microbiota. Developed in the last trimester of intra-uterine life, the skin barrier adapts dynamically after birth. Specific differences in the structure and physiology have been disclosed between infant and adult skin. The stratum corneum of infants is thinner and structured by thicker corneocytes with a more anisotropic surface in comparison to adult skin. Lower levels of the natural moisturizing factor and its constituents, together with the increased protease activity in the epidermis result in dry baby skin and ongoing adaptation of the desquamation to the extra-uterine environment. Infant epidermis is characterized by an accelerated proliferation rate and clinically competent permeability barrier in term neonates, despite the higher baseline values of transepidermal water loss in infants. The skin surface of newborns is less acidic, which could increase susceptibility to diaper and atopic dermatitis. Immediately after birth, skin is colonized by commensal bacteria-a process dependent on the mode of delivery and of major importance for the maturation of the immune system. Skin bacterial diversity and dysbiosis have been related to different pathology such as atopic and seborrheic dermatitis. This paper focuses on the ongoing structural, functional and biochemical adaptation of the human skin barrier after birth. We discuss the interactions on the 'skin barrier/ microbiota/ immune system' axis and their role in the development of competent functional integrity of the epidermal barrier.

Advances in Current Drugs and Formulations for the Management of Atopic Dermatitis

Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease with a complex pathophysiology. Treatment of AD remains challenging owing to the presence of a wide spectrum of clinical phenotypes and limited response to existing therapies. However, recent genetic, immunological, and pathophysiological insights into the disease mechanism resulted in the invention of novel therapeutic drug candidates. This review provides a comprehensive overview of current therapies and assesses various novel drug delivery strategies currently under clinical investigation. Further, this review majorly emphasizes on various topical treatments including emollient therapies, barrier repair agents, topical corticosteroids (TCS), phosphodiesterase 4 (PDE4) inhibitors, calcineurin inhibitors, and Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway inhibitors. It also discusses biological and systemic therapies, upcoming treatments based on ongoing clinical trials. Additionally, this review scrutinized the use of pharmaceutical inactive ingredients in the approved topical dosage forms for AD treatment.

Alterations in epidermal function in type 2 diabetes: Implications for the management of this disease

Epidermal function is regulated by numerous exogenous and endogenous factors, including age, psychological stress, certain skin disorders, ultraviolet irradiation and pollution, and epidermal function itself can regulate cutaneous and extracutaneous functions. The biophysical properties of the stratum corneum reflect the status of both epidermal function and systemic conditions. Type 2 diabetes in both murine models and humans displays alterations in epidermal functions, including reduced levels of stratum corneum hydration and increased epidermal permeability as well as delayed permeability barrier recovery, which can all provoke and exacerbate cutaneous inflammation. Because inflammation plays a pathogenic role in type 2 diabetes, a therapy that improves epidermal functions could be an alternative approach to mitigating type 2 diabetes and its associated cutaneous disorders.

Rosmarinic Acid, as an NHE1 Activator, Decreases Skin Surface pH and Improves the Skin Barrier Function

Stratum corneum (SC) pH regulates skin barrier functions and elevated SC pH is an important factor in various inflammatory skin diseases. Acidic topical formulas have emerged as treatments for impaired skin barriers. Sodium proton exchanger 1 (NHE1) is an important factor in SC acidification. We investigated whether topical applications containing an NHE1 activator could improve skin barrier functions. We screened plant extracts to identify NHE1 activators in vitro and found Melissa officinalis leaf extract. Rosmarinic acid, a component of Melissa officinalis leaf extract, significantly increased NHE1 mRNA expression levels and NHE1 production. Immunofluorescence staining of NHE1 in 3D-cultured skin revealed greater upregulation of NHE1 expression by NHE1 activator cream, compared to vehicle cream. Epidermal lipid analysis revealed that the ceramide level was significantly higher upon application of the NHE1 activator cream on 3D-cultured skin, compared to application of a vehicle cream. In a clinical study of 50-60-year-old adult females (n = 21), application of the NHE1 activator-containing cream significantly improved skin barrier functions by reducing skin surface pH and transepidermal water loss and increasing skin hydration, compared to patients who applied vehicle cream and those receiving no treatment. Thus, creams containing NHE1 activators, such as rosmarinic acid, could help maintain or recover skin barrier functions.

Skin Barrier Function in Infants: Update and Outlook

A good understanding of infant skin should provide a rationale for optimum management of the health of this integument. In this review, we discuss the skin barrier function of infants, particularly with reference to the use of diapers and baby wipes. The skin barrier of newborns continues to develop with age. Two years after birth, the barrier properties of infant skin closely resemble those of adult skin. However, several risk factors may contribute to impaired skin barrier and altered skin permeability in infants. Problems may arise from the use of diapers and baby wipes. The skin covered by a diaper is effectively an occluded environment, and thus is vulnerable to over-hydration. To date there has been no published information regarding dermal absorption of ingredients contained in baby wipes. Similarly, dermal absorption of topical ingredients in infants with underlying skin conditions has not been widely explored. Clearly, there are serious ethical concerns related to conducting skin permeation studies on infant skin. However, the increasing availability of non-invasive methods for in vivo studies is encouraging and offers new directions for studying this important patient group.

STAT3 maintains skin barrier integrity by modulating SPINK5 and KLK5 expression in keratinocytes

Skin barrier dysfunction induces skin inflammation. Signal transducer and activator of transcription 3 (STAT3) is known to be involved in Th17-mediated immune responses and barrier integrity in the cornea and intestine; however, its role in the skin barrier remains largely unknown. In this study, we elucidated the potential role of STAT3 in the skin barrier and its effect on kallikrein-related peptidase 5 (KLK5) and serine protease inhibitor Kazal-type 5 (SPINK5) expression using a mouse model with keratinocyte-specific ablation of STAT3. Keratinocyte-specific loss of STAT3 induced a cutaneous inflammatory phenotype with pruritus and intense scratching behaviour in mice. Transcriptomic analysis revealed that the genes associated with impaired skin barrier function, including KLK5, were upregulated. The effect of STAT3 on KLK5 expression in keratinocytes was not only substantiated by the increase in KLK5 expression following treatment with STAT3 siRNA but also by its decreased expression following STAT3 overexpression. Overexpression and IL-17A-mediated stimulation of STAT3 increased the expression of SPINK5, which was blocked by STAT3 siRNA. These results suggest that the expression of SPINK5 and KLK5 in keratinocytes could be dependent on STAT3 and that STAT3 might play an essential role in the maintenance of skin barrier homeostasis.

Characterization of Permeability Barrier Dysfunction in a Murine Model of Cutaneous Field Cancerization Following Chronic UV-B Irradiation: Implications for the Pathogenesis of Skin Cancer

Simple Summary

In the present work, we developed an experimental preclinical model of skin with cutaneous field cancerization after chronic UV-B light exposure in an immunologically intact mouse model (SKH1 aged mice). We observed impairments in the transepidermal water loss, stratum corneum hydration, and surface pH. We also detected a marked hyperkeratotic hyperplasia of the epidermis, induction of keratinocyte hyperproliferation, incidental actinic keratosis, and in situ squamous cell carcinomas in the UV-B light-irradiated groups. In this context, the association between the permeability barrier impairment and keratinocyte hyperproliferation might be considered a new target in the management of skin with cutaneous field cancerization. As current therapeutic approaches to actinic keratosis and cutaneous field cancerization only focus on the direct antineoplastic, immunomodulatory, or photodynamic effects of approved topical drugs, this mouse model of skin with cutaneous field cancerization might be helpful for both the identification and screening of potentially new preventive strategies or treatments (e.g., skin barrier therapies).

Abstract

Chronic ultraviolet B (UV-B) irradiation is known to be one of the most important hazards acting on the skin and poses a risk of developing photoaging, skin with cutaneous field cancerization (CFC), actinic keratosis (AKs), and squamous cell carcinomas (SCCs). Most of the UV-B light is absorbed in the epidermis, affecting the outermost cell layers, the stratum corneum, and the stratum granulosum, which protects against this radiation and tries to maintain the permeability barrier. In the present work, we show an impairment in the transepidermal water loss, stratum corneum hydration, and surface pH after chronic UV-B light exposure in an immunologically intact mouse model (SKH1 aged mice) of skin with CFC. Macroscopic lesions of AKs and SCCs may develop synchronically or over time on the same cutaneous surface due to both the presence of subclinical AKs and in situ SCC, but also the accumulation of different mutations in keratinocytes. Focusing on skin with CFC, yet without the pathological criteria of AKs or SCC, the presence of p53 immunopositive patches (PIPs) within the epidermis is associated with these UV-B-induced mutations. Reactive epidermis to chronic UV-B exposure correlated with a marked hyperkeratotic hyperplasia, hypergranulosis, and induction of keratinocyte hyperproliferation, while expressing an upregulation of filaggrin, loricrin, and involucrin immunostaining. However, incidental AKs and in situ SCC might show neither hypergranulosis nor upregulation of differentiation markers in the upper epidermis. Despite the overexpression of filaggrin, loricrin, involucrin, lipid enzymes, and ATP-binding cassette subfamily A member 12 (ABCA12) after chronic UV-B irradiation, the permeability barrier, stratum corneum hydration, and surface pH were severely compromised in the skin with CFC. We interpret these results as an attempt to restore the permeability barrier homeostasis by the reactive epidermis, which fails due to ultrastructural losses in stratum corneum integrity, higher pH on skin surface, abundant mast cells in the dermis, and the common presence of incidental AKs and in situ SCC. As far as we know, this is the first time that the permeability barrier has been studied in the skin with CFC in a murine model of SCC induced after chronic UV-B irradiation at high doses. The impairment in the permeability barrier and the consequent keratinocyte hyperproliferation in the skin of CFC might play a role in the physiopathology of AKs and SCCs.

Towards Optimal pH of the Skin and Topical Formulations: From the Current State of the Art to Tailored Products

Acidic pH of the skin surface has been recognized as a regulating factor for the maintenance of the stratum corneum homeostasis and barrier permeability. The most important functions of acidic pH seem to be related to the keratinocyte differentiation process, the formation and function of epidermal lipids and the corneocyte lipid envelope, the maintenance of the skin microbiome and, consequently, skin disturbances and diseases. As acknowledged extrinsic factors that affect skin pH, topically applied products could contribute to skin health maintenance via skin pH value control. The obtained knowledge on skins’ pH could be used in the formulation of more effective topical products, which would add to the development of the so-called products ‘for skin health maintenance’. There is a high level of agreement that topical products should be acidified and possess pH in the range of 4 to 6. However, formulators, dermatologists and consumers would benefit from some more precise guidance concerning favorable products pH values and the selection of cosmetic ingredients which could be responsible for acidification, together with a more extensive understanding of the mechanisms underlaying the process of skin acidification by topical products.

Contact Dermatitis: Classifications and Management

Contact dermatitis (CD) is a common inflammatory skin disease caused by exposure to contact allergens and irritants. It is also the most common reason of occupational dermatitis and contributes greatly to hand dermatitis and facial dermatitis. Besides the two major forms of contact dermatitis: allergic contact dermatitis and irritant contact dermatitis, other subtypes of CD have been recognized including immediate skin reactions, photoinduced contact dermatitis, systemic contact dermatitis, and non-eczematous contact dermatitis. CD is a great imitator which can mimic many kinds of skin diseases, such as atopic dermatitis, lichen planus, and angioedema. For the diagnosis of CD, a complete medical history, including occupational history, is very important. It can give a clue of CD and provide a list of suspected substances. Besides the well-known diagnostic test, patch testing, there are many other diagnostic tests can be used to help diagnosis of CD and identify the causative allergens, including photopatch test, skin tests for detecting of immediate contact reactions, serum allergen-specific IgE test, and qualitative and quantitative testing of allergen in the suspected materials patients exposed to and challenge test. Before the treatment, the suspected irritants or allergens should be avoided completely. This includes both the removal of the patient from the environment that contains those substances and the promotion of the metabolism and expulsion of the allergens that have been absorbed by the body. In addition, it is also important to restore the skin barrier and reduce skin inflammation through multiple treatments, such as emollients, topical corticosteroids, and antihistamines, as well as systemic corticosteroids and immunosuppressants. Early and appropriate treatments are important to prevent further deterioration and persistence of the skin condition.

Improving newborn skin health: Effects of diaper care regimens on skin pH and erythema

BACKGROUND/OBJECTIVE

Newborn infant skin is functional but immature, and diapering products can play a significant role in infant diapered skin health. Previous work demonstrated a regimen consisting of a diaper with an emollient and apertures on the inner liner (topsheet) with an acidic, pH-buffered wipe (Regimen A) lowered newborn skin pH and reduced the enzymatic activity on skin post-stool cleaning versus a regimen without these features (Regimen B). This study extends these findings to determine the impact of Regimen A on diaper area erythema severity over a 2-week use period.

METHODS

This IRB-approved, blinded, randomized, crossover study enrolled newborn infants >7 days and ≤8 weeks. Participants exclusively used two unique diaper and wipe combinations, Regimen A and Regimen B (non-emollient, non-aperture containing topsheet and wipe with limited buffering capacity), each for 14 days and preceded by a 3-day washout regimen.

RESULTS

Diapered skin pH was reduced during Regimen A use to values similar to that of a non-diapered control site (chest), while use of Regimen B was associated with a more alkaline skin pH. Regimen A resulted in significantly fewer severe erythema episodes. At the site of highest erythema, the perianal space, the average erythema score was significantly lower and more newborns were free of erythema while using Regimen A vs. Regimen B (P < .05).

CONCLUSIONS

These findings demonstrate that diapering products can have a significant impact on newborn skin. They reinforce the need to support the physiological normalization of skin pH and protection from skin irritation and damage.

Acidic pH Is Required for the Multilamellar Assembly of Skin Barrier Lipids In Vitro

Lipid membrane remodeling belongs to the most fundamental processes in the body. The skin barrier lipids, which are ceramide dominant and highly rigid, must attain an unusual multilamellar nanostructure with long periodicity to restrict water loss and prevent the entry of potentially harmful environmental factors. Our data suggest that the skin acid mantle, apart from regulating enzyme activities and keeping away pathogens, may also be a prerequisite for the multilamellar assembly of the skin barrier lipids. Atomic force microscopy on monolayers composed of synthetic or human stratum corneum lipids showed multilayer formation (approximately 10-nm step height) in an acidic but not in a neutral environment. X-ray diffraction, Fourier transform infrared spectroscopy, and permeability studies showed markedly altered lipid nanostructure and increased water loss at neutral pH compared with that at acidic pH. These findings are consistent with the data on the altered organization of skin lipids and increased transepidermal water loss under conditions such as inadequate skin acidification, for example, in neonates, the elderly, and patients with atopic dermatitis.

Premature infant skin barrier maturation: status at full-term corrected age

OBJECTIVE

To evaluate the effects of gestational age (GA) and postnatal age on skin barrier integrity by comparing premature infants at full-term corrected age with infants born at term.

STUDY DESIGN

Parallel comparison of chest skin in 36 premature infants with 39 full-term infants using daily measures of transepidermal water loss (TEWL), skin pH, erythema and rash, over 2 weeks.

RESULT

Chest skin pH was significantly lower for premature infants, indicating that acid mantle formation had occurred in the premature versus full-term infants. Chest TEWL was significantly higher for premature versus full-term infants over 2 weeks, suggesting that even 7-8 weeks after birth, skin integrity is poorer in premature infants.

CONCLUSION

Skin barrier properties of premature infants at adjusted full-term age differ from full-term infants, suggesting that epidermal barrier development depends on GA and time from birth. These maturational differences may influence premature infant response to topical agents.

Effects of Exercise on the Skin Epithelial Barrier of Young Elite Athletes-Swimming Comparatively to Non-Water Sports Training Session

The benefits of swimming have been extensively assessed. However, swimming pools contain chlorine and other irritating chemicals that may induce contact dermatitis. To evaluate the effect of a swimming training session on transepidermal water loss (TWEL) in swimmers compared to football players, elite swimmers and football players were invited to participate (58 athletes) in the study, where TEWL was measured before, immediately after, and 30 min after a 2 h training session. The probe was held on the dorsum of the hand, volar forearm, and on the antecubital flexure for 1 min. The volar forearm, antecubital flexure, and hand dorsum showed a significant increase in TEWL in swimmers in both measurements after training compared to baseline (p < 0.001). In football players, an increase in TEWL was observed on the hands' dorsum between baseline and after training measurements. The variations on TEWL levels before and immediately after the training session were higher among swimmers on the volar forearm (p = 0.002) and antecubital flexure (p = 0.019). Our findings support the effect of the training environment-swimming pool versus outdoor sports-on the skin barrier function, with an increase of transepidermal water loss immediately after exercise. Exposure to a swimming pool environment in a 2 h training session may lead to changes in skin barrier function.

Effect of oxybrasion on selected skin parameters

BACKGROUND

Oxybrasion is one of the types of microdermabrasion. This method removes a superficial epidermal layer with the use of a stream of 0.9% saline solution and compressed air.

AIMS

The assessment of skin hydration, sebum, pH, TEWL (transepidermal water loss), and pigmentation using oxybrasion.

MATERIAL AND METHODS

The study involved 27 female subjects. Five treatments were performed every 2 weeks using the oxygen microdermabrasion. Measurements of the skin parameters were taken before each treatment and 2 weeks after the last procedure. The measurement points were on the forehead, the cheek, and on the petal of the nose.

RESULTS

Sebum measurement showed some statistically significant differences between the sebum level on the cheek and the nose after a series of treatments. A higher hydration level was found at all measurement points. There were no statistically significant differences in TEWL parameter. pH measurement showed that the pH value decreased after each of the procedures. Most of the pigmentation measurements differed in a statistically significant way.

CONCLUSION

Results of the study indicate that the oxybrasion treatments increase the skin hydration and they have a significant influence on the decrease of the skin hydrolipid coat and pH.

Use of an emollient-containing diaper and pH-buffered wipe regimen restores skin pH and reduces residual enzymatic activity

BACKGROUND/OBJECTIVES

Diaper dermatitis is one of the most frequent skin conditions affecting infants and is associated with elevated skin pH, exposure to urine and feces, and increased fecal protease and lipase activity, resulting in stratum corneum barrier damage and increased risk of infection. The study aim was to determine the impact of two diaper and wipe regimens on newborn infant skin pH and residual enzyme activity after stool cleaning.

METHODS

Two diaper and wipe regimens were compared in a randomized, single-blinded crossover study. Regimen A paired an emollient-containing diaper with an acidic, pH-buffered wipe. Regimen B was a non-emollient diaper and wipe with limited buffering capacity. A 3-day washout period preceded each 3-day regimen use period. Skin pH at the perianal/buttocks interface (PBI), genital region, and undiapered chest control were measured at baseline and day 3. Skin swabs were collected for residual enzyme activity after a stool cleaning event.

RESULTS

Diapered skin pH at the PBI was similar to undiapered skin after 3 days of use for Regimen A, while PBI pH for Regimen B was elevated versus control. PBI pH was lower for Regimen A versus Regimen B. After a stool cleaning, PBI skin pH for Regimen A was lower immediately and had lower residual enzyme activity versus Regimen B (P < .05), and the pH-lowering effect was sustained up to 60 minutes.

CONCLUSIONS

These results suggest that the use of an emollient-containing diaper with a pH-buffered wipe creates conditions favorable to optimum diapered skin health.

Carbon dioxide ameliorates reduced desquamation in dry scaly skin via protease activation

OBJECTIVE

Scaling, a phenomenon showing an abnormal detachment of the stratum corneum (SC) owing to desquamation dysfunction, is commonly observed in various skin diseases or xerotic skin due to ageing and low humidity. Therefore, it is considered that ameliorating the disturbed desquamatory process of the SC leads to improvement in scaling. Carbon dioxide (CO₂ ) is known to be good for some skin diseases; however, the effect of CO₂ on scaling and its mechanism are not sufficiently clear. We aimed to elucidate the effect of transepidermal application of CO₂ on scaling and its mechanism of action.

METHODS

Twenty healthy men with mild scaling on the cheeks were recruited for a double-blind, placebo-controlled, split-face study. They applied the formulation containing CO₂ twice daily for 1 week. After the study, the SC was collected by tape stripping to analyse desquamatory protease activities and degradation of extracellular corneodesmosomes. Furthermore, the contribution of pH to proteolysis of the corneodesmosome by CO₂ was evaluated using three-dimensional (3D) cultured epidermal models.

RESULTS

The spectroscopic absorbance of tape strips, used as scaling indicators, was decreased, concomitantly with the amelioration of incomplete degradation of desmoglein-1, one of the main corneodesmosomal proteins, and activation of trypsin-like protease in the SC by transepidermal application of CO₂ . Experiments using 3D cultured epidermis showed that pH in the epidermal tissue was lowered by CO₂ , whereas a pH change was not observed with the application of the formulation containing hydrochloric acid, which was added to equalize the pH to that of the CO₂ formulation.

CONCLUSION

The transcutaneous application of CO₂ ameliorates reduced desquamatory process in xerotic skin, with concomitant mild acidification of the SC, thereby leading to improvement in scaling. Thus, CO₂ may have an advantage of efficiently and safely counteracting scaling of various skin disorders.

Aging-associated alterations in epidermal function and their clinical significance

Chronologically-aged skin displays multiple functional changes in both the dermis and the epidermis. It appears that epidermal dysfunction, compromised permeability homeostasis, reduced stratum corneum hydration and elevated skin surface pH predispose to the development of aging-associated cutaneous and extracutaneous disorders. Improvements in epidermal function have been shown to be an effective alternative therapy in the prevention and treatment of some aging-associated cutaneous disorders, including eczematous dermatitis, pruritus, and xerosis. Recent studies demonstrated that epidermal dysfunction leads to the development of chronic, low-grade systemic inflammation, termed ‘inflammaging,’ which is linked to the development of aging-associated systemic disorders. Thus, correction of epidermal dysfunction could comprise a novel strategy in the prevention and treatment of aging-associated systemic disorders as well. In this review, we summarize aging-associated alterations in epidermal function, their underlying mechanisms, and their clinical significance. Regimens to improve epidermal function in the elderly are also discussed.

Could Inflammaging and Its Sequelae Be Prevented or Mitigated?

Aged humans display a chronic and low-grade inflammation, termed “inflammaging”, which has been potentially linked to the subsequent development of some aging-associated systemic disorders, including type 2 diabetes, atherosclerotic cardiovascular disease, Alzheimer’s disease and obesity. Though the origin of aging-associated systemic inflammation is uncertain, epidemiological studies show that inflammatory dermatoses (psoriasis and eczema) are risk factors for some aging-associated systemic disorders, such as type 2 diabetes and atherosclerotic cardiovascular disease. Moreover, recent studies demonstrate that epidermal dysfunction in aged skin not only causes cutaneous inflammation, but also a subsequent increase in circulating levels of proinflammatory cytokines, suggesting that the skin could be a major contributor to inflammaging. This hypothesis is further supported by reductions in circulating levels of proinflammatory cytokines in both aged humans and murine, following improvements in epidermal function with topical emollients. Therefore, correction of epidermal dysfunction could be a novel approach for the prevention and mitigation of certain inflammation-associated chronic disorders in aged humans.

Influence of Buffers of Different pH and Composition on the Murine Skin Barrier, Epidermal Proliferation, Differentiation, and Inflammation

The pH of the skin is tightly regulated by endogenous buffering systems. We examined the influence of buffers of different pH and composition on skin barrier repair, pH, inflammation, and epidermal thickness/proliferation/differentiation. After tape-stripping in hairless mice buffers with pH 4-7 were applied in patch test chambers. After removal of the chambers, skin pH and transepidermal water loss (TEWL) were monitored for 24 h, and biopsies were taken for histology/immunohistology. Hairless mice showed a basal skin pH of about 5.8. Following barrier disruption and application of water, the pH increased by 0.6 units; increase in pH was reduced by the pH 4 glycolate buffer, unchanged by pH 4 citrate and pH 5.5 buffers, and even increased by the pH 7 buffer. pH 5.5, pH 4 citrate, and pH 4 glycolate buffers led to a slight, while the pH 7 buffer led to a significant increase in TEWL after barrier disruption compared to water. The pH 7 buffers led to a significant increase in epidermal thickness/proliferation/differentiation and inflammation after barrier disruption, whereas buffers with pH 4 and 5.5 caused a slight increase. In conclusion, only the pH 4 glycolate buffer significantly reduced the skin barrier disruption-related increase in skin pH. This was accompanied by only slight increase in epidermal thickness and inflammation compared to water. Application of the pH 7 buffer led to a significant increase in the skin pH, TEWL, epidermal thickness, and inflammation. The results are important for the formulation of topical products for effective acidification in pathological skin conditions.

Facial skin mapping: from single point bio-instrumental evaluation to continuous visualization of skin hydration, barrier function, skin surface pH, and sebum in different ethnic skin types

Dry skin is one of the most important concerns of consumers worldwide. Despite huge efforts over several decades, the personal care industry still does not offer a perfect solution to satisfy the unmet needs of consumers for moisturising treatments in different ethnic groups. The paucity of data for the underlying cellular and biochemical problems in, and the effects of moisturisers on photodamaged facial skin may partly explain this. Mainly, single point measurements are used to understand the effects of products on skin physiology even on surrogate skin sites such as the non‐photodamaged volar forearm. Some groups have developed discontinuous facial maps of skin biophysical properties, however, in 2014 a continuous facial analysis of bio‐instrumental evaluations was developed using a heat map approach. These maps enabled a continuous visualization of features that not only revealed an unexpected complexity of facial skin but also indicated that use of surrogate skin sites for facial skin is inappropriate. We have demonstrated that remarkable gradients of skin hydration, TEWL, skin surface pH and sebum exist within short distances across the face and the gradients are distinctive among different ethnic groups. In addition, these studies have demonstrated that darkly‐pigmented individuals do not necessarily have a better skin barrier function than their less‐pigmented counterparts and that Caucasians have a lower facial skin surface pH compared with more pigmented subjects. Overall, there are no correlations between capacitance, TEWL and skin surface pH including individual topology angle values. Novel 3D camera approaches have also been used to facilitate a more precise assignment of measurement sites and visualisation. The 3D facial colour mappings illustrated precisely the local moisturising effects of a moisturising cream. There were subtle ethnic differences in efficacy that may be related to underlying skin biochemistry and/or ethnic differences in product application. A placebo‐controlled study using conductance measurements in Chinese subjects is also reported. Finally, a new whole face statistical approach has been taken to prove differences in skin parameters but also of moisturiser treatment that adds further to our understanding of the ethnic differences in skin physiology and product application. This paper reviews the background of the development and application of this methodology.

Skin acidification with a water-in-oil emulsion (pH 4) restores disrupted epidermal barrier and improves structure of lipid lamellae in the elderly

The pH of the skin surface increases with age and thus reduces epidermal barrier function. Aged skin needs appropriate skin care to counterbalance age‐related pH increase and improve barrier function. This confirmatory randomized study investigated the efficacy of water‐in‐oil (w/o) emulsions with either pH 4 or pH 5.8 in 20 elderly subjects after 4 weeks of treatment. After the treatment, the skin was challenged with a sodium dodecyl sulphate (SDS) solution in order to analyze barrier protection properties of both formulations. The pH 4 w/o emulsion resulted in a significantly lower skin pH compared with the pH 5.8 w/o emulsion and an improved skin hydration after 4‐week treatment. Further, the pH 4 emulsion led to more pronounced improvements in length of intercellular lipid lamellae, lamellar organization as well as lipid levels than the pH 5.8 emulsion. Following SDS‐induced barrier damage to the skin, the pH of all test areas increased, but the area treated with the pH 4 emulsion showed the lowest increase compared with baseline. In addition, even after the SDS challenge the skin area treated with the pH 4 emulsion still maintained a significantly increased length of intercellular lipid lamellae compared with the beginning of the study. This study provides evidence that topical application of a w/o emulsion with pH 4 reacidifies the skin in elderly and has beneficial effects on skin moisturization, regeneration of lipid lamellae and lipid content. Application of a pH 4 emulsion can improve the epidermal barrier as well as the stratum corneum organization in aged skin.

Aging of the skin barrier

The skin barrier is mainly present in the stratum corneum (SC), composed of corneocytes surrounded by intercellular lipid lamellae, and attached by corneodesmosome. The tight junction attached to the lateral walls of keratinocytes in the upper part of the stratum granulosum is also included in the skin barrier. During aging, the following structures and functions of the skin barrier are changed or disturbed: (1) skin barrier structure, (2) permeability barrier function, (3) epidermal calcium gradient, (4) epidermal lipid synthesis and SC lipid processing, (5) cytokine production and response after insults, (6) SC acidity, (7) SC hydration, and (8) antimicrobial barrier. Patients with diabetes also show changes in the skin barrier similar to those in aged skin, and the characteristics of the skin barrier are very similar. Understanding the pathogenic mechanisms of the skin barrier in aging will permit us to develop therapeutic strategies for aged or diabetic skin.

Clinical purpura and elastosis and their correlation with skin tears in an aged population

The previous research reported the results of a prospect cohort study that used logistic regression analysis to construct a risk prediction model for skin tears in individuals aged over 65 years. The model identified three baseline individual characteristics (male gender, history of STs, and history of falls) and two baseline skin manifestations (purpura and elastosis) that predicted the risk of dorsal forearm skin tears. This paper outlines the relationships between baseline skin manifestations and the risk of skin tears. Univariable logistic regression analysis was conducted of all the baseline data collected from the same-study participants to identify variables that significantly predicted purpura and elastosis at baseline. Amongst the 173 participants, 71 (41%) developed one or more skin tears, and in these participants, 52 (73.2%) displayed purpura, 41 (57.8%) had elastosis, and 30 (42.3%) exhibited both manifestations of the dorsal forearm at baseline. Four individual characteristics (age, history of skin tears, history of falls, and antiplatelet therapy) and three skin properties (pH, subepidermal low echogenicity band of the forearms, and skin thickness) were found to predict the risk of purpura. Conversely, three individual variables (age, gender, and smoking), three clinical skin variables (uneven skin pigmentation, cutis rhomboidalis nuchae, and history of actinic keratosis) and one skin property variable (collagen type IV) predicted the risk of skin elastosis. Progressive changes to the skin's structural and mechanical properties from the underlying effects of chronological ageing, and environmental and lifestyle-related influences increased the risk of purpura and elastotic skin manifestations and concomitantly increased risk of skin tears amongst participants.

Age-related and seasonal changes in covalently bound ceramide content in forearm stratum corneum of Japanese subjects: determination of molecular species of ceramides

The stratum corneum (SC) consists of corneocytes surrounded by a neutral lipid-enriched intercellular matrix. Ceramides represent approximately 50% of intercellular lipids, and play important roles in retaining epidermal water. The SC also contains covalently bound ceramides, which are thought to play a crucial role in the formation of lamellar structures, and are involved in maintaining skin barrier function. A previous report showed that levels of free ceramides in human SC changed with the seasons and age, although whether the content of different species of covalently bound ceramides also underwent such temporal changes was unclear. Here, SC samples were taken from 99 healthy individuals of different ages (24-64 years) and during different seasons. The content of different molecular species of covalently bound ceramides in the samples was quantified using HPLC-MS/MS. The levels of total covalently bound ceramides (Total-Cers) significantly decreased approximately 50% in autumn and winter, compared with that of spring and summer. The levels of covalently bound ceramides containing saturated fatty acids (SFA-Cers) in the spring and summer were approximately 2.3-fold higher than that seen in autumn and winter, whereas the level of covalently bound ceramides containing unsaturated fatty acids (USFA-Cers) in spring and summer were approximately 1.6-fold higher than that in autumn and winter. Furthermore, the ratio between SFA-Cers and USFA-Cers was significantly lower in spring and summer than in autumn and winter. The levels of SFA-Cers, but not USFA-Cers, were significantly lower in individuals ≥ 50 years old compared to those who are 30- and 40-years old in the spring. Our study showed for the first time that, similar to free ceramides, the level of covalently bound ceramides changed with the seasons. However, age-related changes in covalently bound ceramide content were limited in that only the amount of SFA-Cers in the spring was lower in older individuals.

Noninvasive measures in atopic dermatitis

PURPOSE OF REVIEW

To summarize the current knowledge on the morphology, functionality and biochemical composition of the skin in allergic reactions. We address novel noninvasive techniques that promise to disclose intimate mechanisms of skin allergy in vivo. Epidermal barrier is not just a static wrap of the organism but rather a dynamic field for immunological, biophysical and biochemical processes and serves as a bio-sensor for exogenous danger signals.

RECENT FINDINGS

Classical biophysical methods are amended by novel in-vivo techniques, such as Raman spectroscopy, analysing the skin microcomposition and develop epidermal profiles. Visualization techniques, such as reflectance spectroscopy and optical coherence tomography (OCT) are employed in studying the micro-morphological changes in the skin of allergic patients.

SUMMARY

The noninvasive assessment of skin functions, micro-morphology and biochemical as well as immunological pathways will help to better understand skin allergies. They will allow to detect subtypes, for example in atopic dermatitis and to develop specific treatment modalities.

Skin care products can aggravate epidermal function: studies in a murine model suggest a pathogenic role in sensitive skin

BACKGROUND

Sensitive skin is defined as a spectrum of unpleasant sensations in response to a variety of stimuli. However, only some skin care products provoke cutaneous symptoms in individuals with sensitive skin. Hence, it would be useful to identify products that could provoke cutaneous symptoms in individuals with sensitive skin.

OBJECTIVE

To assess whether vehicles, as well as certain branded skin care products, can alter epidermal function following topical applications to normal mouse skin.

METHODS

Following topical applications of individual vehicle or skin care product to C57BL/6J mice twice daily for 4 days, transepidermal water loss (TEWL) rates, stratum corneum (SC) hydration and skin surface pH were measured on treated versus untreated mouse skin with an MPA5 device and pH 900 pH meter.

RESULTS

Our results show that all tested products induced abnormalities in epidermal functions of varying severity, including elevations in TEWL and skin surface pH, and reduced SC hydration.

CONCLUSIONS

Our results suggest that mice can serve as a predictive model that could be used to evaluate the potential safety of skin care products in humans with sensitive skin.

Selective Release System for Antioxidative and Anti-Inflammatory Activities Using H2O2-Responsive Therapeutic Nanoparticles

We developed nanoparticles that were degraded by H₂O₂, a reactive oxygen species (ROS), to study a drug delivery system that targets damaged skin cells with oxidative stress and inflammation. In this study, tyrosol-incorporated copolyoxalate (TPOX) was synthesized by using 1,4-cyclohexanedimethanol, 4-(2-hydroxyethyl)phenol (tyrosol), and oxalyl chloride (M_w ∼ 8835 Da). In vitro drug release behavior was assessed by loading nile red, a lipophilic fluorescent material such as quercetin, into the TPOX nanoparticles. The results indicated that the release of TPOX nanopaticles depended on the H₂O₂ concentration, but was pH-independent. We confirmed that TPOX nanoparticles under oxidative conditions in oxidative- or inflammatory-damaged cells selectively released entrapped nile red through the degradation by H₂O₂ for contributing to antioxidant and anti-inflammatory effects. For application, we prepared and evaluated the cytoprotective effect of quercetin-loaded TPOX (QTPOX) nanoparticles against oxidative and inflammatory stress. They showed a strong cytoprotective effect against H₂O₂-induced cell damage in HaCaT and RAW 264.7 cells. Also, QTPOX nanoparticles inhibited the main factors of LPS-induced inflammation, including iNOS, COX-2, IL-1, TNF-α, and NO production. These results suggest that QTPOX as H₂O₂-responsive therapeutic nanoparticles is highly potent and versatile as drug delivery system through selective and intensive drug release mechanism for the treatment of abnormal and inflammatory skin diseases.

Altered expression of epidermal lipid bio-synthesis enzymes in atopic dermatitis skin is accompanied by changes in stratum corneum lipid composition

BACKGROUND

The barrier dysfunction in atopic dermatitis (AD) skin correlates with stratum corneum (SC) lipid abnormalities including reduction of global lipid content, shorter ceramide (CER) as well as free fatty acid (FFA) chain length and altered CER subclass levels. However, the underlying cause of these changes in lipid composition has not been fully investigated.

AIM

We investigated whether the expression of CER and FFA biosynthesis enzymes are altered in AD skin compared with control skin and determine whether changes in enzyme expression can be related with changes in lipid composition.

METHODS

In AD patients and controls the expression of enzymes involved in the biosynthesis of FFAs and CERs was analyzed in relation to the SC lipid composition. These enzymes include stearoyl CoA desaturase (SCD), elongase 1 (ELOVL1) and ELOVL6 involved in FFA synthesis and β-glucocerebrosidase (GBA), acid-sphingomyelinase (aSmase), ceramide synthase 3 (CerS3) involved in CER synthesis. In TH2 treated human skin equivalents (AD HSEs) mimicking lesional AD skin, the mRNA expression of these enzymes was investigated.

RESULTS

The results reveal an altered expression of SCD and ELOVL1 in AD lesional skin. This was accompanied by functional changes displayed by increased unsaturated FFAs (SCD) and reduced FFA C22-C28 (ELOVL1) in AD lesional skin. The expression of GBA, aSmase and CerS3 were also altered in lesional skin. The CER composition in AD lesional skin showed corresponding changes such as increased CER AS and NS (aSmase) and decreased esterified ω-hydroxy CERs (CerS3). In support of the results from AD skin, the AD HSEs showed reduced mRNA ELOVL1, GBA and a Smase levels.

CONCLUSION

This study shows that alterations in the expression of key enzymes involved in SC lipid synthesis contribute to changes in the lipid composition in AD skin and inflammation may influence expression of these enzymes.

The how, why and clinical importance of stratum corneum acidification

In this article, I review the multiple endogenous mechanisms that contribute to the highly acidic pH of normal stratum corneum (SC). Then, I describe how each mechanism potentially impacts specific defensive functions of the SC. Finally, I review the rapidly expanding, clinical implications and potential therapeutic applications of SC acidification.

Natural Endogenous Human Matriptase and Prostasin Undergo Zymogen Activation via Independent Mechanisms in an Uncoupled Manner

The membrane-associated serine proteases matriptase and prostasin are believed to function in close partnership. Their zymogen activation has been reported to be tightly coupled, either as a matriptase-initiated proteolytic cascade or through a mutually dependent mechanism involving the formation of a reciprocal zymogen activation complex. Here we show that this putative relationship may not apply in the context of human matriptase and prostasin. First, the tightly coupled proteolytic cascade between matriptase and prostasin might not occur when modest matriptase activation is induced by sphingosine 1-phospahte in human mammary epithelial cells. Second, prostasin is not required and/or involved in matriptase autoactivation because matriptase can undergo zymogen activation in cells that do not endogenously express prostasin. Third, matriptase is not required for and/or involved in prostasin activation, since activated prostasin can be detected in cells expressing no endogenous matriptase. Finally, matriptase and prostasin both undergo zymogen activation through an apparently un-coupled mechanism in cells endogenously expressing both proteases, such as in Caco-2 cells. In these human enterocytes, matriptase is detected primarily in the zymogen form and prostasin predominantly as the activated form, either in complexes with protease inhibitors or as the free active form. The negligible levels of prostasin zymogen with high levels of matriptase zymogen suggests that the reciprocal zymogen activation complex is likely not the mechanism for matriptase zymogen activation. Furthermore, high level prostasin activation still occurs in Caco-2 variants with reduced or absent matriptase expression, indicating that matriptase is not required and/or involved in prostasin zymogen activation. Collectively, these data suggest that any functional relationship between natural endogenous human matriptase and prostasin does not occur at the level of zymogen activation.

Application of Topical Acids Improves Atopic Dermatitis in Murine Model by Enhancement of Skin Barrier Functions Regardless of the Origin of Acids

BACKGROUND

The acidic pH of the stratum corneum (SC) is important for epidermal permeability barrier homeostasis. Acidification of the skin surface has been suggested as a therapeutic strategy for skin disorders such as atopic dermatitis (AD).

OBJECTIVE

We performed an animal study to evaluate the usefulness of acidification of SC for inhibition of AD lesions and to find out if the therapeutic effect of vinegar is attributable to its herbal contents, rather than its acidity.

METHODS

Five groups of six oxazolone-treated (Ox)-AD mice were treated for three weeks with creams of different acidity: vehicle cream alone (pH 5.5), neutralized vinegar cream (pH 7.4), pH 5.0 vinegar cream, pH 3.5 vinegar cream, and pH 3.5 hydrogen chloride (HCl) cream. Also, we have compared two groups of Ox-AD mice treated with pH 5.5 vehicle cream or pH 5.5 vinegar cream.

RESULTS

Ox-AD mice treated with acidic creams exhibited fewer AD-like lesions, had significantly lower eczema scores, decreased basal by transepidermal water loss (TEWL), and increased SC hydration compared to the groups given only vehicle and neutral cream. There was no significant difference between the acidic vinegar and HCl groups. Between the groups treated with vehicle and pH 5.5 vinegar cream, there was no difference in eczema score, basal TEWL and SC hydration.

CONCLUSION

Application of topical acids, regardless of their source materials, inhibits the development of AD lesions by maintenance of skin surface pH and skin barrier function in murine model.

Commonly Employed African Neonatal Skin Care Products Compromise Epidermal Function in Mice

BACKGROUND

Neonatal mortality is much higher in the developing world than in developed countries. Infections are a major cause of neonatal death, particularly in preterm infants, in whom defective epidermal permeability barrier function facilitates transcutaneous pathogen invasion. The objective was to determine whether neonatal skin care products commonly used in Africa benefit or compromise epidermal functions in murine skin.

METHODS

After twice-daily treatment of 6- to 8-week-old hairless mice with each skin care product for 3 days, epidermal permeability barrier function, skin surface pH, stratum corneum hydration, and barrier recovery were measured using a multiprobe adapter system physiology monitor. For products showing some benefits in these initial tests, the epidermal permeability barrier homeostasis was assessed 1 and 5 hours after a single application to acutely disrupted skin.

RESULTS

All of the skin care products compromised basal permeability barrier function and barrier repair kinetics. Moreover, after 3 days of treatment, most of the products also reduced stratum corneum hydration while elevating skin surface pH to abnormal levels.

CONCLUSION

Some neonatal skin care products that are widely used in Africa perturb important epidermal functions, including permeability barrier homeostasis in mice. Should these products have similar effects on newborn human skin, they could cause a defective epidermal permeability barrier, which can increase body fluid loss, impair thermoregulation, and contribute to the high rates of neonatal morbidity and mortality seen in Africa. Accordingly, alternative products that enhance permeability barrier function should be identified, particularly for use in preterm infants.

Skin pH Is the Master Switch of Kallikrein 5-Mediated Skin Barrier Destruction in a Murine Atopic Dermatitis Model

Elevated skin surface pH has been reported in patients with atopic dermatitis. In this study, we explored the role of skin pH in the pathogenesis of atopic dermatitis using the NC/Tnd murine atopic dermatitis model. Alkalinization of the skin of asymptomatic NC/Tnd mice housed in specific pathogen-free conditions induced kallikrein 5 and activated protease-activated receptor 2, resulting in thymic stromal lymphopoietin secretion and a cutaneous T-helper 2 allergic response. This was associated with increased transepidermal water loss and development of eczematous lesions in these specific pathogen-free NC/Tnd mice, which normally do not suffer from atopic dermatitis. Injection of recombinant thymic stromal lymphopoietin also induced scratching behavior in the specific pathogen-free NC/Tnd mice. Thymic stromal lymphopoietin production and dermatitis induced by alkalinization of the skin could be blocked by the protease-activated receptor 2 antagonist ENMD-1068. In contrast, weak acidification of eczematous skin in conventionally housed NC/Tnd mice reduced kallikrein 5 activity and ameliorated the dermatitis. Onset of the dermatitis was associated with increased epidermal filaggrin expression and impaired activity of the sodium/hydrogen exchanger 1, a known regulator of skin pH. We conclude that alterations in skin pH directly modulate kallikrein 5 activity leading to skin barrier dysfunction, itch, and dermatitis via the protease-activated receptor 2-thymic stromal lymphopoietin pathway.

Skin Physiology of the Neonate and Infant: Clinical Implications

Significance: The skin is a complex and dynamic organ that performs several vital functions. The maturation process of the skin starts at birth with the adaption of the skin to the comparatively dry environment compared to the in utero milieu. This adaptive flexibility results in the unique properties of infant skin. To deliver appropriate care to infant skin, it is necessary to understand that it is evolving with unique characteristics. Recent Advances: The role of biophysical noninvasive techniques in the assessment of skin development underlines the importance of an objective evaluation of skin physiology parameters. Skin hydration, transepidermal water loss, and pH values are measurable with specific instruments that give us an accurate and reproducible assessment during infant skin maturation. The recording of these values, following standard measurement procedures, allows us to evaluate the integrity of the skin barrier and to monitor the functionality of the maturing skin over time. Critical Issues: During the barrier development, impaired skin function makes the skin vulnerable to chemical damage, microbial infections, and skin diseases, possibly compromising the general health of the infant. Preterm newborns, during the first weeks of life, have an even less developed skin barrier and, therefore, are even more at risk. Thus, it is extremely important to evaluate the risk of infection, skin breakdown, topical agent absorption, and the risk of thermoregulation failure. Future Directions: Detailed and objective evaluations of infant skin maturation are necessary to improve infant skin care. The results of these evaluations should be formed into general protocols that will allow doctors and caregivers to give more personalized care to full-term newborns, preterm newborns, and infants.