Stress test of the skin: The cutaneous permeability barrier treadmill

Skin Barrier in Atopic Dermatitis

A compromised permeability barrier is a hallmark of atopic dermatitis (AD). Localized to the outermost skin layer, the stratum corneum (SC) is critically dependent on terminal differentiation of epidermal keratinocytes, which transform into protein-rich corneocytes surrounded by extracellular lamellae of unique epidermal lipids, conferring permeability barrier function. These structures are disrupted in AD. A leaky barrier is prone to environmental insult, which in AD elicits type 2-dominant inflammation, in turn resulting in a vicious cycle further impairing the SC structure. Therapies directed at enforcing SC structure and anti-inflammatory strategies administered by topical and systemic route as well as UV therapy have differential effects on the permeability barrier. The expanding armamentarium of therapeutic modalities for AD treatment warrants optimization of their effects on permeability barrier function.

pH and light dual stimuli-responses of mixed system of 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecyl ammonium bromide) and trans-ortho-hydroxyl cinnamic acid

Stimuli-responsive smart supramolecular self-assembly with controllable morphology and adjustable rheological property has attracted widespread concern of scientists in recent years due to the great potential application in microfluidics, controlled release, biosensors and so on. In this study, a pH and UV light dual stimuli-responsive system was constructed by combining Gemini surfactant 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecyl ammonium bromide) (12-3(OH)-12·2Br^-) with trans-ortho-hydroxyl cinnamic acid (trans-OHCA) in aqueous solution. The phase behavior and stimuli-responsive behavior of the system including the microstructural transition, rheological property, intermolecular interaction, and isomerization reaction were explored by various experiment techniques such as rheometer, UV-vis spectrum, polarized optical microscopy (POM), transmission electron microscopy (TEM), dynamic light scattering (DLS) as well as theoretical calculation. The system displays abundant phase behaviors that supramolecular self-assemblies of different morphologies in different states such as spherical micelle, wormlike micelle, lamellar liquid crystal, and aqueous two phase system (ATPS) were observed even at lower concentration, which provide the research basis on the abundant stimuli-responsiveness of the system. The results prove that the multiple ionization and the photo-isomerization of trans-OHCA endow the system with plentiful responses to pH and UV light stimuli. It is expected that this study on the dual stimuli-responsive system with abundant self-assembly behaviors and adjustable rheological behaviors would be of theoretical and practical importance, which would provide essential guidance in designing and constructing smart materials with multiple stimuli-responses.

Three-Dimensional Skin Tissue Printing with Human Skin Cell Lines and Mouse Skin-Derived Epidermal and Dermal Cells

Since the skin covers most surfaces of the body, it is susceptible to damage, which can be fatal depending on the degree of injury to the skin because it defends against external attack and protects internal structures. Various types of artificial skin are being studied for transplantation to repair damaged skin, and recently, the production of replaceable skin using three-dimensional (3D) bioprinting technology has also been investigated. In this study, skin tissue was produced using a 3D bioprinter with human skin cell lines and cells extracted from mouse skin, and the printing conditions were optimized. Gelatin was used as a bioink, and fibrinogen and alginate were used for tissue hardening after printing. Printed skin tissue maintained a survival rate of 90% or more when cultured for 14 days. Culture conditions were established using 8 mM calcium chloride treatment and the skin tissue was exposed to air to optimize epidermal cell differentiation. The skin tissue was cultured for 14 days after differentiation induction by this optimized culture method, and immunofluorescent staining was performed using epidermal cell differentiation markers to investigate whether the epidermal cells had differentiated. After differentiation, loricrin, which is normally found in terminally differentiated epidermal cells, was observed in the cells at the tip of the epidermal layer, and cytokeratin 14 was expressed in the lower cells of the epidermis layer. Collectively, this study may provide optimized conditions for bioprinting and keratinization for three-dimensional skin production.

A Lipid Mixture Enriched by Ceramide NP with Fatty Acids of Diverse Chain Lengths Contributes to Restore the Skin Barrier Function Impaired by Topical Corticosteroid

INTRODUCTION

The stratum corneum (SC) is a skin barrier that consists of corneocytes, intercellular lipids, and corneodesmosomes. Ceramides are composed of sphingoid bases linked with various types of fatty acids (FAs), and they are an essential constituent of SC intercellular lipids. Among their subtypes, ceramide NP with a phytosphingosine base is especially important. Most of the previous studies on barrier recovery have focused on a specific ceramide with a single chain FA, not with diverse chain lengths. Skin barrier function is impaired by various factors, including topical corticosteroid.

OBJECTIVE

We evaluated whether a lipid mixture enriched by ceramide NP with FAs of diverse chain lengths (CER [NP]*) can restore the skin barrier function impaired by topical corticosteroid.

METHODS

Twenty-seven healthy adult male volunteers were recruited. Topical corticosteroid was applied on both volar forearms of volunteers. Then, the test cream containing a lipid mixture with CER (NP)* was applied on the left forearm, and a vehicle cream without a lipid mixture was applied on the right forearm of each subject. The functional parameters of the skin barrier were compared before and after the treatment. Epidermal differentiation markers, hyaluronic acid synthase 3 (HAS3), cytokine levels, and the lipid profiles in the SC were analyzed.

RESULTS

The functional parameters of the skin barrier, such as barrier recovery rate, SC integrity, and SC hydration were significantly improved in the test cream-applied site compared to the vehicle cream-applied sites. Filaggrin and HAS3 levels were significantly higher in the sites applied with the test cream. Interleukin (IL)-1α levels were also significantly increased in these sites. IL-2, IL-6, IL-10, and IL-13 levels were significantly decreased in the test cream-applied sites. Lipid analyses showed that C18, C20, and total ceramide NP levels significantly increased in the sites where the test cream was applied. Also, C16, C18, C20, C24, and total ceramide NP levels were significantly elevated in the test cream-applied sites after acute barrier disruption.

CONCLUSION

Our results demonstrate that a lipid mixture enriched by CER (NP)* could recover the barrier function impaired by topical corticosteroid.

Adult skin acute stress responses to short-term environmental and internal aggression from exposome factors

Exposome factors that lead to stressed skin can be defined as any disturbance to homeostasis from environmental (meteorological factors, solar radiation, pollution or tobacco smoke) and/or internal exposure (unhealthy diet, hormonal variations, lack of sleep, psychosocial stress). The clinical and biological impact of chronic exposome effects on skin functions has been extensively reviewed, whereas there is a paucity of information on the impact of short‐term acute exposure. Acute stress, which would typically last minutes to hours (and generally no more than a week), provokes a transient but robust neuroendocrine‐immune and tissue remodelling response in the skin and can alter the skin barrier. Firstly, we provide an overview of the biological effects of various acute stressors on six key skin functions, namely the skin physical barrier, pigmentation, defences (antioxidant, immune cell‐mediated, microbial and microbiome maintenance), structure (extracellular matrix and appendages), neuroendocrine and thermoregulation functions. Secondly, we describe the biological and clinical effects on adult skin from individual exposome factors that elicit an acute stress response and their consequences in skin health maintenance. Clinical manifestations of acutely stressed skin may include dry skin that might accentuate fine lines, oily skin, sensitive skin, pruritus, erythema, pale skin, sweating, oedema and flares of inflammatory skin conditions such as acne, rosacea, atopic dermatitis, pigmentation disorders and skin superinfection such as viral reactivation. Acute stresses can also induce scalp sensitivity, telogen effluvium and worsen alopecia.

Atopic dermatitis: Role of the skin barrier, environment, microbiome, and therapeutic agents

Atopic dermatitis (AD) is a chronic, inflammatory skin disorder characterized by eczematous and pruritic skin lesions. In recent decades, the prevalence of AD has increased worldwide, most notably in developing countries. The enormous progress in our understanding of the complex composition and functions of the epidermal barrier allows for a deeper appreciation of the active role that the skin barrier plays in the initiation and maintenance of skin inflammation. The epidermis forms a physical, chemical, immunological, neuro-sensory, and microbial barrier between the internal and external environment. Not only lesional, but also non-lesional areas of AD skin display many morphological, biochemical and functional differences compared with healthy skin. Supporting this notion, genetic defects affecting structural proteins of the skin barrier, including filaggrin, contribute to an increased risk of AD. There is evidence to suggest that natural environmental allergens and man-made pollutants are associated with an increased likelihood of developing AD. A compromised epidermal barrier predisposes the skin to increased permeability of these compounds. Numerous topical and systemic therapies for AD are currently available or in development; while anti-inflammatory therapy is central to the treatment of AD, some existing and novel therapies also appear to exert beneficial effects on skin barrier function. Further research on the skin barrier, particularly addressing epidermal differentiation and inflammation, lipid metabolism, and the role of bacterial communities for skin barrier function, will likely expand our understanding of the complex etiology of AD and lead to identification of novel targets and the development of new therapies.