Topical apigenin improves epidermal permeability barrier homoeostasis in normal murine skin by divergent mechanisms

Improved Skin Barrier Function Along with Hydration Benefits of Viola yedoensis Extract, Aesculin, and Schaftoside and LC-HRMS/MS Dereplication of Its Bio-Active Components

The skin hydration level is a key factor that influences the physical and mechanical properties of the skin. The stratum corneum (SC), the outermost layer of the epidermis, is responsible for the skin's barrier function. In this study, we investigated the role of a unique composition of Viola yedoensis extract for its ability to activate CD44, a cell-surface receptor of hyaluronic acid, and aquaporin-3, a water-transporting protein, in human keratinocytes (HaCaT). An ELISA assay evaluating the protein expression levels of CD44, aquaporin-3 (AQP3), filaggrin, and keratin-10 revealed that V. yedoensis extract upregulated the levels of CD44 and AQP3 by 15% and 78%, respectively. Additionally, V. yedoensis extract demonstrated a comparative effect on water vapor flux in TEWL and lipid perturbation in DSC versus the reference, glycerin. In light of this new biological efficacy, a detailed phytochemical characterization was undertaken using an integrated LC-HRMS/MS-based metabolomics approach, which provided further insights on the chemistry of V. yedoensis. This led to the identification of 29 secondary metabolites, 14 of which are reported here for the first time, including esculetin, aesculin, apigenin and kaempferol C-glycosides, megastigmane glycosides, roseoside, platanionoside B, and an eriojaposide B isomer, along with the rare, calenduloside F and esculetin diglucoside, which are reported for the first time from the genus, Viola. Notably, two active components identified in the V. yedoensis extract, namely, aesculin and schaftoside, showed an upregulation of the protein expression of CD44 in HaCaT cells by 123% and 193% within 24 h of treatment, respectively, while aesculin increased AQP3 levels by 46%. Aesculin and schaftoside also significantly upregulated the expression of K-10 levels by 299% and 116%, which was considerably higher than sodium hyaluronate, the positive control. The rationale used to characterize the new structures is outlined along with the related biosynthetic pathways envisioned to generate roseoside and Eriojaposide B. These findings provide new molecular insights to deepen the understanding of how V. yedoensis extract, along with the biomarkers aesculin and schaftoside, restores the skin barrier and skin hydration benefits.

Apigenin: A Bioflavonoid with a Promising Role in Disease Prevention and Treatment

Apigenin is a powerful flavone compound found in numerous fruits and vegetables, and it offers numerous health-promoting benefits. Many studies have evidenced that this compound has a potential role as an anti-inflammatory and antioxidant compound, making it a promising candidate for reducing the risk of pathogenesis. It has also been found to positively affect various systems in the body, such as the respiratory, digestive, immune, and reproductive systems. Apigenin is effective in treating liver, lung, heart, kidney, neurological diseases, diabetes, and maintaining good oral and skin health. Multiple studies have reported that this compound is capable of suppressing various types of cancer through the induction of apoptosis and cell-cycle arrest, suppressing cell migration and invasion, reduction of inflammation, and inhibiting angiogenesis. When used in combination with other drugs, apigenin increases their efficacy, reduces the risk of side effects, and improves the response to chemotherapy. This review broadly analyzes apigenin's potential in disease management by modulating various biological activities. In addition, this review also described apigenin's interaction with other compounds or drugs and the potential role of nanoformulation in different pathogeneses. Further extensive research is needed to explore the mechanism of action, safety, and efficacy of this compound in disease prevention and treatment.

Benefits of topical natural ingredients in epidermal permeability barrier

Because of the crucial role of epidermal permeability barrier in regulation of cutaneous and extracutaneous functions, great efforts have been made to identify and develop the regimens that can improve epidermal permeability barrier function. Studies have demonstrated that oral administration of natural ingredients can improve epidermal permeability barrier in various skin conditions, including inflammatory dermatoses and UV-irradiation. Moreover, topical applications of some natural ingredients can also accelerate the repair of epidermal permeability barrier after acute barrier disruption and lower transepidermal water loss in the intact skin. Natural ingredient-induced improvements in epidermal permeability barrier function can be attributable to upregulation of keratinocyte differentiation, lipid production, antioxidant, hyaluronic acid production, expression of aquaporin 3 and sodium-hydrogen exchanger 1. In this review, we summarize the benefits of topical natural ingredients in epidermal permeability barrier in normal skin with or without acute barrier disruption and the underlying mechanisms.

The PI3K-Akt-mTOR and Associated Signaling Pathways as Molecular Drivers of Immune-Mediated Inflammatory Skin Diseases: Update on Therapeutic Strategy Using Natural and Synthetic Compounds

The dysregulated phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling pathway has been implicated in various immune-mediated inflammatory and hyperproliferative dermatoses such as acne, atopic dermatitis, alopecia, psoriasis, wounds, and vitiligo, and is associated with poor treatment outcomes. Improved comprehension of the consequences of the dysregulated PI3K/Akt/mTOR pathway in patients with inflammatory dermatoses has resulted in the development of novel therapeutic approaches. Nonetheless, more studies are necessary to validate the regulatory role of this pathway and to create more effective preventive and treatment methods for a wide range of inflammatory skin diseases. Several studies have revealed that certain natural products and synthetic compounds can obstruct the expression/activity of PI3K/Akt/mTOR, underscoring their potential in managing common and persistent skin inflammatory disorders. This review summarizes recent advances in understanding the role of the activated PI3K/Akt/mTOR pathway and associated components in immune-mediated inflammatory dermatoses and discusses the potential of bioactive natural products, synthetic scaffolds, and biologic agents in their prevention and treatment. However, further research is necessary to validate the regulatory role of this pathway and develop more effective therapies for inflammatory skin disorders.

Therapeutic effects and mechanisms of Ku-Gan formula on atopic dermatitis: A pilot clinical study and modular pharmacology analysis with animal validation

ETHNOPHARMACOLOGICAL RELEVANCE

Atopic dermatitis (AD) is a persistent, recurrent inflammatory skin disorder with a rapid upward trend worldwide. The first-line treatment for AD consists of topical medicines such as topical corticosteroids (TCSs). However, long-term use of conventional topical medicine results in side effects and recurrence, presenting therapeutic challenges for the management of AD. Ku-Gan formula (KG) has been extensively used to treat skin diseases since the Song dynasty. In particular, topical administration of the KG alleviates the cutaneous symptoms of AD and reduces recurrence rates with a good safety profile; however, the mechanisms of the KG's action remain unknown.

AIM OF THE STUDY

The current study aimed to evaluate the efficacy and safety of KG in AD patients and to investigate the molecular mechanisms that underlie the efficacy of KG in the treatment of AD.

MATERIALS AND METHODS

A single-arm prospective pilot study with historical controls was conducted. This study evaluated 11 patients with mild to moderate AD, who underwent topical KG treatment. The primary outcome was the change in local eczema area and severity index (EASI) scores. The secondary outcomes included the recurrence rate and safety. The recurrence rate were compared to those of a matched historical control group. Secondly, modular pharmacology analysis was used to elucidate the therapeutic mechanism of KG in AD treatment by identifying the hub genes and kernel pathways. Moreover, we evaluated treatment effects and verified modular pharmacology-based findings using the calcipotriol (MC903)-induced mouse model and bioinformatics analysis.

RESULTS

Our clinical pilot study demonstrated that the KG wet wrapping could effectively ameliorate skin lesions in AD patients with a significant drop from 4.18 to 1.63 in local EASI. Compared to the historical controls, KG had a reduced recurrence rate (36%) and a longer median time to relapse (>12 weeks). Modular pharmacology analysis identified the hub genes including IL6, IL1B, VEGFA, STAT3, JUN, TIMP1 and ARG1, and kernel pathway including IL-17 signaling pathway of KG. Pharmacodynamic results suggested that KG ameliorated skin symptoms and demonstrated no less efficacy than halcinonide (HC) in MC903-induced AD-like mice. In addition, KG regulated the mRNA expression of hub genes as well as the related genes involved in IL-17 signaling pathway including Il25, Il17a,Traf3ip2, and Traf6, in skin lesions of AD-like mice.

CONCLUSION

These results showed that KG is a safe and effective topical treatment for AD with low recurrence. In addition, our study identified potential molecular pathways and therapeutic candidate targets of the KG formula, providing evidence for its clinical applicability in AD.

Regulation of Host Defense Peptide Synthesis by Polyphenols

The rise of antimicrobial resistance has created an urgent need for antibiotic-alternative strategies for disease control and prevention. Host defense peptides (HDPs), which have both antimicrobial and immunomodulatory properties, are an important component of the innate immune system. A host-directed approach to stimulate the synthesis of endogenous HDPs has emerged as a promising solution to treat infections with a minimum risk for developing antimicrobial resistance. Among a diverse group of compounds that have been identified as inducers of HDP synthesis are polyphenols, which are naturally occurring secondary metabolites of plants characterized by the presence of multiple phenol units. In addition to their well-known antioxidant and anti-inflammatory activities, a variety of polyphenols have been shown to stimulate HDP synthesis across animal species. This review summarizes both the in vitro and in vivo evidence of polyphenols regulating HDP synthesis. The mechanisms by which polyphenols induce HDP gene expression are also discussed. Natural polyphenols warrant further investigation as potential antibiotic alternatives for the control and prevention of infectious diseases.

Apigenin: A Therapeutic Agent for Treatment of Skin Inflammatory Diseases and Cancer

The skin is the main barrier between the body and the environment, protecting it from external oxidative stress induced by ultraviolet rays. It also prevents the entrance of infectious agents such as viruses, external antigens, allergens, and bacteria into our bodies. An overreaction to these agents causes severe skin diseases, including atopic dermatitis, pruritus, psoriasis, skin cancer, and vitiligo. Members of the flavonoid family include apigenin, quercetin, luteolin, and kaempferol. Of these, apigenin has been used as a dietary supplement due to its various biological activities and has been shown to reduce skin inflammation by downregulating various inflammatory markers and molecular targets. In this review, we deal with current knowledge about inflammatory reactions in the skin and the molecular mechanisms by which apigenin reduces skin inflammation.

Prenylated Flavonoids in Topical Infections and Wound Healing

The review presents prenylated flavonoids as potential therapeutic agents for the treatment of topical skin infections and wounds, as they can restore the balance in the wound microenvironment. A thorough two-stage search of scientific papers published between 2000 and 2022 was conducted, with independent assessment of results by two reviewers. The main criteria were an MIC (minimum inhibitory concentration) of up to 32 µg/mL, a microdilution/macrodilution broth method according to CLSI (Clinical and Laboratory Standards Institute) or EUCAST (European Committee on Antimicrobial Susceptibility Testing), pathogens responsible for skin infections, and additional antioxidant, anti-inflammatory, and low cytotoxic effects. A total of 127 structurally diverse flavonoids showed promising antimicrobial activity against pathogens affecting wound healing, predominantly Staphylococcus aureus strains, but only artocarpin, diplacone, isobavachalcone, licochalcone A, sophoraflavanone G, and xanthohumol showed multiple activity, including antimicrobial, antioxidant, and anti-inflammatory along with low cytotoxicity important for wound healing. Although prenylated flavonoids appear to be promising in wound therapy of humans, and also animals, their activity was measured only in vitro and in vivo. Future studies are, therefore, needed to establish rational dosing according to MIC and MBC (minimum bactericidal concentration) values, test potential toxicity to human cells, measure healing kinetics, and consider formulation in smart drug release systems and/or delivery technologies to increase their bioavailability.

Optimizing emollient therapy for skin barrier repair in atopic dermatitis

OBJECTIVE

We compared the principal characteristics of over-the-counter moisturizers with physiological lipid-based barrier repair therapy (BRT).

DATA SOURCES

An extended literature reported that moisturizers are considered standard ancillary therapy for anti-inflammatory skin disorders such as atopic dermatitis (AD). Additional studies have found that physiological lipid-based BRT can comprise effective, stand-alone therapy for pediatric AD.

RESULTS

Not all moisturizers are beneficial-some negatively impact skin function, and in doing so, they risk inducing or exacerbating inflammation in patients with AD. The frequent self-reported occurrences of sensitive skin in patients with AD could reflect the potential toxicity of such formulations. A still unanswered question is whether improper formulations could also prove to be counterproductive in other types of sensitive skin, such as rosacea. In contrast, we found how physiological lipid-based BRT (when comprised of the 3 key stratum corneum lipids in sufficient quantities and at an appropriate molar ratio) can correct the barrier abnormality, thereby reducing inflammation in AD and possibly in other inflammatory dermatoses, such as adult eczemas and possibly even psoriasis.

CONCLUSION

We provide guidelines for the appropriate dispensation of moisturizers and physiological lipid-based, BRT for the treatment of AD. Both over-the-counter (Atopalm) and prescription (EpiCeram) products are available in the United States with these characteristics.

Promising Natural Products in New Drug Design, Development, and Therapy for Skin Disorders: An Overview of Scientific Evidence and Understanding Their Mechanism of Action

The skin is the largest organ in the human body, composed of the epidermis and the dermis. It provides protection and acts as a barrier against external menaces like allergens, chemicals, systemic toxicity, and infectious organisms. Skin disorders like cancer, dermatitis, psoriasis, wounds, skin aging, acne, and skin infection occur frequently and can impact human life. According to a growing body of evidence, several studies have reported that natural products have the potential for treating skin disorders. Building on this information, this review provides brief information about the action of the most important in vitro and in vivo research on the use of ten selected natural products in inflammatory, neoplastic, and infectious skin disorders and their mechanisms that have been reported to date. The related studies and articles were searched from several databases, including PubMed, Google, Google Scholar, and ScienceDirect. Ten natural products that have been reported widely on skin disorders were reviewed in this study, with most showing anti-inflammatory, antioxidant, anti-microbial, and anti-cancer effects as the main therapeutic actions. Overall, most of the natural products reported in this review can reduce and suppress inflammatory markers, like tumor necrosis factor-alpha (TNF-α), scavenge reactive oxygen species (ROS), induce cancer cell death through apoptosis, and prevent bacteria, fungal, and virus infections indicating their potentials. This review also highlighted the challenges and opportunities of natural products in transdermal/topical delivery systems and their safety considerations for skin disorders. Our findings indicated that natural products might be a low-cost, well-tolerated, and safe treatment for skin diseases. However, a larger number of clinical trials are required to validate these findings. Natural products in combination with modern drugs, as well as the development of novel delivery mechanisms, represent a very promising area for future drug discovery of these natural leads against skin disorders.

Ameliorated membranous nephropathy activities of two ethanol extracts from corn silk and identification of flavonoid active compounds by LC-MS2

The current study looks to evaluate the effect of corn silk flavonoids on membranous nephropathy (MN). Polyamide resin (PR) can be used to enrich corn silk ethanol extract (CSEE) to obtain flavonoid-rich extract (PR-CSEE), the total flavonoid content (TFC) of which we found to be 57.4%. The results of scanning electron microscope, Fourier-transform infrared, and high-performance liquid chromatography analyses determined that PR-CSEE and CSEE have different structural characteristics, but that PR-CSEE has higher TFC. MN mice models were induced by cationic bovine serum albumin, and we found that PR-CSEE administration reduced urine protein levels markedly, while renal function, glomerular atrophy, inflammatory infiltration, and in-serum immunoglobulin G and complement 3 content were improved. Through LC-MS² spectrometry analysis, we pinpointed the 12 major flavonoid active compounds in PR-CSEE. These findings suggest that PR-CSEE can act as a potential functional food material by which to improve MN.

Improvement of Skin Barrier Dysfunction by Phenolic-containing Extracts of Lycium barbarum via Nrf2/HO-1 Regulation

Lycium barbarum have received an increasing popularity due to its powerful biological activity and medicinal use. However, the effect of Lycium barbarum on skin remains largely uncharacterized. The general purpose of this paper was to characterize the phenolic compounds in Lycium barbarum extract (LBE) using LC-HRMS/QTOF method and to investigate whether topical administration of LBE can repair skin barrier dysfunction in mice. Our data demonstrated that LBE could not only decrease ROS level and matrix metalloproteinase expression, but also strengthen intrinsic antioxidant defense system including SOD, GSH-Px and CAT, thereby resulting in increased skin collagen content and an improvement of UV-induced skin erythema, thickness and wrinkles. Improved skin barrier functions were highly correlated with increased expression of filaggrin, involucrin and loricrin as well as antioxidant proteins such as Nrf2 and HO-1 in UV-irradiated mice, suggesting that LBE may be promising natural products at a lower cost for the topical application in the treatment of skin diseases with defective barrier function.

New Treatments for Atopic Dermatitis Targeting Skin Barrier Repair via the Regulation of FLG Expression

Atopic dermatitis (AD) is one of the most common chronic, inflammatory skin disorders with a complex etiology and a broad spectrum of clinical phenotypes. Despite its high prevalence and effect on the quality of life, safe and effective systemic therapies approved for long-term management of AD are limited. A better understanding of the pathogenesis of atopic dermatitis in recent years has contributed to the development of new therapeutic approaches that target specific pathophysiological pathways. Skin barrier dysfunction and immunological abnormalities are critical in the pathogenesis of AD. Recently, the importance of the downregulation of epidermal differentiation complex (EDC) molecules caused by external and internal stimuli has been extensively emphasized. The purpose of this review is to discuss the innovations in the therapy of atopic dermatitis, including biologics, small molecule therapies, and other drugs by highlighting regulatory mechanisms of skin barrier-related molecules, such as filaggrin (FLG) as a crucial pathway implicated in AD pathogenesis.

Mutations in 3β-hydroxysteroid-δ8, δ7-isomerase paradoxically benefit epidermal permeability barrier homeostasis in mice

Inherited or acquired blockade of distal steps in the cholesterol synthetic pathway results in ichthyosis, due to reduced cholesterol production and/or the accumulation of toxic metabolic precursors, while inhibition of epidermal cholesterol synthesis compromises epidermal permeability barrier homeostasis. We showed here that 3β-hydroxysteroid-δ8, δ7-isomerase-deficient mice (TD), an analog for CHILD syndrome in humans, exhibited not only lower basal transepidermal water loss rates, but also accelerated permeability barrier recovery despite the lower expression levels of mRNA for epidermal differentiation marker-related proteins and lipid synthetic enzymes. Moreover, TD mice displayed low skin surface pH, paralleled by increased expression levels of mRNA for sodium/hydrogen exchanger 1 (NHE1) and increased antimicrobial peptide expression, compared with wild-type (WT) mice, which may compensate for the decreased differentiation and lipid synthesis. Additionally, in comparison with WT controls, TD mice showed a significant reduction in ear thickness following challenges with either phorbol ester or oxazolone. However, TD mice exhibited growth retardation. Together, these results demonstrate that 3β-hydroxysteroid-δ8, δ7-isomerase deficiency does not compromise epidermal permeability barrier in mice, suggesting that alterations in epidermal function depend on which step of the cholesterol synthetic pathway is interrupted. But whether these findings in mice could be mirrored in humans remains to be determined.

Croton urucurana Baillon stem bark ointment accelerates the closure of cutaneous wounds in knockout IL-10 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Croton urucurana Baill. (Euphorbiaceae) is a plant used in Brazilian popular medicine for the treatment of wound healing, inflammatory diseases, gastritis, infections, and hemorrhoids.

AIM

The present study aimed to evaluate the in vivo wound healing activity of an ointment based on ethanolic extract of C. urucurana stem bark, at concentrations of 5% and 10%, and to relate it with compounds that could be associated with this activity.

MATERIALS AND METHODS

Analyses by FIA-ESI-IT-MSⁿ were carried out to investigate the chemical composition of C. urucurana. Knockout IL-10 (n = 60) mice and wild type C57 (n = 12) mice were separated into 6 groups to evaluate the wound healing activity. Knockout IL-10 mice: SAL (0.9% saline); BAS (ointment base); SS (1% silver sulfadiazine); CR1 (ointment with extract of C. urucurana 5%); CR2 (ointment with extract of C. urucurana 10%); and wild mice C57: SALC57 (Saline 0.9%). A circular wound with 10 mm in diameter was generated on the dorsal of the animals. Tissue specimen of the wounds were removed on days 7 and 14 of the treatment for histopathological, oxidative status and analyses of pro-and anti-inflammatory cytokines in scar tissue.

RESULTS

In the phytochemical profile, twelve proanthocyanidins were identified (in the form of monomers, dimers, trimers, and tetramers), based on (epi)catechin and (epi)gallocatechin. Furthermore, two quercetin derivatives and two alkaloids were detected. The groups treated with CR1 and CR2 ointments presented higher rate of wound closure, increased total number of cells, mast cells, blood vessels and higher deposition of type III and I collagen. In addition, they showed increased amount of pro-inflammatory cytokines (IL- 2 and IFN-γ), and anti-inflmatory cytokines (IL-4), on the 7th day of treatment.

CONCLUSION

The results presented support the popular use of preparations based on the bark of C. urucurana as a healing compound.

Novel Anti-Inflammatory Approaches for Cystic Fibrosis Lung Disease: Identification of Molecular Targets and Design of Innovative Therapies

Cystic fibrosis (CF) is the most common genetic disorder among Caucasians, estimated to affect more than 70,000 people in the world. Severe and persistent bronchial inflammation and chronic bacterial infection, along with airway mucus obstruction, are hallmarks of CF lung disease and participate in its progression. Anti-inflammatory therapies are, therefore, of particular interest for CF lung disease. Furthermore, a better understanding of the molecular mechanisms involved in airway infection and inflammation in CF has led to the development of new therapeutic approaches that are currently under evaluation by clinical trials. These new strategies dedicated to CF inflammation are designed to treat different dysregulated aspects such as oxidative stress, cytokine secretion, and the targeting of dysregulated pathways. In this review, we summarize the current understanding of the cellular and molecular mechanisms that contribute to abnormal lung inflammation in CF, as well as the new anti-inflammatory strategies proposed to CF patients by exploring novel molecular targets and novel drug approaches.

Assessment of non-invasive techniques and herbal-based products on dermatological physiology and intercellular lipid properties

Skin is the largest external organ of the human body. It acts as a barrier to protect the human body from environmental pollution, mechanical stress, and excessive water loss. The defensive function resides primarily on top of the epidermis layer commonly known as stratum corneum (SC). Human SC consists of three major lipids, namely ceramide, free fatty acid, and cholesterol that comprise approximately 50%, 25%, and 25% of the total lipid mass, respectively. The optimal composition of SC lipids is the vital epidermal barrier function of the skin. On the other hand, skin barrier serves to limit passive water loss from the body, reduces chemical absorption from the environment, and prevents microbial infection. In contrast, epidermal lipids are important to maintain the cell structure, growth and differentiation, cohesion and desquamation as well as formation of a permeability barrier. Multiple non-invasive in vivo approaches were implemented on a regular basis to monitor skin physiological and intercellular lipid properties. The measurement of different parameters such as transepidermal water loss (TEWL), hydration level, skin elasticity, collagen intensity, melanin content, sebum, pH, and tape stripping is essential to evaluate the epidermal barrier function. Novel non-invasive techniques such as tape stripping, ultrasound imaging, and laser confocal microscopy offer higher possibility of accurate and detailed characterisation of skin barrier. To date, these techniques have also been widely used to determine the effects of herbal plants in dermatology. Herbal plants have been traditionally used for ages to treat a variety of skin diseases, as reported by the World Health Organisation (WHO). Their availability, lower cost, and minimal or no side effects have created awareness among society, thus increase the demand for natural sources as the remedy to treat various skin diseases. This paper reviews several non-invasive techniques and evaluations of herbal-based product in dermatology.

The regulation of protein kinase casein kinase II by apigenin is involved in the inhibition of ultraviolet B-induced macrophage migration inhibitory factor-mediated hyperpigmentation

Ultraviolet (UV) radiation elicits melanogenesis and pigmentation in the skin. Apigenin (4',5,7-trihydroxyflavone [AGN]) is a plant flavone contained in various herbs, fruits, and vegetables. We herein investigated antimelanogenic properties of AGN and the molecular mechanisms of the action of AGN. In UVB-treated mice, AGN inhibited cutaneous hyperpigmentation and macrophage migration inhibitory factor (MIF) expression as a melanogenesis-related key factor. In mouse keratinocytes, AGN inhibited the expression of MIF and also the related factors (e.g., stem cell factor and proteinase-activated receptor 2) induced by MIF. In addition to ellagic acid as a casein kinase II (CK2) inhibitor, AGN suppressed CK2 enzymatic activity and UVB-induced CK2 expression and subsequent phosphorylation of IκB and MIF expression. These results suggest that AGN inhibits UVB-induced hyperpigmentation through the regulation of CK2-mediated MIF expression in keratinocytes.

Insights into atopic dermatitis gained from genetically defined mouse models

Atopic dermatitis (AD) is characterized by severe pruritus and recurrent eczema with a chronic disease course. Impaired skin barrier function, hyperactivated T_H2 cell-type inflammation, and pruritus-induced scratching contribute to the disease pathogenesis of AD. Skin microbial alterations complicate the pathogenesis of AD further. Mouse models are a powerful tool to analyze such intricate pathophysiology of AD, with a caution that anatomy and immunology of the skin differ between human subjects and mice. Here we review recent understanding of AD etiology obtained using mouse models, which address the epidermal barrier, skin microbiome, T_H2 immune response, and pruritus.

Pathomechanism of 'skin-originated' allergic diseases

The skin is outermost barrier of the body and protects us from various kinds of external stimuli. The barrier function of the skin is, however, not wholly perfect but include some 'security holes' where external antigen invades in. Further, external antigens themselves have some specific shunt pathways to breach the skin barrier. Recent studies revealed that percutaneous sensitization is a strong inducer of systemic immune responses and it is now considered that majority of food allergy is sensitized through body surfaces. Thus, to know about the fundamental structure of the skin barrier and its potential weak spots must be important for understanding the pathomechanism of 'skin-originated' allergic diseases. In this review, I overview the fundamental features of the skin barrier, and then, will discuss the pathomechanism how external antigens breach the barrier and induce subsequent systemic allergic reactions.

Moisturizers versus Current and Next-Generation Barrier Repair Therapy for the Management of Atopic Dermatitis

We compare here the principal characteristics of over-the-counter moisturizers with physiologic lipid-based barrier repair therapy. Moisturizers are standard ancillary therapy for anti-inflammatory skin disorders, like atopic dermatitis (AD), and can attenuate the emergence of AD, the initial step in the "atopic march." But not all moisturizers are beneficial; some can make skin function worse, and can even induce inflammation, possibly accounting for the frequent occurrence of "sensitive skin" in women. In contrast, physiologic lipid-based barrier repair therapy, if comprised of the 3 key stratum corneum lipids, in sufficient quantities and at an appropriate molar ratio, can correct the barrier abnormality and reduce inflammation in AD, and perhaps in other inflammatory dermatoses.

Upregulation of FLG, LOR, and IVL Expression by Rhodiola crenulata Root Extract via Aryl Hydrocarbon Receptor: Differential Involvement of OVOL1

Rhodiola species are antioxidative, salubrious plants that are known to inhibit oxidative stress induced by ultraviolet and γ-radiation in epidermal keratinocytes. As certain phytochemicals activate aryl hydrocarbon receptors (AHR) or OVO-like 1 (OVOL1) to upregulate the expression of epidermal barrier proteins such as filaggrin (FLG), loricrin (LOR), and involucrin (IVL), we investigated such regulation by Rhodiola crenulata root extract (RCE). We demonstrated that RCE induced FLG and LOR upregulation in an AHR-OVOL1-dependent fashion. However, RCE-mediated IVL upregulation was AHR-dependent but OVOL1-independent. Coordinated upregulation of skin barrier proteins by RCE via AHR may be beneficial in the management of barrier-disrupted inflammatory skin diseases such as atopic dermatitis.

Protective role of 6-formylindolo[3,2-b]carbazole (FICZ), an endogenous ligand for arylhydrocarbon receptor, in chronic mite-induced dermatitis

BACKGROUND

Chronic eczema such as atopic dermatitis imposes significant socio-econo-psychologic burdens on the affected individuals. In addition to conventional topical treatments, phototherapy is recommended for patients with extensive lesions. Although immunosuppression is believed to explain its primary effectiveness, the underlying mechanisms of phototherapy remain unsolved. Ultraviolet irradiation generates various tryptophan photoproducts including 6-formylindolo[3,2-b]-carbazole (FICZ). FICZ is known to be a potent endogenous agonist for aryl hydrocarbon receptor (AHR); however, the biological role of FICZ in chronic eczema is unknown.

OBJECTIVE

To investigate the effect of FICZ on chronic eczema such as atopic dermatitis.

METHODS

We stimulated HaCaT cells and normal human epidermal keratinocytes (NHEKs) with or without FICZ and then performed quantitative reverse transcriptase polymerase chain reaction, immunofluorescence, and siRNA treatment. We used the atopic dermatitis-like NC/Nga murine model and treated the mice for 2 weeks with either Vaseline® as a control, FICZ ointment, or betamethasone 17-valerate ointment. The dermatitis score, transepidermal water loss, histology, and expression of skin barrier genes and proteins were evaluated.

RESULTS

FICZ significantly upregulated the gene expression of filaggrin in both HaCaT cells and NHEKs in an AHR-dependent manner, but did not affect the gene expression of other barrier-related proteins. In addition, FICZ improved the atopic dermatitis-like skin inflammation, clinical scores, and transepidermal water loss in NC/Nga mice compared with those of control mice. On histology, FICZ significantly reduced the epidermal and dermal thickness as well as the number of mast cells. Topical FICZ also significantly reduced the gene expression of Il22.

CONCLUSION

These findings highlight the beneficial role of FICZ-AHR and provide a new strategic basis for developing new drugs for chronic eczema.

Barrier dysfunction in the skin allergy

The skin is continuously exposed to external pathogens, and its barrier function is critical for skin homeostasis. Previous studies have shown that the barrier dysfunction is one of the most predisposing factors for the development of skin allergic diseases such as atopic dermatitis. In this article, we summarize how the physical barrier of the skin is organized and review its link to the pathomechanism of skin allergic diseases. We describe the formation of the SC barrier in terms of the following five categories: 1) filaggrin metabolism; 2) cornified envelope; 3) intercellular lipids; 4) corneodesmosome; and 5) corneocyte desquamation. New approaches to restoring the skin barrier function are also discussed.

Antioxidant Artemisia princeps Extract Enhances the Expression of Filaggrin and Loricrin via the AHR/OVOL1 Pathway

The Japanese mugwort, Artemisia princeps (yomogi in Japanese), has anti-inflammatory and antioxidant effects. Skin care products containing Artemisia princeps extract (APE) are known to improve dry skin symptoms in atopic dermatitis. Atopic dry skin is associated with a marked reduction of skin barrier proteins, such as filaggrin (FLG) and loricrin (LOR). Recently, aryl hydrocarbon receptor (AHR), and its downstream transcription factor OVO-like 1 (OVOL1), have been shown to regulate the gene expression of FLG and LOR. The focus of this paper is to evaluate the effects of APE on the AHR/OVOL1/FLG or LOR pathway since they have remained unknown to this point. We first demonstrated that non-cytotoxic concentrations of APE significantly upregulated antioxidant enzymes, NAD(P)H dehydrogenase quinone 1 and heme oxygenase 1, in human keratinocytes. Even at these low concentrations, APE induced nuclear translocation of AHR and significantly upregulated CYP1A1 (a specific target gene for AHR activation), FLG, and LOR expression. AHR knockdown downregulated OVOL1 expression. The APE-induced upregulation of FLG and LOR was canceled in keratinocytes with AHR or OVOL1 knockdown. In conclusion, antioxidant APE is a potent phytoextract that upregulates FLG and LOR expression in an AHR/OVOL1-dependent manner and this may underpin the barrier-repairing effects of APE in treating atopic dry skin.

Atopic dermatitis: immune deviation, barrier dysfunction, IgE autoreactivity and new therapies

Atopic dermatitis (AD) is a chronic or chronically relapsing, eczematous, severely pruritic skin disorder mostly associated with IgE elevation and skin barrier dysfunction due to decreased filaggrin expression. The lesional skin of AD exhibits Th2- and Th22-deviated immune reactions that are progressive during disease chronicity. Th2 and Th22 cytokines further deteriorate the skin barrier by inhibiting filaggrin expression. Some IgEs are reactive to self-antigens. The IgE autoreactivity may precipitate the chronicity of AD. Upon activation of the ORAI1 calcium channel, atopic epidermis releases large amounts of thymic stromal lymphopoietin (TSLP), which initiates the Th2 and Th22 immune response. Th2-derived interleukin-31 and TSLP induce an itch sensation. Taken together, TSLP/Th2/Th22 pathway is a promising target for developing new therapeutics for AD. Enhancing filaggrin expression using ligands for the aryl hydrocarbon receptor may also be an adjunctive measure to restore the disrupted barrier function specifically for AD.

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.

Multifactorial skin barrier deficiency and atopic dermatitis: Essential topics to prevent the atopic march

Atopic dermatitis (AD) is the most common inflammatory skin disease in the industrialized world and has multiple causes. Over the past decade, data from both experimental models and patients have highlighted the primary pathogenic role of skin barrier deficiency in patients with AD. Increased access of environmental agents into the skin results in chronic inflammation and contributes to the systemic "atopic (allergic) march." In addition, persistent skin inflammation further attenuates skin barrier function, resulting in a positive feedback loop between the skin epithelium and the immune system that drives pathology. Understanding the mechanisms of skin barrier maintenance is essential for improving management of AD and limiting downstream atopic manifestations. In this article we review the latest developments in our understanding of the pathomechanisms of skin barrier deficiency, with a particular focus on the formation of the stratum corneum, the outermost layer of the skin, which contributes significantly to skin barrier function.

The Potential of Plant Phenolics in Prevention and Therapy of Skin Disorders

Phenolic compounds constitute a group of secondary metabolites which have important functions in plants. Besides the beneficial effects on the plant host, phenolic metabolites (polyphenols) exhibit a series of biological properties that influence the human in a health-promoting manner. Evidence suggests that people can benefit from plant phenolics obtained either by the diet or through skin application, because they can alleviate symptoms and inhibit the development of various skin disorders. Due to their natural origin and low toxicity, phenolic compounds are a promising tool in eliminating the causes and effects of skin aging, skin diseases, and skin damage, including wounds and burns. Polyphenols also act protectively and help prevent or attenuate the progression of certain skin disorders, both embarrassing minor problems (e.g., wrinkles, acne) or serious, potentially life-threatening diseases such as cancer. This paper reviews the latest reports on the potential therapy of skin disorders through treatment with phenolic compounds, considering mostly a single specific compound or a combination of compounds in a plant extract.

Apigenin inhibits COX-2, PGE2, and EP1 and also initiates terminal differentiation in the epidermis of tumor bearing mice

Non-melanoma skin cancer (NMSC) is the most prevalent cancer in the United States. NMSC overexpresses cyclooxygenase-2 (COX-2). COX-2 synthesizes prostaglandins such as PGE2 which promote proliferation and tumorigenesis by engaging G-protein-coupled prostaglandin E receptors (EP). Apigenin is a bioflavonoid that blocks mouse skin tumorigenesis induced by the chemical carcinogens, 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). However, the effect of apigenin on the COX-2 pathway has not been examined in the DMBA/TPA skin tumor model. In the present study, apigenin decreased tumor multiplicity and incidence in DMBA/TPA-treated SKH-1 mice. Analysis of the non-tumor epidermis revealed that apigenin reduced COX-2, PGE2, EP1, and EP2 synthesis and also increased terminal differentiation. In contrast, apigenin did not inhibit the COX-2 pathway or promote terminal differentiation in the tumors. Since fewer tumors developed in apigenin-treated animals which contained reduced epidermal COX-2 levels, our data suggest that apigenin may avert skin tumor development by blocking COX-2.

Gene regulation of filaggrin and other skin barrier proteins via aryl hydrocarbon receptor

Aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor that binds to structurally diverse chemicals including dioxins, coal tar, flavonoids and tryptophan photoproducts. Upon ligation, cytoplasmic AHR translocates to the nucleus, heterodimerizes with aryl hydrocarbon receptor nuclear translocator and mediates numerous biological effects by inducing the transcription of various AHR-responsive genes such as epidermal barrier proteins. The activation of AHR usually generates oxidative stress. However, AHR also mediates antioxidant signaling by a plethora of ligands via nuclear factor-erythroid 2-related factor-2. Both oxidative and antioxidant ligands upregulate the expression of the filaggrin gene. We review the role of AHR signaling in the gene regulation of epidermal barrier proteins.

Apigenin induces dermal collagen synthesis via smad2/3 signaling pathway

Decrease in fibroblast-produced collagen has been proven to be the pivotal cause of skin aging, but there is no satisfactory drug which directly increases dermal thickness and collage density. Here we found that a flavonoid natural product, apigenin, could significantly increase collagen synthesis. NIH/3T3 and primary human dermal fibroblasts (HDFs) were incubated with various concentrations of apigenin, with dimethyl sulfoxide (DMSO) serving as the negative control. Real-time reverse-transcription polymerase chain reaction (PCR), Western Blot, and Toluidine blue staining demonstrated that apigenin stimulated type-I and type-III collagen synthesis of fibroblasts on the mRNA and protein levels. Meanwhile, apigenin did not induce expression of alpha smooth muscle actin (α-SMA) in vitro and in vivo, a fibrotic marker in living tissues. Then the production of collagen was confirmed by Masson’s trichrome stain, Picrosirius red stain and immunohistochemistry in mouse models. We also clarified that this compound induced collagen synthesis by activating smad2/3 signaling pathway. Taken together, without obvious influence on fibroblasts’ apoptosis and viability, apigenin could promote the type-I and type-III collagen synthesis of dermal fibroblasts in vitro and in vivo, thus suggesting that apigenin may serve as a potential agent for esthetic and reconstructive skin rejuvenation.

Topical hesperidin prevents glucocorticoid-induced abnormalities in epidermal barrier function in murine skin

Systemic and topical glucocorticoids (GC) can cause significant adverse effects not only on the dermis, but also on epidermal structure and function. In epidermis, a striking GC-induced alteration in permeability barrier function occurs that can be attributed to an inhibition of epidermal mitogenesis, differentiation and lipid production. As prior studies in normal hairless mice demonstrated that topical applications of a flavonoid ingredient found in citrus, hesperidin, improve epidermal barrier function by stimulating epidermal proliferation and differentiation, we assessed here whether its topical applications could prevent GC-induced changes in epidermal function in murine skin and the basis for such effects. When hairless mice were co-treated topically with GC and 2% hesperidin twice-daily for 9 days, hesperidin co-applications prevented the expected GC-induced impairments of epidermal permeability barrier homoeostasis and stratum corneum (SC) acidification. These preventive effects could be attributed to a significant increase in filaggrin expression, enhanced epidermal β-glucocerebrosidase activity and accelerated lamellar bilayer maturation, the last two likely attributable to a hesperidin-induced reduction in stratum corneum pH. Furthermore, co-applications of hesperidin with GC largely prevented the expected GC-induced inhibition of epidermal proliferation. Finally, topical hesperidin increased epidermal glutathione reductase mRNA expression, which could counteract multiple functional negative effects of GC on epidermis. Together, these results show that topical hesperidin prevents GC-induced epidermal side effects by divergent mechanisms.