An environmental contaminant, benzo(a)pyrene, induces oxidative stress-mediated interleukin-8 production in human keratinocytes via the aryl hydrocarbon receptor signaling pathway

Air pollution and skin diseases: A comprehensive evaluation of the associated mechanism

Air pollutants deteriorate the survival environment and endanger human health around the world. A large number of studies have confirmed that air pollution jeopardizes multiple organs, such as the cardiovascular, respiratory, and central nervous systems. Skin is the largest organ and the first barrier that protects us from the outside world. Air pollutants such as particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs) will affect the structure and function of the skin and bring about the development of inflammatory skin diseases (atopic dermatitis (AD), psoriasis), skin accessory diseases (acne, alopecia), auto-immune skin diseases (cutaneous lupus erythematosus(CLE) scleroderma), and even skin tumors (melanoma, basal cell carcinoma (BCC), squamous-cell carcinoma (SCC)). Oxidative stress, skin barrier damage, microbiome dysbiosis, and skin inflammation are the pathogenesis of air pollution stimulation. In this review, we summarize the current evidence on the effects of air pollution on skin diseases and possible mechanisms to provide strategies for future research.

Tryptophan, an important link in regulating the complex network of skin immunology response in atopic dermatitis

Atopic dermatitis (AD) is a common chronic relapsing inflammatory skin disease, of which the pathogenesis is a complex interplay between genetics and environment. Although the exact mechanisms of the disease pathogenesis remain unclear, the immune dysregulation primarily involving the Th2 inflammatory pathway and accompanied with an imbalance of multiple immune cells is considered as one of the critical etiologies of AD. Tryptophan metabolism has long been firmly established as a key regulator of immune cells and then affect the occurrence and development of many immune and inflammatory diseases. But the relationship between tryptophan metabolism and the pathogenesis of AD has not been profoundly discussed throughout the literatures. Therefore, this review is conducted to discuss the relationship between tryptophan metabolism and the complex network of skin inflammatory response in AD, which is important to elucidate its complex pathophysiological mechanisms, and then lead to the development of new therapeutic strategies and drugs for the treatment of this frequently relapsing disease.

Exosomes released by environmental pollutant-stimulated Keratinocytes/PBMCs can trigger psoriatic inflammation in recipient cells via the AhR signaling pathway

Introduction: Exosomes, pivotal in intercellular communication during skin disease pathogenesis, have garnered substantial attention. However, the impact of environmental pollutants, such as benzo[a]pyrene (BaP) and 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), on exosome release amid inflammatory skin diseases remains unexplored. This study addresses this gap by examining the influence of BaP and TCDD on exosome function, specifically focusing on immune-related pathway alterations in normal recipient keratinocytes and peripheral blood mononuclear cells (PBMCs). Methods: HaCaT cells were treated with exosomes from BaP- or TCDD-treated keratinocytes. Proinflammatory cytokines and chemokines, including TNF-α, IL-1β, IL-6, IL-8, CXCL1, and CXCL5, were assessed. The involvement of the p65NF-κB/p38MAPK/ERK signaling pathway in recipient keratinocytes was investigated. Aryl hydrocarbon receptor (AhR) silencing was employed to elucidate its role in mediating the proinflammatory response induced by exosomes from BaP- or TCDD-treated keratinocytes. Results and discussion: Treatment with exosomes from BaP- or TCDD-treated keratinocytes induced a significant increase in proinflammatory cytokines and chemokines in HaCaT cells. The upregulation implicated the p65NF-κB/p38MAPK/ERK signaling pathway. AhR silencing attenuated this response, suggesting a role for AhR in mediating this response. In PBMCs from healthy controls, exosomes from BaP-stimulated PBMCs of psoriatic patients led to increased expression of proinflammatory cytokines and modulation of Th1/Th17 cell distribution via AhR activation. These findings unveil a novel dimension in the interplay between environmental xenobiotic agents (BaP and TCDD) and exosomal functions. The study establishes their influence on psoriatic inflammatory responses, shedding light on the underlying mechanisms mediated through the AhR signaling pathway in recipient keratinocytes and PBMCs.

Promoting New Approach Methodologies (NAMs) for research on skin color changes in response to environmental stress factors: tobacco and air pollution

Aging is one of the most dynamic biological processes in the human body and is known to carry significant impacts on individuals' self-esteem. Skin pigmentation is a highly heritable trait made possible by complex, strictly controlled cellular and molecular mechanisms. Genetic, environmental and endocrine factors contribute to the modulation of melanin's amount, type and distribution in the skin layers. One of the hallmarks of extrinsic skin aging induced by environmental stress factors is the alteration of the constitutive pigmentation pattern clinically defined as senile lentigines and/or melasma or other pigmentary dyschromias. The complexity of pollutants and tobacco smoke as environmental stress factors warrants a thorough understanding of the mechanisms by which they impact skin pigmentation through repeated and long-term exposure. Pre-clinical and clinical studies demonstrated that pollutants are known to induce reactive oxygen species (ROS) or inflammatory events that lead directly or indirectly to skin hyperpigmentation. Another mechanistic direction is provided by Aryl hydrocarbon Receptors (AhR) which were shown to mediate processes leading to skin hyperpigmentation in response to pollutants by regulation of melanogenic enzymes and transcription factors involved in melanin biosynthesis pathway. In this context, we will discuss a diverse range of New Approach Methodologies (NAMs) capable to provide mechanistic insights of the cellular and molecular pathways involved in the action of environmental stress factors on skin pigmentation and to support the design of raw ingredients and formulations intended to counter their impact and of any subsequently needed clinical studies.

Implications of xenobiotic-response element(s) and aryl hydrocarbon receptor in health and diseases

The effect of air pollution on public health is severely detrimental. In humans; the physiological response against pollutants is mainly elicited via the activation of aryl hydrocarbon receptor (AhR). It acts as a prime sensor of xenobiotic chemicals, also functioning as a transcription factor regulating a variety of gene expressions. Along with AhR, another pivotal element of the pollution stress pathway is Xenobiotic Response Elements (XREs). XRE, as studied are some conserved sequences in the DNA, responsible for the physiological response against pollutants. XRE is present at the upstream of the inducible target genes of AhR and it regulates the function of the AhR. XRE(s) are highly conserved in species as it has only eight specific sequences found so far in humans, mice, and rats. Inhalation of toxicants like dioxins, gaseous industrial effluents, and smoke from burning fuel and tobacco leads to predominant damage to the lungs. However, scientists are exploring the involvement of AhR in chronic diseases for example chronic obstructive pulmonary disease (COPD) and also other lethal diseases like lung cancer. In this review, we summarise what is known at this time about the roles played by the XRE and AhR in our molecular systems that have a defined control in the normal maintenance of homeostasis as well as dysfunctions.

Targeting the aryl hydrocarbon receptor by gut phenolic metabolites: A strategy towards gut inflammation

The Aryl Hydrocarbon Receptor (AHR) is a ligand-dependent transcription factor able to control complex transcriptional processes in several cell types, which has been correlated with various diseases, including inflammatory bowel diseases (IBD). Numerous studies have described different compounds as ligands of this receptor, like xenobiotics, natural compounds, and several host-derived metabolites. Dietary (poly)phenols have been studied regarding their pleiotropic activities (e.g., neuroprotective and anti-inflammatory), but their AHR modulatory capabilities have also been considered. However, dietary (poly)phenols are submitted to extensive metabolism in the gut (e.g., gut microbiota). Thus, the resulting gut phenolic metabolites could be key players modulating AHR since they are the ones that reach the cells and may exert effects on the AHR throughout the gut and other organs. This review aims at a comprehensive search for the most abundant gut phenolic metabolites detected and quantified in humans to understand how many have been described as AHR modulators and what could be their impact on inflammatory gut processes. Even though several phenolic compounds have been studied regarding their anti-inflammatory capacities, only 1 gut phenolic metabolite, described as AHR modulator, has been evaluated on intestinal inflammatory models. Searching for AHR ligands could be a novel strategy against IBD.

Environmental polycyclic aromatic hydrocarbon exposure is associated with low back pain

Several studies have assessed the influence of several often-ignored environmental factors on low back pain (LBP), but the effects of environmental polycyclic aromatic hydrocarbon (PAH) exposure on LBP are unclear. During the 2001-2004 cycle of the National Health and Nutrition Examination Survey (NHANES), our study was given to a representative sample of US participants older than 20 (N = 2743). Environmental PAH exposure was calculated using urinary PAH metabolite concentrations. Weighted logistic regression was performed to assess the connection between PAH levels and LBP, with mediation analysis utilised to explore the underlying mechanism. Levels of 1-hydroxynaphthalene (1-OHNa), 2-hydroxynaphthalene (2-OHNa) and total PAHs had a statistically significant positive association with LBP. The odds ratios per 1-unit increase for log-transformed levels of urinary 1-OHNa, 2-OHNa, and total PAHs with LBP were 1.01 (95% CI 1.02-1.19), 1.19 (95% CI 1.04-1.36) and 1.16 (95% CI 1.03-1.32), respectively. The results revealed a strong dose-response association between 1-OHNa, 2-OHNa, total PAHs, and LBP risk. Subgroup analysis indicated that 2&3-OHPh may increase the risk of LBP in the lower family income subgroup. Gamma-glutamyl transaminase (GGT), known as a biomarker of oxidative stress, was strongly related to PAHs. The relationship between total PAHs and LBP was mediated in part by GGT. Our study demonstrates associations between environmental PAH exposure and LBP that need more research to determine the precise effects of various PAH compounds on LBP.

Galactomyces Ferment Filtrate Potentiates an Anti-Inflammaging System in Keratinocytes

Skincare products play a crucial role in preventing the dry skin induced by various causes. Certain ingredients can help to improve the efficacy of skincare products. Galactomyces ferment filtrate (GFF) is such a functional ingredient. Its use originated from the empirical observation that the hands of sake brewers who deal with yeast fermentation retain a beautiful and youthful appearance. Consequently, skincare products based on GFF are widely used throughout the world. Recent studies have demonstrated that GFF activates an aryl hydrocarbon receptor (AHR) and upregulates the expression of filaggrin, a pivotal endogenous source of natural moisturizing factors, in epidermal keratinocytes. It also activates nuclear factor erythroid-2-related factor 2 (NRF2), the antioxidative master transcription factor, and exhibits potent antioxidative activity against oxidative stress induced by ultraviolet irradiation and proinflammatory cytokines, which also accelerate inflammaging. GFF-mediated NRF2 activation downregulates the expression of CDKN2A, which is known to be overexpressed in senescent keratinocytes. Moreover, GFF enhances epidermal terminal differentiation by upregulating the expression of caspase-14, claudin-1, and claudin-4. It also promotes the synthesis of the antiinflammatory cytokine IL-37 and downregulates the expression of proallergic cytokine IL-33 in keratinocytes. In addition, GFF downregulates the expression of the CXCL14 and IL6R genes, which are involved in inflammaging. These beneficial properties might underpin the potent barrier-protecting and anti-inflammaging effects of GFF-containing skin formulae.

Potential Therapeutic Skin Microbiomes Suppressing Staphylococcus aureus-Derived Immune Responses and Upregulating Skin Barrier Function-Related Genes via the AhR Signaling Pathway

Disruption of the skin microbial balance can exacerbate certain skin diseases and affect prognosis and treatment. Changes in the distribution and prevalence of certain microbial species on the skin, such as Staphylococcus aureus (SA), can impact the development of severe atopic dermatitis (AD) or psoriasis (Pso). A dysfunctional skin barrier develops in AD and Pso due to SA colonization, resulting in keratinization and chronic or progressive chronic inflammation. Disruption of the skin barrier following SA colonization can elevate the production of T helper 2 (Th2)-derived cytokines, which can cause an imbalance in Th1, Th2, and Th17 cells. This study examined the ability of potential therapeutic skin microbiomes, such as Cutibacterium avidum R-CH3 and Staphylococcus hominis R9, to inhibit SA biofilm formation and restore skin barrier function-related genes through the activation of the aryl hydrocarbon receptor (AhR) and the nuclear factor erythroid-2-related factor 2 (Nrf2) downstream target. We observed that IL-4/IL-13-induced downregulation of FLG, LOR, and IVL induced by SA colonization could be reversed by dual AhR/Nrf2 activation. Further, OVOL1 expression may be modulated by functional microbiomes via dual AhR/Nrf2 activation. Our results suggest that our potential therapeutic skin microbiomes can prevent SA-derived Th2-biased skin barrier disruption via IL-13 and IL-4-dependent FLG deregulation, STAT3 activation, and AhR-mediated STAT6 expression.

Aryl Hydrocarbon Receptor in Oxidative Stress as a Double Agent and Its Biological and Therapeutic Significance

The aryl hydrocarbon receptor (AhR) has long been implicated in the induction of a battery of genes involved in the metabolism of xenobiotics and endogenous compounds. AhR is a ligand-activated transcription factor necessary for the launch of transcriptional responses important in health and disease. In past decades, evidence has accumulated that AhR is associated with the cellular response to oxidative stress, and this property of AhR must be taken into account during investigations into a mechanism of action of xenobiotics that is able to activate AhR or that is susceptible to metabolic activation by enzymes encoded by the genes that are under the control of AhR. In this review, we examine various mechanisms by which AhR takes part in the oxidative-stress response, including antioxidant and prooxidant enzymes and cytochrome P450. We also show that AhR, as a participant in the redox balance and as a modulator of redox signals, is being increasingly studied as a target for a new class of therapeutic compounds and as an explanation for the pathogenesis of some disorders.

Integrative analysis to explore the biological association between environmental skin diseases and ambient particulate matter

Although numerous experimental studies have suggested a significant association between ambient particulate matter (PM) and respiratory damage, the etiological relationship between ambient PM and environmental skin diseases is not clearly understood. Here, we aimed to explore the association between PM and skin diseases through biological big data analysis. Differential gene expression profiles associated with PM and environmental skin diseases were retrieved from public genome databases. The co-expression among them was analyzed using a text-mining-based network analysis software. Activation/inhibition patterns from RNA-sequencing data performed with PM_2.5-treated normal human epidermal keratinocytes (NHEK) were overlapped to select key regulators of the analyzed pathways. We explored the adverse effects of PM on the skin and attempted to elucidate their relationships using public genome data. We found that changes in upstream regulators and inflammatory signaling networks mediated by MMP-1, MMP-9, PLAU, S100A9, IL-6, and S100A8 were predicted as the key pathways underlying PM-induced skin diseases. Our integrative approach using a literature-based co-expression analysis and experimental validation not only improves the reliability of prediction but also provides assistance to clarify underlying mechanisms of ambient PM-induced dermal toxicity that can be applied to screen the relationship between other chemicals and adverse effects.

Antioxidant Activities and Mechanisms of Tomentosin in Human Keratinocytes

Tomentosin, one of natural sesquiterpene lactones sourced from Inula viscosa L., exerts therapeutic effects in various cell types. Here, we investigated the antioxidant activities and the underlying action mechanisms of tomentosin in HaCaT cells (a human keratinocyte cell line). Specifically, we examined the involvement of tomentosin in aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathways. Treatment with tomentosin for up to 60 min triggered the production of reactive oxygen species (ROS), whereas treatment for 4 h or longer decreased ROS production. Tomentosin treatment also induced the nuclear translocation of Nrf2 and upregulated the expression of Nrf2 and its target genes. These data indicate that tomentosin induces ROS production at an early stage which activates the Nrf2 pathway by disrupting the Nrf2–Keap1 complex. However, at a later stage, ROS levels were reduced by tomentosin-induced upregulation of antioxidant genes. In addition, tomentosin induced the phosphorylation of mitogen-activated protein kinases (MAPKs) including p38 MAPK and c-Jun N-terminal kinase (JNK). SB203580 (a p38 MAPK inhibitor) and SP600125 (a JNK inhibitor) attenuated the tomentosin-induced phosphorylation of Nrf2, suggesting that JNK and p38 MAPK signaling pathways can contribute to the tomentosin-induced Nrf2 activation through phosphorylation of Nrf2. Furthermore, N-acetyl-_L-cysteine (NAC) treatment blocked both tomentosin-induced production of ROS and the nuclear translocation of Nrf2. These data suggest that tomentosin-induced Nrf2 signaling is mediated both by tomentosin-induced ROS production and the activation of p38 MAPK and JNK. Moreover, tomentosin inhibited the AhR signaling pathway, as evidenced by the suppression of xenobiotic-response element (XRE) reporter activity and the translocation of AhR into nucleus induced by urban pollutants, especially benzo[a]pyrene. These findings suggest that tomentosin can ameliorate skin damage induced by environmental pollutants.

Aryl Hydrocarbon Receptors: Evidence of Therapeutic Targets in Chronic Inflammatory Skin Diseases

The aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, is important for xenobiotic metabolism and binds to various endogenous and exogenous ligands present in the skin. AhR is known to be associated with diseases in various organs; however, its functions in chronic inflammatory skin diseases, such as atopic dermatitis (AD) and psoriasis (PS), have recently been elucidated. Here, we discuss the molecular mechanisms of AhR related to chronic inflammatory skin diseases, such as AD and PS, and the mechanisms of action of AhR on the skin immune system. The importance of AhR molecular biological pathways, clinical features in animal models, and AhR ligands in skin diseases need to be investigated. In conclusion, the therapeutic effects of AhR ligands are demonstrated based on the relationship between AhR and skin diseases. Nevertheless, further studies are required to elucidate the detailed roles of AhR in chronic inflammatory skin diseases.

Antioxidant Effects of Korean Propolis in HaCaT Keratinocytes Exposed to Particulate Matter 10

Air pollution causes oxidative stress that leads to inflammatory diseases and premature aging of the skin. The purpose of this study was to examine the antioxidant effect of Korean propolis on oxidative stress in human epidermal HaCaT keratinocytes exposed to particulate matter with a diameter of less than 10 μm (PM₁₀). The total ethanol extract of propolis was solvent-fractionated with water and methylene chloride to divide into a hydrophilic fraction and a lipophilic fraction. The lipophilic fraction of propolis was slightly more cytotoxic, and the hydrophilic fraction was much less cytotoxic than the total extract. The hydrophilic fraction did not affect the viability of cells exposed to PM₁₀, but the total propolis extract and the lipophilic fraction aggravated the toxicity of PM₁₀. The total extract and hydrophilic fraction inhibited PM₁₀-induced ROS production and lipid peroxidation in a concentration-dependent manner, whereas the lipophilic fraction did not show such effects. High-performance liquid chromatography with photodiode array detection (HPLC-DAD) analysis showed that the hydrophilic fraction contained phenylpropanoids, such as caffeic acid, p-coumaric acid, and ferulic acid, whereas the lipophilic faction contained caffeic acid phenethyl ester (CAPE). The former three compounds inhibited PM₁₀-induced ROS production, lipid peroxidation, and/or glutathione oxidation, and ferulic acid was the most effective among them, but CAPE exhibited cytotoxicity and aggravated the toxicity of PM₁₀. This study suggests that Korean propolis, when properly purified, has the potential to be used as a cosmetic material that helps to alleviate the skin toxicity of air pollutants.

Modeling of Temporal Exposure to the Ambient Environment and Eczema Severity

Atopic eczema is a common and complex disease. Missing genetic hereditability and increasing prevalence in industrializing nations point toward an environmental driver. We investigated the temporal association of weather and pollution parameters with eczema severity. This cross-sectional clinical study was performed between May 2018 and March 2020 and is part of the Tower Hamlets Eczema Assessment. All participants had a diagnosis of eczema, lived in East London, were of Bangladeshi ethnicity, and were aged <31 years. The primary outcome was the probability of having an Eczema Area and Severity Index score > 10 after previous ambient exposure to commonly studied meteorological variables and pollutants. There were 430 participants in the groups with Eczema Area and Severity Index ≤ 10 and 149 in those with Eczema Area and Severity Index > 10. Using logistic generalized additive models and a model selection process, we found that tropospheric ozone averaged over the preceding 270 days was strongly associated with eczema severity alongside the exposure to fine particles with diameters of 2.5 μm or less (fine particulate matter) averaged over the preceding 120 days. In our models and analyses, fine particulate matter appeared to largely act in a supporting role to ozone. We show that long-term exposure to ground-level ozone at high levels has the strongest association with eczema severity.

Siegesbeckiae Herba Extract and Chlorogenic Acid Ameliorate the Death of HaCaT Keratinocytes Exposed to Airborne Particulate Matter by Mitigating Oxidative Stress

Airborne particulate matter with a size of 10 μm or less (PM₁₀) can cause oxidative damages and inflammatory reactions in the skin. This study was conducted to discover natural products that are potentially useful in protecting the skin from PM₁₀. Among the hot water extracts of a total of 23 medicinal plants, Siegesbeckiae Herba extract (SHE), which showed the strongest protective effect against PM₁₀ cytotoxicity, was selected, and its mechanism of action and active constituents were explored. SHE ameliorated PM₁₀-induced cell death, lactate dehydrogenase (LDH) release, lipid peroxidation, and reactive oxygen species (ROS) production in HaCaT cells. SHE decreased the expression of KEAP1, a negative regulator of NRF2, and increased the expression of NRF2 target genes, such as HMOX1 and NQO1. SHE selectively induced the enzymes involved in the synthesis of GSH (GCL-c and GCL-m), the regeneration of GSH (GSR and G6PDH), and GSH conjugation of xenobiotics (GSTκ1), rather than the enzymes that directly scavenge ROS (SOD1, CAT, and GPX1). SHE increased the cellular content of GSH and mitigated the oxidation of GSH to GSSG caused by PM₁₀ exposure. Of the solvent fractions of SHE, the n-butyl alcohol (BA) fraction ameliorated cell death in both the absence and presence of PM₁₀. The BA fraction contained a high amount of chlorogenic acid. Chlorogenic acid reduced PM₁₀-induced cell death, LDH release, and ROS production. This study suggests that SHE protects cells from PM₁₀ toxicity by increasing the cellular antioxidant capacity and that chlorogenic acid may be an active phytochemical of SHE.

Upregulation of CCL7, CCL20, CXCL2, IL-1β, IL-6 and MMP-9 in Skin Samples of PCB Exposed Individuals-A Preliminary Study

Polychlorinated biphenyls (PCBs) are well known immunotoxic and carcinogenic compounds. Although cutaneous symptoms are the hallmark of exposure to these compounds, exact pathophysiologic mechanisms are not well understood. We took skin biopsies from moderately high PCB exposed workers (n = 25) after an informed consent and investigated the expression of immunological markers such as CCL-7, CCL-20, CXCL2, IL-1β and IL-6, as well as the matrix metalloproteinase MMP-9, EPGN and NRF2 by RT-qPCR, and compared expression levels with plasma PCB levels. Statistical analyses showed a significant correlation between CCL-20, CXCL2, IL-6, IL-1β, CCL-7 and MMP-9 and PCB serum levels. EPGN and NRF2 were not correlated to PCB levels in the blood. We found a significant correlation of genes involved in autoimmune, auto-inflammatory and carcinogenesis in skin samples of PCB exposed individuals with elevated plasma PCB levels. Confirmation of these findings needs to be performed in bigger study groups and larger gen-sets, including multiple housekeeping genes. Further study needs to be performed to see whether a chronical exposure to these and similar compounds can cause higher incidence of malignancies and inflammatory disease.

Protective Effects of Maclurin against Benzo[a]pyrene via Aryl Hydrocarbon Receptor and Nuclear Factor Erythroid 2-Related Factor 2 Targeting

Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon formed during the incomplete combustion of organic matter, has harmful effects. Therefore, much research is ongoing to develop agents that can mitigate the effects of B[a]P. The aim of this study was to examine the effect of maclurin, one component of the branches of Morus alba L., on the B[a]P-induced effects in HaCaT cells, a human keratinocyte cell line. Maclurin treatment inhibited aryl hydrocarbon receptor (AHR) signaling as evidenced by reduced xenobiotic response element (XRE) reporter activity, decreased expression of cytochrome P450 1A1 (CYP1A1), and reduced nuclear translocation of AHR. The B[a]P-induced dissociation of AHR from AHR-interacting protein (AIP) was suppressed by maclurin. Maclurin also inhibited the production of intracellular reactive oxygen species (ROS) induced by B[a]P. In addition, the antioxidant property of maclurin itself was demonstrated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Furthermore, maclurin activated antioxidant response element (ARE) signaling through enhancement of ARE luciferase reporter activity and the expression of ARE-dependent genes including nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase-1 (HO-1). Nrf2 activation and its nuclear translocation were promoted by maclurin through p38 MAPK activation. These data indicate that maclurin had antagonistic activity against B[a]P effects through activation of Nrf2-mediated signaling and inhibition of AHR signaling and, suggesting its potential in protecting from harmful B[a]P-containing pollutants.

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.

Metalloproteinase 1 downregulation in neurofibromatosis 1: Therapeutic potential of antimalarial hydroxychloroquine and chloroquine

Neurofibromatosis type 1 is an autosomal dominant genetic disorder caused by mutation in the neurofibromin 1 (NF1) gene. Its hallmarks are cutaneous findings including neurofibromas, benign peripheral nerve sheath tumors. We analyzed the collagen and matrix metalloproteinase 1 (MMP1) expression in Neurofibromatosis 1 cutaneous neurofibroma and found excessive expression of collagen and reduced expression of MMP1. To identify new therapeutic drugs for neurofibroma, we analyzed phosphorylation of components of the Ras pathway, which underlies NF1 regulation, and applied treatments to block this pathway (PD184352, U0126, and rapamycin) and lysosomal processes (chloroquine (CQ), hydroxychloroquine (HCQ), and bafilomycin A (BafA)) in cultured Neurofibromatosis 1 fibroblasts. We found that downregulation of the MMP1 protein was a key abnormal feature in the neurofibromatosis 1 fibroblasts and that the decreased MMP1 was restored by the lysosomal blockers CQ and HCQ, but not by the blockers of the Ras pathway. Moreover, the MMP1-upregulating activity of those lysosomal blockers was dependent on aryl hydrocarbon receptor (AHR) activation and ERK phosphorylation. Our findings suggest that lysosomal blockers are potential candidates for the treatment of Neurofibromatosis 1 neurofibroma.

Molecule-Resolved Visualization of Particulate Matter on Human Skin Using Multimodal Nonlinear Optical Imaging

Precise measurement of particulate matter (PM) on skin is important for managing and preventing PM-related skin diseases. This study aims to directly visualize the deposition and penetration of PM into human skin using a multimodal nonlinear optical (MNLO) imaging system. We successfully obtained PM particle signals by merging two different sources, C–C vibrational frequency and autofluorescence, while simultaneously visualizing the anatomical features of the skin via keratin, collagen, and elastin. As a result, we found morphologically dependent PM deposition, as well as increased deposition following disruption of the skin barrier via tape-stripping. Furthermore, PM penetrated more and deeper into the skin with an increase in the number of tape-strippings, causing a significant increase in the secretion of pro-inflammatory cytokines. Our results suggest that MNLO imaging could be a useful technique for visualizing and quantifying the spatial distribution of PM in ex vivo human skin tissues.

Rapamycin Alleviates 2,3,7,8-Tetrachlorodibenzo-p-dioxin-Induced Aggravated Dermatitis in Mice with Imiquimod-Induced Psoriasis-Like Dermatitis by Inducing Autophagy

Recently, the mTOR signaling has emerged as an important player in the pathogenesis of psoriasis. We previously found that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced psoriatic skin inflammation was related to the inhibition of autophagy in keratinocytes. However, the effects and detailed molecular mechanisms of the mTOR inhibitor rapamycin and TCDD on psoriasis in vivo remain to be elucidated. In this study, we aimed to evaluate the effects of rapamycin and TCDD on skin lesions in imiquimod (IMQ)-induced psoriasis using a mouse model. TCDD aggravated skin inflammation in an IMQ-induced psoriatic mouse model. Furthermore, TCDD increased the expression of aryl hydrocarbon receptor (AHR), CYP1A1, proinflammatory cytokines, oxidative stress markers (NADPH oxidase (Nox) 2, Nox4), and phosphorylated P65NF-ĸB, whereas the expression of autophagy-related factors and the antioxidant marker nuclear factor-erythroid 2-related factor 2 (NRF2) decreased. Rapamycin reduced the aggravated skin inflammation induced by TCDD and restored TCDD-induced autophagy suppression and the increase of AHR expression, oxidative stress, and inflammatory response in the skin lesions of a psoriatic mouse model. In conclusion, we demonstrated that rapamycin alleviates TCDD-induced aggravated dermatitis in mice with imiquimod-induced psoriasis-like dermatitis through AHR and autophagy modulation.

Oleanolic Acid Protects the Skin from Particulate Matter-Induced Aging

The role of particulate matter (PM) in health problems including cardiovascular diseases (CVD) and pneumonia is becoming increasingly clear. Polycyclic aromatic hydrocarbons, major components of PM, bind to aryl hydrocarbon receptor (AhRs) and promote the expression of CYP1A1 through the AhR pathway in keratinocytes. Activation of AhRs in skin cells is associated with cell differentiation in keratinocytes and inflammation, resulting in dermatological lesions. Oleanolic acid, a natural component of L. lucidum, also has anti-inflammation, anticancer, and antioxidant characteristics. Previously, we found that PM₁₀ induced the AhR signaling pathway and autophagy process in keratinocytes. Here, we investigated the effects of oleanolic acid on PM₁₀-induced skin aging. We observed that oleanolic acid inhibits PM₁₀-induced CYP1A1 and decreases the increase of tumor necrosis factor–alpha and interleukin 6 induced by PM₁₀. A supernatant derived from keratinocytes cotreated with oleanolic acid and PM₁₀ inhibited the release of matrix metalloproteinase 1 in dermal fibroblasts. Also, the AhR-mediated autophagy disruption was recovered by oleanolic acid. Thus, oleanolic acid may be a potential treatment for addressing PM₁₀-induced skin aging.

Mechanisms of Resorcinol Antagonism of Benzo[a]pyrene-Induced Damage to Human Keratinocytes

Benzo[a]pyrene (B[a]P) is a polycyclic aromatic hydrocarbon and ubiquitous environmental toxin with known harmful effects to human health. Abnormal phenotypes of keratinocytes are closely associated with their exposure to B[a]P. Resorcinol is a component of argan oil with reported anticancer activities, but its mechanism of action and potential effect on B[a]P damage to the skin is unknown. In this study, we investigated the effects of resorcinol on B[a]P-induced abnormal keratinocyte biology and its mechanisms of action in human epidermal keratinocyte cell line HaCaT. Resorcinol suppressed aryl hydrocarbon receptor (AhR) activity as evidenced by the inhibition of B[a]P-induced xenobiotic response element (XRE)-reporter activation and cytochrome P450 1A1 (CYP1A1) expression. In addition, resorcinol attenuated B[a]P-induced nuclear translocation of AhR, and production of ROS and pro-inflammatory cytokines. We also found that resorcinol increased nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activity. Antioxidant response element (ARE)-reporter activity and expression of ARE-dependent genes NAD(P)H dehydrogenase [quinone] 1 (NQO1), heme oxygenase-1 (HO-1) were increased by resorcinol. Consistently, resorcinol treatment induced nuclear localization of Nrf2 as seen by Western analysis. Knockdown of Nrf2 attenuated the resorcinol effects on ARE signaling, but knockdown of AhR did not affect resorcinol activation of Nrf2. This suggests that activation of antioxidant activity by resorcinol is not mediated by AhR. These results indicate that resorcinol is protective against effects of B[a]P exposure. The mechanism of action of resorcinol is inhibition of AhR and activation of Nrf2-mediated antioxidant signaling. Our findings suggest that resorcinol may have potential as a protective agent against B[a]P-containing pollutants.

A New Insight into the Potential Role of Tryptophan-Derived AhR Ligands in Skin Physiological and Pathological Processes

The aryl hydrocarbon receptor (AhR) plays a crucial role in environmental responses and xenobiotic metabolism, as it controls the transcription profiles of several genes in a ligand-specific and cell-type-specific manner. Various barrier tissues, including skin, display the expression of AhR. Recent studies revealed multiple roles of AhR in skin physiology and disease, including melanogenesis, inflammation and cancer. Tryptophan metabolites are distinguished among the groups of natural and synthetic AhR ligands, and these include kynurenine, kynurenic acid and 6-formylindolo[3,2-b]carbazole (FICZ). Tryptophan derivatives can affect and regulate a variety of signaling pathways. Thus, the interest in how these substances influence physiological and pathological processes in the skin is expanding rapidly. The widespread presence of these substances and potential continuous exposure of the skin to their biological effects indicate the important role of AhR and its ligands in the prevention, pathogenesis and progression of skin diseases. In this review, we summarize the current knowledge of AhR in skin physiology. Moreover, we discuss the role of AhR in skin pathological processes, including inflammatory skin diseases, pigmentation disorders and cancer. Finally, the impact of FICZ, kynurenic acid, and kynurenine on physiological and pathological processes in the skin is considered. However, the mechanisms of how AhR regulates skin function require further investigation.

Aryl Hydrocarbon Receptor and Dioxin-Related Health Hazards-Lessons from Yusho

Poisoning by high concentrations of dioxin and its related compounds manifests variable toxic symptoms such as general malaise, chloracne, hyperpigmentation, sputum and cough, paresthesia or numbness of the extremities, hypertriglyceridemia, perinatal abnormalities, and elevated risks of cancer-related mortality. Such health hazards are observed in patients with Yusho (oil disease in Japanese) who had consumed rice bran oil highly contaminated with 2,3,4,7,8-pentachlorodibenzofuran, polychlorinated biphenyls, and polychlorinated quaterphenyls in 1968. The blood concentrations of these congeners in patients with Yusho remain extremely elevated 50 years after onset. Dioxins exert their toxicity via aryl hydrocarbon receptor (AHR) through the generation of reactive oxygen species (ROS). In this review article, we discuss the pathogenic implication of AHR in dioxin-induced health hazards. We also mention the potential therapeutic use of herbal drugs targeting AHR and ROS in patients with Yusho.

The role of xenobiotics in triggering psoriasis

Psoriasis is a common inflammatory skin disease affecting approximately 2% of the world population. A complex interplay of genetic predisposition and risk factors contributes to the risk of its onset. Several xenobiotics have been implicated in the pathogenesis of psoriasis. Drugs are among the most investigated trigger factors; strong association with disease induction or exacerbation has been reported for β-blockers, lithium, NSAIDs and ACE inhibitors, all of which are commonly used in the management of various comorbidities in psoriasis patients. Furthermore, inhibitors of TNF have a well-documented potential for triggering new-onset psoriasis when used for other indications (e.g. Crohn's disease or rheumatoid arthritis), while post-marketing data have revealed the same association for ustekinumab. Several other drugs have been connected with psoriasis, but the evidence is less compelling. Smoking and alcohol have been reported to increase the risk for occurrence of psoriasis, but can also affect unfavorably the course of the disease and its response to treatment. Furthermore, exposure to secondhand smoke, especially in childhood, also mediates the risk. Emerging data now suggest that air pollution also has a detrimental effect on skin disease, including psoriasis, but this association needs further investigation. Understanding of the toxic effect of xenobiotics on the initiation and clinical course of psoriasis can contribute to its better control, as it can help with the avoidance of triggering factors and, in some cases, influence the success of pharmacological treatment. It, therefore, has an important place in the comprehensive management of psoriasis.

Regulation of Filaggrin, Loricrin, and Involucrin by IL-4, IL-13, IL-17A, IL-22, AHR, and NRF2: Pathogenic Implications in Atopic Dermatitis

Atopic dermatitis (AD) is an eczematous, pruritic skin disorder with extensive barrier dysfunction and elevated interleukin (IL)-4 and IL-13 signatures. The barrier dysfunction correlates with the downregulation of barrier-related molecules such as filaggrin (FLG), loricrin (LOR), and involucrin (IVL). IL-4 and IL-13 potently inhibit the expression of these molecules by activating signal transducer and activator of transcription (STAT)6 and STAT3. In addition to IL-4 and IL-13, IL-22 and IL-17A are probably involved in the barrier dysfunction by inhibiting the expression of these barrier-related molecules. In contrast, natural or medicinal ligands for aryl hydrocarbon receptor (AHR) are potent upregulators of FLG, LOR, and IVL expression. As IL-4, IL-13, IL-22, and IL-17A are all capable of inducing oxidative stress, antioxidative AHR agonists such as coal tar, glyteer, and tapinarof exert particular therapeutic efficacy for AD. These antioxidative AHR ligands are known to activate an antioxidative transcription factor, nuclear factor E2-related factor 2 (NRF2). This article focuses on the mechanisms by which FLG, LOR, and IVL expression is regulated by IL-4, IL-13, IL-22, and IL-17A. The author also summarizes how AHR and NRF2 dual activators exert their beneficial effects in the treatment of AD.

Additive effect of combined pollutants to UV induced skin OxInflammation damage. Evaluating the protective topical application of a cosmeceutical mixture formulation

Since the skin is one of the targets of the harmful effects of environmental insults, several studies have investigated the effects of outdoor stressors on cutaneous tissue. Ozone (O3), particulate matter (PM), and ultraviolet radiation (UV) have all been shown to induce skin damage through disruption of tissue redox homeostasis, resulting in the so called "OxInflammation" condition. However, few studies have explored whether these stressors can act synergistically in cutaneous tissues. In the present work, we evaluated whether O3, PM, and UV, which are the most common environmental skin insults, act synergistically in inducing skin damage, and whether this effect could be prevented through topical application of a cosmeceutical formulation mixture (CF Mix) containing 15% vitamin C (l-ascorbic acid), 1% vitamin E (α-tocopherol), and 0.5% ferulic acid. Human skin explants obtained from three different subjects were sequentially exposed to 200 mJ UV light, 0.25 ppm O3 for 2 h, and 30 min of diesel engine exhaust (DEE), alone or in combination for 4 days (time point D1 and D4). We observed a clear additive effect of O3 and DEE in combination with UV in increasing levels of several oxidative (4HNE, HO-1) and inflammatory (COX2, NF-κB) markers and loss of barrier-associated proteins, such as filaggrin and involucrin. Furthermore, daily topical pre-treatment with the CF Mix prevented upregulation of the inflammatory and oxidative markers and the loss of both involucrin and filaggrin. In conclusion, this study is the first to investigate the combined effects of three of the most harmful outdoor stressors on human skin and suggests that daily topical application may prevent pollution-induced skin damage.

Baicalein Inhibits Benzo[a]pyrene-Induced Toxic Response by Downregulating Src Phosphorylation and by Upregulating NRF2-HMOX1 System

Benzo[a]pyrene (BaP), a major environmental pollutant, activates aryl hydrocarbon receptor (AHR), induces its cytoplasmic-to-nuclear translocation and upregulates the production of cytochrome P450 1A1 (CYP1A1), a xenobiotic metabolizing enzyme which metabolize BaP. The BaP-AHR-CYP1A1 axis generates reactive oxygen species (ROS) and induces proinflammatory cytokines. Although the anti-inflammatory phytochemical baicalein (BAI) is known to inhibit the BaP-AHR-mediated CYP1A1 expression, its subcellular signaling remains elusive. In this study, normal human epidermal keratinocytes and HaCaT keratinocytes were treated with BAI, BaP, or BAI + BaP, and assessed for the CYP1A1 expression, antioxidative pathways, ROS generation, and proinflammatory cytokine expressions. BAI and BAI-containing herbal medicine Wogon and Oren-gedoku-to could inhibit the BaP-induced CYP1A1 expression. In addition, BAI activated antioxidative system nuclear factor-erythroid 2-related factor-2 (NRF2) and heme oxygenase 1 (HMOX1), leading the reduction of BaP-induced ROS production. The BaP-induced IL1A and IL1B was also downregulated by BAI. BAI inhibited the phosphorylation of Src, a component of AHR cytoplasmic complex, which eventually interfered with the cytoplasmic-to-nuclear translocation of AHR. These results indicate that BAI and BAI-containing herbal drugs may be useful for inhibiting the toxic effects of BaP via dual AHR-CYP1A1-inhibiting and NRF2-HMOX1-activating activities.

A novel water-in-oil emulsion with a lecithin-modified bentonite prevents skin damage from urban dust and cedar pollen

OBJECTIVE

Particulate matter (PM), such as air pollutants and pollens, are known to cause skin ageing through skin inflammation. It is important to develop formulations which protect the skin from PM. We previously developed a conventional water-in-oil emulsion with a synthetic surfactant, distearyldimonium chloride, modified bentonite (C-W/O), which protects skin from allergens. In the present study, we developed a novel water-in-oil emulsion with a natural surfactant, lecithin, modified bentonite (N-W/O).

METHODS

The microarray analysis was performed using total RNA extracted from a reconstructed human epidermis (RHE) stimulated with urban aerosols or cedar pollen for 6 h in order to develop an epidermal inflammation model by PM for the evaluation of topical formulations. We then compared the efficacy of N-W/O and C-W/O to prevent epidermal degradation. Tissues and culture media were collected 24 h after the urban aerosol or cedar pollen stimulation for a histological assay, and the quantification of MMP1 and IL-8 secretion.

RESULTS

The expression levels of proinflammatory cytokines and chemokines, such as IL1A and CXCL8, and matrix metalloproteinases, including MMP1, MMP3 and MMP9, were significantly up-regulated by the PM stimulation. As a result of ranking based on the pathway enrichment analysis, oxidative stress-related pathways, such as MAPK-mediated signalling, HIF-1 signalling, IL-1 signalling and ROS-induced cellular signalling, were ranked high in the urban dust- and cedar pollen-treated groups. A thickened stratum corneum, thinned vital layer and cleaved E-cadherin were observed by haematoxylin and eosin staining and immunohistochemical staining of E-cadherin in the PM treated groups. The secretion of MMP1 and IL-8 into the media was significantly increased by the PM stimulation. N-W/O prevented the degradation of epidermal integrity and secretion of inflammatory proteins more effectively than C-W/O.

CONCLUSION

The present results showed that N-W/O made using natural surfactant is useful at protecting skin from PM, such as urban aerosols and cedar pollen.

Aryl Hydrocarbon Receptor Activation Downregulates IL-33 Expression in Keratinocytes via Ovo-Like 1

Background: IL-33, one of the IL-1 superfamily cytokines, has been shown to be associated with pruritus and inflammation in atopic dermatitis (AD). Furthermore, IL-33 production derived from keratinocytes reportedly has a crucial role in the development of AD; however, the mechanism of IL-33 expression has not been fully understood. Methods: We analyzed IL-33 expression in normal human epidermal keratinocytes (NHEKs) treated with IL-4. Results: IL-4 induced the upregulation of IL-33 expression in NHEKs. Based on the findings 1) that ovo-like 1 (OVOL1), a susceptible gene of AD, upregulates filaggrin (FLG) and loricrin (LOR) expression in NHEKs and 2) that reduced expression of FLG and LOR leads to production of IL-1 superfamily cytokines, we examined the involvement of OVOL1 in IL-33 expression in NHEKs. Knockdown of OVOL1 induced upregulation of IL-33 expression. Moreover, because Glyteer, an activator of aryl hydrocarbon receptor (AHR), reportedly upregulates OVOL1 expression, we examined whether treatment with Glyteer inhibited IL-33 expression in NHEKs. Treatment with Glyteer inhibited IL-4-induced upregulation of IL-33 expression, which was canceled by knockdown of either AHR or OVOL1. Conclusions: Activation of the AHR-OVOL1 axis inhibits IL-4-induced IL-33 expression, which could be beneficial for the treatment of AD.

Metabolism and genotoxicity of polycyclic aromatic hydrocarbons in human skin explants: mixture effects and modulation by sunlight

Cutaneous exposure to carcinogenic polycyclic aromatic hydrocarbons (PAH) occurs frequently in the industrialized workplace. In the present study, we addressed this topic in a series of experiments using human skin explants and organic extracts of relevant industrial products. PAH mixtures were applied topically in volumes containing either 10 or 1 nmol B[a]P. We first observed that although mixtures were very efficient at inducing expression of CYP450 1A1, 1A2, and 1B1, formation of adducts of PAH metabolites to DNA, like those of benzo[a]pyrene diol epoxide (BPDE), was drastically reduced as the complexity of the surrounding matrix increased. Interestingly, observation of a nonlinear, dose-dependent response with the least complex mixture suggested the existence of a threshold for this inhibitory effect. We then investigated the impact of simulated sunlight (SSL) on the effects of PAH in skin. SSL was found to decrease the expression of CYP450 genes when applied either after or more efficiently before PAH treatment. Accordingly, the level of DNA-BPDE adducts was reduced in skin samples exposed to both PAH and SSL. The main conclusion of our work is that both increasing chemical complexity of the mixtures and co-exposure to UV radiation decreased the production of adducts between DNA and PAH metabolites. Such results must be taken into account in risk management.

Chloracne and Hyperpigmentation Caused by Exposure to Hazardous Aryl Hydrocarbon Receptor Ligands

Dioxins and dioxin-like compounds are environmental pollutants that are hazardous to human skin. They can be present in contaminated soil, water, and air particles (such as ambient PM_2.5). Exposure to a high concentration of dioxins induces chloracne and hyperpigmentation. These chemicals exert their toxic effects by activating the aryl hydrocarbon receptor (AHR) which is abundantly expressed in skin cells, such as keratinocytes, sebocytes, and melanocytes. Ligation of AHR by dioxins induces exaggerated acceleration of epidermal terminal differentiation (keratinization) and converts sebocytes toward keratinocyte differentiation, which results in chloracne formation. AHR activation potently upregulates melanogenesis in melanocytes by upregulating the expression of melanogenic enzymes, which results in hyperpigmentation. Because AHR-mediated oxidative stress contributes to these hazardous effects, antioxidative agents may be potentially therapeutic for chloracne and hyperpigmentation.

Antagonizing Effects of Clematis apiifolia DC. Extract against Benzo[a]pyrene-Induced Damage to Human Keratinocytes

Background. Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon present in the atmosphere, has cytotoxic and carcinogenic effects. There have been no reports to demonstrate involvement of Clematis apiifolia DC. extract (CAE) in B[a]P-induced effects. This study was conducted to investigate the effect of CAE on B[a]P-induced effects and to elucidate its mechanism of action in HaCaT human keratinocytes. CAE inhibited aryl hydrocarbon receptor (AhR) signaling by decreasing both XRE reporter activity and expression of cytochrome P450 1A1 (CYP1A1) induced by B[a]P treatment in HaCaT cells. We also found that B[a]P-induced nuclear translocation of AhR and production of reactive oxygen species (ROS) and proinflammatory cytokines were attenuated by CAE treatment. CAE treatment suppressed B[a]P-induced phosphorylation of Src (Tyr416). In addition, dasatinib, a Src inhibitor, also inhibited B[a]P-induced nuclear translocation of AhR, similar to CAE treatment. In addition, CAE activated antioxidant response element (ARE) signaling by increasing ARE luciferase reporter activity and expression of ARE-dependent genes such as nuclear factor (erythroid-derived 2)-like 2 (Nrf2), NAD(P)H dehydrogenase [quinone] 1 (NQO1), and heme oxygenase-1 (HO-1). Nuclear translocation of Nrf2 by CAE was demonstrated by Western blot analysis and immunocytochemistry. The effects of CAE on ARE signaling were attenuated by knockdown of the Nrf2 gene. Inhibition of AhR signaling and activation of antioxidant activity by CAE operated in a reciprocally independent manner as evidenced by AhR and Nrf2 siRNA experiments. These findings indicate that CAE exerts protective effects against B[a]P by inhibiting AhR signaling and activating Nrf2-mediated signaling, suggesting its potential in protection from harmful B[a]P-containing pollutants.

Aryl Hydrocarbon Receptor in Atopic Dermatitis and Psoriasis

The aryl hydrocarbon receptor (AHR)/AHR-nuclear translocator (ARNT) system is a sensitive sensor for small molecular, xenobiotic chemicals of exogenous and endogenous origin, including dioxins, phytochemicals, microbial bioproducts, and tryptophan photoproducts. AHR/ARNT are abundantly expressed in the skin. Once activated, the AHR/ARNT axis strengthens skin barrier functions and accelerates epidermal terminal differentiation by upregulating filaggrin expression. In addition, AHR activation induces oxidative stress. However, some AHR ligands simultaneously activate the nuclear factor-erythroid 2-related factor-2 (NRF2) transcription factor, which is a master switch of antioxidative enzymes that neutralizes oxidative stress. The immunoregulatory system governing T-helper 17/22 (Th17/22) and T regulatory cells (Treg) is also regulated by the AHR system. Notably, AHR agonists, such as tapinarof, are currently used as therapeutic agents in psoriasis and atopic dermatitis. In this review, we summarize recent topics on AHR related to atopic dermatitis and psoriasis.

Xenobiotic Receptors and Their Mates in Atopic Dermatitis

Atopic dermatitis (AD) is the most common inflammatory skin disease worldwide. It is a chronic, relapsing and pruritic skin disorder which results from epidermal barrier abnormalities and immune dysregulation, both modulated by environmental factors. AD is strongly associated with asthma and allergic rhinitis in the so-called 'atopic march.' Xenobiotic receptors and their mates are ligand-activated transcription factors expressed in the skin where they control cellular detoxification pathways. Moreover, they regulate the expression of genes in pathways involved in AD in epithelial cells and immune cells. Activation or overexpression of xenobiotic receptors in the skin can be deleterious or beneficial, depending on context, ligand and activation duration. Moreover, their impact on skin might be amplified by crosstalk among xenobiotic receptors and their mates. Because they are activated by a broad range of endogenous molecules, drugs and pollutants owing to their promiscuous ligand affinity, they have recently crystalized the attention of researchers, including in dermatology and especially in the AD field. This review examines the putative roles of these receptors in AD by critically evaluating the conditions under which the proteins and their ligands have been studied. This information should provide new insights into AD pathogenesis and ways to develop new therapeutic interventions.

Environmental Stressors on Skin Aging. Mechanistic Insights

The skin is the main barrier that protects us against environmental stressors (physical, chemical, and biological). These stressors, combined with internal factors, are responsible for cutaneous aging. Furthermore, they negatively affect the skin and increase the risk of cutaneous diseases, particularly skin cancer. This review addresses the impact of environmental stressors on skin aging, especially those related to general and specific external factors (lifestyle, occupation, pollutants, and light exposure). More specifically, we have evaluated ambient air pollution, household air pollutants from non-combustion sources, and exposure to light (ultraviolet radiation and blue and red light). We approach the molecular pathways involved in skin aging and pathology as a result of exposure to these external environmental stressors. Finally, we reflect on how components of environmental stress can interact with ultraviolet radiation to cause cell damage and the critical importance of knowing the mechanisms to develop new therapies to maintain the skin without damage in old age and to repair its diseases.

Cytochrome P450 Monooxygenase-Mediated Metabolic Utilization of Benzo[a]Pyrene by Aspergillus Species

We are increasingly exposed to environmental pollutants, including the carcinogen benzo[a]pyrene (BaP), which has prompted extensive research into human metabolism of toxicants. However, little is known about metabolic mechanisms employed by fungi that are able to use some toxic pollutants as the substrates for growth, leaving innocuous by-products. This study systemically demonstrates that a common soil-dwelling fungus is able to use benzo[a]pyrene as food, which results in expression and metabolic changes associated with growth and energy generation. Importantly, this study reveals key components of the metabolic utilization of BaP, notably a cytochrome P450 monooxygenase and the fungal NF-κB-type transcriptional regulators. Our study advances fundamental knowledge of fungal BaP metabolism and provides novel insight into designing and implementing enhanced bioremediation strategies.

Soil-dwelling fungal species possess the versatile metabolic capability to degrade complex organic compounds that are toxic to humans, yet the mechanisms they employ remain largely unknown. Benzo[a]pyrene (BaP) is a pervasive carcinogenic contaminant, posing a significant concern for human health. Here, we report that several Aspergillus species are capable of degrading BaP. Exposing Aspergillus nidulans cells to BaP results in transcriptomic and metabolic changes associated with cellular growth and energy generation, implying that the fungus utilizes BaP as a growth substrate. Importantly, we identify and characterize the conserved bapA gene encoding a cytochrome P450 monooxygenase that is necessary for the metabolic utilization of BaP in Aspergillus. We further demonstrate that the fungal NF-κB-type velvet regulators VeA and VelB are required for proper expression of bapA in response to nutrient limitation and BaP degradation in A. nidulans. Our study illuminates fundamental knowledge of fungal BaP metabolism and provides novel insights into enhancing bioremediation potential.

The impact of airborne pollution on skin

Indoor and outdoor airborne pollutants modify our environment and represent a growing threat to human health worldwide. Airborne pollution effects on respiratory and cardiac health and diseases have been well established, but its impact on skin remains poorly described. Nonetheless, the skin is one of the main targets of pollutants, which reach the superficial and deeper skin layers by transcutaneous and systemic routes. In this review, we report the outcomes of basic and clinical research studies monitoring pollutant levels in human tissues including the skin and hair. We present a current understanding of the biochemical and biophysical effects of pollutants on skin metabolism, inflammatory processes and oxidative stress, with a focus on polyaromatic hydrocarbons and ground-level ozone that are widespread outdoor pollutants whose effects are mostly studied. We reviewed the literature to report the clinical effects of pollutants on skin health and skin ageing and their impact on some chronic inflammatory skin diseases. We also discuss the potential interactions of airborne pollutants with either ultraviolet radiation or human skin microbiota and their specific impact on skin health.

Particulate Matter-Induced Aryl Hydrocarbon Receptor Regulates Autophagy in Keratinocytes

Particulate matter (PM), which refers to the mixture of particles present in the air, can have harmful effects. Damage to cells by PM, including disruption of organelles and proteins, can trigger autophagy, and the relationship between autophagy and PM has been well studied. However, the cellular regulators of PM-induced autophagy have not been well characterized, especially in keratinocytes. The Aryl Hydrocarbon Receptor (AhR) is expressed in the epidermis and is activated by PM. In this study, we investigated the role of the AhR in PM-induced autophagy in HaCaT cells. Our results showed that PM led to AhR activation in keratinocytes. Activation of the AhR-target gene CYP1A1 by PM was reduced by co-treatment with α-naphthoflavone (α-NF), an AhR inhibitor. We also evaluated activation of the autophagy pathway in PM-treated keratinocytes. In HaCaT cells, treatment with PM treatment led to the induction of microtubules-associated proteins light chain 3 (LC3) and p62/SQSTM1, which are essential components of the autophagy pathway. To study the role of the AhR in mediating PM-induced autophagy, we treated cells with α-NF or used an siRNA against AhR. Expression of LC3-ІІ induced by PM was decreased in a dose dependent manner by α-NF. Furthermore, knockdown of AhR with siAhR diminished PM-induced expression of LC3-ІІ and p62. Together, these results suggest that inhibition of the AhR decreases PM-induced autophagy. We confirmed these results using the autophagy-inhibitors BAF and 3-MA. Taken together, our results indicate that exposure to PM induces autophagy via the AhR in HaCaT keratinocytes.

Tryptophan Photoproduct FICZ Upregulates IL1A, IL1B, and IL6 Expression via Oxidative Stress in Keratinocytes

Ultraviolet B (UVB) irradiation activates the aryl hydrocarbon receptor (AHR), generates the reactive oxygen species (ROS), and induces the production of proinflammatory cytokines such as IL1A, IL1B, and IL6. 6-Formylindolo[3,2-b]carbazole (FICZ) is a tryptophan-derived photoproduct that is induced by UVB irradiation and activates the AHR. However, its role in upregulating proinflammatory cytokine expression has never been investigated. Here, we demonstrated that FICZ enhanced ROS generation in human HaCaT keratinocytes in an AHR-dependent manner. FICZ also upregulated the expression of IL1A and IL1B, as well as the expression of IL6 and the production of its protein product, in an AHR- and ROS-dependent fashion. Here, we demonstrate that the actions of FICZ can substitute for the hazardous effects of UVB exposure, contributing to the further understandings of the mechanisms which UVB harms organisms.

Solar simulated light exposure alters metabolization and genotoxicity induced by benzo[a]pyrene in human skin

Skin is a major barrier against external insults and is exposed to combinations of chemical and/or physical toxic agents. Co-exposure to the carcinogenic benzo[a]pyrene (B[a]P) and solar UV radiation is highly relevant in human health, especially in occupational safety. In vitro studies have suggested that UVB enhances B[a]P genotoxicity by activating the AhR pathway and overexpressing the cytochrome P450 enzymes responsible for the conversion of B[a]P into DNA damaging metabolites. Our present work involved more realistic conditions, namely ex vivo human skin explants and simulated sunlight (SSL) as a UV source. We found that topically applied B[a]P strongly induced expression of cutaneous cytochrome P450 genes and formation of DNA adducts. However, gene induction was significantly reduced when B[a]P was combined with SSL. Consequently, formation of BPDE-adducts was also reduced when B[a]P was associated with SSL. Similar results were obtained with primary cultures of human keratinocytes. These results indicate that UV significantly impairs B[a]P metabolism, and decreases rather than increases immediate toxicity. However, it cannot be ruled out that decreased metabolism leads to accumulation of B[a]P and delayed genotoxicity.

Therapeutic Agents with AHR Inhibiting and NRF2 Activating Activity for Managing Chloracne

Chloracne is the major skin symptom caused by dioxin intoxication. Dioxin activates the aryl hydrocarbon receptor (AHR)–cytochrome p450 1A1 (CYP1A1) system, generates oxidative stress, and induces hyperkeratinization of keratinocytes and sebocytes leading to chloracne. Nuclear factor-erythroid 2-related factor-2 (NRF2) is a master switch that induces the expression of various antioxidative enzymes, such as heme oxygenase-1. Cinnamaldehyde is an antioxidant phytochemical that inhibits AHR–CYP1A1 signaling and activates the NRF2–antioxidative axis. The cinnamaldehyde-containing Kampo herbal medicine Keishibukuryogan is capable of improving chloracne in Yusho patients who are highly contaminated with dioxin. Agents with dual functions in promoting AHR–CYP1A1 inhibition and NRF2 activation may be useful for managing dioxin-related health hazards.

β-carotene and retinol reduce benzo[a]pyrene-induced mutagenicity and oxidative stress via transcriptional modulation of xenobiotic metabolizing enzymes in human HepG2 cell line

Benzo[a]pyrene (B[a]P) is one of the polycyclic aromatic hydrocarbons which is formed due to smoking of foods, incomplete combustion of woods, vehicle exhausts, and cigarettes smokes. B[a]P gets entry into human and animal bodies mainly through their diets. Metabolic activation of B[a]P is required to induce mutagenesis and carcinogenesis in animal and human studies. Carotenoids and retinoids are phytochemicals that if ingested have multiple physiological interferences in the human and animal bodies. In this study, we firstly investigated the protective effects of β-carotene, β-apo-8-carotenal, retinol, and retinoic acid against B[a]P-induced mutagenicity and oxidative stress in human HepG2 cells. Secondly, we tested the hypothesis of modulating xenobiotic metabolizing enzymes (XMEs) by carotenoids and retinoids as a possible mechanism of protection by these micronutrients against B[a]P adverse effects. The obtained results declared that β-carotene and retinol significantly reduced B[a]P-induced mutagenicity and oxidative stress. Tested carotenoids and retinoids reduced B[a]P-induced phase I XMEs and induced B[a]P reduced phase II and III XMEs. Thus, the protective effects of these micronutrients are probably due to their ability of induction of phase II and III enzymes and interference with the induction of phase I enzymes by the promutagen, B[a]P. It is highly recommended to consume foods rich in these micronutrients in the areas of high PAH pollution.

Perillaldehyde Inhibits AHR Signaling and Activates NRF2 Antioxidant Pathway in Human Keratinocytes

The skin covers the outer surface of the body, so the epidermal keratinocytes within it are susceptible to reactive oxygen species (ROS) generated by environmental pollutants such as benzo(a)pyrene (BaP), a potent activator of aryl hydrocarbon receptor (AHR). Antioxidant activity is generally mediated by the nuclear factor-erythroid 2-related factor-2 (NRF2) and heme oxygenase-1 (HO1) axis in human keratinocytes. Perillaldehyde is the main component of Perilla frutescens, which is a medicinal antioxidant herb traditionally consumed in East Asia. However, the effect of perillaldehyde on the AHR/ROS and/or NRF2/HO1 pathways remains unknown. In human keratinocytes, we found that perillaldehyde (1) inhibited BaP-induced AHR activation and ROS production, (2) inhibited BaP/AHR-mediated release of the CCL2 chemokine, and (3) activated the NRF2/HO1 antioxidant pathway. Perillaldehyde is thus potentially useful for managing inflammatory skin diseases or disorders related to oxidative stress.

Exposure to lethal levels of benzo[a]pyrene or cadmium trigger distinct protein expression patterns in earthworms (Eisenia fetida)

Different pollutants induce distinct toxic responses in earthworms (Eisenia fetida). Here, we used proteomics techniques to compare the responses of E. fetida to exposure to the 10% lethal concentration (14d-LC₁₀) of benzo[a]pyrene (BaP) or cadmium (Cd) in natural red soil (China). BaP exposure markedly induced the expression of oxidation-reduction proteins, whereas Cd exposure mainly induced the expression of proteins involved in transcription- and translation-related processes. Furthermore, calmodulin-binding proteins were differentially expressed upon exposure to different pollutants. The calcium (Ca²⁺)-binding cytoskeletal element myosin was down-regulated upon BaP treatment, whereas the Ca²⁺-binding cytoskeletal element tropomyosin-1 was up-regulated upon Cd treatment. Some proteins exhibited opposite responses to the two pollutants. For instance, catalase (CAT) and heat shock protein 70 were up-regulated upon BaP treatment and down-regulated upon Cd treatment. A significant (p<0.05, one-way ANOVA with least-significant difference (LSD) test) increase in the level of reactive oxygen species (ROS) and CAT activity further showed that BaP mainly induces oxidative stress. Real-time PCR analysis showed that mRNA expression often did not correlate well with protein expression in earthworms subjected to Cd or BaP treatment. In addition, the expression of the gene encoding the protein metallothionein, which was not detected in the protein analysis, was induced upon Cd treatment, but slightly reduced upon BaP treatment. Therefore, BaP and Cd have distinct effects on the protein profile of E. Fetida with BaP markedly inducing ROS activity, and Cd mainly triggering genotoxicity.

CAPSULE SUMMARY

Distinct patterns of protein expression are induced in earthworms upon exposure to different pollutants; BaP markedly induces high levels of ROS, while Cd resultes in genotoxicity.

Antioxidants for Healthy Skin: The Emerging Role of Aryl Hydrocarbon Receptors and Nuclear Factor-Erythroid 2-Related Factor-2

Skin is the outermost part of the body and is, thus, inevitably exposed to UV rays and environmental pollutants. Oxidative stress by these hazardous factors accelerates skin aging and induces skin inflammation and carcinogenesis. Aryl hydrocarbon receptors (AHRs) are chemical sensors that are abundantly expressed in epidermal keratinocytes and mediate the production of reactive oxygen species. To neutralize or minimize oxidative stress, the keratinocytes also express nuclear factor-erythroid 2-related factor-2 (NRF2), which is a master switch for antioxidant signaling. Notably, there is fine-tuned crosstalk between AHR and NRF2, which mutually increase or decrease their activation states. Many NRF2-mediated antioxidant phytochemicals are capable of up- and downmodulating AHR signaling. The precise mechanisms by which these phytochemicals differentially affect the AHR and NRF2 system remain largely unknown and warrant future investigation.