Electrophilic Reactivity of Sulfated Alcohols in the Context of Skin Sensitization.

The surfactant sodium lauryl sulfate (SLS), although consistently positive in the murine local lymph node assay (LLNA) for skin sensitization, shows no evidence of being a human sensitizer and is often described as a false positive, lacking structural alerts for sensitization. However, there is evidence of the cinnamyl sulfate anion being the metabolite responsible for the sensitization potential of cinnamyl alcohol to humans and in animal tests. Here, manufacturing chemistry data and physical organic chemistry principles are applied to confirm that SLS is not reactive enough to sensitize, whereas sensitization to cinnamyl alcohol via cinnamyl sulfate is plausible. Sensitization data for several other primary alcohols, including geraniol, farnesol, and possibly hydrocortisone, are also consistent with this mechanism. It seems possible that biosulfation may play a wider role than has previously been recognized in skin sensitization.

Reconstructed human epidermis-based testing strategy of skin sensitization potential and potency classification using epidermal sensitization assay and in silico data.

The hazards and potency of skin sensitizers are traditionally determined using animal tests such as the local lymph node assay (LLNA); however, significant progress has been made in the development of non-animal test methods addressing the first three mechanistic key events of adverse outcome pathway in skin sensitization. We developed the epidermal sensitization assay (EpiSensA), which is a reconstructed human epidermis-based assay, by measuring four genes related to critical keratinocyte responses during skin sensitization. Four in vitro skin sensitization test methods (EpiSensA, direct peptide reactivity assay [DPRA], KeratinoSens™, and human cell line activation test [h-CLAT]) were systematically evaluated using 136 chemicals including lipophilic chemicals and pre/pro-haptens, which may be related to assay-specific limitations. The constructed database included existing and newly generated data. The EpiSensA showed a broader applicability domain and predicted the hazards with 82.4% and 78.8% accuracy than LLNA and human data. The EpiSensA could detect 76 out of 88 sensitizers at lower concentrations than the LLNA, indicating that the EpiSensA has higher sensitivity for the detection of minor sensitizing constituents. These results confirmed the potential use of the EpiSensA in evaluating a mixture of unknown compositions that can be evaluated by animal tests. To combine different information sources, the reconstructed human epidermis-based testing strategy (RTS) was developed based on weighted multiple information from the EpiSensA and TImes MEtabolism Simulator platform for predicting Skin Sensitization (TIMES-SS; RTSv1) or Organization for Economic Cooperation and Development (OECD) QSAR Toolbox automated workflow (RTSv2). The predictivities of the hazards and Globally Harmonized System (GHS) subcategories were equal to or better than the defined approaches (2 out of 3, integrated testing strategy [ITS]v1, and ITSv2) adopted as OECD Guideline 497.

HMGB1-mediated chromatin remodeling attenuates Il24 gene expression for the protection from allergic contact dermatitis.

Dysregulation of inflammatory cytokines in keratinocytes promote the pathogenesis of the skin inflammation, such as allergic contact dermatitis (ACD). High-mobility group box 1 protein (HMGB1) has been implicated in the promotion of skin inflammation upon its extracellular release as a damage-associated molecular pattern molecule. However, whether and how HMGB1 in keratinocytes contributes to ACD and other skin disorders remain elusive. In this study, we generated conditional knockout mice in which the Hmgb1 gene is specifically deleted in keratinocytes, and examined its role in ACD models. Interestingly, the mutant mice showed exacerbated skin inflammation, accompanied by increased ear thickening in 2,4-dinitrofluorobenezene-induced ACDs. The mRNA expression of interleukin-24 (IL-24), a cytokine known to critically contribute to ACD pathogenesis, was elevated in skin lesions of the mutant mice. As with constitutively expressed, IL-4-induced Il24 mRNA, expression was also augmented in the Hmgb1-deficient keratinocytes, which would account for the exacerbation of ACD in the mutant mice. Mechanistically, we observed an increased binding of trimethyl histone H3 (lys4) (H3K4me3), a hallmark of transcriptionally active genes, to the promoter region of the Il24 gene in the hmgb1-deficient cells. Thus, the nuclear HMGB1 is a critical "gate keeper" in that the dermal homeostasis is contingent to its function in chromatin remodeling. Our study revealed a facet of nuclear HMGB1, namely its antiinflammatory function in keratinocytes for the skin homeostasis.

Amino Chemoassay Profiling of Aromatic Aldehydes-Unraveling Drivers of Their Skin Sensitization Potency.

Aromatic aldehydes are ubiquitous in humans' everyday life. As aldehydes, they can form imines (Schiff bases) with amino groups of skin proteins, leading to immune response-triggered allergic contact dermatitis. Many known aromatic aldehydes are considered as weak or nonsensitizers, but others like atranol and chloratranol, two components of the fragrance oak moss absolute, show strong sensitization potency. This large discrepancy in potency and, in particular, the underlying reaction mechanisms are only little understood so far. To reduce this knowledge gap, our chemoassay employing glycine-para-nitroanilide (Gly-pNA) as an amino model nucleophile was applied to 23 aromatic aldehydes. The determined Gly-pNA second-order rate constants for imine formation (k1 ≤ 2.85 L·mol-1·min-1) and the imine stability constant (K ≤ 333 L·mol-1) are on the lower end of the known amino reactivity scale for aldehydes, confirming many aromatic aldehydes as less potent sensitizers in line with animal and human data. The substantially higher sensitization potency of atranol and chloratranol, in turn, is reflected by their unique reaction chemistry profiles, inter alia, identifying them as cross-linkers able to form thermodynamically more stable epitopes with skin proteins (despite low formation kinetics, k1). The discussion further includes a comparison of experimentally determined k1 values with computed reactivity data (Taft σ*), the impact of the substitution pattern of the aryl ring on the reactivity with Gly-pNA, and analytically determined adduct patterns. Overall, this work provides new insights into the reaction of aromatic aldehydes with amino groups under aqueous conditions and fosters a better understanding of the chemistry underlying skin sensitization.

Role of miR-24-3p and miR-146a-5p in dendritic cells' maturation process induced by contact sensitizers.

MiRNAs are non-coding RNA molecules that regulate gene expression at the post-transcriptional level. Although allergic contact dermatitis has been studied extensively, few studies addressed miRNA expression and their role in dendritic cell activation. The main aim of this work was to investigate the role of miRNAs in the underlying mechanism of dendritic cell maturation induced by contact sensitizers of different potency. Experiments were conducted using THP-1-derived immature DCs (iDCs). Contact allergens of different potency were used: p-benzoquinone, Bandrowski's base, and 2,4-dinitrochlorobenzene as extreme; nickel sulfate hexahydrate, diethyl maleate and 2-mercaptobenzothiazole as moderate; and α-hexyl cinnamaldehyde, eugenol, and imidazolidinyl urea as weak. Selective inhibitor and mimic miRNAs were then used and several cell surface markers was evaluated as targets. Also, patients patch tested with nickel were analyzed to determine miRNAs expression. Results indicate an important role of miR-24-3p and miR-146a-5p in DCs activation. miR-24-3p was up-regulated by extreme and weak contact allergens, while miR-146a-5p was up-regulated by weak and moderate contact allergens and down-regulated only by the extreme ones. Also, the involvement of PKCß in contact allergen-induced miR-24-3p and miR-146a-5p expression was demonstrated. Furthermore, the expression of the two miRNAs maintains the same trend of expression in both in vitro and in human conditions after nickel exposure. Results obtained suggest the involvement of miR-24 and miR-146a in DCs maturation process in the proposed in vitro model, supported also by human evidences.

Sensitization properties of acetophenone azine, a new skin sensitizer identified in textile.

BACKGROUND: Acetophenone azine (CAS no. 729-43-1) present in sports equipment (shoes, socks and shin pads) has been suspected to induce skin allergies. Twelve case reports of allergy in children and adults from Europe and North America were published between 2016 and 2021. OBJECTIVES: The objective of this study was to confirm that acetophenone azine is indeed a skin sensitizer based on in vitro/ in vivo testings derived from the Adverse Outcome Pathway (AOP) built for skin sensitization by OECD in 2012. METHODS: Acetophenone azine was tested in vitro according to the human cell line activation test (h-CLAT) and the ARE-Nrf2 Luciferase Test (KeratinoSens) and in vivo using the Local Lymph Nodes Assay (LLNA). RESULTS: Both the h-CLAT and the KeratinoSens were positive whereas the LLNA performed at 5, 2.5 and 1% (wt/vol) of acetophenone azine, was negative. CONCLUSION: Based on these results, acetophenone azine was considered as a skin sensitizer. This was recently confirmed by its classification under the CLP regulation.

CD100 boosts the inflammatory response in the challenge phase of allergic contact dermatitis in mice.

BACKGROUND: Allergic contact dermatitis (ACD) is an inflammatory disease with a complex pathophysiology in which epidermal-resident memory CD8+ T (TRM ) cells play a key role. The mechanisms involved in the activation of CD8+ TRM cells during allergic flare-up responses are not understood. METHODS: The expression of CD100 and its ligand Plexin B2 on CD8+ TRM cells and keratinocytes before and after allergen exposure was determined by flow cytometry and RT-qPCR. The role of CD100 in the inflammatory response during the challenge phase of ACD was determined in a model of ACD in CD100 knockout and wild-type mice. RESULTS: We show that CD8+ TRM cells express CD100 during homeostatic conditions and up-regulate it following re-exposure of allergen-experienced skin to the experimental contact allergen 1-fluoro-2,4-dinitrobenzene (DNFB). Furthermore, Plexin B2 is up-regulated on keratinocytes following exposure to some contact allergens. We show that loss of CD100 results in a reduced inflammatory response to DNFB with impaired production of IFNγ, IL-17A, CXCL1, CXCL2, CXCL5, and IL-1ß and decreased recruitment of neutrophils to the epidermis. CONCLUSION: Our study demonstrates that CD100 is expressed on CD8+ TRM cells and is required for full activation of CD8+ TRM cells and the flare-up response of ACD.

Effects of impermeable and semipermeable glove materials on resolution of inflammation and epidermal barrier impairment after experimental skin irritation.

BACKGROUND: Semipermeable membranes might be suitable for glove liners or comfort gloves in individuals with irritant contact dermatitis (ICD). OBJECTIVES: To evaluate the effects of different glove materials on inflammation and epidermal barrier impairment after experimental skin irritation. METHODS: Nine test areas on the volar forearms of 24 healthy volunteers were irritated with sodium lauryl sulfate (1%) and afterward covered for 6 days (6 or 8 h/day) with semipermeable Sympatex (SYM), vinyl (OCC), combinations of vinyl with Sympatex (SYM/OCC) or cotton (COT/OCC), or left uncovered (CON). Up to day 10, measurements of transepidermal water loss (TEWL), erythema (a*), skin humidity (SH) and visual scoring (VS) were applied. RESULTS: No significant differences in skin parameters were found between COT/OCC and SYM/OCC as well as between each of the combinations and CON. SYM, COT/OCC and SYM/OCC led to better results for most skin parameters than OCC alone. CONCLUSIONS: Occlusive material has a negative impact on skin barrier recovery and inflammation after skin irritation whereas SYM is not inferior to uncovered areas indicating good tolerability. Altogether, the data suggest that SYM is a useful alternative to COT as material for glove liners and comfort gloves in ICD patients.

Common fragrance chemicals activate dendritic cells in coculture with keratinocytes.

BACKGROUND: Fragrances are important contact allergens; however, investigation of their skin sensitization potency has been challenging in new approach methods (NAMs). Many fragrance chemicals are susceptible to autoxidation or can be metabolized by enzymes constitutively expressed in skin keratinocytes. Strong sensitizers can be formed in both of these processes. Further, keratinocytes can modulate the dendritic cell (DC) activation and maturation potential, a key event in the acquisition of contact allergy. OBJECTIVES: To evaluate the 2D coculture model consisting of keratinocytes and DCs using different weak to moderate sensitizing fragrance chemicals. Further, to investigate fragrances and related oxidation products in the in vitro model and compare to in vivo data. METHODS: Chemicals were tested in the coculture activation test (COCAT), consisting of HaCaT keratinocytes and THP-1 cells. THP-1 cell surface expression of costimulatory and adhesion molecules (CD86 and CD54) collected after 24 h incubation with the chemicals was analysed using flow cytometry. RESULTS: Twenty-four molecules were tested positive, three were negative (n = 27). Four pairs were evaluated, with aldehydes showing a 6- to 13-fold stronger responses compared to their corresponding alcohols. CONCLUSIONS: Results provide insight into the activation of DC in their natural environment of keratinocytes. α,ß-Unsaturated alcohols were classified as weaker sensitizers compared to their corresponding aldehydes. In sum, testing of fragrances retrieved results in good agreement with in vivo data.

LncRNA-WAKMAR2 regulates expression of CLDN1 to affect skin barrier through recruiting c-Fos.

BACKGROUND: Chronic actinic dermatitis (CAD) is an immune-mediated photo-allergic skin disease. In the clinic, the treatment of this disease is hampered by the lack of proper understanding of the skin barrier dysfunction mechanism. OBJECTIVE: To illuminate the mechanism of skin barrier dysfunction in CAD. METHODS: Transcriptome sequencing and protein profiling were used to detect skin barrier injury-related genes. RNA pull down, a promoter-reporter gene assay, and chromatin isolation by RNA purification-sequencing were used to elucidate the effect of WAKMAR2 in skin barrier functionality. RESULTS: Transcriptome sequencing from patient's tissues showed a significantly decreased expression of WAKMAR2. Down-regulation of WAKMAR2 destroyed the keratinocyte barrier. Moreover, WAKMAR2 can directly bind to the c-Fos protein. This novel long non-coding RNA (LncRNA)-protein complexes were targeted to the CLDN1 promotor. Overexpression of WAKMAR2 enhanced the promoter activity of CLDN1, while the addition of AP-1 inhibitor could reverse this phenomenon. Furthermore, our in vivo results suggested that expression of WAKMAR2 was required for the repair of skin damage in mice induced by ultraviolet irradiation. CONCLUSIONS: We identified a crucial LncRNA (WAKMAR2) for the protection of the skin barrier in vitro and in vivo. Mechanically, it can specifically interact with c-Fos protein for the regulation of CLDN1, a finding which could be applied for CAD treatment.

Ozonated oil alleviates dinitrochlorobenzene-induced allergic contact dermatitis via inhibiting the FcεRI/Syk signaling pathway. / 医用臭氧油通过抑制FcεRI/Syk信号通路缓解DNCB诱导的变应性接触性皮炎（英文）.

OBJECTIVES: Ozone is widely applied to treat allergic skin diseases such as eczema, atopic dermatitis, and contact dermatitis. However, the specific mechanism remains unclear. This study aims to investigate the effects of ozonated oil on treating 2,4-dinitrochlorobenzene (DNCB)-induced allergic contact dermatitis (ACD) and the underling mechanisms. METHODS: Besides the blank control (Ctrl) group, all other mice were treated with DNCB to establish an ACD-like mouse model and were randomized into following groups: a model group, a basal oil group, an ozonated oil group, a FcεRI-overexpressed plasmid (FcεRI-OE) group, and a FcεRI empty plasmid (FcεRI-NC) group. The basal oil group and the ozonated oil group were treated with basal oil and ozonated oil, respectively. The FcεRI-OE group and the FcεRI-NC group were intradermally injected 25 µg FcεRI overexpression plasmid and 25 µg FcεRI empty plasmid when treating with ozonated oil, respectively. We recorded skin lesions daily and used reflectance confocal microscope (RCM) to evaluate thickness and inflammatory changes of skin lesions. Hematoxylin-eosin (HE) staining, real-time PCR, RNA-sequencing (RNA-seq), and immunohistochemistry were performed to detct and analyze the skin lesions. RESULTS: Ozonated oil significantly alleviated DNCB-induced ACD-like dermatitis and reduced the expressions of IFN-γ, IL-17A, IL-1ß, TNF-α, and other related inflammatory factors (all P<0.05). RNA-seq analysis revealed that ozonated oil significantly inhibited the activation of the DNCB-induced FcεRI/Syk signaling pathway, confirmed by real-time PCR and immunohistochemistry (all P<0.05). Compared with the ozonated oil group and the FcεRI-NC group, the mRNA expression levels of IFN-γ, IL-17A, IL-1ß, IL-6, TNF-α, and other inflammatory genes in the FcεRI-OE group were significantly increased (all P<0.05), and the mRNA and protein expression levels of FcεRI and Syk were significantly elevated in the FcεRI-OE group as well (all P<0.05). CONCLUSIONS: Ozonated oil significantly improves ACD-like dermatitis and alleviated DNCB-induced ACD-like dermatitis via inhibiting the FcεRI/Syk signaling pathway.

IRE1 and PERK signaling regulates inflammatory responses in a murine model of contact hypersensitivity.

BACKGROUND: Contact sensitizers may interfere with correct protein folding. Generation of un-/misfolded proteins can activate the IRE-1 or PERK signaling pathways initiating the unfolded protein response (UPR) and thereby determine inflammatory immune responses. We have analyzed the effect of sensitizers with different potencies on the induction of UPR activation/inhibition and the subsequent generation of a pro-inflammatory micromilieu in vitro as well as the effect of UPR modulation on the inflammatory response in the murine contact hypersensitivity (CHS) in vivo. METHODS: Semi-quantitative and quantitative PCR, fluorescence microscopy, ELISA, NF-κB activation and translocation assays, DC/keratinocyte co-culture assay, FACS, and in vivo CHS experiments were performed. RESULTS: Sensitizers and irritants activate IRE-1 and PERK in murine and human keratinocytes. Synergistic effects occur after combination of different weak sensitizers / addition of irritants. Moreover, tolerogenic dinitrothiocyanobenzene can be converted into a strong sensitizer by pre-activation of the UPR. Blocking UPR signaling results in decreased NF-κB activation and cytokine production in keratinocytes and in activation marker downregulation in a HaCaT/THP-1 co-culture. Interestingly, not only systemic but also topical application of UPR inhibitors abrogates CHS responses in vivo. CONCLUSION: These observations highlight an important role of the UPR in determination of the inflammatory response in vitro and in vivo further underlining the importance of tissue stress and damage responses in the development of ACD and provide mechanistically based concepts as a basis for the development of new therapeutic approaches to treat allergic contact dermatitis.

Juzentaihoto Exerts Anti-Allergic Effects by Inhibiting Effector T-Cell Activation and Inducing and/or Activating Regulatory T Cells in a Murine Model of Contact Hypersensitivity.

BACKGROUND: Juzentaihoto (JTT) is a Kampo prescription that has been used clinically for treating skin diseases such as atopic dermatitis in Japan. We have previously studied the anti-allergic effects of JTT on 2,4,6-trinitrochlorobenzene (TNCB)-induced contact hypersensitivity (CHS) in mice and demonstrated that it significantly suppresses ear swelling in a dose-dependent manner. However, the mechanism underlying the anti-allergic actions of JTT is obscure. METHODS: We investigated the mechanism underlying the anti-allergic effects of JTT using a TNCB-induced murine CHS model and adoptive cell transfer experiments. RESULTS: We showed that the anti-allergic effects of JTT are due to inhibition of effector T-cell activation and induction and/or activation of regulatory T cells. Furthermore, ex vivo experiments confirmed the effect of JTT on the activation of effector T cells and regulatory T cells, as interferon-γ production decreased, whereas interleukin (IL)-10 production increased, in the cultured lymphocytes obtained from 5% TNCB-sensitized mice treated with anti-CD3ε and anti-CD28 monoclonal antibodies. Flow cytometry showed that the CD4+CD25+Foxp3+, CD4+CD25+Foxp3-, and CD8+CD122+ cell population increased after oral administration of JTT. Finally, the anti-allergic effect of JTT by inducing and/or activating regulatory T cells (Tregs) was confirmed to be mediated by IL-10 through in vivo neutralization experiments with anti-IL-10 monoclonal antibodies. CONCLUSION: We suggested that JTT exerts anti-allergic effects by regulating the activation of effector T cells and Tregs involved in murine CHS model.

Exploring neuronal mechanisms involved in the scratching behavior of a mouse model of allergic contact dermatitis by transcriptomics.

BACKGROUND: Allergic contact dermatitis (ACD) is a common skin condition characterized by contact hypersensitivity to allergens, accompanied with skin inflammation and a mixed itch and pain sensation. The itch and pain dramatically affects patients' quality of life. However, still little is known about the mechanisms triggering pain and itch sensations in ACD. METHODS: We established a mouse model of ACD by sensitization and repetitive challenge with the hapten oxazolone. Skin pathological analysis, transcriptome RNA sequencing (RNA-seq), qPCR, Ca2+ imaging, immunostaining, and behavioral assay were used for identifying gene expression changes in dorsal root ganglion innervating the inflamed skin of ACD model mice and for further functional validations. RESULTS: The model mice developed typical ACD symptoms, including skin dryness, erythema, excoriation, edema, epidermal hyperplasia, inflammatory cell infiltration, and scratching behavior, accompanied with development of eczematous lesions. Transcriptome RNA-seq revealed a number of differentially expressed genes (DEGs), including 1436-DEG mRNAs and 374-DEG-long noncoding RNAs (lncRNAs). We identified a number of DEGs specifically related to sensory neuron signal transduction, pain, itch, and neuroinflammation. Comparison of our dataset with another published dataset of atopic dermatitis mouse model identified a core set of genes in peripheral sensory neurons that are exclusively affected by local skin inflammation. We further found that the expression of the pain and itch receptor MrgprD was functionally upregulated in dorsal root ganglia (DRG) neurons innervating the inflamed skin of ACD model mice. MrgprD activation induced by its agonist ß-alanine resulted in exaggerated scratching responses in ACD model mice compared with naïve mice. CONCLUSIONS: We identified the molecular changes and cellular pathways in peripheral sensory ganglia during ACD that might participate in neurogenic inflammation, pain, and itch. We further revealed that the pain and itch receptor MrgprD is functionally upregulated in DRG neurons, which might contribute to peripheral pain and itch sensitization during ACD. Thus, targeting MrgprD may be an effective method for alleviating itch and pain in ACD.

Applicability of amino acid derivative reactivity assay (4 mM) for the prediction of skin sensitization by combining multiple alternative methods to evaluate key events.

The amino acid derivative reactivity assay (ADRA) is an alternative method for evaluating key event 1 (KE-1) in the skin sensitization mechanism included in OECD TG442C (OECD, 2021). Recently, we found that ADRA with a 4-mM test chemical solution had a higher accuracy than the original ADRA (1 mM). However, ADRA (4 mM) has yet to be evaluated using integrated approaches to testing and assessment (IATA), a combination of alternative methods for evaluating KE. In this study, the sensitization potency of three defined approaches (DAs) using ADRA (4 mM) as KE-1 was predicted and compared with those of two additional ADRAs or direct peptide reactivity assay (DPRA): (i) "2 out of 3" approach, (ii) "3 out of 3" approach, and (iii) integrated testing strategy (ITS). In the hazard identification of chemical sensitizers, the accuracy of human data and local lymph node assay (LLNA) remained almost unchanged among the three approaches evaluated. Potency classifications for sensitization were predicted with the LLNA and human data sets using ITS. The potency classifications for the sensitization potency prediction accuracy of LLNA data using any alternative method were almost unchanged, at approximately 70%, and those with ITS were not significantly different. When ITS was performed using DPRA, the prediction accuracy was approximately 73% for human data, which was similar to that of the LLNA data; however, the accuracy tended to increase for all ADRA methods. In particular, when ITS was performed using ADRA (4 mM), the prediction accuracy was approximately 78%, which proved to be a practical level.

Electron paramagnetic resonance and spin trapping to detect free radicals from allergenic hydroperoxides in contact with the skin: From the molecule to the tissue.

A major research topic consists of revealing the contribution of radical-mediated reactions in dermatological diseases related to xenobiotic-induced stress to succeed risk-assessment procedures protecting producers and consumers. Allergic contact dermatitis is the clinically relevant consequence of skin sensitization, one of the most critical occupational and environmental health issues related to xenobiotics exposure. The first key event identified for the skin sensitization process to a chemical is its aptitude to react with epidermal proteins and form antigenic structures that will further trigger the immune response. Many chemical sensitizers are suspected to react through mechanisms involving radical intermediates. This review focuses on the recent progress we have accomplished over the last few years studying radical intermediates derived from skin-sensitizing chemicals by electron paramagnetic resonance in combination with the spin-trapping technique. Our work is carried out "from the molecule", performing studies in solution, "to the tissue", by the development of a methodology on a reconstructed human epidermis model, very close in terms of histology and metabolic/enzymatic activity to real human epidermis, that can be used as suitable biological tissue model. The benefits are to test chemicals under conditions close to human use and real-life sensitization exposures and benefit from the three-dimensional (3D) microenvironment.

mMrgprA3/mMrgprC11/hMrgprX1: Potential therapeutic targets for allergic contact dermatitis-induced pruritus in mice and humans.

BACKGROUND: Although the Mas-related G-protein-coupled receptors (Mrgprs) play essential roles in itch detection, their contribution to allergic contact dermatitis (ACD)-associated itch remains unclear. OBJECTIVES: To investigate whether Mrgprs are involved in ACD and whether Mrgprs can be identified as potential therapeutic targets. METHODS: Mrgpr-clusterΔ-/- mice and human MrgprX1 (hMrgprX1) transgenic mice were used to evaluate the function of Mrgprs in oxazolone-induced ACD. RESULTS: Utilizing an ACD model, we found that Mrgpr-clusterΔ-/- mice display significantly reduced pruritus. Among 12 Mrgprs deleted in Mrgpr-clusterΔ-/- mice, the expression of MrgprC11 and MrgprA3 was significantly increased in the ACD model, which also innervated the skin and spinal cord at higher-than-normal densities. The proportions of dorsal root ganglia neurons responding to bovine adrenal medulla peptide 8-22 and chloroquine were also remarkably increased in the ACD model, resulting in enhanced itch behaviour. To study the function of human Mrgprs in ACD-induced itch, we used hMrgprX1 transgenic mice, which rescued the severe itch defect of Mrgpr-clusterΔ-/- mice in the ACD model. Remarkably, pharmacological blockade of hMrgprX1 significantly attenuates ACD itch in hMrgprX1 transgenic mouse. CONCLUSIONS: Our study provides the first evidence that Mrgprs are involved in ACD-induced chronic itch, which provides new avenues for itch management in ACD.

Effects of skin washing frequency on the epidermal barrier function and inflammatory processes of the epidermis: An experimental study.

BACKGROUND: Increased hand hygiene measures during the COVID-19 pandemic have led to an increased quantum of hand eczema (HE). OBJECTIVES: To examine the effects of varying washing frequencies using current mild cleansing agents-alongside with the effect of a rehydrating cream-on the epidermal barrier function and inflammatory processes of the stratum corneum(SC). METHODS: Standardized skin washings on the volar aspects of the lower arms of skin-healthy volunteers were performed using the automated cleansing device either 5 or 11 times within 4 h for 60 s each with a standard cleanser, a lipid-containing syndet, or a lipid-containing syndet followed by one-time application of a rehydrating cream. Skin bioengineering parameters (transepidermal water loss, SC hydration, erythema, and SC pH) and biochemical/immunological parameters (interleukin-1α, interleukin-1α receptor antagonist and natural moisturizing factor) of SCsamples collected by tape stripping were assessed. RESULTS: All applied washing procedures provided comparable, mild effects on the epidermal barrier function and skin inflammation. CONCLUSION: Occupational skin cleansers seem to have improved regarding skin barrier damaging effects. To further corroborate this, a study design, modified on the basis of our findings, applying longer washing periods for consecutive days seems desirable.

Effects of constant light exposure on allergic and irritant contact dermatitis in mice reared under constant light conditions.

Environmental light levels can affect physiological functions, such as general activity, body temperature and metabolism. Irregular lifestyles, such as those involving exposure to light during the night, can exacerbate the clinical symptoms of several inflammatory skin diseases. However, the effects of constant light exposure on immune responses are not fully understood. This study aimed to elucidate the effects of constant light exposure on two major types of skin reactions, allergic contact dermatitis (ACD) and irritant contact dermatitis (ICD). BALB/c mice were kept under constant light conditions or a normal light and dark cycle, and their ACD and ICD responses were assessed after the topical application of 2,4,6-trinitro-1-chlorobenzene and croton oil, respectively, to the ear skin. Interestingly, in both ACD and ICD, the ear-swelling response and local leukocyte infiltration were aggravated by constant exposure to light, which has previously been shown to severely disturb the behavioural rhythms of mice. In ACD, these findings were accompanied by increases in the numbers of degranulated mast cells and eosinophils. These results suggest that constant light exposure intensifies allergic and non-allergic skin inflammation.

MRGPRX2 sensing of cationic compounds-A bridge between nociception and skin diseases?

Mast cells are innate immune cells located at many barrier sites in the body and known to protect the host against environmental threats and to be involved in allergic diseases. More recently, new studies have investigated their roles in the regulation of skin inflammation and transmission of pain and itch sensations. Mast cell signalling through the Mas-related G protein-coupled receptor (MRGPR) X2 or its mouse orthologue MRGPRB2 has been reported to be one of the major mechanism by which mast cell can regulate such processes. MRGPRX2 and MRGPRB2 can induce mast cell degranulation upon binding to a broad panel of cationic molecules such as neuropeptides, bacteria-derived quorum sensing molecules, venom peptides, host defense peptides and, unfortunately, various FDA-approved drugs. Upon activation, mast cells release granule-associated proteases, lipids and multiple cytokines that can modulate vascular permeability, immune cells recruitment and activation status of tissue-projecting nociceptive sensory neurons (ie nociceptors). Here, we discuss the modality of MRGPRX2-dependent mast cell activation and its different consequences on the patterns of skin inflammation and associated diseases. We notably emphasize how MRGPRX2-dependent skin mast cell activation might trigger various pathological traits such as pruritus, pain and inflammation and therefore become a potential therapeutic target for inflammatory pain, itch, atopic dermatitis and drugs-induced injection site reactions.