A sensory neuron-expressed IL-31 receptor mediates T helper cell-dependent itch: Involvement of TRPV1 and TRPA1

Characterisation of the pruritus responses and pruritic behaviours in an interleukin 31-induced canine model of pruritus

BACKGROUND

Intravenous administration of interleukin (IL)-31 in healthy dogs has been used as a model to assess antipruritic drugs. However, there is no known in-depth characterisation of pruritic behaviours, and the repeatability of the IL-31-induced pruritus in the individual dogs is currently unknown.

OBJECTIVES

To evaluate the immediate/delayed pruritus responses and the pruritic behaviours observed in the IL-31-induced pruritic model in healthy dogs after repeated IL-31 injections.

ANIMALS

Fifteen healthy laboratory beagles.

METHODS

All dogs were video-recorded for 270 min after two intravenous recombinant IL-31 injections (1.75 μg/kg) and vehicle (phosphate-buffered saline, control) injections, respectively; interventions were randomised and performed with a 2 week wash-out period. Two blinded investigators reviewed the pruritic behaviours of all video recordings.

RESULTS

Both canine IL-31 (IL-31_01, IL-31_02) injections significantly increased pruritic seconds and categorical minutes ('YES'/'NO' behaviour per discrete 1 min interval) in healthy dogs compared with both vehicle groups (Vehicle_01, Vehicle_02). The second intravenous canine IL-31 (IL-31_02) administered 14 days after the first IL-31 injection induced a significant increase in pruritic seconds (p = 0.021) and not pruritic categorical minutes (p = 0.231). An increase in pruritic seconds was observed in both IL-31 groups in the first 30 min post-administration, while there was no significant difference between IL-31 and vehicle groups.

CONCLUSIONS AND CLINICAL RELEVANCE

In conclusion, intravenous IL-31 reproducibly induces itch responses in dogs. Future evaluations of the canine IL-31 pruritic model should assess total pruritic behaviours in seconds rather than using a biased 'YES/NO' behaviour per 1 min scoring system.

Staphylococcus aureus: The Bug Behind the Itch in Atopic Dermatitis

Pruritus or itch is a defining symptom of atopic dermatitis (AD). The origins of itch are complex, and it is considered both a defense mechanism and a cause of disease that leads to inflammation and psychological stress. Considerable progress has been made in understanding the processes that trigger itch, particularly the pruritoceptive origins that are generated in the skin. This perspective review discusses the implications of a recent observation that the V8 protease expressed by Staphylococcus aureus can directly trigger sensory neurons in the skin through activation of protease-activated receptor 1. This may be a key to understanding why itch is so common in AD because S. aureus commonly overgrows in this disease owing to deficient antimicrobial defense from both the epidermis and the cutaneous microbiome. Increased understanding of the role of microbes in AD provides increased opportunities for safely improving the treatment of this disorder.

Genetic and Immunological Pathogenesis of Atopic Dermatitis

Type 2 immune-mediated diseases give a clear answer to the issue of nature (genetics) versus nurture (environment). Both genetics and environment play vital complementary roles in the development of atopic dermatitis (AD). As a key component of the atopic march, AD demonstrates the interactive nature of genetic and environmental contributions to atopy. From sequence variants in the epithelial barrier gene encoding FLG to the hygiene hypothesis, AD combines a broad array of contributions into a single syndrome. This review will focus on the genetic contribution to AD and where genetics facilitates the elicitation or enhancement of AD pathogenesis.

Atopic Dermatitis Itch: Scratching for an Explanation

Chronic pruritus is a cardinal symptom of atopic dermatitis (AD). The mechanisms underlying atopic itch involve intricate crosstalk among skin, immune components, and neural components. In this review, we explore these mechanisms, focusing on key players and interactions that induce and exacerbate itch. We discuss the similarities and differences between pruritus and pain in patients with AD as well as the relationship between pruritus and factors such as sweat and the skin microbiome. Furthermore, we explore novel targets that could provide significant itch relief in these patients as well as exciting future research directions to better understand atopic pruritus in darker skin types.

Sensory neuronal control of skin barrier immunity

Peripheral sensory neurons recognize diverse noxious stimuli, including microbial products and allergens traditionally thought to be targets of the mammalian immune system. Activation of sensory neurons by these stimuli leads to pain and itch responses as well as the release of neuropeptides that interact with their cognate receptors expressed on immune cells, such as dendritic cells (DCs). Neuronal control of immune cell function through neuropeptide release not only affects local inflammatory responses but can impact adaptive immune responses through downstream effects on T cell priming. Numerous neuropeptide receptors are expressed by DCs but only a few have been characterized, presenting opportunities for further investigation of the pathways by which cutaneous neuroimmune interactions modulate host immunity.

The relationship and clinical significance of serum cytokine expression level and skin pruritus in patients with Hodgkin lymphoma and angioimmunoblastic T-cell lymphoma

Pruritus of lymphoma is commonly associated with both Hodgkin lymphoma (HL) and angioimmunoblastic T cell lymphoma (AITL) and critically affects the life quality of patient. Recent evidence suggests that the pruritogenic cytokines seem to play a significant role in the genesis of chronic. This study aims to investigate the cytokines associated with itching in lymphoma patients and provide the basis for potential therapeutic targets. Serum samples were collected from 60 lymphoma patients, including 47 with Hodgkin lymphoma (HL) and 13 with angioimmunoblastic T-cell lymphoma (AITL), serving as the observation group (lymphoma group, LP group, n = 60). Additionally, serum samples from 8 healthy donors (HD group, n = 8) were collected for comparison. Within the lymphoma group, patients were stratified into those with pruritus (LWP group, n = 30) and those without pruritus (LWOP group, n = 30) based on the presence of skin pruritus symptoms. Elevated levels of multiple cytokines were significantly observed in the LP group in comparison to the HD group (p < 0.01). Patients in LWP group exhibited higher serum levels of IL-31 (p < 0.001), IL-1β (P = 0.039), and IL-1α (P = 0.037) compared to LWOP group. Notably, serum IL-31 levels were higher in advanced AITL patients (stage IV) than in early AITL patients (stage I-Ⅲ, P < 0.05). In subgroup analysis, patients with pruritus in the AITL group exhibited higher serum levels of MIG and CTACK compared to HL group, whereas PDGF-BB levels were significantly lower (p < 0.05). Elevated serum levels of IL-31, IL-1β, and IL-1α are linked to lymphoma-associated pruritus. Differences in serum cytokine profiles between HL and AITL subgroups are also highlighted. These findings offer valuable insights for clinical intervention in managing lymphoma-related pruritus.

Similarities and differences in peripheral itch and pain pathways in atopic dermatitis

Atopic dermatitis (AD) is predominantly characterized by intense itching, but concomitant skin pain is experienced by more than 40% of patients. Patients with AD display considerable somatosensory aberrations, including increased nerve sensitivity to itch stimuli (hyperknesis), perception of itch from innocuous stimuli (alloknesis), or perception of pain from innocuous stimuli (allodynia). This review summarizes the current understanding of the similarities and differences in the peripheral mechanisms underlying itch and pain in AD. These distinct yet reciprocal sensations share many similarities in the peripheral nervous system, including common mediators (such as serotonin, endothelin-1, IL-33, and thymic stromal lymphopoietin), receptors (such as members of the G protein-coupled receptor family and Toll-like receptors), and ion channels for signal transduction (such as certain members of the transient receptor potential [TRP] cation channels). Itch-responding neurons are also sensitive to pain stimuli. However, there are distinct differences between itch and pain signaling. For example, specific immune responses are associated with pain (type 1 and/or type 3 cytokines and certain chemokine C-C [CCL2, CCL5] and C-X-C [CXCL] motif ligands) and itch (type 2 cytokines, including IL-31, and periostin). The TRP melastatin channels TRPM2 and TRPM3 have a role in pain but no known role in itch. Activation of μ-opioid receptors is known to alleviate pain but exacerbate itch. Understanding the connection between itch and pain mechanisms may offer new insights into the treatment of chronic pain and itch in AD.

A systematic review of interleukin-31 inhibitors in the treatment of prurigo nodularis

BACKGROUND

Prurigo nodularis (PN) is a neuroimmunological skin disease. Severe itching is the most challenging symptom which affects patients' quality of life. T helper 2-derived cytokines, such as interleukin-31 and oncostatin M (OSM), play a crucial role in PN pathogenesis. Nemolizumab and vixarelimab are two biologics acting as IL-31 inhibitors. Vixarelimab also suppresses the OSM activity. This systematic review evaluates the efficacy and safety of nemolizumab and vixarelimab in PN management.

METHODS

A systematic search was conducted in PubMed/Medline, Ovid Embase, and Web of Science up to September 17th, 2023. Clinical trials and cohort studies published in English were included.

RESULTS

Among a total of 96 relevant records, five were included. The results of four studies with 452 patients using nemolizumab showed that a significantly higher percentage of patients treated with nemolizumab demonstrated a reduction in peak pruritus numerical rating scale (PP-NRS) and investigator's global assessment along with improved sleep disturbance (SD) and quality of life than the placebo group. Moreover, one study administered vixarelimab to 49 PN patients, and their finding illustrated a higher rate of subjects who received vixarelimab experienced ≥ 4-point diminution in worst itch NRS, visual analog scale, healing of representative lesions, and SD quality compared to the placebo group.

CONCLUSIONS

IL-31 inhibitors suggest distinct advantages in improving pruritus, sleep quality, and overall quality of life in subjects with moderate-to-severe PN. Further clinical studies are recommended to compare the effectiveness of these biologics to other therapeutic choices.

Molecular and cellular pruritus mechanisms in the host skin

Pruritus, also known as itching, is a complex sensation that involves the activation of specific physiological and cellular receptors. The skin is innervated with sensory nerves as well as some receptors for various sensations, and its immune system has prominent neurological connections. Sensory neurons have a considerable impact on the sensation of itching. However, immune cells also play a role in this process, as they release pruritogens. Disruption of the dermal barrier activates an immune response, initiating a series of chemical, physical, and cellular reactions. These reactions involve various cell types, including keratinocytes, as well as immune cells involved in innate and adaptive immunity. Collective activation of these immune responses confers protection against potential pathogens. Thus, understanding the molecular and cellular mechanisms that contribute to pruritus in host skin is crucial for the advancement of effective treatment approaches. This review provides a comprehensive analysis of the present knowledge concerning the molecular and cellular mechanisms underlying itching signaling in the skin. Additionally, this review explored the integration of these mechanisms with the broader context of itch mediators and the expression of their receptors in the skin.

Neuroimmune interplay during type 2 inflammation: Symptoms, mechanisms, and therapeutic targets in atopic diseases

Type 2 inflammation is characterized by overexpression and heightened activity of type 2 cytokines, mediators, and cells that drive neuroimmune activation and sensitization to previously subthreshold stimuli. The consequences of altered neuroimmune activity differ by tissue type and disease; they include skin inflammation, sensitization to pruritogens, and itch amplification in atopic dermatitis and prurigo nodularis; airway inflammation and/or hyperresponsiveness, loss of expiratory volume, airflow obstruction and increased mucus production in asthma; loss of sense of smell in chronic rhinosinusitis with nasal polyps; and dysphagia in eosinophilic esophagitis. We describe the neuroimmune interactions that underlie the various sensory and autonomic pathologies in type 2 inflammatory diseases and present recent advances in targeted treatment approaches to reduce type 2 inflammation and its associated symptoms in these diseases. Further research is needed to better understand the neuroimmune mechanisms that underlie chronic, sustained inflammation and its related sensory pathologies in diseases associated with type 2 inflammation.

Emerging trends and hotspots of the itch research: A bibliometric and visualized analysis

AIMS

Itch, a common uncomfortable sensory experience, occurs frequently in inflammatory or allergic disorders. In recent years, with the discovery of itch-specific pathways in the peripheral and central nervous system, the association between immunology and neural pathways has gradually emerged as the main mechanism of itch. Although many studies have been conducted on itch, no bibliometric analysis study focusing on this topic has been conducted. This study aimed to explore the research hotspots and trends in the itch field from a bibliometric perspective.

METHODS

Publications relevant to itch, published from 2003 to 2022, were retrieved from the Science Citation Index-Expanded of Web of Science Core Collection. Publications were critically reviewed and analyzed with CiteSpace software, Vosviewer, and the bibliometric online analysis platform. Visual maps were conducted in terms of annual production, collaborating countries or institutions, productive authors, core journals, co-cited references, and keyword bursts.

RESULTS

2395 articles on itch that met our criteria were identified and the quantity of publications has been increasing rapidly since 2012. The USA was the most influential country. University Hospital Münster was the institution with the most publications. Gil Yosipovitch was the most prolific author. Atopic dermatitis (AD), intradermal serotonin, chronic pruritus, mechanical itch, gastrin-releasing peptide, substance p, interleukin-31 receptor, histamine-induced itch, bile acid, scratching behavior, and h-4 receptor were the top 11 clusters in co-citation cluster analysis. Keyword burst analysis suggested that treatment, inflammation, and AD are current research hotspots.

CONCLUSION

Global publications on itch research have increased steadily and rapidly over the past 20 years. Inflammation and AD are current research hotspots. The neuroimmunological and neuroinflammatory mechanisms of itch, as well as clinical assessment methods and therapeutic targets, will be novel research directions in the future. This study provides guidance for further itch research.

Mast cell-sensory neuron crosstalk in allergic diseases

Mast cells (MCs) are tissue-resident immune cells, well-positioned at the host-environment interface for detecting external antigens and playing a critical role in mobilizing innate and adaptive immune responses. Sensory neurons are afferent neurons innervating most areas of the body but especially in the periphery, where they sense external and internal signals and relay information to the brain. The significance of MC-sensory neuron communication is now increasingly becoming recognized, especially because both cell types are in close physical proximity at the host-environment interface and around major organs of the body and produce specific mediators that can activate each other. In this review, we explore the roles of MC-sensory neuron crosstalk in allergic diseases, shedding light on how activated MCs trigger sensory neurons to initiate signaling in pruritus, shock, and potentially abdominal pain in allergy, and how activated sensory neurons regulate MCs in homeostasis and atopic dermatitis associated with contact hypersensitivity and type 2 inflammation. Throughout the review, we also discuss how these 2 sentinel cell types signal each other, potentially resulting in a positive feedback loop that can sustain inflammation. Unraveling the mysteries of MC-sensory neuron crosstalk is likely to unveil their critical roles in various disease conditions and enable the development of new therapeutic approaches to combat these maladies.

Interplay of cytokines in the pathophysiology of atopic dermatitis: insights from Murin models and human

The pathogenesis of atopic dermatitis (AD) is understood to be crucially influenced by three main factors: dysregulation of the immune response, barrier dysfunction, and pruritus. In the lesional skin of AD, various innate immune cells, including Th2 cells, type 2 innate lymphoid cells (ILC2s), and basophils, produce Th2 cytokines [interleukin (IL)-4, IL-5, IL-13, IL-31]. Alarmins such as TSLP, IL-25, and IL-33 are also produced by epidermal keratinocytes, amplifying type 2 inflammation. In the chronic phase, not only Th2 cells but also Th22 and Th17 cells increase in number, leading to suppression of filaggrin expression by IL-4, IL-13, and IL-22, which further deteriorates the epidermal barrier function. Dupilumab, which targets IL-4 and IL-13, has shown efficacy in treating moderate to severe AD. Nemolizumab, targeting IL-31RA, effectively reduces pruritus in AD patients. In addition, clinical trials with fezakinumab, targeting IL-22, have demonstrated promising results, particularly in severe AD cases. Conversely, in murine models of AD, several cytokines, initially regarded as promising therapeutic targets, have not demonstrated sufficient efficacy in clinical trials. IL-33 has been identified as a potent activator of immune cells, exacerbating AD in murine models and correlating with disease severity in human patients. However, treatments targeting IL-33 have not shown sufficient efficacy in clinical trials. Similarly, thymic stromal lymphopoietin (TSLP), integral to type 2 immune responses, induces dermatitis in animal models and is elevated in human AD, yet clinical treatments like tezepelumab exhibit limited efficacy. Therapies targeting IL-1α, IL-5, and IL-17 also failed to achieve sufficient efficacy in clinical trials. It has become clear that for treating AD, IL-4, IL-13, and IL-31 are relevant therapeutic targets during the acute phase, while IL-22 emerges as a target in more severe cases. This delineation underscores the necessity of considering distinct pathophysiological aspects and therapeutic targets in AD between mouse models and humans. Consequently, this review delineates the distinct roles of cytokines in the pathogenesis of AD, juxtaposing their significance in human AD from clinical trials against insights gleaned from AD mouse models. This approach will improve our understanding of interspecies variation and facilitate a deeper insight into the pathogenesis of AD in humans.

The epidermal lipid-microbiome loop and immunity: Important players in atopic dermatitis

BACKGROUND

The promotion of epidermal barrier dysfunction is attributed to abnormalities in the lipid-microbiome positive feedback loop which significantly influences the imbalance of the epithelial immune microenvironment (EIME) in atopic dermatitis (AD). This imbalance encompasses impaired lamellar membrane integrity, heightened exposure to epidermal pathogens, and the regulation of innate and adaptive immunity. The lipid-microbiome loop is substantially influenced by intense adaptive immunity which is triggered by abnormal loop activity and affects the loop's integrity through the induction of atypical lipid composition and responses to dysregulated epidermal microbes. Immune responses participate in lipid abnormalities within the EIME by downregulating barrier gene expression and are further cascade-amplified by microbial dysregulation which is instigated by barrier impairment.

AIM OF REVIEW

This review examines the relationship between abnormal lipid composition, microbiome disturbances, and immune responses in AD while progressively substantiating the crosstalk mechanism among these factors. Based on this analysis, the "lipid-microbiome" positive feedback loop, regulated by immune responses, is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review delves into the impact of adaptive immune responses that regulate the EIME, driving AD, and investigates potential mechanisms by which lipid supplementation and probiotics may alleviate AD through the up-regulation of the epidermal barrier and modulation of immune signaling. This exploration offers support for targeting the EIME to attenuate AD.

A Bispecific, Tetravalent Antibody Targeting Inflammatory and Pruritogenic Pathways in Atopic Dermatitis

Inhibition of IL-4/IL-13 signaling has dramatically improved the treatment of atopic dermatitis (AD). However, in many patients, clinical responses are slow to develop and remain modest. Indeed, some symptoms of AD are dependent on IL-31, which is only partially reduced by IL-4/IL-13 inhibition. Thus, there is an unmet need for AD treatments that concomitantly block IL-4/IL-13 and IL-31 pathways. We engineered NM26-2198, a bispecific tetravalent antibody designed to accomplish this task. In reporter cell lines, NM26-2198 concomitantly inhibited IL-4/IL-13 and IL-31 signaling with a potency comparable with that of the combination of an anti-IL-4Rα antibody (dupilumab) and an anti-IL-31 antibody (BMS-981164). In human PBMCs, NM26-2198 inhibited IL-4-induced upregulation of CD23, demonstrating functional binding to FcγRII (CD32). NM26-2198 also inhibited the secretion of the AD biomarker thymus and activation-regulated chemokine (TARC) in blood samples from healthy human donors. In male cynomolgus monkeys, NM26-2198 exhibited favorable pharmacokinetics and significantly inhibited IL-31-induced scratching at a dose of 30 mg/kg. In a repeat-dose, good laboratory practice toxicology study in cynomolgus monkeys, no adverse effects of NM26-2198 were observed at a weekly dose of 125 mg/kg. Together, these results justify the clinical investigation of NM26-2198 as a treatment for moderate-to-severe AD.

TRP Ion Channels in Immune Cells and Their Implications for Inflammation

The transient receptor potential (TRP) ion channels act as cellular sensors and mediate a plethora of physiological processes, including somatosensation, proliferation, apoptosis, and metabolism. Under specific conditions, certain TRP channels are involved in inflammation and immune responses. Thus, focusing on the role of TRPs in immune system cells may contribute to resolving inflammation. In this review, we discuss the distribution of five subfamilies of mammalian TRP ion channels in immune system cells and how these ion channels function in inflammatory mechanisms. This review provides an overview of the current understanding of TRP ion channels in mediating inflammation and may offer potential avenues for therapeutic intervention.

The IL-31/TRPV1 pathway mediates allergic asthma exacerbated by DINP dermal exposure in OVA-sensitized Balb/c mice

BACKGROUND

The potential role of dermal exposure diisononyl phthalate (DINP) as an adjuvant in allergic inflammation and asthma has been suggested. However, the current findings do not provide enough evidence to support this claim.

OBJECTIVES

The purpose of this investigation was to examine the impact and mechanisms of allergic asthma exacerbation through the dermal exposure to DINP.

METHODS

The study was undertaken using OVA-sensitized mice. Lung histopathology and airway hyperreactivity (AHR) were assessed. Expression levels of immunoglobulins (t-IgE, OVA-IgE and OVA-IgG1), cytokines (IL-31, IL-4, IL-5, IL-6, IL-13 and INF-γ), and TRPV1 were measured. To investigate the mechanism by which allergic asthma worsens due to dermal exposure to DINP, the blockade analysis using the IL-31 antagonist SB-431542 and the TRPV1 antagonist capsazepine (CZP) were performed.

RESULTS

The findings of the study revealed that the simultaneous exposure to DINP and OVA resulted in an increase in inspiratory resistance (Ri) and expiratory resistance (Re), a decrease in the minimum value of lung dynamic compliance (Cldyn), and worsened airway remodeling. Additionally, it was found that this exposure led to an increase in the levels of IL-31 and TRPV1, which are biomarkers of Th2 cytokines (IL-4, IL-5, IL-6, and IL-13), as well as immunoglobulins (Total IgE, OVA-lgE, and OVA-IgG1), while decreasing the biomarker of Th1 cytokines (IFN-γ). However, these impairments showed improvement after the administration of SB-431542 or CZP.

CONCLUSION

The findings of this research indicate that the IL-31/TRPV1 pathway plays a moderating function in OVA-induced allergic asthma worsened by dermal exposure to DINP.

Neuronal BST2: A Pruritic Mediator alongside Protease-Activated Receptor 2 in the IL-27-Driven Itch Pathway

Chronic itch is a common and complex symptom often associated with skin diseases such as atopic dermatitis (AD). Although IL-27 is linked to AD, its role and clinical significance in itch remain undefined. We sought to investigate IL-27 function in itch using tissue-specific transgenic mice, various itch models, behavior scoring, RNA sequencing, and cytokine/kinase array. Our findings show that IL-27 receptors were overexpressed in human AD skin. Intradermal IL-27 injection failed to directly induce itch in mice but upregulated skin protease-activated receptor 2 (PAR2) transcripts, a key factor in itch and AD. IL-27 activated human keratinocytes, increasing PAR2 transcription and activity. Coinjection of SLIGRL (PAR2 agonist) and IL-27 in mice heightened PAR2-mediated itch. In addition, IL-27 boosted BST2 transcription in sensory neurons and keratinocytes. BST2 was upregulated in AD skin, and its injection in mice induced itch-like response. BST2 colocalized with sensory nerve branches in AD skin from both human and murine models. Sensory neurons released BST2, and mice with sensory neuron-specific BST2 knockout displayed reduced itch responses. Overall, this study provides evidence that skin IL-27/PAR2 and neuronal IL-27/BST2 axes are implicated in cutaneous inflammation and pruritus. The discovery of neuronal BST2 in pruritus shed light on BST2 in the itch cascade.

The Effect of Osthole on Transient Receptor Potential Channels: A Possible Alternative Therapy for Atopic Dermatitis

Introduction

Chronic recurrent skin inflammation and severe itching in patients with atopic dermatitis (AD) significantly impair their quality of life. The H4 histamine receptor plays a key role in histamine-induced itching. During the skin inflammation associated with AD, pro-inflammatory mediators (interleukins, cytokines) are released from neurons. Ultimately, a cascade of reactions leads to the activation and sensitization of transient receptor potential channels (TRP), which exacerbate the inflammation and itching associated with AD. Osthole (OST) is a natural coumarin with a proven versatile pharmacological effect: anti-cancer, anti-inflammatory and immunomodulatory. However, the molecular mechanism of OST in relieving inflammation in histamine-mediated itching is not yet clear.

Purpose

In the studies presented, the possible effect of the OST action on the inhibition of the gene expression of the histamine H4 receptor and the key genes of the TRP channels as well as on the concentration of proinflammatory interleukins was analyzed.

Methods

Inflammation was induced in a 3D skin model and a keratinocyte cell line Normal Human Epidermal Keratinocytes (NHEK) identical to that of AD, and then OST was administered at various doses. The concentrations of IL-4/-13 were determined by ELISA. RNA was isolated from the 3D skin cells and the NHEK cell line, and the qPCR method was used to determine the expression of: IL-4α, H4R, TRPV1, TRPV4, TRPM8 analyzed.

Results

The study showed that OST significantly reduced the secretion of IL-4/-13 in a keratinocyte cell line and in a 3D skin model. In addition, OST was found to significantly decrease the gene expression of IL-4α, H4R, TRPV1, TRPV4 and increase TRPM8 in both the NHEK cell line and the organotypic 3D skin model.

Conclusion

The data obtained provide the first in vitro evidence of itch relief following the application of OST to atopic skin. Research on the use of OST as an active component of emollients in the treatment of AD should be continued in the future.

TRPV1 Channel in Human Eosinophils: Functional Expression and Inflammatory Modulation

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel expressed on sensory neurons and immune cells. We hypothesize that TRPV1 plays a role in human eosinophil function and is modulated by inflammatory conditions. TRPV1 expression on human eosinophils was examined by qPCR, flow cytometry, and immunohistochemistry, respectively. TRPV1 functionality was analyzed by investigating calcium flux, apoptosis, modulation by cytokines and acidic pH, and CD69 externalization using flow cytometry. Activation of TRPV1 induced calcium influx and prolonged survival. Although eosinophils were not directly activated by TRPV1 agonists, activation by IL-3 or GM-CSF was mainly restricted to TRPV1-positive eosinophils. TRPV1 surface content was increased by acidic pH, IL-3, IL-31, IL-33, TSLP, TNF-α, BDNF, and NGF-β. Interestingly, TRPV1 was also expressed by eosinophils located in proximity to peripheral nerves in atopic dermatitis (AD) skin. In conclusion, eosinophils express functional TRPV1 channels which are increased by extracellular acidification and AD-related cytokines. Since eosinophils also express TRPV1 in AD skin, our results indicate an important role of TRPV1 for neuroimmune interaction mechanisms in itchy, inflammatory skin diseases, like AD.

Serum IL-31 is related to the severity and 3-month prognosis of patients with Intracerebral hemorrhage

Interleukin (IL)-31/IL-33 axis has been proved to play an important role in the regulation of inflammation, and serum IL-33 was found to be a novel serum prognostic marker of intracerebral hemorrhage (ICH), while the value of serum IL-31 levels on prognosis in patients with ICH remains unknown. The present study was designed to study the value of serum IL-31 levels on prognosis in ICH patients. A total of 200 ICH patients and 50 healthy people were included in this study. We collected clinical data such as demographic data, laboratory data, admission disease scores and medical histories of these participants. We measured serum IL-31 levels using enzyme-linked immunosorbent assay, and assessed the prognosis of ICH patients 3 months after onset by mRS scale, and mRS > 2 was defined as a 3-month poor outcome. The level of IL-31 in ICH patients were significantly higher than that in healthy control people (211.91 ± 61.61 vs 167.64 ± 27.45 pg/mL, P < .001), and levels of IL-31 in ICH patients with 3-month good outcome were significantly lower than that in ICH patients with 3-month poor outcome (196.09 ± 50.84 vs 248.05 ± 41.41 pg/mL, P < .001). Results of correlation analysis suggested that the level of serum IL-31 was positively related to admission NIHSS score (r = 0.627, P < .001), hematoma volume (r = 0.352, P < .001), mRS score (r = 0.515, P < .001), high-density lipoprotein-cholesterol (r = 0.177, P = .012), serum C-reactive protein levels (r = 0.483, P < .001), and serum tumor necrosis factor α levels (r = 0.389, P < .001) in ICH patients, while the level of serum IL-31 was negatively related to the admission GCS score (r = -0.518, P < .001) and triglycerides (r = -0.147, P = .038). Results of multivariate regression analysis shows that serum IL-31 levels are an independent risk factor affecting NIHSS scores (OR = 1.023, 95% CI = 1.010-2.036) and 3-month prognosis (OR = 1.023, 95% CI = 0.982-1.747) in ICH patients. The receiver operating characteristic curve analysis showed that the sensitivity and specificity of serum IL-31 level in evaluating the prognosis of ICH were 85.2% and 76.7%, respectively. A cutoff value of serum IL-31 level > 185.30 pg/mL may indicate a poor prognosis for ICH. Serum IL-31 levels on admission in ICH patients are associated with patient prognosis, and higher serum IL-31 levels are associated with a higher risk of poor prognosis in ICH patients.

Establishment of an experimental model of ovalbumin-induced atopic dermatitis in canines

Introduction

A reliable standard model is required to evaluate the efficacy of new drugs for companion animals, especially dogs. Canine atopic dermatitis (cAD), also known as allergic inflammatory skin disease, is a common condition. Currently, the house dust mite animal model is used in the research of cAD; however, this model exhibits significant individual variation and is difficult to standardize. In this study, we used ovalbumin as an antigen to sensitize and stimulate dogs, thereby establishing a stable model mimicking the T-helper 2 (Th2) response seen in cAD. Our objective was to create a cAD model that could be employed to evaluate the efficacy of novel drugs and mimic the Th2 dominant allergic response observed in the pathogenesis of atopic dermatitis of dogs.

Methods

In this study, six beagles were used. Normal saline was applied to two animals, and ovalbumin to four, on their dorsal skin.

Results

The ovalbumin-treated groups exhibited clinical cAD symptoms, such as pruritus and erythema. Moreover, plasma levels of the cAD markers immunoglobulin E and CCL17 chemokine were higher in the ovalbumin-treated group than in the vehicle control group. The skin thickness of the epidermis was significantly increased in the ovalbumin-treated group, with infiltration of inflammatory cells observed in the thickened dermis region. In conclusion, treatment of canine skin with an optimal concentration of ovalbumin induced typical cAD-like symptoms, and histological and molecular analyses confirmed an enhanced Th2-related immune response.

Conclusion

Therefore, we successfully established a suitable Th2-dominant response mimicking cAD, which will facilitate targeted research of atopic dermatitis in dogs.

Site-Specific Transient Receptor Potential Channel Mechanisms and Their Characteristics for Targeted Chronic Itch Treatment

Chronic itch is a debilitating condition with limited treatment options, severely affecting quality of life. The identification of pruriceptors has sparked a growing interest in the therapeutic potential of TRP channels in the context of itch. In this regard, we provided a comprehensive overview of the site-specific expression of TRP channels and their associated functions in response to a range of pruritogens. Although several potent antipruritic compounds that target specific TRP channels have been developed and have demonstrated efficacy in various chronic itch conditions through experimental means, a more thorough understanding of the potential for adverse effects or interactions with other TRP channels or GPCRs is necessary to develop novel and selective therapeutics that target TRP channels for treating chronic itch. This review focuses on the mechanism of itch associated with TRP channels at specific sites, from the skin to the sensory neuron, with the aim of suggesting specific therapeutic targets for treating this condition.

Exogenous drugs-induced mouse models of atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin disease characterized by intense pruritus. AD is harmful to both children and adults, but its pathogenic mechanism has yet to be fully elucidated. The development of mouse models for AD has greatly contributed to its study and treatment. Among these models, the exogenous drug-induced mouse model has shown promising results and significant advantages. Until now, a large amount of AD-related research has utilized exogenous drug-induced mouse models, leading to notable advancements in research. This indicates the crucial significance of applying such models in AD research. These models exhibit diverse characteristics and are highly complex. They involve the use of various strains of mice, diverse types of inducers, and different modeling effects. However, there is currently a lack of comprehensive comparative studies on exogenous drug-induced AD mouse models, which hinders researchers' ability to choose among these models. This paper provides a comprehensive review of the features and mechanisms associated with various exogenous drug-induced mouse models, including the important role of each cytokine in AD development. It aims to assist researchers in quickly understanding models and selecting the most suitable one for further investigation.

Methotrexate for refractory adult atopic dermatitis leads to alterations in cutaneous IL-31 and IL-31RA expression

BACKGROUND

Methotrexate (MTX) is an alternative treatment for patients with moderate/severe atopic dermatitis (AD).

OBJECTIVE

The authors evaluated the effect of MTX on the cutaneous expression of cytokines and chemokines that are involved in the inflammatory response in adult AD patients who received treatment with methotrexate for 24 weeks.

METHODS

The authors conducted a prospective single-institution cohort study with 12 adults with moderate/severe AD who received oral MTX (15 mg/wk for 24 wks) and 10 non-atopic matched controls. The comparison was made of skin biopsies of lesional and non-lesional skin, pre- and post MTX treatment. The authors analyzed mean epidermal thickness and expression of IL-31, IL-31RA, OSMR, TSLP, Ki67, IL-4 mRNA, IL-6, IL-10, TNF-α, IFN-γ, TARC, and CCL-22.

RESULTS

There was a reduction in mean epidermal thickness (p = 0.021), an increase in IL-31RA expression (immunohistochemistry) in the epidermis (p = 0.016) and a decrease in IL-31 gene expression (p = 0.019) on lesional AD skin post-MTX treatment. No significant changes in the cutaneous expression of the other evaluated markers were identified.

STUDY LIMITATIONS

Small sample size and limited length of follow-up.

CONCLUSIONS

Treatment with MTX in adults with moderate/severe AD reduced epidermal hyperplasia and changed the cutaneous expression of inflammatory cytokines and receptors that are mainly related to pruritus, including IL-31 and IL-31RA.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03327116.

Blockade of OSMRβ signaling ameliorates skin lesions in a mouse model of human atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by severe pruritus and eczematous skin lesions. Although IL-31, a type 2 helper T (Th2)-derived cytokine, is important to the development of pruritus and skin lesions in AD, the blockade of IL-31 signaling does not improve the skin lesions in AD. Oncostatin M (OSM), a member of IL-6 family of cytokines, plays important roles in the regulation of various inflammatory responses through OSM receptor β subunit (OSMRβ), a common receptor subunit for OSM and IL-31. However, the effects of OSM on the pathogenesis of AD remain to be elucidated. When AD model mice were treated with OSM, skin lesions were exacerbated and IL-4 production was increased in the lymph nodes. Next, we investigated the effects of the monoclonal antibody (mAb) against OSMRβ on the pathogenesis of AD. Treatment with the anti-OSMRβ mAb (7D2) reduced skin severity score in AD model mice. In addition to skin lesions, scratching behavior was decreased by 7D2 mAb with the reduction in the number of OSMRβ-positive neurons in the dorsal root ganglia of AD model mice. 7D2 mAb also reduced the serum concentration of IL-4, IL-13, and IgE as well as the gene expressions of IL-4 and IL-13 in the lymph nodes of AD model mice. Blockade of both IL-31 and OSM signaling is suggested to suppress both pruritus and Th2 responses, resulting in the improvement of skin lesions in AD. The anti-OSMRβ mAb may be a new therapeutic candidate for the treatment of AD.

Intrapatient comparison of atopic dermatitis skin transcriptome shows differences between tape-strips and biopsies

BACKGROUND

Our knowledge of etiopathogenesis of atopic dermatitis (AD) is largely derived from skin biopsies, which are associated with pain, scarring and infection. In contrast, tape-stripping is a minimally invasive, nonscarring technique to collect skin samples.

METHODS

To construct a global AD skin transcriptomic profile comparing tape-strips to whole-skin biopsies, we performed RNA-seq on tape-strips and biopsies taken from the lesional skin of 20 moderate-to-severe AD patients and the skin of 20 controls. Differentially expressed genes (DEGs) were defined by fold-change (FCH) ≥2.0 and false discovery rate <0.05.

RESULTS

We detected 4104 (2513 Up; 1591 Down) and 1273 (546 Up; 727 Down) DEGs in AD versus controls, in tape-strips and biopsies, respectively. Although both techniques captured dysregulation of key immune genes, tape-strips showed higher FCHs for innate immunity (IL-1B, IL-8), dendritic cell (ITGAX/CD11C, FCER1A), Th2 (IL-13, CCL17, TNFRSF4/OX40), and Th17 (CCL20, CXCL1) products, while biopsies showed higher upregulation of Th22 associated genes (IL-22, S100As) and dermal cytokines (IFN-γ, CCL26). Itch-related genes (IL-31, TRPV3) were preferentially captured by tape-strips. Epidermal barrier abnormalities were detected in both techniques, with terminal differentiation defects (FLG2, PSORS1C2) better represented by tape-strips and epidermal hyperplasia changes (KRT16, MKI67) better detected by biopsies.

CONCLUSIONS

Tape-strips and biopsies capture overlapping but distinct features of the AD molecular signature, suggesting their respective utility for monitoring specific AD-related immune, itch, and barrier abnormalities in clinical trials and longitudinal studies.

Sensory neuronal STAT3 is critical for IL-31 receptor expression and inflammatory itch

IL-31 receptor blockade suppresses pruritus of atopic dermatitis. However, cell-type-specific contributions of IL-31 receptor to itch, its expression mechanism, and the downstream signaling pathway to induce itch remain unknown. Here, using conditional knockout mice, we demonstrate that IL-31-induced itch requires sensory neuronal IL-31 receptor and STAT3. We find that IL-31 receptor expression is dependent on STAT3 in sensory neurons. In addition, pharmacological experiments suggest that STAT3 activation is important for the itch-inducing signaling downstream of the IL-31 receptor. A cutaneous IL-31 injection induces the nuclear accumulation of activated STAT3 first in sensory neurons that abundantly express IL-31 receptor and then in other itch-transmitting neurons. IL-31 enhances itch induced by various pruritogens including even chloroquine. Finally, pruritus associated with dermatitis is partially dependent on sensory neuronal IL-31 receptor and strongly on sensory neuronal STAT3. Thus, sensory neuronal STAT3 is essential for IL-31-induced itch and further contributes to IL-31-independent inflammatory itch.

Full-body blue light irradiation as treatment for atopic dermatitis: a randomized sham-controlled clinical trial (AD-Blue)

BACKGROUND

Visible blue light (wavelength 400-495 nm) is a promising new treatment option for both psoriasis and atopic dermatitis (AD). Whilst previous clinical trials featured various devices and blue light at a variety of wavelengths, none of these interventions were challenged in objective clinical criteria.

PATIENTS AND METHODS

Eighty-seven patients diagnosed with AD were enrolled in AD-Blue, an international, prospective, double-blinded, three-armed (415 nm vs. 450 nm vs. sham control), randomized trial designed to investigate the safety and efficacy of prototype full-body blue light devices.

RESULTS

Full-body irradiation with 450 nm blue light but not 415 nm had a significant impact on itch (Itch-VAS, -1.6 ± 2.3; p  =  0.023 vs. sham irradiation). PO-SCORAD values also decreased significantly in response to irradiation at 415 nm (-11.5 ± 18.4; p = 0.028 vs. sham irradiation). None of the other outcome measures (EASI, SCORAD, IGA, DLQI) changed significantly. No safety signals were observed. Evaluation of skin transcriptomes, cytokine levels in serum, and ELISpots from peripheral blood mononuclear cells isolated from a subset of patients revealed moderate decreases in IL-31 in response to irradiation with blue light.

CONCLUSIONS

Despite its favorable safety profile and moderate reductions in itch and IL-31 levels, full-body blue light irradiation did not lead to an amelioration of any of the objective measures of AD.

Ganzkörper-Blaulichtbestrahlung zur Behandlung der atopischen Dermatitis: eine randomisierte, placebokontrollierte klinische Studie (AD-Blue)

Hintergrund

Sichtbares blaues Licht (Wellenlänge 400–495 nm) ist eine vielversprechende neue Behandlungsoption sowohl für Psoriasis als auch für atopische Dermatitis (AD). In früheren klinischen Studien wurden zwar verschiedene Geräte und blaues Licht mit unterschiedlichen Wellenlängen eingesetzt, aber keine dieser Prozeduren wurde anhand objektiver klinischer Kriterien geprüft.

Patienten und Methodik

87 Patienten mit AD wurden in die AD‐Blue‐Studie aufgenommen, eine internationale, prospektive, doppelblinde, dreiarmige (415 nm vs. 450 nm vs. Placebo), randomisierte Studie zur Untersuchung der Sicherheit und Wirksamkeit von Prototypen von Ganzkörper‐Blaulicht‐Bestrahlungsgeräten.

Ergebnisse

Die Ganzkörper‐Bestrahlung mit 450 nm blauem Licht, aber nicht mit 415 nm, hatte einen signifikant positiven Einfluss auf den Juckreiz (Pruritus‐VAS, –1,6 ± 2,3; p = 0,023 gegenüber der Placebobestrahlung). Die PO‐SCORAD‐Werte sanken ebenfalls signifikant als Reaktion auf die Bestrahlung bei 415 nm (–11,5 ± 18,4; p = 0,028 im Vergleich zur Placebobestrahlung). Keines der anderen Ergebnisse (EASI, SCORAD, IGA, DLQI) veränderte sich signifikant. Es wurden keine Sicherheitsprobleme beobachtet. Die Auswertung von Hauttranskriptomdaten, Zytokinspiegeln im Serum und ELISpots aus mononukleären Zellen des peripheren Blutes, die von einer Untergruppe von Patienten isoliert wurden, ergab eine moderate Abnahme von IL‐31 als Reaktion auf die Bestrahlung mit blauem Licht.

Schlussfolgerungen

Trotz des günstigen Sicherheitsprofils und der mäßigen Verringerung von Pruritus und IL‐31‐Spiegel führte die Ganzkörper‐Blaulichtbestrahlung bei AD zu keiner Verbesserung der objektiven Parameter zu Krankheitsschwere.

Expert opinion on management of moderate-to-severe atopic dermatitis in Qatar

Atopic dermatitis (AD), a chronic-relapsing inflammatory skin disorder, manifests with intense itching and eczematous lesions impairing quality of life. A heterogeneous population, and regional clinical practices for treating AD warrant the development of guidelines in Qatar. Therefore, guidelines for the management of moderate-to-severe AD in Qatar have been developed and discussed. Experts, including dermatologists and immunologists, used the Delphi technique for developing guidelines. Consensus was defined as ≥75% agreement or disagreement. AD is highly prevalent in primary and tertiary dermatology centers. AD-associated foot eczema and psoriasiform eczema are more frequent in Qatar than in Europe or USA. SCORing Atopic Dermatitis Index quantifies disease severity and itch. Dermatology Life Quality Index assesses the quality of life. Atopic Dermatitis Control Tool assesses long-term disease control. Moderate-severe AD benefits from new topicals like Janus-kinase-inhibitors or PDE4-inhibitors combined with phototherapy. Currently approved systemic agents are dupilumab, baricitinib, abrocitinib, and upadacitinib. New anti-IL-13 and anti-IL-31 therapies will soon be available. Patient education, allergy testing, and comorbidity consideration are critical in the management of AD. The expert panel established a comprehensive and pragmatic approach to managing moderate-to-severe AD, thereby assisting clinical decision-making for healthcare professionals in Qatar.

Efficacy and tolerance of a novel topical TRPV-1 channel antagonist in dogs with allergic pododermatitis

BACKGROUND

Pruritus due to allergic skin disease is one of the most common reasons for dermatological consultations in the veterinary clinic. Treatment is usually multimodal and requires continuous monitoring and reassessment. New therapies are needed to broaden the therapeutic arsenal.

HYPOTHESIS/OBJECTIVES

The aim of this study was to evaluate the efficacy of a novel transient receptor potential vanilloid 1 (TRPV1) channel antagonist for allergic pododermatitis in dogs.

ANIMALS

Twenty-four client-owned dogs with allergic pododermatitis.

MATERIALS AND METHODS

The study was an open, prospective, multi-centre clinical trial with client-owned dogs. All dogs were treated twice daily with a spray containing hydroxymethoxyiodobenzyl glycolamide pelargonate for 28 days. Clinical assessments included pruritus Visual Analog Scale (PVAS), pedal skin lesion score, evaluation of quality of life (QoL), presence of secondary infections and a four-point subjective efficacy assessment by the veterinarian and the dog owner.

RESULTS

There was more than 50% improvement in all scores by the conclusion of the study. Secondary infections were reduced (p < 0.001). Both the veterinarians and dog owners evaluated the efficacy of the product positively. The product was well-tolerated.

CONCLUSIONS AND CLINICAL RELEVANCE

This study demonstrated the tolerability and efficacy of a TRPV1 antagonist on pruritic pododermatitis in 24 dogs.

Interleukin-31 in serum and cerebrospinal fluid of dogs with syringomyelia

BACKGROUND

Syringomyelia is a spinal cord cavity containing cerebrospinal fluid (CSF)-like fluid. If syringomyelia asymmetrically involves the dorsal horn grey matter of the spinal cord, affected dogs show increased signs of dysesthesia and neuropathic pain, like increased itching behaviour. In the dorsal horn, amongst others, receptors for Interleukin-31 (IL-31) can be found. IL-31 is one of the main cytokines involved in the pathogenesis of pruritus in atopic dermatitis in different species. This study investigates suspected elevated levels of IL-31 in serum and CSF of dogs showing signs of pain or increased itching behaviour related to syringomyelia. The IL-31 were measured in archived samples (52 serum and 35 CSF samples) of dogs with syringomyelia (n = 48), atopic dermatitis (n = 3) and of healthy control dogs (n = 11) using a competitive canine IL-31 ELISA.

RESULTS

Mean serum IL-31 level in dogs with syringomyelia was 150.1 pg/ml (n = 39), in dogs with atopic dermatitis 228.3 pg/ml (n = 3) and in healthy dogs 80.7 pg/ml (n = 10). Mean CSF IL-31 value was 146.3 pg/ml (n = 27) in dogs with syringomyelia and 186.2 pg/ml (n = 8) in healthy dogs. Individual patients with syringomyelia (especially dogs with otitis media or otitis media and interna or intervertebral disc herniation) showed high IL-31 levels in serum and CSF samples, but the difference was not statistically significant. IL-31 serum and CSF levels did not differ significantly in dogs with syringomyelia with or without itching behaviour and with or without signs of pain.

CONCLUSION

Based on this study, increased IL-31 levels seem not to be correlated with itching behaviour or signs of pain in dogs with syringomyelia, but might be caused by other underlying diseases.

Molecular mechanisms of pruritus in prurigo nodularis

Pruritus is the most common symptom of dermatological disorders, and prurigo nodularis (PN) is notorious for intractable and severe itching. Conventional treatments often yield disappointing outcomes, significantly affecting patients' quality of life and psychological well-being. The pathogenesis of PN is associated with a self-sustained "itch-scratch" vicious cycle. Recent investigations of PN-related itch have partially revealed the intricate interactions within the cutaneous neuroimmune network; however, the underlying mechanism remains undetermined. Itch mediators play a key role in pruritus amplification in PN and understanding their action mechanism will undoubtedly lead to the development of novel targeted antipruritic agents. In this review, we describe a series of pruritogens and receptors involved in mediating itching in PN, including cytokines, neuropeptides, extracellular matrix proteins, vasculogenic substances, ion channels, and intracellular signaling pathways. Moreover, we provide a prospective outlook on potential therapies based on existing findings.

Experimental Study: Interleukin-31 Augments Morphine-Induced Antinociceptive Activity and Suppress Tolerance Development in Mice

Morphine-induced antinociception is partially reduced in interleukin-31 (IL-31) receptor A (IL-31RA)-deficient mice, indicating that IL-31RA is crucial for morphine-induced peripheral antinociception. Herein, we examined the combined effects of IL-31 and morphine on the antinociceptive activity and itch-associated scratching behavior (LLS) in mice and elucidated the regulatory mechanisms. A hot-plate test was used to assess antinociception. LLS was automatically detected and recorded via a computer. IL-31RA mRNA expression was assessed using real-time polymerase chain reaction. Repeated pre-treatment with IL-31 resulted in significant antinociceptive activity. Repeated administration of morphine decreased the morphine-induced antinociceptive activity, LLS counts, and regular dose and inhibited IL-31-induced LLS. These results suggested that the repeated administration of morphine depleted inter-neuronal IL-31RA levels, preventing morphine-induced antinociception. Therefore, IL-31 may be helpful as an adjunct analgesic to morphine. To explore the benefits of IL-31, its influence on morphine-induced antinociceptive tolerance in mice was examined. An IL-31 and morphine combination increased the analgesic action, which increased the expression of DRG neuronal IL-31RA, elucidating the site of peripheral antinociception of morphine. This site may induce exocytosis of IL-31RA in the sensory nervous system. Collectively, the suppressive effect of IL-31 on morphine-induced antinociceptive tolerance may result from IL-31RA supplementation in sensory nerves.

Oncostatin M suppresses IL31RA expression in dorsal root ganglia and interleukin-31-induced itching

Background

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by intermittent itchy rash. Type 2 inflammatory cytokines such as interleukin (IL)-4, IL-13, and IL-31 are strongly implicated in AD pathogenesis. Stimulation of IL-31 cognate receptors on C-fiber nerve endings is believed to activate neurons in the dorsal root ganglion (DRG), causing itch. The IL-31 receptor is a heterodimer of OSMRβ and IL31RA subunits, and OSMRβ can also bind oncostatin M (OSM), a pro-inflammatory cytokine released by monocytes/macrophages, dendritic cells, and T lymphocytes. Further, OSM expression is enhanced in the skin lesions of AD and psoriasis vulgaris patients.

Objective

The current study aimed to examine the contributions of OSM to AD pathogenesis and symptom expression.

Methods

The expression levels of the OSM gene (OSM) and various cytokine receptor genes were measured in human patient skin samples, isolated human monocytes, mouse skin samples, and mouse DRG by RT-qPCR. Itching responses to various pruritogens were measured in mice by counting scratching episodes.

Results

We confirmed overexpression of OSM in skin lesions of patients with AD and psoriasis vulgaris. Monocytes isolated from the blood of healthy subjects overexpressed OSM upon stimulation with IL-4 or GM-CSF. Systemic administration of OSM suppressed IL31RA expression in the mouse DRG and IL-31-stimulated scratching behavior. In contrast, systemic administration of OSM increased the expression of IL-4- and IL-13-related receptors in the DRG.

Conclusion

These results suggest that OSM is an important cytokine in the regulation of skin monocytes, promoting the actions of IL-4 and IL-13 in the DRG and suppressing the action of IL-31. It is speculated that OSM released from monocytes in skin modulates the sensitivity of DRG neurons to type 2 inflammatory cytokines and thereby the severity of AD-associated skin itch.

Microglia are involved in regulating histamine-dependent and non-dependent itch transmissions with distinguished signal pathways

Although itch and pain have many similarities, they are completely different in perceptual experience and behavioral response. In recent years, we have a deep understanding of the neural pathways of itch sensation transmission. However, there are few reports on the role of non-neuronal cells in itch. Microglia are known to play a key role in chronic neuropathic pain and acute inflammatory pain. It is still unknown whether microglia are also involved in regulating the transmission of itch sensation. In the present study, we used several kinds of transgenic mice to specifically deplete CX3CR1+ microglia and peripheral macrophages together (whole depletion), or selectively deplete microglia alone (central depletion). We observed that the acute itch responses to histamine, compound 48/80 and chloroquine were all significantly reduced in mice with either whole or central depletion. Spinal c-fos mRNA assay and further studies revealed that histamine and compound 48/80, but not chloroquine elicited primary itch signal transmission from DRG to spinal Npr1- and somatostatin-positive neurons relied on microglial CX3CL1-CX3CR1 pathway. Our results suggested that microglia were involved in multiple types of acute chemical itch transmission, while the underlying mechanisms for histamine-dependent and non-dependent itch transmission were different that the former required the CX3CL1-CX3CR1 signal pathway.

Emerging concepts in neuropathic and neurogenic itch

Chronic pruritus has multiple etiologies, ranging from inflammatory to metabolic and neuropathic processes. However, recent advances in itch biology have shed light on potential mechanisms that explain the molecular and cellular basis of these pathologies. Furthermore, new understanding of neuroimmune itch circuits necessitates clarification of terminologies such as "neuropathic" and "neurogenic." This review provides an overview of ways new concepts may better explain the pathophysiology of a variety of chronic pruritic disorders and the rationale for directing emerging novel therapeutic strategies toward them.

IL-31-dependent neurogenic inflammation restrains cutaneous type 2 immune response in allergic dermatitis

Despite robust literature associating IL-31 with pruritic inflammatory skin diseases, its influence on cutaneous inflammation and the interplay between inflammatory and neurosensory pathways remain unmapped. Here, we examined the consequences of disrupting Il31 and its receptor Il31ra in a mouse model of house dust mite (HDM)-induced allergic dermatitis. Il31-deficient mice displayed a deficit in HDM dermatitis-associated scratching, consistent with its well-established role as a pruritogen. In contrast, Il31 deficiency increased the number and proportion of cutaneous type 2 cytokine-producing CD4+ T cells and serum IgE in response to HDM. Furthermore, Il4ra+ monocytes and macrophages capable of fueling a feedforward type 2 inflammatory loop were selectively enriched in Il31ra-deficient HDM dermatitis skin. Thus, IL-31 is not strictly a proinflammatory cytokine but rather an immunoregulatory factor that limits the magnitude of type 2 inflammatory responses in skin. Our data support a model wherein IL-31 activation of IL31RA+ pruritoceptors triggers release of calcitonin gene-related protein (CGRP), which can mediate neurogenic inflammation, inhibit CD4+ T cell proliferation, and reduce T cell production of the type 2 cytokine IL-13. Together, these results illustrate a previously unrecognized neuroimmune pathway that constrains type 2 tissue inflammation in the setting of chronic cutaneous allergen exposure and may explain paradoxical dermatitis flares in atopic patients treated with anti-IL31RA therapy.

The potent analgesia of intrathecal 2R, 6R-HNK via TRPA1 inhibition in LF-PENS-induced chronic primary pain model

BACKGROUND

Chronic primary pain (CPP) is an intractable pain of unknown cause with significant emotional distress and/or dysfunction that is a leading factor of disability globally. The lack of a suitable animal model that mimic CPP in humans has frustrated efforts to curb disease progression. 2R, 6R-hydroxynorketamine (2R, 6R-HNK) is the major antidepressant metabolite of ketamine and also exerts antinociceptive action. However, the analgesic mechanism and whether it is effective for CPP are still unknown.

METHODS

Based on nociplastic pain is evoked by long-term potentiation (LTP)-inducible high- or low-frequency electrical stimulation (HFS/LFS), we wanted to develop a novel CPP mouse model with mood and cognitive comorbidities by noninvasive low-frequency percutaneous electrical nerve stimulation (LF-PENS). Single/repeated 2R, 6R-HNK or other drug was intraperitoneally (i.p.) or intrathecally (i.t.) injected into naïve or CPP mice to investigate their analgesic effect in CPP model. A variety of behavioral tests were used to detect the changes in pain, mood and memory. Immunofluorescent staining, western blot, reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) and calcium imaging of in cultured dorsal root ganglia (DRG) neurons by Fluo-8-AM were used to elucidate the role and mechanisms of 2R, 6R-HNK in vivo or in vitro.

RESULTS

Intrathecal 2R, 6R-HNK, rather than intraperitoneal 2R, 6R-HNK or intrathecal S-Ketamine, successfully mitigated HFS-induced pain. Importantly, intrathecal 2R, 6R-HNK displayed effective relief of bilateral pain hypersensitivity and depressive and cognitive comorbidities in a dose-dependent manner in LF-PENS-induced CPP model. Mechanically, 2R, 6R-HNK markedly attenuated neuronal hyperexcitability and the upregulation of calcitonin gene-related peptide (CGRP), transient receptor potential ankyrin 1 (TRPA1) or vanilloid-1 (TRPV1), and vesicular glutamate transporter-2 (VGLUT2) in peripheral nociceptive pathway. In addition, 2R, 6R-HNK suppressed calcium responses and CGRP overexpression in cultured DRG neurons elicited by the agonists of TRPA1 or/and TRPV1. Strikingly, the inhibitory effects of 2R, 6R-HNK on these pain-related molecules and mechanical allodynia were substantially occluded by TRPA1 antagonist menthol.

CONCLUSIONS

In the newly designed CPP model, our findings highlighted the potential utility of intrathecal 2R, 6R-HNK for preventing and therapeutic modality of CPP. TRPA1-mediated uprgulation of CGRP and neuronal hyperexcitability in nociceptive pathways may undertake both unique characteristics and solving process of CPP.

Type 2 cytokines sensitize human sensory neurons to itch-associated stimuli

Introduction

Chronic itch is a central symptom of atopic dermatitis. Cutaneous afferent neurons express receptors interleukins (IL)-4, IL-13, and IL-33, which are type 2 cytokines that are elevated in atopic dermatitis. These neuronal cytokine receptors were found to be required in several murine models of itch. Prior exposure of neurons to either IL-4 or IL-33 increased their response to subsequent chemical pruritogens in mice but has not been previously examined in humans. The objective of the present study was to determine if type 2 cytokine stimulation sensitizes sensory neurons to future itch stimuli in a fully human ex vivo system.

Methods

We measured calcium flux from human dorsal root ganglia cultures from cadaveric donors in response to pruritogens following transient exposure to type 2 cytokines. We also measured their effect on neuronal calcium flux and changes in gene expression by RNA sequencing.

Results

Type 2 cytokines (IL-4, IL-13, and IL-33) were capable of sensitizing human dorsal root ganglia neurons to both histaminergic and nonhistaminergic itch stimuli. Sensitization was observed after only 2 h of pruritogen incubation. We observed rapid neuronal calcium flux in a small subset of neurons directly in response to IL-4 and to IL-13, which was dependent on the presence of extracellular calcium. IL-4 and IL-13 induced a common signature of upregulated genes after 24 h of exposure that was unique from IL-33 and non-type 2 inflammatory stimuli.

Discussion

This study provides evidence of peripheral neuron sensitization by type 2 cytokines as well as broad transcriptomic effects in human sensory ganglia. These studies identify both unique and overlapping roles of these cytokines in sensory neurons.

Zhenxin Anshen formula ameliorates atopic der-matitis-like skin dysfunction in mice and regulation of transient receptor potential vanilloid 1 and transient receptor potential ankyrin 1 in Neural pathways

OBJECTIVE

To investigate the efficacy of Zhenxin Anshen formula (, ZXAS) on atopic dermatitis (AD) by transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1) signalling pathway in mice and .

METHODS

AD-like lesions were induced by 1-chloro-2,4-dinitrobenzene (DNCB) to the shaved dorsal skin of BALB/c mice. BALB/c mice were divided into five groups: normal control, model control, cetirizine, low-, medium-, and high-dose of ZXAS. After ZXAS in-tervention, the skin lesions and blood samples were collected for hematoxylin and eosin-stained and measuring the concentrations of inflammatory cytokines. Immun-oglobulin E (IgE), interleukin (IL)-4, IL-5, IL-13, and thymic stromal lymphopoietin (TSLP) were de-tected by Enzyme-linked immunosorbent assay (ELISA). The spinal cords were collected for measuring the expression of gastrin-releasing peptide receptor (GRPR), TRPV1, and TRPA1 by using immunohistochemistry, western blotting, and quantitative real-time polymerase chain reaction (qRT-PCR) analyses. In addition, 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay, flow cytometry, ELISA, and Western blotting were conducted for analysis of primary dorsal root ganglia (DRG) neurons .

RESULTS

ZXAS treatment improved DNCB-induced AD-like lesions through reducing dermatitis score, number of scratching and epidermal thickness, accompanied by the de-creased IgE and Th2 inflammatory cytokines. ZXAS also supressed the mRNA and protein expression of GRPR, TRPV1, and TRPA1 in the spinal cord. The medicated sera of ZXAS decreased capsaicin-induced Ca influx and downregulated the expression of TRPV1, TRPA1, and phospholipase C in DRG neurons.

CONCLUSIONS

The therapeutic effect of ZXAS on AD may be related to the regulation of TRPV1 and TRPA1 and inhibition of Ca2+ signals in neurons.

GRPR down-regulation inhibits spermatogenesis through Ca2+ mediated by PLCβ/IP3R signaling pathway in long-term formaldehyde-exposed rats

Formaldehyde (FA), which is known as an air pollutant, has been proven to induce male infertility. However, the underlying mechanism of FA-induced male infertility remains elusive. In this study, 24 male SD rats were exposed to different levels of FA (0, 0.5, 2.46, and 5 mg/m3) for eight consecutive weeks. Through HE staining and sperm smear, we observed that FA exposure resulted in spermatogenic injury and the sperm quality decreased in rats. The qRT-PCR and Western blot analysis further revealed that GRPR was down-regulated in testicular tissues of FA-exposed rats as well as primary spermatogenic cells. Meanwhile, ZDOCK uncovered an interaction between GRPR and PLCβ. In addition, the CCK8, Fluo 3-AM and Flow cytometry results showed that FA exposure suppressed the expression of GRPR, PLCβ and IP3R, consequently reducing the Ca2+ concentration in spermatogenic cells, inducing apoptosis and inhibiting proliferation of spermatogenic cells. Moreover, rescue experiments confirmed that promoting GRPR could improve intracellular Ca2+ concentration by upregulating PLCβ and IP3R, partially reducing the apoptosis and promoting the proliferation of FA-treated spermatogenic cells. These findings revealed that GRPR participates in spermatogenesis through Ca2+ mediated by the PLCβ/IP3R signaling pathway in FA-exposed rats.

Divergent in situ expression of IL-31 and IL-31RA between bullous pemphigoid and pemphigus vulgaris

Bullous pemphigoid (BP) and pemphigus vulgaris (PV) are two major autoimmune blistering skin diseases. Unlike PV, BP is accompanied by intense pruritus, suggesting possible involvement of the pruritogenic cytokine IL-31. However, the underlying mechanisms of the clinical difference between BP and PV in terms of pruritus are not fully understood. To compare the expression levels of IL-31 and its receptor IL-31RA in the lesional skin, including peripheral nerves in BP and PV patients, immunohistochemical staining for IL-31 and IL-31RA was performed in skin samples of BP and PV patients and healthy controls (HC). The IL-31RA-expressing area in epidermis and peripheral nerves was analysed using ImageJ and the percentage of positive cells for IL-31/IL-31RA in dermal infiltrating cells was manually quantified. Quantitative analyses revealed that IL-31/IL-31RA expressions in the epidermis and dermal infiltrate were significantly increased in BP compared to PV and HC. The difference between BP and PV became more obvious when advanced bullous lesions were compared. Peripheral nerves in BP lesions presented significantly higher IL-31RA expression compared to PV lesions. In conclusion, we found significantly augmented expressions of IL-31/IL-31RA in BP lesions, including peripheral nerves, in comparison to PV. These results suggest a possible contribution of IL-31/IL-31RA signalling to the difference between BP and PV in the facilitation of pruritus and local skin inflammation, raising the possibility of therapeutic targeting of the IL-31/IL-31RA pathway in BP patients.

Modulation of Neuroimmune and Epithelial Dysregulation in Patients With Moderate to Severe Prurigo Nodularis Treated With Nemolizumab

Importance

Prurigo nodularis (PN) is a debilitating skin disease characterized by intense pruritus and hyperkeratotic skin nodules. Nemolizumab, a monoclonal antibody targeting interleukin 31 receptor α, is a promising novel therapy for the treatment of moderate to severe PN. The biological mechanisms by which nemolizumab promotes improvement of itch and skin lesions in PN are unknown.

Objective

To characterize changes in plasma protein biomarkers associated with clinical response to nemolizumab in patients with PN.

Design, Setting, and Participants

This multicenter cohort study included patients recruited from Austria, France, Germany, Poland, and the US from a phase 2 clinical trial. Adults diagnosed with moderate to severe PN with severe pruritus for at least 6 months were included in the original trial. Patients in the nemolizumab group were included in the present study if they achieved at least a 4-point decrease in the Peak Pruritus Numerical Rating Scale (PP-NRS) from baseline to week 12 during nemolizumab treatment. Placebo controls did not experience a 4-point decrease in PP-NRS. Mass spectrometry with tandem mass tags to enrich skin-specific protein detection was used to characterize changes in plasma protein expression in nemolizumab and placebo groups. Data were collected from November 2, 2017, to September 26, 2018, and analyzed from December 6, 2019, to April 8, 2022.

Intervention

As part of the clinical trial, patients were treated with 3 doses of nemolizumab or placebo at 0, 4, and 8 weeks.

Main Outcomes and Measures

Changes in plasma and epidermal protein expression in nemolizumab-treated patients compared with the placebo group at 0, 4, and 12 weeks.

Results

Among the 38 patients included in the analysis (22 women and 16 men; mean [SD] age, 55.8 [15.8] years), enrichment analysis of canonical pathways, biological functions, and upstream regulators showed downregulation of terms involving inflammation (IL-6, acute-phase response, signal transducer and activator of transcription 3, and interferon γ), neural processes (synaptogenesis signaling and neuritogenesis), tissue remodeling and fibrosis (transforming growth factor β1 and endothelin-1), and epidermal differentiation (epithelial mesenchymal transition) in the plasma of nemolizumab group.

Conclusions and Relevance

In this cohort study, differences between nemolizumab and placebo groups included modulation of inflammatory signaling, neural development, and epithelial differentiation, suggesting a promising potential approach for clinical management of PN.

IL-31RA and TRPV1 Expression in Atopic Dermatitis Induced with Trinitrochlorobenzene in Nc/Nga Mice

Atopic dermatitis (AD) is a common chronic inflammatory skin disease. Interleukin 31 (IL-31), a novel cytokine in AD, causes pruritus, typically characteristic of AD patients. The transient receptor potential vanilloid type 1 (TRPV1) is a cation channel activated by diverse noxious stimuli that has been studied in a variety of pruritic skin diseases. In this study, the AD animal model was generated by administering the hapten, trinitrochlorobenzene (TNCB), to Nc/Nga mice, and the degree of expression of the IL-31 receptor alpha (IL-31RA) and TRPV1 in the skin of these atopic models was evaluated. The Nc/Nga mice were divided into 3 groups: control, TNCB 2-weeks treated, and TNCB 8-weeks treated. After inducing AD, the skin lesions in each group were scored and compared, and the histology of the skin lesions and the IL-31RA and TRPV1 expression for each group were evaluated by analyzing immunohistochemistry. The results show a significant difference in the skin lesion scores between the groups. The immunohistochemistry evaluation highlighted the remarkable expression of IL-31RA and TRPV1 in the nerve fibers of the TNCB 8-weeks-treated group. We thus confirmed that the long-term application of TNCB induced chronic atopic-like dermatitis and that IL-31RA and TRPV1 were overexpressed in the peripheral nerve fibers in this AD model.

Crisaborole Inhibits Itch and Pain by Preventing Neutrophil Infiltration in a Mouse Model of Atopic Dermatitis

Crisaborole, a phosphodiesterase 4 (PDE4) inhibitor, has been approved for the treatment of mild to moderate atopic dermatitis. Atopic dermatitis is often associated with increased pain. Using a mouse model, this study investigated whether crisaborole suppresses pain associated with atopic dermatitis and the potential mechanisms underlying it. The mouse model for atopic dermatitis was developed by repeatedly applying MC903. MC903-treated mice had increased spontaneous scratching (itch-related behaviour) and wiping behaviour (pain-related behaviour). Crisaborole was topically applied to the cheek skin of MC903-treated mice, and it reduced both itch- and pain-related behaviours in these mice. Immunofluorescence staining revealed that crisaborole reduced neutrophil infiltration and interaction of neutrophils with sensory neurones. Intradermal injection of S100A8/A9, proinflammatory neutrophil mediator, enhanced not only itch-related behaviours evoked by histamine or chloroquine, but also pain-related behaviours evoked by capsaicin. Calcium imaging of mouse dorsal root ganglion neurones revealed that pretreatment with S100A8/A9 significantly increased calcium responses to histamine and capsaicin, and the proportion of chloroquine-sensitive neurones. These findings suggest that the PDE4 inhibitor reduces itch and pain, in part by inhibiting infiltration of S100A8/A9-containing neutrophils in a mouse model of MC903-induced atopic dermatitis.