Periostin, an Emerging Player in Itch Sensation

Prevalence and Mechanisms of Itch in Chronic Wounds: A Narrative Review

Itch is a commonly experienced problem by individuals with chronic wounds and greatly compromises their quality of life. Scratching can further hinder the wound healing process. Despite this being a clinically recognized issue, our knowledge of its exact prevalence in chronic wounds of different types and the molecular mechanisms driving it is limited. The multifactorial nature of wound itch makes its characterization particularly challenging. The present review is based on a thorough PubMed search, and it aims to provide an overview of existing evidence on the epidemiology, impact, and pathophysiology of wound itch, along with general recommendations on its management. Importantly, our work highlights the merit of screening chronic wound patients for associated pruritus and incorporating anti-itch measures in mainstream wound care.

The big four in the pathogenesis and pathophysiology of prurigo nodularis: Interplay among type 2 inflammation, epidermal hyperplasia, dermal fibrosis, and itch from neuroimmune dysregulation

Prurigo nodularis (PN) is a distinct inflammatory dermatosis. It is characterized by intensely pruritic, firm nodules, typically 1 to 2 cm in diameter, which usually develop on the extensor surfaces of the extremities. Histopathologically, the following characteristics are observed in PN lesions: (1) dermal cellular infiltrates composed of type 2 inflammation-associated immune cells with lesional overexpression of type 2 cytokines (including interleukin [IL]-4, IL-13, and IL-31), (2) dermal fibrosis, and (3) epidermal hyperplasia with hyperkeratosis. Additionally, functional and structural alterations of cutaneous sensory nerve fibers profoundly contribute to itch in cooperation with type 2 inflammation. This abnormal interaction is referred to as neuroimmune dysregulation. The scratching behavior induced by itching from neuroimmune dysregulation initiates the development of prurigo nodules. This distinctive pathogenic feature of "itch-first" in PN is distinct from "inflammation-first" in atopic dermatitis, where the skin initially exhibits type 2 inflammation, which is subsequently followed by itching. The interplay between the four elements, namely type 2 inflammation, epidermal hyperplasia, dermal fibrosis, and itch resulting from neuroimmune dysregulation, appears to be pivotal in the pathogenesis and pathophysiology of PN.

Deciphering Pain and Pruritus in Keloids from the Perspective of Neurological Dysfunction: Where Are We Now?

Keloids are a typical skin fibroproliferative disease that can cause severe aesthetic and functional concerns. Pain and pruritus are the most common clinical symptoms of keloids, but the mechanisms underlying these symptoms remain unclear. The peripheral nervous system plays a pivotal role in the transmission of superficial sensation signals. Mounting evidence has shown potential correlations between disturbance in the peripheral nervous system and pain and pruritus in keloids. Here, we summarize the role of neurological dysfunction in the development of pain and pruritus, with a specific focus on neuroanatomical alterations, the dysfunction of sensory nerves, and neurogenic inflammation.

Periostin in Bullous Pemphigoid: A Potential Biomarker of Disease Activity and Severity

Elevated periostin levels are commonly observed in conditions characterised by increased IgE and eosinophilia, such as bullous pemphigoid (BP), which typically presents with eosinophil infiltration and elevated IgE levels. To explore the link between periostin levels and key clinical parameters in BP, serum periostin levels were assessed in 55 classic BP patients and 55 healthy controls using ELISA. Upon admission, the BP Disease Area Index (BPDAI) score, autoantibody levels, and peripheral blood immune cells of BP patients were evaluated. The investigation also employed the Olink proteomic platform to analyse circulating proinflammatory biomarkers. The results indicated significantly higher periostin levels in BP patients, showing a strong positive correlation with BPDAI scores, which was more pronounced compared to the correlation between BPDAI scores and BP 180 IgG or eosinophil counts. Correlation analysis revealed positive links between periostin levels in serum and attributes such as urticaria/erythema lesions, total IgE levels, serum BP180 IgG, BP180 IgE, BP230 IgE, and blood eosinophil counts. The findings from the Olink proteomic analysis provided additional evidence of the connection between periostin and type II inflammation in BP, which was further validated by the observed positive correlation between periostin and IL-13 using ELISA. Furthermore, it was observed that serum periostin levels decreased post-effective treatment. Overall, this study underscores a compelling association between periostin expression and the activity and severity of BP, as well as its reflection of type II inflammation.

Mechanisms of Itch in Atopic Dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disease characterized by recurrent eczematous lesions and intense itch. The pathological mechanism of AD involves a complex interaction between skin barrier dysfunction and a predominantly T helper (Th) 2-skewed immune dysregulation. The dysfunctional skin barrier in AD enhances antigen penetration, exacerbating allergic reactions. Scratching further damages the skin barrier, worsens dryness and increases the release of pro-inflammatory mediators, perpetuating the itch-scratch cycle. Breaking this cycle with appropriate treatments is vital. Th2 cells secrete interleukin (IL)-4, IL-13 and IL-31 which play keys roles in AD pathogenesis. IL-31 directly induces pruritus, while IL-4 and IL-13 enhance itching. An increased density of intraepidermal nerve fibers has been observed in AD lesions in a disease-state-dependent manner. In normal skin, both semaphorin 3A (Sema3A; a nerve repulsion factor) and nerve growth factor (NGF; a nerve elongation factor) are expressed. However, in AD lesions, Sema3A expression decreases while NGF expression increases. These findings suggest that epidermal nerve density is regulated by a fine balance between Sema3A and NGF, with Sema3A playing a key role in itch sensitivity in AD. In healthy skin, Sema3A is produced during the early-stage of differentiation of keratinocytes and moves into the upper epidermis. The levels of Sema3A and the density of epidermal nerve fibers may vary depending on the disease state of AD. Our future research will focus on the regulatory mechanisms of Sema3A in skin, and potential clinical applications.

Biomarkers and patient-related factors associated with clinical outcomes in dupilumab-treated atopic dermatitis

Background

Atopic dermatitis (AD) is a common chronic eczematous skin disease with severe pruritus. Several new therapeutic agents for AD such as dupilumab, an anti-IL-4Rα antibody, have been developed in recent years. We need to predict which agent is the best choice for each patient, but this remains difficult.

Objective

Our aim was to examine clinical background factors and baseline biomarkers that could predict the achievement of improved clinical outcomes in patients with AD treated with dupilumab.

Methods

A multicenter, prospective observational study was conducted on 110 patients with AD. The Eczema Area and Severity Index was used as an objective assessment, and the Patient-Oriented Eczema Measure and Numerical Rating Scale for Pruritus were used as patient-reported outcomes. In addition, some clinical background factors were evaluated.

Results

The achievement of an absolute Eczema Area and Severity Index of 7 or less was negatively associated with current comorbidity of food allergy and baseline serum lactate dehydrogenase (LDH) levels. There were negative associations between achievement of a Patient-Oriented Eczema Measure score of 7 or less and duration of severe AD and between achievement of an itching Numerical Rating Scale for Pruritus score of 1 or less and current comorbidity of allergic conjunctivitis or baseline serum periostin level. Furthermore, signal detection analysis showed that a baseline serum LDH level less than 328 U/L could potentially be used as a cutoff value for predicting the efficacy of dupilumab.

Conclusion

Baseline biomarkers such as LDH and periostin and clinical background factors such as current comorbidity of food allergy and a long period of severe disease may be useful indicators when choosing dupilumab for systemic treatment for AD, as they can predict the efficacy of dupilumab.

Epicutaneous house dust mite (HDM)-induced skin lesions feature early activation of T helper 2 inflammatory and pruritogenic pathways in HDM-nonsensitised dogs

BACKGROUND

Epicutaneously house dust mite-sensitised (HDM-S) healthy dogs are commonly used as canine atopic dermatitis (cAD) models; however, the exact mechanisms of HDM-induced AD immune activation in HDM-S and HDM-nonsensitised (NS) dogs remain unclear.

OBJECTIVES

To characterise the inflammatory and pruritogenic transcriptome of acute epicutaneous HDM-induced skin lesions at 6 h and 24 h in HDM-NS and HDM-S dogs; untreated skin at 0 h from each dog served as control.

ANIMALS

Six HDM-S and six HDM-NS laboratory beagles.

MATERIALS AND METHODS

Processed expression data from GEO deposited by Schamber et al. (G3 (Bethesda), 2014, 4 and 1787) (GSE58442) were downloaded and analysed using R and the Bioconductor package. Significance analysis was performed with the limma package; genes with false discovery rate <0.05 and fold-change ≤/≥1.5 were considered significantly differentially expressed (DEGs).

RESULTS

A 2D principal component analysis revealed no clear separation between HDM-NS and HDM-S dogs at 6 h and 24 h time points. HDM-induced skin lesions in sensitised and nonsensitised dogs at the 24 h time point showed significant upregulation of T helper cell (Th)2 genes (interleukin [IL]-4R, IL-5, IL-13, CCL13 and CCL17), as well as proinflammatory- (LTB, IL-1A and IL-18), Th1- (CXCL10, OASL and MX-1) and Th17-related markers (IL-17B, IL-17F, CCL19 and CCL20). The key Th22-related maker, IL-22, was upregulated only in the HDM-S group at the 24 h time point. Both groups at 24 h featured significant upregulation of several noncytokine pruritogens, such as trypsin, chymase, cathepsin S, periostin and neuromedin B.

CONCLUSIONS AND CLINICAL RELEVANCE

Taken together, we establish that epicutaneous HDM patch application induces immune changes in HDM-NS dogs with Th2 dominance and activates several itch-promoting pathways.

The involvement of keratinocytes in pruritus of chronic inflammatory dermatosis

Frequent itching and incessant scratching are commonly observed in various chronic inflammatory skin conditions, including atopic dermatitis and psoriasis. The persistent and prolonged nature of pruritus can worsen one's quality of life. Keratinocytes (KCs), the predominant cells of the epidermis, have been confirmed to interact with sensory neurons and immune cells and be involved in chronic skin inflammatory diseases associated with pruritus. Initially, KCs and sensory neurons form a unique synapse-like connection within the epidermis, serving as the structural foundation for their interaction. Additionally, several receptors, including toll-like receptors and protease-activated receptor 2, expressed on KCs, become activated in an inflammatory milieu. On the one hand, activated KCs are sources of pro-inflammatory cytokines and neurotrophic factors, such as adenosine triphosphate, thymic stromal lymphopoietin, and nerve growth factor, which directly or indirectly participate in stimulating sensory neurons, thereby contributing to the itch sensations. On the other hand, KCs also function as primary transducers alongside intraepidermal nerve endings, directly initiating pruritic responses. This review summarizes the current literature and highlights the critical role of KCs in the development and persistence of chronic itch in inflammatory skin disorders.

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.

Current and emerging drugs for the treatment of pruritus: an update of the literature

INTRODUCTION

Pruritus, particularly in its chronic form, often imposes significant suffering and reductions in patients' quality of life. The pathophysiology of itch is varied depending on disease context, creating opportunities for unique drug development and multimodal therapy.

AREAS COVERED

The purpose of this article is to provide an update of the literature regarding current and emerging therapeutics in itch. We review the multitudes of drug targets available and corresponding drugs that have shown efficacy in clinical trials, with a particular emphasis on phase 2 and 3 trials and beyond. Broadly, these targets include therapies directed against type 2 inflammation (i.e. Th2 cytokines, JAK/STAT, lipid mediators, T-cell mediators, and other enzymes and receptors) and neural receptors and targets (i.e. PARs, TRP channels, opioid receptors, MRGPRs, GABA receptors, and cannabinoid receptors).

EXPERT OPINION

Therapeutics for itch are emerging at a remarkable pace, and we are entering an era with more and more specialized therapies. Increasingly, these treatments are able to relieve itch beyond their effect on inflammation by directly targeting the neurosensory system.

Exploration of efficacy and mechanism of 0.05% cyclosporine eye drops (II) monotherapy in allergic conjunctivitis-associated dry eye

PURPOSE

To explore the efficacy and relevant mechanism of 0.05% cyclosporine A (CsA) eye drops (II) monotherapy in patients with allergic conjunctivitis-associated dry eye (ACDE).

METHODS

Prospective, randomized, controlled study. Fifty-three patients with mild-to-moderate ACDE were randomly assigned to two groups. The CsA group received 0.05% CsA eye drops (II) monotherapy four times daily. The control group received 0.1% olopatadine twice daily combined with 0.1% preservative-free artificial tears four times daily. Clinical symptoms and signs, tear total IgE, and lymphotoxin-α (LT-α) concentrations were assessed at pre- and post-treatment days 7, 30, and 60. And we further measured six tear cytokines levels using a microsphere-based immunoassay.

RESULTS

The CsA group showed significant improvement in symptoms (Ocular Surface Disease Index and itching scores) and signs (conjunctival hyperaemia, conjunctival oedema, conjunctival papillae, tear break-up time (TBUT), corneal fluorescein staining, and goblet cell density) at each follow-up period compared to pre-treatment (all P < 0.050). And its improvement in itching scores (P7th < 0.001, P30th = 0.039, and P60th = 0.031) and TBUT (P7th = 0.009, P30th = 0.003, and P60th = 0.005) was more significant than the control group at all follow-up periods. The tear total IgE, interleukin (IL)-5, IL-6, periostin, eotaxin-3, and MMP-9 levels significantly decreased in the CsA group at day 60 after treatment (all P < 0.050). And the changed values in tear total IgE were positively correlated with the change in itching scores.

CONCLUSIONS

0.05% CsA eye drops (II) monotherapy can rapidly improve the symptoms and signs, especially in ocular itching and TBUT, in patients with ACDE. And its efficacy is superior to 0.1% olopatadine combined with artificial tears. Moreover, CsA downregulates the expression levels of tear inflammatory cytokines, including tear total IgE, IL-5, IL-6, periostin, eotaxin-3, and MMP-9. Among that, the reduction in tear total IgE levels may reflect the improvement of ocular itching.

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.

What's New in Cutaneous T-Cell Lymphoma-Associated Pruritus

Cutaneous T-cell lymphomas are a heterogenous group of lymphomas that cause various skin manifestations. Severe pruritus occurs frequently in cutaneous T-cell lymphoma and negatively impacts patients' quality of life. The pathophysiology of cutaneous T-cell lymphoma-associated itch is complex and involves various immune cells, inflammatory cytokines, and neuroimmune interactions. Treating cutaneous T-cell lymphoma pruritus can be challenging, and there have been few randomized controlled studies evaluating the use of antipruritic treatments in these patients. Systemic therapies targeting the disease have also been shown to have some antipruritic effects. Furthermore, although biologic therapy has revolutionized the treatment of other pruritic skin conditions, the use of biologics in cutaneous T-cell lymphoma remains controversial.

Cutaneous Components Leading to Pruritus, Pain, and Neurosensitivity in Atopic Dermatitis: A Narrative Review

Atopic dermatitis (AD) is a chronic, relapsing immunoinflammatory skin condition characterized by sensations such as pruritis, pain, and neuronal hypersensitivity. The mechanisms underlying these sensations are multifactorial and involve complex crosstalk among several cutaneous components. This review explores the role these components play in the pathophysiology of atopic dermatitis. In the skin intercellular spaces, sensory nerves interact with keratinocytes and immune cells via myriad mediators and receptors. These interactions generate action potentials that transmit pruritis and pain signals from the peripheral nervous system to the brain. Keratinocytes, the most abundant cell type in the epidermis, are key effector cells, triggering crosstalk with immune cells and sensory neurons to elicit pruritis, pain, and inflammation. Filaggrin expression by keratinocytes is reduced in atopic dermatitis, causing a weakened skin barrier and elevated skin pH. Fibroblasts are the main cell type in the dermis and, in atopic dermatitis, appear to reduce keratinocyte differentiation, further weakening the skin barrier. Fibroblasts and mast cells promote inflammation while dermal dendritic cells appear to attenuate inflammation. Inflammatory cytokines and chemokines play a major role in AD pathogenesis. Type 2 immune responses typically generate pruritis, and the type 1 and type 3 responses generate pain. Type 2 responses and increased skin pH contribute to barrier dysfunction and promote dysbiosis of the skin microbiome, causing the proliferation of Staphyloccocus aureus. In conclusion, understanding the dynamic interactions between cutaneous components in AD could drive the development of therapies to improve the quality of life for patients with AD.

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.

Possible Association of Interleukin-31/-31RA Signalling and Basophils with Itch in Porokeratosis

is missing (Short communication).

Pruritus in keloid scars: mechanisms and treatments

Keloids occur after cutaneous injury and can cause distress due to physical appearance and associated symptoms such as pain and pruritus. Keloid-associated pruritus is a common manifestation and has negative impacts on quality of life. The mechanism underlying this type of pruritus is multifactorial and thought to involve small nerve fiber damage, neurogenic inflammation, and a Th2-predominant inflammatory response. Various agents have been shown to reduce keloid pruritus, including intralesional corticosteroids, botulinum toxin A, 5-fluorouracil, and bleomycin. Other treatment modalities such as cryotherapy and hyperbaric oxygen therapy are also effective. Future treatments targeting the mechanisms involved in keloid-associated itch could provide improvements in pruritus and quality of life in these patients, but further studies on the efficacy of these agents are needed.

Multimodal roles of transient receptor potential channel activation in inducing pathological tissue scarification

Transient receptor potential (TRP) channels are a class of transmembrane proteins that can sense a variety of physical/chemical stimuli, participate in the pathological processes of various diseases and have attracted increasing attention from researchers. Recent studies have shown that some TRP channels are involved in the development of pathological scarification (PS) and directly participate in PS fibrosis and re-epithelialization or indirectly activate immune cells to release cytokines and neuropeptides, which is subdivided into immune inflammation, fibrosis, pruritus and mechanical forces increased. This review elaborates on the characteristics of TRP channels, the mechanism of PS and how TRP channels mediate the development of PS, summarizes the important role of TRP channels in the different pathogenesis of PS and proposes that therapeutic strategies targeting TRP will be important for the prevention and treatment of PS. TRP channels are expected to become new targets for PS, which will make further breakthroughs and provide potential pharmacological targets and directions for the in-depth study of PS.

Basic mechanisms of itch

Pruritus (or itch) is an unpleasant sensation leading to a desire to scratch. In the epidermis, there are selective C or Aδ epidermal nerve endings that are pruriceptors. At their other ends, peripheral neurons form synapses with spinal neurons and interneurons. Many areas in the central nervous system are involved in itch processing. Although itch does not occur solely because of parasitic, allergic, or immunologic diseases, it is usually the consequence of neuroimmune interactions. Histamine is involved in a minority of itchy conditions, and many other mediators play a role: cytokines (eg, IL-4, IL-13, IL-31, IL-33, and thymic stromal lymphopoietin), neurotransmitters (eg, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, neuropeptide Y, NBNP, endothelin 1, and gastrin-releasing peptide), and neurotrophins (eg, nerve growth factor and brain-derived neurotrophic factor). Moreover, ion channels such as voltage-gated sodium channels, transient receptor potential vanilloid 1, transient receptor ankyrin, and transient receptor potential cation channel subfamily M (melastatin) member 8 play a crucial role. The main markers of nonhistaminergic pruriceptors are PAR-2 and MrgprX2. A notable phenomenon is the sensitization to pruritus, in which regardless of the initial cause of pruritus, there is an increased responsiveness of peripheral and central pruriceptive neurons to their normal or subthreshold afferent input in the context of chronic itch.

Binding, Neutralization and Internalization of the Interleukin-13 Antibody, Lebrikizumab

INTRODUCTION

IL-13 is the primary upregulated cytokine in atopic dermatitis (AD) skin and is the pathogenic mediator driving AD pathophysiology. Lebrikizumab, tralokinumab and cendakimab are therapeutic monoclonal antibodies (mAb) that target IL-13.

METHODS

We undertook studies to compare in vitro binding affinities and cell-based functional activities of lebrikizumab, tralokinumab and cendakimab.

RESULTS

Lebrikizumab bound IL-13 with higher affinity (as determined using surface plasma resonance) and slower off-rate. It was more potent in neutralizing IL-13-induced effects in STAT6 reporter and primary dermal fibroblast periostin secretion assays than either tralokinumab or cendakimab. Live imaging confocal microscopy was employed to determine the mAb effects on IL-13 internalization into cells via the decoy receptor IL-13Rα2, using A375 and HaCaT cells. The results showed that only the IL-13/lebrikizumab complex was internalized and co-localized with lysosomes, whereas IL-13/tralokinumab or IL-13/cendakimab complexes did not internalize.

CONCLUSION

Lebrikizumab is a potent, neutralizing high-affinity antibody with a slow disassociation rate from IL-13. Additionally, lebrikizumab does not interfere with IL-13 clearance. Lebrikizumab has a different mode of action to both tralokinumab and cendakimab, possibly contributing to the clinical efficacy observed by lebrikizumab in Ph2b/3 AD studies.

[Translated article] Pruritus in Dermatology: Part 1-General Concepts and Pruritogens

Pruritus is the most common symptom of dermatologic and systemic diseases. The diagnosis of pruritus is clinical, although additional tests may be necessary to identify or confirm the cause. Translational medicine has led to the discovery of new mediators of itch, or pruritogens, as well as new receptors. Knowing how to properly recognize the main pathway that mediates itch in each patient is the key to successful treatment. Although the histaminergic pathway predominates in conditions like urticaria or drug-induced pruritus, it is the nonhistaminergic pathway that predominates in nearly all other skin diseases covered in this review. Part 1 of this 2-part review discusses the classification of pruritus, additional testing, the pathophysiology of itch and the pruritogens implicated (including cytokines and other molecules), and central sensitization to itch.

Allergen sensitization stratifies IL-31 production by memory T cells in atopic dermatitis patients

Background

The role of allergen sensitization in IL-31 production by T cells and specifically in the clinical context of atopic dermatitis (AD) has not been characterized.

Methods

The response to house dust mite (HDM) in purified memory T cells cocultured with epidermal cells from AD patients (n=58) and control subjects (n=11) was evaluated. AD-associated cytokines from culture supernatants, plasma proteins and mRNA expression from cutaneous lesions were assessed and related with the clinical features of the patients.

Results

HDM-induced IL-31 production by memory T cells defined two subsets of AD patients according to the presence or absence of IL-31 response. Patients in the IL-31 producing group showed a more inflammatory profile, and increased HDM-specific (sp) and total IgE levels compared to the IL-31 non-producing group. A correlation between IL-31 production and patient’s pruritus intensity, plasma CCL27 and periostin was detected. When the same patients were analyzed based on sp IgE and total IgE levels, an increased IL-31 in vitro response, as well as type 2 markers in plasma and cutaneous lesions, was found in patients with sp IgE levels &gt; 100 kUA/L and total IgE levels &gt; 1000 kU/L. The IL-31 response by memory T cells was restricted to the cutaneous lymphocyte-associated antigen (CLA)+ T-cell subset.

Conclusion

IgE sensitization to HDM allows stratifying IL-31 production by memory T cells in AD patients and relating it to particular clinical phenotypes of the disease.

How to get rid of itching

Itch is an unpleasant sensation arising from a variety of dermatologic, neuropathic, systemic, and psychogenic etiologies. Various itch pathways are implicated according to the underlying etiology. A variety of pruritogens, or itch mediators, as well as receptors have been identified and provide potential therapeutic targets. Recent research has primarily focused on targeting inflammatory cytokines and Janus kinase signaling, protease-activated receptors, substance P and neurokinin, transient receptor potential-vanilloid ion channels, Mas-related G-protein-coupled receptors (MRGPRX2 and MRGPRX4), the endogenous opioid and cannabinoid balance, and phosphodiesterase 4. Periostin, a newly identified pruritogen, should be further explored with clinical trials. Drugs targeting neural sensitization including the gabergic system and P2X3 are other potential drugs for chronic itch. There is a need for more targeted therapies to improve clinical outcomes and reduce side effects.

IL-31-generating network in atopic dermatitis comprising macrophages, basophils, thymic stromal lymphopoietin, and periostin

BACKGROUND

IL-31 is a type 2 cytokine involved in the itch sensation in atopic dermatitis (AD). The cellular origins of IL-31 are generally considered to be T_H2 cells. Macrophages have also been implicated as cellular sources of IL-31.

OBJECTIVE

We sought to determine the expression of IL-31 by macrophages and to elucidate the productive mechanisms and contributions to itch in AD skin lesions.

METHODS

Expression of IL-31 by macrophages, expressions of thymic stromal lymphopoietin (TSLP) and periostin, and presence of infiltrating basophils in human AD lesions were examined through immunofluorescent staining, and correlations were assessed. Furthermore, mechanisms of inducing IL-31-expressing macrophages were analyzed in an MC903-induced murine model for AD in vivo and in mouse peritoneal macrophages ex vivo.

RESULTS

A significant population of IL-31⁺ cells in human AD lesions was that of CD68⁺ cells expressing CD163, an M2 macrophage marker. The number of IL-31⁺/CD68⁺ cells correlated with epidermal TSLP, dermal periostin, and the number of dermal-infiltrating basophils. In the MC903-induced murine AD model, significant scratching behaviors with enhanced expressions of TSLP and periostin were observed, accompanied by massive infiltration of basophils and IL-31⁺/MOMA-2⁺/Arg-1⁺ cells. Blockade of IL-31 signaling with anti-IL-31RA antibody or direct depletion of macrophages by clodronate resulted in attenuation of scratching behaviors. To effectively reduce lesional IL-31⁺ macrophages and itch, basophil depletion was essential in combination with TSLP- and periostin-signal blocking. Murine peritoneal macrophages produced IL-31 when stimulated with TSLP, periostin, and basophils.

CONCLUSIONS

A network comprising IL-31-expressing macrophages, TSLP, periostin, and basophils plays a significant role in AD itch.

Identification of key immune-related genes in dilated cardiomyopathy using bioinformatics analysis

Dilated cardiomyopathy (DCM) is characterized by the left ventricular dilatation and impaired myocardial systolic dysfunction with high mortality and morbidity. However, the underlying mechanisms remain elusive. We first identified the differentially expressed genes (DEGs) between the DCM and control group using two expression profiles from GSE3585 and GSE84796. Enrichment analysis was conducted to explore the potential mechanisms underlying DCM. A total of four algorithms, including key module of MCODE, degree, maximum neighborhood component (MNC), and maximal clique centrality (MCC), were used to identify the hub genes within Cytoscape. The correlation between hub genes and infiltrated immune cells was evaluated to determine potential immune-related genes. The expression analysis and diagnosis value analysis of potential immune-related genes were performed. Finally, the expression analysis with GSE57338 and relationship analysis with the comparative toxicogenomics database (CTD) were performed to identify the key immune-related genes in DCM. A total of 80 DEGs were screened for DCM. Enrichment analysis revealed that DEGs were involved in the immune-related pathological process. Immune infiltration analysis indicated a potentially abnormal immune response in DCM. Four up-regulated genes (COL1A2, COL3A1, CD53, and POSTN) were identified as potential immune-related genes. Finally, three genes (COL1A2, COL3A1, and POSTN) were determined as the key immune-related genes in DCM via expression analysis with a validation set (GSE57338) and relationship analysis with CTD. Our study suggested that the upregulated COL1A2, COL3A1, and POSTN might be the key immune-related genes for DCM. Further studies are needed to validate the underlying mechanisms.

IL-13, periostin and dipeptidyl-peptidase-4 reveal endotype-phenotype associations in atopic dermatitis

BACKGROUND

The heterogeneous (endo)phenotypes of atopic dermatitis (AD) require precision medicine. Currently, systemic therapy is recommended to patients with an Eczema Area and Severity Index (EASI)≥16. Previous studies have demonstrated an improved treatment response to the anti-interleukin (IL)-13 antibody tralokinumab in AD subgroups with elevated levels of the IL-13-related biomarkers dipeptidyl-peptidase (DPP)-4 and periostin.

METHODS

Herein, 373 AD patients aged≥12 years were stratified by IL-13high , periostinhigh and DPP-4high endotypes using cross-sectional data from the ProRaD cohort Bonn. "High" was defined as >80th quantile of 47 non-atopic controls. We analyzed endotype-phenotype associations using machine-learning gradient boosting compared to logistic regression.

RESULTS

AD severity and eosinophils correlated with IL-13 and periostin levels. Correlations of IL-13 with EASI were stronger in patients with increased (rs=0.482) than with normal (rs=0.342) periostin levels. We identified eosinophilia>6% and an EASI range of 5.5-17 dependent on the biomarker combination to be associated with increasing probabilities of biomarkerhigh endotypes. Also patients with mild-to-low-moderate severity (EASI<16) featured increased biomarkers (IL-13high : 41%, periostinhigh : 48.4%, DPP-4high : 22.3%). Herthoge sign (adjusted Odds Ratio (aOR)=1.89, 95% Confidence Interval (CI) [1.14-3.14]) and maternal allergic rhinitis (aOR=2.79-4.47) increased the probability of an IL-13high -endotype, "dirty neck" (aOR=2.83 [1.32-6.07]), orbital darkening (aOR=2.43 [1.08-5.50]), keratosis pilaris (aOR=2.21 [1.1-4.42]) and perleche (aOR=3.44 [1.72-6.86]) of a DPP-4high -endotype.

CONCLUSIONS

A substantial proportion of patients with EASI<16 featured high biomarker levels suggesting systemic impact of skin inflammation already below the current cut-off for systemic therapy. Our findings facilitate the identification of patients with distinct endotypes potentially linked to response to IL-13-targeted therapy.

Serum Levels of Eosinophil-Derived Neurotoxin, Platelet-Activating Factor and Vascular Endothelial Growth Factor in Adult Patients with Atopic Dermatitis-A Pilot Study

Atopic dermatitis (AD) is a chronic, highly pruritic, relapsing-remitting inflammatory skin disease. The etiology of AD has not been fully explained yet and complex interactions of various small molecules are still being taken into account. The aim of this research was to investigate the serum eosinophil-derived neurotoxin (EDN), platelet activating factor (PAF) and vascular endothelial growth factor (VEGF) concentrations in relation to the disease severity and pruritus intensity in adult patients with AD. This pilot study was performed on 30 participants (15 patients with AD and 15 healthy controls). Blood samples were taken to examine the serum levels of EDN, PAF and VEGF using the enzyme-linked immunosorbent assay (ELISA) test. The severity of disease was assessed by the Scoring Atopic Dermatitis (SCORAD) index. The intensity of pruritus, as a subjective symptom, was determined by the Visual Analogue Scale (VAS). Obtained results revealed that the EDN (p = 0.016) and VEGF (p = 0.032), but not PAF (p = 0.841) concentrations were significantly higher in patients with AD compared with those of the control group. There was positive correlation between the EDN level and the SCORAD index in patients with AD (r = -0.9, p = 0.037) which was not found for the PAF and VEGF levels. Circulating EDN, PAF and VEGF levels were not significantly correlated with the severity of pruritus. Our results suggest that the END and VEGF serum levels are significantly increased in patients with AD compared to control group. Moreover, EDN might be useful to reflect the severity of symptoms.

In vitro models for investigating itch

Itch (pruritus) is a sensation that drives a desire to scratch, a behavior observed in many animals. Although generally short-lasting and not causing harm, there are several pathological conditions where chronic itch is a hallmark symptom and in which prolonged scratching can induce damage. Finding medications to counteract the sensation of chronic itch has proven difficult due to the molecular complexity that involves a multitude of triggers, receptors and signaling pathways between skin, immune and nerve cells. While much has been learned about pruritus from in vivo animal models, they have limitations that corroborate the necessity for a transition to more human disease-like models. Also, reducing animal use should be encouraged in research. However, conducting human in vivo experiments can also be ethically challenging. Thus, there is a clear need for surrogate models to be used in pre-clinical investigation of the mechanisms of itch. Most in vitro models used for itch research focus on the use of known pruritogens. For this, sensory neurons and different types of skin and/or immune cells are stimulated in 2D or 3D co-culture, and factors such as neurotransmitter or cytokine release can be measured. There are however limitations of such simplistic in vitro models. For example, not all naturally occurring cell types are present and there is also no connection to the itch-sensing organ, the central nervous system (CNS). Nevertheless, in vitro models offer a chance to investigate otherwise inaccessible specific cell–cell interactions and molecular pathways. In recent years, stem cell-based approaches and human primary cells have emerged as viable alternatives to standard cell lines or animal tissue. As in vitro models have increased in their complexity, further opportunities for more elaborated means of investigating itch have been developed. In this review, we introduce the latest concepts of itch and discuss the advantages and limitations of current in vitro models, which provide valuable contributions to pruritus research and might help to meet the unmet clinical need for more refined anti-pruritic substances.

Current and Emerging Strategies to Inhibit Type 2 Inflammation in Atopic Dermatitis

Type 2 immunity evolved to combat helminth infections by orchestrating a combined protective response of innate and adaptive immune cells and promotion of parasitic worm destruction or expulsion, wound repair, and barrier function. Aberrant type 2 immune responses are associated with allergic conditions characterized by chronic tissue inflammation, including atopic dermatitis (AD) and asthma. Signature cytokines of type 2 immunity include interleukin (IL)-4, IL-5, IL-9, IL-13, and IL-31, mainly secreted from immune cells, as well as IL-25, IL-33, and thymic stromal lymphopoietin, mainly secreted from tissue cells, particularly epithelial cells. IL-4 and IL-13 are key players mediating the prototypical type 2 response; IL-4 initiates and promotes differentiation and proliferation of naïve T-helper (Th) cells toward a Th2 cell phenotype, whereas IL-13 has a pleiotropic effect on type 2 inflammation, including, together with IL-4, decreased barrier function. Both cytokines are implicated in B-cell isotype class switching to generate immunoglobulin E, tissue fibrosis, and pruritus. IL-5, a key regulator of eosinophils, is responsible for eosinophil growth, differentiation, survival, and mobilization. In AD, IL-4, IL-13, and IL-31 are associated with sensory nerve sensitization and itch, leading to scratching that further exacerbates inflammation and barrier dysfunction. Various strategies have emerged to suppress type 2 inflammation, including biologics targeting cytokines or their receptors, and Janus kinase inhibitors that block intracellular cytokine signaling pathways. Here we review type 2 inflammation, its role in inflammatory diseases, and current and future therapies targeting type 2 pathways, with a focus on AD. INFOGRAPHIC.

Neuro-immune communication regulating pruritus in atopic dermatitis

Atopic dermatitis (AD) is a common, chronic-relapsing inflammatory skin disease with significant disease burden. Genetic and environmental trigger factors contribute to AD, activating two of our largest organs, the nervous and immune system. Dysregulation of neuro-immune circuits plays a key role in the pathophysiology of AD causing inflammation, pruritus, pain, and barrier dysfunction. Sensory nerves can be activated by environmental or endogenous trigger factors transmitting itch stimuli to the brain. Upon stimulation, sensory nerve endings also release neuromediators into the skin contributing again to inflammation, barrier dysfunction and itch. Additionally, dysfunctional peripheral and central neuronal structures contribute to neuroinflammation, sensitization, nerve elongation, neuropathic itch, thus chronification and therapy-resistance. Consequently, neuro-immune circuits in skin and central nervous system may be targets to treat pruritus in AD. Cytokines, chemokines, proteases, lipids, opioids, ions excite/sensitize sensory nerve endings not only induce itch but further aggravate/perpetuate inflammation, skin barrier disruption, and pruritus. Thus, targeted therapies for neuro-immune circuits as well as pathway inhibitors (e.g., kinase inhibitors) may be beneficial to control pruritus in AD either in systemic and/or topical form. Understanding neuro-immune circuits and neuronal signaling will optimize our approach to control all pathological mechanisms in AD, inflammation, barrier dysfunction and pruritus.

Pruritus: A Sensory Symptom Generated in Cutaneous Immuno-Neuronal Crosstalk

Pruritus or itch generated in the skin is one of the most widespread symptoms associated with various dermatological and systemic (immunological) conditions. Although many details about the molecular mechanisms of the development of both acute and chronic itch were uncovered in the last 2 decades, our understanding is still incomplete and the clinical management of pruritic conditions is one of the biggest challenges in daily dermatological practice. Recent research revealed molecular interactions between pruriceptive sensory neurons and surrounding cutaneous cell types including keratinocytes, as well as resident and transient cells of innate and adaptive immunity. Especially in inflammatory conditions, these cutaneous cells can produce various mediators, which can contribute to the excitation of pruriceptive sensory fibers resulting in itch sensation. There also exists significant communication in the opposite direction: sensory neurons can release mediators that maintain an inflamed, pruritic tissue-environment. In this review, we summarize the current knowledge about the sensory transduction of pruritus detailing the local intercellular interactions that generate itch. We especially emphasize the role of various pruritic mediators in the bidirectional crosstalk between cutaneous non-neuronal cells and sensory fibers. We also list various dermatoses and immunological conditions associated with itch, and discuss the potential immune-neuronal interactions promoting the development of pruritus in the particular diseases. These data may unveil putative new targets for antipruritic pharmacological interventions.

Meteorin-β/Meteorin like/IL-41 attenuates airway inflammation in house dust mite-induced allergic asthma

We sought to examine the regulatory effect of Meteorin-β (Metrnβ)/Meteorin like (Metrnl)/IL-41 on lung inflammation in allergic asthma. We found that Metrnβ was elevated significantly in asthmatic patients and in mice with allergic asthma induced by house dust mite (HDM) extract. Upon exposure to HDM, Metrnβ was secreted predominantly by airway epithelial cells and inflammatory cells, including macrophages and eosinophils. The increased Metrnβ effectively blocked the development of airway hyperreactivity (AHR) and decreased inflammatory cell airway infiltration and type 2 cytokine production, which was associated with downregulated DC-mediated adaptive immune responses. Moreover, Metrnβ impaired the maturation and function of bone marrow-derived dendritic cells in vitro. Asthmatic mice adoptively transferred with dendritic cells isolated from Metrnβ-treated allergic mice displayed decreased AHR, airway inflammation, and lung injury. Metrnβ also displayed anti-inflammatory properties in immunodeficient SCID mice with allergic asthma and in in vitro 3D ALI airway models. Moreover, blockade of Metrnβ by anti-Metrnβ antibody treatment promoted the development of allergic asthma. These results revealed the unappreciated protective roles of Metrnβ in alleviating DC-mediated Th2 inflammation in allergic asthma, providing the novel treatment strategy of therapeutic targeting of Metrnβ in allergic asthma.