Neuropeptides in skin from patients with atopic dermatitis: an immunohistochemical study

Expression of calcitonin gene-related peptide in atopic dermatitis and correlation with distress

BACKGROUND

Atopic dermatitis (AD) is a chronic, inflammatory, often severely itching skin disorder. It may worsen due to stress, depression, or anxiety. Calcitonin gene-related peptide (CGRP) may be involved in inflammation signaling. CGRP has also been suggested in relation to stress, depression, and anxiety. This study aimed to investigate the expression of CGRP in the skin of patients with AD.

METHODS

Twenty-seven adult patients with AD, characterized with clinical and psychodemographic parameters, were investigated regarding CGRP expression in skin biopsies, using an immunohistochemical technique.

RESULTS

The total number of CGRP-positive nerve-like fibers was found to be higher in lesional skin than in non-lesional skin. Moreover, more inflammatory cells of dendritic shape intruded into the epidermis in lesional skin compared to non-lesional skin. Keratinocytes showing expression of CGRP were also found in lesional skin. Interestingly, the number of CGRP-positive nerve-like fibers in lesional skin correlated with depressive and anxiety scores. Correlation with depressive score was also found for round CGRP-positive inflammatory cells in the epidermis.

CONCLUSIONS

CGRP may have a role in both the inflammatory process and distress, in AD.

An update on mechanisms of pruritus and their potential treatment in primary cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL), which include mycosis fungoides (MF) and Sézary syndrome (SS), are a group of lymphoproliferative disorders characterized by clonal accumulation of neoplastic T-lymphocytes in the skin. Severe pruritus, one of the most common and distressing symptoms in primary CTCL, can significantly impair emotional well-being, physical functioning, and interpersonal relationships, thus greatly reducing quality of life. Unfortunately, effectively managing pruritus remains challenging in CTCL patients as the underlying mechanisms are, as of yet, not fully understood. Previous studies investigating the mechanisms of itch in CTCL have identified several mediators and their corresponding antagonists used for treatment. However, a comprehensive overview of the mediators and receptors contributing to pruritus in primary CTCL is lacking in the current literature. Here, we summarize and review the mediators and receptors that may contribute to pruritus in primary CTCL to explore the mechanisms of CTCL pruritus and identify effective therapeutic targets using the PubMed and Web of Science databases. Studies were included if they described itch mediators and receptors in MF and SS. Overall, the available data suggest that proteases (mainly tryptase), and neuropeptides (particularly Substance P) may be of greatest interest. At the receptor level, cytokine receptors, MRGPRs, and TRP channels are most likely important. Future drug development efforts should concentrate on targeting these mediators and receptors for the treatment of CTCL pruritus.

IL-20 promotes cutaneous inflammation and peripheral itch sensation in atopic dermatitis

Atopic dermatitis (AD) is a chronic skin disease, which is associated with intense itch, skin barrier dysfunction and eczematous lesions. Aberrant IL‐20 expression has been implicated in numerous inflammatory diseases, including psoriasis. However, the role of IL‐20 in AD remains unknown. Here, RNA‐seq, Q‐PCR, and immunocytochemistry were utilized to examine disease‐driven changes of IL‐20 and its cognate receptor subunits in skin from healthy human subjects, AD patients and murine AD‐models. Calcium imaging, knockdown and cytokine array were used to investigate IL‐20‐evoked responses in keratinocytes and sensory neurons. The murine cheek model and behavioral scoring were employed to evaluate IL‐20‐elicited sensations in vivo. We found that transcripts and protein of IL‐20 were upregulated in skin from human AD and murine AD‐like models. Topical MC903 treatment in mice ear enhanced IL‐20R1 expression in the trigeminal sensory ganglia, suggesting a lesion‐associated and epidermal‐driven mechanism for sensitization of sensory IL‐20 signaling. IL‐20 triggered calcium influx in both keratinocytes and sensory neurons, and promoted their AD‐related molecule release and transcription of itch‐related genes. In sensory neurons, IL‐20 application increased TLR2 transcripts, implicating a link between innate immune response and IL‐20. In a murine cheek model of acute itch, intradermal injection IL‐20 and IL‐13 elicited significant itch‐like behavior, though only when co‐injected. Our findings provide novel insights into IL‐20 function in peripheral (skin‐derived) itch and clinically relevant intercellular neuron‐epidermal communication, highlighting a role of IL‐20 signaling in the pathophysiology of AD, thus forming a new basis for the development of a novel antipruritic strategy via interrupting IL‐20 epidermal pathways.

Current Insights Into the Role of Neuropeptide Y in Skin Physiology and Pathology

Neuropeptide Y is widely distributed within the body and has long been implicated as a contributor to skin disease based on the correlative clinical data. However, until recently, there have been few empirical investigations to determine whether NPY has a pathophysiological role in the skin. Due to appearance-altering phenotypes of atopic dermatitis, psoriasis, and vitiligo, those suffering from these diseases often face multiple forms of negative social attention. This often results in psychological stress, which has been shown to exacerbate inflammatory skin diseases - creating a vicious cycle that perpetuates disease. This has been shown to drive severe depression, which has resulted in suicidal ideation being a comorbidity of these diseases. Herein, we review what is currently known about the associations of NPY with skin diseases and stress. We also review and provide educated guessing what the effects NPY can have in the skin. Inflammatory skin diseases can affect physical appearance to have significant, negative impacts on quality of life. No cure exists for these conditions, highlighting the need for identification of novel proteins/neuropetides, like NPY, that can be targeted therapeutically. This review sets the stage for future investigations into the role of NPY in skin biology and pathology to stimulate research on therapeutic targeting NPY signaling in order to combat inflammatory skin diseases.

Atopic dermatitis: an expanding therapeutic pipeline for a complex disease

Atopic dermatitis (AD) is a common chronic inflammatory skin disease with a complex pathophysiology that underlies a wide spectrum of clinical phenotypes. AD remains challenging to treat owing to the limited response to available therapies. However, recent advances in understanding of disease mechanisms have led to the discovery of novel potential therapeutic targets and drug candidates. In addition to regulatory approval for the IL-4Ra inhibitor dupilumab, the anti-IL-13 inhibitor tralokinumab and the JAK1/2 inhibitor baricitinib in Europe, there are now more than 70 new compounds in development. This Review assesses the various strategies and novel agents currently being investigated for AD and highlights the potential for a precision medicine approach to enable prevention and more effective long-term control of this complex disease.

Recent advances in understanding of the complex phenotype and mechanisms underlying atopic dermatitis (AD) have revealed multiple new potential targets for pharmacological intervention. Here, Bieber reviews therapeutic strategies and assesses the expanding pipeline for the therapy of AD, highlighting the potential for a precision medicine approach to the management of this complex disorder.

The Anti-Inflammatory Effect of Aptamin C on House Dust Mite Extract-Induced Inflammation in Keratinocytes via Regulation of IL-22 and GDNF Production

Atopic dermatitis (AD), a chronic inflammatory skin disease, is characterized by eczemous lesions on the skin that manifest as severe itching and last a long time. AD is thought to be a response to local allergens, including house dust mites (HDMs). Aptamin C is a modified form of vitamin C comprised of aptamers (DNA fragments) that bind specifically to vitamin C and inhibit its oxidation, thereby increasing its stability and antioxidant effects. It is already known that vitamin C shows an anti-inflammatory effect on skin inflammation. Oxidative stress is one of the major causes of inflammatory diseases, including HDM-induced skin inflammation, suggesting that the antioxidant activity of Aptamin C could regulate inflammatory responses to HDMs in the skin keratinocyte cell line HaCaT and primary skin keratinocytes. Aptamin C not only inhibited HDM-induced proliferation of both type of cells, but suppressed HDM-induced increases in interleukin (IL)-1α and IL-6 production by these cells. In addition, Aptamin C suppressed the production of IL-17 and IL-22 by T cells, which are closely associated with AD pathogenesis, as well as HDM-induced IL-22Rα expression. Aptamin C also reduced the production of thymus and activation-regulated chemokine (TARC) by suppressing the interaction between IL-22 and IL-22Rα, as well as reducing T cell migration. Although HDM treatment markedly increased the expression of glial cell line-derived neurotrophic factor (GDNF), which is associated with itching in AD skin lesions, this increase was reduced by Aptamin C treatment. Taken together, these results suggest that Aptamin C can effectively regulate inflammatory lesions, such as AD, by regulating the production of inflammatory cytokines and GDNF induced by HDM.

Gabapentinoids for Pruritus in Older Adults: A Narrative Review

There is currently no standardized algorithm for the treatment of chronic pruritus (CP), or itch lasting more than 6 weeks, in adults aged ≥ 65 years. The antiepileptic agents gabapentin and pregabalin, however, are gaining popularity in the dermatologic community for their efficacy in treating CP of neuropathic origin. Yet the lack of literature specifically looking at the safety and efficacy of these medications in older adults results in limited guidance for providers in the safe use of gabapentinoids. In this paper we discuss special considerations and recommendations for treating older adults with gabapentin and pregabalin and explore the possibility for these drugs to ameliorate CP of multiple etiologies.

Mas-related G protein-coupled receptor X2 and its activators in dermatologic allergies

The Mas-related G protein-coupled receptor X2 (MRGPRX2) is a multiligand receptor responding to various exogenous and endogenous stimuli. Being highly expressed on skin mast cells, MRGPRX2 triggers their degranulation and release of proinflammatory mediators, and it promotes multicellular signaling cascades, such as itch induction and transmission in sensory neurons. The expression of MRGPRX2 by skin mast cells and the levels of the MRGPRX2 agonists (eg, substance P, major basic protein, eosinophil peroxidase) are upregulated in the serum and/or skin of patients with inflammatory and pruritic skin diseases, such as chronic spontaneous urticaria or atopic dermatitis. Therefore, MRGPRX2 and its agonists might be potential biomarkers for the progression of cutaneous inflammatory diseases and the response to treatment. In addition, they may represent promising targets for prevention and treatment of signs and symptoms in patients with skin diseases or drug reactions. To assess this possibility, this review explores the role and relevance of MRGPRX2 and its activators in cutaneous inflammatory disorders and chronic pruritus.

Clinical practice guidelines for the management of atopic dermatitis 2018

Atopic dermatitis (AD) is a disease characterized by relapsing eczema with pruritus as a primary lesion. The current strategies to treat AD in Japan from the perspective of evidence-based medicine consist of three primary measures: (i) the use of topical corticosteroids and tacrolimus ointment as the main treatment for the inflammation; (ii) topical application of emollients to treat the cutaneous barrier dysfunction; and (iii) avoidance of apparent exacerbating factors, psychological counseling and advice about daily life. The guidelines present recommendations to review clinical research articles, evaluate the balance between the advantages and disadvantages of medical activities, and optimize medical activity-related patient outcomes with respect to several important points requiring decision-making in clinical practice.

Substance P and neurokinin 1 receptor are new targets for the treatment of chronic pruritus

BACKGROUND

Chronic pruritus is a distressing symptom associated with various dermatological conditions and systemic diseases. Current treatment options are often inadequate, resulting in impaired quality of life for many patients. An understanding of the underlying mechanisms of itch across pruritic conditions is important for development of effective, targeted treatments for chronic pruritus.

OBJECTIVES

To provide an overview of the pathogenesis of chronic pruritus, focusing on the role of substance P (SP) and neurokinin 1 receptor (NK₁ R) in itch signalling, and to describe data supporting NK₁ R antagonism as a potential strategy for the treatment of chronic pruritus.

METHODS

A PubMed search was conducted to determine what data were available that investigated the role of SP and NK₁ R in itch signalling.

RESULTS

SP is a neuropeptide that is a mediator of itch signalling. One of the target receptors for SP is NK₁ R, which is expressed in the central nervous system and on multiple cell types involved in the initiation and transmission of itch. Studies demonstrating that SP and NK₁ R are overexpressed across multiple chronic itch-inducing conditions and that NK₁ R antagonism disrupts itch signalling and reduces itch provide a rationale for targeting this pathway as a potential treatment of chronic pruritus across multiple diseases.

CONCLUSIONS

A large and growing body of evidence, including recent phase II clinical studies of NK₁ R antagonists, demonstrate that SP and NK₁ R play an important role in itch signalling. Additional studies are ongoing to further evaluate the use of NK₁ R antagonists for the treatment of chronic pruritus. What's already known about this topic? Chronic pruritus has a significant impact on quality of life. Current treatment options for chronic pruritus are inadequate. Substance P (SP) and neurokinin 1 receptor (NK₁ R) have been shown to play a role in itch signalling, and may be a rational target for addressing chronic pruritus. NK₁ R antagonists are being evaluated as potential treatment for chronic pruritus. What does this study add? This review provides a compilation of the most up-to-date data elucidating the role of SP and NK₁ R in itch signalling, which supports targeting this pathway as a potential treatment of chronic pruritus. NK₁ R antagonism disrupts itch signalling and reduces itch. A summary of the latest data on NK₁ R antagonists in the treatment of pruritus is provided.

Tachykinin upregulation in atopic dermatitis

Context: Atopic dermatitis (AD) is a chronic, inflammatory, itching skin disorder, which may worsen due to stress, depression and anxiety. Tachykinins may be involved in inflammation signaling as well as they may have a role in stress, depression and anxiety. Objective: This study aimed to measure the expression of tachykinin markers, in the skin of patients with AD, and the correlation of these tachykinins with clinical and psychodemographic parameters. Materials and methods: Twenty-eight adult patients with AD were investigated regarding tachykinin expression in skin biopsies, using an immunohistochemical technique. The patients were characterized with clinical and psychodemographic parameters. Results: The number of substance P and neurokinin (NK)A positive nerve fibers, as well as NKA positive mononuclear dermal cells, was increased in lesional compared to non-lesional skin. Interestingly, the depression score and the number of dermal NK-1 receptor (R) positive cells in lesional as well as in non-lesional skin showed a correlation. Conclusion: These findings indicate an upregulation of the tachykinergic system in the inflamed skin of AD.

The Genetics of Chronic Itch: Gene Expression in the Skin of Patients with Atopic Dermatitis and Psoriasis with Severe Itch

To identify itch-related mediators and receptors that are differentially expressed in pruritic skin, we used RNA sequencing to analyze the complete transcriptome in skin from paired itchy, lesional and nonitchy, nonlesional skin biopsies from 25 patients with atopic dermatitis and 25 patients with psoriasis and site-matched biopsies from 30 healthy controls. This analysis identified 18,000 differentially expressed genes common between itchy atopic and psoriatic skin compared with healthy skin. Of those, almost 2,000 genes were differentially expressed between itchy and nonitchy skin in atopic and psoriatic subjects. Overexpression of several genes, such as phospholipase A2 IVD, substance P, voltage-gated sodium channel 1.7, and transient receptor potential (TRP) vanilloid 1, in itchy skin was positively correlated with itch intensity ratings in both atopic dermatitis and psoriasis. Cytokines such as IL-17A, IL-23A, and IL-31 had elevated gene transcript levels in both itchy atopic and psoriatic skin. However, expression of genes for TRP vanilloid 2, TRP ankyrin 1, protease-activated receptor 2, protease-activated receptor 4, and IL-10 was found to be increased only in pruritic atopic skin, whereas expression of genes for TRP melastatin 8, TRP vanilloid 3, phospholipase C, and IL-36α/γ was elevated only in pruritic psoriatic skin. This "itchscriptome" analysis will lead to an increased understanding of the molecular mechanisms of chronic pruritus and provide targets for itch treatment irrespective of disease state.

Lack of Galanin Receptor 3 Alleviates Psoriasis by Altering Vascularization, Immune Cell Infiltration, and Cytokine Expression

The neuropeptide galanin is distributed in the central and peripheral nervous systems and in non-neuronal peripheral organs, including the skin. Galanin acts via three G protein-coupled receptors which, except galanin receptor 1, are expressed in various skin structures. The galanin system has been associated with inflammatory processes of the skin and of several other organs. Psoriasis is an inflammatory skin disease with increased neovascularization, keratinocyte hyperproliferation, a proinflammatory cytokine milieu, and immune cell infiltration. In this study, we showed that galanin receptor 3 is present in endothelial cells in human and murine dermal vessels and is co-expressed with nestin in neo-vessels of psoriatic patients. Moreover, in a murine psoriasis model, we showed that C57/BL6 mice lacking galanin receptor 3 display a milder course of psoriasis upon imiquimod treatment, leading to decreased disease severity, delayed neo-vascularization, reduced infiltration of neutrophils, and significantly lower levels of proinflammatory cytokines compared with wild-type mice. In contrast, galanin receptor 2-knockout animals did not differ significantly from wild type mice at both the macroscopic and molecular levels in their inflammatory response to imiquimod treatment. Our data indicate that galanin receptor 3, but not galanin receptor 2, plays an important role in psoriasis-like skin inflammation.

Adjunctive Management of Itch in Atopic Dermatitis

Itch, or pruritus, is a hallmark feature of atopic dermatitis (AD). The impact of AD-related pruritus can range from mildly distressing or distracting to completely disabling. Traditionally, management of itch in AD patients has focused on restoring the altered skin barrier with topical emollients and/or reducing inflammation. A growing emphasis has been placed on directly targeting the neural transmission pathways that mediate itch signaling. Off-label use of neuromodulatory agents has helped reduce this aggravating symptom in atopic patients. This article reviews the current literature on the use of neuromodulatory agents and nonpharmacologic alternative therapies used to treat AD-related pruritus.

Aprepitant for refractory cutaneous T-cell lymphoma-associated pruritus: 4 cases and a review of the literature

Background

Aprepitant is an FDA-approved medication for chemotherapy-induced nausea and vomiting. It blocks substance P binding to neurokinin-1; substance P has been implicated in itch pathways both as a local and global mediator.

Case presentations

We report a series of four patients, diagnosed with cutaneous T-cell lymphoma, who experienced full body pruritus recalcitrant to standard therapies. All patients experienced rapid symptom improvement (within days) following aprepitant treatment.

Conclusion

Aprepitant has been shown in small studies to be efficacious for treating chronic and malignancy-associated pruritus. Prior studies have shown no change in clinical efficacy of chemotherapeutics with concurrent aprepitant administration. These cases further demonstrate that aprepitant can be considered as a therapeutic option in malignancy-associated pruritus and further support the need for larger clinical trials.

The pruritus- and TH2-associated cytokine IL-31 promotes growth of sensory nerves

BACKGROUND

Pruritus is a cardinal symptom of atopic dermatitis, and an increased cutaneous sensory network is thought to contribute to pruritus. Although the immune cell-IL-31-neuron axis has been implicated in severe pruritus during atopic skin inflammation, IL-31's neuropoietic potential remains elusive.

OBJECTIVE

We sought to analyze the IL-31-related transcriptome in sensory neurons and to investigate whether IL-31 promotes sensory nerve fiber outgrowth.

METHODS

In vitro primary sensory neuron culture systems were subjected to whole-transcriptome sequencing, ingenuity pathway analysis, immunofluorescence, and nerve elongation, as well as branching assays after IL-31 stimulation. In vivo we investigated the cutaneous sensory neuronal network in wild-type, Il31-transgenic, and IL-31 pump-equipped mice.

RESULTS

Transgenic Il31 overexpression and subcutaneously delivered IL-31 induced an increase in the cutaneous nerve fiber density in lesional skin in vivo. Transcriptional profiling of IL-31-activated dorsal root ganglia neurons revealed enrichment for genes promoting nervous system development and neuronal outgrowth and negatively regulating cell death. Moreover, the growth cones of primary small-diameter dorsal root ganglia neurons showed abundant IL-31 receptor α expression. Indeed, IL-31 selectively promoted nerve fiber extension only in small-diameter neurons. Signal transducer and activator of transcription 3 phosphorylation mediated IL-31-induced neuronal outgrowth, and pharmacologic inhibition of signal transducer and activator of transcription 3 completely abolished this effect. In contrast, transient receptor potential cation channel vanilloid subtype 1 channels were dispensable for IL-31-induced neuronal sprouting.

CONCLUSIONS

The pruritus- and TH2-associated novel cytokine IL-31 induces a distinct transcriptional program in sensory neurons, leading to nerve elongation and branching both in vitro and in vivo. This finding might help us understand the clinical observation that patients with atopic dermatitis experience increased sensitivity to minimal stimuli inducing sustained itch.

Atopic dermatitis and the intestinal microbiota in humans and dogs

The prevalence of human and canine allergic diseases is commonly perceived to be increasing. Suggested predisposing factors in people and dogs include increased allergen load, increased exposure to pollutants, reduced family size, reduced microbial load and less exposure to infection at a young age, increasingly urbanised environment, and changes in dietary habits. Genetic make‐up may provide a template for phenotypic predisposition which is strongly influenced by our diet and environment leading to constant regulation of gene expression. One way in which diet can alter gene expression is via its effects on the gut flora or microbiota, the collection of microbes residing in the gastrointestinal tract. The resident microbiota is important in maintaining structural and functional integrity of the gut and in immune system regulation. It is an important driver of host immunity, helps protect against invading enteropathogens, and provides nutritional benefits to the host. Disruption of the microbiota (dysbiosis) may lead to severe health problems, both in the gastrointestinal tract and extra‐intestinal organ systems. The precise mechanisms by which the intestinal microbiota exerts its effects are only beginning to be unravelled but research is demonstrating close links between gut microflora and many factors involved in the pathogenesis of atopic dermatitis (AD). AD and indeed any other ‘skin disease’, may be seen as a possible manifestation of a more systemic problem involving gut dysbiosis and increased intestinal permeability, which may occur even in the absence of gastrointestinal signs. Manipulation of the canine intestinal microbiota as a method for modifying atopy, may be attempted in many ways including avoidance of certain foods, supplementation with probiotics and prebiotics, optimising nutrient intake, minimising stress, antimicrobial therapy, correction and prevention of low stomach acid, and faecal microbiota transplantation (FMT).

Immunohistochemical distribution of neuropeptide Y, peptide YY, pancreatic polypeptide-like immunoreactivity and their receptors in the epidermal skin of healthy women

Few studies have suggested that neuropeptide Y (NPY) could play an important role in skin functions. However, the expression of NPY, the related peptides, peptide YY (PYY) and pancreatic polypeptide (PP) and their receptors have not been investigated in human skin. Using specific antisera directed against NPY, PYY, PP and the Y1, Y2, Y4 and Y5 receptor subtypes, we investigated here the expression of these markers. NPY-like immunoreactivity (ir) in the epidermal skin could not be detected. For the first time we report the presence of positive PP-like ir immunofluorescent signals in epidermal cells, i.e. keratinocytes of skin from three areas (abdomen, breast and face) obtained as surgical left-overs. The immunofluorescent signal of PP-like ir varies from very low to high level in all three areas. In contrast, PYY-like ir is only expressed in some cells and with varied level of intensity. Furthermore and for the first time we observed specific Y1 and Y4 receptor-like ir in all epidermal layers, while the Y2 and Y5 subtypes were absent. Interestingly, as seen in human epidermis, in Episkin, a reconstituted human epidermal layer, we detected the presence of PP-like as well as Y1-like and Y4-like ir. These data have shown the presence and distribution of PYY, PP and Y1 and Y4 receptors in the human skin and Episkin, suggesting possible novel roles of NPY related peptides and their receptors in skin homeostasis.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Research in practice: substance P antagonism in chronic pruritus

Pruritus is an unpleasant sensation of the skin, which triggers a desire to scratch or rub. The chronic form (≥6 weeks' duration) often occurs as a side effect of many diseases and is usually accompanied by a high loss in quality of life for patients, especially in cases in which the symptom is chronic without adequate treatment options. In recent years, the situation improved continuously, guidelines for chronic pruritus have been defined and standard medications have been proposed. For many reasons, there are still patients who are unable to obtain relief. New therapeutic approaches are therefore urgently needed. Blocking the neuropeptide substance P is a promising strategy; substance P mediates clinically relevant pro-inflammatory effects by binding to the neurokinin 1 receptor (NK-1R). This led us to hypothesize that NK-1R antagonists are promising therapeutic options for chronic pruritus. Several international case series have meanwhile proven the antipruritic effect of the NK-1R antagonist aprepitant for various forms of chronic pruritus. Initiation of clinical trials with new NK-1R-antagonists as a new therapeutic option continues this trend.

Neurotensin serum levels and skin gene expression are increased in atopic dermatitis

BACKGROUND

Neurotensin (NT) participates in immune responses, but the mechanisms are not known. We have previously shown that NT augments the ability of corticotropin-releasing hormone (CRH) to increase mast-cell-dependent vascular permeability in rodents. We also showed that NT stimulates human mastcell release of vascular endothelial growth factor, and that CRH is increased in the serum of patients with atopic dermatitis (AD), an inflammatory skin condition involving mast cells.

OBJECTIVES

To measure serum levels of NT, and lesional skin expression of NT and the main NT receptor (NTR-1) in AD, and to compare it with skin expression in chronic urticaria (CU) and urticaria pigmentosa (UP).

METHODS

Serum NT was measured with a Milliplex microbead array. Skin NT and NTR-1 gene expression was determined with quantitative polymerase chain reaction. Immunohistochemistry was performed using a mouse monoclonal antibody for NT, and a rabbit polyclonal antibody for NTR-1. Mast cells were counterstained with Leder dye.

RESULTS

Neurotensin is significantly elevated in the serum of patients with AD compared with healthy controls (P = 0.0001). NT gene expression is also significantly increased in lesional skin of patients with AD compared with controls (P = 0.0194). Moreover, immunohistochemistry of AD lesions shows NT > NTR-1 staining of perivascular cells, many of which are identified as mast cells after staining with Leder dye. There was no statistically significant difference in NT and NTR-1 lesional skin gene expression in patients with either CU or UP.

CONCLUSIONS

These results suggest that interactions between NT and mast cells may occur and contribute to AD pathogenesis.

Neurogenic markers of the inflammatory process in atopic dermatitis: relation to the severity and pruritus

Introduction

Atopic dermatitis (AD) is a chronic and relapsing inflammatory skin disease, characterized by eczematous skin lesions and intensive pruritus. Recent studies have shed light on the role of the nervous system in the pathogenesis of AD. It can influence the course of the disease through an altered pattern of cutaneous innervation and abnormal expression of neuropeptides in the lesional skin.

Aim

The aim of the study was to evaluate plasma concentrations of the nerve growth factor (NGF), substance P (SP) and vasoactive intestinal peptide (VIP) in AD patients in comparison to two control groups (healthy volunteers and patients suffering from psoriasis). Correlations between plasma levels of evaluated parameters, severity of the disease and selected clinical parameters (skin prick tests, total and antigen specific IgE levels) were also analysed.

Material and methods

Seventy-five patients with AD, 40 patients with psoriasis and 40 healthy volunteers were included into the study. Patients with AD included 52 persons suffering from an extrinsic and 23 from an intrinsic type of the disease. The severity of skin lesions was assessed with SCORAD index. Pruritus was evaluated on the basis of the questionnaire assessing the extent, frequency and intensity of pruritus. Commercial enzyme-linked immunosorbent assays (SP, NGF: R&D Systems; and VIP: Phoenix Pharmaceuticals) were used to assess the neuropeptide and NGF plasma levels.

Results

Nerve growth factor and VIP plasma concentrations were significantly higher in AD patients compared to psoriatic patients and healthy subjects. Substance P plasma concentrations were elevated in the extrinsic type of AD and psoriasis comparing to healthy volunteers. There were no statistically significant differences in NGF, SP and VIP plasma concentrations between the extrinsic and intrinsic type of AD. There was also no correlation between plasma levels of evaluated parameters (NGF, SP, VIP) and SCORAD index in both types of AD. However, plasma SP concentration correlated with intensity of pruritus in AD patients. Plasma VIP concentrations correlated with intensity of pruritus in the intrinsic type of AD and with IgE-mediated sensitization to moulds in the extrinsic type of disease.

Conclusions

Our findings confirm that NGF and VIP play a prominent role in atopic inflammatory reactions and may serve as good alternative biomarkers of AD. The results of this study also suggest a similar important role of neuroimmune interactions in both variants of AD. Increased SP plasma concentrations in both AD and psoriasis point to its possible role in modulating immune-mediated inflammation in different chronic inflammatory skin diseases. Moreover, SP and VIP seem to influence the course of AD by increasing pruritus, whereas an elevated plasma VIP level in AD patients may be related to a risk of developing IgE-mediated sensitization to certain airborne allergens.

Investigational drugs for pruritus

INTRODUCTION

Chronic pruritus (CP), defined as itch lasting for > 6 weeks, is a burdensome symptom of several different diseases, dermatological and systemic, with a high negative impact on the quality of life of patients. Given the manifold aetiologies of CP, therapy is often difficult. In recent years, however, novel substances have been developed for treatment of certain CP entities and identified targets.

AREAS COVERED

In this review, the authors present a survey of targets currently believed to be promising (H4R, IL-31, MOR, KOR, GRPR, NGF, NK-1R, TRP channels) and related investigational drugs that are in the preclinical or clinical stage of development. Some substances have already undergone clinical testing, but only one of them (nalfurafine) has been licensed so far. Many of them are most likely to exert their effects on the skin and interfere there with the cutaneous neurobiology of CP.

EXPERT OPINION

Currently, the most promising candidates for new therapeutic agents in CP are neurokinin-1 receptor antagonists and substances targeting the kappa- or mu-opioid receptor, or both. They have the potential to target the neuronal pathway of CP and are thus of interest for several CP entities. The goal for the coming years is to validate these concepts and move forward in developing new drugs for the therapy of CP.

PGP 9.5 distribution patterns in biopsies from early lesions of atopic dermatitis

Peripheral nerve fibres are often increased in lesional skin of atopic dermatitis (AD) patients. We attempted to study nerve fibre profiles, using PGP 9.5 as neuronal marker, in early AD lesions in 10 patients, as compared to non-lesional skin in the same patients and skin from healthy controls. The number of PGP 9.5-positive nerve fibre profiles was not different in the biopsies taken from normal-looking AD skin and healthy controls. The total number of PGP 9.5-positive nerve fibre profiles in the whole skin sections was higher in both the epidermis and the dermis in the group of skin biopsies taken from early lesions of AD patients. Further, the number of epidermal PGP 9.5-positive dendritic cells was increased in AD skin. It seems reasonable that PGP 9.5-positive nerve fibres and PGP 9.5-positive dendritic cells have pathological roles in AD. The findings might serve as a basis for further studies in evaluating novel diagnostic and therapeutic approaches.

Role of parasympathetic nerves and muscarinic receptors in allergy and asthma

Parasympathetic nerves control the symptoms and inflammation of allergic diseases primarily by signaling through peripheral muscarinic receptors. Parasympathetic signaling targets classic effector tissues such as airway smooth muscle and secretory glands and mediates acute symptoms of allergic disease such as airway narrowing and increased mucus secretion. In addition, parasympathetic signaling modulates inflammatory cells and non-neuronal resident cell types such as fibroblasts and smooth muscle contributing to chronic allergic inflammation and tissue remodeling. Importantly, muscarinic antagonists are experiencing a rebirth for the treatment of asthma and may be useful for treating other allergic diseases.

Management of itch in atopic dermatitis

Atopic dermatitis is a common, pruritic, inflammatory skin disorder. Chronic, localized, or even generalized pruritus is the diagnostic hallmark of atopic dermatitis, and its management remains a challenge for physicians. The threshold for itch and alloknesis is markedly reduced in these patients, and infections can promote exacerbation and thereby increase the itch. Modern management consists of anti-inflammatory, occasionally antiseptic, as well as antipruritic therapies to address the epidermal barrier as well as immunomodulation or infection. Mild forms of atopic dermatitis may be controlled with topical therapies, but moderate-to-severe forms often require a combination of systemic treatments consisting of antipruritic and immunosuppressive drugs, phototherapy, and topical compounds. In addition, patient education and a therapeutic regimen to help the patient cope with the itch and eczema are important adjuvant strategies for optimized long-term management. This review highlights various topical, systemic, and complementary and alternative therapies, as well as provide a therapeutic ladder for optimized long-term control of itch in atopic dermatitis.

A study of serum concentrations and dermal levels of NGF in atopic dermatitis and healthy subjects

Nerve growth factor (NGF) was reported to be increased in the serum and skin of atopic dermatitis (AD) patients, to the extent that serum nerve growth factor levels were proposed to serve as a marker of disease severity. We studied NGF levels in the serum and dermis using skin microdialysis and attempted to correlate them with disease severity. We also examined if potential differences between morning and evening levels of NGF can explain the phenomenon of nocturnal itch. In addition, neurogenic inflammation and itch were induced using histamine iontophoresis in lesional and non-lesional skin and the effect of experimental itch on dermal NGF concentration was examined. We found that systemic (serum) and eczematous skin levels of NGF in AD are significantly lower in comparison to healthy controls. Serum NGF decreases from morning to late afternoon in both groups. Interestingly, serum NGF levels were correlated to disease severity in the morning in AD, although the NGF concentration in AD were significantly lower than in the healthy group. The local itch and neurogenic inflammation induction via experimental histamine reduced local NGF levels in the eczema and non-lesional skin in atopics, but not in the healthy controls, where it was slightly increased. The higher the clinical severity of the eczema, a significantly less pronounced effect of neurogenic inflammation on the local levels of NGF was found. The availability of measurable NGF might be reduced by a higher expression of NGF receptors. The fluctuations of NGF levels during the day suggest a complex modulation of this neurotrophin, potentially linked to stress or to an altered neurophysiological mechanism.

Expression of tachykinins and their receptors in plaque psoriasis with pruritus

BACKGROUND Various mediators of pruritus have been suggested that might be responsible for the mechanism of pruritus in psoriasis.

OBJECTIVES

To study the expression levels of members of the tachykinin family, substance P and neurokinin (NK) A and their receptors, NK-1 and NK-2, in psoriasis and to correlate their expression with the intensity of pruritus. A possible correlation with chronic stress and depression was also evaluated.

METHODS

Biopsies were obtained from 28 patients with chronic plaque psoriasis; the majority had pruritus. The samples were taken from lesional and nonlesional areas on the back and also from 10 healthy controls, for immunohistochemistry staining, and from lesional skin for radioimmunoassay. Prior to biopsy, the clinical severity of the psoriasis of each patient was assessed by the Psoriasis Area and Severity Index (PASI) and the intensity of pruritus was measured by using a visual analogue scale (VAS). Levels of depression and stress were measured using Beck's Depression Inventory (BDI) and the salivary cortisol test, respectively.

RESULTS

Substance P-, NKA- and NK-2 receptor-immunoreactive nerves, and non-neuronal inflammatory cells positive for substance P and NKA and their respective receptors, NK-1 and NK-2, were numerous in psoriasis compared with healthy controls. The numbers of substance P-positive nerves and NK-2 receptor-positive cells in lesional skin were significantly correlated to pruritus intensity. The cortisol ratio was inversely correlated with the number of NK-1 receptor-immunoreactive inflammatory cells in lesional and nonlesional psoriasis skin. There was also a positive correlation between the BDI score and the number of substance P-positive cells in nonlesional skin and with NK-1 receptor-positive cells in lesional and nonlesional skin.

CONCLUSIONS

Tachykinins may play a role in psoriasis per se, in addition to pruritus in this disease. Targeting the combined NK-1 and NK-2 receptors might be a possible treatment.

Role of spinal neurotransmitter receptors in itch: new insights into therapies and drug development

Targets for antipruritic therapies are now expanding from the skin to the central nervous system. Recent studies demonstrate that various neuronal receptors in the spinal cord are involved in pruritus. The spinal opioid receptor is one of the best-known examples. Spinal administration of morphine is frequently accompanied by segmental pruritus. In addition to μ-opioid receptor antagonists, κ-opioid receptor agonists have recently come into usage as novel antipruritic drugs, and are expected to suppress certain subtypes of itch such as hemodialysis- and cholestasis-associated itch that are difficult to treat with antihistamines. The gastrin-releasing peptide receptor in the superficial dorsal horn of the spinal cord has also received recent attention as a novel pathway of itch-selective neural transmission. The NMDA glutamate receptor appears to be another potential target for the treatment of itch, especially in terms of central sensitization. The development of NMDA receptor antagonists with less undesirable side effects on the central nervous system might be beneficial for antipruritic therapies. Drugs suppressing presynaptic glutamate-release such as gabapentin and pregabalin also reportedly inhibit certain subtypes of itch such as brachioradial pruritus. Spinal receptors of other neuromediators such as bradykinin, substance P, serotonin, and histamine may also be potential targets for antipruritic therapies, given that most of these molecules interfere not only with pain, but also with itch transmission or regulation. Thus, the identification of itch-specific receptors and understanding itch-related circuits in the spinal cord may be innovative strategies for the development of novel antipruritic drugs.

Pathophysiology and therapy of pruritus in allergic and atopic diseases

Pruritus (itch) is a major characteristic and one of the most debilitating symptoms in allergic and atopic diseases and the diagnostic hallmark of atopic dermatitis. Pruritus is regularly defined as an unpleasant sensation provoking the desire to scratch. Although we achieved rather good knowledge about certain inducers of itch such as neuropeptides, amines, mu-opioids, cytokines and proteases, for example, less is known about the pathophysiological specifities among the different diseases, and the therapeutic consequences which may derive thereoff. This review dissects the role of mediators, receptors and itch inhibitors on peripheral nerve endings, dorsal root ganglia, the spinal cord and the CNS leading to the amplification or - vice versa - suppression of pruritus. As the treatment of pruritus in allergic and atopic skin disease is still not satisfactory, knowing these pathways and mechanisms may lead to novel therapeutic approaches against this frequently encountered skin symptom.

Galanin family of peptides in skin function

The skin, the largest organ of the body, functions as a barrier between the body proper and the external environment, as it is constantly exposed to noxious stressors. During the last few years, the concept of an interactive network involving cutaneous nerves, the neuroendocrine axis, and the immune system has emerged. The neuroendocrine system of the skin is composed of locally produced neuroendocrine mediators that interact with specific receptors. Among these mediators are neuropeptides, including members of the galanin peptide family--galanin, galanin-message associated peptide, galanin-like peptide, and alarin--which are produced in neuronal as well as nonneuronal cells in the skin. Here, we review the expression of the galanin peptides and their receptors in the skin, and the known functions of galanin peptides in different compartments of the skin. We discuss these data in light of the role of the galanin peptide family in inflammation and cell proliferation.

Up-regulation of the tight-junction protein ZO-1 by substance P and IGF-1 in A431 cells

The formation of a barrier by tight junctions is important in epithelia of various tissues. Substance P (SP) and insulin-like growth factor (IGF)-1 synergistically promote barrier function in the corneal epithelium. We have now examined the effects of SP and IGF-1 on expression of the tight-junction protein zonula occludens (ZO)-1 in A431 human epidermoid carcinoma cells. Reverse transcription-polymerase chain reaction (RT-PCR) and immunoblot analyses revealed that SP and IGF-1 increased the amounts of ZO-1 mRNA and protein in these cells in a concentration-dependent manner, with neither SP nor IGF-1 alone having such an effect. The SP- and IGF-1-induced up-regulation of ZO-1 was accompanied by phosphorylation of extracellular signal-regulated kinase (ERK), and both of these effects were blocked by PD98059, an inhibitor of ERK activation. SP and IGF-1 also increased the transepithelial electrical resistance (TER) (an indicator of barrier function) of an A431 cell monolayer in a manner sensitive to PD98059. Our results thus suggest that the synergistic induction of ZO-1 expression by SP and IGF-1 may promote barrier function in skin epithelial cells.

Long‐term safety and tolerability of pimecrolimus cream 1% and topical corticosteroids in adults with moderate to severe atopic dermatitis

OBJECTIVE

This randomized, double-blind, multi-centre study compared the long-term safety and tolerability of pimecrolimus cream 1% and topical corticosteroids (TCS) in 658 adults with moderate-severe atopic dermatitis (AD).

METHODS

Patients applied either pimecrolimus or TCS (i.e. 0.1% triamcinolone acetonide cream and/or 1% hydrocortisone acetate cream) twice daily to all affected areas until complete clearance or for up to 1 year. The study was approved by the institutional review board or ethics committee at each centre.

RESULTS

A majority of patients treated with either pimecrolimus or TCS used the drug on a continuous basis over 1 year. In patients who had >30% of the body surface involved by AD, the incidence rate of all skin infections was significantly lower in the pimecrolimus group than in the TCS group (95% CI of the treatment difference: -25.3% to -3.4%). The most frequent application site reaction was burning (25.9% of patients on pimecrolimus and 10.9% on TCS), which was transient and mild-moderate in most cases. Three TCS-treated patients reported skin striae. There were no treatment-related serious or clinically significant systemic adverse events. Efficacy was better in patients on continuous TCS therapy, although patients completing the study were similarly well-controlled in both groups. About 42% of the pimecrolimus-treated patients were maintained for 1 year without TCS.

CONCLUSION

Pimecrolimus demonstrated a favourable safety profile when used to treat adult patients with moderate-severe AD for up to 1 year. A significant proportion of patients could be maintained without TCS for a year.

Skin peptides: biological activity and therapeutic opportunities

The skin provides an effective barrier to the loss of body fluids and environmental assault. In addition to the physical barrier provided by the stratum corneum, the skin also contains a chemical barrier consisting of antimicrobial peptides (AMPs), which control microbial growth on the surface. These AMPs also have multiple roles as mediators of inflammation with effects on epithelial and inflammatory cells, influencing cell proliferation, wound healing, cytokine/chemokine production and chemotaxis. This review describes the range of peptides found in the skin, both constitutive and those induced in response to injury. The role these peptides play in normal skin function and in various skin conditions is described. A better understanding of their role in normal and skin disease may offer new strategies in skin disease, dermatology and as cosmeceuticals.

The role of selected neuropeptides in pathogenesis of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is an inflammatory skin disease of a chronic course. The role of neuropeptides in pathogenesis of this disorder is probably not crucial; however, there is evidence that these substances influence the development and course of AD.

OBJECTIVE

The aim of this study was to evaluate the plasma level of substance P, neuropeptide Y (NPY) and calcitonin gene related peptide (CGRP) in AD patients during exacerbation and remission of the disease.

MATERIAL AND METHODS

Forty-nine patients with AD, aged 17 to 56 years, participated in the study. Among this group, there were 25 males (51%) and 24 females (49%). The disease lasted from 1 to 55 years. The severity of the disease was assessed with SCORAD index. The severity of pruritus was evaluated with Visual Analog Scale and a specially designed questionnaire. Neuropeptides plasma level was detected with radioimmunoassay.

RESULTS

Substance P plasma level in AD patients during exacerbation and remission was significantly higher than in the control group. There was a negative correlation between substance P plasma level and total IgE level. CGRP plasma level during exacerbation of AD was significantly lower than in healthy controls and increased in the remission. Significantly higher CGRP concentration was observed in patients suffering from severe pruritus; however, both in patients with more and less severe pruritus, CGRP plasma level was lower than in controls. Higher CGRP plasma level was also observed in patients with more severe disease. NPY plasma level in patients with AD was significantly increased both during exacerbation and remission. During remission of AD, NPY concentration was higher than during exacerbation.

Further exploring the brain-skin connection: stress worsens dermatitis via substance P-dependent neurogenic inflammation in mice

A neurogenic component in atopy and allergy is evident and potentially of great pathogenic relevance. Stress was recently shown to activate elements of this component and is vividly discussed as a cause of exacerbation. However, to date, scientific proof of stress-induced neuronal plasticity and neuro-immune interaction in atopy or allergy remains lacking. Here we show early evidence that exposure to sound stress and atopic dermatitis-like allergic dermatitis (AD) equipotently raise the number of cutaneous nerve fibers containing the prototypic stress neuropeptide substance P (SP) in mice. Stress increases AD readout parameters by at least 30% (eosinophil infiltration, vascular cell adhesion molecule-positive blood vessels, epidermal thickness). This dramatic pathologic exacerbation is associated with increased neurogenic inflammation (degranulated mast cells; interstitial neuropeptidergic dense core granules, mast cell apoptosis, endothelial gaping). Key features of AD exacerbation could not be induced in mice lacking the neurokinin-1 SP receptor (NK1). Interestingly, stress had no significant additional effect on CD4+ cell number, but shifted the cytokine profile toward TH2 in skin. Thus, we conclude that stress primarily exacerbates AD via SP-dependent cutaneous neurogenic inflammation and subsequent local cytokine shifting and should be considered as a therapeutic target, while it offers a convincing pathogenic explanation to affected patients and their frustrated physicians alike.

Plasma concentration of selected neuropeptides in patients suffering from psoriasis

The aim of this study was to evaluate plasma levels of substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) during psoriasis course.

METHODS

Seventy-three patients with psoriasis and 32 healthy volunteers were included. Detailed demographic and disease anamnesis was obtained from every patient. The disease severity was assessed using the Psoriasis Area and Severity Index score. Plasma levels of SP, CGRP, VIP and NPY were measured radioimmunologically.

RESULTS

Plasma levels of SP and NPY did not significantly differ between patients with psoriasis and controls (median SP: 52.8 and 57.9 pg/ml, respectively; P = 0.32; median NPY: 8.5 and 8.2 pg/ml, respectively; P = 0.67). CGRP plasma concentration was significantly elevated in psoriatic individuals both before (median 43.1 pg/ml) and after treatment (median 45.4 pg/ml), in comparison with healthy donors (median 13.5 pg/ml; P < 0.01 and P = 0.03, respectively). Treatment did not significantly influence plasma CGRP levels (P = 0.3). Median VIP plasma concentration in psoriatics before treatment was significantly higher compared with healthy controls (medians 66.9 and 60.1 pg/ml, respectively; P = 0.04), but the therapy resulted in significant decrease in VIP plasma level (median 19.0 pg/ml; P < 0.001). In psoriatic patients significant correlations were noted between NPY and VIP (R = 0.34; P < 0.01), and VIP and CGRP plasma levels, both before (R = 0.28; P = 0.03) and after the treatment (R = 0.44; P < 0.01).

CONCLUSIONS

Based on our results and previous literature data it could be suggested that neuropeptides may be involved in the development of psoriatic lesions.

Alarin is a vasoactive peptide

Galanin-like peptide (GALP) is a hypothalamic neuropeptide belonging to the galanin family of peptides. The GALP gene is characterized by extensive differential splicing in a variety of murine tissues. One splice variant excludes exon 3 and results in a frame shift leading to a novel peptide sequence and a stop codon after 49 aa. In this peptide, which we termed alarin, the signal sequence of the GALP precursor peptide and the first 5 aa of the mature GALP are followed by 20 aa without homology to any other murine protein. Alarin mRNA was detected in murine brain, thymus, and skin. In accordance with its vascular localization, the peptide exhibited potent and dose-dependent vasoconstrictor and anti-edema activity in the cutaneous microvasculature, as was also observed with other members of the galanin peptide family. However, in contrast to galanin peptides in general, the physiological effects of alarin do not appear to be mediated via the known galanin receptors. Alarin adds another facet to the surprisingly high-functional redundancy of the galanin family of peptides.

The role of neuropeptides in psoriasis

The pathogenesis of psoriasis is incompletely understood but cutaneous neurogenic inflammation is probably involved. This involvement is suggested by a number of clinical and histological observations. Reports about the distribution of cutaneous nerves and the quantification of nerve growth factor and neuropeptides, including calcitonin gene-related peptide and vasoactive intestinal peptide, in lesional and nonlesional psoriatic skin suggest that sensory neuropeptides contribute to the development of psoriasis. This review summarizes what is known about the role of neurogenic markers in psoriasis.