The role of selected neuropeptides in pathogenesis of atopic dermatitis

Propionate alleviates itch in murine models of atopic dermatitis by modulating sensory TRP channels of dorsal root ganglion

BACKGROUND

Itch is the most common symptom of atopic dermatitis (AD) and significantly decreases the quality of life. Skin microbiome is involved in AD pathogenesis, whereas its role in the regulation of itch remains elusive. In this study, we aimed to investigate the effects of skin microbial metabolite propionate on acute and chronic pruritus and to explore the mechanism.

METHODS

Using various mouse models of itch, the roles of propionate were explored by behavioral tests and histopathology/immunofluorescent analysis. Primary-cultured dorsal root ganglion neurons and HEK293 cells expressing recombinant human TRP channels were utilized for in vitro calcium imaging/in vivo miniature two-photon imaging in combination with electrophysiology and molecular docking approaches for investigation of the mechanism.

RESULTS

Propionate significantly alleviated itch and alloknesis in various mouse models of pruritus and AD and decreased the density of intraepidermal nerve fibers. Propionate reduced the responsiveness of dorsal root ganglion neurons to pruritogens in vitro, attenuated the hyper-excitability in sensory neurons in MC903-induced AD model, and inhibited capsaicin-evoked hTRPV1 currents (IC50 = 20.08 ± 1.11 μM) via interacting with the vanilloid binding site. Propionate also decreased the secretion of calcitonin gene-related peptide by nerves in MC903-induced AD mouse model, which further attenuated itch and skin inflammation.

CONCLUSION

Our study revealed a protective effect of propionate against persistent itch through direct modulation of sensory TRP channels and neuropeptide production in neurons. Regulation of itch via the skin microbiome might be a novel strategy for the treatment of AD.

The mind-skin connection: A narrative review exploring the link between inflammatory skin diseases and psychological stress

Inflammatory skin diseases are known to negatively impact patient psychology, with individuals experiencing higher rates of stress and subsequent diminished quality of life, as well as mental health issues including anxiety and depression. Moreover, increased psychological stress has been found to exacerbate existing inflammatory skin diseases. The association between inflammatory skin diseases and psychological stress is a timely topic, and a framework to better understand the relationship between the two that integrates available literature is needed. In this narrative review article, we discuss potential neurobiological mechanisms behind psychological stress due to inflammatory skin diseases, focusing mainly on proinflammatory cytokines in the circulating system (the brain-gut-skin communications) and the default mode network in the brain. We also discuss potential descending pathways from the brain that lead to aggravation of inflammatory skin diseases due to psychological stress, including the central and peripheral hypothalamic-pituitary-adrenal axes, peripheral nerves and the skin barrier function.

Sensory neurons: An integrated component of innate immunity

The sensory nervous system possesses the ability to integrate exogenous threats and endogenous signals to mediate downstream effector functions. Sensory neurons have been shown to activate or suppress host defense and immunity against pathogens, depending on the tissue and disease state. Through this lens, pro- and anti-inflammatory neuroimmune effector functions can be interpreted as evolutionary adaptations by host or pathogen. Here, we discuss recent and impactful examples of neuroimmune circuitry that regulate tissue homeostasis, autoinflammation, and host defense. Apparently paradoxical or conflicting reports in the literature also highlight the complexity of neuroimmune interactions that may depend on tissue- and microbe-specific cues. These findings expand our understanding of the nuanced mechanisms and the greater context of sensory neurons in innate immunity.

Navigating the blurred path of mixed neuroimmune signaling

Evolution has created complex mechanisms to sense environmental danger and protect tissues, with the nervous and immune systems playing pivotal roles. These systems work together, coordinating local and systemic reflexes to restore homeostasis in response to tissue injury and infection. By sharing receptors and ligands, they influence the pathogenesis of various diseases. Recently, a less-explored aspect of neuroimmune communication has emerged: the release of neuropeptides from immune cells and cytokines/chemokines from sensory neurons. This article reviews evidence of this unique neuroimmune interplay and its impact on the development of allergy, inflammation, itch, and pain. We highlight the effects of this neuroimmune signaling on vital processes such as host defense, tissue repair, and inflammation resolution, providing avenues for exploration of the underlying mechanisms and therapeutic potential of this signaling.

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.

Lidocaine alleviates inflammation and pruritus in atopic dermatitis by blocking different population of sensory neurons

BACKGROUND AND PURPOSE

Atopic dermatitis is a common chronic pruritic inflammatory disease of the skin involving neuro-immune communication. Neuronal mechanism-based therapeutic treatments remain lacking. We investigated the efficacy of intravenous lidocaine therapy on atopic dermatitis and the underlying neuro-immune mechanism.

EXPERIMENTAL APPROACH

Pharmacological intervention, immunofluorescence, RNA-sequencing, genetic modification and immunoassay were performed to dissect the neuro-immune basis of itch and inflammation in atopic dermatitis-like mouse model and in patients.

KEY RESULTS

Lidocaine alleviated skin lesions and itch in both atopic dermatitis patients and calcipotriol (MC903)-induced atopic dermatitis model by blocking subpopulation of sensory neurons. QX-314, a charged Na_V blocker that enters through pathologically activated large-pore ion channels and selectivity inhibits a subpopulation of sensory neurons, has the same effects as lidocaine in atopic dermatitis model. Genetic silencing Na_V 1.8-expressing sensory neurons was sufficient to restrict cutaneous inflammation and itch in the atopic dermatitis model. However, pharmacological blockade of TRPV1-positive nociceptors only abolished persistent itch but did not affect skin inflammation in the atopic dermatitis model, indicating a difference between sensory neuronal modulation of skin inflammation and itch. Inhibition of activity-dependent release of calcitonin gene-related peptide (CGRP) from sensory neurons by lidocaine largely accounts for the therapeutic effect of lidocaine in the atopic dermatitis model.

CONCLUSION AND IMPLICATIONS

Na_V 1.8⁺ sensory neurons play a critical role in pathogenesis of atopic dermatitis and lidocaine is a potential anti-inflammatory and anti-pruritic agent for atopic dermatitis. A dissociable difference for sensory neuronal modulation of skin inflammation and itch contributes to further understanding of pathogenesis in atopic dermatitis.

Critical Players and Therapeutic Targets in Chronic Itch

Chronic itch is one of the most prominent clinical characteristics of diverse systematic diseases. It is a devastating sensation in pathological diseases. Despite its importance, there are no FDA-labelled drugs specifically geared toward chronic itch. The associated complex pathogenesis and diverse causes escalate chronic itch to being one of the top challenges in healthcare. Humanized antibodies against IL-13, IL-4, and IL-31 proved effective in treatment of itch-associated atopic dermatitis but remain to be validated in chronic itch. There are still no satisfactory anti-itch therapeutics available toward itch-related neuropeptides including GRP, BNP, SST, CGRP, and SP. The newly identified potential itch targets including OSM, NMB, glutamate, periostin, and Serpin E1 have opened new avenues for therapeutic development. Proof-of-principle studies have been successfully performed on antagonists against these proteins and their receptors in itch treatment in animal models. Their translational interventions in humans need to be evaluated. It is of great importance to summarize and compare the newly emerging knowledge on chronic itch and its pathways to promote the development of novel anti-itch therapeutics. The goal of this review is to analyze the different physiologies and pathophysiologies of itch mediators, whilst assessing their suitability as new targets and discussing future therapeutic development.

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.

Roles of calcitonin gene-related peptide in the skin, and other physiological and pathophysiological functions

Skin immunity is regulated by many mediator molecules. One is the neuropeptide calcitonin gene-related peptide (CGRP). CGRP has roles in regulating the function of components of the immune system including T cells, B cells, dendritic cells (DCs), endothelial cells (ECs), and mast cells (MCs).

Herein we discuss actions of CGRP in mediating inflammatory and vascular effects in various cutaneous models and disorders.

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CGRP can help to recruit immune cells through endothelium-dependent vasodilation.

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CGRP plays an important role in the pathogenesis of neurogenic inflammation.

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Functions of many components in the immune system are influenced by CGRP.

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CGRP regulates various inflammatory processes in human skin by affecting different cell-types.

Therapeutic Potential of MRGPRX2 Inhibitors on Mast Cells

Mast cells (MCs) act as primary effectors in inflammatory and allergic reactions by releasing intracellularly-stored inflammatory mediators in diseases. The two major pathways for MC activation are known to be immunoglobulin E (IgE)-dependent and -independent. Although IgE-dependent signaling is the main pathway to MC activation, IgE-independent pathways have also been found to serve pivotal roles in the pathophysiology of various inflammatory conditions. Recent studies have shown that human and mouse MCs express several regulatory receptors such as toll-like receptors (TLRs), CD48, C300a, and GPCRs, including mas-related GPCR-X2 (MRGPRX2). MRGPRX2 has been reported as a novel GPCR that is expressed in MCs activated by basic secretagogues, neurokinin peptides, host defense antimicrobial peptides, and small molecule compounds (e.g., neuromuscular blocking agents) and leads to MC degranulation and eicosanoids release under in vitro experimental condition. Functional analyses of MRGPRX2 and Mrgprb2 (mouse ortholog) indicate that MRGPRX2 is involved in MC hypersensitivity reactions causing neuroinflammation such as postoperative pain, type 2 inflammation, non-histaminergic itch, and drug-induced anaphylactic-like reactions. In this review, we discuss the roles in innate immunity through functional studies on MRGPRX2-mediated IgE-independent MC activation and also the therapeutic potential of MRGPRX2 inhibitors on allergic and inflammatory diseases.

Intractable Itch in Atopic Dermatitis: Causes and Treatments

Itch or pruritus is the hallmark of atopic dermatitis and is defined as an unpleasant sensation that evokes the desire to scratch. It is also believed that itch is a signal of danger from various environmental factors or physiological abnormalities. Because histamine is a well-known substance inducing itch, H₁-antihistamines are the most frequently used drugs to treat pruritus. However, H₁-antihistamines are not fully effective against intractable itch in patients with atopic dermatitis. Given that intractable itch is a clinical problem that markedly decreases quality of life, its treatment in atopic dermatitis is of high importance. Histamine-independent itch may be elicited by various pruritogens, including proteases, cytokines, neuropeptides, lipids, and opioids, and their cognate receptors, such as protease-activated receptors, cytokine receptors, Mas-related G protein-coupled receptors, opioid receptors, and transient receptor potential channels. In addition, cutaneous hyperinnervation is partly involved in itch sensitization in the periphery. It is believed that dry skin is a key feature of intractable itch in atopic dermatitis. Treatment of the underlying conditions that cause itch is necessary to improve the quality of life of patients with atopic dermatitis. This review describes current insights into the pathophysiology of itch and its treatment in atopic dermatitis.

Involvement of Neuro-Immune Interactions in Pruritus With Special Focus on Receptor Expressions

Pruritus is a common, but very challenging symptom with a wide diversity of underlying causes like dermatological, systemic, neurological and psychiatric diseases. In dermatology, pruritus is the most frequent symptom both in its acute and chronic form (over 6 weeks in duration). Treatment of chronic pruritus often remains challenging. Affected patients who suffer from moderate to severe pruritus have a significantly reduced quality of life. The underlying physiology of pruritus is very complex, involving a diverse network of components in the skin including resident cells such as keratinocytes and sensory neurons as well as transiently infiltrating cells such as certain immune cells. Previous research has established that there is a significant crosstalk among the stratum corneum, nerve fibers and various immune cells, such as keratinocytes, T cells, basophils, eosinophils and mast cells. In this regard, interactions between receptors on cutaneous and spinal neurons or on different immune cells play an important role in the processing of signals which are important for the transmission of pruritus. In this review, we discuss the role of various receptors involved in pruritus and inflammation, such as TRPV1 and TRPA1, IL-31RA and OSMR, TSLPR, PAR-2, NK1R, H1R and H4R, MRGPRs as well as TrkA, with a focus on interaction between nerve fibers and different immune cells. Emerging evidence shows that neuro-immune interactions play a pivotal role in mediating pruritus-associated inflammatory skin diseases such as atopic dermatitis, psoriasis or chronic spontaneous urticaria. Targeting these bidirectional neuro-immune interactions and the involved pruritus-specific receptors is likely to contribute to novel insights into the underlying pathogenesis and targeted treatment options of pruritus.

Keratinocytes-Derived Reactive Oxygen Species Play an Active Role to Induce Type 2 Inflammation of the Skin: A Pathogenic Role of Reactive Oxygen Species at the Early Phase of Atopic Dermatitis

Background

Atopic dermatitis (AD) is characterized by chronic, relapsing skin inflammation (eczema) with itchy sensation. Keratinocytes, which are located at the outermost part of our body, are supposed to play important roles at the early phase of type 2 inflammation including AD pathogenesis.

Objective

The purpose of this study was to evaluate whether keratinocytes-derived reactive oxygen species (ROS) could be produced by the allergens or non-allergens, and the keratinocytes-derived ROS could modulate a set of biomarkers for type 2 inflammation of the skin.

Methods

Normal human epidermal keratinocytes (NHEKs) were treated with an allergen of house dust mites (HDM) or a non-allergen of compound 48/80 (C48/80). Then, biomarkers for type 2 inflammation of the skin including those for neurogenic inflammation were checked by reverse transcriptase-polymerase chain reaction and western immunoblot experiments.

Results

HDM or C48/80 was found to upregulate expression levels of our tested biomarkers, including type 2 T helper-driving pathway (KLK5, PAR2, and NFκB), epithelial-cell-derived cytokines (thymic stromal lymphopoietin, interleukin [IL]-25, IL-33), and neurogenic inflammation (NGF, CGRP). The HDM- or C-48/80-induced expression levels of the biomarkers could be blocked by an antioxidant treatment with 5 mM N-acetyl-cysteine. In contrast, pro-oxidant treatment with 1 mM H₂O₂ could upregulate expression levels of the tested biomarkers in NHEKs.

Conclusion

Our results reveal that keratinocytes-derived ROS, irrespective to their origins from allergens or non-allergens, have a potential to induce type 2 inflammation of AD skin.

House dust mites activate nociceptor-mast cell clusters to drive type 2 skin inflammation

Allergic skin diseases, such as atopic dermatitis (AD), are clinically characterized by severe itching and type 2 immunity-associated hypersensitivity to widely-distributed allergens, including those derived from house dust mites (HDMs). Here we found that HDMs with cysteine-protease activity directly activated peptidergic nociceptors, which are neuropeptide-producing nociceptive sensory neurons, that expressed the ion channel TRPV1 and Tac1, the gene encoding the precursor for the neuropeptide substance P. Intravital imaging and genetic approaches indicated that HDMs-activated nociceptors drove the development of allergic skin inflammation by inducing the degranulation of mast cells contiguous to such nociceptors through the release of substance P and the activation of the cationic molecules receptor MRGPRB2 on mast cells. This data indicates that, after exposure to HDM allergens, activation of TRPV1⁺Tac1⁺ nociceptor-MRGPRB2⁺ sensory clusters represents a key early event in the development of allergic skin reaction.

Skin neurogenic inflammation

The epidermis closely interacts with nerve endings, and both epidermis and nerves produce substances for mutual sustenance. Neuropeptides, like substance P (SP) and calcitonin gene-related protein (CGRP), are produced by sensory nerves in the dermis; they induce mast cells to release vasoactive amines that facilitate infiltration of neutrophils and T cells. Some receptors are more important than others in the generation of itch. The Mas-related G protein-coupled receptors (Mrgpr) family as well as transient receptor potential ankyrin 1 (TRPA1) and protease activated receptor 2(Par2) have important roles in itch and inflammation. The activation of MrgprX1 degranulates mast cells to communicate with sensory nerve and cutaneous cells for developing neurogenic inflammation. Mrgprs and transient receptor potential vanilloid 4 (TRPV4) are crucial for the generation of skin diseases like rosacea, while SP, CGRP, somatostatin, β-endorphin, vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP) can modulate the immune system during psoriasis development. The increased level of SP, in atopic dermatitis, induces the release of interferon (IFN)-γ, interleukin (IL)-4, tumor necrosis factor (TNF)-α, and IL-10 from the peripheral blood mononuclear leukocytes. We are finally starting to understand the intricate connections between the skin neurons and resident skin cells and how their interaction can be key to controlling inflammation and from there the pathogenesis of diseases like atopic dermatitis, psoriasis, and rosacea.

Calcitonin gene-related peptide and pain: a systematic review

BACKGROUND

Calcitonin gene-related peptide (CGRP) is widely distributed in nociceptive pathways in human peripheral and central nervous system and its receptors are also expressed in pain pathways. CGRP is involved in migraine pathophysiology but its role in non-headache pain has not been clarified.

METHODS

We performed a systematic literature search on PubMed, Embase and ClinicalTrials.gov for articles on CGRP and non-headache pain covering human studies including experimental studies and randomized clinical trials.

RESULTS

The literature search identified 375 citations of which 50 contained relevant original data. An association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain was found. In 13 out of 20 studies in somatic pain conditions, CGRP levels had a positive correlation with pain. Increased CGRP levels were reported in plasma, synovial and cerebrospinal fluid in subjects with musculoskeletal pain. A randomized clinical trial on monoclonal antibody, which selectively binds to and inhibits the activity of CGRP (galcanezumab) in patients with osteoarthritis knee pain, failed to demonstrate improvement of pain compared with placebo. No studies to date have investigated the efficacy of monoclonal antibodies against CGRP receptor in non-headache pain conditions.

CONCLUSION

The present review revealed the association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain. These data suggest that CGRP may act as a neuromodulator in non-headache pain conditions. However, more studies are needed to fully understand the role of CGRP in nociceptive processing and therapy of chronic pain.

Neuroendocrine cells derived chemokine vasoactive intestinal polypeptide (VIP) in allergic diseases

Worldwide increase incidences of allergic diseases have heightened the interest of clinicians and researchers to understand the role of neuroendocrine cells in the recruitment and activation of inflammatory cells. Several pieces of evidence revealed the association of neuropeptides in the pathogenesis of allergic diseases. Importantly, one such peptide that is secreted by neuronal cells and immune cells exerts a wide spectrum of immunological functions as cytokine/chemokine is termed as Vasoactive Intestinal Peptide (VIP). VIP mediates immunological function through interaction with specific receptors namely VPAC-1, VPAC-2, CRTH2 and PAC1 that are expressed on several immune cells such as eosinophils, mast cells, neutrophils, and lymphocytes; therefore, provide the basis for the action of VIP on the immune system. Additionally, VIP mediated action varies according to target organ depending upon the presence of specific VIP associated receptor, involved immune cells and the microenvironment of the organ. Herein, we present an integrative review of the current understanding on the role of VIP and associated receptors in allergic diseases, the presence of VIP receptors on various immune cells with particular emphasis on the role of VIP in the pathogenesis of allergic diseases such as asthma, allergic rhinitis, and atopic dermatitis. Being crucial signal molecule of the neuroendocrine-immune network, the development of stable VIP analogue and/or antagonist may provide the future therapeutic drug alternative for the better treatment of these allergic diseases. Taken together, our current review summarizes the current understandings of VIP biology and further explore the significance of neuroendocrine cells derived VIP in the recruitment of inflammatory cells in allergic diseases that may be helpful to the investigators for planning the experiments and accordingly predicting new therapeutic strategies for combating allergic diseases. Summarized graphical abstract will help the readers to understand the significance of VIP in allergic diseases.

Up-regulated expression of substance P in CD8+ T cells and NK1R on monocytes of atopic dermatitis

BACKGROUND

Large numbers of CD8⁺ T cells were observed in atopic dermatitis (AD) skin, and monocytes from AD patients showed increased prostaglandin E2 production. However, little is known about the expression of substance P (SP) and its receptor NK1R in blood leukocytes of patients with AD.

OBJECTIVE

To explore the expression of SP and NK1R in leukocytes of AD and the influence of allergens on SP and NK1R expression.

METHODS

The expression levels of SP and NK1R in patients with AD were examined by flow cytometry, ELISA and a mouse AD model.

RESULTS

The plasma SP level was 4.9-fold higher in patients with AD than in HC subjects. Both the percentage of SP expression in the population and mean fluorescence intensity (MFI) of SP expression were elevated in CD8⁺ T cells in the blood of AD patients. However, both the CD14⁺NK1R⁺ population and MFI of NK1R expression on CD14⁺ cells were enhanced in the blood of AD patients. Allergens ASWE, HDME and PPE failed to up-regulate SP expression in CD8⁺ T cells. However, allergens ASWE and HDME both enhanced NK1R expression on CD14⁺ blood leukocytes regardless of AD or HC subjects. OVA-sensitized AD mice showed an elevated proportion and MFI of SP-expressing CD8⁺ T cells in the blood, which agrees with the SP expression situation in human AD blood. Injection of SP into mouse skin did not up-regulate NK1R expression on monocytes.

CONCLUSIONS

An elevated plasma SP level, up-regulated expression of SP and NK1R indicate that the SP/NK1R complex is important in the development of AD. Therefore, SP and NK1R antagonist or blocker agents may help to treat patients with AD. Trial registration Registration number: ChiCTR-BOC-16010279; Registration date: Dec., 28, 2016; retrospectively registered.

CSP0510 Lotion as a Novel Moisturizer Containing Citric Acid and Trisodium Phosphate Relieves Objective and Subjective Symptoms of Atopic Dermatitis

BACKGROUND

Moisturizers with anti-inflammatory or anti-itch activity should be developed for the safe and effective management of atopic dermatitis (AD).

OBJECTIVE

This study evaluated the efficacy of a newly developed moisturizer, CSP0510 lotion (Twolines Inc., Korea), containing citric acid (CA) and trisodium phosphate (TSP) as active ingredients, in mild to moderate AD.

METHODS AND RESULTS

CSP0510 lotion applied twice daily for 4 weeks to eczematous lesions improved objective and subjective (itch) symptoms of AD. The physician's global assessment (PGA) score for objective symptoms decreased from 2.5±0.6 before application to 1.3±0.5 after application in the CSP0510-treated group (n=42, p<0.001). Also, the PGA score decreased from 2.3±0.6 to 1.9±0.5 by vehicle-treated (without CA and TSP) control group (p=0.001), but there was no statistical difference between CSP0510-treated and vehicle-treated groups (p=0.089). The visual analogue scale score for itch decreased from 4.8±1.3 to 2.0±0.9 in the CSP0510-treated group (p<0.001), and from 4.6±1.1 to 3.5±0.9 in the control group (p=0.075), showing a statistical significance between two groups (p=0.002). Our results in humans were further supported by in vitro and animal experiments. In HaCaT cells treated with compound 48/80 (7.5 µg/ml), CA:TSP (1:1, vol:vol) synergistically suppressed the compound 48/80-induced upregulation of thymic stromal lymphopoietin, nerve grow factor, and calcitonin gene-related peptide. Application of CSP0510 to the dorsal skin of hairless mice for 3 weeks suppressed the oxazolone-induced allergic skin inflammation.

CONCLUSION

In conclusion, CSP0510 lotion has anti-itch and anti-inflammatory activity in the skin, which improves both objective and subjective symptoms of AD.

Are itch and scratching the nausea and vomiting of skin?

The physiologic similarities between itch and nausea may not be evident initially, but they share the role of repelling irritants and toxins from the body by inducting scratching and vomiting, respectively. In addition, itch and nausea frequently occur together in certain conditions such as uraemia. Here we show that the mechanisms underlying itch and nausea overlap and that advances in either field may influence the identification of novel drug targets, particularly for itch.

Gender differences in depression and anxiety among atopic dermatitis patients

Background:

Dermatological patients invariably suffer one or the other psychological problems which may escalate to the extent of a mental disorder. One of the most common dermatological disorders is atopic dermatitis (AD), but the literature has limited data on gender differences for psychiatric morbidity in such patients.

Aims:

To evaluate and compare gender differences in the prevalence of depression and anxiety in AD.

Materials and Methods:

This cross-sectional study with consecutive sampling was done in an outpatient clinic of Dermatology at a Tertiary Care Center. AD subjects giving informed consent were evaluated on a brief semi-structured performa for collecting demographic and clinical information. Primary Care Evaluation of Mental Disorders (PRIME-MD) was used to assess the presence of psychiatric symptoms in these patients. Descriptive analysis was done for the socio-demographic profile and independent sample t-test, Chi-square and Cramer's V test was carried out to find in-between group differences for males and females.

Results:

A total of 81 patients were included in the final analysis (males = 36, females = 45) with no significant difference in mean age between male and female subjects (36.14 ± 17.62 and 33.98 ± 14.49 years, respectively; P = 0.54). When including moderate to severe grade of depression or anxiety, the current study found prevalence rates of 15% and 12% respectively. Females had significantly more anxiety and depression scores than males (P = 0.04 and P = 0.03 respectively).

Conclusions:

There is a female preponderance of depression and anxiety disorder in AD patients.

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.

The itchy scalp--scratching for an explanation

Scalp pruritus is a common complaint that is considered a diagnostically and therapeutically challenging situation. Scalp skin has a unique neural structure that contains densely innervated hair follicles and dermal vasculature. In spite of the recent advances in our understanding of itch pathophysiology, scalp itching has not been studied as yet. In this review, we summarize the current knowledge on the neurobiology of scalp and hair follicles as well as itch mediators and provide a putative mechanism for scalp itch with special emphasis on neuroanatomy and pathophysiology.

Psychoneuroimmunology of psychological stress and atopic dermatitis: pathophysiologic and therapeutic updates

Atopic dermatitis is a chronic inflammatory skin disease characterized by impaired epidermal barrier function, inflammatory infiltration, extensive pruritus and a clinical course defined by symptomatic flares and remissions. The mechanisms of disease exacerbation are still poorly understood. Clinical occurrence of atopic dermatitis is often associated with psychological stress. In response to stress, upregulation of neuropeptide mediators in the brain, endocrine organs, and peripheral nervous system directly affect immune and resident cells in the skin. Lesional and non-lesional skin of patients with atopic dermatitis demonstrates increased mast cells and mast cell-nerve fiber contacts. In the setting of stress, sensory nerves release neuromediators that regulate inflammatory and immune responses, as well as barrier function. Progress towards elucidating these neuroimmune connections will refine our understanding of how emotional stress influences atopic dermatitis. Moreover, psychopharmacologic agents that modulate neuronal receptors or the amplification circuits of inflammation are attractive options for the treatment of not only atopic dermatitis, but also other stress-mediated inflammatory skin diseases.

Pathophysiology of the Behçet's Disease

Behçet's disease (BD) is a multisystemic disease of unknown etiology characterized by chronic relapsing oral-genital ulcers and uveitis. Multiple systemic associations including articular, gastrointestinal, cardiopulmonary, neurologic, and vascular involvement are also observed in BD. Although the etiopathogenesis of the disease remains unknown, increased neutrophil functions such as chemotaxis, phagocytosis, and excessive production of reactive oxygen species (ROS), including superoxide anion, which may be responsible for oxidative tissue damage seen in BD, and also immunological alterations, T lymphocyte abnormalities in both subpopulation and function have been considered to be correlated with the etiopathogenesis of BD. There is some clinical evidence suggesting that emotional stress and hormonal alterations can influence the course and disease activity of BD.

Targeting the neurokinin receptor 1 with aprepitant: a novel antipruritic strategy

BACKGROUND

Chronic pruritus is a global clinical problem with a high impact on the quality of life and lack of specific therapies. It is an excruciating and frequent symptom of e.g. uncurable renal, liver and skin diseases which often does not respond to conventional treatment with e.g. antihistamines. Therefore antipruritic therapies which target physiological mechanisms of pruritus need to be developed. Substance P (SP) is a major mediator of pruritus. As it binds to the neurokinin receptor 1 (NKR1), we evaluated if the application of a NKR1 antagonist would significantly decrease chronic pruritus.

METHODS AND FINDINGS

Twenty hitherto untreatable patients with chronic pruritus (12 female, 8 male; mean age, 66.7 years) were treated with the NKR1 antagonist aprepitant 80 mg for one week. 16 of 20 patients (80%) experienced a considerable reduction of itch intensity, as assessed by the visual analog scale (VAS, range 0 to 10). Considering all patients, the mean value of pruritus intensity was significantly reduced from 8.4 VAS points (SD +/-1.7) before treatment to 4.9 VAS points (SD +/-3.2) (p<0.001, CI 1.913-5.187). Patients with dermatological diseases (e.g. atopic diathesis, prurigo nodularis) had the best profit from the treatment. Side-effects were mild (nausea, vertigo, and drowsiness) and only occurred in three patients.

CONCLUSIONS

The high response rate in patients with therapy refractory pruritus suggests that the NKR1 antagonist aprepitant may indeed exhibit antipruritic effects and may present a novel, effective treatment strategy based on pathophysiology of chronic pruritus. The results are promising enough to warrant confirming the efficacy of NKR1 antagonists in a randomized, controlled clinical trial.

Systemic therapy of atopic dermatitis in children

Atopic dermatitis (AD) is a common disease in childhood that is a serious burden on patients and their families. Most AD is mild and can be managed with the use of emollients and standard therapy consisting of topical corticosteroids or topical calcineurin inhibitors. However, in a subgroup of patients with moderate to severe AD, the disease is recalcitrant to topical therapy and systemic treatments become necessary. Short courses of systemic corticosteroids are often used in clinical practice, but their use is controversial. International guidelines suggest that in the case of acute flare-ups, patients might benefit from a short course of systemic corticosteroids, but long-term use and use in children should be avoided. Ciclosporin is an immunosuppressant agent that acts directly on cells of the immune system, with an inhibitory effect on T cells. When AD cannot be controlled by standard topical therapies, ciclosporin significantly decreases symptom scores, disease extent, pruritus and sleep deprivation, and improves quality of life. The most frequent adverse effects associated with the use of ciclosporin are hypertension and renal dysfunction, but they are usually reversible after drug discontinuation. Ciclosporin has been found to be safely used, effective and well tolerated in children with severe AD. However, studies to assess the long-term effectiveness and safety of ciclosporin in AD are lacking. In patients for whom ciclosporin is not suitable, or when there is a lack of response, alternative drugs should be considered, such as azathioprine or interferon-gamma. Intravenous immunoglobulins and the monoclonal antibody infliximab only have a place in the systemic therapy of AD when other drugs have failed. Mycophenolate mofetil has recently been introduced in the treatment of recalcitrant AD. Efalizumab and omalizumab are monoclonal antibodies with a possible future role in the treatment of AD, but further studies are needed.

What causes itch in atopic dermatitis?

Itch, the hallmark of atopic dermatitis, has a significant impact on quality of life for patients with this disease. Various central and peripheral mediators have been suggested to play a role in the pathophysiology of atopic eczema itch. Significant cross-talk occurs among stratum corneum, keratinocytes, immune cells, and nerve fibers, which are in close proximity to one another and induce itch. The impaired barrier function associated with the itch-scratch cycle further augments this vicious cycle. Recent advances in our understanding of itch pathophysiology shed light on peripheral and central neural sensitization of nerve fibers that contribute significantly to itch in atopic dermatitis. Recently, several new mediators have been described as associated with itch in atopic dermatitis, including serine proteases, interleukin 31, and nerve growth factor. This review covers the peripheral and central mechanisms and mediators involved in pathogenesis of itch in atopic dermatitis.

[Atopic dermatitis and stress? How do emotions come into skin?]

It is widely accepted, that stress can induce or exacerbate atopic dermatitis. The physiological mechanisms that mediate this negative influence of stress on atopic dermatitis are not clearly understood. This topic has been actively investigated in recent years focusing on neuroimmunological, psychoendocrinological studies and examination of integrity and function of skin barrier under stress. Different neuropeptides and neurotrophins seem to play an important role in stress-induced neurogenic inflammation and connection of nervous and immune system. Mast cells play a key role in the development of inflammatory reaction to stress. Skin barrier is altered by stress by means of increased cortisol level. Thereby lamellar body secretion is decreased and epidermal expression of antimicrobial peptides (beta-defensin and cathelicidin) is down-regulated. We review recent investigations in this field.