Pathophysiology and therapy of pruritus in allergic and atopic diseases

Vascular Endothelial Growth Factor a Promotes Chronic Itch via VEGFA-VEGFR2-PI3K-TRPV1 Axis in Allergic Contact Dermatitis

Introduction

Allergic contact dermatitis (ACD), a prevalent skin disorder affecting up to 20% of the population, triggers significant discomfort and health implications. Our research investigates the pivotal role of Vascular Endothelial Growth Factor A (VEGFA) in chronic itching associated with ACD.

Methods

Bioinformatics methods were utilized to identify differentially expressed genes (DEGs) between ACD models and patients. In vivo models of chronic pruritus in mice induced by 2,4-dinitrofluorobenzene (DNFB) were employed. Mice were administered subcutaneously with a VEGFA inhibitor, sFlt1, and compared to a control group. Real-time RT-PCR, Western blot, and immunohistochemical staining were performed to evaluate VEGFA expression and the impact of sFlt1 on itching behavior.

Results

The analysis revealed that VEGFA is significantly upregulated in ACD skin, primarily expressed by keratinocytes. Administration of the VEGFA inhibitor sFlt1 in the ACD mouse model led to a substantial reduction in scratching behavior, indicating that VEGFA may mediate pruritus through the VEGFA-VEGFR2-PI3K-TRPV1 signaling pathway.

Discussion

These findings suggest that VEGFA plays a crucial role in ACD-associated pruritus and may serve as a potential therapeutic target. However, further research is required to validate these findings and to explore additional molecular pathways involved in the pruritic response in ACD.

Pharmacokinetics, pharmacodynamics, and safety of izuforant, an H4R inhibitor, in healthy subjects: A phase I single and multiple ascending dose study

Izuforant is a selective, and potent histamine H4 receptor (H4R) antagonist developed to treat atopic dermatitis (AD). There is an unmet medical need for therapeutic agents to control inflammation and pruritus. Izuforant is a strong candidate for this task based on the findings of non-clinical studies showing that inhibition of the histamine-mediated signaling pathway via H4R by izuforant results in decreased pruritus and inflammation. This study aimed to evaluate the clinical pharmacokinetic (PK) and pharmacodynamic (PD) profiles of izuforant. Dose-block-randomized, double-blind, placebo-controlled, single- and multiple ascending dose studies were conducted in 64 healthy volunteers. For the single ascending dose (SAD) study, 10-600 mg izuforant was administered to the designated groups. For the multiple ascending dose (MAD) study, 100-400 mg izuforant was administered to three groups. The clinical pharmacokinetic (PK) profile of izuforant was evaluated using plasma and urine concentrations. Blood sampling for the PD assay, which measured imetit-induced eosinophil shape changes (ESC), was also conducted. A one-compartment PK model described the distribution and elimination profiles of izuforant. An imetit-induced ESC inhibition test was established and validated for PD evaluation as a measure of the H4R antagonistic effect. ESC inhibition was observed even at doses as low as 10 mg; however, this inhibition became stronger and lasted longer as the dose increased. All izuforant doses were well tolerated, and no discontinuations due to adverse events (AE) or deaths were reported.

Neutrophil-derived oxidative stress contributes to skin inflammation and scratching in a mouse model of allergic contact dermatitis via triggering pro-inflammatory cytokine and pruritogen production in skin

Allergic contact dermatitis (ACD) is a common skin disease featured with skin inflammation and a mixed itch/pain sensation. The itch/pain causes the desire to scratch, affecting both physical and psychological aspects of patients. Nevertheless, the mechanisms underlying itch/pain sensation of ACD still remain elusive. Here, we found that oxidative stress and oxidation-related injury were remarkably increased in the inflamed skin of a mouse model of ACD. Reducing oxidative stress significantly attenuated itch/pain-related scratching, allokonesis and skin inflammation. RNA-Sequencing reveals oxidative stress contributes to a series of skin biological processes, including inflammation and immune response. Attenuating oxidative stress reduces overproduction of IL-1β and IL-33, two critical cytokines involved in inflammation and pain/itch, in the inflamed skin of model mice. Exogenously injecting H2O2 into the neck skin of naïve mice triggered IL-33 overproduction in skin keratinocytes and induced scratching, which was reduced in mice deficient in IL-33 receptor ST2. ACD model mice showed remarkable neutrophil infiltration in the inflamed skin. Blocking neutrophil infiltration reduced oxidative stress and attenuated scratching and skin inflammation. Therefore, our study reveals a critical contribution of neutrophil-derived oxidative stress to skin inflammation and itch/pain-related scratching of ACD model mice via mechanisms involving the triggering of IL-33 overproduction in skin keratinocytes. Targeting skin oxidative stress may represent an effective therapy for ameliorating ACD.

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

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

Cyanoacrylate glue reactions: A systematic review, cases, and proposed mechanisms

OBJECTIVE

Cyanoacrylate glue closure was first used in humans 10 years ago to treat venous reflux of the axial veins. Studies have since shown its clinical efficacy in vein closure. However, great need exists to elucidate further the types of specific adverse reactions that cyanoacrylate glue can cause for better patient selection and to minimize these events. In the present study, we systematically reviewed the literature to identify the types of reported reactions. In addition, we explored the pathophysiology contributing to these reactions and proposed the mechanistic pathway with inclusion of actual cases.

METHODS

We searched the literature for reports of reactions following cyanoacrylate glue use in patients with venous diseases between 2012 and 2022. The search was performed using MeSH (medical subject headings) terms. The terms included cyanoacrylate, venous insufficiency, chronic venous disorder, varicose veins, vein varicosities, venous ulcer, venous wound, CEAP (clinical, etiologic, anatomic, pathophysiologic), vein, adverse events, phlebitis, hypersensitivity, foreign body granuloma, giant cell, endovenous glue-induced thrombosis, and allergy. The search was limited to the literature reported in English. These studies were evaluated for the type of product used and the reactions noted. A systematic review, in accordance with the PRISMA (preferred reporting items for systematic reviews and meta-analyses) method, was performed. Covidence software (Melbourne, VC, Australia) was used for full-text screening and data extraction. Two reviewers reviewed the data, and the content expert served as the tiebreaker.

RESULTS

We identified 102, of which, 37 reported on cyanoacrylate use other than in the context of chronic venous diseases and were excluded. Fifty-five reports were determined appropriate for data extraction. The adverse reactions to cyanoacrylate glue were phlebitis, hypersensitivity, foreign body granuloma, and endovenous glue-induced thrombosis.

CONCLUSIONS

Although cyanoacrylate glue closure for venous reflux is generally a safe and clinically effective treatment choice for patients with symptomatic chronic venous disease and axial reflux, some adverse events could be specific to the properties of the cyanoacrylate product. We propose mechanisms for how such reactions can occur based on histologic changes, published reports, and case examples; however, further exploration is necessary to confirm these theories.

Chronic Pruritus in Atopic Patients Treated with Dupilumab: Real Life Response and Related Parameters in 354 Patients

Chronic pruritus is a major symptom of atopic dermatitis (AD). Its etiopathogenesis is complex, and an understanding of the driving factors of its pathogenesis allows for the development of new molecule-targeted therapies. Dupilumab, targeting and blocking interleukin-4 (IL-4) and interleukin-13 (IL-13) molecules, has shown great efficacy in treating AD symptoms such chronic itching. We performed a retrospective observational study to evaluate possible chronic-itch-related characteristics and parameters in 356 AD patients who received dupilumab. The objective of the study was to evaluate the factors associated with the level of pruritus reported by patients at each of the 1575 detections in the form of the peak pruritus numerical rating scale (NRSpp) and sleep disturbance numerical rating scale (NRSsd). We focused on: the eczema area and severity index (EASI), dermatology life quality index (DLQI), patient-oriented eczema measure (POEMS), eosinophilia, L-lactate dehydrogenase (LDH), immunoglobulin E (IgE) and the time from the start of dupilumab therapy. NRSpp fell from 8.6 (sd 1.7) at baseline to 1.7 (sd 2.3) at 36 months and NRSsd from 7 (sd 3) to 0. Regarding the parameters that correlate with NRSpp, all the parameters analysed were significantly correlated except for eosinophils (p = 0.136). In the multivariate analysis, both considering and not considering treatment duration, the parameters were correlated (p < 0.001); EASI, DLQI, POEM, and LDH significantly correlated with NRSpp (p < 0.001 for each, except for LDH p = 0.003); while IgE tot lost significance (p = 0.337). Similar results were obtained for the parameters correlating with NRSsd. Our results confirm the efficacy of dupilumab on pruritus. The use of questionnaires such as DLQI and POEM is advisable in clinical practice and is adequate for assessing the impact of itching on AD. The low correlation of IgE and eosinophils, the ambiguity of LDH levels with the level of pruritus, and a poor clinical validity and unclear correlation with disease severity suggest a progressive abandonment of monitoring of these values.

Neuro-immune communication regulating pruritus in atopic dermatitis

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

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

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

Atopic dermatitis: Current standards of diagnosis and treatment, including the latest methods of management

Atopic dermatitis (AD) is a chronic relapsing disease which causes characteristic eczematous skin lesions. The most common symptoms of atopic dermatitis are persistent pruritus, xerosis, and skin lesions with a typical location and appearance that changes with the patient’s age. The prevalence of the disease in the pediatric population is estimated at 10% to 30%, while in adults it ranges from 1% to 3%. The number of people who suffer from AD is rising every year. The pathophysiology of the disease is complex and multifactorial. It involves elements of epidermal barrier dysfunction, alterations in cellular immune response, IgE hypersensitivity, and environmental factors. AD significantly reduces the quality of life of both patients and their families. Patients with AD are at higher risk for neuropsychiatric disorders such as depression, attention-deficit/hyperactivity disorder, and headaches. The decreased quality of life of AD patients and their families is associated with the discomfort of recurrent and chronic inflammatory skin lesions, persistent pruritus, and the inconvenience of long-term therapy. It also affects the psychological development of children, contributes to behavioral disorders (hyperactivity, hypersensitivity) and impacts many areas of family life such as sleep, leisure activities, and relationships between family members. The basic treatment of AD is avoidance of potential harmful factors, proper care in the treatment of exacerbations, topical corticosteroids, and calcineurin inhibitors in proactive therapy. In some patients who meet age criteria, phototherapy and cyclosporine should be considered. In individuals with severe AD who do not respond to topical treatment and who will not benefit from general therapy, dupilumab, a biologic drug, is the treatment of choice. Biologic treatment has an increasingly important place in the effective and modern therapy of AD. Currently, new biologic drugs are being researched, which may bring a therapeutic revolution in AD in the future. Allergen immunotherapy in patients with AD should be carefully evaluated on an individual basis, as proper selection of patients with documented IgE-dependent sensitization is important for the success of this therapy. Close collaboration with the patient and their caregivers, education, and psychological support as appropriate are integral to the treatment.

Cyclosporine in cholinergic itch

Cholinergic itch is part of symptom complex that also includes cholinergic erythema and cholinergic urticaria. It mostly occurs during the winters among young adults. It is characterized by onset of severe itching or burning sensation all over body, mostly, on exposure to sunlight, warm atmosphere and in some cases after hot and spicy food intake. In most of the cases, it is poorly responsive to antihistamine therapy.

Genetic priming of sensory neurons in mice that overexpress PAR2 enhances allergen responsiveness

Pruritus is a common symptom of inflammatory skin conditions, including atopic dermatitis (AD). Although primary sensory neurons that transmit pruritic signals are well-cataloged, little is known about the neuronal alterations that occur as a result of skin disruption in AD. To address this question, we examined the molecular and behavioral consequences of challenging Grhl3 ^PAR2/+ mice, which overexpress PAR2 in suprabasal keratinocytes, with serial topical application of the environmental allergen house dust mite (HDM). We monitored behavior and used RNA sequencing, qPCR, and in situ hybridization to evaluate gene expression in trigeminal ganglia (TG), before and after HDM. We found that neither Grhl3 ^PAR2/+ nor wild-type (WT) mice exhibited spontaneous scratching, and pruritogen-induced acute scratching did not differ. In contrast, HDM exacerbated scratching in Grhl3 ^PAR2/+ mice. Despite the absence of scratching in untreated Grhl3 ^PAR2/+ mice, several TG genes in these mice were up-regulated compared to WT. HDM treatment of the Grhl3 ^PAR2/+ mice enhanced up-regulation of this set of genes and induced additional genes, many within the subset of TG neurons that express TRPV1. The same set of genes was up-regulated in HDM-treated Grhl3 ^PAR2/+ mice that did not scratch, but at lesser magnitude. Finally, we recorded comparable transcriptional changes in IL31Tg mice, demonstrating that a common genetic program is induced in two AD models. Taken together, we conclude that transcriptional changes that occur in primary sensory neurons in dermatitis-susceptible animals underlie a genetic priming that not only sensitizes the animal to chronic allergens but also contributes to pruritus in atopic skin disease.

Prospective, comparative clinical pilot study of cold atmospheric plasma device in the treatment of atopic dermatitis

Cold atmospheric plasma generates free radicals through the ionization of air at room temperature. Its effect and safety profile as a treatment modality for atopic dermatitis lesions have not been evaluated prospectively enough. We aimed to investigate the effect and safety of cold atmospheric plasma in patients with atopic dermatitis with a prospective pilot study. Cold atmospheric plasma treatment or sham control treatment were applied respectively in randomly assigned and symmetric skin lesions. Three treatment sessions were performed at weeks 0, 1, and 2. Clinical severity indices were assessed at weeks 0, 1, 2, and 4 after treatment. Additionally, the microbial characteristics of the lesions before and after treatments were analyzed. We included 22 patients with mild to moderate atopic dermatitis presented with symmetric lesions. We found that cold atmospheric plasma can alleviate the clinical severity of atopic dermatitis. Modified atopic dermatitis antecubital severity and eczema area and severity index score were significantly decreased in the treated group. Furthermore, scoring of atopic dermatitis score and pruritic visual analog scales significantly improved. Microbiome analysis revealed significantly reduced proportion of Staphylococcus aureus in the treated group. Cold atmospheric plasma can significantly improve mild and moderate atopic dermatitis without safety issues.

Th2 Modulation of Transient Receptor Potential Channels: An Unmet Therapeutic Intervention for Atopic Dermatitis

Atopic dermatitis (AD) is a multifaceted, chronic relapsing inflammatory skin disease that affects people of all ages. It is characterized by chronic eczema, constant pruritus, and severe discomfort. AD often progresses from mild annoyance to intractable pruritic inflammatory lesions associated with exacerbated skin sensitivity. The T helper-2 (Th2) response is mainly linked to the acute and subacute phase, whereas Th1 response has been associated in addition with the chronic phase. IL-17, IL-22, TSLP, and IL-31 also play a role in AD. Transient receptor potential (TRP) cation channels play a significant role in neuroinflammation, itch and pain, indicating neuroimmune circuits in AD. However, the Th2-driven cutaneous sensitization of TRP channels is underappreciated. Emerging findings suggest that critical Th2-related cytokines cause potentiation of TRP channels, thereby exaggerating inflammation and itch sensation. Evidence involves the following: (i) IL-13 enhances TRPV1 and TRPA1 transcription levels; (ii) IL-31 sensitizes TRPV1 via transcriptional and channel modulation, and indirectly modulates TRPV3 in keratinocytes; (iii) The Th2-cytokine TSLP increases TRPA1 synthesis in sensory neurons. These changes could be further enhanced by other Th2 cytokines, including IL-4, IL-25, and IL-33, which are inducers for IL-13, IL-31, or TSLP in skin. Taken together, this review highlights that Th2 cytokines potentiate TRP channels through diverse mechanisms under different inflammatory and pruritic conditions, and link this effect to distinct signaling cascades in AD. This review strengthens the notion that interrupting Th2-driven modulation of TRP channels will inhibit transition from acute to chronic AD, thereby aiding the development of effective therapeutics and treatment optimization.

Current Insights into Immunology and Novel Therapeutics of Atopic Dermatitis

Atopic dermatitis (AD) is one of the most prevalent inflammatory disease among non-fatal skin diseases, affecting up to one fifth of the population in developed countries. AD is characterized by recurrent pruritic and localized eczema with seasonal fluctuations. AD initializes the phenomenon of atopic march, during which infant AD patients are predisposed to progressive secondary allergies such as allergic rhinitis, asthma, and food allergies. The pathophysiology of AD is complex; onset of the disease is caused by several factors, including strong genetic predisposition, disrupted epidermal barrier, and immune dysregulation. AD was initially characterized by defects in the innate immune system and a vigorous skewed adaptive Th2 response to environmental agents; there are compelling evidences that the disorder involves multiple immune pathways. Symptomatic palliative treatment is the only strategy to manage the disease and restore skin integrity. Researchers are trying to more precisely define the contribution of different AD genotypes and elucidate the role of various immune axes. In this review, we have summarized the current knowledge about the roles of innate and adaptive immune responsive cells in AD. In addition, current and novel treatment strategies for the management of AD are comprehensively described, including some ongoing clinical trials and promising therapeutic agents. This information will provide an asset towards identifying personalized targets for better therapeutic outcomes.

How Do Neurons Signal Itch?

Mechanistic theories of itch are based on neuronal specificity, stimulus intensity, and temporal or spatial discharge patterns. Traditionally, these theories are conceptualized as mutually exclusive, assuming that finding evidence for one theory would exclude the others and could sufficiently explain itch. Current experimental data primarily support the specificity or pattern theory of itch. However, in contrast to an assumed inherent exclusivity, recent results have shown that even within itch-specific pathways in the spinal cord, temporal discharge patterns are important as sustained pruriceptor is required to allow successful transsynaptic signal progression. Also, optogenetic activation of pruriceptors suggest that the combination of neuronal specificity and temporal pattern determines the sensory effect: tonic activation of pruriceptors is required to induce scratching behavior whereas short-lasting stimulation rather causes withdrawal. In addition to the mere duration of discharge, also the temporal pattern or spatial aspects could critically contribute to elicit pruritus instead of pain. Basic neurophysiological studies trying to validate neuronal theories for pruritus in their pure form provide unitary concepts leading from neuronal discharge to the itch sensation. However, the crucial clinical questions have the opposite perspective: which mechanisms explain the chronic itch in a given patient or a given disease? In trying to solve these clinical problems we should not feel bound to the mutual exclusive nature of itch theories, but rather appreciate blending several theories and also accept combinations of itch and pain. Thus, blended versions of itch theories might better suffice for an explanation of chronic itch in patients and will improve the basis for mechanistic treatment options.

Tolerability of and Adherence to Topical Treatments in Atopic Dermatitis: A Narrative Review

Atopic dermatitis (AD) is a common, chronic inflammatory skin disease that oftentimes requires complex therapy. Poor adherence is a major barrier to AD treatment success. An interspecialty, virtual roundtable panel was held, through which clinical dermatologists, allergists, and behavioral and social psychologists discussed AD management and adherence. Relevant literature was reviewed, and the content of this article was organized based on the roundtable discussion. Current guidelines for AD treatment include maintenance and acute therapy for mild-to-severe AD. Therapy is often complex and requires significant patient involvement, which may contribute to poor treatment adherence. Behavioral and social psychology strategies that may help improve adherence include scheduling timely follow-up appointments, using a clearly written eczema action plan (EAP), reducing perceived treatment burden, utilizing anchoring techniques, sharing anecdotes, and rewarding children using positive reinforcement and stickers. There are multiple practical ways by which providers can improve both the management and treatment adherence of patients with AD.

Effectiveness of montelukast for uremic pruritus in hemodialysis patients: A protocol for systematic review and meta-analysis

BACKGROUND

Uremic pruritus (UP) is a common and tormenting symptom in end-stage renal disease patients undergoing maintenance hemodialysis. An increasing number of studies have been published in recent years to support the effectiveness of montelukast for UP. We will conduct a comprehensive systematic review and meta-analysis to evaluate effectiveness of montelukast for UP in hemodialysis patients.

METHODS

The following electronic databases were searched: Pubmed, Embase, Web of Science, Cochrane Library, the China National Knowledge Infrastructure, Chinese Biomedical Literature Database, and China Science and Technology Journal Database. The range of publication time was from the inception of the database to December 2020. Two reviewers will independently conduct article selection, data collection, and assessment of risk of bias. Any disagreement will be resolved by discussion with the third reviewer. Meta-analysis will be performed by Review Manager 5.3. The Cochrane Collaboration tool will be used to assess the risk of bias.

RESULTS

This study will provide a systematic synthesis of current published data to explore the effectiveness of montelukast for UP in hemodialysis patients.

CONCLUSIONS

This systematic review and meta-analysis will provide clinical evidence for the effectiveness of montelukast for UP in hemodialysis patients and inform our understanding of the value of montelukast in improving pruritus symptoms. This study will help clinicians, patients, and policy makers to make better decisions regarding the appropriate role of montelukast as a part of patient management routines.

STUDY REGISTRATION NUMBER

INPLASY2020100043.

The Role of Nociceptive Neurons in the Pathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease. Emerging evidence shows that neurogenic inflammation, induced by nociceptive neurons and T helper 17 cell (Th17) responses, has a fundamental role in maintaining the changes in the immune system due to psoriasis. Nociceptive neurons, specific primary sensory nerves, have a multi-faceted role in detecting noxious stimuli, maintaining homeostasis, and regulating the immunity responses in the skin. Therefore, it is critical to understand the connections and interplay between the nociceptive neurons and the immune system in psoriasis. Here, we review works on the altered innervation that occurs in psoriasis. We examine how these distinct sensory neurons and their signal transducers participate in regulating inflammation. Numerous clinical studies report the dysfunction of nociceptive neurons in psoriasis. We discuss the mechanism behind the inconsistent activation of nociceptive neurons. Moreover, we review how neuropeptides, involved in regulating Th17 responses and the role of nociceptive neurons, regulate immunity in psoriasis. Understanding how nociceptive neurons regulate immune responses enhances our knowledge of the neuroimmunity involved in the pathogenesis of psoriasis and may form the basis for new approaches to treat it.

Itching as the onset of pain (part 3)

Itchy skin is an extremely unpleasant symptom that can provoke insomnia, depression, irritability, loss of appetite. There are several theories of itching. According to one of them, itching is a modified pain caused by a slight irritation of the nerve endings in the skin. According to the second, itching is an independent symptom, in the formation of which nervous, humoral and vascular mechanisms are involved. Other theories consider itching as a reaction of the autonomic nervous system or a hereditary pathological condition. According to recent studies, itchy skin is characterized by the absence of a universal peripheral mediator of itching. The trigger for itching is the action of pruritogen – a mechanical, chemical, thermal or electrical stimulant directly or indirectly through mediators. Free ends of type A delta fibers and type C fibers play a crucial role in itching and pain. If this was previously confirmed only by clinical observations, now there are neurophysiological studies that support the theory that itching and pain fibers are one with different activity thresholds. Today, it is unacceptable that there are separate specific receptors for different sensations. It is now assumed that there are mixed receptors for heat, cold, pain, itching and touch [95]. Systematic use of substances included in the list of drugs and manifested by mental and physical dependence on them – drug addiction, one of the diseases of society. But drug addiction is sometimes forced, according to medical indications, in cases of palliative conditions. Depending on the stage of the person after taking the drug or in the interval between drug use, one of the signs of use may be severe itching of the skin. And after excluding both the main diseases that cause itching and other secondary causes of itching, it can be assumed that a person has idiopathic generalized pruritus (itching) of unknown origin (GPOU). The itching of the elderly, which is quite common in the elderly, as a manifestation of concomitant, often combined, somatic pathology, but may also be due to physiological changes, both on the skin and on the physiological aging of nerve endings.

[Pruritus-a long journey from neurophysiology to the clinic]

BACKGROUND

The mutual exchange of results between basic sciences and clinical research as well as their translation into practice, also with regard to chronic pruritus, is currently to be seen as an ambition or hope rather than established practice.

OBJECTIVE

In view of the rapid developments in the field of neurophysiological basics of pruritus, the aim is to clarify how these new concepts can be brought in line with clinical understanding.

MATERIALS AND METHODS

A review is provided.

RESULTS

After the peripheral and spinal processing pathways for pruritus in the mouse were characterized with molecular markers, we are currently working on the translation of this information to the only functionally defined nerve fiber classes in humans. However, it is still unclear whether these processing pathways are crucial for the explanation of chronic pruritus in patients, since inflammation or neuropathy can significantly alter nerve populations and neuronal networks. Therefore, molecular target structures, which have emerged from results of basic research, need to be verified in patients. The gold standard, however, remains the patient with clinical observation and testing. Specific stimulation methods from neurophysiology can help to test hypotheses from basic research directly on patients, while also providing impulses for further development of research concepts.

CONCLUSIONS

Translation in medical research is now perceived by many researchers as a hackneyed buzzword. In the field of pruritus research, however, the exchange of results and concepts based on the mutual appreciation of expertise appears attractive, highly relevant, and promising.

Does age influence the quality of life in children with atopic dermatitis?

BACKGROUND

Atopic dermatitis (AD) is one of the most common childhood skin diseases that can affect the quality of life (QoL) of children. The QoL of Montenegrin children with AD has not been sufficiently explored. The aim of this study was to assess their QoL with special emphasize on age differences.

METHODS

This cross-sectional study included children with AD seen at the Clinic of Dermatology and Venereology, Clinical Center of Montenegro (CCM) in Podgorica between August 2017 and July 2018. The QoL was assessed with the Infants' Dermatitis Quality of Life Index (IDQOL) and the Children's Dermatology Life Quality Index (CDLQI). Disease severity was measured by the Three Item Severity (TIS) score.

RESULTS

A total of 386 children with AD aged from newborn to 16 years took part in this study. The mean total score of the QoL was 14.7 in infants (0-4 years old), 19.4 in younger children (5-9 years old), and 16.6 in older children (10-16 years old). Age was in negative correlation with the CDLQI score, leisure domain of the CDLQI and CDLQI sleep, and in positive correlation with the IDQOL child mood. TIS score was in positive correlation with both the IDQOL and CDLQI score.

CONCLUSIONS

The QoL measured by CDLQI was more impaired in younger children, whilst IDQOL child mood was more impaired in older infants. The most impaired QoL was seen in children in the age group 5-9 years. Regardless of disease severity, treatment and counseling of children suffering from AD should be tailored specifically to their age.

Tips and Tricks for Controlling Eczema

Eczema is a chronic, relapsing, and remitting disease that can affect patients from infancy through adulthood. Severity of eczema ranges from mild to severe and can be plagued with recurrent flares. These flares can be difficult to treat and may require use of different strategies to address the issue. In this article, the author addresses different therapeutic options that can be used in those patients with difficult-to-treat eczema.

CCL2/CCR2 signaling elicits itch- and pain-like behavior in a murine model of allergic contact dermatitis

Spontaneous itch and pain are the most common symptoms in various skin diseases, including allergic contact dermatitis (ACD). The chemokine (C-C motif) ligand 2 (CCL2, also referred to as monocyte chemoattractant protein 1 (MCP-1)) and its receptor CCR2 are involved in the pathophysiology of ACD, but little is known of the role of CCL2/CCR2 for the itch- and pain-behaviors accompanying the murine model of this disorder, termed contact hypersensitivity (CHS). C57BL/6 mice previously sensitized to the hapten, squaric acid dibutyl ester, applied to the abdomen were subsequently challenged twice with the hapten delivered to either the cheek or to the hairy skin of the hind paw resulting in CHS at that site. By 24 h after the 2nd challenge to the hind paw CCL2 and CCR2 mRNA, protein, and signaling activity were upregulated in the dorsal root ganglion (DRG). Calcium imaging and whole-cell current-clamp recordings revealed that CCL2 directly acted on its neuronal receptor, CCR2 to activate a subset of small-diameter, nociceptive-like DRG neurons retrogradely labeled from the CHS site. Intradermal injection of CCL2 into the site of CHS on the cheek evoked site-directed itch- and pain-like behaviors which could be attenuated by prior delivery of an antagonist of CCR2. In contrast, CCL2 failed to elicit either type of behavior in control mice. Results are consistent with the hypothesis that CHS upregulates CCL2/CCR2 signaling in a subpopulation of cutaneous small diameter DRG neurons and that CCL2 can activate these neurons through neuronal CCR2 to elicit itch- and pain-behavior. Targeting the CCL2/CCR2 signaling might be beneficial for the treatment of the itch and pain sensations accompanying ACD in humans.

Integrating tacrolimus into eutectic oil-based microemulsion for atopic dermatitis: simultaneously enhancing percutaneous delivery and treatment efficacy with relieving side effects

Background: Topical application of tacrolimus (FK506) was effective in treating atopic dermatitis (AD); however, the therapeutic efficiency is hampered by its poor penetration into the skin and local side effects of transient irritation symptoms with a burning sensation, a feeling of warmth or heat. Menthol and camphor have been widely used in topical compound formulations for adjunctive pharmacotherapy for antipruritics and analgesics owing to their cool nature, and both present skin penetration enhancing effects. Moreover, they can form a liquid eutectic oil to solubilize hydrophobic drugs.

Purpose: Taking advantages of menthol/camphor eutectic (MCE), this work aims to integrate FK506 into MCE to construct a microemulsion system, i.e., FK506 MCE ME, which simultaneously enhances the percutaneous delivery and treatment efficacy, while reduces the side effects of FK506.

Methods: The formulation of FK506 MCE ME was optimized and characterized. Different formulations containing FK506 were topically administered to treat 1–chloro–2, 4–dinitrobenzene (DNCB)-induced murine AD.

Results: MCE solubilized FK506. FK506 in MCE ME penetrated skin in vitro more than in the commercial ointment, and MCE predominantly exerted the enhancing effects in MCE ME. FK506 MCE ME or FK506 MCE ME gel had greater effects on clinical symptoms, histological analysis, and IgE than did commercial FK506. The anti-pruritic and down-regulation of substance P effects of MCE ME vehicle mitigated the side effects of FK506 application.

Conclusion: MCE ME presented the excellent properties of simultaneously enhancing the percutaneous delivery and treatment efficacy, while reducing the side effects of FK506 for AD. Therefore, MCE ME is a promising nanoscale system for FK506 to effectively treating AD with low irritation and high medication adherence.

Chemical compounds studied in this article: Tacrolimus (PubChem CID: 445643); menthol (PubChem CID: 1254); camphor (PubChem CID: 2537)

Itch Processing in the Skin

Itching can result from activity of specialized primary afferent neurons (“pruriceptors”) that have been shown to express certain molecular markers such as B-type natriuretic peptide and several members of the Mrgpr-family in rodents. On the other hand, neurons involved in pain processing (“nociceptors”) can also provoke itching when the activation site is restricted to an isolated tiny spot within the epidermis. Individuals classified as having sensitive skin report increased itching and pain sensations upon weak external stimuli that are not painful or itchy in the control group. Numerous possible factors could contribute to sensitive skin along the pathway of transduction of the external stimuli into peripheral neuronal signals, followed by neuronal processing, finally resulting in the perception: (a) reduced local protective factors leading to impaired skin barrier function, (b) increased production of excitatory skin mediators, (c) sensitized peripheral neurons, (d) facilitated spinal and central processing, and (e) reduced descending inhibition from the central nervous system. For all of those pathophysiological mechanisms there are clinical examples such as atopic dermatitis (a,b,c), neuropathic itching (c,e), and restless leg syndrome (d,e). However, none of these factors have been directly linked to the occurrence of sensitive skin. Moreover, individuals reporting sensitive skin are heterogeneous and a subpopulation with defined pathophysiology has not yet been identified. Given that the condition is reported in about 50% of women, and thereby includes many healthy individuals, it appears problematic to assign a definitive pathophysiological mechanism to it.

Neuropathic itch

Neuropathic itch is clinically important but has received much less attention as compared to neuropathic pain. In the past decade, itch-specific pathways have been characterized on a cellular and molecular level, but their exact role in the pathophysiology of neuropathic itch is still unclear. Traditionally, mutually exclusive theories for itch such as labeled line, temporal/spatial pattern, or intensity theory have been proposed, and experimental studies in mice mainly favor the specificity theory of itch. By contrast, results in humans also suggest a role for spatial and temporal patterns in neuropathic itch. Rarefication of skin innervation in neuropathy could provide a "spatial contrast" discharge pattern, and axotomy could induce de novo expression of the itch-specific spinal neuropeptide, gastrin-releasing peptide, in primary afferent nociceptors, thereby modulating itch processing in the dorsal horn. Thus, clinical neuropathy may generate itch by changes in the spatial and temporal discharge patterns of nociceptors, hijacking the labeled line processing of itch and abandoning the canonical scheme of mutual exclusive itch theories. Moreover, the overlap between itch and pain symptoms in neuropathy patients complicates direct translation from animal experiments and, on a clinical level, necessitates collaboration between medical specialities, such as dermatologists, anesthesiologists, and neurologists.

Oral H1 antihistamines as 'add-on' therapy to topical treatment for eczema

BACKGROUND

The symptoms of eczema can lead to sleeplessness and fatigue and may have a substantial impact on quality of life. Use of oral H1 antihistamines (H1 AH) as adjuvant therapy alongside topical agents is based on the idea that combining the anti-inflammatory effects of topical treatments with the blocking action of histamine on its receptors in the skin by H1 AH (to reduce the principal symptom of itch) might magnify or intensify the effect of treatment. Also, it would be unethical to compare oral H1 AH alone versus no treatment, as topical treatment is the standard management for this condition.

OBJECTIVES

To assess the effects of oral H1 antihistamines as 'add-on' therapy to topical treatment in adults and children with eczema.

SEARCH METHODS

We searched the following databases up to May 2018: the Cochrane Skin Group Specialised Register, CENTRAL, MEDLINE, Embase, and the GREAT database (Global Resource of EczemA Trials; from inception). We searched five trials registers and checked the reference lists of included and excluded studies for further references to relevant randomised controlled trials (RCTs). We also searched the abstracts of four conference proceedings held between 2000 and 2018.

SELECTION CRITERIA

We sought RCTs assessing oral H1 AH as 'add-on' therapy to topical treatment for people with eczema compared with topical treatment plus placebo or no additional treatment as add-on therapy.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodological procedures. Primary outcome measures were 'Mean change in patient-assessed symptoms of eczema' and 'Proportion of participants reporting adverse effects and serious adverse events'. Secondary outcomes were 'Mean change in physician-assessed clinical signs', 'Mean change in quality of life', and 'Number of eczema flares'.

MAIN RESULTS

We included 25 studies (3285 randomised participants). Seventeen studies included 1344 adults, and eight studies included 1941 children. Most studies failed to report eczema severity at baseline, but they were conducted in secondary care settings, so it is likely that they recruited patients with more severe cases of eczema. Trial duration was between three days and 18 months. Researchers studied 13 different H1 AH treatments. We could not undertake pooling because of the high level of diversity across studies in terms of duration and dose of intervention, concomitant topical therapy, and outcome assessment. Risk of bias was generally unclear, but five studies had high risk of bias in one domain (attrition, selection, or reporting bias). Only one study measured quality of life, but these results were insufficient for statistical analysis.Although this review assessed 17 comparisons, we summarise here the results of three key comparisons in this review.Cetirizine versus placeboOne study compared cetirizine 0.5 mg/kg/d against placebo over 18 months in 795 children. Study authors did not report patient-assessed symptoms of eczema separately for pruritus. Cetirizine is probably associated with fewer adverse events (mainly mild) (risk ratio (RR) 0.68, 95% confidence interval (CI) 0.46 to 1.01) and the need for slightly less additional H1 AH use as an indication of eczema flare rate (P = 0.035; no further numerical data given). Physician-assessed clinical signs (SCORing Atopic Dermatitis index (SCORAD)) were reduced in both groups, but the difference between groups was reported as non-significant (no P value given). Evidence for this comparison was of moderate quality.One study assessed cetirizine 10 mg/d against placebo over four weeks in 84 adults. Results show no evidence of differences between groups in patient-assessed symptoms of eczema (pruritus measured as part of SCORAD; no numerical data given), numbers of adverse events (RR 1.11, 95% CI 0.50 to 2.45; mainly sedation, other skin-related problems, respiratory symptoms, or headache), or physician-assessed changes in clinical signs, amount of local rescue therapy required, or number of applications as an indicator of eczema flares (no numerical data reported). Evidence for this comparison was of low quality.Fexofenadine versus placeboCompared with placebo, fexofenadine 120 mg/d taken in adults over one week (one study) probably leads to a small reduction in patient-assessed symptoms of pruritus on a scale of 0 to 8 (mean difference (MD) -0.25, 95% CI -0.43 to -0.07; n = 400) and a greater reduction in the ratio of physician-assessed pruritus area to whole body surface area (P = 0.007; no further numerical data given); however, these reductions may not be clinically meaningful. Results suggest probably little or no difference in adverse events (mostly somnolence and headache) (RR 1.05, 95% CI 0.74 to 1.50; n = 411) nor in the amount of 0.1% hydrocortisone butyrate used (co-intervention in both groups) as an indicator of eczema flare, but no numerical data were given. Evidence for this comparison was of moderate quality.Loratadine versus placeboA study of 28 adults compared loratadine 10 mg/d taken over 4 weeks versus placebo. Researchers found no evidence of differences between groups in patient-assessed pruritus, measured by a 100-point visual analogue scale (MD -2.30, 95% CI -20.27 to 15.67); reduction in physician-assessed clinical signs (SCORAD) (MD -4.10, 95% CI -13.22 to 5.02); or adverse events. Study authors reported only one side effect (folliculitis with placebo) (RR 0.25, 95% CI 0.01 to 5.76). Evidence for this comparison was of low quality. Number of eczema flares was not measured for this comparison.

AUTHORS' CONCLUSIONS

Based on the main comparisons, we did not find consistent evidence that H1 AH treatments are effective as 'add-on' therapy for eczema when compared to placebo; evidence for this comparison was of low and moderate quality. However, fexofenadine probably leads to a small improvement in patient-assessed pruritus, with probably no significant difference in the amount of treatment used to prevent eczema flares. Cetirizine was no better than placebo in terms of physician-assessed clinical signs nor patient-assessed symptoms, and we found no evidence that loratadine was more beneficial than placebo, although all interventions seem safe.The quality of evidence was limited because of poor study design and imprecise results. Future researchers should clearly define the condition (course and severity) and clearly report their methods, especially participant selection and randomisation; baseline characteristics; and outcomes (based on the Harmonising Outcome Measures in Eczema initiative).

Matrine inhibits itching by lowering the activity of calcium channel

Sophorae Flavescentis Radix (SFR) is a medicinal herb with many functions that are involved in anti-inflammation, antinociception, and anticancer. SFR is also used to treat a variety of itching diseases. Matrine (MT) is one of the main constituents in SFR and also has the effect of relieving itching, but the antipruritic mechanism is still unclear. Here, we investigated the effect of MT on anti-pruritus. In acute and chronic itch models, MT significantly inhibited the scratching behavior not only in acute itching induced by histamine (His), chloroquine (CQ) and compound 48/80 with a dose-depended manner, but also in the chronic pruritus models of atopic dermatitis (AD) and acetone-ether-water (AEW) in mice. Furthermore, MT could be detected in the blood after intraperitoneal injection (i.p.) and subcutaneous injection (s.c.). Finally, electrophysiological and calcium imaging results showed that MT inhibited the excitatory synaptic transmission from dorsal root ganglion (DRG) to the dorsal horn of the spinal cord by suppressing the presynaptic N-type calcium channel. Taken together, we believe that MT is a novel drug candidate in treating pruritus diseases, especially for histamine-independent and chronic pruritus, which might be attributed to inhibition of the presynaptic N-type calcium channel.

Itching and its related factors in subtypes of eczema: a cross-sectional multicenter study in tertiary hospitals of China

Itching is a leading symptom of eczema or dermatitis and has a great impact on patients' lives. Previous studies on itching have focused mostly on atopic dermatitis (AD). A cross-sectional multicenter study was conducted among outpatients with eczema from 39 tertiary hospitals in mainland China from July 1 to September 30, 2014. This work elaborates on itching in different types of eczema. Itching was very common (97%, 8499/8758) in outpatients with eczema. The severity of the itch increased with age and disease duration (P < 0.001). The top three subtypes of dermatitis with severe itching were atopic dermatitis (30.4%), widespread eczema (30.1%), and asteatotic eczema (27.9%). Widespread eczema refers to the involvement of more than three body parts, without clinical features of other specific types of eczema. The proportion of outpatients without itching was highest in hand eczema (6.8%). Positive correlations were observed between the severity of itching and the proportions of different diseases based on trend tests, including atopic dermatitis (P < 0.001), widespread eczema (P < 0.001), asteatotic eczema (P < 0.001), and autosensitization dermatitis (P < 0.001). Eczema outpatients with older age, longer disease duration, and, especially, a history of allergic diseases might be more prone to itching.

Pruritus: Progress toward Pathogenesis and Treatment

Pruritus, the most common cutaneous symptom, is widely seen in many skin complaints. It is an uncomfortable feeling on the skin and sometimes impairs patients' quality of life. At present, the specific mechanism of pruritus still remains unclear. Antihistamines, which are usually used to relieve pruritus, ineffectively work in some patients with itching. Recent evidence has suggested that, apart from histamine, many mediators and signaling pathways are involved in the pathogenesis of pruritus. Various therapeutic options for itching correspondingly have been developed. In this review, we summarize the updated pathogenesis and therapeutic strategies for pruritus.

New mechanism underlying IL-31-induced atopic dermatitis

BACKGROUND

T_H2 cell-released IL-31 is a critical mediator in patients with atopic dermatitis (AD), a prevalent and debilitating chronic skin disorder. Brain-derived natriuretic peptide (BNP) has been described as a central itch mediator. The importance of BNP in peripheral (skin-derived) itch and its functional link to IL-31 within the neuroimmune axis of the skin is unknown.

OBJECTIVE

We sought to investigate the function of BNP in the peripheral sensory system and skin in IL-31-induced itch and neuroepidermal communication in patients with AD.

METHODS

Ca²⁺ imaging, immunohistochemistry, quantitative real-time PCR, RNA sequencing, knockdown, cytokine/phosphokinase arrays, enzyme immune assay, and pharmacologic inhibition were performed to examine the cellular basis of the IL-31-stimulated, BNP-related itch signaling in dorsal root ganglionic neurons (DRGs) and skin cells, transgenic AD-like mouse models, and human skin of patients with AD and healthy subjects.

RESULTS

In human DRGs we confirmed expression and co-occurrence of oncostatin M receptor β subunit and IL-31 receptor A in a small subset of the neuronal population. Furthermore, IL-31 activated approximately 50% of endothelin-1-responsive neurons, and half of the latter also responded to histamine. In murine DRGs IL-31 upregulated Nppb and induced soluble N-ethylmaleimide-sensitive factor activating protein receptor-dependent BNP release. In Grhl3PAR2^/+ mice house dust mite-induced severe AD-like dermatitis was associated with Nppb upregulation. Lesional IL-31 transgenic mice also exhibited increased Nppb transcripts in DRGs and the skin; accordingly, skin BNP receptor levels were increased. Importantly, expression of BNP and its receptor were increased in the skin of patients with AD. In human skin cells BNP stimulated a proinflammatory and itch-promoting phenotype.

CONCLUSION

For the first time, our findings show that BNP is implicated in AD and that IL-31 regulates BNP in both DRGs and the skin. IL-31 enhances BNP release and synthesis and orchestrates cytokine and chemokine release from skin cells, thereby coordinating the signaling pathways involved in itch. Inhibiting peripheral BNP function might be a novel therapeutic strategy for AD and pruritic conditions.

Beneficial effects of melittin on ovalbumin-induced atopic dermatitis in mouse

Atopic dermatitis (AD) is an inflammatory skin disease characterized by intense pruritus and relapsable eczematous lesions. The hallmarks of AD are defects in the epidermal barrier and immunoglobulin E (IgE)-mediated sensitization to several environmental allergens, as well as an immune disorder mediated by an imbalance toward T-helper-2 response. Melittin, a major component of bee venom, has been studied in various inflammatory diseases. However, the beneficial effects of melittin on mouse with AD-like symptoms have not been explored. Therefore, we investigated the anti-allergic effects of melittin. AD was induced by ovalbumin (OVA) patch. After agent treatment, skin tissues and sera were extracted from the sacrificed mice were used to demonstrate the effects of melittin through various molecular biological methods. The results showed that OVA-induced skin thickening and inflammatory infiltration were decreased in the melittin-treated group. Melittin prevented OVA-induced filaggrin deficiency and imbalanced inflammatory mediators. Furthermore, melittin inhibited IL-4/IL-13-induced filaggrin downregulation through the blockade of STAT3 activation in human keratinocytes. In summary, this study has shown that melittin ameliorated OVA-induced AD-like symptoms from various perspectives. The findings of this study may be the first evidence of the anti-inflammatory effects of melittin on OVA-induced AD.

Current insights into the role of human β-defensins in atopic dermatitis

Anti-microbial peptides or host defence peptides are small molecules that display both anti-microbial activities and complex immunomodulatory functions to protect against various diseases. Among these peptides, the human β-defensins (hBDs) are localized primarily in epithelial surfaces, including those of the skin, where they contribute to protective barriers. In atopic dermatitis skin lesions, altered skin barrier and immune dysregulation are believed to be responsible for reduced hBD synthesis. Impaired hBD expression in the skin is reportedly the leading cause of increased susceptibility to bacterial and viral infection in patients with atopic dermatitis. Although hBDs have considerable beneficial effects as anti-microbial agents and immunomodulators and may ameliorate atopic dermatitis clinically, recent evidence has also suggested the negative effects of hBDs in atopic dermatitis development. In the current review, we provide an overview of the regulation of hBDs and their role in the pathogenesis of atopic dermatitis. The efforts to utilize these molecules in clinical applications are also described.

Inflammatory and Noninflammatory Itch: Implications in Pathophysiology-Directed Treatments

Itch is the main chief complaint in patients visiting dermatologic clinics and has the ability to deeply impair life quality. Itch results from activation of cutaneous nerve endings by noxious stimuli such as inflammatory mediators, neurotransmitters and neuropeptides, causing itch signal transduction from peripheral skin, through the spinal cord and thalamus, to the brain cortex. Primarily noninflammatory diseases, such as uremic pruritus, cause itch through certain pruritogens in the skin. In inflammatory skin diseases, atopic dermatitis (AD) is the prototypic disease causing intensive itch by aberrant skin inflammation and epidermal barrier disruption. Recent understanding of disease susceptibility, severity markers, and mechanisms have helped to develop targeted therapy for itch in AD, including monoclonal antibodies against IL-4, IL-13, thymic stromal lymphopoietin (TSLP), IgE and IL-31. Promising effects have been observed in some of them. In this review, we summarized targeted therapies for inflammatory itch in AD and for managing abnormal itch transductions in other common itching skin diseases.

Cl- channel is required for CXCL10-induced neuronal activation and itch response in a murine model of allergic contact dermatitis

Persistent itch often accompanies allergic contact dermatitis (ACD), but the underlying mechanisms remain largely unexplored. We previously demonstrated that CXCL10/CXCR3 signaling activated a subpopulation of cutaneous primary sensory neurons and mediated itch response after contact hypersensitivity (CHS), a murine model of ACD, induced by squaric acid dibutylester. The purpose of this study was to determine the ionic mechanisms underlying CXCL10-induced neuronal activation and allergic itch. In whole cell recordings, CXCL10 triggered a current in dorsal root ganglion (DRG) neurons innervating the area of CHS. This current was modulated by intracellular Cl^- and blocked by the general Cl^- channel inhibitors. Moreover, increasing Ca²⁺ buffering capacity reduced this current. In addition, blockade of Cl^- channels significantly suppressed CXCL10-induced Ca²⁺ response. In behavioral tests, injection of CXCL10 into CHS site exacerbated itch-related scratching behaviors. Moreover, the potentiating behavioral effects of CXCL10 were attenuated by either of two Cl^- channel blockers. Thus we suggest that the Cl^- channel acts as a downstream target mediating the excitatory and pruritic behavioral effects of CXCL10. Cl^- channels may provide a promising therapeutic target for the treatment of allergic itch in which CXCL10/CXCR3 signaling may participate.NEW & NOTEWORTHY The ionic mechanisms underlying CXCL10-induced neuronal activation and allergic itch are largely unexplored. This study revealed that CXCL10 evoked an ionic current mainly carried by Cl^- channels. We suggest that Cl^- channels are likely key molecular candidates responsible for the CXCL10-evoked neuronal activation and itch-like behaviors in a murine model of allergic contact dermatitis induced by the antigen squaric acid dibutylester. Cl^- channels may emerge as a promising drug target for the treatment of allergic itch in which CXCL10/CXCR3 signaling may participate.

Anti-inflammatory therapies in atopic dermatitis

The pathogenesis of atopic dermatitis (AD) is multifactorial and complex. Consequently, clinical signs and symptoms vary strongly depending on individually relevant trigger factors and the stage of the disease. So far, treatment of AD was commonly limited to topical treatment or, in more severe cases, to systemic drugs mostly approved for other indications than AD. However, emerging data on new anti-inflammatory agents have been published in the recent years. As these new substances specifically focus on immune responses in AD, these are partially considered as possible 'breakthrough' in the treatment of AD. Therapeutic strategies of the future appear to be 'customized' for inflammation in AD as they target pro-inflammatory, highly relevant cytokines and cytokine receptors, such as IL-4Rα, IL-13, IL-31, and IL-17. Further innovative therapeutic approaches aim to block the function of relevant molecules such as thymic stromal lymphopoietin, chemoattractant-receptor homologous molecule expressed on Th2 lymphocytes (CRTh2), and phosphodiesterase (PDE)-4 inhibitors. Recently, anti-inflammatory effects in AD by antagonizing the histamine (H)-4 receptor have also been detected. Finally, specific immunotherapy is under further investigation as treatment option for AD patients with clinically relevant sensitization.

CXCR3 chemokine receptor signaling mediates itch in experimental allergic contact dermatitis

Persistent itch is a common symptom of allergic contact dermatitis (ACD) and represents a significant health burden. The chemokine CXCL10 is predominantly produced by epithelial cells during ACD. Although the chemokine CXCL10 and its receptor CXCR3 are implicated in the pathophysiology of ACD, it is largely unexplored for itch and pain accompanying this disorder. Here, we showed that CXCL10 and CXCR3 mRNA, protein, and signaling activity were upregulated in the dorsal root ganglion after contact hypersensitivity (CHS), a murine model of ACD, induced by squaric acid dibutylester. CXCL10 directly activated a subset of cutaneous dorsal root ganglion neurons innervating the area of CHS through neuronal CXCR3. In behavioral tests, a CXCR3 antagonist attenuated spontaneous itch- but not pain-like behaviors directed to the site of CHS. Injection of CXCL10 into the site of CHS elicited site-directed itch- but not pain-like behaviors, but neither type of CXCL10-evoked behaviors was observed in control mice. These results suggest that CXCL10/CXCR3 signaling mediates allergic itch but not inflammatory pain in the context of skin inflammation. Thus, upregulation of CXCL10/CXCR3 signaling in sensory neurons may contribute to itch associated with ACD. Targeting the CXCL10/CXCR3 signaling might be beneficial for the treatment of allergic itch.

Atopic dermatitis

Atopic dermatitis (also known as atopic eczema) is a chronic inflammatory skin disease that is characterised by intense itching and recurrent eczematous lesions. Although it most often starts in infancy and affects two of ten children, it is also highly prevalent in adults. It is the leading non-fatal health burden attributable to skin diseases, inflicts a substantial psychosocial burden on patients and their relatives, and increases the risk of food allergy, asthma, allergic rhinitis, other immune-mediated inflammatory diseases, and mental health disorders. Originally regarded as a childhood disorder mediated by an imbalance towards a T-helper-2 response and exaggerated IgE responses to allergens, it is now recognised as a lifelong disposition with variable clinical manifestations and expressivity, in which defects of the epidermal barrier are central. Present prevention and treatment focus on restoration of epidermal barrier function, which is best achieved through the use of emollients. Topical corticosteroids are still the first-line therapy for acute flares, but they are also used proactively along with topical calcineurin inhibitors to maintain remission. Non-specific immunosuppressive drugs are used in severe refractory cases, but targeted disease-modifying drugs are being developed. We need to improve understanding of the heterogeneity of the disease and its subtypes, the role of atopy and autoimmunity, the mechanisms behind disease-associated itch, and the comparative effectiveness and safety of therapies.

Dietary deficiencies of unsaturated fatty acids and starch cause atopic dermatitis-like pruritus in hairless mice

Hairless mice fed with a special diet (named HR-AD) show atopic dermatitis (AD)-like pruritic skin inflammation that is almost completely resolved with the supplementation of an unsaturated fatty acid (UFA), the linoleic acid (LA). This suggests that the dietary deficiency of LA is the key cause of this dermatitis. However, because there is no appropriate control diet for HR-AD, the involvement of other dietary ingredients cannot be ruled out. Furthermore, it has not yet been tested whether only UFA deficiency can cause such AD-like pruritus. In this study, using semi-purified custom diets, we attempted to reproduce this syndrome. Four-week-old hairless mice were maintained on a widely used standard diet American Institute of Nutrition-76A (AIN-76A), its modifications, or HR-AD. Several modifications of fat and carbohydrate components revealed that dietary deficiency of both UFAs and cornstarch was required to induce severe skin barrier dysfunction as typically occurred in HR-AD-fed mice. An UFA- and cornstarch-deficient diet caused severe AD-like pruritus comparable to HR-AD, despite weak Th2 immune responses and absence of immunoglobulin E production. On the other hand, a diet lacking UFAs but containing cornstarch significantly alleviated the development of pruritic dermatitis. Furthermore, the supplementation of wheat starch similarly improved skin barrier function. In conclusion, this study showed that a lack of certain starches might also be the cause of diet-induced AD. Our findings could help to reproduce the diet-induced AD itch model and also provide evidence that certain starches can have protective and ameliorative effects on AD-like pruritus.

Expression of Neuropeptides, Neurotrophins, and Neurotransmitters in the Skin of Patients with Atopic Dermatitis and Psoriasis

Expression of neural marker PGP9.5, amphiregulin, semaphorin-3A, calcitonin gene-related peptide and its receptor, nerve growth factor and its receptor, substance P and its receptor, and expression frequency were analyzed in biopsy specimens from patients with atopic dermatitis and psoriasis and healthy volunteers by immunohistochemical method. Nerve fibers penetrated into the epidermis more frequently, and amphiregulin expression was significantly higher in patients with atopic dermatitis and psoriasis comparing to the control. Expression of semaphorin-3A in patients with atopic dermatitis was less frequent than in the control. These findings reflect the involvement of amphiregulin and semaphorin-3A in the improvement of skin innervations and penetration of nerve fibers into the epidermis, and due of which these proteins mediate the development of itch.

Dynamics of expression rates of growth factor proteins in psoriatic patients receiving a phototherapy

Goal. To study the dynamics of expression rates of growth factor proteins in psoriatic patients receiving the PUVA therapy. Materials and methods. The authors conducted a study of 30 patients with psoriasis vulgaris treated with the PUVA therapy. The psoriasis severity and extent of itching were assessed prior to and after the treatment by the PASI index and visual analogue scale, respectively. The expression of semaphorin 3A, amphiregulin, nerve growth factor and PGP 9.5 protein (a nerve fiber marker) in the skin was assessed by the indirect immunofluorescence method. The expression of PGP 9.5 protein was used to assess the quantity and mean length as well as average and total fluorescence intensity of nerve fibers. Results. An increased expression of amphiregulin and nerve growth factor as well as increase in the quantity, mean length and average and total fluorescence intensity of nerve fibers were revealed in the epidermis of psoriatic patients. Following a course of the PUVA therapy, a decrease in the PASI index and extent of itching, reduced expression of amphiregulin and nerve growth factor as well as reduced quantity, mean length and average and total fluorescence intensity of nerve fibers in the epidermis were observed. Direct correlation dependence between the extent of itching, amphiregulin and nerve growth factor expression level and quantity and length of nerve fibers in the epidermis was discovered. Direct correlation dependence between the amphiregulin and nerve growth factor expression level, and average length of nerve fibers in the epidermis was discovered. Conclusion. The itching intensity in psoriatic patients receiving the PUVA therapy is reduced due to the decreased skin expression of the nerve growth factor and amphiregulin.

Use of transcutaneous electrical nerve stimulation for chronic pruritus

Pruritus is a distressing symptom in many dermatological as well as systemic conditions, and it is sometimes very chronic and relapsing. Transcutaneous electrical nerve stimulation (TENS) is an inexpensive form of analgesia that could also ameliorate itching. This study aimed to evaluate TENS efficacy in patients with pruritus due to some types of chronic eczema, and in patients with chronic hepatic disease. Ten patients with atopic dermatitis (AD), 20 patients with lichen simplex chronicus (LSC), and 16 patients with chronic liver disease having chronic distressing pruritus received three sessions of TENS weekly for 12 sessions, and the effect on the visual analogue scale (VAS) scores was recorded after 2 weeks of therapy, at treatment end, and after an additional month for follow up. There was a statistically significant decline in the mean VAS score for studied groups at weeks 2 and 4 of therapy compared to baseline, but the improvement was more significant in patients with AD, and LSC (p < 0.001 for both) than in those with chronic liver disease (p < 0.01) who also showed an early re-elevation of VAS score on follow up. TENS therapy holds promise as a palliative, alternative, safe and inexpensive treatment for patients with some chronic pruritic conditions.