Itch and inflammation induced by intradermally injected interleukin-2 in atopic dermatitis patients and healthy subjects

Type 2 responses determine skin rash during recombinant interleukin-2 therapy

The skin is the organ most often affected by adverse drug reactions. Although these cutaneous adverse drug reactions (CADRs) often are mild, they represent a major burden for patients. One of the drugs inducing CADRs is aldesleukin, a recombinant interleukin-2 (recIL-2) originally approved to treat malignant melanoma and metastatic renal cell carcinoma which frequently led to skin rashes when applied in high doses for anti-cancer therapy. Skin rashes and other side effects, together with poor efficacy led to a drawback of the therapeutic, but modified recIL-2 molecules are on the rise to treat both cancer and inflammatory diseases such as autoimmunity. Still, pathophysiological mechanisms of recIL-2-induced skin rashes are not understood. In the study reported here, a hypothetical literature-based immune-related adverse outcome pathway (irAOP) was developed to identify possible key cells and molecules in recIL-2-induced skin rash. Using this approach, a hypothesis was formed that the induced immune response predominantly is Type 2-driven by T-helper and innate lymphoid cells, leading to the occurrence of cutaneous side effects during recIL-2 therapy. This paper further discusses mechanisms beyond the proposed irAOP which might add to the pathology but currently are less-studied. Together, this hypothetic irAOP forms a basis to clarify possible cellular and molecular interactions leading to recIL-2-induced skin rash. This might be used to adapt existing or develop new test systems to help predict and prevent cutaneous side effects in future IL-2-based or similar therapies.

Clinically uninvolved but not healthy-The skin of patients with atopic dermatitis is primed for itch and inflammation

BACKGROUND

Atopic dermatitis (AD) is a highly prevalent inflammatory skin disorder characterized by episodic exacerbations and remissions. Why the clinically healthy skin of AD patients becomes rapidly inflamed and very pruritic is poorly understood.

OBJECTIVE

To investigate cowhage- and histamine-induced itch and skin expression levels of their target receptors in lesional and non-lesional skin of AD, compared to the skin of patients with psoriasis, chronic spontaneous urticaria (CSU) and healthy subjects.

METHODS

Patients with AD, psoriasis and chronic spontaneous urticaria (CSU) as well as healthy control subjects (HC) (n = 20 each) were assessed for differences in itch parameters, neurogenic flare reaction and local blood flow responses to skin provocations with cowhage and histamine. Skin biopsies from 10 AD, 10 psoriasis,11 CSU and 12 HC were obtained to assess expression of protease-activated receptors 2 and 4 (PAR-2, PAR-4), histamine H1 and H4 receptors (H1R, H4R), and mast cells.

RESULTS

Provocation of non-lesional skin of AD patients with cowhage resulted in prolonged itch (p = 0.020), which was not observed in psoriasis and CSU. Significantly prolonged and more intense cowhage- and histamine-induced itch (for duration, peak and overall intensity) was also observed in lesional AD skin. Diminished neurogenic flare reaction and blood flow after histamine provocation were shown in AD and psoriasis patients. Non-lesional AD skin along with lesional AD and psoriasis skin showed an increased expression of PAR-2 and PAR-4, H1R and H4R. Mast cell number was higher in lesional AD and psoriasis skin (p = 0.006 and p = 0.006, respectively).

CONCLUSION

The non-lesional skin of AD patients markedly differs from healthy skin in cowhage-induced itch responses and the expression of receptors for proteases and histamine. Proactive therapeutic interventions that downregulate these receptors may prevent episodic exacerbation in AD.

Etiopathogenesis of chronic kidney disease-associated pruritus: putting the pieces of the puzzle together

Defined as the unpleasant sensation that causes the desire to scratch, pruritus is the most common skin symptom associated with uremia and appears in almost half of patients with advanced chronic kidney disease (CKD). Beyond its direct impact on quality of life, CKD-associated pruritus (CKD-aP) is an independent predictor of mortality that also has a synergistic effect with other quality of life-related symptoms, such as insomnia, depression, and anxiety. Although different mechanisms have been proposed to explain the origin of Pa-ERC, its etiopathogenesis is still not fully understood. Since new therapeutic targets have been identified and several clinical trials have recently shown promising results, our current understanding of the interrelationships has expanded significantly and the pathophysiological mechanisms underlying CKD-aP are now considered to be multifactorial. The potential triggers of pruritus in patients with CKD are discussed in this review, including hypotheses about skin xerosis, accumulation of uremic toxins, dysregulation of the immune system and systemic inflammation, uremic neuropathy, and imbalances in the endogenous opioid system. Other non-uremic causes of pruritus are also discussed, with the aim of guiding the physicians to apply an adequate aetiopathogenic approach to CKD-aP in their day-to-day clinical practice.

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.

Histamine Is Responsible for the Neuropathic Itch Induced by the Pseudorabies Virus Variant in a Mouse Model

Pseudorabies virus (PRV) is the causative agent of pseudorabies (PR). It can infect a wide range of mammals. PRV infection can cause severe acute neuropathy (the so-called “mad itch”) in nonnatural hosts. PRV can infect the peripheral nervous system (PNS), where it can establish a quiescent, latent infection. The dorsal root ganglion (DRG) contains the cell bodies of the spinal sensory neurons, which can transmit peripheral sensory signals, including itch and somatic pain. Little attention has been paid to the underlying mechanism of the itch caused by PRV in nonnatural hosts. In this study, a mouse model of the itch caused by PRV was elaborated. BALB/c mice were infected intramuscularly with 10⁵ TCID₅₀ of PRV TJ. The frequency of the bite bouts and the durations of itch were recorded and quantified. The results showed that the PRV-infected mice developed spontaneous itch at 32 h postinfection (hpi). The frequency of the bite bouts and the durations of itch were increased over time. The mRNA expression levels of the receptors and the potential cation channels that are relevant to the itch-signal transmission in the DRG neurons were quantified. The mRNA expression levels of tachykinin 1 (TAC1), interleukin 2 (IL-2), IL-31, tryptases, tryptophan hydroxylase 1 (TPH1), and histidine decarboxylase (HDC) were also measured by high-throughput RNA sequencing and real-time reverse transcription PCR. The results showed that the mean mRNA level of the HDC in the DRG neurons isolated from the PRV-infected mice was approximately 25-fold higher than that of the controls at 56 hpi. An immunohistochemistry (IHC) was strongly positive for HDC in the DRG neurons of the PRV-infected mice, which led to the high expression of histamine at the injected sites. The itch of the infected mice was inhibited by chlorphenamine hydrogen maleate (an antagonist for the histamine H1 receptor) in a dose-dependent manner. The mRNA and protein levels of the HDC in the DRG neurons were proportional to the severity of the itch induced by different PRV strains. Taken together, the histamine synthesized by the HDC in the DRG neurons was responsible for the PRV-induced itch in the mice.

Unravelling the pathophysiology of chronic kidney disease-associated pruritus

For decades, itch related to chronic kidney disease (CKDaP) has been a clinical problem, but the aetiology and pathophysiology of CKDaP are still not yet fully understood—currently the underlying pathophysiological mechanisms are thought to be multifactorial. As new therapeutic targets have recently been identified and clinical trials have shown promising results, our current understanding of the interrelationships has expanded significantly. Here we review the pathophysiology and recent findings on modulation and sensitization of itch contributing to the development of CKDaP, covering hypothesis regarding immune system dysfunction, metabolic changes, uremic toxin deposition, peripheral neuropathy and imbalances in the endogenous opioid system.

Chronic Kidney Disease-Associated Itch (CKD-aI) in Children-A Narrative Review

Chronic kidney disease (CKD) is a condition of widespread epidemiology and serious consequences affecting all organs of the organism and associated with significant mortality. The knowledge on CKD is rapidly evolving, especially concerning adults. Recently, more data is also appearing regarding CKD in children. Chronic itch (CI) is a common symptom appearing due to various underlying dermatological and systemic conditions. CI may also appear in association with CKD and is termed chronic kidney disease-associated itch (CKD-aI). CKD-aI is relatively well-described in the literature concerning adults, yet it also affects children. Unfortunately, the data on paediatric CKD-aI is particularly scarce. This narrative review aims to describe various aspects of CKD-aI with an emphasis on children, based on the available data in this population and the data extrapolated from adults. Its pathogenesis is described in details, focusing on the growing role of uraemic toxins (UTs), as well as immune dysfunction, altered opioid transmission, infectious agents, xerosis, neuropathy and dialysis-associated aspects. Moreover, epidemiological and clinical aspects are reviewed based on the few data on CKD-aI in children, whereas treatment recommendations are proposed as well, based on the literature on CKD-aI in adults and own experience in managing CI in children.

Patient-Reported Symptoms and Disease Impacts in Adults With Moderate-to-Severe Atopic Dermatitis: Results From a Phase 2b Study With Abrocitinib

BACKGROUND

Moderate-to-severe atopic dermatitis (AD) is inadequately controlled with current treatments for many patients. Abrocitinib is an oral Janus kinase 1 selective inhibitor under investigation for the treatment of AD.

OBJECTIVE

The aim of the study was to evaluate patient-reported outcomes in a phase 2b study of abrocitinib in adults with moderate-to-severe AD inadequately controlled by topical therapy (NCT02780167).

METHODS

Patients (N = 267) were randomly assigned 1:1:1:1:1 to 12-week, once-daily abrocitinib (200, 100, 30, 10 mg) or placebo. Patient-reported outcomes included pruritus numeric rating scale (average), Patient Global Assessment, Patient-Oriented Eczema Measure, Pruritus and Symptoms Assessment for AD, Dermatology Life Quality Index, and Hospital Anxiety and Depression Scale (HADS).

RESULTS

Abrocitinib 200 or 100 mg resulted in significantly greater improvements from baseline versus placebo in peak pruritus numeric rating scale (by days 2 and 3, respectively), Patient-Oriented Eczema Measure, Pruritus and Symptoms Assessment for AD, Dermatology Life Quality Index, and HADS (200 mg only, by week 1 or 2), and proportions of the patients with Patient Global Assessment clear/almost clear with 2-point or greater improvement (by weeks 1 and 4, respectively) that continued through week 12 (except HADS).

CONCLUSIONS

Abrocitinib treatment resulted in rapid (2 days to 2 weeks) and persistent improvements in AD symptoms and impacts in moderate-to-severe disease.

Molecular and Cellular Mechanisms of Itch in Psoriasis

Itch (or pruritus) was not previously recognized as a serious symptom of psoriasis. However, approximately 60-90% of psoriatic patients with pruritus have stated that it deteriorates their quality of life. Since conventional antipruritic therapies, such as antihistamines, only exert limited effects, the establishment of a treatment option for itch in psoriasis is urgently needed. Although a definitive drug is not currently available, various itch mediators are known to be involved in pruritus in psoriasis. In this review, we describe the clinical features of pruritus in psoriasis, classify a wide range of itch mediators into categories, such as the nervous, immune, endocrine, and vascular systems, and discuss the mechanisms by which these mediators induce or aggravate itch in the pathophysiology of psoriasis.

Role of neuroimmune circuits and pruritus in psoriasis

Psoriasis is a chronic inflammatory skin disease presenting with an array of clinical phenotypes, often associated with pruritus. Environmental and psychological stressors can exacerbate psoriasis symptoms and provoke flares. Recent studies suggest a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis in some patients with psoriasis that can result in immune dysregulation. The immune system, in turn, can communicate with the nervous system to induce, maintain or aggravate psoriasis. In the skin, peripheral sensory as well as autonomic nerves control release of inflammatory mediators from dendritic cells, mast cells, T cells or keratinocytes, thereby modulating inflammatory responses and, in case of sensory nerves, pruritus. In response to the environment or stress, cytokines, chemokines, proteases, and neuropeptides fluctuate in psoriasis and influence immune responses as well as nerve activity. Furthermore, immune cells communicate with sensory nerves which control release of cytokines, such as IL-23, that are ultimately involved in psoriasis pathogenesis. Nerves also communicate with keratinocytes to induce epidermal proliferation. Notably, in contrast to recent years the debilitating problem of pruritus in psoriasis has been increasingly appreciated. Thus, investigating neuroimmune communication in psoriasis will not only expand our knowledge about the impact of sensory nerves in inflammation and pruritus and give new insights into the impact of environmental factors activating neuroimmune circuits or of stress in psoriasis, but may also lead to novel therapies. This review summarizes the relevant literature on the role of neuroimmune circuits, stress and how the central HPA axis and its peripheral equivalent in the skin, impact psoriasis.

Therapeutic plasma exchange as a novel treatment for severe intrahepatic cholestasis of pregnancy: Case series and mechanism of action

INTRODUCTION

Intrahepatic cholestasis of pregnancy is characterised by pruritus and elevated serum bile acids. The pruritus can be severe, and pharmacological options achieve inconsistent symptomatic improvement. Raised bile acids are linearly associated with adverse fetal outcomes, with existing management of limited benefit. We hypothesised that therapeutic plasma exchange removes pruritogens and lowers total bile acid concentrations, and improves symptoms and biochemical abnormalities in severe cases that have not responded to other treatments.

METHODS

Four women with severe pruritus and hypercholanemia were managed with therapeutic plasma exchange. Serial blood biochemistry and visual analogue scores of itch severity were obtained. Blood and waste plasma samples were collected before and after exchange; individual bile acids and sulfated progesterone metabolites were measured with HPLC-MS, autotaxin activity and cytokine profiles with enzymatic methods. Results were analysed using segmental linear regression to describe longitudinal trends, and ratio t tests.

RESULTS

Total bile acids and visual analogue itch scores demonstrated trends to transiently improve following plasma exchange, with temporary symptomatic benefit reported. Individual bile acids (excluding the drug ursodeoxycholic acid), and the sulfated metabolites of progesterone reduced following exchange (P = .03 and P = .04, respectively), whilst analysis of waste plasma demonstrated removal of autotaxin and cytokines.

CONCLUSIONS

Therapeutic plasma exchange can lower potentially harmful bile acids and improve itch, likely secondary to the demonstrated removal of pruritogens. However, the limited current experience and potential complications, along with minimal sustained symptomatic benefit, restrict its current use to women with the most severe disease for whom other treatment options have been exhausted.

Skin provocation tests may help to diagnose atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a common skin disorder. Its diagnosis relies on clinical judgment. Mild and untypical manifestations may cause diagnostic difficulties. Biomarkers for the differential diagnostic workup of AD are needed.

OBJECTIVE

To test whether the results of skin provocation with cowhage, an established model of histamine-independent pruritus, and histamine are different in AD patients and healthy subjects and whether these tests may be used as diagnostic markers of AD.

METHODS

Twenty-two AD patients and 18 healthy controls were subjected to topical cowhage provocation and skin prick testing with histamine and assessed for differences in the quality, intensity, and persistence of itch, for wheal diameter, volume, and flare size and intensity.

RESULTS

Patients with AD, compared with healthy controls, exhibited significantly smaller histamine-induced flares (P < 0.01) and markedly longer itch persistence after provocation with cowhage (P < 0.01). Both parameters showed good diagnostic properties for AD (area under the receiver operating characteristic (ROC) curve 0.78 and 0.80, respectively). The persistence of cowhage-induced itch for at least 30 min and a histamine-induced flare of less than 2 cm in diameter were reliable thresholds for the diagnosis of AD. If combinations of the results of both tests were used, their sensitivity and specificity of diagnosing AD were up to 91% and 94%, respectively.

CONCLUSION

The clinical benefit of cowhage and histamine skin provocation tests should be investigated in further studies. Long persistence of cowhage-induced itch and diminished histamine-induced flare in nonlesional skin may support diagnosis of AD.

Role of cytokines and chemokines in itch

Cytokines classically are secreted "messenger" proteins that modulate cellular function of immune cells. Chemokines attract immune cells to the site where they exert various functions in inflammation, autoimmunity or cancer. Increasing evidence is emerging that cytokines or chemokines can act as "neuro-modulators" by activating high-affinity receptors on peripheral or central neurons, microglia cells or Schwann cells. Very recently, cytokines have been shown to act as pruritogens in rodents and humans, while a role of chemokines in itch has thus far been only demonstrated in mice. Upon stimulation, cytokines are released by skin or immune cells and form a "bridge of communication" between the immune and nervous system. For some cytokines such as IL-31 and TSLP, the evidence for this role is strong in rodents. For cytokines such as IL-4, there is some convincing evidence, while for cytokines such as oncostatin M, IL-2, IL-6, IL-8 and IL-13, direct evidence is currently limited. Current clinical trials support the idea that cytokines and chemokines and their receptors or signalling pathways are promising targets for the future therapy of certain subtypes of itch.

Transient receptor potential channels and itch: how deep should we scratch?

Over the past 30 years, transient receptor potential (TRP) channels have evolved from a somewhat obscure observation on how fruit flies detect light to become the center of drug discovery efforts, triggering a heated debate about their potential as targets for therapeutic applications in humans. In this review, we describe our current understanding of the diverse mechanism of action of TRP channels in the itch pathway from the skin to the brain with focus on the peripheral detection of stimuli that elicit the desire to scratch and spinal itch processing and sensitization. We predict that the compelling basic research findings on TRP channels and pruritus will be translated into the development of novel, clinically useful itch medications.

Neuroimmunological mechanism of pruritus in atopic dermatitis focused on the role of serotonin

Although pruritus is the critical symptom of atopic dermatitis that profoundly affect the patients' quality of life, controlling and management of prurirtus still remains as unmet needs mainly due to the distinctive multifactorial pathogenesis of pruritus in atopic dermatitis. Based on the distinct feature of atopic dermatitis that psychological state of patients substantially influence on the intensity of pruritus, various psychotropic drugs have been used in clinic to relieve pruritus of atopic dermatitis patients. Only several psychotropic drugs were reported to show real antipruritic effects in atopic dermatitis patients including naltrexone, doxepin, trimipramine, bupropion, tandospirone, paroxetine and fluvoxamine. However, the precise mechanisms of antipruritic effect of these psychotropic drugs are still unclear. In human skin, serotonin receptors and serotonin transporter protein are expressed on skin cells such as keratinocytes, melanocytes, dermal fibroblasts, mast cells, T cells, natural killer cells, langerhans cells, and sensory nerve endings. It is noteworthy that serotonergic drugs, as well as serotonin itself, showed immune-modulating effect. Fenfluramine, fluoxetine and 2, 5-dimethoxy-4-iodoamphetamine significantly decreased lymphocyte proliferation. It is still questionable whether these serotonergic drugs exert the immunosuppressive effects via serotonin receptor or serotonin transporter. All these clinical and experimental reports suggest the possibility that antipruritic effects of selective serotonin reuptake inhibitors in atopic dermatitis patients might be at least partly due to their suppressive effect on T cells. Further studies should be conducted to elucidate the precise mechanism of neuroimmunological interaction in pruritus of atopic dermatitis.

Interleukin-31 does not induce immediate itch in atopic dermatitis patients and healthy controls after skin challenge

BACKGROUND

The most intriguing function attributed to interleukin-31 (IL-31) is its ability to induce pruritus in pathologic conditions, such as atopic dermatitis (AD). As of today, this feature of IL-31 was tested in vivo only in animal models.

METHODS

Ten patients with AD and 10 healthy controls were challenged with IL-31 and NaCl (negative control) by skin prick testing. Twenty additional healthy controls were subjected to skin prick testing with histamine. Itch and local inflammatory responses of the skin were assessed for up to 72 h.

RESULTS

All of the histamine-challenged subjects developed immediate pruritus (i.e. within the first 5 min). In contrast, only one IL-31- and two of the NaCl-challenged subjects reported immediate itch at the provocation site (short lasting, for 2-6 min). Nine subjects (five patients with AD) reported late itch responses to IL-31 challenges with a mean delay of 143 min. No subject reported late itch responses to histamine or NaCl testing. There was no significant difference in IL-31-induced itch start time, duration and intensity between patients with AD and healthy volunteers.

CONCLUSION

IL-31 does not induce immediate itch responses in humans. The late onset of IL-31-induced itch supports the notion that IL-31 exerts its pruritic effect indirectly via keratinocytes and secondary mediators, rather than through its receptors on cutaneous nerves.

Neural processing of itch

While considerable effort has been made to investigate the neural mechanisms of pain, much less effort has been devoted to itch, at least until recently. However, itch is now gaining increasing recognition as a widespread and costly medical and socioeconomic issue. This is accompanied by increasing interest in the underlying neural mechanisms of itch, which has become a vibrant and rapidly-advancing field of research. The goal of the present forefront review is to describe the recent progress that has been made in our understanding of itch mechanisms.

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.

Interleukin-2 serum levels are elevated in patients with uremic pruritus: a novel finding with practical implications

BACKGROUND

Uremic pruritus (UP) is still a common tormenting symptom among patients on hemodialysis (HD). The pathogenesis of UP is complex and not fully clarified. Some preliminary studies indicate that UP is a systemic inflammatory disease with a deranged balance of T helper (TH) cell differentiation toward TH1 predominance. The aim of this study was to further elucidate the potential contribution of TH1 cytokines to the pathogenesis of UP.

METHODS

In this study, 112 HD patients were screened for UP. After meeting the required criteria, 31 HD patients with UP were included in the study as case group and 30 age- and sex-matched HD patients without UP were enrolled as controls. The serum levels of interleukin (IL)-2 and interferon-γ (as TH1 cytokines), IL-4 (as a TH-2 cytokine), high-sensitive C-reactive protein (as an inflammatory marker), parathyroid hormone, calcium, phosphate, albumin and ferritin were measured in all patients. Moreover, blood variables including hemoglobin and mean corpuscular volume were also determined. The correlations of measured factors with UP severity were determined as well.

RESULTS

Except for the serum levels of IL-2, which were significantly higher in HD patients with itch versus those without it [0.544 ± 0.126 (U/mL) versus 0.318 ± 0.145 (U/mL); P < 0.0001], no statistically significant difference was observed in the levels of each of the above-mentioned factors between the two groups. Additionally, no correlation was detected between the levels of measured factors and UP severity.

CONCLUSIONS

The results of our study, for the first time, point to the potential important role of IL-2 in UP and further support the notion of TH1 overactivity in its pathogenesis. Our study paves the way for further studies focusing on the contribution of IL-2 to the UP, such as the experimental use of anti-IL-2 receptor antibodies.

Pathogenesis and treatment of pruritus

Classification of itch into four categories-pruritoceptive, neurogenic, neuropathic, and psychogenic-has proven to be of utility to clinicians and investigators. Itch is recognized to be transmitted by dedicated afferent neurons, and a matrix of cerebral cortical loci involved in perception and the desire to scratch has been recognized. This highlights the multidimensional nature of the itch sensation. Some of the many mediators of itch, especially relevant in pruritogenic itch, are the result of cross-talk between dermal mast cells and adjacent cutaneous afferents. Keratinocytes of the epidermis express many neuropeptides, and their receptors are far from passive bystanders in the neurophysiology of itch. Mediators can also act centrally (eg, opioid peptides that act on micro receptors in the central nervous system). The pathophysiology of pruritus in neurogenic itch caused by common systemic diseases is gradually being elucidated, especially in the itch of cholestasis, although the molecular basis of itching in chronic renal failure remains elusive. Better understanding of the mediators of itch and their receptors has led to the imminent development of novel anti-itch compounds, including interleukin-31 inhibitors, histamine H4-receptor antagonists, and neurokinin-1 receptor antagonists.

Pathophysiology and therapy of pruritus in allergic and atopic diseases

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

Skin disorders and sleep in adults: where is the evidence?

Sleep deprivation has been shown to have detrimental effects on behavioural, physiological and psychological functioning. Skin disorders are variably associated with sleep disturbance and sleep deprivation, some associated with specific sleep disorders such as obstructive sleep apnoea. Paradoxically, there is very little literature focussed on the management of sleep problems in the context of skin disorders. Furthermore, randomised controlled trials of treatments for skin conditions are few and rarely measure sleep as an outcome, either subjectively or objectively. This review focuses on common skin disorders and how they affect sleep.

Two Japanese cases of lichen planus pigmentosus-inversus

Case 1 was a 51-year-old Japanese woman. She presented with an asymptomatic brown macule located on the right axilla of 2 months' duration. The smooth macule was 2 cm in diameter with a sharp demarcation (Fig. 1A). Case 2 was a 62-year-old Japanese man. He presented with asymptomatic, symmetric, gray-brown macules located on the groin, axillae, and popliteal region of 6 months' duration. The smooth macules were several millimeters to centimeters in diameter and sharply demarcated (Fig. 1B). Oral or nail lesions, previous inflammatory processes in affected areas, and internal malignancies were absent. A causal relationship with drugs, recent sun exposure, or trauma could not be identified. Findings for work-up, including blood cell count, fasting blood sugar levels, liver function, serum electrolyte levels, serum electrophoresis, urinalysis, antinuclear antibodies, and serological examinations for human hepatitis viruses and syphilis, were within normal limits or negative. The lesions gradually disappeared without medication within 6 months. Biopsy specimens showed a lymphocytic infiltrate with basal vacuolar changes and prominent melanin incontinence in the upper dermis (Fig. 2A). The band-like lymphocytic infiltrate was moderate in Case 1 and mild in Case 2. Immunohistochemistry showed infiltrative CD8(+) T lymphocytes with keratinocytic damage, indicating cytotoxic injury of the keratinocytes (Fig. 2B). Both the epidermis and the upper dermis contained CD1a(+) cells (Fig. 2C). The keratinocytes focally and weakly expressed HLA-DR (Fig. 2D). These findings were identical in samples from both patients.

Neuronal conditions of spinal cord in dermatitis are improved by olopatadine

Intense pruritus and cutaneous reactivity represent cardinal features of eczema. The resulting scratching behaviors alter neuronal conditions of the spinal dorsal horn where the primary sensory afferent fibers transmit cutaneous stimulation and deteriorate eczematous skin lesions. We investigated the effects of olopatadine hydrochloride (olopatadine) on alteration of neuronal conditions of the spinal dorsal horn and eczematous skin lesions induced by contact dermatitis. Eczematous lesions were induced by repeated application of diphenylcyclopropenone (DCP) in BALB/c mice. Olopatadine suppressed scratching behavior caused by repeated application of DCP in mice. Increased expressions of c-Fos and substance P in the spinal dorsal horn following DCP application were improved by olopatadine. Furthermore, olopatadine diminished the number of infiltrating cells and levels of cytokines in eczematous skin lesions resulting from DCP application. Olopatadine improves neurological conditions in the spinal cord and eczematous skin lesions in a murine contact dermatitis model.

Therapeutic effect of topical gamma-linolenic acid on refractory uremic pruritus

BACKGROUND

Pruritus is a bothersome symptom affecting up to 80% of dialysis patients. Lymphocyte and cytokine interaction has an important role in the pathogenesis of uremic pruritus. Gamma-linolenic acid (GLA) is associated with immune modulation of T lymphocytes and lymphokines. The aim of this study is to determine whether topical GLA can attenuate uremic pruritus.

METHODS

Seventeen dialysis patients with refractory uremic pruritus who passed the screening criteria entered a prospective, randomized, double-blind, placebo-controlled, crossover study. They stopped all antipruritic therapy at least 2 weeks before the study and were randomly assigned to treatment with either GLA 2.2% cream or placebo-based cream applied to the entire body after taking a bath once a day and to pruritic sites 3 times a day for 2 weeks, and then the reverse treatment after a 2-week washout period. Severity of pruritus was evaluated by using a traditional visual analogue scale (VAS) and a modified questionnaire method (pruritus score [PS]). Hemogram, aspartate and alanine aminotransferases, bilirubin, albumin, blood urea nitrogen, creatinine, calcium, phosphate, and intact parathyroid hormone were measured.

RESULTS

Sixteen patients completed the study; 1 patient was withdrawn because of an allergic skin reaction. There were no significant differences between groups except for sex distribution. Median VAS and PS values between groups did not differ significantly at baseline. There is a greater antipruritic effect of GLA based on evaluation with both the VAS and PS. There is persistence of a residual effect into the second treatment period after GLA treatment.

CONCLUSION

GLA-rich cream is better than placebo-based cream for alleviating uremic pruritus. It is a useful adjuvant in the management of refractory uremic pruritus.

Induction of scratching behaviour and dermatitis in various strains of mice cohabiting with NC/Nga mice with chronic dermatitis

BACKGROUND

NC/Nga (NC) mice with similar pathological and behavioural features as seen in human atopic dermatitis are used as a model of the disease. Under normal circumstances, spontaneous and persistent scratching occurs in NC mice and this can lead to the onset of skin inflammation.

OBJECTIVES

We examined the induction of scratching behaviour in NC, BALB/c, ICR and C3H/HeN mice, and of dermatitis in NC and BALB/c mice, by cohabitation with mice with dermatitis.

METHODS

NC, BALB/c, ICR and C3H/HeN mice were kept together with NC mice with chronic dermatitis (CNV-NC) for 2 weeks, and the numbers of scratching episodes were counted. NC and BALB/c mice were also kept together with CNV-NC mice for 24 weeks and the skin severity score was assessed. The score was assessed for a further 8 weeks after separation of these mice.

RESULTS

The number of scratching episodes in NC, BALB/c, ICR and C3H/HeN mice was increased by cohabitation with CNV-NC mice. Cohabitation with CNV-NC mice led to dermatitis in both NC and BALB/c mice. The number of scratching episodes and the skin severity score in BALB/c mice were about half of those in NC mice. When cohabitation with CNV-NC mice stopped, the number of scratching episodes and the skin severity score decreased in BALB/c mice, but not in NC mice. Changes in the histopathological data of BALB/c mice supported the severity of skin inflammation.

CONCLUSIONS

Our study demonstrates that scratching behaviour and dermatitis can be induced in various strains of mice by cohabitation with CNV-NC mice, and that cessation of cohabitation leads to a recovery in BALB/c mice but not in NC mice.

Inhibition of scratching behaviour caused by contact dermatitis in histidine decarboxylase gene knockout mice

A neuronal system dedicated to itch consists of primary afferent and spinothalamic projection neurons. Histamine is thought to be one of the main mediators for the transmission of itch sensation. However, there are little available information on the role of histamine in scratching behaviour and sensory transmission of atopic dermatitis and chronic eczema. In the present study, the role of histamine in scratching behaviour and neural conduction of sensation in the chronic eczema model was investigated by using l-histidine decarboxylase (HDC) gene knockout mice lacking histamine. The chronic contact dermatitis was induced with daily application of diphenylcyclopropenone (DCP) on a hind paw of HDC (+/+) and HDC (-/-) mice for 2 months. The observation of scratching behaviour and the hot-plate test were performed in both mice. Histological studies were performed in the skin and spinal cord tissues. Histological examination revealed that both HDC (+/+) and HDC (-/-) mice displayed the similar extent of inflammatory cell infiltration, hyperplastic epidermis and newly spreading of neuronal processes in the skin tissue. Scratching behaviour was exclusively induced in HDC (+/+) mice, whereas it was barely observed in HDC (-/-) mice. The expression of c-Fos was specifically upregulated in HDC (+/+) mice in lamina I of the spinal dorsal horn following repeated DCP application. Scratching behaviour in chronic contact dermatitis in mice was thought mainly mediated with histamine. The afferent pathway of sensation in chronic contact dermatitis model may connect with the central nervous system through lamina I of the spinal dorsal horn.

Pruritogenic mediators in psoriasis vulgaris: comparative evaluation of itch-associated cutaneous factors

BACKGROUND

Although some patients with psoriasis vulgaris also complain of severe pruritus, the data available regarding pruritus in psoriasis are sparse.

OBJECTIVES

To clarify the mechanism and mediators involved in the pruritus of psoriasis vulgaris, we compared itch-associated factors in lesional skin from psoriatic patients vs. skin without pruritus quantitatively using a panel of histological and immunohistological parameters.

PATIENTS AND METHODS

Biopsied specimens were obtained from 38 patients with psoriasis vulgaris who were divided into two groups according to the presence or absence of pruritus.

RESULTS

When compared with psoriatic patients devoid of pruritus, lesional skin from patients with pruritus showed the following characteristic features: (i) a rich innervation both in the epidermis and in the papillary dermis; (ii) an increase in neuropeptide substance P-containing nerve fibres in perivascular areas; (iii) decreased expression of neutral endopeptidase in the epidermal basal layer as well as in the endothelia of blood vessels; (iv) many mast cells showing degranulating processes in the papillary dermis; (v) a strong immunoreactivity for nerve growth factor (NGF) throughout the entire epidermis and an increased NGF content in lesional skin homogenates; (vi) an increase in the expression of high-affinity receptors for NGF (Trk A) in basal keratinocytes and in dermal nerves; (vii) an increased population of interleukin-2-immunoreactive lymphocytes; and (viii) a strong expression of E-selectin on vascular endothelial cells. A significant correlation was observed between the severity of pruritus and protein gene product 9.5-immunoreactive intraepidermal nerve fibres, NGF-immunoreactive keratinocytes, expression of Trk A in the epidermis and the density of immunoreactive vessels for E-selectin. These findings indicate that possible pruritogenic mediators in psoriatic lesional skin are neurogenic factors including innervation, neuropeptide substance P, neuropeptide-degrading enzymes and NGF, activated mast cells, one or more cytokines and endothelial-leucocyte adhesion molecules.

CONCLUSIONS

These data document for the first time itch-related local markers in psoriasis, and suggest complex and multifactorial mechanisms of pruritus in the disease. These results provide the groundwork for further studies to evaluate the efficacy of antipruritic treatment for psoriatic patients.

Analysis of the spontaneous scratching behavior by NC/Nga mice: a possible approach to evaluate antipruritics for subjects with atopic dermatitis

We investigated the spontaneous scratching by NC/Nga mice to design a new method for evaluating the itch of subjects with atopic dermatitis. The numbers of scratchings in various strains of mice were classified based on the duration of the scratching. Prolonged scratching was frequent in skin-lesioned NC/Nga mice, but not in ICR, BALB/c and non-lesioned NC/Nga mice. Pretreatment with dexamethasone or tacrolimus significantly suppressed long-duration scratching in NC/Nga mice but did not suppress short-duration scratching induced by ovalbumin active cutaneous anaphylaxis in BALB/c mice and in ICR mice subcutaneously injected with histamine. In contrast, pretreatment with chlorpheniramine or ketotifen significantly suppressed short-duration scratching induced by ovalbumin active cutaneous anaphylaxis in BALB/c mice and in ICR mice subcutaneously injected with histamine, but not long-duration scratching seen in NC/Nga mice. These findings indicate that the mechanism of spontaneous scratching in NC/Nga mice differs from that induced by several pruritogen injections. This new method shows good correlation with the therapeutic activity of drugs in cases of atopic dermatitis in humans and may serve as a useful model for evaluating antipruritic drugs and for studying mechanisms involved in atopic dermatitis.

Pruritus - Pathophysiologie, Klinik und Therapie - Eine Ubersicht. Pruritus - pathophysiology, clinical features and therapy - an overview

Pruritus is an unpleasant sensory perception of the skin associated with the desire to scratch. As a physiological nociception, pruritus leads to the removal of harmful agents such as parasites and plants from the skin surface. More often, pruritus occurs as a severe and therapy-refractory symptom of various underlying dermatological and systemic diseases. Comparable to chronic pain, chronic pruritus worsens the general condition and may lead to physical and psychological exhaustion. Until the 1990s, pruritus had been regarded as an incomplete pain sensation. Only recently, itch was defined as a separate, pain-independent sensation with its own mediators, spinal neurons and cortical areas. These observations led to the development of new therapeutic modalities. This paper gives an overview of itch pathophysiology, clinical types and therapies.

Sensitivity of human scalp skin to pruritic stimuli investigated by intradermal microdialysis in vivo

BACKGROUND

Although pruritus is common in scalp skin, the forearm has been the main site for investigation in previous experimental studies.

OBJECTIVE

Our purpose was to compare the sensitivity to pruritic stimuli in human scalp and forearm skin.

METHODS

Four microdialysis fibers were inserted intradermally into scalp (n = 10) or forearm skin (n = 10) of healthy male subjects and were perfused with histamine (0.01%) or compound 48/80 (C48/80; 0.05%) for 20 minutes. Total protein content in the dialysate was assessed at 10-minute intervals. Intensity of itching and pain sensation were measured psychophysically.

RESULTS

Histamine- and C48/80-induced protein extravasation was significantly lower in scalp skin. Histamine and C48/80 invariably provoked an itching sensation in the forearm but only in 4 of 10 applications in the scalp.

CONCLUSION

Despite the high prevalence of pruritus, scalp skin is less sensitive to histamine-induced experimental itching. A lower innervation density of pruritic nociceptors and/or different central processing of itching might account for this difference.

Experimental itch in sodium lauryl sulphate-inflamed and normal skin in humans: a randomized, double-blind, placebo-controlled study of histamine and other inducers of itch

BACKGROUND

Investigations of pruritogenic substances in humans have involved intradermal injections in normal skin; itching of inflamed skin has been little studied.

OBJECTIVES

To develop an itch model with provocation of itch in experimentally inflamed skin as well as in normal skin, using subjects as self-controls.

METHODS

In 32 non-atopic volunteers aged 21-30 years, the skin of five selected test sites on one volar forearm was pretreated for 24 h with large Finn chambers containing 1% sodium lauryl sulphate (SLS) used as a standard contact irritant to induce inflammation. Twenty microlitres of different pruritogenic substances [histamine, substance P, neurokinin A, neurokinin B, trypsin, platelet-activating factor (PAF) and serotonin] and saline as control were injected intradermally into the inflamed test sites and in corresponding non-treated sites on the opposite forearm. The test individuals scored itch intensity on a visual analogue scale for 20 min, and weal area was then measured. :

RESULTS

Histamine and substance P induced itch in both normal and inflamed skin compared with a saline reference. Neurokinin A, trypsin, PAF and serotonin only elicited itch in normal skin, and neurokinin B neither elicited itch in normal skin nor in inflamed skin. Itch was induced in normal and SLS-inflamed skin to a similar magnitude. However, weal area after histamine was significantly (P < 0.001) larger in inflamed skin when compared with normal skin.

CONCLUSIONS

Histamine and substance P elicited itch to the same degree in normal skin and inflamed skin pretreated with SLS despite a stronger weal response in inflamed skin. Mediators present in inflamed skin did not potentiate itch, a c-fibre-mediated neuronal response. The weal reaction is based on enhanced vascular permeability (protein extravasation). A greater skin perfusion in inflamed skin may therefore have increased the weal size. We propose an experimental model in humans for testing of itch involving both normal and inflamed skin. The model has the potential for use in evaluating new topical and systemic treatments of itch.

Itch--mediators and mechanisms

A specialized subpopulation of unmyelinated chemonociceptors and dedicated spinal neurons which are responsible for the itch sensation have been identified recently. Under physiological conditions, painful stimuli such as activation of conventional mechano-heat-sensitive ('polymodal') nociceptors (scratching) inhibit the itch sensation via central mechanisms. Conversely, centrally acting pain-inhibiting opioids enhance itch by disinhibition. These mechanisms might well explain the itch in diseases characterized by histamine release like urticaria, and might provide evidence for the role of endogenous opioids as central itch promotors in cholestasis or nephropathy. After the discovery of itch-specific neurons has dramatically improved our understanding of itch mechanisms under experimental conditions, the present task is to correlate these new findings to the clinical situation of itch patients.

Pathophysiology of pruritus in atopic dermatitis: an overview

Pruritus is an essential feature of atopic dermatitis (AD) and the diagnosis of active AD cannot be made without the history of itching. Because of the high impact on life quality, most of the patients measure the severity of eczema by the intensity of pruritus rather than appearance of skin lesions. However, although pruritus is a cardinal symptom of AD, its mechanism and association with the cutaneous nervous system is not completely understood. Recently, a considerable progress has been achieved in clarifying the complex pathophysiology of pruritus in AD. As a cutaneous sensory perception, itch requires excitation of neuropeptide-containing free nerve endings of unmyelinated nociceptor fibers. It is well known that histamine and acetylcholine provoke itch by direct binding to 'itch receptors' and several mediators such as neuropeptides, proteases or cytokines indirectly via histamine release. Interestingly, some variations of these complex mechanisms could be demonstrated in patients with AD. This review highlights the recent knowledge of different mechanisms which may be involved in regulating pruritus in patients with AD potentially leading to new therapeutic applications for the treatment of itch in AD.