Understanding the pathophysiology of itch

The MRGPR family of receptors in immunity

The discovery of Mas-related G protein-coupled receptors (Mrgprs) has opened a compelling chapter in our understanding of immunity and sensory biology. This family of receptors, with their unique expression and diverse ligands, has emerged as key players in inflammatory states and hold the potential to alleviate human diseases. This review will focus on the members of this receptor family expressed on immune cells and how they govern immune and neuro-immune pathways underlying various physiological and pathological states. Immune cell-specific Mrgprs have been shown to control a variety of manifestations, including adverse drug reactions, inflammatory conditions, bacterial immunity, and the sensing of environmental exposures like allergens and irritants.

S. aureus drives itch and scratch-induced skin damage through a V8 protease-PAR1 axis

Itch is an unpleasant sensation that evokes a desire to scratch. The skin barrier is constantly exposed to microbes and their products. However, the role of microbes in itch generation is unknown. Here, we show that Staphylococcus aureus, a bacterial pathogen associated with itchy skin diseases, directly activates pruriceptor sensory neurons to drive itch. Epicutaneous S. aureus exposure causes robust itch and scratch-induced damage. By testing multiple isogenic bacterial mutants for virulence factors, we identify the S. aureus serine protease V8 as a critical mediator in evoking spontaneous itch and alloknesis. V8 cleaves proteinase-activated receptor 1 (PAR1) on mouse and human sensory neurons. Targeting PAR1 through genetic deficiency, small interfering RNA (siRNA) knockdown, or pharmacological blockade decreases itch and skin damage caused by V8 and S. aureus exposure. Thus, we identify a mechanism of action for a pruritogenic bacterial factor and demonstrate the potential of inhibiting V8-PAR1 signaling to treat itch.

Kappa opioid agonists in the treatment of itch: just scratching the surface?

Chronic pruritus is a debilitating condition affecting 23-44 million Americans. Recently, kappa opioid agonists (KOAs) have emerged as a novel class of potent antipruritic agents. In 2021, the Food and Drug Administration approved difelikefalin (Korsuva) for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis. Difelikefalin is a potent, peripherally restricted KOA that is intravenously available. Although promising, difelikefalin is currently available as an intravenous composition only, limiting the scope of use. Oral formulations of difelikefalin did not meet the primary endpoint criteria in recent phase 2 clinical trials; however, additional clinical studies are ongoing. The future for KOAs in the treatment of pruritus is encouraging. Orally active pathway-biased KOAs, such as triazole 1.1, may serve as viable alternatives with broader applications. Extended-release compositions, such as the TP-2021 ProNeura subdermal implant, may circumvent the pharmacokinetic issues associated with peptide-based KOAs. Lastly, dual-acting kappa opioid receptor agonist/mu opioid receptor antagonists are orally bioavailable and may be useful in the treatment of various forms of chronic itch. In this review, we summarize the results of KOAs in clinical and preclinical trials and discuss future directions of drug development.

Skin Infiltrate Composition as a Telling Measure of Responses to Checkpoint Inhibitors

Checkpoint inhibitors treat a variety of tumor types with significant benefits. Unfortunately, these therapies come with diverse adverse events. Skin rash is observed early into treatment and might serve as an indicator of downstream responses to therapy. We studied the cellular composition of cutaneous eruptions and whether their contribution varies with the treatment applied. Skin samples from 18 patients with cancer and 11 controls were evaluated by mono- and multiplex imaging, quantification, and statistical analysis. T cells were the prime contributors to skin rash, with T cells and macrophages interacting and proliferating on site. Among T cell subsets examined, type 1 and 17 T cells were relatively increased among inflammatory skin infiltrates. A combination of increased cytotoxic T cell content and decreased macrophage abundance was associated with dual checkpoint inhibition over PD1 inhibition alone. Importantly, responders significantly separated from nonresponders by greater CD68+ macrophage and either CD11c+ antigen-presenting cell or CD4+ T cell abundance in skin rash. The microenvironment promoted epidermal proliferation and thickening as well. The combination of checkpoint inhibitors used affects the development and composition of skin infiltrates, whereas the combined abundance of two cell types in cutaneous eruptions aligns with responses to checkpoint inhibitor therapy.

Chronic Kidney Disease-Associated Pruritus and Quality of Life: Learning from Our Patients

Chronic kidney disease-associated pruritus is itching directly related to kidney disease that cannot be explained by any other condition. Despite technological advances in the different aspects of dialysis sessions and the best treatment for chronic kidney disease patients, it is still a common problem in our patients. The many complex physiological mechanisms involved, the different hypotheses made over the years on the aetiology of the condition, and the great clinical variability may partially explain the limited knowledge about this problem and the difficulties in treating it. The presence of all these factors leads to the persistence of unpleasant symptoms, which must affect the disease burden and quality of life of kidney patients. Through the presentation of an illustrative clinical case, the aim of this review article is to highlight the need for adequate diagnosis and an improved approach to all aspects of chronic kidney disease-associated pruritus, in view of the heavy burden of the disease and the huge impact on the patient's quality of life.

Odevixibat: A Review of a Bioactive Compound for the Treatment of Pruritus Approved by the FDA

Odevixibat is synthesized through chemical modification of Benzothiazepine's structure. It is a tiny chemical that inhibits the ileal bile acid transporter and is used to treat a variety of cholestatic illnesses, including progressive familial intrahepatic cholestasis (PFIC). For cholestatic pruritus and liver disease development, bile acid transporter inhibition is a unique treatment strategy. Odevixibat reduces enteric bile acid reuptake. Oral odevixibat was also studied in children with cholestatic liver disease. Odevixibat received its first approval in the European Union (EU) in July 2021 for the treatment of PFIC in patients aged 6 months, followed by approval in the USA in August 2021 for the treatment of pruritus in PFIC patients aged 3 months. Bile acids in the distal ileum can be reabsorbed by the ileal sodium/bile acid cotransporter, a transport glycoprotein. Odevixibat is a sodium/bile acid co-transporter reversible inhibitor. An average 3 mg once-daily dose of odevixibat for a week resulted in a 56% reduction in the area under the curve of bile acid. A daily dose of 1.5 mg resulted in a 43% decrease in the area under the curve for bile acid. Odevixibat is also being evaluated in many countries for the treatment of other cholestatic illnesses, including Alagille syndrome and biliary atresia. This article reviews the updated information on odevixibat with respect to its clinical pharmacology, mechanism of action, pharmacokinetics, pharmacodynamics, metabolism, drug-drug interactions, pre-clinical studies, and clinical trials.

[From ocular itching to eye rubbing: a review of the literature]

Ocular itching and eye rubbing are frequent complaints in an ophthalmology practice. Numerous studies address the consequences of eye rubbing, such as keratoconus. However, there are few studies concerning the pathophysiology of itching, its transmission pathways, or its interactions with eye rubbing. Through this literature review, we will address the various clinical, physiological and therapeutic aspects of this pair of symptoms with a variety of ocular consequences. We will then describe the state of the art in itching and scratching in dermatology, in order to draw a parallel between these two vicious cycles. A better understanding of the pathophysiology of ocular itching and eye rubbing, as well as new studies based on dermatological data, might allow more appropriate clinical management of our patients and their symptoms.

A review of psychocutaneous disorders from a psychotherapeutic perspective—Toolkit for the dermatologist

Introduction

The study of psychocutaneous disorders requires a multidisciplinary approach. It is of paramount importance that dermatologists understand the psychiatric premise for these disorders. Mental health professionals can also benefit from a better understanding of the dermatologic manifestations of psychiatric disorders they may encounter in their practice.

Aim

The aim of this study is to elevate the level of understanding regarding psychotherapeutic treatment of psychocutaneous disorders.

Methods

We performed a literature review using the major databases. Four researchers reviewed English, full text, peer-reviewed articles that were published after 2000 using our specific search terms and inclusion/exclusion criteria.

Results

The majority of psychocutaneous disorders seem to be clustered among three DSM-5 disorders: depressive disorders, anxiety disorders, and obsessive-compulsive related disorders.

Conclusions

Better recognition of the underlying psychiatric comorbidities may lead to improved patient outcomes.

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.

How Does Botulinum Toxin Inhibit Itch?

Two decades after reports of the anti-pruritic effects of botulinum neurotoxins (BoNTs), there is still no approved product for the anti-itch indication of BoNTs, and most clinical case reports still focus on the off-label use of BoNTs for various itchy conditions. Few randomized clinical trials have been conducted with controversial results, and the beneficial effects of BoNTs against itch are mainly based on case studies and case series. These studies are valuable in presenting the potential application of BoNTs in chronic pruritic conditions, but due to the nature of these studies, they are categorized as providing lower levels of evidence or lower grades of recommendation. To obtain approval for the anti-pruritic indication of BoNTs, higher levels of evidence are required, which can be achieved through conducting large-scale and well-designed studies with proper control groups and established careful and reliable primary and secondary outcomes. In addition to clinical evidence, presenting the mechanism-based antipruritic action of BoNTs can potentially strengthen, accelerate, and facilitate the current efforts towards further investments in accelerating the field towards the potential approval of BoNTs for itchy conditions. This review, therefore, aimed to provide the state-of-the-art mechanisms underlying the anti-itch effect of BoNTs from basic studies that resemble various clinical conditions with itch as a hallmark. Evidence of the neuronal, glial, and immune modulatory actions of BoNTs in reducing the transmission of itch are presented, and future potential directions are outlined.

Itch Beyond the Skin-Mucosal Itch

Itch is a nociceptive sensation linked with reflexes and cognitive motor actions. We traditionally think of itch as a sensation of the skin related to allergy, an insect sting or interestingly, anxiety and frustration. Less understood and considered are the physiological processes involved in the itching sensation that occurs at mucosal and junctional dermal sites, which is extraordinary as from an evolutionary point of view these sites serve important guardian roles, rich in sensory nerves and inflammatory cells. Despite itch being an ancient reflex and evolutionarily conserved phenomenon, better clinical understanding of the nuances between sites of itch sensation may lead to improved clinical outcomes. This review invites readers to appreciate itch beyond the skin by highlighting several specific itch patterns-nasal, oral, auricular, vulvovaginal, anal, and perineal itch-the pathophysiological mechanisms that underlie them, the clinical patterns these may cause, and some unique treatments.

Effect of scratching and friction on human skin in vivo

OBJECTIVE

To investigate effect of scratching and friction on human skin function and functional differences between scratching and friction.

METHOD

Forty healthy volunteers were enrolled. Scratching and friction behavior was modeled by scalpel and sandpaper simulation to forearm for 80 times, respectively. Noninvasive bioengineering devices were used to measure basic skin physiological parameters and exfoliated stratum corneum collected and protein quantified. Parameters were recorded at baseline (BL) and after every 20 times interventions (20, 40, 60, and 80 times).

RESULTS

Compared to BL, transepidermal water loss (TEWL) value increased significantly at both scratched and friction sites (P < .001) with a significant higher value for friction (P < .001). There was no significant difference in stratum corneum hydration (SCH) value postscratching (P > .05), while it decreased first and then increased significantly at friction site (P < .001). Roughness values (contract (CONT), variety (VAR), and scaliness (SEsc)) were raised significantly at both sites (P < .001). Net change in CONT and SEsc values of friction was higher than scratched sites (P > .05). There was no significant difference in blood flow after both scratching and friction (P > .05). Quantity of keratinocyte protein from friction sites was statistically higher than scratching after 80 times interventions (P < .05).

CONCLUSION

Both noninvasive detections and protein quantification indicated more damage from friction, which may have significance for behavior guidance of patients with pruritus and implication for further investigation.

Pruritus in psoriasis and atopic dermatitis: current treatments and new perspectives

Psoriasis and atopic dermatitis (AD) are two common chronic inflammatory skin diseases. Although showing different etiology and clinical manifestations, patients with either disease suffer from low health-related quality of life due to pruritus (dermal itch). Recent studies have revealed that more than 85% of psoriasis patients suffer from pruritus, and it is also the dominating symptom of AD. However, as this is a non-life treating symptom, it was partly neglected for years. In this review, we focus on current findings as well as the impact and potential treatments of pruritus in these two skin diseases. We first distinguish the type of itch based on involved mediators and modulators. This clear delineation between the types of pruritus based on involved receptors and pathways allows for precise treatment. In addition, insights into recent clinical trials aimed to alleviate pruritus by targeting these receptors are presented. We also report about novel advances in combinatorial treatments, dedicated to the type of pruritus linked to a causal disease. Altogether, we suggest that only a focused treatment tailored to the primary disease and the underlying molecular signals will provide fast and sustained relief of pruritus associated with psoriasis or AD.

Amelioration of Compound 48/80-Mediated Itch and LL-37-Induced Inflammation by a Single-Stranded Oligonucleotide

Numerous inflammatory skin disorders display a high prevalence of itch. The Mas-related G protein coupled receptor X2 (MRGPRX2) has been shown to modulate itch by inducing non-IgE-mediated mast cell degranulation and the release of endogenous inducers of pruritus. Various substances collectively known as basic secretagogues, which include inflammatory peptides and certain drugs, can trigger MRGPRX2 and thereby induce pseudo-allergic reactions characterized by histamine and protease release as well as inflammation. Here, we investigated the capacity of an immunomodulatory single-stranded oligonucleotide (ssON) to modulate IgE-independent mast cell degranulation and, more specifically, its ability to inhibit the basic secretagogues compound 48/80 (C48/80)-and LL-37 in vitro and in vivo. We examined the effect of ssON on MRGPRX2 activation in vitro by measuring degranulation in a human mast cell line (LAD2) and calcium influx in MRGPRX2-transfected HEK293 cells. To determine the effect of ssON on itch, we performed behavioral studies in established mouse models and collected skin biopsies for histological analysis. Additionally, with the use of a rosacea mouse model and RT-qPCR, we investigated the effect on ssON on LL-37-induced inflammation. We reveal that both mast cell degranulation and calcium influx in MRGPRX2 transfected HEK293 cells, induced by the antimicrobial peptide LL-37 and the basic secretagogue C48/80, are effectively inhibited by ssON in a dose-dependent manner. Further, ssON demonstrates a capability to inhibit LL-37 and C48/80 activation in vivo in two mouse models. We show that intradermal injection of ssON in mice is able to block itch induced via C48/80 in a dose-dependent manner. Histological staining revealed that ssON inhibits acute mast cell degranulation in murine skin treated with C48/80. Lastly, we show that ssON treatment ameliorates LL-37-induced inflammation in a rosacea mouse model. Since there is a need for new therapeutics targeting non-IgE-mediated activation of mast cells, ssON could be used as a prospective drug candidate to resolve itch and inflammation in certain dermatoses.

Mechanisms of Cannabinoids and Potential Applicability to Skin Diseases

The legalisation of cannabis in a growing number of jurisdictions has led to increasing interest in its potential therapeutic effects in a range of disorders, including cutaneous conditions. Cannabinoids have been used as natural medicines for centuries; however, their biological activity in the skin is a new area of study. Recent data suggest that cannabinoids are involved in neuro-immuno-endocrine modulation of skin functioning, yet their effect on the features of dermatologic conditions is unclear. This article sought to review the mechanisms by which cannabinoids regulate skin functioning through the lens of relevance to treatment of dermatologic diseases looking at the effects of cannabinoids on a range of cellular activities and dermatologic conditions both in vitro and in vivo. We identified studies demonstrating an inhibitory effect of cannabinoids on skin inflammation, proliferation, fibrosis, pain, and itch-biological mechanisms involved in the pathogenesis of many dermatologic conditions. Cannabinoids have the potential to expand the therapeutic repertoire of a wide spectrum of skin disorders. Given their widespread unregulated use by the general public, basic and clinical studies are required to elucidate the effectiveness and long-term effects of topical and systemic cannabinoids in cutaneous disorders.

Advances in Understanding the Initial Steps of Pruritoceptive Itch: How the Itch Hits the Switch

Pruritoceptive (dermal) itch was long considered an accompanying symptom of diseases, a side effect of drug applications, or a temporary sensation induced by invading pruritogens, as produced by the stinging nettle. Due to extensive research in recent years, it was possible to provide detailed insights into the mechanism of itch mediation and modulation. Hence, it became apparent that pruritus is a complex symptom or disease in itself, which requires particular attention to improve patients’ health. Here, we summarize recent findings in pruritoceptive itch, including how this sensation is triggered and modulated by diverse endogenous and exogenous pruritogens and their receptors. A differentiation between mediating pruritogen and modulating pruritogen seems to be of great advantage to understand and decipher the molecular mechanism of itch perception. Only a comprehensive view on itch sensation will provide a solid basis for targeting this long-neglected adverse sensation accompanying numerous diseases and many drug side effects. Finally, we identify critical aspects of itch perception that require future investigation.

CKD-Associated Pruritus: New Insights Into Diagnosis, Pathogenesis, and Management

Chronic kidney disease–associated pruritus (CKD-aP) is a common, troubling and in some cases debilitating problem for patients with CKD and end-stage renal disease. Despite a prevalence rate of approximately 20% in CKD and 40% in end-stage renal disease, and a clear association with poorer psychosocial and medical outcomes, this condition is often underreported by patients and overlooked by health care providers. This is likely due, in part, to uncertainty regarding its pathogenesis and treatment. Most commonly, CKD-aP is attributed to toxin build-up, peripheral neuropathy, immune system dysregulation, or opioid dysregulation. Prior treatment studies of CKD-aP have targeted these potential etiologies but have been limited by noncontrolled design, small sample size, and non-uniform definitions of CKD-aP. Recently, several large, randomized controlled trials targeting opioid dysregulation have yielded promising results. These trials have spurred new hope for understanding and treating this condition.

Quantitative Characterization of the Neuropeptide Level Changes in Dorsal Horn and Dorsal Root Ganglia Regions of the Murine Itch Models

Chronic itch can be extremely devastating and, in many cases, difficult to treat. One challenge in treating itch disorders is the limited understanding of the multitude of chemical players involved in the communication of itch sensation from the peripheral to the central nervous system. Neuropeptides are intercellular signaling molecules that are known to be involved in the transmission of itch signals from primary afferent neurons, which detect itch in the skin, to higher-order circuits in the spinal cord and brain. To investigate the role of neuropeptides in transmitting itch signals, we generated two mouse models of chronic itch-Acetone-Ether-Water (AEW, dry skin) and calcipotriol (MC903, atopic dermatitis). For peptide identification and quantitation, we analyzed the peptide content of dorsal root ganglia (DRG) and dorsal horn (DH) tissues from chronically itchy mice using liquid chromatography coupled to tandem mass spectrometry. De novo-assisted database searching facilitated the identification and quantitation of 335 peptides for DH MC903, 318 for DH AEW, 266 for DRG MC903, and 271 for DRG AEW. Of these quantifiable peptides, we detected 30 that were differentially regulated in the tested models, after accounting for multiple testing correction (q ≤ 0.1). These include several peptide candidates derived from neuropeptide precursors, such as proSAAS, protachykinin-1, proenkephalin, and calcitonin gene-related peptide, some of them previously linked to itch. The peptides identified in this study may help elucidate our understanding about these debilitating disorders. Data are available via ProteomeXchange with identifier PXD015949.

Interventions for chronic pruritus of unknown origin

BACKGROUND

Pruritus is a sensation that leads to the desire to scratch; its origin is unknown in 8% to 15% of affected patients. The prevalence of chronic pruritus of unknown origin (CPUO) in individuals with generalised pruritus ranges from 3.6% to 44.5%, with highest prevalence among the elderly. When the origin of pruritus is known, its management may be straightforward if an effective treatment for the causal disease is available. Treatment of CPUO is particularly difficult due to its unknown pathophysiology.

OBJECTIVES

To assess the effects of interventions for CPUO in adults and children.

SEARCH METHODS

We searched the following up to July 2019: Cochrane Skin Group Specialised Register, CENTRAL, MEDLINE, Embase, and trials registries. We checked the reference lists of included studies for additional references to relevant trials.

SELECTION CRITERIA

We sought to include randomised controlled trials and quasi-randomised controlled trials that assessed interventions for CPUO, as defined in category VI ('Other pruritus of undetermined origin, or chronic pruritus of unknown origin') of the International Forum for the Study of Itch (IFSI) classification, in children and adults. Eligible interventions were non-pharmacological or topical or systemic pharmacological interventions, and eligible comparators were another active treatment, placebo, sham procedures, or no treatment or equivalent (e.g. waiting list).

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Our primary outcomes were 'Patient- or parent-reported pruritus intensity' and 'Adverse events'. Our secondary outcomes were 'Health-related quality of life', 'Sleep disturbances', 'Depression', and 'Patient satisfaction'. We used GRADE to assess the certainty of evidence.

MAIN RESULTS

We found there was an absence of evidence for the main interventions of interest: emollient creams, cooling lotions, topical corticosteroids, topical antidepressants, systemic antihistamines, systemic antidepressants, systemic anticonvulsants, and phototherapy. We included one study with 257 randomised (253 analysed) participants, aged 18 to 65 years; 60.6% were female. This study investigated the safety and efficacy of three different doses of oral serlopitant (5 mg, 1 mg, and 0.25 mg, once daily for six weeks) compared to placebo for severe chronic pruritus; 25 US centres participated (clinical research centres and universities). All outcomes were measured at the end of treatment (six weeks from baseline), except adverse events, which were monitored throughout. A pharmaceutical company funded this study. Fifty-five per cent of participants suffered from CPUO, and approximately 45% presented a dermatological diagnosis (atopic dermatitis/eczema 37.3%, psoriasis 6.7%, acne 3.6%, among other diagnoses). We unsuccessfully attempted to retrieve outcome data from study authors for the subgroup of participants with CPUO. Participants had pruritus for six weeks or longer. Total study duration was 10 weeks. Participants who received serlopitant 5 mg may have a greater rate of relief of patient-reported pruritus intensity as measured by the visual analogue scale (VAS; a reduction in VAS score indicates improvement) compared to placebo (126 participants, risk ratio (RR) 2.06, 95% confidence interval (CI) 1.27 to 3.35; low-certainty evidence). We are uncertain of the effects of serlopitant 5 mg compared to placebo on the following outcomes due to very low-certainty evidence: adverse events (127 participants; RR 1.48, 95% CI 0.87 to 2.50); health-related quality of life (as measured by the Dermatology Life Quality Index (DLQI); a higher score indicates greater impairment; 127 participants; mean difference (MD) -4.20, 95% CI -11.68 to 3.28); and sleep disturbances (people with insomnia measured by the Pittsburgh Sleep Symptom Questionnaire-Insomnia (PSSQ-I), a dichotomous measure; 128 participants; RR 0.49, 95% CI 0.24 to 1.01). Participants who received serlopitant 1 mg may have a greater rate of relief of patient-reported pruritus intensity as measured by VAS compared to placebo; however, the 95% CI indicates that there may also be little to no difference between groups (126 participants; RR 1.50, 95% CI 0.89 to 2.54; low-certainty evidence). We are uncertain of the effects of serlopitant 1 mg compared to placebo on the following outcomes due to very low-certainty evidence: adverse events (128 participants; RR 1.45, 95% CI 0.86 to 2.47); health-related quality of life (DLQI; 128 participants; MD -6.90, 95% CI -14.38 to 0.58); and sleep disturbances (PSSQ-I; 128 participants; RR 0.38, 95% CI 0.17 to 0.84). Participants who received serlopitant 0.25 mg may have a greater rate of relief of patient-reported pruritus intensity as measured by VAS compared to placebo; however, the 95% CI indicates that there may also be little to no difference between groups (127 participants; RR 1.66, 95% CI 1.00 to 2.77; low-certainty evidence). We are uncertain of the effects of serlopitant 0.25 mg compared to placebo on the following outcomes due to very low-certainty evidence: adverse events (127 participants; RR 1.29, 95% CI 0.75 to 2.24); health-related quality of life (DLQI; 127 participants; MD -5.70, 95% CI -13.18 to 1.78); and sleep disturbances (PSSQ-I; 127 participants; RR 0.60, 95% CI 0.31 to 1.17). The most commonly reported adverse events were somnolence, diarrhoea, headache, and nasopharyngitis, among others. Our included study did not measure depression or patient satisfaction. We downgraded the certainty of evidence for all outcomes due to indirectness (only 55% of study participants had CPUO) and imprecision. We downgraded outcomes other than patient-reported pruritus intensity a further level due to concerns regarding risk of bias in selection of the reported result and some concerns with risk of bias due to missing outcome data (sleep disturbances only). We deemed risk of bias to be generally low.

AUTHORS' CONCLUSIONS

We found lack of evidence to address our review question: for most of our interventions of interest, we found no eligible studies. The neurokinin 1 receptor (NK1R) antagonist serlopitant was the only intervention that we could assess. One study provided low-certainty evidence suggesting that serlopitant may reduce pruritus intensity when compared with placebo. We are uncertain of the effects of serlopitant on other outcomes, as certainty of the evidence is very low. More studies with larger sample sizes, focused on patients with CPUO, are needed. Healthcare professionals, patients, and other stakeholders may have to rely on indirect evidence related to other forms of chronic pruritus when deciding between the main interventions currently used for this condition.

Effectiveness of a music intervention on pruritus: an open randomized prospective study

BACKGROUND

Pruritus is a common symptom in many skin diseases. Music interventions have demonstrated their efficacy in different symptoms or diseases such as pain, depression and anxiety.

OBJECTIVE

To evaluate the effects of a music intervention on pruritus.

PATIENTS AND METHODS

A randomized controlled trial was conducted from November 2018 to April 2019. Fifty inpatients with pruritus intensity ≥3/10 in various chronic skin diseases were randomized in a music group or an emollient group. The primary endpoint was the evolution of pruritus as measured by the Numerical Rating Scale before and one hour after the procedure. The secondary judgement criteria were the effects on patient anxiety, the impact of pruritus on the quality of life and patient satisfaction (NCT03701971).

RESULTS

Fifty patients with chronic pruritus were included, 62% were male, and the average age was 60.7 years. The most common diseases were psoriasis (N = 10), atopic dermatitis (N = 8) and contact eczema (N = 6). The average ItchyQol score was 64.8/110, showing a significant impact on quality of life. The intensity of pruritus decreased more significantly in the music intervention group than in the emollient group: 2.3 (SD 2.1) and 1.2 (SD 1.7), respectively (P < 0.05). There was a decrease in anxiety in both groups, with no statistical significant difference between groups. Among patients who received the music intervention, 64% reported feeling an improvement, 91% would recommend the music intervention, and 64% would like to continue this practice.

DISCUSSION

Pruritus management is complex and requires first-line aetiological treatment. Aetiological or symptomatic treatments do not always provide enough relief; it is useful to find other therapeutic options. The music intervention has shown interest in our study. Its repeated use over the long term will be interesting to evaluate. As in pain, music may work by activating inhibitory neural circuits. The use of music is a simple method to manage chronic pruritus.

Intractable pruritus in chronic myelomonocytic leukaemia and myelodysplastic syndromes: a case series

Intractable pruritus without visible primary skin lesions and refractory to antihistamines as a primary presentation of chronic myelomonocytic leukaemia (CMML) and myelodysplastic syndrome (MDS) is not well recognised. We present two cases of CMML and two cases of MDS with this challenging symptom. In two of them, the pruritus preceded the diagnosis of MDS/CMML by months. Various chemotherapeutic and immunosuppressive options were used with variable success. In one of the cases, the pruritus persisted despite achieving morphological remission of CMML with azacitidine but had a remarkable complete response to cladribine. The pathogenesis of intractable itching in CMML and MDS remains unclear but seems to be linked to the biology of these diseases and could precede definitive diagnostic features. Earlier diagnosis of these myeloid disorders may therefore be aided by increasing awareness among clinicians of the association with pruritus.

Pain and Pruritus: a study of their similarities and differences

Pruritus is one of the most common dermatologic complaints and, as the most common dermatologic symptom, is a major contributor to frequent dermatology visits. Chronic pruritus mirrors another major medical condition faced by millions of Americans each year - chronic pain. In older literature, pain and pruritus were thought to have been conveyed by the same C fiber, and the proportion contributing to pruritus was just a small subset of this general fiber. Overall, pain and pruritus share many integral similarities. Although these sensations both initiate the body's awareness to injury, pain and itch may have evolved for sensing different damages such as a burrowing parasite or a noxious stimulus, respectively. This seems to have been validated through analyses of their pathophysiology, acute and chronic conditions, and treatment modalities. However, their symptoms and intrinsic mechanisms vary considerably. It is important to view pruritus in more of an overall, whole body experience, rather than just the sensory aspect. Future studies should investigate the psychological treatment of chronic pruritus, considering the immense similarities with its chronic pain counterpart.

Breaking the Itch-Scratch Cycle: Topical Options for the Management of Chronic Cutaneous Itch in Atopic Dermatitis

Chronic itch is an unpleasant sensation that triggers a desire to scratch that lasts for six weeks or more. It is a major diagnostic symptom of myriad diseases, including atopic dermatitis for which it is the most prominent feature. Chronic itch can be hugely debilitating for the sufferer, damaging in terms of both the monetary cost of treatment and its socioeconomic effects, and few treatment options exist that can adequately control it. Corticosteroids remain the first line treatment strategy for atopic dermatitis, but due to the risks associated with long-term use of corticosteroids, and the drawbacks of other topical options such as topical calcineurin inhibitors and capsaicin, topical options for itch management that are efficacious and can be used indefinitely are needed. In this review, we detail the pathophysiology of chronic pruritus, its key features, and the disease most commonly associated with it. We also assess the role of the skin and its components in maintaining a healthy barrier function, thus reducing dryness and the itch sensation. Lastly, we briefly detail examples of topical options for the management of chronic pruritus that can be used indefinitely, overcoming the risk associated with long-term use of corticosteroids.

Water-Soluble Extract from Actinidia arguta (Siebold & Zucc.) Planch. ex Miq. and Perilla frutescens (L.) Britton, ACTPER, Ameliorates a Dry Skin-Induced Itch in a Mice Model and Promotes Filaggrin Expression by Activating the AhR Signaling in HaCaT Cells

With a complex etiology involving multiple factors, the condition known as itch is a primary symptom of many skin diseases. Current treatment methods are ineffective for addressing itches caused by dry skin, for example. We developed a botanical extract, ACTPER, made from a mixture of Actinidia arguta and Perilla frutescens, which have traditionally been used to treat itch. The quality of ACTPER as a research agent was controlled in our experiment by cell-based bioassays, as well as by high-performance liquid chromatography (HPLC), using two chemical markers. In the acetone-induced dry skin mice model, the oral administration of ACTPER alleviated dry skin-related skin properties and itching behavior. The RNA and protein expression of the filament aggregating protein (filaggrin) gene, a key factor involved in the regulation of skin barrier function, was significantly increased, as measured by quantitative reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence assay. To understand the underlying mechanism(s) at the molecular level, HaCaT cells, a human keratinocyte-derived cell line, were treated with various concentrations of ACTPER. We found that the protein expression of filaggrin was indeed upregulated by ACTPER in a dose dependent manner. Data from experiments involving the reporter plasmid containing the xenobiotic response element (XRE), and the chemical antagonist for the aryl hydrocarbon receptor (AhR), indicated that the ACTPER-mediated upregulation of filaggrin was controlled through the activation of the AhR signaling pathway. The molecular docking simulation study predicted that ACTPER might contain chemical compounds that bind directly to AhR. Taken together, our results suggest that ACTPER may provide the platform, based upon which a variety of safe and effective therapeutic agents can be developed to treat itch.

The Itch-Scratch Cycle: A Review of the Mechanisms

BACKGROUND

Despite being one of the most common presenting dermatological symptoms, itching continues to perplex health care professionals because it is notoriously difficult to control.

OBJECTIVE

This review gathers evidence to answer the 2-part question, "Why do we itch and scratch?" by exploring the history of itchy disease, the neurobiology of itch, and the 4 different clinical origins of itch: pruritogenic, neurological, neuropathic, and psychological.

RESULTS

The automated scratching reflex and its biological and psychological reasons for existence are complicated and poorly understood. Currently, there are a myriad of treatments available for individuals suffering from this condition; however, many remain symptomatic.

CONCLUSIONS

The itch-scratch cycle is a complex pain-like sensation with a reflex-like response. In the future, continued exploration into the mechanisms behind itch and scratch may open the doors for new therapeutic interventions.

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Drugs on the Horizon for Chronic Pruritus

Chronic pruritus is a common condition that has a detrimental impact on quality of life. As the molecular pathogenesis of itch is elucidated, novel therapies that disrupt itch pathways are being investigated. Emerging treatments include drugs targeting the neural system, drugs targeting the immune system, antihistamines, bile acid transport inhibitors, and topical drugs that work through a variety of mechanisms such as phosphodiesterase-4 inhibition or targeting of nerve ion channels. Many of these therapies show promising results in the treatment of chronic itch of various etiologies, such as atopic dermatitis, psoriasis, uremic pruritus, and cholestatic pruritus.

Pruritus Reduction with Systemic Anti-lymphoma Treatments in Patients with Cutaneous T Cell Lymphoma: A Narrative Review

Cutaneous T-cell lymphomas (CTCL) are a heterogeneous and relatively rare group of non-Hodgkin lymphomas arising from neoplastic skin-homing memory T cells. There is no known cure for CTCL, and current treatments focus on achieving and maintaining remission, controlling symptoms, limiting toxicities and maintaining or improving quality of life. Patients with CTCL often suffer from pruritus (itching), which can be debilitating and can have a significant impact on physical well-being and quality of life. Although progress has been made towards understanding the mechanisms of pruritus, the pathophysiology of CTCL-related pruritus remains unclear. Currently, there is neither a step-wise treatment algorithm for CTCL nor a standardized approach to treating pruritus in patients with CTCL. Treatments which specifically target pruritus have been reported with varying effectiveness. However, systemic treatments that target CTCL have the potential to alleviate pruritus by treating the underlying disease. Several systemic CTCL treatments have reported anti-pruritic properties, some in both objective responders and nonresponders, but the lack of a standardized method to measure and report pruritus makes it difficult to compare the effectiveness of systemic treatments. In this review, we provide an overview of approved and investigational systemic CTCL treatments that report anti-pruritic properties. For each study, the methods used to measure and report pruritus, as well as the study design are examined so that the clinical benefits of each systemic treatment can be more readily evaluated.

Funding: Financial support for medical editorial assistance and article processing charge were provided by Celgene Corporation.

Are itch and scratching the nausea and vomiting of skin?

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

The Regulation of Immunological Processes by Peripheral Neurons in Homeostasis and Disease

The nervous system and the immune system are the principal sensory interfaces between the internal and external environment. They are responsible for recognizing, integrating, and responding to varied stimuli, and have the capacity to form memories of these encounters leading to learned or 'adaptive' future responses. We review current understanding of the cross-regulation between these systems. The autonomic and somatosensory nervous systems regulate both the development and deployment of immune cells, with broad functions that impact on hematopoiesis as well as on priming, migration, and cytokine production. In turn, specific immune cell subsets contribute to homeostatic neural circuits such as those controlling metabolism, hypertension, and the inflammatory reflex. We examine the contribution of the somatosensory system to autoimmune, autoinflammatory, allergic, and infectious processes in barrier tissues and, in this context, discuss opportunities for therapeutic manipulation of neuro-immune interactions.

[Role of the skin expression of neuropeptides, neurotrophins and their receptors in the pathogenesis of dermatoses]

OBJECTIVE

to define the role of neurotransmitters and their receptors in the development of itch and in the maintenance of a skin inflammatory response in patients with psoriasis and atopic dermatitis.

MATERIAL AND METHODS

Skin biopsy specimens from 30 patients with psoriasis and 30 patients with atopic dermatitis were investigated by histological, immunoperoxidase, and indirect immunofluorescence assays. The investigators determined the expression of protein gene product 9.5 (PGP9.5), amphiregulin, semaphorin 3A, calcitonin gene-related peptide (CGRP) and its receptor (CGRP-R), nerve growth factor (NGF) and its receptor TrkA, and substance P (SP) and its receptor SP-R. The indirect immunofluorescence assay was used for quantitative analysis. The findings were statistically analyzed using a Statistica 10 program.

RESULTS

Immunoperoxidase examination of the skin biopsy specimens from patients with atopic dermatitis and psoriasis revealed enhanced expression of amphiregulin, NGF, and PGP9.5, appearance of positively stained epidermal nerve fibers, and decreased expression of the nerve reduction factor semaphorin 3A in all cases. Some patients with atopic dermatitis and psoriasis showed increased expression of CGRP and CGRP-R, SP, SP-R, and TrkA. A pronounced inflammatory response was generally observed in these cases.

CONCLUSION

The investigation performed suggests that atopic dermatitis and psoriasis are characterized by a larger number of epidermal nerve fibers and by a direct correlation between this indicator, disease severity, and itch intensity. The production of neuropeptides and neurotrophins is closely related to the development of a skin inflammatory response irrespective of its cause and dysregulation of these processes is likely to favor the body's sensitization and the chronic pattern the course of diseases.

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.

HTR7 Mediates Serotonergic Acute and Chronic Itch

Chronic itch is a prevalent and debilitating condition for which few effective therapies are available. We harnessed the natural variation across genetically distinct mouse strains to identify transcripts co-regulated with itch behavior. This survey led to the discovery of the serotonin receptor HTR7 as a key mediator of serotonergic itch. Activation of HTR7 promoted opening of the ion channel TRPA1, which in turn triggered itch behaviors. In addition, acute itch triggered by serotonin or a selective serotonin reuptake inhibitor required both HTR7 and TRPA1. Aberrant serotonin signaling has long been linked to a variety of human chronic itch conditions, including atopic dermatitis. In a mouse model of atopic dermatitis, mice lacking HTR7 or TRPA1 displayed reduced scratching and skin lesion severity. These data highlight a role for HTR7 in acute and chronic itch and suggest that HTR7 antagonists may be useful for treating a variety of pathological itch conditions.

Anti-allergic properties of curine, a bisbenzylisoquinoline alkaloid

Curine is a bisbenzylisoquinoline alkaloid isolated from Chondrodendron platyphyllum (Menispermaceae). Recent findings have shed light on the actions of curine in different models of allergy and inflammation. Here we review the properties and mechanisms of action of curine focusing on its anti-allergic effects. Curine pre-treatment significantly inhibited the scratching behavior, paw edema and systemic anaphylaxis induced by either ovalbumin (OVA) in sensitized animals or compound 48/80, through mechanisms of mast cell stabilization and inhibition of mast cell activation to generate lipid mediators. In addition, oral administration of curine significantly inhibited eosinophil recruitment and activation, as well as, OVA-induced airway hyper-responsiveness in a mouse model of asthma, through inhibition of the production of IL-13 and eotaxin, and of Ca²⁺ influx. In conclusion, curine exhibit anti-allergic effects in models of lung, skin and systemic allergy in the absence of significant toxicity, and as such has the potential for anti-allergic drug development.

Neurotrophins and neuropeptides as inflammatory mediators in case of chronic dermatosis

This literature review examines the role of neurotrophins and neuropeptides for the development of skin inflammatory reactions in case of chronic inflammatory dermatoses. The article describes inflammatory effects of neurotrophin, a nerve growth factor, neuropeptide substance P and calcitonin gene-related peptide. Factors affecting the condition of skin innervation and development of inflammation - neurotrophin, a nerve growth factor, amphiregulin, an epidermal growth factor, and semaphorin 3A, a nerve repulsion factor - were examined. Searching for and administering antagonists of proinflammatory effects of neuropeptides, neurotrophins and epidermal growth factor can become new approaches to the treatment of chronic inflammatory dermatoses.

Curine inhibits mast cell-dependent responses in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Curine is a bisbenzylisoquinoline alkaloid and the major constituent isolated from Chondrodendron platyphyllum, a plant that is used to treat inflammatory diseases in Brazilian folk medicine. This study investigates the effectiveness of curine on mast cell-dependent responses in mice.

MATERIALS AND METHODS

To induce mast cell-dependent responses, Swiss mice were subcutaneously sensitized with ovalbumin (OVA-12 μg/mouse) and Al(OH)3 in a 0.9% NaCl solution. Fifteen days later, the animals were challenged with OVA through different pathways. Alternatively, the animals were injected with compound 48/80 or histamine, and several parameters, including anaphylaxis, itching, edema and inflammatory mediator production, were analyzed. Promethazine, cromoglycate, and verapamil were used as control drugs, and all of the treatments were performed 1h before the challenges.

RESULTS

Curine pre-treatment significantly inhibited the scratching behavior and the paw edema induced by either compound 48/80 or OVA, and this protective effect was comparable in magnitude with those associated with treatment with either cromoglycate or verapamil. In contrast, curine was a weak inhibitor of histamine-induced paw edema, which was completely inhibited by promethazine. Curine and verapamil significantly inhibited pleural protein extravasations and prostaglandin D2 (PGD2) and cysteinyl leukotrienes (CysLTs) production following allergen-induced pleurisy. Furthermore, like verapamil, curine inhibited the anaphylactic shock caused by either compound 48/80 or an allergen. In in vitro settings, these treatments also inhibited degranulation as well as PGD2 and CysLT production through IgE-dependent activation of the mast cell lineage RBL-2H3.

CONCLUSION

Curine significantly inhibited immediate allergic reactions through mechanisms more related to mast cell stabilization and activation inhibition than interference with the pro-inflammatory effects of mast cell products. These findings are in line with the hypothesis that the alkaloid curine may be beneficial for the treatment of allergic disorders.

Why we scratch an itch: the molecules, cells and circuits of itch

Itch is described as an irritating sensation that triggers a desire to scratch. However, this definition hardly seems fitting for the millions of people who suffer from intractable itch. Indeed, the Buddhist philosopher Nāgārjuna more aptly stated, "There is pleasure when an itch is scratched. But to be without an itch is more pleasurable still." Chronic itch is widespread and very difficult to treat. In this review we focus on the molecules, cells and circuits in the peripheral and central nervous systems that drive acute and chronic itch transmission. Understanding the itch circuitry is critical to developing new therapies for this intractable disease.