p-Phenylenediamine induces immediate contact allergy and non-histaminergic itch via MRGPRX2.

p-phenylenediamine (PPD) is a common component of hair dye known to induce immediate allergy, even acute dermatitis and contact dermatitis. MAS-related G protein coupled receptor-X2 (MRGPRX2) in mast cells (MCs) mediates small molecular substances-induced pseudo-allergic reactions. However, the role of MRGPRX2 in PPD-induced immediate contact allergy needs further exploration. The aim of this study was to investigate whether PPD activates MCs via MRGPRX2 and induces immediate allergies that contribute to contact dermatitis. Wild-type (WT) and kitw-sh/w-sh mice (MUT) were treated with PPD to observe local inflammation and MC degranulation in vivo. The release of inflammatory mediators was measured in vitro. Histamine 1 receptor (H1R)-/- mice were used to analyze itch type. PPD caused immediate contact allergy in WT mice, induced scratching, and local inflammatory reactions, while exhibiting minimal effects on MUT mice. PPD did not induce histamine release, but induced significant tryptase release in vivo and in vitro. PPD activated MRGPRX2 to induce MC degranulation in vitro. PPD caused immediate contact allergy in WT mice, induced scratching and local inflammatory reactions, while exhibited minimal effect on MUT mice. PPD did not induce histamine release, while induced significant tryptase release in vivo and in vitro. PPD induced immediate contact allergy by MCs activation via MRGPRX2 and lead to tryptase release. The scratching times showed no significant difference in WT mice or H1R-/- mice, which indicated PPD caused non-histaminergic itch. The results showed that PPD activated MCs via MRGPRX2 and induced immediate contact allergy, leading to the release of tryptase without monoamine release, which might induce non-histaminergic itch.

EGFRI-associated health-related quality of life by severity of skin toxicity in metastatic colorectal cancer patients receiving epidermal growth factor receptor inhibitor target therapy.

PURPOSE: The purposes of this study were to assess the levels of symptom distress, body image, and epidermal growth factor receptor inhibitors (EGFRI)-associated health-related quality of life (QoL); identify the factors related to EGFRI-associated health-related QoL; and examine the differences in EGFRI-associated health-related QoL by grade of skin toxicity in mCRC patients receiving target therapy. METHODS: This cross-sectional study examined mCRC patients who received cetuximab-based target therapy from the oncology and CRC inpatient and outpatient departments of a medical center in northern Taiwan. Structured questionnaires were used to measure patients' symptom distress, body image, and EGFRI-associated health-related QoL. RESULTS: Of the 111 mCRC patients studied, 79.2% reported acneiform eruption and 52.2% reported paronychia. The most common symptoms were dry skin and itching. Poor EGFRI-associated health-related QoL was associated with more symptom distress, more negative body image, a higher cumulative dose of target therapy, and being married; these factors explained 66.6% of the variance in EGFRI-associated health-related QoL. CONCLUSION: Patient-specific skin care and emotional support are needed to relieve distressful dermatological symptoms and emotional distress during and post-treatment for mCRC.

Enhanced histamine-induced itch in diacylglycerol kinase iota knockout mice.

Subsets of small-diameter dorsal root ganglia (DRG) neurons detect pruritogenic (itch-causing) and algogenic (pain-causing) stimuli and can be activated or sensitized by chemical mediators. Many of these chemical mediators activate receptors that are coupled to lipid hydrolysis and diacylglycerol (DAG) production. Diacylglycerol kinase iota (DGKI) can phosphorylate DAG and is expressed at high levels in small-diameter mouse DRG neurons. Given the importance of these neurons in sensing pruritogenic and algogenic chemicals, we sought to determine if loss of DGKI impaired responses to itch- or pain-producing stimuli. Using male and female Dgki-knockout mice, we found that in vivo sensitivity to histamine-but not other pruritogens-was enhanced. In contrast, baseline pain sensitivity and pain sensitization following inflammatory or neuropathic injury were equivalent between wild type and Dgki-/- mice. In vitro calcium responses in DRG neurons to histamine was enhanced, while responses to algogenic ligands were unaffected by Dgki deletion. These data suggest Dgki regulates sensory neuron and behavioral responses to histamine, without affecting responses to other pruritogenic or algogenic agents.

Identification of a bilirubin receptor that may mediate a component of cholestatic itch.

Various pathologic conditions result in jaundice, a yellowing of the skin due to a buildup of bilirubin. Patients with jaundice commonly report experiencing an intense non-histaminergic itch. Despite this association, the pruritogenic capacity of bilirubin itself has not been described, and no bilirubin receptor has been identified. Here, we demonstrate that pathophysiologic levels of bilirubin excite peripheral itch sensory neurons and elicit pruritus through MRGPRs, a family of G-protein coupled receptors expressed in primary sensory neurons. Bilirubin binds and activates two MRGPRs, mouse MRGPRA1 and human MRGPRX4. In two mouse models of pathologic hyperbilirubinemia, we show that genetic deletion of either Mrgpra1 or Blvra, the gene that encodes the bilirubin-producing enzyme biliverdin reductase, attenuates itch. Similarly, plasma isolated from hyperbilirubinemic patients evoked itch in wild-type animals but not Mrgpra1-/- animals. Removing bilirubin decreased the pruritogenic capacity of patient plasma. Based on these data, targeting MRGPRs is a promising strategy for alleviating jaundice-associated itch.

Antipruritic Effects of Janus Kinase Inhibitor Tofacitinib in a Mouse Model of Psoriasis.

The Janus kinase 1/3 inhibitor tofacitinib has demonstrated an antipruritic effect in two phase III studies in psoriasis. However, the mechanisms behind this antipruritic effect are still unknown. We presently investigated whether tofacitinib affects spontaneous itch as well as expression of itch-related cytokines and epidermal nerve fiber density (ENFD) in the imiquimod-induced mouse model of psoriasis. Psoriasis-like skin lesions were produced by daily topical application of imiquimod to the back skin. Imiquimod treatment resulted in spontaneous scratching, which was significantly inhibited by tofacitinib treatment. Imiquimod treatment significantly increased mRNA expression of Il22, Il23, and Il31, reduced peptidergic ENFD, and increased nonpeptidergic ENFD compared to naive mice. Tofacitinib significantly decreased the expression of those cytokines and increased peptidergic ENFD without a significant effect on nonpeptidergic ENFD. Tofacitinib may inhibit psoriatic itch through inhibition of cytokine expression as well as modulation of epidermal innervation.

Histopathological diagnosis of persistent pruritic eruptions associated with adult-onset Still's disease.

AIMS: Persistent pruritic eruptions (PPEs), presenting with dyskeratotic keratinocytes histologically, are characteristic skin rash in patients with adult-onset Still's disease (AOSD). The lesions may be histologically similar to other entities that present with dyskeratosis. In the present study, we compared the histopathological features between PPEs and other entities presenting with dyskeratosis. METHODS AND RESULTS: To investigate whether histopathological findings can be used to discriminate among PPEs and other entities presenting with dyskeratotic keratinocytes, cutaneous histopathological changes of PPEs associated with AOSD (n = 26) were compared with those of systemic lupus erythematosus (SLE) (n = 16), dermatomyositis (n = 19), and drug eruption (n = 16). Dyskeratosis was observed in the upper one-third of the epidermal layer in all 26 PPEs. The rate of dyskeratosis for PPEs was higher than that for SLE (18.8%) and dermatomyositis (15.8%). In drug eruptions, the dyskeratotic cells were distributed in all levels of the epidermis. Variable densities of neutrophils were found in the dermis in all PPEs. CONCLUSIONS: Although this was a retrospective study conducted at a single centre, presentation of dyskeratotic keratinocytes in the upper one-third of the epidermal layer is a distinctive histopathological reactive pattern of PPEs. This pattern may be a useful histopathological marker for early diagnosis of AOSD.

NMDA receptor antagonists attenuate intrathecal morphine-induced pruritus through ERK phosphorylation.

Pruritus is the most common complication of intrathecal morphine; however, its exact molecular mechanism is unclear, and treatment is challenging. The analgesic effect of N-methyl-D-aspartate (NMDA) receptor antagonists and the morphine-associated increase in NMDA receptor activation suggest potential role of NMDA receptor in the spinal itch sensation. Male C57BL/6 mice were given intrathecal morphine to induce scratching behavior. The effects of NMDA, ketamine, ifenprodil and U0126 on morphine-induced pruritus and analgesia were evaluated also. The number of scratching responses was counted for 30 min post-injection to evaluate pruritus. A warm-water tail immersion assay was conducted before and until 120 min post-injection at 30-min intervals. Percent of maximal possible effect (%MPE) and area under curve (AUC) were calculated based on tail-flick latency to evaluate analgesic efficacy. Compared with control treatment, intrathecal morphine elicited an obvious scratching response and analgesic effect in a dose dependent manner. Ketamine (1 µg), ifenprodil (0.1 µg) and U0126 (0.1 µg and 1.0 µg) all significantly attenuated morphine induced scratches. Ifenprodil (0.1 µg) injection significantly prolonged the analgesic effect of intrathecal morphine. The ERK1/2 phosphorylation induced by intrathecal morphine was inhibited by ketamine, ifenprodil and U0126 as well. U0126 inhibited morphine-induced pruritus with no effect on its analgesia. Therefore, intrathecal coadministration of morphine with NMDA receptor antagonists ketamine and ifenprodil alleviated morphine-induced scratching. Intrathecal morphine increased ERK phosphorylation in the lumbar spinal dorsal horn, which may be related with morphine-induced pruritus, and was counteracted by NMDA receptor antagonists.

A possible role for CD26/DPPIV enzyme activity in the regulation of psoriatic pruritus.

BACKGROUND: Psoriasis (PSO) is one of the most common chronic inflammatory skin diseases, and pruritus affects approximately 60-90% of patients with PSO. However, the pathogenesis of pruritus in PSO remains unclear. Dipeptidyl peptidase IV (DPPIV) enzyme activity is involved in the regulation of peptide hormones, chemokines and neurotransmitters. OBJECTIVES: Our aim is to evaluate for a potential association between DPPIV and an increased risk of pruritus, and to identify possible underlying treatment targets in affected patients. METHODS: Utilizing clinical serum samples of PSO patients and in vivo experimental pruritus models, we evaluated for a potential association between DPPIV and an increased risk for pruritus, and attempted to identify possible underlying treatment targets in pruritus of PSO. RESULTS: We first showed that levels of DPPIV enzyme activity in sera of patients with PSO were significantly increased compared to those of healthy controls. We next evaluated levels of substance-P (SP), which is a neurotransmitter for pruritus and a substrate for DPPIV enzyme. Truncated form SP cleaved by DPPIV was significantly increased in sera of PSO. In an in vivo pruritus model induced by SP, scratching was decreased by treatment with a DPPIV inhibitor. Moreover, DPPIV-knockout mice showed attenuation of scratching induced by SP. Finally, scratching was decreased following the administration of a DPPIV inhibitor in an imiquimod-induced PSO model. On the other hand, scratching induced by imiquimod was increased in DPPIV overexpressing-mice. CONCLUSIONS: These results suggest that inhibition of DPPIV enzyme activity regulates pruritus in PSO.

Elevated basal serum tryptase identifies a multisystem disorder associated with increased TPSAB1 copy number.

Elevated basal serum tryptase levels are present in 4-6% of the general population, but the cause and relevance of such increases are unknown. Previously, we described subjects with dominantly inherited elevated basal serum tryptase levels associated with multisystem complaints including cutaneous flushing and pruritus, dysautonomia, functional gastrointestinal symptoms, chronic pain, and connective tissue abnormalities, including joint hypermobility. Here we report the identification of germline duplications and triplications in the TPSAB1 gene encoding α-tryptase that segregate with inherited increases in basal serum tryptase levels in 35 families presenting with associated multisystem complaints. Individuals harboring alleles encoding three copies of α-tryptase had higher basal serum levels of tryptase and were more symptomatic than those with alleles encoding two copies, suggesting a gene-dose effect. Further, we found in two additional cohorts (172 individuals) that elevated basal serum tryptase levels were exclusively associated with duplication of α-tryptase-encoding sequence in TPSAB1, and affected individuals reported symptom complexes seen in our initial familial cohort. Thus, our findings link duplications in TPSAB1 with irritable bowel syndrome, cutaneous complaints, connective tissue abnormalities, and dysautonomia.

Hyperactivation of JAK1 tyrosine kinase induces stepwise, progressive pruritic dermatitis.

Skin homeostasis is maintained by the continuous proliferation and differentiation of epidermal cells. The skin forms a strong but flexible barrier against microorganisms as well as physical and chemical insults; however, the physiological mechanisms that maintain this barrier are not fully understood. Here, we have described a mutant mouse that spontaneously develops pruritic dermatitis as the result of an initial defect in skin homeostasis that is followed by induction of a Th2-biased immune response. These mice harbor a mutation that results in a single aa substitution in the JAK1 tyrosine kinase that results in hyperactivation, thereby leading to skin serine protease overexpression and disruption of skin barrier function. Accordingly, treatment with an ointment to maintain normal skin barrier function protected mutant mice from dermatitis onset. Pharmacological inhibition of JAK1 also delayed disease onset. Together, these findings indicate that JAK1-mediated signaling cascades in skin regulate the expression of proteases associated with the maintenance of skin barrier function and demonstrate that perturbation of these pathways can lead to the development of spontaneous pruritic dermatitis.

Topical TrkA Kinase Inhibitor CT327 is an Effective, Novel Therapy for the Treatment of Pruritus due to Psoriasis: Results from Experimental Studies, and Efficacy and Safety of CT327 in a Phase 2b Clinical Trial in Patients with Psoriasis.

Pruritus is an important symptom in psoriasis with no targeted treatment. Tropomyosin-receptor kinase A (TrkA) is associated with pruritus and psoriatic plaque formation. We report the efficacy of a TrkA inhibitor, CT327, on pruritus in psoriasis. A randomised, double-blind, vehicle-controlled Phase 2b clinical trial was conducted in 160 subjects. No effect was found on psoriasis severity using Investigator's Global Assessment (primary endpoint). However, clinically and statistically significant reductions in pruritus were observed in the 108 patient subset reporting at least moderate pruritus at baseline (37.1 mm visual analogue scale improvement (95% CI [-37.5, -6.2], p = 0.0067) for lowest dose; secondary endpoint). Significant modified Psoriasis Area and Severity Index reductions were found in this subset (p < 0.05). Experiments exploring capsaicin-mediated calcium influx, important in pruritus signalling, were performed in sensory neurons. CT327 inhibited capsaicin responses, indicating action at the nerve growth factor-TrkA-TRPV1 pathway. TrkA is a key target in pruritus, and CT327 has potential to become an effective and safe first-in-class treatment.

Attenuation of serotonin-induced itch responses by inhibition of endocannabinoid degradative enzymes, fatty acid amide hydrolase and monoacylglycerol lipase.

Itch and pain are two irritating sensations sharing a lot in common. Considering the antinociceptive effects of blockade of endocannabinoid degrading enzymes in pain states, we attempted to reduce scratching behavior by endocannabinoid modulation, i.e. by inhibiting fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), or cellular uptake of endocannabinoids. Scratching behavior was induced by intradermal injection of serotonin to Balb/c mice. URB597 (10 mg/kg, i.p.), a FAAH inhibitor, JZL184 (16 mg/kg, i.p.), a MAGL inhibitor, and AM404 (10 mg/kg, i.p.), an endocannabinoid transport inhibitor, were given to evaluate the effects of endocannabinoid modulation on scratching responses. Then, the CB1 receptor antagonist, AM251 (1 mg/kg, i.p.), and the CB2 receptor antagonist, SR144528 (1 mg/kg, i.p.), were administered to determine whether cannabinoid receptors mediate these effects. URB597 and JZL184, but not AM404, attenuated serotonin-induced scratches. The inhibitory effect of URB597 was reversed by SR144528, but cannabinoid receptor antagonists had no other effects on modulation by the inhibitors. We propose that augmenting the endocannabinoid tonus by inhibition of degradative enzymes, FAAH and MAGL, but not cellular uptake, may be a novel target for the development of antipruritic agents.

Extracellular signal-regulated kinase (ERK) activation is required for itch sensation in the spinal cord.

BACKGROUND: Itch, chronic itch in particular, can have a significant negative impact on an individual's quality of life. However, the molecular mechanisms underlying itch processing in the central nervous system remain largely unknown. RESULTS: We report here that activation of ERK signaling in the spinal cord is required for itch sensation. ERK activation, as revealed by anti-phosphorylated ERK1/2 immunostaining, is observed in the spinal dorsal horn of mice treated with intradermal injections of histamine and compound 48/80 but not chloroquine or SLIGRL-NH2, indicating that ERK activation only occurs in histamine-dependent acute itch. In addition, ERK activation is also observed in 2, 4-dinitrofluorobenzene (DNFB)-induced itch. Consistently, intrathecal administration of the ERK phosphorylation inhibitor U0126 dramatically reduces the scratching behaviors induced by histamine and DNFB, but not by chloroquine. Furthermore, administration of the histamine receptor H1 antagonist chlorpheniramine decreases the scratching behaviors and ERK activation induced by histamine, but has no effect on DNFB-induced itch responses. Finally, the patch-clamp recording shows that in histamine-, chloroquine- and DNFB-treated mice the spontaneous excitatory postsynaptic current (sEPSC) of dorsal horn neurons is increased, and the decrease of action potential threshold is largely prevented by bathing of U0126 in histamine- and DNFB-treated mice but not those treated with chloroquine. CONCLUSION: Our results demonstrate a critical role for ERK activation in itch sensation at the spinal level.

Potentials of the circulating pruritogenic mediator lysophosphatidic acid in development of allergic skin inflammation in mice: role of blood cell-associated lysophospholipase D activity of autotaxin.

Itching and infiltration of immune cells are important hallmarks of atopic dermatitis (AD). Although various studies have focused on peripheral mediator-mediated mechanisms, systemic mediator-mediated mechanisms are also important in the pathogenesis and development of AD. Herein, we found that intradermal injection of lysophosphatidic acid (LPA), a bioactive phospholipid, induces scratching responses by Institute of Cancer Research mice through LPA1 receptor- and opioid µ receptor-mediating mechanisms, indicating its potential as a pruritogen. The circulating level of LPA in Naruto Research Institute Otsuka Atrichia mice, a systemic AD model, with severe scratching was found to be higher than that of control BALB/c mice, probably because of the increased lysophospholipase D activity of autotaxin (ATX) in the blood (mainly membrane associated) rather than in plasma (soluble). Heparan sulfate proteoglycan was shown to be involved in the association of ATX with blood cells. The sequestration of ATX protein on the blood cells by heparan sulfate proteoglycan may accelerate the transport of LPA to the local apical surface of vascular endothelium with LPA receptors, promoting the hyperpermeability of venules and the pathological uptake of immune cells, aggravating lesion progression and itching in Naruto Research Institute Otsuka Atrichia mice.

Transverse myelitis associated with an itchy rash and hyperckemia: neuromyelitis optica associated with dermatitis herpetiformis.

IMPORTANCE: Neuromyelitis optica is associated with severe neurodisability if not recognized and treated promptly. Several autoimmune disorders are associated with this condition and may vary in their presentation. It is essential that clinicians are aware of the uncommon presenting features of neuromyelitis optica and associated autoimmune conditions. OBSERVATIONS: A 53-year-old woman presented with nausea and vomiting and was noted to have an asymptomatic elevated creatinine kinase level, which improved with conservative management. She had a history of iron-deficiency anemia due to long-standing celiac disease that was managed with a gluten-free diet. She then presented with recurrent transverse myelitis and a vesicobullous rash over her arms and feet that was pruritic and excoriating. Skin biopsy results confirmed a clinical diagnosis of dermatitis herpetiformis and antibody test findings against aquaporin-4 were positive, leading to a diagnosis of neuromyelitis optica spectrum disorder. She was treated with methylprednisolone sodium succinate, plasma exchange, and azathioprine and has remained in remission. CONCLUSIONS AND RELEVANCE: This report highlights the association of neuromyelitis optica with dermatitis herpetiformis, which can present even without clinical features of celiac disease. Nausea, vomiting, and asymptomatic hyperCKemia should be recognized as rare presenting features of neuromyelitis optica.

Topical E6005, a novel phosphodiesterase 4 inhibitor, attenuates spontaneous itch-related responses in mice with chronic atopy-like dermatitis.

Atopic dermatitis is a chronic inflammatory cutaneous disease with difficult-to-treat pruritus. Although phosphodiesterase (PDE) 4 inhibitors have an anti-inflammatory effect on inflammatory skin diseases, such as atopic dermatitis, their acute antipruritic activities remain unclear. Therefore, in this study, we examined whether E6005, a novel PDE4 inhibitor, has antipruritic activity in dermatitis, using a mouse model of atopic dermatitis (NC/Nga mice). A single topical application of E6005 inhibited spontaneous hind-paw scratching, an itch-associated response and spontaneous activity of the cutaneous nerve in mice with chronic dermatitis. The cutaneous concentration of cAMP was significantly decreased in mice with chronic dermatitis, and this decrease was reversed by topical E6005 application. These results suggest that E6005 increases the cutaneous concentration of cAMP to relieve dermatitis-associated itching. Thus, E6005 may be a useful therapy for pruritic dermatitis such as atopic dermatitis.

Surfactant-induced chronic pruritus: Role of L-histidine decarboxylase expression and histamine production in epidermis.

Shampoo and cleansers containing anionic surfactants including sodium dodecyl sulphate (SDS) often cause pruritus in humans. Daily application of 1-10% SDS for 4 days induced hind-paw scratching (an itch-related behaviour) in a concentration-dependent manner, and 10% SDS also caused dermatitis, skin dryness, barrier disruption, and an increase in skin surface pH in mice. SDS-induced scratching was inhibited by the opioid receptor antagonist naloxone and the H histamine receptor antagonist terfenadine. Mast-cell deficiency did not inhibit SDS-induced scratching, although it almost completely depleted histamine in the dermis. Treatment with SDS increased the histamine content of the epidermis, but not that of the dermis. SDS treatment increased the gene expression and post-translation processing of L-histidine decarboxylase in the epidermis. The present results suggest that repeated application of SDS induces itch through increased production of epidermal histamine, which results from an increase in the gene expression and post-translation processing of L-histidine decarboxylase.