Itch is a common symptom in patients with skin and systemic diseases, but the effective treatment is limited. Here, we evaluated the anti-itch effects of the botulinum toxin type A (BoNT/A) using acute and chronic dry skin itch mouse models, which were induced by compound 48/80, chloroquine, and a mixture of acetone-diethylether-water treatment, respectively. Pretreatment of intradermal BoNT/A exerted long-term inhibitory effects on compound 48/80-induced and chloroquine-induced acute itch on days 1, 3, 7, and 14, but not on day 21, in mice. Furthermore, a single injection of BoNT/A reduced the expression of the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), and the transient receptor potential cation channel, subfamily A, member 1 (TRPA1) at both transcriptional and translational levels in the dorsal root ganglia (DRG) in mice. Pretreatment of BoNT/A also attenuated chronic itch induced by acetone-diethylether-water treatment and abolished the upregulation of TRPA1 in the DRG. Thus, it was suggested that downregulation of the expression of TRPA1 and TRPV1 in the DRG may contribute toward the long-term anti-itch effects of a single injection of BoNT/A in mice and BoNT/A treatment may serve as an alternative strategy for anti-itch therapy.

Long-term anti-itch effect of botulinum neurotoxin A is associated with downregulatio of TRPV1 and TRPA1 in the dorsal root ganglia in mice.

Atopic dermatitis (AD) is a Th2-dominated inflammatory skin disease characterized by epidermal thickening. Serum levels of IL-22, a cytokine known to induce keratinocyte proliferation, are elevated in AD, and Th22 cells infiltrate AD skin lesions. We show that application of antigen to mouse skin subjected to tape stripping, a surrogate for scratching, induces an IL-22 response that drives epidermal hyperplasia and keratinocyte proliferation in a mouse model of skin inflammation that shares many features of AD. DC-derived IL-23 is known to act on CD4(+) T cells to induce IL-22 production. However, the mechanisms that drive IL-23 production by skin DCs in response to cutaneous sensitization are not well understood. We demonstrate that IL-23 released by keratinocytes in response to endogenous TLR4 ligands causes skin DCs, which selectively express IL-23R, to up-regulate their endogenous IL-23 production and drive an IL-22 response in naive CD4(+) T cells that mediates epidermal thickening. We also show that IL-23 is released in human skin after scratching and polarizes human skin DCs to drive an IL-22 response, supporting the utility of IL-23 and IL-22 blockade in AD.

IL-23 induced in keratinocytes by endogenous TLR4 ligands polarizes dendritic cells to drive IL-22 responses to skin immunization

ABSTRACT:  Intractable and continuous itch sensations often accompany diseases such as atopic dermatitis, neurogenic lesions, uremia and cholestasis. Lysophosphatidic acid (LPA) is an itch mediator found in cholestatic itch patients and it induces acute itch and pain in experimental rodent models. However, the molecular mechanism by which LPA activates peripheral sensory neurons remains unknown. In this study, we used a cheek injection method in mice to reveal that LPA induced itch-related behaviours but not pain-related behaviours. The LPA-induced itch behaviour and cellular effects were dependent on transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1), which are important for itch signal transduction. We also found that, among the six LPA receptors, the LPA₅ receptor had the greatest involvement in itching. Furthermore, we demonstrated that phospholipase D (PLD) plays a critical role downstream of LPA₅ and that LPA directly and intracellularly activates TRPA1 and TRPV1. These results suggest a unique mechanism by which cytoplasmic LPA produced de novo could activate TRPA1 and TRPV1. We conclude that LPA-induced itch is mediated by LPA₅ , PLD, TRPA1 and TRPV1 signalling, and thus targeting TRPA1, TRPV1 or PLD could be effective for cholestatic itch interventions.

Lysophosphatidic acid-induced itch is mediated by signalling of LPA5 receptor, phospholipase D and TRPA1/TRPV1.

Coding of itch versus pain has been heatedly debated for decades. However, the current coding theories (labeled line, intensity, and selectivity theory) cannot accommodate all experimental observations. Here we identified a subset of spinal interneurons, labeled by gastrin-releasing peptide (Grp), that receive direct synaptic input from both pain and itch primary sensory neurons. When activated, these Grp⁺ neurons generated rarely seen, simultaneous robust pain and itch responses that were intensity dependent. Accordingly, we propose a “leaky gate” model in which Grp⁺ neurons transmit both itch and weak pain signals; however, upon strong painful stimuli, the recruitment of endogenous opioids works to close this gate, reducing overwhelming pain generated by parallel pathways. Consistent with our model, loss of these Grp⁺ neurons increased pain responses while itch was decreased. Our new model serves as an example of non-monotonic coding in the spinal cord and better explains observations in human psychophysical studies.

total_Leaky Gate Model; Intensity-Dependent Coding of Pain and Itch in the Spinal Cord

Background Interleukin-31 may play a role in the pathobiologic mechanism of atopic dermatitis and pruritus. We wanted to assess the efficacy and safety of nemolizumab (CIM331), a humanized antibody against interleukin-31 receptor A, in the treatment of atopic dermatitis. Methods In this phase 2, randomized, double-blind, placebo-controlled, 12-week trial, we assigned adults with moderate-to-severe atopic dermatitis that was inadequately controlled by topical treatments to receive subcutaneous nemolizumab (at a dose of 0.1 mg, 0.5 mg, or 2.0 mg per kilogram of body weight) or placebo every 4 weeks or an exploratory dose of 2.0 mg of nemolizumab per kilogram every 8 weeks. The primary end point was the percentage improvement from baseline in the score on the pruritus visual-analogue scale (on which a negative change indicates improvement) at week 12. Secondary end points included changes in the score on the Eczema Area and Severity Index (EASI, on which a negative change indicates improvement), and body-surface area of atopic dermatitis. Results Of 264 patients who underwent randomization, 216 (82%) completed the study. At week 12, among the patients who received nemolizumab every 4 weeks, changes on the pruritus visual-analogue scale were -43.7% in the 0.1-mg group, -59.8% in the 0.5-mg group, and -63.1% in the 2.0-mg group, versus -20.9% in the placebo group (P<0.01 for all comparisons). Changes on the EASI were -23.0%, -42.3%, and -40.9%, respectively, in the nemolizumab groups, versus -26.6% in the placebo group. Respective changes in body-surface area affected by atopic dermatitis were -7.5%, -20.0%, and -19.4% with nemolizumab, versus -15.7% with placebo. Among the patients receiving nemolizumab every 4 weeks, treatment discontinuations occurred in 9 of 53 patients (17%) in the 0.1-mg group, in 9 of 54 (17%) in the 0.5-mg group, and in 7 of 52 (13%) in the 2.0-mg group, versus in 9 of 53 (17%) in the placebo group. Conclusions In this phase 2 trial, nemolizumab at all monthly doses significantly improved pruritus in patients with moderate-to-severe atopic dermatitis, which showed the efficacy of targeting interleukin-31 receptor A. The limited size and length of the trial preclude conclusions regarding adverse events. (Funded by Chugai Pharmaceutical; XCIMA ClinicalTrials.gov number, NCT01986933 .).

Korean red ginseng (KRG) and ginsenosides exhibit diverse biological effects, including anti-inflammatory and anti-allergic. We aimed to investigate the therapeutic effect of KRG in a murine model of atopic dermatitis (AD) is mediated whether by diminishing the pruritus or by suppressing the inflammation. Thirty NC/Nga mice were randomly divided to 5 groups. AD-like skin lesions were induced by percutaneous challenge with 2,4,6-trinitro-1-chrolobenzene (TNCB) on the ears and backs of NC/Nga mice. KRG extract, evening primrose oil, cyclosporine, and phosphate-buffered saline were administered orally by a gastric tube. Each study group was also divided into scratching-permitted and scratching-restricted subgroups to evaluate the impact of scratching behavior on AD. The effects of KRG and the other agents were assessed by measuring the clinical severity score, ear thickness, extent of transepidermal water loss (TEWL), number of scratching movements, total systemic immunoglobulin E (IgE) and interleukin (IL)-31 levels, histologic changes of cutaneous lesions, and mRNA expression levels of tumor necrosis factor (TNF)-α, interferon (IFN)-γ, thymic stromal lymphopoietin (TSLP), and IL-31. KRG exerts therapeutic effects against AD by inhibiting the T helper 2 (Th2) mediated inflammation as well as by diminishing the itching sensation. Moreover, restricting scratching behavior suppresses the vicious cycle of itching and scratching, thus reducing clinical and systemic inflammation in our murine model of AD.

The challenge of translating findings from animal models to the clinic is well known. An example of this challenge is the striking effectiveness of neurokinin-1 receptor (NK-1R) antagonists in mouse models of inflammation coupled with their equally striking failure in clinical investigations in humans. Here, we provide an explanation for this dichotomy: Mas-related GPCRs (Mrgprs) mediate some aspects of inflammation that had been considered mediated by NK-1R. In support of this explanation, we show that conventional NK-1R antagonists have off-target activity on the mouse receptor MrgprB2 but not on the homologous human receptor MRGPRX2. An unrelated tripeptide NK-1R antagonist has dual activity on MRGPRX2. This tripeptide both suppresses itch in mice and inhibits degranulation from the LAD-2 human mast cell line elicited by basic secretagogue activation of MRGPRX2. Antagonists of Mrgprs may fill the void left by the failure of NK-1R antagonists.

Dual action of neurokinin-1 antagonists on Mas-related GPCRs.

Supporting Datas-Dual action of neurokinin-1 antagonists on Mas rekated Gpcr’s.

Nitroxyl (HNO) is a redox sibling of nitric oxide (NO) that targets distinct signalling pathways with pharmacological endpoints of high significance in the treatment of heart failure. Beneficial HNO effects depend, in part, on its ability to release calcitonin gene-related peptide (CGRP) through an unidentified mechanism. Here we propose that HNO is generated as a result of the reaction of the two gasotransmitters NO and H2S. We show that H2S and NO production colocalizes with transient receptor potential channel A1 (TRPA1), and that HNO activates the sensory chemoreceptor channel TRPA1 via formation of amino-terminal disulphide bonds, which results in sustained calcium influx. As a consequence, CGRP is released, which induces local and systemic vasodilation. H2S-evoked vasodilatatory effects largely depend on NO production and activation of HNO-TRPA1-CGRP pathway. We propose that this neuroendocrine HNO-TRPA1-CGRP signalling pathway constitutes an essential element for the control of vascular tone throughout the cardiovascular system.