Immunoglobulin E-independent activation of mast cell is mediated by Mrg receptors

Corydalis yanhusuo extract and its pharmacological substances alleviate food allergy by inhibiting mast cells activation via PLC/PKC/STAT3 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Food allergies have increasingly become a disease that affects global health and need for corresponding therapeutic drugs urgently. As a traditional Chinses medicine with a wide range of pharmacological effects, however, there was no clear research confirming therapeutic effect and pharmacological substances of Corydalis yanhusuo (YHS) on food allergies. Mast cells (MCs) are the main effector cells which mediate allergic and pseudo-allergic reactions.

MATERIALS AND METHODS

In this study, we investigated the effect of YHS extract on treating food allergy and its underlying mechanism. The inhibitory effect of YHS on MCs activation in vitro was evaluated by Ca2+ influx, degranulation, and cytokine release detection. The in vivo effect was investigated using the passive cutaneous anaphylaxis (PCA), active systemic allergy as well as OVA-induced food allergy mice. Western blot was performed to reveal the signaling pathway.

RESULTS

YHS extract showed an inhibitory effect on MCs activation and food allergy both in vitro and in vivo. PLC/PKC/STAT3 signaling pathway was suppressed by YHS extract in the disease. HPLC analysis revealed YHS extract contains corydaline and tetrahydropalmatine, and both compounds inhibited MCs activation induced by C48/80 in vitro.

CONCLUSION

YHS extract inhibited the MCs activation and food allergy via PLC/PKC/STAT3 pathway.

Chronic Spontaneous Urticaria: Current and Emerging Biologic Agents

Antihistamine refractory chronic spontaneous urticaria (CSU) has a prevalence of up to 50%. Anti-immunoglobulin E (IgE) therapies have revolutionized management of CSU, yet refractory cases persist, suggesting a role for biologic agents that impact alternative routes of mast cell stimulation independent of cross-linking at FcεR1. This review addresses anti-IgE and Th2-targeted therapies in the management of CSU. In addition, we explore novel treatments targeting alternative pathways of mast cell activation including MAS-related G protein-coupled receptor-X2 and sialic acid-binding immunoglobulin-like lectin-6, inhibiting intracellular signaling via Bruton's tyrosine kinase, and disrupting KIT activation by SCF.

Neuroplasticity and neuroimmune interactions in fatal asthma

BACKGROUND

Alteration of airway neuronal function and density and bidirectional interaction between immune cells and sensory peripheral nerves have been proposed to trigger and perpetuate inflammation that contribute to asthma severity. To date, few studies analysed neuroplasticity and neuroinflammation in tissue of asthmatic individuals. We hypothesized that the presence of these phenomena would be a pathological feature in fatal asthma.

METHODS

We have quantified the expression of the pan-neuronal marker PGP9.5 and the neuronal sensory-derived neuropeptide calcitonin gene-related peptide (CGRP) in the large airways of 12 individuals deceased due to an asthma attack and compared to 10 control lung samples. The proximity between nerve bundles to eosinophils, mast cells and CADM1+ cells was also quantified. We have additionally developed a hPSC-derived sensory neuron/mast cell co-culture model, from where mast cells were purified and differences in gene expression profile assessed.

RESULTS

Fatal asthma patients presented a higher PGP9.5 and CGRP positive area in the airways, indicating sensory neuroplasticity. Eosinophils, mast cells and CADM1+ cells were observed in close contact or touching the airway nerve bundles, and this was found to be statistically higher in fatal asthma samples. In vitro co-culture model showed that human mast cells adhere to sensory neurons and develop a distinct gene expression profile characterized by upregulated expression of genes related to heterophilic adhesion, activation and differentiation markers, such as CADM4, PTGS2, C-KIT, GATA2, HDC, CPA3, ATXN1 and VCAM1.

CONCLUSIONS

Our results support a significant role for neuroplasticity and neuroimmune interactions in fatal asthma, that could be implicated in the severity of the fatal attack. Accordingly, the presence of physical neuron and mast cell interaction leads to differential gene expression profile in the later cell type.

The MRGPRX2-substance P pathway regulates mast cell migration

Mast cells (MCs) are tissue-resident immune cells known to degranulate in response to FcεRI crosslinking or MRGPRX2 engagement. MCs are found close to nerves, but the mechanisms that regulate this privileged localization remain unclear. Here, we investigated MRGPRX2 expression patterns and specific activities in MCs. We show that MRGPRX2 expression is heterogeneous in human MC (hMC) progenitors and mature MCs. Substance P (SP) is a rapid and specific activator of MRGPRX2, and long-term supplementation of MCs with SP expands MRGPRX2-expressing cells. While high concentrations of SP induce rapid MC degranulation, low concentrations prompt immature MC chemotaxis. Lastly, we demonstrate that in inflammatory skin conditions like psoriasis, the number of MRGPRX2+ MCs is increased, and during in vitro skin reinnervation, MRGPRX2+ MCs preferentially reside in proximity to and migrate toward SP+ nerve fibers (NFs). This indicates that SP-MRGPRX2 signaling defines MC positioning and relocation within tissues and promotes immune cell-NF communication.

Mast cell modulation: A novel therapeutic strategy for abdominal pain in irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most prevalent gastrointestinal disorders characterized by recurrent abdominal pain and an altered defecation pattern. Chronic abdominal pain represents the hallmark IBS symptom and is reported to have the most bothersome impact on the patient's quality of life. Unfortunately, effective therapeutic strategies reducing abdominal pain are lacking, mainly attributed to a limited understanding of the contributing mechanisms. In the past few years, exciting new insights have pointed out that altered communication between gut immune cells and pain-sensing nerves acts as a hallmark driver of IBS-related abdominal pain. In this review, we aim to summarize our current knowledge on altered neuro-immune crosstalk as the main driver of altered pain signaling, with a specific focus on altered mast cell functioning herein, and highlight the relevance of targeting mast cell-mediated mechanisms as a novel therapeutic strategy for chronic abdominal pain in IBS patients.

CREB Is Critically Implicated in Skin Mast Cell Degranulation Elicited via FcεRI and MRGPRX2

Skin mast cells (MCs) mediate acute allergic reactions in the cutaneous environment and contribute to chronic dermatoses, including urticaria, and atopic or contact dermatitis. The cAMP response element binding protein (CREB), an evolutionarily well conserved transcription factor (TF) with over 4,000 binding sites in the genome, was recently found to form a feedforward loop with KIT, maintaining MC survival. The most selective MC function is degranulation with its acute release of prestored mediators. Herein, we asked whether CREB contributes to the expression and function of the degranulation-competent receptors FcεRI and MRGPRX2. Interference with CREB by pharmacological inhibition (CREBi, 666-15) or RNA interference only slightly affected the expression of these receptors, while KIT was strongly attenuated. Interestingly, MRGPRX2 surface expression moderately increased following CREB-knockdown, whereas MRGPRX2-dependent exocytosis simultaneously decreased. FcεRI expression and function were regulated consistently, although the effect was stronger at the functional level. Preformed MC mediators (tryptase, histamine, β-hexosaminidase) remained comparable following CREB attenuation, suggesting that granule synthesis did not rely on CREB function. Collectively, in contrast to KIT, FcεRI and MRGPRX2 moderately depend on unperturbed CREB function. Nevertheless, CREB is required to maintain MC releasability irrespective of stimulus, insinuating that CREB may operate by safeguarding the degranulation machinery. To our knowledge, CREB is the first factor identified to regulate MRGPRX2 expression and function in opposite direction. Overall, the ancient TF is an indispensable component of skin MCs, orchestrating not only survival and proliferation but also their secretory competence.

Mast cell signaling and its role in urticaria

Chronic urticaria is a mast cell (MC)-driven disease characterized by the development of itching wheals and/or angioedema. In the last decades, outstanding progress has been made in defining the mechanisms involved in MC activation, and novel activating and inhibitory receptors expressed in MC surface were identified and characterized. Besides an IgE-mediated activation through high-affinity IgE receptor cross-linking, other activating receptors, including Mas-related G-protein-coupled receptor-X2, C5a receptor, and protease-activated receptors 1 and 2 are responsible for MC activation. This would partly explain the reason some subgroups of chronic spontaneous urticaria (CSU), the most frequent form of urticaria in the general population, do not respond to IgE target therapies, requiring other therapeutic approaches for improving the management of the disease. In this review, we shed some light on the current knowledge of the immunologic and nonimmunologic mechanisms regulating MC activation in CSU, considering the complex inflammatory scenario underlying CSU pathogenesis, and novel potential MC-targeted therapies, including surface receptors and cytoplasmic signaling proteins.

Inhibition of mast cell degranulation by novel small molecule MRGPRX2 antagonists

BACKGROUND

Mas-related G protein-coupled receptor X2 (MRGPRX2) is a promiscuous receptor on mast cells that mediates IgE-independent degranulation and has been implicated in multiple mast cell-mediated disorders, including chronic urticaria, atopic dermatitis, and pain disorders. Although it is a promising therapeutic target, few potent, selective, small molecule antagonists have been identified, and functional effects of human MRGPRX2 inhibition have not been evaluated in vivo.

OBJECTIVE

We sought to identify and characterize novel, potent, and selective orally active small molecule MRGPRX2 antagonists for potential treatment of mast cell-mediated disease.

METHODS

Antagonists were identified using multiple functional assays in cell lines overexpressing human MRGPRX2, LAD2 mast cells, human peripheral stem cell-derived mast cells, and isolated skin mast cells. Skin mast cell degranulation was evaluated in Mrgprb2em(-/-) knockout and Mrgprb2em(MRGPRX2) transgenic human MRGPRX2 knock-in mice by assessment of agonist-induced skin vascular permeability. Ex vivo skin mast cell degranulation and associated histamine release was evaluated by microdialysis of human skin tissue samples.

RESULTS

MRGPRX2 antagonists potently inhibited agonist-induced MRGPRX2 activation and mast cell degranulation in all mast cell types tested in an IgE-independent manner. Orally administered MRGPRX2 antagonists also inhibited agonist-induced degranulation and resulting vascular permeability in MRGPRX2 knock-in mice. In addition, antagonist treatment dose dependently inhibited agonist-induced degranulation in ex vivo human skin.

CONCLUSIONS

MRGPRX2 small molecule antagonists potently inhibited agonist-induced mast cell degranulation in vitro and in vivo as well as ex vivo in human skin, supporting potential therapeutic utility as a novel treatment for multiple human diseases involving clinically relevant mast cell activation.

A Monoclonal Antibody to PACAP for Migraine Prevention

BACKGROUND

Targeting pituitary adenylate cyclase-activating polypeptide (PACAP) is a new avenue for treating migraine. The efficacy and safety of intravenous Lu AG09222, a humanized monoclonal antibody directed against the PACAP ligand, for migraine prevention are unclear.

METHODS

In a phase 2, double-blind, randomized, placebo-controlled trial, we enrolled adult participants (18 to 65 years of age) with migraine for whom two to four previous preventive treatments had failed to provide a benefit. The trial included a 4-week treatment period and an 8-week follow-up period. Participants were randomly assigned in a 2:1:2 ratio to receive a single-dose baseline infusion of 750 mg of Lu AG09222, 100 mg of Lu AG09222, or placebo. The primary end point was the mean change from baseline in the number of migraine days per month, during weeks 1 through 4, in the Lu AG09222 750-mg group as compared with the placebo group.

RESULTS

Of 237 participants enrolled, 97 received 750 mg of Lu AG09222, 46 received 100 mg of Lu AG09222, and 94 received placebo. The mean number of baseline migraine days per month was 16.7 in the overall population, and the mean change from baseline over weeks 1 through 4 was -6.2 days in the Lu AG09222 750-mg group, as compared with -4.2 days in the placebo group (difference, -2.0 days; 95% confidence interval, -3.8 to -0.3; P = 0.02). Adverse events with a higher incidence in the Lu AG09222 750-mg group than in the placebo group during the 12-week observation period included coronavirus disease 2019 (7% vs. 3%), nasopharyngitis (7% vs. 4%), and fatigue (5% vs. 1%).

CONCLUSIONS

In a phase 2 trial, a single intravenous infusion of 750 mg of Lu AG09222 showed superiority over placebo in reducing migraine frequency over the subsequent 4 weeks. (Funded by H. Lundbeck; HOPE ClinicalTrials.gov number, NCT05133323.).

Mrgprb2-dependent Mast Cell Activation Plays a Crucial Role in Acute Colitis

BACKGROUND & AIMS

Mast cells (MCs) are typically found at mucosal surfaces, where their immunoglobulin E (IgE)-dependent activation plays a central role in allergic diseases. Over the past years, signaling through Mas-related G protein-coupled receptor b2 (Mrgprb2) in mice and MRGPRX2 in humans has gained a lot of interest as an alternative MC activation pathway with high therapeutic potential. The aim of this study was to explore the relevance of such IgE-independent, Mrgprb2-mediated signaling in colonic MCs in the healthy and acutely inflamed mouse colon.

METHODS

Mrgprb2 expression and functionality was studied using a genetic labeling strategy combined with advanced microscopic imaging. Furthermore, Mrgprb2 knockout (Mrgprb2-/-) mice were used to determine the role of this pathway in a preclinical dextran sodium sulphate (DSS) colitis model.

RESULTS

We found that Mrgprb2 acts as a novel MC degranulation pathway in a large subset of connective tissue MCs in the mouse distal colon. Acute DSS colitis induced a pronounced increase of Mrgprb2-expressing MCs, which were found in close association with Substance P-positive nerve fibers. Loss of Mrgprb2-mediated signaling impaired DSS-induced neutrophil influx and significantly impacted on acute colitis progression.

CONCLUSIONS

Our findings uncover a novel, IgE-independent MC degranulation pathway in the mouse colon that plays a central role in acute colitis pathophysiology, mainly by safeguarding acute colitis progression and severity in mice. This pseudo allergic, Mrgprb2-induced signaling is part of a hitherto unconsidered colonic neuro-immune pathway and might have significant potential for the further development of effective therapeutic treatment strategies for gastrointestinal disorders, such as ulcerative colitis.

MrgX2-targeted ligand screening from Artemisia capillaris Thunb. extract and receptor-ligand interaction analysis based on MrgX2-HALO-tag/CMC

Artemisia capillaris Thunb. (A. capillaris) is a well-known traditional Chinese herbal medicine with a wide range of pharmacological effects, such as soothing the liver and gallbladder, heat clearance, and detoxifying. Hence, its extract is commonly added to various traditional Chinese medicine formulas. Traditional Chinese medicine injection (TCMI) is a mature pharmaceutical dosage form developed using TCM theory combined with modern science and technology. Notably, allergic reactions, especially pseudo‑allergic reactions (PARs), greatly limited the use of these injections. Therefore, screening pseudo‑allergic components in A. capillaris extract is clinically significant. In the present study, we proposed a two-dimensional screening and identification system based on mas-related G protein-coupled receptor X2-HALO-tag/cell membrane chromatography (MrgX2-HALO-tag/CMC) high performance liquid chromatography mass spectrometry (HPLC-MS); seven potential active components were screened from 75 % ethanol extract of A. capillaris: NCA, CA, CCA, 1,3-diCQA, ICA-B, ICA-A, and ICA-C. The receptor-ligand interactions between these seven compounds and MrgX2 protein were analyzed using frontal analysis and molecular docking technology. Furthermore, a mast cell degranulation-related assay was used to assess the pseudo‑allergic activity of these compounds. The screened compounds can serve as ligands of MrgX2, and this study provides a research basis for pseudo‑allergic reactions caused by TCMIs containing A. capillaris.

Mas-related G protein-coupled receptors in gastrointestinal dysfunction and inflammatory bowel disease: A review

Inflammatory bowel disease (IBD) is a chronic debilitating condition, hallmarked by persistent inflammation of the gastrointestinal tract. Despite recent advances in clinical treatments, the aetiology of IBD is unknown, and a large proportion of patients are refractory to pharmacotherapy. Understanding IBD immunopathogenesis is crucial to discern the cause of IBD and optimise treatments. Mas-related G protein-coupled receptors (Mrgprs) are a family of approximately 50 G protein-coupled receptors that were first identified over 20 years ago. Originally known for their expression in skin nociceptors and their role in transmitting the sensation of itch in the periphery, new reports have described the presence of Mrgprs in the gastrointestinal tract. In this review, we consider the impact of these findings and assess the evidence that suggests that Mrgprs may be involved in the disrupted homeostatic processes that contribute to gastrointestinal disorders and IBD. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Inhibitory effect of phellodendrine on C48/80-induced allergic reaction in vitro and in vivo

The incidence of allergic reactions has risen steadily in recent years, prompting growing interest in the identification of efficacious and safe natural compounds that can prevent or treat allergic diseases. Phellodendron amurense Rupr. has long been applied as a treatment for allergic diseases, whose primary component is phellodendrine. However, the efficacy of phellodendrine as a treatment for allergic diseases remains to be assessed. Mast cells are the primary effectors of allergic reactions, which are not only activated by IgE-dependent pathway, but also by IgE-independent pathways via human MRGPRX2, rat counterpart MRGPRB3. As such, this study explored the effect and mechanism of phellodendrine through this family receptors in treating allergic diseases in vitro and in vivo. These analyses revealed that phellodendrine administration was sufficient to protect against C48/80-induced foot swelling and Evans blue exudation in mice, and suppressed C48/80-induced RBL-2H3 rat basophilic leukemia cells degranulation, and β-HEX, HIS, IL-4, and TNF-α release. Moreover, phellodendrine could reduce the mRNA expression of MRGPRB3 and responsiveness of MRGPRX2 by altering its structure. It was able to decrease Ca2+ levels, phosphorylation levels of CaMK, PLCβ1, PKC, ERK, JNK, p38, and p65, and inhibit the degradation of IκB-α. These analyses indicate that berberine inhibits the activation of PLC and downregulates the release of Ca2+ in the endoplasmic reticulum by altering the conformation of MRGPRB3/MRGPRX2 protein, thereby inhibiting the activation of PKC and subsequently inhibiting downstream MAPK and NF-κB signaling, ultimately suppressing allergic reactions. There may thus be further value in studies focused on developing phellodendrine as a novel anti-allergic drug.

An optimized method for IgE-mediated degranulation of human lung mast cells

Background

Mast cells are critically involved in IgE-mediated diseases, e.g., allergies and asthma. Human mast cells are heterogeneous, and mast cells from different anatomical sites have been shown to respond differently to certain stimuli and drugs. The origin of the mast cells is therefore of importance when setting up a model system, and human lung mast cells are highly relevant cells to study in the context of asthma. We therefore set out to optimize a protocol of IgE-mediated activation of human lung mast cells.

Methods

Human lung mast cells were extracted from lung tissue obtained from patients undergoing pulmonary resection by enzyme digestion and mechanical disruption followed by CD117 magnetic-activated cell sorting (MACS) enrichment. Different culturing media and conditions for the IgE-mediated degranulation were tested to obtain an optimized method.

Results

IgE crosslinking of human lung mast cells cultured in serum-free media gave a stronger response compared to cells cultured with 10% serum. The addition of stem cell factor (SCF) did not enhance the degranulation. However, when the cells were put in fresh serum-free media 30 minutes prior to the addition of anti-IgE antibodies, the cells responded more vigorously. Maximum degranulation was reached 10 minutes after the addition of anti-IgE. Both CD63 and CD164 were identified as stable markers for the detection of degranulated mast cells over time, while the staining with anti-CD107a and avidin started to decline 10 minutes after activation. The levels of CD203c and CD13 did not change in activated cells and therefore cannot be used as degranulation markers of human lung mast cells.

Conclusions

For an optimal degranulation response, human lung mast cells should be cultured and activated in serum-free media. With this method, a very strong and consistent degranulation response with a low donor-to-donor variation is obtained. Therefore, this model is useful for further investigations of IgE-mediated mast cell activation and exploring drugs that target human lung mast cells, for instance, in the context of asthma.

PACAP38/mast-cell-specific receptor axis mediates repetitive stress-induced headache in mice

BACKGROUND

Pain, an evolutionarily conserved warning system, lets us recognize threats and motivates us to adapt to those threats. Headache pain from migraine affects approximately 15% of the global population. However, the identity of any putative threat that migraine or headache warns us to avoid is unknown because migraine pathogenesis is poorly understood. Here, we show that a stress-induced increase in pituitary adenylate cyclase-activating polypeptide-38 (PACAP38), known as an initiator of allosteric load inducing unbalanced homeostasis, causes headache-like behaviour in male mice via mas-related G protein-coupled receptor B2 (MrgprB2) in mast cells.

METHODS

The repetitive stress model and dural injection of PACAP38 were performed to induce headache behaviours. We assessed headache behaviours using the facial von Frey test and the grimace scale in wild-type and MrgprB2-deficient mice. We further examined the activities of trigeminal ganglion neurons using in vivo Pirt-GCaMP Ca2+ imaging of intact trigeminal ganglion (TG).

RESULTS

Repetitive stress and dural injection of PACAP38 induced MrgprB2-dependent headache behaviours. Blood levels of PACAP38 were increased after repetitive stress. PACAP38/MrgprB2-induced mast cell degranulation sensitizes the trigeminovascular system in dura mater. Moreover, using in vivo intact TG Pirt-GCaMP Ca2+ imaging, we show that stress or/and elevation of PACAP38 sensitized the TG neurons via MrgprB2. MrgprB2-deficient mice showed no sensitization of TG neurons or mast cell activation. We found that repetitive stress and dural injection of PACAP38 induced headache behaviour through TNF-a and TRPV1 pathways.

CONCLUSIONS

Our findings highlight the PACAP38-MrgprB2 pathway as a new target for the treatment of stress-related migraine headache. Furthermore, our results pertaining to stress interoception via the MrgprB2/PACAP38 axis suggests that migraine headache warns us of stress-induced homeostatic imbalance.

MRGPRX2 antagonist GE1111 attenuated DNFB-induced atopic dermatitis in mice by reducing inflammatory cytokines and restoring skin integrity

Introduction

Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterised by itching, erythema, and epidermal barrier dysfunction. The pathogenesis of AD is complex and multifactorial; however,mast cell (MC) activation has been reported to be one of the crucial mechanisms in the pathogenesis of AD. The MC receptor Mas related G protein-coupled receptor-X2 (MRGPRX2) has been identified as a prominent alternative receptor to the IgE receptor in causing MC activation and the subsequent release of inflammatory mediators. The current study aimed to evaluate the therapeutic effect of a novel small molecule MRGPRX2 antagonist GE1111 in AD using in vitro and in vivo approaches.

Methods

We developed an in vitro cell culture disease model by using LAD-2 MC, HaCaT keratinocytes and RAW 264.7 macrophage cell lines. We challenged keratinocytes and macrophage cells with CST-14 treated MC supernatant in the presence and absence of GE1111 and measured the expression of tight junction protein claudin 1, inflammatory cytokines and macrophage phagocytosis activity through immunohistochemistry, western blotting, RT-qPCR and fluorescence imaging techniques. In addition to this, we developed a DFNB-induced AD model in mice and evaluated the protective effect and underlying mechanism of GE1111.

Results and Discussion

Our in vitro findings demonstrated a potential therapeutic effect of GE1111, which inhibits the expression of TSLP, IL-13, MCP-1, TNF-a, and IL-1ß in MC and keratinocytes. In addition to this, GE1111 was able to preserve the expression of claudin 1 in keratinocytes and the phagocytotic activity of macrophage cells. The in vivo results demonstrated that GE1111 treatment significantly reduced phenotypic changes associated with AD (skin thickening, scaling, erythema and epidermal thickness). Furthermore, immunohistochemical analysis demonstrated that GE1111 treatment preserved the expression of the tight junction protein Involucrin and reduced the expression of the inflammatory mediator periostin in the mouse model of AD. These findings were supported by gene and protein expression analysis, where GE1111 treatment reduced the expression of TSLP, IL-13, and IL-1ß, as well as downstream signalling pathways of MRGPRX2 in AD skin lesions. In conclusion, our findings provide compelling in vitro and in vivo evidence supporting the contribution of MRGPRX2-MC interaction with keratinocytes and macrophages in the pathogenesis of AD.

Mast cell degranulation and bradykinin-induced angioedema - searching for the missing link

Initiation of the bradykinin generation cascade is responsible for the occurrence of attacks in some types of angioedema without wheals. Hereditary angioedema due to C1 inhibitor deficiency (HAE-C1-INH) is one such clinical entity. In this paper, we explore the existing evidence that mast cells (MCs) degranulation may contribute to the activation of the kallikrein-kinin system cascade, followed by bradykinin formation and angioedema. We present the multidirectional effects of MC-derived heparin and other polyanions on the major components of the kinin-kallikrein system, particularly on the factor XII activation. Although, bradykinin- and histamine-mediated symptoms are distinct clinical phenomena, they share some common features, such as some similar triggers and a predilection to occur at sites where mast cells reside, namely the skin and mucous membranes. In addition, recent observations indicate a high incidence of hypersensitivity reactions associated with MC degranulation in the HAE-C1-INH patient population. However, not all of these can be explained by IgE-dependent mechanisms. Mast cell-related G protein-coupled receptor-X2 (MRGPRX2), which has recently attracted scientific interest, may be involved in the activation of MCs through a different pathway. Therefore, we reviewed MRGPRX2 ligands that HAE-C1-INH patients may be exposed to in their daily lives and that may affect MCs degranulation. We also discussed the known inter- and intra-individual variability in the course of HAE-C1-INH in relation to factors responsible for possible variability in the strength of the response to MRGPRX2 receptor stimulation. The above issues raise several questions for future research. It is not known to what extent a prophylactic or therapeutic intervention targeting the pathways of one mechanism (mast cell degranulation) may affect the other (bradykinin production), or whether the number of mast cells at a specific body site and their reactivity to triggers such as pressure, allergens or MRGPRX2 agonists may influence the occurrence of HAE-C1-INH attacks at that site.

Fragment-Based Design, Synthesis, and Characterization of Aminoisoindole-Derived Furin Inhibitors

A 1H-isoindol-3-amine was identified as suitable P1 group for the proprotein convertase furin using a crystallographic screening with a set of 20 fragments known to occupy the S1 pocket of trypsin-like serine proteases. Its binding mode is very similar to that observed for the P1 group of benzamidine-derived peptidic furin inhibitors suggesting an aminomethyl substitution of this fragment to obtain a couplable P1 residue for the synthesis of substrate-analogue furin inhibitors. The obtained inhibitors possess a slightly improved picomolar inhibitory potency compared to their benzamidine-derived analogues. The crystal structures of two inhibitors in complex with furin revealed that the new P1 group is perfectly suited for incorporation in peptidic furin inhibitors. Selected inhibitors were tested for antiviral activity against respiratory syncytial virus (RSV) and a furin-dependent influenza A virus (SC35M/H7N7) in A549 human lung cells and demonstrated an efficient inhibition of virus activation and replication at low micromolar or even submicromolar concentrations. First results suggest that the Mas-related G-protein coupled receptor GPCR-X2 could be a potential off-target for certain benzamidine-derived furin inhibitors.

A new MAS-related G protein-coupled receptor X2 cell membrane chromatography analysis model based on HALO-tag technology and its applications

Cell membrane chromatography (CMC) is an effective method for studying receptors with multiple transmembrane structure such as MAS-related G protein-coupled receptor X2 (MrgX2). CMC relies on the maintenance of the complete biological structure of a membrane receptor; however, it needs to be further improved to obtain a more convenient and stable CMC model. In the present study, the haloalkane dehalogenase protein tag (HALO-tag) technology was used to construct a new MrgX2/CMC model. The fusion receptors of MrgX2 with HALO-tag at the C terminus were expressed in HEK293 cells. The silica gel was modified with a substrate of HALO-tag (chloroalkanes) via one-step acylation for the rapid capture of fusion receptors. The new CMC model (MrgX2-HALO-tag/CMC model) was not only quicker to prepare but also more stable and had a longer lifespan than a previous MrgX2-SNAP-tag/CMC model. In combination with the high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) system, the MrgX2-HALO-tag/CMC model was used to screen and identify bioactive components in traditional Chinese medicine. Using this combination, sanggenon C and morusin were identified from Mori Cortex as anti-pseudo-allergic components. The MrgX2-HALO-tag/CMC model alone was also applied to analyze ligand-receptor interaction. The affinity order of four ligands to MrgX2 was as follows: desipramine < imipramine < amitriptyline < clomipramine. This was consistent with the results obtained using the MrgX2-SNAP-tag/CMC model. The MrgX2-HALO-tag/CMC model provides ideas and application prospects for the immobilization of cell membrane that contains receptors with more transmembrane structures.

Mechanisms of histamine release from mast cells beyond the high affinity IgE receptor in severe chronic spontaneous urticaria

There is growing evidence suggesting that in a subset of patients with severe chronic urticaria [CSU] mast cells are activated via mechanisms that bypass the high affinity IgE receptor. This might explain why some patients do not respond at all to anti-IgE therapy [omalizumab]. The present article reviews the pathogenic mechanisms able to lead to histamine release from mast cells described so far in patients with CSU. These include the activation of the coagulation cascade, the activation of the complement system, the activation of the MRGPRX2 receptor, and the platelet activating factor vicious circle. The article suggests some possible interpretations for the clinical events occurring in this specific subset of patients.

Beyond Allergies-Updates on The Role of Mas-Related G-Protein-Coupled Receptor X2 in Chronic Urticaria and Atopic Dermatitis

Mast cells (MCs) are an important part of the immune system, responding both to pathogens and toxins, but they also play an important role in allergic diseases, where recent data show that non-IgE-mediated activation is also of relevance, especially in chronic urticaria (CU) and atopic dermatitis (AD). Skin MCs express Mas-related G-protein-coupled receptor X2 (MRGPRX2), a key protein in non-IgE-dependent MC degranulation, and its overactivity is one of the triggering factors for the above-mentioned diseases, making MRGPRX2 a potential therapeutic target. Reviewing the latest literature revealed our need to focus on the discovery of MRGPRX2 activators as well as the ongoing vast research towards finding specific MRGPRX2 inhibitors for potential therapeutic approaches. Most of these studies are in their preliminary stages, with one drug currently being investigated in a clinical trial. Future studies and improved model systems are needed to verify whether any of these inhibitors may have the potential to be the next therapeutic treatment for CU, AD, and other pseudo-allergic reactions.

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.

Mast-cell-specific receptor mediates alcohol-withdrawal-associated headache in male mice

Rehabilitation from alcohol addiction or abuse is hampered by withdrawal symptoms including severe headaches, which often lead to rehabilitation failure. There is no appropriate therapeutic option available for alcohol-withdrawal-induced headaches. Here, we show the role of the mast-cell-specific receptor MrgprB2 in the development of alcohol-withdrawal-induced headache. Withdrawing alcohol from alcohol-acclimated mice induces headache behaviors, including facial allodynia, facial pain expressions, and reduced movement, which are symptoms often observed in humans. Those behaviors were absent in MrgprB2-deficient mice during alcohol withdrawal. We observed in vivo spontaneous activation and hypersensitization of trigeminal ganglia (TG) neurons in alcohol-withdrawal WT mice, but not in alcohol-withdrawal MrgprB2-deficient mice. Increased mast cell degranulation by alcohol withdrawal in dura mater was dependent on the presence of MrgprB2. The results indicate that alcohol withdrawal causes headache via MrgprB2 of mast cells in dura mater, suggesting that MrgprB2 is a potential target for treating alcohol-withdrawal-related headaches.

Cultures of Human Skin Mast Cells, an Attractive In Vitro Model for Studies of Human Mast Cell Biology

Studies of mast cell biology are dependent on relevant and validated in vitro models. Here, we present detailed information concerning the phenotype of both freshly isolated human skin mast cells (MCs) and of in vitro cultures of these cells that were obtained by analyzing their total transcriptome. Transcript levels of MC-related granule proteins and transcription factors were found to be remarkably stable over a 3-week culture period. Relatively modest changes were also seen for important cell surface receptors including the high-affinity receptor for IgE, FCER1A, the low-affinity receptor for IgG, FCGR2A, and the receptor for stem cell factor, KIT. FCGR2A was the only Fc receptor for IgG expressed by these cells. The IgE receptor increased by 2-5-fold and an approximately 10-fold reduction in the expression of FCGR2A was observed most likely due to the cytokines, SCF and IL-4, used for expanding the cells. Comparisons of the present transcriptome against previously reported transcriptomes of mouse peritoneal MCs and mouse bone marrow-derived MCs (BMMCs) revealed both similarities and major differences. Strikingly, cathepsin G was the most highly expressed granule protease in human skin MCs, in contrast to the almost total absence of this protease in both mouse MCs. Transcript levels for the majority of cell surface receptors were also very low compared to the granule proteases in both mouse and human MCs, with a difference of almost two orders of magnitude. An almost total absence of T-cell granzymes was observed in human skin MCs, indicating that granzymes have no or only a minor role in human MC biology. Ex vivo skin MCs expressed high levels of selective immediate early genes and transcripts of heat shock proteins. In validation experiments, we determined that this expression was an inherent property of the cells and not the result of the isolation process. Three to four weeks in culture results in an induction of cell growth-related genes accompanying their expansion by 6-10-fold, which increases the number of cells for in vitro experiments. Collectively, we show that cultured human skin MCs resemble their ex vivo equivalents in many respects and are a more relevant in vitro model compared to mouse BMMCs for studies of MC biology, in particular human MC biology.

The pharmacotherapeutic management of allergic rhinitis in people with asthma

INTRODUCTION

Up to 90% of asthmatic patients have comorbid allergic rhinitis (AR). Although appropriate therapy of AR can improve asthma symptoms and management, AR is often underdiagnosed and under-treated in asthmatics.A non-systematic literature research was conducted on AR as a comorbidity and risk factor of asthma. Latest international publications in medical databases, international guidelines, and the Internet were reviewed.

AREAS COVERED

Based on the conducted literature research there is proved evidence of the necessity of diagnosis and treatment of AR in patients with asthma because it affects health care utilization. Therefore, it is recommended in national and global guidelines.

EXPERT OPINION

AR increases the risk of asthma development and contributes to the severity of an existing asthma. Early treatment of AR with drugs as intranasal steroids, antihistamines, leukotriene receptor antagonists, and especially allergen-specific immunotherapy can reduce the risk of asthma development and the concomitant medication use in addition to severity of symptoms in AR and asthma.

The Underlying Rab Network of MRGPRX2-Stimulated Secretion Unveils the Impact of Receptor Trafficking on Secretory Granule Biogenesis and Secretion

MRGPRX2, the human member of the MAS-related G-protein-coupled receptors (GPCRs), mediates the immunoglobulin E (IgE)-independent responses of a subset of mast cells (MCs) that are associated with itch, pain, neurogenic inflammation, and pseudoallergy to drugs. The mechanisms underlying the responses of MRGPRX2 to its multiple and diverse ligands are still not completely understood. Given the close association between GPCR location and function, and the key role played by Rab GTPases in controlling discrete steps along vesicular trafficking, we aimed to reveal the vesicular pathways that directly impact MRGPRX2-mediated exocytosis by identifying the Rabs that influence this process. For this purpose, we screened 43 Rabs for their functional and phenotypic impacts on MC degranulation in response to the synthetic MRGPRX2 ligand compound 48/80 (c48/80), which is often used as the gold standard of MRGPRX2 ligands, or to substance P (SP), an important trigger of neuroinflammatory MC responses. Results of this study highlight the important roles played by macropinocytosis and autophagy in controlling MRGPRX2-mediated exocytosis, demonstrating a close feedback control between the internalization and post-endocytic trafficking of MRGPRX2 and its triggered exocytosis.

Neuroimmune communication in allergic rhinitis

The prevalence rate of allergic rhinitis (AR) is high worldwide. The inhalation of allergens induces AR, which is an immunoglobulin E-mediated and type 2 inflammation-driven disease. Recently, the role of neuroimmune communication in AR pathogenesis has piqued the interest of the scientific community. Various neuropeptides, such as substance P (SP), vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), nerve growth factor (NGF), and neuromedin U (NMU), released via "axon reflexes" or "central sensitization" exert regulatory effects on immune cells to elicit "neurogenic inflammation," which contributes to nasal hyperresponsiveness (NHR) in AR. Additionally, neuropeptides can be produced in immune cells. The frequent colocalization of immune and neuronal cells at certain anatomical regions promotes the establishment of neuroimmune cell units, such as nerve-mast cells, nerve-type 2 innate lymphoid cells (ILC2s), nerve-eosinophils and nerve-basophils units. Receptors expressed both on immune cells and neurons, such as TRPV1, TRPA1, and Mas-related G protein-coupled receptor X2 (MRGPRX2) mediate AR pathogenesis. This review focused on elucidating the mechanisms underlying neuroimmune communication in AR.

A Modified Basophil Activation Test for the Clinical Management of Immediate Hypersensitivity Reactions to Paclitaxel: A Proof-of-Concept Study

Immediate hypersensitivity reactions (iHSRs) to taxanes are observed in 6% and 4% of gynecologic and breast cancer patients, respectively. Drug desensitization is the only option, as no comparable alternative therapy is available. Surfactants in the taxane formulation have been implicated in the immunopathogenesis of iHSRs, although sporadic skin test (ST) positivity and iHSRs to nab-paclitaxel have suggested the involvement of the taxane moiety and/or IgE-mediated pathomechanisms. In vitro diagnostic tests might offer insights into mechanisms underlying iHSRs to taxanes. The aim of the present study was to address this unmet need by developing a novel basophil activation test (BAT). The study included patients (n = 31) undergoing paclitaxel/carboplatin therapy. Seventeen patients presented with iHSRs to paclitaxel (iHSR-Taxpos), and eleven were tolerant (iHSR-Taxneg). Fourteen patients presented with iHSRs to carboplatin (iHSR-Plpos), and fourteen were tolerant (iHSR-Plneg). The BAT median stimulation index (SI) values were 1.563 (range, 0.02-4.11; n = 11) and -0.28 (range -4.88-0.07, n = 11) in iHSR-Taxpos and iHSR-Taxneg, respectively. The BAT median SI values were 4.45 (range, 0.1-26.7; n = 14) and 0 (range, -0.51-1.65; n = 12) in iHSR-Plpos and iHSR-Plneg, respectively. SI levels were not associated with iHSR severity grading. Comparing BAT results in iHSR-Taxpos and iHSR-Taxneg showed the area under the receiver operator characteristic (ROC) curve to be 0.9752 (p = 0.0002). The cutoff calculated by the maximized likelihood ratio identified 90.91% of iHSR-Taxpos patients and 90.91% of iHSR-Taxneg patients. Comparing BAT results for iHSR-Plpos and iHSR-Plneg showed the area under the ROC curve to be 0.9286 (p = 0.0002). The cutoff calculated by the maximized likelihood ratio identified 78.57% of iHSR-Plpos patients and 91.67% of iHSR-Plneg patients. Most iHSR-Taxpos patients for which ST was available (10/11) scored ST-negative and BAT-positive, whereas most iHSR-Plpos patients for which ST was available (14/14) scored both BAT- and ST-positive. This suggested the intervention of non-IgE-mediated mechanisms in iHSR-Taxpos patients. Consistent with this view, an in silico molecular docking analysis predicted the high affinity of paclitaxel to the degranulation-competent MRGPRX2 receptor. This hypothesis warrants further in vitro investigations. In conclusion, the present study provides preliminary proof-of-concept evidence that this novel BAT has potential utility in understanding mechanisms underlying iHSRs to taxanes.

Peripheral signaling pathways contributing to non-histaminergic itch in humans

BACKGROUND

Chronic itch (chronic pruritus) is a major therapeutic challenge that remains poorly understood despite the extensive recent analysis of human pruriceptors. It is unclear how the peripheral nervous system differentiates the signaling of non-histaminergic itch and pain.

METHODS

Here we used psychophysical analysis and microneurography (single nerve fiber recordings) in healthy human volunteers to explore the distinct signaling mechanisms of itch, using the pruritogens β-alanine, BAM 8-22 and cowhage extract.

RESULTS

The mode of application (injection or focal application using inactivated cowhage spicules) influenced the itch/pain ratio in sensations induced by BAM 8-22 and cowhage but not β-alanine. We found that sensitizing pre-injections of prostaglandin E2 increased the pain component of BAM 8-22 but not the other pruritogens. A-fibers contributed only to itch induced by β-alanine. TRPV1 and TRPA1 were necessary for itch signaling induced by all three pruritogens. In single-fiber recordings, we found that BAM 8-22 and β-alanine injection activated nearly all CM-fibers (to different extents) but not CMi-fibers, whereas cowhage extract injection activated only 56% of CM-fibers but also 25% of CMi-fibers. A "slow bursting discharge pattern" was evoked in 25% of CM-fibers by β-alanine, in 35% by BAM 8-22, but in only 10% by cowhage extract.

CONCLUSION

Our results indicate that no labeled line exists for these pruritogens in humans. A combination of different mechanisms, specific for each pruritogen, leads to itching sensations rather than pain. Notably, non-receptor-based mechanisms such as spatial contrast or discharge pattern coding seem to be important processes. These findings will facilitate the discovery of therapeutic targets for chronic pruritus, which are unlikely to be treated effectively by single receptor blockade.

MRGPRX2, drug pseudoallergies, inflammatory diseases, mechanisms and distinguishing MRGPRX2- and IgE/FcεRI-mediated events

MRGPRX2, a novel Gaq -coupled human mast cell receptor, mediates non-immune adverse reactions without the involvement of antibody priming. Constitutively expressed by human skin mast cells, MRGPRX2 modulates cell degranulation producing pseudoallergies manifesting as itch, inflammation and pain. The term pseudoallergy is defined in relation to adverse drug reactions in general and immune/non-immune-mediated reactions in particular. A list of drugs with MRGPRX2 activity is presented, including a detailed examination of three important and widely used approved therapies: neuromuscular blockers, quinolones and opioids. For the clinician, the significance of MRGPRX2 is considered as an aid in distinguishing and ultimately identifying specific immune and non-immune inflammatory reactions. Anaphylactoid/anaphylactic reactions, neurogenic inflammation and inflammatory diseases with a clear or strongly suspected association with MRGPRX2 activation are examined. Inflammatory diseases include chronic urticaria, rosacea, atopic dermatitis, allergic contact dermatitis, mastocytosis, allergic asthma, ulcerative colitis and rheumatoid arthritis. MRGPRX2- and allergic IgE/FcεRI-mediated reactions may be clinically similar. Importantly, the usual testing procedures do not distinguish the two mechanisms. Currently, identification of MRGPRX2 activation and diagnosis of pseudoallergic reactions is generally viewed as a process of exclusion once other non-immune and immune processes, particularly IgE/FcεRI-mediated degranulation of mast cells, are ruled out. This does not take into account that MRGPRX2 signals via β-arrestin, which can be utilized to detect MRGPRX2 activation by employing MRGPRX2 transfected cells to assess MRGPRX2 activation via two pathways, the G-protein-independent β-arrestin pathway and the G-protein-dependent Ca2+ pathway. Testing procedures, interpretations for distinguishing mechanisms, patient diagnosis, agonist identification and drug safety evaluations are addressed.

Human Mast Cells Upregulate Cathepsin B, a Novel Marker of Itch in Psoriasis

Mast cells (MCs) contribute to skin inflammation. In psoriasis, the activation of cutaneous neuroimmune networks commonly leads to itch. To dissect the unique contribution of MCs to the cutaneous neuroinflammatory response in psoriasis, we examined their density, distribution, relation to nerve fibres and disease severity, and molecular signature by comparing RNA-seq analysis of MCs isolated from the skin of psoriasis patients and healthy volunteers. In involved psoriasis skin, MCs and Calcitonin Gene-Related Peptide (CGRP)-positive nerve fibres were spatially associated, and the increase of both MC and nerve fibre density correlated with disease severity. Gene set enrichment analysis of differentially expressed genes in involved psoriasis skin showed significant representation of neuron-related pathways (i.e., regulation of neuron projection along with dendrite and dendritic spine morphogenesis), indicating MC engagement in neuronal development and supporting the evidence of close MC-nerve fibre interaction. Furthermore, the analysis of 208 identified itch-associated genes revealed that CTSB, TLR4, and TACR1 were upregulated in MCs in involved skin. In both whole-skin published datasets and isolated MCs, CTSB was found to be a reliable indicator of the psoriasis condition. Furthermore, cathepsin B+ cells were increased in psoriasis skin and cathepsin B+ MC density correlated with disease severity. Therefore, our study provides evidence that cathepsin B could serve as a common indicator of the MC-dependent itch signature in psoriasis.

Mast Cells and Basophils in IgE-Independent Anaphylaxis

Anaphylaxis is a life-threatening or even fatal systemic hypersensitivity reaction. The incidence of anaphylaxis has risen at an alarming rate in the past decades in the majority of countries. Generally, the most common causes of severe or fatal anaphylaxis are medication, foods and Hymenoptera venoms. Anaphylactic reactions are characterized by the activation of mast cells and basophils and the release of mediators. These cells express a variety of receptors that enable them to respond to a wide range of stimulants. Most studies of anaphylaxis focus on IgE-dependent reactions. The mast cell has long been regarded as the main effector cell involved in IgE-mediated anaphylaxis. This paper reviews IgE-independent anaphylaxis, with special emphasis on mast cells, basophils, anaphylactic mediators, risk factors, triggers, and management.

PACAP activates MRGPRX2 on meningeal mast cells to drive migraine-like pain

Migraine ranks among the most prevalent disorders worldwide, leading to disability and decreased quality of life in patients. Recently, neurogenic inflammation has been recognized as a potential underlying pathology contributing to the migraine pain pathway. Mast cells reside in the meninges and have been implicated in contributing to the pathophysiology of migraine. Here we report for the first time that the mouse Mas-Related G-protein-coupled Receptor B2 (MrgprB2), is expressed on meningeal connective tissue mast cells and contributes to Pituitary Adenylate Cyclase Activating Peptide (PACAP)-induced migraine-like pain behavior. We also found that PACAP was able to dose-dependently lead to enzyme release from human mast cells via activation of MRGPRX2; the human homolog of MrgprB2. Using a transgenic MRGPRX2 mouse, we observed significant increases in PACAP-induced migraine-like pain behavior in MRGPRX2+ mice vs mice lacking the receptor. These results reveal both MrgprB2 and MRGPRX2 as important contributors to neuropeptide-induced migraine pain.

[Neuroimmunology of allergic rhinitis part 2 : Interactions of neurons and immune cells and neuroimmunological units]

Allergic rhinitis is an IgE-mediated, type‑2 inflammatory disease. neuropeptides are released by neurons and interact with immune cells. Via colocalization, neuroimmune cell units such as nerve-mast cell units, nerve-type 2 innate lymphoid cell (ILC2) units, nerve-eosinophil units, and nerve-basophil units are formed. Markedly elevated tryptase levels were found in nasal lavage fluid and were strongly associated with neuropeptide levels. A close anatomical connection allows bidirectional communication between immune and neuronal cells. Transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin repeat 1 (TRPA1) are critically involved in immunological reactions in the setting of allergic rhinitis. Neuroimmunological communication plays an important role in the inflammatory process, so that allergic rhinitis can no longer be considered a purely immunological disease, but rather a combined neuroimmunological disease.

MRGPRX2 signaling involves the Lysyl-tRNA synthetase and MITF pathway

MRGPRX2, a G-protein-coupled-seven transmembrane domain receptor, is mainly expressed in mast cells and neurons and is involved in skin immunity and pain. It is implicated in the pathophysiology of non-IgE-mediated immediate hypersensitivity and has been related to adverse drug reactions. Moreover, a role has been proposed in asthma, atopic dermatitis, contact dermatitis, and chronic spontaneous urticaria. Although it has a prominent role in disease, its signaling transduction is poorly understood. This study shows that MRGPRX2 activation with substance P increased Lysyl t-RNA synthetase (LysRS) translocation to the nucleus. LysRS is a moonlighting protein with a dual role in protein translation and IgE signaling in mast cells. Upon allergen- IgE-FcεRI crosslinking, LysRS is translocated to the nucleus and activates microphthalmia-associated transcription factor (MITF) activity. In this study, we found that MRGPRX2 triggering led to MITF phosphorylation and increased MITF activity. Therefore, overexpression of LysRS increased MITF activity after MRGPRX2 activation. MITF silencing reduced MRGPRX2-dependent calcium influx and mast cell degranulation. Furthermore, a MITF pathway inhibitor, ML329, impaired MITF expression, calcium influx, and mast cell degranulation. Moreover, drugs such as atracurium, vancomycin, and morphine, reported to induce MRGPRX2-dependent degranulation, increased MITF activity. Altogether, our data show that MRGPRX2 signaling enhances MITF activity, and its abrogation by silencing or inhibition resulted in defective MRGPRX2 degranulation. We conclude that MRGPRX2 signaling involves the LysRS and MITF pathway. Thus, MITF and MITF-dependent targets may be considered therapeutic approaches to treat pathologies where MRGPRX2 is implicated.

Immediate hypersensitivity reactions to antineoplastic agents - A practical guide for the oncologist

Immediate hypersensitivity reactions (IHRs) to antineoplastic agents occur frequently, and every oncologist will encounter these reactions in their clinical practice at some point. The clinical signature of IHRs can range from mild to life-threatening, and their occurrence can substantially impede the treatment course of patients with cancer. Yet, clear guidelines regarding the diagnosis and management are scarce, especially from an oncologic point of view. Therefore, herein, we review the definition, pathophysiology, epidemiology, diagnosis and management of IHRs to chemotherapeutic agents and monoclonal antibodies. First, we focus on defining the specific entities that comprise IHRs and discuss their underlying mechanisms. Then, we summarize the epidemiology for the antineoplastic agents that represent the most common causes of IHRs, i.e., platinum compounds, taxanes and monoclonal antibodies (mAbs). Next, we describe the possible clinical pictures and the comprehensive diagnostic work-up that should be executed to identify the culprit and safe alternatives for the future. Finally, we finish with reviewing the treatment options in both the acute phase and after recovery, with the aim to improve the oncologic care of patients with cancer.

Secretory and Membrane-Associated Biomarkers of Mast Cell Activation and Proliferation

Mast cells (MCs) are immune cells distributed in many organs and tissues and involved in the pathogenesis of allergic and inflammatory diseases as a major source of pro-inflammatory and vasoactive mediators. MC-related disorders are heterogeneous conditions characterized by the proliferation of MC within tissues and/or MC hyper-reactivity that leads to the uncontrolled release of mediators. MC disorders include mastocytosis, a clonal disease characterized by tissue MC proliferation, and MC activation syndromes that can be primary (clonal), secondary (related to allergic disorders), or idiopathic. Diagnosis of MC disorders is difficult because symptoms are transient, unpredictable, and unspecific, and because these conditions mimic many other diseases. Validation of markers of MC activation in vivo will be useful to allow faster diagnosis and better management of MC disorders. Tryptase, being the most specific MC product, is a widely used biomarker of proliferation and activation. Other mediators, such as histamine, cysteinyl leukotrienes, and prostaglandin D2, are unstable molecules and have limitations in their assays. Surface MC markers, detected by flow cytometry, are useful for the identification of neoplastic MC in mastocytosis but, so far, none of them has been validated as a biomarker of MC activation. Further studies are needed to identify useful biomarkers of MC activation in vivo.

Review article: Functional dyspepsia-a gastric disorder, a duodenal disorder or a combination of both?

BACKGROUND

Functional dyspepsia (FD) is one of the most frequent conditions in gastroenterological outpatient health care. Most recent research in FD has shifted its focus to duodenal pathophysiological mechanisms, although current treatments still focus mainly the stomach.

AIM

The aim of the study was to provide a comprehensive overview of the pathophysiology of FD focusing on a paradigm shift from gastric towards duodenal mechanisms.

METHODS

We conducted a literature search in PubMed for studies describing mechanisms that could possibly cause FD.

RESULTS

The pathophysiology of FD remains incompletely understood. Recent studies show that duodenal factors such as acid, bile salt exposure and eosinophil and mast cell activation correlate with symptom pattern and burden and can be associated with gastric sensorimotor dysfunction. The evolving data identify the duodenum an interesting target for new therapeutic approaches. Furthermore, the current first-line treatment, that is proton pump inhibitors, reduces duodenal low-grade inflammation and FD symptoms.

CONCLUSION

Future research for the treatment of FD should focus on the inhibition of duodenal mast cell activation, eosinophilia and loss of mucosal integrity.

Myricetin served as antagonist for negatively regulate MRGPRX2 mediated pseudo-allergic reactions through CD300f/SHP1/SHP2 phosphorylation

BACKGROUND

Mas-related G protein-coupled receptor X2 (MRGPRX2) plays a vital role in mast cells (MCs) degranulation and pseudo-allergic reactions. Leukocyte mono-immunoglobulin-like receptor 3 (CD300f) can negatively regulate MCs degranulation. Identification of drug candidates which target CD300f represents a promising prospect in drug development. Myricetin is widely distributed in plants and has been reported to inhibit allergic reactions in OVA-induced murine models.

OBJECTIVE

This study aims to determine whether myricetin can activate CD300f to arrest MCs degranulation mediated by MRGPRX2.

RESULTS

Myricetin inhibited the allergic mediator and cytokine release triggered by MRGPRX2 in vivo and in vitro. Under C48/80 stimulation, the release of β-hexosaminidase, TNF-α, IL-8 and MCP-1 in CD300f knockdown in LAD2 cells was significantly increased compared with NC-LAD2 cells. Myricetin displayed good structural affinity (K_D = 7.21 × 10^-5) with CD300f by SPR. Molecular docking results showed that hydrogen bonds were formed between myricetin and CD300f, indicating high binding ability (5.6653). Myricetin can upregulate the phosphorylation of SHP-1 and SHP-2 and dephosphorylation in the MRGPRX2 signaling pathway, involving PLCγ1, AKT, P38, and ERK1/2.

CONCLUSION

In the present study, myricetin is identified as an exogenous ligand for CD300f, which negatively regulates MRGPRX2-mediated MCs activation via CD300f to inhibit MCs degranulation and pseudo-allergic reactions.

Targeting active sites of inflammation using inherent properties of tissue-resident mast cells

Mast cells play a pivotal role in initiating and directing host's immune response. They reside in tissues that primarily interface with the external environment. Activated mast cells respond to environmental cues throughout acute and chronic inflammation through releasing immune mediators via rapid degranulation, or long-term de novo expression. Mast cell activation results in the rapid release of a variety of unique enzymes and reactive oxygen species. Furthermore, the increased density of mast cell unique receptors like mas related G protein-coupled receptor X2 also characterizes the inflamed tissues. The presence of these molecules (either released mediators or surface receptors) are particular to the sites of active inflammation, and are a result of mast cell activation. Herein, the molecular design principles for capitalizing on these novel mast cell properties is discussed with the goal of manipulating localized inflammation. STATEMENT OF SIGNIFICANCE: Mast cells are immune regulating cells that play a crucial role in both innate and adaptive immune responses. The activation of mast cells causes the release of multiple unique profiles of biomolecules, which are specific to both tissue and disease. These unique characteristics are tightly regulated and afford a localized stimulus for targeting inflammatory diseases. Herein, these important mast cell attributes are discussed in the frame of highlighting strategies for the design of bioresponsive functional materials to target regions of inflammations.

Opioid toxicity: histamine, hypersensitivity, and MRGPRX2

Insights into the pathophysiology of many non-immune-mediated drug reactions referred to as toxicities, sensitivities, intolerances, or pseudoallergies have resulted from research identifying the mastocyte-related G-protein-coupled receptor (GPCR) member X2 (MRGPRX2), a human mast cell receptor mediating adverse reactions without the involvement of antibody priming. Opioid-induced degranulation of mast cells, particularly morphine, provoking release of histamine and other preformed mediators and causing hemodynamic and cutaneous changes seen as flushing, headache and wheal and flare reactions in the skin, is an example of results of MRGPRX2 activation. Opioids including morphine, codeine, dextromethorphan and metazocine as well as endogenous prodynorphin opioid peptides activate MRGPRX2 at concentrations causing mast cell degranulation. Unlike the canonical opioid receptors, MRGPRX2 shows stereochemical recognition preference for dextro rather than levo opioid enantiomers. Opioid analgesic drugs (OADs) display a range of histamine-releasing potencies from the strong releaser morphine to doubtful releasers like hydromorphone and the non-releaser fentanyl. Whether there is a correlation between histamine release by individual OADs, MRGPRX2 activation, and presence or absence of adverse cutaneous effects is not known. To investigate the question, ongoing research with recently pursued methodologies and strategies employing basophil and mast cell tests resulting from MRGPRX2 insights should help to elucidate whether or not an opioid's histamine-releasing potency, and its property of provoking an adverse reaction, are each a reflection of its activation of MRGPRX2.

Allergenic and Mas-Related G Protein-Coupled Receptor X2-Activating Properties of Drugs: Resolving the Two

Since the seminal description implicating occupation of the Mas-related G protein-coupled receptor X2 (MRGPRX2) in mast cell (MC) degranulation by drugs, many investigations have been undertaken into this potential new endotype of immediate drug hypersensitivity reaction. However, current evidence for this mechanism predominantly comes from (mutant) animal models or in vitro studies, and irrefutable clinical evidence in humans is still missing. Moreover, translation of these preclinical findings into clinical relevance in humans is difficult and should be critically interpreted. Starting from our clinical priorities and experience with flow-assisted functional analyses of basophils and cultured human MCs, the objectives of this rostrum are to identify some of these difficulties, emphasize the obstacles that might hamper translation from preclinical observations into the clinics, and highlight differences between IgE- and MRPGRX2-mediated reactions. Inevitably, as with any subject still beset by many questions, alternative interpretations, hypotheses, or explanations expressed here may not find universal acceptance. Nevertheless, we believe that for the time being, many questions remain unanswered. Finally, a theoretical mechanistic algorithm is proposed that might advance discrimination between MC degranulation from MRGPRX2 activation and cross-linking of membrane-bound drug-reactive IgE antibodies.

Tachykinin Receptor-Selectivity of the Potential Glioblastoma-Targeted Therapy, DOTA-[Thi8,Met(O2)11]-Substance P

Radiopharmaceutical development hinges on the affinity and selectivity of the biological component for the intended target. An analogue of the neuropeptide Substance P (SP), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-[Thi8,Met(O2)11]-SP (DOTA-[Thi8,Met(O2)11]SP), in the theranostic pair [68Ga]Ga-/ [213Bi]Bi-DOTA-[Thi8,Met(O2)11]SP has shown promising clinical results in the treatment of inoperable glioblastoma. As the theranostic targeting component, modifications to SP that affect the selectivity of the resulting analogue for the intended target (neurokinin-1 receptor [NK1R]) could be detrimental to its therapeutic potential. In addition to other closely related tachykinin receptors (neurokinin-2 receptor [NK2R] and neurokinin-3 receptor [NK3R]), SP can activate a mast cell expressed receptor Mas-related G protein-coupled receptor subtype 2 (MRGPRX2), which has been implicated in allergic-type reactions. Therefore, activation of these receptors by SP analogues has severe implications for their therapeutic potential. Here, the receptor selectivity of DOTA-[Thi8,Met(O2)11]SP was examined using inositol phosphate accumulation assay in HEK293-T cells expressing NK1R, NK2R, NK3R or MRGPRX2. DOTA-[Thi8,Met(O2)11]SP had similar efficacy and potency as native SP at NK1R, but displayed greater NK1R selectivity. DOTA-[Thi8,Met(O2)11]SP was unable to elicit significant activation of the other tachykinin receptors nor MRGPRX2 at high concentrations nor did it display antagonistic behaviour at these receptors. DOTA-[Thi8,Met(O2)11]SP, therefore has high potency and selectivity for NK1R, supporting its potential for targeted theranostic use in glioblastoma multiforme and other conditions characterised by NK1R overexpression.

Allergic and other adverse reactions to drugs used in anesthesia and surgery

The list of drugs patients may be exposed to during the perioperative and postoperative periods is potentially extensive. It includes induction agents, neuromuscular blocking drugs (NMBDs), opioids, antibiotics, sugammadex, colloids, local anesthetics, polypeptides, antifibrinolytic agents, heparin and related anticoagulants, blue dyes, chlorhexidine, and a range of other agents depending on several factors related to individual patients’ clinical condition and progress in the postoperative recovery period. To avoid poor or ultrarapid metabolizers to a particular drug (for example tramadol and codeine) or possible adverse drug reactions (ADRs), some drugs may need to be avoided during or after surgery. This will be the case for patients with a history of anaphylaxis or other adverse events/intolerances to a known drug. Other drugs may be ceased for a period before surgery, e.g., anticoagulants that increase the chance of bleeding; diuretics for patients with acute renal failure; antihypertensives relative to kidney injury after major vascular surgery; and serotonergic drugs that together with some opioids may rarely induce serotonin toxicity. Studies of germline variations shown by genotyping and phenotyping to identify a predisposition of genetic factors to ADRs offer an increasingly important approach to individualize drug therapy. Studies of associations of human leukocyte antigen (HLA) genes with some serious delayed immune-mediated reactions are ongoing and variations of drug-metabolizing cytochrome CYP450 enzymes, P-glycoprotein, and catechol-O -methyltransferase show promise for the assessment of ADRs and non-responses to drugs, particularly opioids and other analgesics. Surveys of ADRs from an increasing number of institutions often cover small numbers of patients, are retrospective in nature, fail to clearly identify culprit drugs, and do not adequately distinguish immune-mediated from non-immune-mediated anaphylactoid reactions. From the many surveys undertaken, the large list of agents identified during and after anesthesia and surgery are examined for their ADR involvement. Drugs are classified into those most often involved, (NMBD and antibiotics); drugs that are becoming more frequently implicated, namely antibiotics (particularly teicoplanin), and blue dyes; those becoming less frequently involved; and drugs more rarely involved in perioperative, and postoperative adverse reactions but still important and necessary to keep in mind for the occasional potential sensitive patient. Clinicians should be aware of the similarities between drug-induced true allergic type I IgE/FcεRI- and pseudoallergic MRGPRX2-mediated ADRs, the clinical features of each, and their distinguishing characteristics. Procedures for identifying MRGPRX2 agonists and diagnosing and distinguishing pseudoallergic from allergic reaction mechanisms are discussed.

Colitis aggravated by Mrgprb2 knockout is associated with altered immune response, intestinal barrier function and gut microbiota

NEW FINDINGS

What is the central question of this study? What is the role of mas-related G protein-coupled receptor X2 (MRGPRX2/Mrgprb2) in ulcerative colitis in relation to the intestinal flora, intestinal barrier and immune response? What is the main finding and its importance? Knockout of mouse Mrgprb2 aggravates dextran sulfate sodium (DSS)-induced colitis, which is associated with altered gut microbiota and immune response and disruption of the intestinal barrier. MRGPRB2 may have a protective effect on DSS-induced colitis.

ABSTRACT

Ulcerative colitis (UC) is a chronic immune-related disease, and changes in the intestinal microbiota and damage to the intestinal barrier contribute to its pathogenesis. Mast cells (MCs) are widely distributed in the gastrointestinal tract and are thought to be related to the pathogenesis of UC. Human mas-related G protein-coupled receptor X2 (MRGPRX2) and its mouse homologue, Mrgprb2, are selectively expressed on MCs to recruit immune cells and modulate host defence against microbial infection. To investigate the role of Mrgprb2 in UC in mice, we compared the differences between Mrgprb2 knockout (b2KO) male mice and wild-type (WT) male mice with dextran sulfate sodium (DSS)-induced colitis in the severity of clinical symptoms, inflammatory cell infiltration, degree of intestinal barrier damage and composition of the intestinal flora. The results showed that weight loss, disease activity index score, colon shortening and colonic pathological damage were significantly increased in b2KO mice while MC activation, cytokine and chemokine secretion, and inflammatory cell infiltration were decreased. In addition, the abundance and diversity of the intestinal microbiota were reduced in b2KO mice. B2KO mice also exhibited a reduction of probiotics such as norank_f_Muribaculaceae and Lactobacillus and increase of harmful bacteria like Escherichia-Shigella. Intestinal mucosal barrier damage of b2KO mice was more severe than that of WT mice due to the attenuated expression of mucin-2 and occludin. These results demonstrated that MRGPRB2 may have a protective effect on DSS-induced colitis by altering the intestinal flora, participating in barrier repair and recruiting inflammatory cells to eliminate pathogens.

Role of PACAP in migraine: An alternative to CGRP?

Migraine is a widespread and debilitating neurological condition affecting more than a billion people worldwide. Thus, more effective migraine therapies are highly needed. In the last decade, two endogenous neuropeptides, calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating peptide (PACAP), were identified to be implicated in migraine. Recently, introduction of monoclonal antibodies (mAbs) blocking the CGRP is the most important advance in migraine therapy for decades. However, 40% of patients are unresponsive to these new drugs. We believe that PACAP may be involved in these patients. Like CGRP, PACAP is located to sensory nerve fibers, it dilates cranial arteries, it causes migraine when infused into patients and it is a peptide that lends itself to antibody therapy. Also, recent studies suggest that the PACAP pathway is independent of the CGRP pathway. Understanding the signaling pathways of PACAP may therefore lead to identification of novel therapeutic targets of particular interest in patients unresponsive to anti-CGRP therapy. Accordingly, neutralizing mAb to PACAP is currently in clinical phase II development. The aim of the present review is, therefore, to give a thorough account of the existing data on PACAP, its receptors and its relation to migraine.

The mast cell: A Janus in kidney transplants

Mast cells (MCs) are innate immune cells with a versatile set of functionalities, enabling them to orchestrate immune responses in various ways. Aside from their known role in allergy, they also partake in both allograft tolerance and rejection through interaction with regulatory T cells, effector T cells, B cells and degranulation of cytokines and other mediators. MC mediators have both pro- and anti-inflammatory actions, but overall lean towards pro-fibrotic pathways. Paradoxically, they are also seen as having potential protective effects in tissue remodeling post-injury. This manuscript elaborates on current knowledge of the functional diversity of mast cells in kidney transplants, combining theory and practice into a MC model stipulating both protective and harmful capabilities in the kidney transplant setting.

Focus on mast cells in the tumor microenvironment: Current knowledge and future directions

Mast cells (MCs) are crucial cells participating in both innate and adaptive immune processes that play important roles in protecting human health and in the pathophysiology of various diseases, such as allergies, cardiovascular diseases, and autoimmune diseases. In the context of tumors, MCs are a non-negligible population of immune cells in the tumor microenvironment (TME). In most tumor types, MCs accumulate in both the tumor tissue and the surrounding tissue. MCs interact with multiple components of the TME, affecting TME remodeling and the tumor cell fate. However, controversy persists regarding whether MCs contribute to tumor progression or trigger an anti-tumor immune response. This review focuses on the context of the TME to explore the specific properties and functions of MCs and discusses the crosstalk that occurs between MCs and other components of the TME, which affect tumor angiogenesis and lymphangiogenesis, invasion and metastasis, and tumor immunity through different mechanisms. We also anticipate the potential role of MCs in cancer immunotherapy, which might expand upon the success achieved with existing cancer therapies.

Hypersensitivity reactions to small molecule drugs

Drug hypersensitivity reactions induced by small molecule drugs encompass a broad spectrum of adverse drug reactions with heterogeneous clinical presentations and mechanisms. These reactions are classified into allergic drug hypersensitivity reactions and non-allergic drug hypersensitivity reactions. At present, the hapten theory, pharmacological interaction with immune receptors (p-i) concept, altered peptide repertoire model, and altered T-cell receptor (TCR) repertoire model have been proposed to explain how small molecule drugs or their metabolites induce allergic drug hypersensitivity reactions. Meanwhile, direct activation of mast cells, provoking the complement system, stimulating or inhibiting inflammatory reaction-related enzymes, accumulating bradykinin, and/or triggering vascular hyperpermeability are considered as the main factors causing non-allergic drug hypersensitivity reactions. To date, many investigations have been performed to explore the underlying mechanisms involved in drug hypersensitivity reactions and to search for predictive and preventive methods in both clinical and non-clinical trials. However, validated methods for predicting and diagnosing hypersensitivity reactions to small molecule drugs and deeper insight into the relevant underlying mechanisms are still limited.

P2X4 receptor stimulation enhances MrgprB2-mediated mast cell activation and pseudoallergic reactions in mice

Pseudoallergies caused by drugs make disease treatment difficult. Mas-relate G protein-coupled receptor X2 (MRGPRX2), which is specifically expressed in mast cells (MCs), has been implicated in pseudoallergies. High concentrations of therapeutic agents are typically required to stimulate MRGPRX2. Although regulatory mechanisms may enhance this response, the factors involved in this regulation are not well-understood. In this study, the effects of extracellular ATP on MC activation induced by MrgprB2, the mouse ortholog of human MRGPRX2, were examined in mouse peritoneal MCs (PMCs). ATP alone induced minimal PMC degranulation but markedly enhanced degranulation induced by the MrgprB2 agonist compound 48/80 (CP48/80), substance P, PAMP-12, and vancomycin. ATP promoted CP48/80-induced increase in intracellular Ca²⁺ in PMCs. This enhancement effect of ATP was absent in PMCs prepared from P2X4 receptor (P2X4R)-deficient mice and inhibited by the PI3K inhibitor wortmannin. In addition, P2X4R deficiency reduced the skin-specific and systemic anaphylactic responses to CP48/80 in vivo. In MC-deficient Kit^W-sh/W-sh mice, reconstitution with MCs obtained from wild-type mice led to a more severe anaphylactic response to CP48/80 compared to that from P2X4R-deficient mice. P2X4R-mediated effect may be involved in MrgprB2-mediated MC activation in vivo and is a potential target for alleviating pseudoallergic reactions.