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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. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Ursolic acid (UA), a pentacyclic triterpene, exhibits diverse pharmacological effects, including potential treatment for allergic diseases. It downregulates thymic stromal lymphopoietin (TSLP) and disrupts mast cell signaling pathways. However, the exact molecular mechanism by which UA interferes with mast cell action remains unclear. Therefore, the current study aimed to uncover molecular entities underlying the effect of UA on mast cells and its potential antipruritic effect, specifically investigating its modulation of key molecules such as TRPV4, PAR2, and MRGPRX2, which are involved in TSLP regulation and sensation. Calcium imaging experiments revealed that UA pretreatment significantly suppressed MRGPRX2 activation (and its mouse orthologue MrgprB2), a G protein-coupled receptor predominantly expressed in mast cells. Molecular docking predictions suggested potential interactions between UA and MRGPRX2/MrgprB2. UA pretreatment also reduced mast cell degranulation through MRGPRX2 and MrgprB2-dependent mechanisms. In a dry skin mouse model, UA administration decreased tryptase and TSLP production in the skin, and diminished TSLP response in the sensory neurons. While PAR2 and TRPV4 activation enhances TSLP production, UA did not inhibit their activity. Notably, UA attenuated compound 48/80-induced scratching behaviors in mice and suppressed spontaneous scratching in a dry skin model. The present study confirms the effective inhibition of UA on MRGPRX2/MrgprB2, leading to reduced mast cell degranulation and suppressed scratching behaviors. These findings highlight the potential of UA as an antipruritic agent for managing various allergy- or itch-related conditions. [Display omitted] • UA interferes with the activity of MRGPRX2/MrgprB2, reducing mast cell degranulation. • UA inhibits TSLP-related itch signaling pathway without affecting TRPV4 and PAR2 in keratinocytes. • UA alleviates scratching induced by MRGPRX2/MrgprB2 agonists, suggesting its antipruritic potential. [ABSTRACT FROM AUTHOR]

Depuis la description séminale impliquant l'occupation du récepteur X2 couplé à la protéine G liée à Mas (MRGPRX2) dans la dégranulation des mastocytes (MCs) par les médicaments, de nombreuses études ont été entreprises sur ce nouvel endotype potentiel de réactions d'hypersensibilité immédiate aux médicaments (RHMIs). Cependant, les preuves actuelles de ce mécanisme proviennent principalement de modèles animaux (mutants) ou d'études in vitro. Des preuves cliniques irréfutables chez l'homme font défaut. De plus, la traduction de ces résultats précliniques en pertinence clinique chez l'homme est difficile et doit être interprétée de manière critique. En partant de nos priorités cliniques et de notre expérience des analyses fonctionnelles des basophiles, MCs et lymphocytes T, l'objectif de cette revue est d'identifier certaines de ces difficultés, de souligner les obstacles qui pourraient entraver la transposition des observations précliniques en clinique et de mettre en évidence les différences entre les réactions médiées par les sIgE et par le MRGPRX2. Finalement, nous proposons un algorithme mécanistique théorique qui pourrait faciliter la discrimination entre la dégranulation des MCs due à l'activation de MRGPRX2 et la réticulation des anticorps IgE liés à la membrane et réactifs aux médicaments. [ABSTRACT FROM AUTHOR]

• The basophil activation test (BAT) has evolved to a safe and reliable diagnostic. • The BAT has some limitations hindering wider application. • The mast cell activation test (MAT) appears a promising adjunct diagnostic. • The MAT does not necessitate viable patients' cells and allows lager batch analyses. • Unlike BAT, MAT can directly reveal potential MRGPRX2 agonistic activity. The basophil activation test (BAT) has emerged as a reliable complementary diagnostic to document IgE-dependent allergies and to study cross-reactivity between structural homologues. However, the BAT has some weaknesses that hinder a wider application. The BAT requires fresh blood samples and is lost as a diagnostic in patients showing a non-responder status of their cells. The BAT is difficult to standardize mainly because of the difficulty to perform batch analyses. In contrast, mast cell activation tests (MATs), using passively sensitized mast cells (MCs) with patients' sera (henceforth indicated as passive MAT; pMAT), use serum samples that can be frozen, stored, and shipped to a reference center experienced in MC lines and/or cultures and capable of offering batch testing. With the recent recognition of the Mas-related G protein-coupled receptor X2 (MRGPRX2) occupation as a putative mechanism of immediate drug hypersensitivity reactions, the MAT has another advantage compared to the BAT. MCs, in contrast to resting basophils, express the MRGPRX2 and can therefore be used to study this IgE-independent mechanism. This review provides a status update of pMAT in the diagnosis of allergic IgE-mediated hypersensitivity and speculates how direct activation of MCs via the MRGPRX2 receptor could advance paradigms for this non-allergic hypersensitivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A phytosphingosine derivative, mYG-II-6, shows strong antipruritic properties. • mYG-II-6 inhibits histamine-induced signals by blocking TRPV1 activity. • The compound also inhibits MRGPRX2, reducing mast cell degranulation. • It effectively suppresses histamine-induced scratching behaviors in mice. • This underscores its potential as an innovative anti-pruritic treatment. Phytosphingosine and its derivative are known for their skin-protective properties. While mYG-II-6, a phytosphingosine derivative, has shown anti-inflammatory and antipsoriatic effects, its potential antipruritic qualities have yet to be explored. This study aimed to investigate mYG-II-6′s antipruritic properties. The calcium imaging technique was employed to investigate the activity of ion channels and receptors. Mast cell degranulation was confirmed through the β-hexosaminidase assay. Additionally, in silico molecular docking and an in vivo mouse scratching behavior test were utilized. Using HEK293T cells transfected with H1R and TRPV1, we examined the impact of mYG-II-6 on histamine-induced intracellular calcium rise, a key signal in itch-mediating sensory neurons. Pretreatment with mYG-II-6 significantly reduced histamine-induced calcium levels and inhibited TRPV1 activity, suggesting its role in blocking the calcium influx channel. Additionally, mYG-II-6 suppressed histamine-induced calcium increase in primary cultures of mouse dorsal root ganglia, indicating its potential antipruritic effect mediated by histamine. Interestingly, mYG-II-6 exhibited inhibitory effects on human MRGPRX2, a G protein-coupled receptor involved in IgE-independent mast cell degranulation. However, it did not inhibit mouse MrgprB2, the ortholog of human MRGPRX2. Molecular docking analysis revealed that mYG-II-6 selectively interacts with the binding pocket of MRGPRX2. Importantly, mYG-II-6 suppressed histamine-induced scratching behaviors in mice. Our findings show that mYG-II-6 can alleviate histamine-induced itch sensation through dual mechanisms. This underscores its potential as a versatile treatment for various pruritic conditions. [ABSTRACT FROM AUTHOR]

The mast cell receptor Mrgprb2, a mouse orthologue of human Mrgprx2, is known as an inflammatory receptor and its elevated expression is associated with various diseases such as ulcerative colitis. We aimed to elucidate the role of Mrgprb2/x2 and the effect of its ligands on a chemically induced murine colitis model. We showed that in Mrgprb2-/- mice, there is a differential regulation of cytokine releases in the blood plasma and severe colonic damages after DSS treatment. Unexpectedly, we demonstrated that known Mrgprb2/x2 agonists (peptide P17, P17 analogues and CST-14) and antagonist (GE1111) similarly increased the survival rate of WT mice subjected to 4% DSS-induced colitis, ameliorated the colonic damages of 2.5% DSS-induced colitis, restored major protein mRNA expression involved in colon integrity, reduced CD68+ and F4/80+ immune cell infiltration and restored cytokine levels. Collectively, our findings highlight the eminent role of Mrpgrb2/x2 in conferring a beneficial effect in the colitis model, and this significance is demonstrated by the heightened severity of colitis with altered cytokine releases and inflammatory immune cell infiltration observed in the Mrgprb2 knockout mice. Elevated expression of Mrgprb2 in WT colitis murine models may represent the organism's adaptive protective mechanism since Mrgprb2 knockout results in severe colitis. On the other hand, both agonist and antagonist of Mrgprb2 analogously mitigated the severity of colitis in DSS-induced colitis model by altering Mrgprb2 expression, immune cell infiltration and inflammatory cytokine releases. [Display omitted] • Mrgprb2-/- results in severe colonic damages and colitis through altered cytokine releases and infiltration of inflammatory immune cells. • WT model shows increased Mrgprb2/x2 expression in colitis animals contrary to the Mrgprb2 receptor knockout findings. • Mrgprb2/x2 ligands (agonist and antagonist) analogously alleviates colitis severity by reducing Mrgprb2 expression. • GE1111 acts as an inverse agonist of Mrgprx2. [ABSTRACT FROM AUTHOR]

P17, a peptide isolated from Tetramorium bicarinatum ant venom, is known to induce an alternative phenotype of human monocyte–derived macrophages via activation of an unknown G protein–coupled receptor (GPCR). We sought to investigate the mechanism of action and the immunomodulatory effects of P17 mediated through MRGPRX2 (Mas-related G protein–coupled receptor X2). To identify the GPCR for P17, we screened 314 GPCRs. Upon identification of MRGPRX2, a battery of in silico , in vitro , ex vivo , and in vivo assays along with the receptor mutation studies were performed. In particular, to investigate the immunomodulatory actions, we used β-hexosaminidase release assay, cytokine releases, quantification of mRNA expression, cell migration and differentiation assays, immunohistochemical labeling, hematoxylin and eosin, and immunofluorescence staining. P17 activated MRGPRX2 in a dose-dependent manner in β-arrestin recruitment assay. In LAD2 cells, P17 induced calcium and β-hexosaminidase release. Quercetin- and short hairpin RNA–mediated knockdown of MRGPRX2 reduced P17-evoked β-hexosaminidase release. In silico and in vitro mutagenesis studies showed that residue Lys8 of P17 formed a cation- π interaction with the Phe172 of MRGPRX2 and [Ala8]P17 lost its activity partially. P17 activated LAD2 cells to recruit THP-1 and human monocytes in Transwell migration assay, whereas MRGPRX2-impaired LAD2 cells cannot. In addition, P17-treated LAD2 cells stimulated differentiation of THP-1 and human monocytes, as indicated by the enhanced expression of macrophage markers cluster of differentiation 11b and TNF-α by quantitative RT-PCR. Immunohistochemical and immunofluorescent staining suggested monocyte recruitment in mice ears injected with P17. Our data provide novel structural information regarding the interaction of P17 with MRGPRX2 and intracellular pathways for its immunomodulatory action. [Display omitted] [ABSTRACT FROM AUTHOR]

Peptide based therapeutics are desirable owing to their high biological specificity. However, a number of these fail in clinical testing due to an adverse inflammatory response. Mast cells play a key role in directing the host response to drugs and related products. Although the role of FcεRI receptor is well known, Mas-related G-protein coupled receptor X2 (MRGPRX2) binding of endogenous peptides, and drugs will activate mast cells independent of FcεRI. Identifying peptides that activate mast cells through MRGPRX2, and their respective activation potency, can be used to reduce the failure rate of peptide therapeutics at clinical trial. Moreover, it will allow for peptide design where mast cell activation is actually desired. It was found that FRKKW and WNKWAL are two motifs that activate human LAD2 cells similar to PAMP-12 controls. Peptide activators of MRGPRX2 could be reduced to X a -(Y) (n ≥ 3) -X b where: X a is an aromatic residue; X b is a hydrophobic residue; and Y is a minimum 3 residue long sequence, containing a minimum of one positively charged residue with the remainder being uncharged residues. Artificial peptides WKKKW and FKKKF were constructed to test this structural functionality and were similar to PAMP-12 controls. Peptides with different activation potentials were found where FRKKW = WKKKW = FKKKF > PAMP-12 = WNKWAL > YKKKY > FRKKANKWALSR = FRKKWNKAALSR > KWKWK > FRKK = WNKWA > KYKYK > NKWALSR = YKKY = WNK. These sequences should be considered when designing peptide-based therapeutics. Mast cells release immune regulating molecules upon activation that direct host's immune response. MRGPRX2 receptor provides an alternate pathway for mast cell activation that is independent of FcεRI receptor. It is thought that mast cell activation through MRGPRX2 plays a critical role in high failure rates of drugs in clinical trials. Identifying peptide sequences that activate mast cells through MRGPRX2 can serve two important purposes, namely, sequences to avoid when designing peptide therapeutics, and artificial peptides with different activation potentials for mast cells. Herein, we have identified a general amino acid sequence that induces mast cell activation through MRGPRX2. Furthermore, by modulating the identified sequence, artificial peptides have been designed which activate mast cells by varying degrees for therapeutic applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Cutaneous mast cells (MCs) express Mas-related G protein–coupled receptor-X2 (MRGPRX2; mouse ortholog MrgprB2), which is activated by an ever-increasing number of cationic ligands. Antimicrobial host defense peptides (HDPs) generated by keratinocytes contribute to host defense likely by 2 mechanisms, one involving direct killing of microbes and the other via MC activation through MRGPRX2. However, its inappropriate activation may cause pseudoallergy and likely contribute to the pathogenesis of rosacea, atopic dermatitis, allergic contact dermatitis, urticaria, and mastocytosis. Gain- and loss-of-function missense single nucleotide polymorphisms in MRGPRX2 have been identified. The ability of certain ligands to serve as balanced or G protein–biased agonists has been defined. Small-molecule HDP mimetics that display both direct antimicrobial activity and activate MCs via MRGPRX2 have been developed. In addition, antibodies and reagents that modulate MRGPRX2 expression and signaling have been generated. In this article, we provide a comprehensive update on MrgprB2 and MRGPRX2 biology. We propose that harnessing MRGPRX2's host defense function by small-molecule HDP mimetics may provide a novel approach for the treatment of antibiotic-resistant cutaneous infections. In contrast, MRGPRX2-specific antibodies and inhibitors could be used for the modulation of allergic and inflammatory diseases that are mediated via this receptor. [ABSTRACT FROM AUTHOR]

Depuis la description séminale impliquant l'occupation du récepteur X2 couplé à la protéine G liée à Mas (MRGPRX2) dans la dégranulation des mastocytes (MCs) par les médicaments, de nombreuses études ont été entreprises sur ce nouvel endotype potentiel de réactions d'hypersensibilité immédiate aux médicaments (RHMIs). Cependant, les preuves actuelles de ce mécanisme proviennent principalement de modèles animaux (mutants) ou d'études in-vitro. Des preuves cliniques irréfutables chez l'homme font défaut. De plus, la traduction de ces résultats précliniques en pertinence clinique chez l'homme est difficile et doit être interprétée de manière critique. En partant de nos priorités cliniques et de notre expérience des analyses fonctionnelles des basophiles, MCs et lymphocytes T, l'objectif de ma présentation est de proposer un algorithme mécanistique théorique qui pourrait faciliter la discrimination entre la dégranulation des MCs due à l'activation du récepteur MRGPRX2 et au pontage des anticorps spécifiques IgE couplés au récepteur FceRI. La nécessité de distinguer les deux endotypes doit principalement être recherchée dans les différences d'approche ainsi que dans les mécanismes et les profils de réactivité croisée. Since the seminal description implicating Mas-linked G protein-coupled receptor X2 (MRGPRX2) occupancy in the degranulation of mast cells (MCs) by drugs, many studies have been undertaken on this potential new endotype of immediate drug hypersensitivity reactions (IDHRs). However, current evidence for this mechanism comes mainly from animal (mutant) models or in-vitro studies. Irrefutable clinical evidence in humans is lacking. Furthermore, translating these preclinical results into clinical relevance in humans is difficult and needs to be interpreted critically. Based on our clinical priorities and our experience with functional analyses of basophils, MCs and T lymphocytes, the aim of my presentation is to propose a theoretical mechanistic algorithm that could facilitate discrimination between MC degranulation due to MRGPRX2 receptor activation and bridging of specific IgE antibodies coupled to the FceRI receptor. Special focus will be paid to the role of in vitro/ex vivo cellular tests. [ABSTRACT FROM AUTHOR]

• Bergapten alleviated airway inflammation. • Bergapten inhibited MRGPRX2-mediated mast cells activation. • NR4A1 was involved in MRGPRX2 pathway. Asthma is a serious global health problem affecting 300 million persons around the world. Mast cells (MCs) play a major role in airway hyperresponsiveness (AHR) and inflammation in asthma, their exact effector mechanisms remain unclear. Here, we aim to investigate the inhibitory effect of Bergapten (BER) on MRGPRX2-mediated MCs activation through asthma model. Mouse model of asthma was established to examine the anti-asthmatic effects of BER. Calcium (Ca2+) influx, β-hexosaminidase and histamine release were used to assess MCs degranulation in vitro. RNA-Seq technique was conducted to study the gene expression profile. RT-PCR and Western Blotting were performed to examine targeting molecules expression. BER inhibited AHR, inflammation, mucous secretion, collagen deposition and lung MCs activation in asthma model. BER dramatically reduced levels of IL4, IL-5, and IL-13 in bronchoalveolar lavage fluid (BALF), as well as inflammatory cells. BER also reduced serum IgE levels. Pretreatment MCs with BER inhibited substance P (SP)-induced Ca2+ influx, degranulation and cytokines release from MCs. BER also reduced the phosphorylation levels of PKC, PLC, IP3R, AKT and ERK, which were induced by SP. Furthermore, RNA-seq analysis showed that SP up-regulated 68 genes in MCs, while were reversed by BER. Among these 68 genes, SP up-regulated NR4A1 expression, and this effect was inhibited by BER. Meanwhile, knockdown of NR4A1 significantly attenuated SP-induced MCs degranulation. In conclusion, NR4A1 plays a major role in MRGPRX2-mediated MCs activation, BER inhibited AHR and inflammation in asthmatic model by inhibiting MCs activation through MRGPRX2-NR4A1 pathway. [ABSTRACT FROM AUTHOR]

Drug-induced anaphylaxis is a hyperacute reaction affecting multiple organs that can be of fatal consequence. Its incidence is increasing, consistent with a global increased sensitization to various allergens and drugs in the population. Few risk factors and mechanisms have been identified from human studies due to the rarity of anaphylactic events and their unpredictability. This systemic reaction is caused by the rapid release of a large range of functionally diverse mediators, including histamine and platelet-activating factor as the main drivers identified. Mechanisms defined from models of experimental anaphylaxis identify drug-specific antibodies of the IgE and IgG class that link the drug to antibody receptors on multiple cell types, causing their activation and mediator release. In the case of drugs with peculiar chemical structures, antibodies may not be necessary because drug-binding receptors, such as Mas-related G protein–coupled receptor member X2, have been identified. This review describes the complex reaction leading to drug-induced anaphylaxis that can involve various antibody classes, various cell types—including mast cells, neutrophils, platelets, basophils, macrophages, and monocytes—and their mediators and receptors that, importantly, can be activated alone or in association to participate in the severity of the reaction. [ABSTRACT FROM AUTHOR]

The Mas-related G protein–coupled receptor X2 (MRGPRX2) is a multiligand receptor responding to various exogenous and endogenous stimuli. Being highly expressed on skin mast cells, MRGPRX2 triggers their degranulation and release of proinflammatory mediators, and it promotes multicellular signaling cascades, such as itch induction and transmission in sensory neurons. The expression of MRGPRX2 by skin mast cells and the levels of the MRGPRX2 agonists (eg, substance P, major basic protein, eosinophil peroxidase) are upregulated in the serum and/or skin of patients with inflammatory and pruritic skin diseases, such as chronic spontaneous urticaria or atopic dermatitis. Therefore, MRGPRX2 and its agonists might be potential biomarkers for the progression of cutaneous inflammatory diseases and the response to treatment. In addition, they may represent promising targets for prevention and treatment of signs and symptoms in patients with skin diseases or drug reactions. To assess this possibility, this review explores the role and relevance of MRGPRX2 and its activators in cutaneous inflammatory disorders and chronic pruritus. [ABSTRACT FROM AUTHOR]

• A novel pseudo-allergic mouse model was developed. • Thimerosal may cause contact dermatitis through the mechanism of pseudo-allergic reaction. • MrgprB2-mediated mast cell activation contributes to pseudo-allergic reaction induced by thimerosal in mice. • Pseudo-allergic reaction induced by thimerosal may be a possible explanation for its clinical irrelevance. Thimerosal has been used as a preservative in many products which may cause contact dermatitis. It is the second most common allergen in positive patch test reactions, though being a clinical irrelevant allergen. Thimerosal-induced contact dermatitis is generally considered to be a delayed-type hypersensitivity reaction, but it is difficult to explain the fact that most patients develop an allergic reaction upon first encounter with thimerosal. Recent studies have demonstrated the association between Mas-related G protein coupled receptor X2 (MRGPRX2) and pseudo-allergic reactions which occur at the first contact with stimulation. This suggests the possibility that thimerosal may cause contact dermatitis via MRGPRX2 mediated mechanism. To investigate the role of Mas-related G-protein coupled receptor B2 (MrgprB2)/MRGPRX2 in contact dermatitis induced by thimerosal. Thimerosal induced pseudo-allergic reactions via MrgprB2/ MRGPRX2 were investigated using a novel skin pseudo-allergic reaction mouse model, footpad swelling and extravasation assays in vivo and mast cell degranulation assay in vitro. Thimerosal induced contact dermatitis in dorsal skin and footpad swelling in wild-type mice, but had no significant effect in MrgprB2-knockout mice. Thimerosal-induced dermatitis is characterized by infiltration of inflammatory cells and elevation of serum histamine and inflammatory cytokines, rather than elevation of serum IgE level. Thimerosal increased the intracellular Ca2+ concentration in HEK293 cells overexpressing MrgprB2/MRGPRX2. Downregulation of MRGPRX2 resulted in the reduced degranulation of LAD2 human mast cells. MrgprB2 mediates thimerosal-induced mast cell degranulation and pseudo-allergic reaction in mice. MRGPRX2 may be a key contributor to human contact dermatitis. [ABSTRACT FROM AUTHOR]

Polymyxin B (PMB) and polymyxin E (PME) are cyclic, peptide antibiotics which derived from various species of Paenibacillus (Bacillus) polymyxa. They are decapeptide antibiotics with an antimicrobial spectrum that includes Gram-negative bacteria, and reused as therapeutic agents due to the emergence of multidrug-resistant (MDR) Gram-positive bacteria. PMB or PME-induced anaphylactoid reactions in the clinic have been documented. However, the mechanism underlying anaphylactoid reaction induced by polymyxin has not yet been reported. Here, we report that human Mas-related G protein-coupled receptor X2 (MRGPRX2) and its mouse homologue Mas-related G protein-coupled receptor B2 (MrgprB2) are the receptors mediating the anaphylactoid response provoked by PMB and PME. We firstly investigated the anaphylactoid reactions induced by PMB and PME in LAD2 cells in vitro and in vivo , and found that treatment with PMB and PME led to significant release of mast cell granules such as histamine and β-hexosaminidase, secretion of pro-inflammatory cytokines, such as TNF-α and PGD2, and provocation of calcium flux in LAD2 cells. Furthermore, treatment with PMB and PME led to reduced release of β-hexosaminidase in MRGPRX2 knockdown-LAD2 cells, and obvious increased calcium release in MRGPRX2 overexpressing HEK293 cells, which suggested that MRGPRX2 are involved in mast cell activation provoked by PMB or PME. In vivo , MRGPRB2 knockout mice exhibited lower pseudo-allergic reactions than wild type mice. Activation of MrgprB2 also triggers increased capillary permeability and paw swelling. Our results elucidated the role of MRGPRX2 in PMB and PME-induced anaphylactoid response and suggested that MRGPRX2 as a potential therapeutic target to control the anaphylactoid reactions which triggered by PMB or PME. • Polymyxin B and E induced degranulation and Ca2+ mobilization of LAD2 cells. • Polymyxin B and E induced Ca2+ mobilization in MRGPRX2 overexpressing HEK293 cells. • Polymyxin B and E caused anaphylactoid responses mediated by MRGPRX2. • Polymyxin B and E induced histamine release, extensive Evans blue extravasation and paw swelling in mice. • MRGPRX2 may be a potential target for preventing Polymyxin B or E caused anaphylactoid reactions. [ABSTRACT FROM AUTHOR]

• Phenothiazine antipsychotics activate calcium mobilization and induce degranulation in mast cells. • Phenothiazine antipsychotics increase serum histamine via Mrgprb2 without Evans blue extravasation or paw swell. • Phenothiazine antipsychotics could interact with H1R and exhibit as antagonists. • MRGPRX2 is essential for the degranulation of mast cells triggered by phenothiazine antipsychotics. • Dual properties of phenothiazine antipsychotics in pseudo-allergic reactions rely on structural specificity. Phenothiazines are a class of antipsychotics that share the same tricyclic structure and are widely used in clinical settings. Adverse reactions from these drugs, however, have been regularly reported, with allergic skin reactions noted in some cases. Nevertheless, the mechanisms underlying anaphylaxis by these drugs have not been described. In the present study, we found that phenothiazine antipsychotics increased calcium mobilization and activated mast cells to release β -hexosaminidase, histamine, and tumor necrosis factor-α via Mas-related G-protein-coupled receptor member X2 (MRGPRX2) in vitro. In addition, they induced histamine release in serum via Mrgprb2 in C57BL/6 mice without Evans blue extravasation or paw swell. Further experiments indicated these drugs had good interaction with the histamine H 1 receptor (H1R) and show an anti-calcium mobilization effect on H 1 R-HEK293 cells, which confirmed a potential antagonist effect of these drugs on the H 1 R. The molecular docking and activity experiments indicated that the N-methyl substitution on the side chain of these drugs played a significant role in activating MRGPRX2, while the phenothiazine tricyclic ring was associated with the inhibiting effect on the H 1 R. Therefore, due to their dual properties of increasing histamine levels without obvious allergic symptoms, clinicians should be highly vigilant for damage from histamine accumulation and long-term inflammatory reactions during the clinical use of phenothiazine antipsychotics. [ABSTRACT FROM AUTHOR]

Pseudo-allergic reactions occurred in patients administered drugs for the first time, seriously threaten man's survival. Due to the frequent reports of pseudo-allergic reactions to Danshen injection, in our previous study, isosalvianolic acid C in Danshen injection was found to trigger off mast cell degranulation. However, the direct involvement and the mechanisms underlying pseudo-allergic reactions have not been elucidated. In this study, the pseudo-allergic reactions induced by isosalvianolic acid C were confirmed by an ear swelling assay, a hindpaw swelling and extravasation assay in vivo and mast cell degranulation assays in vitro. We also evaluated whether the pseudo-allergic effect is related to MRGPRX2, Isosalvianolic acid C induced Ca2+ mobilization was verified as MRGPRX2-related by Ca2+ imaging using mouse peritoneal mast cells (both wild-type and MrgprB2 knockout mice), MRGPRX2-expressing HEK293 and MrgprB2-expressing HEK293 cells. MRGPRX2-related pseudo-allergic reactions induced by Isosalvianolic acid C were further confirmed by MrgprB2 knockout mice and MRGPRX2 knockdown mast cells both exhibited reduced isosalvianolic acid C-induced pseudo-allergic effects. Furthermore, both the frontal analysis and molecular docking assays showed that isosalvianolic acid C has a considerable affinity with MRGPRX2. Based on the above experiments, the western blot analyses were conducted, the results indicated that isosalvianolic acid C induced Ca2+ mobilization and degranulation via the activation of PLC-γ and IP3R, and releasing chemokines via the activation of PLC-γ, PKC and P38. This study should alarm many clinicians that medicines containing isosalvianolic acid C might induce pseudo-allergic reactions, and it may provide guidance on safe dosage of these medicines in the process of production and use. In this study, we first identified and showed that Isosalvianolic acid C induces pseudo-allergic reactions via the mast cell specific receptor MRGPRX2. Unlabelled Image • Isosalvianolic acid C induces pseudo-allergic reactions. • Isosalvianolic acid C activates the human MRGPRX2 receptor. • Isosalvianolic acid C activates the mouse MrgprB2 receptor. • Isosalvianolic acid C-induced pseudo-allergic reactions are mediated by activation of PLC-γ, IP3R, PKC and P38. [ABSTRACT FROM AUTHOR]

Abstract Fluoroquinolones trigger anaphylaxis during clinical applications, affecting the safety of their administration. Mast cells are immune cells that act as sentinels during host defenses, mediating hypersensitivity and anaphylactic reactions. Mas-related G protein-coupled receptor X2 (MRGPRX2) is a mast cell-specific receptor that mediates cell degranulation in anaphylactic reactions. In this study, the mechanism underpinning the anaphylactic reactions caused by fluoroquinolones was investigated. Hypersensitivity was assessed through hindpaw swelling, tissue fluid leakage assays, in vivo and body temperature measurements assay in vivo, and cell calcium mobilization assays, and mast cell degranulation assays in vitro. Mast cell-deficient W-sash c-kit mutant KitW-sh/W-sh mice and MrgprB2 (the orthologous receptor of MRGPRX2 in mice) knockout mice exhibited reduced fluoroquinolone-induced anaphylactic effects. Fluoroquinolones activated mast cells in a dose-dependent manner and reduced degranulation was observed following MRGPRX2 silencing. These results reveal that fluoroquinolone-induced anaphylactic reactions are mediated by mast cells through MRGPRX2. Graphical abstract Unlabelled Image Highlights • The mechanism underpinning the anaphylactic reactions caused by fluoroquinolones is proposed. • Mast cell-deficient KitW-sh/W-sh mice and MrgprB2 knockout mice exhibited reduced anaphylactic effects compared with WT mice. • Fluoroquinolones activated mast cells dose-dependently and reduced degranulation was observed following MRGPRX2 silencing. • The mechanism relies on fluoroquinolones-triggered mast cells activation via MRGPRX2. [ABSTRACT FROM AUTHOR]

Abstract An allergic reaction is a potentially fatal hypersensitivity response caused by mast cell activation, particularly histamine and lipid mediators. Histamine release caused by reaction to drugs is considered a pseudo-allergic reaction. Quercetin is known for its anti-allergic immune effect. However, at present, its anti-pseudo-allergic effect and its mechanism are less investigated. Therefore, the purpose of this study was to evaluate the anti-pseudo-allergic effect of Quercetin in vivo and to explore the mechanism in vitro. The anti-pseudo-allergic activity of Quercetin was evaluated in vivo using a mouse model, while Quercetin mechanism of action was examined in vitro using HEK293 cells expressing Mrgprx2, a mast cell specific receptor, and LAD2 mast cell line. Our in vivo results showed that Quercetin could attenuate Evans blue leakage in the paws and hind paw thickness in C57BL/6 mice in a dose-dependent manner, and could significantly inhibit serum histamine and chemokines release. In addition, it suppressed calcium mobilization and attenuated the release of histamine and MCP-1 in peritoneal mast cells in a dose-dependent manner. Furthermore, it inhibited the vasodilation due to histamine, the release of eosinophils, and the percentage of degranulated mast cells, indicating that Quercetin antagonized mast cell mediators in vivo , histamine-induced vasodilation and eosinophil release. In vitro results showed that Quercetin reduced pseudo-allergic induced calcium influx, suppressed degranulation and chemokines release in a similar way as dexamethasone (100 μM) (mast cell stabilizer) in LAD2 mast cell line. In addition, Quercetin inhibited Mrgprx2-induced both calcium influx and pseudo-allergic reaction in HEK293 cells expressing Mrgprx2. C48/80, a histamine promoter, and Substance P (a neuropeptide) EC 50 was higher when combined with Quercetin compared to the EC 50 of these compounds alone, suggesting that Quercetin could inhibit Mrgprx2-induced pseudo-allergic reaction. Furthermore, Quercetin decreased PLCγ-IP3R signaling pathway activation induced by C48/80 in LAD2 mast cell line. In Mrgprx2 knockdown LAD2 cells, the effect of Quercetin (200 μM) reduced C48/80 induced calcium flux and the release of β‑hexosaminidase, histamine, MCP-1 and IL-8 compared with non-atopic control (NC) transfected LAD2 human mast cells, suggesting that Quercetin anti-pseudo-allergic effect was related to Mrgprx2. The docking results showed that Quercetin had a good binding affinity with Mrgprx2 similar to the one of Substance P and C48/80. Therefore, Quercetin inhibited Mrgprx2-induced pseudo-allergic reaction via PLCγ-IP3R associated Ca2+ fluctuations. Our results validated Quercetin as an effective small molecule inhibiting Mrgprx2-induced pseudo-allergic reaction via PLCγ-IP3R associated Ca2+ fluctuations, thus highlighting a potential candidate to suppress Mrgprx2 induced pseudo-allergic related diseases. Highlights • Quercetin could inhibit C48/80/Substance P-induced pseudo-allergic reaction. • Quercetin anti-pseudo-allergic effect was related to Mrgprx2. • Quercetin inhibited Mrgprx2-induced pseudo-allergic reaction via PLCγ-IP3R associated Ca2+ fluctuations. • Quercetin may be a potential candidate to suppress Mrgprx2 induced pseudo-allergic related diseases. [ABSTRACT FROM AUTHOR]

• SLPI protein expression was upregulated in dermal mast cells in human psoriatic lesions. • · Slpi gene expression in murine mast cells was upregulated by psoriatic skin-derived mediators. • SLPI controlled FcεRI-dependent but not Mrgprb2-dependent mast cell degranulation. • Mrgprb2 gene expression in murine mast cells was downregulated by skin-derived mediators. Psoriasis, which involves mast cells, is a chronic inflammatory skin disorder whose pathophysiology is still not fully understood. We investigated the role of secretory leukocyte protease inhibitor (SLPI), a potential inhibitor of mastocyte serine proteases, on mast cell-dependent processes of relevance to the skin barrier defense in psoriasis. Here, we demonstrate that the dermal mast cells of patients with psoriasis express SLPI but not those of healthy donors. Moreover, SLPI transcripts were found to be markedly upregulated in murine mast cells by mediators derived from psoriasis skin explant cultures. Using mast cells from SLPI-deficient mice and their SLPI+ wild-type controls, we show that SLPI inhibits the activity of serine protease chymase in mastocytes. SLPI was also found to enhance the degranulation of mast cells activated via anti-IgE Abs but not Mrgprb2 ligands. Finally, we demonstrate that the expression and function of Mrgprb2 in mast cells are suppressed by a normal and, to a larger extent, psoriatic skin environment. Together, these findings reveal mechanisms underlying FcεRI– and Mrgprb2-dependent mast cell function that have not been described previously. [ABSTRACT FROM AUTHOR]

Background Pseudo-allergic reactions occur when patients receive muscle relaxants during perioperative anesthesia. These reactions may result in a serious threat to the patient's life, particularly to a child's life. Cisatracurium, a relatively new NMBA, has resulted in bronchospasms and cardiovascular collapse. However, the mechanisms underlying the anaphylactoid reactions caused by cisatracurium have not been fully elucidated. Methods In the present study, the MRGPRX2-related pseudo-allergic reactions induced by cisatracurium were investigated using hindpaw swelling and extravasation assays in vivo and mast cell degranulation assays. Results Cisatracurium caused anaphylactoid reactions in wild-type mice. However, cisatracurium did not induce a similar phenomenon in KitW-sh/W-sh mice. Furthermore, mast cell-related G protein-coupled receptor B2-knockout mice did not display an inflammatory response upon treatment with cisatracurium. Cisatracurium induced LAD2 cell degranulation, leading to the dose-dependent release of β-hexosaminidase, histamine and TNF-α. However, cisatracurium only induced the release of low levels of these mediator LAD2 cells transfected with MRGPRX2 siRNA. Cisatracurium also stimulated intracellular Ca 2+ influx in MRGPRX2-HEK293 cells compared with that in NC-HKE293 cells. Interestingly, cytokine release was not observed in LAD2 cells even with high dose of cisatracurium. Conclusions Cisatracurium activated MRGPRX2 and triggered mast cell degranulation, leading to anaphylactoid reactions. Therefore, strategies targeting MRGPRX2 might potentially block cisatracurium-induced pseudo-allergic reactions. [ABSTRACT FROM AUTHOR]

Mast cell (MC) is the key mediate during allergy accours. The classical MC degranulation pathway is mediated by FcεRI aggregation and varies in strength among subjects, whereas a non-classical but analogous pseudo-allergic way was recently reported to occur via MRGPRX2. However, few therapies can directly target pseudo-allergies and related Mrgprs. Isoliquiritigenin (ISL) exerts anti-inflammatory effect in many diseases. In this study, we investigated the anti-pseudo-allergy effects of ISL and its underlying mechanism. We first examined the effect of ISL on the IgE-independent response using a PCA model,and in vitro cultured MCs. Further, we evaluated whether the anti-pseudo-allergic effect was related to Mrgprs using in vitro MRGPRX2 -expressing HEK293 cells. ISL dose-dependently suppressed compound 48/80 (C48/80)-induced PCA and MC degranulation in mice. Our in vitro studies revealed that ISL reduced C48/80-induced calcium flux and suppressed degranulation in LAD2 cells. ISL dose dependently inhibited C48/80-induced MRGPRX2 -expressing HEK293 cell activation. Our finding that ISL could inhibit IgE-independent allergy, via the Mrgprx2 pathway provides a new insight into pseudo-allergy and its therapy. [ABSTRACT FROM AUTHOR]

Résumé Les mastocytes sont des cellules granulaires du système immunitaire stratégiquement localisées au sein des tissus connectifs et des muqueuses, où ils participent à la régulation des processus inflammatoires. La caractéristique principale des mastocytes est leur capacité à externaliser rapidement leur contenu granulaire cytoplasmique enrichi en molécules bioactives et immunomodulatrices, en réponse à différent signaux activateur. Mieux comprendre comment ces cellules régulent leur dynamique de sécrétion en fonction du récepteur activé est d’un intérêt majeur pour appréhender les réactions inflammatoires dépendantes des mastocytes. Nous nous sommes particulièrement intéressés à l’activation des mastocytes par deux récepteurs jouant un rôle majeur dans divers processus inflammatoires : le FcɛRI (le récepteur de haute affinité aux IgE) et MRGPRX2 (le récepteur des mastocytes aux substances cationiques). Pour pallier aux contraintes technologiques actuelles, nous avons développé une nouvelle approche permettant de visualiser, en temps réel et à l’échelle cellulaire, la dynamique de dégranulation des mastocytes en utilisant la microscopie confocale in vitro et biphotonique in vivo. Nous avons démontré qu’en réponse à une activation par FcɛRI ou MRGPRX2, les mastocytes mettent en place des stratégies de dégranulation bien spécifiques à chaque récepteur, permettant l’externalisation du contenu granulaires avec des caractéristiques physiques distinctes et le développement de réactions inflammatoire de différentes intensités. Nous proposons ici une synthèse des connaissances nouvelles sur les différentes stratégies de dégranulation des mastocytes. Mast cells are granular immune cells strategically located among connective tissues and mucosa, where they participate to the regulation of diverse inflammatory processes. The principal characteristic of mast cells is their capacity to rapidly exteriorize intracellular granular content enriched in bioactive molecules in response to different activation signals. A better understanding of how these cells regulate their secretion dynamics under different stimulatory conditions is crucial to apprehend mast cell-dependent inflammatory reactions. We particularly focused on mast cell activation via two major receptors involved in diverse pathophysiological processes: FcɛRI (the high affinity receptor for IgE) and MRGPRX2 (the mast cell receptor for cationic molecules). To circumvent existing technical constraints, we developed a new approach that permits to monitor, in real-time and at the single cell level, mast cell degranulation dynamics using in vitro confocal microscopy and in vivo two-photon microscopy. We found that mast cell translate FcɛRI- or MRGPRX2-mediated signals into distinct degranulation strategies leading to the release of granular content with specific physical characteristics and the development of mast cell-dependent reactions of different intensities. Here we propose a synthesis of new concept on how mast cells regulate their degranulation strategy in response to activation via different receptors. [ABSTRACT FROM AUTHOR]

Pseudo-allergic reactions-adverse, non-immunologic, anaphylaxis-like sudden onset reactions mediated through an IgE-independent pathway—are activated by various basic compounds and occur at least as frequently as IgE-mediated reactions to drugs. A large family of G protein coupled receptors (Mas-related genes; Mrgprs ) is closely related to pseudo-allergies. However, few therapies can directly target pseudo-allergies and related Mrgprs. Saikosaponin A (SSA) is effective in the treatment of passive cutaneous anaphylaxis (PCA), adjuvant arthritis, and delayed hypersensitiveness. In this study, we investigated the anti-pseudo-allergy effect of SSA and its underlying mechanism. We examined the effect of SSA on both IgE-independent and IgE-dependent responses using PCA and active systemic anaphylaxis models, as well as in vitro -cultured mast cells. We also evaluated whether the anti-allergy effect is related to Mrgprs by using in vitro Mrgprx2 -expressing HEK293 cells. SSA dose dependently suppressed compound 48/80 (C48/80)-induced PCA and mast cell degranulation in mice. When SSA and C48/80 were administered together through the vein, C48/80-induced systemic anaphylaxis did not occur, and C48/80-induced shock ratio decreased dose-dependently upon SSA treatment. However, SSA did not affect IgE-dependent allergy. When administered topically 24 h before antigen challenge, Evans blue leakage and paw swelling were induced in the SSA-treated group and the vehicle group. Our in vitro studies revealed that SSA reduced C48/80-induced calcium flux and suppressed degranulation in LAD2 cells. SSA could also dose-dependently inhibit C48/80-induced Mrgprx2 -expressing HEK293 cell activation. As a conclusion, SSA could inhibits IgE-independent allergy, but not IgE-dependent allergy, and this effect involves the Mrgprx2 pathway. This study provided a new sight on pseudo-allergy and its therapy. [ABSTRACT FROM AUTHOR]

Mast cells are unique immunocytes that function as sentinel cells in host defense reactions such as immediate hypersensitivity responses and anaphylactic responses. The mast cell specific receptor MRGPRX2 (Mas-related G protein-coupled receptor X2) triggers mast cell degranulation—a key process in anaphylactic reactions. We sought to better understand anaphylactic reaction induced by sinomenine hydrochloride (SH). MRGPRX2-related pseudo-allergic reactions induced by SH were investigated using the hindpaw swelling and extravasation assay in vivo and mast cell degranulation assays in vitro . MrgprB2 knockout mice exhibit a reduced SH-induced inflammation effect. Furthermore, MRGPRX2 (the orthologous gene of MrgprB2) related human mast cells are activated by SH in a dose-dependent manner; however, MRGPRX2 knockdown mast cells showed reduced degranulation. The results showed a kind of mechanism that SH-induced anaphylactoid reactions were mediated by MRGPRX2 via activating PLC molecular signaling pathways to provoke mast cells Ca 2+ mobilization and degranulation. [ABSTRACT FROM AUTHOR]

Background Mast cells are important modulators of the human immune system via their release of several inflammatory mediators and proteases. The release can be activated by different pathways: the classical immunoglobulin E-dependent pathway and by the non-immunological immunoglobulin E-independent pathway. MAS-related G protein-coupled receptor X2 (MRGPRX2) is expressed in mast cells and it is one of the endogenous receptor responsible for the IgE-independent activation of human mast cell. The MRGPRX2 is classified as orphan receptor and unlike most GPCRs, the MRGPRX2 recognizes a wide range of basic molecules. Thus, there still might be several unknown ligands for the receptor. Methods MRGPRX2 activating peptides were isolated from human plasma using consecutive HPLC purification steps. The isolation process was monitored with MRGPRX2 transfected HEK 293 cells. The isolated peptides were sequenced by MS and synthetized. The synthetic peptides were used to determine degranulation of the human LAD 2 mast cell line by measuring β-hexosaminidase release. Results Three endogenous MRGPRX2 activating peptides were isolated from human plasma. These peptides are identified as fragments of albumin. The isolated fragments activate MRGPRX2 and degranulate MRGPRX2 expressing LAD 2 cells in dose-dependent manner. Conclusions The isolated basic peptides generated from human albumin are able to degranulate mast cells via the MRGPRX2. General significance These endogenous albumin fragments, cleaved from albumin by mast cell secreted proteases, provide a possible pathway for self-perpetuating mast cell dependent inflammation. [ABSTRACT FROM AUTHOR]

[Display omitted] Drug-induced anaphylaxis is triggered by the direct stimulation of mast cells (MCs) via Mas-related G protein–coupled receptor X2 (MRGPRX2; mouse ortholog MRGPRB2). However, the precise mechanism that links MRGPRX2/B2 to MC degranulation is poorly understood. Dedicator of cytokinesis 2 (DOCK2) is a Rac activator predominantly expressed in hematopoietic cells. Although DOCK2 regulates migration and activation of leukocytes, its role in MCs remains unknown. We aimed to elucidate whether—and if so, how—DOCK2 is involved in MRGPRX2/B2-mediated MC degranulation and anaphylaxis. Induction of drug-induced systemic and cutaneous anaphylaxis was compared between wild-type and DOCK2-deficient mice. In addition, genetic or pharmacologic inactivation of DOCK2 in human and murine MCs was used to reveal its role in MRGPRX2/B2-mediated signal transduction and degranulation. Induction of MC degranulation and anaphylaxis by compound 48/80 and ciprofloxacin was severely attenuated in the absence of DOCK2. Although calcium influx and phosphorylation of several signaling molecules were unaffected, MRGPRB2-mediated Rac activation and phosphorylation of p21-activated kinase 1 (PAK1) were impaired in DOCK2-deficient MCs. Similar results were obtained when mice or MCs were treated with small-molecule inhibitors that bind to the catalytic domain of DOCK2 and inhibit Rac activation. DOCK2 regulates MRGPRX2/B2-mediated MC degranulation through Rac activation and PAK1 phosphorylation, thereby indicating that the DOCK2-Rac-PAK1 axis could be a target for preventing drug-induced anaphylaxis. [ABSTRACT FROM AUTHOR]

Myricetin combined with CD300f to activate the phosphorylation of SHP-1 and SHP-2, while negatively regulating the downstream signal pathway of MRGPRX2. [Display omitted] • Myricetin alleviated C48/80-induced mast cells degranulation and local cutaneous inflammation. • Myricetin served as an exogenous ligand of CD300f. • Myricetin upregulated the phosphorylation of SHP-1 and SHP-2 and dephosphorylation in the MRGPRX2 signaling pathway, involving PLCγ1, AKT, P38, and ERK1/2. 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. This study aims to determine whether myricetin can activate CD300f to arrest MCs degranulation mediated by MRGPRX2. 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. 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. [ABSTRACT FROM AUTHOR]

RA attenuates MRGPRX2-PLCγ1-PKC-NF-κB and PLC-IP3R-Ca2+signaling pathway. [Display omitted] • Rosmarinic acid ameliorates skin inflammation and pruritus in ACD. • RA regulated MRGPRX2-PLCγ1-PKC-NF-κB signaling pathway. • RA directly act on MRGPRX2 receptor expression to ameliorate ACD. Allergic contact dermatitis (ACD) is one of the most common dermatoses, which has high disease burden and quality of life impairment. Anti-histamine is not effective in a part of the ACD patients. Thus, the discovery of novel antipruritic therapy is of highly demand. In this study, we investigated the anti-pruritic effects of rosmarinic acid (RA) and explored the underlying mechanism. SPF Balb/c mice were randomly divided into control group, ACD model group, RA group (1.0 mg/kg) and loratadine (LORA) group (1.5 mg/kg). Back epidermal thickness was recorded. H&E staining was used for pathological observation. Mast cell degranulation was assessed by toluidine blue staining. ELISA assay was employed to detect cytokines levels. Cortistatin-14 (CST-14) and Mas-related G protein-coupled receptor X2 (MRGPRX2) expression was detetcted by RT-PCR and western blot. Molecular docking assay was used to predict the affinity of RA and MRGPRX2. Surface plasmon resonance (SPR) assay was used to verify structure affinity of RA and MRGPRX2. RA treatment significantly decreased epidermal keratinization and inflammatory cell infiltration in ACD mouse model. Administration of RA significantly reduced secretion of histamine, IL-13, and mRNA expression of CST-14. Furthermore, RA treatment increased mRNA expression of MRGPRX2. In addition, Molecular docking results predict that RA has a good affinity with MRGPRX2. RA displayed a structure affinity (K D = 8.89 × 10-4) with MRGPRX2 by SPR. RA inhibited CST-14 and Compound 48/80 (C48/80)-induced mast cell activation via MRGPRX2-PLCγ1-PKC-NF-κB signaling pathway. RA exhibits anti-pruritic and anti-inflammatory effects in ACD mice by inhibiting MRGPRX2-PLCγ1-PKC-NF-κB signaling pathway. RA might emerge as a potential drug for the treatment of pruritus and skin inflammation in the setting of ACD. [ABSTRACT FROM AUTHOR]

The mast cells are integral part of immune system and they have pleiotropic physiological functions in our body. Any type of abnormal stimuli causes the mast cells receptors to spur the otherwise innocuous mast cells to degranulate and release inflammatory mediators like histamine, cytokines, chemokines and prostaglandins. These mediators are involved in various diseases like allergy, asthma, mastocytosis, cardiovascular disorders, etc. Herein, we describe the receptors involved in degranulation of mast cells and are broadly divided into four categories: G-protein coupled receptors, ligand gated ion channels, immunoreceptors and pattern recognition receptors. Although, activation of pattern recognition receptors do not cause mast cell degranulation, but result in cytokines production. Degranulation itself is a complex process involving cascade of events like membrane fusion events and various proteins like VAMP, Syntaxins, DOCK5, SNAP-23, MARCKS. Furthermore, we described these mast cell receptors antagonists or agonists useful in treatment of myriad diseases. Like, omalizumab anti-IgE antibody is highly effective in asthma, allergic disorders treatment and recently mechanistic insight of IgE uncovered; matrix mettaloprotease inhibitor marimistat is under phase III trial for inflammation, muscular dystrophy diseases; ZPL-389 (H4 receptor antagonist) is in Phase 2a Clinical Trial for atopic dermatitis and psoriasis; JNJ3851868 an oral H4 receptor antagonist is in phase II clinical development for asthma, rheumatoid arthritis. Therefore, research is still in inchoate stage to uncover mast cell biology, mast cell receptors, their therapeutic role in myriad diseases. [ABSTRACT FROM AUTHOR]

Molecular mechanism of artemisinic acid in the prevention of substance P-induced chronic urticaria. [Display omitted] • Artemisinic acid have the therapeutic effect in substance P induced urticaria model. • Artemisinic acid regulate the downstream signaling pathway of MRGPRX2 in mast cells. • Artemisinic acid attenuates substance P induced urticaria via Lyn kinase in mast cells. Chronic urticaria (CU) is a common skin disease that affects about 1% of the world's population of all ages and seriously affects patients' quality of life. Therefore, further safe and effective treatments are urgently needed. Therefore, artemisinic acid was investigated in the present study due to its pharmacologic effect on inhibiting mast cell degranulation and chronic urticaria in a mouse model. 4Artemisinic acid decreased the symptoms of substance P-induced chronic urticaria in the mouse model and alleviated secretagogue-induced local cutaneous and systemic anaphylaxis through the Lyn-PLC-p38-NF-κB signaling pathway. Artemisinic acid inhibited mast cell degranulation and pro-inflammatory cytokine production in vitro. Mechanism analysis demonstrated that it could arrest mast cell activation through the Lyn-PLC-p38/ERK1/2/AKT-NF-κB signaling pathway. Based on the results of in vitro kinase assay of Lyn and PLC, artemisinic acid was a potential small molecule inhibitor of Lyn. Artemisinic acid displayed good structural affinity (K D = 2.64 × 10−6) with Lyn SPR results. Artemisinic acid can attenuate substance P/MRGPRX2-mediated chronic urticaria and mast cell activation. Artemisinic acid is an antagonist of Lyn kinase and can be developed as a drug candidate to treat allergic diseases. [ABSTRACT FROM AUTHOR]

Mast cells (MCs), which are granulated tissue-resident cells of hematopoietic lineage, contribute to vascular homeostasis, innate/adaptive immunity, and wound healing. However, MCs are best known for their roles in allergic and inflammatory diseases, such as anaphylaxis, food allergy, rhinitis, itch, urticaria, atopic dermatitis, and asthma. In addition to the high-affinity IgE receptor (FcεRI), MCs express numerous G protein–coupled receptors (GPCRs), which are the largest group of membrane receptor proteins and the most common targets of drug therapy. Antimicrobial host defense peptides, neuropeptides, major basic protein, eosinophil peroxidase, and many US Food and Drug Administration–approved peptidergic drugs activate human MCs through a novel GPCR known as Mas-related G protein–coupled receptor X2 (MRGPRX2; formerly known as MrgX2). Unique features of MRGPRX2 that distinguish it from other GPCRs include their presence both on the plasma membrane and intracellular sites and their selective expression in MCs. In this article we review the possible roles of MRGPRX2 on host defense, drug-induced anaphylactoid reactions, neurogenic inflammation, pain, itch, and chronic inflammatory diseases, such as urticaria and asthma. We propose that host defense peptides that kill microbes directly and activate MCs through MRGPRX2 could serve as novel GPCR targets to modulate host defense against microbial infection. Furthermore, mAbs or small-molecule inhibitors of MRGPRX2 could be developed for the treatment of MC-dependent allergic and inflammatory disorders. [ABSTRACT FROM AUTHOR]

Anaphylaxis is a severe systemic allergic reaction that exhibits multiple clinical symptoms. The Mas-related G protein-coupled receptor X2 (MRGPRX2) is recognized as a key cell receptor mediating allergic diseases and drug-induced anaphylactoid reactions. Thus, it has been a promising target for preventing and treating these reactions. Based on the potential activity of imperatorin and active structural feature of MRGPRX2, we first demonstrated that the synthetic imperatorin derivatives (IDs) could significantly inhibit MRGPRX2 agonist-induced degranulation and cytokine release in LAD2 cells, as well as alleviate local and systemic anaphylaxis in mice. The IC 50 value of the most promising compound is an order of magnitude lower than that of imperatorin. IDs were further identified to display anti-pseudo-allergic activity by binding MRGPRX2 with the tertiary nitrogen substructures, just liking the reported MRGPRX2-ligand. These results would propose evidence for discovery of agents for treating MCs-dependent allergic disorders. [Display omitted] • Imperatorin derivatives inhibit MRGPRX2-agonist induced MC-activation in vitro and in vivo. • ID-15 give outstanding potency with an order of magnitude lower IC 50 than that of imperatorin. • IDs display anti-allergic activity by binding MRGPRX2 with the tertiary nitrogen substructures. • IDs can also alleviate IgE-mediated passive cutaneous anaphylaxis in mice. • These results can aid the discovery of agents for treating MC-dependent allergic disorders. [ABSTRACT FROM AUTHOR]

Chronic prurigo (CPG) is characterized by intensive itch and interactions among nerves, neuropeptides, and mast cells (MCs). The role of some neuropeptides such as cortistatin (CST) and its receptor, Mas-related G protein–coupled receptor X2 (MRGPRX2), in CPG remains poorly investigated. We evaluated first whether CST activates human skin MCs, and second whether CST and MRGPRX2 are expressed in the skin of CPG patients, and by which cells. Skin prick tests and microdialysis with CST were performed in 6 and 1 healthy volunteers, respectively. Degranulation of human skin MCs was assessed using β-hexosaminidase and histamine release assays. Skin samples from 10 patients with CPG and 10 control subjects were stained for CST, MCs, and MRGPRX2 (protein and mRNA) using immunohistochemistry, immunofluorescence, and/or in situ hybridization. Flow cytometry was used to assess CST in human skin MCs. MRGPRX2 levels were measured in serum by ELISA. CST induced concentration-dependent degranulation of human skin MCs in vivo and ex vivo. Skin lesions of CPG patients exhibited markedly higher numbers of CST-expressing cells, CST-expressing MCs, MRGPRX2-expressing cells, and MRGPRX2 mRNA-expressing cells than nonlesional skin. MCs were the main MRGPRX2 mRNA-expressing cells in the lesions of most CPG patients (70%). Stimulation of human skin MCs with anti-IgE led to a release of CST. The number of MRGPRX2-expressing cells correlated with disease severity (r = 0.649, P =.04). MRGPRX2 serum levels in CPG patients correlated with disease severity (r = 0.704, P =.023) and quality-of-life impairment (r = 0.687, P =.028). CST and MRGPRX2 may contribute to the pathogenesis of CPG and should be evaluated in further studies as potential biomarkers and novel therapeutic targets. [ABSTRACT FROM AUTHOR]

[Display omitted] Pseudo-allergic reactions frequently occur following clinical drug use and sometimes even cause mortal danger. Mas-related G-protein-coupled receptor member X2 (MRGPRX2) is a novel receptor that mediates pseudo-allergy and is an important target in the treatment of allergies. However, to date, there are no synthetic small-molecule inhibitors that prevent anaphylactoid reactions through this pathway. Our preliminary research suggested that B10-S and mubritinib effectively inhibited LAD2 cells. Therefore, two novel derivatives were synthesized by integrating the active substructures of B10-S and mubritinib, according to the molecular docking results. The antiallergic inhibitory effects of the two compounds were preliminarily evaluated in vitro using β-hexosaminidase release, histamine release, and intracellular Ca2+ mobilization assays, and their binding sites on MRGPRX2 were analyzed by molecular docking. Both substances inhibited β-hexosaminidase and histamine release in LAD2 cells and decreased intracellular Ca2+ by inhibiting MRGPRX2 in MRGPRX2-HEK293 cells treated with C48/80 in a dose-dependent manner. The docking results suggested that the molecules could competitively bind to the active site on MRGPRX2 and Glu141, which were combined by C48/80. Our study indicated that the two compounds have potential anti-allergic properties, which may provide evidence that will facilitate the development of synthetic molecules with anti-pseudo-allergic activity for clinical use in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] Mas-related G protein-coupled receptor X2 (MRGPRX2) mediates the itch response in neurons and is involved in atopic dermatitis (AD)-associated inflammation and itch. Potent and MRGPRX2-selective ligands are essential to an understanding of the detailed function of the receptor and to develop new therapeutic agents for its related diseases. (+)-TAN-67 (1), the enantiomer of the δ-opioid receptor (DOR) selective ligand (–)-TAN-67 (1), has been reported to activate MRGPRX2, although (+)- 1 also interacts with DOR, which prevents investigators from interrogating the function of MRGPRX2. Here, we have succeeded in developing a novel unnatural morphinan compound (+)- 2a by a transformation based on the structure of (+)- 1 , which removes the DOR binding affinity. (+)- 2a activated both human MRGPRX2 and the mouse orthologue Mrgprb2 in in vitro experiments and induced itch-like behaviors in mice to the same extent as (+)- 1. The (+)- 2a -induced itch response in mice was suppressed by administration of the tripeptide QWF, an MRGPRX2/Mrgprb2 antagonist, or the antipruritic drug nalfurafine. Together, (+)- 2a serves as a useful tool to elucidate the itch-related function/action of MRGPRX2 and its mouse orthologue Mrgprb2. [ABSTRACT FROM AUTHOR]

• MrgprX2 is a key receptor for pseudo-allergic reactions. • PI3K/AKT signaling pathway and PLCγ are important downstream of MrgprX2. • Inhibiting PI3K/AKT signaling pathway and PLCγ remarkable weakened pseudo-allergic reactions both in vivo and in vitro. The G protein-coupled receptor MrgprX2 in mast cells is known to be a crucial receptor for pseudo-allergic reactions. MrgprX2 activation leads to elevated intracellular calcium levels and mast cell degranulation, but the underlying mechanism remains to be elucidated. Herein, we investigated the role of the phosphatidylinositol 3 kinase (PI3K)/serum-threonine kinase (AKT) signaling pathway and phospholipase C gamma (PLCγ) in mast cell degranulation mediated by MrgprX2 in LAD2 human-derived mast cells. The results showed that phosphorylated AKT (p-AKT) and PLCγ up-regulation were accompanied by an increase in intracellular calcium following activation of MrgprX2 by Compound 48/80, an inducer of mast cell degranulation. In contrast, p-AKT and PLCγ were down-regulated and intracellular calcium levels decreased after MrgprX2 knockdown. Mast cell degranulation was clearly suppressed; however, inhibiting PI3K and PLCγ phosphorylation did not influence MrgprX2 expression. The increase in calcium concentration was suppressed and mast cell degranulation was weakened. Furthermore, by inhibiting PI3K and PLCγ phosphorylation in animals, the allergic symptoms caused by C48/80 were obviously reduced. We deduced that during the mast cell degranulation observed in pseudoallergic reactions, MrgprX2 regulated intracellular calcium levels via the PI3K/AKT and PLCγ pathways. [ABSTRACT FROM AUTHOR]

[Display omitted] • Substance P and PAMP(9-20) activated MRGPRX2 and induced different medium release. • Substance P induced more serious degranulation reaction in mice than PAMP(9-20) by release more histamine. • The excited sites of substance P and PAMP(9-20) on MRGPRX2 were different. • Activation of MRGPRX2 by substance P and PAMP(9-20) at different sites induces certain differences in the activation of downstream signaling pathways. MRGPRX2 on mast cells (MCs) is the target that directly mediates MC activation through the activity of small molecular substances. Previous work has attempted to prove that substance P (SP) and PAMP(9-20) induce an MRGPRX2-mediated MC degranulation reaction. However, SP activates MRGPRX2-induced histamine release, which may lead to allergic airway inflammation, while PAMP(9-20)-induced MrgprB2 activation releases more tryptase and fewer monoamines. Due to the lack of direct available comparisons, the different types of sensitizing mediators released by the action of SP and PAMP(9-20) inducing pseudo-allergic reactions via MRGPRX2 are unclear. To investigate whether the action sites of excited MRGPRX2 are different for SP and PAMP(9-20), leading to different effects, the release of inflammatory mediators was measured using MC degranulation reactions and RNA-seq assay in vitro. Mice were treated to observe local inflammation and MC degranulation in vivo. Moreover, site-directed mutagenesis was used to verify the excited sites of SP and PAMP(9-20). SP and PAMP(9-20) both activated MRGPRX2 and led MCs to release inflammatory mediators. Significantly different levels of histamine, tryptase, TNF-α, MCP-1, and other cytokines were released in vivo and in vitro. G165E, D184N, W243R, and H259Y were necessary for SP to activate MRGPRX2, while only D184N and W243R were important for PAMP(9-20). The downstream signaling pathways activated by SP and PAMP(9-20) also differed in the phosphorylation level of PKC. There were differences in the sites via which SP and PAMP(9-20) activate MRGPRX2 and also in the activated downstream signaling pathways, which led to the differences the activation of the pathways and effects of SP- and PAMP(9-20)-induced MRGPRX2 activation. [ABSTRACT FROM AUTHOR]

Immediate drug hypersensitivity reactions (IDHRs) constitute a significant health issue with serious consequences of diagnostic error. The primary diagnostics to document IDHRs usually consists of quantification of drug-specific IgE (sIgE) antibodies and skin tests. Unfortunately, the positive predictive value (PPV) and negative predictive value (NPV) of these tests are not absolutely, which leaves room for new tests. Over the last two decades, the basophil activation test (BAT), in which ex vivo activation of individual basophils is quantified by flow cytometry, has emerged as a reliable complementary diagnostic to document IDHRs, to explore allergenic recognition, to study cross-reactivity and to monitor therapy. However, the BAT is technically challenging requiring specialized personnel and equipment, fresh samples and the technique is lost as a diagnostic in patients showing a non-responder status of their cells. By consequence, the BAT has still not entered mainstream application. In contrast, mast cell activation tests (MATs) use serum samples that can be frozen, stored, and shipped to a recognized reference centre experienced in mast cell (MC) lines and/or cultures and capable of offering batch testing with necessary quality controls. This review does not only highlight the use of the BAT and MAT as diagnostics in IDHRs, but also outlines the potential of both techniques in further exploring and unveiling the mechanisms that govern drug-induced basophil and MC activation and degranulation. [ABSTRACT FROM AUTHOR]

Studies on the mechanisms that govern mast cell (MC) functions are hindered by the difficulties in isolating sufficient numbers of these tissue-resident cells. Therefore, many research groups use cultured human MCs obtained out of progenitor cells. However, these culture methods significantly differ regarding primary source material, culture durations and conditions. Consequently, the finally obtained cells are likely to exhibit morphological, phenotypical and/or functional heterogeneity. To compare the phenotype and functionality of cells cultured from peripheral blood and bone marrow progenitor cells from patients with suspected clonal MC disease. These cells are designated as PBCMCs and BMCMCs, respectively. Twenty paired PBCMCs and BMCMCs cultures starting from CD34+ progenitor cells were compared. Cells were cultured for 4 weeks. Phenotyping included Giemsa and CD117 staining and flow cytometric staining for CD117, CD203c, FcεRI, MRGPRX2, CD300a, CD32, CD63 and CD25. Functional assessment included measurement of the up-regulation of CD63 after cross-linking of the high affinity receptor for IgE (FcεRI) with anti-FcεRI and ligation of MRGPRX2 with substance P. PBCMCs and BMCMCs are phenotypically comparable. Functionally, after activation with anti-FcεRI and substance P, PBCMCs and BMCMCs show similar up-regulation of the lysosomal degranulation marker CD63. However, the yield of PBCMCs is higher than BMCMs and peripheral blood cultures are purer than bone marrow cultures. PBCMCs are an attractive alternative to the more difficult to obtain BMCMCs for the exploration of the complex mechanisms that govern IgE- and MRGPRX2-dependent MC activation and degranulation. Unlike BMCMCs, PBCMCs are easily accessible and enable repetitive analyses. [ABSTRACT FROM AUTHOR]

[Display omitted] • Iohexol induces pseudo-allergic reactions in mice via mast cells. • MRGPRX2 mediates iohexol-induced LAD2 cells activation. • Iodine might be a key player in iohexol-induced pseudo-allergic reactions. • Regulate dosage regimen might be useful to reduce iohexol-induced allergic reactions. Iohexol is a typical iodinated radiocontrast medium and widely used in clinical angiography. Hypersensitivity reactions induced by iohexol are common side effects known to increase the risk for patients. Iodine is the main functional group of iohexol, and it can induce delayed anaphylaxis. However, iohexol also induces immediate-type allergies, but the underlying mechanism is still not clear. MRGPRX2 is a key receptor present on mast cells, which mediates pseudo-allergic reactions induced by various drugs. We aimed to verify the relationship between iohexol-induced anaphylactic reactions and MRGPRX2. MRGPRX2-mediated pseudo-allergic reactions induced by iohexol were investigated in vivo and in vitro using a mouse model of local and systemic anaphylaxis and mast cell degranulation assays, respectively. Iohexol caused pseudo-allergic reactions in wild-type (WT) mice by activating mast cells to release histamine and cytokines. However, it did not induce a similar phenomenon in KitW-sh/W-sh (MUT) mice. Iohexol stimulated intracellular calcium ion (Ca2+) influx in MRGPRX2-HEK293, MrgprB2-HEK293, and LAD2 cells but not in NC-HEK293 cells. After knockdown of MRGPRX2 expression in LAD2 cells, the degree of iohexol-induced degranulation was reduced. In addition, after structural modification of iohexol by removal of iodine, a reduction in iohexol-induced effects, such as local and systemic anaphylaxis in mice and degranulation of LAD2 cells, could be observed. Iohexol was shown to induce immediate-type pseudo-allergic reactions via MRGPRX2, which was dependent on the presence of iodine. Conclusively, inhibition of MRGPRX2-mediated mast cell degranulation and cytokine release is important to prevent iohexol-induced immediate-type pseudo-allergic reactions. [ABSTRACT FROM AUTHOR]

Mast cells (MCs) play a pivotal role in innate and adaptive immune responses. However, MCs are also involved in different pathologic conditions. Studies on the mechanisms that govern human MC functions are impeded by their limited and difficult recovery. Therefore, several research groups have developed protocols to culture human MCs from progenitor cells. These protocols vary with respect to culture duration and used maturation cytokines. How MCs obtained by different protocols differ in phenotype and functionality is currently unknown. To compare different protocols for the generation of human MCs from peripheral blood progenitors. Thirteen paired human MC cultures were investigated. MCs were cultured form CD34+ progenitors cells for 4 or 8 weeks and with or without the addition of IL-6. Phenotyping comprised staining for CD117, CD203c, FcεRI, MRGPRX2, CD300a and CD32. Functional studies included measurements of the up-regulation of CD63 and CD203c after allergen-specific cross-linking of sIgE/FcεRI complexes or ligation of MRGPRX2 with substance P and different drugs. Cell cultures for 4 weeks in the presence of IL-6 consistently yielded the highest numbers of MCs. MCs cultured for 8 weeks with IL-6 showed more autofluorescence significantly impeding correct analyses of FcεRI and CD32. The density of FcεRI and CD32 was comparable between the different culture conditions. MRGPRX2 expression was significantly higher in the 8 week cultures. The density of CD300a was increased in the cultures with IL-6. Cells cultured for 8 weeks were more responsive to MRGPRX2 activation. In contrast, the 4-weeks cultures with IL-6 showed significantly higher allergen-specific activation. Four weeks of culture with IL-6 are sufficient to generate sizeable numbers of human mast cells from blood progenitors, thereby enabling simultaneous exploration of allergen-specific sIgE/FcεRI cross-linking and non-specific activation via MRGPRX2. • Primary human mast cells can be cultured in a four-week culture system. • IL-6 increases the mast cell yield and improves functionality. • The mast cells enable exploration of sIgE/FceRI- and MRGPRX2-dependent activation. [ABSTRACT FROM AUTHOR]