Mateusz Kwitniewski

Background: Recent evidence indicates that the Mas-related G protein–coupled receptor X2 (MRGPRX2) can be activated by several drugs, including neuromuscular blocking agents, fluoroquinolones, and vancomycin. However, the contribution of this mechanism to drug hypersensitivity reactions (DHRs) observed in clinical practice remains incompletely understood. Single-nucleotide polymorphisms (SNPs) in the MRGPRX2 gene may alter receptor reactivity and thereby influence drug tolerance. In this study, we investigated whether selected SNPs—previously described in patients with DHRs (N62S, S313R), known but not previously tested with drugs (S325L, E164R), and predicted in silico (W248L)—affect in vitro responses to representative drug ligands. Methods: RBL-2H3 cells were transiently transfected with wild-type (WT) MRGPRX2 or its variants. Cell-surface expression of MRGPRX2 was assessed by flow cytometry. Intracellular calcium mobilization was measured after stimulation with ciprofloxacin, atracurium, and vancomycin; substance P served as a reference agonist and assay buffer as a negative control. Results: All variants exhibited comparable levels of cell-surface expression. No responses were observed in the presence of assay buffer. The S313R and S325L variants showed responses comparable to WT, with a tendency toward enhanced responses to substance P. In contrast, the E164R variant displayed a loss-of-function phenotype (p < 0.05 for all ligands vs. WT, S313R, and S325L variants), as did the in silico-predicted W248L variant (p < 0.05 for all ligands vs. WT, S313R, and S325L variants). The N62S variant demonstrated slightly reduced responses to the tested agonists compared with WT. Conclusions: Our findings indicate that under the investigated experimental conditions with ciprofloxacin, atracurium, and vancomycin: (1) N62S-transfected RBL-2H3 cells did not exhibit enhanced responses to the tested drug ligands; (2) the W248L variant exhibited the predicted loss-of-function phenotype, suggesting that in silico modeling may help assess the pathogenicity of specific MRGPRX2 variants; and (3) the remaining variants showed only partial concordance with previously published data, possibly reflecting differences in experimental design or assay conditions and highlighting the need for replication studies.

Background Neuromuscular blocking agents (NMBAs) may trigger severe perioperative hypersensitivity reactions. A recently proposed mechanism involves off-target activity of NMBAs. They are thought to directly activate the Mas-related G protein-coupled receptor X2 (MRGPRX2), leading to mast cell degranulation and drug-induced hypersensitivity reactions. This study investigated which NMBAs exert this effect, whether in silico findings are consistent with cell-based experiments, and how the affinity of NMBAs for MRGPRX2 compares with that of fluoroquinolones, known MRGPRX2 agonists. We also sought to predict MRGPRX2 binding-site mutations that might enhance interactions with these drugs. Methods Molecular docking, molecular dynamics (MD) simulations, and molecular mechanics Poisson–Boltzmann surface area binding free-energy calculations were combined with a β-hexosaminidase release assay in MRGPRX2-expressing RBL-2H3 stable cell line. Computational alanine scanning was performed to predict the impact of receptor mutations. Results We demonstrated that atracurium-induced mast cell degranulation can be attributed to its immediate metabolite, laudanosine, which binds strongly to MRGPRX2. Pipecuronium, but not rocuronium, suxamethonium, or vecuronium, exhibited high affinity for MRGPRX2 in MD simulations. Complexes of ciprofloxacin, levofloxacin, and moxifloxacin with MRGPRX2 demonstrated excellent stability in MD simulations. RBL-MX2 responses to NMBAs and fluoroquinolones were highly consistent with our MD findings. Alanine substitutions reduced the affinity of ligands for MRGPRX2. Conclusions In contrast to fluoroquinolones, NMBAs displayed different affinity for MRGPRX2. Cellular responses in bench experiments closely reflected the MD predictions. Alanine scanning revealed that the MRGPRX2 binding pocket exhibits low susceptibility to single-site mutations that enhance receptor responsiveness.

Mast cells (MCs) are immune cells that reside in tissues; particularly in the skin, and in the gastrointestinal and respiratory tracts. In recent years, there has been considerable interest in the Mas-Related G Protein-Coupled Receptor X2 (MRGPRX2), which is present on the surface of MCs and can be targeted by multiple exogenous and endogenous ligands. It is potentially implicated in non-IgE-mediated pseudoallergic reactions and inflammatory conditions such as asthma or atopic dermatitis. In this paper, we review natural products and herbal medicines that may potentially interact with MRGPRX2. They mainly belong to the classes of polyphenols, flavonoids, coumarins, and alkaloids. Representative compounds include rosmarinic acid, liquiritin from licorice extract, osthole, and sinomenine, respectively. While evidence-based medicine studies are still required, these compounds have shown diverse effects, such as antioxidant, analgesic, anti-inflammatory, or neuroprotective. However, despite potential beneficial effects, their use is also burdened with risks of fatal reactions such as anaphylaxis. The role of MRGPRX2 in these reactions is a subject of debate. This review explores the literature on xenobiotic compounds from herbal medicines that have been shown to act as MRGPRX2 ligands, and their potential clinical significance.

Background: Chemerin is a chemoattractant protein with adipokine and antimicrobial properties encoded by the retinoic acid receptor responder 2 (RARRES2) gene. Chemerin bioactivity largely depends on carboxyl-terminal proteolytic processing that generates chemerin isoforms with different chemotactic, regulatory, and antimicrobial potentials. While these mechanisms are relatively well known, the role of alternative splicing in generating isoform diversity remains obscure. Methods and results: Using rapid amplification of cDNA ends (RACE) PCR, we determined RARRES2 transcript variants present in mouse and human tissues and identified novel transcript variant 4 of mouse Rarres2 encoding mChem153K. Moreover, analyses of real-time quantitative PCR (RT-qPCR) and publicly-available next-generation RNA sequencing (RNA-seq) datasets showed that different alternatively spliced variants of mouse Rarres2 are present in mouse tissues and their expression patterns were unaffected by inflammatory and infectious stimuli except brown adipose tissue. However, only one transcript variant of human RARRES2 was present in liver and adipose tissue. Conclusion: Our findings indicate a limited role for alternative splicing in generating chemerin isoform diversity under all tested conditions.

Antimicrobial peptides (AMPs) are important components of innate immunity. Here, we report the antimicrobial properties of a peptide derived from the Male fertility factor kl2 (MFF-kl2) protein of Drosophila melanogaster, which was identified as a functional analog of the mammalian antibacterial chemerin-p4 peptide. The antimicrobial activity of multifunctional chemerin is mainly associated with a domain localized in the middle of the chemerin sequence, Val66-Pro85 peptide (chemerin-p4). Using bioinformatic tools, we found homologs of the chemerin-p4 peptide in the proteome of D. melanogaster. One of them is MFF-p1, which is a part of the MFF kl2 protein, encoded by the gene male fertility factor kl2 (kl-2) located on the long arm of the Y chromosome. The second detected peptide (Z-p1) is a part of the Zizimin protein belonging to DOCK family, which is involved in cellular signaling processes. After testing the antimicrobial properties of both peptides, we found that only MFF-p1 possesses these properties. Here, we demonstrate its antimicrobial potential both in vitro and in vivo after infecting D. melanogaster with bacteria. MFF-p1 strongly inhibits the viable counts of E. coli and B. subtilis after 2 h of treatment and disrupts bacterial cells. The expression of kl-2 is regulated by exposure to bacteria and by the circadian clock.

The members of the ZC3H12/MCPIP/Regnase family of RNases have emerged as important regulators of inflammation. In contrast to Regnase-1, -2 and -4, a thorough characterization of Regnase-3 (Reg-3) has not yet been explored. Here we demonstrate that Reg-3 differs from other family members in terms of NYN/PIN domain features, cellular localization pattern and substrate specificity. Together with Reg-1, the most comprehensively characterized family member, Reg-3 shared IL-6, IER-3 and Reg-1 mRNAs, but not IL-1β mRNA, as substrates. In addition, Reg-3 was found to be the only family member which regulates transcript levels of TNF, a cytokine implicated in chronic inflammatory diseases including psoriasis. Previous meta-analysis of genome-wide association studies revealed Reg-3 to be among new psoriasis susceptibility loci. Here we demonstrate that Reg-3 transcript levels are increased in psoriasis patient skin tissue and in an experimental model of psoriasis, supporting the immunomodulatory role of Reg-3 in psoriasis, possibly through degradation of mRNA for TNF and other factors such as Reg-1. On the other hand, Reg-1 was found to destabilize Reg-3 transcripts, suggesting reciprocal regulation between Reg-3 and Reg-1 in the skin. We found that either Reg-1 or Reg-3 were expressed in human keratinocytes in vitro. However, in contrast to robustly upregulated Reg-1 mRNA levels, Reg-3 expression was not affected in the epidermis of psoriasis patients. Taken together, these data suggest that epidermal levels of Reg-3 are negatively regulated by Reg-1 in psoriasis, and that Reg-1 and Reg-3 are both involved in psoriasis pathophysiology through controlling, at least in part different transcripts.

Chemerin is a chemoattractant protein with adipokine and antimicrobial properties encoded by the retinoic acid receptor responder 2 (RARRES2) gene. Chemerin bioactivity is largely dependent on carboxyl-terminal proteolytic processing that generates chemerin isoforms with the different chemotactive, regulatory and antimicrobial potential.While these mechanisms are relatively well known, a role of alternative splicing in generating isoform diversity remains obscure. Using rapid amplification of cDNA ends (RACE) PCR, we have identified novel transcript variant 4 of mouse RARRES2 encoding mChem153K. Moreover, RT-QPCR results and analysis of publicly available RNA-seq datasets showed that different alternatively spliced variants of mouse RARRES2 are present in mouse tissues, and their expression pattern was not affected by inflammatory nor infectious stimuli. Finally, we demonstratedthat chemerin isoform mChem157S exhibits higher bactericidal but not chemotactic activity compared to mChem156S. Together, our findings highlight the importance of an alternative splicing in generation of chemerin isoforms diversity and activity.

Epithelia in the skin, gut and other environmentally exposed organs display a variety of mechanisms to control microbial communities and limit potential pathogenic microbial invasion. Naturally occurring antimicrobial proteins/peptides and their synthetic derivatives (here collectively referred to as AMPs) reinforce the antimicrobial barrier function of epithelial cells. Understanding how these AMPs are functionally regulated may be important for new therapeutic approaches to combat microbial infections. Some AMPs are subject to redox-dependent regulation. This review aims to: (i) explore cysteine-based redox active AMPs in skin and intestine; (ii) discuss casual links between various redox environments of these barrier tissues and the ability of AMPs to control cutaneous and intestinal microbes; (iii) highlight how bacteria, through intrinsic mechanisms, can influence the bactericidal potential of redox-sensitive AMPs.

A biomarker is a defined characteristic measured as an indicator of normal, biologic, pathogenic processes, or biological responses to an exposure or intervention. Diagnostic biomarkers are used to detect a disease or a subtype of a disease; monitoring biomarkers are measured serially to assess a medical condition; response biomarkers are used to check biologic response following a medical intervention; predictive biomarkers are used to identify patients who are more likely to respond to a medical intervention; and prognostic biomarkers are used to assess the future likelihood of a clinical event. Although biomarkers have been extensively investigated and validated in many diseases and pathologies, very few are currently useful for the diagnosis, evaluation of disease activity, and treatment of hereditary angioedema (HAE). Pathophysiologic pathways involved in HAE reveal a plethora of molecules from the complement, coagulation, and fibrinolysis systems or from the vascular endothelium, which may serve as biomarkers. The most promising candidates, together with their laboratory readout systems, should be evaluated with regard to their analytical and clinical validity and utility. To be highly specific, such biomarkers should be linked to the pathomechanisms of HAE, particularly the bradykinin-generating cascade. Additionally, major advances in high-throughput omics-based technologies may facilitate the discovery of new candidate biomarkers in the future. This review will cover the existing as well as future potential biomarkers that will support the diagnosis, monitor disease activity, and can be used to assess the efficacy of new avenues of therapy of HAE and other forms of angioedema.

Chemerin is a chemoattractant protein with adipokine properties encoded by the retinoic acid receptor responder 2 (RARRES2) gene. It has gained more attention in the past few years due to its multilevel impact on metabolism and immune responses. However, mechanisms controlling the constitutive and regulated expression of RARRES2 in a variety of cell types remain obscure. To our knowledge, this report is the first to show that DNA methylation plays an important role in the cell-specific expression of RARRES2 in adipocytes, hepatocytes, and B lymphocytes. Using luciferase reporter assays, we determined the proximal fragment of the RARRES2 gene promoter, located from − 252 to + 258 bp, to be a key regulator of transcription. Moreover, we showed that chemerin expression is regulated in murine adipocytes by acute-phase cytokines, interleukin 1β and oncostatin M. In contrast with adipocytes, these cytokines exerted a weak, if any, response in mouse hepatocytes, suggesting that the effects of IL-1β and OSM on chemerin expression is specific to fat tissue. Together, our findings highlight previously uncharacterized mediators and mechanisms that control chemerin expression.