Targeting Ca2+ release-activated Ca2+ channel channels and leukotriene receptors provides a novel combination strategy for treating nasal polyposis

Distinct roles of ORAI1 in T cell-mediated allergic airway inflammation and immunity to influenza A virus infection

T cell activation and function depend on Ca2+ signals mediated by store-operated Ca2+ entry (SOCE) through Ca2+ release-activated Ca2+ (CRAC) channels formed by ORAI1 proteins. We here investigated how SOCE controls T cell function in pulmonary inflammation during a T helper 1 (TH1) cell-mediated response to influenza A virus (IAV) infection and TH2 cell-mediated allergic airway inflammation. T cell-specific deletion of Orai1 did not exacerbate pulmonary inflammation and viral burdens following IAV infection but protected mice from house dust mite-induced allergic airway inflammation. ORAI1 controlled the expression of genes including p53 and E2F transcription factors that regulate the cell cycle in TH2 cells in response to allergen stimulation and the expression of transcription factors and cytokines that regulate TH2 cell function. Systemic application of a CRAC channel blocker suppressed allergic airway inflammation without compromising immunity to IAV infection, suggesting that inhibition of SOCE is a potential treatment for allergic airway disease.

International consensus statement on allergy and rhinology: rhinosinusitis 2021

I.

EXECUTIVE SUMMARY

BACKGROUND: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR-RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR-RS-2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence-based findings of the document.

METHODS

ICAR-RS presents over 180 topics in the forms of evidence-based reviews with recommendations (EBRRs), evidence-based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary.

RESULTS

ICAR-RS-2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence-based management algorithm is provided.

CONCLUSION

This ICAR-RS-2021 executive summary provides a compilation of the evidence-based recommendations for medical and surgical treatment of the most common forms of RS.

The Role of TRP Channels in Allergic Inflammation and its Clinical Relevance

Allergy refers to an abnormal adaptive immune response to non-infectious environmental substances (allergen) that can induce various diseases such as asthma, atopic dermatitis, and allergic rhinitis. In this allergic inflammation, various immune cells, such as B cells, T cells, and mast cells, are involved and undergo complex interactions that cause a variety of pathophysiological conditions. In immune cells, calcium ions play a crucial role in controlling intracellular Ca2+ signaling pathways. Cations, such as Na+, indirectly modulate the calcium signal generation by regulating cell membrane potential. This intracellular Ca2+ signaling is mediated by various cation channels; among them, the Transient Receptor Potential (TRP) family is present in almost all immune cell types, and each channel has a unique function in regulating Ca2+ signals. In this review, we focus on the role of TRP ion channels in allergic inflammatory responses in T cells and mast cells. In addition, the TRP ion channels, which are attracting attention in clinical practice in relation to allergic diseases, and the current status of the development of therapeutic agents that target TRP channels are discussed.

Analysis of Mrgprb2 Receptor-Evoked Ca 2+ Signaling in Bone Marrow Derived (BMMC) and Peritoneal (PMC) Mast Cells of TRPC-Deficient Mice

Mast cells are a heterogeneous group of immune cells. The simplest and commonly accepted classification divides them in two groups according to their protease content. We have compared the action of diverse secretagogues on bone marrow derived (BMMC) and peritoneal (PMC) mast cells which represent classical models of mucosal and connective tissue type mast cells in mice. Whereas, antigen stimulation of the FcεRI receptors was similarly effective in triggering elevations of free intracellular Ca²⁺ concentration ([Ca²⁺]_i) in both BMMC and PMC, robust [Ca²⁺]_i rise following Endothelin-1 stimulation was observed only in a fraction of BMMC. Leukotriene C4 activating cysteinyl leukotriene type I receptors failed to evoke [Ca²⁺]_i rise in either mast cell model. Stimulation of the recently identified target of many small-molecule drugs associated with systemic pseudo-allergic reactions, Mrgprb2, with compound 48/80, a mast cell activator with unknown receptor studied for many years, triggered Ca²⁺ oscillations in BMMC and robust [Ca²⁺]_i rise in PMCs similarly to that evoked by FcεRI stimulation. [Ca²⁺]_i rise in PMC could also be evoked by other Mrgprb2 agonists such as Tubocurarine, LL-37, and Substance P. The extent of [Ca²⁺]_i rise correlated with mast cell degranulation. Expression analysis of TRPC channels as potential candidates mediating agonist evoked Ca²⁺ entry revealed the presence of transcripts of all members of the TRPC subfamily of TRP channels in PMCs. The amplitude and AUC of compound 48/80-evoked [Ca²⁺]_i rise was reduced by ~20% in PMC from Trpc1/4/6^−/− mice compared to Trpc1/4^−/− littermatched control mice, whereas FcεRI-evoked [Ca²⁺]_i rise was unaltered. Whole-cell patch clamp recordings showed that the reduction in compound 48/80-evoked [Ca²⁺]_i rise in Trpc1/4/6^−/− PMC was accompanied by a reduced amplitude of Compound 48/80-induced cation currents which exhibited typical features of TRPC currents. Together, this study demonstrates that PMC are an appropriate mast cell model to study mechanisms of Mrgprb2 receptor-mediated mast cell activation, and it reveals that TRPC channels contribute at least partially to Mrgprb2-mediated mast cellactivation but not following FcεRI stimulation. However, the channels conducting most of the Ca²⁺ entry in mast cells triggered by Mrgprb2 receptor stimulation remains to be identified.

CRAC channel regulation of innate immune cells in health and disease

Calcium is a major intracellular signaling messenger in innate immune cells. Similar to other immune cell subsets, the majority of calcium entry into innate immune cells is induced by cell surface receptors that stimulate store-operated calcium entry through calcium-release activated calcium (CRAC) channels. Since the molecular description of the STIM family of calcium sensors and the ORAI family of CRAC channel proteins, the majority of studies support a dominant role for these proteins in calcium signaling in innate cells. In reviewing the literature on CRAC channel function in innate cells, several general themes emerge. All innate cells express multiple members of the STIM and ORAI family members, however the ratio and relative contribution of individual isoforms changes depending on the cell type and activation state of the cell. It is evident that study of functional roles for STIM molecules is clearly ahead of studies of specific ORAI family members in all innate cell types, and that studies of CRAC channels in innate cells are not nearly as advanced as studies in lymphocytes. However, taken together, evidence from both STIM calcium sensors and ORAI channels in innate cells indicates that deficiency of STIM and ORAI proteins tends not to affect the development of any innate cell lineage, but certainly affects their function, in particular activation of the neutrophil oxidase and mast cell activation via IgE receptors. Furthermore, there are clearly hints that therapeutic targeting of CRAC channels in innate cells offers a new approach to various inflammatory and allergic diseases.

The Allergen Der p3 from House Dust Mite Stimulates Store-Operated Ca2+ Channels and Mast Cell Migration through PAR4 Receptors

The house dust mite is the principal source of perennial aeroallergens in man. How these allergens activate innate and adaptive immunity is unclear, and therefore, there are no therapies targeting mite allergens. Here, we show that house dust mite extract activates store-operated Ca²⁺ channels, a common signaling module in numerous cell types in the lung. Activation of channel pore-forming Orai1 subunits by mite extract requires gating by STIM1 proteins. Although mite extract stimulates both protease-activated receptor type 2 (PAR2) and PAR4 receptors, Ca²⁺ influx is more tightly coupled to the PAR4 pathway. We identify a major role for the serine protease allergen Der p3 in stimulating Orai1 channels and show that a therapy involving sub-maximal inhibition of both Der p3 and Orai1 channels suppresses mast cell activation to house dust mite. Our results reveal Der p3 as an important aeroallergen that activates Ca²⁺ channels and suggest a therapeutic strategy for treating mite-induced asthma.

Store-operated calcium entry in disease: Beyond STIM/Orai expression levels

Precise intracellular calcium signaling is crucial to numerous cellular functions. In non-excitable cells, store-operated calcium entry (SOCE) is a key step in the generation of intracellular calcium signals. Tight regulation of SOCE is important, and dysregulation is involved in several pathophysiological cellular malfunctions. The current underlying SOCE, calcium release-activated calcium current (I_CRAC), was first discovered almost three decades ago. Since its discovery, the molecular components of I_CRAC, Orai1 and stromal interaction molecule 1 (STIM1), have been extensively investigated. Several regulatory mechanisms and proteins contribute to alterations in SOCE and cellular malfunctions in cancer, immune and neurodegenerative diseases, inflammation, and neuronal disorders. This review summarizes these regulatory mechanisms, including glycosylation, pH sensing, and the regulatory proteins golli, α-SNAP, SARAF, ORMDL3, CRACR2A, and TRPM4 channels.

Evidence for autocrine and paracrine regulation of allergen-induced mast cell mediator release in the guinea pig airways

Mast cells play an essential role in immediate type hypersensitivity reactions and in chronic allergic diseases of the airways, including asthma. Mast cell mediator release can be modulated by locally released autacoids and circulating hormones, but surprisingly little is known about the autocrine effects of mediators released upon mast cell activation. We thus set out to characterize the autocrine and paracrine effects of mast cell mediators on mast cell activation in the guinea pig airways. By direct measures of histamine, cysteinyl-leukotriene and thromboxane release and with studies of allergen-evoked contractions of airway smooth muscle, we describe a complex interplay amongst these autacoids. Notably, we observed an autocrine effect of the cysteinyl-leukotrienes acting through cysLT₁ receptors on mast cell leukotriene release. We confirmed the results of previous studies demonstrating a marked enhancement of mast cell mediator release following cyclooxygenase inhibition, but we have extended these results by showing that COX-2 derived eicosanoids inhibit cysteinyl-leukotriene release and yet are without effect on histamine release. Given the prominent role of COX-1 inhibition in aspirin-sensitive asthma, these data implicate preformed mediators stored in granules as the initial drivers of these adverse reactions. Finally, we describe the paracrine signaling cascade leading to thromboxane synthesis in the guinea pig airways following allergen challenge, which occurs indirectly, secondary to cysLT₁ receptor activation on structural cells and/ or leukocytes within the airway wall, and a COX-2 dependent synthesis of the eicosanoid. The results highlight the importance of cell-cell and autocrine interactions in regulating allergic responses in the airways.

The role of cysteinyl leukotrienes and their receptors in refractory nasal polyps

Leukotriene signaling is essential in many diseases, including asthma, allergic rhinitis, atherosclerosis and inflammatory bowel disease. Nevertheless, the expression of cysteinyl leukotrienes (CysLTs) and its receptors (CYSLTRs) in different types of nasal polyps (NPs), and the role of their antagonist in the treatment of refractory chronic rhinosinusitis with nasal polyps (CRSwNP) are not well understood. The following study investigates the expression of CysLTs and CYSLTRs in different types of NPs, as well as the role of leukotriene receptor antagonist (montelukast) in refractory NPs. Our data showed that CysLTs and CYSLTRs were significantly elevated in CRSwNP group (p < 0.05), particularly in IL-5⁺NP patients^, compared to patients with chronic rhinosinusitis but without NPs (CRSsNP) and the control group. Furthermore, montelukast have shown the ability to inhibit the expression of MUC5AC, TSLP, IL-4, IL-5, IL-13, and TGF-β in NP explants after treatment with Staphylococcal Enterotoxins B (SEB). In addition, the patients treated by additional montelukast have better outcomes compared to those with INCS only. To conclude, our results demonstrate that the inhibition of CysLTs signaling by montelukast decreases the expression of cytokines and mucin in polyp explants, and in turn promotes the recovery in patients with refractory CRSwNP.

Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) is characterized by the triad of asthma, sinonasal polyposis, and aspirin intolerance. The hallmark of the disease is baseline overproduction of cysteinyl leukotrienes via the 5-lipoxygenase pathway, exacerbated by ingestion of aspirin. Patients with AERD have high rates of recidivistic polyposis following sinus surgery, although the improvement in quality of life following surgery is similar to aspirin-tolerant patients. The diagnosis is secured by a positive aspirin provocation test, usually administered by a medical allergist. Aspirin therapy is a unique treatment consideration for patients with AERD.

Position statement of the Brazilian Academy of Rhinology on the use of antihistamines, antileukotrienes, and oral corticosteroids in the treatment of inflammatory sinonasal diseases

Introduction

Inflammatory conditions of the nose and paranasal sinuses are very prevalent in the general population, resulting in marked loss of quality of life in affected patients, as well as significant work, leisure, and social activity losses. These patients require specific and specialized treatment. A wide range of oral medications are available.

Objective

The present document is aimed to clarify, for professionals treating patients with inflammatory sinonasal diseases, both specialists and general practitioners, specific oral therapies in noninfectious nasal inflammatory conditions.

Methods

The methodology used to create this article included the search for the key words: oral corticosteroids, antihistamines, antileukotrienes, rhinitis, rhinosinusitis in the MEDLINE and EMBASE databases in the last 5 years. Since no relevant article was found for the text on the subject of interest in the last 5 years, the search was extended for another 5 years, and so on, according to the authors’ needs.

Results

Relevant literature was found regarding the use of antihistamines, antileukotrienes and oral corticosteroids in these conditions. The Brazilian Academy of Rhinology emphasizes, after extensive discussion by the collegiate, key points in the treatment with these drugs.

Conclusion

There is support in the literature for the use of these drugs; however, final considerations about the role of each of them have been made.

Cell type-specific glycosylation of Orai1 modulates store-operated Ca2+ entry

N-glycosylation of cell surface proteins affects protein function, stability, and interaction with other proteins. Orai channels, which mediate store-operated Ca(2+) entry (SOCE), are composed of N-glycosylated subunits. Upon activation by Ca(2+) sensor proteins (stromal interaction molecules STIM1 or STIM2) in the endoplasmic reticulum, Orai Ca(2+) channels in the plasma membrane mediate Ca(2+) influx. Lectins are carbohydrate-binding proteins, and Siglecs are a family of sialic acid-binding lectins with immunoglobulin-like repeats. Using Western blot analysis and lectin-binding assays from various primary human cells and cancer cell lines, we found that glycosylation of Orai1 is cell type-specific. Ca(2+) imaging experiments and patch-clamp experiments revealed that mutation of the only glycosylation site of Orai1 (Orai1N223A) enhanced SOCE in Jurkat T cells. Knockdown of the sialyltransferase ST6GAL1 reduced α-2,6-linked sialic acids in the glycan structure of Orai1 and was associated with increased Ca(2+) entry in Jurkat T cells. In human mast cells, inhibition of sialyl sulfation altered the N-glycan of Orai1 (and other proteins) and increased SOCE. These data suggest that cell type-specific glycosylation influences the interaction of Orai1 with specific lectins, such as Siglecs, which then attenuates SOCE. In summary, the glycosylation state of Orai1 influences SOCE-mediated Ca(2+) signaling and, thus, may contribute to pathophysiological Ca(2+) signaling observed in immune disease and cancer.

An essential role of NAD(P)H oxidase 2 in UVA-induced calcium oscillations in mast cells

Solar UVA radiation (320-400 nm) is known to have immunomodulatory effects, but the detailed mechanisms involved are not fully elucidated. UVA irradiation has been shown to induce calcium oscillations in rat peritoneal mast cells due to NAD(P)H oxidase (NOX) activation, but the specific NOX isoforms have not been identified. In the present work effects of UVA irradiation were investigated in isolated rat peritoneal mast cells, in cultured rat mast cell line RBL-2H3, and in mouse bone marrow-derived mast cells (BMMC). It was found that UVA irradiation by alternate 340/380 nm (3.2-5.6 μW cm(-2)) or by LED (380 nm, 80 μW cm(-2)) induced calcium oscillations in isolated rat peritoneal mast cells, in RBL-2H3, and in BMMC. Such UVA-induced calcium oscillations resembled closely those induced by surface IgE receptor (FcεRI) activation. It was found that RBL-2H3 expressed high levels of gp91(phox) (NOX2), p22(phox), p67(phox), p47(phox), p40(phox), Rac1, Rac2, moderate levels of DUOX2, but did not express NOX1, NOX3, NOX4, or DUOX1. The specific cellular localizations of gp91(phox) (NOX2), p22(phox), p47(phox), p67(phox), p40(phox) and Rac1/2 were confirmed by immunocytochemistry. UVA-induced reactive oxygen species (ROS) production in RBL-2H3 was completely suppressed by the NOX inhibitor diphenyleneiodonium chloride (DPI) or by the antioxidant N-acetyl-l-cysteine (NAC). siRNA suppression of gp91(phox) (NOX2), p22(phox) and p47(phox) expression inhibited markedly UVA-induced calcium oscillations, ROS and IL-6/LTC4 production in RBL-2H3. Taken together these data indicate that NOX2 plays an essential role in UVA irradiation-induced calcium oscillations, ROS and mediator production in mast cells.

The Intervention of CRAC Channels Alleviates Inflammatory Responses in Nasal Polyps

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) is associated with Th2-dominant inflammation. However, effective treatments for CRSwNP have not yet been found. This study aimed to investigate the expression of Orai1 in nasal polyps (NP) and the influence on them of the intervention of Ca2+ release-activated Ca2+ (CRAC) channels.

MATERIALS AND METHODS

Nasal samples were obtained from normal subjects or subjects with CRSwNP. We studied the distribution of Orai1 protein in NP and normal mucosa (normal group) using immunohistochemistry. These tissues in cultures were then maintained in the absence (control group) or presence of 2-aminoethoxydiphenyl borate (2-APB) for 24 h. Orai1 was examined by means of enzyme-linked immunosorbent assay (ELISA) and real-time reverse transcription-polymerase chain reaction (RT-PCR). The Ca2+ mean fluorescence intensity (MFI) was evaluated by flow cytometry, and the inflammatory mediators, including interleukin (IL)-4, IL-5, IL-13, Dermatophagoides pteronyssinus-specific IgE, leukotriene C4 and eosinophil cation protein in cultures, were analyzed with ELISA and real-time RT-PCR.

RESULTS

The expression of Orai1 was localized to the cytoplasmic membrane of inflammatory cells, and upregulated in NP compared to that in the normal group. However, Orai1 protein was decreased in polyp tissues after the 2-APB treatment. The levels of Ca2+ MFI and above inflammatory mediators were also elevated in NP, and reduced after the 2-APB administration compared to those in the control group.

CONCLUSIONS

Orai1 and CRAC channels may play a crucial role in NP formation and development, and the 2-APB intervention of Orai1 protein may alleviate inflammatory responses in NP.

Ion channels in innate and adaptive immunity

Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy.

Key role for store-operated Ca2+ channels in activating gene expression in human airway bronchial epithelial cells

Ca²⁺ entry into airway epithelia is important for activation of the NFAT family of transcription factors and expression of genes including epidermal growth factor that help orchestrate local inflammatory responses. However, the identity of epithelial Ca²⁺ channel that activates these transcriptional responses is unclear. In many other non-excitable cells, store-operated Ca²⁺ entry is a major route for Ca²⁺ influx and is mediated by STIM1 and Orai1 proteins. This study was performed to determine if store-operated Ca²⁺ channels were expressed in human bronchial epithelial cells and, if so, whether they coupled Ca²⁺ entry to gene expression. Cytoplasmic Ca²⁺ measurements, patch clamp recordings, RNAi knockdown and functional assays were used to identify and then investigate the role of these Ca²⁺ channels in activating the NFAT and c-fos pathways and EGF expression. STIM1 and Orai1 mRNA transcripts as well as proteins were robustly in epithelial cells and formed functional Ca²⁺ channels. Ca²⁺ entry through the channels activated expression of c-fos and EGF as well as an NFAT-dependent reporter gene. Store-operated Ca²⁺ entry was also important for epithelial cell migration in a scrape wound assay. These findings indicate that store-operated Ca²⁺ channels play an important role in stimulating airway epithelial cell gene expression and therefore comprise a novel potential therapeutic target for the treatment of chronic asthma and related airway disorders.

Ion channels regulating mast cell biology

Mast cells play a central role in the pathophysiology of asthma and related allergic conditions. Mast cell activation leads to the degranulation of preformed mediators such as histamine and the secretion of newly synthesised proinflammatory mediators such as leukotrienes and cytokines. Excess release of these mediators contributes to allergic disease states. An influx of extracellular Ca2+ is essential for mast cell mediator release. From the Ca2+ channels that mediate this influx, to the K+ , Cl- and transient receptor potential channels that set the cell membrane potential and regulate Ca2+ influx, ion channels play a critical role in mast cell biology. In this review we provide an overview of our current knowledge of ion channel expression and function in mast cells with an emphasis on how channels interact to regulate Ca2+ signalling.

Emerging roles of store-operated Ca²⁺ entry through STIM and ORAI proteins in immunity, hemostasis and cancer

Store-operated Ca(2+) entry (SOCE) is an important Ca(2+) influx pathway, which is defined by the fact that depletion of intracellular Ca(2+) stores, mainly the endoplasmic reticulum (ER), triggers the opening of Ca(2+) channels in the plasma membrane. The best characterized SOC channel is the Ca(2+) release-activated Ca(2+) (CRAC) channel, which was first described in cells of the immune system but has since been reported in many different cell types. CRAC channels are multimers of ORAI family proteins, of which ORAI1 is the best characterized. They are activated by stromal interaction molecules (STIM) 1 and 2, which respond to the depletion of intracellular Ca(2+) stores with oligomerization and binding to ORAI proteins. The resulting SOCE is critical for the physiological function of many cell types including immune cells and platelets. Recent studies using cell lines, animal models and primary cells from human patients with defects in SOCE have highlighted the importance of this Ca(2+) entry mechanism in a variety of pathophysiological processes. This review focuses on the role of SOCE in immunity to infection, allergy, hemostasis and cancer.

CRACM/Orai ion channel expression and function in human lung mast cells

BACKGROUND

Influx of extracellular Ca(2+) into human lung mast cells (HLMCs) is essential for the FcεRI-dependent release of preformed granule-derived mediators and newly synthesized autacoids and cytokines. However, the identity of the ion channels underlying this Ca(2+) influx is unknown. The recently discovered members of the CRACM/Orai ion channel family that carries the Ca(2+) release-activated Ca(2+) current are candidates.

OBJECTIVES

To investigate the expression and function of CRACM channels in HLMCs.

METHODS

CRACM mRNA, protein, and functional expression were examined in purified HLMCs and isolated human bronchus.

RESULTS

CRACM1, -2, and -3 mRNA transcripts and CRACM1 and -2 proteins were detectable in HLMCs. A CRACM-like current was detected following FcεRI-dependent HLMC activation and also in HLMCs dialyzed with 30 μM inositol triphosphate. The Ca(2+)-selective current obtained under both conditions was blocked by 10 μM La(3+) and Gd(3+), known blockers of CRACM channels, and 2 distinct and specific CRACM-channel blockers-GSK-7975A and Synta-66. Both blockers reduced FcεRI-dependent Ca(2+) influx, and 3 μM GSK-7975A and Synta-66 reduced the release of histamine, leukotriene C(4), and cytokines (IL-5/-8/-13 and TNFα) by up to 50%. Synta-66 also inhibited allergen-dependent bronchial smooth muscle contraction in ex vivo tissue.

CONCLUSIONS

The presence of CRACM channels, a CRACM-like current, and functional inhibition of HLMC Ca(2+) influx, mediator release, and allergen-induced bronchial smooth muscle contraction by CRACM-channel blockers supports a role for CRACM channels in FcεRI-dependent HLMC secretion. CRACM channels are therefore a potential therapeutic target in the treatment of asthma and related allergic diseases.

Mitochondrial function and malfunction in the pathophysiology of pancreatitis

As a primary energy producer, mitochondria play a fundamental role in pancreatic exocrine physiology and pathology. The most frequent aetiology of acute pancreatitis is either gallstones or heavy alcohol consumption. Repeated episodes of acute pancreatitis can result in the development of chronic pancreatitis and increase the lifetime risk of pancreatic cancer 100-fold. Pancreatic cancer is one of the most common causes of cancer mortality with only about 3-4 % of patients surviving beyond 5 years. It has been shown that acute pancreatitis involves Ca²⁺ overload and overproduction of reactive oxygen species in pancreatic acinar cells. Both factors significantly affect mitochondria and lead to cell death. The pathogenesis of inflammation in acute and chronic pancreatitis is tightly linked to the induction of necrosis and apoptosis. There is currently no specific therapy for pancreatitis, but recent findings of an endogenous protective mechanism against Ca²⁺ overload--and particularly the potential to boost this protection--bring hope of new therapeutic approaches.

Effect of non-steroidal anti-inflammatory drugs and new fenamate analogues on TRPC4 and TRPC5 channels

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used anti-inflammatory therapeutic agents, among which the fenamate analogues play important roles in regulating intracellular Ca²⁺ transient and ion channels. However, the effect of NSAIDs on TRPC4 and TRPC5 is still unknown. To understand the structure-activity of fenamate analogues on TRPC channels, we have synthesized a series of fenamate analogues and investigated their effects on TRPC4 and TRPC5 channels. Human TRPC4 and TRPC5 cDNAs in tetracycline-regulated vectors were transfected into HEK293 T-REx cells. The whole cell current and Ca²⁺ movement were recorded by patch clamp and calcium imaging, respectively. Flufenamic acid (FFA), mefenamic acid (MFA), niflumic acid (NFA) and diclofenac sodium (DFS) showed inhibition on TRPC4 and TRPC5 channels in a concentration-dependent manner. The potency was FFA>MFA>NFA>DFS. Modification of 2-phenylamino ring by substitution of the trifluoromethyl group in FFA with F, CH₃, OCH₃, OCH₂CH₃, COOH, and NO₂ led to the changes in their channel blocking activity. However, 2-(2'-methoxy-5'-methylphenyl)aminobenzoic acid stimulated TRPC4 and TRPC5 channels. Selective COX1-3 inhibitors (aspirin, celecoxib, acetaminophen, and indomethacin) had no effect on the channels. Longer perfusion (> 5 min) with FFA (100 μM) and MFA (100 μM) caused a potentiation of TRPC4 and TRPC5 currents after their initial blocking effects that appeared to be partially mediated by the mitochondrial Ca²⁺ release. Our results suggest that fenamate analogues are direct modulators of TRPC4 and TRPC5 channels. The substitution pattern and conformation of the 2-phenylamino ring could alter their blocking activity, which is important for understanding fenamate pharmacology and new drug development targeting the TRPC channels.

Cysteinyl leukotriene type I receptor desensitization sustains Ca2+-dependent gene expression

A universal mechanism to turn off a biological response is receptor desensitization, where the ability of a physiological trigger to activate a cell is lost despite the continued presence of the stimulus. Receptor desensitization of G protein-coupled receptors involves uncoupling of the receptor from its G protein/second messenger pathway, followed by receptor internalization¹. G protein-coupled cysteinyl leukotriene type I (CysLT1) receptors regulate immune cell function and the receptor is an established therapeutic target for allergies including asthma².

Desensitization of these receptors arises predominantly from protein kinase C-dependent phosphorylation of three serine residues in the receptor C-terminus³. Physiological concentrations of the receptor agonist LTC₄ evoke repetitive cytoplasmic Ca²⁺ oscillations, reflecting regenerative Ca²⁺ release from stores that is sustained by Ca²⁺ entry through store-operated CRAC channels⁴. CRAC channels are tightly linked to expression of the transcription factor c-fos⁵, a regulator of numerous genes important to cell growth and development⁶. Here we show that abolishing leukotriene receptor desensitization suppresses agonist-driven gene expression. Mechanistically, stimulation of non-desensitizing receptors evoked prolonged inositol trisphosphate-mediated Ca²⁺ release, which led to accelerated Ca²⁺-dependent slow inactivation of CRAC channels and a subsequent loss of excitation-transcription coupling. Rather than serving to turn off a biological response, reversible desensitization of a Ca²⁺ mobilizing receptor acts as an ‘on’switch, sustaining long-term signalling in the immune system.

Pharmacology of ORAI channels as a tool to understand their physiological functions

Store-operated Ca(2+) entry is a major Ca(2+) entry mechanism that is present in most cell types. In immune cells, store-operated Ca(2+) entry is almost exclusively mediated by Ca(2+) release-activated Ca(2+) (CRAC) channels. Ca(2+) entry through these channels and the corresponding cytosolic Ca(2+) signals are required for many immune cell functions, including all aspects of T-cell activation. ORAI proteins are the molecular correlates for the CRAC channels. The three human members, ORAI1, ORAI2 and ORAI3, are activated through the stromal interaction molecules (STIM)1 and 2 following depletion of endoplasmic reticulum Ca(2+) stores. Different combinations of STIM and ORAI can form different CRAC channels with distinct biophysical properties. In this article, we review and discuss mechanistic and functional implications of two important CRAC/ORAI inhibitors, 2-APB and BTP2, and the antibiotic G418 that has also been reported to interfere with ORAI channel function. The use of pharmacological tools should help to assign distinct physiological and pathophysiological functions to different STIM-ORAI protein complexes.

Mast cell CRAC channel as a novel therapeutic target in allergy

PURPOSE OF REVIEW

This review describes recent advances in our understanding of a major Ca-entry pathway, the Ca release-activated Ca (CRAC) channel, that is central to mast cell activation.

RECENT FINDINGS

Animals in which the genes encoding the CRAC channel have been deleted have severely compromised mast cell function and reduced allergic responses. These functional consequences reflect the ability of CRAC channels to activate a range of spatially and temporally distinct responses in mast cells, which contribute to both rapid and slow phases of an allergic response. In addition, the cells can sustain their own activation through positive feedback cycles that involve CRAC channels. Drugs that inhibit CRAC channels are proving effective in treatment of allergic responses both in vitro and in animal models of asthma.

SUMMARY

CRAC channels comprise a new therapeutic target for combating allergies including asthma.

Calmodulin protects against alcohol-induced pancreatic trypsinogen activation elicited via Ca2+ release through IP3 receptors

Alcohol abuse is a major global health problem, but there is still much uncertainty about the mechanisms of action. So far, the effects of ethanol on ion channels in the plasma membrane have received the most attention. We have now investigated actions on intracellular calcium channels in pancreatic acinar cells. Our aim was to discover the mechanism by which alcohol influences calcium homeostasis and thereby understand how alcohol can trigger premature intracellular trypsinogen activation, which is the initiating step for alcohol-induced pancreatitis. We used intact or two-photon permeabilized acinar cells isolated from wild-type mice or mice in which inositol trisphosphate receptors of type 2 or types 2 and 3 were knocked out. In permeabilized pancreatic acinar cells even a relatively low ethanol concentration elicited calcium release from intracellular stores and intracellular trypsinogen activation. The calcium sensor calmodulin (at a normal intracellular concentration) markedly reduced ethanol-induced calcium release and trypsinogen activation in permeabilized cells, effects prevented by the calmodulin inhibitor peptide. A calmodulin activator virtually abolished the modest ethanol effects in intact cells. Both ethanol-elicited calcium liberation and trypsinogen activation were significantly reduced in cells from type 2 inositol trisphosphate receptor knockout mice. More profound reductions were seen in cells from double inositol trisphosphate receptor (types 2 and 3) knockout mice. The inositol trisphosphate receptors, required for normal pancreatic stimulus-secretion coupling, are also responsible for the toxic ethanol action. Calmodulin protects by reducing calcium release sensitivity.

Effect of thapsigargin on Ca²+ fluxes and viability in human prostate cancer cells

Effect of the carcinogen thapsigargin on human prostate cancer cells is unclear. This study examined if thapsigargin altered basal [Ca²⁺](i) levels in suspended PC3 human prostate cancer cells by using fura-2 as a Ca²⁺-sensitive fluorescent probe. Thapsigargin at concentrations between 10 nM and 10 µM increased [Ca²⁺](i) in a concentration-dependent fashion. The Ca²⁺ signal was reduced partly by removing extracellular Ca²⁺ indicating that Ca²⁺ entry and release both contributed to the [Ca²⁺](i) rise. This Ca²⁺ influx was inhibited by suppression of phospholipase A2, but not by inhibition of store-operated Ca²⁺ channels or by modulation of protein kinase C activity. In Ca²⁺-free medium, pretreatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-(t-butyl)-1,4-hydroquinone (BHQ) nearly abolished thapsigargin-induced Ca²⁺ release. Conversely, pretreatment with thapsigargin greatly reduced BHQ-induced [Ca²⁺](i) rise, suggesting that thapsigargin released Ca²⁺ from the endoplasmic reticulum. Inhibition of phospholipase C did not change thapsigargin-induced [Ca²⁺](i) rise. At concentrations of 1-10 µM, thapsigargin induced cell death that was partly reversed by chelation of Ca²⁺ with BAPTA/AM. Annexin V/propidium iodide staining data suggest that apoptosis was partly responsible for thapsigargin-induced cell death. Together, in PC3 human prostate cancer cells, thapsigargin induced [Ca²⁺](i) rises by causing phospholipase C-independent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx via phospholipase A2-sensitive Ca²⁺ channels. Thapsigargin also induced cell death via Ca²⁺-dependent pathways and Ca²⁺-independent apoptotic pathways.

Recent advances in antileukotriene therapy

PURPOSE OF REVIEW

Despite profound effects of leukotrienes in experimental models, clinical responses to antileukotriene drugs are highly heterogeneous. This review discusses recent advances concerning the molecular mechanisms of antileukotrienes as well as their efficacy in various clinical scenarios and patient groups.

RECENT FINDINGS

Appreciation of the role of leukotriene E4 and the existence of its distinct receptors may explain the limited efficacy of current leukotriene receptor antagonists. Pharmacogenetic studies highlight the influence of several leukotriene pathway genes on clinical responsiveness. Benefits of addition of antileukotrienes to inhaled corticosteroids in chronic adult asthmatics have been shown, but their role in acute asthma is unclear. Evidence suggests they are not a first-line treatment for allergic rhinitis or urticaria, but may provide useful additional therapy. In children antileukotrienes provide symptomatic benefit in preschool wheezers, but have no clear role in bronchiolitis or acute asthma. Adherence to montelukast appears superior to inhaled corticosteroids. Use in sleep-disordered breathing and eosinophilic gastroenteropathies warrants further investigation. Despite recent concerns thorough analysis of existing data suggests antileukotrienes are well tolerated drugs. The possible link with Churg-Strauss syndrome requires further investigation.

SUMMARY

The leukotriene pathway remains an attractive target in asthma and allergic disease, particularly in light of renewed appreciation of the role of leukotriene E4. Clarification of the clinical role of antileukotrienes is needed.

Is there a role for leukotriene antagonists in the prevention of recurrent nasal polyps?

PURPOSE OF REVIEW

The aim of this review is to provide the current available data for leukotriene receptor antagonists in the treatment of nasal polyps, the use in the postoperative therapy single or as an add-on to standard treatments.

RECENT FINDINGS

Surgical treatment of nasal polyps was refined in the last 30 years by the introduction of functional endoscopic sinus surgery and nasal endoscopy for monitoring nasal polyp patients. As the relapse is the main challenge and as nasal steroids only delay it, a more efficient treatment is needed. Leukotriene antagonists have effects on asthma and allergic rhinitis; preliminary data show some benefits in nasal polyps.

SUMMARY

In the surgery of nasal polyps, recurrence is the main problem. Steroids are the current standard therapy, but the limitations are obvious. The role of leukotrienes in the disorder of nasal polyps is well established now, and with the antagonists available, interest rose in treating nasal polyps. A total of 356 patients took part in several studies involving leukotriene antagonists in the nasal polyp population. Some studies have minor levels of evidence; the data show positive effects for patients in preoperative and postoperative studies and medical treatments. There were benefits as an add-on to steroids and data from allergic rhinitis studies also show possible synergism with antihistamines. There are hints for a positive effect on eosinophil inflammation, clinical symptom scores, nasal airflow, sneezing and postnasal drip. Although some effects are shown, more controlled studies are necessary for reliable data.

Store-operated CRAC channels: function in health and disease

Elevation of cytosolic Ca(2+) levels through the activation of store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels is involved in mediating a disparate array of cellular responses. These include secretion, metabolism and gene expression, as well as cell growth and proliferation. Moreover, emerging evidence points to the involvement of aberrant CRAC channel activity in human diseases, such as certain types of immunodeficiency and autoimmunity disorders, allergy, and inflammatory bowel disease. This article summarizes recent advances in understanding the gating and function of CRAC channels, their links to human disease and key issues for the development of channel blockers.