Characterization of prostanoid receptors mediating inhibition of histamine release from anti-IgE-activated rat peritoneal mast cells

Novel insights regarding anaphylaxis in children - With a focus on prevalence, diagnosis, and treatment

Anaphylaxis is a serious allergic reaction that occurs rapidly and causes a life-threatening response involving the whole body. This reaction often leads to difficulty in breathing and can result in death. The estimated prevalence of anaphylaxis is 0.05%-2%, which is reported to be increasing in children. Although drugs and venom are the most common causes of anaphylaxis in adults, food is the most common cause of anaphylaxis in children. An interesting association between food-dependent exercise-induced anaphylaxis (FDEIA) and oral immunotherapy (OIT) has recently been reported. A provocation test to determine the diagnostic and augmenting factors of FDEIA has been reported in recent years. Remarkably, several articles showed allergic symptoms without exercise in children with FDEIA and in those with FDEIA development after OIT. Regarding OIT, full-dose OIT poses a risk of adverse reactions, including anaphylaxis. Recent trials have shown the efficacy and safety of low-dose OIT in patients with food-induced anaphylaxis. In this review, we summarized the novel insights regarding anaphylaxis in the pediatric population.

How to manage food dependent exercise induced anaphylaxis (FDEIA)

PURPOSE OF REVIEW

In recent years, the number of reports on food-dependent exercise-induced anaphylaxis (FDEIA) has been increasing. This review aims to describe the standard management of FDEIA including provocation tests and identify the issues that remain unclear.

RECENT FINDINGS

Provocation tests with aspirin for FDEIA enable us to confirm the definitive diagnosis and to make differential diagnosis. In some cases, FDEIA symptoms can be induced by aspirin and the causative food without exercise. Exercise may only be an augmenting factor of FDEIA, similar to aspirin or alcohol.

SUMMARY

The mechanisms of FDEIA development remain unclear. It has been suggested that in FDEIA, exercise lowers the threshold of a food allergy. Further research is needed to elucidate the mechanism of FDEIA and to establish strategies for effective disease management.

Prostaglandin E2 prevents hyperosmolar-induced human mast cell activation through prostanoid receptors EP2 and EP4

Background

Mast cells play a critical role in allergic and inflammatory diseases, including exercise-induced bronchoconstriction (EIB) in asthma. The mechanism underlying EIB is probably related to increased airway fluid osmolarity that activates mast cells to the release inflammatory mediators. These mediators then act on bronchial smooth muscle to cause bronchoconstriction. In parallel, protective substances such as prostaglandin E₂ (PGE₂) are probably also released and could explain the refractory period observed in patients with EIB.

Objective

This study aimed to evaluate the protective effect of PGE₂ on osmotically activated mast cells, as a model of exercise-induced bronchoconstriction.

Methods

We used LAD2, HMC-1, CD34-positive, and human lung mast cell lines. Cells underwent a mannitol challenge, and the effects of PGE₂ and prostanoid receptor (EP) antagonists for EP_1–4 were assayed on the activated mast cells. Beta-hexosaminidase release, protein phosphorylation, and calcium mobilization were assessed.

Results

Mannitol both induced mast cell degranulation and activated phosphatidyl inositide 3-kinase and mitogen-activated protein kinase (MAPK) pathways, thereby causing de novo eicosanoid and cytokine synthesis. The addition of PGE₂ significantly reduced mannitol-induced degranulation through EP₂ and EP₄ receptors, as measured by beta-hexosaminidase release, and consequently calcium influx. Extracellular-signal-regulated kinase 1/2, c-Jun N-terminal kinase, and p38 phosphorylation were diminished when compared with mannitol activation alone.

Conclusions

Our data show a protective role for the PGE₂ receptors EP₂ and EP₄ following osmotic changes, through the reduction of human mast cell activity caused by calcium influx impairment and MAP kinase inhibition.

Prostaglandin E2-induced inflammation: Relevance of prostaglandin E receptors

Prostaglandin E2 (PGE2) is one of the most typical lipid mediators produced from arachidonic acid (AA) by cyclooxygenase (COX) as the rate-limiting enzyme, and acts on four kinds of receptor subtypes (EP1-EP4) to elicit its diverse actions including pyrexia, pain sensation, and inflammation. Recently, the molecular mechanisms underlying the PGE2 actions mediated by each EP subtype have been elucidated by studies using mice deficient in each EP subtype as well as several compounds highly selective to each EP subtype, and their findings now enable us to discuss how PGE2 initiates and exacerbates inflammation at the molecular level. Here, we review the recent advances in PGE2 receptor research by focusing on the activation of mast cells via the EP3 receptor and the control of helper T cells via the EP2/4 receptor, which are the molecular mechanisms involved in PGE2-induced inflammation that had been unknown for many years. We also discuss the roles of PGE2 in acute inflammation and inflammatory disorders, and the usefulness of anti-inflammatory therapies that target EP receptors. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Anti-inflammatory and antipruritic effects of luteolin from Perilla (P. frutescens L.) leaves

Perilla (Perilla frutescens L.) leaves have shown therapeutic efficacy in the treatment of inflammatory disorders, allergies, bronchial asthma, and systemic damage due to free radicals. In the present study we analyzed the active constituents in perilla leaves using high-performance liquid chromatography (HPLC) and isolated luteolin, a polyphenolic flavonoid. We investigated the anti-inflammatory and antipruritic properties of luteolin. Luteolin inhibited the secretion of inflammatory cytokines such as interleukin-1β (IL-1 β) and tumor necrosis factor-α (TNF-α) from human mast cells (HMC-1) stimulated with phorbol myristate acetate plus calcium ionophore A23187 in a dose-dependent manner. Luteolin also significantly reduced the histamine release from rat peritoneal mast cells stimulated by compound 48/80, a potent histamine liberator. Furthermore, the administration of luteolin markedly inhibited the scratching behavior and vascular permeability induced by pruritogens, such as compound 48/80 or serotonin, in ICR mice. These results suggested that luteolin has potential as a therapeutic agent against inflammation and itch-related skin diseases.

Aspirin augments IgE-mediated histamine release from human peripheral basophils via Syk kinase activation

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs), especially aspirin, and food additives (FAs) may exacerbate allergic symptoms in patients with chronic idiopathic urticaria and food-dependent exercise-induced anaphylaxis (FDEIA). Augmentation of histamine release from human mast cells and basophils by those substances is speculated to be the cause of exacerbated allergic symptoms. We sought to investigate the mechanism of action of aspirin on IgE-mediated histamine release.

METHODS

The effects of NSAIDs, FAs or cyclooxygenase (COX) inhibitors on histamine release from human basophils concentrated by gravity separation were evaluated.

RESULTS

Benzoate and tartrazine, which have no COX inhibitory activity, augmented histamine release from basophils similar to aspirin. In contrast, ibuprofen, meloxicam, FR122047 and NS-398, which have COX inhibitory activity, did not affect histamine release. These results indicate that the augmentation of histamine release by aspirin is not due to COX inhibition. It was observed that aspirin augmented histamine release from human basophils only when specifically activated by anti-IgE antibodies, but not by A23187 or formyl-methionyl-leucyl-phenylalanine. When the IgE receptor signaling pathway was activated, aspirin increased the phosphorylation of Syk. Moreover, patients with chronic urticaria and FDEIA tended to be more sensitive to aspirin as regards the augmentation of histamine release, compared with healthy controls.

CONCLUSIONS

Aspirin enhanced histamine release from basophils via increased Syk kinase activation, and that the augmentation of histamine release by NSAIDs or FAs may be one possible cause of worsening symptoms in patients with chronic urticaria and FDEIA.

Repeated application of glucocorticoids exacerbate pruritus via inhibition of prostaglandin D2 production of mast cells in a murine model of allergic contact dermatitis

Rebound is known to occur most typically when topical glucocorticoids are abruptly discontinued; however, its frequency and severity are poorly characterized. We previously created a novel murine model of topical glucocorticoid-induced pruritus; however, the mechanism underlying pruritus in this model has not been elucidated. Using this murine model, we aimed to determine the cause of augmentation of pruritus with a focus on the production of prostaglandin (PG) D(2). BALB/c mice with chronic allergic contact dermatitis induced by 5 weeks of repeated application of 2,4,6-trinitro-1-chlorobenzene (TNCB) were treated topically with dexamethasone for 5 weeks immediately after the elicitation of dermatitis and after ear-swelling and scratching behavior were measured. RBL-2H3 mast cells were used to investigate the effect of dexamethasone on degranulation or PGD(2) production in IgE/antigen-stimulated mast cells. The scratching behavior induced by TNCB was augmented by topical application of dexamethasone, but dexamethasone did not have any effect on scratching bouts in mice that had not been treated with TNCB. Topical dexamethasone reduced the PGD(2) level, which increase in TNCB-treated mice, to the baseline level. Moreover, dexamethasone significantly decreased the PGD(2) production in IgE/antigen-stimulated RBL-2H3 mast cells; however, the same concentration of dexamethasone did not have any effect on the degranulation of stimulated mast cells. Topical glucocorticoids may exacerbate pruritus in a mouse model of allergic contact dermatitis via inhibition of PGD(2) production in antigen-mediated activated mast cells in the skin.

Mast cells and the liver aging process

It has now ascertained that the clinical manifestations of liver disease in the elderly population reflect both the cumulative effects of longevity on the liver and the generalized senescence of the organism ability to adjust to metabolic, infectious, and immunologic insults. Although liver tests are not significantly affected by age, the presentation of liver diseases such as viral hepatitis may be subtler in the elderly population than that of younger patients.

Human immunosenescence is a situation in which the immune system, particularly T lymphocyte function, deteriorates with age, while innate immunity is negligibly affected and in some cases almost up-regulated.

We here briefly review the relationships between the liver aging process and mast cells, the key effectors in a more complex range of innate immune responses than originally though.

Prostaglandin D₂ and T(H)2 inflammation in the pathogenesis of bronchial asthma

Prostaglandin D₂ (PGD₂) is a major prostanoid, produced mainly by mast cells, in allergic diseases, including bronchial asthma. PGD₂-induced vasodilatation and increased permeability are well-known classical effects that may be involved in allergic inflammation. Recently, novel functions of PGD₂ have been identified. To date, D prostanoid receptor (DP) and chemoattractant receptor homologous molecule expressed on T(H)2 cells (CRTH2) have been shown to be major PGD₂-related receptors. These two receptors have pivotal roles mediating allergic diseases by regulating the functions of various cell types, such as T(H)2 cells, eosinophils, basophils, mast cells, dendritic cells, and epithelial cells. This review will focus on the current understanding of the roles of PGD₂ and its metabolites in T(H)2 inflammation and the pathogenesis of bronchial asthma.

Lubiprostone reverses the inhibitory action of morphine on mucosal secretion in human small intestine

BACKGROUND AND AIMS

Treatments with morphine or opioid agonists cause constipation. Lubiprostone is approved for treatment of adult idiopathic constipation and constipation-predominant IBS in adult women. We tested whether lubiprostone can reverse morphine-suppression of mucosal secretion in human intestine and explored the mechanism of action.

METHODS

Fresh segments of jejunum discarded during Roux-En-Y gastric bypass surgeries were used. Changes in short-circuit current (ΔIsc) were recorded in Ussing flux chambers as a marker for electrogenic chloride secretion during pharmacological interactions between morphine, prostaglandin receptor antagonists, chloride channel blockers and lubiprostone.

RESULTS

Morphine suppressed basal Isc. Lubiprostone reversed morphine suppression of basal Isc. Lubiprostone, applied to the mucosa in concentrations ranging from 3 nM to 30 μM, evoked increases in Isc in concentration-dependent manner when applied to the mucosal side of muscle-stripped preparations. Blockade of enteric nerves did not change stimulation of Isc by lubiprostone. Removal of chloride or application of bumetanide or NPPB suppressed or abolished responses to lubiprostone. Antagonists acting at CFTR channels and prostaglandin EP(4) receptors, but not at E(1), EP(1-3) receptors, partially suppressed stimulation of Isc by lubiprostone.

CONCLUSIONS

Antisecretory action of morphine results from suppression of excitability of secretomotor neurons in the enteric nervous system. Lubiprostone, which does not affect enteric neurons directly, bypasses the action of morphine by directly opening mucosal chloride channels.

Bone marrow stromal cells inhibit mast cell function via a COX2-dependent mechanism

BACKGROUND

Mast cells (MCs) have a central role in the induction of allergic inflammation, such as seen in asthma, and contribute to the severity of certain autoimmune diseases, such as rheumatoid arthritis. The MC thus represents an important inflammatory cell, and one which has resisted therapeutic attempts to alter its role in disease.

OBJECTIVE

Because bone marrow-derived stromal cells (BMSC, also known as mesenchymal stem cells or MSCs) have been reported to alter allergic inflammation in vivo, we chose to study the interaction between mouse BMSC and mouse bone marrow-derived MCs.

METHODS

MC degranulation, cytokine production and chemotaxis were evaluated in vitro following co-culture with BMSCs either in cell contact or a transwell. In addition, MC degranulation was assessed in vivo following administration of BMSCs in a model of passive cutaneous anaphylaxis and a peritoneal degranulation assay. Mechanisms of MC suppression by BMSCs were determined through use of inhibitors or antibodies to COX1, COX2, nitric oxide, indoleamine 2, 3-dioxygenase, EP1-4 receptors, TGF-β and IL-10. Lastly, we utilized either BMSCs or MCs deficient in COX1, COX2 or EP1-4 receptors to confirm the mechanisms of inhibition of MC function by BMSCs.

RESULTS

We discovered that BMSCs will effectively suppress specific MC functions in vitro as well as in vivo. When MCs are cocultured with BMSCs to allow cell-to-cell contact, BMSCs suppressed MC degranulation, pro-inflammatory cytokine production, chemokinesis and chemotaxis. Similarly, MC degranulation within mouse skin or the peritoneal cavity was suppressed following in vivo administration of BMSCs. Further, we found that these inhibitory effects were dependent on up-regulation of COX2 in BMSCs; and were facilitated through the activation of EP4 receptors on MCs.

CONCLUSION AND CLINICAL RELEVANCE

These observations support the concept that BMSCs have the ability to suppress MC activation and therefore could be the basis for a novel cell based therapeutic approach in the treatment of MC driven inflammatory diseases.

Bone marrow stromal cells inhibit mast cell function via a COX2-dependent mechanism

BACKGROUND

Mast cells (MCs) have a central role in the induction of allergic inflammation, such as seen in asthma, and contribute to the severity of certain autoimmune diseases, such as rheumatoid arthritis. The MC thus represents an important inflammatory cell, and one which has resisted therapeutic attempts to alter its role in disease.

OBJECTIVE

Because bone marrow-derived stromal cells (BMSC, also known as mesenchymal stem cells or MSCs) have been reported to alter allergic inflammation in vivo, we chose to study the interaction between mouse BMSC and mouse bone marrow-derived MCs.

METHODS

MC degranulation, cytokine production and chemotaxis were evaluated in vitro following co-culture with BMSCs either in cell contact or a transwell. In addition, MC degranulation was assessed in vivo following administration of BMSCs in a model of passive cutaneous anaphylaxis and a peritoneal degranulation assay. Mechanisms of MC suppression by BMSCs were determined through use of inhibitors or antibodies to COX1, COX2, nitric oxide, indoleamine 2, 3-dioxygenase, EP1-4 receptors, TGF-β and IL-10. Lastly, we utilized either BMSCs or MCs deficient in COX1, COX2 or EP1-4 receptors to confirm the mechanisms of inhibition of MC function by BMSCs.

RESULTS

We discovered that BMSCs will effectively suppress specific MC functions in vitro as well as in vivo. When MCs are cocultured with BMSCs to allow cell-to-cell contact, BMSCs suppressed MC degranulation, pro-inflammatory cytokine production, chemokinesis and chemotaxis. Similarly, MC degranulation within mouse skin or the peritoneal cavity was suppressed following in vivo administration of BMSCs. Further, we found that these inhibitory effects were dependent on up-regulation of COX2 in BMSCs; and were facilitated through the activation of EP4 receptors on MCs.

CONCLUSION AND CLINICAL RELEVANCE

These observations support the concept that BMSCs have the ability to suppress MC activation and therefore could be the basis for a novel cell based therapeutic approach in the treatment of MC driven inflammatory diseases.

Shear-induced interleukin-6 synthesis in chondrocytes: roles of E prostanoid (EP) 2 and EP3 in cAMP/protein kinase A- and PI3-K/Akt-dependent NF-kappaB activation

Mechanical overloading of cartilage producing hydrostatic stress, tensile strain, and fluid flow can adversely affect chondrocyte function and precipitate osteoarthritis (OA). Application of high fluid shear stress to chondrocytes recapitulates the earmarks of OA, as evidenced by the release of pro-inflammatory mediators, matrix degradation, and chondrocyte apoptosis. Elevated levels of cyclooxygenase-2 (COX-2), prostaglandin (PG) E(2), and interleukin (IL)-6 have been reported in OA cartilage in vivo, and in shear-activated chondrocytes in vitro. Although PGE(2) positively regulates IL-6 synthesis in chondrocytes, the underlying signaling pathway of shear-induced IL-6 expression remains unknown. Using the human T/C-28a2 chondrocyte cell line as a model system, we demonstrate that COX-2-derived PGE(2) signals via up-regulation of E prostanoid (EP) 2 and down-regulation of EP3 receptors to raise intracellular cAMP, and activate protein kinase A (PKA) and phosphatidylinositol 3-kinase (PI3-K)/Akt pathways. PKA and PI3-K/Akt transactivate the NF-kappaB p65 subunit via phosphorylation at Ser-276 and Ser-536, respectively. Binding of p65 to the IL-6 promoter elicits IL-6 synthesis in sheared chondrocytes. Selective knockdown of EP2 or ectopic expression of EP3 blocks PKA- and PI3-K/Akt-dependent p65 activation and markedly diminishes shear-induced IL-6 expression. Similar inhibitory effects on IL-6 synthesis were observed by inhibiting PKA, PI3-K, or NF-kappaB using pharmacological and/or genetic interventions. Reconstructing the signaling network regulating shear-induced IL-6 expression in chondrocytes may provide insights for developing therapeutic strategies for arthritic disorders and for culturing artificial cartilage in bioreactors.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

Prostaglandin as a target molecule for pharmacotherapy of allergic inflammatory diseases

The purpose of this review is to summarize the role of prostaglandins (PGs) in allergic inflammation and to know the value of PGs, as a target molecule for an anti-allergic drug. PGD(2) is the major PG produced by the cyclooxygenase pathway in mast cells. Our and others findings indicate that PGD(2) is one of the potent allergic inflammatory mediators and must be a target molecule of anti-allergic agent. From our data, one of PGD(2) receptor antagonists show clear inhibition of airway hypersensitivity caused by allergic reaction. Concerning the role of PGE(2) in allergic inflammation, conflicting results have been reported. Many experimental data suggest an individual role of each PGE(2) receptor, EP(1), EP(2), EP(3) and EP(4) in allergic reaction. Our results indicate the protective action of PGE(2) on allergic reaction via EP(3). In addition, one of EP(3) agonists clearly inhibits the allergic airway inflammation. These findings indicate the value of EP(3) agonists as an anti-allergic agent. In addition, some investigators including us reported that PGI(2) plays an important role for the protection of the onset of allergic reaction. However, the efficacy of PGI(2) analogue as an anti-allergic agent is not yet fully investigated. Finally, the role of thromboxane A(2) (TxA(2)) in allergic reaction is discussed. Our experimental results suggest a different participation of TxA(2) in allergic reaction of airway and skin. In this review, the role of PGs in allergic inflammation is summarized and the value of PGs as a target molecule for developing a new anti-allergic agent will be discussed.

Presence of SNAP-23 and syntaxin 4 in mouse and hamster peritoneal mast cells

Mast cells (MCs) play a crucial role in inflammatory reactions. Their presence and number in the peritoneal cavity is important to overcome and enhance resistance to peritoneal infection. When MCs are activated they release a variety of biological mediators from their granules, such as histamine, that contribute to the appropriate and rapid local immune response. Granular content is released using a process of compound exocytosis, also termed degranulation. SNAP-23 and syntaxin 4 are plasma membrane proteins involved in degranulation of rat MCs. Their presence, however, has not been studied in MCs of other rodent species. The aim of the present study was to investigate using immunocytochemistry whether SNAP-23 and syntaxin 4 are present in peritoneal MCs of the mouse and hamster. In addition, the diameter, percentage and histamine content of these cells were also analyzed. Our results demonstrate that SNAP-23 and syntaxin 4 are present in the mouse and hamster peritoneal MCs, suggesting that proteins involved in the secretory process in MCs are conserved among species. Likewise, we conclude that peritoneal MCs of mouse and hamster are heterogeneous in size, percentage and histamine content.

Comparison of the influence of NSAIDs with different COX-selectivity on histamine release from mast cells isolated from naïve and sensitized rats

Mast cell stimulation leads to an early response with histamine release and prostaglandin (PGD(2)) production but attempts to link these two events have been contradictory. In IgE-mediated mast cell activation, a late-phase PGD(2)-production is caused by increased cyclooxygenase-2 (COX-2) expression whereas a COX-2 involvement in the early response is uncertain. The present study compares the influence of four COX-inhibitors (NSAIDs) on the histamine release of mast cells from naïve and actively sensitized rats. NSAIDs of different COX-1 vs. COX-2 selectivity were used, i.e. acetylsalicylic acid (ASA), piroxicam, meloxicam, and NS-398, a selective COX-2-inhibitor. All could inhibit antigen-induced histamine release, with 64%, 34%, 27% and 85% inhibition by ASA (5 mM), piroxicam (100 microM), meloxicam (100 microM) and NS-398 (100 microM), respectively. Similar inhibition was found with compound 48/80 without calcium added to the medium whereas compound 48/80 with calcium was affected less by ASA and NS-398 and unaffected by the oxicams. Only small differences between the two kinds of mast cells were found, except with NS-398 which was a significantly more effective inhibitor of naïve than sensitized cells when exposed to compound 48/80 with calcium present. The results do not show any consistent relationship between the influence of the NSAIDs and their COX-2-selectivity. The high NSAID-concentrations required for inhibition cast doubt about an involvement of COX-inhibition and indicate additional or other targets. The results seem to exclude toxic effects on mast cell energy production but are consistent with an interference with the calcium disposition.

Prostaglandin E2 activates EP2 receptors to inhibit human lung mast cell degranulation

The prostanoid, PGE2, is known to inhibit human lung mast cell activity. The aim of the present study was to characterize the EP receptor that mediates this effect. PGE2 (pEC(50), 5.8+/-0.1) inhibited the IgE-mediated release of histamine from mast cells in a concentration-dependent manner. Alternative EP receptor agonists were studied. The EP2-selective agonist, butaprost (pEC50, 5.2+/-0.2), was an effective inhibitor of mediator release whereas the EP1/EP3 receptor agonist, sulprostone, and the EP1-selective agonist, 17-phenyl-trinor-PGE2, were ineffective. The DP agonist PGD2, the FP agonist PGF(2alpha), the IP agonist iloprost and the TP agonist U-46619 were ineffective inhibitors of IgE-mediated histamine release from mast cells. PGE2 induced a concentration-dependent increase in intracellular cAMP levels in mast cells. The effects of the EP1/EP2 receptor antagonist, AH6809, and the EP4 receptor antagonist, AH23848, on the PGE2-mediated inhibition of histamine release were determined. AH6809 (pK(B), 5.6+/-0.1) caused a modest rightward shift in the PGE2 concentration-response curve, whereas AH23848 was ineffective. Long-term (24 h) incubation of mast cells with either PGE2 or butaprost (EP2 agonist), but not sulprostone (EP1/EP3 agonist), caused a significant reduction in the subsequent ability of PGE2 to inhibit histamine release. Collectively, these data suggest that PGE2 mediates effects on human lung mast cells by interacting with EP2 receptors.

Effects of plastoquinones from the brown alga Sargassum micracanthum and a new chromene derivative converted from the plastoquinones on acute gastric lesions in rats

Previously, we reported the anti oxidative and anti viral effects of plastoquinones (compounds 1, 2) extracted from the seaweed Sargassum micracanthum (Kuetzing) Endlicher and a new chromene compound (compound 3), which was converted from the plastoquinones. Recently, we have also demonstrated the antiulcer effects of these compounds and assessed the effects using a rat model of acute gastric lesion and fundus strips isolated from rats. In hydrochloric acid/ethanol rat ulcer tests: 1) oral administrations of compounds 1, 2, and 3 1--10, 3--30 and 10--30 mg/kg, respectively, and omeprazole 3--30 mg/kg showed dose-dependent antiulcer effects: 2) the antiulcer effects after intraduodenal administration of the respective compounds at the dose of 30 mg/kg were found to be significant: and 3) a decrease in the hexosamine level of the gastric mucosa was slightly improved by oral administration of compounds 1, 2, and 3 30 mg/kg. In indomethacin-induced gastric ulcer tests, the antiulcer effects of compounds 1, 2, and 3 10 mg/kg (p.o.) were not significant. Compounds 1, 2, and 3 showed slight contracting effects on the fundus isolated from rats and these effects were inhibited by pretreatment with AH6809, an inhibitor of prostaglandin DP, EP(1), and EP(2) receptors. These results suggest that the protection of the mucosa via endogenous prostaglandins might be related to the antiulcer effects of compounds 1, 2, and 3.

Aspirin-sensitive rhinosinusitis is associated with reduced E-prostanoid 2 receptor expression on nasal mucosal inflammatory cells

BACKGROUND

Impaired braking of inflammatory cell cysteinyl leukotriene production by prostaglandin (PG) E(2) has been implicated in the pathogenesis of aspirin exacerbated airways disease, but the mechanism is obscure. PGE(2) acts via G-protein-coupled receptors, E-prostanoid (EP)(1-4,) but there is little information on the expression of PGE(2) receptors in this condition.

OBJECTIVE

To address the hypothesis that expression of 1 or more EP receptors on nasal mucosal inflammatory cells is deficient in patients with aspirin-sensitive compared with nonaspirin-sensitive polypoid rhinosinusitis.

METHODS

By using specific antibodies, immunohistochemistry, and image analysis, we measured the expression of EP(1-4) in nasal biopsies from patients with aspirin-sensitive (n = 12) and nonaspirin-sensitive (n = 10) polypoid rhinosinusitis and normal controls (n = 9). Double-staining was used to phenotype inflammatory leukocytes expressing EP(1-4).

RESULTS

Global mucosal expression of EP(1) and EP(2), but not EP(3) or EP(4), immunoreactivity was significantly elevated in aspirin-sensitive and nonaspirin-sensitive rhinosinusitis compared with controls (P < .03). This was attributable principally to elevated expression on tubulin(+) epithelial cells and Mucin 5 subtypes A and B (Muc-5AC(+)) goblet cells. In contrast, the percentages of neutrophils, mast cells, eosinophils, and T cells expressing EP(2), but not EP(1), EP(3), or EP(4), were significantly reduced (P < or = .04) in the aspirin-sensitive compared with nonaspirin-sensitive patients.

CONCLUSION

The data suggest a possible role for PGE(2) in mediating epithelial repair in rhinitis and asthma. Because PGE(2) exerts a range of inhibitory actions on inflammatory leukocytes via the EP(2) receptor, its reduced expression in aspirin-sensitive rhinosinusitis may be partly responsible for the increased inflammatory infiltrate and production of cysteinyl leukotrienes that characterize aspirin-sensitive disease.

Age-induced reprogramming of mast cell degranulation

Mast cell degranulation can initiate an acute inflammatory response and contribute to the progression of chronic diseases. Alteration in the cellular programs that determine the requirement for mast cell degranulation would therefore have the potential to dramatically impact disease severity. Mast cells are exposed to increased levels of PGE2 during inflammation. We show that although PGE2 does not trigger the degranulation of dermal mast cells of young animals, in older mice, PGE2 is a potent mast cell stimulator. Intradermal administration of PGE2 leads to an EP3 receptor-dependent degranulation of mast cells, with the number of degranulated cells approaching levels observed in IgE- and Ag-treated controls. Taken together, these studies suggest that the ability of PGE2 to initiate mast cell degranulation changes in the aging animal. Therefore, elevated PGE2 levels might provide an important pathway by which mast cells are engaged to participate in inflammatory responses in the elderly patient.

Suppression of allergic inflammation by the prostaglandin E receptor subtype EP3

Prostaglandins, including PGD(2) and PGE(2), are produced during allergic reactions. Although PGD(2) is an important mediator of allergic responses, aspirin-like drugs that inhibit prostaglandin synthesis are generally ineffective in allergic disorders, suggesting that another prostaglandin-mediated pathway prevents the development of allergic reactions. Here we show that such a pathway may be mediated by PGE(2) acting at the prostaglandin E receptor EP3. Mice lacking EP3 developed allergic inflammation that was much more pronounced than that in wild-type mice or mice deficient in other prostaglandin E receptor subtypes. Conversely, an EP3-selective agonist suppressed the inflammation. This suppression was effective when the agonist was administered 3 h after antigen challenge and was associated with inhibition of allergy-related gene expression. Thus, the PGE(2)-EP3 pathway is an important negative modulator of allergic reactions.

Drug-induced urticaria

Urticaria is characterised by transient swellings of the skin, which fluctuate over hours. Deeper swellings of the subcutaneous and submucosal tissue are known as angio-oedema. Drug-induced urticaria has been reported with a wide range of drugs and vaccines. NSAIDs and antibiotics are the drugs most commonly associated with urticaria, although reliable data from prospectively controlled studies is scarce. Spontaneous reports of drug-induced urticaria to the Committee on Safety of Medicines, UK, over a 40-year period also implicate bupropion, selective serotonin re-uptake inhibitor antidepressants, angiotensin-converting enzyme inhibitors (ACEI), H2 and H1 antihistamines, and systemic antifungals. New evidence suggests that selective COX-2 inhibitors may be tolerated in patients with aspirin-sensitive urticaria. The safety of angiotensin II receptor antagonists in patients with angio-oedema induced by ACEI has not yet been established.

Prostaglandin D2 Inhibits IgE-Mediated Scratching by Suppressing Histamine Release From Mast Cells

Effects of prostaglandin (PG) D(2), PGE(2), and PGI(2) on itch-associated scratching responses of mice and histamine release from the rat basophilic leukemia cell line RBL-2H3 were examined. PGD(2) and ketotifen but not PGE(2) and PGI(2) suppressed the scratching caused by ovalbumin injected into ovalbumin-sensitized mice. Ketotifen also suppressed compound 48/80-induced scratching but not PGD(2), PGE(2), and PGI(2). In vitro, PGD(2) suppressed the antigen-induced histamine release from RBL-2H3 cells, but PGE(2) and PGI(2) did not. These findings suggest that PGD(2) specifically suppressed IgE-mediated scratching by inhibiting IgE-mediated histamine release from mast cells.

Excitatory action of prostanoids on the ferret isolated vagus nerve preparation

We have investigated the actions of various prostanoid receptor agonists on an isolated preparation of the ferret cervical vagus using a grease-gap extracellular recording technique. The potency ranking for depolarization was BW245C (5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropyl) hydantoin; DP-selective, EC50=0.14 microM)>prostaglandin E2 (nonselective EP agonist)>U-46619 (11alpha, 9alpha-epoxymethano-15S-hydroxyprosta-5Z,13E-dienoic acid; TP agonist)>prostaglandin F2alpha (FP receptor agonist). Sulprostone (EP1/EP3-selective), fluprostenol (FP-selective) and cicaprost and iloprost (both IP-selective) had minimal effects. It is likely that DP, EP2/EP4 and TP receptors are present on the vagal fibres of the ferret.

Treatment of acute and chronic gastrointestinal inflammation

Treating inflammation in the equine gastrointestinal tract remains a challenge. Our most potent anti-inflammatory drugs, COX inhibitors and glucocorticoids, have unwanted effects on the gastrointestinal tract and host defense that often limit their use. Newer strategies targeting specific cells and molecules that regulate a subset of the events occurring during inflammation are rapidly becoming available and should allow clinicians to reduce the detrimental effects of inflammation without inhibiting the beneficial aspects.

The DP receptor, allergic inflammation and asthma

Prostaglandin (PG) D(2) is the major cyclooxygenase metabolite of arachidonic acid produced by mast cells in response to allergen in diseases, such as asthma, atopic dermatitis, allergic rhinitis and allergic conjunctivitis. However, whether PGD(2) regulates allergic process per se, and, if so, whether it facilitates or down-regulates the disease process has remained unknown. PGD(2) exerts its actions by binding to two types of specific cell surface receptor. One is DP (the PGD receptor) and the other is chemoattractant receptor-homologous molecule expressed on Th2. Between the two, the DP receptor has been better characterized since its cDNA cloning in 1994, and novel class of DP antagonists have been and are being developed. Furthermore, mice deficient in DP were generated and have been subjected to several models of allergic diseases to reveal the role of PGD(2) in allergy. In this article, we summarize these findings and provide an overview of the current status of the DP receptor research to discuss the therapeutic potential of modulating the PGD(2)-DP pathway in allergic diseases.

Effects of methyl p-hydroxybenzoate (methyl paraben) on Ca2+ concentration and histamine release in rat peritoneal mast cells

1 Mechanisms of methyl p-hydroxybenzoate (methyl paraben) action in allergic reactions were investigated by measuring the intracellular Ca(2+) concentration ([Ca(2+)](i)) and histamine release in rat peritoneal mast cells (RPMCs). 2 In the presence or absence of extracellular Ca(2+), methyl paraben (0.1-10 mM) increased [Ca(2+)](i), in a concentration-dependent manner. Under both the conditions, methyl paraben alone did not evoke histamine release. 3 In RPMCs pretreated with a protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate (PMA) 3 and 10 nM), methyl paraben (0.3-3 mM) induced histamine release. However, a high concentration (10 mM) of the agent did not increase the histamine release. 4 U73122 (0.1 and 0.5 micro M), an inhibitor of phospholipase C (PLC), significantly inhibited the methyl paraben-induced histamine release in PMA-pretreated RPMCs. U73343 (0.5 micro M), an inactive analogue of U73122, did not inhibit the histamine release caused by methyl paraben. 5 In Ca(2+)-free solution, PLC inhibitors (U73122 0.1 and 0.5 micro M, D609 1-10 micro M) inhibited the methyl paraben-induced increase in [Ca(2+)](i), whereas U73343 (0.5 micro M) did not. 6 Xestospongin C (2-20 micro M) and 2 aminoethoxydiphenyl borate (30 and 100 micro M), blockers of the inositol 1,4,5-trisphosphate (IP(3)) receptor, inhibited the methyl paraben-induced increase in [Ca(2+)](i) in Ca(2+)-free solution. 7 In conclusion, methyl paraben causes an increase in [Ca(2+)](i), which may be due to release of Ca(2+) from storage sites by IP(3) via activation of PLC in RPMCs. In addition, methyl paraben possibly has some inhibitory effects on histamine release via unknown mechanisms.

Effects of cannabinoid receptor agonists on immunologically induced histamine release from rat peritoneal mast cells

Immunologic activation of mast cells through the cross-linking of high affinity IgE receptors results in the release of inflammatory mediators which are important in the pathogenesis of allergic reactions. Early studies investigating the effects of palmitoylethanolamide on animal models of inflammation and on rat mast cells led to the hypothesis that endogenous cannabinoids might act as local autacoids which suppressed inflammation by reducing the activation of mast cells. However, more recent studies produced contradicting results. In order to evaluate if cannabinoid receptors are present in mast cells, we studied the effects of endocannabinoids (anandamide and palmitoylethanolamide) and synthetic cannabimimetics (CP 55,940, WIN 55,212-2 and HU-210) on histamine release from rat peritoneal mast cells. When incubated with mast cells alone, only anandamide could induce significant level of histamine release at concentrations higher than 10(-6) M. When mast cells were activated with anti-IgE, the histamine release induced was not affected by anandamide, palmitoylethanolamide and CP 55,940. In contrast, both WIN 55,212-2 and HU-210 enhanced anti-IgE-induced histamine release at 10(-5) M and preincubation did not increase the potency. The histamine releasing action of anandamide and the enhancing effects of WIN 55,212-2 and HU-210 on anti-IgE-induced histamine release were not reduced by the cannabinoid receptor antagonists, AM 281 and AM 630. In conclusion, the present study does not support the hypothesis that cannabinoids suppress mast cell activation. Instead, some of the cannabinoid receptor-directed ligands tested enhanced mast cell activation. However, the high concentrations required and the failure of cannabinoid receptor antagonists to reverse such effects also question the existence of functional cannabinoid receptors in mast cells.

Aspirin sensitivity and urticaria

The relationship of aspirin sensitivity to urticaria is complex. Aspirin sensitivity can cause acute urticaria in some individuals, aggravate pre-existing chronic urticaria in others or, rarely, act as a cofactor with food or exercise to provoke anaphylaxis. Individuals who react with urticaria appear to come from a different population to those who react with asthma, although there is some overlap. Aspirin-sensitive chronic urticaria patients may also react adversely to some food additives. The pharmacological mechanisms of aspirin-sensitive urticaria are not fully understood but probably involve diversion of arachidonic acid metabolism from prostaglandin to cysteinyl leukotriene formation leading to direct effects on blood vessels and delayed mast cell degranulation with release of histamine. Cross-reactivity amongst all nonsteroidal drugs is common in aspirin-aggravated chronic urticaria but appears not to occur with selective cyclo-oxygenase 2 inhibitors.

Receptors and signaling mechanisms required for prostaglandin E2-mediated regulation of mast cell degranulation and IL-6 production

Mast cells are implicated in the pathogenesis of a broad spectrum of immunological disorders. These cells release inflammatory mediators in response to a number of stimuli, including IgE-Ag complexes. The degranulation of mast cells is modified by PGs. To begin to delineate the pathway(s) used by PGs to regulate mast cell function, we examined bone marrow-derived mast cells (BMMC) cultured from mice deficient in the EP(1), EP(2), EP(3), and EP(4) receptors for PGE(2). Although BMMCs express all four of these PGE(2) receptors, potentiation of Ag-stimulated degranulation and IL-6 cytokine production by PGE(2) is dependent on the EP(3) receptor. Consistent with the coupling of this receptor to G(alphai), PGE(2) activation of the EP(3) receptor leads to both inhibition of adenylate cyclase and increased intracellular Ca(2+). The magnitude of increase in intracellular Ca(2+) induced by EP(3) activation is similar to that observed after activation of cells with IgE and Ag. Although PGE alone is not sufficient to initiate BMMC degranulation, stimulation of cells with PGE along with PMA induces degranulation. These actions are mediated by the EP(3) receptor through signals involving Ca(2+) mobilization and/or decreased cAMP levels. Accordingly, these studies identify PGE(2)/EP(3) as a proinflammatory signaling pathway that promotes mast cell activation.

Food-dependent exercise-induced anaphylaxis: influence of concurrent aspirin administration on skin testing and provocation

BACKGROUND

Provocation tests in patients with food-dependent exercise-induced anaphylaxis (FDEIA) are often negative, even after a sufficient quantity of the implicated food and exercise have been taken.

OBJECTIVES

To investigate the effect of aspirin in provocation tests and in skin prick testing (SPT) of patients with FDEIA. Gluten as a major allergen in wheat-dependent FDEIA was also investigated.

METHODS

Provocation tests and SPT with suspected foods were performed in 12 patients with FDEIA. Provocation tests were performed with combinations of foods, exercise and aspirin. Detection of gluten-specific IgE was also performed by the CAP System FEIA radioallergosorbent test, SPT and a histamine release test.

RESULTS

The SPT reaction was enhanced by pretreatment with oral aspirin in five of eight (62.5) patients. Aspirin facilitated provocation in five of seven (71%) patients tested. Ingestion of wheat and aspirin without exercise provoked symptoms in two patients. Aspirin provoked symptoms even with a small amount of wheat and exercise in one patient. Only the combination of aspirin, wheat and exercise provoked anaphylaxis in one patient. Specific IgE, SPT and/or the histamine release test with gluten were positive in nine of 11 patients with wheat-dependent FDEIA.

CONCLUSIONS

Aspirin enhances symptoms of FDEIA, and prior ingestion of aspirin under controlled conditions can be used to confirm FDEIA. In practice, such patients should avoid aspirin ingestion. Gluten appears to be the major allergen in these patients with wheat-dependent FDEIA.

Immunologically induced histamine release from rat peritoneal mast cells is enhanced by low levels of substance P

Although direct activation of mast cells by high concentrations (>10(-6) M) of substance P is well established, the effect of sub-micromolar concentrations of the neuropeptide on mast cell activation has not been reported. We hence investigated if substance P would modulate immunologic activation of mast cells by studying the effect of the neuropeptide on anti-rat immunologlobulin E antibody (anti-IgE)-induced histamine release from purified rat peritoneal mast cells. We observed that substance P could dose-dependently potentiate anti-IgE-induced histamine release from rat peritoneal mast cells at concentrations (3x10(-9) M to 3x10(-7) M) which alone induced insignificant or low level of histamine release. While the potentiating effect of substance P was not suppressed by any of the non-peptide tachykinin receptor antagonists CP99994 ((2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine), SR48968 ((S)-N-methyl-N-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl) butyl-benzamide) and SR142801 ((S)-(N)-(1-[3-(1-benzoyl-3(3,4-dichlorophenyl)piperidine-3-yl)propyl]-4-phenylpiperidin-4-yl)-N-methyl-acetamide), it was mimicked by compound 48/80 and suppressed by benzalkonium chloride. Hence, substance P enhanced anti-IgE-induced histamine release through a similar receptor-independent mechanism as the direct mast cell activating action of polybasic compounds. Since high concentrations of substance P required for directly activating mast cells may not be achievable physiologically, the enhancing actions of the neuropeptide on the immunologic activation of mast cells may be more clinically relevant in the pathogenesis of various inflammatory conditions.

Prostaglandin E2 selectively enhances the IgE-mediated production of IL-6 and granulocyte-macrophage colony-stimulating factor by mast cells through an EP1/EP3-dependent mechanism

PGE(2) is an endogenously synthesized inflammatory mediator that is over-produced in chronic inflammatory disorders such as allergic asthma. In this study, we investigated the regulatory effects of PGE(2) on mast cell degranulation and the production of cytokines relevant to allergic disease. Murine bone marrow-derived mast cells (BMMC) were treated with PGE(2) alone or in the context of IgE-mediated activation. PGE(2) treatment alone specifically enhanced IL-6 production, and neither induced nor inhibited degranulation and the release of other mast cell cytokines, including IL-4, IL-10, IFN-gamma, and GM-CSF. IgE/Ag-mediated activation of BMMC induced the secretion of IL-4, IL-6, and GM-CSF, and concurrent PGE(2) stimulation synergistically increased mast cell degranulation and IL-6 and GM-CSF, but not IL-4, production. A similar potentiation of degranulation and IL-6 production by PGE(2), in the context of IgE-directed activation, was observed in the well-established IL-3-dependent murine mast cell line, MC/9. RT-PCR analysis of unstimulated MC/9 cells revealed the expression of EP(1), EP(3), and EP(4) PGE receptor subtypes, including a novel splice variant of the EP(1) receptor. Pharmacological studies using PGE receptor subtype-selective analogs showed that the potentiation of IgE/Ag-induced degranulation and IL-6 production by PGE(2) is mediated through EP(1) and/or EP(3) receptors. Our results suggest that PGE(2) may profoundly alter the nature of the mast cell degranulation and cytokine responses at sites of allergic inflammation through an EP(1)/EP(3)-dependent mechanism.