Regulation of human mast cell and basophil function by cAMP

Research on the Mechanism and Application of Acupuncture Therapy for Asthma: A Review

Asthma is a high-risk disease based on airway hyperresponsiveness (AHR). In this review, we found that there are many studies on clinical therapy for asthma that focus on the efficacy of acupuncture therapy and its mechanisms, including the functional connectivity of different brain regions, with the aid of functional magnetic resonance imaging (fMRI), immune responses/cell recognition (innate lymphoid cells and balance of Th1/Th2 and Treg/Th17), intracellular mechanism (autophagy, endoplasmic reticulum stress, and epigenetic alteration), and ligand-receptor/chemical signaling pathway (neurotransmitter, hormone, and small molecules). In this review, we summarized the clinical and experimental evidence for the mechanisms of acupuncture therapy in asthma to offer insights into drug discovery and clinical therapy. Given the paucity of clinical studies on the mechanisms of acupuncture in the treatment of asthma, this review notably included studies based on animal models to investigate the mechanisms of acupuncture in the treatment of asthma.

Endocannabinoid modulation of allergic responses: Focus on the control of FcεRI-mediated mast cell activation

Allergic reactions are highly prevalent pathologies initiated by the production of IgE antibodies against harmless antigens (allergens) and the activation of the high-affinity IgE receptor (FcεRI) expressed in the surface of basophils and mast cells (MCs). Research on the mechanisms of negative control of those exacerbated inflammatory reactions has been intense in recent years. Endocannabinoids (eCBs) show important regulatory effects on MC-mediated immune responses, mainly inhibiting the production of pro-inflammatory mediators. However, the description of the molecular mechanisms involved in eCB control of MC activation is far from complete. In this review, we aim to summarize the available information regarding the role of eCBs in the modulation of FcεRI-dependent activation of that cell type, emphasizing the description of the eCB system and the existence of some of its elements in MCs. Unique characteristics of the eCB system and cannabinoid receptors (CBRs) localization and signaling in MCs are mentioned. The described and putative points of cross-talk between CBRs and FcεRI signaling cascades are also presented. Finally, we discuss some important considerations in the study of the effects of eCBs in MCs and the perspectives in the field.

Drug delivery targets and strategies to address mast cell diseases

INTRODUCTION

Current and developing mast cell therapeutics are reliant on small molecule drugs and biologics, but few are truly selective for mast cells. Most have cellular and disease-specific limitations that require innovation to overcome longstanding challenges to selectively targeting and modulating mast cell behavior. This review is designed to serve as a frame of reference for new approaches that utilize nanotechnology or combine different drugs to increase mast cell selectivity and therapeutic efficacy.

AREAS COVERED

Mast cell diseases include allergy and related conditions as well as malignancies. Here, we discuss the targets of existing and developing therapies used to treat these disease pathologies, classifying them into cell surface, intracellular, and extracellular categories. For each target discussed, we discuss drugs that are either the current standard of care, under development, or have indications for potential use. Finally, we discuss how novel technologies and tools can be used to take existing therapeutics to a new level of selectivity and potency against mast cells.

EXPERT OPINION

There are many broadly and very few selectively targeted therapeutics for mast cells in allergy and malignant disease. Combining existing targeting strategies with technology like nanoparticles will provide novel platforms to treat mast cell disease more selectively.

Inhaled β2 Adrenergic Agonists and Other cAMP-Elevating Agents: Therapeutics for Alveolar Injury and Acute Respiratory Disease Syndrome?

Inhaled long-acting β-adrenergic agonists (LABAs) and short-acting β-adrenergic agonists are approved for the treatment of obstructive lung disease via actions mediated by β2 adrenergic receptors (β2-ARs) that increase cellular cAMP synthesis. This review discusses the potential of β2-AR agonists, in particular LABAs, for the treatment of acute respiratory distress syndrome (ARDS). We emphasize ARDS induced by pneumonia and focus on the pathobiology of ARDS and actions of LABAs and cAMP on pulmonary and immune cell types. β2-AR agonists/cAMP have beneficial actions that include protection of epithelial and endothelial cells from injury, restoration of alveolar fluid clearance, and reduction of fibrotic remodeling. β2-AR agonists/cAMP also exert anti-inflammatory effects on the immune system by actions on several types of immune cells. Early administration is likely critical for optimizing efficacy of LABAs or other cAMP-elevating agents, such as agonists of other Gs-coupled G protein-coupled receptors or cyclic nucleotide phosphodiesterase inhibitors. Clinical studies that target lung injury early, prior to development of ARDS, are thus needed to further assess the use of inhaled LABAs, perhaps combined with inhaled corticosteroids and/or long-acting muscarinic cholinergic antagonists. Such agents may provide a multipronged, repurposing, and efficacious therapeutic approach while minimizing systemic toxicity. SIGNIFICANCE STATEMENT: Acute respiratory distress syndrome (ARDS) after pulmonary alveolar injury (e.g., certain viral infections) is associated with ∼40% mortality and in need of new therapeutic approaches. This review summarizes the pathobiology of ARDS, focusing on contributions of pulmonary and immune cell types and potentially beneficial actions of β2 adrenergic receptors and cAMP. Early administration of inhaled β2 adrenergic agonists and perhaps other cAMP-elevating agents after alveolar injury may be a prophylactic approach to prevent development of ARDS.

Humulene Inhibits Acute Gastric Mucosal Injury by Enhancing Mucosal Integrity

This study was designed to determine whether α-humulene, a major constituent in many plants used in fragrances, has a protective role against gastric injury in vivo and in vitro. A rat model of hydrochloric acid (HCl)/ethanol-induced gastritis and human mast cells (HMC-1) were used to investigate the mucosal protective effect of α-humulene. α-Humulene significantly inhibited gastric lesions in HCl/ethanol-induced acute gastritis and decreased gastric acid secretion pyloric ligation-induced gastric ulcers in vivo. In addition, α-humulene reduced the amount of reactive oxygen species and malondialdehyde through upregulation of prostaglandin E2 (PGE2) and superoxide dismutase (SOD). In HMC-1 cells, α-humulene decreased intracellular calcium and increased intracellular cyclic adenosine monophosphate (cAMP) levels, resulting in low histamine levels. α-Humulene also reduced the expression levels of cytokine genes such as interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF) by downregulating nuclear factor-κB (NF-κB) nuclear translocation. Finally, α-humulene upregulated the expression levels of mucin 5AC (Muc5ac), Muc6, trefoil factor 1 (Tff1), trefoil factor 2 (Tff2), and polymeric immunoglobulin receptor (pigr). α-Humulene may attenuate HCl/ethanol-induced gastritis by inhibiting histamine release and NF-κB activation and stimulating antioxidants and mucosal protective factors, particularly Muc5ac and Muc6. Therefore, these data suggest that α-humulene is a potential drug candidate for the treatment of stress-induced or alcoholic gastritis.

Ephedra Herb, Mao, Inhibits Antigen-Induced Mast Cell Degranulation by Induction of the Affinity Receptor for IgE Internalization

PURPOSE

Ephedra herb (Mao) exerts potent anti-allergic effects. This study aimed to examine the underlying mechanisms of Mao on allergic inflammation using in vitro cultured mast cells (MCs) and an in vivo model of MC-dependent anaphylaxis.

METHODS

Bone marrow-derived MCs (BMMCs) were presensitized with anti-2,4-dinitrophenol (DNP) immunoglobulin E (IgE) and challenged with antigens (Ag; DNP-human serum albumin). Degranulation responses and cell surface high-affinity receptor for IgE (FcεRI) expression were assessed with/without Mao treatment. Passive systemic anaphylaxis (PSA)-treated mice were administered Mao and the pathophysiological responses were evaluated.

RESULTS

Mao inhibited Ag-induced BMMC degranulation, but not polyclonal activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin, indicating that Mao inhibits IgE-dependent activation of BMMCs. Mao-treated BMMCs exhibited significant reductions in expression of surface IgE and its receptor FcεRI. Analysis of subcellular localization revealed that Mao induces FcεRI internalization in BMMCs without degranulation. In the PSA mouse model, Mao administration prevented antigen-induced hypothermia. Mao administration significantly reduced cell surface expression of IgE-bound FcεRI on peritoneal MCs.

CONCLUSIONS

Mao induced FcεRI internalization in MCs, thereby inhibiting Ag-induced IgE-dependent degranulation. The inhibitory effects of Mao on MC degranulation may offer a novel therapeutic approach for allergic diseases.

Anti-Allergic and Anti-Inflammatory Effects of Undecane on Mast Cells and Keratinocytes

The critical roles of keratinocytes and resident mast cells in skin allergy and inflammation have been highlighted in many studies. Cyclic adenosine monophosphate (cAMP), the intracellular second messenger, has also recently emerged as a target molecule in the immune reaction underlying inflammatory skin conditions. Here, we investigated whether undecane, a naturally occurring plant compound, has anti-allergic and anti-inflammatory activities on sensitized rat basophilic leukemia (RBL-2H3) mast cells and HaCaT keratinocytes and we further explored the potential involvement of the cAMP as a molecular target for undecane. We confirmed that undecane increased intracellular cAMP levels in mast cells and keratinocytes. In sensitized mast cells, undecane inhibited degranulation and the secretion of histamine and tumor necrosis factor α (TNF-α). In addition, in sensitized keratinocytes, undecane reversed the increased levels of p38 phosphorylation, nuclear factor kappaB (NF-κB) transcriptional activity and target cytokine/chemokine genes, including thymus and activation-regulated chemokine (TARC), macrophage-derived chemokine (MDC) and interleukin-8 (IL-8). These results suggest that undecane may be useful for the prevention or treatment of skin inflammatory disorders, such as atopic dermatitis, and other allergic diseases.

Agarwood Inhibits Histamine Release from Rat Mast Cells and Reduces Scratching Behavior in Mice: Effect of Agarwood on Histamine Release and Scratching Behavior

Objectives:

This study was conducted to clarify the effects of agarwood on histamine release from mast cells in rats and on the scratching behaviors in mice.

Methods:

Histamine release from rat mast cells induced by compound 48/80 or concanavalin A (Con A) and compound 48/80-induced scratching behavior in mice were examined to investigate the effects of agarwood. The hyaluronidase activity and the 3’,5’-cyclic adenosine monophosphate (cAMP) levels in mast cells were examined to investigate the mechanisms for the inhibition of histamine release. The correlation between the inhibitory effects of agarwood on histamine release and the content of its typical ingredients, a 2-(2-phenylethyl)chromone derivatives, was analyzed using thin-layer chromatography.

Results:

Agarwood showed an inhibitory effect on mast-cell histamine release induced by compound 48/80 or Con A without any effect on hyaluronidase activity; this effect involves an increase in the cAMP levels in mast cells. Oral administration of agarwood showed an inhibitory effect on compound 48/80-induced scratching behavior in mice. The inhibitory effects of agarwood on histamine release were quite different, depending on the area where the agarwood was produced, its quality, and its market price. No correlation was found between the inhibitory effects of agarwood on histamine release and the typical ingredients of agarwood, which are 2-(2-phenylethyl)chromone derivatives.

Conclusion:

These results show that agarwood inhibits histamine release from mast cells partially through an increase in the cAMP levels in cells. We suggest that some active ingredients of agarwood must be effective on oral intake and that agarwood can be used to treat patients with a number of conditions, including urticaria, atopic dermatitis, and bronchial asthma, in which an increase in histamine release occurs. Differences in the pharmacological effects of this crude drug among markets may provide important information for the quality control of this herbal medicine.

A standard, single dose of inhaled terbutaline attenuates hyperpnea-induced bronchoconstriction and mast cell activation in athletes

This study provides the first in vivo evidence for a mast cell stabilizing effect of the short-acting inhaled β₂-adrenoceptor agonist terbutaline, when administered prophylactically at a clinically recommended dose (0.5 mg) before bronchial provocation with dry air. Our data therefore support the proposal that β₂-adrenoceptor agonist-mediated mast cell stabilization is a major contributor to bronchoprotection in individuals with exercise-induced bronchoconstriction.

Release of bronchoactive mediators from mast cells during exercise hyperpnea is a key factor in the pathophysiology of exercise-induced bronchoconstriction (EIB). Our aim was to investigate the effect of a standard, single dose of an inhaled β₂-adrenoceptor agonist on mast cell activation in response to dry air hyperpnea in athletes with EIB. Twenty-seven athletes with EIB completed a randomized, double-blind, placebo-controlled, crossover study. Terbutaline (0.5 mg) or placebo was inhaled 15 min prior to 8 min of eucapnic voluntary hyperpnea (EVH) with dry air. Pre- and postbronchial challenge, urine samples were analyzed by enzyme immunoassay for 11β-prostaglandin F_2α (11β-PGF_2α). The maximum fall in forced expiratory volume in 1 s of 14 (12–20)% (median and interquartile range) following placebo was attenuated to 7 (5–9)% with the administration of terbutaline (P < 0.001). EVH caused a significant increase in 11β-PGF_2α from 41 (27–57) ng/mmol creatinine at baseline to 58 (43–72) ng/mmol creatinine at its peak post-EVH following placebo (P = 0.002). The rise in 11β-PGF_2α was inhibited with administration of terbutaline: 39 (28–44) ng/mmol creatinine at baseline vs. 40 (33–58) ng/mmol creatinine at its peak post-EVH (P = 0.118). These data provide novel in vivo evidence of mast cell stabilization following inhalation of a standard dose of terbutaline prior to bronchial provocation with EVH in athletes with EIB.

A novel model of IgE-mediated passive pulmonary anaphylaxis in rats

Mast cells are central effector cells in allergic asthma and are augmented in the airways of asthma patients. Attenuating mast cell degranulation and with it the early asthmatic response is an important intervention point to inhibit bronchoconstriction, plasma exudation and tissue oedema formation. To validate the efficacy of novel pharmacological interventions, appropriate and practicable in vivo models reflecting mast cell-dependent mechanisms in the lung, are missing. Thus, we developed a novel model of passive pulmonary anaphylaxis in rats. Rats were passively sensitized by concurrent intratracheal and intradermal (ear) application of an anti-DNP IgE antibody. Intravenous application of the antigen, DNP-BSA in combination with Evans blue dye, led to mast cell degranulation in both tissues. Quantification of mast cell degranulation in the lung was determined by (1) mediator release into bronchoalveolar lavage, (2) extravasation of Evans blue dye into tracheal and bronchial lung tissue and (3) invasive measurement of antigen-induced bronchoconstriction. Quantification of mast cell degranulation in the ear was determined by extravasation of Evans blue dye into ear tissue. We pharmacologically validated our model using the SYK inhibitor Fostamatinib, the H₁-receptor antagonist Desloratadine, the mast cell stabilizer disodium cromoglycate (DSCG) and the β₂-adrenergic receptor agonist Formoterol. Fostamatinib was equally efficacious in lung and ear. Desloratadine effectively inhibited bronchoconstriction and ear vascular leakage, but was less effective against pulmonary vascular leakage, perhaps reflecting the differing roles for histamine receptor sub-types. DSCG attenuated both vascular leakage in the lung and bronchoconstriction, but with a very short duration of action. As an inhaled approach, Formoterol was more effective in the lung than in the ear. This model of passive pulmonary anaphylaxis provides a tissue relevant readout of early mast cell activity and pharmacological benchmarking broadly reflects responses observed in patients with asthma.

Plp1 gene duplication inhibits airway responsiveness and induces lung inflammation

Mice with Plp1 gene duplication model the most common form of Pelizaeus-Merzbacher disease (PMD), a CNS disease in which patients may suffer respiratory complications. We hypothesized that affected mice would lack airway responsiveness compared to wild-type and carrier mice during methacholine challenge. Wild-type (n = 10), carrier female (n = 6) and affected male (n = 8) mice were anesthetized-paralyzed, tracheostomized and ventilated. Respiratory mechanics were recorded at baseline and during escalating doses of nebulized methacholine followed by albuterol. Lung resistance (RL) was the primary endpoint. Lung tissues were assayed for inflammatory and histological differences. At baseline, phase angles were higher in carrier and affected mice than wild-type. Dose-response RL curves in affected and carrier mice indicated a lack of methacholine response. Albuterol reduced RL in wild-type and carrier, but not affected mice. Affected mice exhibited lower interleukin (IL)-6 tissue levels and alveolar inflammatory infiltrates. Affected and carrier mice, compared to wild-type, lacked airway reactivity during methacholine challenge, but only affected mice exhibited decreased lung tissue levels of IL-6 and inflammation.

The orl rat is more responsive to methacholine challenge than wild type

BACKGROUND

This study presents an animal model of native airway hyperresponsiveness (AHR). AHR is a fundamental aspect of asthma and reflects an abnormal response characterized by airway narrowing following exposure to a wide variety of non-immunological stimuli. Undescended testis (UDT) is one of the most common male congenital anomalies. The orl rat is a Long Evans substrain with inherited UDT. Since boys born with congenital UDT are more likely to manifest asthma symptoms, the main aim of this study was to investigate the alternative hypothesis that orl rats have greater AHR to a methacholine aerosol challenge than wild type rats.

METHODS

Long Evans wild type (n = 9) and orl (n = 13) rats were anesthetized, tracheostomized, and mechanically ventilated at 4 weeks of age. Escalating concentrations of inhaled methacholine were delivered. The methacholine potency and efficacy in the strains were measured. Respiratory resistance was the primary endpoint. After the final methacholine aerosol challenge, the short-acting β2-adrenoceptor agonist albuterol was administered as an aerosol and lung/diaphragm tissues were assayed for interleukin (IL)-4, IL-6, and tumor necrosis factor (TNF)-α. Histological and histomorphometrical analyses were performed.

RESULTS

The methacholine concentration-response curve in the orl group indicated increased sensitivity, hyperreactivity, and exaggerated maximal response in comparison with the wild type group, indicating that orl rats had abnormally greater AHR responses to methacholine. Histological findings in orl rats showed the presence of eosinophils, unlike wild type rats. β2-Adrenoceptor agonist intervention resulted in up-regulation of IL-4 diaphragmatic levels and down-regulation of IL-4 and IL-6 in the lungs of orl rats.

CONCLUSION

orl rats had greater AHR than wild type rats during methacholine challenge, with higher IL-4 levels in diaphragmatic tissue homogenates. Positive immunostaining for IL-4 was detected in lung and diaphragmatic tissue in both strains. This model offers advantages over other pre-clinical murine models for studying potential mechanistic links between cryptorchidism and asthma. This animal model may be useful for further testing of compounds/therapeutics options for treating AHR.

Genome-wide association study in NSAID-induced acute urticaria/angioedema in Spanish and Han Chinese populations

AIM

Acute urticaria/angioedema (AUA) induced by cross-intolerance to NSAIDs is the most frequent clinical entity in hypersensitivity reactions to drugs. In this work, we conducted a genome-wide association study in Spanish and Han Chinese patients suffering from NSAID-induced AUA.

MATERIALS & METHODS

A whole-genome scan was performed on a total of 232 cases (112 Spanish and 120 Han Chinese) with NSAID-induced AUA and 225 unrelated controls (124 Spanish and 101 Han Chinese).

RESULTS

Although no polymorphism reached genome-wide significance, we obtained suggestive associations for three clusters in the Spanish group (RIMS1, BICC1 and RAD51L 1) and one region in the Han Chinese population (ABI3BP). Five regions showed suggestive associations after meta-analysis: HLF, RAD51L1, COL24A1, GalNAc-T13 and FBXL7. A majority of these genes are related to Ca(2+), cAMP and/or P53 signaling pathways.

CONCLUSION

The associations described were different from those related to the metabolism of arachidonic acid and could provide new mechanisms underlying NSAID-induced AUA.

E-prostanoid 2 receptors dampen mast cell degranulation via cAMP/PKA-mediated suppression of IgE-dependent signaling

The experimental administration of PGE(2) for the treatment of asthma dampens clinical symptoms, and similar efficacy has been found in dust mite-induced hypersensitivity reactions in animal models. Here, we investigate the mechanism by which PGE(2) mediates suppression of MC degranulation. We find that the effect of PGE(2) on FcεRI-dependent MC degranulation varies from activating to suppressing, depending on the relative ratio of EP(2) to EP(3) expression on these cells with suppression evident only in cells having increased EP(2) to EP(3) expression. Consistent with a role for EP(2) in suppressing MC responses in vitro, we found that a selective EP(2) agonist, Butaprost, inhibited MC-mediated FcεRI-induced immediate hypersensitivity in a model of PCA. EP(2) engagement on MCs increased cAMP production and inhibited FcεRI-mediated calcium influx. In addition, it also decreased the extent of FcεRI-induced Fyn kinase activity, leading to decreased phosphorylation of key signaling molecules such as Gab2 and Akt. Treatment with an antagonist of cAMP or shRNA down-regulation of PKA (the principal intracellular target of cAMP) reversed the EP(2)-mediated inhibitory effect on MC degranulation and restored calcium influx and phosphorylation of Akt. Collectively, the findings demonstrate that EP(2) suppresses the Fyn-mediated signals that are central to FcεRI-dependent MC degranulation, suggesting that engagement of the EP(2) on MCs may be beneficial in dampening allergic responses.

Gs-coupled adenosine receptors differentially limit antigen-induced mast cell activation

Mast cell activation results in the immediate release of proinflammatory mediators prestored in cytoplasmic granules, as well as initiation of lipid mediator production and cytokine synthesis by these resident tissue leukocytes. Allergen-induced mast cell activation is central to the pathogenesis of asthma and other allergic diseases. Presently, most pharmacological agents for the treatment of allergic disease target receptors for inflammatory mediators. Many of these mediators, such as histamine, are released by mast cells. Targeting pathways that limit antigen-induced mast cell activation may have greater therapeutic efficacy by inhibiting the synthesis and release of many proinflammatory mediators produced in the mast cell. In vitro studies using cultured human and mouse mast cells, and studies of mice lacking A(2B) receptors, suggest that adenosine receptors, specifically the G(s)-coupled A(2A) and A(2B) receptors, might provide such a target. Here, using a panel of mice lacking various combinations of adenosine receptors, and mast cells derived from these animals, we show that adenosine receptor agonists provide an effective means of inhibition of mast cell degranulation and induction of cytokine production both in vitro and in vivo. We identify A(2B) as the primary receptor limiting mast cell degranulation, whereas the combined activity of A(2A) and A(2B) is required for the inhibition of cytokine synthesis.

Lipoic acid suppresses compound 48/80-induced anaphylaxis-like reaction

Alpha-lipoic acid (LA), a naturally occurring dithiol compound, is an essential cofactor in metabolic reactions involved in energy utilization. LA improves glycemic control, reduces diabetic polyneuropathies, atherosclerosis, and allergic inflammation. The effects of LA on mast cell-mediated anaphylactic reactions, however, are unknown. LA dose-dependently inhibited systemic and passive cutaneous anaphylaxis-like reactions in mice induced by compound 48/80, a condensation product of N-methyl-p-methoxyphenethylamine and formaldehyde. Pretreatment with LA, prior to induction of the systemic anaphylaxis-like reaction with compound 48/80, reduced plasma histamine levels in a dose-dependent manner. In our in vitro study, LA decreased histamine release from rat peritoneal mast cells (RPMCs) triggered by compound 48/80. Moreover, an increase in calcium uptake activated by compound 48/80 was inhibited by LA. LA also significantly elevated intracellular cyclic adenosine-3',5' monophosphate (cAMP) levels in RPMCs. This inhibition of mediator release from RPMCs may be due to inhibition of calcium uptake and augmentation of intracellular cAMP levels. Based on these results, we suggest that LA may be a potential remedy for allergy-related diseases.

Impaired nocifensive behaviours and mechanical hyperalgesia, but enhanced thermal allodynia in pituitary adenylate cyclase-activating polypeptide deficient mice

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) and its receptors (PAC1 and VPAC) have been shown in the spinal dorsal horn, dorsal root ganglia and sensory nerve terminals. Data concerning the role of PACAP in central pain transmission are controversial and we have recently published its divergent peripheral effects on nociceptive processes. The aim of the present study was to investigate acute somatic and visceral nocifensive behaviours, partial sciatic nerve ligation-evoked chronic neuropathic, as well as resiniferatoxin-induced inflammatory thermal and mechanical hyperalgesia in PACAP deficient (PACAP(-/-)) mice to elucidate its overall function in pain transmission. Neuronal activation was investigated with c-Fos immunohistochemistry. Paw lickings in the early (0-5 min) and late (20-45 min) phases of the formalin test were markedly reduced in PACAP(-/-) mice. Acetic acid-evoked abdominal contractions referring to acute visceral chemonociception was also significantly attenuated in PACAP knockout animals. In both models, the excitatory role of PACAP was supported by markedly greater c-Fos expression in the periaqueductal grey and the somatosensory cortex. In PACAP-deficient animals neuropathic mechanical hyperalgesia was absent, while c-Fos immunopositivity 20 days after the operation was significantly higher. In this chronic model, these neurons are likely to indicate the activation of secondary inhibitory pathways. Intraplantarly injected resiniferatoxin-evoked mechanical hyperalgesia involving both peripheral and central processes was decreased, but thermal allodynia mediated by only peripheral mechanisms was increased in PACAP(-/-) mice. These data clearly demonstrate an overall excitatory role of PACAP in pain transmission originating from both exteroceptive and interoceptive areas, it is also involved in central sensitization. This can be explained by the signal transduction mechanisms of its identified receptors, both PAC1 and VPAC activation leads to neuronal excitation. In contrast, it is an inhibitory mediator at the level of the peripheral sensory nerve endings and decreases their sensitization to heat with presently unknown mechanisms.

Cyclic adenosine monophosphate induces plasminogen activator inhibitor-1 expression in human mast cells

Plaminogen activator inhibitor-1 (PAI-1), the key physiological inhibitor of the plasmin fibrinolytic system, plays important roles in the pathogenesis of asthma. Mast cells (MCs) are crucial effector cells and a major source of PAI-1 for asthma. Cyclic adenosine monophosphate (cAMP) is the important regulator of MCs; however, its effects on PAI-1 expression in MCs remain unknown. We reported cAMP/protein kinase A pathway positively regulates PAI-1 expression through cAMP-response element binding protein binding to hypoxia response element-1 at -158 to -153bp of human PAI-1 promoter in human MCs. Moreover, cAMP synergistically augments PAI-1 expression with ionomycin- or IgE receptor cross-linking-mediated stimulation.

Effect of chlorogenic acid on mast cell-dependent anaphylactic reaction

Chlorogenic acid (CGA), a naturally occurring polyphenol compound, has a number of biological activities. However, roles of CGA in the mast cell-dependent anaphylactic reaction have not been fully examined. In the present study, the effect and mechanism of CGA on mast cell-dependent anaphylactic reaction were investigated using in vivo and in vitro models. CGA inhibited compound 48/80-induced systemic anaphylactic shock in mice and skin vascular permeability in rats. CGA also inhibited anti-dinitrophenyl (DNP) IgE-mediated passive cutaneous anaphylaxis (PCA). Moreover, CGA dose-dependently reduced histamine and TNF-alpha release from RBL-2H3 cells activated by anti-DNP IgE. Pretreatment with CGA suppressed IgE-antigen complex induced calcium uptake into RBL-2H3 cells. When CGA was added, the level of intracellular cyclic adenosine monophosphate (cAMP) in RBL-2H3 cells was significantly elevated compared with the untreated cells. Decreased calcium uptake and increased cAMP level might be involved in the inhibitory effect of CGA on mast cell activation. These results suggest a possible therapeutic application of CGA in allergic diseases.

Inhibitory effects of curcumin on passive cutaneous anaphylactoid response and compound 48/80-induced mast cell activation

Mast cells participate in allergies and inflammation by secreting a variety of pro-inflammatory mediators. Curcumin, the active component of turmeric, is a polyphenolic phytochemical with anti-tumor, anti-inflammatory, anti-oxidative, and anti-allergic properties. The effects of curcumin on compound 48/80-induced mast cell activation and passive cutaneous anaphylactoid reactions are unknown. In this report, we investigated the influences of curcumin on the passive cutaneous anaphylactoid response in vivo and compound 48/80-induced mast cell activation in vitro. The mechanism of action was examined by calcium uptake measurements and cAMP assays in mast cells. Curcumin significantly attenuated the mast cell-mediated passive cutaneous anaphylactoid reaction in an animal model. In agreement with this in vivo activity, curcumin suppressed compound 48/80-induced rat peritoneal mast cell (RPMC) degranulation and histamine release from RPMCs. Moreover, compound 48/80-elicited calcium uptake into RPMCs was reduced in a dose-dependent manner by curcumin. Furthermore, curcumin increased the level of intracellular cAMP and significantly inhibited the compound 48/80-induced reduction of cAMP in RPMCs. These results corroborate the finding that curcumin may have anti-allergic activity.

Silibinin attenuates mast cell-mediated anaphylaxis-like reactions

Silibinin is known to have hepatoprotective, anti-carcinogenic and anti-inflammatory effects. However, roles of silibinin in the immediate-type allergic reactions (anaphylaxis) have not fully been investigated. In the present study, we have demonstrated that silibinin attenuated mast cell-mediated anaphylaxis-like reactions involved in allergic diseases. Oral administration of silibinin inhibited compound 48/80-induced passive cutaneous anaphylaxis-like reaction in mice. Silibinin also attenuated anti-dinitrophenyl (DNP) immunoglobulin (Ig) E-mediated passive systemic and cutaneous anaphylaxis. Silibinin had no cytotoxicity on rat peritoneal mast cells (RPMC). Silibinin dose-dependently reduced histamine release from RPMC activated by compound 48/80 or anti-DNP IgE. Moreover, silibinin inhibited the secretion of pro-inflammatory cytokines, such as tumor necrosis factor-alpha and interleukin-6 in RPMC. Pretreatment of silibinin suppressed the antigen-stimulated calcium uptake and activation of nuclear factor-kappa B (NF-kappaB) in RPMC. Furthermore, silibinin increased the intracellular cAMP level. Increased cAMP, decreased calcium uptake and suppressed NF-kappaB activity might be involved in the inhibitory effect of silibinin on the secretory response. Our findings provide possibility that silibinin may serve as an effective therapeutic agent for allergic diseases.

Engagement of the EP2 prostanoid receptor closes the K+ channel KCa3.1 in human lung mast cells and attenuates their migration

Human lung mast cells (HLMC) express the Ca(2+)-activated K(+) channel K(Ca)3.1, which plays a crucial role in their migration to a variety of diverse chemotactic stimuli. K(Ca)3.1 activation is attenuated by the beta(2)-adrenoceptor and the adenosine A(2A) receptor through a G(s)-coupled mechanism independent of cyclic AMP. Prostaglandin E(2) promotes degranulation and migration of mouse bone marrow-derived mast cells through the G(i)-coupled EP(3) prostanoid receptor, and induces LTC(4) and cytokine secretion from human cord blood-derived mast cells. However, PGE(2) binding to the G(s)-coupled EP(2) receptor on HLMC inhibits their degranulation. We show that EP(2) receptor engagement closes K(Ca)3.1 in HLMC. The EP(2) receptor-specific agonist butaprost was more potent than PGE(2) in this respect, and the effects of both agonists were reversed by the EP(2) receptor antagonist AH6809. Butaprost markedly inhibited HLMC migration induced by chemokine-rich airway smooth muscle-conditioned media. Interestingly, PGE(2) alone was chemotactic for HLMC at high concentrations (1 microM), but was a more potent chemoattractant for HLMC following EP(2) receptor blockade. Therefore, the G(s)-coupled EP(2) receptor closes K(Ca)3.1 in HLMC and attenuates both chemokine- and PGE(2)-dependent HLMC migration. EP(2) receptor agonists with K(Ca)3.1 modulating function may be useful for the treatment of mast cell-mediated disease.

Effects of IL-4 and IL-13 on adenosine receptor expression and responsiveness of the human mast cell line 1

BACKGROUND

Inhalation of adenosine-5'-monophosphate (AMP) causes bronchoconstriction in asthma but not in healthy subjects. Bronchoconstriction upon AMP inhalation is thought to occur by histamine release and subsequent binding to receptors on airway smooth muscle cells.

METHODS

To explain enhanced sensitivity to AMP in asthma, mast cell expression of the adenosine A2A and A2B receptors and histamine release were measured after incubation of human mast cell line 1 (HMC-1) cells with AMP and the non-specific adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) for 1.5 and 6 h. To establish a Thelper-2 environment resembling the asthma phenotype, HMC-1 cells were additionally cultured with IL-4 and IL-13 alone or stimulated with the combination of both cytokines and AMP and NECA. To study effects of prolonged presence of the inflammatory environment, the cells were pre-incubated overnight (18 h) with IL-4 and IL-13 and additionally stimulated with AMP and NECA for 1.5 or 6 h.

RESULTS

AMP and NECA hardly affected adenosine receptor expression but increased IL-8 secretion. Incubation with IL-4 and IL-13 for 6 h increased adenosine A2A receptor expression and histamine secretion, but decreased IL-8 secretion. The combination of IL-4, IL-13, and AMP/NECA for 6 h increased A2B receptor expression and IL-8 secretion. Overnight stimulation with IL-4, IL-13 and subsequent stimulation with AMP/NECA for 1.5 h decreased A2AR expression which was accompanied by increased histamine secretion.

CONCLUSION

These results suggest a role for decreased A(2A)R expression in enhanced adenosine responsiveness as observed in asthma.

The mast cell and allergic diseases: role in pathogenesis and implications for therapy

Mast cells have long been recognized for their role in the genesis of allergic inflammation; and more recently for their participation in innate and acquired immune responses. Mast cells reside within tissues including the skin and mucosal membranes, which interface with the external environment; as well as being found within vascularized tissues next to nerves, blood vessels and glandular structures. Mast cells have the capability of reacting both within minutes and over hours to specific stimuli, with local and systemic effects. Mast cells express the high affinity IgE receptor (FcepsilonRI) and upon aggregation of FcepsilonRI by allergen-specific IgE, mast cells release and generate biologically active preformed and newly synthesized mediators which are involved in many aspects of allergic inflammation. While mast cells have been well documented to be essential for acute allergic reactions, more recently the importance of mast cells in reacting through pattern recognition receptors in innate immune responses has become recognized. Moreover, as our molecular understanding of the mast cell has evolved, novel targets for modulation have been identified with promising therapeutic potential.

G protein-coupled receptors and the modification of FcepsilonRI-mediated mast cell activation

By releasing multiple pro-inflammatory mediators upon activation, mast cells are critical effector cells in the pathogenesis of allergic inflammation. The traditional viewpoint of antigen-dependent mast cell activation is that of a Th(2)-driven process whereby antigen-specific IgE molecules are produced by B cells followed by binding of the IgE to high affinity IgE receptors (FcepsilonRI) expressed on mast cells. Subsequent antigen-dependent aggregation of the FcepsilonRI initiates an intracellular signalling cascade that culminates in mediator release. Mast cell responses, including cell growth, survival, chemotaxis, and cell adhesion, however, can also be regulated by other receptors expressed on mast cells. Furthermore, FcepsilonRI-mediated mast cell mediator release can be significantly modified by ligation of specific classes of these receptors. One such class of receptors is the G protein-coupled receptors (GPCR). In this review, we describe how sub-populations of GPCRs can either enhance or inhibit FcepsilonRI-mediated mast cell activation depending on the particular G protein utilized for relaying signalling. Furthermore, we discuss the potential mechanisms whereby the signalling responses utilized by the FcepsilonRI for mast cell activation are influenced by those initiated by GPCRs to produce these diverse responses.

Enhanced mast cell activation in mice deficient in the A2b adenosine receptor

Antigen-mediated cross-linking of IgE bound to mast cells via the high affinity receptor for IgE triggers a signaling cascade that results in the release of intracellular calcium stores, followed by an influx of extracellular calcium. The collective increase in intracellular calcium is critical to the release of the granular contents of the mast cell, which include the mediators of acute anaphylaxis. We show that the sensitivity of the mast cell to antigen-mediated degranulation through this pathway can be dramatically influenced by the A2b adenosine receptor. Loss of this G_s-coupled receptor on mouse bone marrow–derived mast cells results in decreased basal levels of cyclic AMP and an excessive influx of extracellular calcium through store-operated calcium channels following antigen activation. Mice lacking the A2b receptor display increased sensitivity to IgE-mediated anaphylaxis. Collectively, these findings show that the A2b adenosine receptor functions as a critical regulator of signaling pathways within the mast cell, which act in concert to limit the magnitude of mast cell responsiveness when antigen is encountered.

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.

Action of Dracocephalum argunense on mast cell-mediated allergy model

The discovery of drugs for the treatment of allergic disease is an important subject in human health. Stimulation of mast cells starts the process of degranulation resulting in releasing of mediators, such as histamine. In this report, we investigated the effect of aqueous extract of Dracocephalum argunense Fisch. (Labiatae) (DAAE) on the mast cell-mediated allergic response and studied its possible mechanisms of action, focusing on the histamine release and pro-inflammatory cytokine secretion in mast cells. DAAE inhibited compound 48/80-induced systemic reactions and serum histamine release in mice. In addition, DAAE attenuated IgE-mediated skin allergic reaction. DAAE dose-dependently reduced IgE-induced histamine release from mast cells. The level of cAMP was transiently increased by treatment of DAAE. DAAE specifically blocked the phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187-induced p38 mitogen-activated protein kinase (MAPK) activation. DAAE decreased the secretion of pro-inflammatory cytokines, such as tumor necrosis factor-alpha and interleukin-6 in mast cells. Our findings provide evidence that DAAE inhibits mast cell derived allergic reactions, and involvement of cAMP for histamine release and p38 MAPK for pro-inflammatory cytokine secretion in these effects.

Inhibitory effects of Selaginella tamariscina on immediate allergic reactions

The anti-allergic effects of a 70% ethanol extract from Selaginella tamariscina herb (EST) were evaluated in this study. EST given at the doses of 500 and 1000 mg/kg can inhibit mouse systemic anaphylactic shock induced by compound 48/80 in a dose-dependent manner. It can also dose-dependently block rat homologous passive cutaneous anaphylaxis and skin reactions caused by exogenous histamine and serotonin with a significant difference observed at the dose of 1000 mg/kg. In addition, EST can reduce histamine release from rat peritoneal mast cells triggered by compound 48/80 and an antigen in vitro. When incubated with rat mast cells, the extract (200 microg/ml) can significantly elevate the intracellular cAMP levels. The finding suggests that EST inhibits mast cell-dependent, immediate allergic reactions. Its effects appear to be mediated by reducing the release of vasoactive amines such as histamine from mast cells via stabilizing the cell membrane and weakening the inflammatory action of these amines. Based on these results, Selaginella tamariscina and one of its active components flavonoids may be useful as potential remedies for allergic rhinitis and other allergy-related diseases.

Gallic Acid Inhibits Histamine Release and Pro-inflammatory Cytokine Production in Mast Cells

The discovery of drugs for the treatment of inflammatory allergic diseases such as, asthma, allergic rhinitis, and sinusitis is a very important subject in human health. Gallic acid (3,4,5-trihydroxybenzoic acid), a polyphenyl natural products from gallnut and green tea, is known to have anti-oxidant, anti-inflammatory, anti-microbial, and radical scavenging activities. The aim of the present study was to elucidate whether gallic acid modulates the inflammatory allergic reaction and to study its possible mechanisms of action. Gallic acid attenuated compound 48/80- or immunoglobulin E (IgE)-induced histamine release from mast cells. The inhibitory effect of gallic acid on the histamine release was mediated by the modulation of cAMP and intracellular calcium. Gallic acid decreased the phorbol 12-myristate 13-acetate plus calcium ionophore A23187-stimulated pro-inflammatory cytokine gene expression and production such as TNF-alpha and IL-6 in human mast cells. The inhibitory effect of gallic acid on the pro-inflammatory cytokine was nuclear factor-kappaB and p38 mitogen-activated protein kinase dependent. In addition, gallic acid inhibited compound 48/80-induced systemic allergic reaction and IgE-mediated local allergic reaction. The inhibitory activity of gallic acid on the allergic reaction and histamine release was found to be similar with disodium cromoglycate. Our findings provide evidence that gallic acid inhibits mast cell-derived inflammatory allergic reactions by blocking histamine release and pro-inflammatory cytokine expression, and suggest the mechanisms of action. Furthermore, in vivo and in vitro anti-allergic effect of gallic acid suggests a possible therapeutic application of this agent in inflammatory allergic diseases.

Amomum xanthiodes inhibits mast cell-mediated allergic reactions through the inhibition of histamine release and inflammatory cytokine production

In this study, we investigated the effect of Amomum xanthiodes (Zingiberaceae) extract (AXE) on the mast cell-mediated allergy model and studied the possible mechanism of action. We found that AXE inhibited compound 48/80-induced systemic reactions and plasma histamine release in mice. Additionally, AXE decreased immunoglobulin E (IgE)-mediated local allergic reactions and passive cutaneous anaphylaxis (PCA), and AXE dose-dependently attenuated the release of histamine from rat peritoneal mast cells (RPMC) activated by compound 48/80 or IgE. The amounts of AXE needed for inhibition of compound 48/80-induced plasma histamine release and PCA were similar to disodium cromoglycate, the known anti-allergic drug. We found that AXE increased the cAMP levels and decreased the compound 48/80-induced intracellular Ca2+. Furthermore, AXE attenuated the phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore (A23187)-stimulated tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-6 secretion in human mast cells. The inhibitory effect of AXE on the proinflammatory cytokines was nuclear factor-kappaB (NF-kappaB)-dependent. In addition, AXE decreased PMA plus A23187-induced degradation of IkappaBalphaand the nuclear translocation of NF-kappaB. Our findings provide evidence that AXE inhibits mast cell-derived immediate-type allergic reactions, and that cAMP, intracellular Ca2+, proinflammatory cytokines, and NF-kappaB are involved in these effects.

Anti-inflammatory potential of CB1-mediated cAMP elevation in mast cells

Cannabinoids are broadly immunosuppressive, and anti-inflammatory properties have been reported for certain marijuana constituents and endogenously produced cannabinoids. The CB2 cannabinoid receptor is an established constituent of immune system cells, and we have recently established that the CB1 cannabinoid receptor is expressed in mast cells. In the present study, we sought to define a role for CB1 in mast cells and to identify the signalling pathways that may mediate the suppressive effects of CB1 ligation on mast cell activation. Our results show that CB1 and CB2 mediate diametrically opposed effects on cAMP levels in mast cells. The observed long-term stimulation of cAMP levels by the Galpha(i/o)-coupled CB1 is paradoxical, and our results indicate that it may be attributed to CB1-mediated transcriptional regulation of specific adenylate cyclase isoenzymes that exhibit superactivatable kinetics. Taken together, these results reveal the complexity in signalling of natively co-expressed cannabinoid receptors and suggest that some anti-inflammatory effects of CB1 ligands may be attributable to sustained cAMP elevation that, in turn, causes suppression of mast cell degranulation.

The anti-anaphylactic effect of the gall of Rhus javanica is mediated through inhibition of histamine release and inflammatory cytokine secretion

The immediate-type allergic reaction (anaphylaxis) is involved in many allergic diseases such as asthma, allergic rhinitis and sinusitis. We investigated the effect of the gall of Rhus javanica (GRJ) on the model of the immediate-type allergic reaction, and studied its possible mechanisms. GRJ inhibited compound 48/80-induced systemic reactions in mice. GRJ attenuated immunoglobulin (Ig) E-mediated local allergic reactions. In addition, GRJ dose dependently decreased histamine release from rat peritoneal mast cells activated by compound 48/80 or IgE. The decreasing effect of GRJ on the histamine release was mediated by the modulation of cAMP and [Ca2+]i in mast cells. Furthermore, GRJ decreased the phorbol 12-myristate 13-acetate plus calcium ionophore A23187-stimulated TNF-alpha and IL-6 secretion in human mast cells. The inhibitory effect of GRJ on the pro-inflammatory cytokine was c-Jun N-terminal kinase and nuclear factor-kappaB dependent. Our findings provide evidence that GRJ inhibits mast cell-derived immediate-type allergic reactions, and suggest the possible mechanisms of action.

Positive interaction of the beta2-agonist CHF 4226.01 with budesonide in the control of bronchoconstriction induced by acetaldehyde in the guinea-pigs

Pretreatment of anaesthetized guinea-pigs with either CHF 4226.01 (8-hydroxy-5-[(1R)-1-hydroxy-2-[N-[(1R)-2-(p-methoxyphenyl)-1-methylethyl]amino]ethyl] carbostyril hydrochloride), formoterol or budesonide reduced acetaldehyde (AcCHO)-evoked responses in the lungs with a rank order of potency CHF 4226.01 (ED(50) values, from 1.88 to 3.31 pmol) > formoterol (ED(50) values, from 3.03 to 5.51 pmol) >> budesonide (ED(50) values, from 335 to 458 nmol). The duration of action of CHF 4226.01 in antagonizing the airway obstruction elicited by AcCHO was also substantially longer than formoterol (area under the curve) at 10 pmol, 763+/-58 and 480+/-34, respectively; P<0.01). Continuous infusion of a subthreshold dose of AcCHO enhanced the intratracheal pressure (ITP) increases caused by subsequent challenges with substance P (from 9.7+/-0.8 to 27.5+/-1.6 cm H(2)O as a peak, P<0.001). Pretreatment with either CHF 4226.01 or formoterol prevented the sensitizing effect of AcCHO on substance P responses (ED(50) values, 2.85 and 6.11 pmol, respectively; P<0.01). The ED(50) value of budesonide (396 nmol) in preventing AcCHO-evoked ITP increase was reduced when this glucocorticoid was combined with 0.1 pmol CHF 4226.01 (ED(50) 76 nmol; P<0.001). CHF 4226.01/budesonide was two-fold more effective (P<0.01) than the formoterol/budesonide combination. These results suggest that CHF 4226.01/budesonide, by optimizing each other's beneficial potential in the control of pulmonary changes caused by AcCHO in the guinea-pigs, may represent a new fixed combination in asthma.

Ephedrae herba in Mao-Bushi-Saishin-To inhibits IgE-mediated histamine release and increases cAMP content in RBL-2H3 cells

Acute effect of Mao-Bushi-Saishin-To (Ma-Huang-Fu-Zi-Xi-Xin-Tang in Chinese: MBS) on histamine release was investigated. The IgE-mediated anaphylaxic response in Wistar rats was significantly suppressed by MBS and Mao. However, Saishin and Bushi had no or little effect on the antigen-mediated anaphylaxic reaction. Mao as well as MBS but not Saishin nor Bushi inhibited IgE-mediated histamine release from rat basophilic leukemia (RBL-2H3) cells. Consistently, MBS and Mao but not Bushi nor Saishin increased cAMP levels in RBL-2H3 cells. However, ephedrine, methylephedrine, and pseudoephedrine, the main components in Mao, did not affect histamine release. From these results, increase of cAMP levels may account for the inhibitory effect of Mao on histamine release. Furthermore, these inhibitory actions of MBS were mainly due to Mao with an ingredient(s) different from ephedrines.

Inhibition of immediate allergic reactions by ethanol extract from Plumbago zeylanica stems

The antiallergic properties of the 70% ethanol extract from Plumbago zeylanica stems (EPZ) were investigated in the present study. The extract (500, 1000 mg/kg, p.o.) dose-dependently inhibited systemic anaphylactic shock induced by compound 48/80 in mice, reduced homologous passive cutaneous anaphylaxis and skin reactions induced by histamine or serotonin in rats, significant differences were observed at the dose of 1000 mg/kg. In vitro, EPZ (5, 20, 50 microg/ml) concentration-dependently reduced histamine release from rat peritoneal mast cells caused by compound 48/80 and antigen. EPZ (50 microg/ml) markedly increased intracellular cAMP content of rat mast cells. These findings demonstrate that EPZ inhibits mast cell-dependent immediate allergic reactions, which is probably mediated by reducing the release of mediators such as histamine from mast cells via elevating intracellular cAMP level and weakening the inflammatory action of mediators.

Differential roles of CB1 and CB2 cannabinoid receptors in mast cells

Cannabinoid modulation of immune responses is a pathological consequence of marijuana abuse and a potential outcome of therapeutic application of the drug. Moreover, endogenous cannabinoids are physiological immune regulators. In the present report, we describe alterations in gene transcription that occur after cannabinoid exposure in a mast cell line, RBL2H3. Cannabinoid exposure causes marked changes in the transcript levels for numerous genes, acting both independently of and in concert with immunoreceptor stimulation via Fc epsilon RI. In two mast cell lines, we observed mRNA and protein expression corresponding to both CB1 and CB2 cannabinoid receptor isoforms, contrary to the prevailing view that CB1 is restricted to the CNS. We show that coexpression of the two isoforms is not functionally redundant in mast cells. Analysis of signaling pathways downstream of cannabinoid application reveals that activation of extracellular signal-regulated kinase, AKT, and a selected subset of AKT targets is accomplished by CB2 ligands and nonselective CB1/CB2 agonists in mast cells. CB1 inhibition does not affect AKT or extracellular signal-regulated kinase activation by cannabinoids, indicating that CB2 is the predominant regulatory receptor for these kinases in this cell context. CB1 receptors are, however, functional in these mast cells, since they can contribute to suppression of secretory responses.

Preformed enzymes in mast cell granules and their potential role in allergic rhinitis

Mast cells not only function as effector cells but also influence nearly every other cell involved in causing allergic rhinitis. Mast cell-derived mediators such as histamine, bradykinin, tryptase, and the arachidonic acid derivatives produce the symptoms of the early-phase reaction of allergic rhinitis and also attract and activate other leukocytes involved in the late-phase reaction. In addition, activated mast cells are known to secrete a number of cytokines, both preformed and newly synthesized, that can modulate T- and B-cell function, propagate the early- and late-phase reactions, and contribute to tissue remodeling. Most currently available therapies work by antagonizing the mediators secreted by mast cells and other leukocytes. With the possible exception of immunotherapy, these therapies do not provide long-term protection against allergic disorders. Exciting new developments in gene-based therapies seem promising in both reducing and reversing the development of allergic rhinitis.

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.

Regulation of phospholipase D and secretion in mast cells by protein kinase A and other protein kinases

Functions attributed to phospholipase (PL) D include the regulation of intracellular trafficking of Golgi-derived vesicles and secretion of granules from mast cells. We have reported that activation of PLD and secretion in a rat mast cell (RBL-2H3) line is substantially enhanced by cholera toxin, a known activator of protein kinase (PK) A. Here we review the evidence that (1) the synergistic interactions of cholera toxin and other pharmacological agents on mast cell secretion are attributable to the synergistic activation of PLD via PKA, CaM kinase II, and PKC and (2) both PLD1 and PLD2 participate in this process. For example, treatment with cholera toxin, thapsigargin, and phorbol 12-myristate 13-acetate (which activate PKA, CaM kinase II, and PKC, respectively) exhibit synergy in the stimulation of both PLD and secretion. These kinases and PLD are likely confined to membrane components, as similar synergistic interactions could be demonstrated in permeabilized cells. The regulation of PLD and secretion by these kinases is also apparent from studies of inhibitors of PKA and other kinases. Also, by overexpression of either PLD1 or PLD2 it is apparent that both isoforms respond to the same stimuli as endogenous PLD, although PLD1 is largely associated with secretory granules and PLD2 with plasma membrane. The studies reveal interesting differences in the regulation of the translocation of granules (regulated by PKA) and the fusion of these granules with the plasma membrane (regulated by Ca(2+) and PKC). The pathological/physiological implications of the regulation of PLD by PKA require further evaluation in other cell systems.