Anti-Allergic Potential of Cinnamaldehyde via the Inhibitory Effect of Histidine Decarboxylase (HDC) Producing Klebsiella pneumonia.

Allergy is an immunological disorder that develops in response to exposure to an allergen, and histamines mediate these effects via histidine decarboxylase (HDC) activity at the intracellular level. In the present study, we developed a 3D model of Klebsiella pneumoniae histidine decarboxylase (HDC) and analyzed the HDC inhibitory potential of cinnamaldehyde (CA) and subsequent anti-allergic potential using a bacterial and mammalian mast cell model. A computational and in vitro study using K. pneumonia revealed that CA binds to HDC nearby the pyridoxal-5'-phosphate (PLP) binding site and inhibited histamine synthesis in a bacterial model. Further study using a mammalian mast cell model also showed that CA decreased the levels of histamine in the stimulated RBL-2H3 cell line and attenuated the release of ß-hexoseaminidase and cell degranulation. In addition, CA treatment also significantly suppressed the levels of pro-inflammatory cytokines TNF-α and IL-6 and the nitric oxide (NO) level in the stimulated mast cells. A gene expression and Western blotting study revealed that CA significantly downregulated the expressions of MAPKp38/ERK and its downstream pro-allergic mediators that are involved in the signaling pathway in mast cell cytokine synthesis. This study further confirms that CA has the potential to attenuate mast cell activation by inhibiting HDC and modifying the process of allergic disorders.

Preventative and Therapeutic Effects of Low-dose Ionizing Radiation on the Allergic Response of Rat Basophilic Leukemia Cells.

The prevalence of allergies has increased over the last four decades. In allergic reactions, mast cells induce a hypersensitive immune response to a substance that is normally harmless. Ionizing radiation has different biological effects depending on the dose and dose rate. In this study, we investigated whether low-dose irradiation before (preventative effect) or after (therapeutic effect) an antigen-antibody reaction has an anti-allergic effect. To test this, we activated rat basophilic leukemia (RBL-2H3) mast cells with anti-2,4-dinitrophenyl IgE (antibody) and 2,4-dinitrophenyl human serum albumin, which served as an antigen. To test for both the potential of a preventative effect and a therapeutic effect, we irradiated mast cells both before and after mast cell activation, and we measured mediator release and signaling pathway activity. Low-dose ionizing radiation suppressed mediator release from RBL-2H3 mast cells activated by the antigen-antibody reaction regardless of when the mast cells were irradiated. These results were due to the suppression of FcεRI expression. Therefore, we suggest that low-dose ionizing radiation has a preventative and therapeutic effect in allergic reactions via the FcεRI-mediated RBL-2H3 mast cell activation system.

CD45 exclusion- and cross-linking-based receptor signaling together broaden FcεRI reactivity.

For many years, the high-affinity receptor for immunoglobulin E (IgE) FcεRI, which is expressed by mast cells and basophils, has been widely held to be the exemplar of cross-linking (that is, aggregation dependent) signaling receptors. We found, however, that FcεRI signaling could occur in the presence or absence of receptor cross-linking. Using both cell and cell-free systems, we showed that FcεRI signaling was stimulated by surface-associated monovalent ligands through the passive, size-dependent exclusion of the receptor-type tyrosine phosphatase CD45 from plasma membrane regions of FcεRI-ligand engagement. Similarly to the T cell receptor, FcεRI signaling could also be initiated in a ligand-independent manner. These data suggest that a simple mechanism of CD45 exclusion-based receptor triggering could function together with cross-linking-based FcεRI signaling, broadening mast cell and basophil reactivity by enabling these cells to respond to both multivalent and surface-presented monovalent antigens. These findings also strengthen the case that a size-dependent, phosphatase exclusion-based receptor triggering mechanism might serve generally to facilitate signaling by noncatalytic immune receptors.

Proteinase 3 Interferes With C1q-Mediated Clearance of Apoptotic Cells.

Proteinase 3 (PR3) is the autoantigen in granulomatosis with polyangiitis, an autoimmune necrotizing vasculitis associated with anti-neutrophil cytoplasmic antibodies (ANCAs). Moreover, PR3 is a serine protease whose membrane expression can potentiate inflammatory diseases such as ANCA-associated vasculitis and rheumatoid arthritis. During apoptosis, PR3 is co-externalized with phosphatidylserine (PS) and is known to modulate the clearance of apoptotic cells through a calreticulin (CRT)-dependent mechanism. The complement protein C1q is one mediator of efferocytosis, the clearance of altered self-cells, particularly apoptotic cells. Since PR3 and C1q are both involved in the clearance of apoptotic cells and immune response modulation and share certain common ligands (i.e., CRT and PS), we examined their possible interaction. We demonstrated that C1q binding was increased on apoptotic rat basophilic leukemia (RBL) cells that expressed PR3, and we demonstrated the direct interaction between purified C1q and PR3 molecules as shown by surface plasmon resonance. To better understand the functional consequence of this partnership, we tested C1q-dependent phagocytosis of the RBL cell line expressing PR3 and showed that PR3 impaired C1q enhancement of apoptotic cell uptake. These findings shed new light on the respective roles of C1q and PR3 in the elimination of apoptotic cells and suggest a novel potential axis to explore in autoimmune diseases characterized by a defect in apoptotic cell clearance and in the resolution of inflammation.

Degranulation Inhibitors from Medicinal Plants in Antigen-Stimulated Rat Basophilic Leukemia (RBL-2H3) Cells.

Mast cells and basophils play important roles in both immediate- and late-phase reactions of type 1 allergy. Histamine, which is released from mast cells and basophils stimulated by an antigen or degranulation inducers, is usually determined as a degranulation marker in experiments on immediate allergic reactions in vitro. ß-Hexosaminidase is also stored in secretory granules of the cells and is released concomitantly with histamine when the cells are immunologically activated, and recently this enzyme activity in the medium has been used as a marker of the degranulation. In this paper, we review our studies on the search for degranulation inhibitors, such as flavonoids, stilbenes, and curcuminoids, from medicinal plants using rat basophilic leukemia (RBL-2H3) cells.

Comparative analysis of lipotoxicity induced by endocrine, pharmacological, and innate immune stimuli in rat basophilic leukemia cells.

Cellular lipotoxicity manifests as the steatotic accumulation of lipid droplets or lipid bodies, and/or induction of phospholipidosis. Lipotoxicity can be induced by hyperinsulinemia/nutrient overload, cationic amphiphilic drugs (CAD), and innate immunological stimuli, all of which are stimuli relevant to mast cell physiology. Hyper-accumulation of mast cell lipid bodies in response to hyperinsulinemia has been documented, but lipotoxicity in response to CAD or innate immunologic stimuli has not been analysed comparatively. Moreover, gaps in our understanding of this steatosis remain, specifically as to whether hyperinsulinemia-driven steatosis in these cells attains lipotoxic levels or is accompanied by phospholipidosis. To compare endocrine, pharmacological, and innate immunological stimuli for their ability to induce steatosis and phospholipidosis in a rat basophilic leukemia mast cell model (RBL2H3), differential fluorescence microscopy staining and quantitation of phospholipidosis and steatosis in the RBL2H3 cell line was examined. The three classes of stimuli differentially induced phospholipidosis and steatosis. PPARγ up-regulation was not uniformly associated with the expansion of the lipid body population. Fluorescence imaging of lipid-enriched structures generated in response to lipotoxic cationic amphiphilic drugs, chronic insulin exposure, and TLR2/4 ligands revealed differential staining patterns when visualized using lipophilic dyes. It is concluded that lipotoxicity-inducing pathways in this model mast cell system are diverse, and include steatotic responses to an endocrine stimulus, as well as phospholipidosis responses to cationic lipophilic drugs not previously described in this cell type.

Use of a rat basophil leukemia (RBL) cell-based immunological assay for allergen identification, clinical diagnosis of allergy, and identification of anti-allergy agents for use in immunotherapy.

Food allergy is an important public health problem that affects an estimated 8% of young children and 2% of adults. With an increasing interest in genetically-engineered foods, there is a growing need for development of sensitive and specific tests to evaluate potential allergenicity of foods and novel proteins as well as to determine allergic responses to ensure consumer safety. This review covers progress made in the field of development of cell models, specifically that involving a rat basophil leukemia (RBL) cell-based immunoassay, for use in allergen identification, diagnosis, and immunotherapy. The RBL assay has been extensively employed for determining biologically relevant cross-reactivities of food proteins, assessing the effect of processing on the allergenicity of food proteins, diagnosing allergic responses to whole-food products, and identifying anti-allergy food compounds. From the review of the literature, one might conclude the RBL cell-based assay is a better test system when compared to wild-type mast cell and basophil model systems for use in allergen identification, diagnosis, and analyses of potential immunotherapeutics. However, it is important to emphasize that this assay will only be able to identify those allergens to which the human has already been exposed, but will not identify a truly novel allergen, i.e. one that has never been encountered as in its preferred (humanized) configuration.

Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor FcεRI.

The interaction of IgE with its high-affinity Fc receptor (FcεRI) followed by an antigenic challenge is the principal pathway in IgE mediated allergic reactions. As a consequence of the high affinity binding between IgE and FcεRI, along with the continuous production of IgE by B cells, allergies usually persist throughout life, with currently no permanent cure available. Horses, especially race horses, which are commonly inbred, are a species of mammals that are very prone to the development of hypersensitivity responses, which can seriously affect their performance. Physiological responses to allergic sensitization in horses mirror that observed in humans and dogs. In this paper we describe the development of an in situ assay system for the quantitative assessment of the release of mediators of the allergic response pertaining to the equine system. To this end, the gene encoding equine FcεRIα was transfected into and expressed onto the surface of parental Rat Basophil Leukemia (RBL-2H3.1) cells. The gene product of the transfected equine α-chain formed a functional receptor complex with the endogenous rat ß- and γ-chains. The resultant assay system facilitated an assessment of the quantity of mediator secreted from equine FcεRIα transfected RBL-2H3.1 cells following sensitization with equine IgE and antigenic challenge using ß-hexosaminidase release as a readout. Mediator release peaked at 36.68% ± 4.88% at 100 ng ml(-1) of antigen. This assay was modified from previous assays used to study human and canine allergic responses. We have also shown that this type of assay system has multiple applications for the development of diagnostic tools and the safety assessment of potential therapeutic intervention strategies in allergic disease.

Use of humanized rat basophil leukemia (RBL) reporter systems for detection of allergen-specific IgE sensitization in human serum.

Determination of allergen-specific IgE levels in human blood samples is an important diagnostic technology for assessment of allergic sensitization. The presence of specific IgE in human serum samples can be measured by sensitizing humanized rat basophil leukemia (RBL) cell lines with diluted serum and measuring cellular activation after challenge with the suspected allergens. This has been traditionally performed by measuring the levels of ß-hexosaminidase released upon RBL degranulation. Here, we describe the use of two recently developed humanized RBL reporter cell lines which offer higher sensitivity and are amenable to high-throughput-scale experiments.

Eicosapentaenoic acid and docosahexaenoic acid suppress Th2 cytokine expression in RBL-2H3 basophilic leukemia cells.

It is known that the intake of omega-3 fatty acids, such as eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), is beneficial for preventing and/or treating allergic diseases. The pathogenesis of allergic diseases is associated with overactivation of Th2-skewed immunity. Basophils generate large amounts of Th2 cytokines such as interleukin (IL)-4 and IL-13, which are critically involved in allergic inflammation. We investigated how EPA and DHA affect Th2 cytokine expression in phorbol 12-myristate 13-acetate- and ionomycin (PI)-activated RBL-2H3 basophilic leukemia cells. EPA and DHA induced a dramatic decrease in the production of IL-4 and IL-13 and their transcription in a dose-dependent manner. Luciferase assays of RBL-2H3 cells stably expressing Il4 and Il13 promoter-reporter plasmids demonstrated a significant suppression of PI-induced promoter activation. Analysis of certain transcription factors revealed that nuclear expression of c-Fos and the mRNA expression were suppressed by EPA and DHA. Furthermore, they significantly inhibited the nuclear expression and translocation of nuclear factor of activated T cells (NF-AT)1. In contrast, the expression levels of nuclear factor kappa-B (NF-κB), GATA-binding proteins (GATAs), and CCAAT/enhancer binding protein alpha (C/EBPα) were not significantly affected by EPA and DHA. Phosphorylation of extracellular signal-related kinase was inhibited by EPA and DHA, and phosphorylation of p38 mitogen-activated protein kinase was decreased by DHA, but not by EPA. Taken together, our data suggest that EPA and DHA may suppress Th2-skewed allergic immune responses by inhibiting the expression of basophilic IL-4 and IL-13.

Sanguinarine suppresses IgE induced inflammatory responses through inhibition of type II PtdIns 4-kinase(s).

The effects of sanguinarine on IgE mediated early signaling mechanisms leading to inflammatory mediators release were investigated. Pretreatment of RBL 2H3 cells with sanguinarine inhibited IgE induced activation of type II PtdIns 4-kinase activity. Concomitant with type II PtdIns 4-kinase inhibition, sanguinarine also inhibited IgE induced degranulation and ß hexosaminidase release in RBL 2H3 cells. In vitro assays showed sanguinarine inhibited type II PtdIns 4-kinase activity in a dose dependent fashion with no effect on PtdIns 3-kinase activity. Fluorescence spectroscopic studies suggested that sanguinarine binds to type II PtdIns 4-kinases α and ß isoforms with a Kd of 2.4 and 1.8µM, respectively. Kinetic studies showed that sanguinarine competes with PtdIns binding site of type II PtdIns 4-kinase ß. These results suggest that the anti-inflammatory effects of sanguinarine on PtdIns 3-kinase signaling pathway are more likely an indirect effect and emphasize the importance of the cross talk between type II PtdIns 4-kinases and PtdIns 3-kinases.

Inhibitory effect of phloretin and biochanin A on IgE-mediated allergic responses in rat basophilic leukemia RBL-2H3 cells.

AIMS: Anti-allergic effects and action mechanism of phloretin (Phl) and biochanin A (BioA) on the IgE-antigen complex-mediated allergic responses in rat basophilic leukemia RBL-2H3 cells were investigated. MAIN METHODS: Cell viability, formation of reactive oxygen species (ROS), DPPH radical-scavenging activity, ß-hexosaminidase release, production of interleukin (IL)-4, IL-13, and tumor necrosis factor-alpha (TNF-α) and phosphorylation of Akt and mitogen-activated protein kinase (MAPK) were determined by MTT assay, 2,7-dichlorofluorescein diacetate (DCF-DA) assay, DPPH radical-scavenging assay, reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and western blot analysis, respectively. KEY FINDINGS: Ph1 and BioA dose-dependently inhibited the formation of ROS and the release of ß-hexosaminidase from the RBL-2H3 cells and also showed DPPH radical-scavenging activity. Ph1 and BioA suppressed the antigen-induced phosphorylation of the downstream signaling intermediates, including MAPK and Akt, which are critical for the production of pro-inflammatory cytokines, and also significantly attenuated the production of IgE-mediated pro-inflammatory cytokines, such as IL-4, IL-13, and TNF-α. SIGNIFICANCE: Phloretin and biochanin A attenuate the degranulation and allergic cytokine production through inhibition of intracellular ROS production and the phosphorylation of Akt and the MAPKs, such as ERK1/2, p38, and JNK. The results of this study suggested that these two plant flavonoids may have potent anti-allergic activity in vitro.

Fc receptor-γ subunits with both polar or non-polar amino acids at position of T22 are capable of restoring surface expression of the high-affinity IgE receptor and degranulation in γ subunit-deficient rat basophilic leukemia cells.

The high-affinity IgE receptor (FcɛRI) is formed by the IgE-binding α subunit, ß subunit and γ subunits homodimer. All three subunits are required for proper expression of the receptor on the plasma membrane of mast cells and basophils. However, the exact molecular mechanism of inter-subunit interactions required for correct expression and function of the FcɛRI complex remains to be identified. A recent study suggested that polar aspartate at position 194 within the transmembrane domain of the α subunit could interact by hydrogen bonding with polar threonine at position 22 in the transmembrane domains of the γ subunits. To verify this, we used previously isolated rat basophilic leukemia (RBL)-2H3 variant cells deficient in the expression of the FcɛRI-γ subunit (FcR-γ), and transfected them with DNA vectors coding for FcR-γ of the wild-type or mutants in which T22 was substituted for nonpolar alanine (T22A mutant) or polar serine (T22S mutant). Analysis of the transfectants showed that both T22A and T22S mutants were capable to restore surface expression of the FcɛRI similar to wild-type FcR-γ. Furthermore, cells transfected with wild-type, T22A or T22S FcR-γ showed comparably enhanced FcɛRI-mediated degranulation. Our data indicate that substitution of FcR-γ T22 with non-polar amino acid does not interfere with surface expression of the FcɛRI and its signaling capacity.

Reaginic antibodies from horses with recurrent airway obstruction produce mast cell stimulation.

Reaginic antibodies (IgE and some IgG subclasses) and mast cells play important roles in the induction of type I immediate hypersensitivity reactions. These antibodies bind through their Fc fragment to high affinity receptors (FcεRI) present in the membrane of mast cells and basophils. The cross-linking of the receptor initiates a coordinated sequence of biochemical and morphological events that results in exocytosis of secretory granules containing pre-formed inflammatory mediators, secretion of newly formed lipid mediators, and secretion of cytokines. Previously, several studies have investigated the role of reaginic antibodies in the pathogenesis of Recurrent Airway Obstruction (RAO). However, whereas the immunological aspects of RAO have been extensively studied, the precise sequence of events involved in the pathogenesis remains not completely understood, and the role of IgE in this disease remains controversial. Therefore, in this study, several bioassays were conducted to determine whether reaginic antibodies from RAO-affected horses have the ability to activate mast cells. These bioassays involved measuring degranulation of rat peritoneal mast cells, activation of NF-κB and morphological changes in basophilic leukemia cells (RBL-2H3) following incubation with horse serum from RAO-affected horses that were sensitive and insensitive to Aspergillus fumigatus (A. fumigatus) or from unaffected horses. Our results show that reaginic antibodies from horses sensitive to A. fumigatus were able to degranulate rat peritoneal mast cells. In additon, there was an increase in the activity of the transcription factor NF-κB in RBL-2H3 cells, and morphological changes were observed in these cells once cross-linking was produced. These findings were not found in horses not sensitive to A. fumigatus and healthy horses. These bioassays demonstrate the ability of reaginic antibodies to stimulate mast cells and indicate that these antibodies could be involved in the immunological mechanisms leading to RAO.

The chemokine receptors CXCR1 and CXCR2 couple to distinct G protein-coupled receptor kinases to mediate and regulate leukocyte functions.

The chemokine receptors, CXCR1 and CXCR2, couple to Gαi to induce leukocyte recruitment and activation at sites of inflammation. Upon activation by CXCL8, these receptors become phosphorylated, desensitized, and internalized. In this study, we investigated the role of different G protein-coupled receptor kinases (GRKs) in CXCR1- and CXCR2-mediated cellular functions. To that end, short hairpin RNA was used to inhibit GRK2, 3, 5, and 6 in RBL-2H3 cells stably expressing CXCR1 or CXCR2, and CXCL8-mediated receptor activation and regulation were assessed. Inhibition of GRK2 and GRK6 increased CXCR1 and CXCR2 resistance to phosphorylation, desensitization, and internalization, respectively, and enhanced CXCL8-induced phosphoinositide hydrolysis and exocytosis in vitro. GRK2 depletion diminished CXCR1-induced ERK1/2 phosphorylation but had no effect on CXCR2-induced ERK1/2 phosphorylation. GRK6 depletion had no significant effect on CXCR1 function. However, peritoneal neutrophils from mice deficient in GRK6 (GRK6(-/-)) displayed an increase in CXCR2-mediated G protein activation but in vitro exhibited a decrease in chemotaxis, receptor desensitization, and internalization relative to wild-type (GRK6(+/+)) cells. In contrast, neutrophil recruitment in vivo in GRK6(-/-) mice was increased in response to delivery of CXCL1 through the air pouch model. In a wound-closure assay, GRK6(-/-) mice showed enhanced myeloperoxidase activity, suggesting enhanced neutrophil recruitment, and faster wound closure compared with GRK6(+/+) animals. Taken together, the results indicate that CXCR1 and CXCR2 couple to distinct GRK isoforms to mediate and regulate inflammatory responses. CXCR1 predominantly couples to GRK2, whereas CXCR2 interacts with GRK6 to negatively regulate receptor sensitization and trafficking, thus affecting cell signaling and angiogenesis.

Review: Diagnostic and therapeutic applications of rat basophilic leukemia cells.

The research into understanding of the immunological processes is often difficult due to several factors complicating the isolation and culturing of primary degranulating cells like mast cells and basophils. The establishment of rat basophilic leukemia (RBL) cell line as an efficient and reliable experimental research tool was considered a major advance toward the understanding of the wild-type mast cell population's biology. The development of sub-clone RBL-IV (HR+) led to the isolation of histamine-secreting RBL-2H3 cell line. Since then, RBL-2H3 cells have been extensively used for studying the IgE high affinity receptor (FcɛRI) interactions with their ligand, the IgE antibody. This cell line has been employed for generating human and more recently canine and equine FcɛRIα-transfected RBL cell lines facilitating an assessment of the residues involved in the complementary interaction between the IgE molecules from these species and their cognate high affinity receptor. A proteomics-based approach to the definition of IgE-receptor-mediated signaling pathways was also carried out using this cell line. Furthermore, RBL-2H3 cells have the potential of being used to assess the potential allergenicity of antigens to humans and other animals like dogs and horses which are known to suffer from similar allergic manifestations.

Saikosaponin-d inhibits ß-conglycinin induced activation of rat basophilic leukemia-2H3 cells.

ß-Conglycinin is one of the major storage proteins in soybean and has been identified as a potential diagnostic marker for severe allergic reactions to soybean. Unfortunately, there is a lack of information on the signal transduction pathways of ß-conglycinin induced mast cell activation and how to alleviate these allergic reactions. Bupleurum falcatum, a traditional oriental medicine, has been widely utilized in the treatment of influenza, fever, malaria and menstrual disorders. Furthermore, it has been reported that saikosaponins, the important principle of B. falcatum, possesses anti-allergic activities. Therefore, the present study investigated whether or not saikosaponin-d, an extract of B. falcatum, was effective in the treatment of allergic reactions cased by ß-conglycinin, using a rat basophilic leukemia-2H3 cell line. There were multiple signaling pathways contributing to the development of ß-conglycinin-mediated rat basophilic leukemia-2H3 cell activation. The intracellular calcium mobilization and tyrosine phosphorylation were early events, which in turn elicited reactive oxygen species production, gene activation of Cdc42 and c-Fos, and ultimately led to ß-hexosaminidase release. Saikosaponin-d inhibited rat basophilic leukemia-2H3 cell degranulation by suppressing these critical incidents in the signal transduction pathway. These results suggest that saikosaponin-d exhibited anti-allergic activity and could become an effective herbal therapy for alleviating soybean allergy.

Protein profiling of the secretome of FcεRI activated RBL-2H3.1 cells.

BACKGROUND: Secretory proteins of IgE receptor activated mast cells and basophils play a pivotal role in the generation of immediate and long term immune responses in allergy and type I hypersensitivity. OBJECTIVE: The present study aims to generate a 2-D map and profile of proteins secreted from a high secretory variant of the rat basophilic leukemia cell line, RBL-2H3.1, which in view of the difficulty associated with gaining adequate numbers of pure primary mast cell and basophiles, represents an accepted model system for the study and standardization of the methodology to characterize the secretome of these cell types. METHODS: A 2-D map of secretory proteins was generated by 2-D PAGE and a shotgun mass spectrometric approach carried out for protein identification. RESULTS: Study resulted into identification of 299 proteins released from resting and IgE receptor activated RBL-2H3.1 cells after 90 s, 30 min and 3 h antigen challenge. Further sequence analysis identified ~53% of total proteins as secretory proteins which could be attributed to classical and non-classical secretory pathways. Additionally, functional classification of classic secretory proteins verified the presence of proteins belonged to cytokines, receptors, membrane proteins, lysosomal proteins and proteins associated with specific sub-cellular localizations such as endoplasmic reticulum, mitochondria, nucleus, cytoplasm and ribosome. According to this data the presence of some secretory proteins such as cytokines (e.g. MCP-2, PF-4, CSF-1 and TGF-ß1) are all subject to Ag challenge which may point to their importance toward pathogenesis in allergic diseases. CONCLUSION: In view of both a beneficial and adverse role of mast cell mediators in health and disease, an identification of temporal changes in the secretory pattern may form the basis for future tailor made intervention strategies that may enable us to harvest the therapeutic potential inherent in mast cell exocytosis while inhibiting/attenuating negative outcomes.

Inhibitory effects of adlay bran (Coix lachryma-jobi L. var. ma-yuen Stapf) on chemical mediator release and cytokine production in rat basophilic leukemia cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Adlay (Job's tears, Coix lachryma-jobi L. var. ma-yuen Stapf) has long been used in China to treat rheumatism. AIM OF THE STUDY: We investigated the anti-allergic effects of adlay bran on rat basophilic leukemia (RBL)-2H3 cells. MATERIALS AND METHODS: To evaluate the anti-allergic effects of adlay bran, the release of histamines and cytokines were measured using ELISA. To explore the mechanism of these effects, the protein expression levels were determined using western blotting. RESULTS: A 40.8µg/mL concentration of the ethyl acetate fraction of the ethanolic extracts of adlay bran (ABE-EtOAc) effectively inhibited mast cell degranulation. The 40-100% EtOAc/Hex subfractions of ABE-EtOAc inhibited histamine release with an IC(50) of 71-87µg/mL. Moreover, the ABE-EtOAc subfractions suppressed the secretion of interleukin (IL)-4, IL-6 and tumor necrosis factor-α in the RBL-2H3 cells, indicating that adlay bran can inhibit cytokine secretion in the late phase of the allergic reaction. In addition, adlay bran reduced the intracellular production of reactive oxygen species, inhibited the phosphorylation of Akt and decreased the expression of protein kinase C. Furthermore, six phenolic acids and one flavone were isolated. Of these compounds, luteolin showed the most potent inhibitory activity (IC(50)=1.5µg/mL). CONCLUSION: Adlay bran extract reduced the release of histamines and cytokines and suppressed the production of Akt. These combined effects influenced the signal transduction in RBL-2H3 cells, thereby revealing the mechanisms of the anti-allergic effects of adlay.

Inhibitory effects of an ellagic acid glucoside, okicamelliaside, on antigen-mediated degranulation in rat basophilic leukemia RBL-2H3 cells and passive cutaneous anaphylaxis reaction in mice.

Degranulation inhibitors in plants are widely used for prevention and treatment of immediate-type allergy. We previously isolated a new ellagic acid glucoside, okicamelliaside (OCS), from Camellia japonica leaves for use as a potent degranulation inhibitor. Crude extracts from leaves also suppressed allergic conjunctivitis in rats. In this study, we evaluated the in vivo effect of OCS using a pure sample and performed in vitro experiments to elucidate the mechanism underlying the extraordinary high potency of OCS and its aglycon. The IC(50) values for degranulation of rat basophilic leukemia cells (RBL-2H3) were 14 nM for OCS and 3 µM for aglycon, indicating that the two compounds were approximately 2 to 3 orders of magnitude more potent than the anti-allergic drugs ketotifen fumarate, DSCG, and tranilast (0.17, 3, and >0.3 mM, respectively). Antigen-induced calcium ion (Ca(2+)) elevation was significantly inhibited by OCS and aglycon at all concentrations tested (p<0.05). Upstream of the Ca(2+) elevation in the principle signaling pathway, phosphorylation of Syk (Tyr525/526) and PLCγ-1 (Tyr783 and Ser1248) were inhibited by OCS and aglycon. In DNA microarray-screening test, OCS inhibited expression of proinflammatory cytokines [interleukin (IL)-4 and IL-13], cytokine-producing signaling factors, and prostaglandin-endoperoxidase 2, indicating that OCS broadly inhibits allergic inflammation. During passive cutaneous anaphylaxis in mice, OCS significantly inhibited vascular hyperpermeability by two administration routes: a single intraperitoneal injection at 10 mg/kg and per os at 5 mg/kg for 7 days (p<0.05). These results suggest the potential for OCS to alleviate symptoms of immediate-type allergy.