Calcium and mast cell activation

Eucalyptus oil reduces allergic reactions and suppresses mast cell degranulation by downregulating IgE-FcεRI signalling

Eucalyptus oil has been used since ancient times for its bactericidal, anti-inflammatory, analgesic and sedative effects. In recent years, the action of Eucalyptus oil has been scientifically proven, and there have been reports that Eucalyptus oil suppresses the production of chemokines, cytokines and lipid mediators in basophils, alveolar macrophages and monocytes. Based on this information, we aimed to verify whether Eucalyptus oil can be used for allergic dermatitis, the incidence of which has been increasing among human skin diseases. This effect was verified using a mouse IgE-mediated local allergic model. In conclusion, topical application of Eucalyptus oil suppressed oedema and vascular permeability enhancement due to IgE-mediated allergic on the skin. In addition, we also verified the degranuration of mast cells, which is a part of its action, and examined whether 1,8-cineole, which is the main component of Eucalyptus oil, suppresses the phosphorylation of PLCγ and p38 directly or indirectly. 1,8-cineole was found to suppress degranulation of mast cells.

Pterostilbene Inhibits FcεRI Signaling through Activation of the LKB1/AMPK Pathway in Allergic Response

In this study, the role and mechanism of pterostilbene (Pts) in mast cell degranulation in vitro and in vivo were investigated. The results showed that Pts inhibited mast cell-mediated local passive allergic reactions in mice. In addition, treatment with Pts reduced both histamine release and calcium influx in rat peritoneal mast cells and RBL-2H3 cells and reduced IgE-mediated mast cell activation. Furthermore, the mechanism underlying Pts inhibition of mast cell signaling was probed via studying the effects of Pts on liver kinase B1 (LKB1), including the use of the LKB1 activator metformin and siRNA knockdown of LKB1. The data showed that Pts reduced the release of inflammatory mediators such as tumor necrosis factor-α, interleukin-6, leukotriene C4, and prostaglandin D2 in mast cells by activating the LKB1/adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway. Furthermore, Pts inhibited phosphorylation of FcεRI and FcεRI-mediated degranulation in RBL-2H3 cells. These effects were attenuated after LKB1 knockdown. Taken together, Pts could inhibit FcεRI signaling through activation of the LKB1/AMPK signaling pathway in IgE-mediated mast cell activation. Thus, Pts might be an effective therapeutic agent for mast cell-mediated allergic diseases.

Pannexin-1 Channels Are Essential for Mast Cell Degranulation Triggered During Type I Hypersensitivity Reactions

Mast cells (MCs) release pro-inflammatory mediators through a process called degranulation response. The latter may be induced by several conditions, including antigen recognition through immunoglobulin E (IgE) or "cross-linking," classically associated with Type I hypersensitivity reactions. Early in this reaction, Ca²⁺ influx and subsequent increase of intracellular free Ca²⁺ concentration are essential for MC degranulation. Several membrane channels that mediate Ca²⁺ influx have been proposed, but their role remains elusive. Here, we evaluated the possible contribution of pannexin-1 channels (Panx1 Chs), well-known as ATP-releasing channels, in the increase of intracellular Ca²⁺ triggered during cross-linking reaction of MCs. The contribution of Panx1 Chs in the degranulation response was evaluated in MCs from wild type (WT) and Panx1 knock out (Panx1^-/-) mice after anti-ovalbumin (OVA) IgE sensitization. Notably, the degranulation response (toluidine blue and histamine release) was absent in Panx1^-/- MCs. Moreover, WT MCs showed a rapid and transient increase in Ca²⁺ signal followed by a sustained increase after antigen stimulation. However, the sustained increase in Ca²⁺ signal triggered by OVA was absent in Panx1^-/- MCs. Furthermore, OVA stimulation increased the membrane permeability assessed by dye uptake, a prevented response by Panx1 Ch but not by connexin hemichannel blockers and without effect on Panx1^-/- MCs. Interestingly, the increase in membrane permeability of WT MCs was also prevented by suramin, a P2 purinergic inhibitor, suggesting that Panx1 Chs act as ATP-releasing channels impermeable to Ca²⁺. Accordingly, stimulation with exogenous ATP restored the degranulation response and sustained increase in Ca²⁺ signal of OVA stimulated Panx1^-/- MCs. Moreover, opening of Panx1 Chs in Panx1 transfected HeLa cells increased dye uptake and ATP release but did not promote Ca²⁺ influx, confirming that Panx1 Chs permeable to ATP are not permeable to Ca²⁺. These data strongly suggest that during antigen recognition, Panx1 Chs contribute to the sustained Ca²⁺ signal increase via release of ATP that activates P2 receptors, playing a critical role in the sequential events that leads to degranulation response during Type I hypersensitivity reactions.

Docosahexaenoyl ethanolamide mitigates IgE-mediated allergic reactions by inhibiting mast cell degranulation and regulating allergy-related immune cells

Docosahexaenoic acid (DHA) is a long-chain polyunsaturated fatty acid mainly found in fish oil. Although several studies have suggested that it can alleviate allergy symptoms, its mechanism of action remains to be elucidated. In the present study, we found that docosahexaenoyl ethanolamide (DHEA), a metabolite of DHA produced in the human body, exerts the anti-allergic activity in vitro and in vivo. DHEA suppressed degranulation of rat basophilic leukemia RBL-2H3 cells and bone marrow-derived mast cells in a dose-dependent manner without cytotoxicity. This occurred due to a decrease in Ca²⁺ influx, which is critical for mast cell degranulation. DHEA also suppressed IgE-mediated passive cutaneous anaphylaxis reaction in mice. In addition, DHEA was demonstrated to lessen an allergic symptom in a mouse model of pollinosis and to alter the production of IgE and cytokines secreted by splenocytes collected from the pollinosis mice. Taken together, this study indicates that DHEA is a promising anti-allergic agent as it inhibits mast cell degranulation and modulates other immune cells.

Areca nut extracts mobilize calcium and release pro-inflammatory cytokines from various immune cells

Betel nut consumption has significant implications for the public health globally, as the wide-spread habit of Areca chewing throughout Asia and the Pacific is associated with a high prevalence of oral carcinoma and other diseases. Despite a clear causal association of betel nut chewing and oral mucosal diseases, the biological mechanisms that link Areca nut-contained molecules, inflammation and cancer remain underexplored. In this study we show that the whole Areca nut extract (ANE) is capable of mobilizing Ca²⁺ in various immune cell lines. Interestingly, none of the four major alkaloids or a range of other known constituents of Areca nut were able to induce such Ca²⁺ signals, suggesting that the active components might represent novel or so far unappreciated chemical structures. The separation of ANE into aqueous and organic fractions has further revealed that the calcium-mobilizing molecules are exclusively present in the aqueous extract. In addition, we found that these calcium signals are associated with the activation of several immune cell lines as shown by the release of pro-inflammatory cytokines and increased cell proliferation. These results indicate that calcium-mobilizing molecules present in the aqueous fraction of the Areca nut may critically contribute to the inflammatory disorders affecting betel nut chewers.

Rifampicin Alleviates Atopic Dermatitis-Like Response in vivo and in vitro

Atopic dermatitis (AD) is a common inflammatory skin disorder mediated by inflammatory cells, such as macrophages and mast cells. Rifampicin is mainly used for the treatment of tuberculosis. Recently, it was reported that rifampicin has anti-inflammatory and immune-suppressive activities. In this study, we investigated the effect of rifampicin on atopic dermatitis in vivo and in vitro. AD was induced by treatment with 2, 4-dinitrochlorobenzene (DNCB) in NC/Nga mice. A subset of mice was then treated with rifampicin by oral administration. The severity score and scratching behavior were alleviated in the rifampicin-treated group. Serum immunoglobulin E (IgE) and interleukin-4 (IL-4) levels were also ameliorated in mice treated with rifampicin. We next examined whether rifampicin has anti-atopic activity via suppression of mast cell activation. Rifampicin suppressed the release of β-hexosaminidase and histamine from human mast cell (HMC)-1 cultures stimulated with compound 48/80. Treatment with rifampicin also inhibited secretion of inflammatory mediators, such tumor necrosis factor-α (TNF-α) and prostaglandin D₂ (PGD₂), in mast cells activated by compound 48/80. The mRNA expression of cyclooxygenase 2 (COX-2) was reduced in the cells treated with rifampicin in a concentration-dependent manner. These results suggest that rifampicin can be used to treat atopic dermatitis.

Calpain-1 contributes to IgE-mediated mast cell activation

Mast cells play a central role in allergy through secretion of both preformed and newly synthesized mediators. Mast cell mediator secretion is controlled by a complex network of signaling events. Despite intensive studies, signaling pathways in the regulation of mast cell mediator secretion remain incompletely defined. In this study, we examined the role of calpain in IgE-dependent mast cell activation. IgE-mediated activation of mouse bone marrow-derived mast cells enhanced calpain activity. Inhibition of calpain activity by a number of calpain inhibitors reduced IgE-mediated mast cell degranulation both in vitro and in vivo. Calpain inhibitors blocked IgE-mediated TNF and IL-6 production in vitro and reduced late-phase allergic response in vivo. Importantly, mouse calpain-1 null bone marrow-derived mast cells showed reduced IgE-mediated mast cell degranulation in vitro and in vivo, diminished cytokine and chemokine production in vitro, and impaired late-phase allergic response in vivo. Further studies revealed that calpain-1 deficiency led to specific attenuation of IκB-NF-κB pathway and IKK-SNAP23 pathway, whereas calcium flux, MAPK, Akt, and NFAT pathway proceed normally in IgE-activated calpain-1 null mast cells. Thus, calpain-1 is identified as a novel regulator in IgE-mediated mast cell activation and could serve as a potential therapeutic target for the management of allergic inflammation.

CBP501-calmodulin binding contributes to sensitizing tumor cells to cisplatin and bleomycin

CBP501 is an anticancer drug currently in randomized phase II clinical trials for patients with non-small cell lung cancer and malignant pleural mesothelioma. CBP501 was originally described as a unique G(2) checkpoint-directed agent that binds to 14-3-3, inhibiting the actions of Chk1, Chk2, mitogen-activated protein kinase-activated protein kinase 2, and C-Tak1. However, unlike a G(2) checkpoint inhibitor, CBP501 clearly enhances the accumulation of tumor cells at G(2)-M phase that is induced by cisplatin or bleomycin at low doses and short exposure. By contrast, CBP501 does not similarly affect the accumulation of tumor cells at G(2)-M that is induced by radiation, doxorubicin, or 5-fluorouracil treatment. Our recent findings point to an additional mechanism of action for CBP501. The enhanced accumulation of tumor cells at G(2)-M upon combined treatment with cisplatin and CBP501 results from an increase in intracellular platinum concentrations, which leads to increased binding of platinum to DNA. The observed CBP501-enhanced platinum accumulation is negated in the presence of excess Ca(2+). Some calmodulin inhibitors behave similarly to, although less potently than, CBP501. Furthermore, analysis by surface plasmon resonance reveals a direct, high-affinity molecular interaction between CBP501 and CaM (K(d) = 4.62 × 10(-8) mol/L) that is reversed by Ca(2+), whereas the K(d) for the complex between CBP501 and 14-3-3 is approximately 10-fold weaker and is Ca(2+) independent. We conclude that CaM inhibition contributes to CBP501's activity in sensitizing cancer cells to cisplatin or bleomycin. This article presents an additional mechanism of action which might explain the clinical activity of the CBP501-cisplatin combination.

Influence of Pseudomonas aeruginosa quorum sensing signal molecule N-(3-oxododecanoyl) homoserine lactone on mast cells

Quorum sensing system is a cell-to-cell communication system that plays a pivotal role in virulence expression in bacteria. Recent advances have demonstrated that the Pseudomonas aeruginosa quorum sensing molecule, N-3-oxododecanoyl homoserine lactone (3OC(12)-HSL), exerts effects on mammalian cells and modulates host immune response. Mast cells (MCs) are strategically located in the tissues that are constantly exposed to external stimulus. Therefore, it is very much possible that 3OC(12)-HSL may interact with MCs. Little is known, however, about specific effects of 3OC(12)-HSL on MCs. To address this, we investigated the influence of 3OC(12)-HSL on cell viability, apoptosis, intracellular calcium and cytokine release in MCs. We found that at high concentrations (100 microM), 3OC(12)-HSL inhibited proliferation and induced apoptosis in P815. The 3OC(12)-HSL treatment significantly increased intracellular calcium release in both P815 and HMC-1. We also observed that 3OC(12)-HSL-induced histamine release and degranulation in HMC-1 cells. Furthermore, 3OC(12)-HSL-induced IL-6 production at lower concentrations (6.25-12.5 microM) but steadily reduced IL-6 production at high concentration (50-100 muM). These data demonstrate that P. aeruginosa 3OC(12)-HSL affects MCs function.

The human inflammatory response

Inflammation is a protective response of vascularized tissue normally elicited toward nonself-determinants or tissue injury. Inflammation functions as part of normal host surveillance mechanisms to destroy or quarantine both harmful agents and damaged tissue. Most forms of inflammation are exaggerated out of proportion to the stimulus, because humoral amplification systems recruit additional components of the immune system initiating the production of proinflammatory mediators, including cytokines synthesized by activated macrophages. These act as secondary messengers to induce synthesis and expression of specific adhesion molecules on endothelial cells and white cells. Polymorphonuclear leukocytes play a central role in the acute inflammatory response. Anaphylaxis, an immediate hypersensitivity reaction to substances administered in the perioperative period, serves as a useful model for some of the problems of acute inflammation because there are important interrelationships with the cardiovascular system, endothelium, and coagulation. Mast cells and basophils produce the acute inflammation associated with anaphylaxis mediated by immunoglobulin E (IgE) antibodies, whereas the immunoglobulin G (IgG)-antigen interaction activates the complement cascade to generate anaphylatoxins, specifically C5a. Activation of white cells causes release of proteolytic enzymes, production of oxygen-derived free radicals, and the synthesis of a variety of lipid mediators. Protamine sulfate is one of the most common causes of life-threatening anaphylactic reactions during cardiac surgery. Differing responses occur, dependent on the presence of either IgE or IgG antibodies with the activation of the mast cell or the complement system, respectively. The many different amplifying pathways that can be recruited during anaphylaxis and the array of mediators involved are important when therapeutic intervention is considered. The challenge for the future will be to identify a pharmacologic agent that will arrest the inflammatory cascade and thus prevent further amplification and resultant host injury.

Activated mast cells are fibrogenic for 3T3 fibroblasts

The extent of mast cell direct involvement in fibrosis is not defined as yet. In the present study we assessed whether long-term co-culture (up to 7 d) of functionally active rat peritoneal mast cells with 3T3 mouse fibroblasts and mass cell activation can affect fibroblast proliferation and collagen production. Co-culture of subconfluent 3T3 fibroblasts with resting mast cells or with mast cells stimulated by alpha IgE (1:35) or repeatedly activated by low concentrations of compound 48/80 (0.25-0.75 microgram/ml) did not alter fibroblast proliferation. However, fibroblast proliferation was increased significantly (100-130%) when mast cells were repeatedly activated with higher concentrations of compound 48/80 (1-3 micrograms/ml). Repeated mast cell activation by compound 48/80 (0.25 microgram/ml) caused a twofold increase in collagen production and this was reduced by 63% by the mast cell stabilizer nedocromil sodium (10(-5) M). At the same time, co-culture of 3T3 fibroblasts with unstimulated or immunologically activated mast cells did not modulate their collagen production. In conclusion, we have demonstrated that mast cell activation, under certain conditions, can enhance significantly 3T3 fibroblast proliferation and collagen production, thus indicating a direct mast cell involvement in the fibrotic processes.

Mechanisms of vancomycin-induced histamine release from rat peritoneal mast cells

The mechanisms of vancomycin (VCM)-induced histamine release were studied with rat peritoneal mast cells. VCM (> 1 x 10(-3) M) released histamine from the isolated mast cells in a dose-dependent and noncytotoxic manner. In the absence of extracellular Ca2+, the histamine release was reduced markedly. When the intracellular Ca2+ was depleted, it was further decreased. The Fura-2-loaded single mast cells showed a biphasic increase in the intracellular Ca2+ concentration ([Ca2+]i) by VCM: the first transient and the second sustained components. In the absence of extracellular Ca2+, the transient component was unchanged, while the sustained component was eliminated completely. The IP3 content in the mast cells increased within 10 s after the application of VCM. These results suggest that VCM release histamine from rat peritoneal mast cells via an IP3 production and increase in [Ca2+]i.

Regulation of human basophil activation. I. Dissociation of cationic dye binding from histamine release in activated human basophils

Human basophil activation was demonstrated by histamine release (HR) and by the decrease of the toluidine blue-positive basophils (TB+). In four experimental systems, TB+ number decreased in the absence of HR (1) in basophils from atopic subjects stimulated by allergen concentrations below the threshold for HR, (2) in basophils sensitized by anti-2,4-dinitrophenyl IgE stimulated by noncovalently linked 2,4-dinitrobenzene sulfonic acid-human serum albumin (also, the threshold for decrease of TB+ required lower concentrations of sensitizing anti-2,4-dinitrophenyl IgE than for HR), (3) in low Ca++ medium, and (4) in the presence of the Na+/H+ exchanger, monensin. These results suggest that (1) there is a lower threshold for TB+ decrease than for HR in allergen concentration, number of membrane IgE molecules, and number of IgE cross-linkings; moreover, external Ca++ requirement is lower for decrease of TB+ than for HR and (2) TB+ decrease reflects either granule exocytosis or, in the absence of HR, biochemical changes (most probably cation exchanges) altering the interaction of the basic dye with the granules. Thus, monitoring decrease in TB+ allows detection of basophil activation in the absence of HR.

Intestinal anaphylaxis in the rat: mediators responsible for the ion transport abnormalities

Antigen challenge of jejunal epithelium from rats sensitized to egg albumin induces an active Cl- secretory process secondary to release of mucosal mast cell mediators. The present study was designed to define the relative role of these mast cell mediators and the enteric nervous system in the transport abnormalities associated with intestinal anaphylaxis. Net ion transport of stripped jejunal tissue from sensitized and sham-treated animals was studied in Ussing chambers. The Cl- secretory response induced by egg albumin during intestinal anaphylaxis was similar to that after addition of 5-hydroxytryptamine (5-HT), histamine, and prostaglandins D2 and E2 to jejunal tissue. Cinanserin, a 5-HT2-receptor antagonist, virtually abolished the response to 5-HT and totally abolished the response to egg albumin. Methysergide, a 5-HT1-receptor antagonist had no effect on either response. Indomethacin, an inhibitor of prostaglandin synthesis, significantly inhibited the 5-HT and egg albumin response. Diphenhydramine, an H1-receptor antagonist and cimetidine, an H2-receptor antagonist both significantly inhibited the histamine response but neither altered the response to egg albumin. Atropine, an anticholinergic, and tetrodotoxin, a nerve blocker, did not inhibit the antigen induced anaphylactic response. These results indicate that 5-HT, acting through 5-HT2 receptors is largely responsible for the transport abnormalities seen in intestinal anaphylaxis induced by egg albumin while prostaglandins appear to play a partial role. The findings do not support a role for the enteric nervous system for the egg albumin induced changes in Cl- secretion.