Caffeic acid phenethyl ester inhibits pseudo-allergic reactions via inhibition of MRGPRX2/MrgprB2-dependent mast cell degranulation.

Mast cells play essential role in allergic reactions through the process called mast cell degranulation. Recent studies have found that a basic secretagogue compound 48/80 (C48/80) induces non-IgE-mediated mast cell degranulation via activation of human Mas-related G protein-coupled receptor X2 (MRGPRX2) and mouse MrgprB2. Although previous studies have revealed that caffeic acid (CA) and its derivatives possess anti-allergic effects via IgE-dependent manner, it is largely elusive whether these compounds have impact on MRGPRX2/MrgprB2 to exert inhibitory effects. Therefore, the present study investigated whether CA as well as its derivatives - rosmarinic acid (RA) and caffeic acid phenethyl ester (CAPE) - has the ability to inhibit the activity of MRGPRX2/MrgprB2 to evoke pseudo-allergic effects. As a result, it was found that CAPE inhibits C48/80-induced activation of MRGPRX2/MrgprB2, but neither CA nor RA showed discernible inhibition. Furthermore, the ß-hexosaminidase release assay showed that CAPE inhibits mouse peritoneal mast cell degranulation in both IgE-dependent and MrgprB2-dependent manners. Additionally, mouse paw edema induced by C48/80 was dramatically suppressed by co-treatment of CAPE, suggesting that CAPE possesses a protective effect on C48/80-evoked pseudo-allergic reactions. The pretreatment of CAPE also significantly decreased scratching bouts of mice evoked by C48/80, demonstrating that CAPE also has an anti-pruritic effect. Therefore, these data implicate that CAPE can suppress pseudo-allergic reactions evoked by C48/80 via MrgprB2-dependent manner. Finally, molecular docking analysis showed that CAPE is predicted to bind to human MRGPRX2 in the region where C48/80 also binds, implying that CAPE can be a competitive inhibitor of MRGPRX2. In conclusion, it is found that CAPE has the ability to inhibit MRGPRX2/MrgprB2, leading to the prevention of mast cell degranulation and further to the alleviation of mast cell reactions. These results indicate that CAPE as a CA derivative could be developed as a new protective agent that exerts dual inhibition of mast cell degranulation mediated by IgE and MRGPRX2/MrgprB2.

Roxithromycin inhibits compound 48/80-induced pseudo-allergy via the MrgprX2 pathway both in vitro and in vivo.

Roxithromycin (ROX) is a macrolide antibiotic with a variety of immunological effects. Mast cells (MCs) play a key role in host defense, mediating hypersensitivity and pseudo-allergic reactions. Mas-related G protein-coupled receptor X2 (MrgprX2) is the main receptor related to pseudo-allergy. In this study, we investigated the anti-pseudo-allergy effect of ROX and its underlying mechanism. The effects of ROX on passive cutaneous anaphylaxis (PCA) and active systemic allergy were examined, degranulation, Ca2+ influx, and cytokine release were studied in vivo and in vitro. Interactions between ROX and MrgprX2 protein were also detected through surface plasmon resonance. The PCA and active systemic allergy induced by compound 48/80 were inhibited by ROX. An intermolecular interaction was detected between the ROX and MrgprX2 protein. In conclusion, ROX could inhibit pseudo-allergic reactions, and this effect involves the Ca2+/PLC/IP3 pathway of MrgprX2. This study provides new insight into the anti-pseudo-allergy effects of ROX.

Inhibitory effect of glycoprotein isolated from Opuntia ficus-indica var. saboten MAKINO on activities of allergy-mediators in compound 48/80-stimulated mast cells.

The present study was performed to investigate the anti-allergy potentials of glycoprotein (90kDa) isolated from Opuntia ficus-indica var. saboten MAKINO (OFI glycoprotein) in vivo (ICR mice) and in vitro (RBL-2H3 cells). At first, to know whether the OFI glycoprotein has an inhibitory ability for allergy in vivo, we evaluated the activities of allergy-related factors such as histamine and beta-hexosaminidase release, lactate dehydrogenase (LDH), and interleukin 4 (IL-4) in compound 48/80 (8 ml/kg BW)-treated ICR mice. After that, we studied to found the effect for anti-allergy in vitro such as nuclear factor kappa B (NF-kappaB) and inducible nitric oxide synthase (iNOS), extracellular signal-regulated kinase (ERK) 1/2, arachidonic acid, and cyclooxygenase-2 (COX-2) in compound 48/80 (5 microg/ml)-treated RBL-2H3 cells. Our results showed that the OFI glycoprotein (5 mg/kg) inhibited histamine and beta-hexosaminidase release, lactate dehydrogenase (LDH), and interleukin 4 (IL-4) in mice serum. Also OFI glycoprotein (25 microg/ml) has suppressive effects on the expression of MAPK (ERK1/2), and on protein expression of anti-allergic proteins (iNOS and COX-2). Thus, we speculate that the OFI glycoprotein is an example of natural compound that blocks anti-allergic signal transduction pathways.

Chitosan-hyaluronic acid nanoparticles loaded with heparin for the treatment of asthma.

The purpose of this study was to produce mucoadhesive nanocarriers made from chitosan (CS) and hyaluronic acid (HA), and containing the macromolecular drug heparin, suitable for pulmonary delivery. For the first time, this drug was tested in ex vivo experiments performed in mast cells, in order to investigate the potential of the heparin-loaded nanocarriers in antiasthmatic therapy. CS and mixtures of HA with unfractionated or low-molecular-weight heparin (UFH and LMWH, respectively) were combined to form nanoparticles by the ionotropic gelation technique. The resulting nanoparticles loaded with UFH were between 162 and 217 nm in size, and those prepared with LMWH were 152 nm. The zeta potential of the nanoparticle formulations ranged from +28.1 to +34.6 mV, and in selected nanosystems both types of heparin were associated with a high degree of efficiency, which was approximately 70%. The nanosystems were stable in phosphate buffered saline (PBS), pH 7.4, for at least 24h, and released 10.8% of UFH and 79.7% of LMWH within 12h of incubation. Confocal microscopy experiments showed that fluorescent heparin-loaded CS-HA nanoparticles were effectively internalized by rat mast cells. Ex vivo experiments aimed at evaluating the capacity of heparin to prevent histamine release in rat mast cells indicated that the free or encapsulated drug exhibited the same dose-response behaviour.

Attenuation of axon reflexes to compound 48/80 after repeated iontophoresis of compound 48/80 in skin of the human forearm.

The aim of this study was to determine whether the iontophoretic administration of the mast cell degranulator compound 48/80 influences axon reflex vasodilatation in the skin of the human forearm. In stage 1, compound 48/80 was administered by iontophoresis to a circular site in the forearm of 9 healthy men and 8 healthy women on four occasions spread over 24 h. Two control sites were also prepared by passing the iontophoretic current through 0.9% saline. Large wheals initially developed at the compound 48/80 site in 8 of the males and in 2 of the females, but wheals were minimal in all subjects by the fourth administration. In stage 2, compound 48/80 iontophoresis provoked substantial flaring at the first control site, whereas saline iontophoresis induced only minor flaring at the second control site, indicating that compound 48/80 induced axon reflex vasodilatation. However, prior treatment with compound 48/80 inhibited flaring to compound 48/80 in subjects who initially developed wheals, consistent with mast cell degranulation. In stage 3, flaring after iontophoresis of histamine was investigated at the site of compound 48/80 pretreatment and at the second control site in 12 subjects. Flaring was impaired only slightly in 6 subjects who initially developed wheals to compound 48/80. The persistence of flaring indicates that repeated administrations of compound 48/80 did not abolish neurogenic inflammation. Transcutaneous iontophoresis of compound 48/80 may be an attractive alternative to intradermal injection in studies that aim at clarifying the function of mast cells in healthy and diseased skin.

Effects of latrunculin reveal requirements for the actin cytoskeleton during secretion from mast cells.

To investigate the role of the actin cytoskeleton in exocytosis, we have tested the effects of latrunculin B, a microfilament-disrupting drug, on secretion from intact and permeabilised rat peritoneal mast cells. The toxin strongly inhibited secretion from intact cells (attached or in suspension) responding to a polybasic agonist, compound 48/80. However, this effect was revealed only after a profound depletion of actin filaments. This was achieved by a long (1 h) exposure of cells to the drug before activation, together with its presence during activation. Maximal inhibition of secretion by such treatment was 85% at 40 microgram/ml latrunculin B. These results indicate that minimal actin structures are essential for the exocytotic response. In contrast, stimulus-induced cell spreading was prevented by latrunculin (5 microgram/ml) applied either before or after activation. The effects of the toxin on intact cells were fully reversible. The responses of permeabilised cells were affected differentially: secretion induced by calcium was more sensitive to latrunculin than that induced by GTP-gamma-S. The calcium response, therefore, is more dependent upon the integrity of the actin cytoskeleton than the response induced by GTP-gamma-S. Again, maximal inhibitory effects (approximately 65 and 25% at 40 microgram/ml) were observed only when cells were exposed to the toxin both before and after permeabilisation. Since the permeabilised cells system focuses on the final steps of exocytosis, the incomplete inhibition suggests that actin plays a modulatory rather than a central role at this stage.

The role of sensorial neuropeptides in the edematogenic responses mediated by B(1) agonist des-Arg(9)-BK in rats pre-treated with LPS.

In the present study we have investigated some of the mechanisms underlying B(1) kinin receptor-induced paw edema formation in rats that had been treated with LPS, paying special attention to the involvement of neurogenic inflammation. Intradermal (i.d.) injection of the B(1) receptor agonist des-Arg(9)-BK (100 nmol/paw) resulted in a marked increase in paw volume in animals pre-treated with LPS (0.40+/-0.06 ml). The co-injection of the selective NK(1) FK888 (1 nmol/paw) or NK(2) SR 48968 (3 nmol/paw) receptor antagonists resulted in a significant inhibition of the edema induced by des-Arg(9)-BK (30+/-4 and 25+/-7%, respectively). The NK(3) SR 142801 (3 nmol/paw) antagonist did not demonstrate any significant effect on B(1) receptor-mediated paw edema. The edema induced by des-Arg(9)-BK was also significantly inhibited (33+/-5%) by the co-injection of the CGRP-receptor antagonist CGRP 8-37 (1 nmol/paw) or by treatment of animals with capsaicin (50 mgkg(-1), s.c., 48 h, prior) (45+/-4%). The pre-treatment of animals with methysergide or with mianserin, 5-HT(1) and 5HT(2) antagonists, respectively (both 10 mgkg(-1), i.p. 30 min), resulted in a significant reduction of the edema mediated by B(1) receptors (23+/-5 and 20+/-3%, respectively). In addition, compound 48/80 (12 microg/paw, 24 h) significantly reduced des-Arg(9)-induced paw edema in rats pre-treated with LPS (23+/-3%), while the treatment of animals with the H(1) receptor antagonist pyrilamine (10 mgkg(-1), i.p., 30 min) failed to affect the edematogenic responses involving B(1) receptors. Finally, the co-injection of NOS inhibitors L-NAME (100 nmol/paw) or 7-NINA (10 nmol/paw) did not affect the rat paw edema caused by des-Arg(9)-BK, whereas they significantly inhibited BK-induced paw edema. Jointly, the results of the present study show that the edematogenic response mediated by the activation of B(1) receptors, in animals pre-treated with LPS, involves the release of tachykinins and CGRP, as well as serotonin, while NO and histamine seem not to be involved. Therefore, these data further support the notion that B(1) receptors have an important role in modulating the inflammatory processes.

Interaction between tachykinins and CGRP in human skin.

Substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP) coexist in nerve fibres in the skin. CGRP causes erythema upon intracutaneous injection. The erythema is independent of axon reflexes and release of mast cell histamine. SP is known to produce a flare reaction that is dependent on axon reflexes and release of mast cell histamine. The flare reaction to NKA is known to depend predominantly on axon reflexes. The purpose of the present study was to investigate possible cooperation between SP and CGRP. SP was found to shorten the duration of the reddening induced by CGRP, injected concomitantly. NKA did not shorten the duration of the CGRP response. Local elimination of mast cells in the skin by treatment with compound 48/80 had the effect that SP lost its ability to shorten CGRP-evoked erythema. These observations support the suggestion that an SP-evoked release of proteolytic enzymes from mast cells could lead to accelerated degradation of CGRP.

Effects of N-acetylcysteine on histamine release by sodium fluoride and compound 48/80 from isolated rat mast cells.

N-acetylcysteine (NAC) enhances the release of histamine induced by the fluoride-calcium system but not by compound 48/80. After preincubation of the cells for 2 h at room temperature (RT) as well as at 37 degrees C, NAC was found to enhance histamine release also when induced by compound 48/80. Both fluoride treatment and prolonged incubation at 37 degrees C (but not at RT) for 2 h decreased the ATP content of the cells. NAC was found to counteract the fall in ATP caused by prolonged incubation of the cells at 37 degrees C but not when induced by exposure to sodium fluoride. The results do not favor the concept that free radicals generated by fluoride treatment are responsible for the subsequent sensitivity of the cells to the secretory action of calcium. On the other hand, it cannot be excluded that free radicals generated during prolonged incubation of the cells at 37 degrees C might be involved in the decrease of the sensitivity of the cells to the secretory action of the fluoride-calcium system and of compound 48/80. This is supported by the finding that the presence of NAC not only activated the secretory response but also counteracted the decrease of the cellular ATP content noted following preincubation of the cells for 2 h at 37 degrees C.

Induction of histamine release and calmodulin antagonism are two distinct properties of compound 48/80.

Compound 48/80, a mixture of oligomers, was fractionated by passing it in the presence of Ca2+ over a calmodulin-Sepharose column. The fraction not retained by the gel was shown by mass spectrometry to consist mainly of trimers, tetramers and pentamers. A second fraction consisting of hexamers and heptamers was eluted from the column at high ionic strength in the presence of Ca2+. Finally, in the presence of EGTA at high ionic strength, a third fraction eluted mainly consisting of higher oligomers (hexamers to dodecamers). The different fractions were characterized by testing their influence on calmodulin-sensitive Ca2+-transporting ATPase and their ability to elicit histamine release from mast cells. The third fraction showed the highest potency as calmodulin antagonist, however, the second fraction was the most potent in inducing histamine secretion. This would imply that the ability of compound 48/80 to evoke histamine release and to inhibit the function of calmodulin are distinct properties of the agent which are unrelated.

The effects of ionophore A23187 on permeability of the frog mesentery microvasculature.

The effects of the divalent cation ionophore A23187, upon microvascular permeability have been investigated in single perfused capillaries and venules in the mesenteries of pithed frogs. In all experiments, the vessels were perfused with Ringer solutions containing the macromolecules Ficoll 70 (40 mg ml-1) and bovine serum albumin (10 mg ml-1). Hydraulic permeability (Lp) of the vessel walls and the effective osmotic pressure (sigma delta pi) exerted across them by the perfusate macromolecules were estimated by the method of Michel (1980). In eleven experiments addition of A23187 to the perfusate raised Lp from a mean value (+/- S.E.M.) of 4.76 (+/- 1.05) x 10(-7) cm s-1 cmH2O-1 to one of 11.97 (+/- 1.96) x 10(-7) cm s-1 cmH2O-1 and reduced sigma delta pi from a mean (+/- S.E.M.) of 16.5 (+/- 2.01) cmH2O to one of 7.6 (+/- 1.93) cmH2O. The effects of A23187 on Lp and sigma delta pi were reversible. A23187 was found to increase Lp and reduce sigma delta pi after the mesentery had been exposed to compound 48/80 to degranulate the mast cells two or more hours previously. A23187 also appeared to be effective in raising Lp and lowering sigma delta pi in the absence of Ca2+ ions from the perfusate and superfusate. The ionophore was found to reduce permeability, however, when Mg2+ ions were removed from the perfusate and superfusate both in the absence and in the presence of Ca2+. This reduction in permeability could be converted into an increase in Lp and fall in sigma delta pi if Mg2+ were restored to the superfusate. It is concluded that A23187 increases vascular permeability in a reversible manner and that Mg2+ ions in the extracellular fluids are necessary for its action.

Ca-dependent and Ca-independent histamine release from mast cells induced by active components of compound 48/80.

Compound 48/80 and 14C-labelled compound 48/80 were synthesized, and fractionated by thin-layer chromatography into 14 components with various histamine-releasing activities and different Ca++ requirements for their actions. The histamine release induced from rat mast cells in vitro by the most active component, fraction D (molecular weight = 2280, a tridecamer composed of 13 monomer units), was greatly elevated by extracellular Ca++, and was partially reduced by pretreatment of the cells with dinitrophenylated Ascaris antiserum, an IgE. In contrast, the histamine release induced by fraction H (molecular weight = 1580, a nonamer composed of 9 monomer units), was higher in Ca-free medium than in Ca-containing medium, and partially suppressed by pretreatment of mast cells with neurotensin or substance P, both Ca-independent releasers. The binding potencies of the 14C-labelled components estimated at 4 degrees C in the presence of Ca++, where no degranulation of the cells occurs, generally paralleled their histamine-releasing activities. However, Ca++ was inhibitory for the binding of 14C-fraction H. The binding of fraction D to [3H]arachidonic-acid-preloaded mast cells induced a rapid accumulation of the labelled arachidonic acid into phosphatidic acid, phosphatidylinositol and phosphatidylcholine, with concomitant decrease of the labelled arachidonic acid from phosphatidylethanolamine prior to the detectable histamine release.

Binding of compound 48/80 by isolated rat mast cells in connection with histamine release.

The binding of compound 48/80 in connection with histamine release from isolated rat mast cells was investigated by a two-step incubation procedure. After incubation of mast cells with known concentrations of compound 48/80, the supernatants were collected and subsequently exposed to fresh mast cells. The response in the second incubation step provided a measure of the amount of compound 48/80 remaining in the supernatants. At noncytotoxic concentrations of the releasing agent, binding capacities for compound 48/80 of up to 4 micrograms/10(5) mast cells (4% w/v) were observed. The binding of compound 48/80 was of high affinity, giving mast cell concentrations of the compound exceeding that in the incubation medium by four orders of magnitude. The binding occurred rapidly with a substantial proportion bound within the first minute. These findings indicate that quantitation of exocytotic events by means of basic dyes may be compromised by competition for granular binding sites by basic releasing agents.

Binding of active components of compound 48/80 to rat peritoneal mast cells.

The binding characteristics of compound 48/80 were examined using rat mast cells and fractionated 14C-labeled compound 48/80 components at 4 degrees C in vitro where no degranulation of the cells occurred. The binding potencies of these components in the presence of Ca2+ generally paralleled their histamine releasing activities, except in the case of fractions G (decamer) and H (nonamer), both Ca2+-independent releasers, for the binding of which Ca2+ was inhibitory. Scatchard analyses and displacement studies indicated that the mast cells had two types of binding sites with high and low affinities for fractions D (tridecamer, Ca2+-dependent releaser, Kd = 3.41 X 10(-8) M and 3.35 X 10(-6) M) and H (Ca2+-independent releaser, Kd = 1.11 X 10(-7) M and 9.11 X 10(-6) M), respectively. These sites partially overlapped each other, and also the fraction D site partially overlapped the IgE site and the fraction H site overlapped the neurotensin or substance P site.

Binding of a spin label analogue of compound 48/80 to rat peritoneal mast cells: correlation of binding properties with surface topography.

A spin label analogue of compound 48/80 has been synthesized and its binding to purified rat peritoneal mast cells has been studied by electron spin resonance spectroscopy. The spin label analogue (SL-48/80) had almost identical biological activity to unlabeled compound 48/80. SL-48/80 was used to estimate the number of binding sites per cell on normal mast cells (7.25 X 10(10)), on mast cells deactivated by sodium azide and 2-deoxyglucose or by heating to 46 degrees for 30 min (1 X 10(10)) and cells from animals actively-sensitized to ovalbumin (5.2 X 10(10)). SL-48/80 was also shown to bind to isolated mast cell granules. Differences in the binding properties of mast cells after the different treatments are related to their surface topography as seen by scanning electron microscopy, and the contribution of the granules to the number of binding sites is discussed.

Cyclic nucleotide involvement in histamine release from mast cells--a reevaluation.

Secretory events in cells in general are accompanied by increased levels of cyclic AMP. In mast cells, however, the pattern is reversed. Thus histamine release is associated with a fall in cAMP. It has been suggested that the lowered levels of cAMP lead to an increase in membrane permeability towards calcium and that an influx of such ions triggers the release mechanisms. It has further been reported that high levels of cAMP inhibit histamine release by decreasing the permeability. However, evidence has now accumulated indicating that this general concept is far too simplistic. Studies are reviewed which imply that there is little or no correlation between histamine release and intracellular levels of cyclic nucleotides. A new working hypothesis with respect to the role of these nucleotides in mast cell secretion is proposed.

Histamine release from rat peritoneal mast cells exposed to ultraviolet light.

After irradiation with ultraviolet light, rat peritoneal mast cells incubated with the histamine liberator compound 48/80 were found to have reduced capacity to release histamine. The action spectrum for histamine release inhibition seemed to be in the wavelength region of UVB. UV-light per se did not induce histamine liberation other than for dosages greater than or equal to 1.45 J/cm2. No such release was observed with the doses of UVA studied (3.4-20.5 J/cm2). The metabolic inhibitor 2.4-dinitrophenol (DNP), which almost completely inhibited compound 48/80-elicited histamine release, did not influence the UV-induced histamine release, indicating that the latter was not a secretory process but due to cytotoxic leakage of histamine from the cells. These results suggest that inhibition of histamine-releasing capacity or reduction of skin histamine due to photolysis of mast cells may explain the beneficial effect of UV in pruritic disorders where histamine release from mast cells is involved.

The effect of concentration on the binding of compound 48/80 to rat mast cells: a fluorescence microscopy study.

A fluorescent analog of the chemical histamine liberator, compound 48/80, has been synthesized by the covalent attachment of rhodamine to the 48/80 polymer (R-48/80). The histamine liberating characteristics of this analog were similar to those of the parent compound. The binding characteristics of R-48/80 to rat peritoneal mast cells were then studied using fluorescence microscopy. At concentrations that caused minimal secretory stimulation (less than 1.0 microgram/ml), R-48/80 bound to the mast cell surface in a diffuse manner, with no indication of patching or capping. When the cells were incubated at higher concentrations, where non-cytotoxic histamine secretion was stimulated, the drug bound heavily to the exposed granules, but not to unexposed granules or other cell organelles. At cytotoxic concentrations, R-48/80 caused extensive cell clumping, with the drug bound to masses of cell debris and released granules. Therefore, although R-48/80 binds initially to the cell membrane, its primary binding site at concentrations that induce secretion becomes the mast cell granule. The properties of these granules should thus be considered when studying the binding of compound 48/80 or other cationic drugs to rat peritoneal mast cells.