Platelet activating factor does not release histamine from human dispersed cutaneous mast cells

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

The benefit of H2 receptors antagonist Rupatadine in treatment for urticaria

Second generation antihistamine drugs are mainly used for the therapy of patients suffering from urticaria; however, they are efficient in 45-60% of cases only. New drugs for treatment of urticaria need to be developed and implemented, and second generation antihistamine drug Rupatadine is one of them. At the same time, Rupatadine efficiently inhibits the inflammatory action of the platelet-activating factor. Due to its double action, Rupatadine used perorally in the dose of 10 mg once a day is an efficient drug for treatment of urticaria, and its safety was confirmed by clinical trials.

Rupatadine inhibits inflammatory mediator release from human laboratory of allergic diseases 2 cultured mast cells stimulated by platelet-activating factor

BACKGROUND

Mast cells are involved in allergy and inflammation by the secretion of multiple mediators, including histamine, cytokines, and platelet-activating factor (PAF), in response to different triggers, including emotional stress. PAF has been associated with allergic inflammation, but there are no clinically available PAF inhibitors.

OBJECTIVE

To investigate whether PAF could stimulate human mast cell mediator release and whether rupatadine (RUP), a dual histamine-1 and PAF receptor antagonist, could inhibit the effect of PAF on human mast cells.

METHODS

Laboratory of allergic diseases 2 cultured mast cells were stimulated with PAF (0.001, 0.01, and 0.1 μmol/L) and substance P (1 μmol/L) with or without pretreatment with RUP (2.5 and 25 μmol/L), which was added 10 minutes before stimulation. Release of β-hexosaminidase was measured in supernatant fluid by spectrophotoscopy, and histamine, interleukin-8, and tumor necrosis factor were measured by enzyme-linked immunosorbent assay.

RESULTS

PAF stimulated a statistically significant release of histamine, interleukin-8, and tumor necrosis factor (0.001-0.1 μmol/L) that was comparable to that stimulated by substance P. Pretreatment with RUP (25 μmol/L) for 10 minutes inhibited this effect. In contrast, pretreatment of laboratory of allergic diseases 2 cells with diphenhydramine (25 μmol/L) did not inhibit mediator release, suggesting that the effect of RUP was not due to its antihistaminic effect.

CONCLUSION

PAF stimulates human mast cell release of proinflammatory mediators that is inhibited by RUP. This action endows RUP with additional properties in treating allergic inflammation.

Platelet-activating factor (PAF) induces wheal and flare skin reactions independent of mast cell degranulation

BACKGROUND

Platelet-activating factor (PAF) causes wheal and flare responses which are abrogated by H1-antihistamines giving rise to the hypothesis that PAF-induced wheal development is secondary to histamine release from dermal mast cells. But is this hypothesis correct?

METHODS

Wheal and flare responses were induced by intradermal injection of PAF, codeine and histamine in 14 healthy volunteers. Dermal histamine and PGD2 contractions were measured using microdialysis.

RESULTS

PAF, unlike histamine and codeine, did not cause a statistically significant rise in mean histamine levels with ten persons showing negligible histamine release. Codeine caused a significant but variable histamine release, ranging from 29 to 282 ng/ml. Codeine, but not PAF or histamine, caused a small but statistically significant release of PGD2.

CONCLUSION

Wheal and flare reactions in human skin induced by PAF are not associated with histamine release and, therefore, appear to be independent of mast cell degranulation.

Activation of human mast cells through the platelet-activating factor receptor

BACKGROUND

In human subjects platelet-activating factor (PAF) concentrations are markedly increased in the plasma after anaphylactic reactions, and these correlate strongly with the severity of the response. The mechanism for the systemic spread of mast cell (MC) activation in anaphylaxis is often assumed to relate to the hematogenous spread of allergen, but this is implausible, and amplification mechanisms need to be considered.

OBJECTIVE

We have investigated the ability of PAF to induce human MC degranulation using skin, lung, and peripheral blood (PB)-derived cultured MCs and the signaling pathways activated in PB-derived MCs in response to PAF.

METHODS

The expression of PAF receptor was investigated by means of RT-PCR and Western blot analysis. Cell-signaling pathways in PB-derived MCs in response to PAF were investigated by analyzing the effect of various inhibitors and the silencing of phospholipase C (PLC) mRNA on PAF-mediated histamine release.

RESULTS

We show for the first time that PAF induces histamine release from human lung MCs and PB-derived MCs but not skin MCs. Activation of PAF receptor-coupled G(alphai) leads to degranulation through PLCgamma1 and PLCbeta2 activation in human MCs. PAF-induced degranulation was rapid, being maximal at 5 seconds, and was partially dependent on extracellular Ca(2+).

CONCLUSION

Our findings provide a mechanism whereby PAF mediates an amplification loop for MC activation in the generation of anaphylaxis.

Effect of intravenous platelet-activating factor on bovine pulmonary mast cells

The effect of platelet-activating factor (PAF) on bovine pulmonary mast cells (MCs) was investigated in calves aged 1-4 months. PAF was administered over a 5-min period at a rate of 50 ng/kg/min to six animals, which were killed approximately 10 min later. No macroscopical lesions were observed in the lung tissue of five control calves. On semi-thin toluidine-blue stained sections, MC cytoplasm showed profuse deep-blue granulation. In the lung tissues of PAF-treated calves, striking interstitial, alveolar and interlobular oedema and emphysema were observed. MC granules occurred at the periphery of the cytoplasm and MC nuclei were easily detectable. Moreover, the number of granules in the MC cytoplasm was remarkably low. A few granules with some metachromatic material were sometimes detected outside the cell limits. Ultrastructurally, the matrix pattern of the MC granules in lung tissues of control calves was either amorphous or granular. In lung tissues of the PAF-treated calves, the granular matrix pattern was pronounced, varying from fine- to coarse-grained, and the MCs were of reduced size, with many filiform processes and exocytotic vesicles. These findings indicate that pulmonary MC degranulation was induced by PAF in healthy calves.

Demonstration that platelet-activating factor is capable of activating mast cells and inducing a chemotactic response

Platelet-activating factor (PAF) is generated in a variety of inflammatory conditions in which mast cells accumulate. However, little is known about the ability of PAF to influence mast cell function directly. In this study we examine the ability of PAF to activate mast cells and regulate mast cell chemotaxis. PAF was found to induce intracellular calcium mobilization and chemotactic responses in both murine and human mast cells. PAF induced transient increases in intracellular Ca2+ concentrations with a 50% effective dose of 1 nM and induced significant migratory responses at PAF concentrations of 1 nM to 1 microM in the human leukaemia mast cell line (HMC-1). Using signal transduction inhibitors, both PAF-induced calcium mobilization and migration of mast cells were shown to require activation of pertussis toxin-sensitive G proteins. PAF-induced calcium and chemotactic responses were cross-desensitized by C5a. Together, these data demonstrate that PAF is capable of activating distinct signalling pathways in mast cells associated with calcium mobilization and cell migration; and that PAF may thus contribute to the regulation of mast cell responses and hyperplasia at sites of inflammation.

Platelet-activating factor induces histamine release from human skin mast cells in vivo, which is reduced by local nerve blockade

BACKGROUND

Intradermal injection of platelet-activating factor (PAF) causes wheal and flare reactions, which are inhibited by antihistamines. However, PAF does not release histamine from human dispersed skin mast cells in vitro. The purpose of this study was to investigate the extent and possible mechanisms of PAF-induced histamine release in human skin in vivo with the use of dermal microdialysis.

METHODS

Hollow dialysis fibers were inserted into the upper dermis in forearm skin and each fiber was perfused with Krebs-Ringer bicarbonate solution at a rate of 3.0 microliters/min. PAF (4.5 to 36 mumol/L), lyso-PAF (36 mumol/L), vehicle (negative control), and codeine 750 or 250 mumol/L (positive control) were injected intradermally above separate fibers. Dialysate was collected in 2-minute fractions for 20 minutes and histamine analyzed spectrofluorometrically.

RESULTS

PAF, but not lyso-PAF, caused statistically significant dose-related histamine release and wheal and flare reactions. Intradermal mepivacaine administration significantly abrogated flare reactions by PAF and codeine and inhibited histamine release and wheal reactions by PAF but not by codeine. Long-term topical capsaicin administration inhibited histamine release and wheal reactions by PAF but not by codeine. It inhibited flare reactions induced by both compounds. PAF did not release histamine from blood basophils.

CONCLUSIONS

These data suggest that PAF induced histamine release from mast cells in intact human skin indirectly via neurogenic activation. Further, on the intradermal injection of PAF histamine release and the skin responses, the wheal and the flare, are differentially regulated by neurogenic components.

Further studies on the actions of endothelin-1 on blood flow in human skin

When injected into human skin, endothelin-1 produces intense vasoconstriction localized to the site of the injection, but this area of vasoconstriction is surrounded by vasodilatation which spreads several centimetres from the injection site. The vasodilatation induced by intradermal injection of endothelin-1 (63 pmol) into human skin is prevented by local anaesthetic. Pretreatment of human skin with capsaicin also inhibits this response. Pretreatment of subjects with the selective histamine H1-receptor antagonist cetirizine, 10 mg orally 4 h before intradermal injections, inhibited vasodilatation caused by the intradermal injection of histamine (750 pmol), endothelin-1 (63 pmol), and carbachol (750 pmol). Endothelin-1 (0.3-10 microM) and carbachol (1-30 microM) failed to induce histamine release from rat peritoneal mast cells. We conclude that the vasodilatation caused by intradermal injection of endothelin-1 into human skin is neurogenic and is probably mediated by neuropeptide-containing primary afferent neurones. Because neither carbachol nor endothelin-1 cause histamine release from mast cells, our data suggest that histamine release from mast cells at the effector end of the axon reflex is responsible for the carbachol- and endothelin-induced vasodilatation in human skin.

Inflammatory effects of platelet activating factor (PAF) in equine skin

Intradermal administration of PAF (0.001-1 micrograms/site), but not lyso-PAF (10 micrograms/site), in the horse caused an increase in cutaneous vascular permeability which was maximal by 32 min. Responses to PAF and histamine were reduced by coadministration of the histamine 1 receptor antagonist chlorpheniramine, although only the inhibition of histamine-induced responses was dose-related and statistically significant. The cyclo-oxygenase inhibitor indomethacin was without effect on PAF-induced increases in vascular permeability. These findings suggest that the actions of PAF on equine skin microvasculature may be partly due to histamine release but not to prostanoid formation. Coadministration of prostaglandin (PG) E2 enhanced the oedematous responses to both PAF and histamine, although PGE2 failed to exert direct permeability-increasing activity. In addition, and in contrast to PAF and histamine, PGE2 increased cutaneous blood flow and skin surface temperature. PAF, but not lyso-PAF, also caused neutrophil infiltration into the skin which was maximal at 2 h. No significant effects on eosinophil or mononuclear cell numbers were apparent up to 24 h after injection of PAF. These results are consistent with the concept that PAF may be a mediator of inflammatory disorders of the skin in the horse.

Endothelin-1 induces a histamine-dependent flare in vivo, but does not activate human skin mast cells in vitro

The role of the mast cell in endothelin-1 induced flare has been investigated by in vivo and in vitro experiments. The intradermal injection of endothelin-1 (10 pmol) into human skin induced a pallor with surrounding axon-reflex flare which is similar to the flare response to histamine (1 nmol). At these doses, chosen to give identical flare areas, blood flow was increased in the area of the endothelin-induced flare over a longer period. A systemic H1-receptor antagonist significantly inhibited the area of both flares, although blood flow in the remaining portion of the endothelin-induced flare remained raised. Endothelin-1 at concentrations up to 3 x 10(-5) M failed to release histamine from human dispersed skin mast cells. We suggest from these results that a major component of endothelin-1 induced flare results from mast cell activation that is secondary to direct stimulation of sensory nerves by the peptide.

Effect of azelastine and ketotifen on the bronchial and skin responses to platelet-activating factor in humans

In a randomized, double-blind placebo-controlled study we investigated the effect of single oral doses of 8 mg azelastine and 2 mg ketotifen on the immediate response to platelet-activating factor (PAF) inhalation and to increasing doses of PAF injected intradermally. Bronchial provocation with 100 micrograms of PAF resulted in marked bronchoconstrictor responses, but neither azelastine nor ketotifen had any significant effect on these responses. Intradermal injection of PAF (100, 200 and 400 ng) resulted in a dose-related weal and flare response. Azelastine and ketotifen both caused significant reductions in this response (P less than 0.002-P less than 0.01). There was no significant difference between the effect of the two drugs.

Eosinophil infiltration: effects of H1 antihistamines

This article reviews the contribution of cell-mediated inflammatory responses to the immediate immunoglobulin E-dependent allergic reaction. Apparently eosinophils play an important part in the pathogenesis of allergic reactions. Some new H1 antihistamines may also have non-H1-mediated antiinflammatory properties. In two double-blind, placebo-controlled, crossover studies of allergic and normal subjects, we showed that oral cetirizine, at dosages of 10 and 20 mg/day, significantly inhibited wheal-and-erythema reactions induced by grass pollen, 48/80, histamine, platelet-activating factor acether, and N-formyl-methionyl-leucyl-phenylalanine. In the first study, cutaneous eosinophil migration was significantly inhibited by cetirizine at pollen and 48/80 skin test sites (61%, p less than 0.01, and 53%, p less than 0.01, respectively), although no change was observed at histamine skin test sites. Inhibition of neutrophil accumulation was also observed at pollen and 48/80 sites (41%, p less than 0.1, and 31%, p less than 0.1, respectively). Monocyte accumulation was not affected by cetirizine. In the second study, cetirizine suppressed the eosinophil influx induced by pollen, platelet-activating factor, 400 ng, and platelet-activating factor, 40 ng (63%, p less than 0.001; 58.5%, p less than 0.001; and 57.8%, p less than 0.01, respectively). This inhibition was effective 2 hours after challenge and persisted through hours 4, 8, and 24. N-Formyl-methionyl-leucyl-phenylalanine induced a weak eosinophil accumulation that was inhibited by cetirizine.