Effects of the platelet activating factor antagonists BN 52021 and BN 50730 on antigen-induced bronchial hyperresponsiveness and eosinophil infiltration in lung from sensitized guinea-pigs

The activity of medicinal plants and secondary metabolites on eosinophilic inflammation

Eosinophils are leukocytes that are present in several body compartments and in the blood at relatively low numbers under normal conditions. However, an increase in the number of eosinophils, in the blood or in the tissues, is observed in allergic or parasitic disorders. Although some progress has been made in understanding the development of eosinophil-mediated inflammation in allergic and parasitic diseases, the discovery of new compounds to control eosinophilia has lagged behind other advances. Plant-derived secondary metabolites are the basis for many drugs currently used to treat pathologic conditions, including eosinophilic diseases. Several studies, including our own, have demonstrated that plant extracts and secondary metabolites can reduce eosinophilia and eosinophil recruitment in different experimental animal models. In this review, we summarize these studies and describe the anti-eosinophilic activity of various plant extracts, such as Ginkgo biloba, Allium cepa, and Lafoensia pacari, as well as those of secondary metabolites (compounds isolated from plant extracts), such as quercetin and ellagic acid. In addition, we highlight the medical potential of these plant-derived compounds for treating eosinophil-mediated inflammation, such as asthma and allergy.

A new method to evaluate spontaneous platelet aggregation in type 2 diabetes by Cellfacts

BACKGROUND

The alterations in the functional activities of platelets in diabetes produce an increase of spontaneous platelet aggregation (SPA) and release of platelet-derived microparticles. Platelet-derived microparticles are shed from platelets during activation by high shear stress, collagen and certain agonists. Although the physiologic role of microparticles has been difficult to assess, the characterization of their biological activity is of interest in view of a possible role in hemostasis and coagulation and their reported involvement in thrombotic disease.

METHODS

We propose a new, simple method to evaluate spontaneous platelet aggregation and release of platelet-derived microparticles by the Cellfacts analyser (Microbial System Limited (MSL), Coventry, England) that uses electrical sensing flow impedance determination to detect the size particles and the cells in a conductive fluid. Platelet-rich plasma (PRP) from type 2 diabetes was employed for this study. The importance of platelet-activating factor (PAF) on spontaneous platelet aggregation was evaluated and the effect of vitamin E and WEB 2086-BS, an antagonist of platelet-activating factor, was measured.

RESULTS AND CONCLUSIONS

Data presented show that Cellfacts could be an easy and fast instrument to check the state of platelets in patients with alterations in the functionality of platelets, and to follow the effect of pharmacological therapy on spontaneous platelet aggregation and the release of platelet-derived microparticles.

The inhaled administration of KF19514, a phosphodiesterase 4 and 1 inhibitor, prevents antigen-induced lung inflammation in guinea pigs

We examined in this study the effect of KF19514, a phosphodiesterase 4 and 1 inhibitor, on antigen-induced lung inflammation by inhaled administration in guinea-pigs. It was previously reported that inhaled KF19514 prevented antigen-induced bronchoconstriction and platelet-activating factor (PAF)-induced lung inflammation. In fact, a variety of factors other than PAF are related to lung inflammation in real subjects with asthma. Guinea-pigs were actively sensitized by exposure to ovalbumin (OA). Fifteen to 20 days later, the guinea pigs were challenged by exposure to aerosols of five successively increasing concentrations of OA (0.01, 0.1, 0.5, 1 and 5 mg/ml). Bronchoalveolar lavages (BALs) were performed 24 h after the antigen challenge, and airway hyperresponsiveness to acetylcholine (ACh) was studied 24 h after the challenge by measuring lung resistance and dynamic compliance. Ovalbumin antigen challenge produced a marked and significant eosinophil accumulation in the BAL fluids and airway hyperresponsiveness to ACh 24 h after the challenge. Inhaled KF19514 (0.01-0.1%) inhibited the eosinophil accumulation significantly and dose-dependently but inhaled rolipram (0.01-0.1%) and aminophylline (0.1-1%) did not. In addition, the development of airway hyperresponsiveness was prevented by inhaled KF19514 (0.01%) but not by inhaled rolipram (0.01%) and aminophylline (0.1%). Based on these data, KF19514 was suggested to be a promising drug in the treatment of asthma by local administration to the lung.

Effects of SR 140333 and SR 48968 on antigen and substance P-induced activation of guinea-pig alveolar macrophages

BACKGROUND

Tachykinins, such as substance P, might be involved in the development of airway hyperresponsiveness and airway inflammation.

OBJECTIVE

This study was designed to investigate the effects of the tachykinin NK1 receptor antagonist SR 140333 (Nolpitantium) and the NK2 receptor antagonist SR 48968 (Saredutant) on the activation of alveolar macrophages in the guinea-pig.

METHODS

Guinea-pigs sensitized and challenged by ovalbumin administered by aerosol or naive guinea-pigs were exposed by aerosol to the neutral endopeptidase, phosphoramidon and, 15 min later, to substance P. Twenty-four hours later, bronchoalveolar lavages were performed and the cell composition of bronchoalveolar lavage fluids and the arachidonate release from alveolar macrophages stimulated in vitro with fMLP were evaluated.

RESULTS

Antigen challenge in sensitized guinea-pigs induced an increase in the total number of cells and granulocytes in the bronchoalveolar lavage fluids that was not reduced by pre-treatment of guinea-pigs with a single dose of SR 140333 or SR 48968 (1 mg/kg). Substance P exposure in phosphoramidon-pretreated guinea-pigs did not induce an increase in the total number of cells. In contrast, antigen or substance P exposure induced a significant increase in the in vitro fMLP-induced arachidonate release from alveolar macrophages. Pre-treatment of the guinea pigs with SR 140333 or SR 48968 did not reduce the increase in arachidonate release from fMLP-stimulated alveolar macrophages from sensitized and challenged guinea-pigs. Pre-treatment of the animals by SR 140333 and SR 48968 reduced the enhanced arachidonate release induced by fMLP from substance P-exposed guinea-pigs.

CONCLUSION

The present data demonstrate the importance of NK1- and NK2-receptor stimulation in the development of substance P-induced increased reactivity of alveolar macrophages.

Anti-inflammatory and bronchodilator properties of KF19514, a phosphodiesterase 4 and 1 inhibitor

We investigated the effects of KF19514 (5-phenyl-3-(3-pyridyl)methyl-3H-imidazo[4,5-c][1,8]naphthyridin-4 (5H)-one) on bronchoconstriction and allergic inflammation in guinea pigs and on tumor necrosis factor-alpha production in mice. KF19514 inhibited phosphodiesterase 4 (IC50 = 0.40 microM) and phosphodiesterase 1 (IC50 = 0.27 microM) derived from canine tracheal smooth muscles. KF19514 relaxed contracted tracheal smooth muscle and had a potent inhibitory effect on antigen-induced bronchoconstriction (EC50 = 0.058 microM) in vitro. Intravenous administration of KF19514 inhibited histamine-induced bronchoconstriction (ID50 = 2.8 microg/kg i.v.). Moreover, oral administration of KF19514 inhibited anaphylactic bronchoconstriction (ID50 = 0.2 mg/kg p.o.), and eosinophil infiltration in airway stimulated with platelet-activating factor (PAF) or antigen. KF19514 also produced a significant inhibition of tumor necrosis factor-alpha production in mice (ID50 = 0.023 mg/kg p.o.). Finally, KF19514 completely inhibited antigen-induced hyperreactivity at 0.1 mg/kg p.o. These results demonstrate that KF19514 may have efficacy in the treatment of asthma.

Role of lipoxygenase metabolites in platelet-activating factor- and antigen-induced bronchial hyperresponsiveness and eosinophil infiltration

The effect of a novel leuktriene B4 receptor antagonist N-[5[[8-(1-hydroxy-2- phenyl)ethyl]dibenzofuran-2yl]5-hydroxypentanoyl]pyrrolidine (PF 10042) has been evaluated in comparison with 2-[3(1-hydroxyhexyl)phenoxymethyl]quinoline hydrochloride (PF 5901), a specific inhibitor of the 5-lipoxygenase pathway of arachidonic acid metabolism, against platelet activating factor (PAF) and allergen induced bronchial hyperresponsiveness and pulmonary eosinophil infiltration in the guinea pig. PF 10042 significantly displaced radiolabelled [3H]leukotriene B4 from binding sites on human neutrophils with an EC50 of 3 muM. PF 10042 (100 mg/kg, i.p.) significantly inhibited PAF and allergen induced bronchial hyperresponsiveness without reducing the concomitant eosinophil infiltration, whereas PF 5901 (100 mg/kg, p.o.) significantly inhibited both PAF and allergen induced bronchial hyperresponsiveness and eosinophil infiltration. We suggest from these results that PAF and allergen induced bronchial hyperresponsiveness may be secondary to the release of leukotriene B4, but this lipoxygenase metabolite does not contribute significantly to the observed eosinophil infiltration.

Role of PAF in the late airway microvascular leakage induced by antigen in IgE-sensitized rat

The effect of the antagonist of platelet-activating factor (PAF), BN 50730, on PAF-and antigen- induced increase in microvascular leakage, using Evans blue dye as an index of permeability, was investigated in rat pulmonary tissues. PAF (1 microgram/kg, iv) induced a marked increase in Evans blue dye content in trachea, main bronchi and small bronchi, that was significantly reduced upon pretreatment of the rats with BN 50730 (25 mg/kg, orally) and by the serotonin antagonist, methysergide (1 mg/kg, iv), only in the small bronchi. Serotonin also induced an increase in microvascular leakage in the three tissues that was significantly inhibited when the animals were treated with methysergide but not by BN 50730. In contrast, histamine and lyso-PAF did not induce significant increase in Evans blue dye content. Intravenous injection of antigen to IgE-sensitized rats induced a biphasic increase in vascular permeability. An early increase in vascular permeability in trachea, main bronchi and small bronchi was observed 10 minutes after the injection of the antigen, and this phenomenon was significantly reduced upon treatment of the rats with methysergide, whereas, BN 50730 was ineffective. A late increase in vascular permeability was noted in the three tissues, with a maximum at 120 minutes and representing 30-40% of the magnitude of the first phase. Administration of BN 50730 (25 mg/kg) to the animals, evoked a significant inhibition of this increase in microvascular leakage, whereas, methysergide only significantly reduced the one induced by antigen in the trachea.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-lasting inhibitory activity of the hetrazepinic BN 50730 on exudation and cellular alterations evoked by PAF and LPS

1. Inhibitory effects of the hetrazepinic derivative BN 50730 on the rat pleural inflammatory response, triggered by PAF or lipopolysaccharides (LPS), were examined. The type of pharmacological blockade exerted by this antagonist in in vitro assays of eosinophil chemotaxis and platelet aggregation were also investigated. 2. Intrathoracic injection of PAF (1 microgram per cavity) caused a 4 fold increase in the extravasated protein within 15 min and led to a marked eosinophil accumulation 24 h post-challenge. BN 50730 (0.5-10 micrograms per cavity) inhibited exudation by PAF dose-dependently without modifying the response induced by histamine, bradykinin or 5-hydroxytryptamine (5-HT). 3. The kinetics of the inhibitory effect on exudation revealed that the actions of WEB 2086 and BN 52021 (10 micrograms per cavity) were over within 2 and 4 h respectively, whereas BN 50730 (10 micrograms per cavity) retained 80% of its inhibitory activity for 4 days. 4. Oral treatment with BN 50730 (10-20 mg kg-1, 1 h beforehand) suppressed the leucocyte accumulation and late eosinophilia observed 6 and 24 h after PAF respectively, but did not modify the eosinophilia induced by leukotriene B4 (LTB4) or bradykinin. BN 50730 also failed to reduce the eosinophil accumulation induced by LPS but drastically inhibited the neutrophil influx. 5. The pre-incubation of rat peritoneal eosinophils for 10 min with BN 50730 (30 nM-1 microM) dose-dependently inhibited the chemotaxis induced by PAF (0.1 microM) in vitro. The IC50 values for BN 52021, WEB 2086 and BN 50730 in this system were 5, 5 and 0.05 microM respectively. 6. In separate assays, rat peritoneal eosinophils and rabbit washed platelets were preincubated with BN 50730 or WEB 2086 (1 pM) then subjected to a series of at least two consecutive washings in order to remove the antagonist from the receptor environment. Under such conditions, only the cells pretreated with WEB 2086 recovered the sensitivity to the lipid.7. We conclude that BN 50730 is a potent, specific and long-acting PAF antagonist and its effect seems to result from a high affinity and non-competitive interaction of the drug with the PAF receptor.

Effects of isozyme-selective phosphodiesterase inhibitors on eosinophil infiltration in the guinea-pig lung

The effects of selective phosphodiesterase isozyme inhibitors on eosinophil infiltration induced by antigen challenge or by exposure to an aerosol of platelet-activating factor (PAF) were investigated in the guinea-pig. Pretreatment 24 h and 3 h before antigen challenge or PAF exposure with theophylline (100 mg/kg), rolipram (5 mg/kg) and Ro 20-1724 (30 mg/kg) significantly reduced the increase in eosinophil numbers in bronchoalveolar lavage fluid. In contrast, milrinone, SK&F 94-120 and zaprinast were ineffective against antigen-induced eosinophil recruitment. Theophylline, rolipram and Ro 20-1724 also significantly reduced the release of eosinophil peroxidase into the bronchoalveolar lavage fluid. It is suggested that inhibitors of type IV phosphodiesterase have anti-inflammatory effects in the airways and may be useful in the treatment of asthma.