The effect of the orally active platelet-activating factor antagonist WEB 2086 in the treatment of asthma

Effect of acyl and alkyl analogs of platelet-activating factor on inflammatory signaling

Platelet-activating factor (PAF), a bioactive ether phospholipid with significant pro-inflammatory properties, was identified almost half a century ago. Despite extensive study of this autocoid, therapeutic strategies for targeting its signaling components have not been successful, including the recent clinical trials with darapladib, a drug that targets plasma PAF-acetylhydrolase (PAF-AH). We recently provided experimental evidence that the previously unrecognized acyl analog of PAF, which is concomitantly produced along with PAF during biosynthesis, dampens PAF signaling by acting both as a sacrificial substrate for PAF-AH and probably as an endogenous PAF-receptor antagonist/partial agonist. If this is the scenario in vivo, PAF-AH needs to catalyze the selective hydrolysis of alkyl-PAF and not acyl-PAF. Accordingly, different approaches are needed for treating inflammatory diseases in which PAF signaling is implicated. The interplay between acyl-PAF, alkyl-PAF, PAF-AH, and PAF-R is complex, and the outcome of this interplay has not been previously appreciated. In this review, we discuss this interaction based on our recent findings. It is very likely that the relative abundance of acyl and alkyl-PAF and their interactions with PAF-R in the presence of their hydrolyzing enzyme PAF-AH may exert a modulatory effect on PAF signaling during inflammation.

Forty Years Since the Structural Elucidation of Platelet-Activating Factor (PAF): Historical, Current, and Future Research Perspectives

In the late 1960s, Barbaro and Zvaifler described a substance that caused antigen induced histamine release from rabbit platelets producing antibodies in passive cutaneous anaphylaxis. Henson described a ‘soluble factor’ released from leukocytes that induced vasoactive amine release in platelets. Later observations by Siraganuan and Osler observed the existence of a diluted substance that had the capacity to cause platelet activation. In 1972, the term platelet-activating factor (PAF) was coined by Benveniste, Henson, and Cochrane. The structure of PAF was later elucidated by Demopoulos, Pinckard, and Hanahan in 1979. These studies introduced the research world to PAF, which is now recognised as a potent phospholipid mediator. Since its introduction to the literature, research on PAF has grown due to interest in its vital cell signalling functions and more sinisterly its role as a pro-inflammatory molecule in several chronic diseases including cardiovascular disease and cancer. As it is forty years since the structural elucidation of PAF, the aim of this review is to provide a historical account of the discovery of PAF and to provide a general overview of current and future perspectives on PAF research in physiology and pathophysiology.

Platelet-activating factor (PAF) mediates NLRP3-NEK7 inflammasome induction independently of PAFR

Platelet-activating factor (PAF) can drive pathophysiological inflammation, but the mechanism remains incompletely understood. Here, Deng et al. report that PAF activates the canonical NLRP3 inflammasome independently of its receptor PAFR.

The role of lipids in inflammasome activation remains underappreciated. The phospholipid, platelet-activating factor (PAF), exerts multiple physiological functions by binding to a G protein–coupled seven-transmembrane receptor (PAFR). PAF is associated with a number of inflammatory disorders, yet the molecular mechanism underlying its proinflammatory function remains to be fully elucidated. We show that multiple PAF isoforms and PAF-like lipids can activate the inflammasome, resulting in IL-1β and IL-18 maturation. This is dependent on NLRP3, ASC, caspase-1, and NEK7, but not on NLRC4, NLRP1, NLRP6, AIM2, caspase-11, or GSDMD. Inflammasome activation by PAF also requires potassium efflux and calcium influx but not lysosomal cathepsin or mitochondrial reactive oxygen species. PAF exacerbates peritonitis partly through inflammasome activation, but PAFR is dispensable for PAF-induced inflammasome activation in vivo or in vitro. These findings reveal that PAF represents a damage-associated signal that activates the canonical inflammasome independently of PAFR and provides an explanation for the ineffectiveness of PAFR antagonist in blocking PAF-mediated inflammation in the clinic.

Trans-basement membrane migration of eosinophils induced by LPS-stimulated neutrophils from human peripheral blood in vitro

In the airways of severe asthmatics, an increase of neutrophils and eosinophils is often observed despite high-dose corticosteroid therapy. We previously reported that interleukin-8-stimulated neutrophils induced trans-basement membrane migration (TBM) of eosinophils, suggesting the link between neutrophils and eosinophils. Concentrations of lipopolysaccharide (LPS) in the airway increase in severe asthma. As neutrophils express Toll-like receptor (TLR)4 and can release chemoattractants for eosinophils, we investigated whether LPS-stimulated neutrophils modify eosinophil TBM. Neutrophils and eosinophils were isolated from peripheral blood of healthy volunteers and severe asthmatics. Eosinophil TBM was examined using a modified Boyden's chamber technique. Eosinophils were added to the upper compartment, and neutrophils and LPS were added to the lower compartment. Migrated eosinophils were measured by eosinophil peroxidase assays. LPS-stimulated neutrophils induced eosinophil TBM (about 10-fold increase), although LPS or neutrophils alone did not. A leukotriene B₄ receptor antagonist, a platelet-activating factor receptor antagonist or an anti-TLR4 antibody decreased eosinophil TBM enhanced by LPS-stimulated neutrophils by almost half. Neutrophils from severe asthmatics induced eosinophil TBM and lower concentrations of LPS augmented neutrophil-induced eosinophil TBM. These results suggest that the combination of neutrophils and LPS leads eosinophils to accumulate in the airways, possibly involved the pathogenesis of severe asthma.

New risk factors for adult-onset incident asthma. A nested case-control study of host antioxidant defense

RATIONALE

Host antioxidant defense, consisting of enzymatic antioxidant activity and nonenzymatic antioxidant micronutrients, is implicated in asthma pathogenesis. Studies of antioxidant defense and adult incident asthma have either used measures of antioxidants estimated from questionnaires or not considered enzymatic aspects of host defense.

OBJECTIVES

We conducted the first study designed and powered to investigate the association of antioxidant defenses on adult incident asthma.

METHODS

In a nested case-control study, we followed Shanghai women (aged 40-70 years) without prevalent asthma at baseline, over 8 years. Subjects with incident asthma were ascertained prospectively by gold standard testing of symptomatic women and matched to two asymptomatic control subjects.

MEASUREMENTS AND MAIN RESULTS

Baseline urinary F2-isoprostanes, plasma concentrations of antioxidant micronutrients (tocopherols, xanthines, carotenes, and lycopene), and antioxidant enzyme activity (platelet-activating factor acetylhydrolase [PAF-AH] and superoxide dismutase) were measured from samples collected before disease onset. Among 65,372 women, 150 (0.24%) developed asthma. F2-isoprostane levels before asthma onset were not different between cases and control subjects. Doubling of α-tocopherol concentrations and PAF-AH activity was associated with 50 and 37% decreased risk of incident asthma (α-tocopherol: adjusted odds ratio = 0.52; 95% confidence interval, 0.32-0.84; PAF-AH: adjusted odds ratio = 0.63; 95% confidence interval, 0.42-0.93).

CONCLUSIONS

In this prospective study, α-tocopherol, within normal reference ranges, and PAF-AH enzymatic activity were associated with decreased asthma development. These modifiable risk factors may be an effective strategy to test for primary asthma prevention.

Platelet-activating factor nasal challenge induces nasal congestion and reduces nasal volume in both healthy volunteers and allergic rhinitis patients

BACKGROUND

Platelet-activating factor (PAF) is a lipid mediator produced by most inflammatory cells. Clinical and experimental findings suggest that PAF participates in allergic rhinitis (AR) pathogenesis. The aim was to assess the PAF ability to induce clinical response in nasal airway after local stimulation.

METHOD

Ten nonatopic healthy volunteers (HVs) and 10 AR patients out of pollen season were enrolled. PAF increasing concentrations (100, 200, and 400 nM) were instilled into both nasal cavities (0, 30, and 60 minutes, respectively). Nasal symptoms (congestion, rhinorrhea, sneezing, itching, and total 4 symptom score and nasal volume between the 2nd and 5th cm (Vol(2-5)) using acoustic rhinometry (AcR), were assessed at -30, 0, 30, 60, 90, 120, and 240 minutes.

RESULT

PAF increased individual and total nasal symptom score in both HVs and seasonal AR (SAR) patients from 30 to 120 minutes (maximum score at 120', p < 0.05). Nasal obstruction was the most relevant and lasting nasal symptom. PAF also induced a significant reduction of Vol(2-5) at 90' (27%), 120' (38.7%), and 240' (36.4%). No differences in the response to PAF nasal challenge were observed between HVs and SAR subjects in either clinical symptoms or AcR.

CONCLUSION

This is the first description of PAF effects on human nasal mucosa using a cumulative dose schedule and evaluated by both nasal symptoms and AcR. Nasal provocation with PAF showed long-lasting effects on nasal symptoms and nasal obstruction in HVs and in patients with SAR. Nasal challenge may be a useful tool to investigate the role of PAF in AR and the potential role of anti-PAF drugs.

The effect of rupatadine on lung histopathology in a murine model of chronic asthma

INTRODUCTION

Rupatadine is a new second-generation antihistamine with H(1) receptor antagonist activity and platelet-activating factor antagonist properties. This study aimed to investigate the effect of rupatadine on histologic changes in the lungs in a murine model of chronic asthma.

MATERIALS AND METHODS

Thirty-five BALB/c mice were divided into five groups of seven mice each: group I (control), group II (placebo [saline]), group III (dexamethasone 1 mg · kg(-1)·d(-1)), group IV (rupatadine 3 mg·kg(-1) d(-1)), and group V (rupatadine 30 mg·kg(-1)·d(-1)). Groups II through V were sensitized and challenged with ovalbumin and treated once per day via the oral route (gavage). Animals were sacrificed 24 h after the last treatment was administered. Airway histopathology was evaluated using light and electron microscopy in all groups.

RESULTS

There were no significant differences observed in any of the histologic parameters between groups II and IV. There were significantly thinner basement membrane, subepithelial smooth muscle layer, and epithelia were significantly thinner in group V than in group II (p < .05). There were no statistically significant differences in the thicknesses of the basement membrane, subepithelial smooth muscle layer and epithelia between groups III and V.

CONCLUSION

Rupatadine had a beneficial effect on histologic changes in a chronic murine model of asthma.

Platelet-activating factor (PAF)-antagonists of natural origin

Presently herbal medicines are being used by about 80% of the world population for primary health care as they stood the test of time for their safety, efficacy, cultural acceptability and lesser side effects. The discovery of platelet activating factor antagonists (PAF antagonists) during these decades are going on with different framework, but the researchers led their efficiency in studying in vitro test models. Since it is assumed that PAF play a central role in etiology of many diseases in humans such as asthma, neuronal damage, migraine, cardiac diseases, inflammatory, headache etc. Present days instinctively occurring PAF antagonist exists as a specific grade of therapeutic agents for the humans against these and different diseases either laid hold of immunological or non-immunological types. Ginkgolide, cedrol and many other natural PAF antagonists such as andrographolide, α-bulnesene, cinchonine, piperine, kadsurenone, different Piper species' natural products and marine origin plants extracts or even crude drugs having PAF antagonist properties are being used currently against different inflammatory pathologies. This review is an attempt to summarize the data on PAF and action of natural PAF antagonists on it, which were evaluated by in vivo and in vitro assays.

Overview of animal models of asthma

Asthma is an inflammatory disease characterized by airways obstruction, airways hyperresponsiveness, excessive mucous secretion and cough. Guinea pig airways display many anatomical, physiological and pharmacological attributes of human airways, making this species ideal for modeling the asthmatic condition. This unit provides an overview of animal models of asthma, including definitions, descriptions of available animal models, and discussion of numerous critical issues to consider before designing a model to study this complex disease.

Asthma: a simple concept but in reality a complex disease

BACKGROUND

Asthma is a disorder of the conducting airways that contract too easily and too much to cause variable airflow obstruction with symptoms of wheeze, cough, chest tightness and shortness of breath. Based on this knowledge, initial treatments were directed to dilating the contracted airways with anticholinergic and adrenergic drugs. The recognition that allergic-type inflammation underlay the hyperresponsive airways in asthma led to the introduction of anti-inflammatory drugs such as sodium cromoglicate and corticosteroids. Over the 2 decades that followed, these drugs have been progressively improved by increasing their therapeutic index and duration of action.

METHODS

A review of the recent literature indicates that since the 1980s, the explosive increase in knowledge of the cell and mediator mechanisms of asthma has only led to modest improvements in therapy including the introduction of leukotriene modifiers and a blocking monoclonal antibody against IgE. Indeed, biologics targeting allergic cytokines and effector cells have on the whole proven disappointing despite initial promise being shown in animal models.

RESULTS

Part of the difficulty lies in the oversimplified concept that asthma is only driven by allergic processes when in reality there are many environmental causes and triggers and the view that it is a homogeneous disorder only varying in severity.

CONCLUSIONS

The more recent views that asthma is a complex disorder made up of different subtypes with differing causes, treatment responses and natural histories creates a new opportunity for stratified medicine in which therapies acting upstream selectively target specific disease subtypes identified by specific diagnostic biomarkers.

Platelet-activating factor antagonists: current status in asthma

Platelet-activating factor (PAF) is a potent lipid-derived mediator of inflammation that is considered to have a potential role in the pathogenesis of asthma. PAF is produced by many cells associated with asthmatic inflammation and has the ability to evoke some of the clinical hallmarks of asthma, such as bronchoconstriction, mucus production and airway hyperresponsiveness (AHR). In addition, PAF has profound chemoattractant properties for eosinophils and neutrophils and it promotes an increase in microvascular permeability and oedema formation within the airways. Nevertheless, the definitive role of PAF in asthma remains elusive. PAF is formed as a result of the action of phospholipase A(2) and acetyltransferase on membrane phospholipids and it is degraded by a PAF-specific acetylhydrolase. The biological effects of PAF are mediated by the activation of specific receptors expressed on effector cell surfaces, although intracellular signalling and paracrine actions have been described. In addition, at least part of the pulmonary effects of PAF could be related to the secondary release of leukotrienes. In the clinical setting, different ways of modifying the activity of PAF have been explored, in particular the inhibitory actions of PAF receptor antagonists. Both natural and synthetic PAF receptor antagonists have shown conflicting results. Although second generation PAF antagonists (apafant, UK-74505, SR-27417A) appear to have a good protective effect against the systemic and pulmonary actions of inhaled PAF, the protective effects of these compounds on allergen-induced responses and AHR are more modest. In the treatment of asthma, PAF receptor antagonists have failed to produce a significant impact in either acute asthma attacks or the maintenance therapy of chronic forms. Other pharmacological interventions of proven efficacy in asthma, such as salbutamol or 5-lipoxygenase antagonists, have shown some anti-PAF effects. Whether the overall negative results with PAF receptor antagonists indicate that extracellular PAF is not a relevant mediator of airway inflammation or that the compounds explored are not capable of blocking the paracrine actions of PAF remains speculative. A PAF synthase inhibitor could be valuable in the elucidation of the role of PAF and it might be a promising and useful complementary therapeutic tool in the future.

Platelet activating factor as a mediator and therapeutic approach in bronchial asthma

Platelet activating factor (PAF) is a potent phospholipid mediator involved in anaphylaxis and chronic inflammatory disorders, including bronchial asthma. PAF is able to act both, directly as a chemotactic factor and indirectly through the release of other inflammatory agents. Apart from its known potent ability to activate platelets, PAF influences other immune and inflammatory cells function involved in asthma, which may be of importance in the pathogenesis of the disease. In addition, PAF administration can mimic some of abnormalities observed in asthma, including bronchoconstriction, bronchial hyper responsiveness, and gas exchange impairment, which may be mediated by leukotrienes acting as secondary mediators of some PAF effects. Therefore, there has been an extensive interest in the role of PAF in human asthma and major efforts have been continued to discover drugs acting thorough inhibition of PAF effects in the disease. Surprisingly, PAF receptor antagonists have not clearly proven their clinical benefits. It may appear that the combined blockage of PAF effects and other mediators involved in asthma is a way to improve clinical efficacy and also an interesting approach to control inflammation in the disease. This review will focus on two main issues: the role of PAF and PAF antagonists in asthma.

Inverse agonist-induced signaling and down-regulation of the platelet-activating factor receptor

Platelet-activating factor (PAF) is a potent phospholipid mediator involved in several diseases such as allergic asthma, atherosclerosis and psoriasis. The human PAF receptor (PAFR) is a member of the G-protein-coupled receptor family. Following stimulation, PAFR becomes rapidly desensitized; this refractory state is dependent on PAFR phosphorylation, internalization and down-regulation. In this report, we show that the PAFR inverse agonist, WEB2086, can induce phosphorylation and down-regulation of PAFR. Using selective inhibitors, we determined that the agonist, PAF, and WEB2086 could induce phosphorylation of PAFR by PKC. Moreover, dominant-negative (DN) mutant of PKC isoforms beta inhibited WEB2086-stimulated PAFR phosphorylation, whereas PAF-stimulated phosphorylation was inhibited by DN PKCalpha and delta. WEB2086 also induced PAFR down-regulation which could be blocked by PKC inhibitors and by DN PKCbeta. WEB2086-induced down-regulation was dynamin-dependent but arrestin-independent. Unlike PAF, WEB2086-stimulated intracellular trafficking of PAFR was independent of Rab5. Specific inhibitors of lysosomal proteases and of proteasomes were both effective in reducing WEB2086-induced PAFR down-regulation, indicating the importance of receptor targeting to both lysosomes and proteasomes in long-term cell desensitization to WEB2086. These results indicate that although both agonists and inverse agonists induce receptor PAFR down-regulation, this may be accomplished through different signal transduction and trafficking pathways.

Endothelin, PAF and thromboxane A2 in allergic pulmonary hyperreactivity in mice

The role of endothelin, PAF and thromboxane A2 in airway hyperreactivity (AHR) to carbachol induced by ovalbumin sensitization and challenge in Balb/c mice was investigated. Ovalbumin sensitization and challenge induced significant AHR to carbachol in actively sensitized and challenged mice. Treatment of these mice with the PAF antagonist CV-3988 (10 microg kg(-1), i.v.) completely abolished OVA-induced AHR to carbachol. Treatment of sensitized mice with the TxA2 antagonist L-654,664 (1 mg kg(-1), i.v.) partially blocked the induction of AHR in OVA-challenged mice. The intranasal administration of 50 pmol of the ET(A) receptor antagonist BQ-123 had no effect on the PIP but produced a significant reduction at the dose of 100 pmol. The intravenous administration of BQ-123 (100 pmol) reduced the PIP only at the highest doses of carbachol. The ET(B) receptor antagonist BQ-788 administered either via the intranasal or intravenous route had no effect on the PIP at the dose of 100 pmol. Naïve mice treated with either U-44069 (25 or 100 microg kg(-1), i.v.), endothelin-1 (100 pmol, intranasally) or the ET(B) receptor agonist IRL-1620 (100 pmol, intranasally) showed a marked increase in airway reactivity to carbachol. These results suggest an important role for endothelin, PAF and thromboxane A2 in AHR in mice actively sensitized and challenged with ovalbumin.

Novel and emerging therapies for asthma

At present, there are a wide variety of novel and emerging therapeutic approaches for the treatment of asthma. Here, we will summarize these state-of-the-art approaches, including specific and nonspecific mediator inhibition-- a quest that has been on going for more than 25 years-- together with cytokine modulation in asthma (primarily attempting to modulate the Th2-Th1 balance in asthma), targeting cell recruitment, angiogenesis, signal transduction and gene transduction pathways. Finally, we will discuss the recently approved anti-IgE therapy for the treatment of allergic asthma and immune modulation using CpG oligodeoxynucleotides.

Investigative bronchoprovocation and bronchoscopy in airway diseases

RATIONALE

Basic and clinical research strategies used for many lung diseases have depended on volunteer subjects undergoing bronchoscopy to establish access to the airways to collect biological specimens and tissue, perhaps with added bronchoprovocation in asthma syndromes. These procedures have yielded a wealth of important scientific information. Since the last critical review more than a decade ago, some of the techniques and applications have changed, and untoward events have occurred, raising safety concerns and increasing institutional review scrutiny.

OBJECTIVES AND METHODS

To reappraise these investigational methods in the context of current knowledge, the National Heart, Lung, and Blood Institute and the National Institute of Allergy and Infectious Diseases of the National Institutes of Health convened a working group to review these procedures used for airway disease research, emphasizing asthma and chronic obstructive pulmonary disease.

MAIN RESULTS

The group reaffirmed the scientific importance of investigative bronchoscopy and bronchoprovocation, even as less invasive technologies evolve. The group also considered the safety of bronchoscopy and bronchoprovocation with methacholine and antigen to be acceptable for volunteer subjects and patients, but stressed the need to monitor this closely and to emphasize proper training of participating medical research personnel. Issues were raised about vulnerable volunteers, especially children who need surrogates for informed consent.

CONCLUSION

This review of investigative bronchoscopy and bronchoprovocation could serve as the basis for future guidelines for the use of these procedures in the United States.

Inverse agonism: more than reverting constitutively active receptor signaling

Seven-transmembrane receptors constitute one of the major families of proteins encoded by the genome. This type of receptor is one of the most important targets of the pharmaceutical industry, and many of the drugs with significant therapeutic action have been shown to be inverse agonists. Concepts regarding the mechanisms by which ligands activate and inactivate receptors are thought to be far more complex that a simple on-off switch. For both drug design and pharmacology principles, it is important to understand the mechanisms by which these drugs achieve their effects. Recent studies have demonstrated intriguing actions of inverse agonists. They have been shown not only to block constitutive responses of receptors but also to activate and regulate seven-transmembrane receptor signaling and trafficking. The activation of pathways by inverse agonists was shown to occur mainly via G-protein-independent mechanisms. These findings emphasize the importance of inverse agonism as a principle of receptor regulation. In this paper, we will review the evidence supporting inverse agonist promoted signaling and trafficking.

Inibidores de fosfodiesterases: novas perspectivas de uma antiga terapia na asma?

A asma é uma doença inflamatória crônica com níveis variados de obstrução ao fluxo aéreo e diferentes formas de apresentação. Seu tratamento vem sendo modificado com a evolução do conhecimento sobre sua patogenia. A inflamação das vias aéreas, que é modulada por determinantes genéticos e ambientais, resulta na alteração definitiva da arquitetura da via aérea (remodelamento). O padrão inflamatório da asma é de natureza multicelular, envolvendo mastócitos, neutrófilos, eosinófilos, linfócitos T, células musculares e epiteliais. Diversas citocinas e quimiocinas contribuem para a orquestração do processo inflamatório. O reconhecimento do papel crítico da inflamação, que está associada à gravidade da doença, vem direcionando o eixo do tratamento para a prevenção ou para o bloqueio das alterações inflamatórias. Nesse sentido, além dos agentes beta2-adrenérgicos, da teofilina e dos corticosteróides, novos fármacos vêm sendo estudados. Dentre eles, os inibidores específicos de fosfodiesterases vêm apresentando resultados promissores. A partir dos resultados obtidos com a segunda geração dessas substâncias, pode-se imaginar que, em breve, elas representarão uma nova opção para o tratamento da asma.

Airway responsiveness to adenosine 5'-monophosphate and exhaled nitric oxide measurements: predictive value as markers for reducing the dose of inhaled corticosteroids in asthmatic subjects

OBJECTIVES

To investigate the utility of the determination of airway responsiveness to inhaled adenosine 5'-monophosphate (AMP) and exhaled nitric oxide (ENO) levels as markers for safely reducing the dose of inhaled corticosteroids (ICS) in patients with asthma well controlled with a moderately high ICS dose.

METHODS

A total of 37 patients with asthma well controlled for at least 3 months by treatment with a moderately high ICS dose (beclomethasone dipropionate, 500 to 1,000 microg or equivalent daily) were included in the study. Patients were treated for a 2-week run-in (baseline) period with their usual dose of ICS. For the next 12 weeks, patients were treated with ICS at half the previous dose, maintaining the same inhalation device. At the end of the baseline period and after 2 weeks, 8 weeks, and 12 weeks of treatment with a reduced dose of ICS, measurements were made in the following order: ENO, spirometry, and AMP challenge. Furthermore, patients completed a diary twice daily recording peak expiratory flow, daytime and nighttime symptoms, and use of rescue albuterol.

RESULTS

Ten patients had an asthma exacerbation. Using a Kaplan-Meier survival analysis, the significant predictors of a failure of ICS reduction were having both bronchoconstriction in response to AMP and ENO levels > or = 15 parts per billion (ppb) at baseline (p = 0.006), as well as having both bronchoconstriction in response to AMP and ENO levels > or = 20 ppb at baseline (p = 0.033). Having a decrease in the provocative concentration of AMP causing a 20% fall in FEV(1) of at least one doubling concentration 2 weeks after the dose of ICS was halved was a borderline significant predictor for failure of ICS reduction (p = 0.062).

CONCLUSION

These observations suggest that in asthmatic patients well controlled with ICS, the determination of AMP responsiveness and ENO levels may be useful to identifying those subjects whose condition will or will not deteriorate when the dose of ICS is reduced.

Pathophysiological mechanisms of asthma. Application of cell and molecular biology techniques

Asthma is a common increasing and relapsing disease that is associated with genetic and environmental factors such as respiratory viruses and allergens. It causes significant morbidity and mortality. The changes occurring in the airways consist of a chronic eosinophilic and lymphocytic inflammation, together with epithelial and structural remodeling and proliferation, and altered matrix proteins, which underlie airway wall narrowing and bronchial hyperresponsiveness (BHR). Several inflammatory mediators released from inflammatory cells such as histamine and cysteinyl-leukotrienes induce bronchoconstriction, mucus production, plasma exudation, and BHR. Increased expression of T-helper 2 (Th2)-derived cytokines such as interleukin-4 and 5 (IL-4, 5) have been observed in the airway mucosa, and these may cause IgE production and terminal differentiation of eosinophils. Chemoattractant cytokines (chemokines) such as eotaxin may be responsible for the chemoattraction of eosinophils to the airways. The initiating events are unclear but may be genetically determined and may be linked to the development of a Th2-skewed allergen-specific immunological memory. The use of molecular biology techniques on tissues obtained from asthmatics is increasing our understanding of the pathophysiology of asthma. With the application of functional genomics and the ability to transfer or delete genes, important pathways underlying the cause if asthma will be unraveled. The important outcome of this is that new preventive and curative treatments may ensue.

Relationship between anxiety, depression, and morbidity in adult asthma patients

BACKGROUND

Symptoms of disease reported by patients reflect the effects of the disease process within the individual and the person's physical and mental ability to tolerate or otherwise cope with the limitations on their functioning. This study examines the relationship between asthma symptoms, disease severity, and psychological status in patients being managed in routine primary healthcare settings.

METHODS

One hundred and fourteen subjects from four GP practices, two inner city and two suburban, were studied. Symptoms were assessed by means of the Asthma Quality of Life questionnaire (AQLQ) and a locally devised Q score, and psychological status with the Hospital Anxiety and Depression (HAD) scale. Spirometric values and details of current asthma treatment (BTS asthma guidelines treatment step) were recorded as markers of asthma severity.

RESULTS

Symptoms as measured by AQLQ correlated with peak expiratory flow (r(S) = 0.40) and with BTS guidelines treatment step (r(S) = 0.25). Similarly, the Q score correlated with peak expiratory flow (r(S) = 0.44) and with BTS guidelines treatment step (r(S) = 0.42). Similar levels of correlation of forced expiratory volume in one second (FEV(1)) with symptoms were reported. HAD anxiety and depression scores also correlated to a similar extent with these two symptom scores, but there was hardly any correlation with lung function. Logistic regression analysis showed that HAD scores help to explain symptom scores over and above the effects of lung function and BTS guidelines treatment step. Symptoms, depression, and anxiety were higher for inner city patients while little difference was observed in objective measures of asthma.

CONCLUSIONS

Asthma guidelines suggest that changing levels of symptoms should be used to monitor the effectiveness of treatment. These data suggest that reported symptoms may be misleading and unreliable because they may reflect non-asthma factors that cannot be expected to respond to changes in asthma treatment.

Effect of suplatast tosilate, a Th2 cytokine inhibitor, on steroid-dependent asthma: a double-blind randomised study. Tokyo Joshi-Idai Asthma Research Group

BACKGROUND

Th2 cytokines play an important part in the pathogenesis of asthma. Our aim was to study the effect of suplatast tosilate, a selective Th2 cytokine inhibitor, on asthma control and asthma exacerbations during reduction of inhaled corticosteroid dose in patients with steroid-dependent asthma.

METHODS

85 patients with moderate to severe asthma taking high doses (> or = 1500 microg per day) of inhaled beclometasone dipropionate, were assigned suplatast tosilate (100 mg three times daily) or placebo for 8 weeks in a double-blind, randomised, parallel-group, multicentre trial. During the first 4 weeks, other medications remained unchanged (add-on phase); during the next 4 weeks, the doses of beclometasone were halved (steroid-reduction phase). Main outcome measures were pulmonary function, asthma symptoms, and use of beta2-agonists.

FINDINGS

Data were available from 77 patients. During the add-on phase, suplatast tosilate treatment, compared with placebo, was associated with higher forced expiratory volume in 1 s (mean difference between groups for changes from baseline at week 4, 0.20 L [95% CI 0.16-0.24], p=0.043), morning peak expiratory flow (18.6 L/min [14.1-23.1], p=0.037), and less diurnal variation in peak expiratory flow rate, asthma symptom scores (7.1 [6.6-7.6], p=0.029), and serum concentrations of eosinophil cationic protein and IgE. In the steroid-reduction phase, pulmonary function, asthma symptoms, and use of beta2-agonist deteriorated significantly more in the placebo group than in the suplatast group.

INTERPRETATION

Treatment with a Th2 cytokine inhibitor in steroid-dependent asthma improves pulmonary function and symptom control, and allows a decrease in dose of inhaled corticosteroid without significant side-effects. Some improvements in pharmacokinetics are, however, needed.

Recombinant human platelet-activating factor-acetylhydrolase inhibits airway inflammation and hyperreactivity in mouse asthma model

Numerous in vitro and in vivo studies in both animal models and human asthmatics have implicated platelet-activating factor (PAF) as an important inflammatory mediator in asthma. In a murine asthma model, we examined the anti-inflammatory activities of recombinant human PAF-acetylhydrolase (rPAF-AH), which converts PAF to biologically inactive lyso-PAF. In this model, mice sensitized to OVA by i.p. and intranasal (i.n.) routes are challenged with the allergen by i.n. administration. The OVA challenge elicits an eosinophil infiltration into the lungs with widespread mucus occlusion of the airways and results in bronchial hyperreactivity. The administration of rPAF-AH had a marked effect on late-phase pulmonary inflammation, which included a significant reduction in airway eosinophil infiltration, mucus hypersecretion, and airway hyperreactivity in response to methacholine challenge. These studies demonstrate that elevating plasma levels of PAF-AH through the administration of rPAF-AH is effective in blocking the late-phase pulmonary inflammation that occurs in this murine allergen-challenge asthma model. These results suggest that rPAF-AH may have therapeutic effects in patients with allergic airway inflammation.

Changes in sputum eosinophils predict loss of asthma control

Exacerbations of asthma are likely to be due to an increase in airway inflammation. We have studied noninvasive markers of airway inflammation in asthma exacerbations induced by reducing the dose of inhaled corticosteroids. Following a 2-wk run-in period, mild exacerbations were induced in subjects with stable asthma controlled with medium- to high-dose inhaled corticosteroids (beclomethasone dipropionate >/= 800 microg or equivalent daily) by switching them to budesonide 200 microg daily given from a dry-powder inhaler (Turbohaler). Fifteen subjects were enrolled and were seen twice weekly for 8 wk after steroid reduction. At each visit, exhaled nitric oxide (NO), and methacholine airway responsiveness were measured and spirometry and sputum induction were performed. Mild exacerbation was defined as: (1) a decrease in morning peak expiratory flow (PEF) of >/= 20% but < 30% on at least two consecutive days as compared with the mean for the last 7 d of the run-in period; (2) awakening on two consecutive nights because of asthma; or (3) increased use of a short-acting beta(2)-agonist to eight or more puffs daily. Eight subjects did not develop exacerbations during the 8-wk study, whereas seven subjects developed mild exacerbations at Week 4 (n = 1), Week 6 (n = 1), and Week 8 (n = 5). The only significant difference between these two groups at baseline was a higher baseline sputum eosinophil count in subjects with subsequent exacerbations (p < 0.05). The increases in sputum eosinophils and exhaled NO were correlated with decreases in airway function, including decreases in morning PEF and FEV(1). However, multiple regression analysis suggested that the change in sputum eosinophils is a potentially useful marker in predicting loss of asthma control reflected by loss of airway function.

Platelet-activating factor (PAF) receptor and genetically engineered PAF receptor mutant mice

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active phospholipid mediator. Although PAF was initially recognized for its potential to induce platelet aggregation and secretion, intense investigations have elucidated potent biological actions of PAF in a broad range of cell types and tissues, many of which also produce the molecule. PAF acts by binding to a unique G-protein-coupled seven transmembrane receptor. PAF receptor is linked to intracellular signal transduction pathways, including turnover of phosphatidylinositol, elevation in intracellular calcium concentration, and activation of kinases, resulting in versatile bioactions. On the basis of numerous pharmacological reports, PAF is thought to have many pathophysiological and physiological functions. Recently advanced molecular technics enable us not only to clone PAF receptor cDNAs and genes, but also generate PAF receptor mutant animals, i.e., PAF receptor-overexpressing mouse and PAF receptor-deficient mouse. These mutant mice gave us a novel and specific approach for identifying the pathophysiological and physiological functions of PAF. This review also describes the phenotypes of these mutant mice and discusses them by referring to previously reported pharmacological and genetical data.

Regulation of platelet-activating factor (PAF) activity in human diseases by phospholipase A2 inhibitors, PAF acetylhydrolases, PAF receptor antagonists and free radical scavengers

The aim of this review is to present recent findings indicating the likely involvement of platelet-activating factor (PAF) in human diseases, and possible ways of alleviating its harmful effects. PAF is a potent proinflammatory mediator and promotes adhesive interactions between leukocytes and endothelial cells, leading to transendothelial migration of leukocytes, by a process of juxtacrine intercellular signalling. This process leads to activation of leukocytes and the release of reactive oxygen radicals, lipid mediators, cytokines and enzymes. These reaction products subsequently contribute to the pathological features of various inflammatory diseases. The reactive oxygen radicals cause low density lipoprotein (LDL) oxidation which mediates the development of atherosclerosis. Oxidized LDL may damage cellular and subcellular membranes, leading to tissue injury and cell death. Among the therapeutic approaches considered are agents that inhibit/degrade proinflammatory mediators and thereby have anti-inflammatory and/or anti-atherogenic potential. These include inhibitors of phospholipase A2 activity, PAF-acetylhydrolases, PAF antagonists and free radical scavengers/antioxidants, the latter protecting against oxidized LDL-induced cytotoxicity.

An observational study of inhaled corticosteroid withdrawal in stable chronic obstructive pulmonary disease. ISOLDE Study Group

Withdrawal of inhaled corticosteroids is known to worsen disease control in bronchial asthma but similar data are lacking in chronic obstructive pulmonary disease (COPD). We hypothesized that clinical exacerbations requiring treatment would occur more often in patients whose inhaled corticosteroids were stopped than in other patients not treated with these agents. We studied 272 patients in mean age 65 (SD 0.8) years, mean FEV1 42.8 (SD 12.6)% predicted, entering the run-in phase of the Inhaled Steroids in Obstructive Lung Disease (ISOLDE) trial. All had been clinically stable for at least 6 weeks and there were no differences in the degree of bronchodilator reversibility, baseline lung function or pack-years of smoking between the 160 patients receiving inhaled corticosteroids and those not so treated. Inhaled corticosteroids were withdrawn in the first week of the study and during the remaining 7 weeks of the study 38% of those previously treated with these drugs had an exacerbation compared to 6% of the chronically untreated group. Patients receiving inhaled corticosteroids reported a longer duration of symptoms but neither this or any other recorded variable predicted the risk of exacerbation. These data suggest that abrupt withdrawal of inhaled corticosteroids should be monitored carefully even in patients with apparently irreversible COPD.

Enhancement of leukotriene B4 release in stimulated asthmatic neutrophils by platelet activating factor

BACKGROUND

The role of platelet activating factor (PAF) in asthma remains controversial. The priming effect of PAF on leukotriene B4 (LTB4) release, 5-lipoxygenase activity, and intracellular calcium levels in asthmatic neutrophils was examined.

METHODS

LTB4 and other lipoxygenase metabolites in neutrophils obtained from 17 asthmatic patients and 15 control subjects were measured by reverse phase-high performance liquid chromatography (RP-HPLC). Intracellular calcium levels were monitored using the fluorescent probe fura-2.

RESULTS

The mean (SD) basal LTB4, release from neutrophils was not significantly different between the two groups (0.05 (0.01) vs 0.03 (0.02) ng/10(6) cells); however, when stimulated with calcium ionophore A23187 (2.5 microM), neutrophils from asthma patients released more LTB4 than cells from control subjects (15.7 (1.2) vs 9.9 (1.6) ng/10(6) cells). Although PAF alone did not alter LTB4 release, it enhanced the response to subsequent A23187 stimulation. This effect was observed following treatment for five minutes with PAF at concentrations > 1.0 microM. The maximal effect was seen with 5.0 microM PAF + 2.5 microM A23187 (62.7 (2.2) vs 18.6 (2.3) ng/10(6) cells). Pretreatment with PAF also increased 5-lipoxygenase activity and intracellular calcium levels in neutrophils from asthmatic patients to a greater extent than in those from non-asthmatic patients.

CONCLUSIONS

These findings indicate that, in neutrophils from asthmatic patients, PAF enhances LTB4 release and increases 5-lipoxygenase activity and intracellular calcium to a greater extent than in neutrophils from non-asthmatic patients.

Inhibitory effect of azelastine hydrochloride on synthesis and release of platelet activating factor from human alveolar macrophages

The effect of azelastine hydrochloride (azelastine) on synthesis and release of platelet activating factor (PAF) in alveolar macrophages obtained from asthmatic and non-asthmatic subjects was examined. Alveolar macrophages (AMs) were preincubated with or without azelastine and stimulated with f-Met-Leu-Phe (fMLP, 10 microM) for 15 min. PAF activity was detected by aggregation of washed guinea pig platelets. PAF activity released from alveolar macrophages (AMs) from asthmatics without preincubation of azelastine was 15.97 [2.17] (mean [SD], ng/10(7) cells) in supernatants and 42.52 [10.16] in cell pellets. After preincubation with 10(-8), 10(-6), and 10(-4) M of azelastine, PAF activity reduced to 10.71 [2.73] (mean [SD], ng/10(7) cells), 7.86 [0.94], and 3.52 [0.31] in the supernatants, and 35.58 [7.37], 21.57 [4.36], and 14.77 [0.99] (n = 15) in the cell pellets, respectively. PAF activity in non-asthmatic subjects without preincubation of azelastine was 8.55 [1.16] (mean [SD], ng/10(7) cells) in supernatants and 32.64 [3.37] in cell pellets. After preincubation with 10(-8), 10(-6), and 10(-4) M of azelastine, PAF activity reduced to 6.68 [0.78] (mean [SD], ng/10(7) cells), 4.47 [0.51], and 2.97 [0.36] in the supernatants, and 29.53 [3.75], 14.78 [1.95], and 6.16 [0.55] (n = 20) in the cell pellets, respectively. Our results showed that preincubation with azelastine caused a dose-dependent inhibition of intra- and extracellular PAF activity from asthmatic and non-asthmatic macrophages in the same manner.

The effect of intravenous administration of WEB 2086 on PAF-induced platelet aggregation in healthy Friesian calves

The in vivo ability of the specific PAF-antagonist WEB 2086, a thienotriazolodiazepine, to inhibit platelet-activating factor (PAF) in cattle was investigated by in vitro determination of platelet aggregation curves. WEB 2086 was infused intravenously into a group of 5 healthy male Friesian calves in a dose of 3 mg/kg over 1 min. The resultant inhibition peaked between 30 min and 1 h after administration of WEB 2086. The inhibition was significantly reduced after 3 h and became non-significant after 6 h, but maximal pre-treatment aggregation had not been restored by 24 h after the injection of WEB 2086. These results confirm previous results obtained in vitro and suggest that WEB 2086 is a potent antagonist of PAF activity in calves. They also suggest that further clinical studies with WEB 2086 in cattle are desirable.

Effects of a potent platelet-activating factor antagonist, SR27417A, on allergen-induced asthmatic responses

Platelet-activating factor (PAF) is a lipid-derived mediator that has been implicated in the pathophysiology of airway inflammation in asthma. Its actions include chemotaxis and activation of inflammatory cells, particularly eosinophils. Inhaled PAF causes bronchoconstriction and increased airway responsiveness in human subjects. However, PAF antagonists have so far failed to show benefits in allergen challenge or in the treatment of chronic asthma. SR27417A is a novel PAF antagonist with increased potency compared with previously tested compounds. Twelve asthmatic subjects received treatment with either SR27417A or placebo for 1 wk in a double-blind crossover study. After treatment each subject underwent allergen challenge. Effects were assessed in terms of early and late asthmatic responses and allergen-induced effects on airway responsiveness. Baseline lung function and airway responsiveness were also examined. Treatment with SR27417A significantly attenuated the late asthmatic response (AUC LAR4-10h: 107 +/- 24 after placebo, 79 +/- 17 after SR27417A, p < 0.05; mean maximal percent fall in FEV1 LAR: 29 +/- 6% after placebo, 23.5 +/- 5.4% after SR27417A, p < 0.05). There were no effects on early asthmatic responses, allergen-induced airway responsiveness, or baseline lung measurements. SR27417A is the most potent PAF antagonist to date, and it has a modest inhibitory effect on the late asthmatic response. This suggests that PAF has a small role in allergic inflammation.

Inhibition of PAF-induced platelet aggregation by WEB 2086 'in-vitro', an antagonist to the receptor for platelet-activating factor, in bovine

The sensitivity of bovine platelet aggregation in response to PAF stimulation and the ability of WEB 2086 (a thieno-triazolodiazepine) to inhibit response to PAF-induced platelet aggregation were investigated in the blood from five healthy male Belgian Blue calves. The recorded response to PAF showed a plateau which was dependent on the PAF concentration. Platelet aggregation induced by PAF consists of two mechanisms: reversible and irreversible aggregations which are accompanied by the release of platelet granule contents. Reversible aggregation occurred above (2 . 10(-9) mol/l) PAF, and irreversible aggregation occurred above (2 . 10(-7) mol/l) PAF. Addition of WEB 2086 to bovine platelets in vitro induced a rightward shift in the dose-response curve to PAF. WEB 2086 inhibited PAF-induced aggregation in a competitive reversible manner (pA2 = 7.61). The results of our study show that PAF induces platelet aggregation in platelet-rich plasma (PRP) and that addition of WEB 2086 to bovine platelets in vitro inhibits PAF-induced Platelet Aggregation.

A study of the effect of a platelet activating factor (PAF) receptor antagonist on antigen challenge of horses with chronic obstructive pulmonary disease

Antigen challenge involving exposure to straw and mouldy hay for 7 h produced lung function changes and neutrophil recruitment to the lungs in horses with chronic obstructive pulmonary disease (COPD). During the challenge, an increase in radiolabelled neutrophils in the lungs occurred, together with increased respiratory rate and pleural pressure. The role of platelet activating factor (PAF) in antigen-induced neutrophil accumulation, and increased pleural pressure and respiratory rate was investigated by administering the PAF receptor antagonist WEB 2086 to asymptomatic COPD horses prior to antigen challenge. WEB 2086 (3 mg/kg i.v.) did not affect antigen-induced changes in either neutrophil accumulation or respiratory function. These results suggest that PAF may not be an important mediator of the response to antigen in equine COPD.

Priming effect of platelet activating factor on leukotriene C4 from stimulated eosinophils of asthmatic patients

BACKGROUND

Eosinophils from asthmatic patients are known to release greater amounts of leukotrienes than normal eosinophils when stimulated by the calcium ionophore A23187. The effect of platelet activating factor (PAF) in priming eosinophils was investigated.

METHODS

Eosinophils were obtained from 18 asthmatic patients and 18 healthy donors. Cells separated by the Percoll gradients were incubated with PAF (C-18) for 30 minutes and then stimulated with the calcium ionophore A23187 (2.5 microM) for 15 minutes. The amount of leukotriene C4 (LTC4) in supernatants was measured using a combination of high pressure liquid chromatography and radioimmunoassay.

RESULTS

The mean (SD) amount of LTC4 released by eosinophils from asthmatic patients upon stimulation with the calcium ionophore A23187 alone was 27.9 (9.9) ng/10(6) cells (n = 6). The amount of LTC4 released following stimulation with the calcium ionophore A23187 after pretreatment with PAF (1, 5, and 10 microM) was 57.2 (8.9), 75.1 (14.3), and 52.6 (10.7) ng/10(6) cells (n = 6), respectively. Trace amounts of LTC4 (0.9 (0.02) ng/10(6) cells, n = 6) were detected in the supernatant of the cells after stimulation by PAF alone (5 microM). The amount of LTC4 released upon stimulation by calcium ionophore A23187 alone in eosinophils from healthy donors was 10.3 (3.7) ng/10(6) cells (n = 4). The amounts of LTC4 released upon stimulation with calcium ionophore A23187 after pretreatment with PAF at concentrations of 1, 5, and 10 microM were 11.9 (3.5), 17.8 (5.6), and 12.7 (5.1) ng/10(6) cells (n = 4), respectively. Trace amounts of LTC4 (0.6 (0.02) ng/10(6) cells, n = 4) were detected in the supernatant of the cells upon stimulation with PAF alone (5 microM). The amounts of LTC4 released upon stimulation with calcium ionophore A23187 after pretreatment with lyso-PAF at concentrations of 1, 5, and 10 microM (n = 4 or 6) were 30.8 (5.2), 22.9 (5.1), and 27.3 (4.3) ng/10(6) cells (n = 6) from the eosinophils of asthmatic patients and 13.7 (3.3), 15.2 (4.9), and 14.7 (3.8) ng/10(6) cells (n = 4) from the eosinophils of healthy donors.

CONCLUSIONS

The results indicated that PAF enhanced LTC4 formation by eosinophils obtained from asthmatic patients stimulated with the calcium ionophore A23187, but not those obtained from normal subjects.

Secretory non-pancreatic phospholipase A2 and cyclooxygenase-2 expression by tracheobronchial smooth muscle cells

Lipid mediators of inflammation, contribute to airway hyper-reactivity in asthma. Since production of lipid mediators is largely regulated by phospholipase A2 (PLA2), and since PLA2 expression in mesenchymal cells is induced by cytokines and other signals, we examined PLA2 expression by rat tracheobronchial smooth muscle cells (TBSMC). PLA2 expression in TBSMC cultures was markedly increased by tumour-necrosis factor (TNF) alpha (130-fold) and interleukin-1beta (IL-1beta) (7.4-fold). Lipopolysaccharide (LPS;100 ng/ml) resulted in a 51-fold increase in extracellular PLA2 activity. PLA2 expression by LPS-stimulated or cytokine-stimulated cells was downregulated by dexamethasone. Whereas forskolin or dibutyrl cAMP increased PLA2 activity, inhibition of protein kinase A but not tyrosine kinase reduced PLA2 expression. Northern blot analysis showed that TNF alpha and IL-1beta increased both PLA2 and inducible cyclooxygenase (Cox-2) mRNA transcription. Addition of dexamethasone substantially blunted the increase in PLA2 and Cox-2 mRNA. In contrast, the level of Cox-1 mRNA was very low and did not change with the various treatments. Since proinflammatory lipid mediators have been implicated in the pathogenesis of asthma and PLA2 activity regulates generation of these lipid mediators, cytokine-stimulated synthesis and release of PLA2 by airway smooth cells may contribute to the potentiation of airway inflammation in asthma.

Asthma

Bronchial asthma is now recognised to be a major cause of morbidity and even mortality in people of all ages. Two important ideas have changed our approach to asthma management. The first is understanding that asthma is a chronic inflammatory disorder which needs regular treatment with anti-inflammatory drugs such as inhaled corticosteroids to prevent further attacks. The second development is the availability of prescribable peak flow meters, which allows both confident diagnosis and early prediction of relapse. Asthma management guidelines provide a logical treatment framework for most patients, but a few difficult cases still consume large amounts of medical time. The commonest problem is one of compliance with treatment which may respond to patient education, although this is not universally so. Other problems include misdiagnosis, acid reflux and, rarely, true corticosteroid-resistant asthma. Several potentially important new treatments have been developed. These include longer acting anticholinergic drugs, drugs with bronchodilator and some anti-inflammatory properties which antagonise or inhibit the production of leukotrienes, sub-types of phosphodiesterase inhibitor with anti-inflammatory properties and immunosuppressive drugs such as cyclosporin. Ultimately these new treatments must be rigorously tested and integrated into a care plan that remains centred on patient education.