Persistent airway eosinophilia after leukotriene (LT) D4 administration in the guinea pig: modulation by the LTD4 receptor antagonist, pranlukast, or an interleukin-5 monoclonal antibody

The role of oxylipins in NSAID-exacerbated respiratory disease (N-ERD)

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyp formation, adult-onset asthma, and hypersensitivity to all cyclooxygenase-1 (COX-1) inhibitors. Oxygenated lipids are collectively known as oxylipins and are polyunsaturated fatty acids (PUFA) oxidation products. The most extensively researched oxylipins being the eicosanoids formed from arachidonic acid (AA). There are four major classes of eicosanoids including leukotrienes, prostaglandins, thromboxanes, and lipoxins. In N-ERD, the underlying inflammatory process of the upper and lower respiratory systems begins and occurs independently of NSAID consumption and is due to the overproduction of cysteinyl leukotrienes. Leukotriene mediators all induce edema, bronchoconstriction, and airway mucous secretion. Thromboxane A2 is a potent bronchoconstrictor and induces endothelial adhesion molecule expression. Elevated Prostaglandin D2 metabolites lead to vasoconstriction, additionally impaired up-regulation of prostaglandin E2 leads to symptoms seen in N-ERD as it is essential for maintaining homeostasis of inflammatory responses in the airway and has bronchoprotective and anti-inflammatory effects. A characteristic feature of N-ERD is diminished lipoxin levels, this decreased capacity to form endogenous mediators with anti-inflammatory properties could facilitate local inflammatory response and expose bronchial smooth muscle to relatively unopposed actions of broncho-constricting substances. Treatment options, such as leukotriene modifying agents, aspirin desensitization, biologic agents and ESS, appear to influence eicosanoid pathways, however more studies need to be done to further understand the role of oxylipins. Besides AA-derived eicosanoids, other oxylipins may also pay a role but have not been sufficiently studied. Identifying pathogenic N-ERD mechanism is likely to define more effective treatment targets.

Leukotriene D4 role in allergic asthma pathogenesis from cellular and therapeutic perspectives

Asthma is a chronic inflammatory and allergic disease that is mainly characterized by reversible airway obstruction and bronchial hyperresponsiveness. The incidence of asthma is increasing with more than 350 million people worldwide are affected. Up to now, there is no therapeutic option for asthma and most of the prescribed drugs aim to ameliorate the symptoms of the disease especially during the acute exacerbations after trigger exposure. Asthma is a heterogonous disease that involves interactions between inflammatory mediators and cellular components within the disease microenvironment including inflammatory and structural cells. Cysteinyl leukotrienes (cys-LTs) are inflammatory lipid mediators that have potent roles in asthma pathogenesis. CysLTs consisting of LTC₄, LTD₄, and LTE₄ are mainly secreted by leukocytes and act through three main G-protein coupled receptors (CysLT₁R, CysLT₂R, and CysLT₃R). LTD₄ is the most potent bronchoconstrictor which gives it the priority to be discussed in detail in this review. LTD₄ binds with high affinity to CysLT₁R and many studies showed that using CysLT₁R antagonists such as montelukast has a beneficial effect for asthmatics especially in corticosteroid refractory cases. Since asthma is a heterogeneous inflammatory disease of many cell types involved in the disease pathogenies and LTD₄ has a special role in inflammation and bronchoconstriction, this review highlights the role of LTD₄ on each cellular component in asthma and the benefits of using CysLT₁R antagonists in ameliorating LTD₄-induced effects.

G Protein-Coupled Receptors in Asthma Therapy: Pharmacology and Drug Action

Asthma is a heterogeneous inflammatory disease of the airways that is associated with airway hyperresponsiveness and airflow limitation. Although asthma was once simply categorized as atopic or nonatopic, emerging analyses over the last few decades have revealed a variety of asthma endotypes that are attributed to numerous pathophysiological mechanisms. The classification of asthma by endotype is primarily routed in different profiles of airway inflammation that contribute to bronchoconstriction. Many asthma therapeutics target G protein-coupled receptors (GPCRs), which either enhance bronchodilation or prevent bronchoconstriction. Short-acting and long-acting β 2-agonists are widely used bronchodilators that signal through the activation of the β 2-adrenergic receptor. Short-acting and long-acting antagonists of muscarinic acetylcholine receptors are used to reduce bronchoconstriction by blocking the action of acetylcholine. Leukotriene antagonists that block the signaling of cysteinyl leukotriene receptor 1 are used as an add-on therapy to reduce bronchoconstriction and inflammation induced by cysteinyl leukotrienes. A number of GPCR-targeting asthma drug candidates are also in different stages of development. Among them, antagonists of prostaglandin D2 receptor 2 have advanced into phase III clinical trials. Others, including antagonists of the adenosine A2B receptor and the histamine H4 receptor, are in early stages of clinical investigation. In the past decade, significant research advancements in pharmacology, cell biology, structural biology, and molecular physiology have greatly deepened our understanding of the therapeutic roles of GPCRs in asthma and drug action on these GPCRs. This review summarizes our current understanding of GPCR signaling and pharmacology in the context of asthma treatment. SIGNIFICANCE STATEMENT: Although current treatment methods for asthma are effective for a majority of asthma patients, there are still a large number of patients with poorly controlled asthma who may experience asthma exacerbations. This review summarizes current asthma treatment methods and our understanding of signaling and pharmacology of G protein-coupled receptors (GPCRs) in asthma therapy, and discusses controversies regarding the use of GPCR drugs and new opportunities in developing GPCR-targeting therapeutics for the treatment of asthma.

Leukotriene receptors as potential therapeutic targets

Leukotrienes, a class of arachidonic acid-derived bioactive molecules, are known as mediators of allergic and inflammatory reactions and considered to be important drug targets. Although an inhibitor of leukotriene biosynthesis and antagonists of the cysteinyl leukotriene receptor are clinically used for bronchial asthma and allergic rhinitis, these medications were developed before the molecular identification of leukotriene receptors. Numerous studies using cloned leukotriene receptors and genetically engineered mice have unveiled new pathophysiological roles for leukotrienes. This Review covers the recent findings on leukotriene receptors to revisit them as new drug targets.

Cysteinyl leukotriene receptor antagonist regulates allergic airway inflammation in an organ- and cytokine-specific manner

Background

Cysteinyl leukotrienes (cys-LTs) are very important factors in the pathophysiology of bronchial asthma. Cys-LT receptor antagonists (LTRAs) decrease allergic airway inflammation. The aim of the present study was to determine the differential effects of LTRAs and corticosteroids on allergic airway inflammation and allergen-specific cytokine production from lymphoid tissues using a murine model of asthma.

Material/Methods

Four groups of female BALB/c mice [control (Cont); Dermatophagoides farinae allergen-sensitized (AS); pranlukast (Prl), an LTRA-treated AS; and dexamethasone (Dex)-treated AS] were examined. Lung pathology and cytokine production by prepared mononuclear cells isolated from mediastinal lymph nodes (MLNs) and spleen were compared among these groups.

Results

AS mice exhibited allergic airway inflammation and significant increases in allergen-specific Th1 and Th2 cytokines in MLNs and spleen. Prl-treated mice showed significant attenuation of allergic airway inflammation concomitant with reduction of Th2 cytokines and IFN-γ in MLNs but not in spleen. In contrast, Dex significantly decreased Th1 and Th2 cytokines in MLNs and also decreased them (except IL-13 and IL-2) in spleen.

Conclusions

The inflammatory effects of cys-LTs could differ in lymphoid organs. LTRAs potentially regulate allergic airway inflammation in an organ- and cytokine-specific manner, while systemic corticosteroid shows nonspecific effects.

Regulation of dendritic cell functions against harmful respiratory pathogens by a cysteinyl leukotrienes receptor antagonist

Cysteinyl leukotriene receptor antagonist (LTRA) is a widely used medicine for asthma. Cysteinyl leukotrienes (cysLTs) are involved in the regulation of dendritic cell (DC) function. However, the effects of LTRA on DC-related antimicrobial immunity against harmful respiratory pathogens remain unknown. The purpose of this study was to examine the effects of LTRA administered in vivo on DC function against representative respiratory pathogens in vitro. Pulmonary DCs were isolated from four groups of mice: control, mite allergen sensitized (AS), and AS mice treated with the corticosteroid dexamethasone (Dex) or with the LTRA pranlukast (Prl). These DCs were incubated with mite allergen, lipopolysaccharide (LPS), Aspergillus fumigatus, or respiratory syncytial virus (RSV). IL-10 and IL-12 production was then determined. Dex treatment significantly inhibited lipopolysaccharide (LPS)-induced IL-10 and IL-12 production as well as baseline IL-12 production in AS mice. The Prl did not significantly inhibit LPS-induced IL-10 and IL-12 production in AS mice. More importantly, Prl significantly increased IL-10 and IL-12 in AS mice after RSV infection. This study shows that LTRA that is used for asthma potentially up-regulates antimicrobial immunity through modulation of DC function against some respiratory infections without immunosuppression.

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.

A geranyl acetophenone targeting cysteinyl leukotriene synthesis prevents allergic airway inflammation in ovalbumin-sensitized mice

Asthma is associated with increased pulmonary inflammation and airway hyperresponsiveness. The current use of corticosteroids in the management of asthma has recently raised issues regarding safety and lack of responsiveness in 5-10% of asthmatic individuals. The aim of the present study was to investigate the therapeutic effect of a non-steroidal small molecule that has cysteinyl leukotriene (cysLT) inhibitory activity, upon attenuation of allergic lung inflammation in an acute murine model. Mice were sensitized with ovalbumin (OVA) and treated with several intraperitoneal doses (100, 20, 2 and 0.2mg/kg) of 2,4,6,-trihydroxy-3-geranylacetophenone (tHGA). Bronchoalveolar lavage was performed, blood and lung samples were obtained and respiratory function was measured. OVA sensitization increased pulmonary inflammation and pulmonary allergic inflammation was significantly reduced at doses of 100, 20 and 2mg/kg with no effect at the lowest dose of 0.2mg/kg. The beneficial effects in the lung were associated with reduced eosinophilic infiltration and reduced secretion of Th2 cytokines and cysLTs. Peripheral blood reduction of total IgE was also a prominent feature. Treatment with tHGA significantly attenuated altered airway hyperresponsiveness as measured by the enhanced pause (Penh) response to incremental doses of methacholine. These data demonstrate that tHGA, a synthetic non-steroidal small molecule, can prevent acute allergic inflammation. This proof of concept opens further avenues of research and development of tHGA as an additional option to the current armamentarium of anti-asthma therapeutics.

Effects of KP-496, a novel dual antagonist for cysteinyl leukotriene receptor 1 and thromboxane A2 receptor, on Sephadex-induced airway inflammation in rats

Bronchial asthma is characterized by chronic airway inflammation. Eosinophils are involved in airway inflammation and play crucial roles in asthma. There is accumulating evidence to suggest contributions of cysteinyl leukotrienes (cysLTs) and thromboxane (TX) A(2) to the recruitment of eosinophils into lung in asthmatics. KP-496 is a novel dual antagonist for CysLT receptor type 1 and TXA(2) receptors. The aim of this study was to evaluate the anti-inflammatory effects of KP-496 on Sephadex-induced airway inflammation. Sephadex suspension was intratracheally injected into rats. Amounts of regulated on activation, normal T cell expressed and secreted (RANTES) and eotaxin, and numbers of infiltrating cells in bronchoalveolar lavage fluid were measured 24 and 48 h after Sephadex injection, respectively. KP-496 (30, 100 microg/head) was intratracheally administered to rats 1 h before and 7 h after Sephadex injection. KP-496 and prednisolone (10 mg/kg, per os) exhibited significant inhibitory effects on infiltration of total cells and eosinophils into lung. Production of RANTES was significantly inhibited by KP-496 and prednisolone. Production of eotaxin was significantly inhibited by prednisolone. KP-496 also inhibited the production of eotaxin, though this effect was not significant. These results demonstrate that KP-496 exhibited the anti-inflammatory effects by inhibiting infiltration of inflammatory cells and productions of RANTES and eotaxin.

Effects of inhaled monoethanolamine on bronchoconstriction

We previously reported a 65-year-old man who aspirated an alkaline detergent containing 3.3% w/v (weight of solute per volume of solution) monoethanolamine (MEA) into his lungs, causing asthma-like symptoms. We presently describe the mechanism of MEA-induced bronchoconstriction according to findings in guinea pigs. In anesthetized, artificially ventilated animals, changes in airway opening pressure (P(ao)) were measured as an index of bronchoconstriction. An aerosol of 3.3% MEA solution (0.1 ml kg(-1)) inhaled through a tracheal cannula induced significantly stronger bronchoconstriction than an aerosol of potassium hydroxide (KOH) solution (0.1 ml kg(-1)) at the same pH. MEA-induced bronchoconstriction was significantly suppressed by premedication with intravenously injected atropine sulfate (3 mg kg(-1)), a muscarinic receptor antagonist, or diphenhydramine hydrochloride (10 mg kg(-1)), a histamine-H(1) receptor antagonist. MEA-induced bronchoconstriction was not enhanced by premedication with an intravenous injection of neostigmine (0.1 mg kg(-1)), an acetylcholinesterase inhibitor. When bronchoconstriction was induced by MEA, histamine concentrations in bronchoalveolar lavage fluid (BALF) were not significantly greater than in BALF after KOH-induced bronchoconstriction or in BALF after inhalation of physiologic saline. In vitro, contraction of trachea denuded of epithelium during superfusion with MEA (10 mm) was suppressed by premedication with pyrilamine maleate, a histamine-H(1) receptor antagonist, at 10 and 100 microm. Contraction of trachea denuded of epithelium during superfusion with MEA (10 mm) was suppressed by premedication with atropine sulfate at 10 and 100 microm. These results suggest that asthma-like symptoms may result partly from agonistic MEA effects at histamine-H(1) receptors and muscarinic receptors.

Cyclooxygenase-2/prostaglandin D2/CRTH2 pathway mediates double-stranded RNA-induced enhancement of allergic airway inflammation

Respiratory RNA viruses responsible for the common cold often worsen airway inflammation and bronchial responsiveness, two characteristic features of human asthma. We studied the effects of dsRNA, a nucleotide synthesized during viral replication, on airway inflammation and bronchial hyperresponsiveness in murine models of asthma. Intratracheal instillation of poly I:C, a synthetic dsRNA, increased the airway eosinophilia and enhanced bronchial hyperresponsiveness to methacholine in OVA-sensitized, exposed rats. These changes were associated with induction of cyclooxygenase-2 (COX-2) expression and COX-2-dependent PGD2 synthesis in the lungs, particularly in alveolar macrophages. The direct intratracheal instillation of PGD2 enhanced the eosinophilic inflammation in OVA-exposed animals, whereas pretreatment with a dual antagonist against the PGD2 receptor-(CRTH2) and the thromboxane A2 receptor, but not with a thromboxane A2 receptor-specific antagonist, nearly completely eliminated the dsRNA-induced worsening of airway inflammation and bronchial hyperresponsiveness. CRTH2-deficient mice had the same degree of allergen-induced airway eosinophilia as wild-type mice, but they did not exhibit a dsRNA-induced increase in eosinophil accumulation. Our data demonstrate that COX-2-dependent production of PGD2 followed by eosinophil recruitment into the airways via a CRTH2 receptor are the major pathogenetic factors responsible for the dsRNA-induced enhancement of airway inflammation and responsiveness.

Using guinea pigs in studies relevant to asthma and COPD

The guinea pig has been the most commonly used small animal species in preclinical studies related to asthma and COPD. The primary advantages of the guinea pig are the similar potencies and efficacies of agonists and antagonists in human and guinea pig airways and the many similarities in physiological processes, especially airway autonomic control and the response to allergen. The primary disadvantages to using guinea pigs are the lack of transgenic methods, limited numbers of guinea pig strains for comparative studies and a prominent axon reflex that is unlikely to be present in human airways. These attributes and various models developed in guinea pigs are discussed.

Effect of TRFK-5 on airway responsiveness in ovalbumin-treated guinea pigs exposed to tobacco smoke

Tobacco smoke (TS) exposure can induce airway hyperresponsiveness, especially in asthma. A feature of asthma is eosinophilia. We hypothesized that tobacco smoke exposure enhances eosinophil responsiveness in sensitized guinea pigs. Tobacco smoke-exposed, ovalbumin (OA)-sensitized guinea pigs were treated with TRFK-5 (1.0 mg/kg, intraperitoneal), an anti-interleukin (IL)-5 agent, or its vehicle. Guinea pigs were challenged with aerosols of OA, capsaicin, histamine, and methacholine. TRFK-5 attenuated airway responsiveness to OA but not to capsaicin, histamine, or methacholine. Bronchial alveolar lavage fluid analysis confirmed TRFK-5 attenuated airway eosinophilia in OA-treated guinea pigs. Therefore, airway responsiveness to OA is enhanced by eosinophils or IL-5 itself.

Promise and pitfalls in animal-based asthma research: building a better mousetrap

Asthma is one of the leading chronic diseases in the world today. An essential component of the asthma research endeavor is the animal-based experimental disease system, which provides knowledge that is not attainable through study of patients alone. Animal research is especially valuable for elucidating pathophysiology, drug testing, and as an adjunct for interpreting the results of human clinical trials. However, controversies surrounding animal systems data and at the interface between animal and human studies raise questions regarding the true utility of experimental asthma research. We consider here the considerable promise and important limitations of animal-based systems and their prospects for the future study asthma.

Factors contributing to nasal allergic late phase eosinophilia

OBJECTIVE

This study focused on factors contributing to eosinophilia after intranasal allergen challenge.

METHODS

Nasal secretions of 13 allergic individuals were gained over a period of 8 hours after nasal allergen challenge. Early and late phase reactions were determined by acoustic rhinometry and changes of volume and total protein in nasal secretions. Eosinophilia was demonstrated by nasal eosinophilic cationic protein. Interleukin (IL)-5; the chemokines IL-8, monocyte chemotactic protein (MCP)-1 and MCP-3, and eotaxin; soluble vascular cell adhesion molecule 1 (sVCAM-1); and the leukotriene C4 (LTC4) were analyzed by enzyme-linked immunosorbent assay for their suggested impacts on tissue eosinophilia.

RESULTS

By means of rhinometry, we observed in 69% an alternating type of late phase response, followed by a bilateral (15%) or unilateral (8%) type. A biphasic kinetic could be demonstrated by changes in nasal volume and total protein of nasal secretions, reflecting the early and late phase responses. A typical late phase kinetic was observed for IL-5, MCP-1, eotaxin, sVCAM-1, and LTC4. Interleukin 8 was characteristic for early phase reaction but increased in late phase as well. We could not detect any MCP-3 in our samples.

CONCLUSIONS

Our data point to a relevant role of the T(H)2 cytokine IL-5; of the chemokines IL-8, MCP-1, and eotaxin; of the adhesion molecule sVCAM-1; and of the leukotriene LTC4 for the allergic late phase eosinophilia.

Treatment of asthma with antileukotrienes: first line or last resort therapy?

Twenty five years after the structure elucidation of slow reacting substance of anaphylaxis, antileukotrienes are established as a new therapeutic modality in asthma. The chapter reviews the biochemistry and pharmacology of leukotrienes and antileukotrienes with particular focus on the different usage of antileukotrienes for treatment of asthma and rhinitis in Europe and the US. Further research needs and new areas for leukotriene involvement in respiratory diseases are also discussed.

The role of leukotrienes in allergic rhinitis

OBJECTIVE

To review the role of cysteinyl leukotrienes (cysLTs) in allergic rhinitis and the scientific rationale for therapy with leukotriene receptor antagonists (LTRAs).

DATA SOURCES

Relevant basic science and clinical articles were identified by a search of the PubMed database for articles published from 1984 to 2004 using the following keywords: allergic rhinitis; nose; immune response; allergen challenge; leukotrienes C, D, and E; cysteinyl leukotriene; cysteinyl leukotriene receptor; cytokine; leukocyte; montelukast; zafirlukast; and pranlukast.

STUDY SELECTION

The authors' expert opinion was used to select studies for inclusion in this review.

RESULTS

CysLTs are synthesized via 5-lipoxygenase metabolism of arachidonic acid by mast cells and basophils during the early-phase response to antigen and by eosinophils and macrophages during the late phase. The cysLT levels in nasal secretions are elevated after short-term allergen instillation and in allergy season in patients with allergic rhinitis. These lipid mediators act locally and systemically by interacting with receptors, particularly the cysLT1 receptor, on target cells. Evidence derived from topical application of cysLTs in the nose and from the effects of LTRAs indicates that cysLTs contribute to nasal mucous secretion, congestion, and inflammation. CysLTs promote allergic inflammation by enhancing immune responses and the production, adhesion, migration, and survival of inflammatory cells such as eosinophils. They also increase the generation of an array of other proinflammatory mediators, such as cytokines, which in turn increase the production of and receptors for cysLTs. Clinical trials have demonstrated that LTRAs have significant but modest efficacy as single agents but additive efficacy when used with other classes of agents.

CONCLUSIONS

CysLTs fulfill the criteria for relevant mediators of allergic rhinitis via their diverse effects on immune, inflammatory, and local structural components of disease. By blocking the cysLT1 receptor responsible for most of these effects, LTRAs represent a useful approach to treatment of this important and prevalent disorder.

Eicosanoids: mediators and therapeutic targets in fibrotic lung disease

Fibrosis is a common end-stage sequella of a number of acute and chronic lung diseases. Current concepts of pathogenesis implicate dysregulated interactions between epithelial cells and mesenchymal cells. Although investigative efforts have documented important roles for cytokines and growth factors in the pathogenesis of fibrotic lung diseases, these observations have not as yet been translated into efficacious therapies, and there is a pressing need for new pathogenetic insights and therapeutic approaches for these devastating disorders. Eicosanoids are lipid mediators derived from arachidonic acid, the most studied of which are the prostaglandins and leukotrienes. Although they are primarily known for their roles in asthma, pain, fever and vascular responses, present evidence indicates that eicosanoids exert relevant effects on immune/inflammatory, as well as structural, cells pertinent to fibrogenesis. In general, leukotrienes promote, whereas prostaglandin E(2) opposes, fibrogenic responses. An imbalance of eicosanoids also exists in pulmonary fibrosis, which favours the production of leukotrienes over prostaglandin E(2). This review highlights the role of this imbalance in the evolution of fibrotic lung disease, discusses the mechanisms by which it may arise and considers approaches for therapeutic targeting of eicosanoids in these conditions.

Evaluating the prophylactic potential of the phtalimide derivative LASSBio 552 on allergen-evoked inflammation in rats

A previous study showed that the novel tetrazolephtalimide derivative LASSBio 552 (2-4-[3-(1H-1,2,3,4-tetraazol-5-yl)propoxy]phenethyl-1,3-isoindolinedione) prevents LTD(4)-evoked tracheal contraction. This led us to examine the putative anti-inflammatory effect of LASSBio 552 in comparison with the leukotriene CysLT(1) receptor antagonist zafirlukast using a model of allergic pleurisy in rats. Treatment with either LASSBio 552 (24-96 micromol/kg, i.p.) or zafirlukast (9-72 micromol/kg, i.p.), 1 h before challenge, inhibited eosinophil and mononuclear cell influx into the pleural cavity 24 h post-challenge, but failed to alter the increased levels of eotaxin, plasma leakage, mast cell degranulation and neutrophil infiltration noted 6 h post-challenge. CD4(+) T cell recruitment 24 h post-challenge was also sensitive to LASSBio 552. This treatment failed to alter cysteinyl leukotriene production at 6 h, but clearly inhibited the phenomenon 24 h and 48 h post-challenge. In in vitro settings LASSBio 552 inhibited allergen-evoked cysteinyl leukotriene generation from isolated mast cells, while histamine release remained unchanged. It also slightly inhibited cysteinyl leukotriene production by eosinophils and mononuclear cells triggered by Ca(+2) ionophore A23187. A leukotriene CysLT(1) receptor transfected cell-based assay revealed that LASSBio 552 did not prevent LTD(4)-evoked Ca(+2) influx, indicating that it was not a leukotriene CysLT(1) receptor antagonist. These findings indicate that LASSBio 552 is able to inhibit eosinophil influx triggered by allergen chalenge in a mechanism at least partially associated with suppression of CD4(+) T cell influx and cysteinyl leukotriene production.

Leukotriene E(4)-induced persistent eosinophilia and airway obstruction are reversed by zafirlukast in patients with asthma

BACKGROUND

We have shown that inhalation of leukotriene (LT) E 4 contributes to specific recruitment of eosinophils to the airway mucosa in patients with asthma at the time of maximal decrease in airway-specific conductance.

OBJECTIVE

We examined the ability of the cysteinyl LT 1 receptor antagonist, zafirlukast, to improve or prevent LT-mediated eosinophilia and airway obstruction in asthma.

METHODS

Bronchial biopsies were taken and pulmonary function was measured before and 4 to 6 hours after the dose of inhaled LTE 4 causing a > or =15% fall in FEV 1 at baseline both at week 0 and after 6-week randomly assigned treatment with a high dose of zafirlukast, 80 mg twice daily.

RESULTS

Leukotriene E 4 inhalation at week 0 doubled the number of eosinophils in the airway mucosa in 21 of 25 patients with mild asthma, increased the numbers of neutrophils and lymphocytes, and decreased FEV 1 (-17%). Zafirlukast reduced both airway eosinophilia and obstruction in FEV 1 , whereas with a double-blind placebo treatment, the effect of LTE 4 on both parameters persisted for 6 weeks. On repeat LTE 4 inhalation challenge after 6 weeks, zafirlukast treatment prevented further airway eosinophilia and decrease in FEV 1 seen in the placebo group.

CONCLUSION

Persistent LTE 4 -induced airway eosinophilia may form the basis of an amplification mechanism for further eosinophil recruitment. Zafirlukast prevents LTE 4 -induced eosinophilic airway inflammation in mild asthma.

Pranlukast, a Leukotriene Receptor Antagonist, Inhibits Interleukin-5 Production via a Mechanism Distinct from Leukotriene Receptor Antagonism

BACKGROUND

Pranlukast, a cysteinyl leukotriene receptor 1 (CysLTR1) antagonist, inhibits not only airway smooth muscle contraction, but also allergic inflammation. The aim of this study was to determine the mechanism of pranlukast-induced interleukin-5 (IL-5) inhibition in allergic inflammation.

METHODS

Surgically resected human lung tissue was passively sensitized in vitro with mite-allergen-sensitized sera, followed by stimulation with mite allergen after pretreatment of the tissue with pranlukast, dexamethasone, or both. The IL-5 protein level in the culture medium was measured, and in situ hybridization of IL-5 and CysLTR1 mRNA was performed using lung tissues.

RESULTS

Pretreatment of lung tissues with pranlukast alone significantly decreased the amount of IL-5 protein in the culture medium by 40%. The combination of pranlukast and dexamethasone synergistically enhanced this effect. Quantitative in situ hybridization with image analysis revealed abundant expression of IL-5 mRNA in eosinophils, lymphocytes, and mast cells in sensitized and allergen-stimulated lung tissues. CysLTR1 mRNA was detected in macrophages, smooth muscle cells, eosinophils, and mast cells, but was less expressed in lymphocytes. Pranlukast-induced inhibition of IL-5 mRNA expression was noted in various cells, irrespective of their CysLTR1 mRNA expression status. In addition, cysteinyl leukotrienes per se failed to upregulate the IL-5 production.

CONCLUSION

Our results indicate that pranlukast inhibits IL-5 synthesis via a mechanism distinct from CysLTR1 antagonism.

Leukotriene D4 stimulates collagen production from myofibroblasts transformed by TGF-beta

BACKGROUND

Airway remodeling has an important role in the pathogenesis of bronchial asthma. Many mediators that influence the pathophysiology of bronchial asthma, especially cysteinyl leukotrienes (CysLTs) and TGF-beta1, are involved in airway remodeling.

OBJECTIVE

To know whether TGF-beta1 alters fibroblast responsiveness to CysLTs, we examined the effects of leukotriene (LT) D4 on collagen production from fibroblasts and from myofibroblasts transformed by TGF-beta1. We also examined whether TGF-beta1 upregulates CysLT1 receptor (CysLT1R) expression in fibroblasts.

METHODS

Concentrations of procollagen in the human fetal lung fibroblast (HFL) 1 cell supernatant were measured by using an enzyme immunoassay kit in the presence or absence of various concentrations of LTD4, TGF-beta1, CysLT1R antagonist, or some combination of these. The mRNA expression of CysLT1R and alpha-smooth muscle actin as a marker of myofibroblasts was measured by means of real-time PCR. Furthermore, protein expression of CysLT1R on fibroblasts was measured by means of flow cytometric analysis.

RESULTS

TGF-beta1 stimulated collagen production from HFL-1 cells, but LTD4 alone did not. LTD4 in combination with TGF-beta1 increased collagen production compared with TGF-beta1 alone. Real-time PCR showed that stimulation with TGF-beta1 significantly upregulated CysLT1R and alpha-smooth muscle actin mRNA expression in HFL-1 cells.

CONCLUSIONS

LTD4 increased collagen production by upregulating CysLT1R induced by TGF-beta1. In the TGF-beta-rich milieu, activated myofibroblasts expressing CysLT1R can respond to CysLTs and produce large amounts of extracellular matrix, thereby contributing to airway remodeling. These data suggest that treatment with leukotriene receptor antagonists might prevent airway remodeling in patients with asthma.

Comparison of glucocorticoid and cysteinyl leukotriene receptor antagonist treatments in an experimental model of chronic airway inflammation in guinea-pigs

BACKGROUND

Leukotriene receptor antagonists have been demonstrated in several studies to possess bronchodilating and anti-inflammatory properties in asthma. However, there are few experimental studies performed to compare the effects of anti-leukotrienes and glucocorticoids, most used anti-inflammatory agents in asthma. In the present study, we evaluated the effects of treatment with dexamethasone or montelukast on eosinophil and mononuclear cell recruitment in an experimental model of allergen-induced chronic airway inflammation in guinea-pigs (GP).

METHODS

GP were submitted to increasing concentrations of aerosols of ovalbumin (OVA) twice a week for 4 weeks. After 2 weeks, animals were treated daily with dexamethasone, montelukast or saline solution. After this period, GP were anaesthetized, tracheostomized, mechanically ventilated and challenged with OVA aerosol.

RESULTS

Maximal changes of respiratory system resistance and elastance induced by OVA challenge were attenuated by dexamethasone (P<0.001), but not by montelukast treatment. Neither dexamethasone nor montelukast significantly influenced bronchial oedema formation. Dexamethasone but not montelukast induced a decrease in mononuclear cells in airways (P<0.001). Eosinophil infiltration in the bronchial wall was reduced by both dexamethasone and montelukast (P<0.005). Only dexamethasone treatment reduced the levels of exhaled nitric oxide (P<0.025).

CONCLUSION

Although leukotriene receptor antagonist treatment reduces eosinophil accumulation induced by multiple antigen challenges, glucocorticoid treatment attenuates both eosinophil and mononuclear cell infiltration.

Clinical efficacy and pharmacokinetics of montelukast in dyspeptic children with duodenal eosinophilia

BACKGROUND

Montelukast, a competitive cysteinyl leucotriene-1 receptor antagonist, reduces airway eosinophilia in asthmatics. We evaluated the effect of this drug in children with eosinophilic duodenitis, defined histologically as duodenal mucosa with peak eosinophil count of more than 10 eosinophils/hpf.

METHODS

Forty children and adolescents (6-18 yr) with dyspepsia and duodenal eosinophilia were enrolled in a double blind, randomized, placebo-controlled, cross-over study of monteleukast therapy. Subjects were randomized to receive either 10 mg montelukast or an identical placebo once daily and were evaluated on day 14 for symptomatic and biochemical responses. Subjects were also randomized to one of two blood sampling schemes to evaluate montelukast pharmacokinetics.

RESULTS

Using a post treatment global pain assessment, a positive clinical response was observed in 62.1% of patients receiving montelukast compared with 32.4% on placebo (p < 0.02). Pain assessment score deteriorated in 45% of montelukast responders (5/11) after cross-over to placebo and improved in 62% (8/13) of placebo non-responders on cross-over to montelukast. In patients with peak duodenal eosinophil counts between 20-29/hpf (n=19), a positive pain assessment response was observed in 84% of patients receiving montelukast compared to 42% receiving placebo (p < 0.01). Response rate did not differ by age, gender or histologic findings at baseline. Pharmacokinetic analysis yielded parameter estimates for absorption rate constant (Ka), apparent volume of distribution (Vd/F) and elimination rate constant (Kel) of 0.42 h, 0.19 L/kg and 0.26 h, respectively. The relative extent of systemic drug exposure was comparable to that observed in previous pediatric investigations with similar weight-adjusted montelukast doses. Neither dose nor calculated drug exposure were associated with the level of post treatment pain assessment or the change in biochemical markers.

CONCLUSIONS

These data suggest a beneficial role for montelukast in the treatment of pediatric patients with dyspepsia associated with duodenal eosinophilia.

The effect of pranlukast on allergen-induced bone marrow eosinophilopoiesis in subjects with asthma

We investigated the mechanisms by which leukotriene receptor antagonists decrease airway eosinophil number. In a randomized, double-blind crossover study, we examined the effects of 2 weeks of treatment with pranlukast 300 mg twice a day or placebo on allergen-induced changes in airway eosinophil number and bone marrow eosinophil progenitors in 15 subjects with mild asthma. Pranlukast treatment for 2 weeks decreased mean sputum eosinophil count from 0.15 x 10(6)/g (5.3% of cells) before treatment to 0.02 x 10(6)/g (0.7% of cells) after treatment (p < 0.05), whereas placebo did not. Pranlukast also decreased the eosinophil count (5.6% at 7 hours and 7.5% at 24 hours) (p < 0.05) after allergen inhalation compared with placebo (13.8% at 7 hours and 15.3% at 24 hours). There was a similar trend for sputum cells immunostaining for EG2, eotaxin, interleukin-5, and regulated upon activation, normal T cell expressed and secreted. Pranlukast also significantly attenuated the allergen-induced increase in the number of bone marrow eosinophil/basophil cfu (mean 0.3) at 24 hours compared with placebo (mean 6.2). The proportion of CD34(+) cells expressing the eotaxin receptor CC chemokine receptor 3, 24 hours after allergen inhalation, was also reduced by pranlukast. We conclude that, the cysteinyl leukotriene receptor antagonist, pranlukast, attenuates allergen-induced increase in airway eosinophils by decreasing bone marrow eosinophilopoiesis and airway chemotactic and eosinophilopoietic cytokines.

Leukotriene receptor antagonist pranlukast suppresses eosinophil infiltration and cytokine production in human nasal mucosa of perennial allergic rhinitis

The purpose of this study was to investigate the influence of pranlukast on eosinophilic inflammation and cytokine production in human nasal mucosa. Twelve patients were treated with pranlukast, and samples were obtained from the nasal mucosa of the inferior turbinate. With respect to cell infiltration, a significant decrease was observed in the percentage of inflammatory cells (secreted eosinophil cationic protein [EG2] and neutrophil elastase) after treatment. The levels of cytokines and chemical mediators (interleukin [IL]-4, IL-5, RANTES [regulated on activation, normal T cell expressed and secreted], cysteinyl leukotrienes, IL-1beta, tumor necrosis factor-alpha, and IL-8) assessed by enzyme-linked immunosorbent assay and enzyme immunoassay were significantly decreased. These results indicate that pranlukast decreased the levels of a majority of the cytokines in nasal mucosa, leading to improvement in subjective nasal symptoms. Furthermore, these results support the hypothesis that pranlukast exerts its therapeutic action primarily by blocking the leukotriene receptors on eosinophils.

Elevations of local leukotriene C4 levels during viral upper respiratory tract infections

BACKGROUND

One potential mechanism by which respiratory viruses trigger illness and complications is via the local elaboration of inflammatory mediators.

OBJECTIVE

To determine whether there is an increase in local leukotriene C4 (LTC4) levels during experimental infection with influenza A virus (FLU), rhinovirus (RV), or respiratory syncytial virus (RSV).

METHODS

Healthy adults were intranasally inoculated with a safety-tested strain of FLU (n = 29), RV (n = 16), or RSV (n = 21). Nasal lavage samples were collected, symptoms were recorded, and expelled nasal secretions were weighed before and then daily after challenge. Lavage samples were submitted for viral culture and assayed for LTC4 levels by radioimmunoassay. Serum antibody titers to the challenge viruses were assayed at baseline and 21 days after challenge.

RESULTS

All subjects were infected as evidenced by viral shedding and/or seroconversion. Following infection, significant increases (P < 0.05 by analysis of variance) in LTC4 levels were measured for each virus. Furthermore, there was a temporal association between the local LTC4 levels and the development of illness.

CONCLUSIONS

The results of this study, which used an adult experimental model, demonstrate elevations in locally produced LTC4 during respiratory infection with FLU, RV, and RSV. Future studies using antileukotriene agents may help elucidate the precise role of leukotrienes in mediating disease expression.

Cytokine levels during symptomatic viral upper respiratory tract infection

BACKGROUND

Previous studies suggest a role for locally produced proinflammatory cytokines in the development and expression of illness during experimental infection with a variety of respiratory viruses. However, most of these studies fail to make comparisons between symptomatic and asymptomatic infected subjects.

OBJECTIVE

To compare the pattern of nasal cytokine elaboration in asymptomatic and symptomatic subjects experimentally infected with rhinovirus-39 (RV-39).

METHODS

Healthy adults underwent experimental intranasal inoculation with a safety-tested clinical isolate of RV-39. Nasal lavages were collected, nasal symptoms were recorded, and expelled nasal secretions were weighed before and then daily for 6 days after challenge. Nasal lavages were submitted for viral culture and assayed for cytokine protein levels by enzyme-linked immunosorbent assay.

RESULTS

Twenty-nine subjects were enrolled in the study. All subjects were infected as evidenced by viral shedding and/or seroconversion. Sixteen subjects were symptomatic and 13 were asymptomatic as evaluated by subject self-report. During infection, significant increases in mean levels of nasal interleukin 6 (IL-6) (P = .01) and IL-1 (P = .02) were observed in symptomatic but not asymptomatic subjects. In symptomatic subjects, these increases were temporally related to the development of nasal symptoms and production of secretions. Mean levels of IL-8, IL-10, and tumor necrosis factor a were not increased in either group during infection.

CONCLUSIONS

The results of this study demonstrate elevations in certain locally produced cytokines during symptomatic but not asymptomatic respiratory infection with RV-39. Future studies using selected anticytokine therapies may help elucidate the precise role of cytokines in mediating disease expression.

TA-270 [4-hydroxy-1-methyl-3-octyloxy-7-sinapinoylamino-2(1H)-quinolinone], an anti-asthmatic agent, inhibits leukotriene production induced by IgE receptor stimulation in RBL-2H3 cells

A novel quinolinone derivative, TA-270 [4-hydroxy-1-methyl-3-octyloxy-7-sinapinoylamino-2(1H)-quinolinone], has been shown to inhibit antigen-induced asthmatic responses including the early-phase bronchoconstriction in actively sensitized guinea pigs. Here we characterized the action mechanisms of TA-270 in cellular level in vitro. In RBL-2H3 mast cells sensitized with dinitrophenol (DNP)-specific IgE, the antigen exhibited several mast cell functions, including hexosaminidase release as a marker of degranulation, production of tumor necrosis factor-alpha, and production of immunologically detective leukotrienes. These antigen-induced actions were associated with the activation of several early signaling events, including inositol phosphate production reflecting phospholipase C activation and extracellular signal-regulated kinase activation. When the cells were treated with TA-270, the antigen-induced leukotriene production was almost completely suppressed, but other antigen-induced actions listed above were hardly affected. This drug also failed to affect the antigen-induced phospholipase A2 activation as evaluated by the total release of arachidonic acid and its metabolites from the cells prelabeled with radioactive arachidonic acid. However, TA-270 clearly changed the arachidonic acid metabolic pathway. It suppressed the accumulation of 5-lipoxygenase products, including leukotrienes, but hardly affected the accumulation of cyclooxygenase products. The inhibitory action of TA-270 on leukotriene production was also observed in human neutrophils and eosinophils. We conclude that TA-270 inhibits 5-lipoxygenase activity and, thereby, suppresses the antigen-induced leukotriene production.

Pranlukast: a review of its use in the management of asthma

Pranlukast (Onon, Azlaire), is an orally administered, selective, competitive antagonist of the cysteinyl leukotrienes (LT) C(4), LTD(4) and LTE(4). It is indicated for the prophylactic treatment of chronic bronchial asthma in paediatric and adult patients. The efficacy of pranlukast 225mg twice daily in adults with mild to moderate asthma was demonstrated in double-blind, placebo- or azelastine-controlled studies of 4 or 8 weeks' duration. The drug at this dosage was superior to both comparators in improving mean attack scores and morning and/or evening peak expiratory flow rates, and decreasing the use of rescue bronchodilators (p < 0.05). In limited clinical studies, pranlukast 225mg twice daily appeared to be as effective as montelukast 10mg once daily and zafirlukast 40mg twice daily in adults with mild to moderate asthma. Tachyphylaxis was absent when the drug was administered for up to 4 years. In patients requiring high-dose inhaled corticosteroid therapy, pranlukast 225 mg twice daily plus a halved dosage of inhaled corticosteroid was as effective as the original dosage of inhaled corticosteroid. Pranlukast was also effective in patients with mild to severe asthma in a clinical practice setting. In a double-blind trial, greater improvements in most outcome measures were observed with pranlukast than with oxatomide in children and adolescents with asthma. In clinical trials, pranlukast was well tolerated in adult and paediatric patients with asthma, with an adverse event profile similar to that of placebo. Gastrointestinal events and hepatic function abnormalities were the most commonly reported adverse events. No clinically significant differences in adverse event profiles between pranlukast, zafirlukast or montelukast were shown in limited comparisons. Although Churg-Strauss syndrome has been noted in pranlukast recipients, a direct causal relationship is unlikely.

CONCLUSIONS

Pranlukast is a well tolerated and effective preventative treatment in adult and paediatric patients with persistent asthma of all severities. In some patients, pranlukast may be beneficial when added to low-dose inhaled corticosteroids; it may also be a viable alternative to increasing inhaled corticosteroid dosages. The efficacy of pranlukast relative to placebo has been confirmed; its efficacy relative to other therapy awaits further investigation. Nonetheless, pranlukast is a useful therapeutic option (with as-required short-acting beta(2)-agonists), either as preventative monotherapy for the treatment of mild persistent asthma or in conjunction with inhaled corticosteroids in the management of moderate or severe persistent asthma.

Cysteinyl leukotrienes induce nuclear factor kappa b activation and RANTES production in a murine model of asthma

BACKGROUND

It has been demonstrated that both cysteinyl leukotrienes (cysLTs) and cytokines are involved in the pathophysiology of bronchial asthma. Nonetheless, the exact mechanism involved in the interaction between these 2 molecules has yet to be determined.

OBJECTIVE

The aim of the present study was to determine the effects of cysLTs on allergic airway inflammation and allergen-specific cytokine production in a murine model of asthma.

METHODS

Four groups of BALB/c mice (control mice, Dermatophagoides farinae allergen-sensitized mice, pranlukast cysLT receptor antagonist-treated allergen-sensitized mice, and dexamethasone-treated allergen-sensitized mice) were examined.

RESULTS

Allergen-sensitized mice exhibited increased airway responsiveness and inflammation. Pranlukast-treated mice showed significant attenuation of these changes concomitant with reduction of T(H)2 cytokine and IFN-gamma production by isolated lung mononuclear cells (MNCs). A much stronger inhibition of all cytokines was noted in dexamethasone-treated mice. Pranlukast also significantly inhibited production of RANTES and activation of nuclear factor kappa B (NF-kappa B) in the isolated lung MNCs. Leukotriene D(4) stimulated isolated lung MNCs to produce RANTES but not any other cytokines and also activated NF-kappa B in these cells.

CONCLUSIONS

Our results suggest that cysLTs activate NF-kappa B and induce RANTES production from isolated lung MNCs, which in turn might cause migration of eosinophils and activated T lymphocytes into the airway.

Up-regulation of cysteinyl leukotriene 1 receptor by IL-13 enables human lung fibroblasts to respond to leukotriene C4 and produce eotaxin

Cysteinyl leukotrienes (CysLTs) play an important role in eosinophilic airway inflammation. In addition to their direct chemotactic effects on eosinophils, indirect effects have been reported. Eotaxin is a potent eosinophil-specific chemotactic factor produced mainly by fibroblasts. We investigated whether CysLTs augment eosinophilic inflammation via eotaxin production by fibroblasts. Leukotriene (LT)C(4) alone had no effect on eotaxin production by human fetal lung fibroblasts (HFL-1). However, LTC(4) stimulated eotaxin production by IL-13-treated fibroblasts, thereby indirectly inducing eosinophil sequestration. Unstimulated fibroblasts did not respond to LTC(4), but coincubation or preincubation of fibroblasts with IL-13 altered the response to LTC(4). To examine the mechanism(s) involved, the expression of CysLT1R in HFL-1 was investigated by quantitative real-time PCR and flow cytometry. Only low levels of CysLT1R mRNA and no CysLT1R protein were expressed in unstimulated HFL-1. In contrast, stimulation with IL-13 at a concentration of 10 ng/ml for 24 h significantly up-regulated both CysLT1R mRNA and protein expression in HFL-1. The synergistic effect of LTC(4) and IL-13 on eotaxin production was abolished by CysLT1R antagonists pranlukast and montelukast. These findings suggest that IL-13 up-regulates CysLT1R expression, which may contribute to the synergistic effect of LTC(4) and IL-13 on eotaxin production by lung fibroblasts. In the Th2 cytokine-rich milieu, such as that in bronchial asthma, CysLT1R expression on fibroblasts might be up-regulated, thereby allowing CysLTs to act effectively and increase eosinophilic inflammation.

The role of chemical mediators in eosinophil infiltration in allergic rhinitis in mice

The involvement of chemical mediators other than histamine in eosinophil infiltration in the nasal mucosa was studied using histamine H(1) receptor-deficient mice. Histamine H(1) receptor-deficient mice and wild-type controls were immunized with ovalbumin and consecutive topical antigen instillation was performed. Histological alterations and eosinophil infiltration into the nasal mucosa of mice were examined. Diffuse infiltration of inflammatory cells and edema after sensitization with antigen were observed in the nasal mucosa in both wild-type and histamine H(1) receptor-deficient mice. The number of eosinophils in the nasal mucosa in mice sensitized with antigen was significantly increased as compared with controls. The number of eosinophils in the nasal mucosa was significantly decreased by cetirizine and epinastine, ramatroban and zafirlukast in wild-type mice. Not only histamine but also thromboxane A(2) and leukotrienes play important roles in allergic rhinitis, especially in the late phase participating in nasal eosinophilia.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

Extending the understanding of leukotrienes in asthma

PURPOSE OF REVIEW

Leukotriene modifiers have recognized utility in the management of asthma. The aim of this review is to put into context recent research findings that extend our understanding of cysteinyl leukotriene synthesis and actions in the pathogenesis of asthma and allergic disease.

RECENT FINDINGS

Previous literature has shown that T helper type 2 cytokines thought to favor asthma and allergic diseases upregulate leukotriene synthesis. Recent findings show that interleukins-4 and -13 also upregulate cysteinyl leukotriene 1 receptor expression. Conversely, the regulation of cytokine expression by leukotrienes has also been explored: cysteinyl leukotrienes upregulate type 2 cytokine expression and decrease type 1 cytokine expression, favoring an allergic phenotype. Genetic determinants of the expression of leukotriene-forming enzymes include polymorphisms of the 5-lipoxygenase and LTC(4) synthase promoters. Novel actions of leukotrienes continue to be recognized, and a role for leukotrienes in the development of airway remodeling accompanying chronic asthma is discussed. Mounting evidence implicates leukotrienes in the pathogenesis of asthma following viral infections. Finally, advances in the measurement of leukotrienes are reviewed.

SUMMARY

Leukotrienes and their receptors play an important role in the pathogenesis of asthma. Advances in our understanding of the synthesis and actions of these lipid mediators provide the scientific rationale for appropriate utilization of leukotriene modifiers and for envisioning novel leukotriene-based therapeutic approaches in the clinical management of asthma.

Cysteinyl leukotriene expression in chronic hyperplastic sinusitis-nasal polyposis: importance to eosinophilia and asthma

BACKGROUND

Chronic hyperplastic eosinophilic sinusitis (CHS) results from the unregulated proliferation of eosinophils, T(H)2-like lymphocytes, goblet cells, mast cells, and fibroblasts and is present in most patients with asthma. The frequent coexpression of these disorders and their shared pathophysiology suggests that these are similar disorders affecting the upper and lower airways.

OBJECTIVE

We evaluated the expression of cysteinyl leukotrienes (CysLTs) in sinus tissue from subjects with CHS compared with that seen in healthy sinus tissue.

METHODS

Nasal polyp and sinus tissue was evaluated from 58 individuals undergoing elective functional endoscopic sinus surgery. The diagnosis of CHS was demonstrated through the presence of eosinophilia and activated (EG2(+)) eosinophils, as determined by means of tissue immunohistochemistry. Data were compared with those from both nasal polyp tissue without eosinophilic inflammation and healthy control sinus tissue obtained from the sinus ostiomeatal complex at the time of surgery for unrelated disorders. CysLTs were quantified by means of ELISA in lipid-extracted tissue. Activation of the metabolic pathway leading to CysLT synthesis was demonstrated by ribonuclease protection. Subjects were genotyped for leukotriene C(4) (LTC(4)) synthase C-to-A promoter polymorphism.

RESULTS

CysLT concentrations were significantly higher in tissue obtained from subjects with CHS (776.7 +/- 201.9 pg/g tissue) compared with that seen in healthy sinus tissue (355.7 +/- 101.6 pg/g tissue, P <.03). CysLT concentrations within noneosinophilic nasal polyps (328.0 +/- 116.4 pg/g tissue) were similar to those in control tissue. The presence of CysLTs in CHS was associated with increased expression of LTC(4) synthase mRNA. The C-to-A promoter polymorphism was associated with trends toward the increased presence of CHS and CysLTs.

CONCLUSIONS

CHS is characterized by the increased presence of CysLTs when compared with concentrations seen in tissue from patients with chronic inflammatory sinusitis or healthy sinus tissue. These studies support the use of LT modifiers as anti-inflammatory agents that might have clinical benefit in patients with these disorders.

Inflammatory cells in asthma: mechanisms and implications for therapy

Recent clinical studies have brought asthma's complex inflammatory processes into clearer focus, and understanding them can help to delineate therapeutic implications. Asthma is a chronic airway inflammatory disease characterized by the infiltration of airway T cells, CD(+) (T helper) cells, mast cells, basophils, macrophages, and eosinophils. The cysteinyl leukotrienes also are important mediators in asthma and modulators of cytokine function, and they have been implicated in the pathophysiology of asthma through multiple mechanisms. Although the role of eosinophils in asthma and their contribution to bronchial hyperresponsiveness are still debated, it is widely accepted that their numbers and activation status are increased. Eosinophils may be targets for various pharmacologic activities of leukotriene receptor antagonists through their ability to downregulate a number of events that may be key to the effector function of these cells.

Cysteinyl leukotriene interactions with other mediators and with glucocorticosteroids during airway inflammation

Unexpected aspects of the antiasthmatic efficacy of leukotriene modifiers and glucocorticosteroids have been observed. For both classes, the observed effects may be partially explainable on the basis of underrecognized interactions involving leukotrienes. This review examines the interactions between leukotrienes and other mediators of asthma. It details the effects of glucocorticosteroids on leukotriene synthesis and on leukocyte populations in asthmatic airways. Unexpected controller effects of the leukotriene modifiers may reflect the fact that leukotrienes and other mediators of asthma, such as T(H)2 cytokines, positively influence each other's generation. The ability of the leukotriene modifiers to disrupt such extensive interactions means that other relevant mediators are targeted indirectly by leukotriene blockade. Among asthma therapies, the glucocorticosteroids have numerous anti-inflammatory activities, but their effects may be unpredictable. Many processes involved in inflammation appear to escape modulation by glucocorticosteroids, including leukotriene synthesis, and leukotriene generation is among them. Understanding whether glucocorticosteroids reduce cysteinyl leukotriene levels in the airway is important in determining the clinical value of combining glucocorticosteroid therapy with leukotriene modifier therapy.

Involvement of the cysteinyl-leukotrienes in allergen-induced airway eosinophilia and hyperresponsiveness in the mouse

The leukotriene modifiers are a novel generation of therapeutic agents in the treatment of allergic asthma. However, the mechanisms by which the cysteinyl (cys) leukotrienes (LTs) participate in allergen-induced airway eosinophilia and airway hyperresponsiveness (AHR) are still unclear. In the present study, we have investigated the role of cys-LTs in ovalbumin (OVA)-induced airway responses in a murine model of asthma. Montelukast (3 or 10 mg/kg), a selective cys-LT1 receptor antagonist, reduced airway eosinophilia and AHR after OVA challenge. The levels of interleukin (IL)-5 and eotaxin in the bronchoalveolar lavage fluid (BALF) from montelukast-treated (3 mg/kg) mice were unaffected, although a decrease in IL-5 was observed with a dose of 10 mg/kg. LTD4 (50 ng) instilled intranasally to immunized mice augmented macrophages in the BALF, but in conjunction with OVA challenge it caused BALF eosinophilia and neutrophilia when given before challenge and BALF neutrophilia but not eosinophilia when given 2 h after challenge. However, there were no increases of IL-5 or eotaxin in BALF following LTD4 treatment. Repeated instillations of LTD4 to immunized mice, mimicking allergen challenge, did not induce AHR but in conjunction with OVA challenge LTD4 enhanced AHR. These results indicate that allergen-induced eosinophilia and AHR are in part mediated by the cys-LT1 receptor, and that, although LTD4 alone has no effect on airway eosinophilia, in conjunction with antigenic stimulation it potentiates the degree of airway inflammation and AHR.

Leukotriene antagonism reduces the generation of endothelin-1 and interferon-gamma and inhibits eosinophilic airway inflammation

The cysteinyl leukotrienes (cysLTs) and the peptide hormone endothelin (ET)-1 are potent bronchoconstrictor substances, and these mediators are also claimed to be implicated in the development of eosinophilic airway inflammation. In the present study, we have investigated the effect of the cysLT1 receptor antagonist montelukaston the development of an eosinophilic airway inflammation 24 h after intratracheal Sephadex (SDX) provocation in rats. Furthermore, the effect of montelukast treatment on the generation of ET-1 and other pro-inflammatory mediators has been studied. The inflammatory response was significantly reduced in the animals receiving SDX + montelukast compared to animals receiving solely SDX, as evaluated by a decrease in bronchoalveolar lavage fluid total cell count (10.3 +/- 1.2 vs. 18.5 +/- 1.8 x 10(4) ml(-1), P<0.001), number of eosinophils (299.7 +/- 43.8 vs. 577.6 +/- 46.6 x 10(2) ml(-1), P<0.001), and lymphocytes (116.8 +/- 20 vs. 222.0 +/- 34.8 x 10(2) ml(-1), P<0.05), as well as the degree of tissue inflammation (P<0.05). Montelukast also inhibited the increase in the concentration of the pro-inflammatory mediators ET-1 (28.5 +/- 75 vs. 40.9 +/- 7.3 x pg ml(-1), P<0.05) and interferon (IFN)-gamma (4.3 +/- 2.2 vs. 15.6+/-8.7 x pg ml(-1), P<0.05), but not tumor necrosis factor-gamma or interleukin-8. In summary, treatment with the cysLT1 receptor antagonist montelukast reduced the inflammatory response during development of an eosinophilic airway inflammation, possibly by inhibiting the release of pro-inflammatory mediators like ET-1 and IFN-gamma.

Montelukast: a review of its therapeutic potential in asthma in children 2 to 14 years of age

Montelukast is a cysteinyl leukotriene receptor antagonist which is used as a preventive treatment for persistent asthma in patients > or =2 years of age. In children aged 6 to 14 years montelukast (5 mg/day) treatment resulted in a significant increase in FEV(1) (forced expiratory volume in 1 second, primary clinical outcome) during an 8-week randomized, double-blind trial. Moreover, significant improvements were observed for a range of secondary endpoints assessing symptoms, exacerbation rates, beta-agonist usage and quality of life. Concomitant administration of montelukast (5 mg/day) and inhaled budesonide (200 microg twice daily) resulted in a trend towards an increase in FEV(1) (p = 0.06, primary endpoint) and a statistically significant reduction in both as-needed beta(2)-agonist usage and the percentage of days with asthma exacerbations compared with budesonide plus placebo. No significant differences were observed in asthma-related quality of life between the two groups. During clinical trials both improvements in lung function and reductions in as-needed beta(2)-agonist usage were generally observed within 1 day after initiation of therapy in children 2 to 14 years of age with persistent asthma. Data from a randomized, nonblind trial in 6- to 11-year-old children and a 6-month extension to this trial suggest that both compliance to therapy and patient satisfaction are greater for montelukast than for either inhaled sodium cromoglycate or inhaled beclomethasone. In addition, patients and parents preferred oral montelukast over sodium cromoglycate. In 2- to 5-year-old children with persistent asthma, montelukast (4 mg/day) treatment resulted in significant improvements in a range of outcomes, such as as-needed beta(2)-agonist usage, symptom scores and percentage of days with asthma symptoms, as assessed during a randomized, double-blind trial primarily designed to assess tolerability. Data from small randomized, double-blind trials suggest that montelukast reduces exercise-induced bronchoconstriction in 6- to 14-year-old children. Montelukast is generally well tolerated. The frequency of adverse events in montelukast-treated children of all ages was comparable to that in patients receiving placebo.

CONCLUSION

Oral montelukast has shown efficacy as a preventive treatment for asthma during clinical trials in children aged 2 to 14 years. The drug offers benefits over more standard therapies such as inhaled sodium cromoglycate and nedocromil in terms of compliance and convenience. In addition, the drug offers significant benefits when added to inhaled corticosteroids (according to secondary endpoints). Montelukast offers an effective, well tolerated and convenient treatment option for children with asthma.

Anti-allergic therapies: effects on eosinophil progenitors

Marked eosinophilic infiltration is the typical inflammatory response associated with allergic inflammation. Previous research involving animal and human models has established a role for the eosinophil/basophil hematopoietic progenitor in a systemic process of allergic inflammation. In this article, we will review the evidence implicating eosinophil/basophil progenitors in this systemic response and will discuss the rationale for targeting this cell in the treatment of allergic disease. In this context, we discuss corticosteroid treatment of allergic diseases, such as asthma and its effects on hematopoietic mechanisms, the effects of therapies that inhibit the actions of cysteinyl leukotrienes, the effects of in vivo blockade of the eosinophil-active cytokine interleukin-5, and the effects of antihistamines on hematopoiesis. It is suggested that several anti-allergic therapies exert their beneficial effects on allergic inflammation by influencing eosinophil production systemically. Therefore, targeting the systemic hematopoietic response may provide additional, more beneficial, therapeutic effects.

Innate immune responses in viral encephalitis

The innate immune system is multifaceted, comprised of preformed factors, cells, and many proteins and lipid mediators produced by those cells. In the CNS these are critical in initiation and amplification of the inflammatory response and in the subsequent elicitation of the specific T cell response to viral encephalitis. Cells that are resident in brain parenchyma and peripheral cells that are recruited both play key roles in the hosts's responses. Unlike the peripheral compartments, in the CNS, non-cytolytic means of eliminating viral infections have been critical, since, in contrast to columnar epithelial cells, neurons are non-renewing. When the innate immune responses are inefficient or absent in viral encephalitis, pathology is more likely. Much more work remains to elucidate all of the critical cells and their mediators, as well as to develop new therapies for infections of the CNS.

Interleukin-2-induced increased airway responsiveness and lung Th2 cytokine expression occur after antigen challenge through the leukotriene pathway

Previous studies have shown that the allergic late airway response (LR) is dependent on the leukotriene (LT) pathway in Brown Norway (BN) rats. In this same model, interleukin-2 (IL-2) has been shown to increase allergic airway responses without increasing LT production. This study examined the relationship between the upregulation of cellular immunity with IL-2 and the LT pathway in ovalbumin-sensitized BN rats. Airway responsiveness to LTD(4) was significantly increased in BN rats pretreated with IL-2 (20,000 U twice a day for 4.5 days). Treatment with montelukast, a cysteinyl LT(1) receptor antagonist, blocked IL-2's induced increase of the LR to ovalbumin challenge. When cytokine expression was assessed either by semiquantitative polymerase chain reaction or in situ hybridization, we found that montelukast decreased the amount of IL-4 mRNA expression in the lungs while increasing the amount of interferon-gamma mRNA expression 8 hours after challenge. These results indicate that upregulation of cellular immunity with IL-2 can increase the sensitivity of the airways to LTD(4) and that inhibition of the LT pathway will block the LR and modulate cytokine expression after antigen challenge.