Effects of prostaglandin E2 and cAMP elevating drugs on GM-CSF release by cultured human airway smooth muscle cells. Relevance to asthma therapy

Myeloid derived suppressor cells in peripheral blood can be a prognostic factor in canine transitional cell carcinoma

Myeloid-derived suppressor cells (MDSCs) are immature cells with immunosuppressive properties found in the tumor microenvironment. MDSCs are divided into two major subsets: polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). Both MDSC subsets contribute to the creation of an immunosuppressive environment for tumor progression. In humans, patients with high levels of MDSCs show worse outcomes for several types of cancers. However, the association between MDSCs and clinical features has rarely been investigated in canine studies. In the present study, we measured the proportion of PMN-MDSCs and M-MDSCs in the peripheral blood and tumor tissue of dogs with hepatocellular carcinoma (HCC), prostate cancer (PC), transitional cell carcinoma (TCC), lymphoma, and pulmonary adenocarcinoma. Additionally, we examined immunosuppressive ability of PMN-MDSCs and M-MDSCs in peripheral blood mononuclear cells of TCC case on CD4+, CD8+ and interferon-γ+ cells and investigated the relationships of MDSCs with clinical features and outcomes. PMN-MDSCs increased in HCC, PC, TCC, and lymphoma. In contrast, M-MDSCs increased in the TCC. Both PMN-MDSCs and M-MDSCs exhibited immunosuppressive effects on CD8+, CD4+ and interferon-γ+ cells. In dogs with TCC, lymph node metastasis was associated with high level of PMN-MDSCs but not with M-MDSCs. High levels of both PMN-MDSCs and M-MDSCs were related to advanced tumor stage. Kaplan-Meier analysis revealed that high levels of both PMN-MDSCs and M-MDSCs were significantly associated with shorter overall survival. In addition, the Cox proportional hazard regression model showed that M-MDSCs and the tumor stage were independent prognostic factors for TCC. These results suggest that PMN-MDSCs and M-MDSCs may be involved in tumor progression and could be prognostic factors and promising therapeutic targets in dogs with TCC.

Prorelaxant E-type Prostanoid Receptors Functionally Partition to Different Procontractile Receptors in Airway Smooth Muscle

Prostaglandin E2 imparts diverse physiological effects on multiple airway cells through its actions on four distinct E-type prostanoid (EP) receptor subtypes (EP1-EP4). Gs-coupled EP2 and EP4 receptors are expressed on airway smooth muscle (ASM), yet their capacity to regulate the ASM contractile state remains subject to debate. We used EP2 and EP4 subtype-specific agonists (ONO-259 and ONO-329, respectively) in cell- and tissue-based models of human ASM contraction-magnetic twisting cytometry (MTC), and precision-cut lung slices (PCLSs), respectively-to study the EP2 and EP4 regulation of ASM contraction and signaling under conditions of histamine or methacholine (MCh) stimulation. ONO-329 was superior (<0.05) to ONO-259 in relaxing MCh-contracted PCLSs (log half maximal effective concentration [logEC50]: 4.9 × 10-7 vs. 2.2 × 10-6; maximal bronchodilation ± SE, 35 ± 2% vs. 15 ± 2%). However, ONO-259 and ONO-329 were similarly efficacious in relaxing histamine-contracted PCLSs. Similar differential effects were observed in MTC studies. Signaling analyses revealed only modest differences in ONO-329- and ONO-259-induced phosphorylation of the protein kinase A substrates VASP and HSP20, with concomitant stimulation with MCh or histamine. Conversely, ONO-259 failed to inhibit MCh-induced phosphorylation of the regulatory myosin light chain (pMLC20) and the F-actin/G-actin ratio (F/G-actin ratio) while effectively inhibiting their induction by histamine. ONO-329 was effective in reversing induced pMLC20 and the F/G-actin ratio with both MCh and histamine. Thus, the contractile-agonist-dependent differential effects are not explained by changes in the global levels of phosphorylated protein kinase A substrates but are reflected in the regulation of pMLC20 (cross-bridge cycling) and F/G-actin ratio (actin cytoskeleton integrity, force transmission), implicating a role for compartmentalized signaling involving muscarinic, histamine, and EP receptor subtypes.

Involvement of the Innate Immune System in the Pathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common, socially significant disease characterized by progressive airflow limitation due to chronic inflammation in the bronchi. Although the causes of COPD are considered to be known, the pathogenesis of the disease continues to be a relevant topic of study. Mechanisms of the innate immune system are involved in various links in the pathogenesis of COPD, leading to persistence of chronic inflammation in the bronchi, their bacterial colonization and disruption of lung structure and function. Bronchial epithelial cells, neutrophils, macrophages and other cells are involved in the development and progression of the disease, demonstrating multiple compromised immune mechanisms.

Can GPCRs Be Targeted to Control Inflammation in Asthma?

Historically, the drugs used to manage obstructive lung diseases (OLDs), asthma, and chronic obstructive pulmonary disease (COPD) either (1) directly regulate airway contraction by blocking or relaxing airway smooth muscle (ASM) contraction or (2) indirectly regulate ASM contraction by inhibiting the principal cause of ASM contraction/bronchoconstriction and airway inflammation. To date, these tasks have been respectively assigned to two diverse drug types: agonists/antagonists of G protein-coupled receptors (GPCRs) and inhaled or systemic steroids. These two types of drugs "stay in their lane" with respect to their actions and consequently require the addition of the other drug to effectively manage both inflammation and bronchoconstriction in OLDs. Indeed, it has been speculated that safety issues historically associated with beta-agonist use (beta-agonists activate the beta-2-adrenoceptor (β₂AR) on airway smooth muscle (ASM) to provide bronchoprotection/bronchorelaxation) are a function of pro-inflammatory actions of β₂AR agonism. Recently, however, previously unappreciated roles of various GPCRs on ASM contractility and on airway inflammation have been elucidated, raising the possibility that novel GPCR ligands targeting these GPCRs can be developed as anti-inflammatory therapeutics. Moreover, we now know that many GPCRs can be "tuned" and not just turned "off" or "on" to specifically activate the beneficial therapeutic signaling a receptor can transduce while avoiding detrimental signaling. Thus, the fledging field of biased agonism pharmacology has the potential to turn the β₂AR into an anti-inflammatory facilitator in asthma, possibly reducing or eliminating the need for steroids.

The Biology of Prostaglandins and Their Role as a Target for Allergic Airway Disease Therapy

Prostaglandins (PGs) are a family of lipid compounds that are derived from arachidonic acid via the cyclooxygenase pathway, and consist of PGD₂, PGI₂, PGE₂, PGF₂, and thromboxane B₂. PGs signal through G-protein coupled receptors, and individual PGs affect allergic inflammation through different mechanisms according to the receptors with which they are associated. In this review article, we have focused on the metabolism of the cyclooxygenase pathway, and the distinct biological effect of each PG type on various cell types involved in allergic airway diseases, including asthma, allergic rhinitis, nasal polyposis, and aspirin-exacerbated respiratory disease.

Cooperativity of E-prostanoid receptor subtypes in regulating signaling and growth inhibition in human airway smooth muscle

Prostaglandin E2 (PGE₂) is produced in the airway during allergic lung inflammation and both promotes and inhibits features of asthma pathology. These mixed effects relate to 4 E-prostanoid (EP) receptor subtypes (EP1, 2, 3 and 4) expressed at different levels on different resident and infiltrating airway cells. Although studies have asserted both EP2 and EP4 expression in human airway smooth muscle (HASM), a recent study asserted EP4 to be the functionally dominant EP subtype in HASM. Herein, we employ recently-developed subtype-selective ligands to investigate singular or combined EP2 and EP4 receptor activation in regulating HASM signaling and proliferation. The subtype specificity of ONO-AE1-259-01 (EP2 agonist) and ONO-AE1-329 (EP4 agonist) was first demonstrated in human embryonic kidney 293 cells stably expressing different EP receptor subtypes. EP receptor knockdown and subtype-selective antagonists demonstrated EP2 and EP4 receptor responsiveness in HASM cells to the specific ONO compounds, whereas PGE₂ appeared to preferentially signal via the EP4 receptor. Both singular EP2 and EP4 receptor agonists inhibited HASM proliferation, and combined EP2 and EP4 receptor agonism exhibited positive cooperativity in both chronic G_s-mediated signaling and inhibiting HASM proliferation. These findings suggest both EP2 and EP4 are functionally important in HASM, and their combined targeting optimally inhibits airway smooth muscle proliferation.-Michael, J. V. Gavrila, A., Nayak, A. P., Pera, T., Liberato, J. R., Polischak, S. R., Shah, S. D., Deshpande, D. A., Penn, R. B. Cooperativity of E-prostanoid receptor subtypes in regulating signaling and growth inhibition in human airway smooth muscle.

Prostaglandins in asthma and allergic diseases

Prostaglandins are synthesized through the metabolism of arachidonic acid via the cyclooxygenase pathway. There are five primary prostaglandins, PGD₂, PGE₂, PGF₂, PGI₂, and thromboxane B₂, that all signal through distinct seven transmembrane, G-protein coupled receptors. The receptors through which the prostaglandins signal determines their immunologic or physiologic effects. For instance, the same prostaglandin may have opposing properties, dependent upon the signaling pathways activated. In this article, we will detail how inhibition of cyclooxygenase metabolism and regulation of prostaglandin signaling regulates allergic airway inflammation and asthma physiology. Possible prostaglandin therapeutic targets for allergic lung inflammation and asthma will also be reviewed, as informed by human studies, basic science, and animal models.

The potential role of phosphodiesterase inhibitors in the management of asthma

Asthma is a chronic inflammatory condition characterised by reversible airflow obstruction and airway hyperreactivity. The course of the illness may be punctuated by exacerbations resulting in deterioration in quality of life and, in some cases, days lost from school or work. That asthma is common and increasingly prevalent magnifies the importance of any potential economic costs, and promoting asthma control represents an important public health agenda. While lifestyle changes represent a valuable contribution in some patients, the majority of asthmatic patients require therapeutic intervention. The recognition of the role of inflammation in the pathogenesis of asthma has led to an emphasis on regular anti-inflammatory therapy, of which inhaled corticosteroid treatment remains the most superior. In selected patients, further improvements in asthma control may be gained by the addition of regular inhaled long-acting beta(2)-adrenoceptor agonists or oral leukotriene receptor antagonists to inhaled corticosteroid therapy. However, a significant minority of patients with asthma remain poorly controlled despite appropriate treatment, suggesting that additional corticosteroid nonresponsive inflammatory pathways may be operative. Furthermore, some patients with asthma display an accelerated decline in lung function, suggesting that active airway re-modeling is occurring. Such observations have focused attention on the potential to develop new therapies which complement existing treatments by targeting additional inflammatory pathways. The central role of phosphodiesterase (PDE), and in particular the PDE4 enzyme, in the regulation of key inflammatory cells believed to be important in asthma - including eosinophils, lymphocytes, neutrophils and airway smooth muscle - suggests that drugs designed to target this enzyme will have the potential to deliver both bronchodilation and modulate the asthmatic inflammatory response. In vivo studies on individual inflammatory cells suggest that the effects are likely to be favorable in asthma, and animal study models have provided proof of concept; however, first-generation PDE inhibitors have been poorly tolerated due to adverse effects. The development of second-generation agents such as cilomilast and roflumilast heralds a further opportunity to test the potential of these agents, although to date only a limited amount of data from human studies has been published, making it difficult to draw firm conclusions.

Prostaglandin E2 induces expression of MAPK phosphatase 1 (MKP-1) in airway smooth muscle cells

Prostaglandin E2 (PGE2) is a prostanoid with diverse actions in health and disease. In chronic respiratory diseases driven by inflammation, PGE2 has both positive and negative effects. An enhanced understanding of the receptor-mediated cellular signalling pathways induced by PGE2 may help us separate the beneficial properties from unwanted actions of this important prostaglandin. PGE2 is known to exert anti-inflammatory and bronchoprotective actions in human airways. To date however, whether PGE2 increases production of the anti-inflammatory protein MAPK phosphatase 1 (MKP-1) was unknown. We address this herein and use primary cultures of human airway smooth muscle (ASM) cells to show that PGE2 increases MKP-1 mRNA and protein upregulation in a concentration-dependent manner. We explore the signalling pathways responsible and show that PGE2-induces CREB phosphorylation, not p38 MAPK activation, in ASM cells. Moreover, we utilize selective antagonists of EP2 (PF-04418948) and EP4 receptors (GW 627368X) to begin to identify EP-mediated functional outcomes in ASM cells in vitro. Taken together with earlier studies, our data suggest that PGE2 increases production of the anti-inflammatory protein MKP-1 via cAMP/CREB-mediated cellular signalling in ASM cells and demonstrates that EP2 may, in part, be involved.

Stimulatory effect of fibroblast-derived prostaglandin E₂ on keratinocyte stratification in the skin equivalent

Epidermal-dermal interaction plays important roles in physiological events such as wound healing. In this study, we examined a double paracrine mechanism between keratinocytes and fibroblasts through interleukin-1 (IL-1) and an IL-1-induced inflammatory mediator prostaglandin E₂ (PGE₂) using the skin equivalent. The epidermal layer of the skin equivalent expressed high levels of IL-1α mRNA (IL1A mRNA) and relatively low levels of IL-1β mRNA (IL1B mRNA). IL1A mRNA was not detected in fibroblasts. Fibroblasts also expressed low but not negligible levels of IL1B mRNA only in the presence of keratinocytes. Expression of prostaglandin-endoperoxide synthase 2 mRNA (PTGS2 mRNA) and production of PGE₂ in three-dimensionally cultured fibroblasts were noticeably stimulated by co-culture with keratinocytes, whereas PTGS2 mRNA expression in the epidermal layer was very low. In addition, hydroxyprostaglandin dehydrogenase 15-(NAD) mRNA was highly expressed in keratinocytes but not in fibroblasts, and exogenous IL-1β stimulated PTGS2 mRNA expression in the dermal equivalent. The thickness of the epidermal layer and the number of MKI67-positive keratinocytes in the skin equivalent were decreased by treatment with indomethacin, and the decrease recovered when exogenous PGE₂ was added. These results indicate that keratinocytes stimulate their own proliferation through a double paracrine mechanism mediated by IL-1 and PGE₂.

The role of prostaglandins in allergic lung inflammation and asthma

Prostaglandins (PGs) are products of the COX pathway of arachidonic acid metabolism. There are five primary PGs, PGD₂, PGE₂, PGF₂, PGI₂ and thromboxane A₂, all of which signal through distinct seven transmembrane, G-protein coupled receptors. Some PGs may counteract the actions of others, or even the same PG may have opposing physiologic or immunologic effects, depending on the specific receptor through which it signals. In this review, we examine the effects of COX activity and the various PGs on allergic airway inflammation and physiology that is associated with asthma. We also highlight the potential therapeutic benefit of targeting PGs in allergic lung inflammation and asthma based on basic science, animal model and human studies.

Crosstalk between beta-2-adrenoceptor and muscarinic acetylcholine receptors in the airway

The M3 and M2 muscarinic acetylcholine receptors (mAChRs) and beta-2-adrenoceptors (β2ARs) are important regulators of airway cell function, and drugs targeting these receptors are among the first line drugs in the treatment of the obstructive lung diseases asthma and chronic obstructive lung disease (COPD). Cross-regulation or crosstalk between mAChRs and β2ARs in airway smooth muscle (ASM) helps determine the contractile state of the muscle, thus airway diameter and resistance to airflow. In this review we will detail mAChR and β2AR-signaling and crosstalk, focusing on events in the ASM cell but also addressing the function of these receptors in other cell types that impact airway physiology. We conclude by discussing how recent advances in GPCR pharmacology offer a unique opportunity to fine tune mAChR and β2AR signaling and their crosstalk, and thereby produce superior therapeutics for obstructive lung and other diseases.

cAMP regulation of airway smooth muscle function

Agonists activating β(2)-adrenoceptors (β(2)ARs) on airway smooth muscle (ASM) are the drug of choice for rescue from acute bronchoconstriction in patients with both asthma and chronic obstructive pulmonary disease (COPD). Moreover, the use of long-acting β-agonists combined with inhaled corticosteroids constitutes an important maintenance therapy for these diseases. β-Agonists are effective bronchodilators due primarily to their ability to antagonize ASM contraction. The presumed cellular mechanism of action involves the generation of intracellular cAMP, which in turn can activate the effector molecules cAMP-dependent protein kinase (PKA) and Epac. Other agents such as prostaglandin E(2) and phosphodiesterase inhibitors that also increase intracellular cAMP levels in ASM, can also antagonize ASM contraction, and inhibit other ASM functions including proliferation and migration. Therefore, β(2)ARs and cAMP are key players in combating the pathophysiology of airway narrowing and remodeling. However, limitations of β-agonist therapy due to drug tachyphylaxis related to β(2)AR desensitization, and recent findings regarding the manner in which β(2)ARs and cAMP signal, have raised new and interesting questions about these well-studied molecules. In this review we discuss current concepts regarding β(2)ARs and cAMP in the regulation of ASM cell functions and their therapeutic roles in asthma and COPD.

PPARγ Ligands Regulate Noncontractile and Contractile Functions of Airway Smooth Muscle: Implications for Asthma Therapy

In asthma, the increase in airway smooth muscle (ASM) can contribute to inflammation, airway wall remodeling and airway hyperresponsiveness (AHR). Targetting peroxisome proliferator-activated receptor γ (PPARγ), a receptor upregulated in ASM in asthmatic airways, may provide a novel approach to regulate these contributions. This review summarises experimental evidence that PPARγ ligands, such as rosiglitazone (RGZ) and pioglitazone (PGZ), inhibit proliferation and inflammatory cytokine production from ASM in vitro. In addition, inhaled administration of these ligands reduces inflammatory cell infiltration and airway remodelling in mouse models of allergen-induced airways disease. PPARγ ligands can also regulate ASM contractility, with acute treatment eliciting relaxation of mouse trachea in vitro through a PPARγ-independent mechanism. Chronic treatment can protect against the loss of bronchodilator sensitivity to β₂-adrenoceptor agonists and inhibit the development of AHR associated with exposure to nicotine in utero or following allergen challenge. Of particular interest, a small clinical trial has shown that oral RGZ treatment improves lung function in smokers with asthma, a group that is generally unresponsive to conventional steroid treatment. These combined findings support further investigation of the potential for PPARγ agonists to target the noncontractile and contractile functions of ASM to improve outcomes for patients with poorly controlled asthma.

Airway smooth muscle in asthma: just a target for bronchodilation?

Airway smooth muscle (ASM) has long been recognized as the main cell type responsible for bronchial hyperresponsiveness. It has, thus, been considered as a target for bronchodilation. In asthma, however, there is a complex relationship between ASM and inflammatory cells, such as mast cells and T lymphocytes. Moreover, the increased ASM mass in asthmatic airways is one of the key features of airway remodeling. This article aims to review the main concepts about the 3 possible roles of ASM in asthma: (1) contractile tone, (2) inflammatory response, and (3) remodeling.

COX inhibitors for airway inflammation

INTRODUCTION

The cyclooxygenase (COX) enzyme, which is responsible for the production of prostaglandins (PGs), key mediators of inflammation, may have the potential to become an attractive target for anti-inflammatory therapy. COX catalyzes the conversion of arachidonic acid (AA) into PGs, which play a significant role in disease. PGs are lipid mediators of central importance in the regulation of inflammation and smooth muscle tone. Airway-resident inflammatory cells release PGs: PGD2 and PDF2a amplify smooth muscle contraction and airway inflammation. Following its conversion from membrane phospholipids by phospholipase, AA enters the prostanoid pathway via COX, which catalyzes the conversion of AA to PGH2. PGH2 is then converted to biologically active PGs by cell-specific PG synthases. As COX is the rate limiting step in the PG pathway, the regulation of this enzyme is of critical importance in PG production.

AREAS COVERED

This review addresses the opportunities and challenges of COX inhibitors as therapeutic targets in airway inflammation. The review covers literature from the past 20 years.

EXPERT OPINION

Current literature favors COX inhibitors as potential targets for airway diseases. However, from the information available, it is not clear whether the COX enzyme by itself can serve as a target in drug development for asthma and COPD. Therefore, additional research is required to elucidate the mechanisms of action of COX metabolites before it can be considered as a target.

N-Benzyl-4-hy-droxy-2-methyl-1,1-dioxo-2H-1λ(6),2-benzothia-zine-3-carboxamide

In the title mol-ecule, C(17)H(16)N(2)O(4)S, the heterocyclic thia-zine ring adopts a half-chair conformation, with the S and N atoms displaced by 0.546 (4) and 0.281 (4) Å, respectively, on opposite sides of the mean plane formed by the remaining ring atoms. The mol-ecular structure is stabilized by an intra-molecular O-H⋯O hydrogen bond. The two aromatic rings are inclined to one another by 42.32 (11)°. In the crystal, mol-ecules are linked by pairs of N-H⋯O hydrogen bonds, forming inversion dimers. The dimers are linked via a series of C-H⋯O inter-actions, leading to the formation of a three-dimensional network.

Noncontractile functions of airway smooth muscle cells in asthma

Although pivotal in regulating bronchomotor tone in asthma, airway smooth muscle (ASM) also modulates airway inflammation and undergoes hypertrophy and hyperplasia, contributing to airway remodeling in asthma. ASM myocytes secrete or express a wide array of immunomodulatory mediators in response to extracellular stimuli, and in chronic severe asthma, increases in ASM mass may render the airway irreversibly obstructed. Although the mechanisms by which ASM secretes cytokines and chemokines are the same as those regulating immune cells, there exist unique ASM signaling pathways that may provide novel therapeutic targets. This review provides an overview of our current understanding of the proliferative as well as the synthetic properties of ASM.

Lipid metabolites as regulators of airway smooth muscle function

Compelling evidence identifies airway smooth muscle (ASM) not only as a target but also a cellular source for a diverse range of mediators underlying the processes of airway narrowing and airway hyperresponsiveness in diseases such as asthma. These include the growing family of plasma membrane phospholipid-derived polyunsaturated fatty acids broadly characterised by the prostaglandins, leukotrienes, lipoxins, isoprostanes and lysophospholipids. In this review, we describe the enzymatic and non-enzymatic biosynthetic pathways of these lipid mediators and how these are influenced by drug treatment, oxidative stress and airways disease. Additionally, we outline their cognate receptors, many of which are expressed by ASM. We describe potential deleterious and protective roles for these lipid mediators in airway inflammatory and remodelling processes by describing their effects on diverse functions of ASM in asthma that have the potential to contribute to asthma pathogenesis and symptoms. These functions include contractile tone development, cytokine and extracellular matrix production, and cellular proliferation and migration.

Airway smooth muscle in asthma: phenotype plasticity and function

Clinical asthma is characterized by reversible airway obstruction which is commonly due to an exaggerated airway narrowing referred to as airway hyperresponsiveness (AHR). Although debate exists on the complex etiology of AHR, it is clear that airway smooth muscle (ASM) mediated airway narrowing is a major contributor to airway dysfunction. More importantly, it is now appreciated that smooth muscle is far from being a simple cell with only contractile ability properties. Rather, it is more versatile with the capacity to exhibit numerous cellular functions as it adapts to the microenvironment to which it is exposed. The emerging ability of individual smooth muscle cells to undergo changes in their phenotype (phenotype plasticity) and function (functional plasticity) in response to physiological and pathological cues is an important and active area of research. This article provides a brief review of the current knowledge and emerging concepts in the field of ASM phenotype and function both under healthy and asthmatic conditions.

Airway smooth muscle as an immunomodulatory cell

Although pivotal in regulating bronchomotor tone in asthma, airway smooth muscle (ASM) also modulates airway inflammation in asthma. ASM myocytes secrete or express a wide array of immunomodulatory mediators in response to extracellular stimuli, and in chronic severe asthma, increases in ASM mass may also render the airway irreversibly obstructed. Although the mechanisms by which ASM secretes cytokines and chemokines are shared with those regulating immune cells, there exist unique ASM signaling pathways that may provide novel therapeutic targets. This review provides an overview of our current understanding of the proliferative as well as synthetic properties of ASM.

Effect of beta2-adrenoceptor agonists and other cAMP-elevating agents on inflammatory gene expression in human ASM cells: a role for protein kinase A

In diseases such as asthma, airway smooth muscle (ASM) cells play a synthetic role by secreting inflammatory mediators such as granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-6, or IL-8 and by expressing surface adhesion molecules, including ICAM-1. In the present study, PGE(2), forskolin, and short-acting (salbutamol) and long-acting (salmeterol and formoterol) beta(2)-adrenoceptor agonists reduced the expression of ICAM-1 and the release of GM-CSF evoked by IL-1beta in ASM cells. IL-1beta-induced IL-8 release was also repressed by PGE(2) and forskolin, whereas the beta(2)-adrenoceptor agonists were ineffective. In each case, repression of these inflammatory indexes was prevented by adenoviral overexpression of PKIalpha, a highly selective PKA inhibitor. These data indicate a PKA-dependent mechanism of repression and suggest that agents that elevate intracellular cAMP, and thereby activate PKA, may have a widespread anti-inflammatory effect in ASM cells. Since ICAM-1 and GM-CSF are highly NF-kappaB-dependent genes, we used an adenoviral-delivered NF-kappaB-dependent luciferase reporter to examine the effects of forskolin and the beta(2)-adrenoceptor agonists on NF-kappaB activation. There was no effect on luciferase activity measured in the presence of forskolin or beta(2)-adrenoceptor agonists. This finding is consistent with the observation that IL-1beta-induced expression of IL-6, a known NF-kappaB-dependent gene in ASM, was also unaffected by beta(2)-adrenoceptor agonists, forskolin, PGE(2), 8-bromo-cAMP, or rolipram. Collectively, these results indicate that repression of IL-1beta-induced ICAM-1 expression and GM-CSF release by cAMP-elevating agents, including beta(2)-adrenoceptor agonists, may not occur through a generic effect on NF-kappaB.

Estrogen receptor beta: expression profile and possible anti-inflammatory role in disease

Estrogen receptor (ER) beta agonists have been demonstrated to possess anti-inflammatory properties in inflammatory disease models. The objective of this study was to determine whether ERbeta agonists affect in vitro and in vivo preclinical models of asthma. mRNA expression assays were validated in human and rodent tissue panels. These assays were then used to measure expression in human cells and our characterized rat model of allergic asthma. ERB-041 [7-ethenyl-2-(3-fluoro-4-hydroxyphenyl)-1,3-benzoxazol-5-ol], an ERbeta agonist, was profiled on cytokine release from interleukin-1beta-stimulated human airway smooth muscle (HASM) cells and in the rodent asthma model. Although ERbeta expression was demonstrated at the gene and protein level in HASM cells, the agonist failed to have an impact on the inflammatory response. Similarly, in vivo, we observed temporal modulation of ERbeta expression after antigen challenge. However, the agonist failed to have an impact on the model endpoints such as airway inflammation, even though plasma levels reflected linear compound exposure and was associated with an increase in receptor activation after drug administration. In these modeling systems of airway inflammation, an ERbeta agonist was ineffective. Although ERbeta agonists are anti-inflammatory in certain models, this novel study would suggest that they would not be clinically useful in the treatment of asthma.

Suppression of cytokine expression by roflumilast and dexamethasone in a model of chronic asthma

BACKGROUND

In a mouse model of mild chronic asthma, both inflammation and remodelling can be suppressed by dexamethasone (a glucocorticoid) and roflumilast (a selective phosphodiesterase-4 inhibitor).

OBJECTIVE

To better understand the underlying molecular mechanisms, we investigated the effects of treatment on airway expression of inflammation-related cytokines, as well as on epithelial expression of growth factors.

METHODS

BALB/c mice systemically sensitized to ovalbumin were challenged with aerosolized antigen for 6 weeks and treated with roflumilast or dexamethasone during the final 2 weeks. Expression of mRNA, for a variety of cytokines and growth factors, was assessed in selectively dissected proximal airways or in airway epithelium obtained by laser capture microdissection.

RESULTS

In the airway wall of vehicle-treated challenged animals, there was significantly elevated expression of mRNA for a variety of pro-inflammatory and T helper type 2 cytokines, as well as for IFN-gamma. All these cytokines were suppressed by dexamethasone. Treatment with roflumilast reduced expression of IL-17A, TNF-alpha, granulocyte-macrophage colony-stimulating factor and IL-6, but did not inhibit other cytokines. Both drugs suppressed the enhanced expression of mRNA for growth factors such as TGF-beta1 and FGF-2 in airway epithelium.

CONCLUSIONS

Whereas dexamethasone non-specifically inhibits numerous mediators involved in inflammation and the immune response, roflumilast selectively inhibits a subset of pro-inflammatory cytokines and growth factors. These mediators and/or the cells that produce them may have critical roles in the pathogenesis of the lesions of chronic asthma.

Airway smooth muscle as a regulator of immune responses and bronchomotor tone

The traditional view of airway smooth muscle (ASM) in asthma, as a purely contractile tissue, seems to be inadequate. Compelling evidence now suggests that ASM plays an important role in regulating bronchomotor tone, in perpetuating airway inflammation, and in remodeling of the airways. This article reviews three distinct functions of ASM cells: the process of excitation-contraction coupling, with a particular focus on the role of cytokines in modulating calcium responses; the processes of smooth muscle cell proliferation and migration; and the synthetic and immunomodulatory function of ASM cells. This article also discusses how altered synthetic function contributes to airway remodeling.

The broken balance in aspirin hypersensitivity

Aspirin was introduced into medicine over a century ago and has become the most popular drug in the world. Although the first hypersensitivity reaction was described soon after aspirin had been marketed, only recently a phenomenon of cysteinyl leukotriene overproduction brought new insights on a balance between pro- and anti-inflammatory mediators derived from arachidonic acid. We describe the most common clinical presentations of aspirin hypersensitivity, i.e. aspirin-induced asthma, rhinosinusitis and aspirin-induced urticaria. We also present their biochemical background. Despite relatively high incidence of these reactions, aspirin hypersensitivity remains underdiagnosed worldwide. Acute reactions of aspirin hypersensitivity are elicited via cyclooxygenase inhibition by non-steroid anti-inflammatory drugs. Coxibs, selective inhibitors of cyclooxygenase-2 isoenzyme, do not precipitate symptoms in susceptible patients. Though hypersensitivity correlates with cyclooxygenase-1 inhibition, diminished tissue expression was described only for cyclooxygenase-2. Aspirin-induced asthma and aspirin-induced urticaria, in a substantial part of the patients, are driven by a release of mediators from activated mast cells. These cells in physiological conditions are under inhibitory control of prostaglandin E2. The origin of aspirin hypersensitivity remains unknown, but accumulating data from genetic studies strongly suggest that environmental factor, possibly a common viral infection, can trigger the disease in susceptible subjects.

Phosphodiesterase inhibitors in airways disease

Phosphodiesterases hydrolyse intracellular cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) into inactive 5' monophosphates, and exist as 11 families. They are found in a variety of inflammatory and structural cells. Inhibitors of PDEs allow the elevation of cAMP and cGMP which lead to a variety of cellular effects including airway smooth muscle relaxation and inhibition of cellular inflammation or of immune responses. PDE4 inhibitors specifically prevent the hydrolysis of cAMP, and PDE4 isozymes are present in inflammatory cells. Selective PDE4 inhibitors have broad spectrum anti-inflammatory effects such as inhibition of cell trafficking, cytokine and chemokine release from inflammatory cells, such as neutrophils, eosinophils, macrophages and T cells. The second generation PDE4 inhibitors, cilomilast and roflumilast, have reached clinical trial stage and have some demonstrable beneficial effects in asthma and chronic obstructive pulmonary disease (COPD). The effectiveness of these PDE4 inhibitors may be limited by their clinical potency using doses that have minimal effects on nausea and vomiting. Topical administration of PDE4 inhibitors may provide a wider effective to side-effect profile. Development of inhibitors of other PDE classes, combined with PDE4 inhibition, may be another way forward. PDE5 is an inactivator of cGMP and may have beneficial effects on hypoxic pulmonary hypertension and vascular remodelling. PDE3 and PDE7 are other cAMP specific inactivators of cAMP. PDE7 is involved in T cell activation and a dual PDE4-PDE7 inhibitor may be more effective in asthma and COPD. A dual PDE3-PDE4 compound may provide more bronchodilator and bronchoprotective effect in addition to the beneficial PDE4 effects.

Evaluation of selective prostaglandin E2 (PGE2) receptor agonists as therapeutic agents for the treatment of asthma

Prostaglandin E2 (PGE2) released in asthmatic airways has bronchodilator properties and inhibits allergen-induced bronchoconstriction and release of inflammatory mediators. Although considered as a potential treatment for asthma, PGE2 also has some proinflammatory properties. PGE2 acts through four different receptor subtypes (EP1, EP2, EP3, and EP4) that may explain some of PGE2's diverse effects. In a mouse model of allergic inflammation in which the four receptors were individually deleted, only EP3(-/-) mice showed an enhancement of inflammation, whereas an EP3 agonist was inhibitory, with PGE2 being inactive. Thus, EP3 agonists may lead to a new approach for the treatment of asthma. However, other PGE2 receptor subtypes may also have beneficial effects, and a greater understanding of the signaling pathways of these receptor subtypes will help to clarify the role of these receptors in asthma.

Ikappa-B kinase-2 inhibitor blocks inflammation in human airway smooth muscle and a rat model of asthma

RATIONALE

Nuclear factor (NF)-kappaB is a transcription factor known to regulate the expression of many inflammatory genes, including cytokines, chemokines, and adhesion molecules. NF-kappaB is held inactive in the cytoplasm, bound to I-kappaB. The removal of I-kappaB, via the actions of inhibitor of kappaB (I-kappaB) kinase-2 (IKK-2), allows NF-kappaB to enter the nucleus.

OBJECTIVES

To determine the impact of inhibiting IKK-2 on in vitro and in vivo models of airway inflammation.

METHODS

The effect of inhibiting IKK-2 was assessed in stimulated, cultured, primary human airway smooth muscle cells and an antigen-driven rat model of lung inflammation.

MEASUREMENTS

The release of cytokines from cultured cells and inflammatory cytokine expression and cellular burden in the lung were determined.

MAIN RESULTS

Two structurally distinct molecules and dominant negative technology demonstrated that inhibition of IKK-2 activity completely blocked cytokine release from cultured cells, whereas the two glucocorticoid comparators had limited impact on granulocyte colony-stimulating factor, interleukin 8, and eotaxin release. In addition, in an in vivo antigen-driven model of airway inflammation, the IKK-2 inhibitor blocked NF-kappaB nuclear translocation, which was associated with a reduction in inflammatory cytokine gene and protein expression, airway eosinophilia, and late asthmatic reaction, similar in magnitude to that obtained with budesonide.

CONCLUSION

This study demonstrates that inhibiting IKK-2 results in a general reduction of the inflammatory response in vitro and in vivo. Compounds of this class could have therapeutic utility in the treatment of asthma and may, in certain respects, possess a beneficial efficacy profile compared with that of a steroid.

PDE4 inhibitors as new anti-inflammatory drugs: effects on cell trafficking and cell adhesion molecules expression

Phosphodiesterase 4 (PDE4) is a major cyclic AMP-hydrolyzing enzyme in inflammatory and immunomodulatory cells. The wide range of inflammatory mechanisms under control by PDE4 points to this isoenzyme as an attractive target for new anti-inflammatory drugs. Selective inhibitors of PDE4 have demonstrated a broad spectrum of anti-inflammatory activities including the inhibition of cellular trafficking and microvascular leakage, cytokine and chemokine release from inflammatory cells, reactive oxygen species production, and cell adhesion molecule expression in a variety of in vitro and in vivo experimental models. The initially detected side effects, mainly nausea and emesis, appear at least partially overcome by the 'second generation' PDE4 inhibitors, some of which like roflumilast and cilomilast are in the later stages of clinical development for treatment of chronic obstructive pulmonary disease. These new drugs may also offer opportunities for treatment of other inflammatory diseases.

Prostanoid receptor expression by human airway smooth muscle cells and regulation of the secretion of granulocyte colony-stimulating factor

The prostanoid receptors on human airway smooth muscle cells (HASMC) that augment the release by IL-1β of granulocyte colony-stimulating factor (G-CSF) have been characterized and the signaling pathway elucidated. PCR of HASM cDNA identified products corresponding to EP2, EP3, and EP4receptor subtypes. These findings were corroborated at the protein level by immunocytochemistry. IL-1β promoted the elaboration of G-CSF, which was augmented by PGE2. Cicaprost (IP receptor agonist) was approximately equiactive with PGE2, whereas PGD2, PGF2α, and U-46619 (TP receptor agonist) were over 10-fold less potent. Neither SQ 29,548 nor BW A868C (TP and DP1receptor antagonists, respectively) attenuated the enhancement of G-CSF release evoking any of the prostanoids studied. With respect to PGE2, the EP receptor agonists 16,16-dimethyl PGE2(nonselective), misoprostol (EP2/EP3selective), 17-phenyl-ω-trinor PGE2(EP1selective), ONO-AE1-259, and butaprost (both EP2selective) were full agonists at enhancing G-CSF release. AH 6809 (10 μM) and L-161,982 (2 μM), which can be used in HASMC as selective EP2and EP4receptor antagonists, respectively, failed to displace to the right the PGE2concentration-response curve that described the augmented G-CSF release. In contrast, AH 6809 and L-161,982 in combination competitively antagonized PGE2-induced G-CSF release. Augmentation of G-CSF release by PGE2was mimicked by 8-BrcAMP and abolished in cells infected with an adenovirus vector encoding an inhibitor protein of cAMP-dependent protein kinase (PKA). These data demonstrate that PGE2facilitates G-CSF secretion from HASMC through a PKA-dependent mechanism by acting through EP2and EP4prostanoid receptors and that effective antagonism is realized only when both subtypes are blocked concurrently.

NSAIDs increase GM-CSF release by human synoviocytes: comparison with nitric oxide-donating derivatives

Non-steroidal anti-inflammatory drugs (NSAIDs) are used to treat the condition of rheumatoid arthritis, where levels of prostaglandin E2 (PGE2) and granulocyte macrophage-colony stimulating factor (GM-CSF) are elevated in the synovial fluid. NO-NSAIDs are a new class of cyclooxygenase (COX)-inhibitors developed by coupling a nitric oxide (NO)-donating moiety to conventional NSAIDs. We show that, in cytokine-treated synoviocytes (from non-rheumatic patients), NO-naproxen and NO-flurbiprofen like their parent compounds concentration-dependently reduce the levels of PGE2 (an index of COX-2 activity), with a corresponding rise in the release of GM-CSF. Unlike acetylsalicylic acid (ASA), NO-ASA reduces the levels of PGE2, without increasing GM-CSF release, although cell viability is reduced at the highest concentration (1 mM). The effects of NSAIDs and NO-NSAIDs on GM-CSF release were attributable to the PGE2 mediated cyclic (c) AMP pathway because PGE2 reversed the effects of COX blockade. Second, phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine (IBMX) and Ro-201724 (both of which elevate cAMP levels) decreased GM-CSF release, in the presence of PGE2. Finally, neither sodium nitroprusside nor zaprinast (both of which elevate cGMP levels) affected GM-CSF or PGE2 release. Our findings demonstrate that GM-CSF is regulated by NSAIDs and NO-NSAIDs via inhibition of COX and appears to be mediated via the cAMP pathway. NO-ASA is the exception, because it does not increase GM-CSF release, although at millimolar concentrations cell viability is reduced.

Synthetic responses in airway smooth muscle

Human airway smooth muscle (ASM) has several properties and functions that contribute to asthma pathogenesis, and increasing attention is being paid to its synthetic capabilities. ASM can promote the formation of the interstitial extracellular matrix, and in this respect, ASM from asthmatic subjects compared with normal subjects responds differently, both qualitatively and quantitatively. Thus, ASM cells are important regulating cells that potentially contribute to the known alterations within the extracellular matrix in asthma. In addition, through integrin-directed signaling, extracellular matrix components can alter the proliferative, survival, and cytoskeletal synthetic function of ASM cells. ASM also functions as a rich source of biologically active chemokines and cytokines that are capable of perpetuating airway inflammation in asthma and chronic obstructive pulmonary disease by promoting recruitment, activation, and trafficking of inflammatory cells in the airway milieu. Emerging evidence shows that airway remodeling may also be a result of the autocrine action of secreted inflammatory mediators, including T(H)2 cytokines, growth factors, and COX-2-dependent prostanoids. Finally, ASM cells contain both beta(2)-adrenergic receptors and glucocorticoid receptors and may represent a key target for beta(2)-adrenergic receptor agonist/corticosteroid interactions. Combinations of long-acting beta(2)-agonists and corticosteroids appear to have additive and/or synergistic effects in inhibiting inflammatory mediator release and the migration and proliferation of ASM cells.

Identification in human airways smooth muscle cells of the prostanoid receptor and signalling pathway through which PGE2 inhibits the release of GM-CSF

1. The prostanoid receptor(s) on human airways smooth muscle (HASM) cells that mediates the inhibitory effect of PGE(2) on interleukin (IL)-1 beta-induced granulocyte/macrophage colony-stimulating factor (GM-CSF) release has been classified. 2. IL-1 beta evoked the release of GM-CSF from HASM cells, which was suppressed by PGE(2), 16,16-dimethyl PGE(2) (nonselective), misoprostol (EP(2)/EP(3)-selective), ONO-AE1-259 and butaprost (both EP(2)-selective) with pIC(50) values of 8.61, 7.13, 5.64, 8.79 and 5.43, respectively. EP-receptor agonists that have selectivity for the EP(1)-(17-phenyl-omega-trinor PGE(2)) and EP(3)-receptor (sulprostone) subtypes as well as cicaprost (IP-selective), PGD(2), PGF(2 alpha) and U-46619 (TP-selective) were poorly active or inactive at concentrations up to 10 microM. 3. AH 6809, a drug that can be used to selectively block EP(2)-receptors in HASM cells, antagonised the inhibitory effect of PGE(2), 16,16-dimethyl PGE(2) and ONO-AE1-259 with apparent pA(2) values of 5.85, 6.09 and 6.1 respectively. In contrast, the EP(4)-receptor antagonists, AH 23848B and L-161,982, failed to displace to the right the concentration-response curves that described the inhibition of GM-CSF release evoked by PGE(2) and ONO-AE1-259. 4. Inhibition of GM-CSF release by PGE(2) and 8-Br-cAMP was abolished in cells infected with an adenovirus vector encoding an inhibitor protein of cAMP-dependent protein kinase (PKA) but not by H-89, a purported small molecule inhibitor of PKA. 5. We conclude that prostanoid receptors of the EP(2)-subtype mediate the inhibitory effect of PGE(2) on GM-CSF release from HASM cells by recruiting a PKA-dependent pathway. In addition, the data illustrate that caution should be exercised when using H-89 in studies designed to assess the role of PKA in biological processes.

Regulation of airway smooth muscle cell immunomodulatory function: role in asthma

General agreement exists that in asthma, airway smooth muscle contracts, narrowing the airway lumen and thereby causing airflow obstruction and dyspnoea. New evidence is emerging that airway smooth muscle may also fulfil an immunomodulatory role by providing a rich source of pro-inflammatory cytokines and chemokines, polypeptide growth factors, extracellular matrix (ECM) proteins, cell adhesion receptors and co-stimulatory molecules. Together, the available data support a role for airway smooth muscle in actively perpetuating airway mucosal inflammatory processes including mast cell and leukocyte (T cell, neutrophil, eosinophil) activation and recruitment. Production of anti-inflammatory mediators by airway smooth muscle such as prostaglandin E(2) suggests that it is also capable of exerting a 'braking' effect on local inflammation. Recognition of this newly described property of airway smooth muscle makes it important to consider therapeutic targets for suppressing the synthesis and secretion of immunomodulatory mediators from this cell. However, it remains imperative to establish to what extent the secretory potential of airway smooth muscle is quantitatively important in vivo and in asthmatic subjects.

Regulation of beta-adrenergic responses in airway smooth muscle

Decreased responsiveness to beta-adrenergic receptor agonists is a characteristic feature of human asthma. This review summarizes data regarding the impact of chronic beta agonist stimulation, cytokines, prostanoids and other factors on beta-adrenergic responses in human airway smooth muscle, as well as the impact of polymorphisms of the beta(2)-adrenergic receptor on these responses. Effects of beta-agonists on both airway smooth muscle relaxation and gene expression are considered. Understanding the regulation of beta-adrenergic responses in airway smooth muscle cells may prove to be an important step in improving the efficacy of beta-agonists for the treatment of asthma.

Airway smooth muscle: immunomodulatory cells that modulate airway remodeling?

Although the pathogenesis of asthma remains unclear, substantial progress has been made over the past decades in the characterization of airway inflammation as a pathogenetic mechanism in asthma. New evidence suggests that airway smooth muscle (ASM), the most important cell modulating bronchomotor tone, plays an important immunomodulatory role in the orchestration and perpetuation of airway inflammation. Evidence now suggests that the signaling pathways that modulate leukocyte function may be disparate from those found in resident effector cells such as ASM, fibroblasts and epithelial cells. Further investigation and understanding of the critical signaling pathways that modulate ASM cell release, secretion of chemokines/cytokines and expression of cell adhesion molecules (CAMs) may offer new therapeutic approaches in the treatment of asthma.

IL-13 and IL-4 promote TARC release in human airway smooth muscle cells: role of IL-4 receptor genotype

The chemokine thymus- and activation-regulated chemokine (TARC) induces selective migration of Th2, but not Th1, lymphocytes and is upregulated in the airways of asthmatic patients. The purpose of this study was to determine whether human airway smooth muscle (HASM) cells produce TARC. Neither IL-4, IL-13, IL-1beta, IFN-gamma, nor TNF-alpha alone stimulated TARC release into the supernatant of cultured HASM cells. However, both IL-4 and IL-13 increased TARC protein and mRNA expression when administered in combination with TNF-alpha but not IL-1beta or IFN-gamma. Macrophage-derived chemokine was not expressed under any of these conditions. TARC release induced by TNF-alpha + IL-13 or TNF-alpha + IL-4 was inhibited by the beta-agonist isoproterenol and by other agents that activate protein kinase A, but not by dexamethasone. To determine whether polymorphisms of the IL-4Ralpha have an impact on the ability of IL-13 or IL-4 to induce TARC release, HASM cells from multiple donors were genotyped for the Ile50Val, Ser478Pro, and Gln551Arg polymorphisms of the IL-4Ralpha. Our data indicate that cells expressing the Val50/Pro478/Arg551 haplotype had significantly greater IL-13- or IL-4-induced TARC release than cells with other IL-4Ralpha genotypes. These data indicate that Th2 cytokines enhance TARC expression in HASM cells in an IL-4Ralpha genotype-dependent fashion and suggest that airway smooth muscle cells participate in a positive feedback loop that promotes the recruitment of Th2 cells into asthmatic airways.

ChTX induces oscillatory contraction in guinea pig trachea: role of cyclooxygenase-2 and PGE2

We examined the possible role of cyclooxygenase (COX) in charybdotoxin (ChTX)-induced oscillatory contraction in guinea pig trachea. Involvement of prostaglandin E(2) (PGE(2)) in ChTX-induced oscillatory contraction was also investigated. ChTX (100 nM) induced oscillatory contraction in guinea pig trachea. The mean oscillatory frequency induced by ChTX was 10.7 +/- 0.8 counts/h. Maximum and minimum tensions within ChTX-induced oscillatory contractions were 68.4 +/- 1.8 and 14.3 +/- 1.7% compared with K(+) (72.7 mM) contractions. ChTX-induced oscillatory contraction was completely inhibited by indomethacin, a nonselective COX inhibitor. Valeryl salicylate, a selective COX-1 inhibitor, did not significantly inhibit this contraction, whereas N-(2-cyclohexyloxy-4-nitro-phenyl)-methanesulfonamide, a selective COX-2 inhibitor, abolished this contraction. Exogenously applied arachidonic acid enhanced ChTX-induced oscillatory contraction. SC-51322, a selective PGE receptor subtype EP(1) antagonist, significantly inhibited ChTX-induced oscillatory contraction. Exogenously applied PGE(2) induced only a slight phasic contraction in guinea pig trachea, but PGE(2) induced strong oscillatory contraction after pretreatment with indomethacin and ChTX. Moreover, ChTX time-dependently stimulated PGE(2) generation. These results suggest that ChTX specifically activates COX-2 and stimulates PGE(2) production and that ChTX-induced oscillatory contraction in guinea pig trachea is mediated by activation of EP(1) receptor.

Aspirin-induced asthma: advances in pathogenesis, diagnosis, and management

In some asthmatic individuals, aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygen-ase 1 (COX-1) exacerbate the condition. This distinct clinical syndrome, called aspirin-induced asthma (AIA), is characterized by an eosinophilic rhinosinusitis, nasal polyposis, aspirin sensitivity, and asthma. There is no in vitro test for the disorder, and diagnosis can be established only by provocation challenges with aspirin or NSAIDs. Recent major advances in the molecular biology of eicosanoids, exemplified by the cloning of 2 cysteinyl leukotriene receptors and the discovery of a whole family of cyclooxygenase enzymes, offer new insights into mechanisms operating in AIA. The disease runs a protracted course even if COX-1 inhibitors are avoided, and the course is often severe, many patients requiring systemic corticosteroids to control their sinusitis and asthma. Aspirin and NSAIDs should be avoided, but highly specific COX-2 inhibitors, known as coxibs, are well tolerated and can be safely used. Aspirin desensitization, followed by daily aspirin treatment, is a valuable therapeutic option in most patients with AIA, particularly those with recurrent nasal polyposis or overdependence on systemic corticosteroids.

GM-CSF increases airway smooth muscle cell connective tissue expression by inducing TGF-beta receptors

Fibrosis around the smooth muscle of asthmatic airway walls leads to irreversible airway obstruction. Bronchial epithelial cells release granulocyte/macrophage colony-stimulating factor (GM-CSF) in asthmatics and are in close proximity to airway smooth muscle cells (ASMC). The findings in this study demonstrate that GM-CSF induces confluent, prolonged, serum-deprived cultures of ASMC to increase expression of collagen I and fibronectin. GM-CSF also induced ASMC to increase the expression of transforming growth factor (TGF)-beta receptors type I, II, and III (TbetaR-I, TbetaR-II, TbetaR-III), but had no detectable effect on the release of TGF-beta1 by the same ASMC. The presence of GM-CSF also induced the association of TGF-beta1 with TbetaR-III, which enhances binding of TGF-beta1 to TbetaR-II. The induction of TbetaRs was parallel to the increased induction of phosphorylated Smad2 (pSmad2) and connective tissue growth factor (CTGF), indicative of TGF-beta-mediated connective tissue synthesis. Dexamethasone decreased GM-CSF-induced TbetaR-I, TbetaR-II, TbetaR-III, pSmad2, CTGF, collagen I, and fibronectin. In conclusion, GM-CSF increases the responsiveness of ASMC to TGF-beta1-mediated connective tissue expression by induction of TbetaRs, which is inhibited by corticosteroids.

Role of protease-activated receptors in airway function: a target for therapeutic intervention?

Protease-activated receptors (PARs) are G-protein-coupled, seven transmembrane domain receptors that act as cellular enzyme sensors. These receptors are activated by the proteolytic cleavage at the amino terminus, enabling interaction between the newly formed "tethered ligand" and the second extracellular loop of the receptor to confer cellular signalling. PARs can also be activated by small peptides that mimic the tethered ligand. In the respiratory tract, PARs may be regulated by endogenous proteases, such as airway trypsin and mast cell tryptase, as well as exogenous proteases, including inhaled aeroallergens such as those from house dust mite faecal pellets. Immunoreactive PARs have been identified in multiple cell types of the respiratory tract, and PAR activation has been reported to stimulate cellular mitogenesis and to promote tissue inflammation. Activation of PARs concurrently stimulates the release of bronchorelaxant and anti-inflammatory mediators, which may serve to induce cytoprotection and to minimise tissue trauma associated with severe chronic airways inflammation. Furthermore, airway inflammatory responses are associated with increased epithelial PAR expression and elevated concentrations of PAR-activating, and PAR-inactivating, proteases in the extracellular space. On this basis, PARs are likely to play a regulatory role in airway homeostasis, and may participate in respiratory inflammatory disorders, such as asthma and chronic obstructive pulmonary disease. Further studies focussing on the effects of newly developed PAR agonists and antagonists in appropriate models of airway inflammation will permit better insight into the role of PARs in respiratory pathophysiology and their potential as therapeutic targets.

Airway smooth muscle: an immunomodulatory cell

Asthma is characterized in part by reversible airflow obstruction, hyperresponsiveness, and inflammation. Chronic obstructive pulmonary disease, which includes chronic bronchitis, emphysema, and possibly bronchiectasis, is defined as predominantly irreversible airflow obstruction associated with abnormal airway inflammation. Traditional concepts concerning airway inflammation have focused on trafficking leukocytes and on the effects of inflammatory mediators, cytokines, and chemokines secreted by these cells. Airway smooth muscle, the major effector cell responsible for bronchomotor tone, has been viewed as a target tissue responding to neurohumoral control and inflammatory mediators. New evidence, however, suggests that airway smooth muscle may secrete cytokines and chemokines and express cellular adhesion molecules that are important in modulating submucosal airway inflammation. Other new evidence suggests that beta-adrenergic agents may inhibit some but not all of the inflammatory responses. In certain circumstances, increasing levels of cyclic adenosine monophosphate in the cytosol of airway smooth muscle promote the secretion of other cytokines or chemokines. The cellular and molecular mechanisms that regulate the immunomodulatory functions of airway smooth muscle may offer new and important therapeutic targets in treating these common lung diseases.

Effects of non-steroidal anti-inflammatory drugs on cyclo-oxygenase and lipoxygenase activity in whole blood from aspirin-sensitive asthmatics vs healthy donors

1. Cyclo-oxygenase (COX) and lipoxygenase (LO) share a common substrate, arachidonic acid. Aspirin and related drugs inhibit COX activity. In a subset of patients with asthma aspirin induces clinical symptoms associated with increased levels of certain LO products, a phenomenon known as aspirin-sensitive asthma. The pharmacological pathways regulating such responses are not known. 2. Here COX-1 and LO activity were measured respectively by the formation of thromboxane B(2) (TXB(2)) or leukotrienes (LT) C(4), D(4) and E(4) in whole blood stimulated with A23187. COX-2 activity was measured by the formation of prostaglandin E(2) (PGE(2)) in blood stimulated with lipopolysaccharide (LPS) for 18 h. 3. No differences in the levels of COX-1, COX-2 or LO products or the potency of drugs were found in blood from aspirin sensitive vs aspirin tolerant patients. Aspirin, indomethacin and nimesulide inhibited COX-1 activity, without altering LO activity. Indomethacin, nimesulide and the COX-2 selective inhibitor DFP [5,5-dimethyl-3-(2-isopropoxy)-4-(4-methanesulfonylphenyl)-2(5H)-furanone] inhibited COX-2 activity. NO-aspirin, like aspirin inhibited COX-1 activity in blood from both groups. However, NO-aspirin also reduced LO activity in the blood from both patient groups. Sodium salicylate was an ineffective inhibitor of COX-1, COX-2 or LO activity in blood from both aspirin-sensitive and tolerant patients. 4. Thus, when COX activity in the blood of aspirin-sensitive asthmatics is blocked there is no associated increase in LO products. Moreover, NO-aspirin, unlike other NSAIDs tested, inhibited LO activity in the blood from both aspirin sensitive and aspirin tolerant individuals. This suggests that NO-aspirin may be better tolerated than aspirin by aspirin-sensitive asthmatics.