Production of PGE2 by bovine cultured airway smooth muscle cells and its inhibition by cyclo-oxygenase inhibitors

Effect of Prostanoids on Human Platelet Function: An Overview

Prostanoids are bioactive lipid mediators and take part in many physiological and pathophysiological processes in practically every organ, tissue and cell, including the vascular, renal, gastrointestinal and reproductive systems. In this review, we focus on their influence on platelets, which are key elements in thrombosis and hemostasis. The function of platelets is influenced by mediators in the blood and the vascular wall. Activated platelets aggregate and release bioactive substances, thereby activating further neighbored platelets, which finally can lead to the formation of thrombi. Prostanoids regulate the function of blood platelets by both activating or inhibiting and so are involved in hemostasis. Each prostanoid has a unique activity profile and, thus, a specific profile of action. This article reviews the effects of the following prostanoids: prostaglandin-D₂ (PGD₂), prostaglandin-E₁, -E₂ and E₃ (PGE₁, PGE₂, PGE₃), prostaglandin F_2α (PGF_2α), prostacyclin (PGI₂) and thromboxane-A₂ (TXA₂) on platelet activation and aggregation via their respective receptors.

Airway relaxation mechanisms and structural basis of osthole for improving lung function in asthma

Overuse of β2-adrenoceptor agonist bronchodilators evokes receptor desensitization, decreased efficacy, and an increased risk of death in asthma patients. Bronchodilators that do not target β2-adrenoceptors represent a critical unmet need for asthma management. Here, we characterize the utility of osthole, a coumarin derived from a traditional Chinese medicine, in preclinical models of asthma. In mouse precision-cut lung slices, osthole relaxed preconstricted airways, irrespective of β2-adrenoceptor desensitization. Osthole administered in murine asthma models attenuated airway hyperresponsiveness, a hallmark of asthma. Osthole inhibited phosphodiesterase 4D (PDE4D) activity to amplify autocrine prostaglandin E₂ signaling in airway smooth muscle cells that eventually triggered cAMP/PKA-dependent relaxation of airways. The crystal structure of the PDE4D complexed with osthole revealed that osthole bound to the catalytic site to prevent cAMP binding and hydrolysis. Together, our studies elucidate a specific molecular target and mechanism by which osthole induces airway relaxation. Identification of osthole binding sites on PDE4D will guide further development of bronchodilators that are not subject to tachyphylaxis and would thus avoid β2-adrenoceptor agonist resistance.

Androgen and Androgen Receptors as Regulators of Monocyte and Macrophage Biology in the Healthy and Diseased Lung

Androgens, the predominant male sex hormones, drive the development and maintenance of male characteristics by binding to androgen receptor (AR). As androgens are systemically distributed throughout the whole organism, they affect many tissues and cell types in addition to those in male sexual organs. It is now clear that the immune system is a target of androgen action. In the lungs, many immune cells express ARs and are responsive to androgens. In this review, we describe the effects of androgens and ARs on lung myeloid immune cells-monocytes and macrophages-as they relate to health and disease. In particular, we highlight the effect of androgens on lung diseases, such as asthma, chronic obstructive pulmonary disease and lung fibrosis. We also discuss the therapeutic use of androgens and how circulating androgens correlate with lung disease. In addition to human studies, we also discuss how mouse models have helped to uncover the effect of androgens on monocytes and macrophages in lung disease. Although the role of estrogen and other female hormones has been broadly analyzed in the literature, we focus on the new perspectives of androgens as modulators of the immune system that target myeloid cells during lung inflammation.

Transient receptor potential ankyrin-1 causes rapid bronchodilation via nonepithelial PGE2

Transient receptor potential ankyrin-1 (TRPA1) is a ligand-gated cation channel that responds to endogenous and exogenous irritants. TRPA1 is expressed on multiple cell types throughout the lungs, but previous studies have primarily focused on TRPA1 stimulation of airway sensory nerves. We sought to understand the integrated physiological airway response to TRPA1 stimulation. The TRPA1 agonists allyl isothiocyanate (AITC) and cinnamaldehyde (CINN) were tested in sedated, mechanically ventilated guinea pigs in vivo. Reproducible bronchoconstrictions were induced by electrical stimulation of the vagus nerves. Animals were then treated with intravenous AITC or CINN. AITC and CINN were also tested on isolated guinea pig and mouse tracheas and postmortem human trachealis muscle strips in an organ bath. Tissues were contracted with methacholine, histamine, or potassium chloride and then treated with AITC or CINN. Some airways were pretreated with TRPA1 antagonists, the cyclooxygenase inhibitor indomethacin, the EP₂ receptor antagonist PF 04418948, or tetrodotoxin. AITC and CINN blocked vagally mediated bronchoconstriction in guinea pigs. Pretreatment with indomethacin completely abolished the airway response to TRPA1 agonists. Similarly, AITC and CINN dose-dependently relaxed precontracted guinea pig, mouse, and human airways in the organ bath. AITC- and CINN-induced airway relaxation required TRPA1, prostaglandins, and PGE₂ receptor activation. TRPA1-induced airway relaxation did not require epithelium or tetrodotoxin-sensitive nerves. Finally, AITC blocked airway hyperreactivity in two animal models of allergic asthma. These data demonstrate that stimulation of TRPA1 causes bronchodilation of intact airways and suggest that the TRPA1 pathway is a potential pharmacological target for bronchodilation.

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.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.

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.

Refractoriness to exercise challenge: a review of the mechanisms old and new

This article discusses the available literature on refractoriness in exercise-induced bronchoconstriction, namely, a decrease in airway responsiveness with repeated exercise challenges. The mechanisms of this naturally occurring protective feature is unknown. Reviewing previous studies together with findings in more recent studies, the authors propose desensitization of the G protein-coupled cysteinyl leukotriene receptor1 as the mechanism of refractoriness and that this desensitization occurs as a result of interplay between leukotrienes and prostaglandins.

Adenosine A(1) and prostaglandin E receptor 3 receptors mediate global airway contraction after local epithelial injury

Epithelial injury and airway hyperresponsiveness are prominent features of asthma. We have previously demonstrated that laser ablation of single epithelial cells immediately induces global airway constriction through Ca(2+)-dependent smooth muscle shortening. The response is mediated by soluble mediators released from wounded single epithelial cells; however, the soluble mediators and signaling mechanisms have not been identified. In this study, we investigated the nature of the epithelial-derived soluble mediators and the associated signaling pathways that lead to the L-type voltage-dependent Ca(2+) channel (VGCC)-mediated Ca(2+) influx. We found that inhibition of adenosine A1 receptors (or removal of adenosine with adenosine deaminase), cyclooxygenase (COX)-2 or prostaglandin E receptor 3 (EP3) receptors, epidermal growth factor receptor (EGFR), or platelet-derived growth factor receptor (PDGFR) all significantly blocked Ca(2+) oscillations in smooth muscle cells and airway contraction induced by local epithelial injury. Using selective agonists to activate the receptors in the presence and absence of selective receptor antagonists, we found that adenosine activated the signaling pathway A1R→EGFR/PDGFR→COX-2→EP3→VGCCs→calcium-induced calcium release, leading to intracellular Ca(2+) oscillations in airway smooth muscle cells and airway constriction.

Motility, survival, and proliferation

Airway smooth muscle has classically been of interest for its contractile response linked to bronchoconstriction. However, terminally differentiated smooth muscle cells are phenotypically plastic and have multifunctional capacity for proliferation, cellular hypertrophy, migration, and the synthesis of extracellular matrix and inflammatory mediators. These latter properties of airway smooth muscle are important in airway remodeling which is a structural alteration that compounds the impact of contractile responses on limiting airway conductance. In this overview, we describe the important signaling components and the functional evidence supporting a view of smooth muscle cells at the core of fibroproliferative remodeling of hollow organs. Signal transduction components and events are summarized that control the basic cellular processes of proliferation, cell survival, apoptosis, and cellular migration. We delineate known intracellular control mechanisms and suggest future areas of interest to pursue to more fully understand factors that regulate normal myocyte function and airway remodeling in obstructive lung diseases.

Regulation of smooth muscle contraction by the epithelium: role of prostaglandins

As an analog to the endothelium situated next to the vascular smooth muscle, the epithelium is emerging as an important regulator of smooth muscle contraction in many vital organs/tissues by interacting with other cell types and releasing epithelium-derived factors, among which prostaglandins have been demonstrated to play a versatile role in governing smooth muscle contraction essential to the physiological and pathophysiological processes in a wide range of organ systems.

Suppressors of cytokine signaling 3 expression in eosinophils: regulation by PGE₂ and Th2 cytokines

Asthma and nonasthmatic eosinophilic bronchitis (NAEB) are respiratory disorders characterized by a predominance of Th2 cells and eosinophilic inflammation. Suppressors of cytokine signaling (SOCS) proteins play an important role in Th2-mediated allergic responses through control of the balance between Th1 and Th2 cells, particularly, SOCS3 and SOCS5. The aim of this study was to analyze SOCS expression in human peripheral blood eosinophils from patients with asthma, NAEB and healthy controls. SOCS expression in eosinophils from subjects was demonstrated by different techniques. Results showed that expression of SOCS3 in eosinophils and CD4 T cells from patients was higher than in healthy subjects. In addition, we demonstrated that prostaglandin E₂ (PGE₂) and Th2 cytokines are able to upregulate SOCS3 production in eosinophils and attenuate its degranulation. In conclusion, eosinophils are able to transcribe and translate SOCS3 protein and can contribute to the regulation of the Th1/Th2 balance through SOCS3 production.

PGE(2) decreases muscle cell proliferation in patients with non-asthmatic eosinophilic bronchitis

Non-asthmatic eosinophilic bronchitis (NAEB) is characterized by chronic cough and sputum eosinophilia without bronchial hyperresponsiveness. The aim of the present study is to determine whether increased levels of PGE(2) from NAEB sputum supernatants play a protective role in airway inflammation and muscular hyperplasia. Twenty-one patients with NAEB, 15 asthmatic patients, and 12 healthy subjects were studied. An up-regulated PGE(2) enzymatic pathway was observed in bronchial biopsies from patients with NAEB as compared with samples from asthmatic patients. Also, EP2 and EP4 receptor expression was increased in these samples. BSMC proliferation was inhibited to a greater extent in NAEB sputum supernatants than in those taken from asthmatic subjects and healthy controls. This inhibition was mostly due to PGE(2) levels, a fact which was confirmed by employing synthetic EP2 and EP4 agonist and antagonist receptors.These findings suggest that PGE(2) inhibits BSMC proliferation entailing a reduction of smooth muscle hyperplasia and thus protecting against the onset of airflow obstruction.

Oxidative stress and airway inflammation after allergen challenge evaluated by exhaled breath condensate analysis

BACKGROUND

Allergen exposure may increase airway oxidative stress, which causes lipid membrane peroxidation and an increased formation of 8-isoprostane.

OBJECTIVE

The aim of the study was to investigate oxidative stress induced by allergen challenge in mild asthmatics, by measuring 8-isoprostane in exhaled breath condensate (EBC), and to examine their relationship with mediators derived from arachidonic acid. Methods 8-isoprostane, cysteinyl leukotrienes (cys-LTs) and prostaglandin E2 (PGE(2) ) concentrations in EBC were measured at baseline and after allergen challenge in 12 patients with mild allergic asthma sensitized to cat allergen.

RESULTS

At 24 h after allergen challenge, compared with baseline values, EBC 8-isoprostane increased [48.64 pg/mL (44.14-53.61) vs. 21.56 pg/mL (19.92, 23.35), P<0.001], cys-LTs increased [27.37 pg/mL (24.09-31.10) vs. 13.28 pg/mL (11.32, 15.57), P<0.001] and PGE(2) decreased [18.69 pg/mL (12.26, 28.50) vs. 39.95 pg/mL (34.37, 46.43), P<0.001]. The trend of increasing 8-isoprostane after allergen challenge was significantly correlated with the trend of increasing cys-LTs (R(2) =0.85, P<0.001) whereas the trend of decreasing PGE(2) after allergen challenge was significantly correlated with the trend of increasing cys-LTs (R(2) =0.52, P=0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

The increase in EBC 8-isoprostane observed after allergen challenge indicates that allergen exposure increases airway oxidative stress in allergic asthma. The strict correlation between cys-LTs and 8-isoprostane underlines the relationship between allergic inflammation and oxidative stress. A shift of arachidonic acid metabolism towards lipoxygenase pathway is induced by the allergen challenge. Airway oxidative stress occurs after allergen challenge even in patients with mild intermittent allergic asthma.

Changes in sputum eicosanoids and inflammatory markers after inhalation challenges with occupational agents

BACKGROUND

An increase in cysteinyl-leukotrienes (LTs) after specific inhalation challenge (SIC) with common allergens in patients with atopic asthma has been shown previously, but there are scarce data with occupational agents. We sought to determine whether there are differences in lower airway inflammatory markers and the production of cytokines and eicosanoids between patients with a positive or negative SIC response to occupational agents.

METHODS

Twenty-six patients with suspected occupational asthma and 13 healthy control subjects were studied. Spirometry, methacholine challenge, and sputum induction were performed at baseline and 24 h after SIC with occupational agents. Several cytokines and inflammatory mediators, including eicosanoids, were measured in sputum.

RESULTS

Twenty-six SICs were carried out with high-molecular-weight or low-molecular-weight agents, and the responses were positive in 18 patients. SIC elicited nine early asthmatic responses, two dual asthmatic responses, and seven isolated late asthmatic responses. Significant increments in sputum eosinophil counts were found only in patients with positive SIC responses compared with baseline values. Interleukin-10 levels were decreased in patients with positive and negative SIC responses compared to those in healthy control subjects. A significant increase (p < 0.05) in the LTC(4)/prostaglandin E(2) (PGE(2)) ratio was observed in patients after positive SIC responses compared to those with negative SIC responses.

CONCLUSIONS

Overexpression of LTC(4), relative underproduction of PGE(2), and greater airway eosinophilia were observed in patients with positive SIC responses.

Changes in the proteome of human bronchial epithelial cells following stimulation with leucotriene E4 and transforming growth factor-beta1

BACKGROUND AND OBJECTIVE

Activated bronchial epithelial cells exert considerable potential to maintain a microenvironment in the airway wall that promotes airway inflammation and remodelling. Cysteinyl leucotrienes (CysLT) and transforming growth factor-beta(1) (TGF-beta(1)) are both increased in asthmatic airways and may influence the pathophysiology of disease. However, the consequences of activation of bronchial epithelial cells by these mediators are not fully understood. A proteomic-based approach was used to characterize the inflammatory pathways in bronchial epithelial cells after stimulation with CysLT and TGF-beta(1).

METHODS

Human bronchial epithelial cells (BEAS-2B) were stimulated with 1 ng/mL TGF-beta(1) and 50 nmol/L leucotriene E(4) (LTE(4)) for 48 h and whole-cell lysates were subjected to two-dimensional gel electrophoresis. Proteins showing statistically significant differential expression were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and database searching.

RESULTS

Stimulation with LTE(4) increased the expression of three proteins and five proteins showed decreased expression. Of the latter group, two were definitively identified as heat shock protein (Hsp90 alpha) and stress-70 protein. Hsp90 alpha forms a heterocomplex with the glucocorticoid receptor (GR) and a significant decrease in GR following LTE(4) stimulation was confirmed. TGF-beta(1) downregulated 18 intracellular proteins, including lamin A/C, glyceraldehyde-3-phosphate dehydrogenase, protein DJ-1, voltage-dependent calcium channel gamma-7 subunit, heterogeneous nuclear ribonucleoprotein A2/B1 and stress-70 protein.

CONCLUSIONS

The current findings suggest that by downregulating GR and Hsp90 alpha, CysLT may interfere with the action of glucocorticoids. Overall, the results confirm the complex role of bronchial epithelium in aspects of airway inflammation and remodelling.

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.

Pharmacology of airway smooth muscle proliferation

Airway smooth muscle thickening is a pathological feature that contributes significantly to airflow limitation and airway hyperresponsiveness in asthma. Ongoing research efforts aimed at identifying the mechanisms responsible for the increased airway smooth muscle mass have indicated that hyperplasia of airway smooth muscle, due in part to airway myocyte proliferation, is likely a major factor. Airway smooth muscle proliferation has been studied extensively in culture and in animal models of asthma, and these studies have revealed that a variety of receptors and mediators contributes to this response. This review aims to provide an overview of the receptors and mediators that control airway smooth muscle cell proliferation, with emphasis on the intracellular signalling mechanisms involved.

Increased prostaglandin E2 levels in the airway of patients with eosinophilic bronchitis

BACKGROUND

Eosinophilic bronchitis is a common cause of chronic cough, which like asthma is characterized by sputum eosinophilia, but unlike asthma there is no variable airflow obstruction or airway hyperresponsiveness. We tested the hypothesis that the different airway function in patients with eosinophilic bronchitis and asthma could be caused by an imbalance in the production of bronchoconstrictor (LTC(4)) and bronchoprotective (prostaglandin E(2); PGE(2)) lipid mediators.

METHODS

We measured cytokines levels, proinflammatory mediators and eicosanoids concentration in sputum from 13 subjects with nonasthmatic eosinophilic bronchitis, 13 subjects with asthma, and 11 healthy control subjects. Cytokines mRNA levels were measured by real time PCR, proinflammatory mediators, PGE(2), and LTC(4) were measured by enzyme immunoassays.

RESULTS

The median sputum eosinophil count was not statistically different in patients with asthma (7.95%) and eosinophilic bronchitis (15.29%). The levels of mRNA specific to interleukin-5 (IL-5), IL-4, IL-10, IL-13, interferon gamma (IFN-gamma), IL-2, vascular endothelial growth factor and transforming growth factor beta were similar in both conditions. In addition, no differences were found between asthma and eosinophilic bronchitis in proinflammatory cytokines, such as IL-8, IFN-gamma and tumor necrosis factor alpha (TNF-alpha) levels. Sputum cysteinyl-leukotrienes concentration was raised both in eosinophilic bronchitis and asthma patients. We found that induced sputum PGE(2) concentrations were significantly increased in subjects with eosinophilic bronchitis (838.3 +/- 612 pg/ml) when compared with asthmatic (7.54 +/- 2.14 pg/ml) and healthy subjects (4 +/- 1.3 pg/ml).

CONCLUSION

This data suggest that the difference in airway function observed in subjects with eosinophilic bronchitis and asthma could be due to differences in PGE(2) production in the airways.

BK-induced COX-2 expression via PKC-δ-dependent activation of p42/p44 MAPK and NF-κB in astrocytes

Bradykinin (BK) is an inflammatory mediator, elevated levels in the region of several brain injury and inflammatory diseases. It has been shown to induce cyclooxygenase-2 (COX-2) expression implicating in inflammatory responses in various cell types. However, the signaling mechanisms underlying BK-induced COX-2 expression in astrocytes remain unclear. First, RT-PCR and Western blotting analysis showed that BK induced the expression of COX-2 mRNA and protein, which was inhibited by B(2) BK receptor antagonist Hoe140, suggesting the involvement of B(2) BK receptors. BK-induced COX-2 expression and translocation of PKC-delta from cytosol to membrane fraction were inhibited by rottlerin, suggesting that PKC-delta might be involved in these responses. This hypothesis was further supported by the transfection with a dominant negative plasmid of PKC-delta significantly blocked BK-induced COX-2 expression. BK-stimulated p42/p44 MAPK phosphorylation, COX-2 mRNA expression, and prostaglandin E(2) (PGE(2)) release were attenuated by PD98059, indicating the involvement of MEK/p42/p44 MAPK in this pathway. Accordingly, BK-stimulated phosphorylation of p42/p44 MAPK was attenuated by rottlerin, indicating that PKC-delta might be an upstream component of p42/p44 MAPK. Moreover, BK-induced COX-2 expression might be mediated through the translocation of NF-kappaB into nucleus which was blocked by helenalin, rottlerin and PD98059, implying the involvement of NF-kappaB. These results suggest that in RBA-1 cells, BK-induced COX-2 expression and PGE(2) release was sequentially mediated through PKC-delta-dependent activation of p42/p44 MAPK and NF-kappaB. Understanding the regulation of COX-2 expression and PGE(2) release induced by BK in astrocytes might provide a new therapeutic strategy of brain injury and inflammatory diseases.

Involvement of cyclooxygenase-2 and prostaglandins in the molecular pathogenesis of inflammatory lung diseases

Inducible cyclooxygenase (COX-2) and its metabolites have diverse and potent biological actions that are important for both physiological and disease states of lung. The wide variety of prostaglandin (PG) products are influenced by the level of cellular activation, the exact nature of the stimulus, and the specific cell type involved in their production. In turn, the anti- and proinflammatory response of PG is mediated by a blend of specific surface and intracellular receptors that mediate diverse cellular events. The complexity of this system is being at least partially resolved by the generation of specific molecular biological research tools that include cloning and characterization of the enzymes distal to COX-2 and the corresponding receptors to the final cellular products of arachidonic metabolism. The most informative of these approaches have employed genetically modified animals and specific receptor antagonists to determine the exact role of specific COX-2-derived metabolites on specific cell types of the lung in the context of inflammatory models. These data have suggested a number of cell-specific, pathway-specific, and receptor-specific approaches that could lead to effective therapeutic interventions for most inflammatory lung diseases.

Airway smooth muscle prostaglandin-EP1 receptors directly modulate beta2-adrenergic receptors within a unique heterodimeric complex

Multiple and paradoxical effects of airway smooth muscle (ASM) 7-transmembrane-spanning receptors activated during asthma, or by treatment with bronchodilators such as beta(2)-adrenergic receptor (beta(2)AR) agonists, indicate extensive receptor crosstalk. We examined the signaling of the prostanoid-EP(1) receptor, since its endogenous agonist prostaglandin E(2) is abundant in the airway, but its functional implications are poorly defined. Activation of EP(1) failed to elicit ASM contraction in mouse trachea via this G(alphaq)-coupled receptor. However, EP(1) activation markedly reduced the bronchodilatory function of beta(2)AR agonist, but not forskolin, indicating an early pathway interaction. Activation of EP(1) reduced beta(2)AR-stimulated cAMP in ASM but did not promote or augment beta(2)AR phosphorylation or alter beta(2)AR trafficking. Bioluminescence resonant energy transfer showed EP(1) and beta(2)AR formed heterodimers, which were further modified by EP(1) agonist. In cell membrane [(35)S]GTPgammaS binding studies, the presence of the EP(1) component of the dimer uncoupled beta(2)AR from G(alphas), an effect accentuated by EP(1) agonist activation. Thus alone, EP(1) does not appear to have a significant direct effect on airway tone but acts as a modulator of the beta(2)AR, altering G(alphas) coupling via steric interactions imposed by the EP(1):beta(2)AR heterodimeric signaling complex and ultimately affecting beta(2)AR-mediated bronchial relaxation. This mechanism may contribute to beta-agonist resistance found in asthma.

Regulatory features of interleukin-1β-mediated prostaglandin E2 synthesis in airway smooth muscle

Exposure of airway smooth muscle (ASM) cells to the cytokine IL-1β results in an induction of PGE2 synthesis that affects numerous cell functions. Current dogma posits induction of COX-2 protein as the critical, obligatory event in cytokine-induced PGE2 production, although PGE2 induction can be inhibited without a concomitant inhibition of COX-2. To explore other putative regulatory features we examined the role of phospholipase A2 (PLA2) and PGE synthase (PGES) enzymes in IL-1β-induced PGE2 production. Treatment of human ASM cultures with IL-1β caused a time-dependent induction of both cytosolic PLA2 (cPLA2) and microsomal PGES (mPGES) similar to that observed for COX-2. Regulation of COX-2 and mPGES induction was similar, being significantly reduced by inhibition of p42/p44 or p38, whereas cPLA2 induction was only minimally reduced by inhibition of p38 or PKC. COX-2 and mPGES induction was subject to feed-forward regulation by PKA, whereas cPLA2 induction was not. SB-202474, an SB-203580 analog lacking the ability to inhibit p38 but capable of inhibiting IL-1β-induced PGE2 production, was effective in inhibiting mPGES but not COX-2 or cPLA2 induction. These data suggest that although COX-2, cPLA2, and mPGES are all induced by IL-β in human ASM cells, regulatory features of cPLA2 are dissociated, whereas those of COX-2 and mPGES are primarily associated, with regulation of PGE2 production. mPGES induction and, possibly, cPLA2 induction appear to cooperate with COX-2 to determine IL-1β-mediated PGE2 production in human ASM cells.

Prostaglandin E2 receptor selective agonists E-prostanoid 2 and E-prostanoid 4 may have therapeutic effects on ovalbumin-induced bronchoconstriction

BACKGROUND

The pharmacologic actions of prostaglandin E(2) (PGE(2)) are mediated through specific E-prostanoid (EP)-1, EP-2, EP-3, and EP-4 receptors. In this study, we determined which PGE(2) receptor subtype(s) contribute to the prevention of allergen-induced bronchoconstriction.

METHODS

We assessed the effects of these receptor agonists in ovalbumin (OA)-sensitized guinea pigs. The prostaglandin E receptor-subtype agonists tested were ONO-DI-004 (EP-1), ONO-AE1-259 (EP-2), ONO-AE-248 (EP-3), ONO-AE1-329 (EP-4), and sulprostone (EP-1 and EP-3) [Ono Pharmaceutical Company; Osaka, Japan]. We treated the animals with either PGE(2) or these agonists 15 min before OA challenge and measured respiratory resistance at 15 min, 1 h, and 3 h.

RESULTS

Allergen-induced bronchoconstriction was significantly (p < 0.01) suppressed at doses > 85 nmol/kg of PGE(2). The respiratory resistance elevations 15 min after OA challenge were significantly (p < 0.01) suppressed by preadministration of EP-2 and EP-4 agonists, but airway responsiveness to inhaled methacholine did not improve. EP-1, EP-3, or EP-1/EP-3 agonists had no effect on any parameter.

CONCLUSIONS

These results suggest that inhibition of OA-induced bronchoconstriction by PGE(2) acts through EP-2 and EP-4 receptors.

Mechanisms underlying the relaxation response induced by bradykinin in the epithelium-intact guinea-pig trachea in vitro

In this study, we investigated some of the signalling pathways involved in bradykinin (BK)-induced relaxation in epithelium-intact strips of the guinea-pig trachea (GPT + E). BK induced time- and concentration-dependent relaxation of GPT + E. Similar responses were observed for prostaglandin E2 (PGE2) or the combination of subthreshold concentrations of BK plus PGE2. The nonselective cyclooxygenase (COX) inhibitors indomethacin or pyroxicam, or the selective COX-2 inhibitors DFU, NS 398 or rofecoxib, but not the selective COX-1 inhibitor SC 560, all abolished BK-induced relaxation. The tyrosine kinase inhibitors herbimycin A and AG 490 also abolished BK-induced relaxation in GPT + E. The nonselective nitric oxide synthase (NOS) inhibitor 7-NINA concentration-dependently inhibited BK effects. BK-induced relaxation was prevented by the selective antagonists for EP3 (L 826266), but not by EP1 (SC 19221), EP1/EP2 (AH 6809) or EP4 (L161982) receptor antagonists. Otherwise, the selective inhibitors of protein kinases A, G and C, mitogen-activated protein kinases, phospholipases C and A2, nuclear factor-kappaB or potassium channels all failed to significantly interfere with BK-mediated relaxation.BK caused a marked increase in PGE2 levels, an effect that was prevented by NS 398, HOE 140 or AG 490. COX-2 expression did not differ in preparations with or without epithelium, and it was not changed by BK stimulation. However, incubation with BK significantly increased the endothelial NOS (eNOS) and neuronal NOS (nNOS) expression, independent of the epithelium integrity. Our results indicate that BK-induced relaxation in GPT + E depends on prostanoids (probably PGE2 acting via EP3 receptors) and NO release and seems to involve complex interactions between kinin B2 receptors, COX-2, nNOS, eNOS and tyrosine kinases.

PI 3-kinase and MAP kinase regulate bradykinin induced prostaglandin E2release in human pulmonary artery by modulating COX-2 activity

Here we studied the role of phosphoinositide 3-kinase (PI 3-kinase) and mitogen activated protein (MAP) kinase in regulating bradykinin (BK) induced prostaglandin E(2) (PGE(2)) production in human pulmonary artery smooth muscle cells (HPASMC). BK increased PGE(2) in a three step process involving phospholipase A(2) (PLA(2)), cyclooxygenase (COX) and PGE synthase (PGES). BK stimulated PGE(2) release in cultured HPASMC was inhibited by the PI 3-kinase inhibitor LY294002 and the p38 MAP kinase inhibitor SB202190. The inhibitory mechanism used by LY294002 did not involve cytosolic PLA(2) activation or COX-1, COX-2 and PGES protein expression but rather a novel effect on COX enzymatic activity. SB202190 also inhibited COX activity.

PPAR gamma ligands, 15-deoxy-delta12,14-prostaglandin J2 and rosiglitazone regulate human cultured airway smooth muscle proliferation through different mechanisms

The influence of two peroxisome proliferator-activated receptor gamma (PPARgamma) ligands, a thiazolidinedione, rosiglitazone (RG) and the prostaglandin D2 metabolite 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) on the proliferation of human cultured airway smooth muscle (HASM) was examined. The increases in HASM cell number in response to basic fibroblast growth factor (bFGF, 300 pm) or thrombin (0.3 U ml-1) were significantly inhibited by either RG (1-10 microM) or 15d-PGJ2 (1-10 microM). The effects of RG, but not 15d-PGJ2, were reversed by the selective PPARgamma antagonist GW9662 (1 microM). Neither RG nor 15d-PGJ2 (10 microM) decreased cell viability, or induced apoptosis, suggesting that the regulation of cell number was due to inhibition of proliferation, rather than increased cell death. Flow-cytometric analysis of HASM cell cycle distribution 24 h after bFGF addition showed that RG prevented the progression of cells from G1 to S phase. In contrast, 15d-PGJ2 caused an increase in the proportion of cells in S phase, and a decrease in G2/M, compared to bFGF alone. Neither RG nor 15d-PGJ2 inhibited ERK phosphorylation measured 6 h post mitogen addition. The bFGF-mediated increase in cyclin D1 protein levels after 8 h was reduced in the presence of 15d-PGJ2, but not RG. Although both RG and 15d-PGJ2 can inhibit proliferation of HASM irrespective of the mitogen used, only the antiproliferative effects of RG appear to be PPARgamma-dependent. The different antimitogenic mechanisms of 15d-PGJ2 and synthetic ligands for PPARgamma may be exploited to optimise the potential for these compounds to inhibit airway remodelling in asthma. British Journal of Pharmacology (2004) 141, 517-525. doi:10.1038/sj.bjp.0705630

Interleukin-1beta, transforming growth factor-beta1, and bradykinin attenuate cyclic AMP production by human pulmonary artery smooth muscle cells in response to prostacyclin analogues and prostaglandin E2 by cyclooxygenase-2 induction and downregulation of adenylyl cyclase isoforms 1, 2, and 4

Increased levels of inflammatory cytokines contribute to the pathophysiology of pulmonary hypertension. Prostacyclin (PGI2) analogues, which relax pulmonary vessels mainly through cAMP elevation, have a major therapeutic role. In this study, we show that prolonged incubation with bradykinin (BK), interleukin-1beta (IL-1beta), and transforming growth factor-beta1 (TGF-beta1) markedly impairs cAMP accumulation in human pulmonary artery smooth muscle cells in response to short-term incubation with prostaglandin E2 (PGE2) and the PGI2 analogues iloprost and carbaprostacyclin. A similar reduction in cAMP accumulation in response to a direct adenylyl cyclase activator, forskolin, suggested that the effect was attributable to downregulation of adenylyl cyclase. Reverse transcriptase-polymerase chain reaction studies showed downregulation of adenylyl cyclase isoforms 1, 2, and 4. The effect of IL-1beta, BK, and TGF-beta1 on cAMP levels was abrogated by the selective COX-2 inhibitor NS398. Furthermore, it was mimicked by prolonged incubation with the COX-2 product PGE2 and PGI2 analogues or the COX substrate arachidonic acid, suggesting that it was mediated by endogenous prostanoids produced by COX-2. Consistent with this, IL-1beta, BK, and TGF-beta1 all induced COX-2 and PGE2 release. These results show that BK, IL-1beta, and TGF-beta1 downregulate adenylyl cyclase in human pulmonary artery smooth muscle cells via COX-2 induction and prostanoid release. This suggests a novel mechanism whereby mediators and cytokines produced in pulmonary hypertension may impair the therapeutic effects of prostacyclin analogues such as iloprost and carbaprostacyclin.

Cyclooxygenase enzymes in allergic inflammation and asthma

The cyclooxygenase enzyme system produces eicosanoids which mediate many important physiological and pathological functions. Experimental and clinical data suggest a role for this enzyme system in the pathogenesis of allergic inflammation and asthma. This article focuses on the function of this pathway in the lung, reviews evidence implicating the involvement of this pathway in asthma and allergic airway inflammation, and discusses implications for the treatment of asthmatics with cyclooxygenase inhibitors.

Cyclooxygenase (COX) inhibitors induce apoptosis in non-small cell lung cancer through cyclooxygenase independent pathways

Cyclooxygenase (COX) inhibitors are chemopreventive in many tumours but the role of COX inhibition in their effects is contentious. Here we determined if COX inhibitors influenced apoptosis in two non-small cell lung cancer cells one which over expresses COX-2 (MOR-P) and one which expresses neither isoform (H-460). NS398, a selective COX inhibitor, and indomethacin, a non-selective COX inhibitor, were cytotoxic in both cell lines, independently of their COX-2 expression. Furthermore, the cytotoxic concentrations were far greater than the concentrations required to inhibit COX. As indomethacin was more effective we used it in mechanistic studies. Indomethacin induced apoptotic cell death assessed as cytochrome c and apoptotic inducing factor (AIF) release, caspase activation, PARP, lamin B and gelsolin cleavage, chromatin condensation and nuclear fragmentation. The pan-caspase inhibitor, z-VAD, attenuated cell death, and blocked caspase activation, PARP cleavage and nuclear fragmentation without preventing cytochrome c release, suggesting that cytochrome c release is upstream of caspase activation. These observations suggest that COX inhibitors induce apoptosis in non-small lung cancer cells through cytochrome c and AIF release, and subsequent caspase activation, independently of COX-2 expression and prostaglandin production.

A clinical pharmacological study of the potential beneficial effects of a propolis food product as an adjuvant in asthmatic patients

The aqueous extract of propolis has been formulated as a nutritional food product and administered, as an adjuvant to therapy, to patients with mild to moderate asthma daily for 2 months in the framework of a comparative clinical study in parallel with a placebo preparation. The diagnosis of asthma was made according to the criteria of patient classification of the National Institutes of Health and Global Initiative for Asthma Management. At inclusion, the pulmonary forced expiratory volume in the first second (FEV1) as a percentage of the forced vital capacity (FVC) was more than 80% in mild persistent cases, and between 60 and 80% in moderate persistent cases, showing an increase in the degree of reversibility of > 15% in FEV1. All patients were on oral theophylline as controller therapy, none was receiving oral or inhaled corticosteroids, none had other comorbidities necessitating medical treatment, and all were from a middle-class community and had suffered from asthma for the last 2-5 years. Twenty-four patients received the placebo, with one drop-out during the study, while 22 received the propolis extract, with no drop-outs. The age range of the patients was 19-52 years; 36 were male and 10 female. The number of nocturnal attacks was recorded on a weekly basis, while pulmonary function tests were performed on all patients at the beginning of the trial, 1 month later and at the termination of the trial. Immunological parameters, including various cytokines and eicosanoids known to play a role in asthma, were measured in all patients at the beginning of the trial and 2 months later. Analysis of the results at the end of the clinical study revealed that patients receiving propolis showed a marked reduction in the incidence and severity of nocturnal attacks and improvement of ventilatory functions. The number of nocturnal attacks dropped from an average of 2.5 attacks per week to only 1. The improvement in pulmonary functions was manifested as a nearly 19% increase in FVC, a 29.5% increase in FEV1, a 30% increase in peak expiratory flow rate (PEFR), and a 41% increase in the forced expiratory flow rate between 25 and 75% of the vital capacity (FEF25-75). The clinical improvement was associated with decreases by 52, 65, 44 and 30%, respectively, of initial values for the pro-inflammatory cytokines tumor necrosis factor (TNF)-alpha, ICAM-1, interleukin (IL)-6 and IL-8, and a 3-fold increase in the 'protective' cytokine IL-10. The levels of prostaglandins E2 and F2alpha and leukotriene D4 were decreased significantly to 36, 39, and 28%, respectively, of initial values. Patients on the placebo preparation showed no significant improvement in ventilatory functions or in the levels of mediators. The findings suggest that the aqueous propolis extract tested is potentially effective as an adjuvant to therapy in asthmatic patients. The benefits may be related to the presence in the extract of caffeic acid derivatives and other active constituents.

Effect of bradykinin, TGF-beta1, IL-1beta, and hypoxia on COX-2 expression in pulmonary artery smooth muscle cells

Prostanoids are major regulators of smooth muscle function that are generated by cyclooxygenase (COX). Here we hypothesized that cytokines and mediators that regulate the pulmonary circulation would alter COX expression and prostanoid generation in pulmonary artery smooth muscle cells. Bradykinin, transforming growth factor-beta1 (TGF-beta1), and interleukin-1beta (IL-1beta) increased inducible COX-2 expression and prostaglandin E(2) (PGE(2)) release. Transfection studies using a COX-2 promoter construct demonstrated that all three agents acted transcriptionally. Constitutive COX-1 protein expression was unchanged. The COX inhibitor indomethacin, the COX-2 inhibitor NS-398, the protein synthesis inhibitor cycloheximide, and the glucocorticoid dexamethasone abrogated the increased PGE(2) levels. Dexamethasone and cycloheximide prevented COX-2 induction. Hypoxia (3% O(2)-5% CO(2)-92% N(2)) for 24 h selectively augmented TGF-beta1-stimulated PGE(2) production and COX-2 induction but had no effect alone. Prolonged hypoxic culture alone for 48 and 72 h enhanced COX-2 induction and increased PGE(2). These studies show that a number of stimuli are capable of inducing COX-2 in pulmonary artery smooth muscle cells. The interaction between hypoxia and TGF-beta1 may be particularly relevant to pulmonary hypertension.

Mechanisms of cytokine effects on G protein-coupled receptor-mediated signaling in airway smooth muscle

Numerous in vitro and in vivo studies have implicated the cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) as mediators of airway inflammation and therefore potentially important substances in the pathogenesis of asthma. In this study, we examined the mechanisms by which IL-1 beta and TNF-alpha affect inhibition of cell growth, G protein-coupled receptor (GPCR) desensitization, and the recently reported adenylyl cyclase sensitization in human airway smooth muscle (HASM) cultures. Our findings demonstrate that adenylyl cyclase sensitization is independent of cytokine-mediated cyclooxygenase type 2 (COX-2) and prostaglandin E(2) (PGE(2)) induction, whereas COX-2 induction appears to be required for both growth inhibition and GPCR desensitization. However, GPCR desensitization was highly dependent on the presence of EGF during chronic treatment with cytokines, which could be explained by a synergistic effect of EGF on cytokine-mediated COX-2 and PGE(2) induction. Interestingly, various agents (including inhibitors of p42/p44 and p38 mitogen-activated protein kinase signaling) were significantly more effective in inhibiting cytokine-mediated PGE(2) induction, GPCR desensitization, and cell growth inhibition than in inhibiting COX-2 induction. These data demonstrate disparity in the requirement and sufficiency of COX-2 induction in promoting different functional effects of IL-1 beta and TNF-alpha in HASM.

Immunohistochemical localization of guinea-pig leukotriene B4 12-hydroxydehydrogenase/15-ketoprostaglandin 13-reductase

We have cloned cDNA for leukotriene B4 12-hydroxydehydrogenase (LTB4 12-HD)/15-ketoprostaglandin 13-reductase (PGR) from guinea-pig liver. LTB4 12-HD catalyzes the conversion of LTB4 into 12-keto-LTB4 in the presence of NADP+, and plays an important role in inactivating LTB4. The cDNA contained an ORF of 987 bp that encodes a protein of 329 amino-acid residues with a 78% identity with porcine LTB4 12-HD. The amino acids in the putative NAD+/NADP+ binding domain are well conserved among the pig, guinea-pig, human, rat, and rabbit enzymes. The guinea-pig LTB4 12-HD (gpLTB4 12-HD) was expressed as a glutathione S-transferase (GST) fusion protein in Escherichia coli, which exhibited similar enzyme activities to porcine LTB4 12-HD. We examined the 15-ketoprostaglandin 13-reductase (PGR) activity of recombinant gpLTB4 12-HD, and confirmed that the Kcat of the PGR activity is higher than that of LTB4 12-HD activity by 200-fold. Northern and Western blot analyses revealed that gpLTB4 12-HD/PGR is widely expressed in guinea-pig tissues such as liver, kidney, small intestine, spleen, and stomach. We carried out immunohistochemical analyses of this enzyme in various guinea-pig tissues. Epithelial cells of calyx and collecting tubules in kidney, epithelial cells of airway, alveoli, epithelial cells in small intestine and stomach, and hepatocytes were found to express the enzyme. These findings will lead to the identification of the unrevealed roles of PGs and LTs in these tissues.

Mechanisms of interleukin 1beta-induced human airway smooth muscle hyporesponsiveness to histamine. Involvement of p38 MAPK NF-kappaB

We have investigated the effect of IL-1beta on histamine H(1)-receptor (H(1)R)-mediated inositol phosphate (IP) accumulation in human airway smooth muscle cells (HASMC) and on histamine-induced contraction of human bronchial rings. Stimulation of HASMC for 24 h with IL-1beta resulted in significant loss of histamine-induced IP formation, which was associated with a reduction of histamine- induced contraction of IL-1beta-treated human bronchial rings. An inhibitor of NF-kappaB activation, pyrrolidine dithiocarbamate, and a p38 MAPK inhibitor, blocked the IL-1beta-induced H(1)R desensitization, whereas anisomycin, an SAPK/JNK and p38 MAPK activator, mimicked the effect of IL-1beta. IL-1beta has been demonstrated to induce cox-2 expression and PGE(2) synthesis. In our study, indomethacin a cox antagonist, completely inhibited the effect of IL-1beta on H(1)R, whereas exogenously added PGE(2) was able to desensitize H(1)R. Furthermore, H-89, a selective PKA inhibitor, antagonized the effect of IL-1beta. Here, we have demonstrated that IL-1beta desensitizes H(1)R, which involves the activation of p38 MAPK and NF-kappaB, leading to the expression of cox-2 and the synthesis of PGE(2). PGE(2) increases intracellular cAMP resulting in PKA activation, which phosphorylates and functionally uncouples H(1)R. Our results suggest that IL-1beta protects airway smooth muscle against histamine-induced contractile responses and that bronchial hyperreactivity to histamine is not associated with proinflammatory cytokine-induced enhancement in H(1)R signaling.

Hyperosmolarity-induced relaxation and prostaglandin release in guinea pig trachea in vitro

In this study, a tracheal perfusion apparatus was used to investigate the nature of the relaxing factor released by hyperosmolarity on the epithelial side of guinea pig trachea. NaCl induced concentration-dependent relaxation. This relaxation was not affected when the trachea was preincubated with a vasoactive intestinal peptide (VIP) receptor antagonist or with the nitric oxide synthesis inhibitor N(G)-monomethyl-L-arginine (L-NMMA). When the prostaglandin synthesis was prevented by preincubation with the phospholipase A(2)-inhibitor quinacrine, or the cyclooxygenase inhibitor indomethacin, the maximal relaxation induced by NaCl was suppressed by 50% (P<0.05). Moreover, the prostaglandin E(2) concentration was four times higher (P<0.05) in the organ bath during the relaxations, whereas the nitric oxide concentration remained unchanged. In conclusion, increased osmolarity on the airway surface leads to the release of prostaglandins, which are involved in part in the hyperosmolarity-induced relaxation of airway smooth muscle. This might be relevant for asthmatic patients since prostaglandin may modulate the bronchoconstrictive response to hyperosmolar stimuli and exercise.

Modulation of airway smooth muscle tone by protease activated receptor-1,-2,-3 and -4 in trachea isolated from influenza A virus-infected mice

Relaxant and contractile effects of the tethered ligand domain sequences of murine PAR-1, PAR-2, PAR-3 and PAR-4, and of the proteases thrombin and trypsin were examined in mouse isolated tracheal preparations. The epithelium- and cyclo-oxygenase-dependence of these effects and the potential modulatory effects of respiratory tract viral infection were also investigated. In carbachol-contracted preparations, trypsin, thrombin, and the tethered ligand domain sequences of murine PAR-1 (SFFLRN-NH(2)), PAR-2 (SLIGRL-NH(2)) and PAR-4 (GYPGKF-NH(2)), but not PAR-3 (SFNGGP-NH(2)), induced transient, relaxant responses that were abolished by the cyclo-oxygenase inhibitor indomethacin. Repeated administration of SFFLRN-NH(2), SLIGRL-NH(2) or GYPGKF-NH(2) (30 microM) was associated with markedly diminished relaxation responses (homologous desensitization), although there was no evidence of cross-desensitization between these peptides. The tethered ligand domain sequences for PAR-1 and PAR-4 induced a rapid, transient contractile response that preceded the relaxant response. Contractions were not inhibited by indomethacin and were not induced by either thrombin or trypsin. Influenza A virus infection did not significantly affect the responses induced by either the proteases or peptides. Furthermore, epithelial disruption caused by mechanical rubbing had no significant effect on responses to these PAR activators in preparations from either virus- or sham-infected mice. In summary, the proteases trypsin and thrombin, and peptide activators of PAR-1, PAR-2 and PAR-4 induced relaxant responses of mouse isolated tracheal smooth muscle preparations, which were mediated by a prostanoid, probably PGE(2). Interestingly, PAR-mediated relaxations were not significantly diminished following acute damage to the epithelium caused by mechanical rubbing and/or the respiratory tract viral pathogen, influenza A. British Journal of Pharmacology (2000) 129, 63 - 70.

Regulation of renal epithelial cell affinity for calcium oxalate monohydrate crystals

The binding and internalization of calcium oxalate monohydrate (COM) crystals by tubular epithelial cells may be a critical step leading to kidney stone formation. Exposure of MDCK cells to arachidonic acid (AA) for 3 days, but not oleic or linoleic acid, decreased COM crystal adhesion by 55%. Exogenous prostaglandin PGE(1) or PGE(2) decreased crystal binding 96% within 8 h, as did other agents that raise intracellular cAMP. Actinomycin D, cycloheximide, or tunicamycin each blocked the action of PGE(2), suggesting that gene transcription, protein synthesis, and N-glycosylation were required. Blockade of crystal binding by AA was not prevented by the cyclooxygenase inhibitor flurbiprofen, and was mimicked by the nonmetabolizable AA analog eicosatetryanoic acid (ETYA), suggesting that generation of PGE from AA is not the pathway by which AA exerts its effect. These studies provide new evidence that binding of COM crystals to renal cells is regulated by physiological signals that could modify exposure of cell surface molecules to which the crystals bind. Intrarenal AA, PGs, and/or other agents that raise the intracellular concentration of cAMP may serve a protective function by preventing crystal adhesion along the nephron, thereby defending the kidney against crystal retention and stone formation.

Cholinergic contraction is altered in nNOS knockouts. Cooperative modulation of neural bronchoconstriction by nNOS and COX

Endogenous nitric oxide (NO) is a bronchodilator but its physiologic role in small airways is not clear. In this study, we investigated the role of endogenous NO in the regulation of bronchiolar tone in the small airways of wild type and NO synthase (NOS) isoform (eNOS and nNOS)-knockout mice. Pretreatment with the cyclooxygenase inhibitor indomethacin significantly enhanced electrical field stimulation (EFS)-induced contraction in the airways from all types of mice by approximately 60 to 170% (n = 8 in each case), whereas pretreatment with the NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) did not (n = 8). Combined pretreatment with L-NAME and indomethacin enhanced airway contraction of wild-type and eNOS-knockout mice to a significantly greater extent (i.e., by 140 to 290%) than did indomethacin alone (n = 8 for each). This potentiation by L-NAME was not seen in nNOS knockout mice (n = 8). Neither indomethacin nor L-NAME alone affected carbachol (CCh) potency or maximal efficacy in the airways of wild-type mice, whereas the combined pretreatment slightly enhanced the maximal response without altering the potency of CCh (n = 6). Our results show that both NO and prostaglandins modulate neuronal contraction of murine small airways. NO is produced by nNOS, which may be located in nerves, and its overall effects are tonically inhibited by cyclooxygenase products.

Protective effects of inhaled PGE2 on allergen-induced airway responses and airway inflammation

Inhalation of prostaglandin E2 (PGE2) had been reported to prevent allergen-induced bronchoconstrictor responses; however, the effects of inhaled PGE2 on allergen-induced airway inflammation or hyperresponsiveness after allergen are unknown. This study examined the effects of inhaled PGE2 on allergen-induced airway responses and inflammation. Eight mild asthmatics with a dual airway response to inhaled allergen were recruited into a double-blind randomized crossover study comparing the effects of inhaled PGE2 (100 microgram) or placebo, on allergen-induced changes in FEV1 measured for 7 h, induced sputum inflammatory cells, obtained at baseline, 7 and 24 h, and methacholine airway responsiveness measured at 24 h after challenge. Inhaled PGE2 attenuated the allergen-induced early fall in FEV1 from 24.4 +/- 3.6% after placebo to 10.3 +/- 2.5% after PGE2 (p = 0.002), the late fall in FEV1 from 21.2 +/- 2.7% after placebo to 12.6 +/- 3.6% after PGE2 (p = 0.03), allergen-induced methacholine airway hyperresponsiveness (p = 0.03) and allergen-induced increases in percent sputum eosinophils from 36.3 +/- 8.8% after placebo to 21.0 +/- 7.3% after PGE2 (p = 0.01), percentage of EG2+ cells (p = 0.02), and percentage of metachromatic cells (p = 0.02). These results indicate that inhaled PGE2 attenuates allergen-induced airway responses, hyperresponsiveness, and inflammation, when given immediately before inhaled allergen.

Airway smooth muscle as a target of glucocorticoid action in the treatment of asthma

Glucocorticoids are highly effective in the control of asthma and suppression of airway inflammation. The cellular and molecular mechanisms involved in the anti-inflammatory actions of glucocorticoids are becoming clearer. Although it is apparent that glucocorticoids have effects on many aspects of inflammation, it is not certain which actions on which cell types are the most critical in controlling asthma. Airway smooth muscle cells represent a significant proportion of all cells present in the airways and might therefore be expected to be a prominent cellular target for inhaled steroids. Despite this, little is known of the action of glucocorticoids on airway smooth muscle. It is becoming clear that in addition to its contractile properties, airway smooth muscle can potentially contribute to the pathogenesis of asthma by increased proliferation and by expression and secretion of pro-inflammatory cytokines and mediators, which in turn may lead to the activation and recruitment of key inflammatory cells in the airways. This review examines the action of glucocorticoids on some of the diverse functions of airway smooth muscle that are implicated in remodeling of the airways in asthma. Glucocorticoids either directly or indirectly modulate contraction of airway smooth muscle by suppressing agonist-induced increases in intracellular calcium levels or by downregulating or uncoupling receptors linked to contraction (e.g., muscarinic M2 or M3, histamine H1 receptors). In addition, glucocorticoids may augment relaxation of airway smooth muscle by increasing activation of either cyclic AMP-dependent (e.g., increased expression of beta2-adrenoceptors, reduced homologous desensitization of beta2-adrenoceptors) or AMP-independent mechanisms (e.g., increased Na+/K+ electrogenic pump activity). In addition to their effects on contraction, glucocorticoids are also effective antiproliferative agents in airway smooth muscle, but under some circumstances may also contribute to proliferation by inhibiting the antiproliferative effect of high concentrations of tumor necrosis factor alpha in these cells. Glucocorticoids also suppress induction of cyclooxygenase-2 in human airway smooth muscle cells and the subsequent synthesis and release of arachidonic acid metabolites, particularly prostaglandin E2. The potential of airway smooth muscle to recruit and activate pro-inflammatory cells such as the eosinophil may also be reduced by glucocorticoids, as they are effective in preventing the release of several cytokines (e.g., RANTES, interleukin-8, and granulocyte macrophage colony-stimulating factor). The possibility exists that as we begin to understand and speculate more about the likely role of airway smooth muscle in the pathogenesis of asthma, it may be necessary to reconsider airway smooth muscle as an important cellular target for the action of glucocorticoids in the treatment of asthma.

Role of cyclo-oxygenase-2 induction in interleukin-1beta induced attenuation of cultured human airway smooth muscle cell cyclic AMP generation in response to isoprenaline

Airway smooth muscle (ASM) in human asthma shows reduced relaxation and cyclic AMP generation in response to beta-adrenoceptor agonists. IL-beta attenuates cyclic AMP generation but the underlying mechanism is unclear. We have reported that IL-1beta induces cyclo-oxygenase-2 (COX-2) in human ASM cells and results in a marked increase in prostanoid generation with PGE2 and PGI2 as the major products. We investigated the role of COX-2 induction and prostanoid release (measured as PGE2) in IL-1beta induced attenuation of cyclic AMP generation in response to the beta-adrenoceptor agonist isoprenaline (ISO). Pre-treatment of human ASM cells with IL-1beta significantly attenuated cyclic AMP generation in response to high concentrations of ISO (1.0-10.0 microM) in a time- and concentration-dependent manner. The effect was accompanied by a high concentration of PGE2 release. The non-selective COX inhibitor indomethacin (Ind), the selective COX-2 inhibitor NS-398, the protein synthesis inhibitors cycloheximide (CHX) and actinomycin D and the steroid dexamethasone (Dex) all abolished the PGE2 release and prevented the attenuated cyclic AMP generation. COX substrate arachidonic acid time- and concentration-dependently mimicked IL-1beta induced attenuation and the effect was prevented by the non-selective COX inhibitors Ind and flurbiprofen, but not by NS-398, CHX and Dex. In contrast to IL-1beta, TNFalpha and IFNgamma, which are ineffective in inducing COX-2 and releasing PGE2 from human ASM cells, did not affect the cyclic AMP formation. Our study demonstrates that COX-2 induction and the consequent release of prostanoids plays a crucial role in IL-1beta induced attenuation of human ASM cell cyclic AMP response to ISO.

Inhibition of serum and transforming growth factor beta (TGF-beta1)-induced DNA synthesis in confluent airway smooth muscle by heparin

1. Airway remodelling occurs in asthma and involves an increase in airway smooth muscle mass through cell proliferation and hypertrophy. Increased eosinophil density in the airways is a feature of asthma. Eosinophils exhibiting activation in the airways of asthmatics also exhibit increased expression of transforming growth factor beta (TGF-beta1). We have examined the capacity of TGF-beta1 and epidermal growth factor (EGF) to influence airway smooth muscle division and the effect of heparin on TGF-beta1. EGF and serum-induced smooth muscle DNA synthesis in confluent airway smooth muscle cells (ASMC) as an indication of entry into S phase preceding mitogenesis. 2. ASMC were obtained from cell populations growing out from explanted bovine trachealis muscle sections. Cell division was monitored in sparse plated cells by direct cell counting following nuclear staining. Cell DNA synthesis in confluent cells was monitored by uptake of [3H]-thymidine. 3. TGF-beta1 (100 microM) inhibited FBS (10%)-induced smooth muscle division in sparsely plated cells (40%). TGF-beta1 (100 pM) increased cell DNA synthesis (200%) in confluent cells in the presence of bovine serum albumin (BSA, 0.25%). EGF (0.7 nM) also increased airway smooth muscle DNA synthesis (69%) in the presence of BSA (0.25%). The facilitatory effect of TGF-beta1 was observed between 1-100 pM, while that of EGF was observed between 20 200 pM. 4. Heparin inhibited serum and TGF-beta1-induced DNA synthesis in confluent ASMC (55%), consistent with our previous observation of inhibition of division in sparsely populated ASMC (Kilfeather et al., 1995a). This action of heparin was observed between concentrations of 1-100 microg ml(-1). Heparin did not inhibit DNA synthesis in response to EGF. An anti-mitogenic effect of heparin was also observed against responses to combined exposure to TGF-beta1 and EGF. 5. There was a clear inhibitory effect of heparin in absolute terms against serum-induced division in cells plated at 10, 20 and 45 x 10(3) cells cm(-2). The inhibitory effect of heparin was also observed at a plating density of 45,000 cells cm(-2) when responses to serum were expressed as fold-stimulation of basal DNA synthesis. 6. These findings demonstrate a potential role of TGF-beta1, EGF and heparin-related molecules in regulation of airway smooth muscle division.

Airway epithelium: more than just a barrier!

Airway hyper-responsiveness and epithelial cell damage are associated commonly with asthma. The airway epithelium is a physical barrier that protects sensory nerves and smooth muscle from stimulation by inhaled irritants. In addition, epithelial cells release mediators that can inhibit bronchoconstriction by relaxing the underlying smooth muscle: so-called 'epithelium-derived relaxing factors' (EpiDRFs). Clear functional evidence for EpiDRFs is provided by experiments where different endogenous mediators induce the relaxation of tracheas containing epithelium, but cause a contraction in preparations lacking this layer. Here, Gert Folkerts and Frans Nijkamp describe the pharmacological relevance of the putative EpiDRFs, prostaglandin E2 and NO, in the modulation of airway tone under basal conditions in vitro and in vivo. Special attention is paid to the role of both EpiDRFs in the development of airway hyper-responsiveness in animal models and in patients with asthma.

PGE2 release by bradykinin in human airway smooth muscle cells: involvement of cyclooxygenase-2 induction

Prostanoids may be involved in bradykinin (BK)-induced bronchoconstriction in asthma. We investigated whether cyclooxygenase (COX)-2 induction was involved in prostaglandin (PG) E2 release by BK in cultured human airway smooth muscle (ASM) cells and analyzed the BK receptor subtypes responsible. BK stimulated PGE2 release, COX activity, and COX-2 induction in a concentration- and time-dependent manner. It also time dependently enhanced arachidonic acid release. In short-term (15-min) experiments, BK stimulated PGE2 generation but did not increase COX activity or induce COX-2. In long-term (4-h) experiments, BK enhanced PGE2 release and COX activity and induced COX-2. The long-term responses were inhibited by the protein synthesis inhibitors cycloheximide and actinomycin D and the steroid dexamethasone. The effects of BK were mimicked by the B2-receptor agonist [Tyr(Me)8]BK, whereas the B1 agonist des-Arg9-BK was weakly effective at high concentrations. The B2 antagonist HOE-140 potently inhibited all the effects, but the B1 antagonist des-Arg9,(Leu8)-BK was inactive. This study is the first to demonstrate that BK can induce COX-2. Conversion of increased arachidonic acid release to PGE2 by COX-1 is mainly involved in the short-term effect, whereas B2 receptor-related COX-2 induction is important in the long-term PGE2 release.

Bradykinin stimulates cAMP synthesis via mitogen-activated protein kinase-dependent regulation of cytosolic phospholipase A2 and prostaglandin E2 release in airway smooth muscle

Bradykinin stimulates cAMP synthesis in cultured airway smooth muscle (ASM) cells. This occurs via a pathway that involves: (1) the protein kinase C (PKC)-dependent activation of mitogen-activated protein kinase (MAPK); (2) the MAPK-dependent phosphorylation and activation of cytosolic phospholipase A2 (cPLA2) and (3) the utilization of cPLA2-derived arachidonate by the cyclo-oxygenase pathway to produce prostaglandin E2 (PGE2). PGE2 is released and binds to cell surface receptors to stimulate intracellular cAMP synthesis. The signalling pathway was confirmed by the use of PD098059 [the inhibitor of MAPK kinase-1 (MEK-1) activation], AACOCF3 (an inhibitor of cPLA2) and indomethacin (an inhibitor of cyclo-oxygenase), which all reduced bradykinin-stimulated cAMP synthesis. Bradykinin also elicits the inhibition of approx. 60% of the total cAMP phosphodiesterase activity in the cell [Stevens, Pyne, Grady and Pyne (1994) Biochem. J. 297, 233-239]. This is likely to decrease the rate of cAMP degradation markedly and therefore to potentiate PGE2-stimulated cAMP synthesis. Acute treatment of ASM cells with PMA (a direct activator of PKC) also stimulated the MAPK-dependent phosphorylation of cPLA2. However, in contrast with bradykinin, PMA did not stimulate arachidonate release, suggesting that additional signals (e.g. Ca2+ ions) are required for phosphorylation by MAPK to activate cPLA2. PMA was also without effect on PGE2 release and cAMP synthesis. Evidence that PKC can also directly regulate adenylate cyclase was obtained by using cells pretreated with cholera toxin. Under these conditions, PMA stimulated cAMP synthesis independently of arachidonate metabolites. Furthermore the combined treatment of cells with PMA (to activate PKC) and PGE2 (to activate Gs) stimulated synergistic cAMP synthesis. This might be due to the presence of the type 2 adenylate cyclase, which is synergistically activated by Gs and PKC.