Reduced expression of the prostaglandin E2 receptor E-prostanoid 2 on bronchial mucosal leukocytes in patients with aspirin-sensitive asthma

Mast cells: The Janus of type 2 inflammation

Mast cells (MCs) are effectors in type 2 immunity, well known for their detrimental roles in allergy. In this issue of Immunity, Alhallak et al. now identify a protective role of MCs against exacerbated immune responses mediated by prostaglandin E2 (PGE2)-driven soluble ST2.

Mast cells control lung type 2 inflammation via prostaglandin E2-driven soluble ST2

Severe asthma and sinus disease are consequences of type 2 inflammation (T2I), mediated by interleukin (IL)-33 signaling through its membrane-bound receptor, ST2. Soluble (s)ST2 reduces available IL-33 and limits T2I, but little is known about its regulation. We demonstrate that prostaglandin E2 (PGE2) drives production of sST2 to limit features of lung T2I. PGE2-deficient mice display diminished sST2. In humans with severe respiratory T2I, urinary PGE2 metabolites correlate with serum sST2. In mice, PGE2 enhanced sST2 secretion by mast cells (MCs). Mice lacking MCs, ST2 expression by MCs, or E prostanoid (EP)2 receptors by MCs showed reduced sST2 lung concentrations and strong T2I. Recombinant sST2 reduced T2I in mice lacking PGE2 or ST2 expression by MCs back to control levels. PGE2 deficiency also reversed the hyperinflammatory phenotype in mice lacking ST2 expression by MCs. PGE2 thus suppresses T2I through MC-derived sST2, explaining the severe T2I observed in low PGE2 states.

Sphingosine-1-phosphate induces airway smooth muscle hyperresponsiveness and proliferation

BACKGROUND

The emerging role of sphingosine-1-phosphate (S1P) in regulating smooth muscle functions has led to the exploration of the possibility that this sphingolipid could represent a potential therapeutic target in asthma and other lung diseases. Several studies in animal surrogates have suggested a role for S1P-mediated signaling in the regulation of airway smooth muscle (ASM) contraction, airway hyperresponsiveness, and airway remodeling, but evidence from human studies is lacking.

OBJECTIVE

We sought to compare the responsiveness of the airways to S1P in healthy and asthmatic individuals in vivo, in isolated human airways ex vivo, and in murine airways dissected from healthy and house dust mite (HDM)-sensitized animals.

METHODS

Airway responsiveness was measured by spirometry during inhalation challenges and by wire myography in airways isolated from human and mouse lungs. Thymidine incorporation and calcium mobilization assays were used to study human ASM cell responses.

RESULTS

S1P did not induce contraction of airways isolated from healthy and HDM-exposed mice, nor in human airways. Similarly, there was no airway constriction observed in healthy and asthmatic subjects in response to increasing concentrations of inhaled S1P. However, a 30-minute exposure to S1P induced a significant concentration-dependent enhancement of airway reactivity to methacholine and to histamine in murine and human airways, respectively. HDM-sensitized mice demonstrated a significant increase in methacholine responsiveness, which was not further enhanced by S1P treatment. S1P also concentration-dependently enhanced proliferation of human ASM cells, an effect mediated through S1P receptor type 2, as shown by selective antagonism and S1P receptor type 2 small-interfering RNA knockdown.

CONCLUSIONS

Our data suggest that S1P released locally into the airways may be involved in the regulation of ASM hyperresponsiveness and hyperplasia, defining a novel target for future therapies.

Mechanisms by which dupilumab normalizes eicosanoid metabolism and restores aspirin-tolerance in AERD: A hypothesis

Aspirin-exacerbated respiratory disease (AERD) is associated with overproduction of proinflammatory cysteinyl leukotrienes (CysLTs), defective generation of anti-inflammatory prostaglandin E₂ (PGE₂), and reduced expression of the EP2 receptor for PGE₂. Reduced PGE₂ synthesis results from the downregulation of inducible COX-2. Because PGE₂ signaling via EP2 inhibits the 5-lipoxygenase/leukotriene C₄ synthase-dependent pathway, the deficient levels of both PGE₂ and EP2 likely contribute to the excessive baseline production of cysteinyl leukotrienes in patients with AERD compared with in patients with aspirin-tolerant asthma. The COX-2 pathway is regulated by an autocrine metabolic loop involving IL-1β, IL-1 receptor type I, EP2, COX-2, membrane-bound PGE₂ prostaglandin E₂ synthase-1, and PGE₂. Previous studies reported that this metabolic loop is dysregulated in patients with AERD. When the downexpressed EP2 receptor is normalized, the entire loop returns to its normal function. Cotreatment of airway cells from healthy subjects with IL-4 and IFN-γ induces alterations in the metabolic loop similar to those seen in patients with AERD. In these patients, IL-4, which is produced in excess in airways of patients with AERD, likely contributes to the alteration of normal functioning of the autocrine metabolic loop involving IL-1β, IL-1 receptor type I, EP2, COX-2, membrane-bound PGE₂ prostaglandin E₂ synthase-1, and PGE₂. We hypothesized that by blocking IL-4 action, dupilumab normalizes EP2 expression and restores the normal functioning of the COX-2 pathway autocrine metabolic loop, thereby normalizing the synthesis of PGE₂ and restoring aspirin tolerance.

Updates on immune mechanisms in aspirin-exacerbated respiratory disease

Aspirin-exacerbated respiratory disease has fascinated and frustrated specialists in allergy/immunology, pulmonology, and otorhinolaryngology for decades. It generally develops in previously healthy young adults and is unremitting and challenging to treat. The classical triad of asthma, nasal polyposis, and pathognomonic respiratory reactions to aspirin and other cyclooxygenase-1 inhibitors is accompanied by high levels of mast cell activation, cysteinyl leukotriene production, platelet activation, and severe type 2 respiratory inflammation. The "unbraking" of mast cell activation and further cysteinyl leukotriene generation induced by cyclooxygenase-1 inhibition reflect an idiosyncratic dependency on cyclooxygenase-1-derived products, likely prostaglandin E2, to maintain a tenuous homeostasis. Although cysteinyl leukotrienes are clear disease effectors, little else was known about their cellular sources and targets, and the contributions from other mediators and type 2 respiratory inflammation effector cells to disease pathophysiology were unknown until recently. The applications of targeted biological therapies, single-cell genomics, and transgenic animal approaches have substantially advanced our understanding of aspirin-exacerbated respiratory disease pathogenesis and treatment and have also revealed disease heterogeneity. This review covers novel insights into the immunopathogenesis of aspirin-exacerbated respiratory disease from each of these lines of research, including the roles of lipid mediators, effector cell populations, and inflammatory cytokines, discusses unanswered questions regarding cause and pathogenesis, and considers potential future therapeutic options.

Machine learning in the diagnosis of asthma phenotypes during coronavirus disease 2019 pandemic

Background

During the coronavirus disease 2019 (COVID‐19) pandemic, it has become a pressing need to be able to diagnose aspirin hypersensitivity in patients with asthma without the need to use oral aspirin challenge (OAC) testing. OAC is time consuming and is associated with the risk of severe hypersensitive reactions. In this study, we sought to investigate whether machine learning (ML) based on some clinical and laboratory procedures performed during the pandemic might be used for discriminating between patients with aspirin hypersensitivity and those with aspirin‐tolerant asthma.

Methods

We used a prospective database of 135 patients with non‐steroidal anti‐inflammatory drug (NSAID)–exacerbated respiratory disease (NERD) and 81 NSAID‐tolerant (NTA) patients with asthma who underwent OAC. Clinical characteristics, inflammatory phenotypes based on sputum cells, as well as eicosanoid levels in induced sputum supernatant and urine were extracted for the purpose of applying ML techniques.

Results

The overall best ML model, neural network (NN), trained on a set of best features, achieved a sensitivity of 95% and a specificity of 76% for diagnosing NERD. The 3 promising models (i.e., multiple logistic regression, support vector machine, and NN) trained on a set of easy‐to‐obtain features including only clinical characteristics and laboratory data achieved a sensitivity of 97% and a specificity of 67%.

Conclusions

ML techniques are becoming a promising tool for discriminating between patients with NERD and NTA. The models are easy to use, safe, and achieve very good results, which is particularly important during the COVID‐19 pandemic.

Polymorphisms in Human IL4, IL10, and TNF Genes Are Associated with an Increased Risk of Developing NSAID-Exacerbated Respiratory Disease

Background: The role of genetics in non-steroidal anti-inflammatory drugs (NSAID) exacerbated respiratory disease (NERD) is unclear, with different candidates involved, such as HLA genes, genes related to leukotriene synthesis, and cytokine genes. This study aimed to determine possible associations between 22 polymorphisms in 13 cytokine genes. Methods: We included 195 patients (85 with NERD and 110 with respiratory disease who tolerate NSAIDs) and 156 controls (non-atopic individuals without a history of asthma, nasal polyposis (NP), or NSAID hypersensitivity). Genotyping was performed by sequence-specific primer polymerase chain reaction (PCR-SSP). Amplicons were analyzed by horizontal gel electrophoresis in 2% agarose. Results: Significant differences in allele and genotype frequency distributions were found in TNF (rs1800629), IL4 (rs2243248 and rs2243250), and IL10 (rs1800896, rs1800871, and rs1800872) genes in patients with NSAID hypersensitivity. In all cases, the minor allele and the heterozygous genotype were more prevalent in NERD. An association of TNF rs1800629 SNP with respiratory disease in NSAID-tolerant patients was also found. Conclusions: Retrospectively recorded, we found strong associations of NERD with polymorphisms in IL4, IL10, and TNF genes, suggesting that these genes could be involved in the inflammatory mechanisms underlying NERD.

Effects of non-steroidal anti-inflammatory drugs and other eicosanoid pathway modifiers on antiviral and allergic responses: EAACI task force on eicosanoids consensus report in times of COVID-19

Non‐steroidal anti‐inflammatory drugs (NSAIDs) and other eicosanoid pathway modifiers are among the most ubiquitously used medications in the general population. Their broad anti‐inflammatory, antipyretic, and analgesic effects are applied against symptoms of respiratory infections, including SARS‐CoV‐2, as well as in other acute and chronic inflammatory diseases that often coexist with allergy and asthma. However, the current pandemic of COVID‐19 also revealed the gaps in our understanding of their mechanism of action, selectivity, and interactions not only during viral infections and inflammation, but also in asthma exacerbations, uncontrolled allergic inflammation, and NSAIDs‐exacerbated respiratory disease (NERD). In this context, the consensus report summarizes currently available knowledge, novel discoveries, and controversies regarding the use of NSAIDs in COVID‐19, and the role of NSAIDs in asthma and viral asthma exacerbations. We also describe here novel mechanisms of action of leukotriene receptor antagonists (LTRAs), outline how to predict responses to LTRA therapy and discuss a potential role of LTRA therapy in COVID‐19 treatment. Moreover, we discuss interactions of novel T2 biologicals and other eicosanoid pathway modifiers on the horizon, such as prostaglandin D2 antagonists and cannabinoids, with eicosanoid pathways, in context of viral infections and exacerbations of asthma and allergic diseases. Finally, we identify and summarize the major knowledge gaps and unmet needs in current eicosanoid research.

Lipid-mediated innate lymphoid cell recruitment and activation in aspirin-exacerbated respiratory disease

OBJECTIVE

To synthesize investigations into the role of lipid-mediated recruitment and activation of group 2 innate lymphoid cells (ILC2s) in aspirin-exacerbated respiratory disease (AERD).

DATA SOURCES

A comprehensive literature review of reports pertaining to cellular mechanisms, cytokine, and lipid mediators in AERD, as well as ILC2 activation and recruitment, was performed using PubMed and Google Scholar.

STUDY SELECTIONS

Selections of studies were based on reports of lipid mediators in AERD, cytokine mediators in AERD, type 2 effector cells in AERD, platelets in AERD, AERD treatment, ILC2s in allergic airway disease, and ILC2 activation, inhibition, and trafficking.

RESULTS

The precise mechanisms of AERD pathogenesis are not well understood. Greater levels of proinflammatory lipid mediators and type 2 cytokines are found in tissues derived from patients with AERD relative to controls. After pathognomonic cyclooxygenase-1 inhibitor reactions, proinflammatory mediator concentrations (prostaglandin D2 and cysteinyl leukotrienes) are rapidly increased, as are ILC2 levels in the nasal mucosa. The ILC2s, which potently generate type 2 cytokines in response to lipid mediator stimulation, may play a key role in AERD pathogenesis.

CONCLUSION

Although the literature suggests that lipid-mediated ILC2 activation may occur in AERD, there is a dearth of definitive evidence. Future investigations leveraging novel next-generation single-cell sequencing approaches along with recently developed AERD murine models will better define lipid mediator-induced ILC2 trafficking in patients with AERD.

Current perspective on eicosanoids in asthma and allergic diseases: EAACI Task Force consensus report, part I

Eicosanoids are biologically active lipid mediators, comprising prostaglandins, leukotrienes, thromboxanes, and lipoxins, involved in several pathophysiological processes relevant to asthma, allergies, and allied diseases. Prostaglandins and leukotrienes are the most studied eicosanoids and established inducers of airway pathophysiology including bronchoconstriction and airway inflammation. Drugs inhibiting the synthesis of lipid mediators or their effects, such as leukotriene synthesis inhibitors, leukotriene receptors antagonists, and more recently prostaglandin D₂ receptor antagonists, have been shown to modulate features of asthma and allergic diseases. This review, produced by an European Academy of Allergy and Clinical Immunology (EAACI) task force, highlights our current understanding of eicosanoid biology and its role in mediating human pathology, with a focus on new findings relevant for clinical practice, development of novel therapeutics, and future research opportunities.

Could Arachidonic Acid-Derived Pro-Resolving Mediators Be a New Therapeutic Strategy for Asthma Therapy?

Asthma represents one of the leading chronic diseases worldwide and causes a high global burden of death and disability. In asthmatic patients, the exacerbation and chronification of the inflammatory response are often related to a failure in the resolution phase of inflammation. We reviewed the role of the main arachidonic acid (AA) specialized pro-resolving mediators (SPMs) in the resolution of chronic lung inflammation of asthmatics. AA is metabolized by two classes of enzymes, cyclooxygenases (COX), which produce prostaglandins (PGs) and thromboxanes, and lypoxygenases (LOX), which form leukotrienes and lipoxins (LXs). In asthma, two primary pro-resolving derived mediators from COXs are PGE₂ and the cyclopentenone prostaglandin15-Deoxy-Delta-12,14-PGJ₂ (15d-PGJ₂) while from LOXs are the LXA₄ and LXB₄. In different models of asthma, PGE₂, 15d-PGJ₂, and LXs reduced lung inflammation and remodeling. Furthermore, these SPMs inhibited chemotaxis and function of several inflammatory cells involved in asthma pathogenesis, such as eosinophils, and presented an antiremodeling effect in airway epithelial, smooth muscle cells and fibroblasts in vitro. In addition, PGE₂, 15d-PGJ₂, and LXs are all able to induce macrophage reprogramming to an alternative M2 pro-resolving phenotype in vitro and in vivo. Although PGE₂ and LXA₄ showed some beneficial effects in asthmatic patients, there are limitations to their clinical use, since PGE₂ caused side effects, while LXA₄ presented low stability. Therefore, despite the strong evidence that these AA-derived SPMs induce resolution of both inflammatory response and tissue remodeling in asthma, safer and more stable analogs must be developed for further clinical investigation of their application in asthma treatment.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Aspirin sensitivity: Lessons in the regulation (and dysregulation) of mast cell function

The idiosyncratic activation of mast cells (MCs) in response to administration of nonselective COX inhibitors is a cardinal feature of aspirin-exacerbated respiratory disease (AERD). Older studies using MC-stabilizing drugs support a critical role for MCs and their products in driving the severe eosinophilic inflammation and respiratory dysfunction that is typical of AERD. Because patients with AERD react to all nonselective COX inhibitors regardless of their chemical structure, the mechanism of MC activation is not caused by classical, antigen-induced cross-linking of IgE receptors. Recent studies in both human subjects and animal models have revealed a complex and multifactorial process culminating in dysregulation of MC function and an aberrant dependency on COX-1-derived prostaglandin E₂ to maintain a tenuous homeostasis. This article reviews the factors most likely to contribute to MC dysregulation in patients with AERD and the potential diagnostic and therapeutic implications.

Unique Effect of Aspirin Therapy on Biomarkers in Aspirin-exacerbated Respiratory Disease. A Prospective Trial

Rationale: Daily high-dose aspirin therapy benefits many patients with aspirin-exacerbated respiratory disease but provides no benefit for aspirin-tolerant patients with asthma. Type 2 inflammation characterizes aspirin-exacerbated respiratory disease.Objectives: To determine whether high-dose aspirin therapy changes biomarkers of type 2 inflammation in aspirin-exacerbated respiratory disease.Methods: Forty-two subjects with aspirin-exacerbated respiratory disease underwent an aspirin desensitization and were placed on high-dose aspirin (1,300 mg daily). Fifteen aspirin-tolerant subjects with asthma were also placed on high-dose aspirin. Biologic specimens and clinical parameters were collected at baseline and after 8 weeks on aspirin. Urinary eicosanoids, plasma tryptase and cytokine levels, platelet-leukocyte aggregates, and granulocyte transcripts were assessed.Measurements and Main Results: Eight weeks of high-dose aspirin decreased nasal symptoms and urinary prostaglandin E metabolite (P < 0.05) and increased urinary leukotriene E4 (P < 0.01) levels in subjects with aspirin-exacerbated respiratory disease, but not in those with aspirin-tolerant asthma. Urinary prostaglandin D2 and thromboxane metabolites decreased in both groups. Only in subjects with aspirin-exacerbated respiratory disease, exhaled nitric oxide (P < 0.05), plasma tryptase (P < 0.01), and blood eosinophil (P < 0.01) and basophil (P < 0.01) counts increased and plasma tryptase correlated with eosinophil counts (Pearson r = 0.514; P < 0.01) on aspirin. After correction for eosinophil counts, aspirin-induced changes in blood granulocyte transcripts did not differ between groups. Aspirin had no effect on platelet-leukocyte aggregates, platelet activation markers, or plasma cytokines in either group.Conclusions: High-dose aspirin therapy for 8 weeks paradoxically increases markers of type 2 inflammation in subjects with aspirin-exacerbated respiratory disease, despite reducing nasal symptoms. This effect of aspirin is unique to aspirin-exacerbated respiratory disease and not observed in subjects with aspirin-tolerant asthma.

Suppression of aspirin-mediated eosinophil activation by prostaglandin E2: Relevance to aspirin and nonsteroidal anti-inflammatory drug hypersensitivity

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is characterized by severe, sometimes life-threatening reactions to nonsteroidal anti-inflammatory drugs (NSAIDs). Mechanisms driving the disease include overproduction of leukotrienes and loss of anti-inflammatory prostaglandin E₂ (PGE₂) production. Many cell types contribute to the disease; however, eosinophils are markedly elevated and are important drivers of pathologic findings.

OBJECTIVE

To investigate the capacity of aspirin and NSAIDs to drive eosinophil activation and the ability of PGE₂ to inhibit this activation.

METHODS

Eosinophils were purified from blood of healthy individuals without AERD and stimulated with lysine aspirin, ketorolac, or sodium salicylate. The role of PGE₂ in altering activation was determined by incubating eosinophils with increasing doses of PGE₂ before lysine aspirin stimulation. Specific PGE₂ receptor use was determined by incubating eosinophils with receptor agonists and antagonists before aspirin stimulation. Cysteinyl leukotrienes (CysLTs), leukotriene B₄ (LTB₄), and eosinophil-derived neurotoxin (EDN) were quantified by enzyme-linked immunosorbent assay.

RESULTS

Stimulation of eosinophils with lysine aspirin, ketorolac, or sodium salicylate resulted in secretion of CysLTs and LTB₄ in the absence of EDN release. Low doses of PGE₂ inhibited LTB₄ and CysLT release, an effect lost at higher PGE₂ concentrations. Use of butaprost, an EP₂ receptor agonist, suppressed lysine aspirin stimulation. This mechanism was supported by blocking activity of the EP₁ and EP₃ receptors.

CONCLUSION

Eosinophils can be directly activated by NSAIDs via cyclooxygenase-independent pathways to produce CysLTs and LTB₄. This effect can be inhibited by PGE₂ acting through the EP₂ receptor. The recognized loss of EP₂ receptor expression combined with low PGE₂ levels explains in part the sensitivity to NSAIDs.

Prostaglandin E2 in NSAID-exacerbated respiratory disease: protection against cysteinyl leukotrienes and group 2 innate lymphoid cells

PURPOSE OF REVIEW

The purpose of this review is to describe the recent advances that have been made in understanding the protective role of prostaglandin E2 (PGE2) in aspirin-exacerbated respiratory disease (AERD), known in Europe as NSAID-exacerbated respiratory disease (N-ERD).

RECENT FINDINGS

Decreased PGE2 signaling through the EP2 receptor in patients with AERD leads to an increase in leukotriene synthesis and signaling. Leukotriene signaling not only directly activates group 2 innate lymphoid cells and mast cells, but it also increases production of IL-33 and thymic stromal lymphopoietin. These cytokines drive Th2 inflammation in a suspected feed-forward mechanism in patients with AERD.

SUMMARY

Recent discoveries concerning the role of PGE2 in leukotriene synthesis and signaling in AERD, as well as downstream effects on group 2 innate lymphoid cells and mast cells, allow for a more comprehensive understanding of the pathogenesis of this disease. These discoveries also identify new paths of potential investigation and possible therapeutic targets for AERD.

Pathogenesis of NSAID-induced reactions in aspirin-exacerbated respiratory disease

It is well-established that following ingestion of aspirin or any other inhibitor of cyclooxygenase-1, patients with Samter's disease, or aspirin-exacerbated respiratory disease (AERD) develop the sudden onset of worsening respiratory clinical symptoms, which usually involves nasal congestion, rhinorrhea, wheezing and bronchospasm. Gastrointestinal distress, nausea, a pruritic rash and angioedema can also occasionally develop. However, the underlying pathologic mechanism that drives these clinical reactions remains elusive. Pretreatment with medications that inhibit the leukotriene pathway decreases the severity of clinical reactions, which points to the involvement of cysteinyl leukotrienes (cysLTs) in the pathogenesis of these aspirin-induced reactions. Furthermore, studies of aspirin challenges in carefully-phenotyped patients with AERD have confirmed that both proinflammatory lipid mediators, predominantly cysLTs and prostaglandin (PG) D₂, and the influx of effector cells to the respiratory tissue, contribute to symptom development during aspirin-induced reactions. Mast cells, which have been identified as the major cellular source of cysLTs and PGD₂, are likely to be major participants in the acute reactions, and are an attractive target for future pharmacotherapies in AERD. Although several recent studies support the role of platelets as inflammatory effector cells and as a source of cysLT overproduction in AERD, it is not yet clear whether platelet activation plays a direct role in the development of the aspirin-induced reactions. To further our understanding of the pathogenesis of aspirin-induced reactions in AERD, and to broaden the pharmacotherapeutic options available to these patients, additional investigations with targeted clinical trials will be required.

Hypersensitivity reactions to nonsteroidal anti-inflammatory drugs: an update on pharmacogenetics studies

Nonsteroidal anti-inflammatory drugs are the medications most frequently involved in hypersensitivity reactions to drugs. These can be induced by specific immunological and nonimmunological mechanisms, being the latter the most frequent. The nonimmunological mechanism is related to an imbalance of inflammatory mediators, which is aggravated by the cyclooxygenase inhibition. Genetic studies suggest that multiples genes and additional mechanisms might be involved. The proposals of this review is summarize the contribution of variations in genes involved in the arachidonic acid, inflammatory and immune pathways as well as the recent genome-wide association studies findings related to cross-intolerant nonsteroidal anti-inflammatory drugs hypersensitivity reactions. In addition, using integration of different genetic studies, we propose new target genes. This will help to understand the underlying mechanism of these reactions.

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.

Role of lipid mediators and control of lymphocyte responses in type 2 immunopathology

Type 2 immunopathology is a cardinal feature of allergic diseases and involves cooperation between adaptive immunity and innate effector responses. Virtually all cell types relevant to this pathology generate leukotriene and/or prostaglandin mediators that derive from arachidonic acid, express receptors for such mediators, or both. Recent studies highlight prominent functions for these mediators in communication between the innate and adaptive immune systems, as well as amplification or suppression of type 2 effector responses. This review focuses on recent advances and insights, and highlights existing and potential therapeutic applications of drugs that target these mediators or their receptors, with a special emphasis on their regulation of the innate and adaptive lymphocytes relevant to type 2 immunopathology.

Lipid Mediators in Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) is a syndrome of severe asthma and rhinosinusitis with nasal polyposis with exacerbations of baseline eosinophil-driven and mast cell-driven inflammation after nonsteroidal antiinflammatory drug ingestion. Although the underlying pathophysiology is poorly understood, dysregulation of the cyclooxygenase and 5-lipoxygenase pathways of arachidonic acid metabolism is thought to be key. Central features of AERD pathogenesis are overproduction of proinflammatory and bronchoconstrictor cysteinyl leukotrienes and prostaglandin (PG) D₂ and inhibition of bronchoprotective and antiinflammatory PGE₂. Imbalance in the ratio of these lipid mediators likely leads to the increased eosinophilic and mast cell inflammatory responses in the respiratory tract.

Prostaglandin E2 suppresses human group 2 innate lymphoid cell function

Background

Group 2 innate lymphoid cells (ILC2s) are involved in the initial phase of type 2 inflammation and can amplify allergic immune responses by orchestrating other type 2 immune cells. Prostaglandin (PG) E₂ is a bioactive lipid that plays protective roles in the lung, particularly during allergic inflammation.

Objective

We set out to investigate how PGE₂ regulates human ILC2 function.

Methods

The effects of PGE₂ on human ILC2 proliferation and intracellular cytokine and transcription factor expression were assessed by means of flow cytometry. Cytokine production was measured by using ELISA, and real-time quantitative PCR was performed to detect PGE₂ receptor expression.

Results

PGE₂ inhibited GATA-3 expression, as well as production of the type 2 cytokines IL-5 and IL-13, from human tonsillar and blood ILC2s in response to stimulation with a combination of IL-25, IL-33, thymic stromal lymphopoietin, and IL-2. Furthermore, PGE₂ downregulated the expression of IL-2 receptor α (CD25). In line with this observation, PGE₂ decreased ILC2 proliferation. These effects were mediated by the combined action of E-type prostanoid receptor (EP) 2 and EP4 receptors, which were specifically expressed on ILC2s.

Conclusion

Our findings reveal that PGE₂ limits ILC2 activation and propose that selective EP2 and EP4 receptor agonists might serve as a promising therapeutic approach in treating allergic diseases by suppressing ILC2 function.

Smoking Cessation as a Possible Risk Factor for the Development of Aspirin-Exacerbated Respiratory Disease in Smokers

BACKGROUND

The pathogenesis of aspirin-exacerbated respiratory disease (AERD) is characterized by the low expression of cyclooxygenase-2 (COX-2) in airway epithelia, which decreases the production of prostaglandin E₂ (PGE₂). Conversely, cigarette smoke stimulates COX-2 expression in airway epithelia. Therefore, it was hypothesized that the development of AERD would be suppressed by elevated PGE₂ levels in smokers, and smoking cessation might increase susceptibility to AERD.

OBJECTIVE

The objective of this study was to evaluate the relationship between smoking and the risk of AERD development.

METHODS

The smoking status of patients with AERD (n = 114) was compared with 2 control groups with aspirin-tolerant asthma (ATA), patients diagnosed by a systemic aspirin provocation test (ATA-1, n = 83) and outpatients randomly selected from a large-scale dataset (ATA-2, n = 914), as well as a healthy control group (HC, n = 2313).

RESULTS

At the age of asthma onset, there was a low frequency of current smokers (9.7%), but a high frequency of past smokers (20.2%) in the AERD group compared with the ATA-1 (20.5% and 12.0% for current and past smokers, respectively), ATA-2 (24.5% and 10.3%, respectively), and HC group (26.2% and 12.6%, respectively). After adjustment for confounding variables, AERD was positively associated with smoking cessation between 1 and 4 years before disease onset compared with the ATA-2 group (adjusted odds ratio [aOR] 4.63, 95% confidence interval [CI]: 2.16-9.93) and the HC group (aOR 4.09, 95% CI: 2.07-8.05), implying that smoking cessation was followed by the development of AERD.

CONCLUSION

Smoking cessation may be a risk factor for the development of AERD.

Cyclooxygenase 2: its regulation, role and impact in airway inflammation

Cyclooxygenase 2 (COX-2: official gene symbol - PTGS2) has long been regarded as playing a pivotal role in the pathogenesis of airway inflammation in respiratory diseases including asthma. COX-2 can be rapidly and robustly expressed in response to a diverse range of pro-inflammatory cytokines and mediators. Thus, increased levels of COX-2 protein and prostanoid metabolites serve as key contributors to pathobiology in respiratory diseases typified by dysregulated inflammation. But COX-2 products may not be all bad: prostanoids can exert anti-inflammatory/bronchoprotective functions in airways in addition to their pro-inflammatory actions. Herein, we outline COX-2 regulation and review the diverse stimuli known to induce COX-2 in the context of airway inflammation. We discuss some of the positive and negative effects that COX-2/prostanoids can exert in in vitro and in vivo models of airway inflammation, and suggest that inhibiting COX-2 expression to repress airway inflammation may be too blunt an approach; because although it might reduce the unwanted effects of COX-2 activation, it may also negate the positive effects. Evidence suggests that prostanoids produced via COX-2 upregulation show diverse actions (and herein we focus on prostaglandin E2 as a key example); these can be either beneficial or deleterious and their impact on respiratory disease can be dictated by local concentration and specific interaction with individual receptors. We propose that understanding the regulation of COX-2 expression and associated receptor-mediated functional outcomes may reveal number of critical steps amenable to pharmacological intervention. These may prove invaluable in our quest towards future development of novel anti-inflammatory pharmacotherapeutic strategies for the treatment of airway diseases.

Eosinophils and Mast Cells in Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) involves overexpression of proinflammatory mediators, including 5-lipoxygenase and leukotriene C₄ synthase (LTC₄S), resulting in constitutive overproduction of cysteinyl leukotrienes. Mast cells and eosinophils have roles in mediating many of the observed effects. Increased levels of both interleukin-4 (IL-4) and interferon (IFN)-γ are present in the tissue of patients with AERD. Previous studies showed that IL-4 is primarily responsible for the upregulation of LTC₄S by mast cells. Our studies show that IFN-γ, but not IL-4, drives this process in eosinophils. This article examines the overall role that eosinophils and mast cells contribute to the pathophysiology of AERD.

Impaired E Prostanoid2 Expression and Resistance to Prostaglandin E2 in Nasal Polyp Fibroblasts from Subjects with Aspirin-Exacerbated Respiratory Disease

Recurrent, rapidly growing nasal polyps are hallmarks of aspirin-exacerbated respiratory disease (AERD), although the mechanisms of polyp growth have not been identified. Fibroblasts are intimately involved in tissue remodeling, and the growth of fibroblasts is suppressed by prostaglandin E2 (PGE2), which elicits antiproliferative effects mediated through the E prostanoid (EP)2 receptor. We now report that cultured fibroblasts from the nasal polyps of subjects with AERD resist this antiproliferative effect. Fibroblasts from polyps of subjects with AERD resisted the antiproliferative actions of PGE2 and a selective EP2 agonist (P < 0.0001 at 1 μM) compared with nasal fibroblasts from aspirin-tolerant control subjects undergoing polypectomy or from healthy control subjects undergoing concha bullosa resections. Cell surface expression of the EP2 receptor protein was lower in fibroblasts from subjects with AERD than in fibroblasts from healthy control subjects and aspirin-tolerant subjects (P < 0.01 for both). Treatment of the fibroblasts with trichostatin A, a histone deacetylase inhibitor, significantly increased EP2 receptor mRNA in fibroblasts from AERD and aspirin-tolerant subjects but had no effect on cyclooxygenase-2, EP4, and microsomal PGE synthase 1 (mPGES-1) mRNA levels. Histone acetylation (H3K27ac) at the EP2 promoter correlated strongly with baseline EP2 mRNA (r = 0.80; P < 0.01). These studies suggest that the EP2 promotor is under epigenetic control, and one explanation for PGE2 resistance in AERD is an epigenetically mediated reduction of EP2 receptor expression, which could contribute to the refractory nasal polyposis typically observed in this syndrome.

Prostanoids in Asthma and COPD: Actions, Dysregulation, and Therapeutic Opportunities

Pathophysiologic gaps in the actions of currently available treatments for asthma and COPD include neutrophilic inflammation, airway remodeling, and alveolar destruction. All of these processes can be modulated by cyclic adenosine monophosphate-elevating prostaglandins E2 and I2 (also known as prostacyclin). These prostanoids have long been known to elicit bronchodilation and to protect against bronchoconstriction provoked by a variety of stimuli. Much less well known is their capacity to inhibit inflammatory responses involving activation of lymphocytes, eosinophils, and neutrophils, as well as to attenuate epithelial injury and mesenchymal cell activation. This profile of actions identifies prostanoids as attractive candidates for exogenous administration in asthma. By contrast, excessive prostanoid production and signaling might contribute to both the increased susceptibility to infections that drive COPD exacerbations and the inadequate alveolar repair that characterizes emphysema. Inhibition of endogenous prostanoid synthesis or signaling, thus, has therapeutic potential for these types of patients. By virtue of their pleiotropic capacity to modulate numerous pathophysiologic processes relevant to the expression and natural history of airway diseases, prostanoids emerge as attractive targets for therapeutic manipulation.

Hypersensitivity to Aspirin and other NSAIDs: Diagnostic Approach in Patients with Chronic Rhinosinusitis

Hypersensitivity to nonsteroidal anti-inflammatory drugs (NSAIDs) associated with chronic rhinosinusitis (CRS) and/or asthma comprises a distinct clinical syndrome referred to as NSAIDs exacerbated respiratory disease (NERD). Patients with NERD tend to have more severe course of both upper (CRS and nasal polyps) and lower airway (asthma) diseases and are usually recalcitrant to conventional treatment modalities. Diagnosing and phenotyping of patients with NERD are critical for prevention of drug-induced adverse reactions and open novel options for management of underlying chronic airway inflammatory diseases. Diagnosis of NERD is based on detailed clinical history confirmed by challenge with aspirin, but new diagnostic approaches are currently being developed. This review article focuses on the diagnostic approach to a patient with CRS and hypersensitivity to NSAIDs, emphasizing the importance of diagnosis for proper patient's management.

Aspirin-intolerant asthma in the population: prevalence and important determinants

BACKGROUND

Population-based studies on aspirin-intolerant asthma (AIA) are very few, and no previous population study has investigated risk factors for the condition.

OBJECTIVE

To investigate the prevalence and risk factors of AIA in the general population.

METHODS

A questionnaire on respiratory health was mailed to 30,000 randomly selected subjects aged 16-75 years in West Sweden, 29,218 could be traced and 18,087 (62%) responded. The questionnaire included questions on asthma, respiratory symptoms, aspirin-induced dyspnoea and possible determinants.

RESULTS

The prevalence of AIA was 0.5%, 0.3% in men and 0.6% in women (P = 0.014). Sick leave, emergency visits due to asthma and all investigated lower respiratory symptoms were more common in AIA than in aspirin-tolerant asthma (ATA). Obesity was a strong risk factor for AIA (BMI > 35: odds ratio (OR) 12.1; 95% CI 2.49-58.5), and there was a dose-response relationship between increasing body mass index (BMI) and risk of AIA. Obesity, airborne occupational exposure and visible mould at home were considerably stronger risk factors for AIA than for ATA. Current smoking was a risk factor for AIA (OR 2.55; 95% CI 1.47-4.42), but not ATA.

CONCLUSION

Aspirin-intolerant asthma identified in the general population was associated with a high burden of symptoms, uncontrolled disease and a high morbidity. Increasing BMI increased the risk of AIA in a dose-response manner. A number of risk factors, including obesity and current smoking, were considerably stronger for AIA than for ATA.

Aspirin-Exacerbated Respiratory Disease Involves a Cysteinyl Leukotriene-Driven IL-33-Mediated Mast Cell Activation Pathway

Aspirin-exacerbated respiratory disease (AERD), a severe eosinophilic inflammatory disorder of the airways, involves overproduction of cysteinyl leukotrienes (cysLTs), activation of airway mast cells (MCs), and bronchoconstriction in response to nonselective cyclooxygenase inhibitors that deplete homeostatic PGE2. The mechanistic basis for MC activation in this disorder is unknown. We now demonstrate that patients with AERD have markedly increased epithelial expression of the alarmin-like cytokine IL-33 in nasal polyps, as compared with polyps from aspirin-tolerant control subjects. The murine model of AERD, generated by dust mite priming of mice lacking microsomal PGE2 synthase (ptges(-/-) mice), shows a similar upregulation of IL-33 protein in the airway epithelium, along with marked eosinophilic bronchovascular inflammation. Deletion of leukotriene C4 synthase, the terminal enzyme needed to generate cysLTs, eliminates the increased IL-33 content of the ptges(-/-) lungs and sharply reduces pulmonary eosinophilia and basal secretion of MC products. Challenges of dust mite-primed ptges(-/-) mice with lysine aspirin induce IL-33-dependent MC activation and bronchoconstriction. Thus, IL-33 is a component of a cysLT-driven innate type 2 immune response that drives pathogenic MC activation and contributes substantially to AERD pathogenesis.

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.

Altered inhibitory function of the E-type prostanoid receptor 4 in eosinophils and monocytes from aspirin-intolerant patients

Prostaglandin (PG) E2 has been implicated in the pathogenesis of aspirin-exacerbated respiratory disease (AERD). E-type prostanoid (EP) receptor 4 is known to confer inhibitory signals to eosinophils and monocytes, amongst others. In this study, we investigated whether the responsiveness of eosinophils and monocytes to PGE2 and EP4 receptor activation is altered in AERD patients. While the expression of the EP4 receptor in eosinophils was unaltered in AERD patients, inhibition of eosinophil chemotaxis by PGE2 or the EP4 agonist CAY10598 was less pronounced in AERD patients as compared to healthy control subjects. In monocytes, we found no changes in basal or lipopolysaccharide (LPS)-stimulated PGE2 synthesis, but the response to EP4 receptor activation with respect to inhibition of LPS-induced tumor necrosis factor-α release was reduced in AERD patients, especially in the presence of aspirin (acetylsalicylic acid). Our data point towards a decreased sensitivity of inhibitory EP4 receptor that may play a role in AERD.

Prostaglandin E2 receptors in asthma and in chronic rhinosinusitis/nasal polyps with and without aspirin hypersensitivity

Chronic rhinosinusitis with nasal polyps (CRSwNP) and asthma frequently coexist and are always present in patients with aspirin exacerbated respiratory disease (AERD). Although the pathogenic mechanisms of this condition are still unknown, AERD may be due, at least in part, to an imbalance in eicosanoid metabolism (increased production of cysteinyl leukotrienes (CysLTs) and reduced biosynthesis of prostaglandin (PG) E2), possibly increasing and perpetuating the process of inflammation. PGE2 results from the metabolism of arachidonic acid (AA) by cyclooxygenase (COX) enzymes, and seems to play a central role in homeostasis maintenance and inflammatory response modulation in airways. Therefore, the abnormal regulation of PGE2 could contribute to the exacerbated processes observed in AERD. PGE2 exerts its actions through four G-protein-coupled receptors designated E-prostanoid (EP) receptors EP1, EP2, EP3, and EP4. Altered PGE2 production as well as differential EP receptor expression has been reported in both upper and lower airways of patients with AERD. Since the heterogeneity of these receptors is the key for the multiple biological effects of PGE2 this review focuses on the studies available to elucidate the importance of these receptors in inflammatory airway diseases.

Association of serum periostin with aspirin-exacerbated respiratory disease

BACKGROUND

Recent studies recommend periostin as a systemic biomarker of eosinophilic airway inflammation to predict responses to novel treatments that targets eosinophilic TH2-driven inflammation in asthmatic patients.

OBJECTIVE

To investigate the clinical implications of serum periostin levels in patients with aspirin-exacerbated respiratory disease (AERD) based on its overlapping TH2-mediated pathogenesis with the eosinophilic asthma.

METHODS

Serum periostin levels were measured by human periostin enzyme-linked immunosorbent assay (ELISA) in serum samples from 277 adults with asthma. Serum periostin levels were compared between patients with AERD and aspirin tolerant asthma (ATA) with other asthma phenotypes, such as severe or nonsevere asthma and eosinophilic or noneosinophilic asthma. The association of serum periostin levels with clinical parameters (including disease severity and comorbid condition) was analyzed.

RESULTS

Serum periostin levels were significantly higher in patients with AERD vs ATA, patients with severe asthma vs nonsevere asthma, and patients with eosinophilic asthma vs noneosinophilic asthma (P=.005, P=.02, and P=.001, respectively). Multivariate regression analysis revealed serum periostin levels as a significant parameter to predict AERD phenotype (P=.006) together with severe asthma phenotype (P=.04). In addition, serum periostin levels correlated with blood eosinophil counts (Spearman ñ = 0.244, P<.001) and sputum eosinophil counts (Spearman ñ = 0.261, P < 0.001). Higher serum periostin levels were noted in comorbid AERD patients with more severe chronic rhinosinusitis (Lund-Mackay stages 3 and 4) than those with less severe chronic rhinosinusitis (Lund-Mackay stages 1 and 2) (P = .03).

CONCLUSION

Serum periostin levels are significantly elevated in AERD patients and associated with AERD phenotype and disease severity.

Cysteinyl leukotrienes and their receptors; emerging concepts

Cysteinyl leukotrienes (cys-LTs) are potent mediators of inflammation derived from arachidonic acid through the 5-lipoxygenase/leukotriene C4 synthase pathway. The derivation of their chemical structures and identification of their pharmacologic properties predated the cloning of their classical receptors and the development of drugs that modify their synthesis and actions. Recent studies have revealed unanticipated insights into the regulation of cys-LT synthesis, the function of the cys-LTs in innate and adaptive immunity and human disease, and the identification of a new receptor for the cys-LTs. This review highlights these studies and summarizes their potential pathobiologic and therapeutic implications.

Prostaglandin E2 resistance in granulocytes from patients with aspirin-exacerbated respiratory disease

BACKGROUND

Aspirin-exacerbated respiratory disease (AERD) is an inflammatory condition of the respiratory tract and is characterized by overproduction of leukotrienes (LT) and large numbers of circulating granulocyte-platelet complexes. LT production can be suppressed by prostaglandin E(2) (PGE(2)) and the cyclic AMP-dependent protein kinase A (PKA).

OBJECTIVE

To determine if PGE(2)-dependent control of LT production by granulocytes is dysregulated in AERD.

METHODS

Granulocytes from well-characterized patients with and without AERD were activated ex vivo and subjected to a range of functional and biochemical analyses.

RESULTS

Granulocytes from subjects with AERD generated more LTB4 and cysteinyl LTs than did granulocytes from controls with aspirin-tolerant asthma and controls without asthma. When compared with controls, granulocytes from subjects with AERD had comparable levels of EP(2) protein expression and PGE(2)-mediated cAMP accumulation, yet were resistant to PGE(2)-mediated suppression of LT generation. Percentages of platelet-adherent neutrophils correlated positively with LTB4 generation and inversely with responsiveness to PGE(2)-mediated suppression of LTB(4). The PKA inhibitor H89 potentiated LTB4 generation by control granulocytes but was inactive in granulocytes from individuals with AERD and had no effect on platelet P-selectin induction. Both tonic PKA activity and levels of PKA catalytic gamma subunit protein were significantly lower in granulocytes from individuals with AERD relative to those from controls.

CONCLUSIONS

Impaired granulocyte PKA function in AERD may lead to dysregulated control of 5-lipoxygenase activity by PGE(2), whereas adherent platelets lead to increased production of LTs, which contributes to the features of persistent respiratory tract inflammation and LT overproduction.

Sinusitis, Rhinitis, Asthma, and the Single Airway Hypothesis

The one airway, one disease hypothesis proposes that the upper and lower airways share the same physiology and histomorphology. Epidemiological clinical studies support a link between rhinosinusitis and asthma. The relationship can occur in both directions, with nasal allergen challenge leading to inflammatory changes in the lower airway and bronchoprovocation studies of the lower airway leading to inflammatory changes in the upper airway. In addition, both similarities and differences exist in the pathogenesis of nasal polyps and asthma. The mechanism for the connection between the upper and lower airways is a matter of great debate. It has been proposed that inflammatory changes in the lower airway may lead to systemic inflammatory effects that play a role in increased bronchial hyperresponsiveness. Similarly, lower airway inflammatory changes may affect nasal airway patency via systemic effects. Moreover, nasopharyngeal-bronchial reflexes may play a non-immunologic role in the interaction between the lower and upper airways. An example of the connection between the upper and lower airways is found in aspirin-exacerbated respiratory disease whereby leukotrienes play a role in the pathology of chronic rhinosinusitis with polyps and asthma. It is also been observed that the treatment of asthma is hindered by untreated rhinosinusitis.

Prostaglandin E2 deficiency causes a phenotype of aspirin sensitivity that depends on platelets and cysteinyl leukotrienes

Aspirin-exacerbated respiratory disease (AERD) is characterized by asthma, tissue eosinophilia, overproduction of cysteinyl leukotrienes (cysLTs), and respiratory reactions to nonselective cyclooxygenase (COX) inhibitors. Ex vivo studies suggest that functional abnormalities of the COX-2/microsomal prostaglandin (PG)E2 synthase-1 system may underlie AERD. We demonstrate that microsomal PGE2 synthase-1 null mice develop a remarkably AERD-like phenotype in a model of eosinophilic pulmonary inflammation. Lysine aspirin (Lys-ASA)-challenged PGE2 synthase-1 null mice exhibit sustained increases in airway resistance, along with lung mast cell (MC) activation and cysLT overproduction. A stable PGE2 analog and a selective E prostanoid (EP)2 receptor agonist blocked the responses to Lys-ASA by ∼90%; EP3 and EP4 agonists were also active. The increases in airway resistance and MC products were blocked by antagonists of the type 1 cysLT receptor or 5-lipoxygenase, implying that bronchoconstriction and MC activation were both cysLT dependent. Lys-ASA-induced cysLT generation and MC activation depended on platelet-adherent granulocytes and T-prostanoid (TP) receptors. Thus, lesions that impair the inducible generation of PGE2 remove control of platelet/granulocyte interactions and TP-receptor-dependent cysLT production, permitting MC activation in response to COX-1 inhibition. The findings suggest applications of antiplatelet drugs or TP receptor antagonists for the treatment of AERD.

Pathogenesis of aspirin-exacerbated respiratory disease and reactions

Physiologic and pharmacologic studies support the hypothesis that aspirin-exacerbated respiratory disease (AERD) involves fundamental dysregulation in the production of and end-organ responsiveness to both antiinflammatory eicosanoids (prostaglandin E2) and proinflammatory effectors (cysteinyl leukotrienes). The acquired nature of AERD implies a disturbance in a potential epigenetic control mechanism of the relevant mediator systems, which may be a result of incompletely clarified environmental factors (eg, viral or bacterial infections, inhaled pollutants).

Role of imbalance of eicosanoid pathways and staphylococcal superantigens in chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a multifactorial disease of the upper airways with a high prevalence (approximately 11%) in the general population. Different immune and inflammatory mechanisms are involved in its pathogenesis. Alterations in the arachidonic acid pathway (leading to an imbalanced production of eicosanoids) have been linked to the pathophysiology of different diseases especially nasal polyposis, asthma, and aspirin-exacerbated respiratory disease. Furthermore, viral and bacterial infections have been identified as important factors amplifying the pro-inflammatory reactions in these pathologies. This review summarizes the impact of an imbalance in the eicosanoid pathway and the effect of Staphylococcus aureus enterotoxins on the regulation of the pro-inflammatory network in CRS and their translation into disease severity.

Prostaglandin E2 deficiency uncovers a dominant role for thromboxane A2 in house dust mite-induced allergic pulmonary inflammation

Prostaglandin E(2) (PGE(2)) is an abundant lipid inflammatory mediator with potent but incompletely understood anti-inflammatory actions in the lung. Deficient PGE(2) generation in the lung predisposes to airway hyperresponsiveness and aspirin intolerance in asthmatic individuals. PGE(2)-deficient ptges(-/-) mice develop exaggerated pulmonary eosinophilia and pulmonary arteriolar smooth-muscle hyperplasia compared with PGE(2)-sufficient controls when challenged intranasally with a house dust mite extract. We now demonstrate that both pulmonary eosinophilia and vascular remodeling in the setting of PGE(2) deficiency depend on thromboxane A(2) and signaling through the T prostanoid (TP) receptor. Deletion of TP receptors from ptges(-/-) mice reduces inflammation, vascular remodeling, cytokine generation, and airway reactivity to wild-type levels, with contributions from TP receptors localized to both hematopoietic cells and tissue. TP receptor signaling ex vivo is controlled heterologously by E prostanoid (EP)(1) and EP(2) receptor-dependent signaling pathways coupling to protein kinases C and A, respectively. TP-dependent up-regulation of intracellular adhesion molecule-1 expression is essential for the effects of PGE(2) deficiency. Thus, PGE(2) controls the strength of TP receptor signaling as a major bronchoprotective mechanism, carrying implications for the pathobiology and therapy of asthma.