Pathogenic Mechanisms and In Vitro Diagnosis of AERD

NSAID-Exacerbated Respiratory Disease (NERD): From Pathogenesis to Improved Care

Nonsteroidal antiinflammatory drug (NSAID)-exacerbated respiratory disease (NERD) is characterized by moderate-to-severe asthma and a higher prevalence of chronic rhinosinusitis/nasal polyps, but is a highly heterogeneous disorder with various clinical manifestations. Two major pathogenic mechanisms are: (1) overproduction of cysteinyl leukotrienes with dysregulation of arachidonic acid metabolism and (2) increased type 2 eosinophilic inflammation affected by genetic mechanisms. Aspirin challenge is the gold standard to diagnose NERD, whereas reliable in vitro biomarkers have yet not been identified. Therapeutic approaches have been done on the basis of disease severity with the avoidance of culprit and cross-reacting NSAIDs, and when indicated, aspirin desensitization is an effective treatment option. Biologic approaches targeting Type 2 cytokines are emerging as potential therapeutic options. Here, we summarize the up-to-date evidence of pathophysiologic mechanisms and diagnosis/management approaches to the patients with NERD with its phenotypic classification.

Integrative information theoretic network analysis for genome-wide association study of aspirin exacerbated respiratory disease in Korean population

BACKGROUND

Aspirin Exacerbated Respiratory Disease (AERD) is a chronic medical condition that encompasses asthma, nasal polyposis, and hypersensitivity to aspirin and other non-steroidal anti-inflammatory drugs. Several previous studies have shown that part of the genetic effects of the disease may be induced by the interaction of multiple genetic variants. However, heavy computational cost as well as the complexity of the underlying biological mechanism has prevented a thorough investigation of epistatic interactions and thus most previous studies have typically considered only a small number of genetic variants at a time.

METHODS

In this study, we propose a gene network based analysis framework to identify genetic risk factors from a genome-wide association study dataset. We first derive multiple single nucleotide polymorphisms (SNP)-based epistasis networks that consider marginal and epistatic effects by using different information theoretic measures. Each SNP epistasis network is converted into a gene-gene interaction network, and the resulting gene networks are combined as one for downstream analysis. The integrated network is validated on existing knowledgebase of DisGeNET for known gene-disease associations and GeneMANIA for biological function prediction.

RESULTS

We demonstrated our proposed method on a Korean GWAS dataset, which has genotype information of 440,094 SNPs for 188 cases and 247 controls. The topological properties of the generated networks are examined for scale-freeness, and we further performed various statistical analyses in the Allergy and Asthma Portal (AAP) using the selected genes from our integrated network.

CONCLUSIONS

Our result reveals that there are several gene modules in the network that are of biological significance and have evidence for controlling susceptibility and being related to the treatment 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.

Aspirin-exacerbated respiratory disease and current treatment modalities

Aspirin-exacerbated respiratory disease (AERD) refers to the combination of asthma, chronic rhinosinusitis with nasal polyposis, and acute upper and lower respiratory tract reactions to the ingestion of aspirin (acetylsalicylic acid, ASA) and other cyclooxygenase-1 inhibiting non-steroidal anti-inflammatory drugs. AERD affects 0.3-0.9 % of the general population. AERD generally occurs due to abnormalities in mediators and expression of arachidonic acid biosynthesis. Local IgE responses to staphylococcal enterotoxins may also be responsible for eosinophilic activation in the nasal polyp tissues of AERD patients. Clinical features of AERD include the onset of nasal congestion with anosmia, progressing to chronic pansinusitis and nasal polyps that regrow rapidly after surgery. Aspirin desensitization, Leukotriene-modifying agents, biologic agents, management of asthma, chronic rhinosinusitis, and nasal polyposis are recommended as treatment modalities. Immunotherapy is prescribed only to those AERD patients who experience clear seasonal or perennial allergy symptoms in addition to the symptoms attributable to chronic nasal polyposis. There are also investigational and dietary therapies. In this review, the important aspects of AERD will be presented, along with a literature survey.

Development of a genetic marker set to diagnose aspirin-exacerbated respiratory disease in a genome-wide association study

We developed a genetic marker set of single nucleotide polymorphisms (SNPs) by summing risk scores of 14 SNPs showing a significant association with aspirin-exacerbated respiratory disease (AERD) from our previous 660 W genome-wide association data. The summed scores were higher in the AERD than in the aspirin-tolerant asthma (ATA) group (P=8.58 × 10(-37)), and were correlated with the percent decrease in forced expiratory volume in 1 s after aspirin challenge (r(2)=0.150, P=5.84 × 10(-30)). The area under the curve of the scores for AERD in the receiver operating characteristic curve was 0.821. The best cutoff value of the summed risk scores was 1.01328 (P=1.38 × 10(-32)). The sensitivity and specificity of the best scores were 64.7% and 85.0%, respectively, with 42.1% positive and 93.4% negative predictive values. The summed risk score may be used as a genetic marker with good discriminative power for distinguishing AERD from ATA.

Prostaglandin D2-supplemented "functional eicosanoid testing and typing" assay with peripheral blood leukocytes as a new tool in the diagnosis of systemic mast cell activation disease: an explorative diagnostic study

BACKGROUND

Systemic mast cell activation disease (MCAD) is characterized by an enhanced release of mast cell-derived mediators, including eicosanoids, which induce a broad spectrum of clinical symptoms. Accordingly, the diagnostic algorithm of MCAD presupposes the proof of increased mast cell mediator release, but only a few mediators are currently established as routine laboratory parameters. We thus initiated an explorative study to evaluate in vitro typing of individual eicosanoid pattern of peripheral blood leukocytes (PBLs) as a new diagnostic tool in MCAD.

METHODS

Using the "functional eicosanoid testing and typing" (FET) assay, we investigated the balance (i.e. the complex pattern of formation, release and mutual interaction) of prostaglandin E2 (PGE2) and peptido-leukotrienes (pLT) release from PBLs of 22 MCAD patients and 20 healthy individuals. FET algorithms thereby consider both basal and arachidonic acid (AA)-, acetylsalicylic acid (ASA)-, and substance P (SP)-triggered release of PGE2 and pLT. The FET assay was further supplemented by analyzing prostaglandin D2 (PGD2), as mast cell-specific eicosanoid.

RESULTS

We observed marked PGE2-pLT imbalances for PBLs of MCAD patients, as indicated by a markedly enhanced mean FET value of 1.75 ± 0.356 (range: 1.14-2.36), compared to 0.53 ± 0.119 (range: 0.36-0.75) for healthy individuals. In addition, mean PGD2 release from PBLs of MCAD patients was significantly, 6.6-fold higher than from PBLs of healthy individuals (946 ± 302.2 pg/ml versus 142 ± 47.8 pg/ml; P < 0.001). In contrast to healthy individuals, PGD2 release from PBLs of MCAD patients was markedly triggered by SP (mean: 1896 ± 389.7 pg/ml; P < 0.001), whereas AA and ASA caused individually varying effects on both PGD2 and pLT release.

CONCLUSIONS

The new in-vitro FET assay, supplemented with analysis of PGD2, demonstrated that the individual patterns of eicosanoid release from PBLs can unambiguously distinguish MCAD patients from healthy individuals. Notably, in our analyses, the FET value and both basal and triggered PGD2 levels were not significantly affected by MCAD-specific medication. Thus, this approach may serve as an in-vitro diagnostic tool to estimate mast cell activity and to support individualized therapeutic decision processes for patients suffering from MCAD.

Emerging targets in lipid-based therapy

The use of prostaglandins and NSAIDS in the clinic has proven that lipid mediators and their associated pathways make attractive therapeutic targets. When contemplating therapies involving lipid pathways, several basic agents come to mind. There are the enzymes and accessory proteins that lead to the metabolism of lipid substrates, provided through diet or through actions of lipases, the subsequent lipid products, and finally the lipid sensors or receptors. There is abundant evidence that molecules along this lipid continuum can serve as prognostic and diagnostic indicators and are in fact viable therapeutic targets. Furthermore, lipids themselves can be used as therapeutics. Despite this, the vernacular dialog pertaining to "biomarkers" does not routinely include mention of lipids, though this is rapidly changing. Collectively these agents are becoming more appreciated for their respective roles in diverse disease processes from cancer to preterm labor and are receiving their due appreciation after decades of ground work in the lipid field. By relating examples of disease processes that result from dysfunction along the lipid continuum, as well as examples of lipid therapies and emerging technologies, this review is meant to inspire further reading and discovery.

Aspirin sensitivity and chronic rhinosinusitis with polyps: a fatal combination

Aspirin-exacerbated respiratory disease (AERD) refers to aspirin sensitivity, chronic rhinosinusitis (CRS), nasal polyposis, asthma, eosinophil inflammation in the upper and lower airways, urticaria, angioedema, and anaphylaxis following the ingestion of NSAIDs. Epidemiologic and pathophysiological links between these diseases are established. The precise pathogenesis remains less defined, even though there is some progress in the understanding of several molecular mechanisms. Nevertheless, these combinations of diseases in patients classified by AERD constitute a fatal combination and may be difficult to treat with standard medical and surgical interventions. This paper reviews in brief the epidemiology, clinical features, diagnosis, molecular pathogenesis, and specific therapies of patients classified by AERD and postulates future attempts to gain new insights into this disease.