Interleukin-4 in the Generation of the AERD Phenotype: Implications for Molecular Mechanisms Driving Therapeutic Benefit of Aspirin Desensitization

Aspirin Actions in Treatment of NSAID-Exacerbated Respiratory Disease

Non-steroidal Anti-inflammatory drugs (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyposis, chronic rhinosinusitis, adult-onset asthma and hypersensitive reactions to cyclooxygenase-1 (COX-1) inhibitors. Among the available treatments for this disease, a combination of endoscopic sinus surgery followed by aspirin desensitization and aspirin maintenance therapy has been an effective approach. Studies have shown that long-term aspirin maintenance therapy can reduce the rate of nasal polyp recurrence in patients with N-ERD. However, the exact mechanism by which aspirin can both trigger and suppress airway disease in N-ERD remains poorly understood. In this review, we summarize current knowledge of aspirin effects in N-ERD, cardiovascular disease, and cancer, and consider potential mechanistic pathways accounting for the effects of aspirin in N-ERD.

The role of aspirin desensitization followed by oral aspirin therapy in managing patients with aspirin-exacerbated respiratory disease: A Work Group Report from the Rhinitis, Rhinosinusitis and Ocular Allergy Committee of the American Academy of Allergy, Asthma & Immunology

Aspirin-exacerbated respiratory disease (AERD) is characterized by the clinical triad of chronic rhinosinusitis with nasal polyps, asthma, and an intolerance to medications that inhibit the cycloxgenase-1 enzyme. Patients with AERD on average have more severe respiratory disease compared with patients with chronic rhinosinusitis with nasal polyps and/or asthma alone. Although patients with AERD traditionally develop significant upper and lower respiratory tract symptoms on ingestion of cycloxgenase-1 inhibitors, most of these same patients report clinical benefit when desensitized to aspirin and maintained on daily aspirin therapy. This Work Group Report provides a comprehensive review of aspirin challenges, aspirin desensitizations, and maintenance aspirin therapy in patients with AERD. Identification of appropriate candidates, indications and contraindications, medical and surgical optimization strategies, protocols, medical management during the desensitization, and recommendations for maintenance aspirin therapy following desensitization are reviewed. Also included is a summary of studies evaluating the clinical efficacy of aspirin therapy after desensitization as well as a discussion on the possible cellular and molecular mechanisms explaining how this therapy provides unique benefit to patients with AERD.

Leukotriene A4 Hydrolase Activation and Leukotriene B4 Production by Eosinophils in Severe Asthma

Asthma is associated with the overproduction of leukotrienes (LTs), including LTB4. Patients with severe asthma can be highly responsive to 5-lipoxygenase (5-LO) inhibition, which blocks production of both the cysteinyl LTs and LTB4. Production of LTB4 has traditionally been ascribed to neutrophils, mononuclear phagocytes, and epithelial cells, and acts as a chemoattractant for inflammatory cells associated with asthma. The source of LTB4 is unclear, especially in eosinophilic asthma. We speculated that the benefit of 5-LO inhibition could be mediated in part by inhibition of eosinophil-derived LTB4. LTB4 concentrations were assayed in BAL fluid from patients with severe asthma characterized by isolated neutrophilic, eosinophilic, and paucigranulocytic inflammation. Expression of LTA4 hydrolase (LTA4H) by airway eosinophils was determined by immunohistochemistry (IHC). Subsequently, peripheral blood eosinophils were activated and secreted LTB4 was quantified by enzyme immunoassay. Blood eosinophil LTA4H expression was determined by flow cytometry, qPCR, and IHC. LTB4 concentrations were elevated in BAL fluid from patients with severe asthma, including those with isolated eosinophilic inflammation, and these eosinophils displayed LTA4H via IHC. LTA4H expression by blood eosinophils was confirmed by flow cytometry, IHC, and qPCR. Robust LTB4 production by blood eosinophils was observed in response to some, but not all, stimuli. We demonstrated that eosinophils express LTA4H transcripts and protein, and can be stimulated to secrete LTB4. We speculate that in many patients with asthma, eosinophil-derived LTB4 is increased, and this may contribute to the efficacy of 5-LO inhibition.

Clinical and Immunological Efficacy of Aspirin Desensitization in Nasal Polyp Patients with Aspirin-Exacerbated Respiratory Disease

This study aimed to investigate the efficacy and the underlining mechanism of aspirin desensitization among patients with Aspirin Exacerbated Respiratory Disease (AERD). Thirty-eight patients, who had undergone an aspirin challenge test and were diagnosed as having AERD, were engaged in a double-blind randomized clinical trial. They were divided into two groups-an active group of patients who went through aspirin desensitization, and the control group, receiving placebo. Clinical symptoms and the quality of life of the patients-in addition to the levels of interleukin 4 and 5 (IL4), (IL5)-were documented at the beginning of the study and again after six months of aspirin desensitization. The quality of life of the patients was significantly higher in the active group after six months (P = 0.001). Medication requirements and symptom score were manifested to be significantly lower in the active group after six months than at the beginning of the study (P = 0.005, 0.017 respectively). Forced expiratory volume in the second one (FEV1) was, also, significantly higher in the active group after six months of the study (P = 0.032). IL5 was found to be significantly lower in the active group after six months (P = 0.019). However, no significant difference was observed in the levels of IL4 between the two groups (P = 0.152). The study revealed that aspirin desensitization can improve the quality of life of patients with AERD, lessen their symptoms and medication requirements, lower their levels of IL5, and improve some pulmonary function tests such as FEV1.

Aspirin-Exacerbated Respiratory Disease as an Endotype of Chronic Rhinosinusitis

Aspirin-Exacerbated Respiratory Disease (AERD) and Chronic Rhinosinusitis with Nasal Polyps (CRSwNP) are both characterized by the presence of chronic sinonasal inflammation and nasal polyps. Unlike in CRSwNP, AERD patients develop respiratory reactions following ingestion of COX-1 inhibitors. AERD patients also, on average, have worse upper respiratory disease with increased sinonasal symptoms, mucosal inflammation and requirements for revision sinus surgery when compared to CRSwNP patients. While no single genetic factor has been identified in either CRSwNP or AERD to date, differences in the metabolism of arachidonic acid as well as innate immune cell activation may uniquely contribute to AERD pathogenesis.

Aspirin induces IL-4 production: augmented IL-4 production in aspirin-exacerbated respiratory disease

Aspirin hypersensitivity is a hallmark of aspirin-exacerbated respiratory disease (AERD), a clinical syndrome characterized by the severe inflammation of the respiratory tract after ingestion of cyclooxygenase-1 inhibitors. We investigated the capacity of aspirin to induce interleukin-4 (IL-4) production in inflammatory cells relevant to AERD pathogenesis and examined the associated biochemical and molecular pathways. We also compared IL-4 production in peripheral blood mononuclear cells (PBMCs) from patients with AERD vs aspirin-tolerant asthma (ATA) upon exposure to aspirin. Aspirin induced IL-4 expression and activated the IL-4 promoter in a report assay. The capacity of aspirin to induce IL-4 expression correlated with its activity to activate mitogen-activated protein kinases, to form DNA-protein complexes on P elements in the IL-4 promoter and to synthesize nuclear factor of activated T cells, critical transcription factors for IL-4 transcription. Of clinical importance, aspirin upregulated IL-4 production twice as much in PBMCs from patients with AERD compared with PBMCs from patients with ATA. Our results suggest that IL-4 is an inflammatory component mediating intolerance reactions to aspirin, and thus is crucial for AERD pathogenesis.

Release of cyclooxygenase-2 and lipoxin A4 from blood leukocytes in aspirin-exacerbated respiratory disease

BACKGROUND

The release of cyclooxygenase-2 (COX-2) and lipoxin A4 (LXA4) from blood mononuclear cells in patients with aspirin-exacerbated respiratory disease (AERD) is only partially understood.

OBJECTIVE

To investigate the presence of COX-2 and LXA4 in peripheral blood mononuclear cells (PBMC) derived from patients with AERD and with nasal polyps (NP) (designated as the AERD-NP group), patients with NP without AERD (the NP group), and healthy controls without sinus disease (the control group).

METHODS

Blood was taken from 14 patients in the AERD-NP group, 6 patients in the NP group, and 8 healthy subjects in the control group. After culturing of human PBMC, the presence of COX-2 protein and LXA4 (ELISA) was detected in the supernatant, and the results were compared among the groups.

RESULTS

COX-2 and LXA4 were detectable after culturing of PBMC in all patients in the AERD-NP and NP groups and in the control subjects. COX-2 was highest in the patients in the AERD-NP group, but the difference was not significant compared with patients with non-AERD polyp and with the control subjects. LXA4 was also highest in the AERD-NP group, but the difference was also not significant compared with the patients who were non-AERD polyp and the control subjects.

CONCLUSION

Neither the release of COX-2 or LXA4 was different between the patients with AERD and with NPs, the patients without AERD and with NPs, and the healthy control group. The release of these proteins in AERD needs further investigation.

Aspirin activation of eosinophils and mast cells: implications in the pathogenesis of aspirin-exacerbated respiratory disease

Reactions to aspirin and nonsteroidal anti-inflammatory drugs in patients with aspirin-exacerbated respiratory disease (AERD) are triggered when constraints upon activated eosinophils, normally supplied by PGE2, are removed secondary to cyclooxygenase-1 inhibition. However, the mechanism driving the concomitant cellular activation is unknown. We investigated the capacity of aspirin itself to provide this activation signal. Eosinophils were enriched from peripheral blood samples and activated with lysine ASA (LysASA). Parallel samples were stimulated with related nonsteroidal anti-inflammatory drugs. Activation was evaluated as Ca2+ flux, secretion of cysteinyl leukotrienes (CysLT), and eosinophil-derived neurotoxin (EDN) release. CD34+ progenitor-derived mast cells were also used to test the influence of aspirin on human mast cells with measurements of Ca2+ flux and PGD2 release. LysASA induced Ca2+ fluxes and EDN release, but not CysLT secretion from circulating eosinophils. There was no difference in the sensitivity or extent of activation between AERD and control subjects, and sodium salicylate was without effect. Like eosinophils, aspirin was able to activate human mast cells directly through Ca2+ flux and PGD2 release. AERD is associated with eosinophils maturing locally in a high IFN-γ milieu. As such, in additional studies, eosinophil progenitors were differentiated in the presence of IFN-γ prior to activation with aspirin. Eosinophils matured in the presence of IFN-γ displayed robust secretion of both EDN and CysLTs. These studies identify aspirin as the trigger of eosinophil and mast cell activation in AERD, acting in synergy with its ability to release cells from the anti-inflammatory constraints of PGE2.

Interleukin-4 and interleukin-13 compromise the sinonasal epithelial barrier and perturb intercellular junction protein expression

BACKGROUND

Altered expression of epithelial intercellular junction proteins has been observed in sinonasal biopsies from nasal polyps and epithelial layers cultured from nasal polyp patients. These alterations comprise a "leaky" epithelial barrier phenotype. We hypothesize that T helper 2 (Th2) cytokines interleukin (IL)-4 and IL-13 modulate epithelial junction proteins, thereby contributing to the leaky epithelial barrier.

METHODS

Differentiated primary sinonasal epithelial layers cultured at the air-liquid interface were exposed to IL-4, IL-13, and controls for 24 hours at 37°C. Epithelial resistance measurements were taken every 4 hours during cytokine exposure. Western blot and immunofluorescence staining/confocal microscopy were used to assess changes in a panel of tight and adherens junction proteins. Western blot densitometry was quantified with image analysis.

RESULTS

IL-4 and IL-13 exposure resulted in a mean decrease in transepithelial resistance at 24 hours to 51.6% (n = 6) and 68.6% (n = 8) of baseline, respectively. Tight junction protein junctional adhesion molecule-A (JAM-A) expression decreased 42.2% with IL-4 exposure (n = 9) and 37.5% with IL-13 exposure (n = 9). Adherens junction protein E-cadherin expression decreased 35.3% with IL-4 exposure (n = 9) and 32.9% with IL-13 exposure (n = 9). Tight junction protein claudin-2 showed more variability but had a trend toward higher expression with Th2 cytokine exposure. There were no appreciable changes in claudin-1, occludin, or zonula occludens-1 (ZO-1) with IL-4 or IL-13 exposure.

CONCLUSION

Sinonasal epithelial exposure to Th2 cytokines IL-4 and IL-13 results in alterations in intercellular junction proteins, reflecting increased epithelial permeability. Such changes may explain some of the phenotypic manifestations of Th2-mediated sinonasal disease, such as edema, nasal discharge, and environmental reactivity.

Sinonasal epithelial wound resealing in an in vitro model: inhibition of wound closure with IL-4 exposure

BACKGROUND

Prolonged healing and persistent inflammation following surgery for rhinosinusitis impacts patient satisfaction and healthcare resources. Cytokines interleukin (IL)-4, IL-5, and IL-13 are important mediators in T-helper 2 (Th2) inflammatory rhinosinusitis. Decreased wound healing has been demonstrated with Th2 cytokine exposure, but this has not been extensively studied in sinonasal epithelium. We hypothesized that in vitro exposure of primary sinonasal epithelial cell cultures to Th2 inflammatory cytokine IL-4 and IL-13 would impair wound resealing and decrease expression of annexin A2 at the wound edge.

METHODS

Following 24-hour exposure to IL-4, IL-5, or IL-13 vs controls, sterile linear mechanical wounds were created in primary sinonasal epithelial cultures (n = 12 wounds per condition). Wounds were followed for 36 hours or until complete closure, and residual wound areas were calculated by image analysis. Group differences in annexin A2 were assessed by immunofluorescence labeling, confocal microscopy, and Western blots.

RESULTS

Significant wound closure differences were identified across cytokine exposure groups (p < 0.001). Mean percentage wound closure at the completion of the 36-hour time course was 98.41% ± 3.43% for control wounds vs 85.02% ± 18.46% for IL-4 exposed wounds. IL-13 did not significantly impair sinonasal epithelial wound resealing in vitro. Annexin A2 protein levels were decreased in IL-4 treated wounds when compared to control wounds (p < 0.01).

CONCLUSION

Th2 cytokine IL-4 decreases sinonasal epithelial wound closure in vitro. Annexin A2 is also diminished with IL-4 exposure. This supports the hypothesis that IL-4 exposure impairs sinonasal epithelial wound healing and may contribute to prolonged healing in Th2 inflammatory rhinosinusitis.

Rhinosinusitis and aspirin-exacerbated respiratory disease

Rhinosinusitis is a feature of aspirin-exacerbated respiratory disease (AERD), which in the initial phase is manifested as nasal congestion, mostly affecting females at the age of around 30 years on average. Subsequently, nasal inflammation progresses to chronic eosinophilic rhinosinusitis, asthma, nasal polyposis, and intolerance to aspirin and to other NSAIDs. While it has been long established that NSAIDs cause inhibition of cyclooxygenase-1 (COX-1), leading to excessive metabolism of arachidonic acid (AA) to cysteinyl-leukotrienes (cys-LTs), there is now evidence that both cytokines and staphylococcus superantigens amplify the inflammatory process exacerbating the disease. This paper gives a brief overview of the development of chronic rhinosinusitis (CRS) in sensitive patients, and we share our experience in the diagnosis and management of CRS in AERD.