Expression of 5‐lipoxygenase and cyclooxygenase pathway enzymes in nasal polyps of patients with aspirin‐intolerant asthma

Abstract

In aspirin-intolerant subjects, adverse bronchial and nasal reactions to cyclooxygenase (COX) inhibitors are associated with over-production of cysteinyl-leukotrienes (cys-LTs) generated by the 5-lipoxygenase (5-LO) pathway. In the bronchi of patients with aspirin-intolerant asthma, we previously linked cys-LT over-production and aspirin hyper-reactivity with elevated immunoexpression in eosinophils of the terminal enzyme for cys-LT production, LTC4 synthase. We investigated whether this anomaly also occurs in the nasal airways of these patients. Immunohistochemical expression of 5-LO and COX pathway proteins was quantified in nasal polyps from 12 patients with aspirin-intolerant asthma and 13 with aspirin-tolerant asthma. In the mucosa of polyps from aspirin-intolerant asthmatic patients, cells immunopositive for LTC4 synthase were four-fold more numerous than in aspirin-tolerant asthmatic patients (p=0.04). There were also three-fold more cells expressing 5-LO (p=0.037), with no differences in 5-LO activating protein (FLAP), COX-1 or COX-2. LTC4 synthase-positive cell counts correlated exclusively with mucosal eosinophils (r=0.94, p<0.001, n=25). Co-localisation confirmed that five-fold higher eosinophil counts (p=0.007) accounted for the increased LTC4 synthase expression in polyps from aspirin-intolerant asthmatic patients, with no alterations in mast cells or macrophages. Within the epithelium, increased counts of eosinophils (p=0.006), macrophages (p=0.097), and mast cells (p=0.034) in aspirin-intolerant asthmatic polyps were associated only with 2.5-fold increased 5-LO-positive cells (p<0.05), while the other enzymes were not different. Our results indicate that a marked over-representation of LTC4 synthase in mucosal eosinophils is closely linked to aspirin intolerance in the nasal airway, as in the bronchial airways.

Cysteinyl leukotriene overproduction in aspirin-exacerbated respiratory disease is driven by platelet-adherent leukocytes

“…Moreover, the remarkable adherence of platelets to eosinophils suggests that platelets could contribute substantially to the accumulation of eosinophils in the tissue by priming them for adhesion and prolonging their survival (and perhaps reducing their sensitivity to steroid-induced apoptosis) via release of GM-CSF. 48 Our study suggests that the selective increases in the proportions of eosinophils expressing LTC 4 S, in bronchial biopsies 9 and nasal polyp mucosa 10 obtained from individuals with AERD relative to ATA controls may have been due, in part, to the presence of adherent platelets on the eosinophils. Our previous studies demonstrated that exogenous cysLTs, including LTE 4 , do not directly cause human platelets to adhere to granulocytes.…”

“…4,9,10 In addition to activating eosinophils, mast cells, and monocytes, 40 aspirin challenges also elicit increases in LTB 4 metabolites in the urine of subjects with AERD that parallel increases in LTE 4 , 41 suggesting that dysregulation of 5-LO activity in neutrophils is another feature of AERD. More than 50% of the LTA 4 synthesized by neutrophils is released unmetabolized into the extracellular milieu, 42 and is only available as a substrate for reuptake by adherent cells because of its extracellular half-life of less than 5 seconds.…”

“…The higher level of trypsin-insensitive LTC 4 S activity in the granulocytes from subjects with AERD ( Figure 4C) is likely because of slightly higher percentage of eosinophils in those samples, and because of increased LTC 4 S activity in eosinophils as suggested by previous immunohistochemical studies. 9,10 Adherent platelets also accounted for a remarkably similar fraction (64 Ϯ 16%) of the cysLTs produced in response to fMLP, which we chose as a physiologic agonist to activate 5-LO in granulocytes by a receptordependent mechanism, thereby providing LTA 4 for conversion to LTC 4 by platelets. We also found that adherent platelets increased the overall activity of the 5-LO pathway in granulocytes, as reflected by the net quantities of all pathway products detected in the supernatants of the A23187-stimulated samples before and after trypsinization.…”

“…However, apart from immunohistochemical studies suggesting that eosinophils in the respiratory tract mucosa express higher levels of LTC 4 S protein in subjects with AERD than in aspirin-tolerant controls, no abnormalities in cysLT generation have been reported in cells from individuals with AERD. 9,10 Moreover, it is not understood how the 5-LO-derived substrate LTA 4 is provided at sufficient quantities to permit the high basal production of cysLTs characteristic of AERD. Of the circulating cells possessing 5-LO activity, neutrophils are by far the most plentiful and can generate quantities of LTA 4 that exceed the capacity of their LTA 4 hydrolase to convert it into LTB 4 .…”

Aspirin-Exacerbated Respiratory Disease: Prevalence, Diagnosis, Treatment, and Considerations for the Future

“…Patients with AERD displayed dramatic upregulation of two essential enzymes involved in CysLT synthesis: 5-lipoxygenase (5-LO) and LTC 4 synthase. [14][15][16] This overexpression drives both the constitutive overproduction of CysLTs and the life-threatening surge that occurs with ingestion of aspirin and other nonselective cyclooxygenase (COX) inhibitors. 17 In addition to their overproduction, these patients display greatly enhanced sensitivity to the CysLTs, which reflects overexpression of the CysLT receptors.…”