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1 Service de Pneumologie, Université René Descartes, Hôpital Cochin, Paris, France. 2 Dept of Otorhinolaryngology, Malmö University Hospital, Malmö, Sweden. 3 Cardiovascular Research Institute, and Dept of Medicine and Physiology, University of California, San Francisco, CA, USA.
CORRESPONDENCE: J.A. Nadel, Cardiovascular Research Institute, Box 0130, University of California San Francisco, San Francisco, CA 94 143-0130, USA. Fax: 01 4154762283. E-mail: janadel@itsa.ucsf.edu
Keywords: Airway epithelium, epidermal growth factor receptor, interleukin-8, leukocyte recruitment, mucous hypersecretion, steroid treatment
Received: February 4, 2004
Accepted May 4, 2004
This work was funded by private funds. P-R. Burgel is a recipient of a grant from "Collège des Professeurs de Pneumologie".
| Abstract |
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expression was assessed in nasal polyps.
In nine subjects, one nasal polyp was removed surgically before treatment and another was removed after 8 weeks of intranasal fluticasone (400 µg·day1). Tissues were processed for in situ hybridisation and immunohistochemical staining. Described effects of fluticasone on nasal polyps (reduction in nasal resistance and in eosinophil infiltration) were evaluated. Morphometric analysis was performed to assess the effect of fluticasone on epithelial-, MUC5AC-, EGFR- and IL-8-stained areas, TNF-
-stained cells, and neutrophil numbers.
Treatment with fluticasone decreased nasal resistance and intra-epithelial eosinophils. The MUC5AC-stained area in the epithelium was unchanged by treatment; MUC5AC mRNA expression was unaffected by treatment. EGFR-stained area, intra-epithelial neutrophil numbers, IL-8 and TNF-
expression were also unchanged by therapy.
Intranasal fluticasone was effective in decreasing nasal airflow resistance and intra-epithelial eosinophils but had no effect on mucin or epidermal growth factor receptor expression or on neutrophil recruitment.
Goblet cell hyperplasia and increased mucin expression arefeatures of nasal polyp epithelium 1, but, currently, no effective therapy for mucus hypersecretion is established. Eosinophil infiltration is a characteristic finding in nasal polyp tissue. Neutrophils are recruited into the airways in hypersecretory airway diseases (e.g. chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, acute asthma) and are also found in nasal polyps 2. Neutrophil chemoattractants are upregulated in the airways of these diseases 3 and expression of the neutrophil chemoattractant interleukin (IL)-8 is reported in nasal polyp tissue 4. Several neutrophil products are reported to play important roles in mucin production, including oxygen free radicals 5 and elastase 6. Eosinophil products also increase mucin production in airway epithelial cells 7. Therefore, both eosinophils and neutrophils have been suspected to play roles in the increased mucin expression found in nasal polyps 1.
Corticosteroids are the recommended medical therapy fornasal polyps. They are effective in decreasing the size of polyps 8, 9 and in inhibiting eosinophil infiltration into polyp tissue 10, but their effect on mucin production is not established.
Several mucins are expressed in human airways. Among these mucins, gel-forming mucins found in airway secretions include MUC2, MUC5AC and MUC5B. MUC2 expression has not been found consistently in immunohistochemical studies 11 and only a small amount of MUC2 protein has been found in airway secretions 12. Although MUC5B is reported to be expressed in goblet cells in normal nasal epithelium, it is believed to be localised preferentially to airway submucosal glands 13. Furthermore, there appear to be no reports of MUC5B protein expression in nasal polyps. In contrast, MUC5AC is consistently reported to be expressed in both nasal and lower airway epithelium 1, 11. We have previously shown that MUC5AC gene and protein areexpressed in nasal polyp epithelium, and that MUC5AC-stained area in nasal polyp epithelium is comparable to AB/PAS-stained area 1. Because both epidermal growth factor receptor (EGFR) activation 14 and leukocyte products have been implicated in mucin production, the effects of intranasal fluticasone on mucin MUC5AC and EGFR expression, and on leukocyte infiltration were examined in this study.
In each subject, one polyp was removed before corticosteroid therapy and a second polyp was removed after 8 weeks of treatment with an intranasal corticosteroid, fluticasone. The effectiveness of fluticasone on the size of polyps (evaluated by nasal airflow resistance) and eosinophil numbers was assessed, both of which are known to be decreased by fluticasone 10. To assess the effect of fluticasone on mucin production and its effect on the EGFR cascade, in situ hybridisation and immunohistochemistry for MUC5AC gene, and protein expression and immunohistochemistry for EGFR protein were performed. Neutrophil infiltration, and expression of IL-8 and tumour necrosis factor (TNF)-
were also examined.
| Methods |
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All studies were approved by the Ethics Committee of the University of Malmö (Malmö, Sweden) and an informed written consent was obtained from each subject.
Rhinomanometry
Nasal airflow resistance was determined for each nostril using active anterior rhinomanometry 18, a method where nasal airflow and pressure are measured at the nostrils during respiration. Before performing rhinomanometry, subjects rested in the sitting position. A pressure catheter was inserted in a nostril that was occluded with a strip of adhesive tape, and the other end was connected to a pressure transducer. Care was taken to insure that the sides of the catheter did not contact any part of the nasal mucosa. Flow was measured at a pressure of 1.5 cmH2O with a pneumotachograph, via a mask held airtight over the nose and mouth by the subject with as little compression as possible. Nasal airflow resistance was expressed in cmH2O·L1·s1.
Tissue processing and immunohistochemistry
Nasal polyps were removed surgically, fixed immediately in 10% formalin, embedded in paraffin and cut into 5-µm sections. The sections were deparaffinised, rehydrated and treated with 0.3% H2O2 in methyl alcohol. PBS containing 0.05% Tween-20 and 1% bovine serum albumin (BSA) was used as diluent for the following antibodies: a monoclonal antibody (mAb) to MUC5AC (clone 45M1; dilution 1:500; Neomarkers, Fremont, CA, USA); a mAb to EGFR (Ab-1; dilution 1:100; Calbiochem, La Jolla, CA, USA); a mAb to eosinophil cationic protein (EG2; dilution 1:1,000; Pharmacia Upjohn, Kalamazoo, MI, USA); a mAb to human neutrophil elastase (NP57; dilution 1:100; DAKO Corp., Carpinteria, CA, USA); a polyclonal Ab to IL-8 (dilution 1:20; Biosource, Camarillo, CA, USA); and a polyclonal rabbit anti-human antibody to TNF-
(dilution 1:1,000; Genzyme Corp, Cambridge, MA, USA).
Tissue sections were incubated with 2% BSA at room temperature for 1 h and were then incubated with primary antibody at room temperature for 2 h. After removing excess Ab by washing with PBS, sections were incubated with a biotinylated horse anti-mouse Ab (dilution 1:200; Vector Laboratories, Burlingame, CA, USA) or with a biotinylated goat anti-rabbit Ab (dilution 1:200; Vector Laboratories) for 1 h at room temperature. Bound Ab was visualised according to standard protocols for avidin-biotin-peroxidase complex method (Elite ABC kit; Vector Laboratories). Tissue sections were counterstained with haematoxylin. Omission of the primary Ab and incubation with an irrelevant mouse immunoglobulin (Ig)G antibody (DAKO) were used as negative controls. Alcian Blue (AB)/PAS was performed for detection of mucous glycoconjugates.
In situ hybridisation for MUC5AC mRNA
MUC5AC gene expression was assessed by in situ hybridisation with 35S-labelled riboprobes. Preparation of the probes and in situ hybridisation were performed as described previously 19.
Eosinophil and neutrophil numbers
Quantification of eosinophil and neutrophil numbers in polyp tissues was performed by counting numbers of human neutrophil elastase (HNE)-stained (for neutrophils) and EG2-stained (for eosinophils) cells in epithelium and subepithelium. Epithelium was defined as the area between cilia and basal membrane. Subepithelium was defined as the area immediately underneath the basal membrane (depth: one high power field at 400x=0.0125 mm). For each layer (epithelium, subepithelium), 10 high-power fields (magnification 400x) were selected randomly and positively stained cells were counted. Results are expressed as the number of cells per mm of basal membrane in epithelium and as the number of cells per mm2 in subepithelium.
Epithelial, and MUC5AC- and EGFR-stained areas
Measurements of epithelial, and MUC5AC- and EGFR-stained areas in polyp epithelium were performed using a semi-automatic imaging system that included a microscope, a video camera and a computer. Because of the heterogeneity ofpolyp epithelium 1, for EGFR- and MUC5AC-stained areas, and total epithelial area, data were obtained from two randomly selected polyp sections in each subject. In each section, first images of all intact epithelium were recorded at 100x magnification. Next, epithelial area was measured on a computer screen using a grid composed of points; intersections of points with epithelium were counted and converted to areas (each point corresponding to a known area) 11. Results obtained in two sections were averaged and expressed as mm2 of epithelium per mm of basal membrane. The median length of epithelium analysed in each section was 15.1 mm (range 4.423.3). Areas of epithelium occupied by MUC5AC- and by EGFR-stained cells were also measured by point counting using a grid (supra vide). Results obtained in two sections were averaged and were expressed as mm2 of MUC5AC or EGFR staining per mm of basal membrane. Results were not different when they were expressed as % positively stained area of epithelium.
IL-8-stained area
Visualisation of staining for IL-8, a small diffusible molecule, required higher magnification than visualisation of MUC5AC and EGFR staining. Therefore, measurements were performed at 400x magnification: ten images of epithelium were randomly obtained, and areas of epithelium occupied by IL8-stained cells were measured by point counting using a grid (supra vide). Results were expressed as mm2 of IL-8 staining per mm of basal membrane.
TNF-
-stained cells
As TNF-
in epithelium was expressed mostly in recruited inflammatory cells but also in epithelial cells (see Results section), this molecule was assessed by counting positively stained cells (both epithelial and inflammatory cells); for each polyp, 10 high-power fields (magnification 400x) were selected randomly in a single section and positively stained cells were counted. Results are expressed as cells per mm of basal membrane.
Statistics
Data obtained from measurements of nasal airflow resistance and from morphometric measurements of epithelial area, MUC5AC-, EGFR- and IL-8-stained areas, and HNE-, EG2- and TNF-
-stained cells before and after steroid treatment were compared using the nonparametric Wilcoxon signed-rank test. A p-value <0.05 for the null hypothesis was accepted as indicating a statistically significant difference. Sections were evaluated by a single observer on two different occasions in coded random order. All intra-observer coefficients of variation for repeated measurements were <9%.
| Results |
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Morphometric analysis of epithelial area and MUC5AC and EGFR expression
The total epithelial area was slightly decreased after treatment with fluticasone, although this did not reach statistical significance (p=0.054; fig. 3a
). As described previously 1, AB/PAS- and MUC5AC-stained areas were not different from one another in polyp epithelium (data not shown). MUC5AC staining was present in epithelial goblet cells, and the MUC5AC-stained area was unaffected by fluticasone (p=0.91) (fig. 3b
). MUC5AC mRNA assessed by in situ hybridisation showed strong signals before and after steroid treatment (fig. 4
). Hybridisation with a sense probe for MUC5AC mRNA showed no signal (data not shown).
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IL-8
Staining for IL-8 was present in nasal polyp epithelium and was localised to basal and ciliated epithelial cells; however, IL-8 was not present in goblet cells. Some inflammatory cells infiltrating airway epithelium also expressed positive staining for IL-8. IL-8-stained area in epithelium was not affected by treatment with fluticasone (p=0.65; fig. 5a
). No significant correlation was found between intra-epithelial neutrophils and IL-8 expression (r=0.051, p=0.84, n=18 polyps, Spearman Rank correlation).
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-expressing cells were regularly found in polyp epithelium, mostly in inflammatory cells infiltrating polyp epithelium; epithelial cells also expressed TNF-
. TNF-
positively stained cell numbers were not different before and after fluticasone treatment (p=0.82; fig. 5b| Discussion |
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Evaluation of the effects of corticosteroids on mucins in subjects with nasal polyps has not been reported, to our knowledge. In lower airway epithelium of asthmatic patients, available studies show conflicting data regarding effect of local steroids on goblet cell metaplasia and mucin expression. Laitinen et al. 21 studied bronchial biopsies obtained before treatment andafter 3 months of treatment with budesonide (600 µg, twice daily) in seven asthmatic subjects. The authors reported significant increase in ciliated-to-goblet cell index after treatment with inhaled budesonide. However, no data were presented concerning mucin gene or protein expression. Groneberg et al. 22 reported no change in mucin content after a month of inhaled budesonide therapy, using a semi-quantitative analysis of MUC5AC mucin staining of bronchial biopsies. Fahy et al. 23 reported that a month of inhaled beclomethasone therapy did not affect mucin-like glycoproteins in the sputum of moderate asthmatics. The present study is the first to assess effects of local steroids in human airway epithelium in vivo on both mucin gene and protein expression, using quantitative morphometric analysis. The data presented here show that mucin protein content in epithelium is unchanged by usual doses of intranasal steroids. The presence of mucus in airway epithelium is related to mucin synthesis (that increases mucin contents) and to mucin secretion (that decreases mucin contents). Therefore, the persistence of mucin protein expression in airway epithelium after treatment with intranasal steroids may be related to effects on mucin synthesis and/or mucin secretion. Importantly, using in situ hybridisation, it was found that MUC5AC gene expression is not abolished by therapy. This study design did not allow for studying mucin secretion. However, MacGregor et al. 24, measuring secreted mucous glycoproteins in nasal lavage fluid in normal subjects, concluded that intranasal steroids potentiate mucin secretion. Taken together, these results suggest that local steroids do not inhibit either mucin synthesis or mucin secretion and that alternative treatment is required to treat mucus hypersecretion.
No data are available regarding the magnitude of the reduction in mucin content that is clinically significant, so the number of subjects necessary to draw negative conclusions could not be determined. Therefore, the possibility that intranasal steroids have small effects on mucin expression cannot be ruled out and studies analysing larger numbers of subjects may show some positive effects.
A small decrease in total epithelial area was found after steroid treatment. Because intranasal steroids had no effect on mucin-producing cells, this finding could be related to effects of steroids on other epithelial cell types (e.g. ciliated cells, basal cells).
EGFR expression and activation have been shown to be involved in mucin production in human airway epithelial cells and in animal models by various molecules, by allergen 14 and by a wide variety of other stimuli 25. The association between EGFR and mucin expression suggests the possibility that an EGFR cascade is responsible for mucin production in polyps 1. Here it is shown that neither EGFR nor mucin expression is affected by intranasal corticosteroid therapy. These results are in agreement with the reported lack of effect of inhaled corticosteroids on EGFR expression in asthmatic airway epithelium 27. TNF-
has been shown to induce EGFR expression in airways 14. TNF-
is absent from normal nasal tissues but is expressed in nasal polyps 1, 28. In this study, the presence of TNF-
in polyp epithelium, mostly in infiltrating inflammatory cells, has been confirmed. Interestingly, both TNF-
and EGFR expression were unaffected by intranasal corticosteroids.
Neutrophils and eosinophils are prominent in airways of patients with various hypersecretory diseases, suggesting roles for these cells in mucin synthesis 29. Studies conducted in animals have shown conflicting data regarding roles of eosinophils in goblet cell metaplasia and mucin synthesis. Using IL-5-deficient mice, Cohn et al. 30 showed that T-helper 2-induced airway mucus production is independent of eosinophils. However, Shen et al. 31 reported that transfer of eosinophils in IL-5-deficient mice restored mucous cell metaplasia in response to ovalbumin challenge. In the present study, inhibition of eosinophil infiltration by intranasal steroids was not associated with a reduction in mucin gene and protein expression, suggesting that mucin synthesis can occur in the absence of eosinophils in polyps. Neutrophil infiltration was unaffected by steroid treatment and could contribute to mucin production.
It was found in this study that nasal polyp epithelium expresses IL-8, a potent neutrophil chemoattractant, confirming a previous report that IL-8 expression is increased in polyps compared to healthy nasal mucosa 4. The persistence of IL-8 and neutrophils after fluticasone therapy is compatible with the hypothesis that IL-8 is responsible, at least in part, for neutrophil recruitment in nasal polyp epithelium. A correlation was not found between intra-epithelial neutrophils and IL-8 expression. However, because neutrophil transmigration in airway epithelium is rapid and because IL-8 expressed in epithelial cells leaves the cells rapidly, a correlation between IL-8 expression and intra-epithelial neutrophils would not necessarily be expected.
In conclusion, treatment with intranasal fluticasone was effective in reducing polyp size and in suppressing eosinophil infiltration. However, this treatment did not affect mucin production, epidermal growth factor receptor expression or neutrophil infiltration. It is suggested that selective inhibitors of epidermal growth factor receptor tyrosine phosphorylation or inhibition of selected neutrophil products could be useful in inhibiting mucus overproduction in nasal polyps and in other hypersecretory diseases. Furthermore, because of their location and accessibility, nasal polyps provide a convenient "model" for evaluating various therapies in the suppression of mucin production in the respiratory system. Appropriate clinical studies are needed to evaluate these therapeutic possibilities.
| Acknowledgements |
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