Bronchial gland duct ectasia in fatal bronchial asthma: association with interstitial emphysema

PAR-2-activated secretion by airway gland serous cells: role for CFTR and inhibition by Pseudomonas aeruginosa

Airway submucosal gland serous cells are important sites of fluid secretion in conducting airways. Serous cells also express the cystic fibrosis (CF) transmembrane conductance regulator (CFTR). Protease-activated receptor 2 (PAR-2) is a G protein-coupled receptor that activates secretion from intact airway glands. We tested if and how human nasal serous cells secrete fluid in response to PAR-2 stimulation using Ca²⁺ imaging and simultaneous differential interference contrast imaging to track isosmotic cell shrinking and swelling reflecting activation of solute efflux and influx pathways, respectively. During stimulation of PAR-2, serous cells exhibited dose-dependent increases in intracellular Ca²⁺. At stimulation levels >EC₅₀ for Ca²⁺, serous cells simultaneously shrank ∼20% over ∼90 s due to KCl efflux reflecting Ca²⁺-activated Cl^- channel (CaCC, likely TMEM16A)-dependent secretion. At lower levels of PAR-2 stimulation (<EC₅₀ for Ca²⁺), shrinkage was not evident due to failure to activate CaCC. Low levels of cAMP-elevating VIP receptor (VIPR) stimulation, also insufficient to activate secretion alone, synergized with low-level PAR-2 stimulation to elicit fluid secretion dependent on both cAMP and Ca²⁺ to activate CFTR and K⁺ channels, respectively. Polarized cultures of primary serous cells also exhibited synergistic fluid secretion. Pre-exposure to Pseudomonas aeruginosa conditioned media inhibited PAR-2 activation by proteases but not peptide agonists in primary nasal serous cells, Calu-3 bronchial cells, and primary nasal ciliated cells. Disruption of synergistic CFTR-dependent PAR-2/VIPR secretion may contribute to reduced airway surface liquid in CF. Further disruption of the CFTR-independent component of PAR-2-activated secretion by P. aeruginosa may also be important to CF pathophysiology.

Polarization of protease-activated receptor 2 (PAR-2) signaling is altered during airway epithelial remodeling and deciliation

Protease-activated receptor 2 (PAR-2) is activated by secreted proteases from immune cells or fungi. PAR-2 is normally expressed basolaterally in differentiated nasal ciliated cells. We hypothesized that epithelial remodeling during diseases characterized by cilial loss and squamous metaplasia may alter PAR-2 polarization. Here, using a fluorescent arrestin assay, we confirmed that the common fungal airway pathogen Aspergillus fumigatus activates heterologously-expressed PAR-2. Endogenous PAR-2 activation in submerged airway RPMI 2650 or NCI-H520 squamous cells increased intracellular calcium levels and granulocyte macrophage-colony-stimulating factor, tumor necrosis factor α, and interleukin (IL)-6 secretion. RPMI 2650 cells cultured at an air-liquid interface (ALI) responded to apically or basolaterally applied PAR-2 agonists. However, well-differentiated primary nasal epithelial ALIs responded only to basolateral PAR-2 stimulation, indicated by calcium elevation, increased cilia beat frequency, and increased fluid and cytokine secretion. We exposed primary cells to disease-related modifiers that alter epithelial morphology, including IL-13, cigarette smoke condensate, and retinoic acid deficiency, at concentrations and times that altered epithelial morphology without causing breakdown of the epithelial barrier to model early disease states. These altered primary cultures responded to both apical and basolateral PAR-2 stimulation. Imaging nasal polyps and control middle turbinate explants, we found that nasal polyps, but not turbinates, exhibit apical calcium responses to PAR-2 stimulation. However, isolated ciliated cells from both polyps and turbinates maintained basolateral PAR-2 polarization, suggesting that the calcium responses originated from nonciliated cells. Altered PAR-2 polarization in disease-remodeled epithelia may enhance apical responses and increase sensitivity to inhaled proteases.

Pulmonary interstitial emphysema in fatal asthma: case report and histopathological review

BACKGROUND

Mortality related to asthma has decreased worldwide since the introduction of inhaled corticosteroid therapy in the past decades. However, there are still some asthma fatalities identified mainly in populations with less access to regular treatment. Pulmonary interstitial emphysema due to alveolar rupture has been rarely described as a complication of an acute severe asthma attack, and its identification in pathological analysis can be difficult. Previous studies reported the association of pulmonary interstitial emphysema and bronchial ductal gland ectasia in asthma.

CASE PRESENTATION

We present the case of a 42-year- old man that died due to a fatal asthma attack. Postmortem computed tomography revealed the unusual finding of acute Pulmonary Interstitial Emphysema, confirmed by pathological analysis. We reviewed 28 cases of fatal asthma tissue and identified the presence of pulmonary interstitial emphysema in 10% of the cases.

CONCLUSIONS

Postmortem computed tomography is a useful complimentary diagnostic tool for autopsies. Pulmonary Interstitial Emphysema in acute exacerbations of asthma seems to be more frequent than reported. Alveolar hyperdistension and bronchial duct gland ectasia causing tissue rupture are possible mechanisms involved in the formation of Pulmonary Interstitial Emphysema. The clinical impact of Pulmonary Interstitial Emphysema in asthma is unknown.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Persistent diffuse pulmonary interstitial emphysema mimicking pulmonary emphysema

A 69-year-old male non-smoker with a history of atopic asthma presented with symptoms suggestive of chronic obstructive pulmonary disease and this appeared to be corroborated by lung function testing and a chest radiograph. However, a chest CT showed no evidence of pulmonary emphysema and instead demonstrated free air along the bronchovascular sheaths indicative of pulmonary interstistial emphysema, possibly caused by repeated prior exacerbations of asthma. His lung function tests and symptoms improved within months of being treated for his airways disease but the CT findings were unchanged after 2 years.

Forensic Lung Pathology

Sudden and unexpected natural deaths and nonnatural deaths may result from various pulmonary conditions. Additionally, several nonpulmonary conditions of forensic significance may be complicated by the development of respiratory lesions. Certain situations with pulmonary pathology are particularly likely to be critically scrutinized and may form the basis of allegations of medical negligence, other personal injury liability, or wrongful death.1

High-resolution computed tomography findings in elderly patients with asthma

OBJECTIVE

Based on the hypothesis that airway remodelling is related to the duration of asthma, HRCT scanning should show greater abnormalities in the early-onset than the late-onset asthmatics. It was, therefore, intended to assess the presence and the frequency of airway and parenchymal abnormalities with high-resolution computed tomography (HRCT) in elderly asthmatic patients, and to determine whether these abnormalities are related to the duration of asthma.

PATIENTS AND METHODS

Sixty-eight clinically stable asthmatic patients aged > or =60 yr were included in this prospective study. The patients were separated into two groups according to the duration of symptoms as late-onset asthma (n=31) with disease duration of <5 yr, and early-onset asthma (n=37) with disease duration of > or =5 yr. All patients were lifelong non-smoker and had been using inhaled beta agonists and inhaled steroids. HRCT-scanning and histamine inhalation test were performed on all patients.

RESULTS

In comparison with late-onset asthmatic patients, those with early-onset asthma had significantly higher frequency of emphysema (21.6% versus 0.0%, p=0.006), bronchial dilatation (13.9% versus 0.0%, p=0.03) and bronchial wall thickness (41.7% versus 12.9%, p=0.01). Multiple logistic regression analysis identified that early-onset of disease was an independent risk factor for the presence of irreversible HRCT-scan abnormalities in elderly asthmatics [odds ratio (OR): 9.4 (2.7-32.7), p=0.00001].

CONCLUSION

Present data suggest that HRCT abnormalities in early-onset elderly asthmatics reflect parenchymal and airway changes that become irreversible throughout the long course of the disease.

Fractal geometry of airway remodeling in human asthma

RATIONALE

Airway wall remodeling is an important aspect of asthma. It has proven difficult to assess quantitatively as it involves changes in several components of the airway wall.

OBJECTIVE

To develop a simple method for quantifying the overall severity of airway wall remodeling in asthmatic airways using fractal geometry.

METHODS

Negative-pressure silicone rubber casts of lungs were made using autopsy material from three groups: fatal asthma, nonfatal asthma, and nonasthma control. All subjects were lifelong nonsmokers. A fractal dimension was calculated on two-dimensional digital images of each cast.

RESULTS

Nonasthma control casts had smooth walls and dichotomous branching patterns with nontapering segments. Asthmatic casts showed many abnormalities, including airway truncation from mucous plugs, longitudinal ridges, and horizontal corrugations corresponding to elastic bundles and smooth muscle hypertrophy, respectively, and surface projections associated with ectatic mucous gland ducts. Fractal dimensions were calculated from digitized images using an information method. The average fractal dimensions of the airways of both the fatal asthma (1.72) and nonfatal asthma (1.76) groups were significantly (p<0.01 and p=0.032, respectively) lower than that of the nonasthma control group (1.83). The lower fractal dimension of asthmatic airways correlated with a decreased overall structural complexity and pathologic severity of disease.

CONCLUSION

Fractal analysis is a simple and useful technique for quantifying the chronic structural changes of airway remodeling in asthma.

Asthma deaths; persistent and preventable mortality

Bronchial asthma remains a significant cause of mortality at all ages, despite the increased understanding of its pathogenesis and the range of drugs available for its treatment. Changes in therapeutic management can influence death rates and constant surveillance, combined with high-quality post mortem investigations, is essential. Disease severity, poor disease management and adverse psychosocial circumstances are all risk factors for asthma mortality. Bronchial asthma causes characteristic histological changes in the mucosa of the airways which are present even before the clinical diagnosis of asthma can be made. These include fibrous thickening of the lamina reticularis of the epithelial basement membrane, smooth muscle hypertrophy and hyperplasia, increased mucosal vascularity and an eosinophil-rich inflammatory cell infiltrate. In addition, mucoid plugging of the airway lumen is frequently associated with fatal asthma. The recognition of these changes can allow the diagnosis of asthma to be made for the first time at autopsy, in those cases where asthma goes undiagnosed in life. Acute severe asthma may be accompanied by pneumothorax and surgical emphysema of the mediastinum. Disorders which may mimic asthma include pulmonary embolism, chronic obstructive pulmonary disease and anaphylaxis, but careful post mortem examination and appropriate investigations should reveal the true cause of death.

Goblet cell and mucin gene abnormalities in asthma

Goblet cell hyperplasia (GCH) has been established as a pathologic characteristic of mild, moderate, and severe asthma. Abnormalities in goblet cell number are accompanied by changes in stored and secreted mucin (MUC). The functional consequences of these changes in MUC stores and secretion can contribute to the pathophysiologic mechanisms for multiple clinical abnormalities in patients with asthma, including sputum production, airway narrowing, exacerbations, and accelerated loss in lung function. CD4(+) T cells and their T-helper type-2 cytokine products are important mediators of GCH, and MUC5AC is the dominant MUC gene that is expressed in goblet cells. The mechanism of cytokine-induced GCH, the relationships between MUC gene up-regulation and GCH, and the role of ion channels are all currently being explored. The process of working out the molecular mechanisms of GCH and goblet cell degranulation should provide new targets for novel therapeutic interventions. Such new treatments are urgently needed, because mucus hypersecretion is an important cause of morbidity and mortality in patients with asthma, and no specific treatments are available.

Assessment of bronchial wall thickening on posteroanterior chest radiographs in acute asthma

A central bronchus that is readily visible end-on in approximately 50% of normal frontal chest radiographs is the bronchus to the anterior segment of either upper lobe. Bronchial wall thickening, or "cuffing," is considered to be a radiographic sign of an asthmatic exacerbation and is cited as a useful sign in a number of leading textbooks; however, to the authors' knowledge, no prior chest radiographic study has quantitatively assessed this specific sign in a population of asthmatics suffering an acute exacerbation. Posterior chest radiographs were reviewed retrospectively for 51 nonasthmatic, nonsmoking control subjects and for 45 adult asthmatic subjects during an acute exacerbation of moderate to severe asthma. Readers were blinded as to whether the radiograph was from an asthmatic or control subject. If visible end-on, the bronchus to the anterior segment of either upper lobe was assessed by measuring the diameter of the lumen and the thickness of the bronchial wall. At least one clearly defined bronchus to the anterior segment of an upper lobe was visible end-on in 22 patients (43%) in the control group and in 21 patients (47%) in the asthma group (p = NS). Mean wall thickness was 0.7 +/- 0.1 mm in the control group and 0.8 +/- 0.1 mm in the asthma group (p = 0.04). Lumen/wall thickness was 3.1 +/- 0.2 (SEM) in the control group and 2.5 +/- 0.2 in the asthma group (p = 0.055). The presence of bronchial wall thickness does not reliably distinguish radiographs of acutely asthmatic from normal individuals.

The relationship between pulmonary interstitial emphysema and clinical features in fatal asthma

Using retrospective histological material and clinical data from the New Zealand National Asthma Mortality Study, we investigated whether there was a relationship between the presence of pulmonary interstitial emphysema (PIE) and different clinical features in fatal asthma, in particular precipitous asthma death. Histological evidence of PIE was determined in sections from 12 of the 60 patients who had died from asthma who fulfilled the pathological criteria for inclusion in the study. No significant correlation was found between the presence of PIE and the different clinical features examined. For example, of the 13 cases with precipitous fatal asthma (i.e., death occurred within 10 min of the onset of the attack), only two had PIE. This suggests that PIE is not an uncommon histological feature of fatal asthma and may, in fact, significantly contribute to an asthma death, but its presence does not appear to be associated with the specific clinical subgroups studied here.