The nature of small-airway obstruction in chronic obstructive pulmonary disease

Polymers of Z alpha1-antitrypsin co-localize with neutrophils in emphysematous alveoli and are chemotactic in vivo

The molecular mechanisms that cause emphysema are complex but most theories suggest that an excess of proteinases is a crucial requirement. This paradigm is exemplified by severe deficiency of the key anti-elastase within the lung: alpha(1)-antitrypsin. The Z mutant of alpha(1)-antitrypsin has a point mutation Glu342Lys in the hinge region of the molecule that renders it prone to intermolecular linkage and loop-sheet polymerization. Polymers of Z alpha(1)-antitrypsin aggregate within the liver leading to juvenile liver cirrhosis and the resultant plasma deficiency predisposes to premature emphysema. We show here that polymeric alpha(1)-anti-trypsin co-localizes with neutrophils in the alveoli of individuals with Z alpha(1)-antitrypsin-related emphysema. The significance of this finding is underscored by the excess of neutrophils in these individuals and the demonstration that polymers cause an influx of neutrophils when instilled into murine lungs. Polymers exert their effect directly on neutrophils rather than via inflammatory cytokines. These data provide an explanation for the accelerated tissue destruction that is characteristic of Z alpha(1)-antitrypsin-related emphysema. The transition of native Z alpha(1)-antitrypsin to polymers inactivates its anti-proteinase function, and also converts it to a proinflammatory stimulus. These findings may also explain the progression of emphysema in some individuals despite alpha(1)-antitrypsin replacement therapy.

Interleukin-1beta causes pulmonary inflammation, emphysema, and airway remodeling in the adult murine lung

The production of the inflammatory cytokine interleukin (IL)-1 is increased in lungs of patients with chronic obstructive pulmonary disease (COPD) or asthma. To characterize the in vivo actions of IL-1 in the lung, transgenic mice were generated in which human IL-1beta was expressed in the lung epithelium with a doxycycline-inducible system controlled by the rat Clara cell secretory protein (CCSP) promoter. Induction of IL-1beta expression in the lungs of adult mice caused pulmonary inflammation characterized by neutrophil and macrophage infiltrates. IL-1beta caused distal airspace enlargement, consistent with emphysema. IL-1beta caused disruption of elastin fibers in alveolar septa and fibrosis in airway walls and in the pleura. IL-1beta increased the thickness of conducting airways, enhanced mucin production, and caused lymphocytic aggregates in the airways. Decreased immunostaining for the winged helix transcription factor FOXA2 was associated with goblet cell hyperplasia in IL-1beta-expressing mice. The production of the neutrophil attractant CXC chemokines KC (CXCL1) and MIP-2 (CXCL2), and of matrix metalloproteases MMP-9 and MMP-12, was increased by IL-1beta. Chronic production of IL-1beta in respiratory epithelial cells of adult mice causes lung inflammation, enlargement of distal airspaces, mucus metaplasia, and airway fibrosis in the adult mouse.

Predominant constitutive CFTR conductance in small airways

BACKGROUND

The pathological hallmarks of chronic obstructive pulmonary disease (COPD) are inflammation of the small airways (bronchiolitis) and destruction of lung parenchyma (emphysema). These forms of disease arise from chronic prolonged infections, which are usually never present in the normal lung. Despite the fact that primary hygiene and defense of the airways presumably requires a well controlled fluid environment on the surface of the bronchiolar airway, very little is known of the fluid and electrolyte transport properties of airways of less than a few mm diameter.

METHODS

We introduce a novel approach to examine some of these properties in a preparation of minimally traumatized porcine bronchioles of about 1 mm diameter by microperfusing the intact bronchiole.

RESULTS

In bilateral isotonic NaCl Ringer solutions, the spontaneous transepithelial potential (TEP; lumen to bath) of the bronchiole was small (mean +/- sem: -3 +/- 1 mV; n = 25), but when gluconate replaced luminal Cl-, the bionic Cl- diffusion potentials (-58 +/- 3 mV; n = 25) were as large as -90 mV. TEP diffusion potentials from 2:1 NaCl dilution showed that epithelial Cl- permeability was at least 5 times greater than Na+ permeability. The anion selectivity sequence was similar to that of CFTR. The bionic TEP became more electronegative with stimulation by luminal forskolin (5 microM)+IBMX (100 microM), ATP (100 microM), or adenosine (100 microM), but not by ionomycin. The TEP was partially inhibited by NPPB (100 microM), GlyH-101* (5-50 microM), and CFTRInh-172* (5 microM). RT-PCR gave identifying products for CFTR, alpha-, beta-, and gamma-ENaC and NKCC1. Antibodies to CFTR localized specifically to the epithelial cells lining the lumen of the small airways.

CONCLUSION

These results indicate that the small airway of the pig is characterized by a constitutively active Cl- conductance that is most likely due to CFTR.

The role of airway smooth muscle in the pathogenesis of airway wall remodeling in chronic obstructive pulmonary disease

Airway wall remodeling processes are present in the small airways of patients with chronic obstructive pulmonary disease, consisting of tissue repair and epithelial metaplasia that contribute to airway wall thickening and airflow obstruction. With increasing disease severity, there is also increased mucous metaplasia and submucosal gland hypertrophy, peribronchial fibrosis, and an increase in airway smooth muscle mass. Apart from its contractile properties, airway smooth muscle produces inflammatory cytokines, proteases, and growth factors, which may contribute to the remodeling process and induce phenotypic changes of the muscle. Airflow limitation responds minimally to beta-agonists and corticosteroid therapy, unlike asthma, perhaps because of alterations in beta-receptor or glucocorticoid receptor numbers, alterations in receptor signaling, or the constrictive limitation imposed by peribronchial fibrosis. Better response is observed with the combination of inhaled long-acting beta-agonists and corticosteroids. This could result from effects at the level of airway smooth muscle. Airway wall remodeling may involve the release of growth factors from inflammatory or resident cells. The influence of smoking cessation or of current therapies on airway wall remodeling is unknown. Specific therapies for airway wall remodeling may be necessary, together with noninvasive methods of imaging small airway wall remodeling to assess responses.

Inhaled Corticosteroids in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a serious illness that affects over 5% of the adult population. It is one of the few conditions for which the mortality and morbidity are still increasing. Experts expect COPD to become the third leading cause of death and the fifth leading cause of disability worldwide by the year 2020. Thus far, the only treatments that have been shown to make a difference to survival are smoking cessation and the use of oxygen supplements for those who are hypoxaemic at rest. The use of inhaled corticosteroids as monotherapy or in combination with a long-acting beta2-adrenoceptor agonist for COPD is controversial. Experimental data indicate that the inflammatory process in COPD may be resistant to the anti-inflammatory effects of corticosteroids. However, several large clinical studies have shown that inhaled corticosteroids in relatively high doses (e.g. budesonide 800 microg/day or fluticasone propionate 1 mg/day) reduce exacerbations by 20-30% and improve the health status of COPD patients by a similar amount compared with placebo. Withdrawal of inhaled corticosteroids may increase clinical exacerbation rates by 50% in COPD patients and by 2-fold in those with severe disease. Combined therapy with inhaled corticosteroids and long-acting beta2-adrenoceptor agonists may be superior to individual component therapy in reducing exacerbations. However, these medications must be used cautiously, as they have been associated with certain adverse effects. Inhaled corticosteroids, for instance, increase the risk for dysphonia and oral thrush by 2- to 3-fold. Skin bruising is also more common in users than in non-users of inhaled corticosteroids. On balance, for those with moderate-to-severe COPD and those who experience frequent exacerbations, judicious use of inhaled corticosteroids alone or in combination with long-acting beta2-adrenoceptor agonists appears reasonable.

Chronic obstructive pulmonary disease: a novel risk factor for cardiovascular disease

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of morbidity and mortality in Canada and elsewhere. It affects 5% of all adult Canadians and is the fourth leading cause of death. Interestingly, the leading causes of hospitalizations and mortality among COPD patients are cardiovascular events. In the Lung Health Study, over 5 800 patients with mild to moderate COPD were studied. Forty-two to 48% of all hospitalizations that occurred over the study's 5-year follow-up period were related to cardiovascular complications. Various population-based studies suggest that independent of smoking, age, and gender, COPD increases the risk of cardiovascular morbidity and mortality twofold. Alarmingly, some bronchodilators, which are commonly used to treat symptoms in COPD, may increase the risk of cardiovascular morbidity and even mortality among COPD patients. In this paper, we discuss the epidemiologic evidence linking COPD and cardiovascular events as well as the potential mechanism(s) which may be responsible for this association.Key words: COPD, FEV1, cardiovascular events, C-reactive protein.

Cell-mediated adaptive immune defense of the lungs

Cell-mediated adaptive immune responses contribute to defense against all classes of pulmonary pathogens and are essential against viruses, mycobacteria, and fungi, including Pneumocystis carinii. Adaptive responses depend on sequential pairwise interactions between three cell types: T cells, natural killer (NK) cells, and dendritic cells (DC). Differential expression of specific adhesion molecules and chemokines regulates the location and timing of these interactions. Primary adaptive responses are triggered by immature myeloid DC, which carry antigen from the lungs to regional lymph nodes. Antigen presentation by these mature DC is required to activate naive CD4 T cells, which are essential to generate polarized type 1 or type 2 effector responses and for robust immunologic memory. Inflammation recruits NK cells and DC that interact in a contact- and tumor necrosis factor-alpha-dependent fashion within injured tissues to initiate immune response polarization. NK cells exposed to IL-12 favor survival of DC that prime for Th1 responses, whereas NK cells exposed to IL-4 do not exert DC selection, leading to tolerogenic or Th2 responses. Naive alphabeta T cells, NK cells, and DC also amplify secondary adaptive responses to previously encountered pathogens. However, secondary responses are accelerated because memory T cells can migrate directly to infected tissues where they can be activated without strenuous costimulatory requirements. Additionally, previous pulmonary infections or immune responses increase numbers of lung DC and populate the lungs with clones of memory B cells and T cells that are immediately available to respond to infections.

Mediators of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem that is now a leading cause of death. COPD is associated with a chronic inflammatory response, predominantly in small airways and lung parenchyma, which is characterized by increased numbers of macrophages, neutrophils, and T lymphocytes. The inflammatory mediators involved in COPD have not been clearly defined, in contrast to asthma, but it is now apparent that many lipid mediators, inflammatory peptides, reactive oxygen and nitrogen species, chemokines, cytokines, and growth factors are involved in orchestrating the complex inflammatory process that results in small airway fibrosis and alveolar destruction. Many proteases are also involved in the inflammatory process and are responsible for the destruction of elastin fibers in the lung parenchyma, which is the hallmark of emphysema. The identification of inflammatory mediators and understanding their interactions is important for the development of anti-inflammatory treatments for this important disease.

An animal model of autoimmune emphysema

Although cigarette smoking is implicated in the pathogenesis of emphysema, the precise mechanisms of chronic progressive alveolar septal destruction are not well understood. We show, in a novel animal model, that immunocompetent, but not athymic, nude rats injected intraperitoneally with xenogeneic endothelial cells (ECs) produce antibodies against ECs and develop emphysema. Immunization with ECs also leads to alveolar septal cell apoptosis and activation of matrix metalloproteases MMP-9 and MMP-2. Anti-EC antibodies cause EC apoptosis in vitro and emphysema in passively immunized mice. Moreover, immunization also causes accumulation of CD4+ T cells in the lung. Adoptive transfer of pathogenic, spleen-derived CD4+ cells into naive immunocompetent animal also results in emphysema. This study shows for the first time that humoral- and CD4+ cell-dependent mechanisms are sufficient to trigger the development of emphysema, suggesting that alveolar septal cell destruction might result from immune mechanisms.

Models of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major global health problem and is predicted to become the third most common cause of death by 2020. Apart from the important preventive steps of smoking cessation, there are no other specific treatments for COPD that are as effective in reversing the condition, and therefore there is a need to understand the pathophysiological mechanisms that could lead to new therapeutic strategies. The development of experimental models will help to dissect these mechanisms at the cellular and molecular level. COPD is a disease characterized by progressive airflow obstruction of the peripheral airways, associated with lung inflammation, emphysema and mucus hypersecretion. Different approaches to mimic COPD have been developed but are limited in comparison to models of allergic asthma. COPD models usually do not mimic the major features of human COPD and are commonly based on the induction of COPD-like lesions in the lungs and airways using noxious inhalants such as tobacco smoke, nitrogen dioxide, or sulfur dioxide. Depending on the duration and intensity of exposure, these noxious stimuli induce signs of chronic inflammation and airway remodelling. Emphysema can be achieved by combining such exposure with instillation of tissue-degrading enzymes. Other approaches are based on genetically-targeted mice which develop COPD-like lesions with emphysema, and such mice provide deep insights into pathophysiological mechanisms. Future approaches should aim to mimic irreversible airflow obstruction, associated with cough and sputum production, with the possibility of inducing exacerbations.

The prediction of small airway dimensions using computed tomography

Chronic obstructive pulmonary disease is characterized by destruction of the lung parenchyma and/or small airway narrowing. To determine whether the dimensions of relatively large airways assessed using computed tomography (CT) reflect small airway dimensions measured histologically, we assessed these variables in nonobstructed or mild to moderately obstructed patients having lobar resection for a peripheral tumor. For both CT and histology, the square root of the airway wall area (Aaw) was plotted versus lumen perimeter to estimate wall thickness. The wall area percentage was calculated as wall area/lumen area + wall area x 100. Although CT overestimated Aaw, the slopes of the relationships between the square root of Aaw and internal perimeter (Pi) measured with both techniques were related (CT slope = 0.2059 histology slope + 0.1701, R2 = 0.32, p < 0.01). The mean wall area percentage measured by CT for airways with a Pi of greater than 0.75 cm predicted the mean dimensions of the small airways with an internal diameter of 1.27 mm (R2 = 0.57, p < 0.01). We conclude that CT measurements of airways with a Pi of 0.75 cm or more could be used to estimate the dimensions of the small conducting airways, which are the site of airway obstruction in chronic obstructive pulmonary disease.

Small airway morphometry and improvement in pulmonary function after lung volume reduction surgery

We examined small airway morphometry from resected lung specimens in 25 patients with severe emphysema undergoing lung volume reduction surgery (LVRS) and correlated their pathologic findings to changes in FEV(1) 6 months after LVRS. Patients were classified into two groups: responders had a more than 12% and a more than 200-ml change in FEV(1) at 6 months, and nonresponders had 12% or less and/or 200 ml or less change in FEV(1). Epithelial height (EH) and perimeters and areas of peribronchial smooth muscle, epithelium, and subepithelial space were measured quantitatively. The degrees of interstitial fibrosis, vascular sclerosis, goblet cell hyperplasia, squamous metaplasia, chronic inflammation, peribronchial fibrosis, and bullous disease were assessed semiquantitatively. Despite similar baseline characteristics, nonresponders had a greater EH (0.045 vs. 0.035 mm, p = 0.025), greater EH adjusted for basement membrane perimeter (0.040 vs. 0.011, p = 0.016), greater epithelial area adjusted for basement membrane area (0.561 vs. 0.499, p = 0.040), and less bullous disease (1.7 vs. 2.6, p = 0.011) compared with responders. We found a linear relationship between percentage change in FEV(1) and bullous disease and inverse relationships between percentage change in FEV(1) and interstitial fibrosis, goblet cell hyperplasia, peribronchial fibrosis, and vascular sclerosis. We conclude that small airway morphometry and lung histopathology in patients with severe emphysema have an important influence on changes in FEV(1) 6 months after LVRS.

Characterization of T lymphocytes in chronic obstructive pulmonary disease

A new study adds to the mounting evidence implicating T cells as an important component of the inflammation in chronic obstructive pulmonary disease

Sequential photodynamic therapy (PDT) and high dose brachytherapy for endobronchial tumour control in patients with limited bronchogenic carcinoma

BACKGROUND

Bulky endobronchial tumours in patients with lung cancer are difficult to treat. Brachytherapy and photodynamic therapy (PDT) are variably effective, and the combination of these treatments is not often recommended. However, cell culture studies and animal studies indicate a possible synergistic effect of combining PDT with ionising radiation. We assessed the safety and effectiveness of combined brachytherapy and PDT in patients with bulky endobronchial lung cancer.

METHODS

Patients with histologically proven non-small cell bronchogenic carcinoma and bulky endobronchial tumours were treated using a combination of PDT (Photofrin, 2 mg/kg) and brachytherapy. Six weeks after PDT, brachytherapy was applied with five fractions of 4 Gy at weekly intervals. Follow up was performed with standard and autofluorescence bronchoscopy and tissue biopsies every 3 months.

RESULTS

Thirty two patients were treated. Tumours were extensive with lengths ranging from 10 to 60 mm along the bronchus and estimated volumes ranging from 40 to 3500 mm3. At a mean follow up of 24 months, 26 patients were free of residual tumour and local recurrence. The remaining patients received a second treatment with PDT, brachytherapy, Nd:YAG laser coagulation, or external beam radiation. Distant metastases (lung, lymph node) developed in two of the six patients. Currently, all 32 patients are well. There is no evidence of residual or local recurrent endobronchial cancer in 28 patients and none had severe complications.

CONCLUSION

The combination of PDT and brachytherapy for treating patients with lung cancer and extensive endobronchial tumour is safe and, in this study, had excellent therapeutic efficacy.

Gene expression profiling of human lung tissue from smokers with severe emphysema

The mechanism by which inhaled smoke causes the anatomic lesions and physiologic impairment of chronic obstructive pulmonary disease remains unknown. We used high-density microarrays to measure gene expression in severely emphysematous lung tissue removed from smokers at lung volume reduction surgery (LVRS) and normal or mildly emphysematous lung tissue from smokers undergoing resection of pulmonary nodules. Class prediction algorithms identified 102 genes that accurately distinguished severe emphysema from non-/mildly emphysematous lung tissue. We also defined a number of genes whose expression levels correlated strongly with lung diffusion capacity for carbon monoxide and/or forced expiratory volume at 1 s. Genes related to oxidative stress, extracellular matrix synthesis, and inflammation were increased in severe emphysema, whereas expression of endothelium-related genes was decreased. To identify candidate genes that might be causally involved in the pathogenesis of emphysema, we linked gene expression profiles to chromosomal regions previously associated with chronic obstructive pulmonary disease in genome-wide linkage analyses. Unsupervised hierarchical clustering of the LVRS samples revealed distinct molecular subclasses of severe emphysema, with body mass index as the only clinical variable that differed between the groups. Class prediction models established a set of genes that predicted functional outcome at 6 mo after LVRS. Our findings suggest that the gene expression profiles from human emphysematous lung tissue may provide insight into pathogenesis, uncover novel molecular subclasses of disease, predict response to LVRS, and identify targets for therapeutic intervention.

Barrier role of actin filaments in regulated mucin secretion from airway goblet cells

Airway goblet cells secrete mucin onto mucosal surfaces under the regulation of an apical, phospholipase C/G(q)-coupled P2Y(2) receptor. We tested whether cortical actin filaments negatively regulate exocytosis in goblet cells by forming a barrier between secretory granules and plasma membrane docking sites as postulated for other secretory cells. Immunostaining of human lung tissues and SPOC1 cells (an epithelial, mucin-secreting cell line) revealed an apical distribution of beta- and gamma-actin in ciliated and goblet cells. In goblet cells, actin appeared as a prominent subplasmalemmal sheet lying between granules and the apical membrane, and it disappeared from SPOC1 cells activated by purinergic agonist. Disruption of actin filaments with latrunculin A stimulated SPOC1 cell mucin secretion under basal and agonist-activated conditions, whereas stabilization with jasplakinolide or overexpression of beta- or gamma-actin conjugated to yellow fluorescent protein (YFP) inhibited secretion. Myristoylated alanine-rich C kinase substrate, a PKC-activated actin-plasma membrane tethering protein, was phosphorylated after agonist stimulation, suggesting a translocation to the cytosol. Scinderin (or adseverin), a Ca(2+)-activated actin filament severing and capping protein was cloned from human airway and SPOC1 cells, and synthetic peptides corresponding to its actin-binding domains inhibited mucin secretion. We conclude that actin filaments negatively regulate mucin secretion basally in airway goblet cells and are dynamically remodeled in agonist-stimulated cells to promote exocytosis.

Pathophysiology of airflow limitation in chronic obstructive pulmonary disease

The airflow limitation that defines chronic obstructive pulmonary disease (COPD) is the result of a prolonged time constant for lung emptying, caused by increased resistance of the small conducting airways and increased compliance of the lung as a result of emphysematous destruction. These lesions are associated with a chronic innate and adaptive inflammatory immune response of the host to a lifetime exposure to inhaled toxic gases and particles. Processes contributing to obstruction in the small conducting airways include disruption of the epithelial barrier, interference with mucociliary clearance apparatus that results in accumulation of inflammatory mucous exudates in the small airway lumen, infiltration of the airway walls by inflammatory cells, and deposition of connective tissue in the airway wall. This remodelling and repair thickens the airway walls, reduces lumen calibre, and restricts the normal increase in calibre produced by lung inflation. Emphysematous lung destruction is associated with an infiltration of the same type of inflammatory cells found in the airways. The centrilobular pattern of emphysematous destruction is most closely associated with cigarette smoking, and although it is initially focused on respiratory bronchioles, separate lesions coalesce to destroy large volumes of lung tissue. The panacinar pattern of emphysema is characterised by a more even involvement of the acinus and is associated with alpha1 antitrypsin deficiency. The technology needed to diagnose and quantitate the individual small airway and emphysema phenotypes present in people with COPD is being developed, and should prove helpful in the assessment of therapeutic interventions designed to modify the progress of either phenotype.

Role of inducible bronchus associated lymphoid tissue (iBALT) in respiratory immunity

Bronchus-associated lymphoid tissue (BALT) is occasionally found in the lungs of mice and humans; however, its role in respiratory immunity is unknown. Here we show that mice lacking spleen, lymph nodes and Peyer's patches generate unexpectedly robust primary B- and T-cell responses to influenza, which seem to be initiated at sites of induced BALT (iBALT). Areas of iBALT have distinct B-cell follicles and T-cell areas, and support T and B-cell proliferation. The homeostatic chemokines CXCL13 and CCL21 are expressed independently of TNFalpha and lymphotoxin at sites of iBALT formation. In addition, mice with iBALT, but lacking peripheral lymphoid organs, clear influenza infection and survive higher doses of virus than do normal mice, indicating that immune responses generated in iBALT are not only protective, but potentially less pathologic, than systemic immune responses. Thus, iBALT functions as an inducible secondary lymphoid tissue for respiratory immune responses.

Inhaled Salmeterol/Fluticasone Propionate

The salmeterol/fluticasone propionate dry powder inhaler (DPI) [Advair Diskus, Seretide Accuhaler] contains the long-acting beta2-adrenoceptor agonist salmeterol and the inhaled corticosteroid fluticasone propionate. In the US, twice-daily salmeterol/fluticasone propionate 50/250 microg is approved for use in adults with chronic obstructive pulmonary disease (COPD) associated with chronic bronchitis, and in the EU, the twice-daily 50/500 microg dosage is approved for use in patients with severe COPD, repeat exacerbations and significant symptoms despite bronchodilator therapy. In patients with moderate-to-severe COPD, twice-daily inhaled salmeterol/fluticasone propionate 50/250 or 50/500 microg for 24-52 weeks improves predose forced expiratory volume in 1 second (FEV1) significantly more than salmeterol monotherapy, improves postdose or postbronchodilator FEV1 significantly more than fluticasone propionate monotherapy and results in clinically significant improvements in health-related quality of life. Salmeterol/fluticasone propionate 50/500 microg significantly reduced annual COPD exacerbations, especially in severe COPD. Some corticosteroid-related adverse events were increased in recipients of fluticasone propionate with or without salmeterol versus salmeterol monotherapy or placebo; withdrawal from fluticasone propionate, including combination therapy, needs careful management to minimise COPD exacerbations. The DPI combining a corticosteroid and long-acting beta2-agonist provides benefits over monotherapy and may encourage patient compliance in COPD.