Induced sputum for the investigation of airway inflammation: evidence for its clinical application

Advances in Evaluation and Treatment of Severe Asthma (Part One)

As many as 15% to 20% of patients with asthma have incompletely or poorly controlled asthma despite treatment with inhaled corticosteroids and long-acting beta-agonist bronchodilators. They are vulnerable to burdensome symptoms, limitations to their exercise capacity, and asthma attacks that can be frightening and potentially life-threatening. This article outlines a systematic approach to their evaluation, attempting to identify remediable factors that are making their asthma more severe than most other persons with asthma. This approach includes an emphasis on ensuring the correct diagnosis, minimizing exposures to stimuli that worsen airway inflammation, alleviating modifiable comorbidities such as chronic rhinosinusitis and gastroesophageal reflux, and supporting regular medication adherence and effective technique for administering inhaled medications. A basic diagnostic laboratory work-up is recommended, to be modified and amplified according to individual patient needs.

Small airways dysfunction in asthma: evaluation and management to improve asthma control

The small airways have been neglected for many years, but interest in the topic has been rekindled with recent advances in measurement techniques to assess this region and also the ability to deliver therapeutics to the distal airways. Current levels of disease control in asthmatic patients remain poor and there are several contributory factors including; poor treatment compliance, heterogeneity of asthma phenotypes and associated comorbidities. However, the proposition that we may not be targeting all the inflammation that is present throughout the whole respiratory tree may also be an important factor. Indeed decades ago, pathologists and physiologists clearly identified the importance of small airways dysfunction in asthmatic patients. With improved inhaler technology to deliver drug to target the whole respiratory tree and more sensitive measures to assess the distal airways, we should certainly give greater consideration to treating the small airway region when seeing our asthmatic patients in clinic. The aim of this review is to address the relevance of small airways dysfunction in the daily clinical management of patients with asthma. In particular the role of small particle aerosols in the management of patients with asthma will be explored.

Assessing and treating small airways disease in asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are chronic inflammatory disorders of the respiratory tract that are characterized by airflow limitation. They are distinct conditions with different causes, structural changes, and immunopathology. The pathophysiology in asthma and COPD involves not only the proximal large airways, but also the distal small airways, and thus the small airways are an important therapeutic target in the treatment of both diseases. The assessment of diseased distal small airways is challenging. Extensive disease can be present in the small airways with little abnormality in conventional pulmonary function tests. Recent advances in imaging technologies have led to better spatial resolution to assess small airways morphology non-invasively. New physiological tests have been developed to detect disease and response to therapy in regional airways. Improving the efficiency of existing aerosolized therapy to direct drug to the appropriate lung regions may improve clinical efficacy. Approaches to target distal lung regions include developing new drug formulations with smaller aerosol particle size or using inhaler devices that emit aerosolized drug at slow inhalation flows. Large studies are needed to determine whether better distal lung deposition leads to improvements in small airways function that are translated into clinically significant patient outcomes.

Determination of the inflammatory component of airway diseases by induced sputum cell counts: use in clinical practice

OBJECTIVE

To evaluate the usefulness of determining the inflammatory component of airway diseases (inflammometry) by induced sputum cell counts, as well as its influence on treatment decisions in a tertiary facility for the treatment of respiratory diseases.

METHODS

We analyzed 151 sputum samples from 132 consecutive patients referred for clinical sputum induction by five pulmonologists between July of 2006 and February of 2007. A structured questionnaire related to the reasons for requesting the test and to the therapeutic decision making based on test results was completed by each attending physician upon receiving the test results. Induced sputum was obtained and processed according to a technique previously described.

RESULTS

The principal motives for ordering the test were inhaled corticosteroid dose titration in patients with moderate-to-severe asthma (in 54.3%), investigation of chronic cough (in 30.5%), and monitoring airway inflammation in patients with bronchiectasis (in 7.3%) or chronic obstructive pulmonary disease (in 6%). Of the 82 patients with asthma, 47 (57%) presented eosinophilic bronchitis (>3% eosinophils). Nonasthmatic eosinophilic bronchitis was diagnosed in 9 (19%) of the 46 patients with chronic cough. Neutrophilic bronchitis (>65% neutrophils) was found in 13 patients, of which 5 had asthma, 2 had chronic cough, and 6 had chronic obstructive pulmonary disease/bronchiectasis. Based on the induced sputum results, the corticosteroid dose was modified in 48 asthma patients (64.7%).

CONCLUSIONS

The systematic application of inflammometry using induced sputum cell counts can be beneficial for patients with airway diseases, particularly those with asthma or chronic cough.

Biomarkers to assess the utility of potential reduced exposure tobacco products

To date, we have no valid biomarkers that serve as proxies for tobacco-related disease to test potential reduced exposure products. This paper represents the deliberations of four workgroups that focused on four tobacco-related heath outcomes: Cancer, nonmalignant pulmonary disease, cardiovascular disease, and fetal toxicity. The goal of these workgroups was to identify biomarkers that offer some promise as measures of exposure or toxicity and ultimately may serve as indicators for future disease risk. Recommendations were based on the relationship of the biomarker to what is known about mechanisms of tobacco-related pathogenesis, the extent to which the biomarker differs among smokers and nonsmokers, and the sensitivity of the biomarker to changes in smoking status. Other promising biomarkers were discussed. No existing biomarkers have been demonstrated to be predictive of tobacco-related disease, which highlights the importance and urgency of conducting research in this area.

Biomarkers to assess the utility of potential reduced exposure tobacco products

To date, we have no valid biomarkers that serve as proxies for tobacco-related disease to test potential reduced exposure products. This paper represents the deliberations of four workgroups that focused on four tobacco-related heath outcomes: Cancer, nonmalignant pulmonary disease, cardiovascular disease, and fetal toxicity. The goal of these workgroups was to identify biomarkers that offer some promise as measures of exposure or toxicity and ultimately may serve as indicators for future disease risk. Recommendations were based on the relationship of the biomarker to what is known about mechanisms of tobacco-related pathogenesis, the extent to which the biomarker differs among smokers and nonsmokers, and the sensitivity of the biomarker to changes in smoking status. Other promising biomarkers were discussed. No existing biomarkers have been demonstrated to be predictive of tobacco-related disease, which highlights the importance and urgency of conducting research in this area.

Airway inflammation, basement membrane thickening and bronchial hyperresponsiveness in asthma

BACKGROUND

There are few data in asthma relating airway physiology, inflammation and remodelling and the relative effects of inhaled corticosteroid (ICS) treatment on these parameters. A study of the relationships between spirometric indices, airway inflammation, airway remodelling, and bronchial hyperreactivity (BHR) before and after treatment with high dose inhaled fluticasone propionate (FP 750 microg bd) was performed in a group of patients with relatively mild but symptomatic asthma.

METHODS

A double blind, randomised, placebo controlled, parallel group study of inhaled FP was performed in 35 asthmatic patients. Bronchoalveolar lavage (BAL) and airway biopsy studies were carried out at baseline and after 3 and 12 months of treatment. Twenty two normal healthy non-asthmatic subjects acted as controls.

RESULTS

BAL fluid eosinophils, mast cells, and epithelial cells were significantly higher in asthmatic patients than in controls at baseline (p<0.01). Subepithelial reticular basement membrane (rbm) thickness was variable, but overall was increased in asthmatic patients compared with controls (p<0.01). Multiple regression analysis explained 40% of the variability in BHR, 21% related to rbm thickness, 11% to BAL epithelial cells, and 8% to BAL eosinophils. The longitudinal data corroborated the cross sectional model. Forced expiratory volume in 1 second improved after 3 months of treatment with FP with no further improvement at 12 months. PD(20) improved throughout the study. BAL inflammatory cells decreased following 3 months of treatment with no further improvement at 12 months (p<0.05 v placebo). Rbm thickness decreased in the FP group, but only after 12 months of treatment (mean change -1.9, 95% CI -3 to -0.7 microm; p<0.01 v. baseline, p<0.05 v. placebo). A third of the improvement in BHR with FP was associated with early changes in inflammation, but the more progressive and larger improvement was associated with the later improvement in airway remodelling.

CONCLUSION

Physiology, airway inflammation and remodelling in asthma are interrelated and improve with ICS. Changes are not temporally concordant, with prolonged treatment necessary for maximal benefit in remodelling and PD(20). Determining the appropriate dose of inhaled steroids only by reference to symptoms and lung function, as specified in current international guidelines, and even against indices of inflammation may be over simplistic. The results of this study support the need for early and long term intervention with ICS, even in patients with relatively mild asthma.

The role of small airways in lung disease

The small airways constitute one of the least understood areas of the lungs. They play a role in many lung diseases, and small airway pathology results in significant morbidity New approaches to their evaluation may provide insights into this major area of lung disease. Asthma is well recognized as a disease of both large and small airways. Physiological and pathological evidence, from techniques such as post-mortem tissue histological analysis, induced sputum and transbronchial biopsies, has reinforced the concept of the involvement of the entire bronchial tree n the inflammatory process in asthma, In addition to describing the airway pathology in asthma, th s review focuses on the pathogenesis and role of small airway obstruction n other diseases, including chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), sarcoidosis and obliterative bronchiolitis (OB). COPD is characterized by the presence of airflow obstruction resulting from lesions in the small airways. In addition, features compatible with small airways disease are common in IPF, sarcoidosis and OB. Recent advances in pulmonary imaging, such as high-resolution computed tomography (HRCT) and magnetic resonance imaging (MRI) with hyperpolarized 3He, have allowed non-invasive reproducible measurements of structure-function relationships to be made for the small airways. These techniques have great potential for diagnosing changes in small airway function and for assessing responses to treatment. New insights into the contribution of small airways to a range of lung diseases may lead to the development of therapies targeted at this part of the bronchial anatomy.

Sputum induction: effect of nebulizer output and inhalation time on cell counts and fluid-phase measures

BACKGROUND

A knowledge of the factors that can affect induced sputum results is essential in order to standardize the procedure.

OBJECTIVE

We investigated the influence of nebulizer output on sputum cell counts and fluid phase measurements at increasing times of sputum induction.

METHODS

Eighteen adults with stable asthma inhaled an aerosol of 3% hypertonic saline to induce sputum after 7, 14 and 21 min on 2 days separated by 48 h. On one day, in random order, the ultrasonic nebulizer used had a relatively low output of 0.87 mL/min (particle size 5.58 microm mass median aerodynamic diameter, MMAD) and, on the other, a higher output of 1.90 mL/min (particle size 4.14 microm MMAD). The sputum was selected from each expectorate and examined blind to the induction procedures.

RESULTS

With both nebulizers, the 14- and 21-min samples were lower in weight, neutrophils, eosinophils, eosinophil cationic protein (ECP) and interleukin (IL)-8 and higher in macrophages. The higher output nebulizer induced sputum with higher cell viability and lower ECP and IL-8.

CONCLUSION

The results identify that the volume of hypertonic saline inhaled in sputum induction influences the fluid-phase measurements. The duration of induction does alter the cell counts and suggests that the later expectorated sputum samples originate from more peripheral airways. The results draw attention to the need to standardize the volume and time of nebulization to accurately interpret and compare results.

Markers of airway inflammation and airway hyperresponsiveness in patients with well-controlled asthma

In steroid-naive asthmatics, airway hyperresponsiveness correlates with noninvasive markers of airway inflammation. Whether this is also true in steroid-treated asthmatics, is unknown. In 31 stable asthmatics (mean age 45.4 yrs, range 22-69; 17 females) taking a median dose of 1,000 microg inhaled corticosteroids (ICS) per day (range 100-3,600 microg x day(-1)), airway responsiveness to the "direct" agent histamine and to the "indirect" agent mannitol, lung function (forced expiratory volume in one second (FEV1), forced vital capacity (FVC), peak expiratory flow (PEF)), exhaled nitric oxide (eNO), and number of inflammatory cells in induced sputum as a percentage of total cell count were measured. Of the 31 subjects, 16 were hyperresponsive to mannitol and 11 to histamine. The dose-response ratio (DRR: % fall in FEV1/cumulative dose) to both challenge tests was correlated (r=0.59, p=0.0004). However, DRR for histamine and DRR for mannitol were not related to basic lung function, eNO, per cent sputum eosinophils and ICS dose. In addition, NO was not related to basic lung function and per cent sputum eosinophils. In clinically well-controlled asthmatics taking inhaled corticosteroids, there is no relationship between markers of airway inflammation (such as exhaled nitric oxide and sputum eosinophils) and airway responsiveness to either direct (histamine) or indirect (mannitol) challenge. Airway hyperresponsiveness in clinically well-controlled asthmatics appears to be independent of eosinophilic airway inflammation.

Mild exacerbations and eosinophilic inflammation in patients with stable, well-controlled asthma after 1 year of follow-up

OBJECTIVES

To determine the time to exacerbation and probability of a mild exacerbation of asthma, and the impact of eosinophilic inflammation on these parameters in patients with stable, well-controlled asthma.

PATIENTS AND METHODS

A cohort of 31 patients with stable, well-controlled asthma receiving inhaled steroid treatment regularly were followed up for 1 year or until a mild exacerbation occurred. Mild exacerbation was defined as symptoms of asthma lasting > 48 h with a fall in peak expiratory flow > 20%. FEV(1), provocative concentration of methacholine causing a 20% fall in FEV(1), eosinophil count, and eosinophilic cationic protein (ECP) levels in blood and in sputum were measured at the first visit and every 2 months.

RESULTS

At baseline, the mean (SD) eosinophil count was 0.39 x 10(9)/L (0.21 x 10(9)/L) in blood and 13% (14%) in sputum; ECP was 30 microg/L (28 microg/L) in blood and 75 microg/L (85 microg/L) in sputum. Thirteen subjects experienced a mild exacerbation during the 1-year follow-up period. The mean time to mild exacerbation was 293 days (95% confidence interval [CI], 248 to 337 days), and the cumulative probability of not experiencing a mild exacerbation in 1 year was 49% (95% CI, 39 to 59%). An increased risk of mild exacerbation was associated with blood eosinophil count > 0.4 x 10(9)/L (relative risk 4.5; 95% CI of relative risk, 1.8 to 38.0), blood ECP > 20 microg/L (relative risk, 2.1; 95% CI of relative risk, 1.0 to 9.2), and sputum ECP > 40 microg/L (relative risk, 2.5; 95% CI of relative risk, 1.2 to 11.2), but was unassociated with other variables.

CONCLUSIONS

Patient with stable, well-controlled asthma are at risk of mild exacerbation during 1 year of follow-up despite regular inhaled steroid treatment. Eosinophilic inflammation expressed as eosinophil count and ECP is associated with higher risk of mild exacerbation.

Induced sputum cell counts in healthy adults

Induced sputum cell counts provide a relatively noninvasive method to evaluate the presence, type, and degree of inflammation in the airways of the lungs. Their interpretation requires a knowledge of normal values from a healthy population. The objective was to examine the total and differential cell counts in induced sputum from a sample of healthy adults. A total of 118 healthy nonsmoking adults were studied. None had asthma or airflow obstruction (negative history, FEV(1) >/= 80% predicted, ratio of FEV(1) to vital capacity [FEV(1)/VC] >/= 80%, methacholine PC(20) >/= 16 mg/ml). Forty-six were atopic. Sputum induction produced an adequate sample in 96 subjects [53 males, mean age (range) 36 (18 to 60) yr]. The expectorate was processed within 2 h; sputum was selected, treated with dithiothreitol, filtered, and examined in a hemocytometer for total cell count and viability and on Wright-stained cytospins for a differential cell count. The mean, median (90th percentile) total cell count was 4.1, 2.4 (9.7) x 10(6) cells/g and cell viability was 69.6, 72.0 (89.7)%. The proportions of eosinophils were 0.4, 0.0 (1.1)%, neutrophils 37.5, 36.7 (64.0)%, macrophages 58.8, 60.8 (86.1)%, lymphocytes 1.0, 0.5 (2.6)%, metachromatic cells 0.0, 0.0 (0.04)%, and bronchial epithelial cells 1.6, 0.3 (4.4)%, respectively. Female gender and atopy were associated with a significant elevation of eosinophils; mean difference between male/female was 0.3% (p = 0.043) and between atopic/nonatopic 0.4% (p = 0.024). This study has identified reference values for total and differential cell counts in induced sputum of healthy adults.

Asthma and asthma-like disorders

Bronchial asthma is defined as a chronic inflammatory disease resulting in a reversible and variable bronchial obstruction. For the clinical diagnosis of the disease there are some key indicators but as there is no 'gold standard' a correct diagnosis will sometimes not be obtained. Examples are patients in a symptom-free stage, current medication interfering with the methods used, patients with asthma-like symptoms reporting lack of effect of bronchodilators and patients who are unable to perform a forced expiration in an airway function test. The prevalence of asthma is reported to be 5-10%. The prevalence of asthma-like symptoms may be double this. The term 'asthma-like' has been used to an increasing extent during the last few years, which may indicate an increasing awareness of the fact that asthma-like symptoms are not always classical asthma. In this overview some disorders with asthma-like symptoms, especially in adults, are presented. The spectrum of differential diagnoses in a clinic may depend on which doctor/specialist the patient is consulting. In an asthma and allergy clinic it has been found that the most common differential diagnoses are chronic obstructive pulmonary disease (COPD), nonasthmatic cough and sensory hyper-reactivity (SHR), a disorder which is sometimes mixed up with asthma due to similar symptoms (heavy breathing, cough, increased secretion, difficulty in getting air etc.) and similar trigger factors (smoke, strong scents, exercise, cold air etc.). Recently it has been suggested that a capsaicin inhalation test may be an objective test for identifying patients with SHR. In asthma effective treatment is available today but in asthma-like disorders, such as SHR, no effective therapy is available, underlining the need of further research for understanding the pathophysiological mechanisms.