Changes in sputum eicosanoids and inflammatory markers after inhalation challenges with occupational agents

Mechanistic and Therapeutic Approaches to Occupational Exposure-Associated Allergic and Non-Allergic Asthmatic Disease

PURPOSE OF REVIEW

Occupational lung disease, including asthma, is a significant cause of disability worldwide. The dose, exposure frequency, and nature of the causal agent influence the inflammatory pathomechanisms that inform asthma disease phenotype and progression. While surveillance, systems engineering, and exposure mitigation strategies are essential preventative considerations, no targeted medical therapies are currently available to ameliorate lung injury post-exposure and prevent chronic airway disease development.

RECENT FINDINGS

This article reviews contemporary understanding of allergic and non-allergic occupational asthma mechanisms. In addition, we discuss the available therapeutic options, patient-specific susceptibility and prevention measures, and recent scientific advances in post-exposure treatment conception. The course of occupational lung disease that follows exposure is informed by individual predisposition, immunobiologic response, agent identity, overall environmental risk, and preventative workplace practices. When protective strategies fail, knowledge of underlying disease mechanisms is necessary to inform targeted therapy development to lessen occupational asthma disease severity and occurrence.

Occupational asthma: clinical phenotypes, biomarkers, and management

PURPOSE OF REVIEW

This review focuses on new findings in the clinical and inflammatory aspects that can help to better identify the different phenotypes of work-related asthma and the development of specific biomarkers useful in diagnosis and follow-up.

RECENT FINDINGS

Studies on phenotyping of occupational asthma, a subtype of work-related asthma, have mainly compared the clinical, physiological, and inflammatory patterns associated with the type of agent causing occupational asthma, namely, high-molecular-weight and low-molecular-weight agents. Most of this research has found that patients with occupational asthma due to high-molecular-weight agents have an associated presence of rhinitis, conjunctivitis, atopy, and a pattern of early asthmatic reactions during specific inhalation challenge. The inflammatory profile (blood eosinophils, sputum cell count, or exhaled nitric oxide) may be similar when occupational asthma is caused by either type of agent. In some studies, severity of asthma and exacerbations have been associated with exposure to low-molecular-weight agents. The most reliable biomarkers in diagnosis and follow-up are eosinophilia in induced sputum and exhaled nitric oxide.

SUMMARY

There are several phenotypes, characterized by its pathogenesis and inflammatory profile. Avoidance of the causative agents does not warrant complete recovery of occupational asthma. Treatment with biologic agents may be considered in severe occupational asthma.

Preschool wheeze, genes and treatment

Preschool wheeze is a common but poorly understood cause of respiratory morbidity that is both distinct from and overlaps with infantile bronchiolitis and school age asthma. Attempts at classification by epidemiology, pathophysiology, therapeutic response and clinical phenotype are imperfect and yet fundamental to both treatment choice and research design. The four main therapeutic classes for preschool wheeze, namely beta₂ agonists, anticholinergics, corticosteroids and leukotriene modifiers are employed with variable and often scanty evidence base, with evidence for a genetic influence on response variations. The article will discuss the pharmacogenetics of the various options, summarise current treatment recommendations, and explore future research directions.

New developments in work-related asthma

INTRODUCTION

Work-related asthma includes two subtypes: occupational asthma or asthma caused by specific agents (sensitizers or irritants) in the workplace, and work-exacerbated asthma or pre-existing asthma worsened by workplace exposures. Areas covered: This review provides an update on the definitions and the clinical features of the different work-related asthma subtypes as well as new insights into their etiology and the pathophysiological mechanisms involved. The diagnosis of work-related asthma should be made on objective basis using a constellation of clinical, physiologic and allergologic tests. Specific inhalation challenge with the suspected occupational agent(s) remains as the reference standard for diagnosis. A literature search was performed using the following terms: work-related asthma, occupational asthma, work-exacerbated asthma, irritant-induced asthma and etiological agents. Expert commentary: Studies focusing on the biological effects and mechanisms of environmental exposures in the development of sensitizer-induced or irritant-induced asthma in various workplace settings are of greatest interest. An integrative approach that combines clinical parameters with component-resolved diagnosis as well as inflammatory biomarkers appears to be very promising. Occupational allergy provides a good opportunity to understand the complex relationships between exposure to allergens in the workplace, interaction with genes and the co-exposures to other factors in the working environment.

Fractional exhaled nitric oxide in the interpretation of specific inhalational challenge tests for occupational asthma

PURPOSE

Fractional exhaled nitric oxide (FENO) measurements are recommended for the assessment of eosinophilic airway inflammation in asthma. Clinically relevant increases in FENO have been reported 24 h after positive specific inhalational challenge (SIC) tests in occupational asthma. We aimed to determine whether positive SICs could be discriminated from control tests, on the basis of change in FENO.

METHODS

We reviewed all positive SICs to a variety of agents performed at our institution 2008-2012 and gathered data on age, sex, asthmatic response (immediate/dual/late), smoking status, inhaled corticosteroid usage, and FENO pre- and 24-h postcontrol and positive SIC from each worker. Changes in FENO after positive SICs were compared with control SICs from each worker, by using paired Student's t tests.

RESULTS

In 16 workers, negative control challenges were associated with mean changes in FENO of 9 % (95 % CI -1.14 to 19.01) or 1.1 ppb (95 % CI -3.59 to 5.84); 2 of 16 (13 %) workers tested showed increases in FENO that were clinically relevant based on recent guidelines. Subsequent positive SICs were associated with mean changes in FENO of 7 % (95 % CI −15.73 to 29.6) or 2.1 ppb (95 % CI -6.07 to 10.19), which were not significantly different to controls; only 2 of 16 (13 %) workers had FENO changes that were clinically relevant.

CONCLUSIONS

FENO changes above the upper confidence limits of ≥20 % or ≥6 ppb may be considered to be outside the range of normality. However, the majority of workers who had clearly positive SICs to common low molecular weight agents also had no statistically or clinically relevant increase in FENO. Therefore, change in FENO does not predict a positive SIC in this group.

Sputum inflammatory profile before and after specific inhalation challenge in individuals with suspected occupational asthma

BACKGROUND

The aim of this study was to establish the sputum inflammatory profile and changes in levels of leukotriene B₄ (LTB₄) and a panel of Th1/Th2 cytokines in subjects with suspected occupational asthma (OA) following specific inhalation challenge (SIC) to high-molecular-weight (HMW) and low-molecular-weight (LMW) agents.

MATERIAL AND METHODS

Fifty-one consecutive subjects undergoing SIC for suspected OA were enrolled. Sputum induction was performed the day before and 24 h after exposure to the offending agent. Total and differential cell counts were assessed. LTB₄ and a 10 Th1/Th2 cytokines were measured in sputum supernatant.

RESULTS

Thirty-four patients tested positive to SIC and were diagnosed with OA (in 10 due to HMW agents and in 24 to LMW agents). SIC was negative in 17 subjects. As compared to baseline an increase was found in the percentage of sputum eosinophils and neutrophils, and in IL-10 concentration after SIC (p = 0.0078, p = 0.0195, and p = 0.046, respectively), and a decrease was seen in LTB₄ level (p = 0.0078) in patients with OA due to HMW agents. An increase in the percentage of sputum neutrophils after SIC (p = 0.0040) was observed in subjects without OA exposed to LMW agents. IL-8 levels after SIC were higher in patients without OA compared with patients with OA (p = 0.0146).

CONCLUSION

When conducting airway inflammation studies in OA, patients should be divided according to the causal agent (HMW or LMW). In OA patients exposed to HMW agents, an increase in the number of neutrophils can be found in parallel to the increase of eosinophils, although this does not contradict an IgE-mediated mechanism. Exposure to LMW agents can result in increased neutrophilic inflammation in patients with airway diseases unrelated to OA. There is variability in the responses observed in patients with OA exposed to LMW agents.

Induced sputum, exhaled NO, and breath condensate in occupational medicine

OBJECTIVE

Studies of fractional exhaled NO (FeNO) or induced sputum are now well standardized and the exponential increase in publications about exhaled breath condensate reflects growing interest in a noninvasive diagnosis of pulmonary diseases in occupational medicine.

METHODS

This review describes current techniques (FeNO, induced sputum, and exhaled breath condensate) for the study of inflammation and oxidative stress biomarkers.

RESULTS

These biomarkers are FeNO, cytokines, H2O2, 8-isoprostane, malondialdehyde, and nitrogen oxides. These techniques also include the study of markers of the toxic burden in the lungs (heavy metals and mineral compounds) that are important in occupational health exposure assessment.

CONCLUSIONS

In occupational medicine, the study of both volatile and nonvolatile respiratory biomarkers can be useful in medical surveillance of exposed workers, the early identification of respiratory diseases, or the monitoring of their development.

Distinctive bronchial inflammation status in athletes: basophils, a new player

The aim of the study was to establish bronchial inflammation status and to measure eicosanoids in sputum obtained from active elite athletes. A total of 68 subjects were enrolled. Twelve were non-athletes and non-asthmatic (NAtNAs), 21 non-athlete asthmatics (NAtAs), 11 athlete non-asthmatics (AtNAs), and 24 athletes with asthma (AtAs) with positive indirect or direct bronchial challenges. Induced sputum was used to measure cells and eicosanoids. Sputum differential cell counts in all the subject groups revealed eosinophilia with the exception of NAtNAs control subjects. Athletes with and without diagnosed asthma showed a significant increase in bronchial epithelial cells and lymphocytes present in their sputum. Also, flow cytometry revealed that a significantly higher number of basophils were present in sputum from athletes (without and with asthma) when compared with non-athletes (without and with asthma). Asthmatic athletes and non-athletes showed a higher increase in LTC(4) levels and PGE(2) metabolites in sputum when compared with healthy controls. The present study identifies basophils as a new player present in athletes bronchial inflammation defining athlete status and not necessarily associated with exercise-induced bronchoconstriction.

EAACI consensus statement for investigation of work-related asthma in non-specialized centres

Work-related asthma (WRA) is a relevant problem in several countries, is cause of disability and socioeconomic consequences for both the patient and the society and is probably still underdiagnosed. A correct diagnosis is extremely important to reduce or limit the consequences of the disease. This consensus document was prepared by a EAACI Task Force consisting of an expert panel of allergologists, pneumologists and occupational physicians from different European countries. This document is not intended to address in detail the full diagnostic work-up of WRA, nor to be a formal evidence-based guideline. It is written to provide an operative protocol to allergologists and physicians dealing with asthma useful for identifying the subjects suspected of having WRA to address them to in-depth investigations in a specialized centre. No evidence-based system could be used because of the low grade of evidence of published studies in this area, and instead, 'key messages' or 'suggestions' are provided based on consensus of the expert panel members.

Changes in exhaled nitric oxide levels after bronchial allergen challenge

BACKGROUND

Fractional exhaled nitric oxide (FeNO) is a marker of inflammation of the airways accompanying changes in the clinical condition of asthma. Allergen exposure has been associated with a delayed elevation of FeNO. The aim of this study was to assess airway inflammation with FeNO measurements during bronchial allergen challenge (BAC), and to determine the diagnostic performance of FeNO changes.

METHODS

Thirty-four patients with asthma and sensitization to inhalant allergens were studied. BAC with common or high-molecular-weight occupational aeroallergens was performed. FeNO was measured before and 24 h after BAC. Receiver operating characteristics curve was built to assess the sensitivity and specificity of increase in FeNO levels associated with BAC outcome.

RESULTS

In 21 patients (61.76%) a positive asthmatic reaction (responders) was observed. A significant increase in postchallenge FeNO was observed in this group of patients compared to the group of nonresponders. A median increase (FeNO postchallenge-FeNO prechallenge) of 14.0 ppb was observed in the group of responders, whereas a -1.0 ppb change was attained in the nonresponder group (P < 0.001). The cutoff point providing maximal sensitivity and specificity for %ΔFeNO after BAC was 12%. This change in FeNO levels has a sensitivity of 0.81 and a specificity of 0.92 for predicting a positive outcome in the BAC.

CONCLUSION

FeNO measurements can be used as a surrogate of airway inflammation accompanying the asthmatic reaction induced by BAC. FeNO measurements may be a useful and reliable tool in the monitoring and interpreting specific bronchial challenge test with allergens.

New causes of occupational asthma

PURPOSE OF REVIEW

This review focuses on new causative agents of occupational asthma published in 2009 and 2010. The recent developments in the diagnostic tools employed in occupational asthma caused by new agents are summarized.

RECENT FINDINGS

Work exposures are a significant contributor to the burden of asthma and, therefore, there is great scientific interest in work-related asthma. Although the majority of cases probably represent work-aggravated asthma, in a relevant proportion of cases asthma is actually caused by one or more agents present in the workplace. The list of causative agents of immunologically mediated occupational asthma is continuously growing, and new agents and professions are described each year. New insights gained in occupational asthma include routine evaluation of airway inflammation and identification of allergenic triggers using molecular diagnosis.

SUMMARY

A variety of novel high and low-molecular-weight agents have been shown to induce occupational asthma. Apart from the identification of the allergenic sources implicated, molecular diagnosis and detailed characterization of the culprit allergens contributes to increase our knowledge into the pathogenic mechanisms of this disorder. Assessment of airway inflammation helps to confirm the diagnosis and to better understand the physiopathology of the different types of occupational asthma.

Airway response to chlorine inhalation (bleach) among cleaning workers with and without bronchial hyperresponsiveness

BACKGROUND

Symptoms of obstructive lung disease in domestic cleaning staff have been related to the use of bleach and other irritant cleaning products.

MATERIAL AND METHODS

Included in the study were thirteen cleaning employees with work-related asthma-like symptoms, three asthmatic controls and three atopic subjects without bronchial hyperresponsiveness (BHR) who had no exposure to cleaning products. The study protocol consisted of a methacholine test, sputum induction and fraction of exhaled nitric oxide measurement (FENO) both at baseline and 24 hr after a 1-hr inhalation challenge with either placebo or bleach at a concentration of 0.4 ppm of chlorine.

RESULTS

The inhalation of the placebo caused no bronchial reactions. Mean maximum fall in FEV(1) during challenge testing with bleach was significantly higher than the values obtained during the placebo challenge. Inhalation challenge with bleach elicited two isolated late asthmatic reactions and one dual asthmatic reaction. Of all the patients who underwent challenge testing with bleach, only one had a ≥2-fold decrease in methacholine PC(20) 24 hr after the challenge. No significant correlation was found between maximum fall in FEV(1) and PC(20) methacholine. Following challenge testing with bleach, no clinically significant changes in sputum cell counts or FENO were detected.

CONCLUSIONS

These results suggest that bleach inhalation at a concentration of 0.4 ppm-a concentration below 8-hr permissible occupational exposure level-brings about a substantial decrease in FEV1 in subjects with and without BHR. Some subjects have a positive challenge response to bleach inhalation.

PGE(2) decreases muscle cell proliferation in patients with non-asthmatic eosinophilic bronchitis

Non-asthmatic eosinophilic bronchitis (NAEB) is characterized by chronic cough and sputum eosinophilia without bronchial hyperresponsiveness. The aim of the present study is to determine whether increased levels of PGE(2) from NAEB sputum supernatants play a protective role in airway inflammation and muscular hyperplasia. Twenty-one patients with NAEB, 15 asthmatic patients, and 12 healthy subjects were studied. An up-regulated PGE(2) enzymatic pathway was observed in bronchial biopsies from patients with NAEB as compared with samples from asthmatic patients. Also, EP2 and EP4 receptor expression was increased in these samples. BSMC proliferation was inhibited to a greater extent in NAEB sputum supernatants than in those taken from asthmatic subjects and healthy controls. This inhibition was mostly due to PGE(2) levels, a fact which was confirmed by employing synthetic EP2 and EP4 agonist and antagonist receptors.These findings suggest that PGE(2) inhibits BSMC proliferation entailing a reduction of smooth muscle hyperplasia and thus protecting against the onset of airflow obstruction.

Oxidative stress and airway inflammation after allergen challenge evaluated by exhaled breath condensate analysis

BACKGROUND

Allergen exposure may increase airway oxidative stress, which causes lipid membrane peroxidation and an increased formation of 8-isoprostane.

OBJECTIVE

The aim of the study was to investigate oxidative stress induced by allergen challenge in mild asthmatics, by measuring 8-isoprostane in exhaled breath condensate (EBC), and to examine their relationship with mediators derived from arachidonic acid. Methods 8-isoprostane, cysteinyl leukotrienes (cys-LTs) and prostaglandin E2 (PGE(2) ) concentrations in EBC were measured at baseline and after allergen challenge in 12 patients with mild allergic asthma sensitized to cat allergen.

RESULTS

At 24 h after allergen challenge, compared with baseline values, EBC 8-isoprostane increased [48.64 pg/mL (44.14-53.61) vs. 21.56 pg/mL (19.92, 23.35), P<0.001], cys-LTs increased [27.37 pg/mL (24.09-31.10) vs. 13.28 pg/mL (11.32, 15.57), P<0.001] and PGE(2) decreased [18.69 pg/mL (12.26, 28.50) vs. 39.95 pg/mL (34.37, 46.43), P<0.001]. The trend of increasing 8-isoprostane after allergen challenge was significantly correlated with the trend of increasing cys-LTs (R(2) =0.85, P<0.001) whereas the trend of decreasing PGE(2) after allergen challenge was significantly correlated with the trend of increasing cys-LTs (R(2) =0.52, P=0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

The increase in EBC 8-isoprostane observed after allergen challenge indicates that allergen exposure increases airway oxidative stress in allergic asthma. The strict correlation between cys-LTs and 8-isoprostane underlines the relationship between allergic inflammation and oxidative stress. A shift of arachidonic acid metabolism towards lipoxygenase pathway is induced by the allergen challenge. Airway oxidative stress occurs after allergen challenge even in patients with mild intermittent allergic asthma.

Occupational asthma caused by triglycidyl isocyanurate

BACKGROUND

Several cases of allergic contact dermatitis, two cases of occupational asthma from over one decade ago and one case of hypersensitivity pneumonitis have been documented in painters who use polyester powder paint containing triglycidyl isocyanurate (TGIC).

METHODS

We report a 28-year-old female who, 4 months after beginning work in a powder-coating factory, developed asthma-like symptoms. In her workplace, aluminium frames were treated with an electrostatic powder paint containing 2.5-10% TGIC.

RESULTS

Serial peak-flow measurements performed during both working and non-working periods demonstrated peak-flow variability of up to 46% on work days. Bronchial methacholine test results also varied between times at work and away from work. PC(20) methacholine was 0.32 mg/ml and fraction of exhaled nitric oxide (FENO) was 18 ppb. A controlled exposure challenge was performed with a placebo yielding no changes in FEV(1) over a 24-hour period. On visit 2, the patient was placed in the chamber and exposed to TGIC (4% in lactose) at a mean concentration of 3.61 mg/m(3) for a total of 15 min. A 20% fall in FEV(1) from baseline was elicited at 10 min, together with cough and wheezing. No late response was demonstrated. Twenty-four hours after the challenge, neither methacholine PC(20) nor FENO levels varied from baseline values. No IgE was detected by ELISA testing and no IgE-binding bands were found by immunoblot analysis of patient and control serum.

CONCLUSIONS

The aforementioned results demonstrate that TGIC inhalation induced immunologic occupational asthma, although no IgE mechanism was evidenced.

Noninvasive methods for assessment of airway inflammation in occupational settings

The present document is a consensus statement reached by a panel of experts on noninvasive methods for assessment of airway inflammation in the investigation of occupational respiratory diseases, such as occupational rhinitis, occupational asthma, and nonasthmatic eosinophilic bronchitis. Both the upper and the lower airway inflammation have been reviewed and appraised reinforcing the concept of 'united airway disease' in the occupational settings. The most widely used noninvasive methods to assess bronchial inflammation are covered: induced sputum, fractional exhaled nitric oxide (FeNO) concentration, and exhaled breath condensate. Nasal inflammation may be assessed by noninvasive approaches such as nasal cytology and nasal lavage, which provide information on different aspects of inflammatory processes (cellular vs mediators). Key messages and suggestions on the use of noninvasive methods for assessment of airway inflammation in the investigation and diagnosis of occupational airway diseases are issued.