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(Chest. 2006;130:1718-1722.)
© 2006 American College of Chest Physicians

Increased Leukotriene E4 in the Exhaled Breath Condensate of Children With Mild Asthma*

Atsushi Shibata, MD; Toshio Katsunuma, MD, PhD; Morimitsu Tomikawa, MD; Aiko Tan, MD; Keisuke Yuki, PhD; Kenichi Akashi, MD and Yoshikatsu Eto, MD, PhD

* From the Department of Pediatrics, The Jikei University School of Medicine, Tokyo, Japan.

Correspondence to: Toshio Katsunuma, MD, PhD, Department of Pediatrics, The Jikei University School of Medicine, 3-25-8, Nishi-Shinbashi, Minato-ku, Tokyo, 105-8461, Japan; e-mail: tkatsunuma{at}jikei.ac.jp

Abstract

Background: Chronic airway inflammation is a feature of asthma. Increased levels of cysteinyl leukotrienes (cys-LTs; leukotriene [LT]C4, LTD4, LTE4) have been shown in the exhaled breath condensate (EBC) of children with moderate-to-severe asthma. The aim of this study was to examine the relationship between EBC cys-LTs (LTE4) levels and bronchial hyperreactivity in children with mild asthma in order to evaluate the clinical utility of measuring EBC cys-LTs levels.

Methods: We measured LTE4 levels in the EBC of children aged 8 to 18 years, including healthy nonasthmatic children (n = 6) and children with mild asthma (n = 37). Patients with mild asthma were classified into the following three groups: group 1, participants who had been asymptomatic (no wheezing/symptoms of asthma) for > 6 months prior to examination (n = 12); group 2, participants who were asymptomatic but had had wheezing/symptoms of asthma within 6 months before examination (n = 18); and group 3, patients with current wheeze and/or mild symptoms of asthma exacerbation at the time of examination.

Results: Exhaled LTE4 levels were increased in all children with mild asthma compared with nonasthmatic control subjects (5.69 ± 9.62 pg/20 min vs 0.74 ± 0.79 pg/20 min, p < 0.05) [mean ± SD]. In particular, the EBC LTE4 levels in group 2 (4.99 ± 6.70 pg/20 min) and group 3 (14.66 ± 17.11 pg/20 min) were increased compared with control subjects and group 1 (1.50 ± 1.69 pg/20 min). The EBC LTE4 levels negatively correlated with the provocative concentration of methacholine causing a 15% fall in FEV1 (r = – 0.454, p = 0.012).

Conclusion: EBC cys-LTs may be useful as a noninvasive marker assessing airway inflammation and hyperreactivity in children with asthma.

Key Words: childhood asthma • exhaled breath condensate • leukotriene E4 • mild asthma

Asthma is characterized by chronic airway inflammation that is evident even in patients with mild disease.1 Several studies23456 describing biopsy patterns of inflammation in children with asthma have been published in the last few years. The safety of the endobronchial biopsy procedure has also been documented.7 In addition, the measurement of levels of exhaled nitric oxide (eNO), reflecting the activity of airway eosinophil, mast cells, and epithelial cells, has been found to be easy, noninvasive, and useful in asthmatic patients.8910

Performing bronchoscopy-guided biopsy, however, is still likely to be difficult in children, at least as a common clinical diagnostic tool. Moreover, elevated eNO levels are not specific for asthma, given that increased eNO is found in other inflammatory respiratory disorders, such as sinus disease and viral upper respiratory tract infection.1112

Increased levels of cysteinyl leukotrienes (cys-LTs) have been detected in the exhaled breath condensate (EBC) of children with moderate-to-severe persistent asthma.1314 The measurement of cys-LTs in the EBC may be useful as a noninvasive way to assess airway inflammation.

Bronchial hyperresponsiveness to methacholine, histamine, or exercise is a key feature of asthma, and may be an indicator of asthma severity. Bronchial hyperreactivity relates closely to asthma severity of asthma and frequency of symptoms, as well as to need for treatment.15

The aim of the present study was to examine the relationship between leukotriene (LT) E4 levels and bronchial hyperreactivity in mild asthma in children. Such a correlation would allow us to evaluate the clinical utility of measuring EBC cys-LTs levels as a marker of airway inflammation in childhood asthma. Finally, we hope to apply the results to the diagnosis of asthma in infants and children < 6 years old, in whom the correct diagnosis of asthma is not easy.

Materials and Methods

Patients
Children (age range, 8 to 18 years) with asthma were recruited from the pediatric clinic of the Jikei University Hospital, Tokyo, Japan. We measured EBC and urinary LTE4 levels of all participants, including healthy nonasthmatic children (n = 6) and children with mild asthma (n = 37). Eosinophil counts and serum IgE were determined from the blood samples collected from the asthmatic children.

Patients with mild asthma were classified into three groups: group 1, subjects who had been asymptomatic (no wheezing/symptoms of asthma) for > 6 months prior to examination (n = 12); group 2, subjects who were asymptomatic but had had wheezing/symptoms of asthma within 6 months before examination (n = 18); and group 3, subjects with current wheeze and/or mild symptoms of asthma exacerbation at the time of examination (n = 7). EBC collection could be performed in group 3 members because their dyspnea was not severe. However, the methacholine provocation test was not performed to prevent inducing serious bronchoconstriction.

Patient characteristics are summarized in Table 1 . There was no significant difference in age between the groups. The number of subjects treated with fluticasone propionate is also summarized in Table 1. No child had been treated with a dose > 200 µg/d (mean daily dose in group 1, 120.8 µg; group 2, 140.6 µg; group 3: 158.3 µg). No patient was taking aspirin before or during EBC collection.


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  		Table 1. Patient Characteristics*

 
The diagnosis of bronchial asthma was based on the criteria of the American Thoracic Society,16 and asthma severity was classified according to the Global Initiative for Asthma guidelines.17 When severity was based on clinical features present and the step of the daily medication with fluticasone (≤ 200 µg/d), all the subjects were considered to have mild intermittent or persistent asthma.

Healthy nonasthmatic control children were recruited from among the children of one of the authors (T.K.) and his friends. It was confirmed by the parent(s), using a questionnaire regarding medical history, that the children in the control group had no history wheezing episode or of allergic disease. The protocol was approved by the Ethics Committee of the Jikei University, and informed consent was obtained from all parents and children recruited into the study.

Study Design
Baseline spirometry followed by collection of EBC and bronchial responsiveness to methacholine were measured. All medications were withheld for at least 12 h, and montelukast and salmeterol were withheld for 36 h before testing.

Measurements of Provocative Concentration of Methacholine Causing a 15% Fall in FEV1
Spirometry (Autospiro AS500; Minato; Osaka, Japan) was performed using standard techniques. Aerosol was delivered using a nebulizer (model 646; Devilbis; Somerset, PA). Subjects inhaled normal saline solution at first as a control. Then increasing doses of methacholine, starting from 0.032 mg/mL and then progressively doubling the concentration to reach 16 mg/mL, were administered. The provocative concentration of methacholine causing a 15% fall in FEV1 (PC15) was calculated.

EBC
EBC was collected by using a handcrafted condenser constructed as per a report by Scheideler et al.18 The validity of measuring LT levels in EBC using our handcrafted condenser was confirmed by the Bland-Altman plot in comparison with Ecoscreen (Jaeger; Hoechberg, Germany).19 Amylase in the EBC was measured by the 2-chloro-4-nitrophenyl maltotrioside method (Kanto Chemical; Tokyo, Japan), with a lower limit of detection of 1.4 IU/L. Amylase was not detected in the EBC samples.

Subjects were asked to breathe through a mouthpiece at a normal frequency and tidal volume for a period of 20 min with a nose clip. Condensate of least 1 mL in volume was collected and immediately stored at –80°C. The mean collected volume of EBC was 4.5 mL.

LT Measurement
The samples were freeze-dried with a freeze-drier (EYELA FDU-2200; Tokyo Rika Kikai; Tokyo, Japan). After freeze-drying, the samples were resolved with 100 µL of water, and LTE4 concentrations were measured with a specific enzyme immunoassay (Cayman Chemical; Ann Arbor, MI). We initially concentrated the EBC samples by freeze-drying in order to improve the sensitivity for detection of LTE4 concentrations.

The lower limit of detection was 30 pg/mL. LTE4 values in EBC were expressed as the total amount (in picograms) expired in 20 min of breath.20

Statistical Analysis
Statistical analysis was performed using the statistical software (SAS version 8.2; SAS Institute; Cary, NC). A Student t test was used to confirm the difference between the control and mild asthma groups for the primary end point of this study. After confirmation of the primary end point, a Tukey multiple comparison tests was used to compare the mean values between control and each asthma groups. Data were expressed as mean ± SD. The correlation between the LTE4 levels and the PC15 was determined by nonparametric Spearman correlation analysis. Statistical significance was defined at p < 0.05.

Results

There were no significant differences among the groups in serum IgE levels or peripheral blood eosinophil counts (Table 1). All the subjects in groups 1 to 3 were atopic, as confirmed by positive levels of serum IgE to at least one of the following antigens: house dust mite, Japanese cedar pollen, or cat dander.

EBC LTE4 levels, however, were increased in all patients with mild asthma (5.69 ± 9.62 pg/20 min; range, 0.41 to 49.4 pg/20 min) vs nonasthmatic control subjects (0.74 ± 0.79 pg/20 min; range, 0.31 to 2.2 pg/20 min; p < 0.05) [Fig 1 ]. In particular, EBC LTE4 levels in group 2 (4.99 ± 6.70 pg/20 min; range, 0.49 to 28.7 pg/20 min) and in group 3 (14.66 ± 17.11 pg/20 min; range, 0.41 to 49.4 pg/20 min) were increased compared with control subjects and with group 1 (1.50 ± 1.69 pg/20 min; range, 0.17 to 6.4 pg/20 min). There were no significant differences in urinary LTE4 levels among the groups (control subjects, 2,610 ± 2,326 pg/mg creatinine; group 1, 1,523 ± 2,140 pg/mg creatinine; group 2, 982 ± 1,628 pg/mg creatinine; group 3, 1,679 ± 1,105 pg/mg creatinine) [Fig 2 ].


Figure 1
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  		Figure 1. Exhaled LTE4 levels in children with mild asthma. Exhaled LTE4 levels were increased in all patients with mild asthma compared with nonasthmatic control (cont) subjects. EBC LTE4 levels in group 2 patients (children who were asymptomatic but had had wheezing/symptoms of asthma within 6 months before examination) and group 3 (children with current wheeze and mild symptoms of asthma at the time of examination) were increased compared with control subjects and with group 1 patients (children who had been asymptomatic, with no wheezing/symptoms of asthma, for > 6 months prior to examination). *p < 0.05; {dagger}p < 0.05 (vs group 1 patients).

 

Figure 2
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  		Figure 2. Urinary LTE4 levels. There were no significant differences in urinary (U) LTE4 levels among the groups. Cr = creatinine. See Figure 1 for expansion of abbreviation.

 
EBC LTE4 levels were negatively correlated with PC15 (r = – 0.454, p = 0.012) [Fig 3 ]. Among group 1 members, EBC LTE4 levels were significantly lower (p < 0.05) and PC15 levels were significantly higher (p < 0.05) than in group 2 members.


Figure 3
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  		Figure 3. EBC LTE4 levels were negatively correlated with methacholine (r = – 0.454, p = 0.012).

 
Discussion

We found a significant increase in EBC LTE4 concentrations in children with mild asthma. In group 2 (those who were asymptomatic but had had wheezing/symptoms of asthma within 6 months prior to examination) and in group 3 (children with current wheeze and/or mild symptoms of asthma exacerbation at the time of examination), EBC LTE4 levels were significantly increased compared with control subjects or group 1 (children who had been asymptomatic for > 6 months prior to the examination), suggesting that EBC LTE4 levels may reflect a clinical instability of asthmatic symptoms based on the latent activity of airway inflammation.

Csoma et al21 found that the concentrations of EBC cys-LTs of asymptomatic children with mild intermittent asthma were not significantly elevated compared to normal subjects, even though EBC cys-LTs of patients with mild persistent, and moderate-to-severe persistent asthma were elevated. One probable explanation for this difference between those results and ours is that Csoma et al21 might have primarily studied patients with mild intermittent asthma and very stable symptoms. In this study, we could not find a significant difference in the EBC LTE4 levels of nonasthmatic control subjects and patients with mild asthma who had been asymptomatic for > 6 months prior to examination.

We also found a significant correlation between EBC LTE4 levels and PC15 in our subjects (r = – 0.454, p = 0.012) [Fig 3]. It is known that airway hyperresponsiveness is a key feature of asthma and can be used as an indicator of asthma severity. This correlation suggests that LT itself may contribute to airway hyperresponsiveness.22

A few previous studies2324 have reported no correlation between the activation of airway inflammatory cells, such as eosinophils and mast cells, and the degree of airway hyperresponsiveness in asthmatic subjects; however, there are also a similar number of studies25262728 that do show a significant correlation. Our result, depicting a significant correlation between EBC LTE4 levels and airway hyperreactivity, suggests that airway hyperreactivity is affected by the extent of airway inflammation. Measurement of EBC LTE4 can be a marker reflecting airway inflammation and hyperreactivity, which may be useful in infants and young children in whom the objective estimation of asthma can be difficult to perform. However, further longitudinal study must be necessary to more thoroughly investigate the clinical utility of EBC LTs.

Cys-LTs are mainly produced by airway mast cells and eosinophils. In this study, we could not determine the exact source of the cys-LTs because there were no significant differences in serum IgE levels and in peripheral eosinophil counts among the groups. This would imply that the function of mast cells and/or eosinophils, rather than the actual number of cells, may more greatly affect EBC LTE4 levels. Some of the subjects had been treated with inhaled fluticasone propionate (≤ 200 µg/d in all users) prior to examination (Table 1). There were no significant differences in frequency of fluticasone users between group 1 and group 2. However, the frequency in group 3 was significantly higher than group 1 and group 2. Mondino et al13 showed that EBC LTE4 levels in children with asthma were reduced by 18% after 4 weeks of treatment with fluticasone. Nevertheless, we found that EBC LTE4 levels in group 3 were increased, not decreased, compared with control subjects and group 1. Therefore, although the higher number of children treated with fluticasone in group 3 might have affected the results, we would predict the effect of fluticasone to be the opposite of what our results show. In fact, we may have found even higher levels of LTE4 if fewer children in group 3 had been treated with fluticasone.

Our results suggest that airway cys-LTs may play a role in the pathogenesis of asthma even in children with mild, asymptomatic asthma, and that levels of airway cys-LTs may reflect degree of airway hyperreactivity, probably based on chronic airway inflammation. Given these perspectives, the current asthma treatment recommendations, as stated in many guidelines, that suggest early intervention with inhaled corticosteroid293031 seem reasonable.

EBC cys-LTs may be useful as a noninvasive marker assessing airway inflammation and hyperreactivity in children with asthma. In the future, we would expect that measuring EBC LTs will become a part of the clinical practice in asthma management in combination with other useful markers such as eNO, especially in infants and young children.

Footnotes

Abbreviations: cys-LT = cysteinyl leukotriene; EBC = exhaled breath concentrate; eNO = exhaled nitric oxide; LT = leukotriene; PC15 = provocative concentration of methacholine causing a 15% fall in FEV1

The authors have no financial or other potential conflicts of interest associated with this study.

Received for publication September 23, 2005. Accepted for publication June 28, 2006.

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