Differences in airway responsiveness to acetaldehyde and methacholine in asthma and chronic bronchitis

Airway responsiveness to indirect challenges in COPD

Patients with chronic obstructive pulmonary disease (COPD) demonstrate airway hyperresponsiveness to a number of indirect stimuli. Hyperresponsiveness to cold air hyperventilation, exercise, and drugs like propranalol and methoxamine seem to be able to distinguish patients with COPD from those with asthma, whereas hyperresponsiveness to stimuli like adenosine 5-monophosphate (AMP) and hypertonic saline seem unable to do so. The relationship of airway responsiveness to indirect stimuli and airway inflammation has received little study. The clinical relevance of hyperresponsiveness to an indirect challenge, including the impact on the natural history, relation to types of bronchitis, baseline airway calibre, and response to treatment need to be studied.

No acute effects of an exposure to 50 ppm acetaldehyde on the upper airways

OBJECTIVE

German MAK value of acetaldehyde has been fixed at 50 ppm to prevent from irritating effects. The threshold value is mainly based on animal experiments. The aim of this study was to evaluate acute effects of an exposure to 50 ppm acetaldehyde on the upper airways of human subjects.

METHODS

Twenty subjects were exposed to 50 ppm acetaldehyde and to air in an exposure chamber for 4 h according to a crossover design. Subjective symptoms were assessed by questionnaire. Olfactory threshold for n-butanol and mucociliary transport time were measured before and after exposure. Concentrations of interleukin 1beta and interleukin 8 were determined in nasal secretions taken after exposure. mRNA levels of interleukins 1beta, 6 and 8, tumour necrosis factor alpha, granulocyte-macrophage colony-stimulating factor, monocyte chemotactic protein 1, and cyclooxygenases 1 and 2 were measured in nasal epithelial cells, gained after exposure. Possible effects were investigated by semiparametric and parametric crossover analyses.

RESULTS

Exposure to acetaldehyde did not cause any subjective irritating symptoms. Olfactory threshold did not change. Mucociliary transport time increased insignificantly after exposure to acetaldehyde. Neither concentrations of interleukins in nasal secretions nor mRNA levels of inflammatory factors were higher after exposure to acetaldehyde.

CONCLUSION

An acute exposure to 50 ppm acetaldehyde did not cause any adverse effects in test subjects.

Clinical implications of airway hyperresponsiveness in COPD

COPD represents one of the leading causes of mortality in the general population. This study aimed at evaluating the relationship between airway hyperresponsiveness (AHR) and COPD and its relevance for clinical practice. We performed a MEDLINE search that yielded a total of 1919 articles. Eligible studies were defined as articles that addressed specific aspects of AHR in COPD, such as prevalence, pathogenesis, or prognosis. AHR appears to be present in at least one out of two individuals with COPD. The occurrence of AHR in COPD is influenced by multiple mechanisms, among which impairment of factors that oppose airway narrowing plays an important role. The main determinants of AHR are reduction in lung function and smoking status. We envision a dual role of AHR: in suspected COPD, specific determinants of AHR, such as reactivity and the plateau response, may help the physician to discriminate COPD from asthma; in definite COPD, AHR may be relevant for the prognosis. Indeed, AHR is an independent predictor of mortality in COPD patients. Smoking cessation has been shown to reduce AHR. Further studies are needed to elucidate whether this functional change is associated with improvement in lung function and respiratory symptoms.

Interleukin-17 in sputum correlates with airway hyperresponsiveness to methacholine

BACKGROUND

Interleukin-17 (IL-17) is a novel cytokine secreted by activated human memory CD4+ T cells. In vivo IL-17 recruits neutrophils into the airways via the release of CXC chemokines (interleukin-8) from bronchial epithelial cells. Since neutrophils are implicated in pathogenesis of chronic obstructive pulmonary disease (COPD) chronic bronchitis (CB) and asthma, we hypothesized that there would be increased concentration of IL-17 in the airways of these patients. To test this hypothesis, we measured levels of IL-17 in induced sputum of COPD patients, chronic bronchitis and asthmatics and compared them with healthy controls.

METHODS

Levels of IL-17 in induced sputum were measured via ELISA method in 19 COPD, 16 CB, 10 asthma and 11 control subjects. Airway responsiveness to methacholine was performed in people with FEV1 higher than 70% of predicted.

RESULTS

There were no significant differences in IL-17 levels between control group and the other groups. However, levels of IL-17 in sputum of COPD patients were significantly lower than in asthma (P=0.004) and in CB (P=0.01) groups. Medians and (ranges) were as follows: asthma--37.6 pg/ml (18.8-55.7 pg/ml), CB 293 pg/ml (18.8-49.7 pg/ml) and COPD 24.6 pg/ml (0-34.1 pg/ml). Comparison of healthy control subjects (PC20 > 8 mg/ml) to a group with bronchial hyperreactivity, which consisted of asthmatics and CB patients, whose PC20 was less than 8 mg/ml, revealed that levels of IL-17 were significantly increased in the second group (P=0.02). Also, levels of IL-17 were significantly increased (P=0.02) in the asthmatic patients with bronchial hyperreactivity compared to healthy subjects. Moreover levels of IL-17 in sputum of all studied subjects correlated negatively with PC20 (r=-0.51, P=0.002).

CONCLUSIONS

According to our results IL-17 is probably not involved in pathogenesis of stable COPD, but it may play a role in people with airway hyperresponsiveness.

Bronchoprovocation testing

Bronchoprovocation testing has been performed for more than 50 years. Challenge testing with nonselective agents has been used widely for the assessment of airflow limitation in patients, and has been used in the research setting to better characterize the pathophysiology of bronchial responsiveness. Based on this large body of literature, detailed guidelines are now available to allow for standardization of testing methodology. Such standardization is critical to achieve safe, accurate, and reproducible test results that may be interpreted meaningfully. Currently, bronchoprovocation testing with direct-acting stimuli such as methacholine is used most frequently in the clinical arena, but, in recent years, considerable interest has been developing in the use of indirect stimuli. (57) It now is recognized that bronchial hyperresponsiveness to indirect stimuli (e.g., exercise, cold air, and AMP) is highly specific for asthma and may have greater clinical relevance than does responsiveness to direct stimuli. (8) As a result, testing with indirect agents may become employed more widely in the future.