Stability of FeNO and airway hyperresponsiveness to mannitol in untreated asthmatics

The use of the mannitol test as an outcome measure in asthma intervention studies: a review and practical recommendations

BACKGROUND

The mannitol test is an indirect bronchial challenge test widely used in diagnosing asthma. Response to the mannitol test correlates with the level of eosinophilic and mast cell airway inflammation, and a positive mannitol test is highly predictive of a response to anti-inflammatory treatment with inhaled corticosteroids. The response to mannitol is a physiological biomarker that may, therefore, be used to assess the response to other anti-inflammatory treatments and may be of particular interest in early phase studies that require surrogate markers to predict a clinical response. The main objectives of this review were to assess the practical aspects of using mannitol as an endpoint in clinical trials and provide the clinical researcher and respiratory physician with recommendations when designing early clinical trials.

METHODS

The aim of this review was to summarise previous uses of the mannitol test as an outcome measure in clinical intervention studies. The PubMed database was searched using a combination of MeSH and keywords. Eligible studies included intervention or repeatability studies using the standard mannitol test, at multiple timepoints, reporting the use of PD₁₅ as a measure, and published in English.

RESULTS

Of the 193 papers identified, 12 studies met the inclusion criteria and data from these are discussed in detail. Data on the mode of action, correlation with airway inflammation, its diagnostic properties, and repeatability have been summarised, and suggestions for the reporting of test results provided. Worked examples of power calculations for dimensioning study populations are presented for different types of study designs. Finally, interpretation and reporting of the change in the response to the mannitol test are discussed.

CONCLUSIONS

The mechanistic and practical features of the mannitol test make it a useful marker of disease, not only in clinical diagnoses, but also as an outcome measure in intervention trials. Measuring airway hyperresponsiveness to mannitol provides a novel and reproducible test for assessing efficacy in intervention trials, and importantly, utilises a test that links directly to underlying drivers of disease.

Airway hyperresponsiveness to inhaled mannitol identifies a cluster of non-eosinophilic asthma patients with high symptom burden

BACKGROUND

Patients with asthma are heterogeneous in clinical presentation and in response to treatment. Despite this, tools to guide treatment are limited and include mainly measures of eosinophilic inflammation and symptoms. Airway hyperresponsiveness (AHR) to mannitol is present in patients across inflammatory phenotypes and improve with inhaled cortico-steroids.

OBJECTIVE

To investigate whether measuring AHR to mannitol in addition to eosinophilic inflammation and symptoms add information to the phenotypic characterization of patients with asthma.

METHODS

A total of 317 patients with asthma from six different cohorts were included in the analysis. All patients had measures of AHR to mannitol, blood eosinophils and ACQ-5 available. A cluster analysis using Wards minimum variance method was performed. The distribution of FeNO, IgE, lung function, induced sputum inflammatory cell count, age of onset and severity of disease was compared between clusters.

RESULTS

Four clusters were identified. Three of the clusters had proportionate levels of AHR, eosinophilic inflammation and symptoms, but one cluster presented with low levels of eosinophilic inflammation and a significant symptom burden. Half of the subjects in this cluster presented with AHR to inhaled mannitol. Lung function, fractional exhaled nitric oxide, Body Mass Index and IgE were normal.

CONCLUSION

Information on AHR to mannitol in addition to blood eosinophils and symptoms identifies a subgroup of asthma patients with symptomatic, non-eosinophilic disease. AHR to mannitol may provide a treatable trait in a subgroup of patients with non-eosinophilic asthma.

Reduction of bronchial response to mannitol after partial switch from conventional tobacco to electronic cigarette consumption

BACKGROUND

Regarding the multiple health effects of e-cigarettes, there are insufficient data on potential effects on bronchial reactivity (BHR). In the present study, we assessed the impact of a switch from conventional to e-cigarettes on BHR under realistic conditions over a period of 3 months.

METHODS

Sixty subjects who declared to reduce or stop their tobacco consumption by inhalation of nicotine-containing liquids via e-cigarette, and 20 volunteers participating in a stop-smoking program were included. Data was analysed using parametric and non-parametric statistical procedures. Spirometry, determinations of exhaled carbon monoxide (eCO) and nitric oxide (FeNO), provocation testing with mannitol as an indirect bronchial stimulus, and cotinine measurements were used to investigate BHR and nicotine abstinence.

RESULTS

BHR to mannitol significantly decreased in the group using e-cigarettes and nicotine-containing liquids over a period of three months in this real-life setting. Participants reduced their tobacco consumption to about 25% or lower, confirmed by a reduction in eCO. Changes in lung function and FeNO were small and not statistically significant, and changes in the stop-smoking group were similar to those in the e-cigarette group.

CONCLUSION

The reduction in BHR that can be expected after a reduction of cigarette consumption was not abolished by the concomitant use of e-cigarettes. Whether the decrease in BHR observed after 3 months is maintained when using e-cigarettes over longer time periods or has an individual prognostic value, must be clarified in long-term studies.

Asthma: A Loss of Post-natal Homeostatic Control of Airways Smooth Muscle With Regression Toward a Pre-natal State

The defining feature of asthma is loss of normal post-natal homeostatic control of airways smooth muscle (ASM). This is the key feature that distinguishes asthma from all other forms of respiratory disease. Failure to focus on impaired ASM homeostasis largely explains our failure to find a cure and contributes to the widespread excessive morbidity associated with the condition despite the presence of effective therapies. The mechanisms responsible for destabilizing the normal tight control of ASM and hence airways caliber in post-natal life are unknown but it is clear that atopic inflammation is neither necessary nor sufficient. Loss of homeostasis results in excessive ASM contraction which, in those with poor control, is manifest by variations in airflow resistance over short periods of time. During viral exacerbations, the ability to respond to bronchodilators is partially or almost completely lost, resulting in ASM being "locked down" in a contracted state. Corticosteroids appear to restore normal or near normal homeostasis in those with poor control and restore bronchodilator responsiveness during exacerbations. The mechanism of action of corticosteroids is unknown and the assumption that their action is solely due to "anti-inflammatory" effects needs to be challenged. ASM, in evolutionary terms, dates to the earliest land dwelling creatures that required muscle to empty primitive lungs. ASM appears very early in embryonic development and active peristalsis is essential for the formation of the lungs. However, in post-natal life its only role appears to be to maintain airways in a configuration that minimizes resistance to airflow and dead space. In health, significant constriction is actively prevented, presumably through classic negative feedback loops. Disruption of this robust homeostatic control can develop at any age and results in asthma. In order to develop a cure, we need to move from our current focus on immunology and inflammatory pathways to work that will lead to an understanding of the mechanisms that contribute to ASM stability in health and how this is disrupted to cause asthma. This requires a radical change in the focus of most of "asthma research."

The Reliability of Adjusting Stepped Care Based on FeNO Monitoring for Patients with Chronic Persistent Asthma

Objective

To examine the feasibility of fractional exhaled nitrous oxide (FeNO) guided stepped care in patients with chronic persistent asthma.

Methods

160 patients with asthma were enrolled and randomly divided into study and control groups, and were given standardized treatment according to GINA 2014. All patients were evaluated every 3 months and their medication was adjusted according to the results of evaluation. The control group was adjusted according to the recommended protocol from GINA, while the study group was adjusted on the basis of the control group and combined with the results of FeNO. The complete control rate, failure rate of stepwise treatment, ACQ score, lung function, and peripheral blood eosinophil count were compared between the two groups.

Results

In both study and control groups, the patient condition was effectively controlled. Strikingly, the failure rate of step therapy in study group was lower than that of control group (P<0.05), although there were no significant differences between the two groups on total control rate, ACQ score, lung function, and peripheral blood eosinophil count (P>0.05). Furthermore, the levels of FeNO positively correlated with ACQ scores and eosinophil counts or negatively with lung function.

Conclusions

The dynamic monitoring of FeNO could effectively guide the medication and reduce the rate of treatment failure, which could be used to inform standardized management of asthma.