Evolving concepts on the value of adenosine hyperresponsiveness in asthma and chronic obstructive pulmonary disease

The role of adenosine as a novel bronchoprovocant in asthma

PURPOSE OF REVIEW

There is evidence that bronchial hyperresponsiveness to inhaled adenosine may be a better marker of airway allergic inflammation than bronchial hyperresponsiveness to other spasmogens. Here the authors review the most recent development in this area of rapidly evolving clinical research, focusing on the putative role of adenosine as a useful bronchoprovocant in asthma.

RECENT FINDINGS

New studies have provided evidence that hyperresponsiveness to AMP strongly correlates with sputum, blood/bronchial tissue eosinophilia and exhaled nitric oxide, whereas hyperresponsiveness to methacholine is related to changes in forced expiratory volume in 1 s, thus reflecting changes in airway caliber and functional state. Other recent studies have emphasized that the state of atopy is critically important in the bronchial response to inhaled AMP. The early finding that in people with asthma treatment with inhaled glucocorticosteroids significantly reduces airway responsiveness to AMP, as compared with other spasmogens such as methacholine or bradykinin, has been confirmed by recent reports which have also outlined that this is an early phenomenon.

SUMMARY

Taken together these studies evidence that hyperresponsiveness to inhaled adenosine may be a better marker of airway allergic inflammation than hyperresponsiveness to other spasmogens. This peculiar property of adenosine suggests that bronchial provocation with inhaled adenosine could provide a reliable noninvasive tool for monitoring asthma activity/progression, and assessing the response to antiinflammatory treatments.

Inhaled Corticosteroids in the Long-Term Management of Patients with Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a major problem in the elderly population, with approximately 10% of the population affected. Since COPD is an inflammatory disorder of the pulmonary system, corticosteroids might be expected to improve clinical outcomes of the disease. Data from large, well designed randomised clinical trials in which approximately one third of patients were > or =65 years of age indicate that inhaled corticosteroids do not modify the natural history of COPD, as measured by the rate of decline in forced expiratory volume in 1 second (FEV1). However, these same studies also suggest that corticosteroids reduce the frequency of clinical exacerbations by nearly a third (compared with placebo). This beneficial effect is particularly pronounced among those with an FEV1 less than 50% of the predicted value. Withdrawal of inhaled corticosteroids, on the other hand, leads to increased symptoms and elevates the risk of exacerbations by 50% above baseline levels. Patients' health-related quality of life is also improved by the use of inhaled corticosteroids. It is clear that inhaled corticosteroids elevate the risk of thrush, dysphonia and skin bruising by 2-fold compared with placebo. In addition, the sum of evidence suggests a modest deleterious effect for inhaled corticosteroids on bone mineral density, especially for formulations that have an increased rate of systemic absorption. However, the clinical evidence of this observation is uncertain. The effect of inhaled corticosteroids on fracture risk is controversial with some observational studies suggesting a possible association. Whether inhaled corticosteroids increase the risk of ophthalmic complications (cataracts and glaucoma) is also uncertain. In conclusion, the current evidence indicates that inhaled corticosteroid therapy produces short- and long-term clinical benefits in COPD patients with moderate-to-severe disease and should be used as adjunctive therapy for elderly patients with COPD who experience frequent exacerbations or have moderately reduced lung function.

Asthma remission: does it exist?

Subjects believed to have grown out of asthma often develop symptoms again later in life. Ongoing airway inflammation may determine the risk of relapse, although the mechanisms involved are still misunderstood. Additionally, patients with asthma during childhood may develop irreversible airflow obstruction ( airway remodeling) as a result of chronic airway inflammation. Recently, airway inflammation and remodeling could be demonstrated in bronchial biopsy specimens from young adults who considered themselves grown out of asthma. It is also shown that evidence of airway inflammation and remodeling can be obtained noninvasively, thereby providing the opportunity to monitor disease activity. If chronic airway inflammation and/or remodeling are consistent findings in asymptomatic subjects with a history of atopic asthma, the question arises whether natural history can be positively altered with prolonged antiinflammatory therapy. Benefits of long-term prognosis are, however, not yet shown. Since epidemiologic work has demonstrated that a certain percentage of subjects with apparently outgrown atopic asthma remains asymptomatic without needing therapy for the rest of their lives, it can be argued that "asthma remission does exist." The question is whether this percentage can be increased with prolonged antiinflammatory therapy and regular control.

Changes in sputum counts and airway hyperresponsiveness after budesonide: monitoring anti-inflammatory response on the basis of surrogate markers of airway inflammation

BACKGROUND

Airway hyperresponsiveness (AHR) to pharmacologic stimuli and sputum eosinophils might be useful in the individual adjustment of long-term asthma management. However, it is not clear whether inhaled glucocorticosteroids (GCSs) provide greater protection against specific surrogate markers of airways inflammation than other means. In addition, detailed longitudinal assessment of changes in airway response with inhaled GCSs has never been carried out.

OBJECTIVES

We compared changes in AHR to inhaled methacholine and adenosine 5'-monophosphate (AMP) after budesonide treatment in a randomized, double-blind, placebo-controlled, crossover study of patients with mild-to-moderate asthma. Subsequently, we undertook a separate study to examine the time course of the changes in AHR in more detail and the changes in sputum cell counts in relation to budesonide treatment.

METHODS

In the phase 1 of the study, patients undertook bronchial provocation studies with increasing doubling concentrations of methacholine (0.06 to 16 mg/mL) and AMP (3.125 to 800 mg/mL) before and after budesonide 0.8 mg/daily for 3 weeks. The bronchial responses to the inhaled agonists were expressed as the provocative concentration causing a 20% decline in FEV(1) (PC(20)). In phase 2 of the study, patients attended the laboratory on 12 separate occasions to investigate changes in PC(20) methacholine, PC(20) AMP, and sputum cell counts before, during, and after withdrawal of therapy with inhaled budesonide 0.8 mg/daily for 6 weeks.

RESULTS

Budesonide treatment for 3 weeks significantly attenuated the constrictor response by 0.8 +/- 0.3 doubling doses for methacholine and by 2.6 +/- 0.5 doubling doses for AMP. These changes were significantly different from each other (P =.003). Significant variation in PC(20) methacholine (P <.05) value, PC(20) AMP (P <.001) value, percentage of sputum eosinophils (P <.001), and percentage of sputum epithelial cells (P <.001) were observed throughout the longitudinal assessment of changes in airway response to budesonide. Compared with the other surrogate markers, PC(20) AMP appears to be useful in promptly detecting early inflammatory changes of the asthmatic airways; a significant change of 1.6 +/- 0.3, 2.2 +/- 0.3, and 2.8 +/- 0.3 doubling doses of PC(20) AMP was observed at 1, 4, and 6 weeks, respectively, in the course of budesonide treatment.

CONCLUSIONS

The present findings underline the exquisite selectivity of diverse surrogate markers of airway inflammation in response to inhaled budesonide. When compared with that to the other markers, AHR to inhaled AMP is an early and sensitive indicator of the beneficial anti-inflammatory effects of topical GCSs.