Indirect challenges act by causing the release of endogenous mediators that cause the airway smooth muscle to contract. This is in contrast to the direct challenges where agonists such as methacholine or histamine cause airflow limitation predominantly via a direct effect on airway smooth muscle.Direct airway challenges have been used widely and are well standardised. They are highly sensitive, but not specific to asthma and can be used to exclude current asthma in a clinic population. Indirect bronchial stimuli, in particular exercise, hyperventilation, hypertonic aerosols, as well as adenosine, may reflect more directly the ongoing airway inflammation and are therefore more specific to identify active asthma. They are increasingly used to evaluate the prevalence of bronchial hyperresponsiveness and to assess specific problems in patients with known asthma, e.g. exercise-induced bronchoconstriction, evaluation before scuba diving.Direct bronchial responsiveness is only slowly and to a modest extent, influenced by repeated administration of inhaled steroids. Indirect challenges may reflect more closely acute changes in airway inflammation and a change in responsiveness to an indirect stimulus may be a clinically relevant marker to assess the clinical course of asthma. Moreover, some of the indirect challenges, e.g. hypertonic saline and mannitol, can be combined with the assessment of inflammatory cells by induction of sputum.

In this pilot safety study of 48 patients with mild or moderate asthma who had bronchial reactivity to adenosine monophosphate, regadenoson was safe and well tolerated.

Asthmatics, unlike healthy subjects, experience bronchoconstriction in response to inhaled adenosine, and extracellular adenosine concentrations are elevated in the bronchoalveolar lavage fluid and exhaled breath condensate of asthmatic subjects. However, little is known about the location and expression of adenosine receptors in asthmatic airways. The aim of the present study was to investigate the distribution of adenosine A 1 receptors in bronchial biopsy specimens from mildly asthmatic steroid-naïve subjects and then compare the degree of expression with that of healthy subjects.Biopsy sections were immunostained using an adenosine A 1 receptor antibody, the selectivity of which was validated in specific experiments. Image analysis was then performed in order to determine differences in immunostaining intensity.Immunostaining of biopsy sections from the asthmatic subjects revealed strong expression of the A 1 receptor, located predominantly in the bronchial epithelium and bronchial smooth muscle. In comparison, very weak immunostaining was observed in biopsy specimens obtained from healthy subjects. Image analysis revealed that the intensity of positive staining of the asthmatic bronchial epithelium and smooth muscle regions was significantly greater than that observed for the healthy epithelium and smooth muscle.In conclusion, the sensitivity of asthmatics to inhaled adenosine coupled with increased adenosine A 1 receptor expression implies that these receptors play a role in the pathophysiology of this disease. KEYWORDS: Adenosine, adenosine A 1 receptor, adenosine A 1 receptor expression, asthma A denosine is a purine nucleoside that is expressed in all cells of the body and involved in a wide range of physiological processes. The effects of adenosine are mediated predominantly through specific cell surface receptors, of which four subtypes (A 1 , A 2A , A 2B and A 3 ) have been described. It is now well recognised that extracellular levels of adenosine markedly increase under metabolically stressful conditions, such as hypoxia and inflammation, and, although an acutely elevated level of extracellular adenosine is considered to mediate anti-inflammatory and protective effects, chronic accumulation has been associated with pathological consequences [1].In asthmatic subjects, it has been demonstrated that adenosine levels in bronchoalveolar lavage fluid and exhaled breath condensate are significantly higher than those occurring in healthy subjects [2,3], and current evidence strongly suggests that they may contribute to the pathophysiology of asthma. For example, it has been recognised since the mid-1980s that inhalation of adenosine 59-monophosphate (AMP; 5'-nucleotidase rapidly hydrolyses AMP to adenosine in the lung) in asthmatic but not healthy subjects results in dose-related bronchoconstriction [4]. This is considered to be mediated predominantly, but not exclusively, by mast cell degranulation via A 2B receptor activation (reviewed in [5]). Furthermore, inhalation of AMP has been shown to i...

Several groups are assessing the use of cationic lipids for administration and at intervals up to 21 days thereafter. respiratory gene therapy. To date no human data are availNo adverse clinical events were seen or any statistically able regarding the safety of intra-pulmonary cationic lipid significant changes in spirometry or gas transfer. There delivery. In preparation for a trial of pulmonary delivery of were no clinically significant changes in any of the blood the CFTR gene, we have assessed the safety of nebulised parameters and no CT changes were seen. Comparisons lipid GL-67/DOPE/DMPE-PEG 5000 (GL-67A), the cationic of the cellular subpopulations (neutrophils, eosinophils, lipid formulation to be used in this study. Fifteen healthy lymphocytes and macrophages) in induced sputum volunteers were given incremental doses of GL-67A via a showed no significant alterations following administration Pari LC Jet nebuliser; three volunteers in each of five dosof the GL-67A. This study suggests that a single appliing cohorts with a week interval between cohorts. Markers cation of aerosol formulation of GL-67A does not result in of safety included clinical assessment, measurement of clinically detectable changes when given by nebulisation lung function, chest CT scan, serological testing and analyinto the lungs of normal volunteers and provides an indisis of induced sputum. Measurements were taken before cation of a lipid dose tolerated in man.

There has been controversy about possible beneficial effects of beta agonists on airway function in asthma, in addition to their effects on airway smooth muscle. We compared the protective effects of terbutaline on bronchoconstrictor responses to methacholine, which constricts smooth muscle directly, adenosine 5'-monophosphate (AMP), which acts indirectly by mast cell activation, and sodium metabisulfite (MBS), which stimulates sensory nerves, in 15 mild asthmatic subjects in a randomized double-blind study carried out in two phases. In the first phase 12 subjects inhaled two doses of 0.5 and 2.5 mg terbutaline or placebo administered as a dry power (Tubohaler) 20 min before challenge with methacholine and AMP. Each subject received increasing doubling doses of methacholine and AMP nebulized from a dosimeter. Challenges were terminated when FEV1 fell by 20% from baseline (PC20). In the second phase 10 subjects (seven of whom had participated in Phase 1) inhaled 0.5 mg terbutaline or placebo before similar challenge with methacholine and MBS. In Phase 1 terbutaline inhibited the bronchoconstrictor response to methacholine by 2.1 and 3.3 doubling doses but caused a significantly greater inhibition of the response to AMP of 3.4 and 4.8 doubling doses after 0.5 and 2.5 mg, respectively. In the second phase 0.5 mg terbutaline had equivalent effects on responses to both methacholine and MBS of 2.6 and 2.2 doubling dilutions, respectively. This effect on methacholine and MBS implies functional antagonism of airway smooth muscle. The enhanced effect on AMP implies an additional non-smooth muscle action that may involve suppression of airway mast cell function.