Asthma phenotypes: consistency of classification using induced sputum.

BACKGROUND AND OBJECTIVE: Asthma can be classified as eosinophilic or non-eosinophilic based on the cell profile of induced sputum. This classification can help determine whether corticosteroid treatment is indicated. We assessed the stability of these phenotypes over time and with different treatment regimens. METHODS: Clinically stable, non-smoking, asthmatic adults were enrolled in one of two studies. In study one, induced sputum cell counts from 28 subjects were analysed after 4 weeks without corticosteroid treatment and after 6 week treatments with placebo, regular inhaled beta-agonist, inhaled corticosteroid, and combined beta-agonist and corticosteroid. In study two, sputum from 26 subjects with non-eosinophilic asthma was analysed after 12 weeks of placebo and after four 2-week corticosteroid washouts. Sputum with <2% eosinophils was classified as non-eosinophilic. RESULTS: Sputum classification changed frequently in both studies. In study one, only one of eight participants with non-eosinophilic sputum after placebo treatment remained non-eosinophilic throughout. In study two, all of participants had at least one eosinophilic sputum sample, despite the fact that all had been non-eosinophilic at recruitment. Neutrophilic asthma was uncommon in both studies and was also inconsistent. CONCLUSIONS: The phenotypic classification of asthma changes frequently. A diagnosis of non-eosinophilic asthma should not be based on a single sputum sample.

Eosinophil peroxidase produces hypobromous acid in the airways of stable asthmatics.

Eosinophil peroxidase and myeloperoxidase use hydrogen peroxide to produce hypobromous acid and hypochlorous acid. These powerful oxidants may damage the lungs if they are produced as part of the inflammatory response in asthma. The aim of this study was to determine if peroxidases generate hypohalous acids in the airways of individuals with stable asthma, and if they affect lung function. Sputum was induced from patients with mild to moderate asthma and from healthy controls. Eosinophil peroxidase, myeloperoxidase, chlorinated and brominated tyrosyl residues, and protein carbonyls were measured in sputum supernatants. Eosinophil peroxidase protein was significantly elevated in asthmatic subjects whereas myeloperoxidase protein was not. There was significantly more 3-bromotyrosine (Br-Tyr) in proteins from the sputum of asthmatics compared to controls (0.79 vs. 0.23 mmol Br-Tyr/mol Tyr; medians p < .0001). Levels of 3-chlorotyrosine (0.23 vs. 0.14 mmol Cl-Tyr/mol Tyr; medians p = .11) and protein carbonyls (0.347 vs. 0.339 nmol/mg protein; medians p = .56) were not significantly increased in asthmatics. Levels of 3-bromotyrosine were strongly correlated with eosinophil peroxidase protein (r = 0.79, p < .0001). There were no significant correlations between the markers of oxidative stress and lung function. We conclude that eosinophil peroxidase produces substantial amounts of hypobromous acid in the airways of stable asthmatics. Although this highly reactive oxidant is a strong candidate for exacerbating inflammatory tissue damage in the lung, its role in asthma remains uncertain.

Bromotyrosines in sputum proteins and treatment effects of terbutaline and budesonide in asthma.

BACKGROUND: Inhaled corticosteroids are widely used in the treatment of persistent asthma, usually combined with inhaled beta2-agonists. Previous research suggests that short-acting beta2-agonists (SABAs) may downregulate the anti-inflammatory effects of inhaled corticosteroids, thereby increasing asthma morbidity. OBJECTIVE: To determine whether 3-bromotyrosine and 3,5-dibromotyrosine levels, specific markers of eosinophil activation, reflect treatment effects on airway inflammation of inhaled corticosteroids and SABAs and support previous conclusions. METHODS: Levels of 3-bromotyrosine and 3,5-dibromotyrosine were measured in sputum supernatants using stable isotope dilution gas chromatography-mass spectrometry in a randomized, placebo-controlled, crossover study of treatment with terbutaline, budesonide, and their combination in patients with persistent asthma. Thirty-four individuals were randomized, and 28 completed the study. RESULTS: Treatment with budesonide lowered median 3-bromotyrosine levels compared with treatment with placebo, terbutaline, and budesonide-terbutaline (0.24 vs 0.64, 0.62, and 0.43 3-bromotyosine/tyrosine [mmol/mol]; P < .05) and lowered median 3,5-dibromotyrosine levels compared with placebo and terbutaline treatments (0.04 vs 0.11 and 0.07 3,5-dibromotyrosine/ tyrosine [mmol/mol], P < .05). Unlike eosinophil numbers, 3-bromotyrosine and 3,5-dibromotyrosine levels did not increase with terbutaline treatment compared with placebo treatment but were significantly raised when terbutaline was added to budesonide treatment. 3-Bromotyrosine levels correlated significantly with eosinophil cationic protein levels in all groups. CONCLUSIONS: 3-Bromotyrosine and 3,5-dibromotyrosine levels reflect treatment effects in asthma and support previous findings that SABAs impair the anti-inflammatory effects of inhaled corticosteroids. In addition to eosinophil numbers and eosinophil cationic protein levels, these modified tyrosine residues provide useful information about the inflammatory state of the airways.

Eosinophils and eosinophilic cationic protein in induced sputum and blood: effects of budesonide and terbutaline treatment.

BACKGROUND: There is a need for easily measurable markers of airway inflammation to guide the use of anti-inflammatory treatment in asthma. Eosinophilic cationic protein (ECP) levels in sputum and blood correlate with clinical severity, and serial measurements of ECP have been proposed as a suitable candidate. AIMS AND METHODS: Our aim was to confirm that sputum and serum ECP measurements would provide a more sensitive indicator of responses to asthma treatment than eosinophil counts per se, in a randomized, placebo-controlled, crossover study of terbutaline, budesonide, and their combination in patients with chronic persistent asthma. We compared the changes in eosinophil counts and ECP in induced sputum and blood during each treatment period. RESULTS: Budesonide and combined treatment caused a significant reduction in sputum eosinophils (-2.7% and -2.3%, respectively, P < 0.05). Sputum eosinophils increased with terbutaline (+3.9%, P = 0.049). In contrast, the changes for sputum ECP were not significant. There was a similar treatment effect on blood eosinophils, but not for serum ECP. Correlations between sputum and blood eosinophils were significant with and without budesonide, but were nonsignificant between sputum and blood ECP during the active treatments. Correlations between sputum eosinophils and ECP, and between blood eosinophils and serum ECP were greatest during treatment with placebo or terbutaline alone: budesonide weakened or abolished these relationships. CONCLUSIONS: Compared with eosinophil counts, ECP measurements in either induced sputum or serum failed to reflect treatment-related changes in chronic asthma. We conclude that ECP is not a sensitive or reliable means of evaluating airway inflammation, and can not be recommended for assessing responses to anti-inflammatory therapy.