The Duffy antigen receptor for chemokines regulates asthma pathophysiology.

BACKGROUND: The Duffy antigen receptor for chemokines (DARC) is an atypical receptor that regulates pro-inflammatory cytokines. However, the role of DARC in asthma pathophysiology is unknown. OBJECTIVE: To determine the role of DARC in allergic airways disease in mice, and the association between DARC single nucleotide polymorphisms (SNPs) and clinical outcomes in patients with asthma. METHODS: Mice with targeted disruption of the Darc gene (Darc∆E2 ) or WT mice were challenged over 3 weeks with house dust mite (HDM) antigen. Allergic airways disease was assessed 24 hours and 7 days following the final challenge. Additionally, associations between DARC SNPs and clinical outcomes were analysed in a cohort of poorly controlled asthmatics. RESULTS: Total airway inflammation following HDM did not differ between Darc∆E2 and WT mice. At 24 hours, Darc∆E2 mice had increased airway hyperresponsiveness; however, at 7 days airway hyperresponsiveness had completely resolved in Darc∆E2 but persisted in WT mice. In poorly controlled asthmatics, DARC SNPs were associated with worse asthma control at randomization and subsequent increased risk of healthcare utilization (odds ratio 3.13(1.37-7.27), P=.0062). CONCLUSIONS AND CLINICAL RELEVANCE: Our animal model and human patient data suggest a novel role for DARC in the temporal regulation in asthma pathophysiology and symptoms.

Genome-wide association study of leukotriene modifier response in asthma.

Heterogeneous therapeutic responses to leukotriene modifiers (LTMs) are likely due to variation in patient genetics. Although prior candidate gene studies implicated multiple pharmacogenetic loci, to date, no genome-wide association study (GWAS) of LTM response was reported. In this study, DNA and phenotypic information from two placebo-controlled trials (total N=526) of zileuton response were interrogated. Using a gene-environment (G × E) GWAS model, we evaluated 12-week change in forced expiratory volume in 1 second (ΔFEV1) following LTM treatment. The top 50 single-nucleotide polymorphism associations were replicated in an independent zileuton treatment cohort, and two additional cohorts of montelukast response. In a combined analysis (discovery+replication), rs12436663 in MRPP3 achieved genome-wide significance (P=6.28 × 10(-08)); homozygous rs12436663 carriers showed a significant reduction in mean ΔFEV1 following zileuton treatment. In addition, rs517020 in GLT1D1 was associated with worsening responses to both montelukast and zileuton (combined P=1.25 × 10(-07)). These findings implicate previously unreported loci in determining therapeutic responsiveness to LTMs.

Mechanisms of airway hyper-responsiveness in asthma: the past, present and yet to come.

Airway hyper-responsiveness (AHR) has long been considered a cardinal feature of asthma. The development of the measurement of AHR 40 years ago initiated many important contributions to our understanding of asthma and other airway diseases. However, our understanding of AHR in asthma remains complicated by the multitude of potential underlying mechanisms which in reality are likely to have different contributions amongst individual patients. Therefore, the present review will discuss the current state of understanding of the major mechanisms proposed to contribute to AHR and highlight the way in which AHR testing is beginning to highlight distinct abnormalities associated with clinically relevant patient populations. In doing so we aim to provide a foundation by which future research can begin to ascribe certain mechanisms to specific patterns of bronchoconstriction and subsequently match phenotypes of bronchoconstriction with clinical phenotypes. We believe that this approach is not only within our grasp but will lead to improved mechanistic understanding of asthma phenotypes and we hoped to better inform the development of phenotype-targeted therapy.

A genome-wide association study of bronchodilator response in asthmatics.

Reversibility of airway obstruction in response to ß2-agonists is highly variable among asthmatics, which is partially attributed to genetic factors. In a genome-wide association study of acute bronchodilator response (BDR) to inhaled albuterol, 534 290 single-nucleotide polymorphisms (SNPs) were tested in 403 white trios from the Childhood Asthma Management Program using five statistical models to determine the most robust genetic associations. The primary replication phase included 1397 polymorphisms in three asthma trials (pooled n=764). The second replication phase tested 13 SNPs in three additional asthma populations (n=241, n=215 and n=592). An intergenic SNP on chromosome 10, rs11252394, proximal to several excellent biological candidates, significantly replicated (P=1.98 × 10(-7)) in the primary replication trials. An intronic SNP (rs6988229) in the collagen (COL22A1) locus also provided strong replication signals (P=8.51 × 10(-6)). This study applied a robust approach for testing the genetic basis of BDR and identified novel loci associated with this drug response in asthmatics.

A polymorphism in the thyroid hormone receptor gene is associated with bronchodilator response in asthmatics.

A pro-asthmatic culture milieu and ß2-agonist (isoproterenol) were previously shown to regulate the expression of select transcription factors (TFs) within human airway epithelial and smooth muscle cells. This study tests 1116 single-nucleotide polymorphisms (SNPs) across 98 of these TF genes for association with bronchodilator response (BDR) in asthma patients. Genotyping was conducted using the Illumina HumanHap550v3 Beadchip in 403 non-Hispanic White asthmatic children and their parents. SNPs were evaluated for association with BDR using family and population-based analyses. Forty-two SNPs providing P-values <0.1 in both analyses were then genotyped in three adult asthma trials. One SNP 5' of the thyroid hormone receptor-ß gene was associated with BDR in the childhood population and two adult populations (P-value=0.0012). This investigation identified a novel locus for inter-individual variability in BDR and represents a translation of a cellular drug-response study to potential personalization of clinical asthma management.

HLA-DQ strikes again: genome-wide association study further confirms HLA-DQ in the diagnosis of asthma among adults.

BACKGROUND: Asthma is a common chronic respiratory disease in children and adults. An important genetic component to asthma susceptibility has long been recognized, most recently through the identification of several genes (e.g., ORMDL3, PDE4D, HLA-DQ, and TLE4) via genome-wide association studies. OBJECTIVE: To identify genetic variants associated with asthma affection status using genome-wide association data. METHODS: We describe results from a genome-wide association study on asthma performed in 3855 subjects using a panel of 455 089 single nucleotide polymorphisms (SNPs). RESULT: The genome-wide association study resulted in the prioritization of 33 variants for immediate follow-up in a multi-staged replication effort. Of these, a common polymorphism (rs9272346) localizing to within 1 Kb of HLA-DQA1 (chromosome 6p21.3) was associated with asthma in adults (P-value = 2.2E-08) with consistent evidence in the more heterogeneous group of adults and children (P-value = 1.0E-04). Moreover, some genes identified in prior asthma GWAS were nominally associated with asthma in our populations. CONCLUSION: Overall, our findings further replicate the HLA-DQ region in the pathogenesis of asthma. HLA-DQA1 is the fourth member of the HLA family found to be associated with asthma, in addition to the previously identified HLA-DRA, HLA-DQB1 and HLA-DQA2.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma.

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

Characteristics of patients with seasonal allergic rhinitis and concomitant asthma.

BACKGROUND: Allergic rhinitis and asthma often co-exist and appear to produce a continuum of airway disease, but whether the clinical characteristics of asthma in patients with seasonal rhinitis differ from those of persistent asthma has not been examined. OBJECTIVE: The aim of this retrospective study was to characterize the clinical features of patients with seasonal allergic rhinitis with concomitant asthma and to compare them with those in patients with persistent asthma. METHODS: The patient populations for this study were derived from nine prospective, placebo-controlled planned clinical trials of similar design. Six studies (958 patients) enrolled patients with seasonal allergic rhinitis and concomitant asthma; three (607 patients) involved patients with persistent asthma. In all studies, patients were excluded from oral corticosteroid therapy in the preceding 3 months, and from inhaled corticosteroids in the preceding month. RESULTS: Patients with seasonal rhinitis and asthma had a significantly (P<0.001) higher total asthma symptom score than those with persistent asthma. In particular, cough was three times more severe. The need for beta(2)-agonist as a rescue medication and the ratio of forced expiratory volume in 1 s/forced vital capacity (FVC) were similar in the two groups whereas forced expiratory fraction 25-75%/FVC was significantly (P<0.02) reduced in the persistent asthmatics. Asthma and nasal symptom severity scores were correlated in patients with seasonal rhinitis and asthma (P<0.0001). CONCLUSIONS: Patients with seasonal allergic rhinitis and concomitant asthma appear to differ from those with persistent asthma. A prospective study should be designed to discover whether patients with seasonal rhinitis and asthma may represent a distinct nosological entity, 'allergic airway disease'.

Strain dependence of airway hyperresponsiveness reflects differences in eosinophil localization in the lung.

Different strains of mice exhibit different degrees of airway hyperresponsiveness after sensitization to and airway challenge with ovalbumin. Antibody responses in BALB/c mice far exceeded those in C57BL/6 mice; in contrast, although responsiveness to methacholine was much higher in the BALB/c mice, the number of eosinophils in the bronchoalveolar lavage fluid was higher in C57BL/6 animals. Sensitized and challenged BALB/c mice developed increases in lung resistance and decreases in dynamic compliance after methacholine or 5-hydroxytryptamine inhalation. C57BL/6 mice only exhibited significant levels of responsiveness when dynamic compliance was monitored in response to inhaled 5-hydroxytryptamine. Eosinophils accumulated in the peribronchial and peripheral lung tissue in BALB/c mice but were distributed diffusely in the peripheral lung tissue of C57BL/6 mice. Thus, in addition to differences in antibody responses and cholinergic agonist reactivity, differences in the responses of large and small airways may reflect the selective distribution of eosinophils in lung tissue.

Distal lung dysfunction at night in nocturnal asthma.

We have previously shown that patients with nocturnal worsening of asthma (nocturnal asthma) exhibit increased parenchymal inflammation at night. To evaluate the functional significance of this parenchymal inflammation, 10 subjects with nocturnal asthma (NA), four subjects with non-nocturnal asthma (NNA), and four normal control subjects underwent bronchoscopy with measurement of peripheral airways resistance (Rp) at 4:00 P.M. and at 4:00 A.M. Employing a wedged bronchoscope technique, Rp was measured. Flow was stopped, and the pressure reached after 10 s of decay was termed the plateau pressure. The time constant of this decay (tau) was measured, and the peripheral compliance (Cp) was calculated as tau/Rp. The NA group exhibited the highest Rp values at 4:00 P.M. and at 4:00 A.M. as compared with the NNA and control groups, but all groups were significantly different from each other at 4:00 P.M.: NA, 0.113 +/- 0.02 cm H(2)O/ml/min; NNA, 0.033 +/- 0.005 cm H(2)O/ml/min; Control subjects, 0.010 +/- 0.001 cm H(2)O/ ml/min; p = 0.0001; and at 4:00 A.M.: NA, 0.129 +/- 0.023 cm H(2)O/ ml/min; NNA, 0.035 +/- 0.007 cm H(2)O/ml/min; Control subjects, 0.009 +/- 0.002 cm H(2)O/ml/min; p = 0.0003. None of the groups exhibited statistically significant differences in Rp between 4:00 P.M. and 4:00 A.M. The plateau pressure increased significantly from 4:00 P.M. to 4:00 A.M., but only in the NA group (7.7 +/- 0.9 cm H(2)O at 4:00 P.M. versus 16.9 +/- 4.6 cm H(2)O at 4:00 A.M.; p = 0.0004). Cp was decreased in the NA group as compared with the NNA and control groups at both 4:00 P.M. (p = 0.0003) and 4:00 A.M. (p = 0.003). The Rp positively correlated with the residual volume at both 4:00 P.M. (r = 0.71, p = 0.004) and 4:00 A.M. (r = 0.59, p = 0.03). We conclude that the distal lung units, specifically the collateral channels, and may be functionally altered at night in NA.

Airway responses to a diluent used in the methacholine challenge test.

BACKGROUND: Inhalation of diluent is often used in performing methacholine challenge tests, but its elimination has been suggested because marked falls in FEV1 after diluent inhalation have not been documented and performing this step is time-consuming. OBJECTIVE: We investigated the frequency and magnitude of response to the inhalation of diluent, and if there were any systematic effects in determining the PC20 using the baseline and postdiluent spirometric measurements. METHODS: All methacholine challenges performed during a 6-year period (N = 3,902) were reviewed retrospectively. RESULTS: The maximum increase and decrease in FEV1 and FVC from baseline were 56.3% and -41.4%, respectively, and 61.7% and -40.3%, respectively. The mean absolute changes from baseline in FEV1 and FVC were -0.018 L and -0.026 L, respectively. There was a highly significant correlation (r2 = 0.96; P < .0001) between the PC20 baseline and PC20 postdiluent values, and a mean difference of 0.041 mg/mL (P < .0001), with the PC20 postdiluent being higher. CONCLUSIONS: These data do not provide strong evidence to support either using or eliminating the diluent stage. It is clear that there are frequent and sometimes large changes in FVC and FEV1 after the inhalation of diluent containing phenol and sodium bicarbonate buffer. If a laboratory intends to report changes in airway function qualitatively (ie, positive or negative), the diluent stage may not be necessary. However, if a laboratory intends to report bronchial challenge data from inhaling methacholine in a quantitative fashion and report a continuous variable such as PC20, a diluent stage is recommended.

Overexpression of tumor necrosis factor-alpha produces an increase in lung volumes and pulmonary hypertension.

Tumor necrosis factor (TNF)-alpha is a key proinflammatory cytokine that is thought to be important in the development of pulmonary fibrosis, whereas its role in pulmonary emphysema has not been as thoroughly documented. In the present study, TNF-alpha was overexpressed in alveolar type II cells under the control of the human surfactant protein C promoter. In this report, we further characterized the pulmonary abnormalities and provided a physiological assessment of these mice. Histopathology of the lungs revealed chronic inflammation, severe alveolar air space enlargement and septal destruction, and bronchiolitis. However, pulmonary fibrosis was very limited and only seen in the subpleural, peribronchiolar, and perivascular regions. Physiological assessment showed an increase in lung volumes and a decrease in elastic recoil characteristic of emphysema; there was no evidence of restrictive lung disease characteristic of pulmonary fibrosis. In addition, the mice raised in ambient conditions in Denver developed pulmonary hypertension. Gelatinase activity was increased in the lavage fluid from these lungs. These results suggest that in these mice TNF-alpha contributed to the development of pulmonary emphysema through chronic lung inflammation and activation of the elastolytic enzymes but by itself was unable to produce significant pulmonary fibrosis.

New insights from lung function.

Asthma is a disease that is, in large part, defined by abnormalities of pulmonary function. Failure of any new treatment modality to improve objective measures of lung function suggests a limited usefulness of such new therapies. The clear dissociation between inflammation and airways responsiveness indicates the latter is not solely dependent on the former. Recent long-term treatment trials suggest that monitoring the degree of airways responsiveness, and returning responsiveness toward a normal value should be an obtainable goal of therapy. The effects of large inhalations and loss of lung volume dependence suggest that linkage between the airways and lung parenchyma are a key to maintenance of airway patency. Measurement of lung function remains the most practical means for the assessment of permanent changes in lung structure. New developments in monitoring lung function, especially using forced oscillation approaches, show particular promise in assessing the lung function of the asthmatic person.

Timing of administration of anti-VLA-4 differentiates airway hyperresponsiveness in the central and peripheral airways in mice.

The development of airway hyperresponsiveness (AHR) is correlated with the infiltration into the lungs of activated eosinophils and T lymphocytes. In large part, influx of eosinophils into the lung is dependent on very late activating antigen-4 (VLA-4) expression. However, the kinetics of eosinophil recruitment and the development of AHR are not fully delineated. Airway function was monitored by changes in lung resistance (RL) and dynamic compliance (Cdyn) to methacholine (MCh) inhalation after anti-VLA-4. After ovalbumin (OVA) sensitization and airway challenge of BALB/c mice, AHR increased as did the number of lung inflammatory cells. Administration of anti-VLA-4 to sensitized mice 2 h before the first (of three) OVA airway challenges significantly prevented changes in RL. Moreover, injection of the antibody from 2 h before the first challenge to 42 h after the last challenge significantly prevented the increases in RL, as well as eosinophil and lymphocyte numbers in the bronchoalveolar lavage fluid (BALF); interleukin-5 (IL-5) and leukotriene concentrations in BALF were also significantly inhibited. Interestingly, treatment with anti-VLA-4 only prevented changes in Cdyn and goblet cell hyperplasia when administered 2 h before the first challenge. These studies demonstrate that the timing of anti-VLA-4 administration can selectively affect pathologic processes that contribute to altered airway function in the central and peripheral airways after allergen challenge.

Effects of cool, dry air stimulation on peripheral lung mechanics in asthma.

We have previously demonstrated that peripheral airway resistance (Rp) rises more in asthmatics than in nonasthmatic control subjects after segmental challenge with cool, dry air. To better understand this rise in Rp, we used a stop-flow method to measure the decay of segment pressure with time that yielded information on airway resistance (Raw), final plateau pressure (Pp), and peripheral lung compliance (Cp). After stop-flow maneuvers in all seven asthmatics and all seven normal subjects, pressure decayed smoothly without an initial sudden drop. This finding suggests that Raw was negligible and that the predominant site of flow resistance was the collateral pathways of the obstructed segment. Asthmatics had a significantly higher Pp and lower Cp at baseline than did normal subjects, but neither Pp nor Cp changed after challenge. Pp and Rp were significantly correlated. When interpreted in terms of a single-compartment nonlinear model, we concluded that Rp is predominantly determined by the resistance of the collateral airways rather than the more proximal airways. We also concluded that, compared with normal subjects, asthmatics have (1) more collateral airway narrowing and closure and lower segmental compliance, and (2) after challenge, increased collateral airway narrowing or closure without a change in compliance of the distal lung parenchyma. These results reflect the fundamental differences in peripheral lung mechanics between asthmatic and nonasthmatic subjects and in their response to directly instilled cool, dry air.