Richard J. Martin

Airway inflammation in chronic obstructive pulmonary disease: Comparisons with asthma

Chronic obstructive pulmonary disease (COPD) is a progressive syndrome of expiratory airflow limitation caused by chronic inflammation of the airways and lung parenchyma. The airway inflammatory response in COPD is initiated by smoking in the overwhelming majority of cases, and chronic exposure to cigarette smoke initiates a series of events that causes damage to central airways, peripheral airways, and terminal airspaces, leading to physiologic and clinical abnormalities. Although COPD shares some clinical features with asthma, another prevalent airway inflammatory disease, there are distinct differences in the phenotypic characteristics of airway inflammation between COPD and asthma. The eosinophil is the most prominent inflammatory cell in asthma, with mast cells, lymphocytes, and macrophages playing important but less prominent roles. In COPD the cellular composition of the airway inflammatory infiltrate differs, with neutrophils, macrophages, and lymphocytes assuming prominence and the eosinophil playing a minor role, except in the setting of exacerbations. The contrasting inflammatory phenotypes of asthma and COPD have important implications for clinical and physiologic manifestations of disease, as well as for therapy.

Plasma histamine, epinephrine, cortisol, and leukocyte β‐adrenergic receptors in nocturnal asthma

Plasma histamine, cortisol, epinephrine, cyclic adenosine monophosphate (cAMP), and leukocyte β‐adrenergic receptors were measured in asthmatic patients with (n = 7) and without (n = 10) nocturnal asthma at 4 PM and 4 AM and compared with those of normal subjects (n = 10). A twofold higher plasma histamine concentration was observed at 4 AM compared with 4 PM in all groups, with no change in plasma cortisol, epinephrine, and cAMP concentrations. At 4 AM compared with 4 PM, only patients with nocturnal asthma had a significant 33% decrease (p < 0.05) in mononuclear and polymorphonuclear leukocyte β‐adrenergic receptor density, with no difference in binding affinity in all three groups. Polymorphonuclear leukocytes from patients with nocturnal asthma had significantly impaired response to iso‐proterenol at 4 AM (17% ± 7.3% SEM increase in cAMP; p < 0.05) compared with those of patients without nocturnal asthma (69.4% ± 13.7%) and normal (80.2% ± 21.3%) subjects. A significant change in β‐adrenergic receptor density and function occurs at night in patients with nocturnal asthma.

TLR2 Signaling Is Critical for Mycoplasma pneumoniae-Induced Airway Mucin Expression

Excessive airway mucin production contributes to airway obstruction in lung diseases such as asthma and chronic obstructive pulmonary disease. Respiratory infections, such as atypical bacterium Mycoplasma pneumoniae (Mp), have been proposed to worsen asthma and chronic obstructive pulmonary disease in part through increasing mucin. However, the molecular mechanisms involved in infection-induced airway mucin overexpression remain to be determined. TLRs have been recently shown to be a critical component in host innate immune response to infections. TLR2 signaling has been proposed to be involved in inflammatory cell activation by mycoplasma-derived lipoproteins. In this study, we show that TLR2 signaling is critical in Mp-induced airway mucin expression in mice and human lung epithelial cells. Respiratory Mp infection in BALB/c mice activated TLR2 signaling and increased airway mucin. A TLR2-neutralizing Ab significantly reduced mucin expression in Mp-infected BALB/c mice. Furthermore, Mp-induced airway mucin was abolished in TLR2 gene-deficient C57BL/6 mice. Additionally, Mp was shown to increase human lung A549 epithelial cell mucin expression, which was inhibited by the overexpression of a human TLR2 dominant-negative mutant. These results clearly demonstrate that respiratory Mp infection increases airway mucin expression, which is dependent on the activation of TLR2 signaling.

Toll-like Receptor 2 Down-regulation in Established Mouse Allergic Lungs Contributes to Decreased Mycoplasma Clearance

RATIONALE Respiratory Mycoplasma pneumoniae (Mp) infection is involved in asthma pathobiology, but whether the established allergic airway inflammation compromises lung innate immunity and subsequently predisposes patients with asthma to Mp infection remains unknown. OBJECTIVES To test whether the established allergic airway inflammation compromises host innate immunity (e.g., Toll-like receptor 2 [TLR2]) to hinder the elimination of Mp from the lungs. METHODS We used mouse models of ovalbumin (OVA)-induced allergic airway inflammation with an ensuing Mp infection, and cultures of mouse primary lung dendritic cells (DCs) and bone marrow-derived DCs. MEASUREMENTS AND MAIN RESULTS Lung Mp clearance in allergic mice and TLR2 and IL-6 levels in lung cells, including DCs as well as cultured primary lung DCs and bone marrow-derived DCs, were assessed. The established OVA-induced allergic airway inflammation, or the prominent Th2 cytokines IL-4 and IL-13, inhibited TLR2 expression and IL-6 production in lung cells, including lung DCs, and eventually led to impaired host defense against Mp. Studies in IL-6 knockout mice indicated that IL-6 directly promoted Mp clearance from the lungs. IL-4- and IL-13-induced suppression of TLR2 was mediated by inhibiting nuclear factor-kappaB activation through signal transducer and activator of transcription 6 (STAT6) signaling pathway. CONCLUSIONS The established OVA-induced allergic airway inflammation impairs TLR2 expression and host defense cytokine (e.g., IL-6) production, and subsequently delays lung bacterial clearance. This could offer novel therapeutic strategies to reinstate TLR2 activation by using TLR2 ligands and/or blocking IL-4 and IL-13 to ameliorate persisting respiratory bacterial infections in allergic lungs.

Elevated serum melatonin is associated with the nocturnal worsening of asthma

BACKGROUND Increased airway inflammation at night contributes to the nocturnal worsening of asthma. In vitro studies have shown exogenous melatonin to be pro-inflammatory in asthma, but it is unknown whether endogenous melatonin levels are a controller of airway inflammation in nocturnal asthma. OBJECTIVE Our aim was to determine 24-hour patterns of serum melatonin and their relationship to overnight decline in physiology in subjects with nocturnal asthma, non-nocturnal asthma, and in healthy controls. METHODS Observational study of pulmonary physiology and melatonin levels in patients with nocturnal asthma (n = 7), non-nocturnal asthma (n = 13), and healthy controls (n = 11). Subjects maintained a constant sleep-wake regimen for 7 days. On day 8, serum melatonin was measured every 2 hours by radioimmunoassay and analyzed by cosinor modeling. The correlation between serum melatonin levels and overnight change in spirometry was evaluated by Spearmans rank correlation analysis. RESULTS In subjects with nocturnal asthma, peak melatonin levels were significantly elevated compared with healthy controls (67.6 +/- 5.0 pg/mL versus 53.5 +/- 4.0 pg/mL, P =.03). Melatonin acrophase was delayed in nocturnal asthma (02:54 versus 01:58 in healthy controls, P =.003, and 02:15 in non-nocturnal asthma, P =.01). In subjects with nocturnal asthma, increasing melatonin levels were significantly and inversely correlated with overnight change in FEV(1) (r = -.79, P =.04), a relationship that was not observed in non-nocturnal asthma or healthy controls. CONCLUSIONS Nocturnal asthma is associated with elevation and phase delay of peak serum melatonin levels. Elevated melatonin levels might contribute to the pathogenesis of nocturnal asthma.

Features of the bronchial bacterial microbiome associated with atopy, asthma, and responsiveness to inhaled corticosteroid treatment

Background Compositional differences in the bronchial bacterial microbiota have been associated with asthma, but it remains unclear whether the findings are attributable to asthma, to aeroallergen sensitization, or to inhaled corticosteroid treatment. Objectives We sought to compare the bronchial bacterial microbiota in adults with steroid‐naive atopic asthma, subjects with atopy but no asthma, and nonatopic healthy control subjects and to determine relationships of the bronchial microbiota to phenotypic features of asthma. Methods Bacterial communities in protected bronchial brushings from 42 atopic asthmatic subjects, 21 subjects with atopy but no asthma, and 21 healthy control subjects were profiled by using 16S rRNA gene sequencing. Bacterial composition and community‐level functions inferred from sequence profiles were analyzed for between‐group differences. Associations with clinical and inflammatory variables were examined, including markers of type 2–related inflammation and change in airway hyperresponsiveness after 6 weeks of fluticasone treatment. Results The bronchial microbiome differed significantly among the 3 groups. Asthmatic subjects were uniquely enriched in members of the Haemophilus, Neisseria, Fusobacterium, and Porphyromonas species and the Sphingomonodaceae family and depleted in members of the Mogibacteriaceae family and Lactobacillales order. Asthma‐associated differences in predicted bacterial functions included involvement of amino acid and short‐chain fatty acid metabolism pathways. Subjects with type 2–high asthma harbored significantly lower bronchial bacterial burden. Distinct changes in specific microbiota members were seen after fluticasone treatment. Steroid responsiveness was linked to differences in baseline compositional and functional features of the bacterial microbiome. Conclusion Even in subjects with mild steroid‐naive asthma, differences in the bronchial microbiome are associated with immunologic and clinical features of the disease. The specific differences identified suggest possible microbiome targets for future approaches to asthma treatment or prevention. Graphical abstract Figure. No Caption available.

Inhaled Fluticasone Propionate Reduces Concentration of Mycoplasma pneumoniae, Inflammation, and Bronchial Hyperresponsiveness in Lungs of Mice

BACKGROUND Mycoplasma pneumoniae has been shown to induce airway inflammation and bronchial hyperresponsiveness (BHR) in mice. Inhaled corticosteroids are the mainstay of asthma treatment, but their effects on M. pneumoniae and associated airway inflammation and BHR are poorly understood. METHODS Four groups of mice were studied to determine whether inhaled fluticasone propionate (FP) could attenuate airway inflammation and BHR by reducing or eliminating M. pneumoniae in lungs. The active group received aerosolized FP once daily for 5 days. Control mice received aerosolized sham solution plus M. pneumoniae, sham solution alone, or FP alone. RESULTS Mice treated with sham solution or FP alone did not develop airway inflammation or BHR. Mice infected with M. pneumoniae (no FP) developed significant lung inflammation and BHR. FP treatment of infected mice reduced neutrophils in bronchoalveolar lavage fluid (BALF), lung inflammation, and BHR. Expression of Toll-like receptor 2 in lung tissue tended to be down-regulated (P=.18) by FP in infected mice. FP reduced M. pneumoniae by up to 20-fold in lung tissue but not in BALF. CONCLUSION Inhaled FP suppresses airway inflammation and BHR, which may be caused, in part, by its ability to reduce concentrations of M. pneumoniae in lung tissue.

Location of airway inflammation in asthma and the relationship to circadian change in lung function.

Nocturnal asthma is an important part of asthma as the majority of patients with asthma have nocturnal worsening in lung function. The etiology of this process is multifactorial and interactive. There are many naturally occurring circadian rhythms, which for the normal individual have only a minor effect on lung function. However, in the asthmatic patient, these day-to-night alterations produce increased airway inflammation and worsening of asthma. Although asthma is considered an airway disease, the location of the inflammatory response may be greater in the alveolar tissue area. If correct, this could alter the therapeutic approach to this disease.

Atypical bacterial pneumonia and asthma risk

The role of respiratory infections in asthma is poorly understood. Atypical bacteria Mycoplasma pneumoniae and Chlamydia pneumoniae are present in the lower airways of approximately 50% of asthmatics. This study tested the hypothesis that early life community‐acquired pneumonia caused by Mycoplasma pneumoniae or Chlamydia pneumoniae is associated with increased asthma prevalence. Thirty‐five subjects with a history of community‐acquired pneumonia (22 due to atypical bacteria, 13 due to nonatypical pathogens) were evaluated by questionnaire 7–9 years after the episode of pneumonia. Subjects with a history of either typical or atypical pneumonia demonstrated increased asthma prevalence. Current or past asthma prevalence was 55% in subjects with atypical bacterial pneumonia and 61.5% in subjects with nonatypical bacterial pneumonia. Significant between‐group differences were not demonstrated with regard to asthma prevalence (risk ratio = 0.89; 95% confidence interval = 0.49–1.61), current bronchodilator use [1.18 (0.44–3.17)], and family history of atopy [1.18 (0.73–1.91)], or asthma [1.63 (0.68–3.88)]. These data suggest that atypical bacterial pneumonia confers a risk of asthma similar to that seen with nonatypical bacterial pneumonia. Prospective studies are warranted to more fully evaluate the importance of atypical bacterial pneumonia as an asthma risk factor.

Circadian Variation in Exhaled Nitric Oxide in Nocturnal Asthma

Asthma is characterized by airway inflammation and shows a circadian variation with nocturnal exacerbations. Because exhaled nitric oxide (ENO) measurement appears to be a noninvasive marker of airway inflammation, we examined the hypothesis that ENO would increase at night. In five nocturnal and five non-nocturnal asthmatics, ENO was measured at 4 P.M., 10 P.M., and 4 A.M. before and after bronchodilator. Both pre- and post-bronchodilator ENO (mean pre- and post-bronchodilator +/- SEM, ppb) unexpectedly fell significantly in nocturnal asthma from 4 P.M. (77.2 +/- 8.2) compared to 10 P.M. (68.4 +/- 8.7, p < 0.003) and 4 A.M. (66.0 +/- 8.5, p < 0.001) with no significant difference between 10 P.M. and 4 A.M.. In contrast, there were no significant differences in mean ENO at 4 P.M., 10 P.M., and 4 A.M. in non-nocturnal asthma. (51.3 +/- 10.8, 57.7 +/- 13.4, 53.8 +/- 12.5 ppb, respectively). Following bronchodilator, ENO rose significantly by 10.5 +/- 1.8 ppb in the nocturnal asthma group alone. The circadian rhythm of ENO differed greatly between nocturnal and non-nocturnal asthma. The significant decrease in ENO in nocturnal asthma may reflect an important chronobiological defect in the endogenous production and/or increased disposition of nitric oxide, which in view of its bronchodilator action, could play a role in nocturnal exacerbations of asthma.