Search

Rationale: Airway narrowing is maintained for a prolonged period after acute bronchoconstriction in humans in the absence of deep inspirations (DIs)., Objectives: To determine whether maintenance of airway smooth muscle (ASM) shortening is responsible for the persistence of airway narrowing in healthy subjects following transient methacholine (MCh)-induced bronchoconstriction., Methods: On two separate visits, five healthy subjects underwent MCh challenges until respiratory system resistance (Rrs) had increased by approximately 1.5 cm H2O/L/s. Subjects took a DI either immediately after or 30 minutes after the last dose. The extent of renarrowing following the bronchodilator effect of DI was used to assess the continued action of MCh (calculated as percent change in Rrs from the pre-DI Rrs). We then used human bronchial rings to determine whether ASM can maintain shortening during a progressive decrease of carbachol concentration., Measurements and Main Results: The increased Rrs induced by MCh was maintained for 30 minutes despite waning of MCh concentration over that period, measured as attenuated renarrowing when the DI was taken 30 minutes after compared with immediately after the last dose (7 min post-DI, -36.2 ± 11.8 vs. 14.4 ± 13.2%; 12 min post-DI, -39.5 ± 9.8 vs. 15.2 ± 17.8%). Ex vivo, ASM shortening was largely maintained during a progressive decrease of carbachol concentration, even down to concentrations that would not be expected to induce shortening., Conclusions: The maintenance of airway narrowing despite MCh clearance in humans is attributed to an intrinsic ability of ASM to maintain shortening during a progressive decrease of contractile stimulation.

Rationale: The mechanism of action of diethylcarbamazine (DEC), an antifilarial drug effective against tropical pulmonary eosinophilia, remains controversial. DEC effects on microfilariae depend on inducible NO synthase (iNOS). In eosinophilic pulmonary inflammation, its therapeutic mechanism has not been established. We previously described the rapid up-regulation of bone marrow eosinophilopoiesis in ovalbumin (OVA)-sensitized mice by airway allergen challenge, and further evidenced the down-regulation of eosinophilopoiesis by iNOS- and CD95L-dependent mechanisms., Objectives: We investigated whether: (1) DEC can prevent the effects of airway challenge of sensitized mice on lungs and bone marrow, and (2) its effectiveness depends on iNOS/CD95L., Methods: OVA-sensitized BALB/c mice were intranasally challenged for 3 consecutive days, with DEC administered over a 12-, 3-, or 2-day period, ending at the day of the last challenge. We evaluated: (1) airway resistance, cytokine (IFN-gamma, IL-4, IL-5, and eotaxin) production, and pulmonary eosinophil accumulation; and (2) bone marrow eosinophil numbers in vivo and eosinophil differentiation ex vivo., Measurements and Main Results: DEC effectively prevented the effects of subsequent challenges on: (1) airway resistance, Th1/Th2 cytokine production, and pulmonary eosinophil accumulation; and (2) eosinophilopoiesis in vivo and ex vivo. Recovery from unprotected challenges included full responses to DEC during renewed challenges. DEC directly suppressed IL-5-dependent eosinophilopoiesis in naive bone marrow. DEC was ineffective in CD95L-deficient gld mice and in mice lacking iNOS activity because of gene targeting or pharmacological blockade., Conclusions: DEC has a strong impact on pulmonary eosinophilic inflammation in allergic mice, as well as on the underlying hemopoietic response, suppressing the eosinophil lineage by an iNOS/CD95L-dependent mechanism.

Rationale: Airways hyperresponsiveness (AHR) is a hallmark feature of asthma, and can be caused by various disparate mechanisms. Mouse models of AHR have been useful for studying these mechanisms in isolation, but such models still typically do not exhibit the same degree of AHR as seen in severe human asthma. We hypothesized that more severe AHR in mice could be achieved by imbuing them with more than one mechanism of AHR., Objectives: We sought to determine if the airway wall thickening accompanying allergic inflammation and the exaggerated smooth muscle shortening induced by intratracheal cationic protein could act together to produce a severe form of AHR., Methods: We used the forced oscillation technique to measure methacholine responsiveness in BALB/c mice that had been sensitized and challenged with ovalbumin followed by an intratracheal instillation of poly-l-lysine., Measurements and Main Results: We found that both ovalbumin and poly-l-lysine treatment alone caused moderate levels of AHR. When the two treatments were combined, however, they synergized in terms of their effect on lung stiffness to an extent that could even be fatal, reflecting a significantly enhanced level of airway closure., Conclusions: Our results suggest that mechanistic synergy between airway wall thickening and exaggerated smooth muscle shortening produces a more germane mouse model of asthma that may have particular relevance to the pathophysiology of the acute severe asthma exacerbation.

Rationale: Clinical trials have demonstrated that probiotics may be effective in the treatment and prevention of atopic disease in children but there have been few reports of therapeutic effects of oral probiotics outside the gastrointestinal tract., Objectives: We investigated the effect of two probiotic organisms on the response to antigen challenge in a mouse model of allergic airway inflammation., Methods: We used an ovalbumin-sensitized asthma model in BALB/c and Toll-like receptor 9-deficient mice. Animals were treated with probiotic organisms via gavaging needle before antigen challenge. After antigen challenge, airway responsiveness to methacholine, influx of inflammatory cells to the lung, and cytokine levels in bronchoalveolar lavage fluid were assessed., Results: Oral treatment with live Lactobacillus reuteri but not Lactobacillus salivarius significantly attenuated the influx of eosinophils to the airway lumen and parenchyma and reduced the levels of tumor necrosis factor, monocyte chemoattractant protein-1, IL-5, and IL-13 in bronchoalveolar lavage fluid of antigen-challenged animals, but there was no change in eotaxin or IL-10. L. reuteri but not L. salivarius also decreased allergen-induced airway hyperresponsiveness. These responses were dependent on Toll-like receptor 9 and were associated with increased activity of indoleamine 2,3-dioxygenase. Killed organisms did not mimic the ability of the live L. reuteri to attenuate inflammation or airway hyperresponsiveness., Conclusion: Oral treatment with live L. reuteri can attenuate major characteristics of an asthmatic response in a mouse model of allergic airway inflammation. These results suggest that oral treatment with specific live probiotic strains may have therapeutic potential in the treatment of allergic airway disease.

The relationship between gastroesophageal reflux and asthma remains unclear. The aim of this study was to analyze the effect of bronchial obstruction on lower esophageal sphincter (LES) motility and reflux in patients with asthma. LES motility and esophageal pH were assessed in eight subjects with intermittent asthma and eight healthy volunteers during three consecutive 30-minute periods: baseline, methacholine-induced bronchospasm, and after inhalation of the beta2-agonist salbutamol. Healthy subjects inhaled 2 mg of methacholine, whereas subjects with asthma inhaled the dose of methacholine causing a 15% fall in FEV(1), as determined by a previous methacholine challenge. LES motility, esophageal pH, and FEV(1) were not significantly different between the three periods in healthy subjects. In patients with asthma, methacholine induced a 21.9 +/- 2.6% decrease in FEV(1) and a concomitant increase in the rate of transient LES relaxation (TLESR) and reflux episodes. Inhalation of salbutamol decreased the rate of TLESRs but not the number of reflux episodes. We conclude that in patients with asthma, methacholine-induced bronchospasm increases the rate of TLESR and the number of reflux episodes. These results support the belief that, in asthma, bronchial obstruction may be responsible for reflux or may aggravate reflux through a mechanism that remains to be further clarified.

Platelet activating factor (PAF) is a potent mediator potentially involved in the pathogenesis of inflammatory disorders, including bronchial asthma. Recently, transgenic mice overexpressing the PAF receptor (PAFR) gene have been established, and exhibit bronchial hyperresponsiveness, one of the cardinal features of asthma. To elucidate the molecular and pathophysiologic mechanisms underlying PAF-associated bronchial hyperreactivity, we studied airway responsiveness to methacholine (MCh) and serotonin (5-hydroxytryptamine; 5-HT) in PAFR-transgenic mice. In addition, we examined the role of the muscarinic receptor in PAF-induced responses and the binding activities of the muscarinic receptor. The PAFR-transgenic mice exhibited hyperresponsiveness to MCh and PAF; however, no significant differences in 5-HT responsiveness were observed between the control and PAFR-transgenic mice. The administration of atropine significantly blocked PAF-induced responses in PAFR-transgenic mice. There were no differences between the two phenotypes in the binding activities of muscarinic receptor. Morphometric analyses demonstrated that PAFR overexpression did not affect airway structure. These findings suggest that the muscarinic pathway may have a key role in airway hyperresponsiveness associated with PAFR gene overexpression. More generally, PAFR-transgenic mice may provide appropriate models for study of the molecular mechanisms underlying PAF-associated diseases.

Although the renin-angiotensin system is activated in patients with asthma during severe acute attacks and angiotensin II has been shown to cause bronchoconstriction in patients with asthma, the role of angiotensin II in patients with asthma is unclear. We investigated the effects of two specific antagonists at type 1 and type 2 angiotensin II receptors, candesartan cilexetil (TCV-116) and PD123319, on antigen-induced airway reactions in guinea pigs. Sixty minutes after intraperitoneal administration of candesartan cilexetil (0.1, 1.0, or 10 mg/kg) or PD123319 (30 mg/kg), animals received an antigen challenge. Airway responsiveness to inhaled methacholine was assessed as the dose of methacholine required to produce a 200% increase in the pressure at the airway opening (PC(200)). Differential cell counts in bronchoalveolar lavage fluids (BALF) were measured 24 h after antigen challenge. Candesartan cilexetil did not inhibit antigen-induced bronchoconstriction in sensitized guinea pigs or alter PC(200) in nonsensitized guinea pigs. Antigen inhalation significantly increased bronchoconstrictor responses to methacholine and increased airway accumulation of eosinophils; both responses showed dose-dependent prevention by candesartan but not by PD123319. These results indicate that endogenous angiotensin II promotes antigen-induced airway hyperresponsiveness and eosinophil accumulation by acting at type 1 receptors.

The relationship between increased airway responsiveness and asthma severity in children is unclear. The Childhood Asthma Management Program (CAMP) with 1,041 children with mild to moderate asthma offers an opportunity to relate the concentration of methacholine that causes a 20% fall in FEV(1) (PC(20)) to level of lung function, occurrence of respiratory symptoms, duration of disease, and assessment of severity by clinical staff. Decreasing PC(20) was found to be associated with lower levels of lung function (prebronchodilator percent predicted FEV(1): r = 0.29, beta = 3.5, p < 0.001), the occurrence of chronic asthma symptoms, persistent wheezing (odds ratio [OR] = 1.66, p < 0.001), subjective clinical staff assessment of asthma severity (p < 0.001), and longer duration of asthma (r = -0.11, beta = -0.20, p < 0.002). These data provide evidence that the degree of airway responsiveness is linked to disease severity in children with mild to moderate asthma.

This longitudinal study (1992-1994) was performed to determine the relation between accidental chlorine exposure and changes in lung function and airway responsiveness in 239 workers in a metal production plant. These workers had taken part in a cross-sectional survey in 1992. In both the initial and the follow-up surveys, history of exposure to chlorine ("puffs"), accidental chlorine inhalation reported to the first-aid unit (gassing incidents), and of chronic symptoms were documented; spirometry and methacholine challenge tests were performed. At follow-up, 211 workers (88.3%) were seen. In workers with 20 pack-years or more of cigarette smoking, the fall in FEV(1) was associated with having had a gassing incident during the follow-up period; the fall in FEV(1)/FVC (%) was predicted by the number of puffs causing mild symptoms between the two assessments. An increase in airway responsiveness (PC(20) decrease > 1.5-fold) was present in 19 workers; it was associated with accidents reported to the first-aid unit during the previous 2 yr (OR: 5.9, 95% CI: 1.1 to 32.3). These findings suggest: (1) an effect on airway function related to the estimated number of puffs with mild symptoms and gassing incidents, mostly among smokers; (2) a detectable increase in airway responsiveness associated with gassing incidents.

We tested the hypothesis that airway wall dimensions are important determinants for the mechanical properties of airways. Lung tissue was obtained from 31 smokers with different degrees of chronic obstructive pulmonary disease (COPD) who were operated on for a solitary lung lesion. Segments of small airways (n = 35) were mounted on cannulas in an organ bath and inflated and deflated cyclically between +15 and -15 cm H(2)O. For each airway this was done at baseline, after methacholine, and after isoprenaline. Specific compliance (sCdyn), specific hysteresis (seta), and pressure at which the airways collapsed (Pcol) were calculated from each recording. Airway wall dimensions were measured morphometrically. Lung function parameters of airflow obstruction were correlated to sCdyn, seta, and Pcol. At baseline, after methacholine, and after isoprenaline sCdyn was 0.059, 0.052, and 0. 085 cm H(2)O(-)(1), seta was 13.5, 12.9, and 7.1%, and Pcol was -3.4, -3.5, and -1.9 cm H(2)O, respectively. Differences between sCdyn, seta, and Pcol after methacholine and after isoprenaline were highly significant (p < 0.001). Of all dimensions studied, smooth muscle area, but not total wall area, was the most important determinant for sCdyn and for seta after methacholine. Specific hysteresis at baseline correlated to residual volume as a fraction of total lung capacity (RV/TLC) (r = 0.5, p = 0.05) and, in the presence of methacholine, to FEV(1)/FVC (r = -0.68, p = 0.02) and RV/TLC (r = 0. 5, p = 0.05). We conclude that, in this study, smooth muscle area and smooth muscle tone, but not total wall area, are determinants for compliance, hysteresis, and collapsibility of isolated airways obtained from smokers.

Airway responsiveness is known to be partly explained by geometric and anatomic factors. This cross-sectional investigation was undertaken to determine whether FEF25-75/FVC as a surrogate measure of airway size relative to lung size is associated with airway responsiveness to methacholine. Posteroanterior chest radiographs and spirometry were performed on a group of 929 middle aged and older men from an ongoing longitudinal study, the Normative Aging Study, who returned for their regularly scheduled examination between 1984 and 1989. Subjects had a mean age of 60.5 +/- 7.7 yr. FEV1, FEF25-75, and FVC were taken from spirometric results and FEF25-75/FVC ratios were obtained. Main bronchus (MB) and tracheal (TR) diameters and lung area (LA) were obtained from chest radiographs, and ratios of MB/LA and TR/LA were calculated for each subject and compared with FEF25-75/ FVC as measures of airway size relative to lung size. In a multiple linear regression model adjusting for age, height, initial FEV1, smoking, eosinophil count, and IgE level, FEF25-75/FVC was significantly related to the degree of methacholine airway responsiveness as measured by Log10 dose response slope (beta = -0.37, p < 0.001). Controlling for the same variables, both MB/LA (beta = -149.07, p < 0.001) and TR/LA (beta = -125.87, p < 0.001) were significant predictors of the degree of bronchial responsiveness in separate regression models; however, their effects were greatly attenuated when FEF25-75/ FVC was present in the same model. Similar results were obtained after excluding subjects with FEV1/ FVC

We examined the reduced responsiveness to beta-adrenergic receptor agonists (beta-agonists) after exposure to beta-agonists, and the mechanisms underlying this phenomenon in isolated human tracheal smooth muscle, using isometric tension records to test the hypothesis that repeated inhalation of beta-agonists leads to reduced responsiveness to beta-agonists. The inhibitory effects of isoproterenol (ISO) on contraction by spasmogens participating in asthma attacks diminished markedly after continuous exposure to ISO (0.0003 to 3 microM) for 45 min; moreover, when ISO was repeatedly applied for 10 min to tissues precontracted by methacholine every 30 min, the relaxant effects of ISO gradually attenuated after these repeated applications. In contrast, reduced beta-adrenergic relaxation after continuous and repeated exposure to agonists did not occur when tissues were preincubated with 2 microg/ ml cholera toxin (CTX), which irreversibly activates guanosine triphosphate (GTP)-binding protein (Gs) coupled with beta-adrenergic receptors, for 6 h. However, the CTX inhibition disappeared in the presence of iberiotoxin, a selective inhibitor of large conductance Ca2+-activated K+ (KCa) channels. Our results demonstrate that continuous and repeated exposure to beta-agonists leads to beta-adrenergic desensitization, and that activation of KCa channels by Gs prevents this desensitization.

Antigen challenge causes beta2-adrenoceptor dysfunction in sensitized human bronchi (Am. J. Respir. Crit. Care Med. 1997;155:1230-1234). This study investigated whether the dysfunction can be prevented by anti-inflammatory agents. Human bronchial rings (2 to 4 mm) from surgery were passively sensitized to house dust mite and challenged (1) with allergen only, (2) with allergen plus indomethacin (10(-)5 M), (3) with allergen plus nedocromil sodium (10(-)7 M to 10(-)5 M), (4) with allergen plus the H1-receptor antagonist cetirizine (10(-)7 M to 10(-)5 M), and (5) with allergen plus the peptido-leukotriene receptor antagonist iralukast (10(-)7 M to 10(-)5 M). Rings were first contracted with 10(-)6 M carbachol and then relaxed with salbutamol (10(-)9 M to 10(-)4 M). The concentration-relaxation curve to salbutamol was shifted significantly to the right in the rings challenged with allergen only compared with control rings. In the rings challenged with allergen plus nedocromil sodium (10(-)6 M and 10(-)5 M) or iralukast (10(-)6 M and 10(-)5 M) the concentration-relaxation curves to salbutamol were significantly shifted to the left compared with rings challenged in saline alone, suggesting a protective effect against beta2-adrenoceptor dysfunction. Neither allergen plus cetirizine nor allergen plus indomethacin shifted significantly the concentration-relaxation curves to salbutamol compared with rings challenged in saline alone. We conclude that the release of peptido-leukotrienes may play a significant role in causing the allergen-induced beta2-receptor dysfunction in passively sensitized human bronchi.

In a guinea pig model of allergic asthma, we have recently established that a deficiency of nitric oxide (NO) contributes to the increased ex vivo responsiveness of isolated perfused tracheae to methacholine after the early asthmatic reaction at 6 h after inhalational challenge of the animals with ovalbumin aerosol. Because this deficiency could be caused by a reaction of NO with enhanced levels of inflammation-induced superoxide anion (O-2), we examined the effect of endogenous O-2 on the regulation of methacholine-induced constriction by NO of intact perfused tracheal tube preparations from unchallenged (control) guinea pigs and from animals 6 h after ovalbumin challenge. In the presence of the NO synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 100 microM), tracheae obtained from unchallenged guinea pigs showed a 1.7-fold increase in the maximal response to intraluminally applied methacholine (p < 0.05). By contrast, the maximal airway response to methacholine was significantly decreased in the presence of the O-2 scavenger superoxide dismutase (SOD; 100 U/ml), by approximately 45% (p < 0.01). The SOD-induced decrease in responsiveness to methacholine was reversed by L-NAME. Tracheal preparations obtained at 6 h after allergen challenge showed a 1. 8-fold increased responsiveness to intraluminally applied methacholine compared with controls (p < 0.001), which was not further enhanced in the presence of L-NAME. SOD had neither an effect on the increased responsiveness nor did it restore the potentiating effect of L-NAME. These results indicate that (1) in normoreactive tracheal preparations, the regulatory role of NO is partially counteracted by endogenous O-2, and ( 2) the deficiency of NO in hyperreactive tracheae obtained at 6 h after ovalbumin challenge is not caused by its reaction with O-2, but rather to decreased cNOS activity. De Boer J, Pouw FMH, Zaagsma J, Meurs H. Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways.

Cyclooxygenase products modulate the expression of nitric oxide synthase (NOS) in certain cell types. We determined the effect of prostaglandins (PG) E2 and F2alpha on exhaled nitric oxide (NO) concentrations measured by chemiluminescence. Inhaled PGE2 and PGF2alpha significantly reduced exhaled NO. After the highest dose of PGE2 (100 micrograms), NO concentrations fell from 6.9 +/- 0.5 ppb to 4.0 +/- 0.8 ppb (p < 0.001), and from 22.9 +/- 2.0 ppb to 12.3 +/- 1. 2 ppb (p < 0.001), whereas after PGF2alpha, it fell from 6.5 +/- 0.6 ppb to 3.0 +/- 0.5 ppb (p < 0.001), and from 26.0 +/- 3.4 ppb to 11. 5 +/- 1.4 ppb (p < 0.001) in normal (n = 7) and asthmatic (n = 8) subjects, respectively. Although the prostaglandins did not change FEV1 in normal subjects, PGE2 caused an increase in asthmatics (from 3.6 +/- 0.3 L to 3.8 +/- 0.4 L, p < 0.05) and PGF2alpha caused a transient reduction in FEV1 from 4.0 +/- 0.2 L to 3.5 +/- 0.2 L (p < 0.05). To further determine the relationship between bronchoconstriction and exhaled NO levels, we examined the effect of inhaled methacholine which did not change exhaled NO concentrations in normal and asthmatic subjects despite a greater than 20% fall in FEV1 in asthmatics. Therefore, PGE2 and PGF2alpha reduce exhaled NO, an effect not related to airway caliber changes but which may result from an inhibition of nitric oxide synthase (NOS), particularly inducible NOS (iNOS).

Airway hyperresponsiveness in asthma has been attributed to impaired ability of deep inspiration (DI) to stretch airway smooth muscle. We have retested this hypothesis by comparing the responses to methacholine of 10 asthmatic and 10 control subjects. After each dose subjects breathed tidally without deep inspiration for 4 min, followed by a forced partial expiration from which flow was measured at a constant volume, 35% baseline VC (Vp 35). This index is independent of both DI and increases in end-inspiratory lung volume (EILV). EILV increased significantly more in the asthmatic group than in the control group (15.0 versus 2.5% of baseline VC, p = 0. 019), a factor that if not taken into account would tend to mask the difference in the two responses. Comparisons were made after a cumulative dose of 50 microg methacholine, which was the highest dose common to all subjects. The asthmatic response was significantly greater than that seen in the control group, with reductions to 25.9 and 72.1% of baseline Vp 35, respectively (p = 0. 0007). We conclude that the sensitivity of asthmatic airways to methacholine is greater than that of normal airways even when DI is prohibited. Therefore, the hyperresponsiveness of asthmatic airways is not attributable simply to an inability of DI to stretch airway smooth muscle.

Inhalational challenges to histamine and methacholine (Mch) are commonly used to measure airway reactivity. In this study, we investigated the serial distribution of individual airway responsiveness in vivo following stimulation with histamine or methacholine by directly measuring airway area with high resolution computed tomography (HRCT). Anesthetized dogs were challenged on separate days to increasing aerosol concentrations of histamine or Mch. Airway areas of 13 or 14 individual airways in each dog ranging in size from 1.1 to 16.9 mm in diameter at baseline were measured. Dose response curves for each agonist showed a similar responsiveness to each agonist over all airway sizes measured. There was a slightly greater individual airway responsiveness to Mch throughout the airway tree, and this greater responsiveness was also present in those airways that are responsible for the decreased Cdyn observed with Mch challenge. We conclude that in vivo aerosol challenges with histamine or methacholine do not lead to preferential construction of large or small airways.