The effect of inflammation on mucociliary clearance in asthma: an overview.

Mucociliary clearance (MCC) is one of the most important nonspecific defense mechanisms of the respiratory tract, and its impairment is a well-documented feature of chronic respiratory diseases, including asthma. In vitro and in vivo data suggest that several inflammatory mediators influence the mucociliary apparatus. Epithelial damage and functional abnormalities have been described in bronchial asthma, along with changes in mucus-secreting cells and the chemical and rheological properties of airway fluid. Although the mechanisms of MCC impairment in asthma are not clearly understood, data in the recent literature suggest that airway inflammation plays a major role. In this article, we review studies on MCC alterations in light of up-to-date findings on pathogenetic mechanisms in asthma.

Relationship between bronchial reversibility and tracheobronchial clearance in patients with chronic bronchitis.

BACKGROUND: Patients with chronic bronchitis show a large intersubject variation in sputum rheology, tracheobronchial clearance, and reversibility of airflow obstruction to beta 2 agonists. The bronchial mediators which are known to cause bronchoconstriction, mucosal oedema, mucus hypersecretion, and cough can also affect mucociliary transport. The aim of this study was to ascertain whether changes in tracheobronchial clearance and sputum rheological properties in patients with chronic bronchitis were associated with a specific degree of airflow reversibility assessed as the bronchial response to an inhaled beta 2 agonist (fenoterol 400 micrograms). METHODS: Bronchial reversibility (percentage change in baseline forced expiratory volume in one second (FEV1)) was measured in 26 patients with chronic bronchitis on three separate occasions, at least one week apart. Tracheobronchial clearance was evaluated by a non-invasive radioaerosol technique, and an oscillatory viscometer was used for measuring sputum apparent viscosity and elasticity. The number of coughs (productive and nonproductive coughs), the wet weight of sputum, and its radioaerosol content were recorded during the six hour clearance period, as well as the 24 hour sputum production. RESULTS: The change in FEV1 after fenoterol was less than 15% in 12 patients and more than 15% in 14. Patients with airways reversibility of more than 15% had faster tracheobronchial clearance, more coughs, lower sputum viscosity and elasticity, and larger 24 hour sputum production than those with airways reversibility of less than 15%. CONCLUSIONS: In patients with chronic bronchitis a large bronchodilator response is associated with faster clearance of mucus by mucociliary transport and coughing.

Effect of temazepam on tracheobronchial mucus clearance.

BACKGROUND: Tracheobronchial clearance of mucus from the lungs is reduced during sleep and, usually, by the administration of opiates. It seemed possible therefore that temazepam, a widely used potent benzodiazepine, retarded clearance. METHODS: The effect of 10 mg temazepam on mucociliary clearance was studied in eight healthy volunteers, aged 18-50 (mean 30) years, in a randomised, placebo controlled, double blind, cross-over study. Six subjects were female and two male. Six were non-smokers and two were light current smokers. Clearance was assessed from the change in radio-activity in the lungs after inhalation of 5 microns diameter polystyrene particles, labelled with technetium-99m, under controlled conditions. RESULTS: Tracheobronchial clearance was reduced by 22% after temazepam by comparison with placebo during the first three hours after drug ingestion; this is the period when circulating drug concentrations are highest. CONCLUSION: Temazepam should be prescribed with caution in patients with impaired lung mucociliary transport.

Suitability of cryopreserved samples for pharmacological studies of ciliary activity.

The effect of terbutaline sulfate on the ciliary activity of fresh and cryopreserved human nasal epithelium was evaluated. Cryopreservation had no effect on baseline ciliary beat frequency. Both fresh and cryopreserved samples exposed to 10(-4) M terbutaline showed a statistically significant increase in ciliary beat frequency (27 and 25%, respectively). When the percentage changes after drug challenge for fresh and cryopreserved samples were compared no statistical difference emerged. It is concluded that cryopreservation in liquid nitrogen at -196 degrees C does not affect membrane receptors, at least beta-adrenergic receptors, and therefore cryopreserved samples are suitable for pharmacological studies of ciliary activity.

Effect of amiloride on human bronchial ciliary activity in vitro.

Amiloride (AM) reduces mucociliary transport in the frog palate in vitro preparation, whereas in vivo inhalation of AM enhances mucociliary and cough clearance in cystic fibrosis patients. AM influences the bioelectric properties of the respiratory mucosa, and since electrical activity and ciliary activity are strictly related in the beating cell, an effect on ciliary function cannot be excluded. We have, therefore, investigated the effect of AM (10(-7) to 10(-3) M) in vitro on the ciliary activity of ten samples of healthy human bronchial epithelium at 37 degrees C. The baseline ciliary beat frequency was 13.7 +/- (SD) 1.0 Hz. At concentrations of AM of 10(-4) and 10(-3) M, small statistically significant (p less than 0.01) increases in ciliary beat frequency were recorded only after 1 min of exposure to the drug, with changes of +8.2 and +7.6%, respectively. We conclude that (1) AM affects the ciliary activity of the beating cell, but (2) because of the weakness and short duration of the effect, it is unlikely that AM plays a major role on mucociliary transport.

The effect of cryopreservation on ciliary beat frequency of human respiratory epithelium.

The effect of cryopreservation on ciliary activity of human nasal respiratory epithelium was evaluated. Samples were cryopreserved in a solution containing nutrient medium, 10% fetal calf serum, and two different concentrations (10 or 20%) of dimethyl sulfoxide and stored in liquid nitrogen at -196 degrees C for 2 weeks. Ciliary beat frequencies (CBF) of the samples before and after cryopreservation were compared. Mean CBF values did not differ significantly with both concentrations of dimethyl sulfoxide. The mean intrasample coefficient of variation of the CBF decreased significantly after cryopreservation. After thawing, CBF remained unchanged for at least 4 hr. It is concluded that normal ciliated epithelial cells can be frozen and stored in liquid nitrogen at 196 degrees C while maintaining their CBF.

Effect of four-week treatment with oxitropium bromide on lung mucociliary clearance in patients with chronic bronchitis or asthma.

The effect of oxitropium bromide on lung mucociliary clearance, pulmonary function and viscoelastic properties of sputum was investigated in 10 asthmatics and 10 chronic bronchitics. A controlled, double-blind, crossover study was performed. Following a baseline (B) measurement the patients were, in a random order, allocated placebo (P) or oxitropium bromide (O; 0.1 mg/puff), administered from metered dose inhalers, which they used for 4 weeks at a dose of 2 puffs t.d.s. This test medication was used in conjunction with their normal medication. At the end of the treatment period the patients were assessed, the treatments were then crossed over and a final assessment made 4 weeks later. The administration of oxitropium bromide resulted in (1) small but statistically significant increases in pulmonary function (less than 10% vs. placebo); (2) increased penetrance of radioaerosol into the lungs (mean +/- SEM alveolar deposition: 35 +/- 3, 26 +/- 3 and 24 +/- 3% for the O, P and B runs respectively; p less than 0.025); (3) no significant change in particle clearance rate from the lungs despite their deeper penetration (mean +/- SEM area under the tracheobronchial clearance curves between 0 and 6 h: 317 +/- 26, 324 +/- 25 and 287 +/- 25%.h for the O, P and B runs respectively; p greater than 0.1); (4) no alteration in sputum production, and (5) no significant changes in apparent viscosity (mean +/- SEM: 640 +/- 162, 446 +/- 79 and 557 +/- 115 mPa.s for the O, P and B runs, respectively; p greater than 0.1) and elasticity (mean +/- SEM: 3,682 +/- 1,383, 1,779 +/- 353 and 2,061 +/- 366 mPa for the O, P and B runs, respectively; p greater than 0.1) of sputum. When the two groups, i.e. the chronic bronchitics and asthmatics, were studied separately, no significant differences in any parameter measured (other than radioaerosol penetrance which was significantly enhanced on oxitropium bromide in chronic bronchitics) were noted between the three assessments.

Mucus as a natural barrier.

The airway mucus varies in amount, composition and physical properties at different levels of the airways and thus variation in types and/or degree of defence are expected. The mucus barrier, that is the barrier provided by the secretory products from the mucous membrane, comprises three compartments: the epiphase (gel layer); the hypophase (sol layer), and the glycocalyx. The epiphase is the best characterized of the three and, because of its direct contact with the external environment, is the more complex and can act as a physical, chemical and biological barrier. The hypophase and the glycocalyx barriers are less well known in terms of composition, origin, control and functions. The periciliary/sol layer, apart from providing a suitable environment for the cilia, can further dilute substances which have crossed the gel layer. The glycocalyx represents the last protective barrier for the cell membrane and is likely to play an important role in the defence of the surface epithelium. A better understanding of their origin, composition and control, both in health and disease, will help us to choose the appropriate therapeutic agent for enhancing their efficacy as natural barriers.

Variability and reproducibility in the measurement of tracheobronchial clearance in healthy subjects and patients with different obstructive lung diseases.

The purpose of this study was to establish the inter- and intra-subject/patient variability of tracheobronchial clearance, measured for 6 h, using a radioaerosol technique. Inter-subject variability was evaluated in five groups: 33 healthy non-smokers (NS); 19 asymptomatic smokers (S); 40 asthmatics (A); 27 chronic bronchitics (CB) and 12 bronchiectatics (B). Intra-subject variability was evaluated in 16 A and 27 CB who were studied twice. The inter-subject/patient coefficient of variation (CoV) of tracheobronchial clearance was 13% for NS and 28-39% for the remaining four groups. The intra-patient CoV was about half of the inter-patient CoV. Inter-subject CoV (for A and CB) appeared to be independent of initial tracheobronchial deposition of radioaerosol and frequency of cough. We were also able to estimate the approximate number of patients required for a crossover study in order to avoid statistical, type II errors when investigating the effect of a drug or of a therapeutic intervention on tracheobronchial clearance.

Impaired mucus clearance in patients with chronic bronchial sepsis, sinusitis and dextrocardia.

Published reports have indicated that patients with Kartagener's syndrome (dextrocardia, sinusitis and bronchiectasis) have no significant lung mucociliary clearance. With a radioaerosol technique we measured over a 6-hour observation period the tracheobronchial clearance of 8 patients with dextrocardia, chronic bronchial sepsis and chronic sinusitis (DC). The tracheobronchial clearance of these patients was significantly reduced (p less than 0.02) compared with that of 29 healthy subjects of similar age. However, even when allowance was made for productive coughing during the observation period, the reduced clearance was much better than anticipated from published reports in patients with Kartagener's syndrome, which confined their observations to a 2-hour period. The tracheobronchial clearance of the DC patients, adjusted for productive coughing, was as bad as that found in an older group of patients with chronic obstructive airways disease who refrained from expectorating during the equivalent test period. Our study implies one or more of the following possibilities: (a) a spectrum of mucociliary impairment in patients with DC; (b) an effective cough clearance deeper in the lung than hitherto believed, and (c) two-phase flow of mucus cephalad as an effective clearance mechanism in patients with DC.

Effect of terbutaline administered from metered dose inhaler (2 mg) and subcutaneously (0.25 mg) on tracheobronchial clearance in mild asthma.

Tracheobronchial mucus clearance was measured in nine mild asthmatics, using an objective radioaerosol technique, on 3 separate days at intervals of 1 week. Immediately after radioaerosol inhalation, drug or placebo was administered via subcutaneous injection (SC) plus metered dose inhaler (MDI)--2 puffs. Three randomized treatments were used: saline placebo SC plus 2 mg terbutaline by MDI (1 mg per puff); 0.25 mg terbutaline SC plus placebo (propellants and surfactant only) by MDI; and double placebo. Changes in lung mucociliary clearance showed an inverse relationship to baseline clearance of both proximal and distal ciliated airways following inhaled terbutaline, whereas terbutaline SC related inversely only to baseline clearance of the distal ciliated airways. This may reflect the surface concentrations of drug, established by each route.

Impaired tracheobronchial clearance in bronchiectasis.

Tracheobronchial clearance was measured by a radioaerosol technique in 12 patients with bronchiectasis, seven patients with chronic obstructive lung disease expectorating mucoid sputum daily (group X), eight patients with chronic obstructive lung disease but negligible sputum expectoration (group Y), and 10 healthy subjects. The patients with bronchiectasis all expectorated purulent sputum daily (mean wet weight 47 g/day), had reduced forced expiratory volume in one second (FEV1) (mean 47.5% predicted), and were unable to avoid coughing during the six hour observation period. None of the patients with bronchiectasis or the healthy subjects were current smokers. There were five current smokers in group X and six in group Y. The mean FEV1 in group X was 41% predicted and in group Y 52% predicted, both values similar to that of the patients with bronchiectasis. Tracheobronchial clearance in the first six hours after inhalation of radioaerosol was significantly (p less than 0.01) slower in patients with bronchiectasis than in matched healthy subjects despite more proximal deposition of radioaerosol (p = 0.01) and more coughing (p less than 0.01) in the former. Tracheobronchial clearance in patients with bronchiectasis was impaired to a similar degree to that in patients with chronic obstructive lung disease but no bronchiectasis.

Mucus clearance from peripheral airways.

Mucociliary clearance data obtained with 5 microns radioaerosol particles have been analyzed for asymptomatic young cigarette smokes and non-smokers. The rate and the amount of peripheral zone clearance were both considered in relationship to the overall depth of radioaerosol lung penetration. In the smokers, but not in the non-smokers, the forms of relationship found appeared compatible with prediction based on simple mathematical modelling of aerosol deposition sites within the lung. We suggest that the results found in the non-smokers are attributable to poor mucociliary defence (which is rarely required) of their more distal peripheral airways--due presumably to low levels of cross-linked glycoprotein mucus in these airways--whilst those in the smokers functionally reflect the presence of an increased supply of mucus appropriate for mucociliary transport.

General review of tracheobronchial clearance.

The human tracheobronchial tree possesses several mechanisms for keeping itself clean and sterile. Mucociliary clearance results from the beating action of cilia lining the conducting airways and propelling the overlying mucus cephalad. Locally produced biological debris and inhaled, insoluble material are swept with the mucus and removed from healthy lungs within one day. Cough augments the often impaired mucociliary clearance of patients with excessive secretions. Cough is limited in is efficacy to the proximal airways. Energy transfer from airflow to mucus transport in airways lined with excessive secretions has been put forward as a third mechanism (two-phase gas-liquid flow) for the removal of lung secretions. Other mechanisms that have been proposed for clearance of lung secretions are: 'milking', 'squeezing' and peristalsis.

Biochemical basis of physical properties of respiratory tract secretions.

The physical properties of respiratory tract secretion (RTS) play a prominent rôle in the non-specific defence mechanisms of the lung. Viscosity and elasticity, that is flow and deformation, are only two of the physical properties of RTS. Spinability, pourability, adhesiveness and tackiness are starting to be recognised as physical properties of RTS and its is likely that they may be relevant in the pathogenesis of airways obstruction. RTS is a gel, which consists of a cross-linked polymer network dispersed in a liquid solvent. The polymeric structure of the epithelial glycoprotein can be explained in terms of covalent (disulphide) linkages and/or physical entanglement between glycoproteins subunits. Other constituents of RTS such as proteins, lipids, ions and water can influence the physical properties of RTS.

Mediators and mucociliary clearance in asthma.

Lung mucociliary clearance is significantly reduced in asthmatic patients compared to healthy controls even during clinical remission. Further retardation in mucous clearance occurs during sleep per se and this may be a contributing factor to nocturnal asthma. Chemical mediators of anaphylaxis appear to have various and, sometimes opposing effects on the two essential components for mucociliary clearance, namely cilia and mucus. Some mediators such as leukotrienes C4 and D4 are potent secretagogues and histamine increases the water flux into the lumen of the airways from the mucosa. Slow-reacting substance of anaphylaxis (SRS-A) reduces mucus transport whereas histamine enhances it. Ciliostimulation has been reported following allergen challenge and this contrasts with the cilioinhibitory effect of asthmatics' sputa. It appears however, that the net effect of the various chemicals of anaphylaxis is one of impairment of mucus clearance. Some pharmacological agents, used for the relief of bronchospasm and control of asthma, also stimulate mucociliary transport, a desirable additional effect.

Protective effect of methylxanthines against carbachol-induced bronchoconstriction in normal subjects.

The bronchoprotective effect of bioequivalent doses of theophylline (TH; 234 mg) and a combination of TH, proxyphylline (PPH) and diprophylline (DPH) in the proportion 2:3:3 (Neo-Biphyllin, NB; 600 mg) against carbachol-induced bronchoconstriction was studied in 10 healthy non-smokers in a randomised controlled double-blind cross-over trial. The subjects were on a methylxanthine-free diet 4 days prior to and during each study day. Bronchial provocation tests were conducted in the morning and afternoon of the three separate study days--control and two medication days--using a standardised technique. On the control day, the dose of carbachol required to reduce the partial expiratory flow volume at 25% of vital capacity (V25p) by at least 25% was established. A significant protective effect was achieved with both TH (p less than 0.05) and NB (p less than 0.001) as measured by V25p. Bronchoprotection was achieved with low maintenance serum levels of TH.

Development of the airway epithelium and submucosal glands in the pig lung: changes in epithelial glycoprotein profiles.

Glycoproteins in the normal airway surface epithelium and submucosal glands of 13 Large White pigs were studied from birth to adult life using alcian blue (AB) staining at pH 2.6 or at pH 1.0, with and without sialidase digestion, and by the combination of AB and PAS (AB/PAS) stains. Immediately after birth the percentage of cells producing acidic and neutral glycoproteins increased in both airway surface epithelium and submucosal glands. In the airway surface epithelium, the percentage of mucus-secreting cells producing sulphated glycoprotein increased with age, whereas in the submucosal glands the glycoproteins were mainly sulfated between birth and 3 days and sialylated between 3 days and adult life. The percentage of cells producing neutral glycoprotein in the airway surface epithelium increased during the first 24 h of life after which there was little change with age. In the submucosal glands, however, the greatest increase in the percentage of cells producing neutral glycoprotein occurred between 7 days and adult life. The rapid increase of intracellular glycoprotein production at birth and the presence of the same types of glycoprotein in the immature pig and mature human lung, suggest that the pig may be a useful model in which to study mechanisms and changes of glycoprotein synthesis and secretion during lung development.