Neurokinin receptors subserving airways secretion

Mucus secretion can be induced in the airways by activation of nerves. The principal mechanism mediating neurogenic mucus secretion is cholinergic. However, a small but significant secretory response remains after adrenoceptor and cholinoceptor blockade. The identity of this nonadrenergic, noncholinergic (NANC) neural mechanism is unclear but includes an orthodromic pathway and a capsaicin-sensitive "sensory-efferent" (or "local effector") pathway. The orthodromic pathway comprises cholinergic nerves (and to a much lesser extent adrenergic nerves) in which neuropeptides, including vasoactive intestinal peptide (VIP) and neuropeptide tyrosine (NPY), are colocalised and coreleased with the classical neurotransmitter. Investigation of the contribution of the orthodromic neural pathway to neurogenic secretion awaits development of selective receptor antagonists for VIP and NPY. The neurotransmitters of the sensory-efferent neural pathway include calcitonin gene related peptide and the tachykinin receptor agonists indicates that the tachykinin NK1 receptor is ubiquitous for airway secretory processes, including mucus secretion and ion transport. Antagonist studies show that the great proportion of the NANC neural mucus secretory response is mediated via NK1 receptors, with little or no contribution from NK2 receptors. The relevance of the sensory-efferent neural pathway in health is equivocal, but it may have increasing importance in chronic inflammatory bronchial diseases associated with mucus hypersecretion, for example, asthma and chronic bronchitis, in which there is some evidence for the potential for increased sensory-efferent neural activity.     

The relationship of chronic mucin secretion to airway disease in normal and CFTR-deficient mice

In the cystic fibrosis (CF) patient, lung function decreases throughout life as a result of continuous cycles of infection, particularly with Pseudomonas aeruginosa and Staphylococcus aureus. The mechanism underlying the pathophysiology of the disease in humans has not been established. However, it has been suggested that abnormal, tenacious mucus, resulting perhaps from improper hydration from loss of Cl- secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) protein, impairs clearance of bacteria from the CF airway and provides an environment favorable to bacterial growth. If this hypothesis is correct, it could explain the absence of respiratory disease in CFTR-deficient mice, since mice have only a single submucosal gland and display few goblet cells in their lower airways, even when exposed to bacteria. To test this hypothesis further, we induced allergic airway disease in CFTR-deficient mice. We found that induction of allergic airway disease in mice, unlike bacterial infection, results in an inflammatory response characterized by goblet cell hyperplasia, increased mucin gene expression, and increased production of mucus. However, we also found that disease progression and resolution is identical in Cftr-/- mice and control animals. Furthermore, we show that the presence of mucus in the Cftr-/- airway does not lead to chronic airway disease, even upon direct inoculation with S. aureus and P. aeruginosa. Therefore, factors in addition to the absence of high levels of mucus secretion protect the mouse from the airway disease seen in human CF patients.     

The natural history of chronic airflow obstruction

A prospective epidemiological study of the early stages of the development of chronic obstructive pulmonary disease was performed on London working men. The findings showed that forced expiratory volume in one second (FEV1) falls gradually over a lifetime, but in most non-smokers and many smokers clinically significant airflow obstruction never develops. In susceptible people, however, smoking causes irreversible obstructive changes. If a susceptible smoker stops smoking he will not recover his lung function, but the average further rates of loss of FEV1 will revert to normal. Therefore, severe or fatal obstructive lung disease could be prevented by screening smokers' lung function in early middle age if those with reduced function could be induced to stop smoking. Infective processes and chronic mucus hypersecretion do not cause chronic airflow obstruction to progress more rapidly. There are thus two largely unrelated disease processes, chronic airflow obstruction and the hypersecretory disorder (including infective processes).     

New drugs in asthma treatment. Leukotriene receptor blockers and leukotriene synthesis inhibitors

Asthma is an inflammatory airway disease. The patient is characterised by increased mucus secretion, mucosal oedema, bronchial obstruction of varying degree and bronchial hyperresponsiveness. Several cell types and a large number of mediators are involved in asthma-related inflammation and constriction of the airways. The leukotrienes constitute an important group of mediators in asthmatic inflammation. The study of specific leukotriene receptor antagonists and biosynthesis inhibitors has not only shed light on the underlying mechanisms in asthma, but also opened up the way to new treatment alternatives. As zafirlukast, a leukotriene receptor antagonist has just been licensed in Finland, it is a suitable opportunity to review the importance of leukotrienes in asthma and the use of agents that affect them.     

Evidence for periciliary liquid layer depletion, not abnormal ion composition, in the pathogenesis of cystic fibrosis airways disease

The pathogenesis of cystic fibrosis (CF) airways infection is unknown. Two hypotheses, "hypotonic [low salt]/defensin" and "isotonic volume transport/mucus clearance," attempt to link defects in cystic fibrosis transmembrane conductance regulator-mediated ion transport to CF airways disease. We tested these hypotheses with planar and cylindrical culture models and found no evidence that the liquids lining airway surfaces were hypotonic or that salt concentrations differed between CF and normal cultures. In contrast, CF airway epithelia exhibited abnormally high rates of airway surface liquid absorption, which depleted the periciliary liquid layer and abolished mucus transport. The failure to clear thickened mucus from airway surfaces likely initiates CF airways infection. These data indicate that therapy for CF lung disease should not be directed at modulation of ionic composition, but rather at restoring volume (salt and water) on airway surfaces.     

Aspects of chronic airflow obstruction

This report questions several commonly used definitions and commonly accepted concepts. It suggest that the term, "chronic airflow obstructions," should replace the terms, "chronic obstructive pulmonary disease," "chronic obstructive lung disease," or "chronic airway obstruction," because it is flow that is obstructed. It is suggested the term, "chronic mucous hypersecretion," be used, rather than "chronic bronchitis," and that the latter be avoided. Chronic bronchitis should not be equated with narrowing of the airway and emphysema with loss of elastic recoil. Chronic bronchitis, emphysema, and lesions of the small airways probably occur together more frequently than chance will allow because of a common etiologic agent, tobacco smoke. Chronic mucous hypersecretion without other airway or parenchymal lesions seldom produces airflow obstruction and does not impair prognosis significantly. Central airways are important in chronic airflow obstruction. It is time that someone found out what is happening in subjects with abnormal results on tests of the function of small airways. The definition of "destruction" as it occurs in emphysema is deceptive, and loss of recoil and emphysema may be separate conditions. The dysfunction that occurs in emphysematous lungs is due mainly to associated airway lesions and may perhaps be due in part to the site and nature of emphysematous lesions (as opposed to loss of elastic recoil).     

Effect of heparin on airway goblet cell secretion in sensitized guinea pigs

Heparin and related proteoglycans are released from mast cells and possess anti-inflammatory and anti-complement activities. To elucidate whether heparin affects goblet cell secretion in asthmatic airways and, if so, what the mechanism of action is, we studied guinea pigs sensitized with ovalbumin (OVA) by determining the mucus score (MS) of tracheal goblet cells stained with Alcian blue and PAS. Inhalation of OVA caused a rapid decrease in MS in a dose-dependent manner, with the maximal decrease being from 545 +/- 26 to 192 +/- 35 (p < 0.001), indicating an increase in goblet cell mucus discharge. This effect was selectively inhibited by the histamine H2 receptor blockade with cimetidine. Prior inhalation of heparin inhibited OVA-induced goblet cell secretion in a dose-dependent fashion, but had no effect on histamine-induced goblet cell secretion. The OVA-induced histamine release from the tracheal tissue was likewise inhibited by heparin. These results suggest that allergic challenge stimulates airway goblet cell secretion mainly through the release of histamine and the concomitant activation of histamine H2 receptors on goblet cells, and that heparin protects against this effect by inhibiting the histamine release from mast cells.     

Regulation of airway neurogenic inflammation by neutral endopeptidase

Airway neurogenic inflammation is caused by tachykinins released from peripheral nerve endings of sensory neurons within the airways, and is characterized by plasma protein extravasation, airway smooth muscle contraction and increased secretion of mucus. Tachykinins are degraded and inactivated by neutral endopeptidase (NEP), a membrane-bound metallopeptidase, which is located mainly at the surface of airway epithelial cells, but is also present in airway smooth muscle cells, submucosal gland cells and fibroblasts. The key role of NEP in limiting and regulating the neurogenic inflammation provoked by different stimuli has been demonstrated in a large series of studies published in recent years. It has also been shown that a variety of factors, which are relevant for airway diseases, including viral infections, allergen exposure, inhalation of cigarette smoke and other respiratory irritants, is able to reduce NEP activity, thus enhancing the effects of tachykinins within the airways. On the basis of these observations, the reduction of neutral endopeptidase activity may be regarded as a factor that switches neurogenic airway responses from their physiological and protective functions to a detrimental role that increases and perpetuates airway inflammation. However, further studies are needed to assess the role of neutral endopeptidase down regulation in the pathogenesis of asthma and other inflammatory airway diseases.     

A novel role for murine IL-4 in vivo: induction of MUC5AC gene expression and mucin hypersecretion

Mucus hypersecretion and plugging of lower respiratory tract airways contributes to the morbidity and mortality associated with asthma. Interleukin (IL)-4 plays a putative role in some forms of asthma. Thus, transgenic mice that overexpress murine IL-4 selectively within the lung were used to study the effect of IL-4 on mucus glycoprotein gene expression and mucin release. Histologic examination of lung sections from IL-4 mice revealed that nonciliated epithelial cells from conducting airways were hypertrophic, due at least in part to the accumulation of mucus glycoprotein. The cytoplasm of these cells stained positively for glycoproteins using mucicarmine, alcian blue (AB), and periodic acid-Schiff (PAS). Ciliated cells were also enlarged but did not show any mucin-specific staining. Inclusion granules typically found in nonciliated (Clara) cells of control mice were absent in the IL-4 transgenic mice. Northern blot analysis of total RNA from lung tissue revealed that the expression of the MUC5AC, but not MUC2, mucin gene was distinctly upgraded in IL-4 transgenic mice compared to transgene-negative controls. In addition, a 5- to 10-fold increase in AB- and PAS-positive material was found in lavage fluid from IL-4 overexpressing mice compared to transgene-negative controls. Thus, the overexpression of IL-4 locally within the lung enhances mucus glycoprotein synthesis by altering gene expression, results in the accumulation of mucus glycoprotein in nonciliated epithelial cells, and induces the release of mucus into the airway lumen. We therefore hypothesize that the overproduction of mucus seen in some patients with asthma may be a direct result of the action of IL-4 within the inflamed lung.     

Ion composition of airway surface liquid of patients with cystic fibrosis as compared with normal and disease-control subjects

To test whether a major contribution of airways epithelial ion transport to lung defense reflects the regulation of airway surface liquid (ASL) ionic composition, we measured ASL composition using the filter paper technique. On nasal surfaces, the Cl- concentration (approximately 125 meq/liter) was similar to plasma, but the Na+ concentration (approximately 110 meq/liter) was below plasma, and K+ concentration (approximately 30 meq/liter) above plasma. The resting ASL osmolarity [2(Na+ + K+); 277 meq/liter] approximated isotonicity. There were no detectable differences between cystic fibrosis (CF) and normal subjects. In the lower airways, the Na+ concentrations were 80-85 meq/liter, K+ levels approximately 15 meq/liter, and Cl- concentrations 75-80 meq/liter. Measurements of Na+ activity with Na(+)-selective electrodes and osmolality with freezing point depression yielded values consistent with the monovalent cation measurements. Like the nasal surfaces, no differences in cations were detected between CF, normal, or chronic bronchitis subjects. The tracheobronchial ASL hypotonicity was hypothesized to reflect collection-induced gland secretion, a speculation consistent with observations in which induction of nasal gland secretion produced hypotonic secretions. We conclude that there are no significant differences in ASL ion concentrations between CF, normal, and chronic bronchitis subjects and, because ASL ion concentrations exceed values consistent with defensin activity, the failure of CF lung defense may reflect predominantly factors other than salt-dependent defensins.     

Retinoic acid-regulated cellular differentiation and mucin gene expression in isolated rabbit tracheal-epithelial cells in culture

Rabbit tracheal epithelial cells were cultured in a serum-free and hormone-supplemented medium with and without retinoic acid. The cells showed time-dependent mucin gene expression when cultured in the medium with retinoic acid. In the absence of retinoic acid, however, mucin mRNA was barely detectable in the cells. When retinoic acid was added back to the medium, the mucin message was prominent again. Actinomycin D and cycloheximide did not inhibit mucin gene expression. The mucin message was slightly elevated by cAMP agonists. A mucin antisense oligomer inhibited the retinoic acid-induced mucin mRNA expression and secretion, thus offering an alternate approach in the management of mucus hypersecretion in upper airway respiratory diseases such as chronic bronchitis, asthma, and cystic fibrosis.     

Induction of airway mucus production By T helper 2 (Th2) cells: a critical role for interleukin 4 in cell recruitment but not mucus production

Airway inflammation is believed to stimulate mucus production in asthmatic patients. Increased mucus secretion is an important clinical symptom and contributes to airway obstruction in asthma. Activated CD4 Th1 and Th2 cells have both been identified in airway biopsies of asthmatics but their role in mucus production is not clear. Using CD4 T cells from mice transgenic for the OVA-specific TCR, we studied the role of Th1 and Th2 cells in airway inflammation and mucus production. Airway inflammation induced by Th2 cells was comprised of eosinophils and lymphocytes; features found in asthmatic patients. Additionally, there was a marked increase in mucus production in mice that received Th2 cells and inhaled OVA, but not in mice that received Th1 cells. However, OVA-specific Th2 cells from IL-4-deficient mice were not recruited to the lung and did not induce mucus production. When this defect in homing was overcome by administration of TNF-alpha, IL-4 -/- Th2 cells induced mucus as effectively as IL-4 +/+ Th2 cells. These studies establish a role for Th2 cells in mucus production and dissect the effector functions of IL-4 in these processes. These data suggest that IL-4 is crucial for Th2 cell recruitment to the lung and for induction of inflammation, but has no direct role in mucus production.     

Leukotriene activity modulation in asthma

Leukotrienes constitute a class of inflammatory mediators synthesised from arachidonic acid, a product of cell membrane metabolism. Synthesis occurs in the 5-lipoxygenase enzyme pathway, which produces several species of leukotrienes, each with characteristic biological activities. With regard to asthma, the leukotrienes are particularly important because of their ability to directly and potently mediate bronchoconstriction; in addition, they specifically stimulate the secretion of mucus into the airways and the extravasation of fluids and proteins into the airway tissues, both of which contribute to airway obstruction. A number of antileukotriene agents have been developed with the goal of modulating the inflammatory process in various disease states. These agents fall into 2 general classes: leukotriene receptor antagonists and leukotriene synthesis inhibitors. Results of antileukotriene agents in preclinical and clinical trials indicate that antileukotriene agents attenuate the response to challenges with inhaled leukotrienes, cold air, exercise, aspirin and allergen; in addition, they have shown efficacy in clinical asthma and have not been associated with serious adverse effects. Although results to date indicate that these medications are well tolerated and effective in the treatment of asthma, the recent approval by the FDA of 2 antileukotriene agents will give physicians further insight into how patients with asthma respond to them.     

The effects of irritation at various levels of the airway upon tracheal mucus secretion in the cat

1. Sulphated glycoprotein output from the trachea, isolated in situ, has been measured in anaesthetized cats by a radio-isotopic method. The effects of irritation of various parts of the airway on this mucus output were studied. 2. Mechanical stimulation of the nose and nasopharynx increased tracheal mucus output by reflexes which involved parasympathetic and probably also sympathetic motor pathways. 3. Laryngeal stimulation had a similar through the same motor pathways. 4. Inhalation of ammonia vapour into the lower airways reflexly increased mucus output from the isolated trachea. The efferent pathway for this reflex was mainly or entirely parasympathetic. It is argued that the afferent pathway involved cough receptors. 5. Lung inflation, inhalation of histamine aerosol and intravenous injection of phenyl diguanide (which excite mainly lung stretch receptors, lung 'irritant' receptors and alveolar 'J-receptors' respectively) had no consistent effect on tracheal mucus secretion. 6. The afferent and efferent pathways of these reflexes are discussed.     

Bronchographic features of chronic bronchitis in normal men

As part of a study of mucous transport in the airways, tantalum bronchography was performed on 13 normal, asymptomatic men who had normal findings on pulmonary function studies. Most of the subjects demonstrated some of the bronchographic features which have been regarded as specific for chronic bronchitis. Eight men showed opacification of the ducts of mucous glands; 12 had visible secretions in the airways; three had moderate-to-marked irregularity of airways. The clearance of tantalum from the airways in all but two subjects was more rapid than anticipated and thus could not be correlated with the bronchographic features of chronic bronchitis. Two subjects who previously had symptoms of respiratory tract infection showed markedly delayed peripheral airway clearance of tantalum. The bronchographic features of chronic bronchitis can be seen in normal subjects or may indicate airway abnormalities that are not manifested functionally.     

A comparison of sensory nerve function in human, guinea-pig, rabbit and marmoset airways

We have investigated the role of sensory nerves in regulating airway smooth muscle function in the guinea-pig, marmoset, rabbit and man. Tissue levels of the sensory neuropeptides CGRP and substance P in the airways of the guinea-pig were significantly greater compared with the rabbit and marmoset. The relative order of tissue content was guinea-pig > rabbit = marmoset. Marmoset bronchial and tracheal preparations responded weakly to exogenously administered substance P and neurokinin A but contracted to methacholine and demonstrated atropine-sensitive cholinergic responses. In marmoset, rabbit and human airway preparations, capsaicin mediated weak contractile responses to exogenously administered capsaicin. However, high concentrations of capsaicin elicited a relaxation response that was epithelium-independent, cyclo-oxygenase-insensitive, not involving nitric oxide and not dependent on the activation of capsaicin-sensitive afferents. These results suggest that rabbit and marmoset airways respond functionally in a similar way to human airway preparations and maybe more relevant than guinea-pig airways with regard to understanding the role of sensory neuropeptides in airways.     

Demographic characteristics of patients undergoing aortic valve replacement for stenosis: relation to valve morphology

Mucoid enteropathy is a serious disease of rabbits, the cause of which is unknown. Ligation of the cecum has been reported to cause a mucoid enteropathy-like syndrome in 70% of conventional rabbits. The goal of this study was to evaluate this model of mucoid enteropathy in Pasteurella-free, coccidia-free rabbits for use in future studies. Five rabbits served as unoperated controls (group 1). Eight rabbits underwent ligation of the cecum, with large vessels and nerves spared (group 2). In six rabbits the distal branch of the ileocecocolic vessels and nerve were incorporated into the cecal ligature (group 3). At necropsy 3 to 5 days after surgery, all group-3 rabbits had copious amounts of clear, gelatinous mucus in the colon. Only one group-2 rabbit had grossly evident mucus hypersecretion, whereas none of the group-1 rabbits did. Group-3 rabbits had areas of necrosis in the cecum; this was not seen in group-1 or group-2 rabbits. Rabbits of groups 2 and 3 had inflammation of the distal portion of the colon. In specific-pathogen-free rabbits cecal ligation alone did not reliably stimulate mucus hypersecretion but induced a disease similar to natural mucoid enteropathy. Cecal ligation including vessels provided a reproducible syndrome of mucus hypersecretion; however, the severe cecal necrosis was not consistent with the naturally acquired disease.     

Relationship between fundic endocrine cells and gastric acid secretion in hypersecretory duodenal ulcer diseases

BACKGROUND: Acid hypersecretion is associated with duodenal ulcer disease in the following conditions: Zollinger-Ellison syndrome (ZES) and antral gastrin cell hyperfunction (AGCH) due to hypergastrinaemia, or hypersecretory duodenal ulcer (HDU) without hypergastrinaemia. AIM: To evaluate whether quantitative changes in fundic ECL and D cells may be involved in acid hypersecretion. PATIENTS AND METHODS: Seven ZES, six AGCH and six HDU Helicobacter pylori-positive patients were compared. Basal (BAO) and pentagastrin-stimulated gastric acid secretions (PAO), and morphometry of fundic ECL and D cells were performed. The six AGCH and six HDU patients were investigated again using the same tests 1 year after H. pylori eradication. RESULTS: Median PAO values were no different in all the hypersecretory conditions studied. The median volume density of ECL cells in ZES was significantly higher than in controls (2.75, range 1.74-5.8 vs. 0.73, 0.52-1.11: P < 0.05), whereas it was in the control range in AGCH and HDU patients (0.77, range 0.20-1.39 and 0.99, range 0.42-1.51; respectively). The count of fundic D cells was significantly lower in AGCH patients than in all other investigated groups (median 0.16, range 0.1-0.52; P < 0.05). Cure of infection in AGCH and HDU patients did not modify the ECL cell volume density, whereas a significant increase in the count of fundic D cells was observed in AGCH patients. Thus, the ECL/D cell index was significantly affected in AGCH patients (P < 0.05), being higher during H. pylori infection (median 6, range 0.7-9.25) than after the cure (median 2.12, range 1.10-3.5). BAO and PAO were not affected by H. pylori eradication in either group. CONCLUSIONS: The study provides evidence, for the first time, that quantitative alterations in the fundic endocrine cells are not involved in acid hypersecretion of patients with hypersecretory states, and that eradication of H. pylori does not restore normal acid secretion values.     

Morphometric approaches for evaluating pulmonary toxicity in mammals: implications for risk assessment

Recent advances in quantitative morphology provide all the tools necessary to obtain structural information in the lung that can be quantified and interpreted in the three-dimensional world of toxicology. Structural hierarchies of conducting airways and parenchyma of the lung provide: (1) numbers of cells per airway, lobe, or lung; (2) surface areas of cells, airways, and alveoli; (3) length of airways and vessels; and (4) volumes of cells, alveoli, airways, vessels, and individual lobes or the entire lung. Unbiased sampling of these subcompartments of the lung requires fractionation of lobes or individual airways. Individual airways of proximal and distal generations are obtained by airway microdissection along one axial pathway and comparisons made between airway generations. Vertical sections of selected airways are used to sample epithelium and interstitium. Using this unbiased approach of quantitative morphology, we have shown that inhalation of low ambient concentrations of ozone ([O3]0.15 ppm) near or at the United States National Ambient Air Quality Standard (NAAQS) (0.12 ppm O3) induces significant alterations in bronchiolar epithelium and interstitium in nonhuman primates but not rats. The alterations do not appear to be concentration- or time-dependent, thereby bringing into question the current NAAQS that may be at or above the threshold for distal airway injury in primates. Unbiased morphometric methods are critical in a quantitative evaluation of toxicological injury of mammalian tracheobronchial airways.     

Gross periostitis ossificans in mandibular osteomyelitis. Review of the English literature and radiographic variation

BACKGROUND: Although the airway epithelium participates in inflammation and repair, the circadian expression of epithelial cell markers involved in these processes has not been investigated. OBJECTIVE: We sought to determine whether expression of CD51 (vitronectin and fibronectin receptor), CD54 (intercellular adhesion molecule-1), HLA-DR (activation marker), CD29 (beta1 integrin), CD49b (collagen receptor), and CD11b (complement receptor) exhibit a circadian rhythm in asthma. METHODS: Eleven patients with nocturnal asthma (NA), 9 subjects with nonnocturnal asthma (NNA), and 10 control subjects underwent bronchoscopy at 4 PM and 4 AM in a random order 1 week apart, with brushing of the proximal and distal airways. The percentage of cells staining for a particular marker was determined. RESULTS: At 4 PM, HLA-DR in the proximal airways and CD54 in the distal airways was significantly greater in control subjects as compared with asthmatic subjects (HLA-DR, control subjects: 10.0% [range, 5.0% to 21.0%]; NNA: 8.0% [range, 4.0% to 14.5%] NA: 3.5% [range, 2.0% to 6.0%], P = .01; CD54, control subjects: 17.0% [range, 8.0% to 25.0%], NNA: 8.0% [range, 5.3% to 11.5%], NA: 7.0% [range, 4.0% to 15.0%], P = .O;). At 4 AM, CD51 in the distal airways was significantly greater in patients with NA as compared with patients with NNA and control subjects (control subjects, 23.0% [range, 13.8% to 30.5%]; NNA, 32.0% [range, 13.0% to 35.0%]; NA, 40.0% [range, 23.0% to 50.0%], P = .05). Expression of CD51 in the distal airways correlated with the degree of airway obstruction (r = -0.57, P = .001). Control subjects exhibited significant circadian variation in the expression of HLA-DR in the proximal airways and CD54 in the distal airways. CONCLUSION: The increased CD51 at night in patients with NA may be related to increased airway inflammation and repair processes in response to injury. The circadian changes in CD54 and HLA-DR in control subjects require further study to determine their significance. (J Allergy Clin