Density gradient analysis of secretions produced in vitro by human and canine airway mucosa: identification of lipids and proteoglycans in such secretions

Surface rheological properties alter aerosol formation from mucus mimetic surfaces

The effects of surface tension and surface viscoelastic properties on the formation of aerosol droplets generated from mucus-like viscoelastic gels (mucus mimetics) during shearing with a high velocity air stream were investigated. Mucus mimetic samples were formulated with similar composition (94% water and 6% dissolved solids, consisting of mucins, proteins, and ions), surface tension (via the addition of surfactant to the mimetic surface) and bulk viscoelastic properties (via crosslinking of mucin macromolecules in the mimetic) to that of native non-diseased tracheal mucus. The surface tension of the mucus mimetic was decreased by spreading one of two surfactants, dipalmitoyl phosphatidylcholine (DPPC) or calf lung surfactant (Infasurf®), on the mimetic surface. Aerosols were generated from the mimetic surfaces during simulated coughing using an enhanced simulated cough machine (ESCM) operating under controlled environmental conditions. The size distribution of aerosol droplets generated during simulated coughing from the surfactant-coated mimetic surfaces was multimodal, while no droplets were generated from the bare mimetic surface due to its high surface viscoelastic properties and high surface tension. The concentration of aerosols generated from the DPPC-coated mimetic was higher than that of the Infasurf®-coated mimetic, even though the surface tension of the two interfaces was the same. The experimental results suggest that a balance of surface elastic behavior and surface viscous behavior is required for the generation of aerosols from the viscoelastic surfaces.

Lipoid pneumonia in an orangutan (Pongo abelii) with chronic respiratory problems

An orangutan (Pongo abelii) presented with chronic respiratory problems. Cytological evaluation of the bronchoalveolar lavage fluids revealed macrophages with well-circumscribed intracytoplasmic clear vacuoles and lipid droplets in the background, confirmed by Oil Red O staining. The findings were indicative of lipoid pneumonia. This is the first report of lipoid pneumonia in an orangutan.

Synthetic tracheal mucus with native rheological and surface tension properties

In this study, the development of a model tracheal mucus with chemical composition and physical properties (bulk viscoelasticity and surface tension) matched to that of native tracheal mucus is described. The mucus mimetics (MMs) were formulated using components that are abundant in tracheal mucus (glycoproteins, proteins, lipids, ions, and water) at concentrations similar to those found natively. Pure solutions were unable to achieve the gel behavior observed with native mucus. The addition of a bifunctional cross-linking agent enabled control over the viscoelastic properties of the MMs by tailoring the concentration of the cross-linking agent and the duration of cross-linking. Three MM formulations with different bulk viscoelastic properties, all within the normal range for nondiseased tracheal mucus, were chosen for investigation of surfactant spreading at the air-mimetic interface. Surfactant spread quickly and completely on the least viscoelastic mimetic surface, enabling the surface tension of the mimetic to be lowered to match native tracheal mucus. However, surfactant spreading on the more viscoelastic mimetics was hindered, suggesting that the bulk properties of the mimetics dictate the range of surface properties that can be achieved.

Mucociliary dysfunction in COPD: effect of current pharmacotherapeutic options

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide. COPD comprises multiple components which, as well as a systemic component, include pulmonary inflammation, airway remodelling and mucociliary dysfunction. The latter features contribute to the development of chronic, progressive airflow limitation. The mucociliary dysfunction component of COPD is due to mucus hypersecretion coupled with a decrease in mucus transport, and represents an important pathophysiological feature requiring appropriate treatment. Current international guidelines do not recommend the use of mucolytics in the treatment of stable COPD. In contrast, bronchodilators are central to symptomatic management of COPD, and include beta(2)-adrenoceptor agonists, anti-cholinergics and methylxanthines. Interestingly, long-acting beta(2)-agonists (LABAs), rather than short-acting beta(2)-agonists, have the potential to improve the mucociliary component of COPD, in addition to providing symptomatic treatment by their bronchodilator action. Combination therapy with a LABA and an inhaled corticosteroid has the potential to more fully address the multicomponent nature of COPD by providing important anti-inflammatory activity, which may indirectly further improve mucociliary clearance. Theoretically, anti-cholinergics are likely to have mixed effects on mucociliary function, but clinically these effects have been difficult to demonstrate. Finally, a number of novel targets for the treatment of airway mucociliary dysfunction have been identified, and targeting agents are currently in development.

Phosphatidylcholine metabolism of rat trachea in relation to lung parenchyma and surfactant

Pulmonary surfactant prevents alveolar collapse and contributes to airway patency by reducing surface tension. Although alveolar surfactant, consisting mainly of phospholipids (PL) together with neutral lipids and surfactant-specific proteins, originates from type II pneumocytes, the contribution of airway epithelia to the PL fraction of conductive airway surfactant is still debated. We, therefore, analyzed the composition, synthesis, and release of phosphatidylcholine (PC) molecular species as the main surfactant PL of the rat trachea compared with the lung. Analyses of individual PC molecular species with HPLC and electrospray ionization mass spectrometry revealed that the rat trachea contained and synthesized much more palmitoyloleoyl-PC, palmitoyllinoleoyl-PC, and palmitoylarachidonoyl-PC, together with increased amounts of alkylacyl-PC, and less surfactant-specific species such as dipalmitoyl-PC than the lung. Organ cultures with [methyl-3H]choline as precursor of PC revealed that, in the trachea, synthesized PC was retained in the tissue, rather than secreted. [Methyl-3H]choline-labeled dipalmitoyl-PC was a negligible component in the trachea, and, in contrast to the lungs, palmitoyloleoyl-PC was enriched in tracheal secretions. We conclude that the surfactant fraction in the airways does not originate from the airways but is produced in the alveolar space and transported upward.

Effect of chondroitinase ABC on purulent sputum from cystic fibrosis and other patients

Cystic fibrosis (CF) patients develop chronic lung infections associated with airway obstruction by viscous and insoluble mucus secretions. Although mucus glycoproteins (mucins) are thought to be responsible for mucus plugs, other glycoconjugate components of airway secretions have not been systematically evaluated. The aim of the present study was to determine whether chondroitin sulfate proteoglycans (CSPG) contribute to the insolubility of CF sputum. Sputa obtained from 18 CF patients were incubated with chondroitinase ABC (ChABC) or buffer (control) for 18 h at 37 degrees C, and after centrifugation at 12,000 g, the volume of the insoluble pellet and turbidity of the supernatant were determined as measures of solubility. ChABC caused a 70-90% reduction in supernatant turbidity and a 60-70% decrease in pellet volume of the 13 purulent CF sputa, but had much less effect on the five nonpurulent CF sputa tested. Similar results were obtained with two non-CF purulent and two non-CF, nonpurulent sputa. Gel electrophoresis, Western blot, and slot blot immunoassays with antichondroitin sulfate and antimucin antibodies revealed that purulent sputa (CF and non-CF) contained more CSPG and less mucin than nonpurulent sputa. In vitro mixing experiments showed that mucin in nonpurulent sputa was reduced upon incubation with purulent sputa, presumably because of degradation or a loss of immunoreactive mucin epitopes from leukocyte and/or bacterial enzymes present in purulent sputa. Our results suggest that CSPG contribute more significantly than mucins to the insolubility of purulent tracheobronchial secretions from CF patients. Because purulent sputa from non-CF patients showed a similar pattern, our observations with CF sputa may have wider applicability.

Airway mucus: its components and function

The airway surface liquid (ASL), often referred to as mucus, is a thin layer of fluid covering the luminal surface of the airway. The major function of mucus is to protect the lung through mucociliary clearance against foreign particles and chemicals entering the lung. The mucus is comprised of water, ions, and various kinds of macromolecules some of which possess the protective functions such as anti-microbial, anti-protease, and anti-oxidant activity. Mucus glycoproteins or mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for the effective mucociliary clearance. There are at least eight mucin genes identified in the human airways, which will potentially generate various kinds of mucin molecules. At present, neither the exact structures of mucin proteins nor their regulation are understood although it seems likely that different types of mucins are involved in different functions and might also be associated with certain airway diseases. The fact that mucins are tightly associated with various macromolecules present in ASL seems to suggest that the defensive role of ASL is determined not only by these individual components but rather by a combination of these components. Collectively, mucins in ASL may be compared to aircraft carriers carrying various types of weapons in defense of airbome enemies.

Retargeting the coxsackievirus and adenovirus receptor to the apical surface of polarized epithelial cells reveals the glycocalyx as a barrier to adenovirus-mediated gene transfer

Lumenal delivery of adenovirus vectors (AdV) results in inefficient gene transfer to human airway epithelium. The human coxsackievirus and adenovirus receptor (hCAR) was detected by immunofluorescence selectively at the basolateral surfaces of freshly excised human airway epithelial cells, suggesting that the absence of apical hCAR constitutes a barrier to adenovirus-mediated gene delivery in vivo. In transfected polarized Madin-Darby canine kidney cells, wild-type hCAR was expressed selectively at the basolateral membrane, whereas hCAR lacking the transmembrane and/or cytoplasmic domains was expressed on both the basolateral and apical membranes. Cells expressing apical hCAR still were not efficiently transduced by AdV applied to the apical surface. However, after the cells were treated with agents that remove components of the apical surface glycocalyx, AdV transduction occurred. These results indicate that adenovirus can infect via receptors located at the apical cell membrane but that the glycocalyx impedes interaction of AdV with apical receptors.

Dysregulation of proteoglycan production by intrahepatic biliary epithelial cells bearing defective (delta-f508) cystic fibrosis transmembrane conductance regulator

Hepatic dysfunction in cystic fibrosis (CF) has been attributed to accumulation of viscous mucoid secretions in intrahepatic bile ducts. The purpose of our study was to compare glycoconjugate secretion by intrahepatic biliary epithelial (IBE) cells derived from normal livers and livers of CF patients with the delta F508 mutation of the cystic fibrosis transmembrane conductance regulator (CFTR). Confluent cells were incubated with 3H-glucosamine (GlcN) for 16 hours, and radiolabeled macromolecules were analyzed for the amount and type of glycoconjugates. Incorporation of 3H-GlcN into macromolecular glycoconjugates was two- to threefold higher in CF cells versus normals, as was uptake of 3H-Glcn into the cytoplasm of CF cells. Gel exclusion chromatography on Sepharose Cl 4B revealed that the secreted glycoconjugates from CF cells eluted entirely in the excluded fraction (molecular weight > 2 x 10(6)), while, in the normal cells, 60% of the glycoconjugates eluted as lower-molecular-weight species. The high-molecular-weight glycoconjugates in both CF and normal cells were identified as chondroitin sulfates, as evidenced by susceptibility to beta elimination, chondroitinase digestion, and amino acid composition. Western blotting of IBE cell secretions with a polyclonal antibody to chondroitin sulfate revealed proteoglycan bands at 100 and 210 kd. Our results indicate that secretion of chondroitin sulfate is markedly increased in CF biliary epithelium in vitro compared with non-CF cells. Increased uptake of precursor 3H-GlcN may contribute to enhanced glycosylation of chondroitin sulfate in CF cells.

Heterogeneity of the composition and thickness of tracheal mucus in rats

Inability to preserve airway mucus in situ has limited our understanding of its structure and function. This light- and transmission electron-microscopic study of rat tracheal mucus used a nonaqueous fixative that retains mucus (epiphase) over a lucent layer (hypophase). The fixative is a 1% solution of osmium tetroxide dissolved in a perfluorocarbon. The mean thickness of rat tracheal epiphase was 5 microns, with significant variation (0.1-50 microns) around the tracheal circumference. Tracheal mucus was thickest at the trachealis muscle region and contained cells, cellular debris, and a variable amount of surfactant and lipid, estimated at 4-16% of the total epiphase in five rats, with a mean composition of 9%. Lipid was observed on the surface of the epiphase, embedded within mucus, and at the epiphase-hypophase interface. Refined study of developmental, physiological, and pathological alterations to the airway coat may benefit from this approach.

Effect of antigen on the glycoconjugate profile of tracheal secretions and the epithelial glycocalyx in allergic sheep

To characterize the glycoconjugate composition of tracheal secretions and the apical glycocalyx of the tracheal epithelium under baseline conditions and after antigen challenge, sheep allergic to Ascaris suum were intubated with a double-balloon nasotracheal tube to create a tracheal chamber. After an initial tracheal lavage, the animals were either exposed to intratracheally nebulized phosphate-buffered saline (PBS) (3 ml, n = 6) or A. suum antigen (251,000 protein nitrogen units in 3 ml of PBS, n = 6). Tracheal lavage was repeated 2 hours later, and the animals were killed. An enzyme-linked lectin assay and lectin histochemical analysis were used to characterize carbohydrate residues in lyophilized, resuspended tracheal secretions and the apical glycocalyx of the tracheal epithelium, respectively. Eight lectins were used to detect GalNAc, alpha-Gal, beta-Gal, alpha-Fuc (1-3)Man, alpha-Man/Glu, alpha-Man, and alpha-(2-3)sialyl residues. The amounts of total nondialyzable solids, proteins, and lipids in tracheal secretions were approximately twice as high after exposure to A. suum than after exposure to PBS. All carbohydrate residues were present in tracheal secretions after exposure to PBS and A. suum, but the reactivity was higher after exposure to A. suum for beta-Gal (+125%), alpha-Man/Glu (+150%), alpha-(1-3)Man (+287%), alpha-(2-3)sialyl (+353%), and alpha-Man (+448%) (p < 0.05). Likewise, the apical glycocalyx contained all carbohydrate residues after exposure to PBS and A. suum; afer exposure to A. suum, the reactivity was greater for alpha-GalNAc (+18%), alpha-(2-3)sialyl (+90%), beta-Gal(1-3)GalNAc (+433%), and alpha-(1-3)Man (+482%) (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Lectin-detectable glycoconjugate profile of the tracheal secretions and epithelial glycocalyx in sheep. Effect of muscarinic stimulation

Reflex mucus secretion in the airways serves a defense function that includes the binding of bacteria to mucus glycoconjugates thereby preventing bacterial adherence to the epithelium. We therefore compared the lectin-detectable glycoconjugate profile of the epithelial glycocalyx and luminal secretions under baseline conditions and after muscarinic receptor stimulation in the sheep trachea. The sheep were intubated with a double-balloon nasotracheal tube to create a tracheal chamber for collection of secretions. After an initial lavage of the chamber to clear it of secretions, the sheep received an intravenous injection of normal saline, 0.5 mg/kg pilocarpine, or 0.5 mg/kg pilocarpine after pretreatment with 0.2 mg/kg atropine. Tracheal lavage was repeated 2 h later, and the sheep were then killed. An enzyme-linked lectin assay and lectin histochemistry were used to characterize glycoconjugate residues in tracheal secretions and in the apical epithelial glycocalyx, respectively. Eight different lectins were used to detect N-acetyl galactosamine, alpha-galactose, alpha-galactose-N-acetyl galactosamine, beta-galactose, beta-galactose-N-acetyl galactosamine, alpha-fucose, alpha-glucose, alpha-mannose and alpha-(2-3)sialyl residues. After normal saline, reactivity was present for all glycoconjugates in secretions and in the glycocalyx.(ABSTRACT TRUNCATED AT 250 WORDS)

Surfactant apoprotein A secretion by human tracheobronchial epithelial cells

To determine whether surfactant apoproteins are produced locally by the airway walls, we used a two-site simultaneous immunoassay with monoclonal antibodies and measured the surfactant apoprotein-A (SP-A) content in media cultured with human airway explants or cultured epithelial cells. Tracheobronchial explants were cultured for 2 successive periods (periods I and II). Significant SP-A concentrations were detected in both periods. Methacholine (MCh) or isoproterenol (ISP), added to the medium at the beginning of period II, reduced the ratio of SP-A concentration in period II to that in period I, compared to samples without treatment. The SP-A concentration in the medium at the confluent period of cultured epithelial cells was significantly higher than at the mid-period, indicating that SP-A secretion is dependent on the cell number. The supernatant from explants stimulated by MCh was capable of reducing SP-A secretion from cultured epithelial cells. Immunohistochemical study of SP-A using monoclonal antibody demonstrated positive immunoperoxidase staining in the cytoplasm of epithelial cells. Further, Western blots of electrophoresed proteins from epithelial cells showed the characteristic properties of SP-A. These findings indicate that tracheobronchial epithelium can secrete SP-A.

Secretory proteins and glycoconjugates synthesized by human tracheal gland cells in culture

To study the proteins and glycoconjugates synthesized by serous cells from human tracheal glands (HTG), isolated HTG cells were cultured in the presence of radiolabeled precursors 14C-proline, Na2(35)SO4, and 3H-fucose. The secretory 14C/35S/3H-radiolabeled proteins and glycoproteins, de novo synthesized by HTG cells, were analyzed by gel filtration chromatography. We observed the incorporation of 14C-proline into antileukoprotease and an unknown 30 kD protein, and the incorporation of 35SO4-- and 3H-fucose into high molecular weight glycoconjugates and sulfoconjugates (M(r) > 1,000,000) and into components with apparent M(r) of approximately 250 and 100 kD. After specific chemical and enzymatic treatment, the 35S- and 3H-glycoconjugates were shown to be -O-linked mucin-like glycoproteins and proteoglycans. These results show that cultured HTG cells synthesize some of the macromolecules identified in bronchial secretions.

Release of mucus glycoconjugates by Pseudomonas aeruginosa rhamnolipid into feline trachea in vivo and human bronchus in vitro

Pseudomonas aeruginosa colonizes the lower respiratory tracts of patients with severe bronchiectasis, including cystic fibrosis, a condition associated with increased airway mucus output. We have shown that an extract containing chloroform-soluble extracellular products of P. aeruginosa releases glycoconjugates into the cat trachea in vivo. This activity was not related to pyocyanin, a major component of the extract, but was associated with the rhamnolipids. Purified monorhamnolipid (100 micrograms/ml) released radiolabeled and periodic acid-Schiff (PAS)-reactive glycoconjugates (delta 3H = +490 +/- 70%, delta 35S = +170 +/- 40%, delta PAS = +8.6 +/- 1.7 micrograms/min; n = 6, P less than 0.02 for each). Dirhamnolipid (200 micrograms/ml) was also effective (delta 3H = +640 +/- 70%, delta 35S = +130 +/- 20%, delta PAS = +9.3 +/- 1.5 micrograms/min; n = 6, P less than 0.02 for each). Monorhamnolipid (100 micrograms/ml) also released 35S-labeled and PAS-reactive glycoconjugates from human bronchial tissue in vitro (delta 35S = +189 +/- 47%, delta PAS = +26.3 +/- 8.5 micrograms/min; n = 7, P less than 0.001 versus control tissues in which no stimulus was given). The cat tracheal glycoconjugates released by the rhamnolipids differed from those released by pilocarpine 50 microM, in having a higher 3H:35S ratio (P less than 0.001). After gel chromatography on a Sepharose CL-4B column, the void volume fractions of the glycoconjugates also had different profiles in a cesium chloride density gradient. Those released by rhamnolipid banded at 1.62 g/ml, while those released by pilocarpine banded mainly at 1.50 g/ml, with some of the higher density material also present.(ABSTRACT TRUNCATED AT 250 WORDS)

Chondroitin sulfate in sputum from patients with cystic fibrosis and chronic bronchitis

In order to ascertain whether or not the presence of glycosaminoglycans in sputa of patients suffering from chronic bronchial disorders was related to tracheobronchial infection, an electrophoretic procedure was set up. The different acidic macromolecular components of sputum, namely nucleic acids, glycosaminoglycans, and bronchial glycopeptides could be identified in proteolyzed sputum using agarose electrophoresis before and after the action of different enzymes: nucleases, chondroitinases, hyaluronidase and heparinase. This procedure was used to analyze 13 sputum samples from patients suffering from cystic fibrosis (CF) and 12 sputum samples from patients suffering from chronic bronchitis. Chondroitin sulfate was identified in 11 infected sputum samples from patients with CF and also in the noninfected sputum from a patient with chronic bronchitis. These data suggest a relationship between the presence of chondroitin sulfate proteoglycans in sputum and severe tracheobronchial infection in CF.

Mucus glycoproteins from cystic fibrotic sputum. Macromolecular properties and structural 'architecture'

Mucus glycoproteins (mucins) were isolated from sputum of patients with cystic fibrosis (CF) after separation into sol and gel phases. The mucus gel was solubilized with gentle stirring in 6 M-guanidinium chloride supplemented with proteinase inhibitors, and purification of mucins was subsequently achieved by isopycnic density-gradient centrifugation in CsCl/guanidinium chloride. Density-gradient centrifugation also revealed a heterogeneity of the macromolecules, the pattern of which varied between individuals, and mucins from the gel phase was pooled as 'heavy' and 'light' fractions. Gel chromatography on Sepharose CL-2B showed that the heavy fraction contained a larger proportion of smaller species than the 'light' fraction and that the gel phase mucins were much larger than those from the sol. An apparently homogeneous high-Mr mucin population from one individual contained approx. 70% (w/w) carbohydrate, the major sugars being N-acetylglucosamine (17.8%), N-acetylgalactosamine (6.7%), galactose (20.7%), fucose (13.2%) and sialic acid (11.4%). These mucins had an S020.w of 47 S, and an Mr of 15 x 10(6) -20 x 10(6), and rate-zonal centrifugation revealed a polydisperse size distribution [range (5-30) x 10(6)] with a weight-average Mr of 17 x 10(6). The whole mucins were visualized with electron microscopy as linear and apparently flexible threads, disperse in size. Reduction produced subunits which were included on Sepharose CL-2B, and subsequent trypsin digestion yielded high-Mr glycopeptides which were further retarded. The size distributions and fragmentation patterns of mucin from two other CF patients were the same, as studied by gel chromatography, rate-zonal centrifugation and electron microscopy. We conclude that CF mucins are heterogeneous in both size and buoyant density and that the various populations, though differing in buoyant density, share the same architecture and macromolecular properties and are, in this respect, similar to mucins from normal respiratory secretions [Thornton, Davies, Kraayenbrink, Richardson, Sheehan & Carlstedt (1990) Biochem. J. 265, 179-186] and human cervical mucus [Carlstedt & Sheehan (1989) SEB Symp. XLIII 289-316].

Mucins in cat airway secretions

Mucous secretions were obtained from cat tracheas that had received [3H]glucose and [35S]sulphate to radiolabel mucus glycoproteins biosynthetically. Samples were collected under resting ('basal') conditions as well as after pilocarpine stimulation and were separated into gel and sol phases by centrifugation. Macromolecules were partially purified by using gel chromatography on Sepharose CL-4B, and the species that were eluted with the void volume were then separated into two major populations with isopycnic density-gradient centrifugation in CsCl. The major component from the gel phase of pilocarpine-induced secretions had a buoyant density typical of mucins and was observed as linear and apparently flexible chains by electron microscopy. Reduction of disulphide bonds gave subunits that could be further cleaved by trypsin digestion into components of approximately the same size as the high-Mr glycopeptides obtained from other mucins after this treatment. In contrast, the dominant species in the gel phase of the 'basal' secretion had a significantly higher buoyant density than expected for mucins and was largely unaffected by reduction, as studied by gel chromatography. The macromolecules were fragmented by trypsin, suggesting that they contain a polypeptide backbone. This more dense component also predominated in the sol phase both from the 'basal' secretions and from the pilocarpine-released secretions. Digestion with DNAase, chondroitin ABC lyase or heparan sulphate lyase had no effect, which shows that this component is not DNA, a dermatan sulphate/chondroitin sulphate or a heparan sulphate proteoglycan. In contrast, endo-beta-galactosidase and keratanase caused some fragmentation, suggesting that the molecules contain some linkages of the poly-(N-acetyl-lactosamine) type, although the degradation was not as extensive as expected for keratan sulphate. Treatment with alkaline borohydride resulted in extensive fragmentation of the high-Mr glycopeptides from both components, indicating that the glycans were oligosaccharides that were probably O-linked. The monosaccharide compositions of both components were consistent with that expected for mucins. The data are in keeping with the major component from the pilocarpine-stimulated gel secretions being a mucus glycoprotein and the more dense component being a mucin-like molecule, possibly related to the keratanase-sensitive material isolated from canine trachea by Varsano, Basbaum, Forsberg, Borson, Caughey & Nadel [(1987) Exp. Lung Res. 13, 157-184].

Sulfated O-glycoproteins secreted by guinea pig trachea in organ culture

Organ culture of guinea pig trachea was performed in the presence of [35S]sulfate in order to characterize the sulfated glycoproteins released from the respiratory epithelium and mucosa. The sulfated macromolecules that were synthesized during a 6-h incorporation were separated by CsBr density-gradient centrifugation and gel-filtration chromatography successively. Most of the sulfated secreted macromolecules corresponded to a population of glycoproteins sensitive to reductive beta-elimination but resistant to both chondroitinase ABC and heparinase. These glycoproteins had different buoyant densities (ranging from 1.48 g/ml to 1.16 g/ml) and could be subfractionated according to molecular mass. A major part of the radioactivity was incorporated into high-molecular-mass mucins that were excluded from a Sepharose CL-2B column and did not penetrate into polyacrylamide gel in PAGE. However, a mixture of sulfated O-glycoproteins of much lower molecular mass was also characterized in addition to low amounts of chondroitin sulfate. Epithelial goblet cells are the predominant mucin-containing cells of the respiratory guinea pig trachea. Our results suggest that a wide range of sulfated O-glycoproteins are secreted by the guinea pig tracheal mucosa.

Lipids in airway mucus of acute quadriplegic patients

Quadriplegic patients have difficulty in clearing lung mucus due to paralysis of muscles of respiration. In about 25% of these patients, excessive mucus in the airway necessitates tracheostomy, and in some patients it is fatal. In others there is spontaneous recovery. To determine if the excessive mucus results from secretion of abnormal mucus or from accumulation of normal mucus, we analyzed the lipids in mucus from eight quadriplegic patients. Lipids were separated from other constituents of the mucus by density gradient ultracentrifugation, extracted with chloroform-methanol (2:1), and examined by high-performance thin-layer chromatography (HPTLC). Cholesterol was the major neutral lipid; phosphatidylethanolamine, phosphatidylcholine, and sphingomyelin were the main phospholipids. Glycolipids were predominant, lactosylceramide (CDH) being the highest in amount. Two-dimensional HPTLC as well as high-performance lipid chromatography also revealed the presence of gangliosides: comparison with standards indicated the presence of GM1, GM2, GM3, and some unidentified gangliosides. In normal mucus, cholesterol is the predominant lipid; phospholipid is present in smaller amounts but glycolipids are not identified. Thus, results of our lipid analysis show that mucus from the quadriplegic patients is abnormal and similar to that in hypersecretory diseases such as chronic bronchitis and cystic fibrosis. Unlike these latter cases, hypersecretion in the quadriplegic has a rapid onset and, often, spontaneous recovery, suggesting that this is due to abnormal stimulation rather than an increase in the population of secretory cells.

Mucus glycoproteins from 'normal' human tracheobronchial secretion

Mucous secretions were collected from tracheas of patients undergoing minor surgery under general anaesthesia with tracheal intubation, and mucus glycoproteins were isolated by using isopycnic density-gradient centrifugation in CsCl/guanidinium chloride. 'Whole' mucins were excluded from a Sepharose CL-2B gel, whereas subunits obtained after reduction were included. Trypsin digestion of subunits afforded high-Mr glycopeptides (T-domains), which were further included in the gel. The latter fragments are heterogeneous and comprise two or three populations, as indicated by gel chromatography and ion-exchange h.p.l.c. Rate-zonal centrifugation showed that the 'whole' mucins are polydisperse in size, with a weight-average Mr of (14-16) x 10(6). The macromolecules were observed by electron microscopy, as linear and apparently flexible thread-like structures. Subunits and T-domains had weight-average contour lengths of 490 nm and 160 nm respectively. It is concluded that mucus glycoproteins are present in secretions from the healthy lower respiratory tract. The 'whole' tracheal mucins are assembled from subunits, which in turn can be fragmented into high-Mr glycopeptides corresponding to the oligosaccharide domains typically found in mucus glycoproteins. The size and macromolecular architecture of the tracheal mucins is thus similar to that observed for mucins from human cervical mucus, chronic bronchitic sputum and pig stomach, providing yet another example of this general design of these macromolecules, i.e. subunits assembled end-to-end into very large linear and flexible macromolecules.

The uptake of radiolabelled precursors of mucus glycoconjugates by secretory tissues in the feline trachea

1. We gave one of three radiolabelled precursors of mucus glycoconjugates ([3H]proline, [3H]glucose and [35S]sulphate) into the tracheas of anaesthetized cats for 3 h. In other cats [35S]sulphate was given by intravenous injection. 2. After a further 2 h, tracheas were removed and fixed. Serial actions were cut and alternate sections were stained with Haematoxylin and Eosin or prepared as unstained autoradiographs. Points on submucosal gland and surface epithelium were chosen with a grid on photomicrographs of the stained sections. Absorbance, which is proportional to autoradiographic grain density, was estimated on corresponding points on unstained autoradiographs by flying-spot microdensitometry. 3. With [3H]proline as precursor, the grain densities were greater over surface epithelium than over submucosal gland. With [3H]glucose, grain densities were greater over the surface epithelium in three cases, equal in one and greater over submucosal gland in the last. [35S]Sulphate, given either into the tracheal segment or intravenously, yielded grain densities that were greater over the submucosal glands than over surface epithelium. 4. The areas of submucosal gland the surface epithelium were estimated by point counting and the total content of radioactivity in the two structures estimated by multiplying mean absorbance by area. Ratios of the total radiolabel in surface epithelium to that in submucosal gland were consistently high when [3H]proline was the precursor and low with [35S]sulphate, given by either route. [3H]Glucose gave intermediate ratios. 5. Secretions washed from the trachea were subjected to gel-exclusion chromatography. Washings from tracheas labelled with [3H]proline contained some molecules eluting in the void volume of a Sepharose CL-4B column (suggesting a relative molecular mass of greater than 10(6) Da), but more of the radiolabel eluted in three peaks in the partially included volume. Density gradient ultracentrifugation of the void volume material gave radiolabelled peaks at densities of approximately 1.60 and 1.50 g ml-1, consistent with glycosylated proteins, as well as less dense material (less than 1.30 g ml-1), probably proteins with little or no glycosylation. 6. We discuss the justification of using these radiolabelled precursors to give relatively selective labelling of secretory products from submucosal gland and surface epithelium.

Secretions from primary hamster tracheal surface epithelial cells in culture: mucin-like glycoproteins, proteoglycans, and lipids

Surface epithelial cells dissociated from hamster tracheas and grown on a thick collagen gel in the presence of 5% fetal bovine serum become highly enriched with secretory cells at confluence. In the present communication, we have analyzed secretory products from this primary hamster tracheal surface epithelial (HTSE) cell culture. The secreted glycoconjugates included high-molecular-weight mucin-like glycoproteins (HMW MLGP) and proteoglycans that comprised 22% and 5% of the total [3H]glycoconjugates secreted when [3H]glucosamine was added as a metabolic precursor. Among the proteoglycans were hyaluronic acids (53%), heparan sulfate proteoglycans (29%), and chrondroitin sulfate proteoglycans (18%). Chondroitin sulfates were mostly 4-sulfated. On the other hand, the secreted lipids included cholesterol, phospholipids, and glycolipids, and most of them were associated with HMW MLGP.

Comparison of mucus flow rate, radiolabelled glycoprotein output and smooth muscle contraction in the ferret trachea in vitro

1. The concentration-response curves for rate of mucus output, labelled-glycoprotein output and smooth muscle contraction in response to methacholine, phenylephrine and salbutamol were determined in the ferret trachea in vitro. 2. The potencies of methacholine and phenylephrine are both in order: smooth muscle contraction, glycoprotein output, rate of mucus output. 3. At lower concentrations methacholine is more potent than is phenylephrine on smooth muscle contraction, glycoprotein output and rate of mucus output. 4. Concentration-response curves for salbutamol show very little change in rate of mucus output but a large increase in glycoprotein output. 5. It is concluded that the glycoprotein output induced by salbutamol may come from a source different from those induced by methacholine and phenylephrine.

Glycoconjugates secreted by bovine tracheal serous cells in culture

Glycoconjugates secreted by bovine tracheal gland serous cells in culture were characterized after incorporation of radioactive precursor [1-14C]glucosamine and stimulation with isoproterenol. Under dissociative conditions, glycoconjugates eluted in both the void and included volumes on Sepharose Cl-4B. Fractionated by anion-exchange chromatography, the high-molecular-weight (Sepharose Cl-4B; V0) glycoconjugates gave two acidic fractions eluting at 0.5 and 2.0 M NaCl; low-molecular-weight glycoconjugates of the included volumes gave a neutral fraction and two acidic fractions eluting at 0.5 and 2.0 M NaCl. Based on chemical analysis and specific enzymatic digestions, the material eluting in the void volume was shown to contain hyaluronic acid and chondroitin sulfate proteoglycan. In addition, the presence of small amounts of galactose, fucose, sialic acid, glucosamine, and galactosamine suggest the presence of O-glycosidically linked glycoproteins in the void volume. The identification of galactosaminitol in beta-eliminated oligosaccharides from this material confirms this notion. The material eluting in the included volume was shown to contain N-linked glycoproteins with glycans of complex type in the neutral fraction and chondroitin sulfate proteoglycans in the two acidic fractions. Significant N-sulfation of amino sugars was detected in the 0.5 M acidic fraction, indicating the presence of heparan sulfate. Hyaluronic acid and chondroitin sulfate proteoglycan have recently been identified in tracheal secretions; our results suggest that these components originate at least in part from tracheal gland serous cells.

Transition from normal to hypersecretory bronchial mucus in a canine model of bronchitis: changes in yield and composition

Density-gradient analysis was used to follow the transition from normal to hypersecretory bronchial mucus in a model of bronchitis induced in dogs by chronic exposure to SO2 gas. Aspirates of saline bronchial lavage were obtained by fiberoptic bronchoscopy from dogs before, during a 6- to 9-month exposure period to SO2 gas, and during a recovery period of similar duration. Prior to SO2 exposure, aspirates from all animals had a low yield of nondialyzable macromolecules (15 +/- 6 mg/aspirate) and similar composition. Specifically, epithelial glycoprotein of typical buoyant density was not detected; rather a glycoconjugate of higher buoyant density with features of both proteoglycan and glycoprotein was identified. Neutral lipids were predominant with lesser amounts of phospholipids; no glycolipids were detected. During the SO2 exposure period, aspirates from five of the eight dogs contained components similar in buoyant density to human bronchitic glycoprotein. Glycoprotein isolated from the canine aspirates was similar to glycoprotein isolated from human chronic bronchitic sputum, having the same carbohydrate composition and range of oligosaccharide size. Further, during and after SO2 exposure some aspirates contained appreciable amounts of glycolipids. These data demonstrate substantial similarities in composition between normal human and canine mucus and in mucus isolated from dogs with chronic airway inflammation induced by repeated irritant exposure and from human patients with chronic bronchitis.

Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases

To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.