Rheological Properties Of Mucus Research Articles

The impact of long-acting muscarinic antagonists on mucus hypersecretion and cough in chronic obstructive pulmonary disease: a systematic review.

Patients suffering from chronic obstructive pulmonary disease (COPD) clinically manifest airway mucus hypersecretion as sputum expectoration and cough. Evidence accumulated in the past decade has shown that the cholinergic system not only regulates airway smooth muscle contraction but also the activity of inflammatory and airway epithelial cells, including goblet cells, and submucosal gland activity. Long-acting muscarinic antagonists (LAMAs) with the most favourable M3/M2 muscarinic acetylcholine (ACh) receptors residency properties are not only excellent bronchodilators but potentially also mucus-modifying agents, able to positively impact on mucus hypersecretion and cough. The aim of this systematic review was to investigate the impact of LAMAs on mucus hypersecretion and cough in COPD patients. The evidence confirmed that LAMAs, mainly tiotropium and aclidinium, improved sputum production and cough in moderate to severe COPD. Thus, LAMAs not only antagonise the ACh-induced bronchoconstriction of the airways but also appear to limit the production of mucus secreted in response to ACh by airway goblet cells and/or submucosal glands. Further clinical studies are necessary to evaluate the impact of LAMAs exclusively on sputum symptoms and cough as primary end-points and to investigate whether LAMAs have a modulatory action on the rheological properties of mucus.

Effect of N-acetylcysteine on mucosal immunity of respiratory tract.

The outcome of diseases accompanied or caused by mucostasis depends both on the restoration of drainage function of the airways and on the effectiveness of immune mechanisms against pathogens. N-acetylcysteine (NAC) is widely used as mucolytic and antioxidant remedy in clinical practice. In this regard, the data of the scientific literature on the direct and indirect effects of NAC on the mucosal immunity of the respiratory tract have been reviewed. NAC possesses pleiotropic immunomodulating properties, most of which contribute to the regression of clinical manifestations of acute and chronic inflammatory diseases of the respiratory tract. Biological and pharmacological effects of NAC include improvement in rheological properties of mucus, reduction of excess mucin production, restoration of mucociliary clearance and production of sIgA, suppression of excess production of IgE and IgG4, destruction of biofilms and inhibition of their formation, suppression of adhesion of pathogenic bacteria to epithelial cells, antioxidant activity, regulation of the production of pro-inflammatory and profibrotic cytokines. There was no convincing evidence that NAC is able to suppress any component of mucosal immunity. For final conclusions on this subject, further research are required.

The biology of mucus: Composition, synthesis and organization.

In this review we discuss mucus, the viscoelastic secretion from goblet or mucous producing cells that lines the epithelial surfaces of all organs exposed to the external world. Mucus is a complex aqueous fluid that owes its viscoelastic, lubricating and hydration properties to the glycoprotein mucin combined with electrolytes, lipids and other smaller proteins. Electron microscopy of mucosal surfaces reveals a highly convoluted surface with a network of fibers and pores of varying sizes. The major structural and functional component, mucin is a complex glycoprotein coded by about 20 mucin genes which produce a protein backbone having multiple tandem repeats of Serine, Threonine (ST repeats) where oligosaccharides are covalently O-linked. The N- and C-terminals of this apoprotein contain other domains with little or no glycosylation but rich in cysteines leading to dimerization and further multimerization via SS bonds. The synthesis of this complex protein starts in the endoplasmic reticulum with the formation of the apoprotein and is further modified via glycosylation in the cis and medial Golgi and packaged into mucin granules via Ca2+ bridging of the negative charges on the oligosaccharide brush in the trans Golgi. The mucin granules fuse with the plasma membrane of the secretory cells and following activation by signaling molecules release Ca2+ and undergo a dramatic change in volume due to hydration of the highly negatively charged polymer brush leading to exocytosis from the cells and forming the mucus layer. The rheological properties of mucus and its active component mucin and its mucoadhesivity are briefly discussed in light of their importance to mucosal drug delivery.

Effect of Fluid Viscosity on the Cilia-Generated Flow on a Mouse Tracheal Lumen.

Mucous flow in a tracheal lumen is generated by the beat motion of ciliated cells to provide a clearance function by discharging harmful dust particles and viruses. Due to its physiological importance, the cilia-generated flow and the rheological properties of mucus have been investigated intensively. The effects of viscosity on the cilia-generated flow, however, have not been fully clarified. In this study, we measured bulk background velocity of ciliary flow using a micro particle tracking velocimetry method under various viscosity conditions in mice. The results showed that the flow velocity decreased as the increase with viscosity of ambient fluid. Moreover, no previous study has clarified the pump power generated by cilia, which provides important information with regard to understanding the molecular motor properties of cilia. Measurements of both the ciliary flow and the ciliary motion were conducted to determine the cilia pump power. Our results indicated that the cilia pump during the effective stroke did not drive the ciliary flow efficiently under high viscosity conditions; these findings are necessary to resolve the clearance function.

Model for mucus transport in the airways due to air motion — Effect of slipperiness

In this paper, a circular three-layer flow model is proposed to study mucus transport in the airways due to air motion caused by mild forced expiration or mild coughing. Mucus is represented by four-parameter viscoelastic fluid, a combination of Maxwell and Voigt elements, whereas air and serous fluid are taken as Newtonian fluids (incompressible). The pressure gradient generated in the fluid layers is assumed to be given by a time-dependent function representing mild forced expiration or mild cough in the airways causing laminar flow. The effect of slip velocity at the mucus–serous interface caused by the presence of surfactant and at the top surface caused by immotile cilia are also taken into account. The roles of rheological properties of mucus on its transport are studied. The effect of serous fluid and its viscosity on mucus transport is also considered.

Preparation and characterization of mucus-penetrating papain/poly(acrylic acid) nanoparticles for oral drug delivery applications

Particle diffusion through the intestinal mucosal barrier is restricted by the viscoelastic and adhesive properties of the mucus gel layer, preventing their penetration to the underlying absorptive endothelial cells. To overcome this natural barrier, we developed nanoparticles which have a remarkable ability to cleave mucoglycoprotein substructures responsible for the structural and rheological properties of mucus. After rheological screening of various mucolytic proteases, nanoparticles composed of poly(acrylic acid) and papain were prepared and characterized regarding particle size and zeta potential. Analysis of nanoparticles showed mean diameters sub-200 nm (162.8–198.5 nm) and negative zeta potentials advancing the mobility in mucus gel. Using diffusion chamber studies and the rotating diffusion tubes method, we compared the transport rates of papain modified (PAPC) and unaltered poly(acrylic acid) (PAA) particles through freshly excised intestinal porcine mucus. Results of the diffusion assays demonstrated strongly enhanced permeation behavior of PAPC particles owing to local mucus disruption by papain. Improved transport rates, reduction in mucus viscosity and the retarded release of hydrophilic macromolecular compounds make proteolytic enzyme functionalized nanoparticles of substantial interest for improved targeted drug delivery at mucosal surfaces. Although cytotoxicity tests of the nanoparticles could not be performed, safety of papain and PAA was already verified making PAPC particles a promising candidate in the pharmaceutical field of research. The focus of the present study was the development of particles which penetrate the mucus barrier to approach the underlying epithelium. Improvements of particles that penetrate the mucus followed by cell uptake in this direction are ongoing.

Ewe breed differences in fertility after cervical AI with frozen–thawed semen and associated differences in sperm penetration and physicochemical properties of cervical mucus

The objective of this study was to examine sperm penetration through cervical mucus and associated physicochemical properties of cervical mucus from Belclare and Suffolk ewes – two breeds with divergent pregnancy rate following cervical AI using frozen–thawed semen. In Experiment 1, sperm penetration through cervical mucus was assessed in 15 Belclare and 15 Suffolk ewes at 30, 48 and 57 h post sponge removal. In Experiment 2, rheological properties of mucus from 17 Belclare and 19 Suffolk ewes at 48 and 57 h post sponge removal were determined. In Experiment 3, 20 Belclare and 20 Suffolk ewes were used to assess mucus ferning and pH collected at 42, 48, 57 and 65 h post sponge removal. In Experiment 1, a higher number of sperm penetrated cervical mucus from Belclare ewes at 48 h, reflected by a breed by time interaction ( P = 0.05). In Experiment 2, mucus from Suffolk ewes tended to have higher elastic and complex moduli than that from Belclare ewes ( P = 0.06) regardless of time of collection. There was no effect of ewe breed on the viscous modulus. In Experiment 3, there was a significant effect of time post sponge removal on ferning ( P < 0.01), but there was no effect of breed. There was no effect of time or breed on mucus pH. It is concluded that breed differences in the rheological properties of cervical mucus affect the ability of sperm to swim through cervical mucus and this may explain breed differences in fertility observed after cervical AI using frozen–thawed semen.

Glycan Profiling of Gel Forming Mucus Layer from the Scleractinian Symbiotic Coral Oculina arbuscula

The gel forming mucus layer surrounding scleractinian corals play fundamental functions in the maintenance of a favorable microenvironment required for the survival of these organisms. In particular, it harbors a rich partially species-specific symbiotic community through yet poorly understood molecular interactions. However, removal or contamination of this community by exogenous bacteria is closely linked to the worldwide bleaching events that are presently devastating coral colonies. The present study investigates the structure of major high molecular weight glycoconjugates that are responsible for both rheological properties of mucus and sugar-protein interactions with microbial communities. We demonstrated that it is composed by two distinct types of sulfated macromolecules: mucin type glycoproteins densely substituted by short unusual O-linked glycans and repetitive polysaccharides.

Macrolides as Biological Response Modifiers in Cystic Fibrosis and Bronchiectasis

For 50 years, macrolide antibiotics have been used to treat community acquired pneumonia and atypical infections such as Chlamydia pneumonia and Mycoplasma. In the late 1960s it was noted that when the 14-member ring macrolide antibiotic troleandomycin was given to asthma patients who required large doses of systemic corticosteroids, they could often reduce their steroid dose or even stop steroids completely without exacerbation of their asthma. Because of this experience, Prof. S. Kodoh and colleagues first used erythromycin as an immunomodulatory agent to treat diffuse panbronchiolitis (DPB). DPB is a cystic fibrosis (CF)-like condition seen predominantly in young, nonsmoking adults in Japan and Korea. The introduction of erythromycin profoundly improved survival, and in many of these very ill patients the illness disappeared. Since then, research has focused attention on many non-antibacterial, disease modifying effects of this class of compounds. These include downregulation of proinflammatory cytokines via an effect on nuclear transcription factors, reduction in adhesion molecule expression, suppression of inducible nitric oxide synthase (iNOS), reduced neutrophil chemotaxis and degranulation, inhibition of neutrophil elastase, cytoprotection against bioactive phospholipids, improvement in the rheological properties of mucus, reduction in bronchial hyperreactivity, and, perhaps, modulation of neutrophil death by apoptosis pathways, and in the end, airway remodeling. Additionally, they have unconventional effects on microorganisms, including inhibiting Pseudomonas aeruginosa twitching motility and thus biofilm formation. There are small case series and three large randomized controlled trials that have established unequivocal evidence of benefit in CF. There is less evidence for an immunomodulatory effect in bronchiectasis. Future work is likely to focus on the development of macrolides with disease-specific modes of action.

Effects of chelating agents on the rheological property of cervical mucus

As an ongoing effort to elucidate the mechanisms involved in the calcium-dependent fertility regulation process, the viscoelastic properties of the mucus obtained from lamb cervix and human semen, as well as their water and total protein contents after exposure to EDTA, a chelating agent, or Nonoxynol-9 (N-9), a spermicidal agent, were examined. The viscosity was measured using a Cone Plate Digital Viscometer, while the water and total protein contents were determined by the lyophilization process and the Lowry method, respectively. The significant changes in the rheological properties of mucus, such as its viscosity and the water content, upon exposure to EDTA were demonstrated. The viscosity of cervical mucus and human semen were significantly increased by EDTA treatment (as compared to the controls): lamb cervical mucus (2.9 ± 0.3 vs. 2.2 ± 0.3 cps) and human semen (5.0 ± 0.3 vs. 4.3 ± 0.3 cps), respectively. The hydration rate was decreased by EDTA treatment as compared with the control (93.6 ± 0.7 vs. 96.8 ± 0.8%). Among tested samples, the reduction in the percentage of sperm penetration through the cervical mucus was the highest in the mucus containing EDTA, which had the lowest water content (93.6 ± 0.7%), indicating that there is a positive relationship between the hydration rate of the cervical mucus and its ability to permit the penetration of spermatozoa. This result indicates that spermicidal activity exerted by high concentrations of EDTA is in part due to its effect on the rheological properties of cervical mucus or semen.

Mucolytic treatment with N-acetylcysteine L-lysinate metered dose inhaler in dogs: airway epithelial function changes.

N-acetylcysteine L-lysinate Nacystelyn (L-NAC) is a newly synthesized mucolytic agent, of which the action in vivo has not been well defined. In six healthy mongrel dogs, the rheological properties of mucus, its mucociliary and cough clearability, and the transepithelial potential difference (PD) of the tracheobronchial epithelium were evaluated after placebo and L-NAC metered dose inhaler (MDI) aerosols. The principal index of mucus rigidity, log G*, decreased at all airway sites with L-NAC administration, i.e. the mucus became less rigid and more deformable (the overall change in G* was 0.29 log units, i.e. ca. twofold decrease). The viscoelasticity-derived mucus transportability parameters, mucociliary (MCI) and cough (CCI) clearability indices, increased with L-NAC MDI, particularly CCI, which predicts the effect of mucus rheology on cough clearability. PD increased significantly with L-NAC administration at all measurement sites, which appears to be a novel effect for a direct acting mucolytic agent. Tracheal mucus linear velocity (TMV) increased after L-NAC compared with placebo, as did the normalized frog palate transport rate (NFPTR). The increase in NFPTR was greater than that predicted from the mucus rheological properties alone, suggesting that L-NAC still resident in the collected mucus stimulated the frog palate cilia. The index of mucus flux, the collection rate in mg.min-1, was higher with L-NAC compared with placebo. From our results, we conclude that L-NAC shows potential benefit in terms of improving mucus rheological properties and clearability. It may act, in part, by stimulating the fresh secretion of mucus of lower viscoelasticity. The stimulation of mucociliary clearance could be related to ion flux changes, as indicated by the increase in PD.

Effects of MR889, a cyclic thiolic neutrophil elastase inhibitor, on rheologic properties of mucus

MR889 is a synthetic inhibotor of human neutrophil elastase with potential in clinical conditions characterized by a high load of this proteolytic enzyme, mainly chronic obstructive pulmonary disease. On the basis of its mechanism of inhibition, it has been suggested that MR889, upon reaction with elastase, would generate new free thiol groups. The aim of this study was to investigate whether MR889, upon reaction with elastase, may modify rheologic properties, i.e. apparent viscosity and elasticity, of both human sputum and porcine stomach mucus, in ex-vivo and in vitro experiments. MR889 10 −4 M alone had no effect rheologic properties of samples, whereas an agent with free thiol group, n-acetylcysteine 10 −4 M reduced both viscosity and elasticity. MR889 10 −4 M upon reaction with elastase 0.03 nMol (giving 83% of elastase inhibition) had no effect on rheologic properties of samples, whereas upon reaction with elastase 0.15 nMol (49% inhibition) yielded a marked decrease in viscosity. This result would suggest that MR889, in the presence of a high load of elastase, may acquire direct mucus modifying capacity, likely because of its greater utilization upon reaction with the enzyme.

Bromhexine plus oxytetracycline: the effect of combined administration upon the rheological properties of mucus from the mini-pig.

Three adult mini-pigs were employed to assess the effects of a twice daily dosage (40 mg kg-1) of oxytetracycline hydrochloride (OTC) and a combination of OTC with (0.5 mg kg-1) bromhexine hydrochloride (BHC) on the rheological properties and wet weight of secreted tracheal mucus. Mucus was collected daily from open-ended tracheal pouches established surgically in the mini-pigs. After a five day control period, either OTC or OTC plus BHC was administered twice daily with the normal diet. Each study period was followed by a five day washout period when mucus was collected but no drug given. The viscoelastic properties of each mucus sample were determined using creep compliance analysis. OTC was shown to increase the residual shear viscosity IP < 0.01) and increase the instantaneous compliance (P < 0.01). An increase in the wet weight of the collected mucus occurred in one pig only (P < 0.01). When BHC was co-administered with OTC, all of these changes were abolished. Evidence was obtained to suggest that BHC increased the concentration of OTC within the secreted mucus. BHC appeared to reverse the mucospissic activity of OTC in-vivo.

Nimesulide in the treatment of chronic bronchitis.

Hypersecretion of mucus is the main feature of chronic bronchitis and is associated with an increased susceptibility to bronchial infections. Although airway inflammation is present in patients with chronic bronchitis and is recognised as a contributing factor in the development of bronchial hyper-reactivity and obstruction, the role of anti-inflammatory drugs in the treatment of chronic bronchitis has not been established. Nimesulide is a nonsteroidal anti-inflammatory drug that can modulate the function of neutrophils and block the effects of several inflammatory mediators. We found that a 3-week treatment course of nimesulide in patients with chronic mucus hypersecretion decreased sputum viscosity, thus significantly improving symptoms. The effect of nimesulide on the rheological properties of mucus was slower and weaker than that of classic mucolytics and was more likely to be related to a reduction in bronchovascular permeability. The clinical usefulness of nimesulide in chronic bronchitis deserves further investigation.

Autoregulation of Beat Frequency in Respiratory Ciliated Cells: Demonstration by Viscous Loading

As opposed to the virtually constant load exerted by water on the cilia of ciliated protozoa, the hydrodynamic load on respiratory cilia can undergo broad variations because of changes in the rheologic properties of mucus. When water-rowing ciliated cells are exposed to increased viscosity (1 to 50 cP), their beat frequency decreases exponentially. According to Newton's fluid dynamic theory, this outcome is expected for an engine that generates constant force. However, the findings reported here indicate that when mucus-propelling respiratory ciliated cells are exposed to high viscous loads, ranging from 12 to 150 cP, the frequency of ciliary beat decreases only slightly, whereas the beat amplitude remains virtually constant. These observations suggest that ciliated cells of the respiratory tract have a functional reserve that allows them to autoregulate their mechanical output in response to the changes in viscosity to which they are normally exposed in the airway.

Mucolytics: When dispensable, when necessary?

Many patients with chest disease have difficulty in clearing their chests of sputum. A variety of substances have been used in an attempt to help them. Mucolytic drugs can alter the rheological properties of mucus by acting directly on the secretions or by modifying the metabolic activity of the mucus secreting cells. Many physicians and patients are certain to reap a benefit. This paper will discuss the effectiveness of mucolytic therapy.

Mucus transport in the airways by two-phase gas-liquid flow mechanism: continuous flow model.

Mucus transport speed induced by two-phase gas-liquid interaction was measured in the continuous two-phase annular flow tube models, and factors influencing the transport speed were assessed in conjunction with rheological properties of mucus. The flow model was made with 1.0-cm-ID glass tubes and positioned either vertically or horizontally. During a continuous passage of airflow through the model tube, mucus stimulants were supplied into the tube at a rate of 0.5-2.0 ml/min. The advancing speed of the leading edge of the mucous layer and mean mucous layer thickness were then measured. The transport speed in the vertical tube model ranged from 1.1 to 3.1 cm/min with a mucus feed rate of 0.5 ml/min at airflow rates of 0.33-1.17 l/s and increased with increasing airflow rates but decreased rapidly with increasing viscosity of mucus. The transport speed increased almost proportionally with increasing mucus feed rate. Elasticity of mucus did not affect the transport speed itself. However, more elastic mucus caused lower flow resistance and thereby could be transported with a much reduced work load. The transport speed in the horizontal tube model was 5-60% faster than that in the vertical tube model. The mean mucous layer thickness in the vertical tube model was found to be in the range of 0.5-1.5 mm in the experimental conditions used, and decreased rapidly with increasing airflow rate and decreasing viscosity of mucus. From these data the transport speed could be functionally related to airway diameter, mucous layer thickness, and mucus production rate.

Biorheological matching: mucociliary interaction and epithelial clearance.

In mucociliary clearance mucus has been found to be essential as coupler between ciliary beat and transport. The rheological properties of mucus are carefully matched to this task. It has to be an incipient gel and deviations from this state, to a sol or to a stiff gel, both render it defective in function. The known rheological properties of normal mucus are shown to be consistent with our understanding of how a periodically interacting set of cilia produce mucus layer flow. A dual requirement has to be met: Adequate tip penetration and adequate force transfer laterally. As a result any biorheologically properly matched system can replace mucus. Mucociliary clearance is a clear cut, rather well understood case of a general principle of biorheological matching.

Modification of the rheological properties of mucus by drugs.

The rheological properties of mucus secretions from various sites in the body are related to their particular physiological function. Although in normal circumstances the body produces secretions with optimal rheological properties to fulfil such functions, during disease the mucus produced may be too thick or too thin and in both cases may behave sub-optimally. In such situations it becomes attractive to administer chemical agents or drugs, either locally or systemically, which modify the rheological properties in an attempt to correct function. Furthermore, in certain cases it may be desirable to artificially manipulate the consistency of the mucus in order to produce a specific effect.KeywordsRheological PropertyCreep ComplianceChlormadinone AcetateBronchial MucusCysteine DerivativeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Control of mucus hydration as a Donnan equilibrium process.

The physical properties of the mucus secreted by the uterine cervix of primates and other animals undergo periodic changes which are important in the regulation of fertility. During the luteal phase of the sexual cycle, cervical mucus is thick, rubbery and impenetrable by spermatozoa; by the time of ovulation, it is a watery gel easily penetrated by spermatozoa. Although these changes in the rheological properties of mucus have been attributed to variations in the covalent cross-linking between long chains of glycoproteins, the main macromolecular constituent of cervical mucus1,2, recent studies3,4 suggest that the macromolecular matrix of cervical mucus is probably not covalently cross-linked. Rather it is an entangled random network of long mucins3, in which case the observed changes in the physical properties of mucus would be explained by varying degrees of hydration, the mechanism of which is not understood5. We now describe experiments which show that the hydration of cervical mucus may be controlled by a Donnan equilibrium process.