Scintigraphic measurement of tracheal mucus velocity in vivo

Mucus clears from the trachea in a helix: a new twist to understanding airway diseases

BACKGROUND

Mucociliary clearance (MCC) is critical to lung health and is impaired in many diseases. The path of MCC may have an important impact on clearance but has never been rigorously studied. The objective of this study is to assess the three-dimensional path of human tracheal MCC in disease and health.

METHODS

Tracheal MCC was imaged in 12 ex-smokers, 3 non-smokers (1 opportunistically imaged during acute influenza and repeated after recovery) and 5 individuals with primary ciliary dyskinesia (PCD). Radiolabelled macroaggregated albumin droplets were injected into the trachea via the cricothyroid membrane. Droplet movement was tracked via scintigraphy, the path of movement mapped and helical and axial models of tracheal MCC were compared.

MEASUREMENTS AND MAIN RESULTS

In 5/5 participants with PCD and 1 healthy participant with acute influenza, radiolabelled albumin coated the trachea and did not move. In all others (15/15), mucus coalesced into globules. Globule movement was negligible in 3 ex-smokers, but in all others (12/15) ascended the trachea in a helical path. Median cephalad tracheal MCC was 2.7 mm/min ex-smokers vs 8.4 mm/min non-smokers (p=0.02) and correlated strongly to helical angle (r=0.92 (p=0.00002); median 18o ex-smokers, 47o non-smokers (p=0.036)), but not to actual speed on helical path (r=0.26 (p=0.46); median 13.6 mm/min ex-smokers vs 13.9 mm/min non-smokers (p=1.0)).

CONCLUSION

For the first time, we show that human tracheal MCC is helical, and impairment in ex-smokers is often caused by flattened helical transit, not slower movement. Our methodology provides a simple method to map tracheal MCC and speed in vivo.

Mucociliary Clearance is Impaired in Small Airways of Cystic Fibrosis Pigs

Rationale

Cystic fibrosis is a genetic disorder characterized by recurrent airway infections, inflammation, and progressive decline in lung function. Autopsy and spirometry data suggest that cystic fibrosis may start in the small airways which, due to the fractal nature of the airways, account for most of the airway tree surface area. However, they are not easily accessible for testing.

Objectives

Here, we tested the hypothesis that mucociliary clearance is abnormal in the small airways of newborn cystic fibrosis pigs.

Methods

Current mucociliary clearance assays are limited therefore we developed a dynamic positron emission tomography scan assay with high spatial and temporal resolution. Each study was accompanied by a high-resolution computed tomography scan that helped identify the thin outer region of the lung that contained small airways.

Measurements and Main Results

Clearance of aerosolized [ 68 Ga]macro aggregated albumin from distal airways occurred within minutes after delivery and followed a two-phase process. In cystic fibrosis pigs, both early and late clearance rates were slower. Stimulation of the cystic fibrosis airways with the purinergic agonist UTP further impaired late clearance. Only 1 cystic fibrosis pig treated with UTP out of 6 cleared more than 20% of the delivered dose.

Conclusions

These data indicate that mucociliary transport in the small airways is fast and can easily be missed if the acquisition is not fast enough. The data also indicate that mucociliary transport is impaired in small airways of cystic fibrosis pigs. This defect is exacerbated by stimulation of mucus secretions with purinergic agonists.

An operative framework to model mucus clearance in silico by coupling cilia motion with the liquid environment

Mucociliary clearance is the first defense mechanism of the respiratory tract against inhaled particles. This mechanism is based on the collective beating motion of cilia at the surface of epithelial cells. Impaired clearance, either caused by malfunctioning or absent cilia, or mucus defects, is a symptom of many respiratory diseases. Here, by exploiting the lattice Boltzmann particle dynamics technique, we develop a model to simulate the dynamics of multiciliated cells in a two-layer fluid. First, we tuned our model to reproduce the characteristic length- and time-scales of the cilia beating. We then check for the emergence of the metachronal wave as a consequence of hydrodynamic mediated correlations between beating cilia. Finally, we tune the viscosity of the top fluid layer to simulate the mucus flow upon cilia beating, and evaluate the pushing efficiency of a carpet of cilia. With this work, we build a realistic framework that can be used to explore several important physiological aspects of mucociliary clearance.

Models using native tracheobronchial mucus in the context of pulmonary drug delivery research: Composition, structure and barrier properties

Mucus covers all wet epithelia and acts as a protective barrier. In the airways of the lungs, the viscoelastic mucus meshwork entraps and clears inhaled materials and efficiently removes them by mucociliary escalation. In addition to physical and chemical interaction mechanisms, the role of macromolecular glycoproteins (mucins) and antimicrobial constituents in innate immune defense are receiving increasing attention. Collectively, mucus displays a major barrier for inhaled aerosols, also including therapeutics. This review discusses the origin and composition of tracheobronchial mucus in relation to its (barrier) function, as well as some pathophysiological changes in the context of pulmonary diseases. Mucus models that contemplate key features such as elastic-dominant rheology, composition, filtering mechanisms and microbial interactions are critically reviewed in the context of health and disease considering different collection methods of native human pulmonary mucus. Finally, the prerequisites towards a standardization of mucus models in a regulatory context and their role in drug delivery research are addressed.

Chemical and Physical Characterisation of Macroaggregated Human Serum Albumin: Strength and Specificity of Bonds with 99mTc and 68Ga

BACKGROUND

Macroaggregated human serum albumin (MAA) properties are widely used in nuclear medicine, labelled with 99mTc. The aim of this study is to improve the knowledge about the morphology, size, dimension and physical-chemical characteristics of MAA and their bond with 99mTc and 68Ga.

METHODS

Commercial kits of MAA (Pulmocis®) were used. Characterisation through experiments based on SEM, DLS and Stokes' Law were carried out. In vitro experiments for Langmuir isotherms and pH studies on radiolabelling were performed and the stability of the radiometal complex was verified through competition reactions.

RESULTS

The study settles the MAA dimension within the range 43-51 μm. The Langmuir isotherm reveals for [99mTc]MAA: Bmax (46.32), h (2.36); for [68Ga]MAA: Bmax (44.54), h (0.893). Dual labelling reveals that MAA does not discriminate different radioisotopes. Experiments on pH placed the optimal pH for labelling with 99mTc at 6.

CONCLUSION

Radiolabelling of MAA is possible with high efficiency. The nondiscriminatory MAA bonds make this drug suitable for radiolabelling with different radioisotopes or for dual labelling. This finding illustrates the need to continue investigating MAA chemical and physical characteristics to allow for secure labelling with different isotopes.

Development of a simulated lung fluid leaching method to assess the release of potentially toxic elements from volcanic ash

Freshly erupted volcanic ash contains a range of soluble elements, some of which can generate harmful effects in living cells and are considered potentially toxic elements (PTEs). This work investigates the leaching dynamics of ash-associated PTEs in order to optimize a method for volcanic ash respiratory hazard assessment. Using three pristine (unaffected by precipitation) ash samples, we quantify the release of PTEs (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, Zn) and major cations typical of ash leachates (Mg, Na, Ca, K) in multiple simulated lung fluid (SLF) preparations and under varying experimental parameters (contact time and solid to liquid ratio). Data are compared to a standard water leach (WL) to ascertain whether the WL can be used as a simple proxy for SLF leaching. The main findings are: PTE concentrations reach steady-state dissolution by 24 h, and a relatively short contact time (10 min) approximates maximum dissolution; PTE dissolution is comparatively stable at low solid to liquid ratios (1:100 to 1:1000); inclusion of commonly used macromolecules has element-specific effects, and addition of a lung surfactant has little impact on extraction efficiency. These observations indicate that a WL can be used to approximate lung bioaccessible PTEs in an eruption response situation. This is a useful step towards standardizing in vitro methods to determine the soluble-element hazard from inhaled ash.

Inorganic nanomaterials with rapid clearance for biomedical applications

Inorganic nanomaterials that have inherently exceptional physicochemical properties (e.g., catalytic, optical, thermal, electrical, or magnetic performance) that can provide desirable functionality (e.g., drug delivery, diagnostics, imaging, or therapy) have considerable potential for application in the field of biomedicine. However, toxicity can be caused by the long-term, non-specific accumulation of these inorganic nanomaterials in healthy tissues, preventing their large-scale clinical utilization. Over the past several decades, the emergence of biodegradable and clearable inorganic nanomaterials has offered the potential to prevent such long-term toxicity. In addition, a comprehensive understanding of the design of such nanomaterials and their metabolic pathways within the body is essential for enabling the expansion of theranostic applications for various diseases and advancing clinical trials. Thus, it is of critical importance to develop biodegradable and clearable inorganic nanomaterials for biomedical applications. This review systematically summarizes the recent progress of biodegradable and clearable inorganic nanomaterials, particularly for application in cancer theranostics and other disease therapies. The future prospects and opportunities in this rapidly growing biomedical field are also discussed. We believe that this timely and comprehensive review will stimulate and guide additional in-depth studies in the area of inorganic nanomedicine, as rapid in vivo clearance and degradation is likely to be a prerequisite for the future clinical translation of inorganic nanomaterials with unique properties and functionality.

Effect of hypertonic saline on mucociliary clearance and clinical outcomes in chronic bronchitis

Background

Mucus dehydration and impaired mucus clearance are common features of cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). In CF, inhaled hypertonic saline (HS) improves lung function and produces sustained increases in mucociliary clearance (MCC). We hypothesised that administration of HS (7% NaCl) twice daily for 2 weeks would improve clinical outcomes and produce sustained increases in MCC in COPD subjects with a chronic bronchitis (CB) phenotype.

Methods

Twenty-two CB subjects completed a double-blinded, crossover study comparing inhaled HS to a hypotonic control solution (0.12% saline) administered via nebuliser twice daily for 2 weeks. Treatment order was randomised. During each treatment period, symptoms and spirometry were measured. MCC was measured at baseline, shortly after initial study agent administration, and approximately 12 h after the final dose.

Results

HS was safe and well tolerated but overall produced no significant improvements in spirometry or patient-reported outcomes. CB subjects had slower baseline MCC than healthy subjects. The MCC rates over 60 min (Ave60Clr) in CB subjects following 2 weeks of HS were not different from 0.12% saline but were slower than baseline (Ave60Clr was 9.1±6.3% at baseline versus 5.3±6.9% after HS; p<0.05). Subgroup analyses determined that subjects with residual baseline central lung clearance (14 subjects) had improved spirometry and symptoms following treatment with HS, but not 0.12% saline, treatment.

Conclusions

Inhaled HS appeared to be safe in a general CB population. A specific phenotypic subgroup may benefit from HS but requires additional study.

Cilia and centrosomes: Ultrastructural and mechanical perspectives

Cilia and centrosomes of eukaryotic cells play important roles in cell movement, fluid transport, extracellular sensing, and chromosome division. The physiological functions of cilia and centrosomes are generated by their dynamics, motions, and forces controlled by the physical, chemical, and biological environments. How an individual cilium achieves its beat pattern and induces fluid flow is governed by its ultrastructure as well as the coordination of associated molecular motors. Thus, a bottom-up understanding of the physiological functions of cilia and centrosomes from the molecular to tissue levels is required. Correlations between the structure and motion can be understood in terms of mechanics. This review first focuses on cilia and centrosomes at the molecular level, introducing their ultrastructure. We then shift to the organelle level and introduce the kinematics and mechanics of cilia and centrosomes. Next, at the tissue level, we introduce nodal ciliary dynamics and nodal flow, which play crucial roles in the organogenetic process of left-right asymmetry. We also introduce respiratory ciliary dynamics and mucous flow, which are critical for protecting the epithelium from drying and exposure to harmful particles and viruses, i.e., respiratory clearance function. Finally, we discuss the future research directions in this field.

Excess mucus viscosity and airway dehydration impact COPD airway clearance

The mechanisms by which cigarette smoking impairs airway mucus clearance are not well understood. We recently established a ferret model of cigarette smoke-induced chronic obstructive pulmonary disease (COPD) exhibiting chronic bronchitis. We investigated the effects of cigarette smoke on mucociliary transport (MCT).Adult ferrets were exposed to cigarette smoke for 6 months, with in vivo mucociliary clearance measured by technetium-labelled DTPA retention. Excised tracheae were imaged with micro-optical coherence tomography. Mucus changes in primary human airway epithelial cells and ex vivo ferret airways were assessed by histology and particle tracking microrheology. Linear mixed models for repeated measures identified key determinants of MCT.Compared to air controls, cigarette smoke-exposed ferrets exhibited mucus hypersecretion, delayed mucociliary clearance (-89.0%, p<0.01) and impaired tracheal MCT (-29.4%, p<0.05). Cholinergic stimulus augmented airway surface liquid (ASL) depth (5.8±0.3 to 7.3±0.6 µm, p<0.0001) and restored MCT (6.8±0.8 to 12.9±1.2 mm·min-1, p<0.0001). Mixed model analysis controlling for covariates indicated smoking exposure, mucus hydration (ASL) and ciliary beat frequency were important predictors of MCT. Ferret mucus was hyperviscous following smoke exposure in vivo or in vitro, and contributed to diminished MCT. Primary cells from smokers with and without COPD recapitulated these findings, which persisted despite the absence of continued smoke exposure.Cigarette smoke impairs MCT by inducing airway dehydration and increased mucus viscosity, and can be partially abrogated by cholinergic secretion of fluid secretion. These data elucidate the detrimental effects of cigarette smoke exposure on mucus clearance and suggest additional avenues for therapeutic intervention.

Biodistribution, Clearance, and Long-Term Fate of Clinically Relevant Nanomaterials

Realization of the immense potential of nanomaterials for biomedical applications will require a thorough understanding of how they interact with cells, tissues, and organs. There is evidence that, depending on their physicochemical properties and subsequent interactions, nanomaterials are indeed taken up by cells. However, the subsequent release and/or intracellular degradation of the materials, transfer to other cells, and/or translocation across tissue barriers are still poorly understood. The involvement of these cellular clearance mechanisms strongly influences the long-term fate of used nanomaterials, especially if one also considers repeated exposure. Several nanomaterials, such as liposomes and iron oxide, gold, or silica nanoparticles, are already approved by the American Food and Drug Administration for clinical trials; however, there is still a huge gap of knowledge concerning their fate in the body. Herein, clinically relevant nanomaterials, their possible modes of exposure, as well as the biological barriers they must overcome to be effective are reviewed. Furthermore, the biodistribution and kinetics of nanomaterials and their modes of clearance are discussed, knowledge of the long-term fates of a selection of nanomaterials is summarized, and the critical points that must be considered for future research are addressed.

Transport and Mixing Induced by Beating Cilia in Human Airways

The fluid transport and mixing induced by beating cilia, present in the bronchial airways, are studied using a coupled lattice Boltzmann-Immersed Boundary solver. This solver allows the simulation of both single and multi-component fluid flows around moving solid boundaries. The cilia are modeled by a set of Lagrangian points, and Immersed Boundary forces are computed onto these points in order to ensure the no-slip velocity conditions between the cilia and the fluids. The cilia are immersed in a two-layer environment: the periciliary layer (PCL) and the mucus above it. The motion of the cilia is prescribed, as well as the phase lag between two cilia in order to obtain a typical collective motion of cilia, known as metachronal waves. The results obtained from a parametric study show that antiplectic metachronal waves are the most efficient regarding the fluid transport. A specific value of phase lag, which generates the larger mucus transport, is identified. The mixing is studied using several populations of tracers initially seeded into the pericilary liquid, in the mucus just above the PCL-mucus interface, and in the mucus far away from the interface. We observe that each zone exhibits different chaotic mixing properties. The larger mixing is obtained in the PCL layer where only a few beating cycles of the cilia are required to obtain a full mixing, while above the interface, the mixing is weaker and takes more time. Almost no mixing is observed within the mucus, and almost all the tracers do not penetrate the PCL layer. Lyapunov exponents are also computed for specific locations to assess how the mixing is performed locally. Two time scales are introduced to allow a comparison between mixing induced by fluid advection and by molecular diffusion. These results are relevant in the context of respiratory flows to investigate the transport of drugs for patients suffering from chronic respiratory diseases.

Model Calculations of Regional Deposition and Disposition for Single Doses of Inhaled Liposomal and Dry Powder Ciprofloxacin

BACKGROUND

Model predictions of regional deposition in the respiratory tract are useful in assessing factors that influence the effectiveness of aerosol delivery. Regional deposition models have previously been coupled with models of mucous production and clearance to estimate initial concentrations of drug deposited in the airway surface liquid (ASL) lining tracheobronchial airways.

METHODS

Established models of regional deposition and ASL volumes were used to provide input to a new model evaluating the disposition of drug resulting from dissolution or release, absorption, and mucociliary clearance. Additional modeling of oral absorption, distribution, and elimination allowed prediction of systemic exposure. Herein, predicted ASL and plasma concentrations of free (dissolved or unencapsulated) ciprofloxacin over time are reported for a healthy, adult lung model following inhalation of single doses of nebulized liposomal (6 mL of liposomal ciprofloxacin for inhalation, 50 mg/mL, or 6 mL of Pulmaquin, 210 mg; Aradigm) and dry powder (32.5 and 65 mg doses; Bayer) formulations.

RESULTS

Over a range of mucous production rates and tracheal clearance velocities, peak ASL concentrations of free ciprofloxacin were consistently greater for Pulmaquin than for other formulations investigated, owing to the presence of free drug in the nebulized Pulmaquin formulation. The time that ASL concentrations of free drug remained above the minimum inhibitory concentration for Pseudomonas aeruginosa was similar for all four formulations. Predicted plasma ciprofloxacin concentration profiles were in good agreement with available data from Phase I trials in healthy volunteers.

CONCLUSIONS

Predictions of ASL drug concentrations over time are valuable in elucidating the roles of deposition, drug release or dissolution, and disposition on the effectiveness of inhaled aerosol therapies. For inhaled ciprofloxacin, the present results predict similar ASL concentrations of free drug over time following single doses of inhaled liposomal and dry powder formulations. The impact of multiple doses and airway disease warrants further consideration.

A ferret model of COPD-related chronic bronchitis

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death in the US. The majority of COPD patients have symptoms of chronic bronchitis, which lacks specific therapies. A major impediment to therapeutic development has been the absence of animal models that recapitulate key clinical and pathologic features of human disease. Ferrets are well suited for the investigation of the significance of respiratory diseases, given prior data indicating similarities to human airway physiology and submucosal gland distribution. Here, we exposed ferrets to chronic cigarette smoke and found them to approximate complex clinical features of human COPD. Unlike mice, which develop solely emphysema, smoke-exposed ferrets exhibited markedly higher numbers of early-morning spontaneous coughs and sporadic infectious exacerbations as well as a higher level of airway obstruction accompanied by goblet cell metaplasia/hyperplasia and increased mucus expression in small airways, indicative of chronic bronchitis and bronchiolitis. Overall, we demonstrate the first COPD animal model exhibiting clinical and pathologic features of chronic bronchitis to our knowledge, providing a key advance that will greatly facilitate the preclinical development of novel treatments for this disease.

Control of lung defence by mucins and macrophages: ancient defence mechanisms with modern functions

Owing to the need to balance the requirement for efficient respiration in the face of tremendous levels of exposure to endogenous and environmental challenges, it is crucial for the lungs to maintain a sustainable defence that minimises damage caused by this exposure and the detrimental effects of inflammation to delicate gas exchange surfaces. Accordingly, epithelial and macrophage defences constitute essential first and second lines of protection that prevent the accumulation of potentially harmful agents in the lungs, and under homeostatic conditions do so effectively without inducing inflammation. Though epithelial and macrophage-mediated defences are seemingly distinct, recent data show that they are linked through their shared reliance on airway mucins, in particular the polymeric mucin MUC5B. This review highlights our understanding of novel mechanisms that link mucus and macrophage defences. We discuss the roles of phagocytosis and the effects of factors contained within mucus on phagocytosis, as well as newly identified roles for mucin glycoproteins in the direct regulation of leukocyte functions. The emergence of this nascent field of glycoimmunobiology sets forth a new paradigm for considering how homeostasis is maintained under healthy conditions and how it is restored in disease.

Magnetic Nanodrug Delivery Through the Mucus Layer of Air-Liquid Interface Cultured Primary Normal Human Tracheobronchial Epithelial Cells

Superparamagnetic iron oxide (Fe₃O₄) and highly anisotropic barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were coated with an anti-inflammatory drug and magnetically transported through mucus produced by primary human airway epithelial cells. Using wet planetary ball milling, dl-2-amino-3-phosphonopropionic acid-coated BaFe₁₂O₁₉ nano-particles (BaNPs) of 1-100 nm in diameter were prepared in water. BaNPs and conventional 20-30-nm Fe₃O₄ nanoparticles (FeNPs) were then encased in a polymer (PLGA) loaded with dexamethasone (Dex) and tagged for imaging. PLGA-Dex-coated BaNPs and FeNPs were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. Both PLGA-Dex-coated BaNPs and FeNPs were transferred to the surface of a ~100-μm thick mucus layer of air-liquid interface cultured primary normal human tracheobronchial epithelial (NHTE) cells. Within 30 min, the nanoparticles were pulled successfully through the mucus layer by a permanent neodymium magnet. The penetration time of the nanomedicine was monitored using confocal microscopy and tailored by varying the thickness of the PLGA-Dex coating around the particles.

Acquired Cystic Fibrosis Transmembrane Conductance Regulator Dysfunction in Chronic Bronchitis and Other Diseases of Mucus Clearance

Chronic obstructive pulmonary disease (COPD) is a major public health problem. No therapies alter the natural history of the disease. Chronic bronchitis is perhaps the most clinically troublesome phenotype. Emerging data strongly suggest that cigarette smoke and its components can lead to acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. Findings in vitro, in animal models, and in smokers with and without COPD also show acquired CFTR dysfunction, which is associated with chronic bronchitis. This abnormality is also present in extrapulmonary organs, suggesting that CFTR dysfunction may contribute to smoking-related systemic diseases.

Cigarette smoke and CFTR: implications in the pathogenesis of COPD

Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder consisting of chronic bronchitis and/or emphysema. COPD patients suffer from chronic infections and display exaggerated inflammatory responses and a progressive decline in respiratory function. The respiratory symptoms of COPD are similar to those seen in cystic fibrosis (CF), although the molecular basis of the two disorders differs. CF is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding a chloride and bicarbonate channel (CFTR), leading to CFTR dysfunction. The majority of COPD cases result from chronic oxidative insults such as cigarette smoke. Interestingly, environmental stresses including cigarette smoke, hypoxia, and chronic inflammation have also been implicated in reduced CFTR function, and this suggests a common mechanism that may contribute to both the CF and COPD. Therefore, improving CFTR function may offer an excellent opportunity for the development of a common treatment for CF and COPD. In this article, we review what is known about the CF respiratory phenotype and discuss how diminished CFTR expression-associated ion transport defects may contribute to some of the pathological changes seen in COPD.

Factors Affecting Magnetic Retention of Particles in the Upper Airways: An In Vitro and Ex Vivo Study

This paper presents the results of experiments using an in vitro model and an ex vivo animal model (Rana catesbeiana) to study magnetic particle retention in the conducting airways, specifically the trachea and bronchi. The purpose of these experiments was to determine the significant factors for retention of magnetic particles deposited from an aerosol at the airway surface using a magnetic field. The results indicate that the apparent viscosity of the mucus layer at low shear rates is the most significant obstacle to particle retention. The results also show that particle size and aggregation play major roles in particle retention. The mucus transport rate, unlike the effect of fluid velocity in intravenous applications, did not appear to be a determining factor for particle retention. It was also found that a suitably designed magnetic system, aside from having a high intensity, needs to exert a strong radial field to promote particle aggregation. The findings suggest that one possible approach to magnetic particle retention could be delivery of a mucolytic agent along with the drug particles. This study provides the fundamentals needed for development of a targeted magnetic drug delivery system for inhaled therapeutic aerosol particles.

Rotation frequency of human bronchial and nasal epithelial spheroids as an indicator of mucociliary function

BACKGROUND

We evaluated a new in vitro model for mucociliary transport function. Spheroids of human respiratory epithelium show beating cilia at their surface. When cultured in their own mucus, spheroids can rotate along their axis due to coordinated ciliary beating.

OBJECTIVE AND METHODS

To assess whether this setup yields meaningful results we measured rotation frequency (RF) of human bronchial or nasal epithelial spheroids under different temperatures and concentrations of isoproterenol. Isoproterenol was administered either as caged compound releasing active isoproterenol after illumination with UV light, or through a permeable membrane in a two-chamber system.

RESULTS

Under stable conditions, RF remained constant over 200 min. Between 27 and 35 degrees C, there was a temperature-dependent increase: RF(27)( degrees )(C) = 0.27 +/- 0.08 s(-1), and RF(37)( degrees )(C) = 0.43 +/- 0.10 s(-1) (means +/- SEM). Isoproterenol (10(-5), 10(-4) and 10(-3) mmol/l) induced concentration-dependent increases in RF (9, 20 and 25%, respectively; medians) if applied in the two-chamber system. The experiments with caged isoproterenol did not yield conclusive results, probably because the byproducts from photolysis negatively affected ciliary function. The transport velocity at the surface of bronchial and nasal spheroids was estimated to be 2.96 and 3.62 mm/min (medians), respectively, which is in the same range as mucus transport velocity measured in vivo in humans.

CONCLUSIONS

This setup can be used to study mucociliary transport function under controlled conditions in vitro, in particular as RF is likely to reflect not only ciliary beat frequency, but also the coordination of ciliary beating and the properties of the mucus.