Amiloride inhalation therapy in cystic fibrosis. Influence on ion content, hydration, and rheology of sputum

Endocytosis and Transcytosis of SARS-CoV-2 Across the Intestinal Epithelium and Other Tissue Barriers

Since 2003, the world has been confronted with three new betacoronaviruses that cause human respiratory infections: SARS-CoV, which causes severe acute respiratory syndrome (SARS), MERS-CoV, which causes Middle East respiratory syndrome (MERS), and SARS-CoV-2, which causes Coronavirus Disease 2019 (COVID-19). The mechanisms of coronavirus transmission and dissemination in the human body determine the diagnostic and therapeutic strategies. An important problem is the possibility that viral particles overcome tissue barriers such as the intestine, respiratory tract, blood-brain barrier, and placenta. In this work, we will 1) consider the issue of endocytosis and the possibility of transcytosis and paracellular trafficking of coronaviruses across tissue barriers with an emphasis on the intestinal epithelium; 2) discuss the possibility of antibody-mediated transcytosis of opsonized viruses due to complexes of immunoglobulins with their receptors; 3) assess the possibility of the virus transfer into extracellular vesicles during intracellular transport; and 4) describe the clinical significance of these processes. Models of the intestinal epithelium and other barrier tissues for in vitro transcytosis studies will also be briefly characterized.

Mucociliary Respiratory Epithelium Integrity in Molecular Defense and Susceptibility to Pulmonary Viral Infections

Mucociliary defense, mediated by the ciliated and goblet cells, is fundamental to respiratory fitness. The concerted action of ciliary movement on the respiratory epithelial surface and the pathogen entrapment function of mucus help to maintain healthy airways. Consequently, genetic or acquired defects in lung defense elicit respiratory diseases and secondary microbial infections that inflict damage on pulmonary function and may even be fatal. Individuals living with chronic and acute respiratory diseases are more susceptible to develop severe coronavirus disease-19 (COVID-19) illness and hence should be proficiently managed. In light of the prevailing pandemic, we review the current understanding of the respiratory system and its molecular components with a major focus on the pathophysiology arising due to collapsed respiratory epithelium integrity such as abnormal ciliary movement, cilia loss and dysfunction, ciliated cell destruction, and changes in mucus rheology. The review includes protein interaction networks of coronavirus infection-manifested implications on the molecular machinery that regulates mucociliary clearance. We also provide an insight into the alteration of the transcriptional networks of genes in the nasopharynx associated with the mucociliary clearance apparatus in humans upon infection by severe acute respiratory syndrome coronavirus-2.

Understanding SARS-CoV-2 endocytosis for COVID-19 drug repurposing

The quest for the effective treatment against coronavirus disease 2019 pneumonia caused by the severe acute respiratory syndrome (SARS)‐coronavirus 2(CoV‐2) coronavirus is hampered by the lack of knowledge concerning the basic cell biology of the infection. Given that most viruses use endocytosis to enter the host cell, mechanistic investigation of SARS‐CoV‐2 infection needs to consider the diversity of endocytic pathways available for SARS‐CoV‐2 entry in the human lung epithelium. Taking advantage of the well‐established methodology of membrane trafficking studies, this research direction allows for the rapid characterisation of the key cell biological mechanism(s) responsible for SARS‐CoV‐2 infection. Furthermore, 11 clinically approved generic drugs are identified as potential candidates for repurposing as blockers of several potential routes for SARS‐CoV‐2 endocytosis. More broadly, the paradigm of targeting a fundamental aspect of human cell biology to protect against infection may be advantageous in the context of future pandemic outbreaks.

Role of mucins in lung homeostasis: regulated expression and biosynthesis in health and disease

In humans and mice, the first line of innate defense against inhaled pathogens and particles in the respiratory tract is airway mucus. The primary solid components of the mucus layer are the mucins MUC5AC and MUC5B, polymeric glycoproteins whose changes in abundance and structure can dramatically affect airway defense. Accordingly, MUC5AC/Muc5ac and MUC5B/Muc5b are tightly regulated at a transcriptional level by tissue-specific transcription factors in homeostasis and in response to injurious and inflammatory triggers. In addition to modulated levels of mucin gene transcription, translational and post-translational biosynthetic processes also exert significant influence upon mucin function. Mucins are massive macromolecules with numerous functional domains that contribute to their structural composition and biophysical properties. Single MUC5AC and MUC5B apoproteins have molecular masses of >400 kDa, and von Willebrand factor D-like as well as other cysteine-rich domain segments contribute to mucin polymerization and flexibility, thus increasing apoprotein length and complexity. Additional domains serve as sites for O-glycosylation, which increase further mucin mass several-fold. Glycosylation is a defining process for mucins that is specific with respect to additions of glycans to mucin apoprotein backbones, and glycan additions influence the physical properties of the mucins via structural modifications as well as charge interactions. Ultimately, through their tight regulation and complex assembly, airway mucins follow the biological rule of 'form fits function' in that their structural organization influences their role in lung homeostatic mechanisms.

Influenza virus infection alters ion channel function of airway and alveolar cells: mechanisms and physiological sequelae

The cystic fibrosis transmembrane conductance regulator (CFTR) and the amiloride-sensitive epithelial sodium channels (ENaC) are located in the apical membranes of airway and alveolar epithelial cells. These transporters play an important role in the regulation of lung fluid balance across airway and alveolar epithelia by being the conduits for chloride (Cl^-) and bicarbonate ([Formula: see text]) secretion and sodium (Na⁺) ion absorption, respectively. The functional role of these channels in the respiratory tract is to maintain the optimum volume and ionic composition of the bronchial periciliary fluid (PCL) and alveolar lining fluid (ALF) layers. The PCL is required for proper mucociliary clearance of pathogens and debris, and the ALF is necessary for surfactant homeostasis and optimum gas exchange. Dysregulation of ion transport may lead to mucus accumulation, bacterial infections, inflammation, pulmonary edema, and compromised respiratory function. Influenza (or flu) in mammals is caused by influenza A and B viruses. Symptoms include dry cough, sore throat, and is often followed by secondary bacterial infections, accumulation of fluid in the alveolar spaces and acute lung injury. The underlying mechanisms of flu symptoms are not fully understood. This review summarizes our present knowledge of how influenza virus infections alter airway and alveolar epithelial cell CFTR and ENaC function in vivo and in vitro and the role of these changes in influenza pathogenesis.

Pharmacological Approaches to Correcting the Ion Transport Defect in Cystic Fibrosis

Cystic fibrosis (CF) is a lethal genetic disease caused by a mutation in a membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), which mainly (but not exclusively) functions as a chloride channel. The main clinical symptoms are chronic obstructive lung disease, which is responsible for most of the morbidity and mortality associated with CF, and pancreatic insufficiency. About 1000 mutations of the gene coding for CFTR are currently known; the most common of these, present in the great majority of the patients (Delta508) results in the deletion of a phenylalanine at position 508. In this mutation, the aberrant CFTR is not transported to the membrane but degraded in the ubiquitin-proteasome pathway. The aim of this review is to give an overview of the pharmacologic strategies currently used in attempts to overcome the ion transport defect in CF. One strategy to develop pharmacologic treatment for CF is to inhibit the breakdown of DeltaF508-CFTR by interfering with the chaperones involved in the folding of CFTR. At least in in vitro systems, this can be accomplished by sodium phenylbutyrate, or S-nitrosoglutathione (GSNO), and also by genistein or benzo[c]quinolizinium compounds. It is also possible to stimulate CFTR or its mutated forms, when present in the plasma membrane, using xanthines, genistein, and various other compounds, such as benzamidizoles and benzoxazoles, benzo[c]quinolizinium compounds or phenantrolines. Experimental results are not always unambiguous, and adverse effects have been incompletely tested. Some clinical tests have been done on sodium phenyl butyrate, GSNO and genistein, mostly in respect to other diseases, and the results demonstrate that these drugs are reasonably well tolerated. Their efficiency in the treatment of CF has not yet been demonstrated, however. An alternative strategy is to compensate for the defective chloride transport by CFTR by stimulation of other chloride channels. This can be done via purinergic receptors. A phase I study using a stable uridine triphosphate analog has recently been completed. A second alternative strategy is to attempt to maintain hydration of the airway mucus by inhibiting Na(+) uptake by the epithelial Na(+) channel using amiloride or stable analogs of amiloride. Clinical tests so far have been inconclusive. A number of other suggestions are currently being explored. The minority of patients with CF who have a stop mutation may benefit from treatment with gentamicin. The difficulties in finding a pharmacologic treatment for CF may be due to the fact that CFTR has additional functions besides chloride transport, and interfering with CFTR biosynthesis or activation implies interference with central cellular processes, which may have undesirable adverse effects.

[Antisense oligonucleotides for therapy of cystic fibrosis. Inhibition of sodium absorption mediated by ENaC in nasal epithelial cells]

BACKGROUND

The genetic disease cystic fibrosis (CF) is characterised by reduced chloride secretion mediated by the cystic fibrosis transmembrane conductance regulator (CFTR) and Na(+) hyperabsorption through amiloride-sensitive epithelial sodium channels (ENaC). Mutations in CFTR cause the accumulation of thick mucus and dysfunction of mucociliary clearance in the respiratory tract.

MATERIAL AND METHODS

In this project it was investigated whether Na(+) hyperabsorption is inhibited by the use of antisense oligonucleotides (AON). For functional analyses monolayers of human non-CF and CF nasal epithelial cells were measured in modified Ussing chambers. To analyse the AON effects on the protein level Western blotting analyses were carried out.

RESULTS

AON transfection significantly inhibits Na(+) absorption via ENaC in non-CF and CF cells. Furthermore, Western blot analyses demonstrate a suppression of the ENaC protein in AON transfected human non-CF cells.

CONCLUSION

The inhibition of ENaC associated Na(+) absorption by specific AON could offer a new perspective for the regulation of the Na(+) hyperabsorption in CF patients.

Specific inhibition of epithelial Na+ channels by antisense oligonucleotides for the treatment of Na+ hyperabsorption in cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) respiratory epithelia are characterized by a defect Cl(-) secretion and an increased Na(+) absorption through epithelial Na(+) channels (ENaC). The present study aimed to find an effective inhibitor of human ENaC with respect to replacing amiloride therapy for CF patients. Therefore, we developed specific antisense oligonucleotides (AON) that efficiently suppress Na(+) hyperabsorption by inhibiting the expression of the alpha-ENaC subunit.

METHODS

We heterologously expressed ENaC in oocytes of Xenopus laevis for mass screening of AON. Additionally, primary cultures of human nasal epithelia were transfected with AON and were used for Ussing chamber experiments, as well as biochemical and fluorescence optical analyses.

RESULTS

Screening of several AON by co-injection or sequential microinjection of AON and ENaC mRNA in X. laevis oocytes led to a sustained decrease in amiloride-sensitive current and conductance. Using primary cultures of human nasal epithelia, we show that AON effectively suppress amiloride-sensitive Na(+) absorption mediated by ENaC in CF and non-CF tissues. In western blot experiments, it could be shown that the amount of ENaC protein is effectively reduced after AON transfection.

CONCLUSIONS

Our data comprise an initial step towards a preclinical test with AON to reduce Na(+) hyperabsorption in CF epithelia.

Primary ciliary dyskinesia: prospects for new therapies, building on the experience in cystic fibrosis

Primary ciliary dyskinesia (PCD) is a genetic disease associated with abnormal ciliary structure and function, leading to impaired mucociliary clearance, an important primary innate defense mechanism that protects the lungs. Drugs that can effectively treat PCD should overcome the defect in ciliary function and increase the mucociliary clearance. However, there are currently no therapeutic strategies that correct the inborn error of ciliary dysfunction to restore mucociliary clearance. It is unclear if osmolar agents like hypertonic saline or mannitol, therapies that increase the respiratory surface hydration like ion-channel regulators, or therapies aimed at reducing inflammation or mucus production, or softening the mucus will be effective in PCD. Many of these modalities are used in cystic fibrosis, yet no evidence exists to support their routine use in PCD. Newer genetic modifiers show an exciting potential for personalized medication, combining selection of patients with a common genetic mutation and a drug treatment that has been specifically designed to overcome that mutation, and will greatly enhance the therapeutic arsenal for PCD. This review summarizes current and future prospects for these therapeutic options.

Tobramycin and FDA-approved iron chelators eliminate Pseudomonas aeruginosa biofilms on cystic fibrosis cells

The ability of Pseudomonas aeruginosa to form antibiotic-resistant biofilms is thought to account for the inability of current therapies to resolve bacterial infections in the lungs of patients with cystic fibrosis (CF). We recently described a system in which highly antibiotic-resistant P. aeruginosa biofilms grow on human CF airway epithelial cells, and using this system we showed that enhanced iron release from CF cells facilitates the development of such highly antibiotic-resistant biofilms. Given the positive role for iron in biofilm development, we investigated whether the FDA-approved iron chelators deferoxamine and deferasirox would enhance the ability of tobramycin, the primary antibiotic used to treat CF lung infections, to eliminate P. aeruginosa biofilms. The combination of tobramycin with deferoxamine or deferasirox reduced established biofilm biomass by approximately 90% and reduced viable bacteria by 7-log units. Neither tobramycin nor deferoxamine nor deferasirox alone had such a marked effect. The combination of tobramycin and FDA-approved iron chelators also prevented the formation of biofilms on CF airway cells. These data suggest that the combined use of tobramycin and FDA-approved iron chelators may be an effective therapy to treat patients with CF and other lung disease characterized by antibiotic-resistant P. aeruginosa biofilms.

Role of magnesium in the failure of rhDNase therapy in patients with cystic fibrosis

BACKGROUND

In the management of cystic fibrosis (CF), rhDNase-I inhalation is widely used to facilitate the removal of the highly viscous and elastic mucus (often called sputum) from the lungs. However, an important group of CF patients does not benefit from rhDNase-I treatment. A study was undertaken to elucidate the reason for the failure of rhDNase-I in these patients and to evaluate strategies to overcome this.

METHODS

The biochemical properties, physical properties, and degradation by rhDNase-I of sputum obtained from clinical responders and non-responders to rhDNase-I were compared, and the ability of magnesium to reactivate rhDNase-I in DNA solutions and in sputum was investigated. The effect of oral magnesium supplements on magnesium levels in the sputum of patients with CF was also examined.

RESULTS

Sputum from clinical responders was extensively degraded in vitro on incubation with rhDNase-I, while sputum from clinical non-responders was not degraded: the median decrease in sputum elasticity in the two groups was 32% and 5%, respectively. Sputum from clinical responders contained significantly higher concentrations of magnesium than sputum from non-responders (2.0 mM v 1.3 mM; p = 0.020). Sputum that could not be degraded by rhDNase-I became degradable after preincubation with magnesium. The effect of magnesium on rhDNase-I activity was mediated through actin. Oral intake of magnesium enhanced the magnesium concentration in the sputum of CF patients.

CONCLUSION

Increasing the magnesium concentration in sputum by, for example, oral magnesium supplements may be a promising new strategy to overcome the failure of rhDNase-I in patients with CF.

A physical linkage between cystic fibrosis airway surface dehydration and Pseudomonas aeruginosa biofilms

A vexing problem in cystic fibrosis (CF) pathogenesis has been to explain the high prevalence of Pseudomonas aeruginosa biofilms in CF airways. We speculated that airway surface liquid (ASL) hyperabsorption generates a concentrated airway mucus that interacts with P. aeruginosa to promote biofilms. To model CF vs. normal airway infections, normal (2.5% solids) and CF-like concentrated (8% solids) mucus were prepared, placed in flat chambers, and infected with an approximately 5 x 10(3) strain PAO1 P. aeruginosa. Although bacteria grew to 10(10) cfu/ml in both mucus concentrations, macrocolony formation was detected only in the CF-like (8% solids) mucus. Biophysical and functional measurements revealed that concentrated mucus exhibited properties that restrict bacterial motility and small molecule diffusion, resulting in high local bacterial densities with high autoinducer concentrations. These properties also rendered secondary forms of antimicrobial defense, e.g., lactoferrin, ineffective in preventing biofilm formation in a CF-like mucus environment. These data link airway surface liquid hyperabsorption to the high incidence of P. aeruginosa biofilms in CF via changes in the hydration-dependent physical-chemical properties of mucus and suggest that the thickened mucus gel model will be useful to develop therapies of P. aeruginosa biofilms in CF airways.

Reduced Three-Dimensional Motility in Dehydrated Airway Mucus Prevents Neutrophil Capture and Killing Bacteria on Airway Epithelial Surfaces

Cystic fibrosis (CF) lung disease is characterized by persistent lung infection. Thickened (concentrated) mucus in the CF lung impairs airway mucus clearance, which initiates bacterial infection. However, airways have other mechanisms to prevent bacterial infection, including neutrophil-mediated killing. Therefore, we examined whether neutrophil motility and bacterial capture and killing functions are impaired in thickened mucus. Mucus of three concentrations, representative of the range of normal (1.5 and 2.5% dry weight) and CF-like thickened (6.5%) mucus, was obtained from well-differentiated human bronchial epithelial cultures and prepared for three-dimensional studies of neutrophil migration. Neutrophil chemotaxis in the direction of gravity was optimal in 1.5% mucus, whereas 2.5% mucus best supported neutrophil chemotaxis against gravity. Lateral chemokinetic movement was fastest on airway epithelial surfaces covered with 1.5% mucus. In contrast, neutrophils exhibited little motility in any direction in thickened (6.5%) mucus. In in vivo models of airway mucus plugs, neutrophil migration was inhibited by thickened mucus (CF model) but not by normal concentrations of mucus ("normal" model). Paralleling the decreased neutrophil motility in thickened mucus, bacterial capture and killing capacity were decreased in CF-like thickened mucus. Similar results with each mucus concentration were obtained with mucus from CF cultures, indicating that inhibition of neutrophil functions was mucus concentration dependent not CF source dependent. We conclude that concentrated ("thick") mucus inhibits neutrophil migration and killing and is a key component in the failure of defense against chronic airways infection in CF.

Inositol polyphosphate derivative inhibits Na+ transport and improves fluid dynamics in cystic fibrosis airway epithelia

Amiloride-sensitive, epithelial Na(+) channel (ENaC)-mediated, active absorption of Na(+) is elevated in the airway epithelium of cystic fibrosis (CF) patients, resulting in excess fluid removal from the airway lumen. This excess fluid/volume absorption corresponds to CF transmembrane regulator-linked defects in ENaC regulation, resulting in the reduced mucociliary clearance found in CF airways. Herein we show that INO-4995, a synthetic analog of the intracellular signaling molecule, D-myo-inositol 3,4,5,6-tetrakisphosphate, inhibits Na(+) and fluid absorption across CF airway epithelia, thus alleviating this critical pathology. This conclusion was based on electrophysiological studies, fluid absorption, and (22)Na(+) flux measurements in CF airway epithelia, contrasted with normal epithelia, and on electrophysiological studies in Madin-Darby canine kidney cells and 3T3 cells overexpressing ENaC. The effects of INO-4995 were long-lasting, dose-dependent, and more pronounced in epithelia from CF patients vs. controls. These findings support preclinical development of INO-4995 for CF treatment and demonstrate for the first time the therapeutic potential of inositol polyphosphate derivatives.

DNA binding: a novel function of Pseudomonas aeruginosa type IV pili

The opportunistic pathogen Pseudomonas aeruginosa produces multifunctional, polar, filamentous appendages termed type IV pili. Type IV pili are involved in colonization during infection, twitching motility, biofilm formation, bacteriophage infection, and natural transformation. Electrostatic surface analysis of modeled pilus fibers generated from P. aeruginosa strain PAK, K122-4, and KB-7 pilin monomers suggested that a solvent-exposed band of positive charge may be a common feature of all type IV pili. Several functions of type IV pili, including natural transformation and biofilm formation, involve DNA. We investigated the ability of P. aeruginosa type IV pili to bind DNA. Purified PAK, K122-4, and KB-7 pili were observed to bind both bacterial plasmid and salmon sperm DNA in a concentration-dependent and saturable manner. PAK pili had the highest affinity for DNA, followed by K122-4 and KB-7 pili. DNA binding involved backbone interactions and preferential binding to pyrimidine residues even though there was no evidence of sequence-specific binding. Pilus-mediated DNA binding was a function of the intact pilus and thus required elements present in the quaternary structure. However, binding also involved the pilus tip as tip-specific, but not base-specific, antibodies inhibited DNA binding. The conservation of a Thr residue in all type IV pilin monomers examined to date, along with the electrostatic data, implies that DNA binding is a conserved function of type IV pili. Pilus-mediated DNA binding could be important for biofilm formation both in vivo during an infection and ex vivo on abiotic surfaces.

Ionic interaction of amiloride and uridine 5'-triphosphate in nebulizer solutions

Combination therapy using nebulized amiloride hydrochloride and uridine-5'-triphosphate (UTP) trisodium salt aerosols has been investigated for the treatment of cystic fibrosis (CF). Amiloride in aqueous solution precipitates in the presence of UTP, reducing drug concentrations. Interactions between these drugs and NaCl in solution were studied using phase-solubility techniques monitored by UV spectrophotometry. Elemental analyses were employed for precipitate characterization. Amiloride solubility was reduced by more than 85% in saline. Amiloride solubility decreased with increasing UTP concentration, resulting in formation of a precipitated complex. The theoretical molar ratio of complexes range from 1-3 amiloride:1 UTP. At most concentrations only 3 amiloride:1 UTP complex was observed in precipitate. This is a reflection of low Ksp for the 3:1 complex of 2.92 x 10(-11) M4 compared with 2.09 x 10(-4) M2 for amiloride alone. Equilibration over excess bulk solid resulted in higher solubility estimates and different phase solubility diagrams than solubility studies utilizing precipitation technique. This may be explained by the absence of amiloride in the solid state and its impact on complex equilibria with UTP. The solubility suppressing effects of UTP and saline were largely additive. A number of ionic interactions increase complex solubility profile of amiloride hydrochloride in the presence of UTP and NaCl.

Protein composition of apical surface fluid from the human airway cell line Calu-3: effect of ion transport mediators

BACKGROUND

Analysis of the protein components of airway secretions is a potential means of detecting and characterizing biochemical alterations associated with airway diseases.

METHODS

We evaluated airway protein secretions using the airway epithelial cell line Calu-3 grown at an air-liquid interface. To observe changes in apically secreted proteins, we analyzed the protein content of apical surface fluid (ASF) washings of Calu-3 monolayers treated with ion transport mediators.

RESULTS

Immunoassay screening for antibacterial and inflammatory proteins indicated the presence of measurable levels of lysozyme and IL-8 in Calu-3 ASF. RT-PCR and immunoassay studies indicated that Calu-3 cells do not produce clara cell 10 kDa protein (CC10). The total protein secretion of Calu-3 was not altered by bradykinin, but amiloride and adenosine significantly increased Calu-3 protein secretion. Lysozyme secretion was not altered by bradykinin, but amiloride and adenosine significantly reduced lysozyme secretion. IL-8 secretion was not altered by bradykinin or adenosine, but amiloride significantly decreased IL-8 secretion.

CONCLUSION

Our results demonstrate the presence of antibacterial protein lysozyme and the pro-inflammatory cytokine IL-8 in Calu-3 ASF and that ion transport mediators such as bradykinin, amiloride and adenosine influence the secretion of Calu-3 ASF proteins.

Prostasin, a membrane-anchored serine peptidase, regulates sodium currents in JME/CF15 cells, a cystic fibrosis airway epithelial cell line

Prostasin is a tryptic peptidase expressed in prostate, kidney, lung, and airway. Mammalian prostasins are related to Xenopus channel-activating protease, which stimulates epithelial Na+channel (ENaC) activity in frogs. In human epithelia, prostasin is one of several membrane peptidases proposed to regulate ENaC. This study tests the hypothesis that prostasin can regulate ENaC in cystic fibrosis epithelia in which excessive Na+uptake contributes to salt and water imbalance. We show that prostasin mRNA and protein are strongly expressed by human airway epithelial cell lines, including immortalized JME/CF15 nasal epithelial cells homozygous for the ΔF508 cystic fibrosis mutation. Epithelial cells transfected with vectors encoding recombinant soluble prostasin secrete active, tryptic peptidase that is highly sensitive to inactivation by aprotinin. When studied as monolayers in Ussing chambers, JME/CF15 cells exhibit amiloride-sensitive, transepithelial Na+currents that are markedly diminished by aprotinin, suggesting regulation by serine-class peptidases. Overproduction of membrane-anchored prostasin in transfected JME/CF15 cells does not augment Na+currents, and trypsin-induced increases are small, suggesting that baseline serine peptidase-dependent ENaC activation is maximal in these cells. To probe prostasin’s involvement in basal ENaC activity, we silenced expression of prostasin using short interfering RNA targeting of prostasin mRNA’s 3′-untranslated region. This drops ENaC currents to 26 ± 9% of baseline. These data predict that prostasin is a major regulator of ENaC-mediated Na+current in ΔF508 cystic fibrosis epithelia and suggest that airway prostasin is a target for therapeutic inhibition to normalize ion current in cystic fibrosis airway.

Pharmacotherapy of the ion transport defect in cystic fibrosis: role of purinergic receptor agonists and other potential therapeutics

Cystic fibrosis (CF), is an autosomal recessive disease frequently seen in the Caucasian population. It is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CF is characterized by enhanced airway Na(+) absorption, mediated by epithelial Na(+) channels (ENaC), and deficient Cl(-) transport. In addition, other mechanisms may contribute to the pathophysiological changes in the CF lung, such as defective regulation of HCO(3)(-) secretion. In other epithelial tissues, epithelial Na(+) conductance is either increased (intestine) or decreased (sweat duct) in CF. CFTR is a cyclic AMP-regulated epithelial Cl(-) channel, and appears to control the activity of several other transport proteins. Accordingly, defective epithelial ion transport in CF is likely to be a combination of defective Cl(-) channel function and impaired regulator function of CFTR, which in turn is linked to impaired mucociliary clearance and development of chronic lung disease. As the clinical course of CF is determined primarily by progressive lung disease, novel pharmacological strategies for the treatment of CF focus on correction of the ion transport defect in the airways. In recent years, it has been demonstrated that activation of purinergic receptors in airway epithelia by extracellular nucleotides (adenosine triphosphate/uridine triphosphate) has beneficial effects on mucus clearance in CF. Activation of the dominant class of metabotropic purinergic receptors, P2Y(2) receptors, appears to have a 2-fold benefit on ion transport in CF airways; excessive Na(+) absorption is attenuated, most likely by inhibition of the ENaC and, simultaneously, an alternative Ca(2+)-dependent Cl(-) channel is activated that may compensate for the CFTR Cl(-) channel defect. Thus activation of P2Y(2) receptors is expected to lead to improved hydration of the airway surface liquid in CF. Furthermore, purinergic activation has been shown to promote other components of mucociliary clearance such as ciliary beat frequency and mucus secretion. Clinical trials are under way to test the effect of synthetic purinergic compounds, such as the P2Y(2) receptor agonist INS37217, on the progression of lung disease in patients with CF. Administration of these compounds alone, or in combination with other drugs that inhibit accelerated Na(+) transport and help recover or increase residual activity of mutant CFTR, is most promising as successful therapy to counteract the ion transport defect in the airways of CF patients.

Hyperosmolar solutions stimulate mucus secretion in the ferret trachea

STUDY OBJECTIVES

Inhalation of hypertonic saline or mannitol solutions acutely increases mucociliary clearance. Because increased clearance is often coupled with increased mucus secretion, we hypothesized that hyperosmolar agents would stimulate mucus secretion.

SETTING AND SUBJECTS

The isolated tracheae of healthy young adult ferrets were studied in a basic research laboratory.

MEASUREMENTS AND RESULTS

We demonstrated that there was a dose-dependent increase in mucin secretion by enzyme-linked lectin assay after incubation with 1.69 g/dL (597 mOsm/L), 3.69 g/dL (1,192 mOsm/L), 5.69 g/dL (1,823 mOsm/L), and 10.69 g/dL (3,612 mOsm/L) of saline solution over Krebs-Henseleit solution control (288 mOsm/L) [p < 0.01 for 1.69 g/dL of saline solution and p < 0.0001 for others]. Mannitol solution, 15 g/dL (1,040 mOsm/L), also significantly increased mucin secretion (n = 4, p < 0.005). There was a 47% and 54% increase in secretion of the serous cell product lysozyme after exposure to 3.69 g/dL (1,192 mOsm/L) and 10.69 g/dL (3,612 mOsm/L) saline solutions, respectively (n = 5, p < 0.05). Secretion was only stimulated when the hyperosmolar exposure was on the luminal side of the epithelium. Mucin secretion was induced within minutes of 3.69 g/dL of saline solution exposure, and this increased mucin secretion quickly peaked. The ratio of mucin to lysozyme secretion was approximately 2. This ratio appeared to be independent of the osmotic concentration of the stimulus and therefore of secretory rate.

CONCLUSIONS

Mucus secretion is markedly stimulated in response to hyperosmolarity. This may be a protective response. These results also suggest that the therapeutic use of hyperosmolar aerosols should be evaluated with care when used for patients with mucus hypersecretion and impaired mucus clearance.

Effect of osmolality on mucociliary transportability and rheology of cystic fibrosis and bronchiectasis sputum

OBJECTIVE

Water is the main constituent of mucus, and its concentration is likely to be important in all aspects of mucus function, including ciliary clearance. The objective of this study was to investigate the effect of water content and osmolality of the mucus on mucociliary transportability.

METHODOLOGY

Rheology and ciliary transportability of 10 sputum samples that had been subjected to various manipulations were measured using a mucus-depleted bovine trachea model.

RESULTS

It was shown that addition of sodium chloride 0.2 Osmoles/kg (0.585% weight for weight) increased the transportability by 41% (P < 0.01). Evaporation of the sputum to 50% of its original weight caused a 118% increase in transportability (P < 0.0006), but iso-osmolal removal of 50% of the liquid with filter cards led to a non-significant, 25% increase in transportability. Parallel plate viscoelasticity was approximately doubled in both the evaporated and liquid-depleted samples, but was not changed by the addition of 0.2 Osmoles/kg of sodium chloride. The correlation between the osmolality of sputum and ciliary transportability (r = 0.54, P= 0.005) was better than the correlations between the viscosity (r = 0.21, P= 0.27) or elasticity (r = 0.23, P= 0.23) and ciliary transportability.

CONCLUSIONS

These results suggest that the osmolality of sputum exerts a greater influence on mucociliary clearance than its viscoelastic properties.

Pharmaceutical and biotechnological aerosols for cystic fibrosis therapy

This review addresses different aerosol therapies used to treat the underlying cause and symptoms of cystic fibrosis (CF) during the past two decades. A summary of the current methods of aerosol delivery and suggestions that may improve the efficacy of the current treatments are provided.

Effects of intravenous furosemide on mucociliary transport and rheological properties of patients under mechanical ventilation

The use of intravenous (IV) furosemide is common practice in patients under mechanical ventilation (MV), but its effects on respiratory mucus are largely unknown. Furosemide can affect respiratory mucus either directly through inhibition of the NaK(Cl)2 co-transporter on the basolateral surface of airway epithelium or indirectly through increased diuresis and dehydration. We investigated the physical properties and transportability of respiratory mucus obtained from 26 patients under MV distributed in two groups, furosemide (n = 12) and control (n = 14). Mucus collection was done at 0, 1, 2, 3 and 4 hours. The rheological properties of mucus were studied with a microrheometer, and in vitro mucociliary transport (MCT) (frog palate), contact angle (CA) and cough clearance (CC) (simulated cough machine) were measured. After the administration of furosemide, MCT decreased by 17 +/- 19%, 24 +/- 11%, 18 +/- 16% and 18 +/- 13% at 1, 2, 3 and 4 hours respectively, P < 0.001 compared with control. In contrast, no significant changes were observed in the control group. The remaining parameters did not change significantly in either group. Our results support the hypothesis that IV furosemide might acutely impair MCT in patients under MV.

Tracheobronchial mucus viscoelasticity during environmental challenge in horses with recurrent airway obstruction

The goal of this study was to compare the rheological properties of mucus from horses with recurrent airway obstruction (RAO) to that from healthy controls during environmental challenge by stabling in stalls with straw as bedding and hay as feed. We determined viscoelasticity (log G* dyn/cm2, at 10 radian/s) and calculated mucociliary clearability index (MCI) and cough clearability index (CCI), which are derivative parameters of G* and the ratio of viscosity and elasticity measured at 1 and 100 radian/s, respectively. We also investigated the solids content of mucus, and cytology of bronchoalveolar lavage fluid (BALF). Samples were obtained before (0 h) and 6, 24 and 48 h after environmental challenge. The central findings were rheological changes in airway mucus, which occurred over time in RAO-affected animals, but not in controls. Mucus rheology was similar in both groups at 0 and 6 h. In RAO-affected horses, mucus viscoelasticity, as measured by log G*, increased from 2.49 +/- 0.18 dyn/cm2 (mean +/- s.e.) at 0 h to 3.05 +/- 0.13 dyn/cm2 at 24 h after environmental challenge, and was accompanied by significant decreases in MCI and CCI. Percent solids of mucus did not differ significantly between the 2 groups, nor over time. Rheological values did not correlate with BALF cytology. We conclude that viscoelastic properties of tracheal mucus samples from RAO horses in remission do not differ from those of normal horses. However, environmental challenge causes clinical signs of small airway disease and a concurrent increase in mucus viscoelasticity only in RAO horses. Therefore, we infer that unfavourable changes in mucus rheology may contribute to stasis and accumulation of mucus in RAO horses in exacerbation, but not in clinical remission.

Influenza virus inhibits amiloride-sensitive Na+ channels in respiratory epithelia

Many pathogens causing diarrhea do so by modulating ion transport in the gut. Respiratory pathogens are similarly associated with disturbances of fluid balance in the respiratory tract, although it is not known whether they too act by altering epithelial ion transport. Here we show that influenza virus A/PR/8/34 inhibits the amiloride-sensitive Na(+) current across mouse tracheal epithelium with a half-time of about 60 min. We further show that the inhibitory effect of the influenza virus is caused by the binding of viral hemagglutinin to a cell-surface receptor, which then activates phospholipase C and protein kinase C. Given the importance of epithelial Na(+) channels in controlling the amount of fluid in the respiratory tract, we suggest that down-regulation of Na(+) channels induced by influenza virus may play a role in the fluid transport abnormalities that are associated with influenza infections.

Pharmacological modulation of ion transport across wild-type and DeltaF508 CFTR-expressing human bronchial epithelia

Forskolin, UTP, 1-ethyl-2-benzimidazolinone (1-EBIO), NS004, 8-methoxypsoralen (Methoxsalen; 8-MOP), and genistein were evaluated for their effects on ion transport across primary cultures of human bronchial epithelium (HBE) expressing wild-type (wt HBE) and DeltaF508 (DeltaF-HBE) cystic fibrosis transmembrane conductance regulator. In wt HBE, the baseline short-circuit current (I(sc)) averaged 27.0 +/- 0.6 microA/cm(2) (n = 350). Amiloride reduced this I(sc) by 13.5 +/- 0.5 microA/cm(2) (n = 317). In DeltaF-HBE, baseline I(sc) was 33.8 +/- 1.2 microA/cm(2) (n = 200), and amiloride reduced this by 29.6 +/- 1.5 microA/cm(2) (n = 116), demonstrating the characteristic hyperabsorption of Na(+) associated with cystic fibrosis (CF). In wt HBE, subsequent to amiloride, forskolin induced a sustained, bumetanide-sensitive I(sc) (DeltaI(sc) = 8.4 +/- 0.8 microA/cm(2); n = 119). Addition of acetazolamide, 5-(N-ethyl-N-isopropyl)-amiloride, and serosal 4, 4'-dinitrostilben-2,2'-disulfonic acid further reduced I(sc), suggesting forskolin also stimulates HCO(3)(-) secretion. This was confirmed by ion substitution studies. The forskolin-induced I(sc) was inhibited by 293B, Ba(2+), clofilium, and quinine, whereas charybdotoxin was without effect. In DeltaF-HBE the forskolin I(sc) response was reduced to 1.2 +/- 0.3 microA/cm(2) (n = 30). In wt HBE, mucosal UTP induced a transient increase in I(sc) (Delta I(sc) = 15. 5 +/- 1.1 microA/cm(2); n = 44) followed by a sustained plateau, whereas in DeltaF-HBE the increase in I(sc) was reduced to 5.8 +/- 0. 7 microA/cm(2) (n = 13). In wt HBE, 1-EBIO, NS004, 8-MOP, and genistein increased I(sc) by 11.6 +/- 0.9 (n = 20), 10.8 +/- 1.7 (n = 18), 10.0 +/- 1.6 (n = 5), and 7.9 +/- 0.8 microA/cm(2) (n = 17), respectively. In DeltaF-HBE, 1-EBIO, NS004, and 8-MOP failed to stimulate Cl(-) secretion. However, addition of NS004 subsequent to forskolin induced a sustained Cl(-) secretory response (2.1 +/- 0.3 microA/cm(2), n = 21). In DeltaF-HBE, genistein alone stimulated Cl(-) secretion (2.5 +/- 0.5 microA/cm(2), n = 11). After incubation of DeltaF-HBE at 26 degrees C for 24 h, the responses to 1-EBIO, NS004, and genistein were all potentiated. 1-EBIO and genistein increased Na(+) absorption across DeltaF-HBE, whereas NS004 and 8-MOP had no effect. Finally, Ca(2+)-, but not cAMP-mediated agonists, stimulated K(+) secretion across both wt HBE and DeltaF-HBE in a glibenclamide-dependent fashion. Our results demonstrate that pharmacological agents directed at both basolateral K(+) and apical Cl(-) conductances directly modulate Cl(-) secretion across HBE, indicating they may be useful in ameliorating the ion transport defect associated with CF.

Ion composition and rheology of airway liquid from cystic fibrosis fetal tracheal xenografts

The composition of airway surface liquid (ASL) is partly determined by active ion and water transport through the respiratory epithelium. It is usually stated that in cystic fibrosis (CF), CF transmembrane conductance regulator protein abnormality results in imbalanced ion composition and dehydration of ASL, leading to abnormal rheologic and transport properties. To explore the relationship between ion composition, water content, and viscosity of airway liquid (AL), we used a human xenograft model of fetal airways developed in severe combined immunodeficiency (SCID) mice. Six non-CF and six CF portions of fetal tracheas were engrafted subcutaneously in the flanks of SCID mice raised in pathogen-free conditions. AL accumulated in the closed cylindric grafts was harvested 9 to 17 wk after implantation. At the time of AL sampling, all tracheal grafts displayed well-differentiated pseudostratified surface epithelium and submucosal glands. The viscosity of AL was measured using a controlled-stress rheometer. The ion composition of AL was quantified by X-ray microanalysis. No significant difference was observed for AL viscosity between non-CF (0.6 +/- 0.5 Pa. s) and CF (0.2 +/- 0.1 Pa. s) samples. In AL from non-CF and CF samples, the ion concentrations were Na: 63.9 +/- 7.6, 79.7 +/- 11.6; Cl: 64.9 +/- 13.2, 82.6 +/- 15.7; Mg: 1.9 +/- 0.3, 2.2 +/- 0.4; S: 4.9 +/- 1. 3, 4.8 +/- 0.5; K: 2.4 +/- 0.5, 3.2 +/- 1.6; and Ca: 1.2 +/- 0.3, 2.6 +/- 0.8 mmol/liter, respectively. The ion composition of AL from CF versus non-CF xenografts was not significantly different. These results suggest that prior to inflammation and infection, the viscosity and ion composition of the fetal AL do not differ in CF and non-CF.

Role of CFTR in airway disease

Role of CFTR in Airway Disease. Physiol. Rev. 79, Suppl.: S215-S255, 1999. - Cystic fibrosis (CF) is caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), which accounts for the cAMP-regulated chloride conductance of airway epithelial cells. Lung disease is the chief cause of morbidity and mortality in CF patients. This review focuses on mechanisms whereby the deletion or impairment of CFTR chloride channel function produces lung disease. It examines the major themes of the channel hypothesis of CF, which involve impaired regulation of airway surface fluid volume or composition. Available evidence indicates that the effect of CFTR deletion alters physiological functions of both surface and submucosal gland epithelia. At the airway surface, deletion of CFTR causes hyperabsorption of sodium chloride and a reduction in the periciliary salt and water content, which impairs mucociliary clearance. In submucosal glands, loss of CFTR-mediated salt and water secretion compromises the clearance of mucins and a variety of defense substances onto the airway surface. Impaired mucociliary clearance, together with CFTR-related changes in the airway surface microenvironment, leads to a progressive cycle of infection, inflammation, and declining lung function. Here, we provide the details of this pathophysiological cascade in the hope that its understanding will promote the development of new therapies for CF.

Sputum rheology changes in cystic fibrosis lung disease following two different types of physiotherapy: flutter vs autogenic drainage

OBJECTIVE

The aim of the present study was to investigate the efficacy of two frequently used physiotherapies (PTs) for the removal of bronchial secretions in cystic fibrosis (CF) lung disease: autogenic drainage (AD) and the Flutter (Desitin in Germany). AD is believed to improve mucus clearance from peripheral to central airways due to airway caliber changes in combination with a special breathing technique. The Flutter is an easy-to-use physiotherapy device based on oscillations of a steel ball during expiration through a pipe-type device.

MATERIALS AND METHODS

To evaluate the acute and chronic physiotherapy effects of these two techniques, 14 CF patients underwent either twice daily AD or Flutter treatment for 4 consecutive weeks in a randomized crossover design. Prior to each therapy interval, for a 1-week wash-out period, no PT was administered, but patients continued regular medication. At the beginning and end of each 4-week interval, pulmonary function was measured before and after an acute 30-min therapy. At the end of the PT session, sputum was collected, weighed, and deep frozen until analyzed. The viscoelasticity of the sputum was evaluated using a magnetic microrheometer.

RESULTS

No significant changes were noted for FVC, FEV1, or sputum volume throughout the study. Sputum viscoelasticity (rigidity index), however, was significantly lower (p<0.01) after therapy with the Flutter in comparison with AD, predicting improvements in mucociliary and cough clearability of the secretions. In a companion in vitro experiment, oscillations generated by passing humidified air over CF sputum lining an acrylic tube connected to a Flutter de-ice were found to decrease sputum elasticity, as measured by a filancemeter. These findings suggest that applied oscillations are capable of decreasing mucus viscoelasticity within the airways at frequencies and amplitudes achievable with the Flutter device, and provide direct evidence that PT can reduce the viscoelasticity of sputum.

Effects of topically delivered benzamil and amiloride on nasal potential difference in cystic fibrosis

The raised nasal transepithelial potential difference (PD) in cystic fibrosis (CF) reflects accelerated active transport of Na+, and is inhibited by topical administration of the Na+ channel blocker, amiloride. The aim of this study was to investigate the dose-effect and time course of topically administered Na+ conductance inhibitors to inhibit nasal PD, including benzamil, an analog of amiloride. We measured the magnitude of drug inhibition of Na+ transport [percent inhibition of baseline PD (DeltaPD%)] and duration of inhibition of PD, defined as the time when drug inhibition of PD had recovered by 50% (effective time = ET50). Amiloride [10(-)3 M (n = 16), 3 x 10(-)3 M (n = 9), 6 x 10(-)3 M (n = 7), 10(-)2 M (n = 3)] or benzamil [1.7 x 10(-)3 M (n = 7), and 7 x 10(-)3 M (n = 5)] were administered to the nasal surface via an aerosol generated by a jet nebulizer and a nasal mask. The concentration-dependent magnitude (DeltaPD%) of inhibition was similar for amiloride and benzamil ( approximately 67- 77%), whereas the duration of inhibition (ET50) was about two-and-a-half times longer after benzamil administration as compared with equivalent concentrations of amiloride [1.6 +/- 0. 06 versus 4.5 +/- 0.6 h (ET50 +/- SEM), at 6-7 x 10(-)3 M]. In vitro studies of cultured normal nasal epithelia demonstrated directly that benzamil induced an approximately 2-fold more prolonged inhibition of active Na+ transport than amiloride. These data suggest aerosolized benzamil is a candidate long-duration Na+ channel blocker for CF.

Improved clearability of cystic fibrosis sputum with dextran treatment in vitro

Most patients with cystic fibrosis (CF) are infected by Pseudomonas aeruginosa. Dextran exhibits anti-adhesive effects in preventing attachment of P. aeruginosa to epithelial cells (1). The initial purpose of this study was to evaluate the potential of dextran to alter the rheology and ciliary transportability of CF sputum prior to initiation of a clinical trial in patients with CF. Sputum samples were collected from 25 patients with CF not receiving rhDNase therapy for use in in vitro testing. Aliquots of CF sputum were treated with 10% vol. Ringer's or the same volume of Dextran 4000 to give a final concentration of 0.4% (4 mg/ml) or 4% (40 mg/ml) dextran in the sputum. Dog mucus samples were collected from seven healthy, anesthetized dogs from the endotracheal tube cuff. Aliquots of dog mucus were subjected to the same concentrations of dextran as the CF sputum. All treated samples were incubated for 30 min at 37 degrees C, and their rheologic properties (viscoelasticity) were evaluated by magnetic microrheometry. For 17 of the sputum samples, frog palate mucociliary transportability was determined from sputum movement on the ciliated, mucus-depleted frog palate, relative to native frog mucus control. Spinnability (cohesiveness) was evaluated by the filancemeter technique for eight sputum samples. Overall, whether for CF sputum or healthy dog mucus, Dextran 4000 treatment significantly reduced viscoelasticity and increased predicted mucociliary and cough clearability. Direct measurements of sputum mucociliary clearability on frog palate increased significantly with 0.4% dextran and 4% dextran compared with saline control. Sputum spinnability (cohesiveness) decreased significantly with both dextran concentrations, too. The effects on viscoelasticity and spinnability were greater at 4% than at 0.4%. There was a significant positive correlation between spinnability and viscoelasticity, and negative relationships between spinnability and both forms of clearability as predicted from viscoelastic measurements. This study suggests that treatment with Dextran 4000 can reduce the crosslink density and cohesiveness of CF and improve mucociliary and cough clearability. Dextran 4000 is an inexpensive and nontoxic agent that may be of benefit in patients with CF lung disease and perhaps in other respiratory disease where mucus retention is an important feature.

Inhibition of airway liquid secretion and its effect on the physical properties of airway mucus

The combination of both Cl- and HCO3- secretion inhibitors causes an accumulation of mucins within the submucosal gland ducts of acetylcholine (ACh)-treated bronchi [S. K. Inglis, M. R. Corboz, A. E. Taylor, and S. T. Ballard. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L372-L377, 1997], suggesting indirectly that these agents block airway gland liquid secretion. The present study tested the hypotheses that ACh-stimulated liquid secretion is driven by Cl- and HCO3- secretion and that inhibition of this process leads to secretion of a dehydrated mucus with altered rheological properties. Excised distal bronchi from pigs were pretreated with either a combination of Cl- and HCO3- secretion inhibitors (bumetanide, acetazolamide, dimethylamiloride, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) or the dimethyl sulfoxide vehicle and were then treated with ACh to induce secretion. The rate of mucus liquid secretion was substantially reduced when the airways were pretreated with the anion secretion inhibitors. Mucus liquid from inhibitor-pretreated airways contained almost threefold more nonvolatile solids than the control liquid. Rheological analysis revealed that mucus liquid from inhibitor-pretreated airways expressed a significantly greater log G* (rigidity factor), whereas tangent delta (recoil factor) was significantly reduced. These results suggest that 1) ACh-induced liquid secretion in bronchi is driven by both Cl- and HCO3- secretion and 2) inhibition of ACh-induced liquid secretion results in the secretion of mucus with a reduced water content and altered rheological properties.

Aerosolized amiloride: dose effect on nasal bioelectric properties, pharmacokinetics, and effect on sputum expectoration in patients with cystic fibrosis

Aerosolized amiloride normalizes the excessive sodium absorption cystic fibrosis (CF) respiratory epithelium. The aims of this study were to assess the dose-effect relationship and the duration for which amiloride inhibits Na+ transport, to determine acute and chronic pharmacokinetics, and to test the effect of acute aerosolized amiloride on the amount of sputum expectorated. The effect of inhaled amiloride was assessed principally by nasal potential difference (PD) measurements. Amiloride serum levels were measured in 23 patients after inhalation of different doses of aerosolized amiloride. Twenty CF patients inhaled amiloride (10(-3)M) or a placebo in a double-blinded, randomized order, and sputum production was quantitated. The results of this study showed that maximal initial PD inhibition was achieved by 6 x 10(-3)M of amiloride. The duration of inhibition of PD (effective time until return to 50% delta PD [ET50] after nasal administration) was dose dependent (10(-3)M, 39 +/- 0.8 minutes; 10(-2)M; 133 +/- 14 minutes). Amiloride serum levels were below 2.5 ng/ml in 20 of 28 patients; levels were above 5 ng/ml only within 4 hours after high dose inhalation (10(-2)M). In the double-blinded, crossover study, more sputum was expectorated after amiloride inhalation as compared with that after a placebo (P < 0.05). In conclusion, the bioelectric effects of amiloride and serum levels after inhalation are dose dependent, and amiloride is effective at inducing sputum expectoration in CF.

Amiloride-induced contraction of isolated guinea pig, mouse, and human fetal airways

Nebulized amiloride has been proposed as therapy in cystic fibrosis to block Na+ hyperabsorption in airway epithelium and prevent dehydration of secretions. Patients with cystic fibrosis often have reaction airways. Bovine and canine trachea relax to amiloride in vitro, suggesting another benefit as a bronchodilator, whereas guinea pig trachea, a useful model of human airways, does not. We hypothesized that human airways would respond like guinea pig airways. Airway ring segments from guinea pigs, mice, and human fetuses were constricted with the concentration of acetylcholine producing 50-75% maximum contraction. Subsequent changes in isometric tension to cumulative additions of amiloride (10(-8)-10(-4) M) were measured. Guinea pig airways contracted 29 +/- 5%, mouse airways contracted 23 +/- 6%, and human fetal airways contracted 30 +/- 8%. Contraction to amiloride was mimicked by dimethylamiloride, a more selective inhibitor of the Na+/H+ antiporter, and was attenuated by protein kinase C (PKC) inhibition with GF109203X and staurosporine. The present study indicates that amiloride-induced airway contraction in guinea pigs and mice closely parallels the response in isolated human airways and that the mechanism may involve the Na+/H+ antiporter and PKC.

Airway deposition and clearance and systemic pharmacokinetics of amiloride following aerosolization with an ultrasonic nebulizer to normal airways

STUDY OBJECTIVES

Airway epithelial ion transport is an important component of the airway defense mechanism, and new therapies that target ion transport are being developed. Amiloride is an example of such a new drug, exerting a dose-dependent action to inhibit Na+ transport. Amiloride may be useful in cystic fibrosis, blocking the characteristic airway epithelial Na+ hyperabsorption that occurs in the disease. To evaluate airway and systemic delivery of amiloride via an ultrasonic nebulizer (Omron NE-UO7), we measured the airway surface concentrations of amiloride in normal volunteers via a novel approach, together with the systemic pharmacokinetics of amiloride.

DESIGN

Direct measurement of airway surface liquid, plasma, and urine amiloride concentrations following ultrasonic nebulization.

PARTICIPANTS/INTERVENTIONS

Seven normal subjects were studied in the General Clinical Research Center of the University of North Carolina. Following inhalation with amiloride (1 mg/mL, 4.5 mL) for approximately 12 min, a bronchoscopy was performed. Amiloride deposition and clearance from airway surfaces over 1 h were evaluated by transbronchoscopic sampling using preweighed filter papers. Pulmonary and systemic absorption was assessed by measuring drug concentrations in blood and urine.

RESULTS

The mean volume aerosolized was 3.5+/-0.3 mL during 12 min of aerosolization time; the mean initial concentration of amiloride on airway surfaces after nebulization was 1.6 x 10(-4) mol/L, with an elimination half life of approximately 23 min. Peak plasma concentrations of amiloride (30 min, 3.36+/-0.70 ng/mL) suggest early absorption across lung surfaces, rather than via the GI route. Mean urinary excretion of amiloride over 72 h was 0.63+/-0.07 mg, with 87% excreted in the first 24 h.

CONCLUSIONS

The ultrasonic nebulizer rapidly delivers amiloride to normal conducting airways as assessed by the transbronchoscopic sampling technique. Early blood concentrations of amiloride probably reflect initial absorption across lung surfaces and are a useful index of the efficiency of the machine.

Interaction between ion transporters and the mucociliary transport system in dog and baboon

To gain insight into the role of epithelial ion channels, pumps, and cotransporters in regulating airway water and mucociliary transport, we administered inhibitors of the Na+ channel (amiloride), 3Na-2K-adenosinetriphosphatase (acetylstrophanthidin), and Na-K-2Cl cotransporter (furosemide) to anesthetized dogs and/or baboons. Tracheal ciliary beat frequency was measured by using heterodyne laser light scattering. Tracheal mucus velocity (TMV) and bronchial mucociliary clearance (BMC) or lung mucociliary clearance were measured by using radioaerosols and nuclear imaging. Respiratory tract fluid output was collected by using a secretion-collecting endotracheal tube. In six dogs, amiloride aerosol -lung deposition, 96 +/- 11 microg (means +/- SE)- had minimal effect, whereas acetylstrophanthidin aerosol (lung deposition, 71 +/- 9 microg) increased BMC, and furosemide (40 mg iv) markedly increased TMV. In five baboons, TMV increased after iv furosemide administration (2 mg/kg) as well as by aerosol (lung deposition, 20 +/- 3 mg), coincident with increases in ciliary-mucus coupling from 11.5 +/- 0. 1 to 29.5 +/- 0.4 and 46.5 +/- 0.7 microm/beat, respectively. Furosemide also increased lung mucociliary clearance in baboons. In dogs, respiratory tract fluid output increased after intravenous furosemide from 2.2 +/- 0.5 to 6.8 +/- 1.7 mg/min. When combined with dry-air inhalation, furosemide failed to stimulate TMV and reversed the inhibition of BMC by dry air. Thus pharmacological manipulation of the Na-K-2Cl cotransporter and the 3Na-2K-adenosinetriphosphatase pump may provide increases of clinical relevance in airway hydration and mucociliary transport.

End-of-life care in cystic fibrosis

OBJECTIVE

End-of-life clinical care in cystic fibrosis (CF) differs substantially from terminal care in childhood cancer. To examine this difference, we reviewed the medical care of a cohort of CF patients treated at Children's Hospital, Boston, to document the use of preventive, therapeutic, and palliative care in the month preceding death.

PATIENTS

We reviewed the medical records of 44 patients older than 5 years who died of CF-related respiratory failure for the years 1984 to 1993.

RESULTS

Thirty-eight patients (86%) received opiates for the treatment of severe dyspnea and pain; the duration of opiate use varied from less than 1 hour to greater than 1 month. The dose of opiates varied from less than 5 mg per hour to greater than 30 mg per hour. Thirty-three patients (75%) continued to receive intravenous antibiotics in the last 12 hours of life; 32 (72%) continued to receive preventive or therapeutic oral medications in the last 12 hours of life. All patients were designated as do not resuscitate at the time of death; 43 of the patients died in the hospital with 1 patient dying at home under hospice care.

CONCLUSIONS

The model of comfort care developed in childhood cancer does not adequately describe the combination of preventive, therapeutic, and palliative care given at the end of life for CF at our institution. The majority of CF patients continued to receive intravenous antibiotics and/or oral vitamin preparations while being treated with opiates for terminal pain and dyspnea. Small doses of opiates seem to be effective in the treatment of the pain and dyspnea at the end of life in CF.

Revisited physicochemical and transport properties of respiratory mucus in genotyped cystic fibrosis patients

We investigated the physicochemical and transport properties of sputum samples collected in physiotherapy from a well-documented group of 27 cystic fibrosis (CF) patients with identified CF genotypes. Sputum samples were characterized ex vivo for their water content, surface properties (surface tension and contact angle), rheologic properties (viscosity and elastic modulus), and transport properties (mucociliary and cough transport). These data were analyzed in relation to the clinical status of the patients (FEV1, FVC, Shwachman score, Brasfield score, nutritional status), their genotype, and the degree of infection of their sputa (leukocyte and Pseudomonas aeruginosa counts). We observed negative and significant correlations between mucociliary transport and elastic modulus of the patients' sputum (r = -0.63, p < 0.01), and between the cough transport and contact angle of the sputum (r = -0.81, p < 0.0001), respectively. The P. aeruginosa count was also significantly correlated with the sputum water content (r = -0.53, p < 0.02) as well as with the cough transport of the sputum (r = -0.62, p < 0.01). In CF patients with a sputum leukocyte count > 2,000/mm3, the sputum water content (p < 0.02), FEV1 (p < 0.05) and FVC (p < 0.02) were significantly lower than those of CF patients with a leukocyte count < or = 2,000/mm3. CF patients with a homozygous delta F 508 genotype had significantly greater values of sputum water content (p < 0.05), and cough-transport capacity (p < 0.05) than did heterozygous patients. No correlation was observed between the sputum properties and any of the clinical data. These results suggest that the control of infection should be emphasized in CF, since it can directly or indirectly modulate the degree of hydration, and therefore the physicochemical and transport properties, of airway secretions.

Rheology of cystic fibrosis sputum after in vitro treatment with hypertonic saline alone and in combination with recombinant human deoxyribonuclease I

Treatment with recombinant human deoxyribonuclease I (rhDNase) is currently used as therapy for cystic fibrosis (CF) lung disease. Hypertonic saline (HS) acts as an expectorant promoting mucus secretion and augmenting the volume of sputum. We evaluated the individual and combined effects of HS and rhDNase in vitro on the viscoelasticity of CF sputum. Sputum samples were collected from nine CF patients to use for in vitro testing. Aliquots of CF sputum (0.20 to 0.40 g) were subjected to the following protocols: (1) negative control sample without any treatment; (2) positive control sample, adding 10% volume of normal saline (0.9% NaCl); (3) application of hypertonic saline (HS-3% NaCl); (4) combining approximately 100 nM concentration of rhDNase with protocols 2 and 3. The samples in protocols 2 through 4 were incubated for 30 min at 37 degrees C. For each protocol, CF sputum was analyzed at baseline and at 30 min for spinnability by filancemeter and viscoelasticity by magnetic microrheometry. Spinnability decreased for the sputum samples that were treated with rhDNase, in combination with either HS or normal saline. Treatment with HS alone and combined treatment with rhDNase and HS decreased log G* (the principal viscoelasticity index) to the same degree. Saline alone and rhDNase in normal saline both increased the predicted cough clearability of the sputum; however, the combined treatment with rhDNase and hypertonic saline had the best overall effect on cough clearability. The change in predicted mucociliary clearability, although greatest after HS, was not significant. These in vitro results suggest that combined treatment with rhDNase and HS should be evaluated further as a potential mucotropic approach to augment the clearance of purulent sputum in CF lung disease.

[New prospects in cystic fibrosis treatment]

Only a few years ago, cystic fibrosis (CF) was considered the most frequent genetic disease in childhood, although survival has increased considerably in recent years owing to improved treatment. We discuss treatments that are still relevant as well as others that are under investigation now, aiming for better understanding of the disease and the therapies that have improved quality of life for CF patients.

Sodium chloride increases the ciliary transportability of cystic fibrosis and bronchiectasis sputum on the mucus-depleted bovine trachea

Mucus retention in the lungs is an important feature of several respiratory diseases (Regnis, J.A., M. Robinson, D.L. Bailey, P. Cook, P. Hooper, H.K. Chan, I. Gonda, G. Bautovich, and P.T.P. Bye. 1994. Am. J. Respir. Crit. Care Med. 150:66-71 and Currie, D.C., D. Pavia, J.E. Agnew, M.T. Lopez-Vidriero, P.D. Diamond, P.J. Cole, and S.W. Clarke. 1987. Thorax. 42:126-130). On the mucus-depleted bovine trachea, the ciliary transport rate of sputum from patients with cystic fibrosis and bronchiectasis of other causes was slow, but the rate was doubled by increasing the sodium chloride content by 90 mM. Increasing the sputum osmolality by inspissation or by the addition of nonelectrolytes had a similar effect. The viscoelasticity of sputum, but not the bovine ciliary beat frequency, was markedly saline dependent over the pathophysiological range. This suggests that low mucus salinity, not (as is generally assumed) its under-hydration, contributes to its retention in bronchiectasis due to cystic fibrosis and other causes, probably by affecting its rheology. It also indicates how the genetic defect in cystic fibrosis might lead to impaired mucus clearance. Therapies that increase the osmolality of lung mucus might benefit patients with mucus retention.

A comparison of a new mucolytic N-acetylcysteine L-lysinate with N-acetylcysteine: airway epithelial function and mucus changes in dog

A newly synthesized mucolytic agent, N-acetylcysteine L-lysinate (Nacystelyn) was studied. Tracheal mucus velocity (TMV), transepithelial potential difference (PD), rheological properties, and ion content of collected airway secretions were evaluated in six healthy mongrel dogs after placebo, Nacystelyn (NAL) and acetylcysteine (NAC) metered dose inhaler (MDI) aerosols. Although TMV was increased and viscoelasticity decreased after both treatments, the treatment effect with NAL was significantly greater. Furthermore, NAL increased the negative PD and CI- content of secretions in the trachea, an effect not observed after NAC. Both compounds increased ciliary beat frequency (CBF) on the frog palate at a concentration range similar to that approximated in dog airways. The increased mucociliary clearance could be partially explained by favourable rheological changes combined with stimulation of CBF. Since both compounds break disulfide bonds in mucus polymers, the greater change in mucus rheology and clearance rate after NAL, without change in water content, could be explained by the increase in CI- content. Nacystelyn appears to combine different modes of action which synergistically cause an increase in the clearance rate of airway secretions.

Defining topological similarities among ion transport proteins with anti-amiloride antibodies

The structural features of amiloride binding sites on amiloride-sensitive transport proteins have received limited characterization. An antibody that recognizes limited regions of amiloride and can mimic, in binding specificity, certain amiloride-sensitive transport proteins was used as a model to elucidate potential amino acid residue relationships that might define putative amiloride contact sites. Analysis of the structure of this antibody has allowed us to identify sequence relationships among several Na+ selective transport proteins. A structure-based relational database was employed to re-examine sequence homologies among these ion transport proteins. A search of the protein sequence databank identified representative amino acid tracts among amiloride sensitive proteins involving planar residues that might be involved in interacting with amiloride. Computer models of sites within transmembrane domains of NHE1 and NHE2 isoforms of the Na+/H+ exchanger reflective of these planar tracts indicate that amiloride probably spans two helices for interaction with the Na+/H+ exchanger. Structural analysis of this monoclonal anti-amiloride antibody appears to mimic some of the salient features of amiloride binding sites on these proteins.