Mucus Clearance Research Articles

Adaptive control of airway pressure during the expectoration process in a cough assist system.

Existing Mechanical Insufflation-Exsufflation (MI-E) devices often overlook the impact of cough airflow pressure on mucus clearance, particularly lacking in control over airway pressure during the expiratory phase, which can lead to airway collapse and other types of airway damage. This study optimizes the design of cough assist system and explores the effectiveness of PID and adaptive control methods in regulating airway pressure. The adaptive control method compensates for hose pressure drop by online estimation of the ventilatory hose characteristics. It achieves precise tracking of target pressure and ensures the generation of peak flow rates effective for mucus clearance, even in the absence of known patient lung physiological states and unknown hose leakage parameters. Through a series of comparative experiments, this paper confirms the significant advantages of adaptive control in reducing oscillations and overshoot, capable of more stable and precise airway pressure adjustments. This improved control strategy not only enhances clinical safety but also significantly improves therapeutic outcomes and reduces the risk of complications. The findings indicate that the revamped cough assist system, employing an adaptive control strategy, can effectively prevent airway damage during assisted coughing, offering a safer and more effective sputum clearance solution for critically ill patients with expectoration disorders.

Molecular and Seroepidemiologic Characteristics ofStaphylococcus aureus in Children with Cystic Fibrosis

Abstract Background Cystic fibrosis (CF), through altered sodium and chloride transport across the CF transmembrane receptor (CFTR), is associated with poor mucus clearance, bacterial colonization of the lower airway, chronic pulmonary disease punctuated by acute exacerbations, and chronic inflammation. With increased use of CFTR modulators, changes in the CF pulmonary microbiome have been observed, including decreased prevalence of Pseudomonas colonization; however, overall S. aureus prevalence remains largely unchanged. An important remaining question is whether changes in the CF pulmonary microbiome, while not affecting the overall prevalence of S. aureus colonization, has led to changes in S. aureus diversity or the strain types that are most frequently recovered from children with CF. It is also unknown whether the humoral immune response to S. aureus is altered in the presence of CFTR modulator therapy. Methods Genomic DNA was extracted from S. aureus isolates obtained from two cohorts: a historic cohort, comprised of children not receiving CFTR modulators, and a modern cohort, comprised of children receiving CFTR modulator therapy. Multilocus sequence typing (MLST) and whole genome sequencing (WGS) were used to identify clonotype and characterize virulence factors of interest. Serum was obtained from participants and antibody titers to the extracellular toxins LukAB and LukED were measured. Results One hundred participants were enrolled: 50 in cohort 1 (historic) and 50 in cohort 2 (modern). Compared to cohort 1, isolates identified in cohort 2 were less likely to contain ACME and mecA; similarly, cohort 2 isolates were more likely to contain PVL, sek, and sak. The frequency of specific clonotypes changed over time, with increased prevalence of CC8 and decreased prevalence of CC1, CC5, CC15, and CC30 in cohort 2 compared to cohort 1 (Figure 1A). Serum antibody concentrations to LukAB, a conserved toxin across S. aureus, were similar across cohorts (Figure 1B). Conclusion Over time, the clonotypes responsible for S. aureus colonization in patients receiving CFTR modulators have changed. Despite changes in clonotypes and receipt of CFTR modulators, serum concentrations of LukAB-specific antibodies did not differ. These data suggest that staphylococcal colonization in patients with CF is dynamic over time and may be modified based on the receipt of CFTR modulator therapy. Figure 1. (A) S. aureus clonal complexes, over time, demonstrating a relative increase in CC8 between 2012 and 2022; (B) serum concentrations of LukAB antibodies from 2012 (historic) and 2022 (modern) cohorts. No significant difference was observed in median anti-LukAB concentrations.

Effect of prednisone on woodsmoke-induced sputum inflammation in healthy volunteers: A randomized, placebo-controlled pilot study

Inhalation of biomass smoke is associated with adverse respiratory effects in those with chronic pulmonary conditions. There are few published data regarding the effects of anti-inflammatory interventions on these outcomes. Our aim was to assess the effects of postexposure prednisone on woodsmoke (WS)-induced sputum neutrophilia. We carried out a randomized, placebo-controlled, crossover pilot study assessing the effect of a postexposure dose of 60 mg prednisone on induced sputum inflammation after controlled exposure to WS (500 μg/m3 for 2 hours) in healthy adults who had been identified in a separate screening protocol as being "PMN responsive" to WS. Secondary end points were sputum cytokine level and mucociliary clearance as measured by γ-scintigraphy. A total of 11 subjects yielded complete data for the primary analysis. At 24 hours after WS exposure, there was a significant increase in sputum percentage of PMNs (%PMN) versus at baseline after placebo (median= 42% [IQR= 31%-53%]) (P= .02) but not after prednisone (median= 32% [IQR= 18%-40%]) (P= .09). Prednisone reduced Δ%PMN at 24 hours, but this difference did not reach statistical significance. However, for the 8 of 11 subjects who were PMN responsive after placebo, prednisone reduced Δ%PMN significantly (P= .05). Prednisone had no significant effects on sputum levels of IL-1β, IL-6, IL-8, or TNF-α. WS exposure tended to reduce mucociliary clearance in the placebo arm but not in the prednisone arm. Prednisone taken immediately after exposure to WS mitigated short-term increase in sputum %PMN among healthy volunteers selected for their underlying inflammatory responsiveness to WS. Our data support future studies assessing anti-inflammatory interventions and the role of mucus clearance in WS-induced respiratory health effects.

Modelling Mucus Clearance in Sinuses: Thin-Film Flow Inside a Fluid-Producing Cavity Lined with an Active Surface

The paranasal sinuses are a group of hollow spaces within the human skull, surrounding the nose. They are lined with an epithelium that contains mucus-producing cells and tiny hairlike active appendages called cilia. The cilia beat constantly to sweep mucus out of the sinus into the nasal cavity, thus maintaining a clean mucus layer within the sinuses. This process, called mucociliary clearance, is essential for a healthy nasal environment and disruption in mucus clearance leads to diseases such as chronic rhinosinusitis, specifically in the maxillary sinuses, which are the largest of the paranasal sinuses. We present here a continuum mathematical model of mucociliary clearance inside the human maxillary sinus. Using a combination of analysis and computations, we study the flow of a thin fluid film inside a fluid-producing cavity lined with an active surface: fluid is continuously produced by a wall-normal flux in the cavity and then is swept out, against gravity, due to an effective tangential flow induced by the cilia. We show that a steady layer of mucus develops over the cavity surface only when the rate of ciliary clearance exceeds a threshold, which itself depends on the rate of mucus production. We then use a scaling analysis, which highlights the competition between gravitational retention and cilia-driven drainage of mucus, to rationalise our computational results. We discuss the biological relevance of our findings, noting that measurements of mucus production and clearance rates in healthy sinuses fall within our predicted regime of steady-state mucus layer development.

Design of an oral formulation combining PVA nanofibers and PEGylated liposomes for enhanced drug delivery

Modifying the surface properties of nanoparticles is crucial for enhancing the oral absorption of encapsulated drugs. Although both mucoadhesion and mucus permeability are essential properties for improving oral absorption, their opposing characteristics render their combination in a single formulation challenging. The present study aimed to integrate both strategies and design a novel oral formulation by creating nanofibers from a mucoadhesive polymer solution containing approximately 100 nm PEGylated liposomes. First, we evaluated the physicochemical properties of PEGylated liposomes released from nanofibers made of sodium carboxymethylcellulose (CMC-Na) and polyvinyl alcohol (PVA), as well as from PVA alone nanofibers. Liposomes released from CMC-Na/PVA nanofibers had a particle size of 533.9 ± 85.0 nm, showing aggregation, while those from PVA nanofibers maintained a particle size without aggregation (142.8 ± 7.31 nm). To increase the liposome content in PVA nanofibers, we used hydroxypropyl-β-cyclodextrin (HPβCD) as a cryoprotectant, converting the suspension to powder and increasing liposome content by approximately 30-fold. PVA nanofibers increasing liposome content had a fiber diameter of 355.5 ± 77.1 nm, and liposomes released from nanofibers retained their morphology. We then used the flow-through method to evaluate the formulation's adhesive properties, and our findings confirmed its better mucosal adhesion and reduced excretion by mucus clearance (about 1/10) compared to a liposome suspension. Subsequent application to rat intestinal tissue showed that the mucus partially dissolved the nanofibers, allowing PEGylated liposomes to penetrate the mucus layer. Oral administration to rats showed improved gastrointestinal retention, thereby confirming that this novel oral formulation may improve drug oral absorption.

Ivacaftor for Chronic Obstructive Pulmonary Disease - Results from a Phase 2, Randomized Controlled Trial.

Patients with chronic obstructive pulmonary disease (COPD) exhibit acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. CFTR modulators may improve outcomes in patients with COPD, although recent data regarding magnitude of benefit have been inconclusive and effects on mucociliary clearance are unknown. We conducted a phase 2, randomized, double blind placebo control trial to determine safety and tolerability, and explore the potential mechanism of ivacaftor for the treatment of COPD. We randomized 40 patients with moderate to severe COPD and symptoms of chronic bronchitis to ivacaftor (N=30) or placebo (N=10) 150mg BID for 12 weeks. Primary endpoints included evaluation of safety of ivacaftor and pharmacokinetics (PK). Secondary endpoints included measures of CFTR activity and clinical outcomes. Ivacaftor was safe and tolerable with similar rates of adverse events rates between groups. Most common adverse event was diarrhea in the ivacaftor group and acute COPD exacerbation in the placebo group. PK analysis found the mean area under the curve over 12 hours (AUC12) to be 72% of the previously reported AUC12 in cystic fibrosis (CF). Treatment with ivacaftor did not improve sweat chloride, whole lung mucociliary clearance, lung function or respiratory symptoms. Ivacaftor was safe and well tolerated, but did not improve measures of CFTR activity or mucus clearance. As serum concentrations achieved were lower than observed in CF at the same dose, and modulation of wild type CFTR differs from G551D, further dose determination studies are needed to better understand treatment efficacy of CFTR potentiators in COPD. Clinical trial registration available at www. gov, ID: NCT03085485.

Cross-species comparison of airway epithelium transcriptomics

Studies of lung transcriptomics across species are essential for understanding the complex biology and disease mechanisms of this vital organ. Single-cell RNA sequencing (scRNA-seq) has emerged as a key tool for understanding cell dynamics across various species. However, comprehensive cross-species comparisons are limited. Therefore, the aims of this study was to investigate the transcriptomic similarities and differences in lung cells across four species—humans, monkeys, mice, and rats—in healthy and asthma conditions using scRNA-seq. The results revealed significant transcriptomic similarities between monkeys and humans and significant cross-species conservation of cell-specific marker genes, transcription factors (TFs), and biological pathways. Additionally, we explored sex differences, identifying distinct sex-specific expression patterns that may influence disease susceptibility. These insights refine our understanding of the mechanism underlying airway cell biology across species and have important implications for studying lung diseases, particularly the mechanisms of mucus clearance in asthma.

Paediatric donor lung preservation using Paragonix BAROguard.

Paediatric lung transplantation is a lifesaving option in selected patients with end-stage lung disease. Favourable long-term outcomes are limited by impaired mucus clearance, increased risk of infection resulting from immunosuppression, and chronic lung allograft dysfunction. Organ preservation techniques play an important role in the quality of donated organs. Barotrauma to donated lungs may arise from a combination of excessive recruitment manoeuvres and altitude change during air transportation. The Paragonix BAROguard Donor Lung Preservation System is an FDA-approved advanced organ recovery system that maintains continuous airway pressure of 15 cm of water during transportation of the donated lung(s) to the recipient. The Paragonix LUNGguard monitors temperature during transportation of donor lung(s), while the new BAROguard monitors both temperature and pressure during transportation of donor lung(s). In this publication, we present technical aspects of advanced preservation of paediatric donor lungs using the Paragonix BAROguard Donor Lung Preservation System.

Primary ciliary dyskinesia: Meeting the challenges of diagnosis in South Africa.

Primary ciliary dyskinesia (PCD) is an inherited ciliopathy that results in impaired mucous clearance and affects primarily the respiratory tract, causing upper airway disease, bronchial inflammation and bronchiectasis. The prevalence of PCD in low- and middle-income settings, including South Africa (SA), is unknown, largely owing to challenges with diagnosis, and identifying children or adults with PCD is challenging in a setting with a high prevalence of other infectious diseases, including lower respiratory tract infections and tuberculosis. No single test is diagnostic of PCD, and while some tests are costly, others are labour intensive and require highly specialised laboratory expertise. In the SA setting, awareness and opportunities for the diagnosis of PCD need to be created. In this commentary, we provide a pragmatic approach to identifying which children and adults require further investigations for PCD using a range of diagnostic tests or tools that are available. Furthermore, we recommend that designated centres of expertise for PCD diagnosis are created in SA. This would be an important step towards improving accessibility of diagnostic tests and developing local expertise to improving PCD diagnosis, especially in early childhood, to prevent long-term irreversible respiratory sequelae.

High ionic strength vector formulations enhance gene transfer to airway epithelia.

A fundamental challenge for cystic fibrosis (CF) gene therapy is ensuring sufficient transduction of airway epithelia to achieve therapeutic correction. Hypertonic saline (HTS) is frequently administered to people with CF to enhance mucus clearance. HTS transiently disrupts epithelial cell tight junctions, but its ability to improve gene transfer has not been investigated. Here, we asked if increasing the concentration of NaCl enhances the transduction efficiency of three gene therapy vectors: adenovirus, AAV, and lentiviral vectors. Vectors formulated with 3-7% NaCl exhibited markedly increased transduction for all three platforms, leading to anion channel correction in primary cultures of human CF epithelial cells and enhanced gene transfer in mouse and pig airways in vivo. The mechanism of transduction enhancement involved tonicity but not osmolarity or pH. Formulating vectors with a high ionic strength solution is a simple strategy to greatly enhance efficacy and immediately improve preclinical or clinical applications.

Reduced sialylation of airway mucin impairs mucus transport by altering the biophysical properties of mucin

Mucus stasis is a pathologic hallmark of muco-obstructive diseases, including cystic fibrosis (CF). Mucins, the principal component of mucus, are extensively modified with hydroxyl (O)-linked glycans, which are largely terminated by sialic acid. Sialic acid is a negatively charged monosaccharide and contributes to the biochemical/biophysical properties of mucins. Reports suggest that mucin sialylation may be altered in CF; however, the consequences of reduced sialylation on mucus clearance have not been fully determined. Here, we investigated the consequences of reduced sialylation on the charge state and conformation of the most prominent airway mucin, MUC5B, and defined the functional consequences of reduced sialylation on mucociliary transport (MCT). Reduced sialylation contributed to a lower charged MUC5B form and decreased polymer expansion. The inhibition of total mucin sialylation de novo impaired MCT in primary human bronchial epithelial cells and rat airways, and specific α-2,3 sialylation blockade was sufficient to recapitulate these findings. Finally, we show that ST3 beta-galactoside alpha-2,3-sialyltransferase (ST3Gal1) expression is downregulated in CF and partially restored by correcting CFTR via Elexacaftor/Tezacaftor/Ivacaftor treatment. Overall, this study demonstrates the importance of mucin sialylation in mucus clearance and identifies decreased sialylation by ST3Gal1 as a possible therapeutic target in CF and potentially other muco-obstructive diseases.

Insights into metachronal propulsion's influence on Ellis fluid flow across tri‐layers amid dynamic thermal transport: Theoretical study

AbstractCilia‐based therapies are emerging for treating ciliopathies, such as inhalable drugs to propel mucus out of the lungs of patients with cystic fibrosis. This has motivated scientists and researchers to investigate cilia motion mechanics and viscoelastic fluid properties for biomedical engineering applications and disease treatments. In line with the diverse biological implications, this study focuses on the mass and heat transfer flow of tri‐layered non‐Newtonian fluids propelled by ciliary beating in a cylindrical tube. The fluid remains incompressible, with distinct layers that do not mix. The study considers the impact of mass and heat transfer in three distinct regimes, ensuring continuity at the interfaces. Mathematical modeling incorporating the lubrication approximation, small Reynolds number, and long wavelength approximation is employed for simplification. The resulting differential equations, along with boundary conditions, yield accurate solutions for temperature, velocity, and concentration fields in the three fluid layers and are discussed graphically. Key findings demonstrate that velocity and temperature fields are most pronounced in the inner fluid layer (PCL), while the concentration profile is most prominent in the outer layers (ACL), with moderate behavior in the central region. The implications of this research extend to diverse fields, including mucus clearance from the respiratory tract, microfluidics, esophageal transport, biofluid mechanics, and other areas of physiology. The insights gained from this study have promising applications in developing new treatments and biomedical engineering solutions.

Use of inhaled solution of hypertonic saline combined with high-molecular-weight hyaluronic acid in patients with lower respiratory tract diseases

Resolution of the Council of ExpertsNovember 17, 2023Respiratory diseases (acute and chronic bronchitis, chronic obstructive pulmonary disease (COPD), bronchiectasis, cystic fibrosis (CF), bronchial asthma, etc.) are often accompanied by impaired mucus clearance. In this regard, mucoactive drugs are most commonly used for the treatment. Hypertonic saline plus high-molecular-weight hyaluronic acid is one of the affordable and effective agents that can help with thinning and removal of bronchial secretions. The effect of 3%, 6%, 7% hypertonic saline on the respiratory system is multifaceted: it stimulates the osmotic fluid flow, breaks bonds linking polymers in the sputum, reduces swelling in the mucous membranes, stimulates ciliary beat frequency, and reduces the neutrophilic inflammation severity. The molecular size of HA plays an important role in the effectiveness of inhalation therapy with hypertonic saline combined with hyaluronic acid (HA). External administration of high-molecular-weight hyaluronic acid inhibits neutrophil elastase and metalloproteinase, potentiates hydration of bronchial secretions and has anti-inflammatory properties. In addition to clinical studies, real-life clinical practice in patients with cystic fibrosis, bronchiectasis and acute bronchitis also demonstrated the effectiveness of hypertonic saline combined with high-molecular-weight hyaluronic acid. The rationale for the use of hypertonic saline was reflected in the international GOLD (Global Initiative for Chronic Obstructive Lung Disease) guidelines in 2023. Therefore, due to high interest in the hypertonic saline combined with high-molecular-weight hyaluronic acid, it is important to expand the evidence base: to initiate a Russian multicenter study evaluating the effectiveness and safety of this combination in patients with chronic bronchitis and COPD in the Russian Federation. It will allow us to recommend hypertonic saline combined with high-molecular-weight hyaluronic acid to be included in the Russian clinical guidelines on treatment of chronic bronchitis and COPD as a mucoactive drug.

Clinical Outcomes Following SARS-CoV-2 Infection in Pediatric Cystic Fibrosis Patients.

Background Cystic fibrosis (CF) is a genetic disorder of the cystic fibrosis transmembrane conductance regulator chloride channel that leads to impaired mucus clearance in the airways, which leads to deteriorations in lung function and chronic respiratory infection. These effects of CF contribute to the hypothesis that patients with CF may be at increased risk of complications when they catch coronavirus disease 2019 (COVID-19), which swept the world in a global pandemic starting in 2019. Overall, however, the role of CF in COVID-19 has not been well studied, particularly in pediatric patients. Methods In this retrospective review, pediatric patients with CF who contracted COVID-19 (3/1/2020-3/1/2023) (N=69) were compared to two equally sized control cohorts of patients with only CF or COVID-19 matched based on demographics and clinical baselines. Occurrences of adverse outcomes (emergency room visits, hospitalizations, CF pulmonary exacerbations, etc.) were assessed for each subject. The mean percentage of predicted forced expiratory volume in 1 second (FEV1%pred) was also assessed for CF patients. Fisher's exact test assesseddifferences between the proportions of subjects who experienced each outcome. Independent two-variable t-testing assessed mean FEV1%pred differences. Analysis was conducted using IBMSPSSStatistics for Windows, Version 29 (Released 2023; IBM Corp., Armonk, New York, United States)with a significance α=0.05. Ad hoc power analysis was conducted using G*Powerv3.1. Results Overall, CF/COVID subjects fared similarly to control groups without either CF or COVID-19 history, including among subgroups stratified based on baseline respiratory function,P. aeruginosacolonization status, and COVID-19 vaccination status. One notable finding was that CF/COVID subjects experienced significantly fewer pulmonary exacerbations compared to CF-only subjects (p=0.004). Conclusion In conclusion, pediatric CF patients performed similarly to their peers without CF with regardto COVID-19and generally did not demonstrate significant deteriorations in pulmonary function following infection. Lower incidence of pulmonary exacerbations in CF/COVID subjects could be explained by stringent monitoring by parents, quarantine, or close pulmonology follow-up. These findings will provide guidance on management and care for pediatric CF patients with COVID-19.

Reduced Sialylation of Airway Mucin Impairs Mucus Transport by Altering the Biophysical Properties of Mucin.

Mucus stasis is a pathologic hallmark of muco-obstructive diseases, including cystic fibrosis (CF). Mucins, the principal component of mucus, are extensively modified with hydroxyl (O)-linked glycans, which are largely terminated by sialic acid. Sialic acid is a negatively charged monosaccharide and contributes to the biochemical/biophysical properties of mucins. Reports suggest that mucin sialylation may be altered in CF; however, the consequences of reduced sialylation on mucus clearance have not been fully determined. Here, we investigated the consequences of reduced sialylation on the charge state and conformation of the most prominent airway mucin, MUC5B, and defined the functional consequences of reduced sialylation on mucociliary transport (MCT). Reduced sialylation contributed to a lower charged MUC5B form and decreased polymer expansion. The inhibition of total mucin sialylation de novo impaired MCT in primary human bronchial epithelial cells and rat airways, and specific α-2,3 sialylation blockade was sufficient to recapitulate these findings. Finally, we show that ST3 beta-galactoside alpha-2,3-sialyltransferase (ST3Gal1) expression is downregulated in CF and partially restored by correcting CFTR via Elexacaftor/Tezacaftor/Ivacaftor treatment. Overall, this study demonstrates the importance of mucin sialylation in mucus clearance and identifies decreased sialylation by ST3Gal1 as a possible therapeutic target in CF and potentially other muco-obstructive diseases.

Heat and concentration analysis of two-layered muco-ciliary third grade fluid flow in human airways

Understanding the mechanisms involved in the movement and clearance of mucus within the human airways is important from a physiological perspective. A mathematical model of muco-ciliary two-layered fluid flow in a finite two-dimensional channel is proposed. Due to the presence of both the airway ciliary layer (ACL) and the periciliary liquid layer (PCL) in airways epithelial cells, the two-layered model is adopted. The third grade fluid models is used to characterize the viscoelastic nature of mucus secreted in the airways. The mathematical modeling of two-layer flow problem is simplified by using long wavelength and small Reynolds number approximation. A formulated set of partial differential equations (PDEs) is solved for series-form solutions of velocity, temperature, concentration, and pressure gradient by using the Adomian decomposition method (ADM). The analysis delineated that with an increase in pressure gradient at airways entrance ξ the velocity and temperature increases while concentration decreases. Deborah numbers impact ACL and PCL velocities differently, with De(A) influencing flow direction and De(P) causing fluid to flow faster in the forward direction. It also emphasizes the significance of the rate of thermal diffusion, viscous dissipation, and relaxation time. The results showed that the suggested two-layered muco-ciliary model provides a better description of mucus transport in the human airways. The pressure gradient at the airways entrance has a significant impact on mucus transport through the airways.

Adenylate cyclase 6 targets in Mucociliary Clearance

Background. Mucociliary clearance (MCC) is a frontline airway defense mechanism that relies on the appropriate interactions between the epithelium, ciliary beat frequency, and the quantity and quality of mucus. MCC is severely impaired in cystic fibrosis (CF) and drives lung function decline and ultimate respiratory failure and death. A great need remains to identify the key molecular players that regulate MCC in CF outside the scope of FDA approved CFTR therapy and to specifically target MCC dysfunction in CF using small molecules. Results. We discover a novel key role of cAMP-synthesizing enzyme Adenylate cyclase 6 (AC6) in MCC via (a) regulation of CFTR chloride channels in the secretory cells that generate airway surface liquid (ASL) component of MCC and (b) AC6 mediated regulation of ciliary beat frequency in the ciliated cells that is required for the mechanical clearance. Specific activators of AC6 (C20: Top candidate) were developed and improved MCC process ex vivo in CF explant tissues and cells. Together these mechanisms and small molecule approach that improve airway fluid balance and cilia function could be beneficial in CF and other respiratory diseases. Experimental Approach. We performed CFTR functional assessment in normal and CF patient derived airway epithelial cells by adapting patch-sequencing approach and using the specific activators of AC6. The effect of AC6 activators on MCC will be evaluated ex vivo in patient derived lung explant tissues , in vivo (micro-CT) in CF rat models and in vitro (ciliary beat frequency and bead flow measurements) in air-liquid interface airway epithelial cultures. Overall, these studies will be mechanistic and translational involving human disease specimens, animal models, drug development and computational analysis. Significance of the results. The proposed research can improve our understanding of epithelial biology and advance activators of AC6 as therapeutic agents to treat mucus clearance defects. These findings can be leveraged to modulate CFTR function and cilia-generate flow, presenting a potential therapeutic avenue for conditions that involve CFTR and cilia dysregulation associated with several respiratory diseases. National Institutes of Health (NIH) DK080834 and P30-DK117467 and HL147351 (to APN). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The role of electrogenic and electroneutral monocarboxylate transport in airway clearance

Introduction: Monocarboxylates can be transported by the electrogenic Na+-coupled system (SMCTs/SLC5 family) and the electroneutral H+-coupled system (MCTs/SLC16 family). Previously, MCTs have been described in human bronchial epithelium but there is no evidence of SMCTs activity in airways. We describe here for first time that SMCT1/SCL5A8 is functionally expressed in mouse tracheal epithelium. We hypothesized that monocarboxylate transport activity might downregulate airway clearance in mouse tracheas as increased Na+-absorption reduce airway surface liquid (ASL), and increased H+-secretion acidify ASL. Methods: Short-circuit current ( ISC) recordings were performed in bicarbonate buffer with and without Na+, videomicroscopy of particle track speed (PTS) and mucus transport speed were performed in mouse tracheas. Animals (C57BL6/J) were housed at CECs-Animal facility under controlled temperature, humidity and free access to water and food. All protocols were approved (IACUC, #CECs-2022-04), in accordance with relevant regulations. Results: 10 mM apical L-lactate, D-lactate, pyruvate, propionate or acetate induced a negative current ( ISC~ -35 μA·cm−2; n=4-5 each group) and reduced (p<0.05 rank-sum test) when Na+ was replaced. L-lactate or pyruvate, transported by SMCTs and MCTs increased PTS (2.1±0.1 control vs 3.28±0.4 μm·s−1* for L-lactate and 3.31±0.1 μm·s−1* for pyruvate; n=3 each group; * indicates p<0.05 rank-sum test) and inhibited by 30 μM of the MCT inhibitor AR-C155858 (1.9±0.1 μm·s−1). D-lactate, transported by SMCTs only, did not affected PTS (2.03±0.1 μm·s−1; p>0.05; n=3 each group). We observed a reduction of amiloride-sensitive Na+-absorptive currents in tissues incubated with L-lactate compared to non-incubated ( ISC -17±4 μA·cm−2 vs -5±4 μA·cm−2; p<0.05 rank-sum test; n=4 each group). Finally, analysis of mucus transport determined that L- but not D-lactate increased the speed of mucus, that was prevented when tissues were incubated with AR-C155858 (control 1.06 ± 0.05 μm·s−1 vs L-lactate 1.24 ± 0.08 μm·s−1*, vs L-lactate + AR-C155858 1.02 ± 0.06 μm·s−1; * indicates p<0.05 ANOVA on ranks; n=4 each group). Real time PCR determined that the only SMCT expressed in airway epithelium is SLC5A8. Conclusion: SLC5A8 Na+-dependent D-lactate transport didn't affect mucus clearance. This is explained by the fact that ENaC Na+ absorption competes with SMCTs for basolateral Na+ transport, suggesting that both ENaC and SLC5A8 localize in the same cells. On the other hand, monocarboxylates that increase PTS and mucus speed transport might be explained by MCT-dependent H+ removal (alkalization) from ASL. Since alkalization of the airway surface can restore airway clearance, the use of MCTs transportable substrates might help alleviate mucostasis in muco-obstructive diseases. Funded by FONDECYT 1221257 (C.A.F.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Postnasal Drip

Postnasal drip (PND) is a common symptom encountered when evaluating subjects with sinonasal disease; it may be present without sinonasal disease or as a symptom of laryngopharyngeal reflux (LPR). It is postulated that PND stems from dysfunction of normal mucus clearance mechanisms, however, there is no definitive evidence elucidating an exact pathophysiology. Compounding the uncertainties surrounding PND is the lack of an objective assessment tool. Instead, treating physicians must rely on subjective complaints and investigators utilize validated patient reported outcome instruments, such as the sino-nasal outcome test (SNOT), to determine treatment efficacy. This review seeks to discuss the current understanding of PND and evidence regarding effective treatment strategies.

Highly distinctive linear and nonlinear rheological behaviors of mucin-based protein solutions as simulated normal and asthmatic human airway mucus

Mucus on the human airway surface normally provides a fluid barrier to trap and remove inhaled hazardous particulates such as viruses and bacteria, a physiological function known as mucus clearance. This function, however, can fail if the mucus has abnormal rheological properties, as in the case of certain lung diseases such as asthma. Despite its importance, airway mucus rheology has not been well studied so far, largely because of its complex nature and limited availability. Therefore, in this study, we prepared mucin-based protein solutions as simulated normal and asthmatic airway mucus (NM and AM, respectively) and subsequently studied them in both linear and nonlinear rheological conditions using either conventional steady-state or large amplitude oscillatory shear experiments together with nonlinear multi-mode Giesekus model analysis. We also examined the microscopic structure of the simulated airway mucus by optical or atomic force microscopy. We found that both NM and AM exhibited typical nonlinear rheological behaviors of protein solutions. However, as compared to NM, AM was much more solid-like, and the viscosity, yield stress, and dynamic modulus were more than ten times that of NM. These differences in macroscopic rheological behaviors between NM and AM could be attributed to their different microstructures. Taken together, this study provides evidence that airway mucus may dramatically change its rheological behaviors with changing chemical composition and microstructure as occurring in diseased conditions such as AM. Thus, the presented rheological assessment and modeling analysis, together with the microscopic characterization of simulated airway mucus, may have important values for better understanding the critical roles of mucus rheology in the determination of the mucus clearance function in health and disease as well as the development of pulmonary drug delivery systems.