Cilia and Mucociliary Clearance

Epithelial cell dysfunction in chronic rhinosinusitis: the epithelial-mesenchymal transition

INTRODUCTION

Epithelial-mesenchymal transition (EMT) is a type of epithelial cell dysfunction, which is widely present in the nasal mucosa of patients with chronic rhinosinusitis (CRS), especially CRS with nasal polyps, and contributes to pathogenesis of the disease. EMT is mediated via complex mechanisms associated with multiple signaling pathways.

AREAS COVERED

We have summarized the underlying mechanisms and signaling pathways promoting EMT in CRS. Strategies or drugs/agents targeting the genes and pathways related to the regulation of EMT are also discussed for their potential use in the treatment of CRS and asthma. A literature search of studies published in English from 2000 to 2023 was conducted using the PubMed database, employing CRS, EMT, signaling, mechanisms, targeting agents/drugs, as individual or combinations of search terms.

EXPERT OPINION

EMT in nasal epithelium not only leads to epithelial cell dysfunction but also plays an important role in nasal tissue remodeling in CRS. A comprehensive understanding of the mechanisms underlying EMT and the development of drugs/agents targeting these mechanisms may provide new treatment strategies for CRS.

Advanced approaches to overcome biological barriers in respiratory and systemic routes of administration for enhanced nucleic acid delivery to the lung

INTRODUCTION

Numerous delivery strategies, primarily novel nucleic acid delivery carriers, have been developed and explored to enable therapeutically relevant lung gene therapy. However, its clinical translation is yet to be achieved despite over 30 years of efforts, which is attributed to the inability to overcome a series of biological barriers that hamper efficient nucleic acid transfer to target cells in the lung.

AREAS COVERED

This review is initiated with the fundamentals of nucleic acid therapy and a brief overview of previous and ongoing efforts on clinical translation of lung gene therapy. We then walk through the nature of biological barriers encountered by nucleic acid carriers administered via respiratory and/or systemic routes. Finally, we introduce advanced strategies developed to overcome those barriers to achieve therapeutically relevant nucleic acid delivery efficiency in the lung.

EXPERT OPINION

We are now stepping close to the clinical translation of lung gene therapy, thanks to the discovery of novel delivery strategies that overcome biological barriers via comprehensive preclinical studies. However, preclinical findings should be cautiously interpreted and validated to ultimately realize meaningful therapeutic outcomes with newly developed delivery strategies in humans. In particular, individual strategies should be selected, tailored, and implemented in a manner directly relevant to specific therapeutic applications and goals.

Pulmonary delivery of mucus-traversing PF127-modified silk fibroin nanoparticles loading with quercetin for lung cancer therapy

The mucosal barrier remains a major barrier in the pulmonary drug delivery system, as mucociliary clearance in the airway accelerates the removal of inhaled nanoparticles (NPs). Herein, we designed and developed the inhalable Pluronic F127-modified silk fibroin NPs loading with quercetin (marked as QR-SF (PF127) NPs), aiming to solve the airway mucus barrier and improve the cancer therapeutic effect of QR. The PF127 coating on the SF NPs could attenuate the interaction between NPs and mucin proteins, thus facilitating the diffusion of SF(PF127) NPs in the mucus layer. The QR-SF (PF127) NPs had particle sizes of approximately 200 nm with negatively charged surfaces and showed constant drug release properties. Fluorescence recovery after photobleaching (FRAP) assay and transepithelial transport test showed that QR-SF (PF127) NPs exhibited superior mucus-penetrating ability in artificial mucus and monolayer Calu-3 cell model. Notably, a large amount of QR-SF (PF127) NPs distributed uniformly in the mice airway section, indicating the good retention of NPs in the respiratory tract. The mice melanoma lung metastasis model was established, and the therapeutic effect of QR-SF (PF127) NPs was significantly improved in vivo. PF127-modified SF NPs may be a promising strategy to attenuate the interaction with mucin proteins and enhance mucus penetration efficiency in the pulmonary drug delivery system.

Bovine Airway Models: Approaches for Investigating Bovine Respiratory Disease

Bovine respiratory disease (BRD) is a multifactorial condition where different genera of bacteria, such as Mannheimia haemolytica, Histophilus somni, Pasteurella multocida, and Mycoplasma bovis, and viruses, like bovine respiratory syncytial virus, bovine viral diarrhea virus, and bovine herpes virus-1, infect the lower respiratory tract of cattle. These pathogens can co-infect cells in the respiratory system, thereby making specific treatment very difficult. Currently, the most common models for studying BRD include a submerged tissue culture (STC), where monolayers of epithelial cells are typically covered either in cellular or spent biofilm culture medium. Another model is an air-liquid interface (ALI), where epithelial cells are exposed on their apical side and allowed to differentiate. However, limited work has been reported on the study of three-dimensional (3D) bovine models that incorporate multiple cell types to represent the architecture of the respiratory tract. The roles of different defense mechanisms in an infected bovine respiratory system, such as mucin production, tight junction barriers, and the production of antimicrobial peptides in in vitro cultures require further investigation in order to provide a comprehensive understanding of the disease pathogenesis. In this report, we describe the different aspects of BRD, including the most implicated pathogens and the respiratory tract, which are important to incorporate in disease models assembled in vitro. Although current advancements of bovine respiratory cultures have led to knowledge of the disease, 3D multicellular organoids that better recapitulate the in vivo environment exhibit potential for future investigations.

Nanoparticle Diffusion in Respiratory Mucus Influenced by Mucociliary Clearance: A Review of Mathematical Modeling

Background: Inhalation and deposition of particles in human airways have attracted considerable attention due to importance of particulate pollutants, transmission of infectious diseases, and therapeutic delivery of drugs at targeted areas. We summarize current state-of-the art research in particle deposition on airway surface liquid (ASL) influenced by mucociliary clearance (MCC) by identifying areas that need further investigation. Methodology: We aim to review focus on governing and constitutive equations describing MCC geometry followed by description of mathematical modeling of ciliary forces, mucus rheology properties, and numerical approaches to solve modified time-dependent Navier-Stokes equations. We also review mathematical modeling of particle deposition in ASL influenced by MCC, particle transport in ASL in terms of Eulerian and Lagrangian approaches, and discuss the corresponding mass transport issues in this layer. Whenever required, numerical predictions are contrasted with the pertinent experimental data. Results: Results indicate that mean mucus and periciliary liquid velocities are strongly influenced by mucus rheological characteristics as well as ciliary abnormalities. However, most of the currently available literature on mucus fiber spacing, ciliary beat frequency, and particle surface chemistry is based on particle deposition on ASL by considering a fixed value of ASL velocity. The effects of real ASL flow regimes on particle deposition in this layer are limited. In addition, no other study is available on modeling nonhomogeneous and viscoelastic characteristics of mucus layer on ASL drug delivery. Conclusion: Simplification of assumptions on governing equations of drug delivery in ASL influenced by MCC leads to imposing some limitations on numerical results.

Intranasal Drug Administration in Alzheimer-Type Dementia: Towards Clinical Applications

Alzheimer-type dementia (ATD) treatments face limitations in crossing the blood-brain barrier and systemic adverse effects. Intranasal administration offers a direct route to the brain via the nasal cavity's olfactory and trigeminal pathways. However, nasal physiology can hinder drug absorption and limit bioavailability. Therefore, the physicochemical characteristics of formulations must be optimized by means of technological strategies. Among the strategies that have been explored, lipid-based nanosystems, particularly nanostructured lipid carriers, are promising in preclinical investigations with minimal toxicity and therapeutic efficacy due to their ability to overcome challenges associated with other nanocarriers. We review the studies of nanostructured lipid carriers for intranasal administration in the treatment of ATD. Currently, no drugs for intranasal administration in ATD have marketing approval, with only three candidates, insulin, rivastigmine and APH-1105, being clinically investigated. Further studies with different candidates will eventually confirm the potential of the intranasal route of administration in the treatment of ATD.

Influenza virus reduces ubiquitin E3 ligase MARCH10 expression to decrease ciliary beat frequency

Respiratory viruses, such as influenza, decrease airway cilia function and expression, which leads to reduced mucociliary clearance and inhibited overall immune defense. Ubiquitination is a posttranslational modification using E3 ligases, which plays a role in the assembly and disassembly of cilia. We examined the role of membrane-associated RING-CH (MARCH) family of E3 ligases during influenza infection and determined that MARCH10, specifically expressed in ciliated epithelial cells, is significantly decreased during influenza infection in mice, human lung epithelial cells, and human lung tissue. Cellular depletion of MARCH10 in differentiated human bronchial epithelial cells (HBECs) using CRISPR/Cas9 showed a decrease in ciliary beat frequency. Furthermore, MARCH10 cellular knockdown in combination with influenza infection selectively decreased immunoreactive levels of the ciliary component, dynein axonemal intermediate chain 1. Cellular overexpression of MARCH10 significantly decreased influenza hemagglutinin protein levels in the differentiated HBECs and knockdown of MARCH10 increased IL-1β cytokine expression, whereas overexpression had the reciprocal effect. These findings suggest that MARCH10 may have a protective role in airway pulmonary host defense and innate immunity during influenza infection.

Novel insight into the underlying dysregulation mechanisms of immune cell-to-cell communication by analyzing multitissue single-cell atlas of two COVID-19 patients

How does SARS-CoV-2 cause lung microenvironment disturbance and inflammatory storm is still obscure. We here performed the single-cell transcriptome sequencing from lung, blood, and bone marrow of two dead COVID-19 patients and detected the cellular communication among them. Our results demonstrated that SARS-CoV-2 infection increase the frequency of cellular communication between alveolar type I cells (AT1) or alveolar type II cells (AT2) and myeloid cells triggering immune activation and inflammation microenvironment and then induce the disorder of fibroblasts, club, and ciliated cells, which may cause increased pulmonary fibrosis and mucus accumulation. Further study showed that the increase of T cells in the lungs may be mainly recruited by myeloid cells through ligands/receptors (e.g., ANXA1/FPR1, C5AR1/RPS19, and CCL5/CCR1). Interestingly, we also found that certain ligands/receptors (e.g., ANXA1/FPR1, CD74/COPA, CXCLs/CXCRs, ALOX5/ALOX5AP, CCL5/CCR1) are significantly activated and shared among lungs, blood and bone marrow of COVID-19 patients, implying that the dysregulation of ligands/receptors may lead to immune cell's activation, migration, and the inflammatory storm in different tissues of COVID-19 patients. Collectively, our study revealed a possible mechanism by which the disorder of cell communication caused by SARS-CoV-2 infection results in the lung inflammatory microenvironment and systemic immune responses across tissues in COVID-19 patients.

E-cigarette aerosols of propylene glycol impair BK channel activity and parameters of mucociliary function

Propylene glycol (PG) is a common delivery vehicle for nicotine and flavorings in e-cigarette (e-cig) liquids and is largely considered safe for ingestion. However, little is known about its effects as an e-cig aerosol on the airway. Here, we investigated whether pure PG e-cig aerosols in realistic daily amounts impact parameters of mucociliary function and airway inflammation in a large animal model (sheep) in vivo and primary human bronchial epithelial cells (HBECs) in vitro. Five-day exposure of sheep to e-cig aerosols of 100% PG increased mucus concentrations (% mucus solids) of tracheal secretions. PG e-cig aerosols further increased the activity of matrix metalloproteinase-9 (MMP-9) in tracheal secretions. In vitro exposure of HBECs to e-cig aerosols of 100% PG decreased ciliary beating and increased mucus concentrations. PG e-cig aerosols further reduced the activity of large conductance, Ca2+-activated, and voltage-dependent K+ (BK) channels. We show here for the first time that PG can be metabolized to methylglyoxal (MGO) in airway epithelia. PG e-cig aerosols increased levels of MGO and MGO alone reduced BK activity. Patch-clamp experiments suggest that MGO can disrupt the interaction between the major pore-forming BK subunit human Slo1 (hSlo1) and the gamma regulatory subunit LRRC26. PG exposures also caused a significant increase in mRNA expression levels of MMP9 and interleukin 1 beta (IL1B). Taken together, these data show that PG e-cig aerosols cause mucus hyperconcentration in sheep in vivo and HBECs in vitro, likely by disrupting the function of BK channels important for airway hydration.

Cystic fibrosis and primary ciliary dyskinesia: Similarities and differences

Cystic fibrosis (CF) and Primary ciliary dyskinesia (PCD) are both rare chronic diseases, inherited disorders associated with multiple complications, namely respiratory complications, due to impaired mucociliary clearance that affect severely patients' lives. Although both are classified as rare diseases, PCD has a much lower prevalence than CF, particularly among Caucasians. As a result, CF is well studied, better recognized by clinicians, and with some therapeutic approaches already available. Whereas PCD is still largely unknown, and thus the approach is based on consensus guidelines, expert opinion, and extrapolation from the larger evidence base available for patients with CF. Both diseases have some clinical similarities but are very different, necessitating different treatment by specialists who are familiar with the complexities of each disease.This review aims to provide an overview of the knowledge about the two diseases with a focus on the similarities and differences between both in terms of disease mechanisms, common clinical manifestations, genetics and the most relevant therapeutic options. We hoped to raise clinical awareness about PCD, what it is, how it differs from CF, and how much information is still lacking. Furthermore, this review emphasises the fact that both diseases require ongoing research to find better treatments and, in particular for PCD, to fill the medical and scientific gaps.

International consensus statement on allergy and rhinology: Allergic rhinitis - 2023

BACKGROUND

In the 5 years that have passed since the publication of the 2018 International Consensus Statement on Allergy and Rhinology: Allergic Rhinitis (ICAR-Allergic Rhinitis 2018), the literature has expanded substantially. The ICAR-Allergic Rhinitis 2023 update presents 144 individual topics on allergic rhinitis (AR), expanded by over 40 topics from the 2018 document. Originally presented topics from 2018 have also been reviewed and updated. The executive summary highlights key evidence-based findings and recommendation from the full document.

METHODS

ICAR-Allergic Rhinitis 2023 employed established evidence-based review with recommendation (EBRR) methodology to individually evaluate each topic. Stepwise iterative peer review and consensus was performed for each topic. The final document was then collated and includes the results of this work.

RESULTS

ICAR-Allergic Rhinitis 2023 includes 10 major content areas and 144 individual topics related to AR. For a substantial proportion of topics included, an aggregate grade of evidence is presented, which is determined by collating the levels of evidence for each available study identified in the literature. For topics in which a diagnostic or therapeutic intervention is considered, a recommendation summary is presented, which considers the aggregate grade of evidence, benefit, harm, and cost.

CONCLUSION

The ICAR-Allergic Rhinitis 2023 update provides a comprehensive evaluation of AR and the currently available evidence. It is this evidence that contributes to our current knowledge base and recommendations for patient evaluation and treatment.

Immunomodulatory Properties of Vitamin D in the Intestinal and Respiratory Systems

Vitamin D plays a crucial role in modulating the innate immune response by interacting with its intracellular receptor, VDR. In this review, we address vitamin D/VDR signaling and how it contributes to the regulation of intestinal and respiratory microbiota. We additionally review some components of the innate immune system, such as the barrier function of the pulmonary and intestinal epithelial membranes and secretion of mucus, with their respective modulation by vitamin D. We also explore the mechanisms by which this vitamin D/VDR signaling mounts an antimicrobial response through the transduction of microbial signals and the production of antimicrobial peptides that constitute one of the body’s first lines of defense against pathogens. Additionally, we highlight the role of vitamin D in clinical diseases, namely inflammatory bowel disease and acute respiratory distress syndrome, where excessive inflammatory responses and dysbiosis are hallmarks. Increasing evidence suggests that vitamin D supplementation may have potentially beneficial effects on those diseases.

The role of potassium current in the pulmonary response to environmental oxidative stress

Exposure of human lung epithelial cells (A549 cell line) to the oxidant pollutant ozone (O₃) alters cell membrane currents inducing its decrease, when the cell undergoes to a voltage-clamp protocol ranging from -90 to +70mV. The membrane potential of these cells is mainly maintained by the interplay of potassium and chloride currents. Our previous studies indicated the ability of O₃ to activate ORCC (Outward Rectifier Chloride Channel) and consequently increases the chloride current. In this paper our aim was to understand the response of potassium current to oxidative stress challenge and to identify the kind potassium channel involved in O₃ induced current changes. After measuring the total membrane current using an intracellular solution with or without potassium ions, we obtained the contribution of potassium to the overall membrane current in control condition by a mathematical approach. Repeating these experiments after O₃ treatment we observed a significant decrease of I_potassium. Treatment of the cells with Iberiotoxin (IbTx), a specific inhibitor of BK channel, we were able to verify the presence and the functionality of BK channels. In addition, the administration of 4-Aminopyridine (an inhibitor of voltage dependent K channels but not BK channels) and Tetraethylammonium (TEA) before and after O₃ treatment we observed the formation of BK oxidative post-translation modifications. Our data suggest that O₃ is able to inhibit potassium current by targeting BK channel. Further studies are needed to better clarify the role of this BK channel and its interplay with the other membrane channels under oxidative stress conditions. These findings can contribute to identify the biomolecular pathway induced by O₃ allowing a possible pharmacological intervention against oxidative stress damage in lung tissue.

Impact of Bepanthen® and dexpanthenol on human nasal ciliary beat frequency in vitro

BACKGROUND

Dexpanthenol-containing ointments/fluids are recommended to restore impaired nasal mucosa. To date, there are no data about the influence of dexpanthenol or formulations including dexpanthenol on ciliary beat frequency (CBF) of nasal epithelial cells.

METHODS

We tested the ciliary beat frequency of human nasal epithelial cells in RPMI 1640 cell solution using in vitro high-frequency video microscopy every 60 s over a period of 15 min (min). Bepanthen^® solution and dexpanthenol in two clinically relevant concentrations (1.67% and 3.33%) were added to the cells. Addition of sterile water served as control group. To get a better overview, the measurements after 1 min, 5 min and 15 min were combined.

RESULTS

The CBF in the control group (n = 17) after 15 min was 7.3 ± 2.6 Hz. In comparison, the CBF after 15 min was 1.8 ± 1.0 Hz in the 3.33% Bepanthen^® group (n = 17) and 3.2 ± 1.2 Hz in the 1.67% group, which was statistically significantly lower in both groups (p < 0.001). With regard to the dexpanthenol group (n = 17) a CBF of 6.0 ± 2.6 Hz with 3.33% and 6.1 ± 2.4 Hz with 1.67% dexpanthenol, was detected, which was again statistically significantly lower (p = 0.06) compared to the control group except CBF at 15 min with 1.57% (n = 17; p = 0.04). In general, the effect on CBF was less pronounced with dexpanthenol compared with Bepanthen^® with a statistically significant difference between the two formulations. The results were verified by calculating an analysis of variance (ANOVA).

CONCLUSIONS

Bepanthen^® as an ointment, solution or inhalation is commonly used in ENT for mucosal care. Our results have shown that both substances reduce CBF in clinically relevant concentrations, although the effect was more pronounced with Bepanthen^® compared to dexpanthenol solution, which could be related to additives or change of physical properties in the solution. Further research is needed to assess potential clinical relevance.

Aerosolized nicotine from e-cigarettes alters gene expression, increases lung protein permeability, and impairs viral clearance in murine influenza infection

E-cigarette use has rapidly increased as an alternative means of nicotine delivery by heated aerosolization. Recent studies demonstrate nicotine-containing e-cigarette aerosols can have immunosuppressive and pro-inflammatory effects, but it remains unclear how e-cigarettes and the constituents of e-liquids may impact acute lung injury and the development of acute respiratory distress syndrome caused by viral pneumonia. Therefore, in these studies, mice were exposed one hour per day over nine consecutive days to aerosol generated by the clinically-relevant tank-style Aspire Nautilus aerosolizing e-liquid containing a mixture of vegetable glycerin and propylene glycol (VG/PG) with or without nicotine. Exposure to the nicotine-containing aerosol resulted in clinically-relevant levels of plasma cotinine, a nicotine-derived metabolite, and an increase in the pro-inflammatory cytokines IL-17A, CXCL1, and MCP-1 in the distal airspaces. Following the e-cigarette exposure, mice were intranasally inoculated with influenza A virus (H1N1 PR8 strain). Exposure to aerosols generated from VG/PG with and without nicotine caused greater influenza-induced production in the distal airspaces of the pro-inflammatory cytokines IFN-γ, TNFα, IL-1β, IL-6, IL-17A, and MCP-1 at 7 days post inoculation (dpi). Compared to the aerosolized carrier VG/PG, in mice exposed to aerosolized nicotine there was a significantly lower amount of Mucin 5 subtype AC (MUC5AC) in the distal airspaces and significantly higher lung permeability to protein and viral load in lungs at 7 dpi with influenza. Additionally, nicotine caused relative downregulation of genes associated with ciliary function and fluid clearance and an increased expression of pro-inflammatory pathways at 7 dpi. These results show that (1) the e-liquid carrier VG/PG increases the pro-inflammatory immune responses to viral pneumonia and that (2) nicotine in an e-cigarette aerosol alters the transcriptomic response to pathogens, blunts host defense mechanisms, increases lung barrier permeability, and reduces viral clearance during influenza infection. In conclusion, acute exposure to aerosolized nicotine can impair clearance of viral infection and exacerbate lung injury, findings that have implications for the regulation of e-cigarette products.

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

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

Mucociliary Wnt signaling promotes cilia biogenesis and beating

It is widely thought that Wnt/Lrp6 signaling proceeds through the cytoplasm and that motile cilia are signaling-inert nanomotors. Contrasting both views, we here show in the mucociliary epidermis of X. tropicalis embryos that motile cilia transduce a ciliary Wnt signal that is distinct from canonical β-catenin signaling. Instead, it engages a Wnt-Gsk3-Ppp1r11-Pp1 signaling axis. Mucociliary Wnt signaling is essential for ciliogenesis and it engages Lrp6 co-receptors that localize to cilia via a VxP ciliary targeting sequence. Live-cell imaging using a ciliary Gsk3 biosensor reveals an immediate response of motile cilia to Wnt ligand. Wnt treatment stimulates ciliary beating in X. tropicalis embryos and primary human airway mucociliary epithelia. Moreover, Wnt treatment improves ciliary function in X. tropicalis ciliopathy models of male infertility and primary ciliary dyskinesia (ccdc108, gas2l2). We conclude that X. tropicalis motile cilia are Wnt signaling organelles that transduce a distinct Wnt-Pp1 response.

In Vitro Characteristics of Canine Primary Tracheal Epithelial Cells Maintained at an Air-Liquid Interface Compared to In Vivo Morphology

Culturing respiratory epithelial cells at an air-liquid interface (ALI) represents an established method for studies on infection or toxicology by the generation of an in vivo-like respiratory tract epithelial cellular layer. Although primary respiratory cells from a variety of animals have been cultured, an in-depth characterization of canine tracheal ALI cultures is lacking despite the fact that canines are a highly relevant animal species susceptible to various respiratory agents, including zoonotic pathogens such as severe acute respiratory coronavirus 2 (SARS-CoV-2). In this study, canine primary tracheal epithelial cells were cultured under ALI conditions for four weeks, and their development was characterized during the entire culture period. Light and electron microscopy were performed to evaluate cell morphology in correlation with the immunohistological expression profile. The formation of tight junctions was confirmed using transepithelial electrical resistance (TEER) measurements and immunofluorescence staining for the junctional protein ZO-1. After 21 days of culture at the ALI, a columnar epithelium containing basal, ciliated and goblet cells was seen, resembling native canine tracheal samples. However, cilia formation, goblet cell distribution and epithelial thickness differed significantly from the native tissue. Despite this limitation, tracheal ALI cultures could be used to investigate the pathomorphological interactions of canine respiratory diseases and zoonotic agents.

Mucoadhesive drug delivery systems: a promising noninvasive approach to bioavailability enhancement. Part II: formulation considerations

INTRODUCTION

Mucoadhesive drug delivery systems (MDDS) are specifically designed to interact and bind to the mucosal layer of the epithelium for localized, prolonged, and/or targeted drug delivery. Over the past 4 decades, several dosage forms have been developed for localized as well as systemic drug delivery at different anatomical sites.

AREAS COVERED

The objective of this review is to provide a detailed understanding of the different aspects of MDDS. Part II describes the origin and evolution of MDDS, followed by a discussion of the properties of mucoadhesive polymers. Finally, a synopsis of the different commercial aspects of MDDS, recent advances in the development of MDDS for biologics and COVID-19 as well as future perspectives are provided.

EXPERT OPINION

A review of the past reports and recent advances reveal MDDS as highly versatile, biocompatible, and noninvasive drug delivery systems. The rise in the number of approved biologics, the introduction of newer highly efficient thiomers, as well as the recent advances in the field of nanotechnology have led to several excellent applications of MDDS, which are predicted to grow significantly in the future.

Antimicrobial materials for endotracheal tubes: A review on the last two decades of technological progress

Ventilator-associated pneumonia (VAP) is an unresolved problem in nosocomial settings, remaining consistently associated with a lack of treatment, high mortality, and prolonged hospital stay. The endotracheal tube (ETT) is the major culprit for VAP development owing to its early surface microbial colonization and biofilm formation by multiple pathogens, both critical events for VAP pathogenesis and relapses. To combat this matter, gradual research on antimicrobial ETT surface coating/modification approaches has been made. This review provides an overview of the relevance and implications of the ETT bioburden for VAP pathogenesis and how technological research on antimicrobial materials for ETTs has evolved. Firstly, certain main VAP attributes (definition/categorization; outcomes; economic impact) were outlined, highlighting the issues in defining/diagnosing VAP that often difficult VAP early- and late-onset differentiation, and that generate misinterpretations in VAP surveillance and discrepant outcomes. The central role of the ETT microbial colonization and subsequent biofilm formation as fundamental contributors to VAP pathogenesis was then underscored, in parallel with the uncovering of the polymicrobial ecosystem of VAP-related infections. Secondly, the latest technological developments (reported since 2002) on materials able to endow the ETT surface with active antimicrobial and/or passive antifouling properties were annotated, being further subject to critical scrutiny concerning their potentialities and/or constraints in reducing ETT bioburden and the risk of VAP while retaining/improving the safety of use. Taking those gaps/challenges into consideration, we discussed potential avenues that may assist upcoming advances in the field to tackle VAP rampant rates and improve patient care. STATEMENT OF SIGNIFICANCE: The use of the endotracheal tube (ETT) in patients requiring mechanical ventilation is associated with the development of ventilator-associated pneumonia (VAP). Its rapid surface colonization and biofilm formation are critical events for VAP pathogenesis and relapses. This review provides a comprehensive overview on the relevance/implications of the ETT biofilm in VAP, and on how research on antimicrobial ETT surface coating/modification technology has evolved over the last two decades. Despite significant technological advances, the limited number of gathered reports (46), highlights difficulty in overcoming certain hurdles associated with VAP (e.g., persistent colonization/biofilm formation; mechanical ventilation duration; hospital length of stay; VAP occurrence), which makes this an evolving, complex, and challenging matter. Challenges and opportunities in the field are discussed.

Role of mucociliary clearance system in respiratory diseases

Mucociliary clearance system is the primary innate defense mechanism of the lung. It plays a vital role in protecting airways from microbes and irritants infection. Mucociliary clearance system, which is mediated by the actions of airway and submucosal gland epithelial cells, plays a critical role in a multilayered defense system via secreting fluids, electrolytes, antimicrobial and anti-inflammatory proteins, and mucus onto airway surfaces. Changes in environment, drugs or diseases can lead to mucus overproduction and cilia dysfunction, which in turn decrease the rate of mucociliary clearance and enhance mucus gathering. The dysfunction of mucociliary clearance system often occurs in several respiratory diseases, such as primary ciliary dysfunction, cystic fibrosis, asthma and chronic obstructive pulmonary disease, which are characterized by goblet cell metaplasia, submucosal gland cell hypertrophy, mucus hypersecretion, cilia adhesion, lodging and loss, and airway obstruction.

Mouth breathing, dry air, and low water permeation promote inflammation, and activate neural pathways, by osmotic stresses acting on airway lining mucus

Respiratory disease and breathing abnormalities worsen with dehydration of the upper airways. We find that humidification of inhaled air occurs by evaporation of water over mucus lining the upper airways in such a way as to deliver an osmotic force on mucus, displacing it towards the epithelium. This displacement thins the periciliary layer of water beneath mucus while thickening topical water that is partially condensed from humid air on exhalation. With the rapid mouth breathing of dry air, this condensation layer, not previously reported while common to transpiring hydrogels in nature, can deliver an osmotic compressive force of up to around 100 cm H2O on underlying cilia, promoting adenosine triphosphate secretion and activating neural pathways. We derive expressions for the evolution of the thickness of the condensation layer, and its impact on cough frequency, inflammatory marker secretion, cilia beat frequency and respiratory droplet generation. We compare our predictions with human clinical data from multiple published sources and highlight the damaging impact of mouth breathing, dry, dirty air and high minute volume on upper airway function. We predict the hypertonic (or hypotonic) saline mass required to reduce (or amplify) dysfunction by restoration (or deterioration) of the structure of ciliated and condensation water layers in the upper airways and compare these predictions with published human clinical data. Preserving water balance in the upper airways appears critical in light of contemporary respiratory health challenges posed by the breathing of dirty and dry air.

Towards an atomic model of a beating ciliary axoneme

The axoneme of motile cilia and eukaryotic flagella is an ordered assembly of hundreds of proteins that powers the locomotion of single cells and generates flow of liquid and particles across certain mammalian tissues. The symmetric and organized structure of the axoneme has invited structural biologists to unravel its intricate architecture at different scales. In the last few years, single-particle cryo-electron microscopy provided high-resolution structures of axonemal complexes that comprise dozens of proteins and are key to cilia function. This review summarizes unique structural features of the axoneme and the framework they provide to understand cilia assembly, the mechanism of ciliary beating, and clinical conditions associated with impaired cilia motility.

Novel analytical tools reveal that local synchronization of cilia coincides with tissue-scale metachronal waves in zebrafish multiciliated epithelia

Motile cilia are hair-like cell extensions that beat periodically to generate fluid flow along various epithelial tissues within the body. In dense multiciliated carpets, cilia were shown to exhibit a remarkable coordination of their beat in the form of traveling metachronal waves, a phenomenon which supposedly enhances fluid transport. Yet, how cilia coordinate their regular beat in multiciliated epithelia to move fluids remains insufficiently understood, particularly due to lack of rigorous quantification. We combine experiments, novel analysis tools, and theory to address this knowledge gap. To investigate collective dynamics of cilia, we studied zebrafish multiciliated epithelia in the nose and the brain. We focused mainly on the zebrafish nose, due to its conserved properties with other ciliated tissues and its superior accessibility for non-invasive imaging. We revealed that cilia are synchronized only locally and that the size of local synchronization domains increases with the viscosity of the surrounding medium. Even though synchronization is local only, we observed global patterns of traveling metachronal waves across the zebrafish multiciliated epithelium. Intriguingly, these global wave direction patterns are conserved across individual fish, but different for left and right noses, unveiling a chiral asymmetry of metachronal coordination. To understand the implications of synchronization for fluid pumping, we used a computational model of a regular array of cilia. We found that local metachronal synchronization prevents steric collisions, i.e., cilia colliding with each other, and improves fluid pumping in dense cilia carpets, but hardly affects the direction of fluid flow. In conclusion, we show that local synchronization together with tissue-scale cilia alignment coincide and generate metachronal wave patterns in multiciliated epithelia, which enhance their physiological function of fluid pumping.

The RSPH4A Gene in Primary Ciliary Dyskinesia

The radial spoke head protein 4 homolog A (RSPH4A) gene is one of more than 50 genes that cause Primary ciliary dyskinesia (PCD), a rare genetic ciliopathy. Genetic mutations in the RSPH4A gene alter an important protein structure involved in ciliary pathogenesis. Radial spoke proteins, such as RSPH4A, have been conserved across multiple species. In humans, ciliary function deficiency caused by RSPH4A pathogenic variants results in a clinical phenotype characterized by recurrent oto-sino-pulmonary infections. More than 30 pathogenic RSPH4A genetic variants have been associated with PCD. In Puerto Rican Hispanics, a founder mutation (RSPH4A (c.921+3_921+6delAAGT (intronic)) has been described. The spectrum of the RSPH4A PCD phenotype does not include laterality defects, which results in a challenging diagnosis. PCD diagnostic tools can combine transmission electron microscopy (TEM), nasal nitric oxide (nNO), High-Speed Video microscopy Analysis (HSVA), and immunofluorescence. The purpose of this review article is to provide a comprehensive overview of current knowledge about the RSPH4A gene in PCD, ranging from basic science to human clinical phenotype.

Nebulized Menthol Impairs Mucociliary Clearance via TRPM8 and MUC5AC/MUC5B in Primary Airway Epithelial Cells

Flavorings enhance the palatability of e-cigarettes (e-cigs), with menthol remaining a popular choice among e-cig users. Menthol flavor remains one of the only flavors approved by the United States FDA for use in commercially available, pod-based e-cigs. However, the safety of inhaled menthol at the high concentrations used in e-cigs remains unclear. Here, we tested the effects of menthol on parameters of mucociliary clearance (MCC) in air-liquid interface (ALI) cultures of primary airway epithelial cells. ALI cultures treated with basolateral menthol (1 mM) showed a significant decrease in ciliary beat frequency (CBF) and airway surface liquid (ASL) volumes after 24 h. Menthol nebulized onto the surface of ALI cultures similarly reduced CBF and increased mucus concentrations, resulting in decreased rates of mucociliary transport. Nebulized menthol further increased the expression of mucin 5AC (MUC5AC) and mRNA expression of the inflammatory cytokines IL1B and TNFA. Menthol activated TRPM8, and the effects of menthol on MCC and inflammation could be blocked by a specific TRPM8 antagonist. These data provide further evidence that menthol at the concentrations used in e-cigs could cause harm to the airways.

SARS-CoV-2 replication in airway epithelia requires motile cilia and microvillar reprogramming

How SARS-CoV-2 penetrates the airway barrier of mucus and periciliary mucins to infect nasal epithelium remains unclear. Using primary nasal epithelial organoid cultures, we found that the virus attaches to motile cilia via the ACE2 receptor. SARS-CoV-2 traverses the mucus layer, using motile cilia as tracks to access the cell body. Depleting cilia blocks infection for SARS-CoV-2 and other respiratory viruses. SARS-CoV-2 progeny attach to airway microvilli 24 h post-infection and trigger formation of apically extended and highly branched microvilli that organize viral egress from the microvilli back into the mucus layer, supporting a model of virus dispersion throughout airway tissue via mucociliary transport. Phosphoproteomics and kinase inhibition reveal that microvillar remodeling is regulated by p21-activated kinases (PAK). Importantly, Omicron variants bind with higher affinity to motile cilia and show accelerated viral entry. Our work suggests that motile cilia, microvilli, and mucociliary-dependent mucus flow are critical for efficient virus replication in nasal epithelia.

The effects of acute hydrogen peroxide exposure on respiratory cilia motility and viability

COVID-19 has seen the propagation of alternative remedies to treat respiratory disease, such as nebulization of hydrogen peroxide (H₂O₂). As H₂O₂ has known cytotoxicity, it was hypothesised that H₂O₂ inhalation would negatively impact respiratory cilia function. To test this hypothesis, mouse tracheal samples were incubated with different H₂O₂ concentrations (0.1-1%) then cilia motility, cilia generated flow, and cell death was assessed 0-120 min following H₂O₂ treatment. 0.1-0.2% H₂O₂ caused immediate depression of cilia motility and complete cessation of cilia generated flow. Higher H₂O₂ concentrations (≥0.5%) caused immediate complete cessation of cilia motility and cilia generated flow. Cilia motility and flow was restored 30 min after 0.1% H₂O₂ treatment. Cilia motility and flow remained depressed 120 min after 0.2-0.5% H₂O₂ treatment. No recovery was seen 120 min after treatment with ≥1% H₂O₂. Live/dead staining revealed that H₂O₂ treatment caused preferential cell death of ciliated respiratory epithelia over non-ciliated epithelia, with 1% H₂O₂ causing 35.3 ± 7.0% of the ciliated epithelia cells to die 120 min following initial treatment. This study shows that H₂O₂ treatment significantly impacts respiratory cilia motility and cilia generated flow, characterised by a significant impairment in cilia motility even at low concentrations, the complete cessation of cilia motility at higher doses, and a significant cytotoxic effect on ciliated respiratory epithelial cells by promoting cell death. While this data needs further study using in vivo models, it suggests that extreme care should be taken when considering treating respiratory diseases with nebulised H₂O₂.

Cystic Fibrosis: Back to the Basics

Cystic fibrosis (CF) is the most common genetic disorder in Caucasian individuals, with an incidence of 1/2,500-3,500 live births. When CF was first described in 1938, most children died in infancy. Currently, the average lifespan is 28-47.7 years. Although new breakthroughs have occurred, CF is still incurable. Both early diagnosis and treatment by multidisciplinary teams are essential to optimize short- and long-term outcomes. It is imperative for neonatal clinicians to keep up to date on the most current research, treatment, and management of CF to provide the best outcomes. This article offers clinicians an updated review of the pathophysiology and clinical manifestations of CF, as well as current evidence-based diagnostics and treatment regimens.

Analysis of motility and mucociliary function of tracheal epithelial cilia

The airway epithelium contains numerous multiciliated cells. The apical surface of multiciliated cells is covered with cilia that move at 15-25Hz. Ciliary movement is not a simple reciprocal movement and distinctly has forward and reverse movements called effective and recovery strokes, respectively. These "asymmetric" ciliary strokes push away the mucus covering the mucosa of the airway epithelium. Mucus flow created by ciliary stroke is important for capturing and expelling dust, pollen, PM2.5, pathogens, and other particles that enter the airways from outside the body. This mechanism for protecting the airways produced by ciliary movement is called mucociliary function. Defects in ciliary motility lead to impairment of mucociliary function, resulting in recurrent airway infections such as bronchitis and pneumonia, and consequently, bronchiectasis. While the analysis of ciliary beat frequency is relatively easy, the analyses of the amplitude, velocities of strokes, and the asymmetric level require specific techniques and tips. In this chapter, we present methods for the analysis of ciliary movements of a group of cilia on the luminal surface of the trachea ex vivo and individually isolated and ATP-reactivated cilia in vitro. In addition, a method for the analysis of mucociliary function is also presented.

Methods to study motile ciliated cell types in the zebrafish brain

Cilia are well conserved hair-like structures that have diverse sensory and motile functions. In the brain, motile ciliated cells, known as ependymal cells, line the cerebrospinal fluid (CSF) filled ventricles, where their beating contribute to fluid movement. Ependymal cells have gathered increasing interest since they are associated with hydrocephalus, a neurological condition with ventricular enlargement. In this article, we highlight methods to identify and characterize motile ciliated ependymal lineage in the brain of zebrafish using histological staining and transgenic reporter lines.

Light-sheet laser speckle imaging for cilia motility assessment

Mucociliary clearance is an important innate defense mechanism predominantly mediated by ciliated cells in the upper respiratory tract. Ciliary motility on the respiratory epithelium surface and mucus pathogen trapping assist in maintaining healthy airways. Optical imaging methods have been used to obtain several indicators for assessing ciliary movement. Light-sheet laser speckle imaging (LSH-LSI) is a label-free and non-invasive optical technique for three-dimensional and quantitative mapping of velocities of microscopic scatterers. Here, we propose to use an inverted LSH-LSI platform to study cilia motility. We have experimentally confirmed that LSH-LSI can reliably measure the ciliary beating frequency and has the potential to provide many additional quantitative indicators for characterizing the ciliary beating pattern without labeling. For example, the asymmetry between the power stroke and the recovery stroke is apparent in the local velocity waveform. PIV (particle imaging velocimetry) analysis of laser speckle data could determine the cilia motion directions in different phases.

Estimating inhalation bioavailability for peptides and proteins 1 to 10 kDa in size

Inhalation is a critical route for occupational exposure. To protect workers from adverse effects, health-based exposure limits (HBELs) are derived using chemical-specific information including inhalation bioavailability. Inhalation bioavailability of large proteins is well studied and generally accepted to be 1% or less. However, the inhalation bioavailability of peptides and proteins 1-10 kDa in size is not well defined. The goal of this study was to expand upon previous analyses and evaluate the inhalation bioavailability of small peptides. Inhalation bioavailability data for 72 peptides and protein samples ranging from 1.1 to 10.9 kDa in size were evaluated. The median inhalation bioavailability was 20%, which is in agreement with previously published analyses. Inhalation bioavailabilities for the vast majority were below 50%. Interestingly, species, peptide size, and peptide identity did not correlate with inhalation bioavailability. Other factors including inhalation dosimetry, peptide degradation, and chemical characteristics also decrease the amount of peptide available for absorption. Together, the median bioavailability of 20% is likely an appropriate estimate of systemic exposure and is sufficiently protective in most cases for the purposes of occupational exposure safety. Thus, in the absence of peptide-specific data or concerns, an inhalation bioavailability default of 20% is recommended for 1-10 kDa peptide and proteins.

Towards an artificial human lung: modelling organ-like complexity to aid mechanistic understanding

Respiratory diseases account for over 5 million deaths yearly and are a huge burden to healthcare systems worldwide. Murine models have been of paramount importance to decode human lung biology in vivo, but their genetic, anatomical, physiological and immunological differences with humans significantly hamper successful translation of research into clinical practice. Thus, to clearly understand human lung physiology, development, homeostasis and mechanistic dysregulation that may lead to disease, it is essential to develop models that accurately recreate the extraordinary complexity of the human pulmonary architecture and biology. Recent advances in micro-engineering technology and tissue engineering have allowed the development of more sophisticated models intending to bridge the gap between the native lung and its replicates in vitro Alongside advanced culture techniques, remarkable technological growth in downstream analyses has significantly increased the predictive power of human biology-based in vitro models by allowing capture and quantification of complex signals. Refined integrated multi-omics readouts could lead to an acceleration of the translational pipeline from in vitro experimental settings to drug development and clinical testing in the future. This review highlights the range and complexity of state-of-the-art lung models for different areas of the respiratory system, from nasal to large airways, small airways and alveoli, with consideration of various aspects of disease states and their potential applications, including pre-clinical drug testing. We explore how development of optimised physiologically relevant in vitro human lung models could accelerate the identification of novel therapeutics with increased potential to translate successfully from the bench to the patient's bedside.

Variable phenotypes and penetrance between and within different zebrafish ciliary transition zone mutants

Meckel syndrome, nephronophthisis, Joubert syndrome and Bardet-Biedl syndrome are caused by mutations in proteins that localize to the ciliary transition zone (TZ). The phenotypically distinct syndromes suggest that these TZ proteins have differing functions. However, mutations in a single TZ gene can result in multiple syndromes, suggesting that the phenotype is influenced by modifier genes. We performed a comprehensive analysis of ten zebrafish TZ mutants, including mks1, tmem216, tmem67, rpgrip1l, cc2d2a, b9d2, cep290, tctn1, nphp1 and nphp4, as well as mutants in ift88 and ift172. Our data indicate that variations in phenotypes exist between different TZ mutants, supporting different tissue-specific functions of these TZ genes. Further, we observed phenotypic variations within progeny of a single TZ mutant, reminiscent of multiple disease syndromes being associated with mutations in one gene. In some mutants, the dynamics of the phenotype became complex with transitory phenotypes that are corrected over time. We also demonstrated that multiple-guide-derived CRISPR/Cas9 F0 'crispant' embryos recapitulate zygotic null phenotypes, and rapidly identified ciliary phenotypes in 11 cilia-associated gene candidates (ankfn1, ccdc65, cfap57, fhad1, nme7, pacrg, saxo2, c1orf194, ttc26, zmynd12 and cfap52).

Mechanisms and challenges of nanocarriers as non-viral vectors of therapeutic genes for enhanced pulmonary delivery

With the rapid development of biopharmaceuticals and the outbreak of COVID-19, the world has ushered in a frenzy to develop gene therapy. Therefore, therapeutic genes have received enormous attention. However, due to the extreme instability and low intracellular gene expression of naked genes, specific vectors are required. Viral vectors are widely used attributed to their high transfection efficiency. However, due to the safety concerns of viral vectors, nanotechnology-based non-viral vectors have attracted extensive investigation. Still, issues of low transfection efficiency and poor tissue targeting of non-viral vectors need to be addressed. Especially, pulmonary gene delivery has obvious advantages for the treatment of inherited lung diseases, lung cancer, and viral pneumonia, which can not only enhance lung targeting and but also reduce enzymatic degradation. For systemic diseases therapy, pulmonary gene delivery can enhance vaccine efficacy via inducing not only cellular, humoral immunity but also mucosal immunity. This review provides a comprehensive overview of nanocarriers as non-viral vectors of therapeutic genes for enhanced pulmonary delivery. First of all, the characteristics and therapeutic mechanism of DNA, mRNA, and siRNA are provided. Thereafter, the advantages and challenges of pulmonary gene delivery in exerting local and systemic effects are discussed. Then, the inhalation dosage forms for nanoparticle-based drug delivery systems are introduced. Moreover, a series of materials used as nanocarriers for pulmonary gene delivery are presented, and the endosomal escape mechanisms of nanocarriers based on different materials are explored. The application of various non-viral vectors for pulmonary gene delivery are summarized in detail, with the perspectives of nano-vectors for pulmonary gene delivery.

Airway surface hyperviscosity and defective mucociliary transport by IL-17/TNF-α are corrected by β-adrenergic stimulus

The fluid covering the surface of airway epithelia represents a first barrier against pathogens. The chemical and physical properties of the airway surface fluid are controlled by the activity of ion channels and transporters. In cystic fibrosis (CF), loss of CFTR chloride channel function causes airway surface dehydration, bacterial infection, and inflammation. We investigated the effects of IL-17A plus TNF-α, 2 cytokines with relevant roles in CF and other chronic lung diseases. Transcriptome analysis revealed a profound change with upregulation of several genes involved in ion transport, antibacterial defense, and neutrophil recruitment. At the functional level, bronchial epithelia treated in vitro with the cytokine combination showed upregulation of ENaC channel, ATP12A proton pump, ADRB2 β-adrenergic receptor, and SLC26A4 anion exchanger. The overall result of IL-17A/TNF-α treatment was hyperviscosity of the airway surface, as demonstrated by fluorescence recovery after photobleaching (FRAP) experiments. Importantly, stimulation with a β-adrenergic agonist switched airway surface to a low-viscosity state in non-CF but not in CF epithelia. Our study suggests that CF lung disease is sustained by a vicious cycle in which epithelia cannot exit from the hyperviscous state, thus perpetuating the proinflammatory airway surface condition.

Basal bodies bend in response to ciliary forces

Motile cilia beat with an asymmetric waveform consisting of a power stroke that generates a propulsive force and a recovery stroke that returns the cilium back to the start. Cilia are anchored to the cell cortex by basal bodies (BBs) that are directly coupled to the ciliary doublet microtubules (MTs). We find that, consistent with ciliary forces imposing on BBs, bending patterns in BB triplet MTs are responsive to ciliary beating. BB bending varies as environmental conditions change the ciliary waveform. Bending occurs where striated fibers (SFs) attach to BBs and mutants with short SFs that fail to connect to adjacent BBs exhibit abnormal BB bending, supporting a model in which SFs couple ciliary forces between BBs. Finally, loss of the BB stability protein Poc1, which helps interconnect BB triplet MTs, prevents the normal distributed BB and ciliary bending patterns. Collectively, BBs experience ciliary forces and manage mechanical coupling of these forces to their surrounding cellular architecture for normal ciliary beating.

Coordination of Cilia Movements in Multi-Ciliated Cells

Multiple motile cilia are formed at the apical surface of multi-ciliated cells in the epithelium of the oviduct or the fallopian tube, the trachea, and the ventricle of the brain. Those cilia beat unidirectionally along the tissue axis, and this provides a driving force for directed movements of ovulated oocytes, mucus, and cerebrospinal fluid in each of these organs. Furthermore, cilia movements show temporal coordination between neighboring cilia. To establish such coordination of cilia movements, cilia need to sense and respond to various cues, including the organ's orientation and movements of neighboring cilia. In this review, we discuss the mechanisms by which cilia movements of multi-ciliated cells are coordinated, focusing on planar cell polarity and the cytoskeleton, and highlight open questions for future research.

Biallelic DAW1 variants cause a motile ciliopathy characterized by laterality defects and subtle ciliary beating abnormalities

PURPOSE

The clinical spectrum of motile ciliopathies includes laterality defects, hydrocephalus, and infertility as well as primary ciliary dyskinesia when impaired mucociliary clearance results in otosinopulmonary disease. Importantly, approximately 30% of patients with primary ciliary dyskinesia lack a genetic diagnosis.

METHODS

Clinical, genomic, biochemical, and functional studies were performed alongside in vivo modeling of DAW1 variants.

RESULTS

In this study, we identified biallelic DAW1 variants associated with laterality defects and respiratory symptoms compatible with motile cilia dysfunction. In early mouse embryos, we showed that Daw1 expression is limited to distal, motile ciliated cells of the node, consistent with a role in left-right patterning. daw1 mutant zebrafish exhibited reduced cilia motility and left-right patterning defects, including cardiac looping abnormalities. Importantly, these defects were rescued by wild-type, but not mutant daw1, gene expression. In addition, pathogenic DAW1 missense variants displayed reduced protein stability, whereas DAW1 loss-of-function was associated with distal type 2 outer dynein arm assembly defects involving axonemal respiratory cilia proteins, explaining the reduced cilia-induced fluid flow in particle tracking velocimetry experiments.

CONCLUSION

Our data define biallelic DAW1 variants as a cause of human motile ciliopathy and determine that the disease mechanism involves motile cilia dysfunction, explaining the ciliary beating defects observed in affected individuals.

Gene therapy for cystic fibrosis: Challenges and prospects

Cystic fibrosis (CF) is a life-threatening autosomal-recessive disease caused by mutations in a single gene encoding cystic fibrosis transmembrane conductance regulator (CFTR). CF effects multiple organs, and lung disease is the primary cause of mortality. The median age at death from CF is in the early forties. CF was one of the first diseases to be considered for gene therapy, and efforts focused on treating CF lung disease began shortly after the CFTR gene was identified in 1989. However, despite the quickly established proof-of-concept for CFTR gene transfer in vitro and in clinical trials in 1990s, to date, 36 CF gene therapy clinical trials involving ∼600 patients with CF have yet to achieve their desired outcomes. The long journey to pursue gene therapy as a cure for CF encountered more difficulties than originally anticipated, but immense progress has been made in the past decade in the developments of next generation airway transduction viral vectors and CF animal models that reproduced human CF disease phenotypes. In this review, we look back at the history for the lessons learned from previous clinical trials and summarize the recent advances in the research for CF gene therapy, including the emerging CRISPR-based gene editing strategies. We also discuss the airway transduction vectors, large animal CF models, the complexity of CF pathogenesis and heterogeneity of CFTR expression in airway epithelium, which are the major challenges to the implementation of a successful CF gene therapy, and highlight the future opportunities and prospects.

Subacute Pulmonary Toxicity of Glutaraldehyde Aerosols in a Human In Vitro Airway Tissue Model

Glutaraldehyde (GA) has been cleared by the Center for Devices and Radiological Health (CDRH) of the Food and Drug Administration (FDA) as a high-level disinfectant for disinfecting heat-sensitive medical equipment in hospitals and healthcare facilities. Inhalation exposure to GA is known to cause respiratory irritation and sensitization in animals and humans. To reproduce some of the known in vivo effects elicited by GA, we used a liquid aerosol exposure system and evaluated the tissue responses in a human in vitro airway epithelial tissue model. The cultures were treated at the air interface with various concentrations of GA aerosols on five consecutive days and changes in tissue function and structure were evaluated at select timepoints during the treatment phase and after a 7-day recovery period. Exposure to GA aerosols caused oxidative stress, inhibition of ciliary beating frequency, aberrant mucin production, and disturbance of cytokine and matrix metalloproteinase secretion, as well as morphological transformation. Some effects, such as those on goblet cells and ciliated cells, persisted following the 7-day recovery period. Of note, the functional and structural disturbances observed in GA-treated cultures resemble those found in ortho-phthaldehyde (OPA)-treated cultures. Furthermore, our in vitro findings on GA toxicity partially and qualitatively mimicked those reported in the animal and human survey studies. Taken together, observations from this study demonstrate that the human air-liquid-interface (ALI) airway tissue model, integrated with an in vitro exposure system that simulates human inhalation exposure, could be used for in vitro-based human hazard identification and the risk characterization of aerosolized chemicals.

Allergic Inflammation: Effect of Propolis and Its Flavonoids

The incidence of allergic diseases and their complications are increasing worldwide. Today, people increasingly use natural products, which has been termed a "return to nature". Natural products with healing properties, especially those obtained from plants and bees, have been used in the prevention and treatment of numerous chronic diseases, including allergy and/or inflammation. Propolis is a multi-component resin rich in flavonoids, collected and transformed by honeybees from buds and plant wounds for the construction and adaptation of their nests. This article describes the current views regarding the possible mechanisms and multiple benefits of flavonoids in combating allergy and allergy-related complications. These benefits arise from flavonoid anti-allergic, anti-inflammatory, antioxidative, and wound healing activities and their effects on microbe-immune system interactions in developing host responses to different allergens. Finally, this article presents various aspects of allergy pathobiology and possible molecular approaches in their treatment. Possible mechanisms regarding the antiallergic action of propolis on the microbiota of the digestive and respiratory tracts and skin diseases as a method to selectively remove allergenic molecules by the process of bacterial biotransformation are also reported.

Effects of Extracts and Flavonoids from Drosera rotundifolia L. on Ciliary Beat Frequency and Murine Airway Smooth Muscle

Extracts from Drosera rotundifolia are traditionally used to treat cough symptoms during a common cold. The present study aimed to investigate the impact of extracts from D. rotundifolia and active compounds on the respiratory tract. Tracheal slices of C57BL/6N mice were used ex vivo to examine effects on airway smooth muscle (ASM) and ciliary beat frequency (CBF). Phosphodiesterase (PDE) inhibition assays were carried out to test whether PDE1 or PDE4 are targeted by the active compounds. An ethanol–water extract, as well as an aqueous fraction of this extract, exerted antispasmodic properties against acetylcholine-induced contractions. In addition, contractions induced by 60 mM K⁺ were abrogated by the aqueous fraction. Effects on ASM could be attributed to the flavonoids quercetin, 2″-O-galloylhyperoside and hyperoside. Moreover, the Drosera extract and the aqueous fraction increased the CBF of murine tracheal slices. Quercetin and 2″-O-galloylhyperoside were identified as active compounds involved in the elevation of CBF. Both compounds inhibited PDE1A and PDE4D. The elevation of CBF was mimicked by the subtype-selective PDE inhibitor rolipram (PDE4) and by 8-methoxymethyl-IBMX. In summary, our study shows, for the first time, that a Drosera extract and its flavonoid compounds increase the CBF of murine airways while antispasmodic effects were transferred to ASM.

Physiology and pathophysiology of human airway mucus

The mucus clearance system is the dominant mechanical host defense system of the human lung. Mucus is cleared from the lung by cilia and airflow, including both two-phase gas-liquid pumping and cough-dependent mechanisms, and mucus transport rates are heavily dependent on mucus concentration. Importantly, mucus transport rates are accurately predicted by the gel-on-brush model of the mucociliary apparatus from the relative osmotic moduli of the mucus and periciliary-glycocalyceal (PCL-G) layers. The fluid available to hydrate mucus is generated by transepithelial fluid transport. Feedback interactions between mucus concentrations and cilia beating, via purinergic signaling, coordinate Na+ absorptive vs Cl- secretory rates to maintain mucus hydration in health. In disease, mucus becomes hyperconcentrated (dehydrated). Multiple mechanisms derange the ion transport pathways that normally hydrate mucus in muco-obstructive lung diseases, e.g., cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), non-CF bronchiectasis (NCFB), and primary ciliary dyskinesia (PCD). A key step in muco-obstructive disease pathogenesis is the osmotic compression of the mucus layer onto the airway surface with the formation of adherent mucus plaques and plugs, particularly in distal airways. Mucus plaques create locally hypoxic conditions and produce airflow obstruction, inflammation, infection, and, ultimately, airway wall damage. Therapies to clear adherent mucus with hydrating and mucolytic agents are rational, and strategies to develop these agents are reviewed.

Transient Receptor Potential (TRP) Channels in Airway Toxicity and Disease: An Update

Our respiratory system is exposed to toxicants and pathogens from both sides: the airways and the vasculature. While tracheal, bronchial and alveolar epithelial cells form a natural barrier in the airways, endothelial cells protect the lung from perfused toxic compounds, particulate matter and invading microorganism in the vascular system. Damages induce inflammation by our immune response and wound healing by (myo)fibroblast proliferation. Members of the transient receptor potential (TRP) superfamily of ion channel are expressed in many cells of the respiratory tract and serve multiple functions in physiology and pathophysiology. TRP expression patterns in non-neuronal cells with a focus on TRPA1, TRPC6, TRPM2, TRPM5, TRPM7, TRPV2, TRPV4 and TRPV6 channels are presented, and their roles in barrier function, immune regulation and phagocytosis are summarized. Moreover, TRP channels as future pharmacological targets in chronic obstructive pulmonary disease (COPD), asthma, cystic and pulmonary fibrosis as well as lung edema are discussed.

Associative evidence for the potential of humidification as a non-pharmaceutical intervention for influenza and SARS-CoV-2 transmission

BACKGROUND

Both influenza and SARS-CoV-2 viruses show a strong seasonal spreading in temperate regions. Several studies indicated that changes in indoor humidity could be one of the key factors explaining this.

OBJECTIVE

The purpose of this study is to quantify the association between relevant epidemiological metrics and humidity in both influenza and SARS-CoV-2 epidemic periods.

METHODS

The atmospheric dew point temperature serves as a proxy for indoor relative humidity. This study considered the weekly mortality rate in the Netherlands between 1995 and 2019 to determine the correlation between the dew point and the spread of influenza. During influenza epidemic periods in the Netherlands, governmental restrictions were absent; therefore, there is no need to control this confounder. During the SARS-CoV-2 pandemic, governmental restrictions strongly varied over time. To control this effect, periods with a relatively constant governmental intervention level were selected to analyze the reproduction rate. We also examine SARS-CoV-2 deaths in the nursing home setting, where health policy and social factors were less variable. Viral transmissibility was measured by computing the ratio between the estimated daily number of infectious persons in the Netherlands and the lagged mortality figures in the nursing homes.

RESULTS

For both influenza and SARS-CoV-2, a significant correlation was found between the dew point temperature and the aforementioned epidemiological metrics. The findings are consistent with the anticipated mechanisms related to droplet evaporation, stability of virus in the indoor environment, and impairment of the natural defenses of the respiratory tract in dry air.

SIGNIFICANCE

This information is helpful to understand the seasonal pattern of respiratory viruses and motivate further study to what extent it is possible to alter the seasonal pattern by actively intervening in the adverse role of low humidity during fall and winter in temperate regions.

IMPACT

A solid understanding and quantification of the role of humidity on the transmission of respiratory viruses is imperative for epidemiological modeling and the installation of non-pharmaceutical interventions. The results of this study indicate that improving the indoor humidity by humidifiers could be a promising technology for reducing the spread of both influenza and SARS-CoV-2 during winter and fall in the temperate zone. The identification of this potential should be seen as a strong motivation to invest in further prospective testing of this non-pharmaceutical intervention.

Nanoparticle-Based Inhalation Therapy for Pulmonary Diseases

The lung is exposed to various pollutants and is the primary site for the onset of various diseases, including infections, allergies, and cancers. One possible treatment approach for such pulmonary diseases involves direct administration of therapeutics to the lung so as to maintain the topical concentration of the drug. Particles with nanoscale diameters tend to reach the pulmonary region. Nanoparticles (NPs) have garnered significant interest for applications in biomedical and pharmaceutical industries because of their unique physicochemical properties and biological activities. In this article, we describe the biological and pharmacological activities of NPs as well as summarize their potential in the formulation of drugs employed to treat pulmonary diseases. Recent advances in the use of NPs in inhalation chemotherapy for the treatment of lung diseases have also been highlighted.

Progress in Respiratory Gene Therapy

The prospect of gene therapy for inherited and acquired respiratory disease has energized the research community since the 1980s, with cystic fibrosis, as a monogenic disorder, driving early efforts to develop effective strategies. The fact that there are still no approved gene therapy products for the lung, despite many early phase clinical trials, illustrates the scale of the challenge: In the 1990s, first-generation non-viral and viral vector systems demonstrated proof-of-concept but low efficacy. Since then, there has been steady progress toward improved vectors with the capacity to overcome at least some of the formidable barriers presented by the lung. In addition, the inclusion of features such as codon optimization and promoters providing long-term expression have improved the expression characteristics of therapeutic transgenes. Early approaches were based on gene addition, where a new DNA copy of a gene is introduced to complement a genetic mutation: however, the advent of RNA-based products that can directly express a therapeutic protein or manipulate gene expression, together with the expanding range of tools for gene editing, has stimulated the development of alternative approaches. This review discusses the range of vector systems being evaluated for lung delivery; the variety of cargoes they deliver, including DNA, antisense oligonucleotides, messenger RNA (mRNA), small interfering RNA (siRNA), and peptide nucleic acids; and exemplifies progress in selected respiratory disease indications.

Effect of invasive mechanical ventilation on the diversity of the pulmonary microbiota

Pulmonary microbial diversity may be influenced by biotic or abiotic conditions (e.g., disease, smoking, invasive mechanical ventilation (MV), etc.). Specially, invasive MV may trigger structural and physiological changes in both tissue and microbiota of lung, due to gastric and oral microaspiration, altered body posture, high O2 inhalation-induced O2 toxicity in hypoxemic patients, impaired airway clearance and ventilator-induced lung injury (VILI), which in turn reduce the diversity of the pulmonary microbiota and may ultimately lead to poor prognosis. Furthermore, changes in (local) O2 concentration can reduce the diversity of the pulmonary microbiota by affecting the local immune microenvironment of lung. In conclusion, systematic literature studies have found that invasive MV reduces pulmonary microbiota diversity, and future rational regulation of pulmonary microbiota diversity by existing or novel clinical tools (e.g., lung probiotics, drugs) may improve the prognosis of invasive MV treatment and lead to more effective treatment of lung diseases with precision.