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

Pulmonary Vascular Dysfunctions in Cystic Fibrosis

Cystic fibrosis (CF) is an inherited disorder caused by a deleterious mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Given that the CFTR protein is a chloride channel expressed on a variety of cells throughout the human body, mutations in this gene impact several organs, particularly the lungs. For this very reason, research regarding CF disease and CFTR function has historically focused on the lung airway epithelium. Nevertheless, it was discovered more than two decades ago that CFTR is also expressed and functional on endothelial cells. Despite the great strides that have been made in understanding the role of CFTR in the airway epithelium, the role of CFTR in the endothelium remains unclear. Considering that the airway epithelium and endothelium work in tandem to allow gas exchange, it becomes very crucial to understand how a defective CFTR protein can impact the pulmonary vasculature and overall lung function. Fortunately, more recent research has been dedicated to elucidating the role of CFTR in the endothelium. As a result, several vascular dysfunctions associated with CF disease have come to light. Here, we summarize the current knowledge on pulmonary vascular dysfunctions in CF and discuss applicable therapies.

Aspiration Pneumonia

Aspiration pneumonia is a lower respiratory tract infection that results from inhalation of foreign material, often gastric and oropharyngeal contents. It is important to distinguish this from a similar entity, aspiration with chemical pneumonitis, as treatment approaches may differ. An evolving understanding of the human microbiome has shed light on the pathogenesis of aspiration pneumonia, suggesting that dysbiosis, repetitive injury, and inflammatory responses play a role in its development. Risk factors for aspiration events involve a complex interplay of anatomical and physiological dysfunctions in the nervous, gastrointestinal, and pulmonary systems. Current treatment strategies have shifted away from anaerobic organisms as leading pathogens. Prevention of aspiration pneumonia primarily involves addressing oropharyngeal dysphagia, a significant risk factor for aspiration pneumonia, particularly among elderly individuals and those with cognitive and neurodegenerative disorders.

Mucus Structure, Viscoelastic Properties, and Composition in Chronic Respiratory Diseases

The respiratory mucus, a viscoelastic gel, effectuates a primary line of the airway defense when operated by the mucociliary clearance. In chronic respiratory diseases (CRDs), such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), the mucus is overproduced and its solid content augments, changing its structure and viscoelastic properties and determining a derangement of essential defense mechanisms against opportunistic microbial (virus and bacteria) pathogens. This ensues in damaging of the airways, leading to a vicious cycle of obstruction and infection responsible for the harsh clinical evolution of these CRDs. Here, we review the essential features of normal and pathological mucus (i.e., sputum in CF, COPD, and asthma), i.e., mucin content, structure (mesh size), micro/macro-rheology, pH, and osmotic pressure, ending with the awareness that sputum biomarkers (mucins, inflammatory proteins and peptides, and metabolites) might serve to indicate acute exacerbation and response to therapies. There are some indications that old and novel treatments may change the structure, viscoelastic properties, and biomarker content of sputum; however, a wealth of work is still needed to embrace these measures as correlates of disease severity in association with (or even as substitutes of) pulmonary functional tests.

Potential systemic effects of acquired CFTR dysfunction in COPD

Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation, respiratory symptoms, inflammation of the airways, and systemic manifestations of the disease. Genetic susceptibility and environmental factors are important in the development of the disease, particularly exposure to cigarette smoke which is the most notable risk factor. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are the cause of cystic fibrosis (CF), which shares several pathophysiological pulmonary features with COPD, including airway obstruction, chronic airway inflammation and bacterial colonization; in addition, both diseases also present systemic defects leading to comorbidities such as pancreatic, gastrointestinal, and bone-related diseases. In patients with COPD, systemic CFTR dysfunction can be acquired by cigarette smoking, inflammation, and infection. This dysfunction is, on average, about half of that found in CF. Herein we review the literature focusing on acquired CFTR dysfunction and the potential role in the pathogenesis of comorbidities associated with COPD and chronic bronchitis.

Infection, Allergy, and Inflammation: The Role of Aspergillus fumigatus in Cystic Fibrosis

Aspergillus fumigatus (Af) is a mold frequently detected in airway samples from people with cystic fibrosis (pwCF). Abnormal airway mucus may allow Af to germinate, resulting in airway infection or an allergic response. While Af is known to increase morbidity in pwCF, individual responses and the degree of impact on lung disease vary. Improved approaches to diagnosis, treatment, and prevention of Af, particularly the persistent Af infection, are needed. This update highlights our current understanding of Af pathophysiology in the CF airway, the effects of Af on pwCF, and areas of research needed to improve clinical outcomes.

Alcohol-Induced Mucociliary Dysfunction: Role of Defective CFTR Channel Function

Excessive alcohol use is thought to increase the risk of respiratory infections by impairing mucociliary clearance (MCC). In this study, we investigate the hypothesis that alcohol reduces the function of CFTR, the protein that is defective in individuals with cystic fibrosis, thus altering mucus properties to impair MCC and the airway's defense against inhaled pathogens.

Methods

Sprague Dawley rats with wild type CFTR (+/+), matched for age and sex, were administered either a Lieber-DeCarli alcohol diet or a control diet with the same number of calories for eight weeks. CFTR activity was measured using nasal potential difference (NPD) assay and Ussing chamber electrophysiology of tracheal tissue samples. In vivo MCC was determined by measuring the radiographic clearance of inhaled Tc99 particles and the depth of the airway periciliary liquid (PCL) and mucus transport rate in excised trachea using micro-optical coherence tomography (μOCT). The levels of rat lung MUC5b and CFTR were estimated by protein and mRNA analysis.

Results

Alcohol diet was found to decrease CFTR ion transport in the nasal and tracheal epithelium in vivo and ex vivo. This decrease in activity was also reflected in partially reduced full-length CFTR protein levels but not, in mRNA copies, in the lungs of rats. Furthermore, alcohol-fed rats showed a significant decrease in MCC after 8 weeks of alcohol consumption. The trachea from these rats also showed reduced PCL depth, indicating a decrease in mucosal surface hydration that was reflected in delayed mucus transport. Diminished MCC rate was also likely due to the elevated MUC5b expression in alcohol-fed rat lungs.

Conclusions

Excessive alcohol use can decrease the expression and activity of CFTR channels, leading to reduced airway surface hydration and impaired mucus clearance. This suggests that CFTR dysfunction plays a role in the compromised lung defense against respiratory pathogens in individuals who drink alcohol excessively.

Ivacaftor therapy post myocardial infarction augments systemic inflammation and evokes contrasting effects with respect to tissue inflammation in brain and lung

Acquired cystic fibrosis transmembrane regulator (CFTR) dysfunctions have been associated with several conditions, including myocardial infarction (MI). Here, CFTR is downregulated in brain, heart, and lung tissue and associates with inflammation and degenerative processes. Therapeutically increasing CFTR expression attenuates these effects. Whether potentiating CFTR function yields similar beneficial effects post-MI is unknown. The CFTR potentiator ivacaftor is currently in clinical trials for treatment of acquired CFTR dysfunction associated with chronic obstructive pulmonary disease and chronic bronchitis. Thus, we tested ivacaftor as therapeutic strategy for MI-associated target tissue inflammation that is characterized by CFTR alterations. MI was induced in male C57Bl/6 mice by ligation of the left anterior descending coronary artery. Mice were treated with ivacaftor starting ten weeks post-MI for two consecutive weeks. Systemic ivacaftor treatment ameliorates hippocampal neuron dendritic atrophy and spine loss and attenuates hippocampus-dependent memory deficits occurring post-MI. Similarly, ivacaftor therapy mitigates MI-associated neuroinflammation (i.e., reduces higher proportions of activated microglia). Systemically, ivacaftor leads to higher frequencies of circulating Ly6C⁺ and Ly6C^hi cells compared to vehicle-treated MI mice. Likewise, an ivacaftor-mediated augmentation of MI-associated pro-inflammatory macrophage phenotype characterized by higher CD80-positivity is observed in the MI lung. In vitro, ivacaftor does not alter LPS-induced CD80 and tumor necrosis factor alpha mRNA increases in BV2 microglial cells, while augmenting mRNA levels of these markers in mouse macrophages and differentiated human THP-1-derived macrophages. Our results suggest that ivacaftor promotes contrasting effects depending on target tissue post-MI, which may be largely dependent on its effects on different myeloid cell types.

Nicotine aerosols diminish airway CFTR function and mucociliary clearance

Electronic cigarettes (e-cigs) are often promoted as safe alternatives to smoking based on the faulty perception that inhaling nicotine is safe until other harmful chemicals in cigarette smoke are absent. Previously, others and we have reported that, similar to cigarette smoke, e-cig aerosols decrease CFTR-mediated ion transport across airway epithelium. However, it is unclear whether such defective epithelial ion transport by e-cig aerosols occurs in vivo and what the singular contribution of inhaled nicotine is to impairments in mucociliary clearance (MCC), the primary physiologic defense of the airways. Here, we tested the effects of nicotine aerosols from e-cigs in primary human bronchial epithelial (HBE) cells and two animal models, rats and ferrets, known for their increasing physiologic complexity and potential for clinical translation, followed by in vitro and in vivo electrophysiologic assays for CFTR activity and micro-optical coherence tomography (μOCT) image analyses for alterations in airway mucus physiology. Data presented in this report indicate nicotine in e-cig aerosols causes 1) reduced CFTR and epithelial Na+ channel (ENaC)-mediated ion transport, 2) delayed MCC, and 3) diminished airway surface hydration, as determined by periciliary liquid depth analysis. Interestingly, the common e-cig vehicles vegetable glycerin and propylene glycol did not affect CFTR function or MCC in vivo despite their significant adverse effects in vitro. Overall, our studies contribute to an improved understanding of inhaled nicotine effects on lung health among e-cig users and inform pathologic mechanisms involved in altered host defense and increased risk for tobacco-associated lung diseases.

Extracellular Vesicles' Role in the Pathophysiology and as Biomarkers in Cystic Fibrosis and COPD

In keeping with the extraordinary interest and advancement of extracellular vesicles (EVs) in pathogenesis and diagnosis fields, we herein present an update to the knowledge about their role in cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Although CF and COPD stem from a different origin, one genetic and the other acquired, they share a similar pathophysiology, being the CF transmembrane conductance regulator (CFTR) protein implied in both disorders. Various subsets of EVs, comprised mainly of microvesicles (MVs) and exosomes (EXOs), are secreted by various cell types that are either resident or attracted in the airways during the onset and progression of CF and COPD lung disease, representing a vehicle for metabolites, proteins and RNAs (especially microRNAs), that in turn lead to events as such neutrophil influx, the overwhelming of proteases (elastase, metalloproteases), oxidative stress, myofibroblast activation and collagen deposition. Eventually, all of these pathomechanisms lead to chronic inflammation, mucus overproduction, remodeling of the airways, and fibrosis, thus operating a complex interplay among cells and tissues. The detection of MVs and EXOs in blood and biological fluids coming from the airways (bronchoalveolar lavage fluid and sputum) allows the consideration of EVs and their cargoes as promising biomarkers for CF and COPD, although clinical expectations have yet to be fulfilled.

Nanocarrier-based approaches to combat chronic obstructive pulmonary disease

Abnormalities in airway mucus lead to chronic disorders in the pulmonary system such as asthma, fibrosis and chronic obstructive pulmonary disease (COPD). Among these, COPD is more prominent worldwide. Various conventional approaches are available in the market for the treatment of COPD, but the delivery of drugs to the target site remains a challenge with conventional approaches. Nanocarrier-based approaches are considered the best due to their sustained release properties to the target site, smaller size, high surface-to-volume ratio, patient compliance, overcoming airway defenses and improved pharmacotherapy. This article provides updated information about the treatment of COPD along with nanocarrier-based approaches as well as the potential of gene therapy and stem cell therapy to combat the COPD.

Vegetable glycerin e-cigarette aerosols cause airway inflammation and ion channel dysfunction

Vegetable glycerin (VG) and propylene glycol (PG) serve as delivery vehicles for nicotine and flavorings in most e-cigarette (e-cig) liquids. Here, we investigated whether VG e-cig aerosols, in the absence of nicotine and flavors, impact parameters of mucociliary function in human volunteers, a large animal model (sheep), and air-liquid interface (ALI) cultures of primary human bronchial epithelial cells (HBECs). We found that VG-containing (VG or PG/VG), but not sole PG-containing, e-cig aerosols reduced the activity of nasal cystic fibrosis transmembrane conductance regulator (CFTR) in human volunteers who vaped for seven days. Markers of inflammation, including interleukin-6 (IL6), interleukin-8 (IL8) and matrix metalloproteinase-9 (MMP9) mRNAs, as well as MMP-9 activity and mucin 5AC (MUC5AC) expression levels, were also elevated in nasal samples from volunteers who vaped VG-containing e-liquids. In sheep, exposures to VG e-cig aerosols for five days increased mucus concentrations and MMP-9 activity in tracheal secretions and plasma levels of transforming growth factor-beta 1 (TGF-β1). In vitro exposure of HBECs to VG e-cig aerosols for five days decreased ciliary beating and increased mucus concentrations. VG e-cig aerosols also reduced CFTR function in HBECs, mechanistically by reducing membrane fluidity. Although VG e-cig aerosols did not increase MMP9 mRNA expression, expression levels of IL6, IL8, TGFB1, and MUC5AC mRNAs were significantly increased in HBECs after seven days of exposure. Thus, VG e-cig aerosols can potentially cause harm in the airway by inducing inflammation and ion channel dysfunction with consequent mucus hyperconcentration.

The molecular evolution of function in the CFTR chloride channel

The ATP-binding cassette (ABC) transporter superfamily includes many proteins of clinical relevance, with genes expressed in all domains of life. Although most members use the energy of ATP binding and hydrolysis to accomplish the active import or export of various substrates across membranes, the cystic fibrosis transmembrane conductance regulator (CFTR) is the only known animal ABC transporter that functions primarily as an ion channel. Defects in CFTR, which is closely related to ABCC subfamily members that bear function as bona fide transporters, underlie the lethal genetic disease cystic fibrosis. This article seeks to integrate structural, functional, and genomic data to begin to answer the critical question of how the function of CFTR evolved to exhibit regulated channel activity. We highlight several examples wherein preexisting features in ABCC transporters were functionally leveraged as is, or altered by molecular evolution, to ultimately support channel function. This includes features that may underlie (1) construction of an anionic channel pore from an anionic substrate transport pathway, (2) establishment and tuning of phosphoregulation, and (3) optimization of channel function by specialized ligand–channel interactions. We also discuss how divergence and conservation may help elucidate the pharmacology of important CFTR modulators.

Elexacaftor is a CFTR potentiator and acts synergistically with ivacaftor during acute and chronic treatment

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), which lead to early death due to progressive lung disease. The development of small-molecule modulators that directly interact with CFTR to aid in protein folding (“correctors”) and/or increase channel function (“potentiators”) have proven to be highly effective in the therapeutic treatment of CF. Notably, incorporation of the next-generation CFTR corrector, elexacaftor, into a triple combination therapeutic (marketed as Trikafta) has shown tremendous clinical promise in treating CF caused by F508del-CFTR. Here, we report on a newly-described role of elexacaftor as a CFTR potentiator. We explore the acute and chronic actions, pharmacology, and efficacy of elexacaftor as a CFTR potentiator in restoring function to multiple classes of CFTR mutations. We demonstrate that the potentiating action of elexacaftor exhibits multiplicative synergy with the established CFTR potentiator ivacaftor in rescuing multiple CFTR class defects, indicating that a new combination therapeutic of ivacaftor and elexacaftor could have broad impact on CF therapies.

Effects of environmental air pollutants on CFTR expression and function in human airway epithelial cells

The airway epithelium is exposed to a variety of air pollutants, which have been associated with the onset and worsening of respiratory diseases. These air pollutants can vary depending on their composition and associated chemicals, leading to different molecular interactions and biological effects. Mucociliary clearance is an important host defense mechanism against environmental air pollutants and this process is regulated by various ion transporters including the cystic fibrosis transmembrane conductance regulator (CFTR). With evidence suggesting that environmental air pollutants can lead to acquired CFTR dysfunction, it may be possible to leverage therapeutic approaches used in cystic fibrosis (CF) management. The aim of our study was to test whether environmental air pollutants tobacco smoke extract, urban particulate matter, and diesel exhaust particles lead to acquired CFTR dysfunction and whether it could be rescued with pharmacological interventions. Human airway epithelial cells (Calu-3) were exposed to air pollutant extracts for 24 h, with and without pharmacological interventions, with readouts of CFTR expression and function. We demonstrate that both tobacco smoke extract and diesel exhaust particles led to acquired CFTR dysfunction and that rescue of acquired CFTR dysfunction is possible with pharmacological interventions in diesel exhaust particle models. Our study emphasizes that CFTR function is not only important in the context of CF but may also play a role in other respiratory diseases impacted by environmental air pollutants. In addition, the pharmacological interventions approved for CF management may be more broadly leveraged for chronic respiratory disease management.

Breathe-Your immune system is counting on it

Always, but especially in these times of COVID pandemic, we know the dangers of breathing into our lungs a deadly pathogen. Fortunately, healthy lungs are equipped with an innate immune system that works to clear those pathogens. A study in this issue (2021. J. Exp. Med.https://doi.org/10.1084/jem.20201831) shows, for the first time, that breathing-induced changes in the pH of the airway surface contribute to bacterial killing, pointing to new therapeutic strategies for maintaining pulmonary health.

Intestinal current measurement and nasal potential difference to make a diagnosis of cases with inconclusive CFTR genetics and sweat test

Background

Nasal potential difference (NPD) and intestinal current measurements (ICM) are cystic fibrosis transmembrane conductance regulator (CFTR) biomarkers recommended to make a diagnosis in individuals with inconclusive sweat test and CFTR genetics and a clinical suspicion for cystic fibrosis (CF) or CFTR-related disorder (CFTR-RD).

Methods

NPD and ICM were measured according to standard operating procedures of the European Cystic Fibrosis Society Diagnostic Network Working Group.

Results

We assessed 219 individuals by NPD or ICM who had been referred to our laboratory due to clinical symptoms suggestive of CF, but inconclusive sweat test and CFTR genetics (median age: 16.3 years, range 0.4 to 76 years). CF or CFTR-related disorder was diagnosed in 22 of 29 patients (76%) with a CFTR genotype of unknown or variable clinical significance and in 51 of 190 carriers (27%) of one (35/42) or no (16/148) identified CFTR mutation. If two CFTR sequence variants had been identified, the outcome of NPD and ICM was consistent with the classification of the CFTR2 database. Moreover, a suspected false-positive diagnosis of CF was confirmed in seven and withdrawn in eight patients. Of 26 individuals assessed by both NPD and ICM, eleven individuals exhibited discordant tracings of ICM and NPD, with one measurement being in the CF range and the other in the normal range.

Conclusion

The majority of patients whom we diagnosed with CF or CFTR-RD by extended electrophysiology are carriers of the wild-type CFTR coding sequence on at least one of their CF alleles. The disease-causing genetic lesions should reside in the non-coding region of CFTR or elsewhere in the genome, affecting the regulation of CFTR expression in a tissue-depending fashion which may explain the large within-group variability of CFTR activity in the respiratory and intestinal epithelium seen in this group.

Autophagy Augmentation to Alleviate Immune Response Dysfunction, and Resolve Respiratory and COVID-19 Exacerbations

The preservation of cellular homeostasis requires the synthesis of new proteins (proteostasis) and organelles, and the effective removal of misfolded or impaired proteins and cellular debris. This cellular homeostasis involves two key proteostasis mechanisms, the ubiquitin proteasome system and the autophagy–lysosome pathway. These catabolic pathways have been known to be involved in respiratory exacerbations and the pathogenesis of various lung diseases, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), idiopathic pulmonary fibrosis (IPF), acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and coronavirus disease-2019 (COVID-19). Briefly, proteostasis and autophagy processes are known to decline over time with age, cigarette or biomass smoke exposure, and/or influenced by underlying genetic factors, resulting in the accumulation of misfolded proteins and cellular debris, elevating apoptosis and cellular senescence, and initiating the pathogenesis of acute or chronic lung disease. Moreover, autophagic dysfunction results in an impaired microbial clearance, post-bacterial and/or viral infection(s) which contribute to the initiation of acute and recurrent respiratory exacerbations as well as the progression of chronic obstructive and restrictive lung diseases. In addition, the autophagic dysfunction-mediated cystic fibrosis transmembrane conductance regulator (CFTR) immune response impairment further exacerbates the lung disease. Recent studies demonstrate the therapeutic potential of novel autophagy augmentation strategies, in alleviating the pathogenesis of chronic obstructive or restrictive lung diseases and exacerbations such as those commonly seen in COPD, CF, ALI/ARDS and COVID-19.

CFTR targeted therapies: recent advances in cystic fibrosis and possibilities in other diseases of the airways

Cystic fibrosis transmembrane conductance regulator (CFTR) is an ion transporter that regulates mucus hydration, viscosity and acidity of the airway epithelial surface. Genetic defects in CFTR impair regulation of mucus homeostasis, causing severe defects of mucociliary clearance as seen in cystic fibrosis. Recent work has established that CFTR dysfunction can be acquired in chronic obstructive pulmonary disease (COPD) and may also contribute to other diseases that share clinical features of cystic fibrosis, such as asthma, allergic bronchopulmonary aspergillosis and bronchiectasis. Protean causes of CFTR dysfunction have been identified including cigarette smoke exposure, toxic metals and downstream effects of neutrophil activation pathways. Recently, CFTR modulators, small molecule agents that potentiate CFTR or restore diminished protein levels at the cell surface, have been successfully developed for various CFTR gene defects, prompting interest in their use to treat diseases of acquired dysfunction. The spectrum of CFTR dysfunction, strategies for CFTR modulation, and candidate diseases for CFTR modulation beyond cystic fibrosis will be reviewed in this manuscript.

CFTR dysfunction may be part of the pathophysiology of many diseases of the airways. Exploration of mechanisms of dysfunction and options for CFTR-directed therapies are examined in this article. http://bit.ly/33o6nDu

Development of an Innovative, Carrier-Based Dry Powder Inhalation Formulation Containing Spray-Dried Meloxicam Potassium to Improve the In Vitro and In Silico Aerodynamic Properties

Most of the marketed dry powder inhalation (DPI) products are traditional, carrier-based formulations with low drug concentrations deposited in the lung. However, due to their advantageous properties, their development has become justified. In our present work, we developed an innovative, carrier-based DPI system, which is an interactive physical blend of a surface-modified carrier and a spray-dried drug with suitable shape and size for pulmonary application. Meloxicam potassium, a nonsteroidal anti-inflammatory drug (NSAID), was used as an active ingredient due to its local anti-inflammatory effect and ability to decrease the progression of cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). The results of the in vitro and in silico investigations showed high lung deposition in the case of this new formulation, confirming that the interparticle interactions were changed favorably.

Revealing the molecular signaling pathways of mucus stasis in cystic fibrosis

Mucus obstruction is a hallmark of cystic fibrosis (CF) airway disease, leading to chronic infection, dysregulated inflammation, and progressive lung disease. As mucus hyperexpression is a key component in the initiation and perpetuation of airway obstruction, the triggers underlying mucin release must be identified and understood. In this issue of the JCI, Chen et al. sought to delineate the mechanisms that allow IL-1α/IL-1β to perpetuate the mucoinflammatory environment characteristic of the CF airway. The authors demonstrated that IL-1α and IL-1β stimulated non-CF human bronchial epithelial (HBE) cells to upregulate and secrete both MUC5B and MUC5AC in a dose-dependent manner, an effect that was neutralized by the inhibition of the IL-1α/IL-1β receptor (IL-1R1). Further experiments using mouse models and excised lung tissue identified contributors that drive a vicious feedback cycle of hyperconcentrated mucus secretions and persistent inflammation in the CF airway, factors that are likely at the nidus of progressive lung disease.

The Effects of the Anti-aging Protein Klotho on Mucociliary Clearance

α-klotho (KL) is an anti-aging protein and has been shown to exert anti-inflammatory and anti-oxidative effects in the lung and pulmonary diseases such as chronic obstructive pulmonary disease (COPD) and cystic fibrosis. The current study investigated the direct effect of KL on the bronchial epithelium in regards to mucociliary clearance parameters. Primary human bronchial and murine tracheal epithelial cells, cultured, and differentiated at the air liquid interface (ALI), were treated with recombinant KL or infected with a lentiviral vector expressing KL. Airway surface liquid (ASL) volume, airway ion channel activities, and expression levels were analyzed. These experiments were paired with ex vivo analyses of mucociliary clearance in murine tracheas from klotho deficient mice and their wild type littermates. Our results showed that klotho deficiency led to impaired mucociliary clearance with a reduction in ASL volume in vitro and ex vivo. Overexpression or exogenous KL increased ASL volume, which was paralleled by increased activation of the large-conductance, Ca2+-activated, voltage-dependent potassium channel (BK) without effect on the cystic fibrosis transmembrane conductance regulator (CFTR). Furthermore, KL overexpression downregulated IL-8 levels and attenuated TGF-β-mediated downregulation of LRRC26, the γ subunit of BK, necessary for its function in non-excitable cells. In summary, we show that KL regulates mucociliary function by increasing ASL volume in the airways possibly due to underlying BK activation. The KL mediated BK channel activation may be a potentially important target to design therapeutic strategies in inflammatory airway diseases when ASL volume is decreased.

Use of low field nuclear magnetic resonance to monitor lung inflammation and the amount of pathological components in the sputum of cystic fibrosis patients

PURPOSE

To develop a novel approach to monitor lung ventilation/inflammation in cystic fibrosis (CF) patients. Lung assessment in CF patients is relevant given that most patients succumb to respiratory failure. Respiratory functional tests (forced expiratory volume in the first second; FEV₁ ) and inflammatory markers are used to test pulmonary ventilation/inflammation, respectively. However, FEV₁ is effort dependent and might be uncomfortable for CF patients. Furthermore, inflammatory marker detection is costly and not rapid. To overcome these limitations, we propose the measurement, by means of low field nuclear magnetic resonance, of the spin-spin relaxation time (T_2m ) of water hydrogens present in CF patient sputum. In CF sputum, different biological components are pathologically increased and inversely related to lung functionality. Moreover, we showed that these components alter in a dose-dependent manner the T_2m in synthetic CF sputum.

METHODS

Sputum samples were obtained from 42 CF subjects by voluntary expectoration; FEV₁ , C-reactive protein (CRP), blood neutrophil counts together with cytokine (tumor necrosis factor alpha [TNFα], interleukin [IL]-1β, IL-4, and vascular endothelial growth factor) quantifications were then evaluated.

RESULTS

In sputum samples, we observe that T_2m directly correlates (r_FEV1 = 0.44; P < 10^-4 ; 169 samples) with FEV₁ . Moreover, T_2m inversely correlates with the circulating inflammation markers CRP/neutrophil number (r_CRP = -0.44, P < 10^-4 ; r_NC = -0.37, P < 2 * 10^-4 ; 103 and 86 samples, respectively) and with the sputum inflammatory cytokines TNFα/IL-β1 (r_TNFα = -0.72, P < 10^-4 ; r_IL-1β = -0.685, P < 10^-4 ; 27 samples). T_2m variations also correspond to FEV₁ values over time in defined patients.

CONCLUSION

These findings, together with the fast, reliable, and simple determination of T_2m , make our approach a novel tool potentially usable in the real world of CF patients.

Phosphorylation-dependent modulation of CFTR macromolecular signalling complex activity by cigarette smoke condensate in airway epithelia

Genetic and acquired loss-of-function defect of the cystic fibrosis transmembrane conductance regulator (CFTR) compromise airway surface liquid homeostasis and mucociliary clearance (MCC), culminating in recurrent lung inflammation/infection. While chronic cigarette smoke (CS), CS extract (CSE; water-soluble compounds) and CS condensate (CSC; particulate, organic fraction) exposure inhibit CFTR activity at transcriptional, biochemical, and functional levels, the acute impact of CSC remains incompletely understood. We report that CSC transiently activates CFTR chloride secretion in airway epithelia. The comparable CFTR phospho-occupancy after CSC- and forskolin-exposure, determined by affinity-enriched tandem mass spectrometry and pharmacology, suggest that localised cAMP-dependent protein kinase (PKA) stimulation by CSC causes the channel opening. Due to the inhibition of the MRP4/ABCC4, a cAMP-exporter confined to the CFTR macromolecular signalling-complex, PKA activation is accomplished by the subcompartmentalised elevation of cytosolic cAMP. In line, MRP4 inhibition results in CFTR activation and phospho-occupancy similar to that by forskolin. In contrast, acute CSC exposure reversibly inhibits the phosphorylated CFTR both in vivo and in phospholipid bilayers, without altering its cell surface density and phospho-occupancy. We propose that components of CSC elicit both a transient protective CFTR activation, as well as subsequent channel block in airway epithelia, contributing to the subacute MCC defect in acquired CF lung diseases.

Cardiopulmonary and Muscular Interactions: Potential Implications for Exercise (In)tolerance in Symptomatic Smokers Without Chronic Obstructive Pulmonary Disease

Smoking and physical inactivity are important preventable causes of disability and early death worldwide. Reduced exercise tolerance has been described in smokers, even in those who do not fulfill the extant physiological criteria for chronic obstructive pulmonary disease (COPD) and are not particularly sedentary. In this context, it is widely accepted that exercise capacity depends on complex cardio-pulmonary interactions which support oxygen (O₂) delivery to muscle mitochondria. Although peripheral muscular factors, O₂ transport disturbances (including the effects of increased carboxyhemoglobin) and autonomic nervous system unbalance have been emphasized, other derangements have been more recently described, including early microscopic emphysema, pulmonary microvascular disease, ventilatory and gas exchange inefficiency, and left ventricular diastolic dysfunction. Using an integrative physiological approach, the present review summarizes the recent advances in knowledge on the effects of smoking on the lung-heart-muscle axis under the stress of exercise. Special attention is given to the mechanisms connecting physiological abnormalities such as early cardio-pulmonary derangements, inadequate oxygen delivery and utilization, and generalized bioenergetic disturbances at the muscular level with the negative sensations (sense of heightened muscle effort and breathlessness) that may decrease the tolerance of smokers to physical exercise. A deeper understanding of the systemic effects of smoking in subjects who did not (yet) show evidences of COPD and ischemic heart disease - two devastating smoking related diseases - might prove instrumental to fight their ever-growing burden.

Cystic fibrosis transmembrane conductance regulator (CFTR) and autophagy: hereditary defects in cystic fibrosis versus gluten-mediated inhibition in celiac disease

Cystic Fibrosis (CF) is the most frequent lethal monogenetic disease affecting humans. CF is characterized by mutations in cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel whose malfunction triggers the activation of transglutaminase-2 (TGM2), as well as the inactivation of the Beclin-1 (BECN1) complex resulting in disabled autophagy. CFTR inhibition, TGM2 activation and BECN1 sequestration engage in an ‘infernal trio’ that locks the cell in a pro-inflammatory state through anti-homeostatic feedforward loops. Thus, stimulation of CFTR function, TGM2 inhibition and autophagy stimulation can be used to treat CF patients. Several studies indicate that patients with CF have a higher incidence of celiac disease (CD) and that mice bearing genetically determined CFTR defects are particularly sensitive to the enteropathogenic effects of the orally supplied gliadin (a gluten-derived protein). A gluten/gliadin-derived peptide (P31–43) inhibits CFTR in mouse intestinal epithelial cells, causing a local stress response that contributes to the immunopathology of CD. In particular, P31–43-induced CFTR inhibition elicits an epithelial stress response perturbing proteostasis. This event triggers TGM2 activation, BECN1 sequestration and results in molecular crosslinking of CFTR and P31-43 by TGM2. Importantly, stimulation of CFTR function with a pharmacological potentiator (Ivacaftor), which is approved for the treatment of CF, could attenuate the autophagy-inhibition and pro-inflammatory effects of gliadin in preclinical models of CD. Thus, CD shares with CF a common molecular mechanism involving CFTR inhibition that might respond to drugs that intercept the "infernal trio". Here, we highlight how drugs available for CF treatment could be repurposed for the therapy of CD.

Variation in Cilia Protein Genes and Progression of Lung Disease in Cystic Fibrosis

RATIONALE

Cystic fibrosis, like primary ciliary dyskinesia, is an autosomal recessive disorder characterized by abnormal mucociliary clearance and obstructive lung disease. We hypothesized that genes underlying the development or function of cilia may modify lung disease severity in persons with cystic fibrosis.

OBJECTIVES

To test this hypothesis, we compared variants in 93 candidate genes in both upper and lower tertiles of lung function in a large cohort of children and adults with cystic fibrosis with those of a population control dataset.

METHODS

Variants within candidate genes were tested for association using the SKAT-O test, comparing cystic fibrosis cases defined by poor (n = 127) or preserved (n = 127) lung function with population controls (n = 3,269 or 3,148, respectively). Associated variants were then tested for association with related phenotypes in independent datasets.

RESULTS

Variants in DNAH14 and DNAAF3 were associated with poor lung function in cystic fibrosis, whereas variants in DNAH14 and DNAH6 were associated with preserved lung function in cystic fibrosis. Associations between DNAH14 and lung function were replicated in disease-related phenotypes characterized by obstructive lung disease in adults.

CONCLUSIONS

Genetic variants within DNAH6, DNAH14, and DNAAF3 are associated with variation in lung function among persons with cystic fibrosis.

Mucociliary Clearance in Former Tobacco Smokers with Both Chronic Obstructive Pulmonary Disease and Chronic Bronchitis and the Effect of Roflumilast

Background: Little is known of the repeatability and reliability of mucociliary clearance (MCC) in former tobacco smokers who have both chronic obstructive pulmonary disease (COPD) and chronic bronchitis (CB). Less is known of the effect of roflumilast, a selective inhibitor of PDE4, on MCC in these patients. Methods: Former tobacco smokers with COPD and CB were treated for 4 weeks with either roflumilast, or placebo, in a randomized, crossover trial. The following were measured on two baseline and two posttreatment visits: MCC values through 90 minutes, following inhalation of ^99mtechnetium sulfur colloid and gamma camera imaging; outer:inner (O:I) deposition ratio; forced expiratory volume in 1 second (FEV₁); and symptom scores. Comparisons included: MCC measures through 30 minutes (MCC30), 60 minutes (MCC60), and 90 minutes (MCC90) on the two baseline visits (n = 9) and mean change [(roflumilast - baseline)-(placebo - baseline)] for MCC30, MCC60, MCC90, and FEV₁ (n = 8). Associations between MCC measurements, FEV₁ and O:I ratio with symptom scores were also examined. Results: Pearson correlation tests indicated good repeatability for baseline measures of MCC30, MCC60, and MCC90 and intraclass correlation coefficients indicated good reliability. Only FEV₁ (percent predicted) improved significantly following roflumilast treatment. There were no statistically significant correlations between MCC measures and symptom scores. Lower FEV₁ values were significantly associated with increased shortness of breath (dyspnea), and lower O:I ratios (more inner region deposition) were significantly associated with increased cough and sputum. Conclusions: Measurements of MCC30, MCC60, and MCC90 are repeatable and reliable in former tobacco smokers with both COPD and CB. One month of treatment with roflumilast did not improve MCC in this limited study. Airway narrowing in the larger, central airways of these subjects could lead to decreased FEV₁, increased inner region deposition of the radiolabeled particles, and the associated increase in symptoms of dyspnea, cough, and sputum.

A pathogenic role for cystic fibrosis transmembrane conductance regulator in celiac disease

Intestinal handling of dietary proteins usually prevents local inflammatory and immune responses and promotes oral tolerance. However, in ~ 1% of the world population, gluten proteins from wheat and related cereals trigger an HLA DQ2/8‐restricted T_H1 immune and antibody response leading to celiac disease. Prior epithelial stress and innate immune activation are essential for breaking oral tolerance to the gluten component gliadin. How gliadin subverts host intestinal mucosal defenses remains elusive. Here, we show that the α‐gliadin‐derived LGQQQPFPPQQPY peptide (P31–43) inhibits the function of cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel pivotal for epithelial adaptation to cell‐autonomous or environmental stress. P31–43 binds to, and reduces ATPase activity of, the nucleotide‐binding domain‐1 (NBD1) of CFTR, thus impairing CFTR function. This generates epithelial stress, tissue transglutaminase and inflammasome activation, NF‐κB nuclear translocation and IL‐15 production, that all can be prevented by potentiators of CFTR channel gating. The CFTR potentiator VX‐770 attenuates gliadin‐induced inflammation and promotes a tolerogenic response in gluten‐sensitive mice and cells from celiac patients. Our results unveil a primordial role for CFTR as a central hub orchestrating gliadin activities and identify a novel therapeutic option for celiac disease.

Acquired cystic fibrosis transmembrane conductance regulator dysfunction

Sinonasal respiratory epithelium is a highly regulated barrier that employs mucociliary clearance (MCC) as the airways first line of defense. The biological properties of the airway surface liquid (ASL), combined with coordinated ciliary beating, are critical components of the mucociliary apparatus. The ASL volume and viscosity is modulated, in part, by the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR is an anion transporter of chloride (Cl⁻) and bicarbonate (HCO₃⁻) that is located on the apical surface of respiratory epithelium and exocrine glandular epithelium. Improved understanding of how dysfunction or deficiency of CFTR influences the disease process in both genetically defined cystic fibrosis (CF) and acquired conditions has provided further insight into potential avenues of treatment. This review discusses the latest data regarding acquired CFTR deficiency and use of CFTR specific treatment strategies for CRS and other chronic airway diseases.

Precision medicine in united airways disease: A "treatable traits" approach

United airways disease (UAD) is the concept that the upper and lower airways, which are anatomically and immunologically related, form a single organ. According to this concept, upper and lower airway diseases are frequently comorbid because they reflect manifestations of a single underlying disease at different sites of the respiratory tract. Allergic asthma-allergic rhinitis is the archetypal UAD, but emerging data indicate that UAD is a heterogeneous condition and consists of multiple phenotypes (observable clinical characteristics) and endotypes (pathobiologic mechanisms). The UAD paradigm also extends to myriad sinonasal diseases (eg, chronic rhinosinusitis with or without nasal polyps) and lower airway diseases (eg, bronchiectasis, chronic obstructive pulmonary disease). Here, we review currently known phenoendotypes of UAD and propose a "treatable traits" approach for the classification and management of UAD, wherein pathophysiological mechanisms and factors contributing to disease are identified and targeted for treatment. Treatable traits in UAD can be analyzed according to a framework comprising airway inflammation (eosinophilic, neutrophilic), impaired airway mucosal defense (impaired mucociliary clearance, antibody deficiency), and exogenous cofactors (allergic sensitizers, tobacco smoke, microbes). Appreciation of treatable traits is necessary in advancing the effort to deliver precise treatments and achieve better outcomes in patients with UAD.

Cigarette Smoke-Induced Acquired Dysfunction of Cystic Fibrosis Transmembrane Conductance Regulator in the Pathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a disease state characterized by airflow limitation that is not fully reversible. Cigarette smoke and oxidative stress are main etiological risks in COPD. Interestingly, recent studies suggest a considerable overlap between chronic bronchitis (CB) phenotypic COPD and cystic fibrosis (CF), a common fatal hereditary lung disease caused by genetic mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Phenotypically, CF and COPD are associated with an impaired mucociliary clearance and mucus hypersecretion, although they are two distinct entities of unrelated origin. Mechanistically, the cigarette smoke-increased oxidative stress-induced CFTR dysfunction is implicated in COPD. This underscores CFTR in understanding and improving therapies for COPD by altering CFTR function with antioxidant agents and CFTR modulators as a great promising strategy for COPD treatments. Indeed, treatments that restore CFTR function, including mucolytic therapy, antioxidant ROS scavenger, CFTR stimulator (roflumilast), and CFTR potentiator (ivacaftor), have been tested in COPD. This review article is aimed at summarizing the molecular, cellular, and clinical evidence of oxidative stress, particularly the cigarette smoke-increased oxidative stress-impaired CFTR function, as well as signaling pathways of CFTR involved in the pathogenesis of COPD, with a highlight on the therapeutic potential of targeting CFTR for COPD treatment.

Tandem mass tags labeled quantitative proteomics to study the effect of tobacco smoke exposure on the rat lung

BACKGROUND

The causal link between tobacco smoke exposure (TSE) and numerous severe respiratory system diseases (RSD), including chronic bronchitis, chronic obstructive pulmonary disease, and lung cancer, is well established. However, the pathogenesis of TSE-induced RSD remains incompletely understood. This research aims to detect the pathogenetic mechanisms and potential therapeutic targets of TSE-induced RSD.

METHODS

This study employed TSE model which rats were exposed to a concentration of 60% tobacco smoke in a toxicant exposure system for four weeks. Tandem mass tags (TMT) labeled quantitative proteomics combined with off-line high pH reversed-phase fractionation, and nano-liquid chromatography-mass spectrometry method (off-line high pH RPF-nano-LC-MS/MS) were adopted to detect differentially expressed proteins (DEPs) in the lung tissues of the TSE model rats and to compare them with those in control. The accuracy of the results was verified by western blot.

RESULTS

Compared with the control group, 33 proteins in the TSE model group's lung tissues showed significant differential expression. Analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways indicated that, several biological pathways, such as the steroid biosynthesis pathway, were involved and played significant roles in the pathogenesis of the experimental group's TSE.

CONCLUSIONS

These findings make a crucial contribution to the search for a comprehensive understanding of TSE-induced RSD's pathogenesis, and furthermore provide guidance for the diagnosis and treatment of TSE-induced RSD.

Seeing cilia: imaging modalities for ciliary motion and clinical connections

The respiratory tract is lined with multiciliated epithelial cells that function to move mucus and trapped particles via the mucociliary transport apparatus. Genetic and acquired ciliopathies result in diminished mucociliary clearance, contributing to disease pathogenesis. Recent innovations in imaging technology have advanced our understanding of ciliary motion in health and disease states. Application of imaging modalities including transmission electron microscopy, high-speed video microscopy, and micron-optical coherence tomography could improve diagnostics and be applied for precision medicine. In this review, we provide an overview of ciliary motion, imaging modalities, and ciliopathic diseases of the respiratory system including primary ciliary dyskinesia, cystic fibrosis, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis.

Sinus Microanatomy and Microbiota in a Rabbit Model of Rhinosinusitis

Background: Rabbits are useful for preclinical studies of sinusitis because of similar physiologic features to humans. The objective of this study is to develop a rabbit model of sinusitis that permits assessment of microanatomy and sampling for evaluating shifts in the sinus microbiota during the development of sinusitis and to test how the mucociliary clearance (MCC) defect might lead to dysbiosis and chronic rhinosinusitis (CRS).

Methods: Generation of CRS was accomplished with an insertion of a sterile sponge into the left middle meatus of New Zealand white rabbits (n = 9) for 2 weeks. After sponge removal, 4 rabbits were observed for another 10 weeks and evaluated for CRS using endoscopy, microCT, visualization of the functional micro-anatomy by micro-optical coherence tomography (μOCT), and histopathological analysis of the sinus mucosa. Samples were taken from the left middle meatus and submitted for microbiome analysis.

Results: CT demonstrated opacification of all left sinuses at 2 weeks in all rabbits (n = 9), which persisted in animals followed for another 12 weeks (n = 4). Histology at week 2 showed mostly neutrophils. On week 14, significant infiltration of plasma cells and lymphocytes was noted with increased submucosal glands compared to controls (p = 0.02). Functional microanatomy at 2 weeks showed diminished periciliary layer (PCL) depth (p < 0.0001) and mucus transport (p = 0.0044) compared to controls despite a thick mucus layer. By 12 weeks, the thickened mucus layer was resolved but PCL depletion persisted in addition to decreased ciliary beat frequency (CBF; p < 0.0001). The mucin fermenting microbes (Lactobacillales, Bacteroidales) dominated on week 2 and there was a significant shift to potential pathogens (e.g., Pseudomonas, Burkholderia) by week 14 compared to both controls and the acute phase (p < 0.05).

Conclusion: We anticipate this reproducible model will provide a means for identifying underlying mechanisms of airway-surface liquid (ASL) depletion and fundamental changes in sinus microbial communities that contribute to the development of CRS. The rabbit model of sinusitis exhibited diminished PCL depth with delayed mucus transport and significant alterations and shift in the sinus microbiome during the development of chronic inflammation.

The EGFR-ADAM17 Axis in Chronic Obstructive Pulmonary Disease and Cystic Fibrosis Lung Pathology

Chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) share molecular mechanisms that cause the pathological symptoms they have in common. Here, we review evidence suggesting that hyperactivity of the EGFR/ADAM17 axis plays a role in the development of chronic lung disease in both CF and COPD. The ubiquitous transmembrane protease A disintegrin and metalloprotease 17 (ADAM17) forms a functional unit with the EGF receptor (EGFR), in a feedback loop interaction labeled the ADAM17/EGFR axis. In airway epithelial cells, ADAM17 sheds multiple soluble signaling proteins by proteolysis, including EGFR ligands such as amphiregulin (AREG), and proinflammatory mediators such as the interleukin 6 coreceptor (IL-6R). This activity can be enhanced by injury, toxins, and receptor-mediated external triggers. In addition to intracellular kinases, the extracellular glutathione-dependent redox potential controls ADAM17 shedding. Thus, the epithelial ADAM17/EGFR axis serves as a receptor of incoming luminal stress signals, relaying these to neighboring and underlying cells, which plays an important role in the resolution of lung injury and inflammation. We review evidence that congenital CFTR deficiency in CF and reduced CFTR activity in chronic COPD may cause enhanced ADAM17/EGFR signaling through a defect in glutathione secretion. In future studies, these complex interactions and the options for pharmaceutical interventions will be further investigated.

The therapeutic potential of CFTR modulators for COPD and other airway diseases

Airways diseases, especially chronic obstructive pulmonary disease (COPD) and asthma, are common causes of morbidity and mortality worldwide. There is an ongoing unmet need for novel and effective therapies. There is an established pathophysiological link and phenotypic similarity between the chronic bronchitis phenotype of COPD and cystic fibrosis (CF). New evidence suggests that CFTR dysfunction may play a role in other common airways diseases such as COPD, non-atopic asthma and non-CF bronchiectasis. Newly approved and investigational drugs that target both mutant and wild-type CFTR channels have provided a new treatment opportunity addressing the mucus defect in pulmonary diseases that share the same pathophysiology with CF.

Roflumilast reverses CFTR-mediated ion transport dysfunction in cigarette smoke-exposed mice

BACKGROUND

Dysfunction in cystic fibrosis transmembrane conductance regulator (CFTR) can be elicited by cigarette smoke and is observed in patients with chronic bronchitis. We have previously demonstrated in human airway epithelial cell monolayers that roflumilast, a clinically approved phosphodiesterase 4 inhibitor that reduces the risk of exacerbations in chronic obstructive pulmonary disease patients with chronic bronchitis and a history of exacerbations, activates CFTR-dependent chloride secretion via a cAMP-mediated pathway, partially restores the detrimental effects of cigarette smoke on CFTR-mediated ion transport, and increases CFTR-dependent gastrointestinal fluid secretion in isolated murine intestine segments. Based on these findings, we hypothesized that roflumilast could improve CFTR-mediated chloride transport and induce secretory diarrhea in mice exhibiting cigarette smoke-induced CFTR dysfunction.

METHODS

A/J mice expressing wild type CFTR (+/+) were exposed to cigarette smoke or air with or without roflumilast and the effect of treatment on CFTR-dependent chloride transport was quantified using nasal potential difference (NPD) measurements in vivo and short-circuit current (Isc) analysis of trachea ex vivo. Stool specimen were collected and the wet/dry ratio measured to assess the effect of roflumilast on secretory diarrhea.

RESULTS

Acute roflumilast treatment increased CFTR-dependent chloride transport in both smoke- and air-exposed mice (smoke, -2.0 ± 0.4 mV, 131.3 ± 29.3 μA/cm², P < 0.01 and air, 3.9 ± 0.8 mV, 147.7 ± 38.0 μA/cm², P < 0.01 vs. vehicle -0.3 ± 0.7 mV, 10.4 ± 7.0 μA/cm²). Oral administration of roflumilast over five weeks completely reversed the deleterious effects of cigarette smoke on CFTR function in smoke-exposed animals, in which CFTR-dependent chloride transport was 64% that of air controls (roflumilast, -15.22 ± 2.7 mV vs. air, -14.45 ± 1.4 mV, P < 0.05). Smoke exposure increased the wet/dry ratio of stool specimen to a level beyond which roflumilast had little additional effect.

CONCLUSIONS

Roflumilast effectively rescues CFTR-mediated chloride transport in vivo, further implicating CFTR activation as a mechanism through which roflumilast benefits patients with bronchitis.

A ferret model of COPD-related chronic bronchitis

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