A Barrier to Defend - Models of Pulmonary Barrier to Study Acute Inflammatory Diseases

Diagnostic biomarkers and miRNAs in prognosis of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a disease of the lung and/or extrapulmonary system characterized by acute, progressive breathing difficulty and refractory hypoxemia. After years of revision, the 2012 International Expert Conference developed a new diagnostic standard for ARDS, known as the Berlin definition, which provides good guidance on how to define and judge the disease in clinical practice. Despite the establishment of diagnostic standards and treatment improvements, ARDS mortality rate still remains high. The primary reason is that the pathophysiology has not been fully elucidated. In patients with ARDS, damage to the alveolar capillary membrane may occur, leading to increased vascular permeability and the occurrence of pulmonary edema. Therefore, exploring the pathogenesis of ARDS from the perspective of microvascular permeability and identification of effective targets may be key factors in the diagnosis and treatment of ARDS. This review presents the current literature regarding the role of miRNAs (micro ribonucleic acids) in early detection and prediction of ARDS outcome.

Effects of remote ischemic preconditioning on early markers of intestinal injury in experimental hemorrhage in rats

The maintenance of intestinal integrity and barrier function under conditions of restricted oxygen availability is crucial to avoid bacterial translocation and local inflammation. Both lead to secondary diseases after hemorrhagic shock and might increase morbidity and mortality after surviving the initial event. Monitoring of the intestinal integrity especially in the early course of critical illness remains challenging. Since microcirculation and mitochondrial respiration are main components of the terminal stretch of tissue oxygenation, the evaluation of microcirculatory and mitochondrial variables could identify tissues at risk during hypoxic challenges, indicate an increase of intestinal injury, and improve our understanding of regional pathophysiology during acute hemorrhage. Furthermore, improving intestinal microcirculation or mitochondrial respiration, e.g. by remote ischemic preconditioning (RIPC) that was reported to exert a sufficient tissue protection in various tissues and was linked to mediators with vasoactive properties could maintain intestinal integrity. In this study, postcapillary oxygen saturation (µHbO2), microvascular flow index (MFI) and plasmatic D-lactate concentration revealed to be early markers of intestinal injury in a rodent model of experimental hemorrhagic shock. Mitochondrial function was not impaired in this experimental model of acute hemorrhage. Remote ischemic preconditioning (RIPC) failed to improve intestinal microcirculation and intestinal damage during hemorrhagic shock.

A prospects tool in virus research: Analyzing the applications of organoids in virus studies

Organoids have emerged as a powerful tool for understanding the biology of the respiratory, digestive, nervous as well as urinary system, investigating infections, and developing new therapies. This article reviews recent progress in the development of organoid and advancements in virus research. The potential applications of these models in studying virul infections, pathogenesis, and antiviral drug discovery are discussed.

The development and characterization of in vivo-like three-dimensional models of bronchial epithelial cell lines

In vitro models of differentiated respiratory epithelium that allow high-throughput screening are an important tool to explore new therapeutics for chronic respiratory diseases. In the present study, we developed in vivo-like three-dimensional (3-D) models of bronchial epithelial cell lines that are commonly used to study chronic lung disease (16HBE14o-, CFBE41o- and CFBE41o- 6.2 WT-CFTR). To this end, cells were cultured on porous microcarrier beads in the rotating wall vessel (RWV) bioreactor, an optimized suspension culture method that allows higher throughput experimentation than other physiologically relevant models. Cell differentiation was compared to conventional two-dimensional (2-D) monolayer cultures and to the current gold standard in the respiratory field, i.e. air-liquid interface (ALI) cultures. Cellular differentiation was assessed in the three model systems by evaluating the expression and localization of markers that reflect the formation of tight junctions (zonula occludens 1), cell polarity (intercellular adhesion molecule 1 at the apical side and collagen IV expression at the basal cell side), multicellular complexity (acetylated α-tubulin for ciliated cells, CC10 for club cells, keratin-5 for basal cells) and mucus production (MUC5AC) through immunostaining and confocal laser scanning microscopy. Results were validated using Western Blot analysis. We found that tight junctions were expressed in 2-D monolayers, ALI cultures and 3-D models for all three cell lines. All tested bronchial epithelial cell lines showed polarization in ALI and 3-D cultures, but not in 2-D monolayers. Mucus secreting goblet-like cells were present in ALI and 3-D cultures of CFBE41o- and CFBE41o- 6.2 WT-CFTR cells, but not in 16HBE14o- cells. For all cell lines, there were no ciliated cells, basal cells, or club cells found in any of the model systems. In conclusion, we developed RWV-derived 3-D models of commonly used bronchial epithelial cell lines and showed that these models are a valuable alternative to ALI cultures, as they recapitulate similar key aspects of the in vivo parental tissue.

Autophagy/Mitophagy in Airway Diseases: Impact of Oxidative Stress on Epithelial Cells

Autophagy is the key process by which the cell degrades parts of itself within the lysosomes. It maintains cell survival and homeostasis by removing molecules (particularly proteins), subcellular organelles, damaged cytoplasmic macromolecules, and by recycling the degradation products. The selective removal or degradation of mitochondria is a particular type of autophagy called mitophagy. Various forms of cellular stress (oxidative stress (OS), hypoxia, pathogen infections) affect autophagy by inducing free radicals and reactive oxygen species (ROS) formation to promote the antioxidant response. Dysfunctional mechanisms of autophagy have been found in different respiratory diseases such as chronic obstructive lung disease (COPD) and asthma, involving epithelial cells. Several existing clinically approved drugs may modulate autophagy to varying extents. However, these drugs are nonspecific and not currently utilized to manipulate autophagy in airway diseases. In this review, we provide an overview of different autophagic pathways with particular attention on the dysfunctional mechanisms of autophagy in the epithelial cells during asthma and COPD. Our aim is to further deepen and disclose the research in this direction to stimulate the develop of new and selective drugs to regulate autophagy for asthma and COPD treatment.

Optimization of Primary Human Bronchial Epithelial 3D Cell Culture with Donor-Matched Fibroblasts and Comparison of Two Different Culture Media

In vitro airway models are increasingly important for pathomechanistic analyses of respiratory diseases. Existing models are limited in their validity by their incomplete cellular complexity. We therefore aimed to generate a more complex and meaningful three-dimensional (3D) airway model. Primary human bronchial epithelial cells (hbEC) were propagated in airway epithelial cell growth (AECG) or PneumaCult ExPlus medium. Generating 3D models, hbEC were airlifted and cultured on a collagen matrix with donor-matched bronchial fibroblasts for 21 days comparing two media (AECG or PneumaCult ALI (PC ALI)). 3D models were characterized by histology and immunofluorescence staining. The epithelial barrier function was quantified by transepithelial electrical resistance (TEER) measurements. The presence and function of ciliated epithelium were determined by Western blot and microscopy with high-speed camera. In 2D cultures, an increased number of cytokeratin 14-positive hbEC was present with AECG medium. In 3D models, AECG medium accounted for high proliferation, resulting in hypertrophic epithelium and fluctuating TEER values. Models cultured with PC ALI medium developed a functional ciliated epithelium with a stable epithelial barrier. Here, we established a 3D model with high in vivo-in vitro correlation, which has the potential to close the translational gap for investigations of the human respiratory epithelium in pharmacological, infectiological, and inflammatory research.

A multiplex inhalation platform to model in situ like aerosol delivery in a breathing lung-on-chip

Prolonged exposure to environmental respirable toxicants can lead to the development and worsening of severe respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD) and fibrosis. The limited number of FDA-approved inhaled drugs for these serious lung conditions has led to a shift from in vivo towards the use of alternative in vitro human-relevant models to better predict the toxicity of inhaled particles in preclinical research. While there are several inhalation exposure models for the upper airways, the fragile and dynamic nature of the alveolar microenvironment has limited the development of reproducible exposure models for the distal lung. Here, we present a mechanistic approach using a new generation of exposure systems, the Cloud α AX12. This novel in vitro inhalation tool consists of a cloud-based exposure chamber (VITROCELL) that integrates the breathing ^AXLung-on-chip system (AlveoliX). The ultrathin and porous membrane of the AX12 plate was used to create a complex multicellular model that enables key physiological culture conditions: the air-liquid interface (ALI) and the three-dimensional cyclic stretch (CS). Human-relevant cellular models were established for a) the distal alveolar-capillary interface using primary cell-derived immortalized alveolar epithelial cells (^AXiAECs), macrophages (THP-1) and endothelial (HLMVEC) cells, and b) the upper-airways using Calu3 cells. Primary human alveolar epithelial cells (^AXhAEpCs) were used to validate the toxicity results obtained from the immortalized cell lines. To mimic in vivo relevant aerosol exposures with the Cloud α AX12, three different models were established using: a) titanium dioxide (TiO2) and zinc oxide nanoparticles b) polyhexamethylene guanidine a toxic chemical and c) an anti-inflammatory inhaled corticosteroid, fluticasone propionate (FL). Our results suggest an important synergistic effect on the air-blood barrier sensitivity, cytotoxicity and inflammation, when air-liquid interface and cyclic stretch culture conditions are combined. To the best of our knowledge, this is the first time that an in vitro inhalation exposure system for the distal lung has been described with a breathing lung-on-chip technology. The Cloud α AX12 model thus represents a state-of-the-art pre-clinical tool to study inhalation toxicity risks, drug safety and efficacy.

COVID-19 Mimics Pulmonary Dysfunction in Muscular Dystrophy as a Post-Acute Syndrome in Patients

Although progressive wasting and weakness of respiratory muscles are the prominent hallmarks of Duchenne muscular dystrophy (DMD) and long-COVID (also referred as the post-acute sequelae of COVID-19 syndrome); however, the underlying mechanism(s) leading to respiratory failure in both conditions remain unclear. We put together the latest relevant literature to further understand the plausible mechanism(s) behind diaphragm malfunctioning in COVID-19 and DMD conditions. Previously, we have shown the role of matrix metalloproteinase-9 (MMP9) in skeletal muscle fibrosis via a substantial increase in the levels of tumor necrosis factor-α (TNF-α) employing a DMD mouse model that was crossed-bred with MMP9-knockout (MMP9-KO or MMP9^-/-) strain. Interestingly, recent observations from clinical studies show a robust increase in neopterin (NPT) levels during COVID-19 which is often observed in patients having DMD. What seems to be common in both (DMD and COVID-19) is the involvement of neopterin (NPT). We know that NPT is generated by activated white blood cells (WBCs) especially the M1 macrophages in response to inducible nitric oxide synthase (iNOS), tetrahydrobiopterin (BH4), and tetrahydrofolate (FH4) pathways, i.e., folate one-carbon metabolism (FOCM) in conjunction with epigenetics underpinning as an immune surveillance protection. Studies from our laboratory, and others researching DMD and the genetically engineered humanized (hACE2) mice that were administered with the spike protein (SP) of SARS-CoV-2 revealed an increase in the levels of NPT, TNF-α, HDAC, IL-1β, CD147, and MMP9 in the lung tissue of the animals that were subsequently accompanied by fibrosis of the diaphragm depicting a decreased oscillation phenotype. Therefore, it is of interest to understand how regulatory processes such as epigenetics involvement affect DNMT, HDAC, MTHFS, and iNOS that help generate NPT in the long-COVID patients.