Human lung-on-chips: Advanced systems for respiratory virus models and assessment of immune response

Comprehensive analysis of resilience of human airway epithelial barrier against short-term PM2.5 inorganic dust exposure using in vitro microfluidic chip and ex vivo human airway models

BACKGROUND AND OBJECTIVE

The updated World Health Organization (WHO) air quality guideline recommends an annual mean concentration of fine particulate matter (PM2.5) not exceeding 5 or 15 μg/m3 in the short-term (24 h) for no more than 3-4 days annually. However, more than 90% of the global population is currently exposed to daily concentrations surpassing these limits, especially during extreme weather conditions and due to transboundary dust transport influenced by climate change. Herein, the effect of respirable

METHODS

Silica particles at an average size of 1 μm, referred to as

RESULTS

In the AEB-on-a-chip platform, short-term exposure to 800 μg/mL PM2.5 disrupted AEB integrity via increasing barrier permeability, decreasing cell adhesion-barrier markers such as ZO-1, Vinculin, ACE2, and CD31, impaired cell viability and increased the expression levels of proinflammatory markers; IFNs, IL-6, IL-1s, TNF-α, CD68, CD80, and Inos, mostly under dynamic conditions. Besides, decreased tissue viability, impaired tissue integrity via decreasing of Vinculin, ACE2, β-catenin, and E-cadherin, and also proinflammatory response with elevated CD68, IL-1α, IL-6, IFN-Ɣ, Inos, and CD80 markers, were observed after PM2.5 exposure in ex vivo tissue.

CONCLUSION

The duration and concentration of PM2.5 that can be exposed during extreme weather conditions and natural events aligns with our exposure model (0-800 μg/mL 72 h). At this level of exposure, the resilience of the epithelial barrier is demonstrated by both AEB-on-a-chip platform emulating dynamic forces in the body and ex vivo bronchial biopsy slices. Lung-on-a-chip models will serve as reliable exposure models in this context.

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Key Words

• PM2.5
• airway epithelial barrier
• microfluidic systems
• particulate matter
• silica particles

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MESH Headings Collapse

Grants

• 2019K12-149080 Presidency of the Republic of Turkey Strategy and Budget Department
• 1139B412102522 Scientific and Technological Research Council of Turkey (TUBITAK)

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Affiliation(s)

Ozlem Goksel Department of Pulmonary Medicine, Division of Immunology and Allergy, Laboratory of Occupational & Environmental Respiratory Diseases and Asthma, Faculty of Medicine, Ege University, Izmir, Turkey Translational Pulmonary Research Center (EgeSAM), Ege University, Izmir, Turkey
Meryem Irem Sipahi Department of Biotechnology and Biomedicine, Technical University of Denmark, Kongens Lyngby, Denmark
Sena Yanasik Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey
Pelin Saglam-Metiner Translational Pulmonary Research Center (EgeSAM), Ege University, Izmir, Turkey Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey
Sema Benzer Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey
Leila Sabour-Takanlou Department of Medical Biology, Faculty of Medicine, Ege University, Izmir, Turkey
Maryam Sabour-Takanlou Department of Medical Biology, Faculty of Medicine, Ege University, Izmir, Turkey
Cigir Biray-Avci Department of Medical Biology, Faculty of Medicine, Ege University, Izmir, Turkey
Ozlem Yesil-Celiktas Translational Pulmonary Research Center (EgeSAM), Ege University, Izmir, Turkey Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey METU MEMS Center, Ankara, Turkey

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Organotypic lung tissue culture as a preclinical model to study host- influenza A viral infection: A case for repurposing of nafamostat mesylate

Reliable and effective models for recapitulation of host-pathogen interactions are imperative for the discovery of potential therapeutics. Ex vivo models can fulfill these requirements as the multicellular native environment in the tissue is preserved and be utilized for toxicology, vaccine, infection and drug efficacy studies due to the presence of immune cells. Drug repurposing involves the identification of new applications for already approved drugs that are not related to the prime medical indication and emerged as a strategy to cope with slow pace of drug discovery due to high costs and necessary phases to reach the patients. Within the scope of the study, broad-spectrum serine protease inhibitor nafamostat mesylate was repurposed to inhibit influenza A infection and evaluated by a translational ex vivo organotypic model, in which human organ-level responses can be achieved in preclinical safety studies of potential antiviral agents, along with in in vitro lung airway culture. The safe doses were determined as 10 µM for in vitro, whereas 22 µM for ex vivo to be applied for evaluation of host-pathogen interactions, which reduced virus infectivity, increased cell/tissue viability, and protected total protein content by reducing cell death with the inflammatory response. When the gene expression levels of specific pro-inflammatory, anti-inflammatory and cell surface markers involved in antiviral responses were examined, the significant inflammatory response represented by highly elevated mRNA gene expression levels of cytokines and chemokines combined with CDH5 downregulated by 5.1-fold supported the antiviral efficacy of NM and usability of ex vivo model as a preclinical infection model.

Human organoids-on-chips for biomedical research and applications

Human organoids-on-chips (OrgOCs) are the synergism of human organoids (HOs) technology and microfluidic organs-on-chips (OOCs). OOCs can mimic extrinsic characteristics of organs, such as environmental clues of living tissue, while HOs are more amenable to biological analysis and genetic manipulation. By spatial cooperation, OrgOCs served as 3D organotypic living models allowing them to recapitulate critical tissue-specific properties and forecast human responses and outcomes. It represents a giant leap forward from the regular 2D cell monolayers and animal models in the improved human ecological niche modeling. In recent years, OrgOCs have offered potential promises for clinical studies and advanced the preclinical-to-clinical translation in medical and industrial fields. In this review, we highlight the cutting-edge achievements in OrgOCs, introduce the key features of OrgOCs architectures, and share the revolutionary applications in basic biology, disease modeling, preclinical assay and precision medicine. Furthermore, we discuss how to combine a wide range of disciplines with OrgOCs and accelerate translational applications, as well as the challenges and opportunities of OrgOCs in biomedical research and applications.

In vitro high-content tissue models to address precision medicine challenges

The field of precision medicine allows for tailor-made treatments specific to a patient and thereby improve the efficiency and accuracy of disease prevention, diagnosis, and treatment and at the same time would reduce the cost, redundant treatment, and side effects of current treatments. Here, the combination of organ-on-a-chip and bioprinting into engineering high-content in vitro tissue models is envisioned to address some precision medicine challenges. This strategy could be employed to tackle the current coronavirus disease 2019 (COVID-19), which has made a significant impact and paradigm shift in our society. Nevertheless, despite that vaccines against COVID-19 have been successfully developed and vaccination programs are already being deployed worldwide, it will likely require some time before it is available to everyone. Furthermore, there are still some uncertainties and lack of a full understanding of the virus as demonstrated in the high number new mutations arising worldwide and reinfections of already vaccinated individuals. To this end, efficient diagnostic tools and treatments are still urgently needed. In this context, the convergence of bioprinting and organ-on-a-chip technologies, either used alone or in combination, could possibly function as a prominent tool in addressing the current pandemic. This could enable facile advances of important tools, diagnostics, and better physiologically representative in vitro models specific to individuals allowing for faster and more accurate screening of therapeutics evaluating their efficacy and toxicity. This review will cover such technological advances and highlight what is needed for the field to mature for tackling the various needs for current and future pandemics as well as their relevancy towards precision medicine.

Integration of immune cells in organs-on-chips: a tutorial

Viral and bacterial infections continue to pose significant challenges for numerous individuals globally. To develop novel therapies to combat infections, more insight into the actions of the human innate and adaptive immune system during infection is necessary. Human in vitro models, such as organs-on-chip (OOC) models, have proven to be a valuable addition to the tissue modeling toolbox. The incorporation of an immune component is needed to bring OOC models to the next level and enable them to mimic complex biological responses. The immune system affects many (patho)physiological processes in the human body, such as those taking place during an infection. This tutorial review introduces the reader to the building blocks of an OOC model of acute infection to investigate recruitment of circulating immune cells into the infected tissue. The multi-step extravasation cascade in vivo is described, followed by an in-depth guide on how to model this process on a chip. Next to chip design, creation of a chemotactic gradient and incorporation of endothelial, epithelial, and immune cells, the review focuses on the hydrogel extracellular matrix (ECM) to accurately model the interstitial space through which extravasated immune cells migrate towards the site of infection. Overall, this tutorial review is a practical guide for developing an OOC model of immune cell migration from the blood into the interstitial space during infection.

Design, synthesis, and evaluation of 4'-phosphonomethoxy pyrimidine ribonucleosides as potential anti-influenza agents

Influenza viruses belong to the Orthomyxoviridae family and cause acute respiratory distress in humans. The developed drug resistance toward existing drugs and the emergence of viral mutants that can escape vaccines mandate the search for novel antiviral drugs. Herein, the synthesis of epimeric 4'-methyl-4'-phosphonomethoxy [4'-C-Me-4'-C-(O-CH₂ P═O)] pyrimidine ribonucleosides, their phosphonothioate [4'-C-Me-4'-C-(O-CH₂ P═S)] derivatives, and their evaluation against an RNA viral panel are described. Selective formation of the α- l-lyxo epimer, [4'-C-(α)-Me-4'-C-(β)-(O-CH₂ -P(═O)(OEt)₂ )] over the β- d-ribo epimer [4'-C-(β)-Me-4'-C-(α)-(O-CH₂ -P(═O)(OEt)₂ )] was explained by DFT equilibrium geometry optimizations studies. Pyrimidine nucleosides having the [4'-C-(α)-Me-4'-C-(β)-(O-CH₂ -P(═O)(OEt)₂ )] framework showed specific activity against influenza A virus. Significant anti-influenza virus A (H1N1 California/07/2009 isolate) was observed with the 4'-C-(α)-Me-4'-C-(β)-O-CH₂ -P(═O)(OEt)₂ -uridine derivative 1 (EC₅₀  = 4.56 mM, SI₅₀  > 56), 4-ethoxy-2-oxo-1(2H)-pyrimidin-1-yl derivative 3 (EC₅₀  = 5.44 mM, SI₅₀  > 43) and the cytidine derivative 2 (EC₅₀  = 0.81 mM, SI₅₀  > 13), respectively. The corresponding thiophosphonates 4'-C-(α)-Me-4'-C-(β)-(O-CH₂ -P( S)(OEt)₂ ) and thionopyrimidine nucleosides were devoid of any antiviral activity. This study shows that the 4'-C-(α)-Me-4'-(β)-O-CH₂ -P(═O)(OEt)₂ ribonucleoside can be further optimized to provide potent antiviral agents.

Advances of microfluidic lung chips for assessing atmospheric pollutants exposure

Atmospheric pollutants, including particulate matters, nanoparticles, bioaerosols, and some chemicals, have posed serious threats to the environment and the human's health. The lungs are the responsible organs for providing the interface betweenthecirculatory system and the external environment, where pollutant particles can deposit or penetrate into bloodstream circulation. Conventional studies to decipher the mechanismunderlying air pollution and human health are quite limited, due to the lack of reliable models that can reproduce in vivo features of lung tissues after pollutants exposure. In the past decade, advanced near-to-native lung chips, combining cell biology with bioengineered technology, present a new strategy for atmospheric pollutants assessment and narrow the gap between 2D cell culture and in vivo animal models. In this review, the key features of artificial lung chips and the cutting-edge technologies of the lung chip manufacture are introduced. The recent progresses of lung chip technologies for atmospheric pollutants exposure assessment are summarized and highlighted. We further discuss the current challenges and the future opportunities of the development of advanced lung chips and their potential utilities in atmospheric pollutants associated toxicity testing and drug screening.

Lung-on-chip microdevices to foster pulmonary drug discovery

Respiratory diseases account for unprecedented mortality owing to a lack of personalized or insufficient therapeutic interventions. Fostering pulmonary research into managing pulmonary threat requires a potential alternative approach that can mimick the in vivo complexities of the human body. The in vitro miniaturized bionic simulation of the lung holds great potential in the quest for a successful therapeutic intervention. This review discusses the emerging roles of lung-on-chip microfluidic simulator devices in fostering translational pulmonary drug discovery and personalized medicine. This review also explicates how the lung-on-chip model emulates the breathing patterns, elasticity, and vascularization of lungs in creating a 3D pulmonary microenvironment.

Microbiome as an immune regulator in health, disease, and therapeutics

New discoveries in drugs and drug delivery systems are focused on identifying and delivering a pharmacologically effective agent, potentially targeting a specific molecular component. However, current drug discovery and therapeutic delivery approaches do not necessarily exploit the complex regulatory network of an indispensable microbiota that has been engineered through evolutionary processes in humans or has been altered by environmental exposure or diseases. The human microbiome, in all its complexity, plays an integral role in the maintenance of host functions such as metabolism and immunity. However, dysregulation in this intricate ecosystem has been linked with a variety of diseases, ranging from inflammatory bowel disease to cancer. Therapeutics and bacteria have an undeniable effect on each other and understanding the interplay between microbes and drugs could lead to new therapies, or to changes in how existing drugs are delivered. In addition, targeting the human microbiome using engineered therapeutics has the potential to address global health challenges. Here, we present the challenges and cutting-edge developments in microbiome-immune cell interactions and outline novel targeting strategies to advance drug discovery and therapeutics, which are defining a new era of personalized and precision medicine.

3D Lung-on-Chip Model Based on Biomimetically Microcurved Culture Membranes

A comparatively straightforward approach to accomplish more physiological realism in organ-on-a-chip (OoC) models is through substrate geometry. There is increasing evidence that the strongly, microscale curved surfaces that epithelial or endothelial cells experience when lining small body lumens, such as the alveoli or blood vessels, impact their behavior. However, the most commonly used cell culture substrates for modeling of these human tissue barriers in OoCs, ion track-etched porous membranes, provide only flat surfaces. Here, we propose a more realistic culture environment for alveolar cells based on biomimetically microcurved track-etched membranes. They recreate the mainly spherical geometry of the cells’ native microenvironment. In this feasibility study, the membranes were given the shape of hexagonally arrayed hemispherical microwells by an innovative combination of three-dimensional (3D) microfilm (thermo)forming and ion track technology. Integrated in microfluidic chips, they separated a top from a bottom cell culture chamber. The microcurved membranes were seeded by infusion with primary human alveolar epithelial cells. Despite the pronounced topology, the cells fully lined the alveoli-like microwell structures on the membranes’ top side. The confluent curved epithelial cell monolayers could be cultured successfully at the air−liquid interface for 14 days. Similarly, the top and bottom sides of the microcurved membranes were seeded with cells from the Calu-3 lung epithelial cell line and human lung microvascular endothelial cells, respectively. Thereby, the latter lined the interalveolar septum-like interspace between the microwells in a network-type fashion, as in the natural counterpart. The coculture was maintained for 11 days. The presented 3D lung-on-a-chip model might set the stage for other (micro)anatomically inspired membrane-based OoCs in the future.

A drug-responsive multicellular human spheroid model to recapitulate drug-induced pulmonary fibrosis

Associated with a high mortality rate, pulmonary fibrosis (PF) is the end stage of several interstitial lung diseases. Although many factors are linked to PF progression, initiation of the fibrotic process remains to be studied. Current research focused on generating new strategies to gain a better understanding of the underlying disease mechanism as the animal models remain insufficient to reflect human physiology. Herein, to account complex cellular interactions within the fibrotic tissue, a multicellular spheroid (MCS) model where human bronchial epithelial cells incorporated with human lung fibroblasts was generated and treated with bleomycin (BLM) to emulate drug-induced PF. Recapitulating the epithelial-interstitial microenvironment, the findings successfully reflected the PF disease, where excessive alpha smooth muscle actin (α-SMA) and collagen type I secretion were noted along with the morphological changes in response to BLM. Moreover, increased levels of fibrotic linked COL13A1, MMP2, WNT3 and decreased expression level of CDH1 provide evidence for the model reliability on fibrosis modelling. Subsequent administration of the FDA approved nintedanib and pirfenidone anti-fibrotic drugs proved the drug-responsiveness of the model.

Emergence of debubblers in microfluidics: A critical review

Bubbles in microfluidics-even those that appear to be negligibly small-are pervasive and responsible for the failure of many biological and chemical experiments. For instance, they block current conduction, damage cell membranes, and interfere with detection results. To overcome this unavoidable and intractable problem, researchers have developed various methods for capturing and removing bubbles from microfluidics. Such methods are multifarious and their working principles are very different from each other. In this review, bubble-removing methods are divided into two broad categories: active debubblers (that require external auxiliary equipment) and passive debubblers (driven by natural processes). In each category, three main types of methods are discussed along with their advantages and disadvantages. Among the active debubblers, those assisted by lasers, acoustic generators, and negative pressure pumps are discussed. Among the passive debubblers, those driven by buoyancy, the characteristics of gas-liquid interfaces, and the hydrophilic and hydrophobic properties of materials are discussed. Finally, the challenges and prospects of the bubble-removal technologies are reviewed to refer researchers to microfluidics and inspire further investigations in this field.

Barrier-on-a-Chip with a Modular Architecture and Integrated Sensors for Real-Time Measurement of Biological Barrier Function

Biological barriers are essential for the maintenance of organ homeostasis and their dysfunction is responsible for many prevalent diseases. Advanced in vitro models of biological barriers have been developed through the combination of 3D cell culture techniques and organ-on-chip (OoC) technology. However, real-time monitoring of tissue function inside the OoC devices has been challenging, with most approaches relying on off-chip analysis and imaging techniques. In this study, we designed and fabricated a low-cost barrier-on-chip (BoC) device with integrated electrodes for the development and real-time monitoring of biological barriers. The integrated electrodes were used to measure transepithelial electrical resistance (TEER) during tissue culture, thereby quantitatively evaluating tissue barrier function. A finite element analysis was performed to study the sensitivity of the integrated electrodes and to compare them with conventional systems. As proof-of-concept, a full-thickness human skin model (FTSm) was grown on the developed BoC, and TEER was measured on-chip during the culture. After 14 days of culture, the barrier tissue was challenged with a benchmark irritant and its impact was evaluated on-chip through TEER measurements. The developed BoC with an integrated sensing capability represents a promising tool for real-time assessment of barrier function in the context of drug testing and disease modelling.

Erratum: "Human lung-on-chips: Advanced systems for respiratory virus models and assessment of immune response" [Biomicrofluidics 15, 021501 (2021)]

[This corrects the article DOI: 10.1063/5.0038924.].