Titanium dioxide nanoparticles exaggerate respiratory syncytial virus-induced airway epithelial barrier dysfunction

Airway epithelial-derived exosomes induce acute asthma exacerbation after respiratory syncytial virus infection

Acute asthma exacerbation refers to the progressive deterioration of asthma symptoms that is always triggered by virus infection represented by respiratory syncytial virus (RSV). After RSV infection, exaggerated Th2-mediated pulmonary inflammation is the critical pathological response of asthmatic patients with acute exacerbation. Significantly, airway epithelial cells, being the primary targets of RSV infection, play a crucial role in controlling the pulmonary inflammatory response by releasing airway epithelial cell-derived exosomes (AEC-Exos), which potentially influence the development of asthma. However, the specific role of AEC-Exos in acute asthma exacerbation after RSV infection remains obscure. The purpose of this study was to determine the distinct function of AEC-Exos in exacerbating acute asthma following RSV infection. Blockade of exosomes by GW reduce the enhanced pulmonary inflammation significantly. Specifically, the enhanced Th2 inflammation was induced by AEC-Exos thorough transportation of hsa-miR-155-5p-Sirtuin 1 (SIRT1) pathway during acute asthma exacerbation. Targeted inhibition of hsa-miR-155-5p blocks the exaggerated Th2 inflammation effectively in mice with acute asthma exacerbation. In summary, our study showed that during acute asthma exacerbation after RSV infection, AEC-Exos promote the enhanced Th2 inflammation through transportation of increased hsa-miR-155-5p, which was mediated partly through SIRT1-mediated pathway. hsa-miR-155-5p is a potential biomarker for early prediction of acute asthma exacerbation.

Molecular Mechanisms of N-Acetylcysteine in RSV Infections and Air Pollution-Induced Alterations: A Scoping Review

N-acetylcysteine (NAC) is a mucolytic agent with antioxidant and anti-inflammatory properties. The respiratory syncytial virus (RSV) is one of the most important etiological factors of lower respiratory tract infections, and exposure to air pollution appears to be additionally associated with higher RSV incidence and disease severity. We aimed to systematically review the existing literature to determine which molecular mechanisms mediate the effects of NAC in an RSV infection and air pollution, and to identify the knowledge gaps in this field. A search for original studies was carried out in three databases and a calibrated extraction grid was used to extract data on the NAC treatment (dose, timing), the air pollutant type, and the most significant mechanisms. We identified only 28 studies conducted in human cellular models (n = 18), animal models (n = 7), and mixed models (n = 3). NAC treatment improves the barrier function of the epithelium damaged by RSV and air pollution, and reduces the epithelial permeability, protecting against viral entry. NAC may also block RSV-activated phosphorylation of the epidermal growth factor receptor (EGFR), which promotes endocytosis and facilitates cell entry. EGFR also enhances the release of a mucin gene, MUC5AC, which increases mucus viscosity and causes goblet cell metaplasia; the effects are abrogated by NAC. NAC blocks virus release from the infected cells, attenuates the cigarette smoke-induced shift from necrosis to apoptosis, and reverses the block in IFN-γ-induced antiviral gene expression caused by the inhibited Stat1 phosphorylation. Increased synthesis of pro-inflammatory cytokines and chemokines is induced by both RSV and air pollutants and is mediated by the nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways that are activated in response to oxidative stress. MCP-1 (monocyte chemoattractant protein-1) and RANTES (regulated upon activation, expressed and secreted by normal T cells) partially mediate airway hyperresponsiveness (AHR), and therapeutic (but not preventive) NAC administration reduces the inflammatory response and has been shown to reduce ozone-induced AHR. Oxidative stress-induced DNA damage and cellular senescence, observed during RSV infection and exposure to air pollution, can be partially reversed by NAC administration, while data on the emphysema formation are disputed. The review identified potential common molecular mechanisms of interest that are affected by NAC and may alleviate both the RSV infection and the effects of air pollution. Data are limited and gaps in knowledge include the optimal timing or dosage of NAC administration, therefore future studies should clarify these uncertainties and verify its practical use.

Potential mitigation of titanium dioxide nanoparticles against 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis through inhibiting the canonical NF-κB pathway

Titanium dioxide nanoparticles (TiO2 NPs) have been widely employed in various industry fields, which makes consumers concerned about their health impact. Our previous work displayed that TiO2 NPs participated in the mitigation of TNBS-induced colitis, but the mechanism is still unknown. This work aimed to explore the role of oxidative stress and NF-κB pathway in the effect of TiO2 NPs on TNBS-induced colitis. The results showed that TiO2 NPs administration reduced the DAI score of colitis mice after TNBS enema. TiO2 NPs did not alter oxidative stress status (GSH/GSSG), but repaired the gut dysbacteriosis and inhibited the canonical NF-κB pathway activation in TNBS-induced colitis mice, manifested as a decrease in pathogenic bacteria and an increase in beneficial bacteria, as well as down-regulation of toll-like receptors (TLRs), IKKα, IKKβ, p65 and pro-inflammatory cytokines (IL-1β, IL-6, TNF-α and IFN-γ) in mRNA level, and the increased transcription of anti-inflammatory cytokines (IL-10, TGF-β, and IL-12), along with the declined protein level of TNF-α in TiO2 NPs treated colitis mice. The present study suggested that oral TiO2 NPs administration inhibited the canonical NF-κB pathway activation by repairing gut dysbacteriosis, which made a predominant role in alleviating colitis. These findings provided a new perspective for exploring the safety of TiO2 NPs.

8-Bromo-cAMP attenuates human airway epithelial barrier disruption caused by titanium dioxide fine and nanoparticles

Titanium dioxide fine particles (TiO2-FPs) and nanoparticles (TiO2-NPs) are the most widely used whitening pigments worldwide. Inhalation of TiO2-FPs and TiO2-NPs can be harmful as it triggers toxicity in the airway epithelial cells. The airway epithelium serves as the respiratory system's first line of defense in which airway epithelial cells are significant targets of inhaled pathogens and environmental particles. Our group previously found that TiO2-NPs lead to a disrupted barrier in the polarized airway epithelial cells. However, the effect of TiO2-FPs on the respiratory epithelial barrier has not been examined closely. In this study, we aimed to compare the effects of TiO2-FPs and TiO2-NPs on the structure and function of the airway epithelial barrier. Additionally, we hypothesized that 8-Bromo-cAMP, a cyclic adenosine monophosphate (cAMP) derivative, would alleviate the disruptive effects of both TiO2-FPs and TiO2-NPs. We observed increased epithelial membrane permeability in both TiO2-FPs and TiO2-NPs after exposure to 16HBE cells. Immunofluorescent labeling showed that both particle sizes disrupted the structural integrity of airway epithelial tight junctions and adherens junctions. TiO2-FPs had a slightly more, but insignificant impact on the epithelial barrier disruption than TiO2-NPs. Treatment with 8-Bromo-cAMP significantly attenuated the barrier-disrupting impact of both TiO2-FPs and TiO2-NPs on cell monolayers. Our study demonstrates that both TiO2-FPs and TiO2-NPs cause comparable barrier disruption and suggests a protective role for cAMP signaling. The observed effects of TiO2-FPs and TiO2-NPs provide a necessary understanding for characterizing the pathways involved in the defensive role of the cAMP pathway on TiO2-induced airway barrier disruption.

Nanotechnology-based fungal detection and treatment: current status and future perspective

Fungal infections impose a significant impact on global health and encompass major expenditures in medical treatments. Human mycoses, a fungal co-infection associated with SARS-CoV-2, is caused by opportunistic fungal pathogens and is often overlooked or misdiagnosed. Recently, there is increasing threat about spread of antimicrobial resistance in fungus, mostly in hospitals and other healthcare facilities. The diagnosis and treatment of fungal infections are associated with several issues, including tedious and non-selective detection methods, the growth of drug-resistant bacteria, severe side effects, and ineffective drug delivery. Thus, a rapid and sensitive diagnostic method and a high-efficacy and low-toxicity therapeutic approach are needed. Nanomedicine has emerged as a viable option for overcoming these limitations. Due to the unique physicochemical and optical properties of nanomaterials and newer biosensing techniques, nanodiagnostics play an important role in the accurate and prompt differentiation and detection of fungal diseases. Additionally, nano-based drug delivery techniques can increase drug permeability, reduce adverse effects, and extend systemic circulation time and drug half-life. This review paper is aimed at highlighting recent, promising, and unique trends in nanotechnology to design and develop diagnostics and treatment methods for fungal diseases.

Electronic cigarette exposure disrupts airway epithelial barrier function and exacerbates viral infection

The use of electronic cigarettes (e-cigs), especially among teenagers, has reached alarming and epidemic levels, posing a significant threat to public health. However, the short- and long-term effects of vaping on the airway epithelial barrier are unclear. Airway epithelial cells are the forefront protectors from viruses and pathogens. They contain apical junctional complexes (AJCs), which include tight junctions (TJs) and adherens junctions (AJs) formed between adjacent cells. Previously, we reported respiratory syncytial virus (RSV) infection, the leading cause of acute lower respiratory infection-related hospitalization in children and high-risk adults, induces a "leaky airway" by disrupting the epithelial AJC structure and function. We hypothesized chemical components of e-cigs disrupt airway epithelial barrier and exacerbate RSV-induced airway barrier dysfunction. Using confluent human bronchial epithelial (16HBE) cells and well-differentiated normal human bronchial epithelial (NHBE) cells, we found that exposure to extract and aerosol e-cig nicotine caused a significant decrease in transepithelial electrical resistance (TEER) and the structure of the AJC even at noncytotoxic concentrations. Western blot analysis of 16HBE cells exposed to e-cig nicotine extract did not reveal significant changes in AJC proteins. Exposure to aerosolized e-cig cinnamon or menthol flavors also induced barrier disruption and aggravated nicotine-induced airway barrier dysfunction. Moreover, preexposure to nicotine aerosol increased RSV infection and the severity of RSV-induced airway barrier disruption. Our findings demonstrate that e-cig exposure disrupts the airway epithelial barrier and exacerbates RSV-induced damage. Knowledge gained from this study will provide awareness of adverse e-cig respiratory effects and positively impact the mitigation of e-cig epidemic.NEW & NOTEWORTHY Electronic cigarette (e-cig) use, especially in teens, is alarming and at epidemic proportions, threatening public health. Our study shows that e-cig nicotine exposure disrupts airway epithelial tight junctions and increases RSV-induced barrier dysfunction. Furthermore, exposure to aerosolized flavors exaggerates e-cig nicotine-induced airway barrier dysfunction. Our study confirms that individual and combined components of e-cigs deleteriously impact the airway barrier and that e-cig exposure increases susceptibility to viral infection.

Oxidative stress and ROS-mediated cellular events in RSV infection: potential protective roles of antioxidants

Respiratory syncytial virus (RSV), a member of the Pneumoviridae family, can cause severe acute lower respiratory tract infection in infants, young children, immunocompromised individuals and elderly people. RSV is associated with an augmented innate immune response, enhanced secretion of inflammatory cytokines, and necrosis of infected cells. Oxidative stress, which is mainly characterized as an imbalance in the production of reactive oxygen species (ROS) and antioxidant responses, interacts with all the pathophysiologic processes above and is receiving increasing attention in RSV infection. A gradual accumulation of evidence indicates that ROS overproduction plays an important role in the pathogenesis of severe RSV infection and serves as a major factor in pulmonary inflammation and tissue damage. Thus, antioxidants seem to be an effective treatment for severe RSV infection. This article mainly reviews the information on oxidative stress and ROS-mediated cellular events during RSV infection for the first time.

Effect of altered human exposome on the skin and mucosal epithelial barrier integrity

Pollution in the world and exposure of humans and nature to toxic substances is continuously worsening at a rapid pace. In the last 60 years, human and domestic animal health has been challenged by continuous exposure to toxic substances and pollutants because of uncontrolled growth, modernization, and industrialization. More than 350,000 new chemicals have been introduced to our lives, mostly without any reasonable control of their health effects and toxicity. A plethora of studies show exposure to these harmful substances during this period with their implications on the skin and mucosal epithelial barrier and increasing prevalence of allergic and autoimmune diseases in the context of the "epithelial barrier hypothesis". Exposure to these substances causes an epithelial injury with peri-epithelial inflammation, microbial dysbiosis and bacterial translocation to sub-epithelial areas, and immune response to dysbiotic bacteria. Here, we provide scientific evidence on the altered human exposome and its impact on epithelial barriers.

Vitamin D3 protects against respiratory syncytial virus-induced barrier dysfunction in airway epithelial cells via PKA signaling pathway

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infection in infants and young children globally and is responsible for hospitalization and mortality in the elderly population. Virus-induced airway epithelial barrier damage is a critical step during RSV infection, and emerging studies suggest that RSV disrupts the tight junctions (TJs) and adherens junctions (AJs) between epithelial cells, increasing the permeability of the airway epithelial barrier. The lack of commercially available vaccines and effective antiviral drugs for RSV emphasizes the need for new management strategies. Vitamin D3 is a promising intervention for viral infection due to its critical role in modulating innate immune responses. However, there is limited evidence on the effect of vitamin D3 on RSV pathogenies. Here, we investigated the impact of vitamin D3 on RSV-induced epithelial barrier dysfunction and the underlying mechanisms. We found that pre-incubation with 1,25(OH)2D3, the active form of vitamin D3, alleviated RSV-induced epithelial barrier disruption in a dose-dependent manner without affecting viability in 16HBE cells. 1,25(OH)2D3 induced minor changes in the protein expression level of TJ/AJ proteins in RSV-infected cells. We observed increased CREB phosphorylation at Ser133 during 1,25(OH)2D3 exposure, indicating that vitamin D3 triggered protein kinase A (PKA) activity in 16HBE. PKA inhibitors modified the restoration of barrier function by 1,25(OH)2D3 in RSV-infected cells, implying that PKA signaling is responsible for the protective effects of vitamin D3 against RSV-induced barrier dysfunction in airway epithelial cells. Our findings suggest vitamin D3 as a prophylactic intervention to protect the respiratory epithelium during RSV infections.

TiO2 nanoparticles affect spermatogenesis and adhesion junctions via the ROS-mediated mTOR signalling pathway in Eriocheir sinensis testes

Recent findings found that TiO₂ nanoparticles (TiO₂-NPs) have male reproductive toxicity. However, few reports have studied the toxicity of TiO₂-NPs in crustaceans. In this study, we first chose the freshwater crustacean Eriocheir sinensis (E. sinensis) to explore the male toxicity of TiO₂-NP exposure and the underlying mechanisms. Three nm and 25 nm TiO₂-NPs at a dose of 30 mg/kg bw induced apoptosis and damaged the integrity of the haemolymph-testis-barrier (HTB, a structure similar to the blood-testis-barrier) and the structure of the seminiferous tubule. The 3-nm TiO₂-NPs caused more severe spermatogenesis dysfunction than the 25-nm TiO₂-NPs. We initially confirmed that TiO₂-NP exposure affected the expression patterns of adherens junctions (α-catenin and β-catenin) and induced tubulin disorganization in the testis of E. sinensis. TiO₂-NP exposure caused reactive oxygen species (ROS) generation and an imbalance of mTORC1-mTORC2 (mTORC1/rps6/Akt levels were increased, while mTORC2 activity was not changed). After using the ROS scavenger NAC to inhibit ROS generation, both the mTORC1-mTORC2 imbalance and alterations in AJs were rescued. More importantly, the mTORC1 inhibitor rapamycin abolished mTORC1/rps6/Akt hyperactivation and partially restored the alterations in AJs and tubulin. Collectively, the mTORC1-mTORC2 imbalance induced by TiO₂-NPs was involved in the mechanism of AJ and HTB disruption, resulting in spermatogenesis in E. sinensis.

Lung-Targeted Transgene Expression of Nanocomplexed Ad5 Enhances Immune Response in the Presence of Preexisting Immunity

Recombinant adenovirus serotype 5 (Ad5) vector has been widely applied in vaccine development targeting infectious diseases, such as Ebola virus disease and coronavirus disease 2019 (COVID-19). However, the high prevalence of preexisting anti-vector immunity compromises the immunogenicity of Ad5-based vaccines. Thus, there is a substantial unmet need to minimize preexisting immunity while improving the insert-induced immunity of Ad5 vectors. Herein, we address this need by utilizing biocompatible nanoparticles to modulate Ad5-host interactions. We show that positively charged human serum albumin nanoparticles ((+)HSAnp), which are capable of forming a complex with Ad5, significantly increase the transgene expression of Ad5 in both coxsackievirus-adenovirus receptor-positive and -negative cells. Furthermore, in charge- and dose-dependent manners, Ad5/(+)HSAnp complexes achieve robust (up to 227-fold higher) and long-term (up to 60 days) transgene expression in the lungs of mice following intranasal instillation. Importantly, in the presence of preexisting anti-Ad5 immunity, complexed Ad5-based Ebola and COVID-19 vaccines significantly enhance antigen-specific humoral response and mucosal immunity. These findings suggest that viral aggregation and charge modification could be leveraged to engineer enhanced viral vectors for vaccines and gene therapies.

Nanomaterial-induced toxicity in pathophysiological models representative of individuals with pre-existing medical conditions

The integration of nanomaterials (NMs) into an ever-expanding number of daily used products has proven to be highly desirable in numerous industries and applications. Unfortunately, the same "nano" specific physicochemical properties, which make these materials attractive, may also contribute to hazards for individuals exposed to these materials. In 2021, it was estimated that 7 out of 10 deaths globally were accredited to chronic diseases, such as chronic liver disease, asthma, and cardiovascular-related illnesses. Crucially, it is also understood that a significant proportion of global populace numbering in the billions are currently living with a range of chronic undiagnosed health conditions. Due to the significant number of individuals affected, it is important that people suffering from chronic disease also be considered and incorporated in NM hazard assessment strategies. This review examined and analyzed the literature that focused on NM-induced adverse health effects in models which are representative of individuals exhibiting pre-existing medical conditions with focus on the pulmonary, cardiovascular, hepatic, gastrointestinal, and central nervous systems. The overall objective of this review was to outline available data, highlighting the important role of pre-existing disease in NM-induced toxicity with the aim of establishing a weight of evidence approach to inform the public on the potential hazards posed by NMs in both healthy and compromised persons in general population.

Antiviral Electrospun Polyamide Three-Layered Mask Filter Containing Metal Oxide Nanoparticles and Black Seed Oil

Upon the tremendous spread of coronavirus, there is a need to develop biodegradable, multifunctional, antiviral masks that can be safely used without polluting the environment as conventional surgical masks do. In this study, a three-layered mask filter is designed and fabricated. The first two layers contain electrospun polyamide with dispersed nanoparticles (NPs) of TiO₂ and ZnO prepared via breakdown anodization. The third layer is composed of Nigella sativa oil (black seed oil) electrospun with polyamide and blended with chitosan to form an effective antiviral three-layered mask filter. The morphological characterization revealed the nanoscale features of the fabricated nanofibers with the ZnO and TiO₂ NPs being embedded in the polymeric matrix. The specimens showed good wettability, which is necessary for virus attachment and its subsequent decay. The assembled mask has shown very good mechanical properties. The cytotoxicity results revealed that the proposed mask filter has less cytotoxic effect on the A549 cell line than the commercial KN95 mask filter with maintaining a cell viability of 65.3%. The antiviral activity test showed a variable virucidal effect against human adenovirus on A549 cells. The proposed mask showed the highest effect on the virus followed by PA-ZnO and PA-TiO₂ films, which supports the assumption that the used NPs may have broad and promising effects on viruses when combined with the electrospun films.

Airway Epithelial Cell Junctions as Targets for Pathogens and Antimicrobial Therapy

Intercellular contacts between epithelial cells are established and maintained by the apical junctional complexes (AJCs). AJCs conserve cell polarity and build epithelial barriers to pathogens, inhaled allergens, and environmental particles in the respiratory tract. AJCs consist of tight junctions (TJs) and adherens junctions (AJs), which play a key role in maintaining the integrity of the airway barrier. Emerging evidence has shown that different microorganisms cause airway barrier dysfunction by targeting TJ and AJ proteins. This review discusses the pathophysiologic mechanisms by which several microorganisms (bacteria and viruses) lead to the disruption of AJCs in airway epithelial cells. We present recent progress in understanding signaling pathways involved in the formation and regulation of cell junctions. We also summarize the potential chemical inhibitors and pharmacological approaches to restore the integrity of the airway epithelial barrier. Understanding the AJCs-pathogen interactions and mechanisms by which microorganisms target the AJC and impair barrier function may further help design therapeutic innovations to treat these infections.

Molecular Mechanisms of RSV and Air Pollution Interaction: A Scoping Review

RSV is one of the major infectious agents in paediatrics, and its relationship with air pollution is frequently observed. However, the molecular basis of this interaction is sparsely reported. We sought to systematically review the existing body of literature and identify the knowledge gaps to answer the question: which molecular mechanisms are implied in the air pollutants-RSV interaction? Online databases were searched for original studies published before August 2022 focusing on molecular mechanisms of the interaction. The studies were charted and a narrative synthesis was based upon three expected directions of influence: a facilitated viral entry, an altered viral replication, and an inappropriate host reaction. We identified 25 studies published between 1993 and 2020 (without a noticeable increase in the number of studies) that were performed in human (n = 12), animal (n = 10) or mixed (n = 3) models, and analysed mainly cigarette smoke (n = 11), particulate matter (n = 4), nanoparticles (n = 3), and carbon black (n = 2). The data on a damage to the epithelial barrier supports the hypothesis of facilitated viral entry; one study also reported accelerated viral entry upon an RSV conjugation to particulate matter. Air pollution may result in the predominance of necrosis over apoptosis, and, as an effect, an increased viral load was reported. Similarly, air pollution mitigates epithelium function with decreased IFN-γ and Clara cell secretory protein levels and decreased immune response. Immune response might also be diminished due to a decreased viral uptake by alveolar macrophages and a suppressed function of dendritic cells. On the other hand, an exuberant inflammatory response might be triggered by air pollution and provoke airway hyperresponsiveness (AHR), prolonged lung infiltration, and tissue remodeling, including a formation of emphysema. AHR is mediated mostly by increased IFN-γ and RANTES concentrations, while the risk of emphysema was related to the activation of the IL-17 → MCP-1 → MMP-9 → MMP-12 axis. There is a significant lack of evidence on the molecular basics of the RSV-air pollution interaction, which may present a serious problem with regards to future actions against air pollution effects. The major knowledge gaps concern air pollutants (mostly the influence of cigarette smoke was investigated), the mechanisms facilitating an acute infection or a worse disease course (since it might help plan short-term, especially non-pharmacological, interventions), and the mechanisms of an inadequate response to the infection (which may lead to a prolonged course of an acute infection and long-term sequelae). Thus far, the evidence is insufficient regarding the broadness and complexity of the interaction, and future studies should focus on common mechanisms stimulated by various air pollutants and a comparison of influence of the different contaminants at various concentrations.

Respiratory syncytial virus disrupts the airway epithelial barrier by decreasing cortactin and destabilizing F-actin

Respiratory syncytial virus (RSV) infection is the leading cause of acute lower respiratory tract infection in young children worldwide. Our group recently revealed that RSV infection disrupts the airway epithelial barrier in vitro and in vivo. However, the underlying molecular pathways were still elusive. Here, we report the critical roles of the filamentous actin (F-actin) network and actin-binding protein cortactin in RSV infection. We found that RSV infection causes F-actin depolymerization in 16HBE cells, and that stabilizing the F-actin network in infected cells reverses the epithelial barrier disruption. RSV infection also leads to significantly decreased cortactin in vitro and in vivo. Cortactin-knockout 16HBE cells presented barrier dysfunction, whereas overexpression of cortactin protected the epithelial barrier against RSV. The activity of Rap1 (which has Rap1A and Rap1B forms), one downstream target of cortactin, declined after RSV infection as well as in cortactin-knockout cells. Moreover, activating Rap1 attenuated RSV-induced epithelial barrier disruption. Our study proposes a key mechanism in which RSV disrupts the airway epithelial barrier via attenuating cortactin expression and destabilizing the F-actin network. The identified pathways will provide new targets for therapeutic intervention toward RSV-related disease. This article has an associated First Person interview with the first author of the paper.

Role of air pollutants in airway epithelial barrier dysfunction in asthma and COPD

Chronic exposure to environmental pollutants is a major contributor to the development and progression of obstructive airway diseases, including asthma and COPD. Understanding the mechanisms underlying the development of obstructive lung diseases upon exposure to inhaled pollutants will lead to novel insights into the pathogenesis, prevention and treatment of these diseases. The respiratory epithelial lining forms a robust physicochemical barrier protecting the body from inhaled toxic particles and pathogens. Inhalation of airborne particles and gases may impair airway epithelial barrier function and subsequently lead to exaggerated inflammatory responses and airway remodelling, which are key features of asthma and COPD. In addition, air pollutant-induced airway epithelial barrier dysfunction may increase susceptibility to respiratory infections, thereby increasing the risk of exacerbations and thus triggering further inflammation. In this review, we discuss the molecular and immunological mechanisms involved in physical barrier disruption induced by major airborne pollutants and outline their implications in the pathogenesis of asthma and COPD. We further discuss the link between these pollutants and changes in the lung microbiome as a potential factor for aggravating airway diseases. Understanding these mechanisms may lead to identification of novel targets for therapeutic intervention to restore airway epithelial integrity in asthma and COPD.

Exposure to air pollution induces airway epithelial barrier dysfunction through several mechanisms including increased oxidative stress, exaggerated cytokine responses and impaired host defence, which contributes to development of asthma and COPD. https://bit.ly/3DHL1CA

Role of necroptosis of alveolar macrophages in acute lung inflammation of mice exposed to titanium dioxide nanoparticles

Titanium dioxide (TiO₂) nanoparticles are indispensable for daily life but induce acute inflammation, mainly via inhalation exposure. TiO₂ nanoparticles can be phagocytosed by alveolar macrophages (AMs) in vivo and cause necroptosis of exposed cells in vitro. However, the relationship between localization of TiO₂ nanoparticles in the lungs after exposure and their biological responses including cell death and inflammation remains unclear. This study was conducted to investigate the intra/extracellular localization of TiO₂ nanoparticles in murine lungs at 24 h after intratracheal exposure to rutile TiO₂ nanoparticles and subsequent local biological reactions, specifically necroptosis of AMs and lung inflammation. We found that TiO₂ exposure induced leukocyte migration into the alveolar region and increased the secretion of C-C motif ligand (CCL) 3 in the bronchoalveolar lavage (BAL) fluid. A combination of Raman spectroscopy and staining of cell and tissue samples confirmed that AMs phagocytose TiO₂. AMs that phagocytosed TiO₂ nanoparticles showed necroptosis, characterized by the expression of phosphorylated mixed lineage kinase domain-like protein and translocation of high mobility group box-1 from the cell nucleus to the cytoplasm. In primary cultured AMs, TiO₂ also induced necroptosis and increased the secretion of CCL3. Necroptosis inhibitors suppressed the increase in CCL3 secretion in both the BAL fluid and culture supernatant of AMs and suppressed the increase in leukocytes in the BAL fluid. These data suggest that necroptosis of AMs that phagocytose TiO₂ nanoparticles is involved as part of the mechanism by which TiO₂ induces acute lung inflammation.

Engineered nanomaterials induce alterations in biological barriers: focus on paracellular permeability

Engineered nanoparticles (ENPs) are widely used in medical diagnosis and treatment, as food additives and as energy materials. ENPs may exert adverse or beneficial effects on the human body, which may be linked to interactions with biological barriers. In this review, the authors summarize the influences of four typical metal/metal oxide nanomaterials (Ag, TiO₂, Au, ZnO nanoparticles) on the paracellular permeability of biological barriers. Disruptions on tight junctions, adhesion junctions, gap junctions and desmosomes via complex signaling pathways, such as the MAPK, PKC and ROCK signaling pathways, affect paracellular permeability. Reactive oxygen species and cytokines underlie the mechanism of ENP-triggered alterations in paracellular permeability. This review provides the information necessary for the cautious application of nanoparticles in medicine and life sciences in the future.

The Impact of Environmental Pollutants on Barrier Dysfunction in Respiratory Disease

Respiratory epithelial cells form a selective barrier between the outside environment and underlying tissues. Epithelial cells are polarized and form specialized cell-cell junctions, known as the apical junctional complex (AJC). Assembly and disassembly of the AJC regulates epithelial morphogenesis and remodeling processes. The AJC consists of tight and adherens junctions, functions as a barrier and boundary, and plays a role in signal transduction. Endothelial junction proteins play important roles in tissue integrity and vascular permeability, leukocyte extravasation, and angiogenesis. Air pollutants such as particulate matter, ozone, and biologic contaminants penetrate deep into the airways, reaching the bronchioles and alveoli before entering the bloodstream to trigger airway inflammation. Pollutants accumulating in the lungs exacerbate the symptoms of respiratory diseases, including asthma and chronic obstructive lung disease. Biological contaminants include bacteria, viruses, animal dander and cat saliva, house dust mites, cockroaches, and pollen. Allergic inflammation develops in tissues such as the lung and skin with large epithelial surface areas exposed to the environment. Barrier dysfunction in the lung allows allergens and environmental pollutants to activate the epithelium and produce cytokines that promote the induction and development of immune responses. In this article, we review the impact of environmental pollutants on the cell barrier in respiratory diseases.

Effects of Air Pollutants on Airway Diseases

Air pollutants include toxic particles and gases emitted in large quantities from many different combustible materials. They also include particulate matter (PM) and ozone, and biological contaminants, such as viruses and bacteria, which can penetrate the human airway and reach the bloodstream, triggering airway inflammation, dysfunction, and fibrosis. Pollutants that accumulate in the lungs exacerbate symptoms of respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Asthma, a heterogeneous disease with complex pathological mechanisms, is characterized by particular symptoms such as shortness of breath, a tight chest, coughing, and wheezing. Patients with COPD often experience exacerbations and worsening of symptoms, which may result in hospitalization and disease progression. PM varies in terms of composition, and can include solid and liquid particles of various sizes. PM concentrations are higher in urban areas. Ozone is one of the most toxic photochemical air pollutants. In general, air pollution decreases quality of life and life expectancy. It exacerbates acute and chronic respiratory symptoms in patients with chronic airway diseases, and increases the morbidity and risk of hospitalization associated with respiratory diseases. However, the mechanisms underlying these effects remain unclear. Therefore, we reviewed the impact of air pollutants on airway diseases such as asthma and COPD, focusing on their underlying mechanisms.

RSV attenuates epithelial cell restitution by inhibiting actin cytoskeleton-dependent cell migration

The airway epithelium's ability to repair itself after injury, known as epithelial restitution, is an essential mechanism enabling the respiratory tract's normal functions. Respiratory Syncytial Virus (RSV) is the leading cause of lower respiratory tract infections worldwide. We sought to determine whether RSV delays the airway epithelium wound repair process both in vitro and in vivo. We found that RSV infection attenuated epithelial cell migration, a step in wound repair, promoted stress fiber formation, and mediated assembly of large focal adhesions (FA). Inhibition of Rho kinase (ROCK), a master regulator of actin function, reversed these effects. There was increased RhoA and phospho-myosin light chain (pMLC2) following RSV infection. In vivo, mice were intraperitoneally inoculated with naphthalene to induce lung injury, followed by RSV infection. RSV infection delayed re-epithelialization. There were increased concentrations of pMLC2 in day 7 naphthalene plus RSV animals which normalized by day 14. This study suggests a key mechanism by which RSV infection delays wound healing.

Airway tight junctions as targets of viral infections

The apical junctional complexes (AJCs) of airway epithelial cells are a key component of the innate immune system by creating barriers to pathogens, inhaled allergens, and environmental particles. AJCs form between adjacent cells and consist of tight junctions (TJs) and adherens junctions (AJs). Respiratory viruses have been shown to target various components of the AJCs, leading to airway epithelial barrier dysfunction by different mechanisms. Virus-induced epithelial permeability may allow for allergens and bacterial pathogens to subsequently invade. In this review, we discuss the pathophysiologic mechanisms leading to disruption of AJCs and the potential ensuing ramifications. We focus on the following viruses that affect the pulmonary system: respiratory syncytial virus, rhinovirus, influenza viruses, immunodeficiency virus, and other viruses such as coxsackievirus, adenovirus, coronaviruses, measles, parainfluenza virus, bocavirus, and vaccinia virus. Understanding the mechanisms by which viruses target the AJC and impair barrier function may help design therapeutic innovations to treat these infections.