Nitric oxide inhibits IFN regulatory factor 1 and nuclear factor-kappaB pathways in rhinovirus-infected epithelial cells

NO in Viral Infections: Role and Development of Antiviral Therapies

Nitric oxide is a ubiquitous signaling radical that influences critical body functions. Its importance in the cardiovascular system and the innate immune response to bacterial and viral infections has been extensively investigated. The overproduction of NO is an early component of viral infections, including those affecting the respiratory tract. The production of high levels of NO is due to the overexpression of NO biosynthesis by inducible NO synthase (iNOS), which is involved in viral clearance. The development of NO-based antiviral therapies, particularly gaseous NO inhalation and NO-donors, has proven to be an excellent antiviral therapeutic strategy. The aim of this review is to systematically examine the multiple research studies that have been carried out to elucidate the role of NO in viral infections and to comprehensively describe the NO-based antiviral strategies that have been developed thus far. Particular attention has been paid to the potential mechanisms of NO and its clinical use in the prevention and therapy of COVID-19.

Human Metapneumovirus Induces IRF1 via TANK-Binding Kinase 1 and Type I IFN

The innate immune and host-protective responses to viruses, such as the airway pathogen human metapneumovirus (HMPV), depend on interferons (IFNs) that is induced through TANK-binding kinase 1 (TBK1) and IFN regulatory factors (IRFs). The transcription factor IRF1 is important for host resistance against several viruses and has a key role in induction of IFN-λ at mucosal surfaces. In most cell types IRF1 is expressed at very low levels, but its mRNA is rapidly induced when the demand for IRF1 activity arises. Despite general recognition of the importance of IRF1 to antiviral responses, the molecular mechanisms by which IRF1 is regulated during viral infections are not well understood. Here we identify the serine/threonine kinase TBK1 and IFN-β as critical regulators of IRF1 mRNA and protein levels in human monocyte-derived macrophages. We find that inhibition of TBK1 activity either by the semi-selective TBK1/IKKε inhibitor BX795 or by siRNA-mediated knockdown abrogates HMPV-induced expression of IRF1. Moreover, we show that canonical NF-κB signaling is involved in IRF1 induction and that the TBK1/IKKε inhibitor BX795, but not siTBK1 treatment, impairs HMPV-induced phosphorylation of the NF-κB subunit p65. At later time-points of the infection, IRF1 expression depended heavily on IFN-β-mediated signaling via the IFNAR-STAT1 pathway. Hence, our results suggest that TBK1 activation and TBK1/IKKε-mediated phosphorylation of the NF-κB subunit p65 control transcription of IRF1. Our study identifies a novel mechanism for IRF1 induction in response to viral infection of human macrophages that could be relevant not only to defense against HMPV, but also to other viral, bacterial and fungal pathogens.

Nitric oxide and viral infection: Recent developments in antiviral therapies and platforms

Nitric oxide (NO) is a gasotransmitter of great significance to developing the innate immune response to many bacterial and viral infections, while also modulating vascular physiology. The generation of NO from the upregulation of endogenous nitric oxide synthases serves as an efficacious method for inhibiting viral replication in host defense and warrants investigation for the development of antiviral therapeutics. With increased incidence of global pandemics concerning several respiratory-based viral infections, it is necessary to develop broad therapeutic platforms for inhibiting viral replication and enabling more efficient host clearance, as well as to fabricate new materials for deterring viral transmission from medical devices. Recent developments in creating stabilized NO donor compounds and their incorporation into macromolecular scaffolds and polymeric substrates has created a new paradigm for developing NO-based therapeutics for long-term NO release in applications for bactericidal and blood-contacting surfaces. Despite this abundance of research, there has been little consideration of NO-releasing scaffolds and substrates for reducing passive transmission of viral infections or for treating several respiratory viral infections. The aim of this review is to highlight the recent advances in developing gaseous NO, NO prodrugs, and NO donor compounds for antiviral therapies; discuss the limitations of NO as an antiviral agent; and outline future prospects for guiding materials design of a next generation of NO-releasing antiviral platforms.

HONEY DRESSING IN WOUND TREATMENT: A SYSTEMATIC REVIEW

OBJECTIVE

The use of honey for wound treatment and care purposes is based on thousands of years of history. The development of science and in vitro/in vivo studies have demonstrated that honey contributes to wound healing by showing therapeutic effects by means of the bioactive compounds it contains. The aim of this systematic review was to evaluate the place of honey in wound treatment by investigating the randomized controlled studies.

METHOD

30 publications which were obtained as a result of the scans in the databases and which comply with the evaluation criteria were included in the review.

RESULTS

In the results of the study, it was reported that honey in acute and chronic wounds provided rapid epithelization and wound contraction in wound healing, had anti-inflammatory and debridement effect, decreased the pain, ensured infection control, shortened the time of wound healing and was cost-effective.

HRV16 Impairs Macrophages Cytokine Response to a Secondary Bacterial Trigger

Human rhinovirus is frequently seen as an upper respiratory tract infection but growing evidence proves the virus can cause lower respiratory tract infections in patients with chronic inflammatory lung diseases including chronic obstructive pulmonary disease (COPD). In addition to airway epithelial cells, macrophages are crucial for regulating inflammatory responses to viral infections. However, the response of macrophages to HRV has not been analyzed in detail. We used in vitro monocyte-derived human macrophages to study the cytokine secretion of macrophages in response to the virus. Our results showed that macrophages were competent at responding to HRV, as a robust cytokine response was detected. However, after subsequent exposure to non-typeable Haemophilus influenzae (NTHi) or to LPS, HRV-treated macrophages secreted reduced levels of pro-inflammatory or regulatory cytokines. This “paralyzed” phenotype was not mimicked if the macrophages were pre-treated with LPS or CpG instead of the virus. These results begin to deepen our understanding into why patients with COPD show HRV-induced exacerbations and why they mount a defective response toward NTHi.

Rhinovirus and Bacteria Synergistically Induce IL-17C Release from Human Airway Epithelial Cells To Promote Neutrophil Recruitment

Virus-bacteria coinfections are associated with more severe exacerbations and increased risk of hospital readmission in patients with chronic obstructive pulmonary disease (COPD). The airway epithelium responds to such infections by releasing proinflammatory and antimicrobial cytokines, including IL-17C. However, the regulation and role of IL-17C is not well understood. In this study, we examine the mechanisms regulating IL-17C production and its potential role in COPD exacerbations. Human bronchial epithelial cells (HBE) obtained from normal, nontransplanted lungs or from brushings of nonsmokers, healthy smokers, or COPD patients were exposed to bacteria and/or human rhinovirus (HRV). RNA and protein were collected for analysis, and signaling pathways were assessed with pharmacological agonists, inhibitors, or small interfering RNAs. HBE were also stimulated with IL-17C to assess function. HRV-bacterial coinfections synergistically induced IL-17C expression. This induction was dependent on HRV replication and required NF-κB-mediated signaling. Synergy was lost in the presence of an inhibitor of the p38 MAP kinase pathway. HBE exposed to IL-17C show increased gene expression of CXCL1, CXCL2, NFKBIZ, and TFRC, and release CXCL1 protein, a neutrophil chemoattractant. Knockdown of IL-17C significantly reduced induction of CXCL1 in response to HRV-bacterial coinfection as well as neutrophil chemotaxis. HBE from healthy smokers release less IL-17C than cells from nonsmokers, but cells from COPD patients release significantly more IL-17C compared with either nonsmokers or healthy smokers. These data suggest that IL-17C may contribute to microbial-induced COPD exacerbations by promoting neutrophil recruitment.

Rhinovirus-bacteria coexposure synergistically induces CCL20 production from human bronchial epithelial cells

Exacerbations of chronic obstructive pulmonary disease are triggered by viral or bacterial pathogens, with human rhinovirus (HRV) and nontypeable Hemophilus influenzae (NTHI) among the most commonly detected pathogens. Patients who suffer from concomitant viral and bacterial infection have more severe exacerbations. The airway epithelial cell is the initial site of viral and bacterial interactions, and CCL20 is an epithelial chemokine that attracts immature dendritic cells to the airways and can act as an antimicrobial. As such, it contributes to innate and adaptive immune responses to infection. We used primary cultures of human bronchial epithelial cells and the BEAS-2B cell line to examine the effects of bacterial-viral coexposure, as well as each stimulus alone, on epithelial expression of CXCL8 and, in particular, CCL20. HRV-bacterial coexposure induced synergistic production of CXCL8 and CCL20 compared with the sum of each stimulus alone. Synergistic induction of CCL20 did not require viral replication and occurred with two different HRV serotypes that use different viral receptors. Synergy was also seen with either NTHI or Pseudomonas aeruginosa Synergistic induction of CCL20 was transcriptionally regulated. Although NF-κB was required for transcription, it did not regulate synergy, but NF-IL-6 did appear to contribute. Among MAPK inhibitors studied, neither SB203580 nor PD98059 had any effect on synergy, whereas U0126 prevented synergistic induction of CCL20 by HRV and bacteria, apparently via "off-target" effects. Thus bacterial-viral coexposure synergistically increases innate immune responses compared with individual infections. We speculate that this increased inflammatory response leads to worse clinical outcomes.

Rhinovirus Delays Cell Repolarization in a Model of Injured/Regenerating Human Airway Epithelium

Rhinovirus (RV), which causes exacerbation in patients with chronic airway diseases, readily infects injured airway epithelium and has been reported to delay wound closure. In this study, we examined the effects of RV on cell repolarization and differentiation in a model of injured/regenerating airway epithelium (polarized, undifferentiated cells). RV causes only a transient barrier disruption in a model of normal (mucociliary-differentiated) airway epithelium. However, in the injury/regeneration model, RV prolongs barrier dysfunction and alters the differentiation of cells. The prolonged barrier dysfunction caused by RV was not a result of excessive cell death but was instead associated with epithelial-to-mesenchymal transition (EMT)-like features, such as reduced expression of the apicolateral junction and polarity complex proteins, E-cadherin, occludin, ZO-1, claudins 1 and 4, and Crumbs3 and increased expression of vimentin, a mesenchymal cell marker. The expression of Snail, a transcriptional repressor of tight and adherence junctions, was also up-regulated in RV-infected injured/regenerating airway epithelium, and inhibition of Snail reversed RV-induced EMT-like features. In addition, compared with sham-infected cells, the RV-infected injured/regenerating airway epithelium showed more goblet cells and fewer ciliated cells. Inhibition of epithelial growth factor receptor promoted repolarization of cells by inhibiting Snail and enhancing expression of E-cadherin, occludin, and Crumbs3 proteins, reduced the number of goblet cells, and increased the number of ciliated cells. Together, these results suggest that RV not only disrupts barrier function, but also interferes with normal renewal of injured/regenerating airway epithelium by inducing EMT-like features and subsequent goblet cell hyperplasia.

Virus-induced modulation of lower airway diseases: pathogenesis and pharmacologic approaches to treatment

Uncomplicated upper respiratory viral infections are the most common cause of days lost from work and school and exert a major economic burden. In susceptible individuals, however, common respiratory viruses, particularly human rhinoviruses, also can have a major impact on diseases that involve the lower airways, including asthma, chronic obstructive pulmonary diseases (COPD) and cystic fibrosis (CF). Respiratory virus-induced wheezing illnesses in early life are a significant risk factor for the subsequent development of asthma, and virus infections may also play a role in the development and progression of airway remodeling in asthma. It is clear that upper respiratory tract virus infections can spread to the lower airway and trigger acute attacks of asthma, COPD or CF. These exacerbations can be life-threatening, and exert an enormous burden on health care systems. In recent years we have gained new insights into the mechanisms by which respiratory viruses may induce acute exacerbations of lower airway diseases, as well as into host defense pathways that may regulate the outcomes to viral infections. In the current article we review the role of viruses in lower airway diseases, including our current understanding on pathways by which they may cause remodeling and trigger acute exacerbations. We also review the efficacy of current and emerging therapies used to treat these lower airway diseases on the outcomes due to viral infection, and discuss alternative therapeutic approaches for the management of virus-induced airway inflammation.

Human rhinovirus-induced ISG15 selectively modulates epithelial antiviral immunity

Human rhinovirus (HRV) infections trigger exacerbations of lower airway diseases. HRV infects human airway epithelial cells and induces proinflammatory and antiviral molecules that regulate the response to HRV infection. Interferon (IFN)-stimulated gene of 15 kDa (ISG15) has been shown to regulate other viruses. We now show that HRV-16 infection induces both intracellular epithelial ISG15 expression and ISG15 secretion in vitro. Moreover, ISG15 protein levels increased in nasal secretions of subjects with symptomatic HRV infections. HRV-16-induced ISG15 expression is transcriptionally regulated via an IFN regulatory factor pathway. ISG15 does not directly alter HRV replication but does modulate immune signaling via the viral sensor protein RIG-I to impact production of CXCL10, which has been linked to innate immunity to viruses. Extracellular ISG15 also alters CXCL10 production. We conclude that ISG15 has a complex role in host defense against HRV infection, and that additional studies are needed to clarify the role of this molecule.

Carotenoids, inflammation, and oxidative stress--implications of cellular signaling pathways and relation to chronic disease prevention

Several epidemiologic studies have shown that diets rich in fruits and vegetables reduce the risk of developing several chronic diseases, such as type 2 diabetes, atherosclerosis, and cancer. These diseases are linked with systemic, low-grade chronic inflammation. Although controversy persists on the bioactive ingredients, several secondary plant metabolites have been associated with these beneficial health effects. Carotenoids represent the most abundant lipid-soluble phytochemicals, and in vitro and in vivo studies have suggested that they have antioxidant, antiapoptotic, and anti-inflammatory properties. Recently, many of these properties have been linked to the effect of carotenoids on intracellular signaling cascades, thereby influencing gene expression and protein translation. By blocking the translocation of nuclear factor κB to the nucleus, carotenoids are able to interact with the nuclear factor κB pathway and thus inhibit the downstream production of inflammatory cytokines, such as interleukin-8 or prostaglandin E2. Carotenoids can also block oxidative stress by interacting with the nuclear factor erythroid 2-related factor 2 pathway, enhancing its translocation into the nucleus, and activating phase II enzymes and antioxidants, such as glutathione-S-transferases. In this review, which is organized into in vitro, animal, and human investigations, we summarized current knowledge on carotenoids and metabolites with respect to their ability to modulate inflammatory and oxidative stress pathways and discuss potential dose-health relations. Although many pathways involved in the bioactivity of carotenoids have been revealed, future research should be directed toward dose-response relations of carotenoids, their metabolites, and their effect on transcription factors and metabolism.

EGFR activation suppresses respiratory virus-induced IRF1-dependent CXCL10 production

Airway epithelial cells are the primary cell type involved in respiratory viral infection. Upon infection, airway epithelium plays a critical role in host defense against viral infection by contributing to innate and adaptive immune responses. Influenza A virus, rhinovirus, and respiratory syncytial virus (RSV) represent a broad range of human viral pathogens that cause viral pneumonia and induce exacerbations of asthma and chronic obstructive pulmonary disease. These respiratory viruses induce airway epithelial production of IL-8, which involves epidermal growth factor receptor (EGFR) activation. EGFR activation involves an integrated signaling pathway that includes NADPH oxidase activation of metalloproteinase, and EGFR proligand release that activates EGFR. Because respiratory viruses have been shown to activate EGFR via this signaling pathway in airway epithelium, we investigated the effect of virus-induced EGFR activation on airway epithelial antiviral responses. CXCL10, a chemokine produced by airway epithelial cells in response to respiratory viral infection, contributes to the recruitment of lymphocytes to target and kill virus-infected cells. While respiratory viruses activate EGFR, the interaction between CXCL10 and EGFR signaling pathways is unclear, and the potential for EGFR signaling to suppress CXCL10 has not been explored. Here, we report that respiratory virus-induced EGFR activation suppresses CXCL10 production. We found that influenza virus-, rhinovirus-, and RSV-induced EGFR activation suppressed IFN regulatory factor (IRF) 1-dependent CXCL10 production. In addition, inhibition of EGFR during viral infection augmented IRF1 and CXCL10. These findings describe a novel mechanism that viruses use to suppress endogenous antiviral defenses, and provide potential targets for future therapies.

Interferon regulatory factor-1 in flagellin-induced reprogramming: potential protective role of CXCL10 in cornea innate defense against Pseudomonas aeruginosa infection

PURPOSE

We previously showed that pre-exposure of the cornea to Toll-like receptor (TLR)5 ligand flagellin induces strong protective innate defense against microbial pathogens and hypothesized that flagellin modulates gene expression at the transcriptional levels. Thus, we sought to determine the role of one transcription factor, interferon regulatory factor (IRF1), and its target gene CXCL10 therein.

METHODS

Superarray was used to identify transcription factors differentially expressed in Pseudomonas aeruginosa-challenged human corneal epithelial cells (CECs) with or without flagellin pretreatment. The expression of CXCL10, IRF1, LI-8(CXCL2), and IFNγ was determined by PCR, immunohistochemistry, Western/dot blotting, and/or ELISA. IRF1 knockout mice, CXCL10 and IFNγ neutralization, and NK cell depletion were used to define in vivo regulation and function of CXCL10. The severity of P. aeruginosa was assessed using clinical scoring, slit-lamp microscopy, bacterial counting, polymorphonuclear leukocytes (PMN) infiltration, and macrophage inflammatory protein 2/Chemokine (C-X-C motif) ligand 2 (MIP-2/CXCL2) expression.

RESULTS

Flagellin pretreatment drastically affected P. aeruginosa-induced IRF1 expression in human CECs. However, flagellin pretreatment augmented the P. aeruginosa-induced expression of Irf1 and its target gene Cxcl10 in B6 mouse corneas. Irf1 deficiency reduced infection-triggered CXCL10 expression, increased keratitis severity, and attenuated flagellin-elicited protection compared to values in wild-type (WT) controls. CXCL10 neutralization in the cornea of WT mice displayed pathogenesis similar to that of IRF1⁻/⁻ mice. IFNγ receptor neutralization and NK cell depletion prevented flagellin-augmented IRF1 and CXCL10 expression and increased the susceptibility to P. aeruginosa infection in mouse corneas.

CONCLUSIONS

IRF1 plays a role in the corneal innate immune response by regulating CXCL10 expression. IFNγ-producing NK cells augment the epithelial expression of IRF1 and CXCL10 and thus contribute to the innate defense of the cornea against P. aeruginosa infection.

Gaseous nitric oxide reduces influenza infectivity in vitro

Gaseous nitric oxide (gNO) is an approved vasodilator drug for inhalation up to a maximum dose of 80 ppm. While gNO has been shown, in vitro, to be an effective antibacterial agent (at 160 ppm), NO-donor compounds have been shown to inhibit a variety of viruses at varying stages of replication. This research was done in order to determine whether gNO at 80 or 160 ppm possesses an antiviral effect on influenza viruses. Three strains of influenza (A and B) were exposed to gNO for up to 180 min, before and after infection of MDCK cells. In search for possible mechanism of antiviral action, Neuraminidase (NA) inhibition assay of H1N1 that was exposed to gNO was performed. Results show that when virions were exposed to gNO prior to infection a complete inhibition of infectivity was achieved for all three strains. Post infection exposure of influenza with gNO resulted in about 30% inhibition of infectivity. Further testing showed that when eliminating the pH effect by exposing a dried virus to gNO, 90% inhibition was found after 2h exposure. NA activity, of whole dried H1N1 virus, was found to be inhibited by gNO (80%). These results suggest that 80 and 160 ppm gNO have a time dependent antiviral effect on influenza strains of viruses during various stages of cellular infection, which are not due to concomitant changes in pH in the surrounding milieu. Viral NA inhibition by gNO was shown and may be responsible for this antiviral effect.

Epithelial cells and airway diseases

The airway epithelial cell is the initial cell type impacted both by inhaled environmental factors, such as pathogens, allergens, and pollutants, and inhaled medications for airway diseases. As such, epithelial cells are now recognized to play a central role in the regulation of airway inflammatory status, structure, and function in normal and diseased airways. This article reviews our current knowledge regarding the roles of the epithelial cell in airway inflammation and host defense. The interactions of inhaled environmental factors and pathogens with epithelial cells are also discussed, with an emphasis on epithelial innate immune responses and contributions of epithelial cells to immune regulation. Recent evidence suggesting that epithelial cells play an active role in inducing several of the structural changes, collectively referred to airway remodeling, seen in the airways of asthmatic subjects is reviewed. Finally, the concept that the epithelium is a major target for the actions of a number of classes of inhaled medications is discussed, as are the potential mechanisms by which selected drugs may alter epithelial function.

The airway epithelium: soldier in the fight against respiratory viruses

The airway epithelium acts as a frontline defense against respiratory viruses, not only as a physical barrier and through the mucociliary apparatus but also through its immunological functions. It initiates multiple innate and adaptive immune mechanisms which are crucial for efficient antiviral responses. The interaction between respiratory viruses and airway epithelial cells results in production of antiviral substances, including type I and III interferons, lactoferrin, β-defensins, and nitric oxide, and also in production of cytokines and chemokines, which recruit inflammatory cells and influence adaptive immunity. These defense mechanisms usually result in rapid virus clearance. However, respiratory viruses elaborate strategies to evade antiviral mechanisms and immune responses. They may disrupt epithelial integrity through cytotoxic effects, increasing paracellular permeability and damaging epithelial repair mechanisms. In addition, they can interfere with immune responses by blocking interferon pathways and by subverting protective inflammatory responses toward detrimental ones. Finally, by inducing overt mucus secretion and mucostasis and by paving the way for bacterial infections, they favor lung damage and further impair host antiviral mechanisms.

Modulation of epithelial biology by rhinovirus infection: role in inflammatory airway diseases

The human airway epithelial cell is the primary site of human rhinovirus (HRV) infection in both the upper and lower airways, but HRV infection does not cause overt epithelial cytotoxicity at either location. Therefore, it is thought that HRV infections induce symptoms of the common cold or exacerbate lower airway diseases, such as asthma and chronic obstructive pulmonary disease, by altering epithelial cell biology. This premise has led to intense investigation of the interactions of HRV with epithelial cells. This article reviews current knowledge regarding how HRV induces epithelial induction of proinflammatory cytokines and chemokines. In addition, the contributions of epithelial cells to host antiviral responses will be reviewed along with evidence that HRV-infected epithelial cells may contribute to the airway remodeling that is a characteristic feature of asthma.

dsRNA-induced expression of thymic stromal lymphopoietin (TSLP) in asthmatic epithelial cells is inhibited by a small airway relaxant

RATIONALE

Thymic Stromal Lymphopoietin (TSLP) is considered a hub cytokine that activates dendritic cells and T-cells producing asthma-like Th₂-inflammation. Viral stimuli, a major cause of asthma exacerbations, have been shown to induce overexpression of TSLP in asthmatic epithelium. Capsazepine has multiple effects and is of interest because it relaxes human small airways. Here we have explored effects of capsazepine on viral surrogate (dsRNA)-induced TSLP and other cytokines (TNF-alpha, IL-8) in human bronchial epithelial cells (HBEC) from healthy and asthmatic donors.

METHODS

HBEC obtained from healthy and asthmatic subjects were grown and stimulated with dsRNA. Cells pre-treated with capsazepine (3-30 μM), dexamethasone (0.1-10 μM) or an IkappaB-kinase inhibitor (PS1145, 30 μM) were also exposed to dsRNA (10 μg/ml). Cells and supernatants were harvested for analyses of gene expression (RT-qPCR) and protein production (ELISA,Western blot).

RESULTS

dsRNA-induced TSLP, TNF-alpha, and IL-8 in asthmatic and non-asthmatic HBEC. Dexamethasone attenuated gene expression and protein release whereas capsazepine dose-dependently, and similar to a non-relaxant NFkB inhibitor (PS1145), completely inhibited dsRNA-induced TSLP and TNF-alpha in both healthy and asthmatic HBEC. Capsazepine reduced dsRNA-induced IL-8 and it prevented dsRNA-induced loss of the NF-κB repressor protein IkBα.

CONCLUSION

Additional to its human small airway relaxant effects we now demonstrate that capsazepine has potent anti-inflammatory effects on viral stimulus-induced cytokines in HBEC from healthy as well as asthmatic donors. Based on these data we suggest that exploration of structure-activity amongst the multifaceted capsazepinoids is warranted in search for compounds of therapeutic value in viral-induced, steroid-resistant asthma.