Danger-associated molecular patterns (DAMPs) in acute lung injury

Toll-like receptors in kidney ischemia-reperfusion injury: Modulating macrophage responses for therapeutic insights

Kidney ischemia-reperfusion (I/R) injury is an acute clinical condition associated with inflammation and tissue damage during and after ischemia and reperfusion periods. In I/R injury, macrophages contribute to injury, and a family of proteins called toll-like receptors seem to have an immune modulatory role. When activated, TLRs initiate a series of signaling pathways, including MyD88 and TRIF. These pathways regulate the activation of tissue macrophages into either 'classically activated' M1 or 'alternatively activated' M2 phenotypes. Indeed, the relative abundance of these macrophage phenotypes defines the tissue injury level, which consequently requires reparative processes. The initial effector pro-inflammatory M1 macrophages aggravate tissue injury. Conversely, tissue reparative and anti-inflammatory M2 macrophages promote tissue repair and resolution-increased TLR signalling results in increased inflammation, prolonged healing and even renal failure. New evidence indicates that the change of macrophage responses through pharmacological targeting of the TLR pathways that regulate inflammation and tissue repair may have therapeutic implications. Some experimental treatment methods, in which early phases have been elaborated through experimental animal models, are TLR antagonists, small molecule inhibitors and nanotechnology-based delivery systems for Antisense oligonucleotide. Nevertheless, because the pathways regulated by TLRs and the subsets of macrophages are so countless and entangled, more extensive study is needed to provide more targeted actions. These findings shed light on the role and regulation of TLRs in macrophages during kidney I/R injury and investigate potential treatments with the potential to enhance care in this highly damaging condition.

Acute respiratory distress syndrome (ARDS): from mechanistic insights to therapeutic strategies

Acute respiratory distress syndrome (ARDS) is a clinical syndrome of acute hypoxic respiratory failure caused by diffuse lung inflammation and edema. ARDS can be precipitated by intrapulmonary factors or extrapulmonary factors, which can lead to severe hypoxemia. Patients suffering from ARDS have high mortality rates, including a 28-day mortality rate of 34.8% and an overall in-hospital mortality rate of 40.0%. The pathophysiology of ARDS is complex and involves the activation and dysregulation of multiple overlapping and interacting pathways of systemic inflammation and coagulation, including the respiratory system, circulatory system, and immune system. In general, the treatment of inflammatory injuries is a coordinated process that involves the downregulation of proinflammatory pathways and the upregulation of anti-inflammatory pathways. Given the complexity of the underlying disease, treatment needs to be tailored to the problem. Hence, we discuss the pathogenesis and treatment methods of affected organs, including 2019 coronavirus disease (COVID-19)-related pneumonia, drowning, trauma, blood transfusion, severe acute pancreatitis, and sepsis. This review is intended to provide a new perspective concerning ARDS and offer novel insight into future therapeutic interventions.

Association of Inflammatory Profile During Ex Vivo Lung Perfusion With High-Grade Primary Graft Dysfunction: A Systematic Review and Meta-Analysis

PGD3 is the manifestation of ischemia-reperfusion injury which results from inflammation and cell death and is associated with poor outcome. This systematic-review and meta-analysis of non-randomized controlled trials on patients undergoing Ltx with reconditioned lungs via EVLP, aims to assess the association between the levels of proinflammatory biomarkers during EVLP and PGD3 development within the firsts 72 h post-Ltx. Biomarkers were categorized by timing (1-hour, T0 and 4-hours, Tend from EVLPstart) and by their biological function (adhesion molecules, chemokines, cytokines, damage-associated-molecular-patterns, growth-factors, metabolites). We employed a four-level mixed-effects model with categorical predictors for biomarker groups to identify differences between patients with PGD3 and others. The single study and individual measurements were considered random intercepts. We included 8 studies (610 measurements at T0 and 884 at Tend). The pooled effect was 0.74 (p = 0.021) at T0, and 0.90 (p = 0.0015) at Tend. The four-level model indicated a large pooled correlation between developing PGD3 at 72 h post-Ltx and inflammatory biomarkers values, r = 0.62 (p = 0.009). Chemokine group showed the strongest association with the outcome (z-value = 1.26, p = 0.042). Pooled panels of inflammation markers, particularly chemokines, measured at T0 or at Tend, are associated with the development of PGD3 within the first 72 h after Ltx.

Systematic Review Registration

https://osf.io/gkxzh/.

Regulated Cell Death of Alveolar Macrophages in Acute Lung Inflammation: Current Knowledge and Perspectives

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a common and serious clinical lung disease characterized by extensive alveolar damage and inflammation leading to impaired gas exchange. Alveolar macrophages (AMs) maintain homeostatic properties and immune defenses in lung tissues. Several studies have reported that AMs are involved in and regulate ALI/ARDS onset and progression via different regulated cell death (RCD) programs, such as pyroptosis, apoptosis, autophagic cell death, and necroptosis. Notably, the effects of RCD in AMs in disease are complex and variable depending on the environment and stimuli. In this review, we provide a comprehensive perspective on how regulated AMs death impacts on ALI/ARDS and assess its potential in new therapeutic development. Additionally, we describe the crosstalk between different RCD types in ALI, and provide new perspectives for the treatment of ALI/ARDS and other severe lung diseases.

Airway epithelium in lung transplantation: a potential actor for post-transplant complications?

Lung transplantation, a critical intervention for end-stage lung diseases, is frequently challenged by post-transplant complications. Indeed, primary graft dysfunction, anastomotic complications, infections and acute and chronic rejections pose significant hurdles in lung transplantation. While evidence regarding the role of airway epithelium after lung transplantation is still emerging, its importance is becoming increasingly recognised. This review looks at the complex involvement of airway epithelium in various post-transplant complications, while emphasising the utility of airway epithelial culture as a research model. In summary, by elucidating the involvement of airway epithelium in each post-transplant complication and explaining these intricate processes, the review aims to guide specific future research efforts and therapeutic strategies aimed at improving lung transplant outcomes and enhancing patient care.

Pathogenic mechanisms and latest therapeutic approaches for radiation-induced lung injury: A narrative review

The treatment of thoracic tumors with ionizing radiation can cause radiation-induced lung injury (RILI), which includes radiation pneumonitis and radiation-induced pulmonary fibrosis. Preventing RILI is crucial for controlling tumor growth and improving quality of life. However, the serious adverse effects of traditional RILI treatment methods remain a major obstacle, necessitating the development of novel treatment options that are both safe and effective. This review summarizes the molecular mechanisms of RILI and explores novel treatment options, including natural compounds, gene therapy, nanomaterials, and mesenchymal stem cells. These recent experimental approaches show potential as effective prevention and treatment options for RILI in clinical practice.

Mechanisms of Bleomycin-induced Lung Fibrosis: A Review of Therapeutic Targets and Approaches

Pulmonary toxicity is a serious side effect of some specific anticancer drugs. Bleomycin is a well-known anticancer drug that triggers severe reactions in the lungs. It is an approved drug that may be prescribed for the treatment of testicular cancers, Hodgkin's and non-Hodgkin's lymphomas, ovarian cancer, head and neck cancers, and cervical cancer. A large number of experimental studies and clinical findings show that bleomycin can concentrate in lung tissue, leading to massive oxidative stress, alveolar epithelial cell death, the proliferation of fibroblasts, and finally the infiltration of immune cells. Chronic release of pro-inflammatory and pro-fibrotic molecules by immune cells and fibroblasts leads to pneumonitis and fibrosis. Both fibrosis and pneumonitis are serious concerns for patients who receive bleomycin and may lead to death. Therefore, the management of lung toxicity following cancer therapy with bleomycin is a critical issue. This review explains the cellular and molecular mechanisms of pulmonary injury following treatment with bleomycin. Furthermore, we review therapeutic targets and possible promising strategies for ameliorating bleomycin-induced lung injury.

A prediction model for secondary invasive fungal infection among severe SARS-CoV-2 positive patients in ICU

Background

The global COVID-19 pandemic has resulted in over seven million deaths, and IFI can further complicate the clinical course of COVID-19. Coinfection of COVID-19 and IFI (secondary IFI) pose significant threats not only to healthcare systems but also to patient lives. After the control measures for COVID-19 were lifted in China, we observed a substantial number of ICU patients developing COVID-19-associated IFI. This creates an urgent need for predictive assessment of COVID-19 patients in the ICU environment for early detection of suspected fungal infection cases.

Methods

This study is a single-center, retrospective research endeavor. We conducted a case-control study on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positive patients. The cases consisted of patients who developed any secondary IFI during their ICU stay at Jilin University China-Japan Union Hospital in Changchun, Jilin Province, China, from December 1st, 2022, to August 31st, 2023. The control group consisted of SARS-CoV-2 positive patients without secondary IFI. Descriptive and comparative analyses were performed, and a logistic regression prediction model for secondary IFI in COVID-19 patients was established. Additionally, we observed an increased incidence of COVID-19-associated pulmonary aspergillosis (CAPA) during this pandemic. Therefore, we conducted a univariate subgroup analysis on top of IFI, using non-CAPA patients as the control subgroup.

Results

From multivariate analysis, the prediction model identified 6 factors that are significantly associated with IFI, including the use of broad-spectrum antibiotics for more than 2 weeks (aOR=4.14, 95% CI 2.03-8.67), fever (aOR=2.3, 95%CI 1.16-4.55), elevated log IL-6 levels (aOR=1.22, 95% CI 1.04-1.43) and prone position ventilation (aOR=2.38, 95%CI 1.15-4.97) as independent risk factors for COVID-19 secondary IFI. High BMI (BMI ≥ 28 kg/m2) (aOR=0.85, 95% CI 0.75-0.94) and the use of COVID-19 immunoglobulin (aOR=0.45, 95% CI 0.2-0.97) were identified as independent protective factors against COVID-19 secondary IFI. The Receiver Operating Curve (ROC) area under the curve (AUC) of this model was 0.81, indicating good classification.

Conclusion

We recommend paying special attention for the occurrence of secondary IFI in COVID-19 patients with low BMI (BMI < 28 kg/m2), elevated log IL-6 levels and fever. Additionally, during the treatment of COVID-19 patients, we emphasize the importance of minimizing the duration of broad-spectrum antibiotic use and highlight the potential of immunoglobulin application in reducing the incidence of IFI.

Diterpene Coronarin Attenuates Lipopolysaccharide-Induced Acute Lung Injury in Both In Vivo and In Vitro Models

Acute lung injury (ALI) is a clinical condition occurs due to severe systemic inflammatory response for clinical stimulus like pneumonia, sepsis, trauma, aspiration, inhalation of toxic gases, and pancreatitis. Disruption of alveolar barriers, activation of macrophages, infiltration of neutrophils, and proinflammatory cytokines are the vital events occurs during ALI. The drugs which inhibit these inflammatory response can protect lungs from inflammatory insults. In this study, we examined the potency of phytochemical coronarin, a diterpene which have been proven to possess anti-inflammatory, antioxidant, antiangiogenic, and antitumor activities. Healthy BALB/c mice were induced to acute lung injury with intra-tracheal administration of LPS and then treated with 5 and 10 mg/kg concentration of coronarin. The wet/dry lung weight of mice were estimated to assess the induction of pulmonary edema. BALF fluid was analyzed for protein concentrations and immune cells count. Myeloperoxidase activity and levels of chemokines MCP-2 and MIP-2, iNOS, COX-2, and PGE-2 were quantified to assess the immunomodulatory effect of coronarin against LPS-induced ALI. The levels of proinflammatory cytokines was measured to examine the anti-inflammatory property of coronarin, and it was confirmed with histopathological analysis of the lung tissue. Murine RAW 264.7 cells were utilized for the in vitro analysis. Cell cytoxicity and cytoprotective property of coronarin was assessed with MTT assay in LPS-treated Murine RAW 264.7. The anti-inflammatory property of coronarin was further confirmed in in vitro condition by estimating the levels of pro-inflammatory cytokines in coronarin-treated and untreated LPS-induced cells. Overall, our in vivo and in vitro results confirm coronarin significantly inhibited the infiltration of neutrophils prevented immunodulatory activity and synthesis of proinflammatory cytokines and alleviated the acute lung injury induced by LPS. Coronarin is a potent anti-inflammatory drug which can be subjected to further research to be prescribed as drug for ALI.

Bidirectional pressure: a mini review of ventilator-lung-kidney interactions

Acute kidney injury and respiratory failure that requires mechanical ventilation are both common complications of critical illnesses. Failure of either of these organ systems also increases the risk of failure to the other. As a result, there is a high incidence of patients with concomitant acute kidney injury and the need for mechanical ventilation, which has a devasting impact on intensive care unit outcomes, including mortality. Despite decades of research into the mechanisms of ventilator-lung-kidney interactions, several gaps in knowledge remain and current treatment strategies are primarily supportive. In this review, we outline our current understanding of the mechanisms of acute kidney injury due to mechanical ventilation including a discussion of; 1) The impact of mechanical ventilation on renal perfusion, 2) activation of neurohormonal pathways by positive pressure ventilation, and 3) the role of inflammatory mediators released during ventilator induced lung injury. We also provide a review of the mechanisms by which acute kidney injury increases the risk of respiratory failure. Next, we outline a summary of the current therapeutic approach to preventing lung and kidney injury in the critically ill, including fluid and vasopressor management, ventilator strategies, and treatment of acute kidney injury. Finally, we conclude with a discussion outlining opportunities for novel investigations that may provide a rationale for new treatment approaches.

Exploring immune-related pathogenesis in lung injury: Providing new insights Into ALI/ARDS

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) represent a significant global burden of morbidity and mortality, with lung injury being the primary cause of death in affected patients. The pathogenesis of lung injury, however, remains a complex issue. In recent years, the role of the immune system in lung injury has attracted extensive attention worldwide. Despite advancements in our understanding of various lung injury subtypes, significant limitations persist in both prevention and treatment. This review investigates the immunopathogenesis of ALI/ARDS, aiming to elucidate the pathological processes of lung injury mediated by dendritic cells (DCs), natural killer (NK) cells, phagocytes, and neutrophils. Furthermore, the article expounds on the critical contributions of gut microbiota, inflammatory pathways, and cytokine storms in the development of ALI/ARDS.

COVID-19 cooling: Nanostrategies targeting cytokine storm for controlling severe and critical symptoms

As severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants continue to wreak havoc worldwide, the "Cytokine Storm" (CS, also known as the inflammatory storm) or Cytokine Release Syndrome has reemerged in the public consciousness. CS is a significant contributor to the deterioration of infected individuals. Therefore, CS control is of great significance for the treatment of critically ill patients and the reduction of mortality rates. With the occurrence of variants, concerns regarding the efficacy of vaccines and antiviral drugs with a broad spectrum have grown. We should make an effort to modernize treatment strategies to address the challenges posed by mutations. Thus, in addition to the requirement for additional clinical data to monitor the long-term effects of vaccines and broad-spectrum antiviral drugs, we can use CS as an entry point and therapeutic target to alleviate the severity of the disease in patients. To effectively combat the mutation, new technologies for neutralizing or controlling CS must be developed. In recent years, nanotechnology has been widely applied in the biomedical field, opening up a plethora of opportunities for CS. Here, we put forward the view of cytokine storm as a therapeutic target can be used to treat critically ill patients by expounding the relationship between coronavirus disease 2019 (COVID-19) and CS and the mechanisms associated with CS. We pay special attention to the representative strategies of nanomaterials in current neutral and CS research, as well as their potential chemical design and principles. We hope that the nanostrategies described in this review provide attractive treatment options for severe and critical COVID-19 caused by CS.

Gut lymph purification alleviates acute lung injury induced by intestinal ischemia-reperfusion in rats by removing danger-associated molecular patterns from gut lymph

Background

The potential effect of removing danger-associated molecular patterns (DAMPs) from gut lymph on reducing acute lung injury (ALI) induced by gut ischemia-reperfusion injury (GIRI) is uncertain. This study aimed to investigate whether gut lymph purification (GLP) could improve GIRI-induced acute lung injury in rats by clearing danger-associated molecular patterns.

Materials and methods

Rats were divided into four groups: Sham, GIRI, GIRI + gut lymph drainage (GLD), and GIRI + GLP. After successful modeling, lung tissue samples were collected from rats for hematoxylin-eosin (HE) staining and detection of apoptotic indexes. We detected the DAMPs levels in blood and lymph samples. We observed the microstructure of AEC Ⅱ and measured the expression levels of apoptosis indexes.

Results

The GIRI group showed destruction of alveolar structure, thickened alveolar walls, and inflammatory cell infiltration. This was accompanied by significantly increased levels of high mobility group protein-1 (HMGB-1) and Interleukin-6 (IL-6), while reduced levels of heat shock protein 70 (HSP 70) and Interleukin-10 (IL-10) in both lymph and serum. In contrast, the lung tissue damage in the GIRI + GLP group was significantly improved compared to the GIRI group. This was evidenced by a reduction in the expression levels of HMGB-1 and IL-6 in both lymph and serum and an increase in HSP 70 and IL-10 levels. Additionally, organelle structure of AEC II was significantly improved in the GIRI + GLP group compared to the GIRI group.

Conclusions

GLP inhibits inflammation and cell apoptosis in GIRI-induced ALI by blocking the link between DAMPs and mononuclear phagocytes, reducing the severity of ALI.

Advances and Applications of Lung Organoids in the Research on Acute Respiratory Distress Syndrome (ARDS)

Acute Respiratory Distress Syndrome (ARDS) is a sudden onset of lung injury characterized by bilateral pulmonary edema, diffuse inflammation, hypoxemia, and a low P/F ratio. Epithelial injury and endothelial injury are notable in the development of ARDS, which is more severe under mechanical stress. This review explains the role of alveolar epithelial cells and endothelial cells under physiological and pathological conditions during the progression of ARDS. Mechanical injury not only causes ARDS but is also a side effect of ventilator-supporting treatment, which is difficult to model both in vitro and in vivo. The development of lung organoids has seen rapid progress in recent years, with numerous promising achievements made. Multiple types of cells and construction strategies are emerging in the lung organoid culture system. Additionally, the lung-on-a-chip system presents a new idea for simulating lung diseases. This review summarizes the basic features and critical problems in the research on ARDS, as well as the progress in lung organoids, particularly in the rapidly developing microfluidic system-based organoids. Overall, this review provides valuable insights into the three major factors that promote the progression of ARDS and how advances in lung organoid technology can be used to further understand ARDS.

Mesenchymal Stromal Cells Primed by Toll-like Receptors 3 and 4 Enhanced Anti-Inflammatory Effects against LPS-Induced Macrophages via Extracellular Vesicles

Although it has been suggested that toll-like receptor (TLR) 3 and TLR4 activation alters mesenchymal stromal cells (MSCs)' immunoregulatory function as anti- or pro-inflammatory phenotypes, we have previously confirmed that TLR4-primed hUCB-MSCs alleviate lung inflammation and tissue injury in an E. coli-induced acute lung injury (ALI) mouse model. Therefore, we hypothesized that strong stimulation of TLR3 or TLR4 prompts hUCB-MSCs to exhibit an anti-inflammatory phenotype mediated by extracellular vesicles (EVs). In this study, we compared the anti-inflammatory effect of TLR3-primed and TLR4-primed hUCB-MSCs against an LPS-induced ALI in vitro model by treating MSCs, MSC-derived conditioned medium (CM), and MSC-derived extracellular vesicles (EVs). LPS-induced rat primary alveolar macrophage and RAW 264.7 cells were treated with naïve, TLR3-, and TLR4-primed MSCs and their derived CM and EVs. Flow cytometry and ELISA were used to evaluate M1-M2 polarization of macrophages and pro-inflammatory cytokine levels, respectively. LPS-stimulated macrophages showed significantly increased pro-inflammatory cytokines compared to those of the normal control, and the percentage of M2 macrophage phenotype was predominantly low. In reducing the inflammatory cytokines and enhancing M2 polarization, TLR3- and TLR4-primed MSCs were significantly more effective than the naïve MSCs, and this finding was also observed with the treatment of MSC-derived CMs and EVs. No significant difference between the efficacy of TLR3- and TLR-primed MSCs was observed. Strong stimulation of TLR3- and TLR4-stimulated hUCB-MSCs significantly reduced pro-inflammatory cytokine secretion from LPS-induced macrophages and significantly enhanced the M2 polarization of macrophages. We further confirmed that TLR-primed MSC-derived EVs can exert anti-inflammatory and immunosuppressive effects alone comparable to MSC treatment. We hereby suggest that in the LPS-induced macrophage in vitro model, EVs derived from both TLR3 and TLR4-primed MSCs can be a therapeutic candidate by promoting the M2 phenotype.

Sustained induction of IP-10 by MRP8/14 via the IFNβ-IRF7 axis in macrophages exaggerates lung injury in endotoxemic mice

Background

As a damage-associated molecular pattern, the myeloid-related protein 8/14 (MRP8/14) heterodimer mediates various inflammatory diseases, such as sepsis. However, how MRP8/14 promotes lung injury by regulating the inflammatory response during endotoxemia remains largely unknown. This study aims at illuminating the pathological functions of MRP8/14 in endotoxemia.

Methods

An endotoxemic model was prepared with wild-type and myeloid cell-specific Mrp8 deletion (Mrp8ΔMC) mice for evaluating plasma cytokine levels. Lung injury was evaluated by hematoxylin and eosin (H&E) staining, injury scoring and wet-to-dry weight (W/D) ratio. The dynamic profile of interferon γ (IFNγ)-inducible protein 10 (IP-10) mRNA expression induced by macrophage MRP8/14 was determined by quantitative real-time polymerase chain reaction (qPCR). Immunoblotting was used to evaluate the increase in IP-10 level induced by activation of the JAK-STAT signaling pathway. Luciferase reporter assay was performed to detect the involvement of IRF7 in Ip-10 gene transcription. In vivo air pouch experiments were performed to determine the biological function of IP-10 induced by MRP8/14.

Results

Experiments with Mrp8ΔMC mice showed that MRP8/14 promoted the production of cytokines, including IP-10, in the bronchoalveolar lavage fluid (BALF) and lung injury in endotoxic mice. The result of qPCR showed sustained expression of Ip-10 mRNA in macrophages after treatment with MRP8/14 for 12 h. Neutralization experiments showed that the MRP8/14-induced Ip-10 expression in RAW264.7 cells was mediated by extracellular IFNβ. Western blotting with phosphorylation-specific antibodies showed that the JAK1/TYK2-STAT1 signaling pathway was activated in MRP8/14-treated RAW264.7 cells, leading to the upregulation of Ip-10 gene expression. IRF7 was further identified as a downstream regulator of the JAK-STAT pathway that mediated Ip-10 gene expression in macrophages treated with MRP8/14. In vivo air pouch experiments confirmed that the IFNβ-JAK1/TYK2-STAT1-IRF7 pathway was required for chemokine (C-X-C motif) receptor 3 (CXCR3)+ T lymphocyte migration, which promoted lung injury in the context of endotoxemia.

Conclusions

In summary, our study demonstrates that MRP8/14 induces sustained production of IP-10 via the IFNβ-JAK1/TYK2-STAT1-IRF7 pathway to attract CXCR3+ T lymphocytes into lung tissues and ultimately results in lung injury by an excessive inflammatory response in the context of endotoxemia.

Different TLR signaling pathways drive pathology in experimental cerebral malaria vs. malaria-driven liver and lung pathology

Malaria infection causes multiple organ-specific lethal pathologies, including cerebral malaria, and severe liver and lung pathologies by inducing strong inflammatory responses. Gene polymorphism studies suggest that TLR4 and TLR2 contribute to severe malaria, but the roles of these signaling molecules in malaria pathogenesis remain incompletely understood. We hypothesize that danger-associated molecular patterns produced in response to malaria activate TLR2 and TLR4 signaling and contribute to liver and lung pathologies. By using a mouse model of Plasmodium berghei NK65 infection, we show that the combined TLR2 and TLR4 signaling contributes to malaria liver and lung pathologies and mortality. Macrophages, neutrophils, natural killer cells, and T cells infiltrate to the livers and lungs of infected wild-type mice more than TLR2,4-/- mice. Additionally, endothelial barrier disruption, tissue necrosis, and hemorrhage were higher in the livers and lungs of infected wild-type mice than in those of TLR2,4-/- mice. Consistent with these results, the levels of chemokine production, chemokine receptor expression, and liver and lung pathologic markers were higher in infected wild-type mice than in TLR2,4-/- mice. In addition, the levels of HMGB1, a potent TLR2- and TLR4-activating danger-associated molecular pattern, were higher in livers and lungs of wild-type mice than TLR2,4-/- mice. Treatment with glycyrrhizin, an immunomodulatory agent known to inhibit HMGB1 activity, markedly reduced mortality in wild-type mice. These results suggest that TLR2 and TLR4 activation by HMGB1 and possibly other endogenously produced danger-associated molecular patterns contribute to malaria liver and lung injury via signaling mechanisms distinct from those involved in cerebral malaria pathogenesis.

PGE2 Produced by Exogenous MSCs Promotes Immunoregulation in ARDS Induced by Highly Pathogenic Influenza A through Activation of the Wnt-β-Catenin Signaling Pathway

Acute respiratory distress syndrome is an acute respiratory failure caused by cytokine storms; highly pathogenic influenza A virus infection can induce cytokine storms. The innate immune response is vital in this cytokine storm, acting by activating the transcription factor NF-κB. Tissue injury releases a danger-associated molecular pattern that provides positive feedback for NF-κB activation. Exogenous mesenchymal stem cells can also modulate immune responses by producing potent immunosuppressive substances, such as prostaglandin E2. Prostaglandin E2 is a critical mediator that regulates various physiological and pathological processes through autocrine or paracrine mechanisms. Activation of prostaglandin E2 results in the accumulation of unphosphorylated β-catenin in the cytoplasm, which subsequently reaches the nucleus to inhibit the transcription factor NF-κB. The inhibition of NF-κB by β-catenin is a mechanism that reduces inflammation.

Persisting Cryptococcus yeast species Vishniacozyma victoriae and Cryptococcus neoformans elicit unique airway inflammation in mice following repeated exposure

Background

Allergic airway disease (AAD) is a growing concern in industrialized nations and can be influenced by fungal exposures. Basidiomycota yeast species such as Cryptococcus neoformans are known to exacerbate allergic airway disease; however, recent indoor assessments have identified other Basidiomycota yeasts, including Vishniacozyma victoriae (syn. Cryptococcus victoriae), to be prevalent and potentially associated with asthma. Until now, the murine pulmonary immune response to repeated V. victoriae exposure was previously unexplored.

Objective

This study aimed to compare the immunological impact of repeated pulmonary exposure to Cryptococcus yeasts.

Methods

Mice were repeatedly exposed to an immunogenic dose of C. neoformans or V. victoriae via oropharyngeal aspiration. Bronchoalveolar lavage fluid (BALF) and lungs were collected to examine airway remodeling, inflammation, mucous production, cellular influx, and cytokine responses at 1 day and 21 days post final exposure. The responses to C. neoformans and V. victoriae were analyzed and compared.

Results

Following repeated exposure, both C. neoformans and V. victoriae cells were still detectable in the lungs 21 days post final exposure. Repeated C. neoformans exposure initiated myeloid and lymphoid cellular infiltration into the lung that worsened over time, as well as an IL-4 and IL-5 response compared to PBS-exposed controls. In contrast, repeated V. victoriae exposure induced a strong CD4+ T cell-driven lymphoid response that started to resolve by 21 days post final exposure.

Discussion

C. neoformans remained in the lungs and exacerbated the pulmonary immune responses as expected following repeated exposure. The persistence of V. victoriae in the lung and strong lymphoid response following repeated exposure were unexpected given its lack of reported involvement in AAD. Given the abundance in indoor environments and industrial utilization of V. victoriae, these results highlight the importance to investigate the impact of frequently detected fungal organisms on the pulmonary response following inhalational exposure. Moreover, it is important to continue to address the knowledge gap involving Basidiomycota yeasts and their impact on AAD.

NF-κB mediated regulation of tumor cell proliferation in hypoxic microenvironment

Hypoxia is caused by a cancer-promoting milieu characterized by persistent inflammation. NF-κB and HIF-1α are critical participants in this transition. Tumor development and maintenance are aided by NF-κB, while cellular proliferation and adaptability to angiogenic signals are aided by HIF-1α. Prolyl hydroxylase-2 (PHD-2) has been hypothesized to be the key oxygen-dependent regulator of HIF-1α and NF-transcriptional B's activity. Without low oxygen levels, HIF-1α is degraded by the proteasome in a process dependent on oxygen and 2-oxoglutarate. As opposed to the normal NF-κB activation route, where NF-κB is deactivated by PHD-2-mediated hydroxylation of IKK, this method actually activates NF-κB. HIF-1α is protected from degradation by proteasomes in hypoxic cells, where it then activates transcription factors involved in cellular metastasis and angiogenesis. The Pasteur phenomenon causes lactate to build up inside the hypoxic cells. As part of a process known as lactate shuttle, MCT-1 and MCT-4 cells help deliver lactate from the blood to neighboring, non-hypoxic tumour cells. Non-hypoxic tumour cells use lactate, which is converted to pyruvate, as fuel for oxidative phosphorylation. OXOPHOS cancer cells are characterized by a metabolic switch from glucose-facilitated oxidative phosphorylation to lactate-facilitated oxidative phosphorylation. Although PHD-2 was found in OXOPHOS cells. There is no clear explanation for the presence of NF-kappa B activity. The accumulation of the competitive inhibitor of 2-oxo-glutarate, pyruvate, in non-hypoxic tumour cells is well established. So, we conclude that PHD-2 is inactive in non-hypoxic tumour cells due to pyruvate-mediated competitive suppression of 2-oxo-glutarate. This results in canonical activation of NF-κB. In non-hypoxic tumour cells, 2-oxoglutarate serves as a limiting factor, rendering PHD-2 inactive. However, FIH prevents HIF-1α from engaging in its transcriptional actions. Using the existing scientific literature, we conclude in this study that NF-κB is the major regulator of tumour cell growth and proliferation via pyruvate-mediated competitive inhibition of PHD-2.

Immunotherapy strategies and prospects for acute lung injury: Focus on immune cells and cytokines

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a disastrous condition, which can be caused by a wide range of diseases, such as pneumonia, sepsis, traumas, and the most recent, COVID-19. Even though we have gained an improved understanding of acute lung injury/acute respiratory distress syndrome pathogenesis and treatment mechanism, there is still no effective treatment for acute lung injury/acute respiratory distress syndrome, which is partly responsible for the unacceptable mortality rate. In the pathogenesis of acute lung injury, the inflammatory storm is the main pathological feature. More and more evidences show that immune cells and cytokines secreted by immune cells play an irreplaceable role in the pathogenesis of acute lung injury. Therefore, here we mainly reviewed the role of various immune cells in acute lung injury from the perspective of immunotherapy, and elaborated the crosstalk of immune cells and cytokines, aiming to provide novel ideas and targets for the treatment of acute lung injury.

Regulation of CD18 stability by SIGIRR-modulated ubiquitination: new insights into the relationship between innate immune response and acute lung injury

Inappropriate accumulation of alveolar macrophages (AMs) and subsequent excessive production of immune responses play critical roles in the pathogenesis of acute lung injury (ALI), but the core negative regulators governing innate signalling in AMs are ill defined. We have previously shown that single immunoglobin IL-1 receptor-related protein (SIGIRR), a negative regulator of IL-1 receptor and Toll-like receptor signalling, inhibits lipopolysaccharide (LPS)-induced inflammatory responses in AMs. To address the biological relevance of SIGIRR in vivo, we generated a murine ALI model via intratracheal instillation of LPS. Intriguingly, SIGIRR expression was observed to be decreased in resident and recruited macrophages during ALI. This decrease was associated with parallel induction in CD18 protein levels in LPS-challenged lung tissues. Through intranasal injection of SIGIRR lentiviral particles studies, we showed that the overexpression of SIGIRR attenuated recruitment of macrophages and neutrophils, decreased production of inflammatory cytokines and ameliorated pathological changes in lungs. Whilst exploring the basis for this phenotype, SIGIRR was found to be coexpressed with CD18 in AMs, and SIGIRR potentiated the instability of CD18 protein via enhancement of its ubiquitination and proteasome degradation. Conversely, by using CD18^-/- mice, we further observed that CD18 deletion completely abolished the therapeutic effects of overexpression of SIGIRR on LPS-induced ALI. Mover, overexpression of CD18 in AMs promoted adhesion to ECM components, enhanced TLR4-mediated inflammasome activation and thereby potentiated IL-1β production. These data collectively identify SIGIRR/CD18 as a key negative regulatory circuit maintaining innate immune homeostasis in AMs along the pathogenesis of ALI.

MSCs interaction with the host lung microenvironment: An overlooked aspect?

Mesenchymal stromal cells (MSCs) were identified more than 50 years ago, and research advances have promoted the translation of pre-clinical studies into clinical settings in several diseases. However, we are only starting to uncover the local factors that regulate cell phenotype, cell function, and cell viability across tissues following administration in different diseases. Advances in pre-clinical and translational studies suggest that the host environment, especially inflammatory active environments, plays a significant role in directing the infused MSCs towards different phenotypes with different functions. This can significantly effect their therapeutic efficacy. One way to study this interaction between the host environment and the infused cells is to expose MSCs ex vivo to patient samples such as serum or bronchoalveolar lavage fluid. Using this approach, it has been demonstrated that MSCs are very sensitive to different host factors such as pathogens, inflammatory cytokines, and extra cellular matrix properties. By understanding how different local host factors effect MSC function it will open possibilities to select specific patient sub-groups that are more likely to respond to this type of treatment and will also open possibilities to prime the local host environment to increase viability and to enrich for a specific MSC phenotype. Here, we aim to review the current understanding of the interaction of MSCs with the host microenvironment. To narrow the scope of this mini review, the focus will be on the pulmonary microenvironment, with a specific focus on the diseases acute respiratory distress syndrome (ARDS) and cystic fibrosis (CF).

Lung injury following cardiopulmonary bypass: a clinical update

INTRODUCTION

Cardiopulmonary bypass (CPB) is an integral component of cardiac surgery; however, one of its most critical complications is acute lung injury induced by multiple factors including systemic inflammatory response.

AREAS COVERED

The objective of this review is to investigate the multiple factors that can lead to CPB-induced lung injury. These include contact of blood components with the artificial surface of the CPB circuit, local and systemic inflammatory response syndrome (SIRS), lung ischemia/re-perfusion injury, arrest of ventilation, and circulating endotoxins. We also focus on possible interventions to curtail the negative impact of CPB, such as off-pump surgery, impregnation of the circuit with less biologically active substances, leukocyte depletion filters and ultrafiltration, and pharmacological agents such as steroids and aprotinin.

EXPERT OPINION

Although many aspects of CPB are proposed to contribute to lung injury, its overall role is still not clear. Multiple interventions have been introduced to reduce the risk of pulmonary dysfunction, with many of these interventions having shown promising results, significantly attenuating inflammatory mediators and improving post-operative outcome. However, since lung injury is multifactorial and affected by inextricably linked components, multiple interventions tackling each of them is required.

Acute respiratory distress syndrome: causes, pathophysiology, and phenotypes

Acute respiratory distress syndrome (ARDS) is a common clinical syndrome of acute respiratory failure as a result of diffuse lung inflammation and oedema. ARDS can be precipitated by a variety of causes. The pathophysiology of ARDS is complex and involves the activation and dysregulation of multiple overlapping and interacting pathways of injury, inflammation, and coagulation, both in the lung and systemically. Mechanical ventilation can contribute to a cycle of lung injury and inflammation. Resolution of inflammation is a coordinated process that requires downregulation of proinflammatory pathways and upregulation of anti-inflammatory pathways. The heterogeneity of the clinical syndrome, along with its biology, physiology, and radiology, has increasingly been recognised and incorporated into identification of phenotypes. A precision-medicine approach that improves the identification of more homogeneous ARDS phenotypes should lead to an improved understanding of its pathophysiological mechanisms and how they differ from patient to patient.

SARS-CoV-2 pneumonia and bacterial pneumonia patients differ in a second hit immune response model

Secondary infections have been shown to complicate the clinical course and worsen the outcome of critically ill patients. Severe Coronavirus Disease 2019 (COVID-19) may be accompanied by a pronounced cytokine release, and immune competence of these patients towards most pathogenic antigens remains uncompromised early in the disease. Patients with bacterial sepsis also exhibit excessive cytokine release with systemic hyper-inflammation, however, typically followed by an anti-inflammatory phase, causing immune paralysis. In a second hit immune response model, leukocyte activation capacity of severely ill patients with pneumonia caused by SARS-CoV-2 or by bacteria were compared upon ICU admission and at days 4 and 7 of the ICU stay. Blood cell count and release of the pro-inflammatory cytokines IL-2, IFNγ and TNF were assessed after whole-blood incubation with the potent immune stimulus pokeweed mitogen (PWM). For comparison, patients with bacterial sepsis not originating from pneumonia, and healthy volunteers were included. Lymphopenia and granulocytosis were less pronounced in COVID-19 patients compared to bacterial sepsis patients. After PWM stimulation, COVID-19 patients showed a reduced release of IFNγ, while IL-2 levels were found similar and TNF levels were increased compared to healthy controls. Interestingly, concentrations of all three cytokines were significantly higher in samples from COVID-19 patients compared to samples from patients with bacterial infection. This fundamental difference in immune competence during a second hit between COVID-19 and sepsis patients may have implications for the selection of immune suppressive or enhancing therapies in personalized medicine.

COVID-19 and Fungal Infections: A Double Debacle

Fungal infections remain hardly treatable because of unstandardized diagnostic tests, limited antifungal armamentarium, and more specifically, potential toxic interactions between antifungals and immunosuppressants used during anti-inflammatory therapies, such as those set up in critically ill COVID-19 patients. Taking into account pre-existing difficulties in treating vulnerable COVID-19 patients, any co-occurrence of infectious diseases like fungal infections constitutes a double debacle for patients, healthcare experts, and the public economy. Since the first appearance of SARS-CoV-2, a significant rise in threatening fungal co-infections in COVID-19 patients has been testified in the scientific literature. Better management of fungal infections in COVID-19 patients is, therefore, a priority and requires highlighting common risk factors, relationships with immunosuppression, as well as challenges in fungal diagnosis and treatment. The present review attempts to highlight these aspects in the three most identified causative agents of fungal co-infections in COVID-19 patients: Aspergillus, Candida, and Mucorales species.

Inflammation resolution in environmental pulmonary health and morbidity

Inflammation and resolution are dynamic processes comprised of inflammatory activation and neutrophil influx, followed by mediator catabolism and efferocytosis. These critical pathways ensure a return to homeostasis and promote repair. Over the past decade research has shown that diverse mediators play a role in the active process of resolution. Specialized pro-resolving mediators (SPMs), biosynthesized from fatty acids, are released during inflammation to facilitate resolution and are deficient in a variety of lung disorders. Failed resolution results in remodeling and cellular deposition through pro-fibrotic myofibroblast expansion that irreversibly narrows the airways and worsens lung function. Recent studies indicate environmental exposures may perturb and deregulate critical resolution pathways. Environmental xenobiotics induce lung inflammation and generate reactive metabolites that promote oxidative stress, injuring the respiratory mucosa and impairing gas-exchange. This warrants recognition of xenobiotic associated molecular patterns (XAMPs) as new signals in the field of inflammation biology, as many environmental chemicals generate free radicals capable of initiating the inflammatory response. Recent studies suggest that unresolved, persistent inflammation impacts both resolution pathways and endogenous regulatory mediators, compromising lung function, which over time can progress to chronic lung disease. Chronic ozone (O3) exposure overwhelms successful resolution, and in susceptible individuals promotes asthma onset. The industrial contaminant cadmium (Cd) bioaccumulates in the lung to impair resolution, and recurrent inflammation can result in chronic obstructive pulmonary disease (COPD). Persistent particulate matter (PM) exposure increases systemic cardiopulmonary inflammation, which reduces lung function and can exacerbate asthma, COPD, and idiopathic pulmonary fibrosis (IPF). While recurrent inflammation underlies environmentally induced pulmonary morbidity and may drive the disease process, our understanding of inflammation resolution in this context is limited. This review aims to explore inflammation resolution biology and its role in chronic environmental lung disease(s).

Overview of COVID-19-Associated Invasive Fungal Infection

Purpose of Review

Invasive fungal infections are a complication of COVID-19 disease. This article reviews literature characterizing invasive fungal infections associated with COVID-19.

Recent Findings

Multiple invasive fungal infections including aspergillosis, candidiasis, pneumocystosis, other non-Aspergillus molds, and endemic fungi have been reported in patients with COVID-19. Risk factors for COVID-19-associated fungal disease include underlying lung disease, diabetes, steroid or immunomodulator use, leukopenia, and malignancy. COVID-19-associated pulmonary aspergillosis (CAPA) and COVID-19-associated mucormycosis (CAM) are the most common fungal infections described. However, there is variability in the reported incidences related to use of differing diagnostic algorithms.

Summary

Fungal pathogens are important cause of infection in patients with COVID-19, and the diagnostic strategies continue to evolve. Mortality in these patients is increased, and providers should operate with a high index of suspicion. Further studies will be required to elucidate the associations and pathogenesis of these diseases and best management and prevention strategies.

Pathophysiological Role of Vimentin Intermediate Filaments in Lung Diseases

Vimentin intermediate filaments, a type III intermediate filament, are among the most widely studied IFs and are found abundantly in mesenchymal cells. Vimentin intermediate filaments localize primarily in the cytoplasm but can also be found on the cell surface and extracellular space. The cytoplasmic vimentin is well-recognized for its role in providing mechanical strength and regulating cell migration, adhesion, and division. The post-translationally modified forms of Vimentin intermediate filaments have several implications in host-pathogen interactions, cancers, and non-malignant lung diseases. This review will analyze the role of vimentin beyond just the epithelial to mesenchymal transition (EMT) marker highlighting its role as a regulator of host-pathogen interactions and signaling pathways for the pathophysiology of various lung diseases. In addition, we will also examine the clinically relevant anti-vimentin compounds and antibodies that could potentially interfere with the pathogenic role of Vimentin intermediate filaments in lung disease.

Fungal Infections Other Than Invasive Aspergillosis in COVID-19 Patients

Invasive fungal disease (IFD) associated with Coronavirus Disease 2019 (COVID-19) has focussed predominantly on invasive pulmonary aspergillosis. However, increasingly emergent are non-Aspergillus fungal infections including candidiasis, mucormycosis, pneumocystosis, cryptococcosis, and endemic mycoses. These infections are associated with poor outcomes, and their management is challenged by delayed diagnosis due to similarities of presentation to aspergillosis or to non-specific features in already critically ill patients. There has been a variability in the incidence of different IFDs often related to heterogeneity in patient populations, diagnostic protocols, and definitions used to classify IFD. Here, we summarise and address knowledge gaps related to the epidemiology, risks, diagnosis, and management of COVID-19-associated fungal infections other than aspergillosis.

COVID-19 associated mucormycosis: evolving technologies for early and rapid diagnosis

The post-coronavirus disease (COVID-19) mucormycosis is a deadly addition to the pandemic spectrum. Although it’s a rare, aggressive, and opportunistic disease, the associated morbidity and mortality are significant. The complex interplay of factors aggravating CAM is uncontrolled diabetes, irrational and excessive use of antibiotics, steroids, and an impaired immune system. Recently, India has been witnessing a rapid surge in the cases of coronavirus disease-associated mucormycosis (CAM), since the second wave of COVID-19. The devastating and lethal implications of CAM had now become a matter of global attention. A delayed diagnosis is often associated with a poor prognosis. Therefore, the rapid and early diagnosis of infection would be life-saving. Prevention and effective management of mucormycosis depend upon its early and accurate diagnosis followed by a multimodal therapeutic approach. The current review summarizes an array of detection methods and highlights certain evolving technologies for early and rapid diagnosis of CAM. Furthermore, several potential management strategies have also been discussed, which would aid in tackling the neglected yet fatal crisis of mucormycosis associated with COVID-19.

Innate Immunity as an Executor of the Programmed Death of Individual Organisms for the Benefit of the Entire Population

In humans, over-activation of innate immunity in response to viral or bacterial infections often causes severe illness and death. Furthermore, similar mechanisms related to innate immunity can cause pathogenesis and death in sepsis, massive trauma (including surgery and burns), ischemia/reperfusion, some toxic lesions, and viral infections including COVID-19. Based on the reviewed observations, we suggest that such severe outcomes may be manifestations of a controlled suicidal strategy protecting the entire population from the spread of pathogens and from dangerous pathologies rather than an aberrant hyperstimulation of defense responses. We argue that innate immunity may be involved in the implementation of an altruistic programmed death of an organism aimed at increasing the well-being of the whole community. We discuss possible ways to suppress this atavistic program by interfering with innate immunity and suggest that combating this program should be a major goal of future medicine.

Citrullinated Histone H3 Mediates Sepsis-Induced Lung Injury Through Activating Caspase-1 Dependent Inflammasome Pathway

Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to infection that often results in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). An emerging mechanism of sepsis-induced ARDS involves neutrophils/macrophages undergoing cell death, releasing nuclear histones to cause tissue damage that exacerbates pulmonary injury. While published studies focus on unmodified histones, little is known about the role of citrullinated histone H3 (CitH3) in the pathogenesis of sepsis and ALI. In this study, we found that levels of CitH3 were elevated in the patients with sepsis-induced ARDS and correlated to PaO2/FiO2 in septic patients. Systematic administration of CitH3 peptide in mice provoked Caspase-1 activation in the lung tissue and caused ALI. Neutralization of CitH3 with monoclonal antibody improved survival and attenuated ALI in a mouse sepsis model. Furthermore, we demonstrated that CitH3 induces ALI through activating Caspase-1 dependent inflammasome in bone marrow derived macrophages and bone marrow derived dendritic cells. Our study suggests that CitH3 is an important mediator of inflammation and mortality during sepsis-induced ALI.

The mechanism of nicotinamide on reducing acute lung injury by inhibiting MAPK and NF-κB signal pathway

Background

Acute lung injury is an important factor that leads to the death of patients with pneumonia. Previous studies have shown that nicotinamide (NAM) plays a role in reducing cell damage, so this study explored the mechanism by which NAM functions in acute lung injury.

Methods

We explored the mechanism by which NAM affects acute lung injury in vivo and in vitro by qRT-PCR, western blotting and ELISA.

Results

The results showed that NAM could significantly reduce lung injury and proinflammatory mediator accumulation. Further mechanistic studies showed that NAM could significantly inhibit the MAPK and AKT/NF-κB signaling pathways.

Conclusion

These results suggested that NAM may reduce the release of proinflammatory mediators by inhibiting the MAPK and AKT/NF-κB signaling pathways and ultimately alleviate lung injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00376-2.

Risk Factors for Fungal Co-Infections in Critically Ill COVID-19 Patients, with a Focus on Immunosuppressants

Severe cases of coronavirus disease 2019 (COVID-19) managed in the intensive care unit are prone to complications, including secondary infections with opportunistic fungal pathogens. Systemic fungal co-infections in hospitalized COVID-19 patients may exacerbate COVID-19 disease severity, hamper treatment effectiveness and increase mortality. Here, we reiterate the role of fungal co-infections in exacerbating COVID-19 disease severity as well as highlight emerging trends related to fungal disease burden in COVID-19 patients. Furthermore, we provide perspectives on the risk factors for fungal co-infections in hospitalized COVID-19 patients and highlight the potential role of prolonged immunomodulatory treatments in driving fungal co-infections, including COVID-19-associated pulmonary aspergillosis (CAPA), COVID-19-associated candidiasis (CAC) and mucormycosis. We reiterate the need for early diagnosis of suspected COVID-19-associated systemic mycoses in the hospital setting.

Targeting TLR4 Signaling to Blunt Viral-Mediated Acute Lung Injury

Respiratory viral infections have been a long-standing global burden ranging from seasonal recurrences to the unexpected pandemics. The yearly hospitalizations from seasonal viruses such as influenza can fluctuate greatly depending on the circulating strain(s) and the congruency with the predicted strains used for the yearly vaccine formulation, which often are not predicted accurately. While antiviral agents are available against influenza, efficacy is limited due to a temporal disconnect between the time of infection and symptom development and viral resistance. Uncontrolled, influenza infections can lead to a severe inflammatory response initiated by pathogen-associated molecular patterns (PAMPs) or host-derived danger-associated molecular patterns (DAMPs) that ultimately signal through pattern recognition receptors (PRRs). Overall, these pathogen-host interactions result in a local cytokine storm leading to acute lung injury (ALI) or the more severe acute respiratory distress syndrome (ARDS) with concomitant systemic involvement and more severe, life threatening consequences. In addition to traditional antiviral treatments, blocking the host's innate immune response may provide a more viable approach to combat these infectious pathogens. The SARS-CoV-2 pandemic illustrates a critical need for novel treatments to counteract the ALI and ARDS that has caused the deaths of millions worldwide. This review will examine how antagonizing TLR4 signaling has been effective experimentally in ameliorating ALI and lethal infection in challenge models triggered not only by influenza, but also by other ALI-inducing viruses.

Role of DAMPs in respiratory virus-induced acute respiratory distress syndrome-with a preliminary reference to SARS-CoV-2 pneumonia

When surveying the current literature on COVID-19, the "cytokine storm" is considered to be pathogenetically involved in its severe outcomes such as acute respiratory distress syndrome, systemic inflammatory response syndrome, and eventually multiple organ failure. In this review, the similar role of DAMPs is addressed, that is, of those molecules, which operate upstream of the inflammatory pathway by activating those cells, which ultimately release the cytokines. Given the still limited reports on their role in COVID-19, the emerging topic is extended to respiratory viral infections with focus on influenza. At first, a brief introduction is given on the function of various classes of activating DAMPs and counterbalancing suppressing DAMPs (SAMPs) in initiating controlled inflammation-promoting and inflammation-resolving defense responses upon infectious and sterile insults. It is stressed that the excessive emission of DAMPs upon severe injury uncovers their fateful property in triggering dysregulated life-threatening hyperinflammatory responses. Such a scenario may happen when the viral load is too high, for example, in the respiratory tract, "forcing" many virus-infected host cells to decide to commit "suicidal" regulated cell death (e.g., necroptosis, pyroptosis) associated with release of large amounts of DAMPs: an important topic of this review. Ironically, although the aim of this "suicidal" cell death is to save and restore organismal homeostasis, the intrinsic release of excessive amounts of DAMPs leads to those dysregulated hyperinflammatory responses-as typically involved in the pathogenesis of acute respiratory distress syndrome and systemic inflammatory response syndrome in respiratory viral infections. Consequently, as briefly outlined in this review, these molecules can be considered valuable diagnostic and prognostic biomarkers to monitor and evaluate the course of the viral disorder, in particular, to grasp the eventual transition precociously from a controlled defense response as observed in mild/moderate cases to a dysregulated life-threatening hyperinflammatory response as seen, for example, in severe/fatal COVID-19. Moreover, the pathogenetic involvement of these molecules qualifies them as relevant future therapeutic targets to prevent severe/ fatal outcomes. Finally, a theory is presented proposing that the superimposition of coronavirus-induced DAMPs with non-virus-induced DAMPs from other origins such as air pollution or high age may contribute to severe and fatal courses of coronavirus pneumonia.

The Preventive Effects of Lactobacillus casei on Acute Lung Injury Induced by Lipopolysaccharide

Lactobacillus has been reported to inhibit acute lung injury (ALI). However, the molecular mechanism of Lactobacillus casei (L. casei) in preventing ALI has not been identified, so we investigated whether L. casei pretreatment could inhibit the activation of TLR4/MyD88/NF-κB signaling pathway following ALI. ALI model was established by intraperitoneal injection of 2 mg/kg lipopolysaccharide (LPS) to female BALB/c mice. In L. casei LC2W group, mice were intragastrically administrated L. casei LC2W for a week, before the ALI modeling. The serum of normal BALB/c mice after intragastric administration of L. casei LC2W was used for in vitro cell assays. The serum was pre-incubated with mouse macrophage cell line (RAW264.7) and human lung cell line (HLF-A), then LPS was added to co-incubate. Compared with ALI model group, L. casei LC2W pretreatment significantly reduced lung pathological damage, the number of neutrophils and total cells in bronchoalveolar lavage fluid. Besides, L. casei LC2W pretreatment could significantly reverse the abnormal expression of ICAM-1, IL-6, TNF-α and IL-10 in lung tissue and serum, plus, L. casei LC2W significantly reduced the phosphorylation levels of IRAK-1 and NF-κB p65. In vitro, the serum decreased the up-regulation of IL-6 and TNF-α in cell lines induced by LPS. In conclusion, L. casei LC2W intragastric administration pretreatment could significantly improve LPS-induced ALI in mice, probably through circulation to reach the lungs so as to inhibit the inflammatory response induced by activation of TLR4/MyD88/NF-κB signaling pathway.

Changes of Damage Associated Molecular Patterns in COVID-19 Patients

Background

The development of severe coronavirus disease 2019 (COVID-19) is associated with systemic hyperinflammation, which drives multi-organ failure and death. Disease deterioration tends to occur when the virus is receding; however, whether other factors besides viral products are involved in the inflammatory cascade remains unclear.

Methods

Twenty-eight COVID-19 patients with laboratory-confirmed SARS-CoV-2 infection hospitalized at the Fifth Medical Center of Chinese PLA General Hospital from January 23 to February 20, 2020 and nine healthy donors during the same period were recruited in the study. COVID-19 patients were grouped as mild, moderate, severe based on disease severity. Plasma damage-associated molecular patterns (DAMPs), including high mobility group box 1 (HMGB1), calprotectin (S100A8/A9), surfactant protein A (SP-A), cold-inducible RNA-binding protein (CIRBP), and Histone H4 were detected by ELISA assay, and analyzed in combination with clinical data. Plasma cytokines, chemokines and lymphocytes were determined by flow cytometry.

Results

Plasma levels of HMGB1 (38292.3 ± 4564.4 vs. 32686.3 ± 3678.1, P = 0.002), S100A8/A9 (1490.8 ± 819.3 vs. 742.2 ± 300.8, P = 0.015), and SP-A (6713.6 ± 1708.7 vs. 5296.3 ± 1240.4, P = 0.048) were increased in COVID-19 patients compared to healthy donors, while CIRBP (57.4 ± 30.7 vs. 111.9 ± 55.2, P = 0.004) levels decreased. Five DAMPs did not vary among mild, moderate, and severe patients. Moreover, SP-A levels correlated positively with inflammatory cytokines and negatively with time elapsed after symptom onset, whereas CIRBP showed an opposite pattern.

Conclusions

These findings suggest SP-A may involve in the inflammation of COVID-19, while CIRBP likely plays a protective role. Therefore, DAMPs represent a potential target in the prevention or treatment of COVID-19.

The Immune System in Transfusion-Related Acute Lung Injury Prevention and Therapy: Update and Perspective

As an initiator of respiratory distress, transfusion-related acute lung injury (TRALI) is regarded as one of the rare complications associated with transfusion medicine. However, to date, the pathogenesis of TRALI is still unclear, and specific therapies are unavailable. Understanding the mechanisms of TRALI may promote the design of preventive and therapeutic strategies. The immune system plays vital roles in reproduction, development and homeostasis. Sterile tissue damage, such as physical trauma, ischemia, or reperfusion injury, induces an inflammatory reaction that results in wound healing and regenerative mechanisms. In other words, in addition to protecting against pathogens, the immune response may be strongly associated with TRALI prevention and treatment through a variety of immunomodulatory strategies to inhibit excessive immune system activation. Immunotherapy based on immune cells or immunological targets may eradicate complications. For example, IL-10 therapy is a promising therapeutic strategy to explore further. This review will focus on ultramodern advances in our understanding of the potential role of the immune system in TRALI prevention and treatment.

COVID-19 Impairs Immune Response to Candida albicans

Infection with SARS-CoV-2 can lead to Coronavirus disease-2019 (COVID-19) and result in severe acute respiratory distress syndrome (ARDS). Recent reports indicate an increased rate of fungal coinfections during COVID-19. With incomplete understanding of the pathogenesis and without any causative therapy available, secondary infections may be detrimental to the prognosis. We monitored 11 COVID-19 patients with ARDS for their immune phenotype, plasma cytokines, and clinical parameters on the day of ICU admission and on day 4 and day 7 of their ICU stay. Whole blood stimulation assays with lipopolysaccharide (LPS), heat-killed Listeria monocytogenes (HKLM), Aspergillus fumigatus, and Candida albicans were used to mimic secondary infections, and changes in immune phenotype and cytokine release were assessed. COVID-19 patients displayed an immune phenotype characterized by increased HLA-DR+CD38+ and PD-1+ CD4+ and CD8+ T cells, and elevated CD8+CD244+ lymphocytes, compared to healthy controls. Monocyte activation markers and cytokines IL-6, IL-8, TNF, IL-10, and sIL2Rα were elevated, corresponding to monocyte activation syndrome, while IL-1β levels were low. LPS, HKLM and Aspergillus fumigatus antigen stimulation provoked an immune response that did not differ between COVID-19 patients and healthy controls, while COVID-19 patients showed an attenuated monocyte CD80 upregulation and abrogated release of IL-6, TNF, IL-1α, and IL-1β toward Candida albicans. This study adds further detail to the characterization of the immune response in critically ill COVID-19 patients and hints at an increased susceptibility for Candida albicans infection.

Innate Receptor Activation Patterns Involving TLR and NLR Synergisms in COVID-19, ALI/ARDS and Sepsis Cytokine Storms: A Review and Model Making Novel Predictions and Therapeutic Suggestions

Severe COVID-19 is characterized by a “cytokine storm”, the mechanism of which is not yet understood. I propose that cytokine storms result from synergistic interactions among Toll-like receptors (TLR) and nucleotide-binding oligomerization domain-like receptors (NLR) due to combined infections of SARS-CoV-2 with other microbes, mainly bacterial and fungal. This proposition is based on eight linked types of evidence and their logical connections. (1) Severe cases of COVID-19 differ from healthy controls and mild COVID-19 patients in exhibiting increased TLR4, TLR7, TLR9 and NLRP3 activity. (2) SARS-CoV-2 and related coronaviruses activate TLR3, TLR7, RIG1 and NLRP3. (3) SARS-CoV-2 cannot, therefore, account for the innate receptor activation pattern (IRAP) found in severe COVID-19 patients. (4) Severe COVID-19 also differs from its mild form in being characterized by bacterial and fungal infections. (5) Respiratory bacterial and fungal infections activate TLR2, TLR4, TLR9 and NLRP3. (6) A combination of SARS-CoV-2 with bacterial/fungal coinfections accounts for the IRAP found in severe COVID-19 and why it differs from mild cases. (7) Notably, TLR7 (viral) and TLR4 (bacterial/fungal) synergize, TLR9 and TLR4 (both bacterial/fungal) synergize and TLR2 and TLR4 (both bacterial/fungal) synergize with NLRP3 (viral and bacterial). (8) Thus, a SARS-CoV-2-bacterium/fungus coinfection produces synergistic innate activation, resulting in the hyperinflammation characteristic of a cytokine storm. Unique clinical, experimental and therapeutic predictions (such as why melatonin is effective in treating COVID-19) are discussed, and broader implications are outlined for understanding why other syndromes such as acute lung injury, acute respiratory distress syndrome and sepsis display varied cytokine storm symptoms.

Cysteinyl leukotriene D4 (LTD4) promotes airway epithelial cell inflammation and remodelling

OBJECTIVE

Cysteinyl leukotrienes (CysLTs), a group of inflammatory lipid mediators, are found elevated in obese-asthmatic patients. Leukotriene D4 (LTD4), a representative CysLT, is implicated in promoting lung inflammation and remodelling in allergic asthma, but its role in non-allergic asthma, especially in obese-asthmatic patients, is not known. Here, using primary human small airway epithelial cells (SAECs) we have investigated the mechanism of LTD4-induced inflammation and remodelling and assessed high proneness of obese mice to develop asthma upon challenge with allergen ovalbumin (OVA).

METHODS

Primary human small airway epithelial cells (SAECs) were stimulated with different concentrations of LTD4 for different time intervals and various inflammatory markers were measured through cytokine array, membrane-based ELISA and Western blotting. An air-liquid interface (ALI) model of SAECs was used to study the effects of LTD4-induced remodelling in SAECs using Western blotting, H&E staining and PAS staining. Further, OVA-based murine model was used to examine the propensity of high-fat diet (HFD)-fed obese mice to develop asthma symptoms by studying the infiltration of inflammatory cells (assessed by bronchioalveolar lavage (BAL) cytology) and airway remodelling (assessed by histopathology) upon allergen exposure.

RESULTS

The human primary small airway epithelial cells (SAECs) treated with LTD4 showed significant alterations in the levels of inflammatory markers such as GM-CSF, TNF-α, IL-1β, EGF and eotaxin in dose- and time-dependent manner. Further, LTD4 enhanced the activation of inflammasomes as evidenced by increased levels of NALP3, cleaved caspase-1 and IL-1β. LTD4 also enhanced inflammation by increasing the expression of COX-2 in SAECs. The airway remodelling markers Vimentin and Muc5AC were found elevated in ALI culture of SAECs when stimulated with LTD4, as it also increased TGF-β levels and activation of Smad2/3 phosphorylation in SAECs. Last, sensitization and challenge of HFD-fed obese mice with OVA showed increased infiltration of inflammatory cells in BAL and enhanced levels of remodeling phenotypes like loss of cilia, mucus cell metaplasia and collagen deposition in mice lung tissues.

CONCLUSION

The results suggest that LTD4 could induce inflammatory response in human airway epithelial cell by activating NALP3 inflammasome. LTD4 could further promote airway epithelial cells' remodelling through TGF-β/smad2/3-mediated pathway. Our in vivo results suggested that obesity predisposed the OVA challenged mice to develop lung inflammation and remodelling akin to asthma-like phenotypes during obesity.

Autophagy alleviates mitochondrial DAMP-induced acute lung injury by inhibiting NLRP3 inflammasome

AIM

Acute lung injury (ALI) is characterized by alveolar macrophage overactivation and uncontrolled pulmonary inflammation. Mitochondrial damage-associated molecular patterns (MTDs), one type of damage-associated molecular patterns (DAMPs) released from ruptured mitochondrial, can induce inflammation which participates in the pathogenesis of ALI. Despite the critical role of autophagy in inflammatory response, little is known about its function in MTDs-induced ALI. Herein we have studied how autophagy attenuates MTDs-induced ALI in vitro and in vivo.

MAIN METHODS

Exogenous MTDs were injected into mice through tail vein injection or directly treated with cultured alveolar macrophage cell lines to construct MTDs-induced ALI models. Rapamycin and 3-MA were used to regulate autophagy in vivo and in vitro. The expressions of Caspase-1, IL-1β, and their precursor were measured. Inhibition the activation of NLRP3 inflammasome to discover the candidate targets and potential molecular pathways involved in autophagy mitigating the MTDs-induced ALI.

KEY FINDINGS

After treatment with MTDs the expression levels of inflammatory cytokines and NLRP3 inflammasome-associated proteins were gradually increased in vitro and in vivo. Most importantly, with autophagy enhanced by rapamycin, all the secretion of inflammation cytokine, the level of lung injury, and the expression level of NLRP3 inflammasome-associated proteins were greatly decreased in MTDs-induced mouse model. MTDs-induced inflammation and lung injury were alleviated by autophagy enhancement. Autophagy can function as an effective way to alleviate inflammation in MTDs-induced ALI by inhibiting NLRP3 inflammasome and may represent a therapeutic target in modulating MTDs-induced inflammatory response.

Bone marrow-derived mesenchymal stem cells attenuate pulmonary inflammation and lung damage caused by highly pathogenic avian influenza A/H5N1 virus in BALB/c mice

BACKGROUND

The highly pathogenic avian influenza A/H5N1 virus is one of the causative agents of acute lung injury (ALI) with high mortality rate. Studies on therapeutic administration of bone marrow-derived mesenchymal stem cells (MSCs) in ALI caused by the viral infection have been limited in number and have shown conflicting results. The aim of the present investigation is to evaluate the therapeutic potential of MSC administration in A/H5N1-caused ALI, using a mouse model.

METHODS

MSCs were prepared from the bone marrow of 9 to 12 week-old BALB/c mice. An H5N1 virus of A/turkey/East Java/Av154/2013 was intranasally inoculated into BALB/c mice. On days 2, 4, and 6 after virus inoculation, MSCs were intravenously administered into the mice. To evaluate effects of the treatment, we examined for lung alveolar protein as an indicator for lung injury, PaO₂/FiO₂ ratio for lung functioning, and lung histopathology. Expressions of NF-κB, RAGE (transmembrane receptor for damage associated molecular patterns), TNFα, IL-1β, Sftpc (alveolar cell type II marker), and Aqp5+ (alveolar cell type I marker) were examined by immunohistochemistry. In addition, body weight, virus growth in lung and brain, and duration of survival were measured.

RESULTS

The administration of MSCs lowered the level of lung damage in the virus-infected mice, as shown by measuring lung alveolar protein, PaO₂/FiO₂ ratio, and histopathological score. In the MSC-treated group, the expressions of NF-κB, RAGE, TNFα, and IL-1β were significantly suppressed in comparison with a mock-treated group, while those of Sftpc and Aqp5+ were enhanced. Body weight, virus growth, and survival period were not significantly different between the groups.

CONCLUSION

The administration of MSCs prevented further lung injury and inflammation, and enhanced alveolar cell type II and I regeneration, while it did not significantly affect viral proliferation and mouse morbidity and mortality. The results suggested that MSC administration was a promissing strategy for treatment of acute lung injuries caused by the highly pathogenic avian influenza A/H5N1 virus, although further optimization and combination use of anti-viral drugs will be obviously required to achieve the goal of reducing mortality.

A Perspective on Erythropoietin as a Potential Adjuvant Therapy for Acute Lung Injury/Acute Respiratory Distress Syndrome in Patients with COVID-19

The novel coronavirus 2019-nCoV (SARS-CoV-2) infection that emerged in China in December 2019 has rapidly spread to become a global pandemic. This article summarizes the potential benefits of erythropoietin (EPO) in alleviating SARS-CoV-2 pathogenesis which is now called COVID-19. As with other coronavirus infection, the lethality of COVID-19 is associated with respiratory dysfunction due to overexpression of proinflammatory cytokines induced by the host immune responses. The resulting cytokine storm leads to the development of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Erythropoietin, well known for its role in the regulation of erythropoiesis, may have protective effects against ALI/ARDS induced by viral and other pathogens. EPO exerts antiapoptotic and cytoprotective properties under various pathological conditions. With a high safety profile, EPO promotes the production of endothelial progenitor cells and reduce inflammatory processes through inhibition of the nuclear factor-κB (NF-κB) and JAK-STAT3 signaling pathways. Thus, it may be considered as a safe drug candidate for COVID-19 patients if given at the early stage of the disease. The potential effects of erythropoietin on different aspects of ALI/ARDS associated with SARS-CoV-2 infection are reviewed.

Echinacea polysaccharide alleviates LPS-induced lung injury via inhibiting inflammation, apoptosis and activation of the TLR4/NF-κB signal pathway

Lung injury is a common critical life-threatening syndrome. Inflammation is a key factor in the pathogenesis of lung injury. It is reported that Echinacea Polysaccharides (EP) has anti-inflammatory activity. However, the effect of EP on lung injury remains unclear. In our study, murine model of lung injury was induced with 2.5 mg/kg LPS before administration of 5 mg/kg or 10 mg/kg EP. EP ameliorated LPS-induced lung pathological damage, along with reduction in lung wet/dry weight ratio and myeloperoxidase activity. EP decreased the number of leukocytes, eosinophils, neutrophils, lymphocytes and macrophages in bronchoalveolar lavage fluid, and the release of tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) in LPS-treated lung. EP suppressed LPS-induced apoptosis along with down-regulation of Bcl2-associated X (Bax) and cleaved caspase-3 (CC3), and elevated B-cell lymphoma-2 (Bcl-2). Besides, RAW 264.7 cells were treated with EP 100 μg/ml for 1 h and then incubated with 1 μg/ml LPS for 24 h. TNF-α, IL-6 and IL-1β levels were lowered by treatment of EP in LPS-treated RAW 264.7 cells. Moreover, EP down-regulated the expression of toll-like receptor 4 (TLR4), myeloid differentiating factor 88 (MyD88), p-IκBα, nuclear factor kappa-B (NF-κB), p-NF-κB, and up-regulated the inhibitor of NF-κB (IκBα) in vivo and in vitro following LPS induction, which is consistent with the effect of TAK-242. In conclusion, EP may alleviate LPS-induced lung injury via inhibiting inflammation, apoptosis and activation of TLR4/NF-κB signal pathway.