Early disruption of the alveolar-capillary barrier in a ricin-induced ARDS mouse model: neutrophil-dependent and -independent impairment of junction proteins

Short- and long-term outcomes of pulmonary exposure to a sublethal dose of ricin in mice

Ricin, an extremely potent toxin produced from the seeds of castor plant, Ricinus communis, is ribosome-inactivating protein that blocks cell-protein synthesis. It is considered a biological threat due to worldwide availability of castor beans, massive quantities as a by-product of castor oil production, high stability and ease of production. The consequence of exposure to lethal dose of ricin was extensively described in various animal models. However, it is assumed that in case of aerosolized ricin bioterror attack, the majority of individuals would be exposed to sublethal doses rather than to lethal ones. Therefore, the purpose of current study was to assess short- and long-term effects on physiological parameters and function following sublethal pulmonary exposure. We show that in the short-term, sublethal exposure of mice to ricin resulted in acute lung injury, including interstitial pneumonia, cytokine storm, neutrophil influx, edema and cellular death. This damage was manifested in reduced lung performance and physiological function. Interestingly, although in the long-term, mice recovered from acute lung damage and restored pulmonary and physiological functionality, the reparative process was associated with lasting fibrotic lesions. Therefore, restriction of short-term acute phase of the disease and management of long-term pulmonary fibrosis by medical countermeasures is expected to facilitate the quality of life of exposed survivors.

Research hotspots and evolving trends of barrier dysfunction in acute lung injury and acute respiratory distress syndrome

Endothelial and epithelial barrier dysfunction due to increased permeability and heightened inflammatory reactions influences the emergence of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Nevertheless, bibliometric research comparing endothelial and epithelial barriers is limited. Therefore, this bibliometric study analyzed the Web of Science Core Collection (WoSCC) of the Science Citation Index Expanded literature to explore present research priorities and development tendencies within this field. We conducted a comprehensive search (October 18, 2023) on WoSCC from January 1, 2010, to October 18, 2023, focusing on articles related to endothelial and epithelial barriers in ALI and ARDS. Retrieved data were visualized and analyzed using R-bibliometrix, VOS viewer 1.6.19, and CiteSpace 6.2. R4. Functional enrichment analysis of gene targets identified in the keyword list using Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene ontology databases, and based on the STRING database to construct a PPI network to predict core genes. A total of 941 original articles and reviews were identified. The United States had the highest number of publications and citations and the highest H-index and G-index. According to the Collaboration Network Analysis graph, the United States and China had the strongest collaboration. Birukova AA had the most publications and citations among all authors, while eight of the top ten institutions with mediator centrality were located in the United States. The American Journal of Physiology-Lung Cellular and Molecular Physiology was the leading journal and had the most well-established publication on endothelial and epithelial barriers in ALI and ARDS. Bibliometric analysis revealed that the most frequently used keywords were acute lung injury, ARDS, activation, expression, and inflammation. RHOA appeared most frequently among gene-related keywords, and the PI3K-AKT signaling pathway had the highest count in KEGG pathway enrichment. Research on endothelial versus epithelial barriers in ALI and ARDS remains preliminary. This bibliometric study examined cooperative network connections among countries, authors, journals, and network associations in the cited references. Investigation of the functions of the endothelial and epithelial barriers in ALI/ARDS associated with COVID-19 has recently gained significant attention.

Songorine inhibits oxidative stress-related inflammation through PI3K/AKT/NRF2 signaling pathway to alleviate lipopolysaccharide-induced septic acute lung injury

OBJECTIVE

The present study aimed to investigate the protective action and mechanism of songorine on sepsis-induced acute lung injury (ALI).

METHODS

The sepsis-induced ALI mouse and cell models were established by lipopolysaccharide (LPS) induction. Lung injury was assayed by hematoxylin and eosin staining, lung injury score, and lung wet-to-dry (W/D) weight ratio. Apoptosis in lung tissues was evaluated by TUNEL assay, and the expression of apoptosis-related markers (Bcl2, Bax, and caspase-3) was measured by western blotting. Levels of pro-inflammatory factors and oxidative stress markers in the bronchoalveolar lavage fluid (BALF) of mice were measured by ELISA and RT-qPCR. The expression of PI3K/AKT/NRF2 pathway-related proteins was analyzed by western blotting.

RESULTS

Songorine treatment at 40 mg/kg mitigated sepsis-induced ALI, characterized by improved histopathology, lung injury score, and lung W/D weight ratio (p < 0.05). Moreover, songorine markedly attenuated sepsis-induced apoptosis in lung tissues; this was evidenced by an increase in Bcl2 levels and a decrease in Bax and caspase-3 levels (p < 0.01). Also, songorine reduced levels of proinflammatory cytokines (TNF-α, IL-6, IL-1β and MPO) and oxidative stress regulators (SOD and GSH) in the BALF of LPS-induced sepsis mice and RAW264.7 cells (p < 0.05). In addition, songorine upregulated the PI3K/AKT/NRF2 pathway-related proteins in LPS-induced sepsis mice and RAW264.7 cells (p < 0.05). Furthermore, LY294002 (a PI3K inhibitor) treatment reversed the protective effect of songorine on sepsis-induced ALI.

CONCLUSION

Songorine inhibits oxidative stress-related inflammation in sepsis-induced ALI via the activation of the PI3K/AKT/NRF2 signaling pathway.

Host gastric corpus microenvironment facilitates Ascaris suum larval hatching and infection in a murine model

Ascariasis (roundworm) is the most common parasitic helminth infection globally and can lead to significant morbidity in children including chronic lung disease. Children become infected with Ascaris spp. via oral ingestion of eggs. It has long been assumed that Ascaris egg hatching and larval translocation across the gastrointestinal mucosa to initiate infection occurs in the small intestine. Here, we show that A. suum larvae hatched in the host stomach in a murine model. Larvae utilize acidic mammalian chitinase (AMCase; acid chitinase; Chia) from chief cells and acid pumped by parietal cells to emerge from eggs on the surface of gastric epithelium. Furthermore, antagonizing AMCase and gastric acid in the stomach decreases parasitic burden in the liver and lungs and attenuates lung disease. Given Ascaris eggs are chitin-coated, the gastric corpus would logically be the most likely organ for egg hatching, though this is the first study directly evincing the essential role of the host gastric corpus microenvironment. These findings point towards potential novel mechanisms for therapeutic targets to prevent ascariasis and identify a new biomedical significance of AMCase in mammals.

The Na/K-ATPase role as a signal transducer in lung inflammation

Acute respiratory distress syndrome (ARDS) is marked by damage to the capillary endothelium and alveolar epithelium following edema formation and cell infiltration. Currently, there are no effective treatments for severe ARDS. Pathologies such as sepsis, pneumonia, fat embolism, and severe trauma may cause ARDS with respiratory failure. The primary mechanism of edema clearance is the epithelial cells' Na/K-ATPase (NKA) activity. NKA is an enzyme that maintains the electrochemical gradient and cell homeostasis by transporting Na+ and K+ ions across the cell membrane. Direct injury on alveolar cells or changes in ion transport caused by infections decreases the NKA activity, loosening tight junctions in epithelial cells and causing edema formation. In addition, NKA acts as a receptor triggering signal transduction in response to the binding of cardiac glycosides. The ouabain (a cardiac glycoside) and oleic acid induce lung injury by targeting NKA. Besides enzymatic inhibition, the NKA triggers intracellular signal transduction, fostering proinflammatory cytokines production and contributing to lung injury. Herein, we reviewed and discussed the crucial role of NKA in edema clearance, lung injury, and intracellular signaling pathway activation leading to lung inflammation, thus putting the NKA as a protagonist in lung injury pathology.

Spatiotemporal single-cell transcriptomic profiling reveals inflammatory cell states in a mouse model of diffuse alveolar damage

Diffuse alveolar damage (DAD) triggers neutrophilic inflammation in damaged tissues of the lung, but little is known about the distinct roles of tissue structural cells in modulating the recruitment of neutrophils to damaged areas. Here, by combining single-cell and spatial transcriptomics, and using quantitative assays, we systematically analyze inflammatory cell states in a mouse model of DAD-induced neutrophilic inflammation after aerosolized intratracheal inoculation with ricin toxin. We show that homeostatic resident fibroblasts switch to a hyper-inflammatory state, and the subsequent occurrence of a CXCL1-CXCR2 chemokine axis between activated fibroblasts (AFib) as the signal sender and neutrophils as the signal receiver triggers further neutrophil recruitment. We also identify an anatomically localized inflamed niche (characterized by a close-knit spatial intercellular contact between recruited neutrophils and AFib) in peribronchial regions that facilitate the pulmonary inflammation outbreak. Our findings identify an intricate interplay between hyper-inflammatory fibroblasts and neutrophils and provide an overarching profile of dynamically changing inflammatory microenvironments during DAD progression.

Jinzhen Oral Liquid alleviates lipopolysaccharide-induced acute lung injury through modulating TLR4/MyD88/NF-κB pathway

BACKGROUND

Acute lung injury (ALI) has the attribution of excessive inflammation of the lung. Jinzhen oral liquid (JO), a famous Chinese recipe used to treat ALI, has a favorable therapeutic effect on ALI. However, its anti-inflammatory mechanism has not been extensively studied.

PURPOSE

This study was to elucidate the effects of JO on lipopolysaccharide (LPS)-induced ALI and its molecular mechanism.

METHODS

An ALI model was established by intratracheal instillation of LPS (2 mg/50 μl). The open field experiment was carried out to explore the spontaneous movement and exploratory behavior of ALI mice. Cytokines levels concentrations (IL-6, IL-10 and TNF-α) were determined by enzyme-linked immunosorbent assay (ELISA). Network pharmacology was used to predict the mechanism of JO against ALI. Immunofluorescence, co-immunoprecipitation, fluorescence resonance energy transfer (FRET), Western blot and RT-PCR were used to verify the molecular mechanisms of JO.

RESULTS

The in vivo results suggested that JO (1, 2, 4 g/kg) dose-dependently improved the exercise performance of mice and reduced the lung W/D weight ratio as well as the production of IL-6 and TNF-α, but increased the release of IL-10 in the ALI group. The network pharmacological analysis demonstrated that the Toll-like receptor (TLR) pathway might be the fundamental action mechanisms of JO against ALI. Immunofluorescence staining and co-immunoprecipitation analysis showed that JO decreased the expression levels of TLR4 and MyD88 and reduced their interaction in the lung tissue of ALI mice. Meanwhile, JO decreased nuclear translocation and phosphorylation of NF-κB P65. The results from cellular experiments were in line with those in vivo. The FRET experiment also confirmed that JO disturbed the interaction of TLR4 and MyD88. Subsequently, we also found that the six indicative components of JO have the similar therapeutic effect as JO.

CONCLUSIONS

In summary, we suggested that JO suppressed the TLR4/MyD88/NF-κB signaling pathway, thus inhibiting LPS-induced ALI in vitro and in vivo. The clarified mechanism provided an important theoretical basis and a novel treatment strategy for the ALI treatment of JO.

PGLYRP1-mIgG2a-Fc inhibits macrophage activation via AKT/NF-κB signaling and protects against fatal lung injury during bacterial infection

Severe bacterial pneumonia leads to acute respiratory distress syndrome (ARDS), with a high incidence rate and mortality. It is well-known that continuous and dysregulated macrophage activation is vital for aggravating the progression of pneumonia. Here, we designed and produced an antibody-like molecule, peptidoglycan recognition protein 1-mIgG2a-Fc (PGLYRP1-Fc). PGLYRP1 was fused to the Fc region of mouse IgG2a with high binding to macrophages. We demonstrated that PGLYRP1-Fc ameliorated lung injury and inflammation in ARDS, without affecting bacterial clearance. Besides, PGLYRP1-Fc reduced AKT/nuclear factor kappa-B (NF-κB) activation via the Fc segment bound Fc gamma receptor (FcγR)-dependent mechanism, making macrophage unresponsive, and immediately suppressed proinflammatory response upon bacteria or lipopolysaccharide (LPS) stimulus in turn. These results confirm that PGLYRP1-Fc protects against ARDS by promoting host tolerance with reduced inflammatory response and tissue damage, irrespective of the host's pathogen burden, and provide a promising therapeutic strategy for bacterial infection.

Comparative Aspects of Ricin Toxicity by Inhalation

The pathogenesis of ricin toxicity following inhalation has been investigated in many animal models, including the non-human primate (predominantly the rhesus macaque), pig, rabbit and rodent. The toxicity and associated pathology described in animal models are broadly similar, but variation appears to exist. This paper reviews the published literature and some of our own unpublished data and describes some of the possible reasons for this variation. Methodological variation is evident, including method of exposure, breathing parameters during exposure, aerosol characteristics, sampling protocols, ricin cultivar, purity and challenge dose and study duration. The model species and strain used represent other significant sources of variation, including differences in macro- and microscopic anatomy, cell biology and function, and immunology. Chronic pathology of ricin toxicity by inhalation, associated with sublethal challenge or lethal challenge and treatment with medical countermeasures, has received less attention in the literature. Fibrosis may follow acute lung injury in survivors. There are advantages and disadvantages to the different models of pulmonary fibrosis. To understand their potential clinical significance, these factors need to be considered when choosing a model for chronic ricin toxicity by inhalation, including species and strain susceptibility to fibrosis, time it takes for fibrosis to develop, the nature of the fibrosis (e.g., self-limiting, progressive, persistent or resolving) and ensuring that the analysis truly represents fibrosis. Understanding the variables and comparative aspects of acute and chronic ricin toxicity by inhalation is important to enable meaningful comparison of results from different studies, and for the investigation of medical countermeasures.

Serum antibody profiling identifies vaccine-induced correlates of protection against aerosolized ricin toxin in rhesus macaques

Inhalation of the biothreat agent, ricin toxin (RT), provokes a localized inflammatory response associated with pulmonary congestion, edema, neutrophil infiltration, and severe acute respiratory distress. The extreme toxicity of RT is the result of the toxin's B chain (RTB) promoting rapid uptake into alveolar macrophages and lung epithelial cells, coupled with the A chain's (RTA) potent ribosome-inactivating properties. We previously reported that intramuscular vaccination of rhesus macaques with a lyophilized, alum-adsorbed recombinant RTA subunit vaccine (RiVax®) was sufficient to confer protection against a lethal dose of aerosolized RT. That study implicated RT-specific serum IgG, toxin-neutralizing activity (TNA), and epitope-specific responses as being associated with immunity. However, it was not possible to define actual correlates of protection (COP) because all vaccinated animals survived the RT challenge. We addressed the issue of COP in the current study, by vaccinating groups of rhesus macaques with RiVax® following the previously determined protective regimen (100 µg on study days 0, 30 and 60) or one of two anticipated suboptimal regimens (100 µg on study days 30 and 60; 35 µg on study days 0, 30, and 60). Two unvaccinated animals served as controls. The animals were challenged with ~5 × LD50s of aerosolized RT on study day 110. We report that all vaccinated animals seroconverted prior to RT challenge, with the majority also having measurable TNA, although neither antibody levels nor TNA reached statistical significance with regard to a correlation with protection. By contrast, survival correlated with pre-challenge, epitope-specific serum IgG levels, derived from a competitive sandwich ELISA using a panel of toxin-neutralizing monoclonal antibodies directed against distinct epitopes on RiVax®. The identification of a species-neutral, competitive ELISA that correlates with vaccine-induced protection against RT in nonhuman represents an important advance in the development of medical countermeasures (MCM) against a persistent biothreat.

Characterization of Lung Injury following Abrin Pulmonary Intoxication in Mice: Comparison to Ricin Poisoning

Abrin is a highly toxic protein obtained from the seeds of the rosary pea plant Abrus precatorius, and it is closely related to ricin in terms of its structure and chemical properties. Both toxins inhibit ribosomal function, halt protein synthesis and lead to cellular death. The major clinical manifestations following pulmonary exposure to these toxins consist of severe lung inflammation and consequent respiratory insufficiency. Despite the high similarity between abrin and ricin in terms of disease progression, the ability to protect mice against these toxins by postexposure antibody-mediated treatment differs significantly, with a markedly higher level of protection achieved against abrin intoxication. In this study, we conducted an in-depth comparison between the kinetics of in vivo abrin and ricin intoxication in a murine model. The data demonstrated differential binding of abrin and ricin to the parenchymal cells of the lungs. Accordingly, toxin-mediated injury to the nonhematopoietic compartment was shown to be markedly lower in the case of abrin intoxication. Thus, profiling of alveolar epithelial cells demonstrated that although toxin-induced damage was restricted to alveolar epithelial type II cells following abrin intoxication, as previously reported for ricin, it was less pronounced. Furthermore, unlike following ricin intoxication, no direct damage was detected in the lung endothelial cell population following abrin exposure. Reduced impairment of intercellular junction molecules following abrin intoxication was detected as well. In contrast, similar damage to the endothelial surface glycocalyx layer was observed for the two toxins. We assume that the reduced damage to the lung stroma, which maintains a higher level of tissue integrity following pulmonary exposure to abrin compared to ricin, contributes to the high efficiency of the anti-abrin antibody treatment at late time points after exposure.

A New Immortalized Human Alveolar Epithelial Cell Model to Study Lung Injury and Toxicity on a Breathing Lung-On-Chip System

The evaluation of inhalation toxicity, drug safety and efficacy assessment, as well as the investigation of complex disease pathomechanisms, are increasingly relying on in vitro lung models. This is due to the progressive shift towards human-based systems for more predictive and translational research. While several cellular models are currently available for the upper airways, modelling the distal alveolar region poses several constraints that make the standardization of reliable alveolar in vitro models relatively difficult. In this work, we present a new and reproducible alveolar in vitro model, that combines a human derived immortalized alveolar epithelial cell line (^AXiAEC) and organ-on-chip technology mimicking the lung alveolar biophysical environment (^AXlung-on-chip). The latter mimics key features of the in vivo alveolar milieu: breathing-like 3D cyclic stretch (10% linear strain, 0.2 Hz frequency) and an ultrathin, porous and elastic membrane. ^AXiAECs cultured on-chip were characterized for their alveolar epithelial cell markers by gene and protein expression. Cell barrier properties were examined by TER (Transbarrier Electrical Resistance) measurement and tight junction formation. To establish a physiological model for the distal lung, ^AXiAECs were cultured for long-term at air-liquid interface (ALI) on-chip. To this end, different stages of alveolar damage including inflammation (via exposure to bacterial lipopolysaccharide) and the response to a profibrotic mediator (via exposure to Transforming growth factor β1) were analyzed. In addition, the expression of relevant host cell factors involved in SARS-CoV-2 infection was investigated to evaluate its potential application for COVID-19 studies. This study shows that ^AXiAECs cultured on the ^AXlung-on-chip exhibit an enhanced in vivo-like alveolar character which is reflected into: 1) Alveolar type 1 (AT1) and 2 (AT2) cell specific phenotypes, 2) tight barrier formation (with TER above 1,000 Ω cm²) and 3) reproducible long-term preservation of alveolar characteristics in nearly physiological conditions (co-culture, breathing, ALI). To the best of our knowledge, this is the first time that a primary derived alveolar epithelial cell line on-chip representing both AT1 and AT2 characteristics is reported. This distal lung model thereby represents a valuable in vitro tool to study inhalation toxicity, test safety and efficacy of drug compounds and characterization of xenobiotics.

Differential ER stress as a driver of cell fate following ricin toxin exposure

Inhalation of trace amounts of ricin toxin, a plant-derived ribosome-inactivating protein, results in ablation of alveolar macrophages, widespread epithelial damage, and the onset of acute respiratory distress syndrome (ARDS). While ricin's receptors are ubiquitous, certain cell types are more sensitive to ricin-induced cell death than others for reasons that remain unclear. For example, we demonstrate in side-by-side studies that macrophage-like differentiated THP-1 (dTHP-1) cells are hyper-sensitive to ricin, while lung epithelium-derived A549 cells are relatively insensitive, even though both cell types experience similar degrees of translational inhibition and p38 MAPK activation in response to ricin. Using a variety of small molecule inhibitors, we provide evidence that ER stress contributes to ricin-mediated cytotoxicity of dTHP-1 cells, but not A549 cells. On the other hand, the insensitivity of A549 cells to ricin was overcome by the addition of (TNF)-related apoptosis-inducing ligand (TRAIL; CD253), a known stimulator of extrinsic programmed cell death. These results have implications for understanding the complex pathophysiology of ricin-induced ARDS in that they demonstrate that intrinsic (e.g., ER stress) and extrinsic (e.g., TRAIL) factors may ultimately determine the fate of specific cell types following ricin intoxication.

Transient Ascaris suum larval migration induces intractable chronic pulmonary disease and anemia in mice

Ascariasis is one of the most common infections in the world and associated with significant global morbidity. Ascaris larval migration through the host’s lungs is essential for larval development but leads to an exaggerated type-2 host immune response manifesting clinically as acute allergic airway disease. However, whether Ascaris larval migration can subsequently lead to chronic lung diseases remains unknown. Here, we demonstrate that a single episode of Ascaris larval migration through the host lungs induces a chronic pulmonary syndrome of type-2 inflammatory pathology and emphysema accompanied by pulmonary hemorrhage and chronic anemia in a mouse model. Our results reveal that a single episode of Ascaris larval migration through the host lungs leads to permanent lung damage with systemic effects. Remote episodes of ascariasis may drive non-communicable lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and chronic anemia in parasite endemic regions.

Ascariasis is the most common helminth infection and leads to significant global morbidity. Transient Ascaris larval migration through the host’s lungs is essential for larval development but leads to an exaggerated type-2 host immune response. Our work demonstrates that transient Ascaris spp. larval migration through the lungs has significant long-term consequences including changes in lung structure and function as well as vascular damage causing chronic lung disease and anemia. We propose that Ascaris spp. larval migration through the host lungs is a risk factor for the development of chronic lung disease and anemia in parasite-endemic regions globally.

Neutrophil extracellular traps are associated with altered human pulmonary artery endothelial barrier function

Introduction: Acute respiratory response syndrome (ARDS) leads to increased permeability of the endothelial-epithelial barrier, which in turn promotes edema formation and hypoxemic respiratory failure. Although activated neutrophils are thought to play a significant role in mediating ARDS, at present the contribution of neutrophil extracellular traps (NETs) to lung endothelial barrier function is unclear. Methods: To clarify their role, we co-cultured in vitro NETs induced by phorbol myristate acetate (PMA)–activated neutrophils with lung endothelial cell monolayers and examined the barrier function of lung endothelial cells by immunofluorescence microscopy and albumin permeability in a double-chamber culture method. Results: Co-culture with stimulated neutrophils increased the albumin permeability of the human pulmonary artery endothelial cell (HPAEC) monolayer and altered cytoskeleton F-actin and vascular endothelial-cadherin in cell-cell junctions. Hyperpermeability to albumin and histological alterations were prevented by inhibition of NET formation with peptidyl arginine deiminase inhibitor or a neutrophil elastase inhibitor and were also prevented by increased degradation of NET structure with DNase. Conclusion: This in vitro experiment shows that altered HPAEC barrier function and increased albumin permeability are caused by the direct effect of PMA-induced NETs and their components. NET formation may be involved in the increased vascular permeability of the lung, which is a common feature in ARDS of various etiologies. These insights may help generate novel approaches for medical interventions.

Network-Based Integrated Analysis of Transcriptomic Studies in Dissecting Gene Signatures for LPS-Induced Acute Lung Injury

Acute lung injury (ALI) is a type of serious clinical syndrome leading to morbidity and mortality. However, the precise pathogenesis of ALI remains elusive. Here, we implemented an integrative meta-analysis of six GEO microarray studies with 76 samples in the ALI mouse model. A total of 958 differentially expressed genes (DEGs) were identified in LPS relative to normal samples. Then, a network-based meta-analysis was used to mine core DEGs and to unfold the interactions among these genes. We found that Ebi3 was the top upregulated genes in the LPS-induced ALI. GO, KEGG, and GSEA analyses were performed for functional annotation. qRT-PCR revealed augmented expression of six candidate genes (Stat1, Syk, Jak3, Rac2, Ripk1, and Traf6) in the established ALI mouse model with LPS exposure. Taken together, our study investigated comprehensively hub DEGs and their networks for LPS-stimulated ALI, which might afford an additional approach to determine biomarkers and therapeutic targets and explore the molecular pathophysiology toward ALI.

Intramuscular Exposure to a Lethal Dose of Ricin Toxin Leads to Endothelial Glycocalyx Shedding and Microvascular Flow Abnormality in Mice and Swine

Ricin toxin isolated from the castor bean (Ricinus communis) is one of the most potent and lethal molecules known. While the pathophysiology and clinical consequences of ricin poisoning by the parenteral route, i.e., intramuscular penetration, have been described recently in various animal models, the preceding mechanism underlying the clinical manifestations of systemic ricin poisoning has not been completely defined. Here, we show that following intramuscular administration, ricin bound preferentially to the vasculature in both mice and swine, leading to coagulopathy and widespread hemorrhages. Increased levels of circulating VEGF and decreased expression of vascular VE-cadherin caused blood vessel impairment, thereby promoting hyperpermeability in various organs. Elevated levels of soluble heparan sulfate, hyaluronic acid and syndecan-1 were measured in blood samples following ricin intoxication, indicating that the vascular glycocalyx of both mice and swine underwent extensive damage. Finally, by using side-stream dark field intravital microscopy imaging, we determined that ricin poisoning leads to microvasculature malfunctioning, as manifested by aberrant blood flow and a significant decrease in the number of diffused microvessels. These findings, which suggest that glycocalyx shedding and microcirculation dysfunction play a major role in the pathology of systemic ricin poisoning, may serve for the formulation of specifically tailored therapies for treating parenteral ricin intoxication.

Novel insights into the pathogenesis of virus-induced ARDS: review on the central role of the epithelial-endothelial barrier

Introduction: Respiratory viruses can directly or indirectly damage the pulmonary defense barrier, potentially contributing to acute respiratory distress syndrome (ARDS). Despite developments in the understanding of the pathogenesis of ARDS, the underlying pathophysiology still needs to be elucidated.Areas covered: The PubMed database was reviewed for relevant papers published up to 2021. This review summarizes the currently immunological and clinical studies to provide a systemic overview of the epithelial-endothelial barrier, given the recently published immunological profiles upon viral pneumonia, and the potentially detrimental contribution to respiratory function caused by damage to this barrier.Expert opinion: The biophysical structure of host pulmonary defense is intrinsically linked with the ability of alveolar epithelial and capillary endothelial cells, known as the epithelial-endothelial barrier, to respond to, and instruct the delicate immune system to protect the lungs from infections and injuries. Recently published immunological profiles upon viral infection, and its contributions to the damage of respiratory function, suggest a central role for the pulmonary epithelial and endothelial barrier in the pathogenesis of ARDS. We suggest a central role and common pathways by which the epithelial-endothelial barrier contributes to the pathogenesis of ARDS.

Mice with induced pulmonary morbidities display severe lung inflammation and mortality following exposure to SARS-CoV-2

Mice are normally unaffected by SARS coronavirus 2 (SARS-CoV-2) infection since the virus does not bind effectively to the murine version of the angiotensin-converting enzyme 2 (ACE2) receptor molecule. Here, we report that induced mild pulmonary morbidities rendered SARS-CoV-2–refractive CD-1 mice susceptible to this virus. Specifically, SARS-CoV-2 infection after application of low doses of the acute lung injury stimulants bleomycin or ricin caused severe disease in CD-1 mice, manifested by sustained body weight loss and mortality rates greater than 50%. Further studies revealed markedly higher levels of viral RNA in the lungs, heart, and serum of low-dose ricin–pretreated mice compared with non-pretreated mice. Furthermore, lung extracts prepared 2–3 days after viral infection contained subgenomic mRNA and virus particles capable of replication only when derived from the pretreated mice. The deleterious effects of SARS-CoV-2 infection were effectively alleviated by passive transfer of polyclonal or monoclonal antibodies generated against the SARS-CoV-2 receptor binding domain (RBD). Thus, viral cell entry in the sensitized mice seems to depend on viral RBD binding, albeit by a mechanism other than the canonical ACE2-mediated uptake route. This unique mode of viral entry, observed over a mildly injured tissue background, may contribute to the exacerbation of coronavirus disease 2019 (COVID-19) pathologies in patients with preexisting morbidities.

Structural Analysis of Toxin-Neutralizing, Single-Domain Antibodies that Bridge Ricin's A-B Subunit Interface

Ricin toxin kills mammalian cells with notorious efficiency. The toxin's B subunit (RTB) is a Gal/GalNAc-specific lectin that attaches to cell surfaces and promotes retrograde transport of ricin's A subunit (RTA) to the trans Golgi network (TGN) and endoplasmic reticulum (ER). RTA is liberated from RTB in the ER and translocated into the cell cytoplasm, where it functions as a ribosome-inactivating protein. While antibodies against ricin's individual subunits have been reported, we now describe seven alpaca-derived, single-domain antibodies (V_HHs) that span the RTA-RTB interface, including four Tier 1 V_HHs with IC₅₀ values <1 nM. Crystal structures of each V_HH bound to native ricin holotoxin revealed three different binding modes, based on contact with RTA's F-G loop (mode 1), RTB's subdomain 2γ (mode 2) or both (mode 3). V_HHs in modes 2 and 3 were highly effective at blocking ricin attachment to HeLa cells and immobilized asialofetuin, due to framework residues (FR3) that occupied the 2γ Gal/GalNAc-binding pocket and mimic ligand. The four Tier 1 V_HHs also interfered with intracellular functions of RTB, as they neutralized ricin in a post-attachment cytotoxicity assay (e.g., the toxin was bound to cell surfaces before antibody addition) and reduced the efficiency of toxin transport to the TGN. We conclude that the RTA-RTB interface is a target of potent toxin-neutralizing antibodies that interfere with both extracellular and intracellular events in ricin's cytotoxic pathway.

Influence of fine particulate matter and its pure particulate fractions on pulmonary immune cells and cytokines in mice

Particulate matter with a diameter ≤2.5 µm (PM^2.5) has a complex composition and has been associated with the incidence of cardiopulmonary disease and premature death in humans. However, whether pure particulate fractions of PM^2.5 (PPP^2.5), which are composed primarily of carbon, are responsible for the toxicity caused by ambient particulate matter (original PM^2.5 particles, OPP^2.5) is currently unclear. The present study assessed the acute toxic effects of OPP^2.5 sampled in Beijing, China and of its PPP^2.5 fraction in male BALB/c mice. The mice were intratracheally instilled with a single dose of aerosolized OPP^2.5 or PPP^2.5. Blood, lungs and bronchoalveolar lavage fluid were collected after 24 h for histopathology, flow cytometry and the measurement of pro-inflammatory cytokines/chemokines and other biochemical factors. Both OPP^2.5 and PPP^2.5 caused acute toxicity, particularly inflammatory responses, including an increase in the levels of pro-inflammatory cytokines and an accumulation of numerous immune cells in the lungs. OPP^2.5 induced a stronger inflammatory response than PPP^2.5. The complex components adsorbed into the solid core granules of OPP^2.5 and the granules themselves contributed to the toxic effects.

Analysis of the microRNA and mRNA expression profile of ricin toxin-treated RAW264.7 cells reveals that miR-155-3p suppresses cell inflammation by targeting GAB2

Ricin toxin (RT) is one of the most lethal toxins derived from the seed of castor beans. In addition to its main toxic mechanism of inhibiting the synthesis of cellular proteins, RT can induce the production of inflammatory cytokines. MicroRNAs (miRNAs) play a key role in regulating both innate and adaptive immunity. To elucidate the regulation of miRNAs in RT-induced inflammation injury, the RNA high-throughput sequencing (RNA-Seq) technology was used to analyze the expression profile of miRNAs and mRNAs in RT-treated RAW264.7 cells. Results showed that a total of 323 mRNAs and 19 miRNAs differentially expressed after RT treated. Meanwhile, 713 miRNA-mRNA interaction pairs were identified by bioinformatics analysis. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed that those interaction pairs were mainly involved in JAK-STAT, T cell receptor, and MAPK signaling pathways. Moreover, we further predicted and determined the targeting relationship between miR-155-3p and GAB2 through TargetScan and dual-luciferase reporter assay. Mechanically, overexpression of miR-155-3p can reduce the secretion of TNF-α in RAW264.7 cells, revealing a possible mechanism of miR-155-3p regulating RT-induced inflammatory injury. This study provides a new perspective for clarifying the mechanism of RT-induced inflammatory injury and reveals the potential role of miRNAs in innate immune regulation.

Attenuation of pulmonary injury by an inhaled MMP inhibitor in the endotoxin lung injury model

Acute respiratory distress syndrome (ARDS) is characterized by pulmonary edema and poor gas exchange resulting from severe inflammatory lung injury. Neutrophilic infiltration and increased pulmonary vascular permeability are hallmarks of early ARDS and precipitate a self-perpetuating cascade of inflammatory signaling. The biochemical processes initiating these events remain unclear. Typically associated with extracellular matrix degradation, recent data suggest matrix metalloproteinases (MMPs) are regulators of pulmonary inflammation. To demonstrate that inhalation of a broad MMP inhibitor attenuates LPS induced pulmonary inflammation. Nebulized CGS27023AM (CGS) was administered to LPS-injured mice. Pulmonary CGS levels were examined by mass spectroscopy. Inflammatory scoring of hematoxylin-eosin sections, examination of vascular integrity via lung wet/dry and bronchoalveolar lvage/serum FITC-albumin ratios were performed. Cleaved caspase-3 levels were also assessed. Differential cell counts and pulse-chase labeling were utilized to determine the effects of CGS on neutrophil migration. The effects of CGS on human neutrophil migration and viability were examined using Boyden chambers and MTT assays. Nebulization successfully delivered CGS to the lungs. Treatment decreased pulmonary inflammatory scores, edema, and apoptosis in LPS treated animals. Neutrophil chemotaxis was reduced by CGS treatment, with inhalation causing significant reductions in both the total number and newly produced bromodeoxyuridine-positive cells infiltrating the lung. Mechanistic studies on cells isolated from humans demonstrate that CGS-treated neutrophils exhibit decreased chemotaxis. The protective effect observed following treatment with a nonspecific MMP inhibitor indicates that one or more MMPs mediate the development of pulmonary edema and neutrophil infiltration in response to LPS injury. In accordance with this, inhaled MMP inhibitors warrant further study as a potential new therapeutic avenue for treatment of acute lung injury.

Time-course transcriptome analysis of lungs from mice exposed to ricin by intratracheal inoculation

In this study, a ricin toxin (RT)-induced pulmonary intoxication model was established in mice by intratracheal-delivered RT at a dose of 2× LD₅₀. Based on this model, the histopathological evaluation of the lungs at 24 h and 48 h post-exposure was executed, and the genome-wide transcriptome of the lungs at 4, 12, 24 and 48 h post-exposure was analyzed. Histopathological analysis showed that a large number of neutrophils infiltrated the lungs at 24 h post-exposure, and slight pulmonary edema and perivascular-peribronchiolar edema appeared in the lungs at 48 h. Transcriptome analysis showed that the expression of a large number of genes related to leukocyte migration and chemotaxis consistently increased in the lungs upon exposure to RT, and the expression of genes that participate in acute phase immune and/or inflammatory response, also increased within 12 h of exposure to RT, which could be confirmed by the measurement of cytokines, such as IL-1β, TNF-α and IL-6, in bronchoalveolar lavage fluid. While the expression of genes related to cellular components of the extracellular matrix and cell membrane integrity consistently decreased in the lungs, and the expression of genes related to antioxidant activity also decreased within the first 12 h. There are 17 differentially expressed genes (DEGs) that participate in ribotoxic stress response, endoplasmic reticulum stress response or immune response in the lungs at 4 h post-exposure. The expression of these DEGs was upregulated, and the number of these DEGs accounted for about 59 % of all DEGs at 4 h. The 17 DEGs may play an important role in the occurrence and development of inflammation. Notably, Atf3, Egr1, Gdf15 and Osm, which are poorly studied, may be important targets for the subsequent research of RT-induced pulmonary intoxication. This study provides new information and insights for RT-induced pulmonary intoxication, and it can provide a reference for the subsequent study of the toxicological mechanism and therapeutic approaches for RT-induced pulmonary intoxication.

Disease-modifying treatment of chemical threat agent-induced acute lung injury

Acute respiratory distress syndrome (ARDS) is a highly morbid lung pathology induced by exposure to chemical warfare agents, including vesicants, phosgene, chlorine, and ricin. In this review, we describe the pathology associated with the development of ARDS in humans and experimental models of acute lung injury following animal exposure to these high-priority threat agents. Potential future approaches to disease-modifying treatment used in preclinical animal studies, including antioxidants, anti-inflammatories, biologics, and mesenchymal stem cells, are also described. As respiratory pathologies, including ARDS, are the major cause of morbidity and mortality following exposure to chemical threat agents, understanding mechanisms of disease pathogenesis is key to the development of efficacious therapeutics beyond the primary intervention principle, which remains mechanical ventilation.

Cross-Talk Between Alveolar Macrophages and Lung Epithelial Cells is Essential to Maintain Lung Homeostasis

The main function of the lung is to perform gas exchange while maintaining lung homeostasis despite environmental pathogenic and non-pathogenic elements contained in inhaled air. Resident cells must keep lung homeostasis and eliminate pathogens by inducing protective immune response and silently remove innocuous particles. Which lung cell type is crucial for this function is still subject to debate, with reports favoring either alveolar macrophages (AMs) or lung epithelial cells (ECs) including airway and alveolar ECs. AMs are the main immune cells in the lung in steady-state and their function is mainly to dampen inflammatory responses. In addition, they phagocytose inhaled particles and apoptotic cells and can initiate and resolve inflammatory responses to pathogens. Although AMs release a plethora of mediators that modulate immune responses, ECs also play an essential role as they are more than just a physical barrier. They produce anti-microbial peptides and can secrete a variety of mediators that can modulate immune responses and AM functions. Furthermore, ECs can maintain AMs in a quiescent state by expressing anti-inflammatory membrane proteins such as CD200. Thus, AMs and ECs are both very important to maintain lung homeostasis and have to coordinate their action to protect the organism against infection. Thus, AMs and lung ECs communicate with each other using different mechanisms including mediators, membrane glycoproteins and their receptors, gap junction channels, and extracellular vesicles. This review will revisit characteristics and functions of AMs and lung ECs as well as different communication mechanisms these cells utilize to maintain lung immune balance and response to pathogens. A better understanding of the cross-talk between AMs and lung ECs may help develop new therapeutic strategies for lung pathogenesis.

Endpoint and epitope-specific antibody responses as correlates of vaccine-mediated protection of mice against ricin toxin

The successful licensure of vaccines for biodefense is contingent upon the availability of well-established correlates of protection (CoP) in at least two animal species that can be applied to humans, without the need to assess efficacy in the clinic. In this report we describe a multivariate model that combines pre-challenge serum antibody endpoint titers (EPT) and values derived from an epitope profiling immune-competition capture (EPICC) assay as a predictor in mice of vaccine-mediated immunity against ricin toxin (RT), a Category B biothreat. EPICC is a modified competition ELISA in which serum samples from vaccinated mice were assessed for their ability to inhibit the capture of soluble, biotinylated (b)-RT by a panel of immobilized monoclonal antibodies (mAbs) directed against four immunodominant toxin-neutralizing regions on the enzymatic A chain (RTA) of RT. In a test cohort of mice (n = 40) vaccinated with suboptimal doses of the RTA subunit vaccine, RiVax®, we identified two mAbs, PB10 and SyH7, which had EPICC inhibition values in pre-challenge serum samples that correlated with survival following a challenge with 5 × LD₅₀ of RT administered by intraperitoneal (IP) injection. Analysis of a larger cohort of mice (n = 645) revealed that a multivariate model combining endpoint titers and EPICC values for PB10 and SyH7 as predictive variables had significantly higher statistical power than any one of the independent variables alone. Establishing the correlates of vaccine-mediated protection in mice represents an important steppingstone in the development of RiVax® as a medical countermeasure under the United States Food and Drug Administration's "Animal Rule."

Study on Intervention Mechanism of Yiqi Huayu Jiedu Decoction on ARDS Based on Network Pharmacology

Background

Yiqi Huayu Jiedu (YQHYJD) is a traditional Chinese medicine decoction made up of eight traditional Chinese medicines. Although YQHYJD is effectively used to prevent and treat ARDS/acute lung injury (ALI) in rats, the molecular mechanisms supporting its clinical application remain elusive. The purpose of the current study was to understand its lung protective effects at the molecular level using network pharmacology approach.

Methods

In an ARDS animal model, the beneficial pharmacological activities of YQHYJD were confirmed by reduced lung tissue damage levels observed on drug treated rats versus control group. We then proposed a network analysis to discover the key nodes based on drugs and disease network. Subsequently, we analyzed interaction networks and screened key targets. Using Western blot to detect the expression level of key targets, the intervention effect of changes in expression level of key targets on ARDS was evaluated.

Results

Pathway enrichment analysis of highly ranked genes showed that ErbB pathways were highly related to ARDS. Finally, western blot results showed decreased level of the AKT1 and KRAS/NRAS/HRAS protein in the lung after treatment which confirmed the hypothesis.

Conclusion

In conclusion, our results suggest that YQHYJD can exert lung tissue protective effect against the severe injury through multiple pathways, including the endothelial cells permeability improvement, inflammatory reaction inhibition, edema, and lung tissue hemorrhage reduction.

The low density receptor-related protein 1 plays a significant role in ricin-mediated intoxication of lung cells

Ricin, a highly lethal plant-derived toxin, is a potential biological threat agent due to its high availability, ease of production and the lack of approved medical countermeasures for post-exposure treatment. To date, no specific ricin receptors were identified. Here we show for the first time, that the low density lipoprotein receptor-related protein-1 (LRP1) is a major target molecule for binding of ricin. Pretreating HEK293 acetylcholinesterase-producer cells with either anti-LRP1 antibodies or with Receptor-Associated Protein (a natural LRP1 antagonist), or using siRNA to knock-down LRP1 expression resulted in a marked reduction in their sensitivity towards ricin. Binding assays further demonstrated that ricin bound exclusively to the cluster II binding domain of LRP1, via the ricin B subunit. Ricin binding to the cluster II binding domain of LRP1 was significantly reduced by an anti-ricin monoclonal antibody, which confers high-level protection to ricin pulmonary-exposed mice. Finally, we tested the contribution of LRP1 receptor to ricin intoxication of lung cells derived from mice. Treating these cells with anti-LRP1 antibody prior to ricin exposure, prevented their intoxication. Taken together, our findings clearly demonstrate that the LRP1 receptor plays an important role in ricin-induced pulmonary intoxications.

Intracellular Neutralization of Ricin Toxin by Single-domain Antibodies Targeting the Active Site

The extreme potency of the plant toxin, ricin, is due to its enzymatic subunit, RTA, which inactivates mammalian ribosomes with near-perfect efficiency. Here we characterized, at the functional and structural levels, seven alpaca single-domain antibodies (VHHs) previously reported to recognize epitopes in proximity to RTA's active site. Three of the VHHs, V2A11, V8E6, and V2G10, were potent inhibitors of RTA in vitro and protected Vero cells from ricin when expressed as intracellular antibodies ("intrabodies"). Crystal structure analysis revealed that the complementarity-determining region 3 (CDR3) elements of V2A11 and V8E6 penetrate RTA's active site and interact with key catalytic residues. V2G10, by contrast, sits atop the enzymatic pocket and occludes substrate accessibility. The other four VHHs also penetrated/occluded RTA's active site, but lacked sufficient binding affinities to outcompete RTA-ribosome interactions. Intracellular delivery of high-affinity, single-domain antibodies may offer a new avenue in the development of countermeasures against ricin toxin.toxin, antibody, structure, intracellular.

Passive immunization with an extended half-life monoclonal antibody protects Rhesus macaques against aerosolized ricin toxin

Inhalation of ricin toxin (RT), a Category B biothreat agent, provokes an acute respiratory distress syndrome marked by pro-inflammatory cytokine and chemokine production, neutrophilic exudate, and pulmonary edema. The severity of RT exposure is attributed to the tropism of the toxin's B subunit (RTB) for alveolar macrophages and airway epithelial cells, coupled with the extraordinarily potent ribosome-inactivating properties of the toxin's enzymatic subunit (RTA). While there are currently no vaccines or treatments approved to prevent RT intoxication, we recently described a humanized anti-RTA IgG1 MAb, huPB10, that was able to rescue non-human primates (NHPs) from lethal dose RT aerosol challenge if administered by intravenous (IV) infusion within hours of toxin exposure. We have now engineered an extended serum half-life variant of that MAb, huPB10-LS, and evaluated it as a pre-exposure prophylactic. Five Rhesus macaques that received a single intravenous infusion (25 mg/kg) of huPB10-LS survived a lethal dose aerosol RT challenge 28 days later, whereas three control animals succumbed to RT intoxication within 48 h. The huPB10-LS treated animals remained clinically normal in the hours and days following toxin insult, suggesting that pre-existing antibody levels were sufficient to neutralize RT locally. Moreover, pro-inflammatory markers in sera and BAL fluids collected 24 h following RT challenge were significantly dampened in huPB10-LS treated animals, as compared to controls. Finally, we found that all five surviving animals, within days after RT exposure, had anti-RT serum IgG titers against epitopes other than huPB10-LS, indicative of active immunization by residual RT and/or RT-immune complexes.

Intramuscular Ricin Poisoning of Mice Leads to Widespread Damage in the Heart, Spleen, and Bone Marrow

Ricin, a lethal toxin derived from castor oil beans, is a potential bio-threat due to its high availability and simplicity of preparation. Ricin is prepared according to simple recipes available on the internet, and was recently considered in terrorist, suicide, or homicide attempts involving the parenteral route of exposure. In-depth study of the morbidity developing from parenteral ricin poisoning is mandatory for tailoring appropriate therapeutic measures to mitigate ricin toxicity in such instances. The present study applies various biochemical, hematological, histopathological, molecular, and functional approaches to broadly investigate the systemic effects of parenteral intoxication by a lethal dose of ricin in a murine model. Along with prompt coagulopathy, multi-organ hemorrhages, and thrombocytopenia, ricin induced profound morpho-pathological and functional damage in the spleen, bone marrow, and cardiovascular system. In the heart, diffuse hemorrhages, myocyte necrosis, collagen deposition, and induction in fibrinogen were observed. Severe functional impairment was manifested by marked thickening of the left ventricular wall, decreased ventricular volume, and a significant reduction in stroke volume and cardiac output. Unexpectedly, the differential severity of the ricin-induced damage did not correlate with the respective ricin-dependent catalytic activity measured in the various organs. These findings emphasize the complexity of ricin toxicity and stress the importance of developing novel therapeutic strategies that will combine not only anti-ricin specific therapy, but also will target ricin-induced indirect disturbances.

Rescue of rhesus macaques from the lethality of aerosolized ricin toxin

Ricin toxin (RT) ranks at the top of the list of bioweapons of concern to civilian and military personnel alike, due to its high potential for morbidity and mortality after inhalation. In nonhuman primates, aerosolized ricin triggers severe acute respiratory distress characterized by perivascular and alveolar edema, neutrophilic infiltration, and severe necrotizing bronchiolitis and alveolitis. There are currently no approved countermeasures for ricin intoxication. Here, we report the therapeutic potential of a humanized mAb against an immunodominant epitope on ricin's enzymatic A chain (RTA). Rhesus macaques that received i.v. huPB10 4 hours after a lethal dose of ricin aerosol exposure survived toxin challenge, whereas control animals succumbed to ricin intoxication within 30 hours. Antibody intervention at 12 hours resulted in the survival of 1 of 5 monkeys. Changes in proinflammatory cytokine, chemokine, and growth factor profiles in bronchial alveolar lavage fluids before and after toxin challenge successfully clustered animals by treatment group and survival, indicating a relationship between local tissue damage and experimental outcome. This study represents the first demonstration, to our knowledge, in nonhuman primates that the lethal effects of inhalational ricin exposure can be negated by a drug candidate, and it opens up a path forward for product development.