Inhibition of pulmonary nuclear factor kappa-B decreases the severity of acute Escherichia coli pneumonia but worsens prolonged pneumonia

Transcriptome analysis revealed that ischemic post-conditioning suppressed the expression of inflammatory genes in lung ischemia-reperfusion injury

Introduction

Ischemic post-conditioning (I-post C) is a recognized therapeutic strategy for lung ischemia/reperfusion injury (LIRI). However, the specific mechanisms underlying the lung protection conferred by I-post C remain unclear. This study aimed to investigate the protective mechanisms and potential molecular regulatory networks of I-post C on lung tissue.

Methods

Transcriptome analysis was performed on rat lung tissues obtained from Sham, ischemia-reperfusion (IR), and I-post C groups using RNA-seq to identify differentially expressed genes (DEGs). Subsequently, gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and gene set enrichment analysis (GSEA) were conducted to elucidate significantly enriched pathways in the IR and I-post C groups. Additionally, protein-protein interaction (PPI) network analysis was carried out to examine associations among the DEGs. Pathological changes in lung tissues were assessed using hematoxylin-eosin (H&E) staining. The expression levels of CXCL1 and CXCL6 in the IR and I-post C groups were evaluated through immunofluorescence and Western blotting.

Results

Our results showed that I-post C significantly attenuated both pulmonary edema and inflammatory cell infiltration. Transcriptome analysis identified 38 DEGs in the I-post C group compared to the IR group, comprising 21 upregulated and 17 downregulated genes. Among these, seven inflammation-related DEGs exhibited co-expression patterns with the Sham and IR groups, with notable downregulation of Cxcl1 and Cxcl6. GO analysis primarily linked these DEGs to neutrophil activation, chemotaxis, cytokine activity, and CCR chemokine receptor binding. KEGG analysis revealed enriched pathways, including the IL-17, TNF, and NF-κB signaling pathways. GSEA indicated downregulation of neutrophil chemotaxis and the IL-17 signaling pathway, correlating with reduced expression of Cxcl1 and Cxcl6. Validation of Cxcl1 and Cxcl6 mRNA expression via immunofluorescence and Western blotting supported the RNA-seq findings. Furthermore, a PPI network was constructed to elucidate interactions among the 29 DEGs.

Conclusions

Through RNA-Seq analysis, we concluded that I-post C may reduce inflammation and suppress the IL-17 signaling pathway, thereby protecting against lung damage caused by LIRI, potentially involving neutrophil extracellular traps.

A Systematic Review of Gene Expression Studies in Critically Ill Patients with Sepsis and Community-Acquired Pneumonia

(1) Background: Sepsis is present in nearly 90% of critically ill patients with community-acquired pneumonia (CAP). This systematic review updates the information on studies that have assessed gene expression profiles in critically ill septic patients with CAP. (2) Methods: We searched for studies that satisfied the following criteria: (a) expression profile in critically ill patients with sepsis due to CAP, (b) presence of a control group, and (c) adult patients. Over-representation analysis was performed with clusterProfiler using the Hallmark and Reactome collections. (3) Results: A total of 4312 differentially expressed genes (DEGs) and sRNAs were included in the enrichment analysis. In the Hallmark collection, genes regulated by nuclear factor kappa B in response to tumor necrosis factor, genes upregulated by signal transducer and activator of transcription 5 in response to interleukin 2 stimulation, genes upregulated in response to interferon-gamma, genes defining the inflammatory response, a subgroup of genes regulated by MYC-version 1 (v1), and genes upregulated during transplant rejection were significantly enriched in critically ill septic patients with CAP. Moreover, 88 pathways were identified in the Reactome database. (4) Conclusions: This study summarizes the reported DEGs in critically ill septic patients with CAP and investigates their functional implications. The results highlight the complexity of immune responses during CAP.

Arabincoside B isolated from Caralluma arabica as a potential anti-pneumonitis in LPS mice model

Acute lung injury (ALI) is a life-threatening condition usually associated with poor therapeutic outcomes and a high mortality rate. Since 2019, the situation has worsened due to the COVID-19 pandemic. ALI had approximately 40% of deaths before COVID-19, mainly due to the dysfunction of the blood-gas barrier that led to lung edema, failure of gas exchange, and dyspnea. Many strategies have been taken to mitigate the disease condition, such as diuretics, surfactants, antioxidants, glucocorticoids, heparin, and ventilators with concomitant sedatives. However, until now, there is no available effective therapy for ALI. Thus, we are presenting a new compound termed Arabincoside B (AR-B), recently isolated from Caralluma arabica, to be tested in such conditions. For that, the lipopolysaccharide (LPS) mice model was used to investigate the capability of the AR-B compound to control the ALI compared to standard dexamethasone. The results showed that AR-B had a significant effect on retrieving ALI. A further mechanistic study carried out in the serum, lung homogenate, histological, and immunohistochemistry sections revealed that the AR-B either in 50 mg/kg or 75 mg/kg dose inhibited pro-inflammatory cytokines such as IL-6, IL-13, NF-κB, TNFα, and NO and stimulated regulatory cytokines IL-10. Moreover, AR-B showed a considerable potential to protect the pulmonary tissue against oxidative stress by decreasing MDA and increasing catalase and Nrf2. Also, the AR-B exhibited an anti-apoptotic effect on the lung epithelium, confirmed by reducing COX and BAX expression and upregulating Bcl-2 expression. These results pave its clinical application for ALI.

Aerosolized Pulmonary Delivery of mRNA Constructs Attenuates Severity of Escherichia coli Pneumonia in the Rat

Acute respiratory distress syndrome (ARDS), a rapid onset inflammatory lung disease with no effective specific therapy, typically has pathogenic etiology termed pneumonia. In previous studies nuclear factor-κB (NF-κB) inhibitor α super-repressor (IκBα-SR) and extracellular superoxide dismutase 3 (SOD3) reduced pneumonia severity when prophylactically delivered by viral vector. In this study, mRNA coding for green fluorescent protein, IκBα-SR, or SOD3 was complexed with cationic lipid, passed through a vibrating mesh nebulizer, and delivered to cell culture or directly to rats undergoing Escherichia coli pneumonia. Injury level was then assessed at 48 h. In vitro, expression was observed as early as 4 h in lung epithelial cells. IκBα-SR and wild-type IκBα mRNAs attenuated inflammatory markers, while SOD3 mRNA induced protective and antioxidant effects. In rat E. coli pneumonia, IκBα-SR mRNA reduced arterial carbon dioxide (pCO2) and reduced lung wet/dry ratio. SOD3 mRNA improved static lung compliance and alveolar-arterial oxygen gradient (AaDO2) and decreased bronchoalveolar lavage (BAL) bacteria load. White cell infiltration and inflammatory cytokine concentrations in BAL and serum were reduced by both mRNA treatments compared to scrambled mRNA controls. These findings indicate nebulized mRNA therapeutics are a promising approach to ARDS therapy, with rapid expression of protein and observable amelioration of pneumonia symptoms.

Oleocanthal alleviated lipopolysaccharide-induced acute lung injury in chickens by inhibiting TLR4/NF-κB pathway activation

This study aimed to investigate the ameliorative effect of oleocanthal (OC) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in chickens and its possible mechanisms. In total, 20 chickens were randomly divided into 4 groups: control (CON) group, LPS group, LPS + OC group, and OC group. LPS + OC and OC groups were intragastrically administered a 5 mg/kg·d OC dose for 7 d. On d 8, the LPS group and LPS + OC group were intratracheally administered 2 mg/kg LPS for 12 h. It was found that OC ameliorated the pathological morphology and significantly suppressed apoptosis after OC treatment in LPS-induced ALI chicken (P < 0.01). Antioxidant capacity was higher in the LPS + OC group compared with the LPS group (P < 0.01). OC downregulated the related genes and proteins expression of toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) pathway in LPS group (P < 0.01). In conclusion, OC supplementation can alleviate LPS-induced ALI in chickens by suppressing apoptosis, enhancing lung antioxidant capacities and inhibiting TLR4/NF-κB pathway activation.

Cell cycle kinase CHEK2 in macrophages alleviates the inflammatory response to Staphylococcus aureus-induced pneumonia

BACKGROUND

Excessive macrophage-mediated inflammation participates in the development of Staphylococcus aureus (S. aureus)-induced pneumonia. Checkpoint kinase 2 (Chek2) was screened out as macrophage-related infantile pneumonia gene after the differentially expressed analysis of RNAseq data derived from pam3CSK4 stimulated bone marrow-derived macrophages (BMDMs).

METHODS

RAW264.7 macrophage cells were transfected with Chek2-specific gRNA, which were further overexpressed with wide-type Chek2 or Chek2 kinase activity mutant (Chek2 KD, D368N). At the same time, the relative protein and mRNA expression of inflammatory cytokines were determined. C57BL/6J WT mice were intranasally infected with S. aureus to induce S. aureus-induced pneumonia, which was treated with BML-277, an inhibitor of Chek2. The symptoms of pneumonia mice and inflammatory cytokines associated with the nuclear factor kappa B (NF-κB) signaling pathways were further examined.

RESULTS

In vivo, BML-277 significantly promoted pneumonia symptoms, including mortality, lung infiltration of immune cells, and the abundance of lung pro-inflammatory cytokines. Mechanically, BML-277 did not affect BMDMs survival but up-regulated the mRNA expression of tumor necrosis factor (Tnf), nitric oxide synthase 2 (Nos2), interleukin (Il)23a, and the secretion of Tnf-α and Il-23a. At the same time, genetic complementation experiment testified that Chek2 KD did not inhibit NF-κB and relevant inflammatory cytokines expression.

CONCLUSION

Chek2 functions through the kinase mechanism to down-regulate the NF-κB pathway in macrophages to alleviate S. aureus-induced pneumonia in mice.

Nuclear factor-kappa B and its role in inflammatory lung disease

Nuclear factor-kappa B, involved in inflammation, host immune response, cell adhesion, growth signals, cell proliferation, cell differentiation, and apoptosis defense, is a dimeric transcription factor. Inflammation is a key component of many common respiratory disorders, including asthma, chronic obstructive pulmonary disease (COPD), bronchiectasis, and acute respiratory distress syndrome. Many basic transcription factors are found in NF-κB signaling, which is a member of the Rel protein family. Five members of this family c-REL, NF-κB2 (p100/p52), RelA (p65), NF-κB1 (p105/p50), RelB, and RelA (p65) produce 5 transcriptionally active molecules. Proinflammatory cytokines, T lymphocyte, and B lymphocyte cell mitogens, lipopolysaccharides, bacteria, viral proteins, viruses, double-stranded RNA, oxidative stress, physical exertion, various chemotherapeutics are the stimulus responsible for NF-κB activation. NF-κB act as a principal component for several common respiratory illnesses, such as asthma, lung cancer, pulmonary fibrosis, COPD as well as infectious diseases like pneumonia, tuberculosis, COVID-19. Inflammatory lung disease, especially COVID-19, can make NF-κB a key target for drug production.

Purified β-glucans from the Shiitake mushroom ameliorates antibiotic-resistant Klebsiella pneumoniae-induced pulmonary sepsis

Bacterial infection remains the main cause of acute respiratory distress syndrome and is a leading cause of death and disability in critically ill patients. Here we report on the use of purified β-glucan (lentinan) extracts from Lentinus edodes (Shiitake) mushroom that can reduce infection by a multidrug-resistant clinical isolate of Klebsiella pneumoniae in a rodent pneumonia model, likely through immunomodulation. Adult male Sprague-Dawley rats were subjected to intra-tracheal administration of K. pneumoniae to induce pulmonary sepsis and randomized to three groups; vehicle control (Vehicle, n = 12), commercial lentinan (CL, n = 8) or in-house extracted lentinan (IHL, n = 8) were administered intravenously 1 h postinfection. Physiological parameters and blood gas analysis were measured, bacterial counts from bronchoalveolar-lavage (BAL) were determined, along with differential staining of white cells and measurement of protein concentration in BAL 48 h after pneumonia induction. Use of IHL extract significantly decreased BAL CFU counts. Both CL and IHL extractions reduced protein concentration in BAL. Use of IHL resulted in an improvement in physiological parameters compared to controls and CL. In conclusion, administration of lentinan to treat sepsis-induced lung injury appears safe and effective and may exert its effects in an immunomodulatory manner.

Extracellular Vesicles from Interferon-γ-primed Human Umbilical Cord Mesenchymal Stromal Cells Reduce Escherichia coli-induced Acute Lung Injury in Rats

BACKGROUND

Human umbilical cord mesenchymal stromal cells possess considerable therapeutic promise for acute respiratory distress syndrome. Umbilical cord mesenchymal stromal cells may exert therapeutic effects via extracellular vesicles, while priming umbilical cord mesenchymal stromal cells may further enhance their effect. The authors investigated whether interferon-γ-primed umbilical cord mesenchymal stromal cells would generate mesenchymal stromal cell-derived extracellular vesicles with enhanced effects in Escherichia coli (E. coli) pneumonia.

METHODS

In a university laboratory, anesthetized adult male Sprague-Dawley rats (n = 8 to 18 per group) underwent intrapulmonary E. coli instillation (5 × 10 colony forming units per kilogram), and were randomized to receive (a) primed mesenchymal stromal cell-derived extracellular vesicles, (b) naïve mesenchymal stromal cell-derived extracellular vesicles (both 100 million mesenchymal stromal cell-derived extracellular vesicles per kilogram), or (c) vehicle. Injury severity and bacterial load were assessed at 48 h. In vitro studies assessed the potential for primed and naïve mesenchymal stromal cell-derived extracellular vesicles to enhance macrophage bacterial phagocytosis and killing.

RESULTS

Survival increased with primed (10 of 11 [91%]) and naïve (8 of 8 [100%]) mesenchymal stromal cell-derived extracellular vesicles compared with vehicle (12 of 18 [66.7%], P = 0.038). Primed-but not naïve-mesenchymal stromal cell-derived extracellular vesicles reduced alveolar-arterial oxygen gradient (422 ± 104, 536 ± 58, 523 ± 68 mm Hg, respectively; P = 0.008), reduced alveolar protein leak (0.7 ± 0.3, 1.4 ± 0.4, 1.5 ± 0.7 mg/ml, respectively; P = 0.003), increased lung mononuclear phagocytes (23.2 ± 6.3, 21.7 ± 5, 16.7 ± 5 respectively; P = 0.025), and reduced alveolar tumor necrosis factor alpha concentrations (29 ± 14.5, 35 ± 12.3, 47.2 ± 6.3 pg/ml, respectively; P = 0.026) compared with vehicle. Primed-but not naïve-mesenchymal stromal cell-derived extracellular vesicles enhanced endothelial nitric oxide synthase production in the injured lung (endothelial nitric oxide synthase/β-actin = 0.77 ± 0.34, 0.25 ± 0.29, 0.21 ± 0.33, respectively; P = 0.005). Both primed and naïve mesenchymal stromal cell-derived extracellular vesicles enhanced E. coli phagocytosis and bacterial killing in human acute monocytic leukemia cell line (THP-1) in vitro (36.9 ± 4, 13.3 ± 8, 0.1 ± 0.01%, respectively; P = 0.0004) compared with vehicle.

CONCLUSIONS

Extracellular vesicles from interferon-γ-primed human umbilical cord mesenchymal stromal cells more effectively attenuated E. coli-induced lung injury compared with extracellular vesicles from naïve mesenchymal stromal cells, potentially via enhanced macrophage phagocytosis and killing of E. coli.

Umbilical cord-derived CD362+ mesenchymal stromal cells for E. coli pneumonia: impact of dose regimen, passage, cryopreservation, and antibiotic therapy

Background

Mesenchymal stromal cells (MSCs) demonstrate considerable promise for acute respiratory distress syndrome (ARDS) and sepsis. However, standard approaches to MSC isolation generate highly heterogeneous cell populations, while bone marrow (BM) constitutes a limited and difficult to access MSC source. Furthermore, a range of cell manufacturing considerations and clinical setting practicalities remain to be explored.

Methods

Adult male rats were subject to E. coli-induced pneumonia and administered CD362⁺ umbilical cord (UC)-hMSCs using a variety of cell production and clinical relevance considerations. In series 1, animals were instilled with E. coli and randomized to receive heterogeneous BM or UC-hMSCs or CD362⁺ UC-hMSCs. Subsequent series examined the impact of concomitant antibiotic therapy, MSC therapeutic cryopreservation (cryopreserved vs fresh CD362⁺ UC-hMSCs), impact of cell passage on efficacy (passages 3 vs 5 vs 7 vs 10), and delay of administration of cell therapy (0 h vs 6 h post-injury vs 6 h + 12 h) following E. coli installation.

Results

CD362⁺ UC-hMSCs were as effective as heterogonous MSCs in reducing E. coli-induced acute lung injury, improving oxygenation, decreasing bacterial load, reducing histologic injury, and ameliorating inflammatory marker levels. Cryopreserved CD362⁺ UC-hMSCs recapitulated this efficacy, attenuating E. coli-induced injury, but therapeutic relevance did not extend beyond passage 3 for all indices. CD362⁺ UC-hMSCs maintained efficacy in the presence of antibiotic therapy and rescued the animal from E. coli injury when delivered at 6 h + 12 h, following E. coli instillation.

Conclusions

These translational studies demonstrated the efficacy of CD362⁺ UC-hMSCs, where they decreased the severity of E. coli-induced pneumonia, maintained efficacy following cryopreservation, were more effective at early passage, were effective in the presence of antibiotic therapy, and could continue to provide benefit at later time points following E. coli injury.

Syndecan-2-positive, Bone Marrow-derived Human Mesenchymal Stromal Cells Attenuate Bacterial-induced Acute Lung Injury and Enhance Resolution of Ventilator-induced Lung Injury in Rats

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Human mesenchymal stromal cells demonstrate promise for acute respiratory distress syndrome, but current studies use highly heterogenous cell populations. We hypothesized that a syndecan 2 (CD362)-expressing human mesenchymal stromal cell subpopulation would attenuate Escherichia coli-induced lung injury and enhance resolution after ventilator-induced lung injury.

METHODS

In vitro studies determined whether CD362 human mesenchymal stromal cells could modulate pulmonary epithelial inflammation, wound healing, and macrophage phagocytosis. Two in vivo rodent studies determined whether CD362 human mesenchymal stromal cells attenuated Escherichia coli-induced lung injury (n = 10/group) and enhanced resolution of ventilation-induced injury (n = 10/group).

RESULTS

CD362 human mesenchymal stromal cells attenuated cytokine-induced epithelial nuclear factor kappa B activation, increased epithelial wound closure, and increased macrophage phagocytosis in vitro. CD362 human mesenchymal stromal cells attenuated Escherichia coli-induced injury in rodents, improving arterial oxygenation (mean ± SD, 83 ± 9 vs. 60 ± 8 mmHg, P < 0.05), improving lung compliance (mean ± SD: 0.66 ± 0.08 vs. 0.53 ± 0.09 ml · cm H2O, P < 0.05), reducing bacterial load (median [interquartile range], 1,895 [100-3,300] vs. 8,195 [4,260-8,690] colony-forming units, P < 0.05), and decreasing structural injury compared with vehicle. CD362 human mesenchymal stromal cells were more effective than CD362 human mesenchymal stromal cells and comparable to heterogenous human mesenchymal stromal cells. CD362 human mesenchymal stromal cells enhanced resolution after ventilator-induced lung injury in rodents, restoring arterial oxygenation (mean ± SD: 113 ± 11 vs. 89 ± 11 mmHg, P < 0.05) and lung static compliance (mean ± SD: 0.74 ± 0.07 vs. 0.45 ± 0.07 ml · cm H2O, P < 0.05), resolving lung inflammation, and restoring histologic structure compared with vehicle. CD362 human mesenchymal stromal cells efficacy was at least comparable to heterogenous human mesenchymal stromal cells.

CONCLUSIONS

A CD362 human mesenchymal stromal cell population decreased Escherichia coli-induced pneumonia severity and enhanced recovery after ventilator-induced lung injury.

Calpeptin attenuates cigarette smoke-induced pulmonary inflammation via suppressing calpain/IκBα signaling in mice and BEAS-2B cells

Exposure to cigarette smoke including secondhand smoking is the most important risk factor in the development of chronic obstructive pulmonary disease where incidence has substantially increased in recent decades. The mechanisms responsible for cigarette smoke-induced pulmonary inflammation remain unclear, and thus lack of effective treatment. The present study investigated the effect of calpeptin on attenuating cigarette smoke induced pulmonary inflammation and its potential mechanism and function. When BALB/c mice were exposed to cigarette smoke and received calpeptin intraperitoneally injection after 90 days, calpeptin histologically attenuated the accumulation of neutrophils (P < 0.001), eosinophils (P < 0.001), macrophages (P < 0.01), fibrinous exudation and proliferation within the interstitial and alveolar spaces. BEAS-2B cells were added with cigarette smoke extract in vitro and treated with calpeptin for 24 h in the treatment group. The markedly upregulation of μ-calpain (P < 0.01), m-calpain (P < 0.001) and IκBα (P < 0.01) in cigarette smoke-induced lungs were simultaneously decreased by calpeptin treatment (P < 0.05). The increased expression of μ-calpain, m-calpain and IκBα (P < 0.05) in cigarette smoke extract-stimulated BEAS-2B cells were also decreased by calpeptin treatment (P < 0.05). These data indicated that calpeptin attenuated cigarette smoke-induced pulmonary inflammation by suppressing the pathway of μ-calpain, m-calpain and IκBα in vivo and in vitro. Calpeptin might have a potential for prevention of the development of inflammatory pulmonary diseases and warrant further pharmaceutical investigation.

Tsr Chemoreceptor Interacts With IL-8 Provoking E. coli Transmigration Across Human Lung Epithelial Cells

Bacterial colonization of epithelial surfaces and subsequent transmigration across the mucosal barrier are essential for the development of infection. We hypothesized that the methyl-accepting proteins (MCPs), known as chemoreceptors expressed on Escherichia coli (E. coli) bacterial surface, play an important role in mediating bacterial transmigration. We demonstrated a direct interaction between human interleukin-8 (IL-8) and Tsr receptor, a major MCP chemoreceptor. Stimulation of human lung epithelial cell monolayer with IL-8 resulted in increased E. coli adhesion and transmigration of the native strain (RP437) and a strain expressing only Tsr (UU2373), as compared to a strain (UU2599) with Tsr truncation. The augmented E. coli adhesion and migration was associated with a higher expression of carcinoembryonic antigen-related cell adhesion molecule 6 and production of inflammatory cytokines/chemokines, and a lower expression of the tight junction protein claudin-1 and the plasma membrane protein caveolin-1 in lung epithelial cells. An increased E. coli colonization and pulmonary cytokine production induced by the RP437 and UU2373 strains was attenuated in mice challenged with the UU2599 strain. Our results suggest a critical role of the E. coli Tsr chemoreceptor in mediating bacterial colonization and transmigration across human lung epithelium during development of pulmonary infections.

Hypercapnic acidosis attenuates pulmonary epithelial stretch-induced injury via inhibition of the canonical NF-κB pathway

BACKGROUND

Hypercapnia, with its associated acidosis (HCA), is a consequence of respiratory failure and is also seen in critically ill patients managed with conventional "protective" ventilation strategies. Nuclear factor kappa-B (NF-κB), a pivotal transcription factor, is activated in the setting of injury and repair and is central to innate immunity. We have previously established that HCA protects against ventilation-induced lung injury in vivo, potentially via a mechanism involving inhibition of NF-κB signaling. We wished to further elucidate the role and mechanism of HCA-mediated inhibition of the NF-κB pathway in attenuating stretch-induced injury in vitro.

METHODS

Initial experiments examined the effect of HCA on cyclic stretch-induced inflammation and injury in human bronchial and alveolar epithelial cells. Subsequent experiments examined the role of the canonical NF-κB pathway in mediating stretch-induced injury and the mechanism of action of HCA. The contribution of pH versus CO2 in mediating this effect of HCA was also examined.

RESULTS

Pulmonary epithelial high cyclic stretch (22 % equibiaxial strain) activated NF-κB, enhanced interleukin-8 (IL-8) production, caused cell injury, and reduced cell survival. In contrast, physiologic stretch (10 % strain) did not activate inflammation or cause cell injury. HCA reduced cyclic mechanical stretch-induced NF-κB activation, attenuated IL-8 production, reduced injury, and enhanced survival, in bronchial and alveolar epithelial cells, following shorter (24 h) and longer (120 h) cyclic mechanical stretch. Pre-conditioning with HCA was less effective than when HCA was applied after commencement of cell stretch. HCA prevented the stretch-induced breakdown of the NF-κB cytosolic inhibitor IκBα, while IκBα overexpression "occluded" the effect of HCA. These effects were mediated by a pH-dependent mechanism rather than via CO2 per se.

CONCLUSIONS

HCA attenuates adverse mechanical stretch-induced epithelial injury and death, via a pH-dependent mechanism that inhibits the canonical NF-κB activation by preventing IκBα breakdown.

Aerosol-mediated delivery of AAV2/6-IκBα attenuates lipopolysaccharide-induced acute lung injury in rats

Inhibition of the proinflammatory transcription factor NF-κB has previously been shown to attenuate the inflammatory response in tissue after injury. However, the feasibility and efficacy of aerosolized adeno-associated viral (AAV) vector-delivered transgenes to inhibit the NF-κB pathway are less clear. Initial studies optimized the AAV vector for delivery of transgenes to the pulmonary epithelium. The effect of repeated nebulization on the integrity and transduction efficacy of the AAV vector was then examined. Subsequent in vivo studies examined the efficacy of aerosolized rAAV2/6 overexpressing the NF-κB inhibitor IκBα in a rodent endotoxin-induced lung injury model. Initial in vitro investigations indicated that rAAV2/6 was the most effective vector to transduce the lung epithelium, and maintained its integrity and transduction efficacy after repeated nebulization. In our in vivo studies, animals that received aerosolized rAAV2/6-IκBα demonstrated a significant increase in total IκBα levels in lung tissue relative to null vector-treated animals. Aerosolized rAAV2/6-IκBα attenuated endotoxin-induced bronchoalveolar lavage-detected neutrophilia, interleukin-6 and cytokine-induced neutrophil chemoattractant-1 levels, as well as total protein content, and decreased histologic indices of injury. These results demonstrate that aerosolized AAV vectors encoding human IκBα significantly attenuate endotoxin-mediated lung injury and may be a potential therapeutic candidate in the treatment of acute lung injury.

Human mesenchymal stromal cells decrease the severity of acute lung injury induced by E. coli in the rat

BACKGROUND

Mesenchymal stromal cells (MSCs) demonstrate considerable promise in preclinical acute respiratory distress syndrome models. We wished to determine the efficacy and mechanisms of action of human MSCs (hMSCs) in the setting of acute lung injury induced by prolonged Escherichia coli pneumonia in the rat.

METHODS

Adult male Sprague Dawley rats underwent intratracheal instillation of E. coli bacteria in all experiments. In Series 1, animals were randomised to intravenous administration of: (1) vehicle (phosphate buffered saline (PBS), 300 μL); (2) 1×10(7) fibroblasts/kg; (3) 1×10(7) hMSCs/kg or (4) 2×10(7) hMSCs/kg. Series 2 determined the lowest effective hMSC dose. Series 3 compared the efficacy of intratracheal versus intravenous hMSC administration, while Series 4 examined the efficacy of cryopreserved hMSC. Series 5 examined the efficacy of the hMSC secretome. Parallel in vitro experiments further assessed the potential for hMSCs to secrete LL-37 and modulate macrophage phagocytosis.

RESULTS

hMSC therapy reduced the severity of rodent E. coli pneumonia, improving survival, decreasing lung injury, reducing lung bacterial load and suppressing inflammation. Doses as low as 5×10(6) hMSCs/kg were effective. Intratracheal hMSC therapy was as effective as intravenous hMSC. Cryopreserved hMSCs were also effective, while the hMSC secretome was less effective in this model. hMSC therapy enhanced macrophage phagocytic capacity and increased lung and systemic concentrations of the antimicrobial peptide LL37.

CONCLUSIONS

hMSC therapy decreased E. coli induced pneumonia injury and reduced lung bacterial burden, potentially via enhanced macrophage phagocytosis and increased alveolar LL-37 concentrations.

Year in review 2013: Critical Care--sepsis

This review presents key publications from the research field of sepsis published in Critical Care and other relevant journals during 2013. The results of these experimental studies and clinical trials are discussed in the context of current scientific and clinical background. The discussion highlights and summarises articles on four main topics: sepsis pathogenesis, diagnostic and prognostic biomarkers, potential new therapies, and epidemiologic and outcome studies.

Pulmonary overexpression of inhibitor κBα decreases the severity of ventilator-induced lung injury in a rat model

BACKGROUND

Activation of the nuclear factor-κB (NF-κB) pathway is central to the pathogenesis of lung injury and inflammation. We determined whether targeted overexpression of inhibitor-κBα (IκBα) in the lung could decrease the severity of ventilator-induced lung injury (VILI).

METHODS

Anaesthetized adult male Sprague-Dawley rats were randomly allocated to undergo intratracheal instillation of: (i) vehicle alone (surfactant, n=10); (ii) 1×10(10) adeno-associated virus encoding IκBα (AAV-IκBα, n=10); (iii) 5×10(10) AAV-IκBα (n=10); and (iv) 1×10(10) AAV-Null (n=5). This was followed by 4 h of injurious mechanical ventilation. Subsequent experiments examined the effect of IκBα overexpression in animals undergoing 'protective' mechanical ventilation.

RESULTS

IκBα overexpression increased survival duration at both the lower [3.8 h (0.4)] and higher [3.6 h (0.7)] doses compared with vehicle [2.7 h (1.0)] or the null transgene [2.2 h (0.8)]. IκBα overexpression reduced the alveolar-arterial oxygen gradient (kPa) at both the lower [53 (21)] and higher [52 (19)] doses compared with vehicle [75 (8.5)] or the null transgene [70 (15)], decreased alveolar neutrophil infiltration, and reduced alveolar concentrations of interleukin (IL)-1β and IL-10. The lower IκBα dose was as effective as the higher dose. IκBα overexpression had no effect in the setting of protective lung ventilation.

CONCLUSIONS

Inhibition of pulmonary NF-κB activity by IκBα overexpression reduced the severity of VILI in a rat model.

Acidosis in the critically ill - balancing risks and benefits to optimize outcome

Acidosis is associated with poor outcome in critical illness. However, acidosis - both hypercapnic and metabolic - has direct effects that can limit tissue injury induced by many causes. There is also a clear potential for off-target harm with acute exposure (for example, raised intracranial pressure, pulmonary hypertension), and with exposure for prolonged periods (for example, increased risk of infection) or at high doses. Ongoing comprehensive determination of molecular, cellular and physiologic impact across a range of representative pathologies will allow us to understand better the risks and benefits of hypercapnia and acidosis during critical illness.

The dichotomy of inhibiting nuclear factor kappa-B in pneumonia

Activation of nuclear factor kappa-B (NF-κB) results in its translocation from the cytoplasm to the nucleus and binding to the promoters of a large number of genes, including those encoding proinflammatory cytokines and other mediators that can contribute to organ system dysfunction in severe infection. While inhibition of NF-κB activation has been proposed as a therapeutic approach in critical illness, several studies have indicated that such an approach may have deleterious effects in persistent infectious states, such as pneumonia. A new report from Devaney and colleagues shows that while inhibition of NF-κB may be useful in severe pneumonia associated with rapid progression to mortality, it leads to worsened pulmonary injury with increased bacterial numbers in the lungs in a model of prolonged pneumonia. Such data raise concerns about therapeutic approaches targeting NF-κB in critically ill patients with persistent infection.