Pre-Treatment with Ten-Minute Carbon Dioxide Inhalation Prevents Lipopolysaccharide-Induced Lung Injury in Mice via Down-Regulation of Toll-Like Receptor 4 Expression

Intraoperative partial pressure of arterial carbon dioxide levels and adverse outcomes in patients undergoing lung transplantation

OBJECTIVE

Patients undergoing lung transplantation (LTx) often experience abnormal hypercapnia or hypocapnia. This study aimed to investigate the association between intraoperative PaCO2 and postoperative adverse outcomes in patients undergoing LTx.

METHODS

We retrospectively reviewed the medical records of 151 patients undergoing LTx. Patients' demographics, perioperative clinical factors, and pre- and intraoperative PaCO2 data after reperfusion were collected and analyzed. Based on the PaCO2 levels, patients were classified into three groups: hypocapnia (≤35 mmHg), normocapnia (35.1-55 mmHg), and hypercapnia (>55 mmHg). Univariate and multivariable logistic regressions were used to identify independent risk factors for postoperative composite adverse events and in-hospital mortality.

RESULTS

Intraoperative hypercapnia occurred in 69 (45.7%) patients, and hypocapnia in 17 (11.2%). Patients with intraoperative PaCO2 of 35.1-45 mmHg showed a lower incidence of composite adverse events (53.3%) and mortality (6.2%) (P < 0.001). There was no significant difference in composite adverse events and mortality among preoperative PaCO2 groups (P > 0.05). Compared with intraoperative PaCO2 at 35.1-45 mmHg, the risk of composite adverse events in hypercapnia group increased: the adjusted OR was 3.07 (95% confidence interval [CI]: 1.36-6.94; P = 0.007). The risk of death was significantly higher in hypocapnia group than normocapnia group, the adjusted OR was 7.69 (95% CI: 1.68-35.24; P = 0.009). Over ascending ranges of PaCO2, PaCO2 at 55.1-65 mmHg had the strongest association with composite adverse events, the adjusted OR was 6.40 (95% CI: 1.18-34.65; P = 0.031).

CONCLUSION

These results demonstrate that intraoperative hypercapnia independently predicts postoperative adverse outcomes in patients undergoing LTx. Intraoperative hypocapnia shows predictive value for postoperative in-hospital mortality in LTx.

Carbon dioxide and MAPK signalling: towards therapy for inflammation

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

Identification of macrophage-related genes in sepsis-induced ARDS using bioinformatics and machine learning

Sepsis-induced acute respiratory distress syndrome (ARDS) is one of the leading causes of death in critically ill patients, and macrophages play very important roles in the pathogenesis and treatment of sepsis-induced ARDS. The aim of this study was to screen macrophage-related biomarkers for the diagnosis and treatment of sepsis-induced ARDS by bioinformatics and machine learning algorithms. A dataset including gene expression profiles of sepsis-induced ARDS patients and healthy controls was downloaded from the gene expression omnibus database. The limma package was used to screen 325 differentially expressed genes, and enrichment analysis suggested enrichment mainly in immune-related pathways and reactive oxygen metabolism pathways. The level of immune cell infiltration was analysed using the ssGSEA method, and then 506 macrophage-related genes were screened using WGCNA; 48 showed differential expression. PPI analysis was also performed. SVM-RFE and random forest map analysis were used to screen 10 genes. Three key genes, SGK1, DYSF and MSRB1, were obtained after validation with external datasets. ROC curves suggested that all three genes had good diagnostic efficacy. The nomogram model consisting of the three genes also had good diagnostic efficacy. This study provides new targets for the early diagnosis of sepsis-induced ARDS.

Intermittent Exposure of Hypercapnia Suppresses Allograft Rejection via Induction of Treg Differentiation and Inhibition of Neutrophil Accumulation

Background: In the management of major burn wounds, allogeneic skin transplantation is a critical procedure to improve wound repair. Our previous works found that intermittent exposure to carbon dioxide leads to permissive hypercapnia (HCA) and prolongs skin allograft survival. However, the modulatory effects of HCA exposure on the immune system are not well understood. Objectives: Our purpose was to investigate how intermittent exposure to HCA can effectively reduce the immune reaction to allogeneic skin graft rejection. Methods: A fully major histocompatibility complex-incompatible skin transplant from BALB/c to C57BL/6 mice model was utilized. Immune cells from splenic and draining lymph nodes were analyzed by flow cytometry. Serum proinflammatory cytokines were analyzed by ELISA. Results: Serum levels of IFN-γ, IL-2, IL-6, and TNF-α were significantly decreased in the HCA group. Additionally, the percentage of CD8+ cells in draining lymph nodes was significantly lower in HCA than in the control group. Moreover, the generation rate of FoxP3+ regulatory T cells (Tregs) from spleen naïve CD4+ T cells was increased by intermittent exposure to carbon dioxide. The infiltrated neutrophils were also eliminated by HCA. Taken together, we concluded that intermittent hypercapnia exposure could effectively suppress skin rejection by stimulating Treg cell generation and suppressing immune reactions.

Carbon dioxide inhibits COVID-19-type proinflammatory responses through extracellular signal-regulated kinases 1 and 2, novel carbon dioxide sensors

Mitogen-activated protein kinase (MAPK) signalling pathways are crucial for developmental processes, oncogenesis, and inflammation, including the production of proinflammatory cytokines caused by reactive oxygen species and upon severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. There are no drugs that can effectively prevent excessive inflammatory responses in endothelial cells in the lungs, heart, brain, and kidneys, which are considered the main causes of severe coronavirus disease 2019 (COVID-19). In this work, we demonstrate that human MAPKs, i.e. extracellular signal-regulated kinases 1 and 2 (ERK1/2), are CO₂ sensors and CO₂ is an efficient anti-inflammatory compound that exerts its effects through inactivating ERK1/2 in cultured endothelial cells when the CO₂ concentration is elevated. CO₂ is a potent inhibitor of cellular proinflammatory responses caused by H₂O₂ or the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. ERK1/2 activated by the combined action of RBD and cytokines crucial for the development of severe COVID-19, i.e. interferon-gamma (IFNγ) and tumour necrosis factor-α (TNFα), are more effectively inactivated by CO₂ than by dexamethasone or acetylsalicylic acid in human bronchial epithelial cells. Previously, many preclinical and clinical studies showed that the transient application of 5–8% CO₂ is safe and effective in the treatment of many diseases. Therefore, our research indicates that CO₂ may be used for the treatment of COVID-19 as well as the modification of hundreds of cellular pathways.

All‑trans retinoic acid promotes macrophage phagocytosis and decreases inflammation via inhibiting CD14/TLR4 in acute lung injury

Acute lung injury (ALI) is a common clinical emergency and all-trans retinoic acid (ATRA) can alleviate organ injury. Therefore, the present study investigated the role of ATRA in ALI. Lipopolysaccharide (LPS)-induced ALI rats were treated with ATRA and the arterial partial pressure of oxygen (PaO₂), lung wet/dry weight (W/D) ratio and protein content in the bronchial alveolar lavage fluid (BALF) were measured to evaluate the effect of ATRA on ALI rats. Alveolar macrophages were isolated from the BALF. The phagocytic function of macrophages was detected using the chicken erythrocyte phagocytosis method and flow cytometry. The viability of macrophages was measured using a Cell Counting Kit-8 assay, and apoptosis was analyzed using a TUNEL assay and flow cytometry. The expression levels of Toll-like receptor 4 (TLR4) and cluster of differentiation (CD)14 on the macrophage membrane were detected by immunofluorescence staining. The protein levels of TLR4, CD14, phosphorylated (p)-65, p65, p-IκBα and IκBα were analyzed using western blotting. The concentrations of IL-6, IL-1β and macrophage inflammatory protein-2 in the plasma of rats were detected by ELISA. Macrophages were treated with IAXO-102 (TLR4 inhibitor) to verify the involvement of CD14/TLR4 in the effect of ATRA on ALI. ATRA provided protection against LPS-induced ALI, as evidenced by the increased PaO₂ and reduced lung W/D ratio and protein content in the BALF. ATRA enhanced macrophage phagocytosis and viability and reduced apoptosis and inflammation in ALI rats. Mechanically, ATRA inhibited CD14 and TLR4 expression and NF-κB pathway activation. ATRA enhanced macrophage phagocytosis and reduced inflammation by inhibiting the CD14/TLR4-NF-κB pathway in LPS-induced ALI. In summary, ATRA inactivated the NF-κB pathway by inhibiting the expression of CD14/TLR4 receptor in the alveolar macrophages of rats, thus enhancing the phagocytic function of macrophages in ALI rats, improving the activity of macrophages, inhibiting apoptosis, reducing the levels of inflammatory factors, and consequently playing a protective role in ALI model rats. This study may offer novel insights for the clinical management of ALI.

Trelagliptin Alleviates Lipopolysaccharide (LPS)-Induced Inflammation and Oxidative Stress in Acute Lung Injury Mice

Acute lung injury (ALI) is an urgent disease lacking effective therapies, resulting in relatively high morbidity and mortality. The pathological mechanism of ALI is reported to be related to excessive inflammation and activated oxidative stress. The present study aims to investigate the protective effects of the DPP-4 inhibitor Trelagliptin against lipopolysaccharide (LPS)-induced ALI and the underlying mechanism. LPS was used to induce ALI mice models. The pathological condition of ALI mice was evaluated using MPO activity assay, lung wet to dry weight ratio detection, and HE staining on the lung tissues. Lung function was assessed using a spirometer. The oxidative stress level in the lung tissues was checked by MDA measurement and GPx detection using commercial kits. The leukocyte and neutrophil numbers were determined using a hemocytometer and the total concentration of protein in the BALF was detected using a bicinchoninic acid method. The expression levels of TNF-α, IL-6, and CXCL2 in the lung tissues were evaluated using qRT-PCR and ELISA. Western blot analysis was used to determine the expression levels of TLR4 and p-NF-κB p65. LPS-induced elevated MPO activity, pulmonary wet to dry weight ratio, airway resistance (RAW), the total number of leukocytes and neutrophils, production of inflammatory factors, decreased pulmonary dynamic compliance (Cdyn), and peak expiratory flow (PEF), and an aggravated histopathological state (such as disordered alveolar structure, significant pulmonary interstitial edema, and large numbers of red blood cells and inflammatory cells in the alveolar cavity) were significantly reversed by the administration of Trelagliptin. The TLR4/NF-κB signaling pathway was activated and oxidative stress was induced by stimulation with LPS; however, both effects were suppressed by the administration of Trelagliptin. Trelagliptin might alleviate LPS-induced inflammation and oxidative stress in acute lung injury mice.

Carbon dioxide-dependent signal transduction in mammalian systems

Carbon dioxide (CO2) is a fundamental physiological gas known to profoundly influence the behaviour and health of millions of species within the plant and animal kingdoms in particular. A recent Royal Society meeting on the topic of 'Carbon dioxide detection in biological systems' was extremely revealing in terms of the multitude of roles that different levels of CO2 play in influencing plants and animals alike. While outstanding research has been performed by leading researchers in the area of plant biology, neuronal sensing, cell signalling, gas transport, inflammation, lung function and clinical medicine, there is still much to be learned about CO2-dependent sensing and signalling. Notably, while several key signal transduction pathways and nodes of activity have been identified in plants and animals respectively, the precise wiring and sensitivity of these pathways to CO2 remains to be fully elucidated. In this article, we will give an overview of the literature relating to CO2-dependent signal transduction in mammalian systems. We will highlight the main signal transduction hubs through which CO2-dependent signalling is elicited with a view to better understanding the complex physiological response to CO2 in mammalian systems. The main topics of discussion in this article relate to how changes in CO2 influence cellular function through modulation of signal transduction networks influenced by pH, mitochondrial function, adenylate cyclase, calcium, transcriptional regulators, the adenosine monophosphate-activated protein kinase pathway and direct CO2-dependent protein modifications. While each of these topics will be discussed independently, there is evidence of significant cross-talk between these signal transduction pathways as they respond to changes in CO2. In considering these core hubs of CO2-dependent signal transduction, we hope to delineate common elements and identify areas in which future research could be best directed.

Hypercapnia in the critically ill: insights from the bench to the bedside

Carbon dioxide (CO2) has long been considered, at best, a waste by-product of metabolism, and at worst, a toxic molecule with serious health consequences if physiological concentration is dysregulated. However, clinical observations have revealed that 'permissive' hypercapnia, the deliberate allowance of respiratory produced CO2 to remain in the patient, can have anti-inflammatory effects that may be beneficial in certain circumstances. In parallel, studies at the cell level have demonstrated the profound effect of CO2 on multiple diverse signalling pathways, be it the effect from CO2 itself specifically or from the associated acidosis it generates. At the whole organism level, it now appears likely that there are many biological sensing systems designed to respond to CO2 concentration and tailor respiratory and other responses to atmospheric or local levels. Animal models have been widely employed to study the changes in CO2 levels in various disease states and also to what extent permissive or even directly delivered CO2 can affect patient outcome. These findings have been advanced to the bedside at the same time that further clinical observations have been elucidated at the cell and animal level. Here we present a synopsis of the current understanding of how CO2 affects mammalian biological systems, with a particular emphasis on inflammatory pathways and diseases such as lung specific or systemic sepsis. We also explore some future directions and possibilities, such as direct control of blood CO2 levels, that could lead to improved clinical care in the future.

Oxyberberine Prevented Lipopolysaccharide-Induced Acute Lung Injury through Inhibition of Mitophagy

Acute lung injury (ALI) is a serious respiratory syndrome characterized with uncontrolled inflammatory response. Oxyberberine has strong potential for clinical usage since it showed strong anti-inflammatory, antifungal, and antiarrhythmic effects in various diseases. In the present study, we evaluated whether oxyberberine can inhibit lipopolysaccharide- (LPS-) induced ALI in vivo and further evaluated the possible involvement of mitophagy in vitro by using A549 cells, a human lung epithelial cell line. Our in vivo study shows that oxyberberine significantly inhibited LPS-induced lung pathological injury and lung edema, as indicated by the changes in lung wet/dry ratio and total protein levels in the BALF in mice. Moreover, oxyberberine inhibited inflammation, as indicated by the changes of neutrophil accumulation and production of proinflammatory cytokines including tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6 in both the lung and bronchoalveolar lavage fluid (BALF) in ALI mice. Our in vitro study shows that LPS significantly decreased the protein level of mitochondrial proteins, including cytochrome c oxidase subunit IV (COX IV), p62, and mitofusin-2 (Mfn2) in A549 cells. In addition, LPS induced significant Parkin1 translocation from cytoplasm to mitochondria. These changes were significantly inhibited by oxyberberine. Notably, the inhibitory effect of oxyberberine was almost totally lost in the presence of lysosome fusion inhibitor bafilomycin A1 (Baf), a mitophagy inhibitor. In conclusion, the present study demonstrated that oxyberberine alleviated LPS-induced inflammation in ALI via inhibition of Parkin-mediated mitophagy.

Iridin Prevented Against Lipopolysaccharide-Induced Inflammatory Responses of Macrophages via Inactivation of PKM2-Mediated Glycolytic Pathways

Purpose

Abnormal glycolysis of immune cells contributed to the development of inflammatory response. Inhibition of this Warburg phenotype could be a promising strategy for preventing various inflammatory diseases. Iridin (IRD) is a natural isoflavone, and exerts anticancer, antioxidant, and anti-inflammatory effects. However, the underlying mechanism of IRD on acute inflammation remains unknown. In this study, the protective effects of IRD against lipopolysaccharide (LPS)-induced inflammation were investigated in murine macrophage RAW264.7 cells and in mice.

Methods

The inhibition of IRD on NO production in culture medium was detected by Griess assay while the levels of TNF-α, IL-1β, and MCP-1 were detected by ELISA assay. The effects of IRD on OCR and ECAR levels in LPS-treated macrophages were monitored by using Seahorse Analyzer. The apoptosis rate as well as the release of ROS and NO of RAW264.7 cells were analyzed by flow cytometric assay. The protective effects of IRD were investigated on LPS-induced inflammation in mice. The expressions of PKM2 and its downstream (p-JAK1, p-STAT1, p-STAT3, p-p65, iNOS, and COX2) in cells and in lung tissues were detected by Western blotting analysis.

Results

IRD treatment at the concentrations of 12.5-50 μM significantly inhibited the productions of TNF-α, IL-1β, MCP-1, and ROS, and suppressed the levels of glucose uptake and lactic acid in LPS-treated RAW264.7 cells. Oral administration with IRD (20-80 mg/kg) inhibited LPS-induced acute lung injury as well as inflammatory cytokine production in mice. Moreover, IRD targeted pyruvate kinase isozyme type M2 (PKM2) and suppressed its downstream p-JAK1, p-STAT1, p-STAT3, p-p65, iNOS, and COX2, which could be abolished by PKM2 agonist DASA-58 and antioxidant N-acetyl-L-cysteine, but partly be reversed by NF-κB activator CUT129 and JAK1 activator RO8191.

Conclusion

IRD alleviated LPS-induced inflammation through suppressing PKM2-mediated pathways, and could be a potential candidate for the prevention of inflammatory diseases.

Ischemia-reperfusion Injury in the Transplanted Lung: A Literature Review

Lung ischemia-reperfusion injury (LIRI) and primary graft dysfunction are leading causes of morbidity and mortality among lung transplant recipients. Although extensive research endeavors have been undertaken, few preventative and therapeutic treatments have emerged for clinical use. Novel strategies are still needed to improve outcomes after lung transplantation. In this review, we discuss the underlying mechanisms of transplanted LIRI, potential modifiable targets, current practices, and areas of ongoing investigation to reduce LIRI and primary graft dysfunction in lung transplant recipients.

Humidified Warmed CO2 Treatment Therapy Strategies Can Save Lives With Mitigation and Suppression of SARS-CoV-2 Infection: An Evidence Review

The coronavirus disease (COVID-19) outbreak has presented enormous challenges for healthcare, societal, and economic systems worldwide. There is an urgent global need for a universal vaccine to cover all SARS-CoV-2 mutant strains to stop the current COVID-19 pandemic and the threat of an inevitable second wave of coronavirus. Carbon dioxide is safe and superior antimicrobial, which suggests it should be effective against coronaviruses and mutants thereof. Depending on the therapeutic regime, CO2 could also ameliorate other COVID-19 symptoms as it has also been reported to have antioxidant, anti-inflammation, anti-cytokine effects, and to stimulate the human immune system. Moreover, CO2 has beneficial effects on respiratory physiology, cardiovascular health, and human nervous systems. This article reviews the rationale of early treatment by inhaling safe doses of warmed humidified CO2 gas, either alone or as a carrier gas to deliver other inhaled drugs may help save lives by suppressing SARS-CoV-2 infections and excessive inflammatory responses. We suggest testing this somewhat counter-intuitive, but low tech and safe intervention for its suitability as a preventive measure and treatment against COVID-19. Overall, development and evaluation of this therapy now may provide a safe and economical tool for use not only during the current pandemic but also for any future outbreaks of respiratory diseases and related conditions.

Chemo-photodynamic therapy by pulmonary delivery of gefitinib nanoparticles and 5-aminolevulinic acid for treatment of primary lung cancer of rats

Lung cancer is a severe disease with high mortality. Chemotherapy is one major treatment for lung cancer. However, systemic chemotherapeutics usually distribute throughout the body without specific lung distribution so that serious side effects are unavoidable. Photodynamic therapy (PDT) is occasionally used for lung cancer treatment but photosensitizers are also systemically administered and the bronchoscopic intervention under anesthesia may hurt lung tissues. Here, we combined inhaled chemotherapeutics and photosensitizers for chemo-photodynamic therapy (CPDT) of primary lung cancer of rats with external laser light irradiation. Gefitinib PLGA nanoparticles (GNPs) were prepared. The anti-cancer effects of GNPs and/or a common photosensitizer 5-aminolevulinic acid (5-ALA) were explored on A549 cells (adenocarcinomic human alveolar basal epithelial cells) and primary lung cancer rats after intratracheal administration. External light irradiation was applied due to its higher safety compared to internal light irradiation that may result in injuries after a laser optic fiber was intubated into the lung. The remarkable synergistic effect of CPDT was confirmed although the single therapies were also effective, where the high anti-lung cancer effects were shown and some typical lung cancer markers, including CD31, VEGF, NF-κB p65 and Bcl-2, significantly decreased. Moreover, the treatments attenuated inflammation with the downregulation of TNF-α. The combination of pulmonary drug delivery and chemo-photodynamic therapy is a promising strategy for treatment of lung cancer.