The nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate/D-NO), increases survival by attenuating hyperoxia-compromised innate immunity in bacterial clearance in a mouse model of ventilator-associated pneumonia

GAT107-mediated α7 nicotinic acetylcholine receptor signaling attenuates inflammatory lung injury and mortality in a mouse model of ventilator-associated pneumonia by alleviating macrophage mitochondrial oxidative stress via reducing MnSOD-S-glutathionylation

Supraphysiological concentrations of oxygen (hyperoxia) can compromise host defense and increase susceptibility to bacterial and viral infections, causing ventilator-associated pneumonia (VAP). Compromised host defense and inflammatory lung injury are mediated, in part, by high extracellular concentrations of HMGB1, which can be decreased by GTS-21, a partial agonist of α7 nicotinic acetylcholine receptor (α7nAChR). Here, we report that a novel α7nAChR agonistic positive allosteric modulator (ago-PAM), GAT107, at 3.3 mg/kg, i.p., significantly decreased animal mortality and markers of inflammatory injury in mice exposed to hyperoxia and subsequently infected with Pseudomonas aeruginosa. The incubation of macrophages with 3.3 μM of GAT107 significantly decreased hyperoxia-induced extracellular HMGB1 accumulation and HMGB1-induced macrophage phagocytic dysfunction. Hyperoxia-compromised macrophage function was correlated with impaired mitochondrial membrane integrity, increased superoxide levels, and decreased manganese superoxide dismutase (MnSOD) activity. This compromised MnSOD activity is due to a significant increase in its level of glutathionylation. The incubation of hyperoxic macrophages with 3.3 μM of GAT107 significantly decreases the levels of glutathionylated MnSOD, and restores MnSOD activity and mitochondrial membrane integrity. Thus, GAT107 restored hyperoxia-compromised phagocytic functions by decreasing HMGB1 release, most likely via a mitochondrial-directed pathway. Overall, our results suggest that GAT107 may be a potential treatment to decrease acute inflammatory lung injury by increasing host defense in patients with VAP.

Using Restricted Cubic Splines to Study the Duration of Antibiotic Use in the Prognosis of Ventilator-Associated Pneumonia

Background: Ventilator-associated pneumonia (VAP) is the most widespread and life-threatening nosocomial infection in intensive care units (ICUs). The duration of antibiotic use is a good predictor of prognosis in patients with VAP, but the ideal duration of antibiotic therapy for VAP in critically ill patients has not been confirmed. Research is therefore needed into the optimal duration of antibiotic use and its impact on VAP.

Methods: The Medical Information Mart for Intensive Care database included 1,609 patients with VAP. Chi-square or Student’s t-tests were used to compare groups, and Cox regression analysis was used to investigate the factors influencing the prognoses of patients with VAP. Nonlinear tests were performed on antibiotic use lasting <7, 7–10, and >10 days. Significant factors were included in the model for sensitivity analysis. For the subgroup analyses, the body mass indexes (BMIs) of patients were separated into BMI <30 kg/m2 and BMI ≥30 kg/m2, with the criterion of statistical significance set at p < 0.05. Restricted cubic splines were used to analyze the relationship between antibiotic use duration and mortality risk in patients with VAP.

Results: In patients with VAP, the effects of antibiotic use duration on the outcomes were nonlinear. Antibiotic use for 7–10 days in models 1–3 increased the risk of antibiotic use by 2.6020-, 2.1642-, and 2.3263-fold relative to for >10 days, respectively. The risks in models 1–3 for <7 days were 2.6510-, 1.9933-, and 2.5151-fold higher than those in models with >10 days of antibiotic use, respectively. These results were robust across the analyses.

Conclusions: The duration of antibiotic treatment had a nonlinear effect on the prognosis of patients with VAP. Antibiotic use durations of <7 days and 7–10 days both presented risks, and the appropriate duration of antibiotic use can ensure the good prognosis of patients with VAP.

Nrf2 Is Required for Optimal Alveolar-Macrophage-Mediated Apoptotic Neutrophil Clearance after Oxidant Injury

Recognition and clearance of apoptotic cells by phagocytes (also known as efferocytosis), primarily mediated by macrophages, are essential to terminate lung inflammatory responses and promote tissue repair after injury. The Nrf2 transcription factor is crucial for cytoprotection and host defense. Previously, we showed sustained neutrophilic lung inflammation in Nrf2-deficient (Nrf2^−/−) mice after hyperoxia-induced lung injury in vivo, but the mechanisms underlying this abnormal phenotype remain unclear. To examine whether Nrf2 regulates apoptotic neutrophil clearance, we used the alveolar macrophages (AMФs) and bone-marrow-derived macrophages (BMDMФs) of wild-type (WT) and Nrf2^−/− mice. We found that the efferocytic ability of AMФ was impaired in hyperoxia-exposed mice’s lungs, but the effect was more pronounced in Nrf2^−/− mice. Importantly, AMФ-mediated efferocytosis remained impaired in Nrf2^−/− mice recovering from injury but was restored to the basal state in the wild-type counterparts. Hyperoxia affected apoptotic neutrophil binding, not internalization, in both WT and Nrf2^−/− BMDMФs, but the effect was more significant in the latter cells. Augmenting Nrf2 activity restored hyperoxia attenuated efferocytosis in WT, but not in Nrf2^−/− macrophages. However, the loss of Nrf2 in neutrophils affected their uptake by WT macrophages. Collectively, these results demonstrate that Nrf2 is required for optimal macrophage-mediated efferocytosis and that activating Nrf2 may provide a physiological way to accelerate apoptotic cell clearance after oxidant injury.

WSV056 Inhibits Shrimp Nitric Oxide Synthase Activity by Downregulating Litopenaeus vannamei Sepiapterin Reductase to Promote White Spot Syndrome Virus Replication

Sepiapterin reductase (Spr) plays an essential role in the biosynthesis of tetrahydrobiopterin (BH4), a key cofactor of multiple enzymes involved in various physiological and immune processes. Suppression of Spr could result in BH4 deficiency-caused diseases in human and murine models. However, information on the biological function of Spr in invertebrates is limited. In this study, two Sprs (CG12116 and Sptr) from Drosophila melanogaster were found to be downregulated in transgenic flies overexpressing white spot syndrome virus (WSSV) immediate-early protein WSV056. CG12116 and Sptr exerted an inhibitory effect on the replication of the Drosophila C virus. A Litopenaeus vannamei Spr (LvSpr) exhibiting similarity of 64.1–67.5% and 57.3–62.2% to that of invertebrate and vertebrate Sprs, respectively, were cloned. L. vannamei challenged with WSSV revealed a significant decrease in LvSpr transcription and Spr activity in hemocytes. In addition, the BH4 co-factored nitric oxide synthase (Nos) activity in shrimp hemocytes was reduced in WSSV-infected and LvSpr knockdown shrimp, suggesting WSSV probably inhibits the LvNos activity through LvSpr downregulation to limit the production of nitric oxide (NO). Knockdown of LvSpr and LvNos caused the reduction in NO level in hemocytes and the increase of viral copy numbers in WSSV-infected shrimp. Supplementation of NO donor DETA/NO or double gene knockdown of WSV056 + LvSpr and WSV056 + LvNos recovered the NO production, whereas the WSSV copy numbers were decreased. Altogether, the findings demonstrated that LvSpr and LvNos could potentially inhibit WSSV. In turn, the virus has evolved to attenuate NO production via LvSpr suppression by WSV056, allowing evasion of host antiviral response to ensure efficient replication.

2-O, 3-O desulfated heparin (ODSH) increases bacterial clearance and attenuates lung injury in cystic fibrosis by restoring HMGB1-compromised macrophage function

BACKGROUND

High mobility group box 1 protein (HMGB1) is an alarmin following its release by immune cells upon cellular activation or stress. High levels of extracellular HMGB1 play a critical role in impairing the clearance of invading pulmonary pathogens and dying neutrophils in the injured lungs of cystic fibrosis (CF) and acute respiratory distress syndrome (ARDS). A heparin derivative, 2-O, 3-O desulfated heparin (ODSH), has been shown to inhibit HMGB1 release from a macrophage cell line and is efficacious in increasing bacterial clearance in a mouse model of pneumonia. Thus, we hypothesized that ODSH can attenuate the bacterial burden and inflammatory lung injury in CF and we conducted experiments to determine the underlying mechanisms.

METHODS

We determined the effects of ODSH on lung injury produced by Pseudomonas aeruginosa (PA) infection in CF mice with the transmembrane conductance regulator gene knockout (CFTR-/-). Mice were given ODSH or normal saline intraperitoneally, followed by the determination of the bacterial load and lung injury in the airways and lung tissues. ODSH binding to HMGB1 was determined using surface plasmon resonance and in silico docking analysis of the interaction of the pentasaccharide form of ODSH with HMGB1.

RESULTS

CF mice given 25 mg/kg i.p. of ODSH had significantly lower PA-induced lung injury compared to mice given vehicle alone. The CF mice infected with PA had decreased levels of nitric oxide (NO), increased levels of airway HMGB1 and HMGB1-impaired macrophage phagocytic function. ODSH partially attenuated the PA-induced alteration in the levels of NO and airway HMGB1 in CF mice. In addition, ODSH reversed HMGB1-impaired macrophage phagocytic function. These effects of ODSH subsequently decreased the bacterial burden in the CF lungs. In a surface plasmon resonance assay, ODSH interacted with HMGB1 with high affinity (KD = 3.89 × 10-8 M) and induced conformational changes that may decrease HMGB1's binding to its membrane receptors, thus attenuating HMGB1-induced macrophage dysfunction.

CONCLUSIONS

The results suggest that ODSH can significantly decrease bacterial infection-induced lung injury in CF mice by decreasing both HMGB1-mediated impairment of macrophage function and the interaction of HMGB1 with membrane receptors. Thus, ODSH could represent a novel approach for treating CF and ARDS patients that have HMGB1-mediated lung injury.

The Positive Allosteric Modulation of alpha7-Nicotinic Cholinergic Receptors by GAT107 Increases Bacterial Lung Clearance in Hyperoxic Mice by Decreasing Oxidative Stress in Macrophages

Supplemental oxygen therapy with supraphysiological concentrations of oxygen (hyperoxia; >21% O2) is a life-saving intervention for patients experiencing respiratory distress. However, prolonged exposure to hyperoxia can compromise bacterial clearance processes, due to oxidative stress-mediated impairment of macrophages, contributing to the increased susceptibility to pulmonary infections. This study reports that the activation of the α7 nicotinic acetylcholine receptor (α7nAChR) with the delete allosteric agonistic-positive allosteric modulator, GAT107, decreases the bacterial burden in mouse lungs by improving hyperoxia-induced lung redox imbalance. The incubation of RAW 264.7 cells with GAT107 (3.3 µM) rescues hyperoxia-compromised phagocytic functions in cultured macrophages, RAW 264.7 cells, and primary bone marrow-derived macrophages. Similarly, GAT107 (3.3 µM) also attenuated oxidative stress in hyperoxia-exposed macrophages, which prevents oxidation and hyper-polymerization of phagosome filamentous actin (F-actin) from oxidation. Furthermore, GAT107 (3.3 µM) increases the (1) activity of superoxide dismutase 1; (2) activation of Nrf2 and (3) the expression of heme oxygenase-1 (HO-1) in macrophages exposed to hyperoxia. Overall, these data suggest that the novel α7nAChR compound, GAT107, could be used to improve host defense functions in patients, such as those with COVID-19, who are exposed to prolonged periods of hyperoxia.

Nitric oxide-releasing compounds for the treatment of lung infections

The spread of acquired drug resistance and of microorganisms naturally resistant to antibiotics is a major threat to global health, leading to an urgent need for novel antimicrobial compounds. Exogenous nitric oxide (NO) represents an attractive and promising antimicrobial approach, showing both bactericidal and biofilm dispersal activities. Numerous studies have been performed to develop NO donor scaffolds, including small molecules, macromolecular compounds, nanoparticles (NPs), and polymeric materials. This approach has resulted in successful outcomes, with some NO-releasing compounds entering clinical practice. In this review, we highlight the importance of this strategy, with a focus on lung infections.

The α7 nicotinic acetylcholine receptor agonist GTS-21 improves bacterial clearance in mice by restoring hyperoxia-compromised macrophage function

BACKGROUND

Mechanical ventilation, in combination with supraphysiological concentrations of oxygen (i.e., hyperoxia), is routinely used to treat patients with respiratory distress, such as COVID-19. However, prolonged exposure to hyperoxia compromises the clearance of invading pathogens by impairing macrophage phagocytosis. Previously, we have shown that the exposure of mice to hyperoxia induces the release of the nuclear protein high mobility group box-1 (HMGB1) into the pulmonary airways. Furthermore, extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 (3-(2,4-dimethoxybenzylidene) anabaseine), an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could (1) inhibit hyperoxia-induced HMGB1 release into the airways; (2) enhance macrophage phagocytosis and (3) increase bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia.

METHOD

GTS-21 (0.04, 0.4, and 4 mg/kg) or saline were administered by intraperitoneal injection to mice that were exposed to hyperoxia (≥ 99% O₂) and subsequently challenged with PA.

RESULTS

The systemic administration of 4 mg/kg i.p. of GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1 compared to the saline control. To determine the mechanism of action of GTS-21, RAW 264.7 cells, a macrophage-like cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O₂. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from RAW 264.7 cells and attenuated hyperoxia-induced NF-κB activation in macrophages and mouse lungs exposed to hyperoxia and infected with PA.

CONCLUSIONS

Our results indicate that GTS-21 is efficacious in improving bacterial clearance and reducing acute lung injury via enhancing macrophage function by inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.