Hyaluronic acid plasma levels during high versus low tidal volume ventilation in a porcine sepsis model

Background Shedding of the endothelial glycocalyx can be observed regularly during sepsis. Moreover, sepsis may be associated with acute respiratory distress syndrome (ARDS), which requires lung protective ventilation with the two cornerstones of application of low tidal volume and positive end-expiratory pressure. This study investigated the effect of a lung protective ventilation on the integrity of the endothelial glycocalyx in comparison to a high tidal volume ventilation mode in a porcine model of sepsis-induced ARDS. Methods After approval by the State and Institutional Animal Care Committee, 20 male pigs were anesthetized and received a continuous infusion of lipopolysaccharide to induce septic shock. The animals were randomly assigned to either low tidal volume ventilation, high tidal volume ventilation, or no-LPS-group groups and observed for 6 h. In addition to the gas exchange parameters and hematologic analyses, the serum hyaluronic acid concentrations were determined from central venous blood and from pre- and postpulmonary and pre- and postcerebral circulation. Post-mortem analysis included histopathological evaluation and determination of the pulmonary and cerebral wet-to-dry ratios. Results Both sepsis groups developed ARDS within 6 h of the experiment and showed significantly increased serum levels of hyaluronic acid in comparison to the no-LPS-group. No significant differences in the hyaluronic acid concentrations were detected before and after pulmonary and cerebral circulation. There was also no significant difference in the serum hyaluronic acid concentrations between the two sepsis groups. Post-mortem analysis showed no significant difference between the two sepsis groups. Conclusion In a porcine model of septic shock and ARDS, the serum hyaluronic acid levels were significantly elevated in both sepsis groups in comparison to the no-LPS-group. Intergroup comparison between lung protective ventilated and high tidal ventilated animals revealed no significant differences in the serum hyaluronic acid levels.

Sphingosine Kinase 1 Plays an Important Role in Atorvastatin-Mediated Anti-Inflammatory Effect against Acute Lung Injury

Atorvastatin is a 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) inhibitor and inhibits cholesterol synthesis. Recently, atorvastatin also showed anti-inflammatory effect in acute lung injury, ameliorating pulmonary gas-blood exchanging function. Sphingosine kinase 1 plays a central role in endothelial (EC) cytoskeleton rearrangement and EC barrier integrity regulation. In this study, the role of sphingosine kinase 1 in atorvastatin anti-inflammatory effect against acute lung injury was investigated. Both wild-type (WT) and SphK1-/- mice were challenged with high tidal volume ventilation (40 ml/kg body weight, 65 breathing/min, 4 hours). The acute lung injury was evaluated and the mechanisms were explored. In WT mice, atorvastatin treatment significantly decreased acute lung injury responding to high tidal volume ventilation (HT), including protein, cellular infiltration, and cytokine releasing; comparing to WT mice, SphK1-/- mice showed significantly worsen pulmonary injuries on HT model. Moreover, the atorvastatin-mediated anti-inflammatory effect was diminished in SphK1-/- mice. To further confirm the role of SphK1 in VILI, we then compared the inflammatory response of endothelial cells that were isolated from WT and SphK1-/- mice to cyclic stretching. Similarly, atorvastatin significantly decreased cytokine generation from WT EC responding to cyclic stretching. Atorvastatin also significantly preserved endothelial junction integrity in WT EC against thrombin challenge. However, the inhibitory effect of atorvastatin on cytokine generation induced by cyclic stretching was abolished on SphK1-/- mice EC. The endothelial junction integrity effects of atorvastatin also diminished on SphK1-/- mouse EC. Signal analysis indicated that atorvastatin inhibited JNK activation induced by cyclic stretch. SphK1 knockout also blocked atorvastatin-mediated VE-cadherin junction enhancement. In summary, by inhibition of MAPK activity and maintenance of EC junction homeostasis, SphK1 plays a critical role in atorvastatin-mediated anti-inflammatory effects in both cellular and in vivo model. This study also offers an insight into mechanical stress-mediated acute lung injury and potential therapy in the future.

Lung-protective ventilation increases cerebral metabolism and non-inflammatory brain injury in porcine experimental sepsis

Background Protective ventilation with lower tidal volumes reduces systemic and organ-specific inflammation. In sepsis-induced encephalopathy or acute brain injury the use of protective ventilation has not been widely investigated (experimentally or clinically). We hypothesized that protective ventilation would attenuate cerebral inflammation in a porcine endotoxemic sepsis model. The aim of the study was to study the effect of tidal volume on cerebral inflammatory response, cerebral metabolism and brain injury. Nine animals received protective mechanical ventilation with a tidal volume of 6 mL × kg−1 and nine animals were ventilated with a tidal volume of 10 mL × kg−1. During a 6-h experiment, the pigs received an endotoxin intravenous infusion of 0.25 µg × kg−1 × h−1. Systemic, superior sagittal sinus and jugular vein blood samples were analysed for inflammatory cytokines and S100B. Intracranial pressure, brain tissue oxygenation and brain microdialysis were sampled every hour. Results No differences in systemic or sagittal sinus levels of TNF-α or IL-6 were seen between the groups. The low tidal volume group had increased cerebral blood flow (p < 0.001) and cerebral oxygen delivery (p < 0.001), lower cerebral vascular resistance (p < 0.05), higher cerebral metabolic rate (p < 0.05) along with higher cerebral glucose consumption (p < 0.05) and lactate production (p < 0.05). Moreover, low tidal volume ventilation increased the levels of glutamate (p < 0.01), glycerol (p < 0.05) and showed a trend towards higher lactate to pyruvate ratio (p = 0.08) in cerebral microdialysate as well as higher levels of S-100B (p < 0.05) in jugular venous plasma compared with medium–high tidal volume ventilation. Conclusions Contrary to the hypothesis, protective ventilation did not affect inflammatory cytokines. The low tidal volume group had increased cerebral blood flow, cerebral oxygen delivery and cerebral metabolism together with increased levels of markers of brain injury compared with medium–high tidal volume ventilation.

SARS-CoV-2 infection reduces Krüppel-Like Factor 2 in human lung autopsy

ABSTRACTAcute respiratory distress syndrome (ARDS) occurred in ~12% of hospitalized COVID-19 patients in a recent New York City cohort. Pulmonary endothelial dysfunction, characterized by increased expression of inflammatory genes and increased monolayer permeability, is a major component of ARDS. Vascular leak results in parenchymal accumulation of leukocytes, protein, and extravascular water, leading to pulmonary edema, ischemia, and activation of coagulation associated with COVID-19. Endothelial inflammation further contributes to uncontrolled cytokine storm in ARDS. We have recently demonstrated that Krüppel-like factor 2 (KLF2), a transcription factor which promotes endothelial quiescence and monolayer integrity, is significantly reduced in experimental models of ARDS. Lung inflammation and high-tidal volume ventilation result in reduced KLF2, leading to pulmonary endothelial dysfunction and acute lung injury. Mechanistically, we found that KLF2 is a potent transcriptional activator of Rap guanine nucleotide exchange factor 3 (RAPGEF3) which orchestrates and maintains vascular integrity. Moreover, KLF2 regulates multiple genome-wide association study (GWAS)-implicated ARDS genes. Whether lung KLF2 is regulated by SARS-CoV-2 infection is unknown. Here we report that endothelial KLF2 is significantly reduced in human lung autopsies from COVID-19 patients, which supports that ARDS due to SARS-CoV-2 is a vascular phenotype possibly attributed to KLF2 down-regulation. We provide additional data demonstrating that KLF2 is down-regulated in SARS-CoV infection in mice.

Lung-Protective Ventilation Increases Cerebral Metabolism and Non-Inflammatory Brain Injury in Porcine Experimental Sepsis

Background: Protective ventilation with lower tidal volumes reduces systemic and organ-specific inflammation. In sepsis-induced encephalopathy or acute brain injury the use of protective ventilation has not been widely investigated (experimentally or clinically). We hypothesized that protective ventilation would attenuate cerebral inflammation in a porcine endotoxemic sepsis model. The aim of the study was to study the effect of tidal volume on cerebral inflammatory response, cerebral metabolism and brain injury. Nine animals received protective mechanical ventilation with a tidal volume of 6 mL x kg-1 and nine animals were ventilated with a tidal volume of 10 mL x kg-1. During a 6-hour experiment, the pigs received an endotoxin intravenous infusion of 0.25 µg x kg-1 x h-1. Systemic, superior sagittal sinus and jugular vein blood samples were analysed for inflammatory cytokines and S100B. Intracranial pressure, brain tissue oxygenation and brain microdialysis were sampled every hour. Results: No differences in systemic or sagittal sinus levels of TNF-α or IL-6 were seen between the groups. The low tidal volume group had increased cerebral blood flow (p<0.001) and cerebral oxygen delivery (p<0.001), lower cerebral vascular resistance (p<0.05), higher cerebral metabolic rate (p<0.05) along with higher cerebral glucose consumption (p<0.05) and lactate production (p<0.05). Moreover, low tidal volume ventilation increased the levels of glutamate (p<0.01), glycerol (p<0.08) and showed a trend towards higher lactate to pyruvate ratio (p=0.08) in cerebral microdialysate as well as higher levels of S-100B (p<0.05) in jugular venous plasma compared with medium-high tidal volume ventilation.Conclusions: Contrary to the hypothesis, protective ventilation did not affect inflammatory cytokines. The low tidal volume group had increased cerebral blood flow, cerebral oxygen delivery and cerebral metabolism together with increased levels of markers of brain injury compared with medium-high tidal volume ventilation.

Effects of high-tidal-volume mechanical ventilation on the expression of P2X7 receptor and inflammatory response in lung tissue of rats

Ventilator-induced lung injury is a severe complication mainly caused from mechanical ventilation (MV), associated with the upregulation of inflammation response. The mechanism still remains unclear. This study aims to explore the effects of pathological damage, neutrophil infiltration, expression of P2X7 receptor, and activation of Caspase-1 in lung tissue using a rat model. Sprague Dawley (SD) rats were randomly divided into sham group, conventional MV group, and high-tidal-volume ventilation group and fed with clean water and rat food. The sham group received tracheotomy without MV; conventional MV group was given 7 mL/kg tidal volume ventilation, and high-tidal-volume MV group was given 28 mL/kg tidal volume ventilation. All the rats were sacrificed after 4 h of ventilation or spontaneous breath. Lung wet/dry ratio was measured, and paraffin sections were prepared for pathological injury assessment and immunohistochemistry of P2X7 and myeloperoxidase levels. Lung homogenate was used for Western blot analysis of P2X7 receptor and Caspase-1 levels and real-time polymerase chain reaction (PCR) analysis of P2X7 gene expression level. Compared to sham group and conventional MV group, high-tidal-volume MV led to an increase in lung wet/dry ratio and histology score. High-tidal-volume ventilation also led to chemotaxis of neutrophils. The expression levels of protein and messenger RNA (mRNA) of P2X7 receptor were significantly upregulated. Cleaved-caspase-1 expression was also upregulated. All data provide the evidence that high-tidal-volume MV can lead to lung injury, neutrophils infiltration, and upregulation of cleaved-Caspase-1 level. This result may be related to the upregulation of P2X7 receptor expression.