Geartsje Jongsma

High Levels of S100A8/A9 Proteins Aggravate Ventilator-Induced Lung Injury via TLR4 Signaling

Background Bacterial products add to mechanical ventilation in enhancing lung injury. The role of endogenous triggers of innate immunity herein is less well understood. S100A8/A9 proteins are released by phagocytes during inflammation. The present study investigates the role of S100A8/A9 proteins in ventilator-induced lung injury. Methods Pulmonary S100A8/A9 levels were measured in samples obtained from patients with and without lung injury. Furthermore, wild-type and S100A9 knock-out mice, naive and with lipopolysaccharide-induced injured lungs, were randomized to 5 hours of spontaneously breathing or mechanical ventilation with low or high tidal volume (VT). In addition, healthy spontaneously breathing and high VT ventilated mice received S100A8/A9, S100A8 or vehicle intratracheal. Furthermore, the role of Toll-like receptor 4 herein was investigated. Results S100A8/A9 protein levels were elevated in patients and mice with lung injury. S100A8/A9 levels synergistically increased upon the lipopolysaccharide/high VT MV double hit. Markers of alveolar barrier dysfunction, cytokine and chemokine levels, and histology scores were attenuated in S100A9 knockout mice undergoing the double-hit. Exogenous S100A8/A9 and S100A8 induced neutrophil influx in spontaneously breathing mice. In ventilated mice, these proteins clearly amplified inflammation: neutrophil influx, cytokine, and chemokine levels were increased compared to ventilated vehicle-treated mice. In contrast, administration of S100A8/A9 to ventilated Toll-like receptor 4 mutant mice did not augment inflammation. Conclusion S100A8/A9 proteins increase during lung injury and contribute to inflammation induced by HVT MV combined with lipopolysaccharide. In the absence of lipopolysaccharide, high levels of extracellular S100A8/A9 still amplify ventilator-induced lung injury via Toll-like receptor 4.

Pre-treatment with allopurinol or uricase attenuates barrier dysfunction but not inflammation during murine ventilator-induced lung injury.

Introduction Uric acid released from injured tissue is considered a major endogenous danger signal and local instillation of uric acid crystals induces acute lung inflammation via activation of the NLRP3 inflammasome. Ventilator-induced lung injury (VILI) is mediated by the NLRP3 inflammasome and increased uric acid levels in lung lavage fluid are reported. We studied levels in human lung injury and the contribution of uric acid in experimental VILI. Methods Uric acid levels in lung lavage fluid of patients with acute lung injury (ALI) were determined. In a different cohort of cardiac surgery patients, uric acid levels were correlated with pulmonary leakage index. In a mouse model of VILI the effect of allopurinol (inhibits uric acid synthesis) and uricase (degrades uric acid) pre-treatment on neutrophil influx, up-regulation of adhesion molecules, pulmonary and systemic cytokine levels, lung pathology, and regulation of receptors involved in the recognition of uric acid was studied. In addition, total protein and immunoglobulin M in lung lavage fluid and pulmonary wet/dry ratios were measured as markers of alveolar barrier dysfunction. Results Uric acid levels increased in ALI patients. In cardiac surgery patients, elevated levels correlated significantly with the pulmonary leakage index. Allopurinol or uricase treatment did not reduce ventilator-induced inflammation, IκB-α degradation, or up-regulation of NLRP3, Toll-like receptor 2, and Toll-like receptor 4 gene expression in mice. Alveolar barrier dysfunction was attenuated which was most pronounced in mice pre-treated with allopurinol: both treatment strategies reduced wet/dry ratio, allopurinol also lowered total protein and immunoglobulin M levels. Conclusions Local uric acid levels increase in patients with ALI. In mice, allopurinol and uricase attenuate ventilator-induced alveolar barrier dysfunction.

High-dose acetylsalicylic acid is superior to low-dose as well as to clopidogrel in preventing lipopolysaccharide-induced lung injury in mice.

Background Use of aspirin (acetylsalicylic acid [ASA]) was found to improve outcome in animal models of acute lung injury (ALI) or its more severe form, acute respiratory distress syndrome. In patients with acute respiratory distress syndrome, data indicating a protective effect of ASA are less convincing. We hypothesize that ASA in a high dose is superior to low-dose ASA in preventing lung injury. Also, the effect on lung injury of inhibiting platelet activation by clopidogrel was investigated. Methods Acute lung injury was induced by intranasal instillation of 10 &mgr;g lipopolysaccharide (LPS). Before LPS, BALB/c mice were pretreated with either high dose of ASA (100 &mgr;g/g intraperitoneally, low-dose ASA (12.5 &mgr;g/g i.p), clopidogrel (50 &mgr;g/g i.p), or clopidogrel in combination with low dose of ASA. Controls received vehicle or LPS without intervention. Five hours after LPS, bronchoalveolar lavage fluid (BALF) and plasma were obtained. Measurements and Main Results All treatment regimens reduced neutrophil influx in the BALF compared with LPS controls (high-dose ASA 75% ± 2% [mean ± SD], low-dose ASA 86% ± 3%, clopidogrel 82% ± 1%, and low-dose ASA–clopidogrel 82% ± 3% vs. LPS control 88% ± 2%; P ⩽ 0.05). High-dose ASA reduced BALF levels of protein compared with LPS controls (median [interquartile range], 0.2 [15] vs. 75 [20] pg/mL; P < 0.01), to a greater extent than after low-dose ASA (48 [32] pg/mL), clopidogrel (37 [23] pg/mL), or low-dose ASA–clopidogrel (57 [8] pg/mL). Conclusions High-dose ASA is superior to low-dose ASA, clopidogrel, and to a combination of clopidogrel and low-dose ASA in attenuating LPS-induced lung injury in mice, suggesting high-dose ASA to be the antiplatelet therapy of choice in further research on preventing ALI.

TLR2 deficiency aggravates lung injury caused by mechanical ventilation

ABSTRACT Innate immunity pathways are found to play an important role in ventilator-induced lung injury. We analyzed pulmonary expression of Toll-like receptor 2 (TLR2) in humans and mice and determined the role of TLR2 in the pathogenesis of ventilator-induced lung injury in mice. Toll-like receptor 2 gene expression was analyzed in human bronchoalveolar lavage fluid (BALF) cells and murine lung tissue after 5 h of ventilation. In addition, wild-type (WT) and TLR2 knockout (KO) mice were ventilated with either lower tidal volumes (VT) of 7 mL/kg with positive end-expiratory pressure (PEEP) or higher VT of 15 mL/kg without PEEP for 5 h. Spontaneously breathing mice served as controls. Total protein and immunoglobulin M levels in BALF, neutrophil influx into the alveolar compartment, and interleukin 6 (IL-6), IL-1&bgr;, and keratinocyte-derived chemokine concentrations in lung tissue homogenates were measured. We observed enhanced TLR2 gene expression in BALF cells of ventilated patients and in lung tissue of ventilated mice. In WT mice, ventilation with higher VT without PEEP resulted in lung injury and inflammation with higher immunoglobulin M levels, neutrophil influx, and levels of inflammatory mediators compared with controls. In TLR2 KO mice, neutrophil influx and IL-6, IL-1&bgr;, and keratinocyte-derived chemokine were enhanced by this ventilation strategy. Ventilation with lower VT with PEEP only increased neutrophil influx and was similar in WT and TLR2 KO mice. In summary, injurious ventilation enhances TLR2 expression in lungs. Toll-like receptor 2 deficiency does not protect lungs from ventilator-induced lung injury. In contrast, ventilation with higher VT without PEEP aggravates inflammation in TLR2 KO mice.