Holger Müller-Redetzky

Mechanical ventilation drives pneumococcal pneumonia into lung injury and sepsis in mice: protection by adrenomedullin

IntroductionVentilator-induced lung injury (VILI) contributes to morbidity and mortality in acute respiratory distress syndrome (ARDS). Particularly pre-injured lungs are susceptible to VILI despite protective ventilation. In a previous study, the endogenous peptide adrenomedullin (AM) protected murine lungs from VILI. We hypothesized that mechanical ventilation (MV) contributes to lung injury and sepsis in pneumonia, and that AM may reduce lung injury and multiple organ failure in ventilated mice with pneumococcal pneumonia.MethodsWe analyzed in mice the impact of MV in established pneumonia on lung injury, inflammation, bacterial burden, hemodynamics and extrapulmonary organ injury, and assessed the therapeutic potential of AM by starting treatment at intubation.ResultsIn pneumococcal pneumonia, MV increased lung permeability, and worsened lung mechanics and oxygenation failure. MV dramatically increased lung and blood cytokines but not lung leukocyte counts in pneumonia. MV induced systemic leukocytopenia and liver, gut and kidney injury in mice with pneumonia. Lung and blood bacterial burden was not affected by MV pneumonia and MV increased lung AM expression, whereas receptor activity modifying protein (RAMP) 1–3 expression was increased in pneumonia and reduced by MV. Infusion of AM protected against MV-induced lung injury (66% reduction of pulmonary permeability p < 0.01; prevention of pulmonary restriction) and against VILI-induced liver and gut injury in pneumonia (91% reduction of AST levels p < 0.05, 96% reduction of alanine aminotransaminase (ALT) levels p < 0.05, abrogation of histopathological changes and parenchymal apoptosis in liver and gut).ConclusionsMV paved the way for the progression of pneumonia towards ARDS and sepsis by aggravating lung injury and systemic hyperinflammation leading to liver, kidney and gut injury. AM may be a promising therapeutic option to protect against development of lung injury, sepsis and extrapulmonary organ injury in mechanically ventilated individuals with severe pneumonia.

Dynamics of pulmonary endothelial barrier function in acute inflammation: mechanisms and therapeutic perspectives

The lungs provide a large inner surface to guarantee respiration. In lung alveoli, a delicate membrane formed by endo- and epithelial cells with their fused basal lamina ensures rapid and effective gas exchange between alveolar and vascular compartments while concurrently forming a robust barrier against inhaled particles and microbes. However, upon infectious or sterile inflammatory stimulation, tightly regulated endothelial barrier leakiness is required for leukocyte transmigration. Further, endothelial barrier disruption may result in uncontrolled extravasation of protein-rich fluids. This brief review summarizes some important mechanisms of pulmonary endothelial barrier regulation and disruption, focusing on the role of specific cell populations, coagulation and complement cascades and mediators including angiopoietins, specific sphingolipids, adrenomedullin and reactive oxygen and nitrogen species for the regulation of pulmonary endothelial barrier function. Further, current therapeutic perspectives against development of lung injury are discussed.

Intermedin Stabilized Endothelial Barrier Function and Attenuated Ventilator-induced Lung Injury in Mice

Background Even protective ventilation may aggravate or induce lung failure, particularly in preinjured lungs. Thus, new adjuvant pharmacologic strategies are needed to minimize ventilator-induced lung injury (VILI). Intermedin/Adrenomedullin-2 (IMD) stabilized pulmonary endothelial barrier function in vitro. We hypothesized that IMD may attenuate VILI-associated lung permeability in vivo. Methodology/Principal Findings Human pulmonary microvascular endothelial cell (HPMVEC) monolayers were incubated with IMD, and transcellular electrical resistance was measured to quantify endothelial barrier function. Expression and localization of endogenous pulmonary IMD, and its receptor complexes composed of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs) 1–3 were analyzed by qRT-PCR and immunofluorescence in non ventilated mouse lungs and in lungs ventilated for 6 h. In untreated and IMD treated mice, lung permeability, pulmonary leukocyte recruitment and cytokine levels were assessed after mechanical ventilation. Further, the impact of IMD on pulmonary vasoconstriction was investigated in precision cut lung slices (PCLS) and in isolated perfused and ventilated mouse lungs. IMD stabilized endothelial barrier function in HPMVECs. Mechanical ventilation reduced the expression of RAMP3, but not of IMD, CRLR, and RAMP1 and 2. Mechanical ventilation induced lung hyperpermeability, which was ameliorated by IMD treatment. Oxygenation was not improved by IMD, which may be attributed to impaired hypoxic vasoconstriction due to IMD treatment. IMD had minor impact on pulmonary leukocyte recruitment and did not reduce cytokine levels in VILI. Conclusions/Significance IMD may possibly provide a new approach to attenuate VILI.

Antihistone Properties of C1 Esterase Inhibitor Protect against Lung Injury

&NA; Rationale: Acute respiratory distress syndrome is characterized by alveolar epithelial cell injury, edema formation, and intraalveolar contact phase activation. Objectives: To explore whether C1 esterase inhibitor (C1INH), an endogenous inhibitor of the contact phase, may protect from lung injury in vivo and to decipher the possible underlying mechanisms mediating protection. Methods: The ability of C1INH to control the inflammatory processes was studied in vitro and in vivo. Measurements and Main Results: Here, we demonstrate that application of C1INH alleviates bleomycin‐induced lung injury via direct interaction with extracellular histones. In vitro, C1INH was found to bind all histone types. Interaction with histones was independent of its protease inhibitory activity, as demonstrated by the use of reactive‐center‐cleaved C1INH, but dependent on its glycosylation status. C1INH sialylated‐N‐ and ‐O‐glycans were not only essential for its interaction with histones but also to protect against histone‐induced cell death. In vivo, histone‐C1INH complexes were detected in bronchoalveolar lavage fluid from patients with acute respiratory distress syndrome and multiple models of lung injury. Furthermore, reactive‐center‐cleaved C1INH attenuated pulmonary damage evoked by intravenous histone instillation. Conclusions: Collectively, C1INH administration provides a new therapeutic option for disorders associated with histone release.

Moxifloxacin is not anti-inflammatory in experimental pneumococcal pneumonia

OBJECTIVES Anti-inflammatory functions of antibiotics may counteract deleterious hyperinflammation in pneumonia. Moxifloxacin reportedly exhibits immunomodulatory properties, but experimental evidence in pneumonia is lacking. Therefore, we investigated moxifloxacin in comparison with ampicillin regarding pneumonia-associated pulmonary and systemic inflammation and lung injury. METHODS Ex vivo infected human lung tissue and mice with pneumococcal pneumonia were examined regarding local inflammatory response and bacterial growth. In vivo, clinical course of the disease, leucocyte dynamics, pulmonary vascular permeability, lung pathology and systemic inflammation were investigated. In addition, transcellular electrical resistance of thrombin-stimulated endothelial cell monolayers was quantified. RESULTS Moxifloxacin reduced cytokine production in TNF-α-stimulated, but not in pneumococci-infected, human lung tissue. In vivo, moxifloxacin treatment resulted in reduced bacterial load as compared with ampicillin, whereas inflammatory parameters and lung pathology were not different. Moxifloxacin-treated mice developed less pulmonary vascular permeability during pneumonia, but neither combination therapy with moxifloxacin and ampicillin in vivo nor examination of endothelial monolayer integrity in vitro supported direct barrier-stabilizing effects of moxifloxacin. CONCLUSIONS The current experimental data do not support the hypothesis that moxifloxacin exhibits potent anti-inflammatory properties in pneumococcal pneumonia.

Targeting neutrophil extracellular traps in acute lung injury: a novel therapeutic approach in acute respiratory distress syndrome?

725 April 2015 T he pathogenesis of organ injury, including acute respiratory distress syndrome (ARDS), includes the liberation of endogenous molecular structures called “danger-associated molecular patterns” that are associated with inflammation and tissue injury. Targeting danger-associated molecular patterns thus may be a potential approach for novel ARDS therapies. extracellular deoxyribonucleic acid (DNA) forms neutrophil extracellular traps (NeT), which act like a danger-associated molecular pattern in that they are associated with inflammation and tissue injury. however, we have learned from the blockade of specific cytokines or the use of activated protein C in sepsis and ARDS that there are very narrow therapeutic opportunities, and a single therapy may not be useful for these syndromes caused by partly very distinct pathomechanisms. Given this background, the current study in animals by Yildiz et al.1 investigated the role of NeTs in the pathogenesis of acute lung injury in mice. They used a double-hit model of intratracheal lipopolysaccharide challenge followed by ventilator-induced lung injury (VILI). In this widely used model, they found correlates for VILI-induced NeT formation in vivo; however, NeT degradation by DNase treatment had no impact on the development of lung injury. hence, the authors propose that NeTs do not contribute functionally to the pathogenesis of lung injury in this animal model. Neutrophil extracellular traps are decondensed DNA expelled mainly by neutrophils during a process termed NeTosis. NeTosis is a tightly controlled cell death pathway requiring among others neutrophil elastase, myeloperoxidase, and reactive oxygen species. Various intracellular components such as histones, proteases, and antimicrobial peptides are bound to the expelled DNA. NeTs can bind various pathogens, immobilize or “trap” them, and ultimately promote their killing.2 They trap bacteria during bacteremia, thereby counteracting the dissemination of infections.3,4 Patients with chronic granulomatous disease (lacking reactive oxygen species production due to NADPh oxidase NOX2 deficiency) or complete myeloperoxidase deficiency cannot form NeTs. Their enhanced susceptibility to fungal infections may be explained by the lack of NeTs, as hyphae of Candida species escape phagocytosis due to their size and require NeTs for clearance.5 however, NeTs also exhibit harmful effects. NeTs and especially NeT-bound components such as histones are cytotoxic causing endothelial damage and vascular permeability.6 NeTs are also potent activators of coagulation and have been identified as drivers of organ failure in sepsis due to disruption of the microcirculation.3 The role of NeTs in sterile organ damage such as VILI is not fully understood. In the current study, Yildiz et al. addressed this important question in a well-established VILI model. They found that lipopolysaccharide induced infiltration of neutrophils regardless of additional VILI. however, the combination of lipopolysaccharide and high tidal volume ventilation induced a significant increase in DNA content in the bronchoalveolar lavage. Together with enhanced amounts of citrullinated histone 3, they concluded that NeTosis is induced by VILI in lipopolysaccharide-treated animals. When they next treated Targeting Neutrophil Extracellular Traps in Acute Lung Injury

Therapeutic strategies in pneumonia: going beyond antibiotics

Dysregulation of the innate immune system drives lung injury and its systemic sequelae due to breakdown of vascular barrier function, harmful hyperinflammation and microcirculatory failure, which contribute to the unfavourable outcome of patients with severe pneumonia. A variety of promising therapeutic targets have been identified and numerous innovative therapeutic approaches demonstrated to improve lung injury in experimental preclinical studies. However, at present specific preventive or curative strategies for the treatment of lung failure in pneumonia in addition to antibiotics are still missing. The aim of this mini-review is to give a short overview of some, but not all, adjuvant therapeutic strategies for pneumonia and its most important complications, sepsis and acute respiratory distress syndrome, and briefly discuss future perspectives. A review of preclinical and clinical research on adjuvant therapies for pneumonia http://ow.ly/OeiN3

Self-extracellular RNA acts in synergy with exogenous danger signals to promote inflammation

Self-extracellular RNA (eRNA), released from stressed or injured cells upon various pathological situations such as ischemia-reperfusion-injury, has been shown to act as an alarmin by inducing procoagulatory and proinflammatory responses. In particular, M1-polarization of macrophages by eRNA resulted in the expression and release of a variety of cytokines, including tumor necrosis factor (TNF)-α or interleukin-6 (IL-6). The present study now investigates in which way self-eRNA may influence the response of macrophages towards various Toll-like receptor (TLR)-agonists. Isolated agonists of TLR2 (Pam2CSK4), TLR3 (PolyIC), TLR4 (LPS), or TLR7 (R848) induced the release of TNF-α in a concentration-dependent manner in murine macrophages, differentiated from bone marrow-derived stem cells by mouse colony stimulating factor. Here, the presence of eRNA shifted the dose-response curve for Pam2CSK4 (Pam) considerably to the left, indicating that eRNA synergistically enhanced the cytokine liberation from macrophages even at very low Pam-levels. The synergistic activation of TLR2 by eRNA/Pam was duplicated by other TLR2-agonists such as FSL-1 or Pam3CSK4. In contrast, for TLR4-agonists such as LPS a synergistic effect of eRNA was much weaker, and was not existent for TLR3-, or TLR7-agonists. The synergistic eRNA/Pam action was dependent on the NFκB-signaling pathway as well as on p38MAP- and MEK1/ERK-kinases and was prevented by predigestion of eRNA with RNase1 or by antibodies against TLR2. Thus, the presence of self-eRNA as alarming molecule sensitizes innate immune responses towards pathogen-associated molecular patterns (PAMPs) in a synergistic way and may thereby contribute to the differentiated outcome of inflammatory responses.

Neue pathogenetische Konzepte und pharmakologische Studien zur adjuvanten Therapie bei schwerer Pneumonie

Acute lung injury secondary to pneumonia results from inadequate activation of the innate immune system with hyperinflammation and alveolar-capillary barrier dysfunction. To date, effective strategies for prevention or treatment of acute lung injury in pneumonia besides antibiotics are lacking. In preclinical studies, promising therapeutic targets have been identified and novel strategies demonstrated to protect against lung failure in pneumonia. This review highlights some adjuvant therapeutic strategies for modulation of inflammation and stabilization of lung barrier function in pneumonia.

The Lung Endothelial Barrier in Acute Inflammation

In the lungs, alveolar endo- and epithelial cells and their merged basal laminae form a delicate membrane, which allows rapid and effective gas exchange between alveolar and vascular lumen and, at the same time, provides a barrier to protect against inhaled particles and pathogens. Following infectious or sterile inflammatory conditions, strictly controlled endothelial leakiness is required for leukocyte transmigration. However, increased permeability caused by host-dependent inflammatory mechanisms or pathogen-induced endothelial injury may lead to uncontrolled protein-rich fluid extravasation, lung edema and finally acute respiratory distress syndrome (ARDS), which still carries an unacceptably high mortality rate. This chapter gives an overview of major mechanisms underlying pulmonary endothelial barrier regulation and disruption, focusing on the role of specific cell populations, complement and coagulation systems and mediators including angiopoietins, sphingolipids, adrenomedullin, as well as reactive oxygen and nitrogen species in the regulation of pulmonary vascular permeability. Further, current therapeutic strategies targeting the pulmonary endothelial barrier to improve barrier function are discussed.