Prognostic and Pathogenic Role of Angiopoietin-1 and -2 in Pneumonia.

RATIONALE: During pneumonia, pathogen-host interaction evokes inflammation and lung barrier dysfunction. Tie2 activation by angiopoietin-1 reduces, whereas Tie2 blockade by angiopoietin-2 increases, inflammation and permeability during sepsis. The role of angiopoietin-1/-2 in pneumonia remains unidentified. OBJECTIVES: To investigate the prognostic and pathogenic impact of angiopoietins in regulating pulmonary vascular barrier function and inflammation in bacterial pneumonia. METHODS: Serum angiopoietin levels were quantified in pneumonia patients of two independent cohorts (n = 148, n = 395). Human postmortem lung tissue, pneumolysin- or angiopoietin-2-stimulated endothelial cells, isolated perfused and ventilated mouse lungs, and mice with pneumococcal pneumonia were investigated. MEASUREMENTS AND MAIN RESULTS: In patients with pneumonia, decreased serum angiopoietin-1 and increased angiopoietin-2 levels were observed as compared with healthy subjects. Higher angiopoietin-2 serum levels were found in patients with community-acquired pneumonia who died within 28 days of diagnosis compared with survivors. Receiver operating characteristic analysis revealed improved prognostic accuracy of CURB-65 for 28-day survival, intensive care treatment, and length of hospital stay if combined with angiopoietin-2 serum levels. In vitro, pneumolysin enhanced endothelial angiopoietin-2 release, angiopoietin-2 increased endothelial permeability, and angiopoietin-1 reduced pneumolysin-evoked endothelial permeability. Ventilated and perfused lungs of mice with angiopoietin-2 knockdown showed reduced permeability on pneumolysin stimulation. Increased pulmonary angiopoietin-2 and reduced angiopoietin-1 mRNA expression were observed in Streptococcus pneumoniae-infected mice. Finally, angiopoietin-1 therapy reduced inflammation and permeability in murine pneumonia. CONCLUSIONS: These data suggest a central role of angiopoietin-1/-2 in pneumonia-evoked inflammation and permeability. Increased angiopoietin-2 serum levels predicted mortality and length of hospital stay, and angiopoietin-1 may provide a therapeutic target for severe pneumonia.

Sphingosine Kinase 1 Regulates Inflammation and Contributes to Acute Lung Injury in Pneumococcal Pneumonia via the Sphingosine-1-Phosphate Receptor 2.

OBJECTIVES: Severe pneumonia may evoke acute lung injury, and sphingosine-1-phosphate is involved in the regulation of vascular permeability and immune responses. However, the role of sphingosine-1-phosphate and the sphingosine-1-phosphate producing sphingosine kinase 1 in pneumonia remains elusive. We examined the role of the sphingosine-1-phosphate system in regulating pulmonary vascular barrier function in bacterial pneumonia. DESIGN: Controlled, in vitro, ex vivo, and in vivo laboratory study. SUBJECTS: Female wild-type and SphK1-deficient mice, 8-10 weeks old. Human postmortem lung tissue, human blood-derived macrophages, and pulmonary microvascular endothelial cells. INTERVENTIONS: Wild-type and SphK1-deficient mice were infected with Streptococcus pneumoniae. Pulmonary sphingosine-1-phosphate levels, messenger RNA expression, and permeability as well as lung morphology were analyzed. Human blood-derived macrophages and human pulmonary microvascular endothelial cells were infected with S. pneumoniae. Transcellular electrical resistance of human pulmonary microvascular endothelial cell monolayers was examined. Further, permeability of murine isolated perfused lungs was determined following exposition to sphingosine-1-phosphate and pneumolysin. MEASUREMENTS AND MAIN RESULTS: Following S. pneumoniae infection, murine pulmonary sphingosine-1-phosphate levels and sphingosine kinase 1 and sphingosine-1-phosphate receptor 2 expression were increased. Pneumonia-induced lung hyperpermeability was reduced in SphK1 mice compared with wild-type mice. Expression of sphingosine kinase 1 in macrophages recruited to inflamed lung areas in pneumonia was observed in murine and human lungs. S. pneumoniae induced the sphingosine kinase 1/sphingosine-1-phosphate system in blood-derived macrophages and enhanced sphingosine-1-phosphate receptor 2 expression in human pulmonary microvascular endothelial cell in vitro. In isolated mouse lungs, pneumolysin-induced hyperpermeability was dose dependently and synergistically increased by sphingosine-1-phosphate. This sphingosine-1-phosphate-induced increase was reduced by inhibition of sphingosine-1-phosphate receptor 2 or its downstream effector Rho-kinase. CONCLUSIONS: Our data suggest that targeting the sphingosine kinase 1-/sphingosine-1-phosphate-/sphingosine-1-phosphate receptor 2-signaling pathway in the lung may provide a novel therapeutic perspective in pneumococcal pneumonia for prevention of acute lung injury.

Vasculotide reduces pulmonary hyperpermeability in experimental pneumococcal pneumonia.

BACKGROUND: Community-acquired pneumonia (CAP) is a significant cause of morbidity and mortality worldwide. Despite effective antimicrobial therapy, CAP can induce pulmonary endothelial hyperpermeability resulting in life-threatening lung failure due to an exaggerated host-pathogen interaction. Treatment of acute lung injury is mainly supportive because key elements of inflammation-induced barrier disruption remain undetermined. Angiopoietin-1 (Ang-1)-mediated Tie2 activation reduces, and the Ang-1 antagonist Ang-2 increases, inflammation and endothelial permeability in sepsis. Vasculotide (VT) is a polyethylene glycol-clustered Tie2-binding peptide that mimics the actions of Ang-1. The aim of our study was to experimentally test whether VT is capable of diminishing pneumonia-induced lung injury. METHODS: VT binding and phosphorylation of Tie2 were analyzed using tryptophan fluorescence spectroscopy and phospho-Tie-2 enzyme-linked immunosorbent assay. Human and murine lung endothelial cells were investigated by immunofluorescence staining and electric cell-substrate impedance sensing. Pulmonary hyperpermeability was quantified in VT-pretreated, isolated, perfused, and ventilated mouse lungs stimulated with the pneumococcal exotoxin pneumolysin (PLY). Furthermore, Streptococcus pneumoniae-infected mice were therapeutically treated with VT. RESULTS: VT showed dose-dependent binding and phosphorylation of Tie2. Pretreatment with VT protected lung endothelial cell monolayers from PLY-induced disruption. In isolated mouse lungs, VT decreased PLY-induced pulmonary permeability. Likewise, therapeutic treatment with VT of S. pneumoniae-infected mice significantly reduced pneumonia-induced hyperpermeability. However, effects by VT on the pulmonary or systemic inflammatory response were not observed. CONCLUSIONS: VT promoted pulmonary endothelial stability and reduced lung permeability in different models of pneumococcal pneumonia. Thus, VT may provide a novel therapeutic perspective for reduction of permeability in pneumococcal pneumonia-induced lung injury.