Evans blue dye as a marker of albumin clearance in cultured endothelial monolayer and isolated lung

Activated protein C binds directly to Tie2: possible beneficial effects on endothelial barrier function

Activated protein C (APC) is a natural anticoagulant with strong anti-inflammatory, anti-apoptotic, and barrier stabilizing properties. These cytoprotective properties of APC are thought to be exerted through its pathway involving the binding of APC to endothelial protein C receptor and cleavage of protease-activated receptors. In this study, we found that APC enhanced endothelial barrier integrity via a novel pathway, by binding directly to and activating Tie2, a transmembrane endothelial tyrosine kinase receptor. Binding assays demonstrated that APC competed with the only known ligands of Tie2, the angiopoietins (Angs). APC bound directly to Tie2 (Kd ~3 nM), with markedly stronger binding affinity than Ang2. After binding, APC rapidly activated Tie2 to enhance endothelial barrier function as shown by Evan's blue dye transfer across confluent cell monolayers and in vivo studies. Blocking Tie2 restricted endothelial barrier integrity. This study highlights a novel mechanism by which APC binds directly to Tie2 to enhance endothelial barrier integrity, which helps to explain APC's protective effects in vascular leakage-related pathologies.

Simple bioconjugate chemistry serves great clinical advances: albumin as a versatile platform for diagnosis and precision therapy

Albumin is the most abundant circulating protein in plasma and has recently emerged as a versatile protein carrier for drug targeting and for improving the pharmacokinetic profile of peptide or protein based drugs. Three drug delivery technologies related to albumin have been developed, which include the coupling of low-molecular weight drugs to exogenous or endogenous albumin, conjugating bioactive proteins by albumin fusion technology (AFT), and encapsulation of drugs into albumin nanoparticles. This review article starts with a brief introduction of human serum albumin (HSA), and then summarizes the mainstream chemical strategies of developing HSA binding molecules for coupling with drug molecules. Moreover, we also concisely condense the recent progress of the most important clinical applications of HSA-binding platforms, and specify the current challenges that need to be met for a bright future of HSA-binding.

Role of Dopamine and D2 Dopamine Receptor in the Pathogenesis of Inflammatory Bowel Disease

BACKGROUND

VEGF-induced vascular permeability and blood vessels remodeling are key features of inflammatory bowel disease (IBD) pathogenesis. Dopamine through D2 receptor (D2R) inhibits VEGF/VPF-mediated vascular permeability and angiogenesis in tumor models. In this study, we tested the hypothesis that pathogenesis of IBD is characterized by the disturbance of dopaminergic system and D2R activity.

METHODS

IL-10 knockout (KO) mice and rats with iodoacetamide-induced ulcerative colitis (UC) were treated intragastrically with D2R agonists quinpirole (1 mg/100 g) or cabergoline (1 or 5 µg/100 g). Macroscopic, histologic, and clinical features of IBD, colonic vascular permeability, and angiogenesis were examined.

RESULTS

Although colonic D2R protein increased, levels of tyrosine hydroxylase and dopamine transporter DAT decreased in both models of IBD. Treatment with quinpirole decreased the size of colonic lesions in rats with iodoacetamide-induced UC (p < 0.01) and reduced colon wet weight in IL-10 KO mice (p < 0.05). Quinpirole decreased colonic vascular permeability (p < 0.001) via downregulation of c-Src and Akt phosphorylation. Cabergoline (5 µg/100 g) reduced vascular permeability but did not affect angiogenesis and improved signs of iodoacetamide-induced UC in rats (p < 0.05).

CONCLUSIONS

Treatment with D2R agonists decreased the severity of UC in two animal models, in part, by attenuation of enhanced vascular permeability and prevention of excessive vascular leakage. Hence, the impairment dopaminergic system seems to be a feature of IBD pathogenesis.

Unexpected Role for Adaptive αβTh17 Cells in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a devastating disorder characterized by increased alveolar permeability with no effective treatment beyond supportive care. Current mechanisms underlying ARDS focus on alveolar endothelial and epithelial injury caused by products of innate immune cells and platelets. However, the role of adaptive immune cells in ARDS remains largely unknown. In this study, we report that expansion of Ag-specific αβTh17 cells contributes to ARDS by local secretion of IL-17A, which in turn directly increases alveolar epithelial permeability. Mice with a highly restrictive defect in Ag-specific αβTh17 cells were protected from experimental ARDS induced by a single dose of endotracheal LPS. Loss of IL-17 receptor C or Ab blockade of IL-17A was similarly protective, further suggesting that IL-17A released by these cells was responsible for this effect. LPS induced a rapid and specific clonal expansion of αβTh17 cells in the lung, as determined by deep sequencing of the hypervariable CD3RβVJ region of the TCR. Our findings could be relevant to ARDS in humans, because we found significant elevation of IL-17A in bronchoalveolar lavage fluid from patients with ARDS, and rIL-17A directly increased permeability across cultured human alveolar epithelial monolayers. These results reveal a previously unexpected role for adaptive immune responses that increase alveolar permeability in ARDS and suggest that αβTh17 cells and IL-17A could be novel therapeutic targets for this currently untreatable disease.

Adiponectin protects against hyperoxic lung injury and vascular leak

Adiponectin (Ad), an adipokine exclusively secreted by the adipose tissue, has emerged as a paracrine metabolic regulator as well as a protectant against oxidative stress. Pharmacological approaches of protecting against clinical hyperoxic lung injury during oxygen therapy/treatment are limited. We have previously reported that Ad inhibits the NADPH oxidase-catalyzed formation of superoxide from molecular oxygen in human neutrophils. Based on this premise, we conducted studies to determine whether (i) exogenous Ad would protect against the hyperoxia-induced barrier dysfunction in the lung endothelial cells (ECs) in vitro, and (ii) endogenously synthesized Ad would protect against hyperoxic lung injury in wild-type (WT) and Ad-overexpressing transgenic (AdTg) mice in vivo. The results demonstrated that exogenous Ad protected against the hyperoxia-induced oxidative stress, loss of glutathione (GSH), cytoskeletal reorganization, barrier dysfunction, and leak in the lung ECs in vitro. Furthermore, the hyperoxia-induced lung injury, vascular leak, and lipid peroxidation were significantly attenuated in AdTg mice in vivo. Also, AdTg mice exhibited elevated levels of total thiols and GSH in the lungs as compared with WT mice. For the first time, our studies demonstrated that Ad protected against the hyperoxia-induced lung damage apparently through attenuation of oxidative stress and modulation of thiol-redox status.

In Vivo Labeling of Serum Albumin for PET

The purpose of this study was to develop a novel in vivo albumin-labeling method to allow PET of cardiac function after myocardial infarction and vascular leakage and increased permeability in inflammatory diseases and malignant tumors.

METHODS

To label albumin in vivo, we synthesized a NOTA (1,4,7-triazacyclononane-N,N',N″-triacetic acid)-conjugated truncated form of Evans blue (NEB). (18)F labeling was achieved by the formation of an (18)F-aluminum fluoride ((18)F-AlF) complex, and (64)Cu labeling was obtained by a standard chelation method. Sixty-minute dynamic PET imaging was performed on normal mice to evaluate the distribution of (18)F-AlF-NEB, which was compared with in vitro-labeled mouse serum albumin ((18)F-fluorobenzyl-MSA). Electrocardiography-gated PET imaging was performed in a mouse model of myocardial infarction. Both dynamic and static PET scans were obtained in a mouse inflammation model induced by local injection of turpentine to evaluate vascular leakage. Tumor permeability was studied by dynamic and late-point static PET using (64)Cu-NEB in a UM-22B xenograft model.

RESULTS

NEB was successfully synthesized, and (18)F labeling including work-up took about 20-30 min, with a radiochemical purity greater than 95% without the need for high-performance liquid chromatography purification. Most of the radioactivity was retained in the circulation system at 60 min after injection (26.35 ± 1.52 percentage injected dose per gram [%ID/g]). With electrocardiography-gated PET, ventricles of the heart and major arteries were clearly visualized. The myocardial infarction mice showed much lower left ventricular ejection fraction than the control mice. Inflammatory muscles showed significantly higher tracer accumulation than the contralateral healthy ones. UM-22B tumor uptake of (64)Cu-NEB gradually increased with time (5.73 ± 1.11 %ID/g at 1 h and 8.03 ± 0.77 %ID/g at 2 h after injection).

CONCLUSION

The distribution and local accumulation of serum albumin can be noninvasively visualized and quantified by (18)F-AlF-NEB and (64)Cu-NEB PET. The simple labeling and broad applications make these imaging probes attractive for clinical translation.

The neuraminidase inhibitor oseltamivir is effective against A/Anhui/1/2013 (H7N9) influenza virus in a mouse model of acute respiratory distress syndrome

BACKGROUND

 High mortality and uncertainty about the effectiveness of neuraminidase inhibitors (NAIs) in humans infected with influenza A(H7N9) viruses are public health concerns.

METHODS

 Susceptibility of N9 viruses to NAIs was determined in a fluorescence-based assay. The NAI oseltamivir (5, 20, or 80 mg/kg/day) was administered to BALB/c mice twice daily starting 24, 48, or 72 hours after A/Anhui/1/2013 (H7N9) virus challenge.

RESULTS

 All 12 avian N9 and 3 human H7N9 influenza viruses tested were susceptible to NAIs. Without prior adaptation, A/Anhui/1/2013 (H7N9) caused lethal infection in mice that was restricted to the respiratory tract and resulted in pulmonary edema and acute lung injury with hyaline membrane formation, leading to decreased oxygenation, all characteristics of human acute respiratory distress syndrome. Oseltamivir at 20 and 80 mg/kg protected 80% and 88% of mice when initiated after 24 hours, and the efficacy decreased to 70% and 60%, respectively, when treatment was delayed by 48 hours. Emergence of oseltamivir-resistant variants was not detected.

CONCLUSIONS

 H7N9 viruses are comparable to currently circulating influenza A viruses in susceptibility to NAIs. Based on these animal studies, early treatment is associated with improved outcomes.

NF-κB activation in myeloid cells mediates ventilator-induced lung injury

Background

Although use of the mechanical ventilator is a life-saving intervention, excessive tidal volumes will activate NF-κB in the lung with subsequent induction of lung edema formation, neutrophil infiltration and proinflammatory cytokine/chemokine release. The roles of NF-κB and IL-6 in ventilator-induced lung injury (VILI) remain widely debated.

Methods

To study the molecular mechanisms of the pathogenesis of VILI, mice with a deletion of IкB kinase in the myeloid cells (IKKβ^△mye), IL-6^-/- to WT chimeric mice, and C57BL/6 mice (WT) were placed on a ventilator for 6 hr.

WT mice were also given an IL-6-blocking antibody to examine the role of IL-6 in VILI.

Results

Our results revealed that high tidal volume ventilation induced pulmonary capillary permeability, neutrophil sequestration, macrophage drifting as well as increased protein in bronchoalveolar lavage fluid (BALF). IL-6 production and IL-1β, CXCR2, and MIP2 expression were also increased in WT lungs but not in those pretreated with IL-6-blocking antibodies. Further, ventilator-induced protein concentrations and total cells in BALF, as well as lung permeability, were all significantly decreased in IKKβ^△mye mice as well as in IL6^-/- to WT chimeric mice.

Conclusion

Given that IKKβ^△mye mice demonstrated a significant decrease in ventilator-induced IL-6 production, we conclude that NF-κB–IL-6 signaling pathways induce inflammation, contributing to VILI, and IкB kinase in the myeloid cells mediates ventilator-induced IL-6 production, inflammation, and lung injury.

Permeability of endothelial barrier: cell culture and in vivo models

The methods for assessment of endothelial barrier permeability are vital tools of experimental biology. They allow us to measure permeability of endothelial monolayer in cell culture and in lung vessels or to determine formation of tissue edema resulting from increased permeability of vasculature. This chapter provides an overview of the most common protocols.

Peritonitis-induced peroxynitrite and lung damage depends on c-Jun NH2-terminal kinase signaling of hematopoietic cells

OBJECTIVES

Abdominal sepsis is a common, life-threatening condition in critically ill patients, and pseudomonas peritonitis remains a serious clinical complication of peritoneal dialysis. This study was performed to determine whether peritonitis induces lung damage through the c-Jun NH2-terminal kinase.

DESIGN

: Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Peritonitis models in the mice.

INTERVENTIONS

Wild-type, c-Jun NH2-terminal kinase1, and c-Jun NH2-terminal kinase1 mice were subjected to peritonitis. A c-Jun NH2-terminal kinase inhibitor, SP600125 or leflunomide, was administered to mice immediately after peritonitis.

MEASUREMENTS AND MAIN RESULTS

The changes of plasma dihydrorhodamine 123 oxidation level, the myeloperoxidase activity, and extravasations of Evans blue dye of lung in wild-type mice with or without c-Jun NH2-terminal kinase inhibitor; c-Jun NH2-terminal kinase1 mice and c-Jun NH2-terminal kinase1 mice; and chimeric mice (wild-type --> wild-type, c-Jun NH2-terminal kinase1 --> wild-type) with Pseudomonas aeruginosa-induced peritonitis were determined to evaluate the role of c-Jun NH2-terminal kinase signaling of the hematopoietic cells in peritonitis-induced lung damage. Our results showed that peritonitis induced dihydrorhodamine 123 oxidation, myeloperoxidase activity, activator protein-1 (AP-1) DNA binding activity, phosphorylated-c-Jun NH2-terminal kinase and inducible nitric oxide synthase expression, and Evans blue dye extravasations in lungs, and administration of specific c-Jun NH2-terminal kinase inhibitor decreased the peritonitis-induced dihydrorhodamine 123 oxidation and lung damage. Also, both c-Jun NH2-terminal kinase1 and c-Jun NH2-terminal kinase1 mice showed a decreased dihydrorhodamine 123 oxidation and lung damage after peritonitis. Finally, dihydrorhodamine 123 oxidation, reactive oxygen species, inducible nitric oxide synthase expression, and lung damage were decreased in c-Jun NH2-terminal kinase1 --> wild-type but not in wild-type --> c-Jun NH2-terminal kinase1 chimeric mice.

CONCLUSIONS

Collectively, our data suggest that peritonitis-induced inducible nitric oxide synthase expression, peroxynitrite production, and lung damage depend on the c-Jun NH2-terminal kinase signaling of the hematopoietic cells.

Real-time photoacoustic tomography of cortical hemodynamics in small animals

For the first time, the hemodynamics within the entire cerebral cortex of a mouse were studied by using photoacoustic tomography (PAT) in real time. The PAT system, based on a 512-element full-ring ultrasound array, received photoacoustic signals primarily from a slice of 2-mm thickness. This system can provide high-resolution brain vasculature images. We also monitored the fast wash-in process of a photoacoustic contrast agent in the mouse brain. Our results demonstrated that PAT is a powerful imaging modality that can be potentially used to study small animal neurofunctional activities.

Real-time photoacoustic tomography of cortical hemodynamics in small animals

For the first time, the hemodynamics within the entire cerebral cortex of a mouse were studied by using photoacoustic tomography (PAT) in real time. The PAT system, based on a 512-element full-ring ultrasound array, received photoacoustic signals primarily from a slice of 2-mm thickness. This system can provide high-resolution brain vasculature images. We also monitored the fast wash-in process of a photoacoustic contrast agent in the mouse brain. Our results demonstrated that PAT is a powerful imaging modality that can be potentially used to study small animal neurofunctional activities.

High-speed dynamic 3D photoacoustic imaging of sentinel lymph node in a murine model using an ultrasound array

Noninvasive photoacoustic sentinel lymph node (SLN) mapping with high spatial resolution has the potential to improve the false negative rate and eliminate the use of radioactive tracers in SLN identification. In addition, the demonstrated high spatial resolution may enable physicians to replace SLN biopsy with fine needle aspiration biopsy, and thus reduce the risk of associated morbidity. The primary goal of this study is to demonstrate the feasibility of high-speed 3D photoacoustic imaging of the uptake and clearance dynamics of Evans blue dye in SLNs. The photoacoustic imaging system was developed with a 30 MHz ultrasound array and a kHz repetition rate laser system. It acquires one 3D photoacoustic image of 166 B-scan frames in 1 s, with axial, lateral, and elevational resolutions of 25, 70, and 200 microm, respectively. With optic-fiber based light delivery, the entire system is compact and is convenient to use. Upon injection of Evans blue, a blue dye currently used in clinical SLN biopsy, SLNs in mice and rats were accurately and noninvasively mapped in vivo using our imaging system. In our experiments, the SLNs were found to be located at approximately 0.65 mm below the skin surface in mice and approximately 1.2 mm in rats. In some cases, lymph vessels and lymphatic valves were also imaged. The dye dynamics--accumulation and clearance--in SLNs were quantitatively monitored by sequential 3D imaging with temporal resolution of as high as approximately 6 s. The demonstrated capability suggests that high-speed 3D photoacoustic imaging should facilitate the understanding of the dynamics of various dyes in SLNs and potentially help identify SLNs with high accuracy.

Evans blue dye-enhanced capillary-resolution photoacoustic microscopy in vivo

Complete and continuous imaging of microvascular networks is crucial for a wide variety of biomedical applications. Photoacoustic tomography can provide high resolution microvascular imaging using hemoglobin within red blood cells (RBCs) as an endogenic contrast agent. However, intermittent RBC flow in capillaries results in discontinuous and fragmentary capillary images. To overcome this problem, we use Evans blue (EB) dye as a contrast agent for in vivo photoacoustic imaging. EB has strong optical absorption and distributes uniformly in the blood stream by chemically binding to albumin. With the help of EB, complete and continuous microvascular networks--especially capillaries--are imaged. The diffusion dynamics of EB leaving the blood stream and the clearance dynamics of the EB-albumin complex are also quantitatively investigated.

Peroxynitrite-dependent activation of protein phosphatase type 2A mediates microvascular endothelial barrier dysfunction

Aims

We investigated the mechanism by which proinflammatory stimulation induces microvascular endothelial barrier dysfunction. Since protein phosphatase type 2A (PP2A) can mediate paracellular leak and can be inactivated by tyrosine phosphorylation in its catalytic subunit (PP2Ac), we hypothesized that microvascular endothelial cells exposed to proinflammatory stimulation produce peroxynitrite that nitrates PP2Ac, and this nitration inhibits tyrosine phosphorylation of PP2Ac and thereby increases PP2A activity to mediate endothelial barrier dysfunction.

Methods and results

Exposure of mouse skeletal muscle microvascular endothelial cell monolayers to a proinflammatory stimulus [lipopolysaccharide (LPS) + interferon (IFN)γ] increased permeability to albumin, and this barrier dysfunction was attenuated by PP2A inhibitor okadaic acid or by siRNA (small interfering ribonucleic acid) against PP2Ac. LPS + IFNγ increased synthesis of peroxynitrite precursors nitric oxide (NO) and superoxide by inducible NO synthase (iNOS) and NADPH oxidase, respectively. PP2Ac immunoprecipitates isolated from LPS + IFNγ- or peroxynitrite-treated cells showed increased tyrosine nitration, decreased tyrosine phosphorylation and increased phosphatase activity. 3-Nitrotyrosine immunoprecipitates from LPS + IFNγ-stimulated cells also exhibited increased PP2A activity. Further, iNOS inhibitor 1400W, iNOS deficiency, NADPH oxidase inhibitor apocynin, or p47phox deficiency prevented the increase in PP2A activity and preserved barrier function.

Conclusion

LPS + IFNγ stimulates endothelial cells to produce iNOS-derived NO and NADPH oxidase-derived superoxide, which form peroxynitrite that nitrates tyrosine residues in PP2Ac and inhibits their phosphorylation. This nitration in PP2Ac is correlated with PP2A activation that mediates endothelial barrier dysfunction.

Interleukin-1 mediates thermal injury-induced lung damage through C-Jun NH2-terminal kinase signaling

OBJECTIVE

The molecular mechanisms of lung damage following thermal injury are not clear. The purpose of this study was to determine whether interleukin (IL)-1 mediates burn-induced inducible nitric oxide synthase (iNOS) expression, peroxynitrite production, and lung damage through c-Jun NH2-terminal kinase (JNK) signaling.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Thermal injury models in the mice.

INTERVENTIONS

IL-1 receptor type 1 (IL-1R1) mice, Tnfrsf1a mice, and wild-type (WT) mice were subjected to 30% total body surface area third-degree burn. The JNK inhibitor, SP600125, was given to mice to study the involvement of the JNK pathway in thermal injury-induced lung damage. WT --> WT, WT --> IL-1R1, and IL-1R1 --> WT chimeric mice were generated to determine the role of hematopoietic cells in IL-1-mediated lung damage. Neutrophils were harvested and treated in vitro with N-formyl-methionyl-leucyl-phenylalanine (fMLP).

MEASUREMENTS AND MAIN RESULTS

IL-1R1 mice rather than Tnfrsf1a mice showed less thermal injury-induced lung damage. IL-1R1 mice displayed less lung JNK activity; intercellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM), chemokine receptor 2 (CXCR2), and macrophage inflammatory protein-2 (MIP2), messenger RNA expression; myeloperoxidase activity; and neutrophil p38 mitogen-activated protein kinase (MAPK) phosphorylation after thermal injury. SP600125 significantly reduced thermal injury-induced blood dihydrorhodamine (DHR) 123 oxidation, iNOS expression, and lung permeability in WT mice but not in IL-1R1 mice. IL-1R1 --> WT chimeric mice rather than WT --> IL-1R1 chimeric mice showed less thermal injury-induced lung damage. fMLP increased reactive oxygen species (ROS) production of neutrophils in WT mice but not in IL-1R1 mice. SP600125 decreased ROS production of neutrophils in WT mice but not in IL-1R1 mice.

CONCLUSIONS

Thermal injury-induced lung JNK activation; lung ICAM, VCAM, CXCR2, and MIP2 expression; and DHR 123 oxidation are IL-1 dependent. JNK inhibition decreases IL-1-mediated thermal injury-induced lung damage. Given that the IL-1 receptor is critical in thermal injury-induced p38 MAPK phosphorylation and ROS production of neutrophils, we conclude that IL-1 mediates thermal injury-induced iNOS expression and lung damage through the JNK signaling pathway.

Thermal injury-induced peroxynitrite production and pulmonary inducible nitric oxide synthase expression depend on JNK/AP-1 signaling

OBJECTIVE

To determine whether burn-induced peroxynitrite production and expression of lung inducible nitric oxide synthase (iNOS), intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, CXCR2, macrophage inflammatory protein (MIP)-2, and neutrophil chemokine (KC) are mediated by the c-Jun NH2-terminal kinase (JNK).

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Thermal injury models in the mice.

INTERVENTIONS

In experiment 1, specific pathogen-free C57/BL6 mice were subjected to 30% total body surface area third-degree burn over shaved back. At 0 hr, 2 hrs, 4 hrs, and 6 hrs after burn, lung tissues of those mice were harvested for JNK activity assay, AP-1 DNA-binding activity, and pJNK immunohistochemistry. In experiment 2, a specific JNK inhibitor, SP600125, was given (30 mg/kg intraperitoneally) to mice immediately postburn to suppress the JNK activity. At 8 hrs after burn, blood was assayed for the peroxynitrite-mediated dihydrorhodamine (DHR) 123 oxidation. Lung tissues were harvested for myeloperoxidase (MPO) determination, ICAM-1, VCAM-1, CXCR2, KC, MIP-2, interleukin-1beta, and interleukin-6 messenger RNA expression; iNOS immunohistochemical staining; and histologic studies. Pulmonary microvascular dysfunction was quantified by measuring the extravasations of Evans blue dye.

MEASUREMENTS AND MAIN RESULTS

The JNK activity and AP-1 DNA-binding activity of lung tissue significantly increased to a peak at 2 hrs and 4 hrs, respectively, after thermal injury. Immunohistochemical study demonstrated that the increase of the pJNK was mostly from the bronchiole epithelial cells. This increase of MPO activity in lung, blood DHR 123 oxidation level, and lung permeability increased six-fold, nine-fold, and four-fold after burn. SP600125 administration obliterated the thermal injury-induced JNK activity, AP-1 DNA-binding activity, and iNOS expression in lung tissue. SP600125 treatment also significantly decreased MPO activity, blood DHR 123 oxidation, and lung permeability by 54%, 8%, and 47%, respectively, and markedly decreased the thermal injury-induced perivascular and interstitial inflammatory cell infiltration and septum edema. Furthermore, SP600125 abolished thermal injury-induced ICAM-1, VCAM-1, CXCR2, MIP-2, and KC but not interleukin-1beta and interleukin-6 messenger RNA levels of lung tissues.

CONCLUSIONS

Thermal injury induces lung tissue JNK activation and AP-1 DNA-binding activity mainly from airway epithelial cells. Thermal injury-induced peroxynitrite production and lung iNOS, ICAM-1, and VCAM-1 expression are mediated by the JNK signaling. JNK inhibition decreases thermal injury-induced lung neutrophil infiltration and subsequently pulmonary hyperpermeability.

Hyperresponsiveness to inhaled but not intravenous methacholine during acute respiratory syncytial virus infection in mice

Background

To characterise the acute physiological and inflammatory changes induced by low-dose RSV infection in mice.

Methods

BALB/c mice were infected as adults (8 wk) or weanlings (3 wk) with 1 × 10⁵ pfu of RSV A2 or vehicle (intranasal, 30 μl). Inflammation, cytokines and inflammatory markers in bronchoalveolar lavage fluid (BALF) and airway and tissue responses to inhaled methacholine (MCh; 0.001 – 30 mg/ml) were measured 5, 7, 10 and 21 days post infection. Responsiveness to iv MCh (6 – 96 μg/min/kg) in vivo and to electrical field stimulation (EFS) and MCh in vitro were measured at 7 d. Epithelial permeability was measured by Evans Blue dye leakage into BALF at 7 d. Respiratory mechanics were measured using low frequency forced oscillation in tracheostomised and ventilated (450 bpm, flexiVent) mice. Low frequency impedance spectra were calculated (0.5 – 20 Hz) and a model, consisting of an airway compartment [airway resistance (Raw) and inertance (Iaw)] and a constant-phase tissue compartment [coefficients of tissue damping (G) and elastance (H)] was fitted to the data.

Results

Inflammation in adult mouse BALF peaked at 7 d (RSV 15.6 (4.7 SE) vs. control 3.7 (0.7) × 10⁴ cells/ml; p < 0.001), resolving by 21 d, with no increase in weanlings at any timepoint. RSV-infected mice were hyperresponsive to aerosolised MCh at 5 and 7 d (PC₂₀₀ Raw adults: RSV 0.02 (0.005) vs. control 1.1 (0.41) mg/ml; p = 0.003) (PC₂₀₀ Raw weanlings: RSV 0.19 (0.12) vs. control 10.2 (6.0) mg/ml MCh; p = 0.001). Increased responsiveness to aerosolised MCh was matched by elevated levels of cysLT at 5 d and elevated VEGF and PGE₂ at 7 d in BALF from both adult and weanling mice. Responsiveness was not increased in response to iv MCh in vivo or EFS or MCh challenge in vitro. Increased epithelial permeability was not detected at 7 d.

Conclusion

Infection with 1 × 10⁵ pfu RSV induced extreme hyperresponsiveness to aerosolised MCh during the acute phase of infection in adult and weanling mice. The route-specificity of hyperresponsiveness suggests that epithelial mechanisms were important in determining the physiological effects. Inflammatory changes were dissociated from physiological changes, particularly in weanling mice.

Ventilation-induced neutrophil infiltration and apoptosis depend on apoptosis signal-regulated kinase 1 pathway*

OBJECTIVE

Positive pressure ventilation with large tidal volumes has been shown to cause release of cytokines, including macrophage inflammatory protein (MIP)-2, a functional equivalent of human interleukin-8, neutrophil infiltration, and apoptosis. The mechanisms regulating ventilation-induced cytokine production and lung cell death are unclear. Based on our previous in vitro and in vivo models of lung cell stretch, we hypothesized that high tidal volume ventilation-induced MIP-2 production, neutrophil infiltration, and apoptosis are dependent on the activation of apoptosis signal-regulated kinase 1 (ASK1), the upstream activator of c-Jun N-terminal kinase (JNK).

DESIGN

: Prospective, controlled animal experiment.

SETTING

University research laboratory.

SUBJECTS

Male C57BL/6 mice, weighting 20-25 g.

INTERVENTIONS

C57BL/6 mice were exposed to high tidal volume (30 mL/kg) or low tidal volume (6 mL/kg) mechanical ventilation for 15 mins to 5 hrs.

MEASUREMENTS AND MAIN RESULTS

High tidal volume ventilation induced MIP-2 messenger RNA expression, MIP-2 protein production, neutrophil migration into the lung, airway epithelial cell apoptosis, and activation of ASK1, JNK, and activator protein (AP)-1 DNA binding in a dose-dependent and time-dependent manner. ASK1 inhibition with thioredoxin attenuated high tidal volume ventilation-induced MIP-2 messenger RNA expression, MIP-2 protein production, neutrophil migration into the lung, airway epithelial cell apoptosis, activation of JNK, and AP-1 DNA binding.

CONCLUSIONS

Our data showed that high tidal volume ventilation-induced MIP-2 production, neutrophil sequestration, and apoptotic cell death were dependent, in part, on activation of the ASK1/JNK/AP-1 pathway.

Evans blue is a specific antagonist of the human epithelial Na+ channel delta-subunit

The epithelial Na(+) channel (ENaC) regulates Na(+) homeostasis in cells and across epithelia. Four homologous ENaC subunits (alpha, beta, gamma, and delta) have been isolated in mammals. Combination of alpha-, beta-, and gamma-subunits or delta-, beta-, and gamma-subunits forms fully functional channels. Amiloride is a well known blocker of the ENaC family that inhibits both channel complexes. However, no specific antagonists are currently known that distinguish them. Here, we show that Evans blue, a diagnostic aid for the measurement of blood volume and vascular permeability, inhibits the activity of the delta-subunit expressed in Xenopus oocytes. The inward currents at a holding potential of -60 mV in human ENaCdeltabetagamma-expressing oocytes were inhibited by the application of Evans blue in a concentration-dependent manner with an IC(50) value of 143 muM. Evans blue markedly inhibited the delta-subunit current but did not block the alpha-subunit current. In conclusion, Evans blue is the first known delta-subunit-specific antagonist of ENaC. This finding provides us with a key compound for elucidating the physiological and pathological functions of ENaCdelta in humans and for drug development in the ENaC family.

Inducible nitric oxide synthase contributes to ventilator-induced lung injury

RATIONALE

Inducible nitric oxide synthase (iNOS) has been implicated in the development of acute lung injury. Recent studies indicate a role for mechanical stress in iNOS and endothelial NOS (eNOS) regulation.

OBJECTIVES

This study investigated changes in lung NOS expression and activity in a mouse model of ventilator-induced lung injury.

METHODS

C57BL/6J (wild-type [WT]) and iNOS-deficient (iNOS(-/-)) mice received spontaneous ventilation (control) or mechanical ventilation (MV; VT of 7 and 20 ml/kg) for 2 hours, after which NOS gene expression and activity were determined and pulmonary capillary leakage assessed by the Evans blue albumin assay.

RESULTS

iNOS mRNA and protein expression was absent in iNOS(-/-) mice, minimal in WT control mice, but significantly upregulated in response to 2 hours of MV. In contrast, eNOS protein was decreased in WT mice, and nonsignificantly increased in iNOS(-/-) mice, as compared with control animals. iNOS and eNOS activities followed similar patterns in WT and iNOS(-/-) mice. MV caused acute lung injury as suggested by cell infiltration and nitrotyrosine accumulation in the lung, and a significant increase in bronchoalveolar lavage cell count in WT mice, findings that were reduced in iNOS(-/-) mice. Finally, Evans blue albumin accumulation in lungs of WT mice was significant (50 vs. 15% increase in iNOS(-/-) mice compared with control animals) in response to MV and was prevented by treatment of the animals with the iNOS inhibitor aminoguanidine.

CONCLUSION

Taken together, our results indicate that iNOS gene expression and activity are significantly upregulated and contribute to lung edema in ventilator-induced lung injury.

Adrenomedullin reduces Staphylococcus aureus alpha-toxin-induced rat ileum microcirculatory damage

OBJECTIVE

Increased microvascular permeability and perfusion mismatch are hallmarks of sepsis or septic shock. The intestinal mucosa is very sensitive to tissue hypoxia. Intestinal mucosa dysfunction may allow translocation of bacteria and their products, thereby perpetuating sepsis and inflammation. Staphylococcus aureus alpha-toxin is a major pathogenicity determinant of this bacterium, provoking cardiovascular collapse. Current evidence suggests that the endogenous peptide adrenomedullin stabilizes circulatory homeostasis in systemic inflammatory response. Using alpha-toxin as a well-defined strong initiator of an inflammatory reaction, we tested the hypothesis that exogenously applied adrenomedullin stabilizes gut microcirculation.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Isolated, perfused ileum from male Sprague-Dawley rats and human umbilical vein endothelial cells.

INTERVENTIONS

Administration of S. aureus alpha-toxin before or after infusion of adrenomedullin.

MEASUREMENTS AND MAIN RESULTS

Injection of a bolus of 1 microg of alpha-toxin in the superior mesenteric artery in a constant-flow, blood-perfused preparation of rat ileum increased perfusion pressure and relative hemoglobin concentration and decreased mucosal hemoglobin oxygen saturation. Continuous infusion of adrenomedullin (0.1 micromol/L) significantly reduced these alpha-toxin-related effects. Severe microvascular hyperpermeability observed in alpha-toxin-exposed ileum was abolished by adrenomedullin pretreatment. In addition, adrenomedullin blocked alpha-toxin-induced endothelial myosin light chain phosphorylation, endothelial cell contraction, and subsequent loss of endothelial barrier function in vitro. Treatment of alpha-toxin (infusion of 0.05 microg/mL)-exposed ileum with adrenomedullin (0.1 micromol/L) started 10 mins after onset of toxin application also significantly reduced superior mesenteric artery pressure and permeability increase.

CONCLUSIONS

In summary, these data suggest that exogenous adrenomedullin protects ileum by reducing alpha-toxin-induced microcirculatory disturbances and by stabilizing endothelial barrier function.

Protective effects of sphingosine 1-phosphate in murine endotoxin-induced inflammatory lung injury

Our prior in vitro studies indicate that sphingosine 1-phosphate (S1P), a phospholipid angiogenic factor, produces endothelial cell barrier enhancement through ligation of endothelial differentiation gene family receptors. We hypothesized that S1P may reduce the vascular leak associated with acute lung injury and found that S1P infusion produced a rapid and significant reduction in lung weight gain (more than 50%) in the isolated perfused murine lung. The effect of S1P was next assessed in a murine model of LPS-mediated microvascular permeability and inflammation with marked increases in parameters of lung injury at both 6 and 24 hours after intratracheal LPS. Each parameter assessed was significantly reduced by intravenous S1P (1 microM final) and in selected experiments by the S1P analogue FTY720 (0.1 mg/kg, intraperitoneally) delivered 1 hour after LPS. S1P produced an approximately 40-50% reduction in LPS-mediated extravasation of Evans blue dye albumin, bronchoalveolar lavage protein content, and lung tissue myeloperoxidase activity (reflecting phagocyte infiltration). Consistent with systemic barrier enhancement, S1P significantly decreased Evans blue dye albumin extravasation and myeloperoxidase content in renal tissues of LPS-treated mice. These studies indicate that S1P significantly decreases pulmonary/renal vascular leakage and inflammation in a murine model of LPS-mediated acute lung injury and may represent a novel therapeutic strategy for vascular barrier dysfunction.

Matrix metalloproteinase inhibition decreases ischemia-reperfusion injury after lung transplantation

Increased microvascular permeability and extravasation of inflammatory cells are key events of lung ischemia-reperfusion (IR) injury. The purpose of this study was to investigate the role of matrix metalloproteinases (MMP) in IR-induced alveolar capillary membrane disruption after experimental lung transplantation. We used a rat model of lung orthotopic transplantation (n = 86) with a prolonged cold ischemic phase. MMP2 and MMP9 were elevated 4 h after the onset of ischemia and further increased during reperfusion. Compared to sham values, the alveolar-capillary membrane permeability increased by 105% and 82.6% after 4 h of ischemia and 2 h or 24 h of reperfusion, respectively. A 4- and 5-fold increase of the infiltration of ischemic tissue by neutrophils was also observed after 2 h and 24 h of reperfusion. The PO2/FIO2 ratio dropped significantly from 244 to 76.6 after 2 h of reperfusion and from 296.4 to 127.6 after 24 h of reperfusion. A nonselective inhibitor of MMP, administered to the rats and added to the preservation solution, reduced significantly the alveolar-capillary leakage, the transmigration of neutrophils and improved gas exchanges in animals submitted to 4 h of ischemia combined with 2 h or 24 h of reperfusion. We conclude that inhibition of MMP attenuates IR injury after experimental lung transplantation.

Peroxynitrite is an important mediator in thermal injury-induced lung damage

OBJECTIVE

Intestinal ischemia and reperfusion injury was known to cause postinjury multiple organ failure by neutrophil and unclear nonneutrophil factors. Peroxynitrite formed by the rapid reaction between superoxide and nitric oxide, is a toxic substance that contributes to tissue injury in a number of biological systems. In this study, the role of nitric oxide and neutrophils on lung damage after burn was investigated.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Thermal injury models in the rat.

INTERVENTIONS

In experiment 1, specific pathogen-free Sprague-Dawley rats underwent 35% total body surface area burn. At 4, 8, 16, and 24 hrs after burn, intestinal mucosa and lung tissue were harvested for myeloperoxidase (MPO) assay, blood was collected for measurement of peroxynitrite-mediated oxidation of dihydrorhodamine 123, and pulmonary microvascular dysfunction was quantified by measuring the extravasation of Evans blue dye. In experiment 2, polymorphonuclear granulocyte antibody (0.12 mL/100 g administered intraperitoneally 16 hrs before burn), S-methylisothiourea (7.5 mg/kg, intraperitoneally, immediately after burn), a specific inducible nitric oxide synthase inhibitor, and sterile saline (15 mL/kg, intraperitoneally, immediately after burn) were given to different groups of thermally injured animals individually. The plasma dihydrorhodamine 123 oxidation level, intestinal and lung MPO activity, lung permeability, and lung histology were evaluated at 8 hrs after burn. The cellular localization of nitrotyrosine, a marker for peroxynitrite reactivity, was also examined by immunostaining. In experiment 3, 3-morpholinosydnonimine (10 mM, intraperitoneally), a peroxynitrite donor, was given to nonburned rats to examine the peroxynitrite effect on lung inducible nitric oxide synthase expression.

MEASUREMENTS AND MAIN RESULTS

The level of MPO activity in intestine and lung, blood dihydrorhodamine 123 oxidation, and lung permeability were increased up to 2-fold, 2.5-fold, 2-fold, and 2-fold of normal, respectively, at 8 hrs after burn. S-methylisothiourea injection significantly decreased (p <.05) 31% of the lung MPO activity, 41% of the blood peroxynitrite level, 54% of the lung permeability, and the lung peroxynitrite production in burned rats. Polymorphonuclear granulocyte antibody pretreatment significantly decreased 60% of the intestinal MPO, 92% of the blood peroxynitrite level, and 56% the lung MPO activity in burned rats, but the lung permeability was only slightly decreased by polymorphonuclear granulocyte antibody pretreatment. Furthermore, 3-morpholinosydnonimine increased the lung inducible nitric oxide synthase messenger RNA levels.

CONCLUSIONS

Thermal injury induces blood dihydrorhodamine 123 oxidation, intestinal and lung neutrophil deposition, lung nitrotyrosine production, and lung damage. Both specific inhibition of inducible nitric oxide synthase and polymorphonuclear granulocyte antibody pretreatment decrease blood dihydrorhodamine 123 oxidation and intestinal and lung neutrophil deposition, but only inducible nitric oxide synthase inhibition with S-methylisothiourea reduces lung peroxynitrite production and thermal injury-induced lung damage. Nitric oxide and the ensuing peroxynitrite production in lung play a more important role than neutrophil in contributing to thermal injury-induced lung damage.

Role of inducible nitric oxide synthase in pulmonary microvascular protein leak in murine sepsis

The effects of nitric oxide (NO) from calcium-independent NO synthase (iNOS) on microvascular protein leak in acute lung injury (ALI) are uncertain, possibly because of disparate effects of iNOS-derived NO from different cells. We assessed the contribution of iNOS from inflammatory versus parenchymal cells to pulmonary protein leak in murine cecal ligation and perforation-induced ALI. We studied iNOS+/+, iNOS-/-, and two reciprocally bone marrow-transplanted iNOS chimeric mice groups: + to - (iNOS+/+ donor bone marrow-transplanted into iNOS-/- recipient mice) and - to +. Sepsis-induced ALI was characterized by pulmonary leukocyte infiltration, increased pulmonary iNOS activity, and increased pulmonary microvascular protein leak, as assessed by Evans blue (EB) dye. Despite equal neutrophil infiltration, sepsis-induced EB-protein leak was eliminated in iNOS-/- mice and in - to + iNOS chimeras (parenchymal cell-localized iNOS) but was preserved in + to - chimeric mice (inflammatory cell-localized iNOS). EB-protein leak was also prevented by pretreatment with allopurinol and superoxide dismutase. Microvascular protein leak in sepsis-induced ALI is uniquely dependent on iNOS in inflammatory cells with no obvious contribution of iNOS in pulmonary parenchymal cells. Pulmonary protein leak is also dependent on superoxide, suggesting an effect of peroxynitrite rather than NO itself.

Regulation of endothelial barrier function by the cAMP-dependent protein kinase

Elevation of cAMP promotes the endothelial cell (EC) barrier and protects the lung from edema development. Thus, we tested the hypothesis that both increases and decreases in PKA modulate EC function and coordinate distribution of regulatory, adherence, and cytoskeletal proteins. Inhibition of PKA activity by RpcAMPS and activation by cholera toxin was verified by assay of kemptide phosphorylation in digitonin permeabilized EC. Inhibition of PKA by RpcAMPS or overexpression of the endogenous inhibitor, PKI, decreased monolayer electrical impedance and exacerbated the decreases produced by agonists (thrombin and PMA). RpcAMPS directly increased F-actin content and organization into stress fibers, increased co-staining of actin with both phosphatase 2B and myosin light chain kinase (MLCK), caused reorganization of focal adhesions, and decreased catenin at cell borders. These findings are similar to those evoked by thrombin. In contrast, cholera toxin prevented the agonist-induced resistance decrease and protein redistribution. Although PKA activation attenuated thrombin-induced myosin light chain (MLC) phosphorylation, PKA inhibition per se did not cause MLC phosphorylation or affect [Ca2+]i. These studies indicate that a decrease in PKA activity alone can produce disruption of barrier function via mechanisms not involving MLCK and support a central role for cAMP/PKA in regulation of cytoskeletal and adhesive protein function in EC which correlates with altered barrier function.

Contrast medium-induced pulmonary vascular hyperpermeability is aggravated in a rat climacterium model

Tominaga K, Kataoka Y, Sendo T, et al. Contrast medium-induced pulmonary vascular hyperpermeability is aggravated in a rat climacterium model. Invest Radiol 2001;36:131-135.

RATIONALE AND OBJECTIVES

To test whether climacterium influences adverse pulmonary reactions to contrast media, the authors investigated the effect of ioxaglate on pulmonary vascular permeability in ovariectomized rats as a climacterium model.

METHODS

From 7 days after surgery, ovariectomized rats were treated with estradiol valerate or vehicle once per week for 3 weeks. At 28 days after surgery, ioxaglate, an ionic contrast medium, was intravenously injected at 1.5 mL/min in rats. Pulmonary vascular permeability was evaluated by measuring the amount of Evans blue dye in the lung tissue.

RESULTS

Ioxaglate dose-dependently increased pulmonary vascular permeability in sham-operated and ovariectomized rats. Ovariectomized rats showed a 2.6-fold increased aggravation of vascular permeability by ioxaglate 4 g I/kg compared with sham-operated rats. Estradiol valerate (0.2-5.0 mg/kg) dose-dependently blocked ioxaglate-increased vascular permeability in ovariectomized rats.

CONCLUSIONS

These findings suggest that climacterium is included, at least in part, in the risk factors for contrast-induced adverse pulmonary reactions, and this risk is lowered by estrogen replacement therapy.

Nitric oxide protects against contrast media-increased pulmonary vascular permeability in rats

RATIONALE AND OBJECTIVES

Nitric oxide (NO) regulation of endothelial function is involved in the development of acute lung injury. The role of NO in contrast media-induced increases in pulmonary vascular permeability was investigated in a rat model.

METHODS

Nonionic (iohexol) and ionic (ioxaglate) contrast media were intravenously injected at 1.5 mL/min in rats. Pulmonary vascular permeability was evaluated by measuring the amount of Evans blue dye uptake as a quantitative marker of albumin extravasation in lung tissue.

RESULTS

Intravenous injections of contrast media at doses of 4 and 6 g I/kg induced a dose-dependent increase in pulmonary vascular permeability. L-Arginine (an NO synthase substrate) and N(G)-nitro-L-arginine (L-NNA) (an NO synthase inhibitor) prevented and aggravated, respectively, the increase in pulmonary vascular permeability induced by the contrast medium. An aggravating action of L-NNA was confirmed by morphological and histological observations, this action being blocked by L-arginine (300 mg/kg) but not by D-arginine. Isosorbide dinitrate (1-20 mg/kg), an NO donor, had a dose-dependent protective effect on ioxaglate-increased vascular permeability.

CONCLUSIONS

Our experimental findings suggest that contrast media at high doses produce pulmonary edema by inhibiting endothelial NO production, and nitrovasodilators protect against this adverse effect in rats.

A codominant role of Fc gamma RI/III and C5aR in the reverse Arthus reaction

Recent attempts to specify the relative contribution of FcR and complement in various experimental systems of immune complex disease have led to opposing conclusions. As concluded in IgG FcRgamma-/- mice, manifestation of disease is almost exclusively determined by FcgammaR on effector cells, arguing for a minor role of complement. In contrast, data obtained with C5aR-/- mice suggested that, dependent on the tissue site, complement is more important than FcgammaR. In this paper, we demonstrate that, in response to IgG immune complex formation, FcgammaRI/III- and C5aR-mediated pathways are both necessary and only together are they sufficient to trigger the full expression of inflammation in skin and lung. Moreover, both effector systems are not entirely independent, suggesting an interaction between FcgammaR and C5aR. Therefore, FcgammaR-mediated responses can be integrated through C5aR activation, which may explain why these two receptor pathways have previously been considered to dominate each other.

Intestinal ischemia and reperfusion impairs vasomotor functions of pulmonary vascular bed

OBJECTIVE

To investigate the effects of intestinal ischemia and reperfusion (I/R) on the pulmonary vascular endothelium and smooth muscle.

SUMMARY BACKGROUND DATA

Respiratory failure is an important cause of death and complications after intestinal I/R. Although the mechanism of respiratory failure in this setting is complex and poorly understood, recent studies of lung injury suggest that endothelial dysfunction may play a significant role.

METHODS

A rat model of acute lung injury was studied after 60 minutes of superior mesenteric arterial occlusion followed by either 120 or 240 minutes of reperfusion. The pulmonary vasomotor function was examined in isolated lungs perfused at a constant flow rate.

RESULTS

Sixty minutes of intestinal ischemia followed by 120 or 240 minutes of reperfusion led to a significant reduction in the ability of the pulmonary vasculature to respond to angiotensin II, acetylcholine, and calcium ionophore but not to nitroglycerin. The vasoconstriction response to N(G)-nitro-L-arginine methyl ester, which is a measure of basal nitric oxide release, was diminished in the 240-minute reperfusion group. Intestinal I/R was also associated with pulmonary leukosequestration and increased pulmonary microvascular leakage.

CONCLUSIONS

Basal and agonist-stimulated release of nitric oxide from the pulmonary vascular endothelium and the ability of pulmonary smooth muscle to contract in response to angiotensin II were impaired by intestinal I/R. Such functional impairment in both pulmonary vascular endothelium and smooth muscle may contribute to the alveolocapillary dysfunction and pulmonary hypertension found in acute lung injury after intestinal I/R.

In vitro evaluation of vascular permeability to contrast media using cultured endothelial cell monolayers

OBJECTIVE

The efficiency of contrast agents in medical imaging depends on their distribution into vascular and interstitial compartments. The aim of this study was to compare in vitro endothelial permeability to different classes of contrast agents with various vascular persistence properties: a triiodinated nonionic monomer (ioversol), an iodinated dextran polymer (P604), and an iron oxide nanoparticle (sinerem).

METHODS

Permeability studies, through collagen-coated filters with or without porcine aortic endothelial cell monolayer, were carried out by placing each filter-ring (luminal chamber) into a beaker containing a culture medium (abluminal chamber). Contrast media, diluted in the culture medium, were added to the luminal chamber. Aliquots were sampled from the abluminal chamber for contrast agent determinations. The volume cleared of the compound was calculated from the luminal side to the abluminal side. Parallel permeability tests to [3H]-H2O and Evans blue albumin were performed as references. Finally, the modulatory effect of bradykinin on endothelial permeability to albumin or to contrast agents was studied.

RESULTS

The volume cleared of ioversol, P604, and sinerem through membrane filters was decreased by 19.6%, 32.1%, and 52.0%, respectively, in the presence of a cell monolayer. Bradykinin (10(-6) M) significantly increased permeability to albumin, ioversol, and sinerem. Ioversol and sinerem induced a significant decrease in permeability to albumin.

CONCLUSIONS

A relation between the molecular size of the contrast agents tested and their endothelial permeability can be established with this in vitro model.

Group B streptococcal beta-hemolysin promotes injury of lung microvascular endothelial cells

Group B streptococci (GBS) are the leading cause of pneumonia and sepsis in human newborns. Exudative pulmonary edema and alveolar hemorrhage seen in GBS pneumonia indicate vascular damage, and we reported that GBS injure lung microvascular endothelial cells (LMvEC) both in vivo and in vitro. The specific GBS factors causing LMvEC injury are uncertain, but GBS beta-hemolysin activity is associated with lung epithelial cell injury. We hypothesized that GBS beta-hemolysin contributes to LMvEC injury and exudative pulmonary edema. To test this hypothesis we used isogenic nonhemolytic and hyperhemolytic GBS mutants derived by transposon insertional mutagenesis from three different wild-type strains. Hemolytic titers for each strain were calculated using live GBS and Tween 80/starch-stabilized extracts of log-phase GBS. All nonhemolytic mutants lacked detectable hemolytic activity, whereas hyperhemolytic mutants produced 4-16 times the hemolytic activity of their parent strains. LMvEC injury was assayed by light microscopy, the release of lactate dehydrogenase, trypan blue nuclear staining and Evans blue-albumin flux. Compared with the parent strains, all nonhemolytic mutants caused significantly reduced, and all hyperhemolytic mutants caused significantly greater lactate dehydrogenase release from and trypan blue nuclear staining of LMvEC. Moreover, a nonhemolytic mutant caused reduced and a hyperhemolytic mutant caused increased Evans-blue albumin flux across polar LMvEC monolayers. These findings were corroborated by light microscopic evidence of hemolysin-associated damage to the LMvEC monolayers. We conclude that GBS beta-hemolysin promotes LMvEC injury and increases permeability in vitro, and speculate that GBS beta-hemolysin contributes to the pathogenesis of alveolar edema and hemorrhage in early onset GBS pneumonia.

Phospholipase A2 mediates nitric oxide production by alveolar macrophages and acute lung injury in pancreatitis

OBJECTIVE

Reportedly, nitric oxide (NO) derived from alveolar macrophages (AMs) and increased serum phospholipase A2 (PLA2) activity are associated with the pathogenesis of lung injury in acute pancreatitis. The authors examined the possibility that PLA2 causes, in part, the induction of NO production by AMs in pancreatitis.

METHODS

Pancreatitis was induced in rats by selective pancreatic duct ligation (SPL). AMs were stimulated with PLA2 or SPL rat serum, with or without administration of the PLA2 inhibitor quinacrine. Then NO production from the AMs was measured by the Griess method, inducible NO synthase mRNA expression of AMs was analyzed by the reverse transcription-polymerase chain reaction, and cytotoxic effects of AMs on human umbilical vein endothelial cells was examined by a 51Cr release assay. In vivo, the effect of quinacrine on lung injury was determined by measuring the arterial blood oxygen pressure (PaO2), lung weight, and lung permeability using Evans blue dye concentration of SPL rat.

RESULTS

In vitro, the serum with high PLA2 activity induced NO production by rat AMs. PLA2 (50 ng/ml) induced significant amounts of NO production, inducible NO synthase mRNA expression, and cytotoxicity toward the human umbilical vein endothelial cells in normal rat AMs, and these activities were significantly inhibited by quinacrine. In vivo, rats with pancreatitis that were given quinacrine showed decreased concentrations of NO2- and NO3- in the bronchoalveolar lavage fluid, and the PaO2, lung edema, and lung permeability were improved significantly.

CONCLUSION

PLA2 induces AMs to release NO, which contributes to lung injury in acute pancreatitis. This lung injury was prevented by the administration of the PLA2 inhibitor quinacrine.

Role of tyrosine phosphorylation in thrombin-induced endothelial cell contraction and barrier function

Thrombin-induced endothelial cell (EC) barrier dysfunction is highly dependent upon phosphorylation of serine and threonine residues present on myosin light chains (MLC) catalyzed by a novel EC myosin light chain kinase (MLCK) isoform. In this study, we examined the participation of tyrosine protein phosphorylation in EC contraction, gap formation and barrier dysfunction. We first determined that thrombin significantly increases protein tyrosine kinase activity and protein tyrosine phosphorylation in bovine pulmonary artery EC. Tyrosine kinase inhibitors, genistein and 2,5 DHC, reduced EC tyrosine kinase activities, however, only genistein significantly attenuated thrombin-mediated increases in albumin clearance and reductions in transendothelial electrical resistance. Similarly, genistein but not 2,5 DHC, decreased basal and thrombin-induced Ca2+ increases and MLC phosphorylation in the absence of alterations in Type 1 or 2A serine/threonine phosphatase activities. Immunoprecipitation of the EC MLCK isoform revealed a 214 kD immunoreactive phosphotyrosine protein and genistein pretreatment significantly reduced MLCK activity in MLCK immunoprecipitates. Although thrombin induced the translocation of p60src from the cytosol to the EC cytoskeleton, a detectable increase in the level of MLCK tyrosine phosphorylation was not noted after thrombin challenge. Taken together, our data suggest that genistein-sensitive tyrosine kinase activities are involved in thrombin-mediated EC MLCK activation, MLC phosphorylation, and barrier dysfunction.

Stimulation of large-conductance Ca2+-activated K+ channels by Evans blue in cultured endothelial cells of human umbilical veins

The effect of Evans blue (EB) on large-conductance Ca2+-activated K+ (BKCa) channels was investigated in cultured endothelial cells of human umbilical veins. In whole-cell configuration, EB (50 microM) reversibly increased the amplitude of K+ outward currents (IK). When the patch pipettes were filled with 10 mM EGTA, its stimulatory effect on IK was unaltered. Further application of EB in the presence of suramin, a blocker of P2-purinergic receptor, or AOPCP, an inhibitor of 5'-nucleotidase, still increased IK. However, charybdotoxin (100 nM) suppressed EB-induced increase in IK. In inside-out configuration, bath application of EB (50 microM) did not change single channel conductance but significantly increased the activity of BKCa channels. The EB-induced increase in the activity of BKCa channels was independent on internal Ca2+. EB (50 microM) shifted the activation curve of BKCa channels to less positive membrane potentials by approximately 20 mV. The change in the kinetic behavior of BKCa channels caused by EB in these cells is due to an increase in mean open time and a decrease in mean closed time. These results indicate that EB can stimulate the activity of BKCa channel in endothelial cells. This effect is unrelated to its blockade of P2-purinergic receptors or inhibition of 5'-nucleotidase. The direct stimulation of these ionic channels by EB may contribute to its effect on capillary permeability.

Gut-derived mesenteric lymph but not portal blood increases endothelial cell permeability and promotes lung injury after hemorrhagic shock

OBJECTIVE

To determine whether gut-derived factors leading to organ injury and increased endothelial cell permeability would be present in the mesenteric lymph at higher levels than in the portal blood of rats subjected to hemorrhagic shock. This hypothesis was tested by examining the effect of portal blood plasma and mesenteric lymph on endothelial cell monolayers and the interruption of mesenteric lymph flow on shock-induced lung injury.

SUMMARY BACKGROUND DATA

The absence of detectable bacteremia or endotoxemia in the portal blood of trauma victims casts doubt on the role of the gut in the generation of multiple organ failure. Nevertheless, previous experimental work has clearly documented the connection between shock and gut injury as well as the concept of gut-induced sepsis and distant organ failure. One explanation for this apparent paradox would be that gut-derived inflammatory factors are reaching the lung and systemic circulation via the gut lymphatics rather than the portal circulation.

METHODS

Human umbilical vein endothelial cell monolayers, grown in two-compartment systems, were exposed to media, sham-shock, or postshock portal blood plasma or lymph, and permeability to rhodamine (10K) was measured. Sprague-Dawley rats were subjected to 90 minutes of sham or actual shock and shock plus lymphatic division (before and after shock). Lung permeability, pulmonary myeloperoxidase levels, alveolar apoptosis, and bronchoalveolar fluid protein content were used to quantitate lung injury.

RESULTS

Postshock lymph increased endothelial cell monolayer permeability but not postshock plasma, sham-shock lymph/plasma, or medium. Lymphatic division before hemorrhagic shock prevented shock-induced increases in lung permeability to Evans blue dye and alveolar apoptosis and reduced pulmonary MPO levels. In contrast, division of the mesenteric lymphatics at the end of the shock period but before reperfusion ameliorated but failed to prevent increased lung permeability, alveolar apoptosis, and MPO accumulation.

CONCLUSIONS

Gut barrier failure after hemorrhagic shock may be involved in the pathogenesis of shock-induced distant organ injury via gut-derived factors carried in the mesenteric lymph rather than the portal circulation.

Regulation of endothelial cell myosin light chain phosphorylation and permeability by vanadate

The involvement of tyrosine protein phosphorylation in the regulation of endothelial cell (EC) contraction and barrier function is poorly understood. We have previously shown that myosin light chain (MLC) phosphorylation catalyzed by a novel 214 kDa EC myosin light chain kinase (MLCK) isoform is a key event in EC contraction and barrier dysfunction [Garcia et al. (1995): J Cell Physiol 163:510-522; Garcia et al. (1997): Am J Respir Cell Mol Biol 16:487-491]. In this study, we tested the hypothesis that tyrosine phosphatases participate in the regulation of EC contraction and barrier function via modulation of MLCK activity. The tyrosine phosphatase inhibitor, sodium orthovanadate (vanadate), significantly decreased electrical resistance across bovine EC monolayers and increased albumin permeability consistent with EC barrier impairment. Vanadate significantly increased EC MLC phosphorylation in a time-dependent manner (maximal increase observed at 10 min) and augmented both the MLC phosphorylation and permeability responses produced by thrombin, an agonist which rapidly increases tyrosine kinase activities. The vanadate-mediated increase in MLC phosphorylation was not associated with alterations in either phosphorylase A Ser/Thr phosphatase activities or in cytosolic [Ca2+] but was strongly associated with significant increases in EC MLCK phosphotyrosine content. These data suggest that tyrosine phosphatase activities may participate in EC contractile and barrier responses via the regulation of the tyrosine phosphorylation status of EC MLCK.

Increased vascular endothelial growth factor production in the lungs of rats with hypoxia-induced pulmonary hypertension

Vascular endothelial growth factor (VEGF) is a potent mitogenic and permeability factor targeting predominantly endothelial cells. At least two tyrosine kinase receptors, Flk-1 and Flt-1, mediate its action and are mostly expressed by endothelial cells. VEGF and VEGF receptor expression are upregulated by hypoxia in vivo and the role of VEGF in hypoxia-induced angiogenesis has been extensively studied in a variety of disease entities. Although VEGF and its receptors are abundantly expressed in the lung, their role in hypoxic pulmonary hypertension and the accompanying vascular remodeling are incompletely understood. We report in this in vivo study that hypoxia increases mRNA levels for both VEGF and Flk-1 in the rat lung. The kinetics of the hypoxic response differ between receptor and ligand: Flk-1 mRNA showed a biphasic response to hypoxia with a significant, but transient, rise in mRNA levels observed after 9-15 h of hypoxic exposure and the highest levels noted after 3 wk. In contrast, VEGF mRNA levels did not show a significant increase with acute hypoxia, but increased progressively after 1-3 wk of hypoxia. By in situ hybridization, VEGF mRNA was localized predominantly in alveolar epithelial cells with increased signal in the lungs of hypoxic animals compared with controls. Immunohistochemical staining with anti-VEGF antibodies localized VEGF peptide throughout the lung parenchyma and was increased in hypoxic compared with normoxic animals. Furthermore, hypoxic animals had significantly higher circulating VEGF concentrations compared with normoxic controls. Lung vascular permeability as measured by extravasation of Evans Blue dye was not significantly different between normoxic and hypoxic animals, although a tendency for increased permeability was seen in the hypoxic animals. These findings suggest a possible role for VEGF in the pulmonary response to hypoxia.

Different effects of calcium antagonists on fluid filtration of large arteries and albumin permeability in spontaneously hypertensive rats

OBJECTIVE

To compare the effects of chronic administration of two dihydropyridines, nifedipine and amlodipine, and the non-dihydropyridine Ca2+ antagonist mibefradil on fluid filtration of large arteries and extravasation of albumin in spontaneously hypertensive rats.

METHODS

Spontaneously hypertensive rats aged 2 months were randomly allocated to oral treatment once a day with 30 mg/kg mibefradil (n=12), 100 mg/kg nifedipine (n=12), 20 mg/kg amlodipine (n=12) or placebo (n=12) for 1 month. Instantaneous blood pressure of rats under pentobarbital anaesthesia was recorded at the end of the treatment Fluid filtration across the carotid arterial wall was determined in situ in the isolated carotid artery. Extravasation of 25 mg/kg Evans Blue dye that had been injected intravenously was used to assess whole vascular permeability to albumin after chronic treatment with mibefradil.

RESULTS

Similar reductions in mean arterial pressure were obtained in all Ca2+ antagonist-treated rats. Heart rate was similar in rats in control, nifedipine and amlodipine groups but was significantly lower in mibefradil-treated rats (by 19%, P< 0.001). Fluid filtration across the carotid wall was greater in all Ca2+ antagonist-treated animals. However, fluid filtration was significantly less in mibefradil-treated rats than it was in nifedipine-treated, and amlodipine-treated rats. Furthermore, administration of mibefradil did not significantly modify extravasation of albumin in all tested tissues (pancreas, testis, spleen, lung, kidney, intestine, liver, skeletal muscle) except for cardiac and brain tissues, in which the permeability of albumin was increased by 24 and 33%, respectively, compared with values for the control group (P < 0.05).

CONCLUSION

These results indicate that Ca2+ antagonists increase fluid filtration through large arteries from spontaneously hypertensive rats. That the lower fluid filtration in mibefradil-treated rats was associated with no change in extravasation of albumin in most tissues and especially in skeletal muscle suggests that vascular permeability in hypertensive rats was impaired less by mibefradil treatment than it was by dihydropyridine Ca2+ antagonist treatments.

Thrombin-mediated focal adhesion plaque reorganization in endothelium: role of protein phosphorylation

Endothelial cell (EC) gap formation and barrier function are subject to dual regulation by (1) axial contractile forces, regulated by myosin light chain kinase activity, and (2) tethering forces, represented by cell-cell and cell-substratum adhesions. We examined whether focal adhesion plaque proteins (vinculin and talin) and focal adhesion kinase, p125FAK (FAK), represent target regulatory sites involved in thrombin-mediated EC barrier dysfunction. Histologically, thrombin produced dramatic rearrangement of EC actin, vinculin, and FAK in parallel with the evolution of gap formation and barrier dysfunction. Vinculin and talin were in vitro substrates for phosphorylation by EC PKC, a key effector enzyme involved in thrombin-induced EC barrier dysfunction. Although vinculin and talin were phosphorylated in situ under basal conditions in 32P-labeled EC, thrombin failed to alter the basal level of phosphorylation of these proteins. Phosphotyrosine immunoblotting showed that neither vinculin nor talin was significantly phosphorylated in situ on tyrosine residues in unstimulated ECs, and this was not further increased after thrombin. In contrast, both thrombin and the thrombin receptor-activating peptide (TRAP) produced an increase in FAK phosphotyrosine levels (corrected for immunoreactive FAK content) present in EC immunoprecipitates. Ionomycin, which produces EC barrier dysfunction in a myosin light chain kinase-independent manner, was used to increase intracellular Ca2+ and evaluate the Ca2+ sensitivity of this observation. In contrast to thrombin, ionomycin effected a dramatic decrease in the phosphotyrosine-to-immunoreactive FAK ratios, suggesting distinct effects of the two agents on FAK phosphorylation and function. These data indicate that modulation of cell tethering via phosphorylation of focal adhesion proteins is complex, agonist-specific, and may be a relevant mechanism of EC barrier dysfunction in permeability models that do not depend on an increase in myosin 20-kD regulatory light chain phosphorylation.