Adult respiratory distress syndrome - an update

Endocan and the respiratory system: a review

Endocan, formerly called endothelial cell-specific molecule 1, is an endothelial cell-associated proteoglycan that is preferentially expressed by renal and pulmonary endothelium. It is upregulated by proangiogenic molecules as well as by pro-inflammatory cytokines, and since it reflects endothelial activation and dysfunction, it is regarded as a novel tissue and blood-based relevant biomarker. As such, it is increasingly being researched and evaluated in a wide spectrum of healthy and disease pathophysiological processes. Here, we review the present scientific knowledge on endocan, with emphasis on the evidence that underlines its possible clinical value as a prognostic marker in several malignant, inflammatory and obstructive disorders of the respiratory system.

Delivery of the high-mobility group box 1 box A peptide using heparin in the acute lung injury animal models

In this study, the efficacy of the high-mobility group box-1 box A (HMGB1A)/heparin complex was evaluated for the treatment of acute lung injury (ALI). HMGB1A is an antagonist against wild-type high-mobility group box-1 (wtHMGB1), a pro-inflammatory cytokine that is involved in ALIs. HMGB1A has positive charges and can be captured in the mucus layer after intratracheal administration. To enhance the delivery and therapeutic efficiency of HMGB1A, the HMGB1A/heparin complex was produced using electrostatic interactions, with the expectation that the nano-sized complex with a negative surface charge could efficiently penetrate the mucus layer. Additionally, heparin itself had an anti-inflammatory effect. Complex formation with HMGB1A and heparin was confirmed by atomic force microscopy. The particle size and surface charge of the HMGB1A/heparin complex at a 1:1 weight ratio were 113nm and -25mV, respectively. Intratracheal administration of the complex was performed into an ALI animal model. The results showed that the HMGB1A/heparin complex reduced pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β, more effectively than HMGB1A or heparin alone. Hematoxylin and eosin staining confirmed the decreased inflammatory reaction in the lungs after delivery of the HMGB1A/heparin complex. In conclusion, the HMGB1A/heparin complex might be useful to treat ALI.

Role of pulmonary microvascular endothelial cell apoptosis in murine sepsis-induced lung injury in vivo

Background

Sepsis remains a common and serious condition with significant morbidity and mortality due to multiple organ dysfunction, especially acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Sepsis-induced ALI is characterized by injury and dysfunction of the pulmonary microvasculature and pulmonary microvascular endothelial cells (PMVEC), resulting in enhanced pulmonary microvascular sequestration and pulmonary infiltration of polymorphonuclear leukocytes (PMN) as well as disruption of the normal alveolo-capillary permeability barrier with leak of albumin-rich edema fluid into pulmonary interstitium and alveoli. The role of PMVEC death and specifically apoptosis in septic pulmonary microvascular dysfunction in vivo has not been established.

Methods

In a murine cecal ligation/perforation (CLP) model of sepsis, we quantified and correlated time-dependent changes in pulmonary microvascular Evans blue (EB)-labeled albumin permeability with (1) PMVEC death (propidium iodide [PI]-staining) by both fluorescent intravital videomicroscopy (IVVM) and histology, and (2) PMVEC apoptosis using histologic fluorescent microscopic assessment of a panel of 3 markers: cell surface phosphatidylserine (detected by Annexin V binding), caspase activation (detected by FLIVO labeling), and DNA fragmentation (TUNEL labeling).

Results

Compared to sham mice, CLP-sepsis resulted in pulmonary microvascular barrier dysfunction, quantified by increased EB-albumin leak, and PMVEC death (PI+ staining) as early as 2 h and more marked by 4 h after CLP. Septic PMVEC also exhibited increased presence of all 3 markers of apoptosis (Annexin V+, FLIVO+, TUNEL+) as early as 30 mins – 1 h after CLP-sepsis, which all similarly increased markedly until 4 h. The time-dependent changes in septic pulmonary microvascular albumin-permeability barrier dysfunction were highly correlated with PMVEC death (PI+; r = 0.976, p < 0.01) and PMVEC apoptosis (FLIVO+; r = 0.991, p < 0.01). Treatment with the pan-caspase inhibitor Q-VD prior to CLP reduced PMVEC death/apoptosis and attenuated septic pulmonary microvascular dysfunction, including both albumin-permeability barrier dysfunction and pulmonary microvascular PMN sequestration (p < 0.05). Septic PMVEC apoptosis and pulmonary microvascular dysfunction were also abrogated following CLP-sepsis in mice deficient in iNOS (Nos2^−/−) or NADPH oxidase (p47^phox−/− or gp91^phox−/−) and in wild-type mice treated with the NADPH oxidase inhibitor, apocynin.

Conclusions

Septic murine pulmonary microvascular dysfunction in vivo is due to PMVEC death, which is mediated through caspase-dependent apoptosis and iNOS/NADPH-oxidase dependent signaling.

Penetrating thorax injury leads to mild systemic activation of neutrophils without inflammatory complications

INTRODUCTION

Trauma is one of the major causes of morbidity and mortality. Thoracic injuries are associated with inflammatory complications such as ARDS. The pathogenesis of this complication after pulmonary injury is incompletely understood, but neutrophils are thought to play a pivotal role. The aim of this project was to gain more insight in the role of thoracic injuries in the pathophysiological processes that link systemic neutrophil activation with inflammatory complications after trauma.

METHODS

In this prospective cohort study fifty-five patients with isolated penetrating thoracic injury were included at a level one Trauma Unit. Blood samples were analysed for neutrophil phenotype with the use of flowcytometry within 3 h of trauma and repeated six and 24 h after injury. The presence of inflammatory complications (e.g. ARDS or sepsis/septic shock) was assessed during admission, and this was related to the neutrophil phenotpe.

RESULTS

The clinical follow-up of fifty-three patients was uneventful. Only two patients developed an inflammatory complication. Within 3 h after trauma, neutrophils showed a decreased expression of FcγRII (p=0.007) and FcγRIII (p=0.001) compared to healthy individuals. After 6 h, expression of active FcγRII (p=0.017), C5aR (p=0.004) and CAECAM8 (p=0.043) increased, whereas L-selectin (p=0.002) decreased. After 24 h also CXCR-2 (CD182) expression increased compared to healthy individuals (p=0.001).

CONCLUSIONS

Penetrating thoracic trauma leads to a distinct primed activation status of circulating neutrophils within hours. In addition to activation of cells, both young and reverse migrated neutrophils are released into the circulation. This degree of systemic inflammation does not exceed a threshold of inflammation that is needed for the development of inflammatory complications like ARDS.

Imaging Plasmodium immunobiology in the liver, brain, and lung

Plasmodium falciparum malaria is responsible for the deaths of over half a million African children annually. Until a decade ago, dynamic analysis of the malaria parasite was limited to in vitro systems with the typical limitations associated with 2D monocultures or entirely artificial surfaces. Due to extremely low parasite densities, the liver was considered a black box in terms of Plasmodium sporozoite invasion, liver stage development, and merozoite release into the blood. Further, nothing was known about the behavior of blood stage parasites in organs such as the brain where clinical signs manifest and the ensuing immune response of the host that may ultimately result in a fatal outcome. The advent of fluorescent parasites, advances in imaging technology, and availability of an ever-increasing number of cellular and molecular probes have helped illuminate many steps along the pathogenetic cascade of this deadly tropical parasite.

Multiple anti-inflammatory pathways triggered by resveratrol lead to amelioration of staphylococcal enterotoxin B-induced lung injury

BACKGROUND AND PURPOSE

Inhalation of the superantigen,staphylococcal enterotoxin B (SEB), leads to the activation of the host T and invariant natural killer (iNK) T cells, thereby resulting in acute lung inflammation and respiratory failure but the underlying mechanism(s) of disease remain elusive, with limited treatment options. In this study, we investigated the therapeutic effectiveness of resveratrol, a plant polyphenol, during SEB-induced lung inflammation.

EXPERIMENTAL APPROACH

C57BL/6 mice were exposed to SEB (50 µg·per mouse), administered intranasally, and were treated with resveratrol (100 mg·kg(-1)) before or after SEB exposure. Lung injury was studied by measuring vascular permeability, histopathological examination, nature of infiltrating cells, inflammatory cytokine induction in the bronchoalveolar fluid (BALF), apoptosis in SEB-activated T cells and regulation of SIRT1 and NF-κB signalling pathways.

KEY RESULTS

Pretreatment and post-treatment with resveratrol significantly reduced SEB-induced pulmonary vascular permeability, and inflammation. Resveratrol significantly reduced lung infiltrating cells and attenuated the cytokine storm in SEB-exposed mice, which correlated with increased caspase-8-dependent apoptosis in SEB-activated T cells. Resveratrol treatment also markedly up-regulated Cd11b+ and Gr1+ myeloid-derived suppressor cells (MDSCs) that inhibited SEB-mediated T cell activation in vitro. In addition, resveratrol treatment was accompanied by up-regulation of SIRT1 and down-regulation of NF-κB in the inflammatory cells of the lungs.

CONCLUSIONS AND IMPLICATIONS

The current study demonstrates that resveratrol may constitute a novel therapeutic modality to prevent and treat SEB-induced lung inflammation inasmuch because it acts through several pathways to reduce pulmonary inflammation.

Sphingosine 1-phosphate has dual functions in the regulation of endothelial cell permeability and Ca2+ metabolism

Ca2+ signaling plays an important role in endothelial cell (EC) functions including the regulation of barrier integrity. Recently, the endogenous lipid derivative, sphingosine-1-phosphate (S1P), has emerged as an important modulator of EC barrier function. We investigated the role of endogenously generated S1P in Ca2+ metabolism and barrier function in human umbilical endothelial cells (HUVECs) stimulated by thrombin, histamine, or other agonists. Barrier function was assessed by dextran diffusion through HUVEC monolayers, and Ca2+ transients were measured using a fluoroprobe. Thrombin or histamine increased Ca2+ release from the endoplasmic reticulum (ER) and Ca2+ entry through store-operated channels (SOCs) that was accompanied by increased EC permeability. Inhibition of S1P synthesis by a specific sphingosine kinase inhibitor (SKI) decreased thrombin or histamine-induced increased permeability and decreased Ca2+ entry via SOC in a concentration-dependent fashion. SKI had minuscule effects on thrombin or histamine-induced Ca2+ release from ER. SKI also inhibited thapsigargin or ionomycin-induced Ca2+ entry via SOC without affecting Ca2+ release from the ER. In contrast to the effects of endogenously generated S1P, when S1P was administered externally, it initiated Ca2+ release from ER similar to thrombin and histamine while decreasing EC permeability. These observations indicate that after agonist-induced conditions, endogenously generated S1P functions as a positive modulator of Ca2+ entry via SOC and a mediator of increased cell permeability. In contrast, extracellular exposure to S1P has different signaling mechanisms and effects. Thus, the potential dual roles of endogenous and exogenous S1P on EC function need to be considered in pharmacological studies targeting sphingosine metabolism.

Mice lacking NKCC1 are protected from development of bacteremia and hypothermic sepsis secondary to bacterial pneumonia

The contribution of the Na(+)-K(+)-Cl(-) transporter (NKCC1) to fluid in ion transport and fluid secretion in the lung and in other secretory epithelia has been well established. Far less is known concerning the role of this cotransporter in the physiological response of the pulmonary system during acute inflammation. Here we show that mice lacking this transporter are protected against hypothermic sepsis and bacteremia developing as a result of Klebsiella pneumoniae infection in the lung. In contrast, this protection was not observed in NKCC1(-/-) mice with K. pneumoniae-induced peritonitis. Although overall recruitment of cells to the lungs was not altered, the number of cells present in the airways was increased in the NKCC1(-/-) animals. Despite this robust inflammatory response, the increase in vascular permeability observed in this acute inflammatory model was attenuated in the NKCC1(-/-) animals. Our studies suggest that NKCC1 plays a unique and untoward unrecognized role in acute inflammatory responses in the lung and that specific inhibition of this NKCC isoform could be beneficial in treatment of sepsis.

Cell-based Angiopoietin-1 Gene Therapy for Acute Lung Injury

RATIONALE

The acute respiratory distress syndrome is a significant cause of morbidity and mortality in critically ill patients. Angiopoietin-1 (Ang-1), a ligand for the endothelial Tie2 receptor, is an endothelial survival and vascular stabilization factor that reduces endothelial permeability and inhibits leukocyte-endothelium interactions.

OBJECTIVES

We hypothesized that Ang-1 counteracts vascular inflammation and pulmonary vascular leak in experimental acute lung injury.

METHODS

We used cell-based gene therapy in a rat model of ALI. Transgenic mice overexpressing Ang-1 or deficient in the Tie2 receptor were also studied to better elucidate the mechanisms of protection.

MEASUREMENTS AND MAIN RESULTS

The present report provides data that support a strong protective role for the Ang-1/Tie2 system in two experimental models of LPS-induced acute lung injury. In a rat model, cell-based Ang-1 gene transfer improved morphological, biochemical, and molecular indices of lung injury and inflammation. These findings were confirmed in a gain-of-function conditional, targeted transgenic mouse model, in which Ang-1 reduced endothelial cell activation and the expression of adhesion molecules, associated with a marked improvement in airspace inflammation and intraalveolar septal thickening. Moreover, heterozygous Tie2-deficient mice demonstrated enhanced evidence of lung injury and increased early mortality.

CONCLUSIONS

These results support a critical role for the Ang-1/Tie2 axis in modulating the pulmonary vascular response to lung injury and suggest that Ang-1 therapy may represent a potential new strategy for the treatment and/or prevention of acute respiratory distress syndrome in critically ill patients.

Integrin alphavbeta5 regulates lung vascular permeability and pulmonary endothelial barrier function

Increased lung vascular permeability is an important contributor to respiratory failure in acute lung injury (ALI). We found that a function-blocking antibody against the integrin alphavbeta5 prevented development of lung vascular permeability in two different models of ALI: ischemia-reperfusion in rats (mediated by vascular endothelial growth factor [VEGF]) and ventilation-induced lung injury (VILI) in mice (mediated, at least in part, by transforming growth factor-beta [TGF-beta]). Knockout mice homozygous for a null mutation of the integrin beta5 subunit were also protected from lung vascular permeability in VILI. In pulmonary endothelial cells, both the genetic absence and blocking of alphavbeta5 prevented increases in monolayer permeability induced by VEGF, TGF-beta, and thrombin. Furthermore, actin stress fiber formation induced by each of these agonists was attenuated by blocking alphavbeta5, suggesting that alphavbeta5 regulates induced pulmonary endothelial permeability by facilitating interactions with the actin cytoskeleton. These results identify integrin alphavbeta5 as a central regulator of increased pulmonary vascular permeability and a potentially attractive therapeutic target in ALI.

Acute necrotizing encephalopathy of childhood in non-Asian patients: report of three cases and literature review

Acute necrotizing encephalopathy of childhood is a novel type of parainfectious encephalopathy with a racial and geographic predilection, rarely reported from other than East Asian areas. The objective was to describe the clinical, imaging, and other laboratory findings of non-Asian patients with acute necrotizing encephalopathy. Data were collected from three patients diagnosed in Athens over a 4-year period plus 16 cases reported from other European and North American countries. One of the Greek children died, and the other two had a normal outcome. A neuropathologic examination in the fatal case showed edematous necrosis without inflammatory, reactive, or proliferative changes. Data from Greek and other non-Asian patients support the homogeneity of the disease worldwide.

Respuesta inflamatoria y apoptosis en la lesión pulmonar aguda

One of the principal mechanisms of pulmonary injury in acute respiratory distress is due to the effects of the precipitated inflammatory response. The damage produced to the alveolar epithelium and underlying endothelium depends on the sequestration and activation of inflammatory cells, which in turn exert their actions through mediators. On the other hand, apoptosis is a mechanism responsible for epithelial damage and regulation of inflammation. Response of the lung tissue subjected to mechanical ventilation stimulus is added to the previous mechanisms. All these processes flow into a series of common pathways of cellular activation. Knowledge of these mechanisms could serve to identify which patients would benefit from a specific treatment before applying therapies that act indiscriminately in the inflammatory response.

Expression and role of the hyaluronan receptor RHAMM in inflammation after bleomycin injury

Lung injury is associated with increased concentrations of hyaluronan (hyaluronic acid, HA). HA modifies cell behavior through interaction with cell-associated receptors such as receptor for HA-mediated motility (RHAMM, CD168). Using a function blocking anti-RHAMM antibody (R36), we investigated the expression and role of RHAMM in the inflammatory response to intratracheal bleomycin in rats. Immunostaining showed increased expression of RHAMM in macrophages 4-7 d after injury. Surface biotin labeling of cells isolated by lavage confirmed increased surface expression of a 70-kD RHAMM after lung injury, and in situ hybridization demonstrated increased RHAMM mRNA in macrophages responding to injury. Time-lapse cinemicrography demonstrated a 5-fold increase in motility of alveolar macrophages from bleomycin-treated animals that was completely blocked by R36 in vitro. Further, HA-stimulated macrophage chemotaxis was also inhibited by R36. Daily administration of R36 to injured animals resulted in a 40% decrease in macrophage accumulation 7 d after injury. Further, H&E staining of tissue sections showed that bleomycin-mediated changes in lung architecture were improved with R36 treatment. Taken together with previous results showing the inhibitory effects of HA-binding peptide on inflammation and fibrosis, we conclude that the interaction of RHAMM with HA is a critical component of the recruitment of inflammatory cells to the lung after injury.

Neither neutrophils nor reactive oxygen species contribute to tissue damage during Pneumocystis pneumonia in mice

Neutrophils are implicated in the damage of lung tissue in many disease states, including infectious diseases and environmental insults. These effects may be due to oxidative or nonoxidative functions of the neutrophil or both. We examined the role of neutrophils in pulmonary damage during infection with the opportunistic fungal pathogen Pneumocystis sp. in four mouse models of neutrophil dysfunction. These were (i) a knockout of the gp91(phox) component of NADPH oxidase, in which reactive oxygen species (ROS) production is greatly reduced; (ii) a double knockout of gp91(phox) and inducible nitric oxide synthase, in which ROS and nitric oxide production is greatly decreased; (iii) a knockout of the chemokine receptor CXCR2, in which accumulation of intra-alveolar neutrophils is severely diminished; and (iv) antibody depletion of circulating neutrophils in wild-type mice with the monoclonal antibody RB6. Surprisingly, in each case, indicators of pulmonary damage (respiratory rates, arterial oxygen partial pressures, and intra-alveolar albumin concentrations) were the same in knockout mice and comparable wild-type mice. Therefore, whereas neutrophils are a valid correlative marker of lung damage during Pneumocystis infection, neither neutrophils nor ROS appear to be the causative agent of tissue damage. We also show that there is no difference in Pneumocystis burdens between wild-type and knockout mice, which supports the idea that neutrophils do not have a major role in the clearance of this organism.

Pulmonary endothelium in acute lung injury: from basic science to the critically ill

BACKGROUND

Pulmonary endothelium is an active organ possessing numerous physiological, immunological, and metabolic functions. These functions may be altered early in acute lung injury (ALI) and further contribute to the development of acute respiratory distress syndrome (ARDS). Pulmonary endothelium is strategically located to filter the entire blood before it enters the systemic circulation; consequently its integrity is essential for the maintenance of adequate homeostasis in both the pulmonary and systemic circulations. Noxious agents that affect pulmonary endothelium induce alterations in hemodynamics and hemofluidity, promote interactions with circulating blood cells, and lead to increased vascular permeability and pulmonary edema formation.

OBJECTIVE

We highlight pathogenic mechanisms of pulmonary endothelial injury and their clinical implications in ALI/ARDS patients.

Platelets stimulate fibroblast-mediated contraction of collagen gels

BACKGROUND

Platelets are thought to play a role in a variety of inflammatory conditions in the lung, some of which may lead to fibrosis. In the current study we tested the hypothesis that whole platelets and platelet lysate can mediate remodelling of extracellular matrix in vitro by affecting fibroblast-mediated contraction of a collagen gel. We also sought to determine to what extent platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) contribute to this effect.

METHODS

Washed platelets, isolated from healthy blood donors, and platelet lysate (freezing and thawing), were cast together with human lung fibroblasts in three-dimensional collagen gels. The gels were then released and cultured for four days. PDGF and TGF-beta1 concentrations were measured in culture supernatants by ELISA.

RESULTS

Both platelets and platelet lysate augmented fibroblast-mediated gel contraction in a time and concentration dependent manner (19.9% +/- 0.1 (mean +/- SEM) of initial area vs. 48.0% +/- 0.4 at 48 hours; P < 0.001 and 41.5% +/- 0.6 vs. 60.6% +/- 0.3 at 48 hours; P < 0.001, respectively). Fixed platelets had no effect in the system. Both TGF-beta1 and PDGF-AA/AB were released in co-culture. PDGF-AA/AB had a maximum release at 24 hours whereas TGF-beta1 release increased with longer culture periods. Neutralising antibodies to these mediators partially inhibited platelet-induced gel contraction.

CONCLUSION

We conclude that platelets may promote remodelling of extracellular matrix in vitro and that PDGF and TGF-beta partially mediate this effect, also indicating a role for other mediators. The findings may be an important mechanism in regulating repair processes after injury.

Cyclooxygenase-inhibition enhances the effects of rSP-C surfactant therapy in a rat lavage model of acute respiratory distress syndrome (ARDS)

The effects of additional i.v. therapy with a cyclooxygenase-inhibitor Eltenac to a recombinant surfactant protein C (rSP-C) based surfactant were investigated in a rat lung lavage model of acute lung injury. Treatment was done at 60 min after the induction of acute lung injury by lavage. The influence of the different treatments were tested with regard to improving oxygenation, histopathological changes (hyaline membrane formation and alveolar influx of neutrophil leukocytes). These effects were further compared to a fixed combination of Eltenac with rSP-C surfactant which was administered intratracheally (i.tr.), 60 min after lavage. To prove that fibrinogen is involved in the formation of hyaline membranes in this animal model confocal microscopy was applied. Furthermore, for selected cases the influence of Eltenac or rSP-C surfactant on fibrinogen leakage was investigated by using confocal microscopy. Results of additional i.v. therapy exhibited an improved oxygenation with rSP-C surfactant, while a high dose of Eltenacalone did not influence oxygenation as compared to untreated controls. Addition of Eltenac lead to improved oxygenation using the low dose of rSP-C surfactant. The rSP-C surfactant prevented further hyaline membrane formation. Furthemore, addition of Eltenac to the low dose of rSP-C surfactant lead to improved hyaline membrane formation at a dose of 100 micromol/kg b.w. Results of combined i.tr. therapy confirmed the results of the additional therapy. Again, rSP-C surfactant improved oxygenation and further hyaline membrane formation, while even the high dose of i.tr. administered Eltenacalone only prevented further hyaline membrane formation. Using the low dose of rSP-C surfactant, combined treatment with Eltenac showed additional effects on oxygenation and inhibition of hyaline membrane formation. The maximum therapeutic effect of combined treatment was achieved at 0.3 mg Eltenac per kg b.w. which is equivalent to approximately 1 micromol. The inflammatory cell infiltration into the lung was not influenced by any of the therapeutic approaches. Confocal microscopy gave evidence that fibrinogen is involved in hyaline membrane formation in this animal model. Furthermore, as was shown by the explorative investigations with confocal microscopy, addition of the cyclooxygenase-inhibitor decreases the diffuse interstitial leakage of fibrinogen into the lung while surfactant monotherapy did not exhibit any influence on the fibrinogen influx into the alveoli.

CONCLUSIONS

Confocal microscopy may be an effective method to investigate the connection between fibrinogen leakage and hyaline membrane formation. Effects of additional or combined treatment were superior when compared to each treatment alone leading to the conclusion that a rSP-C surfactant containing a cyclooxygenase-inhibitor, acts synergistically in this animal model of acute lung injury. Lower doses of Eltenac could be used to reach similar effects on oxygenation and prevention of hyaline membrane after combined i.tr. treatment than after additional i.v. treatment together with surfactant. This leads to the conclusion that a fixed combination of rSP-C surfactant and a cyclooxygenase-inhibitor may be an effective treatment. Further testing may be warranted to prove whether this is a promising treatment for patients with acute lung injury.

Inhaled nitric oxide inhibits platelet-leukocyte interactions in patients with acute respiratory distress syndrome

INTRODUCTION

In addition to its effects on platelet function, recent studies suggest that inhaled nitric oxide (NO) also influences the function of circulating leukocytes. Therefore, the aim of this work was to investigate the formation of platelet-leukocyte aggregates (PLAs) and platelet and leukocyte cell surface receptor expression during NO therapy in patients with acute respiratory distress syndrome.

METHODS

In 16 patients responding to NO therapy with an improvement in oxygenation (NO group) and in four nonresponders (control), platelet P-selectin expression, platelet fibrinogen binding, the expression CD11a on leukocytes, and the formation of PLAs were investigated at 0, 60, 120, and 180 mins of therapy or at corresponding time points by means of flow cytometry. In addition, PLA was investigated in 30 healthy volunteers during NO inhalation, in five mechanically ventilated patients without acute respiratory distress syndrome and without NO inhalation, and during NO incubation in platelet-rich plasma of ten healthy volunteers in vitro.

RESULTS

NO therapy inhibited PLA formation at 60 (13% +/- 4% in the NO group vs. 19% +/- 7% in the control group, p <.01) and 120 mins (14% +/- 4% vs. 18% +/- 7%, p <.05) and slightly decreased CD11a expression at 60 mins (152 +/- 22 arbitrary units vs. 187 +/- 36 arbitrary units, p <.05). Furthermore, besides inhibiting platelet fibrinogen binding, NO also led to a significant inhibition of P-selectin expression at 120 (38% +/- 4% vs. 43% +/- 5%, p <.05) and 180 mins (34% +/- 5% vs. 43% +/- 6%, p <.01), demonstrating a significant correlation between changes in P-selectin expression and PLA formation. In contrast, PLA formation was not influenced by mechanical ventilation in patients without acute respiratory distress syndrome. These results were further supported by additional studies showing inhibition of PLA formation in healthy volunteers as well.

CONCLUSIONS

NO-dependent inhibition of PLA formation in patients with acute respiratory distress syndrome can be explained by the inhibition in platelet P-selectin expression. Thus, this study provides rational evidence of systemic antileukocytic and antiplatelet properties of NO therapy in the clinical setting.

Oxygen-sensing mechanisms and the regulation of redox-responsive transcription factors in development and pathophysiology

How do organisms sense the amount of oxygen in the environment and respond appropriately when the level of oxygen decreases? Oxygen sensing and the molecular stratagems underlying the process have been the focus of an endless number of investigations trying to find an answer to the question: "What is the identity of the oxygen sensor?" Dynamic changes in pO2 constitute a potential signaling mechanism for the regulation of the expression and activation of reduction-oxidation (redox)-sensitive and oxygen-responsive transcription factors, apoptosis-signaling molecules and inflammatory cytokines. The transition from placental to lung-based respiration causes a relatively hyperoxic shift or oxidative stress, which the perinatal, developing lung experiences during birth. This variation in DeltapO2, in particular, differentially regulates the compartmentalization and functioning of the transcription factors hypoxia-inducible factor-1alpha (HIF-1alpha) and nuclear factor-kappaB (NF-kappaB). In addition, oxygen-evoked regulation of HIF-1alpha and NF-kappaB is closely coupled with the intracellular redox state, such that modulating redox equilibrium affects their responsiveness at the molecular level (expression/transactivation). The differential regulation of HIF-1alpha and NF-kappaB in vitro is paralleled by oxygen-sensitive and redox-dependent pathways governing the regulation of these factors during the transition from placental to lung-based respiration ex utero. The birth transition period in vivo and ex utero also regulates apoptosis signaling pathways in a redox-dependent manner, consistent with NF-kappaB being transcriptionally regulated in order to play an anti-apoptotic function. An association is established between oxidative stress conditions and the augmentation of an inflammatory state in pathophysiology, regulated by the oxygen- and redox-sensitive pleiotropic cytokines.

Pharmaco-redox regulation of cytokine-related pathways: from receptor signaling to pharmacogenomics

Cytokines represent a multi-diverse family of polypeptide regulators; they are relatively low molecular weight (< 30 kDa), pharmacologically active proteins that are secreted by one cell for the purpose of altering either its own functions (autocrine effect) or those of adjacent cells (paracrine effect). Cytokines are small, nonenzymatic glycoproteins whose actions are both diverse and overlapping (specificity/redundancy) and may affect diverse and overlapping target cell populations. In many instances, individual cytokines have multiple biological activities. Different cytokines can also have the same activity, which provides for functional redundancy (network) within the inflammatory and immune systems. As biological cofactors that are released by specific cells, cytokines have specific effects on cell-cell interaction, communication, and behavior of other cells. As a result, it is infrequent that loss or neutralization of one cytokine will markedly interfere with either of these systems. The biological effect of one cytokine is often modified or augmented by another. Because an interdigitating, redundant network of cytokines is involved in the production of most biological effects, both under physiologic and pathologic conditions, it usually requires more than a single defect in the network to alter drastically the outcome of the process. This fact, therefore, may have crucial significance in the development of therapeutic strategies for biopharmacologic intervention in cytokine-mediated inflammatory processes and infections.

Killing of Klebsiella pneumoniae by human alveolar macrophages

We investigated putative mechanisms by which human surfactant protein A (SP-A) effects killing of Klebsiella pneumoniae by human alveolar macrophages (AMs) isolated from bronchoalveolar lavagates of patients with transplanted lungs. Coincubation of AMs with human SP-A (25 microg/ml) and Klebsiella resulted in a 68% decrease in total colony forming units by 120 min compared with AMs infected with Klebsiella in the absence of SP-A, and this SP-A-mediated effect was abolished by preincubation with N(G)-monomethyl-L-arginine. Incubation of transplant AMs with SP-A increased intracellular Ca(2+) concentration ([Ca(2+)](i)) by 70% and nitrite and nitrate (NO(x)) production by 45% (from 0.24 +/- 0.02 to 1.3 +/- 0.21 nmol small middle dot 10(6) AMs(-1).h(-1)). Preincubation with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester inhibited the increase in [Ca(2+)](i) and abrogated the SP-A-mediated Klebsiella phagocytosis and killing. In contrast, incubation of AMs from normal volunteers with SP-A decreased both [Ca(2+)](i) and NO(x) production and did not result in killing of Klebsiella. Significant killing of Klebsiella was also seen in a cell-free system by sustained production of peroxynitrite (>1 microM/min) at pH 5 but not at pH 7.4. These findings indicate that SP-A mediates pathogen killing by AMs from transplant lungs by stimulating phagocytosis and production of reactive oxygen-nitrogen intermediates.

Nitric oxide and cyclic guanosine monophosphate stimulate apoptosis via activation of the Fas-FasL pathway

BACKGROUND

Inappropriately exaggerated response of pulmonary vascular cells to inflammatory mediators may be one mechanism that leads to acute (or adult) respiratory distress syndrome. Nitric oxide (NO) is induced following such exaggerated responses and may have a variety of biological effects, including induction of apoptosis. The mechanism by which NO causes apoptosis is unknown; however, Fas (CD95) and Fas ligand (FasL) (CD95L) have been implicated. We hypothesized that NO-induced apoptosis in pulmonary vascular smooth muscle cells is mediated through a Fas-FasL pathway.

MATERIALS AND METHODS

Cultured human and rat pulmonary artery smooth muscle cells (PASMCs) were exposed to soluble FasL (0-5 ng/ml), the NO donor S(G)-nitroso-N-acetyl pencillamine (SNAP) (0-50 microg/ml), and/or anti-FasL (0-100 microg/ml) for 12 h. Apoptosis was measured using in situ DNA nick end labeling and flow cytometry. Changes in Fas and FasL protein levels were assessed via Western blot analysis. Messenger RNA (mRNA) abundance of apoptosis-related genes was determined using a ribonuclease protection assay.

RESULTS

Rat PASMCs exposed to FasL show a dose-dependent increase in apoptosis. Human PASMCs are less responsive to FasL. Addition of anti-FasL to rat PASMCs treated with 10(-5) M SNAP decreases apoptosis levels compared to SNAP treated alone. FasL and Fas receptor proteins are increased in response to 10(-3) to 10(-4) M SNAP or 10(-6) M 8-bromo-cyclic guanosine monophosphate (cGMP). The mRNA abundance of Fas, FasL, and other apoptosis-related genes is increased in response to 10(-6) M 8-bromo-cGMP but not 8-bromo-cyclic adenosine monophosphate.

CONCLUSIONS

Nitric oxide-induced apoptosis in rat and human PASMCs is mediated, at least in part, through the Fas-FasL pathway, with cGMP increasing the expression of Fas and FasL.

Modulation of chemokine production in lung microvascular endothelial cells by dopamine is mediated via an oxidative mechanism

Serum concentrations of catecholamines are high in patients with sepsis or acute respiratory distress syndrome (ARDS). Because chemokines mediate the recruitment of neutrophils into inflammatory sites, we addressed the question of whether dopamine (DA) is able to influence chemokine production in endothelial cells under basal and proinflammatory conditions. To this end, lung microvascular endothelial cells (LMVEC) were stimulated or not for 24 h with the bacterial toxins lipopolysaccharide (LPS) (1 microg/ml) or lipoteichonic acid (LTA) (10 microg/ml) in the presence or absence of various concentrations of DA (1-100 microg/ml). Whereas under basal and stimulatory conditions, the addition of DA to endothelial cells dose-dependently increased IL-8 production, the production of ENA-78 and Gro-alpha was significantly inhibited (P < 0.01). This effect could still be demonstrated when the cells were stimulated for up to 3 h with LPS before DA administration. Similar findings were detected for the mRNA expression of these chemokines. The influence of DA on chemokine production was not receptor mediated and could be prevented by antioxidants or radical scavengers. Moreover, addition of H(2)O(2) to endothelial cells gave results similar to those observed with DA stimulation, suggesting a pivotal role for reactive oxygen species in DA-mediated modulation of chemokine production in endothelial cells. Our data thus demonstrate that DA administration results in the induction of oxidative stress, with profound effects on endothelial chemokine production.

Pulmonary and systemic host response to Streptococcus pneumoniae and Klebsiella pneumoniae bacteremia in normal and immunosuppressed mice

Mortality related to bacteremic pneumonia remains high, and the role of sepsis in inflammation, pulmonary injury, and death remains unclear, mostly in leukopenic states. In the present study, the microbiology, histopathology, and host response to Streptococcus pneumoniae and Klebsiella pneumoniae infection were determined in an experimental model of bacteremia in immunocompetent and leukopenic mice. Leukocyte depletion by cyclophosphamide did not impair the early clearance of pneumococci from blood but facilitated growth in lungs. By contrast, klebsiellae rapidly grew in blood of leukopenic mice. These observations suggest that tissue-based phagocytes and circulating leukocytes, respectively, play prominent roles in S. pneumoniae and K. pneumoniae eradication. The kinetics of leukocyte recruitment in lungs during S. pneumoniae bacteremia suggested early strong inflammation in immunocompetent mice that is associated with tumor necrosis factor alpha release and histological disorders, including cell debris and surfactant in alveolar spaces. Leukocyte depletion further stimulated pulmonary capillary leakage both in S. pneumoniae and K. pneumoniae bacteremia, which seemed attributable to bacterial virulence factors. Nitric oxide production did not differ significantly among groups. Leukopenia and low platelet counts characterized the late stage of bacteremia for both strains, but only K. pneumoniae altered renal function. Understanding the pathogenesis of bacteremia will help establish beneficial therapies for both sepsis and pneumonia.

Hantavirus infection induces the expression of RANTES and IP-10 without causing increased permeability in human lung microvascular endothelial cells

Sin Nombre virus (SNV) and Hantaan virus (HTN) infect endothelial cells and are associated with different patterns of increased vascular permeability during human disease. It is thought that such patterns of increased vascular permeability are a consequence of endothelial activation and subsequent dysfunction mediated by differential immune responses to hantavirus infection. In this study, the ability of hantavirus to directly induce activation of human lung microvascular endothelial cells (HMVEC-Ls) was examined. No virus-specific modulation in the constitutive or cytokine-induced expression of cellular adhesion molecules (CD40, CD54, CD61, CD62E, CD62P, CD106, and major histocompatibility complex classes I and II) or in cytokines and chemokines (eotaxin, tumor necrosis factor alpha, interleukin 1beta [IL-1beta], IL-6, IL-8, MCP-1, MIP-1alpha, and MIP-1beta) was detected at either the protein or message level in hantavirus-infected HMVEC-Ls. Furthermore, no virus-specific enhancement of paracellular or transcellular permeability or changes in the organization and distribution of endothelial intercellular junctional proteins was observed. However, infection with either HTN or SNV resulted in detectable levels of the chemokines RANTES and IP-10 (the 10-kDa interferon-inducible protein) in HMVEC-Ls within 72 h and was associated with nuclear translocation of interferon regulatory factor 3 (IRF-3) and IRF-7. Gamma interferon (IFN-gamma)-induced expression of RANTES and IP-10 could also be detected in uninfected HMVEC-Ls and was associated with nuclear translocation of IRF-1 and IRF-3. Treatment of hantavirus-infected HMVEC-Ls with IFN-gamma for 24 h resulted in a synergistic enhancement in the expression of both RANTES and IP-10 and was associated with nuclear translocation of IRF-1, IRF-3, IRF-7, and NF-kappaB p65. These results reveal a possible mechanism by which hantavirus infection and a TH1 immune response can cooperate to synergistically enhance chemokine expression by HMVEC-Ls and trigger immune-mediated increases in vascular permeability.

Development of a new method of analysing chemotactic deactivation of human neutrophil granulocytes

Measurement of chemotactic migration of human neutrophil granulocytes (PMN) induced by chemotaxins serves as a simple and reliable method for assessing the expression of chemotaxin receptors. Incubation of PMN with a certain chemotaxin leads to a diminished chemotactic migration towards this chemotaxin. This is called chemotactic deactivation. We developed a new deactivation chamber to determine chemotaxis and chemotactic deactivation of human PMN. This novel chamber is a modification of the commercially available acrylic 48-well microchemotaxis chamber consisting of an upper block with wells drilled all the way through the block and a blind-well lower block. Both blocks are separated by a polycarbonate membrane. PMN from the wells in the upper block migrate through the pores of the membrane into the wells of the lower block containing the chemoattractants. Migrated PMN on the lower side of the PC membrane were quantified after staining by measuring specific light absorbance. The chemotactic activity is quantified as a ratio of stimulated migration and random migration (chemotactic index=CI). For our novel chamber, only the upper blocks of this commercial chamber were connected like a sandwich, including a polyvinylpyrrolidone-free polycarbonate membrane with a pore size of 3 microm. The wells in the upper compartment were filled with 5 x 10(4) PMN and deactivating chemotaxin. The lower block was then filled with the chemotactic stimulus and the chamber was then incubated in humidified air with 5% CO2 atmosphere at 37 degrees C. The influence of cell concentration, incubation time, chemotactic factor concentration, pore size and alkaline treatment of polycarbonate membranes on migrational activity of PMN have been investigated. The technique was rigorously standardized in order to optimize the assay conditions. The method is relatively simple, sensitive and fast. The determination of chemotaxis and deactivation are performed in the same chamber, thus avoiding cell loss due to nonspecific adherence in other incubation tubes. The chamber can be used to characterize the chemotactic activity of chemoattractants of unknown structure via known and unknown receptors. This new chamber can be very helpful in detecting unknown chemotactic stimuli, which are not detectable by, for example, antibodies.

Chemioxyexcitation (delta pO2/ROS)-dependent release of IL-1 beta, IL-6 and TNF-alpha: evidence of cytokines as oxygen-sensitive mediators in the alveolar epithelium

The signalling mechanisms in oxidative stress mediated by cytokines in the perinatal alveolar epithelium are not well known. In an in vitro model of fetal alveolar type II epithelial cells, we investigated the profile of cytokines in response to ascending Deltap O(2)regimen (oxyexcitation). The peak of TNF-alpha (4 h) preceded IL-1beta and IL-6 (6-9 h), indicating a positive feedback autocrine loop confirmed by exogenous rmTNF-alpha. Reactive oxygen species (ROS) induced a dose-dependent release of cytokines, an effect specifically obliterated by selective antioxidants of the hydroxyl radical (*OH) and superoxide anion (O(2)-). Actinomycin and cycloheximide blocked the induced production of cytokines, implicating transcriptional and translational control. Whilst the dismutating enzymes superoxide dismutase (SOD) and catalase were ineffective in reducing ROS-induced cytokines, MnP, a cell-permeating SOD mimetic, abrogated xanthine/xanthine oxidase-dependent cytokine release. Desferrioxamine mesylate, which inhibits the iron-catalysed generation of *OH via the Fenton reaction, exhibited a mild effect on the release of cytokines. Dynamic variation in alveolar p O(2)constitutes a potential signalling mechanism within the perinatal lung allowing upregulation of cytokines in an ROS-dependent manner.

The lung HETEs (and EETs) up

Arachidonic acid metabolites of the cyclooxygenase and lipoxygenase pathways have a variety of important lung functions. Recent observations indicate that cytochrome P-450 (P-450) monooxygenases are also expressed in the lung, localized to specific pulmonary cell types (e.g., epithelium, endothelium, and smooth muscle), and may modulate critical lung functions. This review summarizes recent data on the presence and biological activity of P-450-derived eicosanoids in the pulmonary vasculature and airways, including effects on pulmonary vascular and bronchial smooth muscle tone and airway epithelial ion transport. We hypothesize a number of potential functions of P-450-derived arachidonate metabolites in the lungs such as contribution to hypoxic pulmonary vasoconstriction, regulation of bronchomotor tone, control of the composition of airway lining fluid, and limitation of pulmonary inflammation. Finally, we describe a number of emerging technologies, including congenic and transgenic strains of experimental animals, P-450 isoform-specific inhibitors and inhibitory antibodies, eicosanoid analogs, and vectors for delivery of P-450 cDNAs and antisense oligonucleotides. These tools will facilitate further studies on the contribution of endogenously formed P-450 eicosanoid metabolites to lung function, under both normal and pathological conditions.

Additive effects of phosphodiesterase-4 inhibition on effects of rSP-C surfactant

We have tested the effects of combined treatment with a recombinant surfactant protein C based surfactant (rSP-C surfactant) containing a phosphodiesterase-4 (PDE-4) inhibitor, roflumilast, in a lung lavage model of acute lung injury. The following groups were tested: (1) controls receiving sham exposure; (2) PDE-4 inhibitor (6.0 mg/kg body weight, intratracheally) alone; (3, 4) rSP-C surfactant (25 and 100 mg phospholipids [PL] per kg body weight) alone; and (5, 6 ) treatment with rSP-C surfactant (25 and 100 mg PL per kg body weight) combined with the PDE-4 inhibitor at a dose of 6.0 mg/kg body weight. The different groups were compared with respect to improving oxygenation and histopathologic changes, e.g., hyaline membrane (HM) formation. Both doses of rSP-C surfactant improved oxygenation while even this high dose of the PDE-4 inhibitor alone did not influence oxygenation compared with untreated control animals. Addition of the PDE-4 inhibitor led to improved oxygenation based on both doses of rSP-C surfactant. The PDE-4 inhibitor alone prevented further HM formation and infiltration of neutrophil leukocytes. The rSP-C surfactant was able to prevent further HM formation. Based on both doses of rSP-C surfactant, addition of the PDE-4 inhibitor showed additional effects on oxygenation and inhibition of HM formation. The effects of combined treatment were superior to each treatment alone, leading to the conclusion that a rSP-C surfactant containing a PDE-4 inhibitor may act synergistically in this animal model of acute lung injury. We conclude that combined treatment with rSP-C surfactant and a PDE-4 inhibitor may be an effective treatment for patients with acute lung injury.

Actin cytoskeleton and cell signaling

The role of the actin cytoskeleton in the function of eukaryotic cells is ubiquitous. Regulation of actin polymerization allows cells to control their shape, to move, divide, secrete, and phagocytose. Actin filaments provide strength, connections to other cells and the extracellular matrix, paths for intracellular transport and a scaffold for generating force. Recently, a number of signal transduction pathways have been identified that regulate actin polymerization and contractility. GTP-binding proteins, protein kinases, phosphoinositide kinases, and protein phosphatases all play important roles in determining the location and extent of actin polymerization and contractility of actin/myosin filaments. These pathways allow cells to respond to extracellular signals to regulate movement, the tone of vascular smooth muscle cells, secretion, and phagocytosis. Some pathogens use signal transduction pathways that regulate actin polymerization to invade cells. The signal transduction pathways that regulate actin-dependent events are the focus of this review.