Function of the alveolar epithelial barrier under pathologic conditions

Staphylococcal phosphatidylinositol-specific phospholipase C potentiates lung injury via complement sensitisation

Staphylococcus aureus is frequently isolated from patients with community-acquired pneumonia and acute respiratory distress syndrome (ARDS). ARDS is associated with staphylococcal phosphatidylinositol-specific phospholipase C (PI-PLC); however, the role of PI-PLC in the pathogenesis and progression of ARDS remains unknown. Here, we showed that recombinant staphylococcal PI-PLC possesses enzyme activity that causes shedding of glycosylphosphatidylinositol-anchored CD55 and CD59 from human umbilical vein endothelial cell surfaces and triggers cell lysis via complement activity. Intranasal infection with PI-PLC-positive S. aureus resulted in greater neutrophil infiltration and increased pulmonary oedema compared with a plc-isogenic mutant. Although indistinguishable proinflammatory genes were induced, the wild-type strain activated higher levels of C5a in lung tissue accompanied by elevated albumin instillation and increased lactate dehydrogenase release in bronchoalveolar lavage fluid compared with the plc^- mutant. Following treatment with cobra venom factor to deplete complement, the wild-type strain with PI-PLC showed a reduced ability to trigger pulmonary permeability and tissue damage. PI-PLC-positive S. aureus induced the formation of membrane attack complex, mainly on type II pneumocytes, and reduced the level of CD55/CD59, indicating the importance of complement regulation in pulmonary injury. In conclusion, S. aureus PI-PLC sensitised tissue to complement activation leading to more severe tissue damage, increased pulmonary oedema, and ARDS progression.

A literature review of immersion pulmonary edema

IMPORTANCE

Immersion pulmonary edema (IPE) is a rare but important complication associated with surface swimming and underwater diving. It tends to reoccur and can be fatal. It is not very well-known to clinicians involved in the care of individuals participating in aquatic activities. We performed a systematic review of immersion pulmonary edema to describe the condition and provide guidelines for its management.

EVIDENCE REVIEW

We searched PubMed to identify case reports and studies using the MeSH terms "immersion," "pulmonary edema," "cold-induced," "exercise," "hemodynamics," "water immersion,'' "cardiovascular response," alone and in combinations. We identified 121 relevant articles including 54 case reports. We reviewed in detail 24 studies and all 54 case reports.

FINDINGS

The incidence of IPE is estimated to be around 1.1- 1.8%. The risk factors for IPE include age >50 years, female sex, overhydration before exercise, tight wetsuits, cold water exposure and physically trained individuals such as endurance athletes. Individuals with pre-existing heart disease are at increased risk, however, IPE is seen even in healthy individuals. Symptoms such as cough, sputum production, hemoptysis and shortness of breath can occur immediately after immersion. Combination of water immersion, cold exposure, and exercise lead to an increase in pulmonary capillary pressures and eventual pulmonary capillary stress failure that leads to the flooding of alveolar spaces and edema. Conclusion and relevance: Clinicians should be aware of IPE to avoid overestimating the severity of coronary or valvular conditions sometimes coincidentally present in IPE victims. Management is usually supportive. Functional and clinical recovery usually happens spontaneously within 24 h to 2 days, with or without diuretic therapy and a beta-adrenergic agonist. IPE can be recurrent and fatal, hence subjects with a history of IPE should undergo extensive cardiopulmonary investigation and should avoid cold water and physically demanding swimming events or avoid immersion activities.

Pathobiology of acute respiratory distress syndrome

The unique characteristics of pulmonary circulation and alveolar-epithelial capillary-endothelial barrier allow for maintenance of the air-filled, fluid-free status of the alveoli essential for facilitating gas exchange, maintaining alveolar stability, and defending the lung against inhaled pathogens. The hallmark of pathophysiology in acute respiratory distress syndrome is the loss of the alveolar capillary permeability barrier and the presence of protein-rich edema fluid in the alveoli. This alteration in permeability and accumulation of fluid in the alveoli accompanies damage to the lung epithelium and vascular endothelium along with dysregulated inflammation and inappropriate activity of leukocytes and platelets. In addition, there is uncontrolled activation of coagulation along with suppression of fibrinolysis and loss of surfactant. These pathophysiological changes result in the clinical manifestations of acute respiratory distress syndrome, which include hypoxemia, radiographic opacities, decreased functional residual capacity, increased physiologic deadspace, and decreased lung compliance. Resolution of acute respiratory distress syndrome involves the migration of cells to the site of injury and re-establishment of the epithelium and endothelium with or without the development of fibrosis. Most of the data related to acute respiratory distress syndrome, however, originate from studies in adults or in mature animals with very few studies performed in children or juvenile animals. The lack of studies in children is particularly problematic because the lungs and immune system are still developing during childhood and consequently the pathophysiology of pediatric acute respiratory distress syndrome may differ in significant ways from that seen in acute respiratory distress syndrome in adults. This article describes what is known of the pathophysiologic processes of pediatric acute respiratory distress syndrome as we know it today while also presenting the much greater body of evidence on these processes as elucidated by adult and animal studies. It is also our expressed intent to generate enthusiasm for larger and more in-depth investigations of the mechanisms of disease and repair specific to children in the years to come.

Idiopathic pulmonary fibrosis: from epithelial injury to biomarkers--insights from the bench side

Idiopathic pulmonary fibrosis (IPF) is the most frequent fibrotic diffuse parenchymal lung disease. Its prognosis is devastating: >50% of the patients die within 3 years after diagnosis. Options for the treatment of IPF are limited and lung transplantation is the only 'curative' therapy. Currently, in the absence of validated indicators of disease progression/activity and diagnostic tools, the clinical management of IPF remains a major challenge. A better understanding of the pathogenesis of IPF is critical for the identification of new therapeutic targets as well as molecules that may serve as surrogate markers for clinically significant endpoints. The current paradigm on the mechanisms leading from a normal to a fibrotic lung postulates that chronic epithelial lesion leads to aberrant wound healing activation, which is characterized by deregulated fibroblast proliferation and activation together with an uncontrolled extracellular matrix synthesis. In this review, we shed light on the role of epithelial cell damage in the pathogenesis of fibrosis. Finally, we examine the markers of epithelial damage and their potential use as biomarkers and the future of this continuously expanding field.

Lung endothelial cells strengthen, but brain endothelial cells weaken barrier properties of a human alveolar epithelium cell culture model

The blood-air barrier in the lung consists of the alveolar epithelium, the underlying capillary endothelium, their basement membranes and the interstitial space between the cell layers. Little is known about the interactions between the alveolar and the blood compartment. The aim of the present study was to gain first insights into the possible interplay between these two neighbored cell layers. We established an in vitro Transwell model of the alveolar epithelium based on human cell line H441 and investigated the influence of conditioned medium obtained from human lung endothelial cell line HPMEC-ST1.6R on the barrier properties of the H441 layers. As control for tissue specificity H441 layers were exposed to conditioned medium from human brain endothelial cell line hCMEC/D3. Addition of dexamethasone was necessary to obtain stable H441 cell layers. Moreover, dexamethasone increased expression of cell type I markers (caveolin-1, RAGE) and cell type II marker SP-B, whereas decreased the transepithelial electrical resistance (TEER) in a concentration dependent manner. Soluble factors obtained from the lung endothelial cell line increased the barrier significantly proven by TEER values and fluorescein permeability on the functional level and by the differential expression of tight junctional proteins on the molecular level. In contrast to this, soluble factors derived from brain endothelial cells weakened the barrier significantly. In conclusion, soluble factors from lung endothelial cells can strengthen the alveolar epithelium barrier in vitro, which suggests communication between endothelial and epithelial cells regulating the integrity of the blood-air barrier.

Alveolocapillary model system to study alveolar re-epithelialization

In the present study an in vitro bilayer model system of the pulmonary alveolocapillary barrier was established to investigate the role of the microvascular endothelium on re-epithelialization. The model system, confluent monolayer cultures on opposing sides of a porous membrane, consisted of a human microvascular endothelial cell line (HPMEC-ST1.6R) and an alveolar type II like cell line (A549), stably expressing EGFP and mCherry, respectively. These fluorescent proteins allowed the real time assessment of the integrity of the monolayers and the automated analysis of the wound healing process after a scratch injury. The HPMECs significantly attenuated the speed of re-epithelialization, which was associated with the proximity to the A549 layer. Examination of cross-sectional transmission electron micrographs of the model system revealed protrusions through the membrane pores and close contact between the A549 cells and the HPMECs. Immunohistochemical analysis showed that these close contacts consisted of heterocellular gap-, tight- and adherens-junctions. Additional analysis, using a fluorescent probe to assess gap-junctional communication, revealed that the HPMECs and A549 cells were able to exchange the fluorophore, which could be abrogated by disrupting the gap junctions using connexin mimetic peptides. These data suggest that the pulmonary microvascular endothelium may impact the re-epithelialization process.

Human epidermal growth factor receptor signaling in acute lung injury

Acute lung injury (ALI) is a syndrome marked by increased permeability across the pulmonary epithelium resulting in pulmonary edema. Recent evidence suggests that members of the human epidermal growth factor receptor (HER) family are activated in alveolar epithelial cells during ALI and regulate alveolar epithelial barrier function. These tyrosine kinase receptors, which also participate in the pathophysiology of pulmonary epithelial malignancies, regulate cell growth, differentiation, and migration as well as cell-cell adhesion, all processes that influence epithelial injury and repair. In this review we outline mechanisms of epithelial injury and repair in ALI, activation patterns of this receptor family in pulmonary epithelial cells as a consequence injury, how receptor activation alters alveolar permeability, and the possible intracellular signaling pathways involved. Finally, we propose a theoretical model for how HER-mediated modulation of alveolar permeability might affect lung injury and repair. Understanding how these receptors signal has direct therapeutic implications in lung injury and other diseases characterized by altered epithelial barrier function.

Human epidermal growth factor receptor signaling in acute lung injury

Acute lung injury (ALI) is a syndrome marked by increased permeability across the pulmonary epithelium resulting in pulmonary edema. Recent evidence suggests that members of the human epidermal growth factor receptor (HER) family are activated in alveolar epithelial cells during ALI and regulate alveolar epithelial barrier function. These tyrosine kinase receptors, which also participate in the pathophysiology of pulmonary epithelial malignancies, regulate cell growth, differentiation, and migration as well as cell-cell adhesion, all processes that influence epithelial injury and repair. In this review we outline mechanisms of epithelial injury and repair in ALI, activation patterns of this receptor family in pulmonary epithelial cells as a consequence injury, how receptor activation alters alveolar permeability, and the possible intracellular signaling pathways involved. Finally, we propose a theoretical model for how HER-mediated modulation of alveolar permeability might affect lung injury and repair. Understanding how these receptors signal has direct therapeutic implications in lung injury and other diseases characterized by altered epithelial barrier function.

Bronchoalveolar lavage neuregulin-1 is elevated in acute lung injury and correlates with inflammation

Shedding of neuregulin (NRG)-1 from the pulmonary epithelium leads to activation of the epithelial human epidermal growth factor receptor (HER)2 receptor, increased pulmonary epithelial permeability and acute lung injury (ALI). We sought to determine whether NRG-1 was detectable and elevated in bronchoalveolar lavage (BAL) and plasma from patients with ALI compared with controls and to determine whether a correlation exists between NRG-1 and inflammation and outcome in ALI. Matched BAL and plasma samples were obtained from 23 ALI patients requiring intubation and mechanical ventilation. Control patients (n=5) included healthy volunteers. NRG-1 and indices of inflammation were measured in BAL and plasma via ELISA. The mean±sd BAL NRG-1 concentration in ALI patients was 187.0±21.35 pg·mL(-1) compared with 85.50±9.2 pg·mL(-1) in controls (p=0.001). Increased BAL NRG-1 was associated with markers of inflammation, and inversely correlated with ventilator-free days (VFDs; r= -0.51, p=0.015). Plasma NRG-1 was elevated in ALI patients compared with controls (611.7±354.2 versus 25.17±19.33 pg·mL(-1), p<0.001) and inversely correlated with VFDs (r= -0.51, p=0.04). These results confirm shedding of NRG-1 in ALI and suggest that the NRG-1-HER2 pathway is active in patients with ALI.

Pulmonary-intestinal cross-talk in mucosal inflammatory disease

Chronic obstructive pulmonary disease (COPD) and inflammatory bowel diseases (IBDs) are chronic inflammatory diseases of mucosal tissues that affect the respiratory and gastrointestinal tracts, respectively. They share many similarities in epidemiological and clinical characteristics, as well as in inflammatory pathologies. Importantly, both conditions are accompanied by systemic comorbidities that are largely overlooked in both basic and clinical research. Therefore, consideration of these complications may maximize the efficacy of prevention and treatment approaches. Here, we examine both the intestinal involvement in COPD and the pulmonary manifestations of IBD. We also review the evidence for inflammatory organ cross-talk that may drive these associations, and discuss the current frontiers of research into these issues.

Neuregulin-1-human epidermal receptor-2 signaling is a central regulator of pulmonary epithelial permeability and acute lung injury

The mechanisms behind the loss of epithelial barrier function leading to alveolar flooding in acute lung injury (ALI) are incompletely understood. We hypothesized that the tyrosine kinase receptor human epidermal growth factor receptor-2 (HER2) would be activated in an inflammatory setting and participate in ALI. Interleukin-1β (IL-1β) exposure resulted in HER2 activation in human epithelial cells and markedly increased conductance across a monolayer of airway epithelial cells. Upon HER2 blockade, conductance changes were significantly decreased. Mechanistic studies revealed that HER2 trans-activation by IL-1β required a disintegrin and metalloprotease 17 (ADAM17)-dependent shedding of the ligand neuregulin-1 (NRG-1). In murine models of ALI, NRG-1-HER2 signaling was activated, and ADAM17 blockade resulted in decreased NRG-1 shedding, HER2 activation, and lung injury in vivo. Finally, NRG-1 was detectable and elevated in pulmonary edema fluid from patients with ALI. These results suggest that the ADAM17-NRG-1-HER2 axis modulates the alveolar epithelial barrier and contributes to the pathophysiology of ALI.

Effect of continuous positive airway pressure combined to nebulization on lung deposition measured by urinary excretion of amikacin

Continuous positive airway pressure (CPAP) is frequently used in patients attending emergency units. Its combination with nebulization is sometimes necessary in those patients presenting with a CPAP dependency.

STUDY OBJECTIVE

To compare lung deposition of amikacin delivered by a classical jet nebulizer (SideStream; Medic-Aid; West Sussex, UK) used alone (SST) or coupled to a CPAP device (Boussignac; Vygon; Belgium).

METHOD

Amikacin (1g) was nebulized with both devices in six healthy subjects during 5 min on spontaneous breathing. A 1-week wash-out period between each nebulization was applied. Lung deposition was indirectly assessed by urinary monitoring of excreted amount of amikacin.

RESULTS

Total daily amount of amikacin excreted in the urine was significantly lower with CPAP than with SST (1.97% initial dose versus 4.88% initial dose, p<0.001) with a corresponding mean ratio CPAP/SST of 0.41. The residual amount of amikacin in the nebulizer was higher with CPAP than with SST (607 mg versus 541 mg) but the difference was not significant (p=0.35).

CONCLUSION

These data suggest that the amount of amikacin delivered to healthy lungs is 2.5-fold lower with CPAP than with SST for the same nebulization time and that the nebulization time when using CPAP should be increased to reach the same amount of drug delivered with a classical jet nebulizer.

Alveolar fluid clearance in acute lung injury: what have we learned from animal models and clinical studies?

Background

Acute lung injury and the acute respiratory distress syndrome continue to be significant causes of morbidity and mortality in the intensive care setting. The failure of patients to resolve the alveolar edema associated with these conditions is a major contributing factor to mortality; hence there is continued interest to understand the mechanisms of alveolar edema fluid clearance.

Discussion

The accompanying review by Vadász et al. details our current understanding of the signaling mechanisms and cellular processes that facilitate clearance of edema fluid from the alveolar compartment, and how these signaling processes may be exploited in the development of novel therapeutic strategies. To complement that report this review focuses on how intact organ and animal models and clinical studies have facilitated our understanding of alveolar edema fluid clearance in acute lung injury and acute respiratory distress syndrome. Furthermore, it considers how what we have learned from these animal and organ models and clinical studies has suggested novel therapeutic avenues to pursue.

Comparison of Lung Deposition of Amikacin by Intrapulmonary Percussive Ventilation and Jet Nebulization by Urinary Monitoring

The intrapulmonary percussive ventilation (IPV), frequently coupled with a nebulizer, is increasingly used as a physiotherapy technique; however, its physiologic and clinical values have been poorly studied. The aim of this study was to compare lung deposition of amikacin by the nebulizer of the IPV device (Percussionaire; Percussionaire Corporation; Sandpoint, ID) and that of standard jet nebulization (SST; SideStream; Medic-Aid; West Sussex, UK). Amikacin was nebulized with both devices in a group of five healthy subjects during spontaneous breathing. The deposition of amikacin was measured by urinary monitoring. Drug output of both devices was measured. Respiratory frequency (RF) was significantly lower when comparing the IPV device with SST (8.2 +/- 1.6 breaths/min vs. 12.6 +/- 2.5 breaths/min, p < 0.05). The total daily amount of amikacin excreted in the urine was significantly lower with IPV than with SST (0.8% initial dose vs. 5.6% initial dose, p < 0.001). Elimination halflife was identical with both devices. Drug output was lower with IPV than with SST. The amount of amikacin delivered to the lung is sixfold lower with IPV than with SST, although a lower respiratory frequency was adopted by the subjects with the IPV. Therefore, the IPV seems unfavorable for the nebulization of antibiotics.

Molecular mechanisms of hexavalent chromium-induced apoptosis in human bronchoalveolar cells

Hexavalent chromium (Cr[VI]) is classified by the International Agency for Research on Cancer as a group I carcinogen. Although the U.S. Occupational Safety and Health Administration was obliged to reduce the permissible exposure limit (PEL), it was reported that U.S. workers continue to be exposed to dangerously high Cr(VI) levels. In this study, we examined the role of p53 and target genes in a bronchoalveolar carcinoma isogenic cell line system and in primary human bronchial epithelial cells. p53-Negative parental H358 cell line, the same line in which the wild-type p53 expression vector (pC53-SN3) was introduced, and cells obtained from biopsies of human bronchus were exposed to chromate. Induction of DNA strand breaks were evaluated by alkaline elution assay, and apoptosis was analyzed by gel ladder, annexin V-PI staining, and ELISA, whereas p53 and target genes were evaluated by Western blots. Although Cr(VI) induced DNA strand breaks in both H358 cell clones, apoptosis was present only in the p53-transfected cells (H358p53(+/+)). In these cells, Cr(VI)-induced apoptosis is mediated by p53 upregulation of p53-upregulated modulator of apoptosis (PUMA), BAX translocation to mitochondria, cytochrome c release, and caspase-3 activation. In primary human bronchial epithelial cells expressing functional p53, Cr(VI) induced expression of PUMA and Noxa, which promote apoptosis through BAX. This result establishes p53 as the "necessary" player in Cr(VI)-induced apoptosis. To the best of our knowledge, this is the first report indicating strict correlation of Cr(VI) apoptosis to PUMA induction on primary human bronchoalveolar cells in short-term cultures.

Understanding the mechanisms of drug-associated interstitial lung disease

Drugs have been implicated in lung injury as a result of direct pharmacological action, persistence or metabolism in the tissue, or via the production of a reactive metabolite or metabolites. The result of this apparent drug-associated injury ranges from cellular dysfunction through to cell death (apoptosis) and alteration of repair mechanisms that are essential in replacing critical tissue elements and function. There is limited knowledge on how timing of drug administration or drug interactions may interfere with the repair mechanisms or modulate the expression of pulmonary toxicity. Chemotherapeutic drugs and novel agents, such as those targeting the epidermal growth factor receptor (EGFR), appear to affect both normal and neoplastic cells. However, unlike chemotherapy, where the actions are systemic and directly as a result of biotransformation or cell injury, it has been postulated that effects of EGFR-targeting agents are more likely to be focused on epithelia via a pharmacological effect. Furthermore, risk factors for the development of adverse pulmonary reactions, as well as biological markers indicating incipient toxicity, need to be prospectively identified. Proteomics, through the identification of ⩾1000 proteins or peptides in blood samples, will hopefully identify candidates for this role.

H2O2 inhibits alveolar epithelial wound repair in vitro by induction of apoptosis

Reactive oxygen species (ROS) are released into the alveolar space and contribute to alveolar epithelial damage in patients with acute lung injury. However, the role of ROS in alveolar repair is not known. We studied the effect of ROS in our in vitro wound healing model using either human A549 alveolar epithelial cells or primary distal lung epithelial cells. We found that H2O2 inhibited alveolar epithelial repair in a concentration-dependent manner. At similar concentrations, H2O2 also induced apoptosis, an effect seen particularly at the edge of the wound, leading us to hypothesize that apoptosis contributes to H2O2-induced inhibition of wound repair. To learn the role of apoptosis, we blocked caspases with the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp (zVAD). In the presence of H2O2, zVAD inhibited apoptosis, particularly at the wound edge and, most importantly, maintained alveolar epithelial wound repair. In H2O2-exposed cells, zVAD also maintained cell viability as judged by improved cell spreading and/or migration at the wound edge and by a more normal mitochondrial potential difference compared with cells not treated with zVAD. In conclusion, H2O2 inhibits alveolar epithelial wound repair in large part by induction of apoptosis. Inhibition of apoptosis can maintain wound repair and cell viability in the face of ROS. Inhibiting apoptosis may be a promising new approach to improve repair of the alveolar epithelium in patients with acute lung injury.

Lung epithelial cell lines in coculture with human pulmonary microvascular endothelial cells: development of an alveolo-capillary barrier in vitro

We have established a coculture system of human distal lung epithelial cells and human microvascular endothelial cells in order to study the cellular interactions of epithelium and endothelium at the alveolocapillary barrier in both pathogenesis and recovery from acute lung injury. The aim was to determine conditions for the development of functional cellular junctions and the formation of a tight epithelial barrier similar to that observed in vivo. The in vitro coculture system consisted of monolayers of human lung epithelial cell lines (A549 or NCI H441) and primary human pulmonary microvascular endothelial cells (HPMEC) on opposite sides of a permeable filter membrane. A549 failed to show sufficient differentiation with respect to formation of a tight epithelial barrier with intact cell-cell junctions. Stimulated with dexamethasone, the cocultures of NCI H441 and HPMEC established contact-inhibited differentiated monolayers, with NCI H441 showing a continuous, circumferential immunostaining of the tight junctional protein, ZO-1 and the adherens junction protein, E-cadherin. The generation of a polarized epithelial cell monolayer with typical junctional structures was confirmed by transmission electron microscopy. Dexamethasone treatment resulted in average transbilayer electrical resistance (TER) values of 500 Omega cm(2) after 10-12 days of cocultivation and correlated with a reduced flux of the hydrophilic permeability marker, sodium-fluorescein. In addition, basolateral distribution of the proinflammatory cytokine tumour necrosis factor-alpha caused a significant reduction of TER-values after 24 h exposure. This decrease in TER could be re-established to control level by removal of the cytokine within 24 h. Thus, the coculture system of the NCI H441 with HPMEC should be a suitable in vitro model system to examine epithelial and endothelial interactions in the pathogenesis of acute lung injury, infectious lung diseases and toxic lung injury. In addition, it could be used to improve techniques of lung drug delivery that also requires a functional barrier.

Early elevation of plasma soluble intercellular adhesion molecule-1 in pediatric acute lung injury identifies patients at increased risk of death and prolonged mechanical ventilation

OBJECTIVE

To determine whether soluble intercellular adhesion molecule (sICAM)-1, a biological marker of alveolar epithelial and lung endothelial injury and alveolar macrophage activation, is elevated in the plasma of pediatric patients with acute lung injury and to examine whether elevated plasma sICAM-1 levels correlate with two clinically relevant outcomes, mortality and the duration of mechanical ventilation.

DESIGN

Prospective cohort study.

SETTING

Pediatric intensive care units at an urban children's hospital and a tertiary university medical center.

PATIENTS

Eighty-three pediatric patients with acute lung injury and five intubated controls.

INTERVENTIONS

Plasma sICAM-1 levels were measured on days 1 and 2 of acute lung injury in pediatric patients and on day 1 of mechanical ventilation in control patients.

MEASUREMENTS AND MAIN RESULTS

Plasma sICAM-1 levels were significantly higher in patients with acute lung injury compared with controls (966 +/- 830 vs. 251 +/- 168 ng/mL, p <.05). Levels of sICAM-1 were also significantly higher on days 1 and 2 of acute lung injury in nonsurvivors and in patients requiring prolonged duration of mechanical ventilation. Also, plasma sICAM-1 levels >1000 ng/mL had a high specificity for identifying nonsurvivors of acute lung injury.

CONCLUSIONS

Early elevation of sICAM-1 in the plasma of pediatric patients with acute lung injury is associated with increased risk of death or prolonged duration of mechanical ventilation.

Lung deposition and efficiency of nebulized amikacin during Escherichia coli pneumonia in ventilated piglets

Lung tissue deposition and antibacterial efficiency of nebulized and intravenous amikacin (AMK) were compared in anesthetized and ventilated piglets suffering from a bronchopneumonia produced by the intrabronchial inoculation of Escherichia coli. AMK was administered 24 hours after the inoculation either through an ultrasonic nebulizer (45 mg x kg-1, n = 10) or by intravenous infusion (15 mg x kg-1, n = 8). Piglets were killed 1 hour after a second AMK administration performed 24 hours after the first one, and lung tissue concentrations of AMK and lung bacterial burden were assessed on multiple lung specimens. The amount of nebulized AMK reaching the tracheobronchial tree represented 38 +/- 6% of the initial nebulizer AMK charge. After nebulization, AMK lung tissue concentrations were 3- to 30-fold higher than after intravenous administration and were influenced by the severity of lung lesions: 188 +/- 175 microg x g-1 in lung segments with mild bronchopneumonia versus 40 +/- 65 microg x g-1 in lung segments with severe bronchopneumonia (p < 0.01). Lung bacterial burden was significantly lower in the aerosol group than in the intravenous group (median = 0 colony forming units. g-1 versus median = 5 x 10(2) colony forming units x g-1, p < 0.001). In conclusion, the deposition of AMK in infected lung parenchyma and the efficiency of bacterial killing were greater after nebulization than after intravenous administration.

Pulmonary edema associated with scuba diving : case reports and review

Acute pulmonary edema has been associated with cold-water immersion in swimmers and divers. We report on eight divers using a self-contained underwater breathing apparatus (scuba) who developed acute pulmonary edema manifested by dyspnea, hypoxemia, and characteristic chest radiographic findings. All cases occurred in cold water. All scuba divers were treated with complete resolution, and three have returned to diving without further episodes. Mechanisms that would contribute to a raised capillary transmural pressure or to a reduced blood-gas barrier function or integrity are discussed. Pulmonary edema in scuba divers is multifactorial, and constitutional factors may play a role. Physicians should be aware of this potential, likely underreported, problem in scuba divers.

Interleukin-1beta augments in vitro alveolar epithelial repair

Biologically active interleukin (IL)-1beta is present in the pulmonary edema fluid obtained from patients with acute lung injury and has been implicated as an important early mediator of nonpulmonary epithelial wound repair. Therefore, we tested the hypothesis that IL-1beta would enhance wound repair in cultured monolayers from rat alveolar epithelial type II cells. IL-1beta (20 ng/ml) increased the rate of in vitro alveolar epithelial repair by 118 +/- 11% compared with that in serum-free medium control cells (P < 0.01). IL-1beta induced cell spreading and migration at the edge of the wound but not proliferation. Neutralizing antibodies to epidermal growth factor (EGF) and transforming growth factor-alpha or inhibition of the EGF receptor by tyrphostin AG-1478 or genistein inhibited IL-1beta-induced alveolar epithelial repair, indicating that IL-1beta enhances in vitro alveolar epithelial repair by an EGF- or transforming growth factor-alpha-dependent mechanism. Moreover, the mitogen-activated protein kinase pathway is involved in IL-1beta-induced alveolar epithelial repair because inhibition of extracellular signal-regulated kinase activation by PD-98059 inhibited IL-1beta-induced alveolar epithelial repair. In conclusion, IL-1beta augments in vitro alveolar epithelial repair, indicating a possible novel role for IL-1beta in the early repair process of the alveolar epithelium in acute lung injury.

Hypoxia decreases proteins involved in epithelial electrolyte transport in A549 cells and rat lung

Fluid reabsorption from alveolar space is driven by active Na reabsorption via epithelial Na channels (ENaCs) and Na-K-ATPase. Both are inhibited by hypoxia. Here we tested whether hypoxia decreases Na transport by decreasing the number of copies of transporters in alveolar epithelial cells and in lungs of hypoxic rats. Membrane fractions were prepared from A549 cells exposed to hypoxia (3% O(2)) as well as from whole lung tissue and alveolar type II cells from rats exposed to hypoxia. Transport proteins were measured by Western blot analysis. In A549 cells, alpha(1)- and beta(1)-Na-K-ATPase, Na/K/2Cl cotransport, and ENaC proteins decreased during hypoxia. In whole lung tissue, alpha(1)-Na-K-ATPase and Na/K/2Cl cotransport decreased. alpha- and beta-ENaC mRNAs also decreased in hypoxic lungs. Similar results were seen in alveolar type II cells from hypoxic rats. These results indicate a slow decrease in the amount of Na-transporting proteins in alveolar epithelial cells during exposure to hypoxia that also occurs in vivo in lungs from hypoxic animals. The reduced number of transporters might account for the decreased transport activity and impaired edema clearance in hypoxic lungs.

Effects of ATP-sensitive potassium channel opener on potassium transport and alveolar fluid clearance in the resected human lung

Since the effect of an ATP-sensitive potassium channel (KATP channel) opener on the function of alveolar epithelial cells is unknown, the effect of YM934, a newly synthesized KATP channel opener, on potassium influx into the alveolar spaces and alveolar fluid clearance was determined in the resected human lung. An isosmolar albumin solution with a low potassium concentration was instilled into the distal airspaces of resected human lungs. Alveolar fluid clearance was measured by the progressive increase in alveolar protein concentration. Net potassium transport was measured by the change in potassium concentration and alveolar fluid volume. YM934 (10(-4) M) increased net influx of potassium by 140% into the alveolar spaces and also increased alveolar fluid clearance by 60% in the experiments with a potassium concentration of 0.3 mEq/1. Glibenclamide (10(-4) M), a KATP channel blocker, inhibited the YM934-increased influx of potassium transport and the increase in alveolar fluid clearance. Also amiloride (10(-5) M), an inhibitors of apical sodium uptake, blocked the YM934 stimulated increase in net alveolar fluid clearance. These results indicate that a KATP channel opener can effect potassium transport and net vectorial fluid movement across the human alveolar epithelium.

The American-European Consensus Conference on ARDS, part 2: Ventilatory, pharmacologic, supportive therapy, study design strategies, and issues related to recovery and remodeling. Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last 10 years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathologic features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

The American-European Consensus Conference on ARDS, part 2. Ventilatory, pharmacologic, supportive therapy, study design strategies and issues related to recovery and remodeling

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last ten years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathological features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

Increased alveolar fluid clearance following thoracotomy: report of a case and results of an analysis

Alveolar fluid clearance was studied in the resected lung of a 58-year-old man who had undergone exploratory thoracotomy 9 days earlier. An isosmolar albumin solution was instilled into the distal air spaces, and the albumin and electrolyte concentrations were measured over 4 h. Alveolar sodium and fluid clearance had increased by nearly 200% from the control values in the resected lungs of patients without prior thoracotomy (n = 5), and histological examination showed that the number of alveolar type II epithelial cells was markedly elevated. These results suggest that an increase in the number of alveolar type II cells may accelerate alveolar fluid clearance under certain clinical conditions.

Hypothermia inhibits the alveolar epithelial injury caused by hyposmotic albumin solution during preservation of the resected human lung

This study was conducted to determine whether hypothermia inhibited alveolar epithelial injury in the resected human lung during preservation. Hyposmotic albumin solution, 248 mOsm/kg, was instilled into the alveolar spaces of resected human lungs which were inflated with an airway pressure of 7 cmH2O and stored at either 37 degrees C or 8 degrees C for 4 h. Alveolar fluid was aspirated and the influx of lactate dehydrogenase (LDH) and globulin into the alveolar spaces, as markers of alveolar epithelial injury, was measured. Ion transport and fluid clearance across the alveolar epithelium were calculated by the changes in electrolyte and albumin concentrations in the alveolar fluid, respectively. While the LDH levels and globulin concentrations increased significantly in the hyposmotic experiments at 37 degrees C, hypothermia inhibited these increases. Alveolar fluid clearance at 37 degrees C increased to 20% in the hyposmotic experiments compared with 12% in the control isosmotic experiments; however, sodium and chloride transport in the hyposmotic experiments was not significantly different from that in the isosmotic experiments. Thus, we conclude that hypothermia at 8 degrees C inhibits alveolar epithelial injury caused by the hyposmotic solution in resected human lungs. Moreover, alveolar ion and fluid clearance mechanisms were preserved across the injured alveolar epithelial cells.

Dopamine stimulates sodium transport and liquid clearance in rat lung epithelium

Pulmonary edema clearance is driven primarily by active sodium transport out of the alveoli, mediated predominantly by apical sodium channels and the basolateral NA,K-ATPase. We postulated that dopamine, analogous to its effects in other transporting epithelia, could regulate these sodium transport mechanisms and affect lung liquid clearance. We therefore studied the effects of dopamine on sodium transport and liquid clearance in isolated perfused rat lungs. Instillation of dopamine into the airways caused a dose-dependent increase in liquid clearance from isolated rat lungs of up to 33% above control values at 10(-8) to 10(-4) M concentrations. 10(-6) M amiloride, which selectively inhibits apical sodium channels, decreased basal liquid clearance by 34% but did not inhibit the dopamine-mediated stimulation of lung liquid clearance. Instillation of 10(-4) M amiloride into rat airways, which inhibits other sodium transport mechanisms non-selectively, decreased basal lung liquid clearance by 49% and inhibited the dopamine-mediated stimulation of lung liquid clearance. Perfusion of rat lungs with 5 x 10(-4) M ouabain to specifically inhibit Na,K-ATPase reduced both basal clearance (by 55%) and the dopamine-stimulated increase in lung fluid clearance. Conceivably, the stimulation of lung liquid clearance by dopamine is due to a modulation of Na,K-ATPase in the pulmonary epithelium.

Terbutaline stimulates alveolar fluid resorption in hyperoxic lung injury

Alveolar fluid resorption occurs by active epithelial sodium transport and is accelerated by terbutaline in healthy lungs. We investigated the effect of terbutaline on the rate of alveolar fluid resorption from rat lungs injured by hyperoxia. Rats exposed to > 95% O2 for 60 h, sufficient to increase wet-to-dry lung weight and cause alveolar edema, were compared with air-breathing control rats. After anesthesia, the animals breathed 100% O2 for 10 min through a tracheostomy. Ringer solution was instilled into the alveoli, and the steady-state rate of volume resorbed at 6 cmH2O pressure was measured via a pipette attached to the tracheostomy tubing. Ringer solution in some animals contained terbutaline (10(-3) M), ouabain (10(-3) M), or both. Normoxic animals resorbed 49 +/- 6 microliters.kg-1.min-1; ouabain reduced this by 39%, whereas terbutaline increased the rate by 75%. The effect of terbutaline was blocked by ouabain. Hyperoxic animals absorbed 78 +/- 9 microliters.kg-1.min-1; ouabain reduced this by 44%. Terbutaline increased the rate by a mean of 39 microliters.kg-1.min-1, similar to the absolute effect seen in the normoxic group, and this was blocked by ouabain. Terbutaline accelerates fluid resorption from both normal and injured rat lungs via its effects on active sodium transport.

Early detection and markers of sepsis

In vitro and animal models of sepsis have provided a template for studies of the pathogenesis of sepsis in patients at risk for and with the syndrome. Numerous potential markers have been identified in these models and then looked for in patients. No single marker or combination of markers convincingly identifies sepsis, predicts the development of sepsis, predicts the development of complications of sepsis, or predicts mortality. As discussed, the clinical studies have been complicated by many confounding variables, including the lack of adherence to rigorous definitions, differences in assay methods, differences in timing of the studies, and differences in outcome variables analyzed. In spite of the limitations, the studies have been critical in helping determine the pathogenesis of sepsis in humans. As new mediators and modulators of inflammation are identified, it will be important to study their role as markers, individually and in combination, in human disease.

Acute respiratory distress syndrome: diagnosis and management

This review will attempt to put together the voluminous studies and concepts that have been published during the past 25 years following the description of the acute respiratory distress syndrome (ARDS) regarding diagnosis and management. The initial discussion will focus on how to clinically diagnose ARDS based recommendations. This also gives the current definition of acute lung injury and when to call it ARDS. The radiographic and hemodynamic characteristics are discussed including oxygenation parameters. The management outlines the conventional as well as new therapies intended to improve survival of this devastating disease.

Effects of hypothermia and hyperpotassium on alveolar fluid clearance in the resected human lung

The effect of hypothermia and hyperpotassium on alveolar fluid clearance in the resected human lung was examined by instilling an isosmotic albumin solution with a potassium concentration of 0.3 mEq/l or 20 mEq/l into one segment of a resected lobe within 10 min of surgical removal for bronchogenic carcinoma. The experiments were carried out at 37 degrees C, 25 degrees C, and and 8 degrees C over 4 hr, after which the alveolar fluid was aspirated. Alveolar fluid clearance was calculated by a simple equation using the changes in the albumin concentration of the alveolar fluid. It was found that although hypothermia at 8 degrees C abolished alveolar fluid clearance completely, alveolar fluid clearance at 25 degrees C was not different from that at 37 degrees C. Moreover, although the potassium concentration increased in the alveolar fluid at 37 degrees C and 8 degrees C, hyperpotassium did not affect the alveolar fluid clearance. These findings indicate that the net transport of potassium leans to influx from the alveolar epithelial cells into the alveolar spaces when the alveolar potassium concentration is low, and to efflux from the alveolar spaces when the alveolar potassium concentration is high. Thus, we conclude that hypothermia abolishes alveolar fluid clearance in resected human lungs, but that the potassium concentration in alveolar fluid does not affect alveolar fluid clearance.