Protective effect of endogenous beta-adrenergic tone on lung fluid balance in acute bacterial pneumonia in mice

Using the sympathetic system, beta blockers and alpha-2 agonists, to address acute respiratory distress syndrome

Acute Respiratory Distress Syndrome (ARDS) manifests as an acute inflammatory lung injury characterized by persistent hypoxemia, featuring a swift onset, high mortality, and predominantly supportive care as the current therapeutic approach, while effective treatments remain an area of active investigation. Adrenergic receptors (AR) play a pivotal role as stress hormone receptors, extensively participating in various inflammatory processes by initiating downstream signaling pathways. Advancements in molecular biology and pharmacology continually unveil the physiological significance of distinct AR subtypes. Interventions targeting these subtypes have the potential to induce specific alterations in cellular and organismal functions, presenting a promising avenue as a therapeutic target for managing ARDS. This article elucidates the pathogenesis of ARDS and the basic structure and function of AR. It also explores the relationship between AR and ARDS from the perspective of different AR subtypes, aiming to provide new insights for the improvement of ARDS.

Are beta blockers effective in preventing stroke associated infections? - a systematic review and meta-analysis

BACKGROUND

Excessive sympathoexcitation could lead to stroke associated infection. Inhibiting sympathetic excitation may reduce the infection risk after stroke. Thus, the present study aimed to determine the protective effect of beta blockers on stroke associated infection through systematic review and meta-analysis.

METHODS

A systematic search of multiple databases were performed up to February 2022. The included studies required beta blockers therapy in stroke patients and assessed the incidence of stroke-associated infections. Outcomes of interest included infections, pneumonia, urinary tract infection and sepsis. Random-effects model was used for analysis. Heterogeneity was evaluated using I2 statistics and publication bias was evaluated by the funnel plot.

RESULT

A total of 83 potentially relevant publications was identified in the initial search. Six studies met the inclusion criteria for meta-analysis. The risk of bias in the included articles satisfies the quality requirement of meta-analysis. No significant associations between beta blockers therapy and the prevention of stroke associated infection, stroke associated pneumonia and septicemia were found, However, subgroup analyses revealed an association between beta blockers treatment and the increased risk of post-stroke urinary tract infection or stroke associated pneumonia in some stroke patients (OR = 1.69 [1.33, 2.14], P < 0.0001; OR = 1.85 [1.51, 2.26], P < 0.0001).

CONCLUSION

Due to the lack of robust evidence, this meta-analysis may not support the preventive effect of beta blockers on stroke associated infection. But beta blockers treatment may be associated with development of post-stroke urinary tract infection and stroke associated pneumonia in some stroke patients.

Inhaled β2 Adrenergic Agonists and Other cAMP-Elevating Agents: Therapeutics for Alveolar Injury and Acute Respiratory Disease Syndrome?

Inhaled long-acting β-adrenergic agonists (LABAs) and short-acting β-adrenergic agonists are approved for the treatment of obstructive lung disease via actions mediated by β2 adrenergic receptors (β2-ARs) that increase cellular cAMP synthesis. This review discusses the potential of β2-AR agonists, in particular LABAs, for the treatment of acute respiratory distress syndrome (ARDS). We emphasize ARDS induced by pneumonia and focus on the pathobiology of ARDS and actions of LABAs and cAMP on pulmonary and immune cell types. β2-AR agonists/cAMP have beneficial actions that include protection of epithelial and endothelial cells from injury, restoration of alveolar fluid clearance, and reduction of fibrotic remodeling. β2-AR agonists/cAMP also exert anti-inflammatory effects on the immune system by actions on several types of immune cells. Early administration is likely critical for optimizing efficacy of LABAs or other cAMP-elevating agents, such as agonists of other Gs-coupled G protein-coupled receptors or cyclic nucleotide phosphodiesterase inhibitors. Clinical studies that target lung injury early, prior to development of ARDS, are thus needed to further assess the use of inhaled LABAs, perhaps combined with inhaled corticosteroids and/or long-acting muscarinic cholinergic antagonists. Such agents may provide a multipronged, repurposing, and efficacious therapeutic approach while minimizing systemic toxicity. SIGNIFICANCE STATEMENT: Acute respiratory distress syndrome (ARDS) after pulmonary alveolar injury (e.g., certain viral infections) is associated with ∼40% mortality and in need of new therapeutic approaches. This review summarizes the pathobiology of ARDS, focusing on contributions of pulmonary and immune cell types and potentially beneficial actions of β2 adrenergic receptors and cAMP. Early administration of inhaled β2 adrenergic agonists and perhaps other cAMP-elevating agents after alveolar injury may be a prophylactic approach to prevent development of ARDS.

Phosphodiesterase 4 mediates interleukin-8-induced heterologous desensitization of the β2 -adrenergic receptor

Acute respiratory distress syndrome (ARDS) is a life-threatening illness characterized by decreased alveolar-capillary barrier function, pulmonary edema consisting of proteinaceous fluid, and inhibition of net alveolar fluid transport responsible for resolution of pulmonary edema. There is currently no pharmacotherapy that has proven useful to prevent or treat ARDS, and two trials using beta-agonist therapy to treat ARDS demonstrated no effect. Prior studies indicated that IL-8-induced heterologous desensitization of the beta2-adrenergic receptor (β₂ -AR) led to decreased beta-agonist-induced mobilization of cyclic adenosine monophosphate (cAMP). Interestingly, phosphodiesterase (PDE) 4 inhibitors have been used in human airway diseases characterized by low intracellular cAMP levels and increases in specific cAMP hydrolyzing activity. Therefore, we hypothesized that PDE4 would mediate IL-8-induced heterologous internalization of the β₂ -AR and that PDE4 inhibition would restore beta-agonist-induced functions. We determined that CINC-1 (a functional IL-8 analog in rats) induces internalization of β₂ -AR from the cell surface, and arrestin-2, PDE4, and β₂ -AR form a complex during this process. Furthermore, we determined that cAMP associated with the plasma membrane was adversely affected by β₂ -AR heterologous desensitization. Additionally, we determined that rolipram, a PDE4 inhibitor, reversed CINC-1-induced derangements of cAMP and also caused β₂ -AR to successfully recycle back to the cell surface. Finally, we demonstrated that rolipram could reverse CINC-1-mediated inhibition of beta-agonist-induced alveolar fluid clearance in a murine model of trauma-shock. These results indicate that PDE4 plays a role in CINC-1-induced heterologous internalization of the β₂ -AR; PDE4 inhibition reverses these effects and may be a useful adjunct in particular ARDS patients.

Specialized Pro-resolving Mediators Regulate Alveolar Fluid Clearance during Acute Respiratory Distress Syndrome

Objective

Acute respiratory distress syndrome (ARDS) is an acute and lethal clinical syndrome that is characterized by the injury of alveolar epithelium, which impairs active fluid transport in the lung, and impedes the reabsorption of edema fluid from the alveolar space. This review aimed to discuss the role of pro-resolving mediators on the regulation of alveolar fluid clearance (AFC) in ARDS.

Data Sources

Articles published up to September 2017 were selected from the PubMed, with the keywords of "alveolar fluid clearance" or "lung edema" or "acute lung injury" or "acute respiratory distress syndrome", and "specialized pro-resolving mediators" or "lipoxin" or "resolvin" or "protectin" or "maresin" or "alveolar epithelial cells" or "aspirin-triggered lipid mediators" or "carbon monoxide and heme oxygenase" or "annexin A1".

Study Selection

We included all relevant articles published up to September 2017, with no limitation of study design.

Results

Specialized pro-resolving mediators (SPMs), as the proinflammatory mediators, not only upregulated epithelial sodium channel, Na,K-ATPase, cystic fibrosis transmembrane conductance regulator (CFTR), and aquaporins levels, but also improved Na,K-ATPase activity to promote AFC in ARDS. In addition to the direct effects on ion channels and pumps of the alveolar epithelium, the SPMs also inhibited the inflammatory cytokine expression and improved the alveolar epithelial cell repair to enhance the AFC in ARDS.

Conclusions

The present review discusses a novel mechanism for pulmonary edema fluid reabsorption. SPMs might provide new opportunities to design "reabsorption-targeted" therapies with high degrees of precision in controlling ALI/ARDS.

Albuterol Improves Alveolar-Capillary Membrane Conductance in Healthy Humans

BACKGROUND

Beta-2 adrenergic receptors (β₂ARs) are located throughout the body including airway and alveolar cells. The β₂ARs regulate lung fluid clearance through a variety of mechanisms including ion transport on alveolar cells and relaxation of the pulmonary lymphatics. We examined the effect of an inhaled β₂-agonist (albuterol) on alveolar-capillary membrane conductance (DM) and pulmonary capillary blood volume (V_C) in healthy humans.

METHODS

We assessed the diffusing capacity of the lungs for carbon monoxide (DLCO) and nitric oxide (DLNO) at baseline, 30 minutes, and 60 minutes following nebulized albuterol (2.5 mg, diluted in 3 mL normal saline) in 45 healthy subjects. Seventeen subjects repeated these measures following nebulized normal saline (age = 27 ± 9 years, height = 165 ± 21 cm, weight = 68 ± 12 kg, BMI = 26 ± 9 kg/m²). Cardiac output (Q), heart rate, systemic vascular resistance (SVR), blood pressure, oxygen saturation, forced expiratory volume at one-second (FEV₁), and forced expiratory flow at 50% of forced vital capacity (FEF₅₀) were assessed at baseline, 30 minutes, and 60 minutes following the administration of albuterol or saline.

RESULTS

Albuterol resulted in a decrease in SVR, and an increase in Q, FEV₁, and FEF₅₀ compared to saline controls. Albuterol also resulted in a decrease in V_C at 60 minutes post albuterol. Both albuterol and normal saline resulted in no change in DLCO or DM when assessed alone, but a significant increase was observed in DM when accounting for changes in V_C.

CONCLUSION

These data suggest that nebulized albuterol improves pulmonary function in healthy humans, while nebulization of both albuterol and saline results in an increase in DM/V_C.

Synergistic Inhibition of β2-adrenergic Receptor-mediated Alveolar Epithelial Fluid Transport by Interleukin-8 and Transforming Growth Factor-β

BACKGROUND

Patients with acute respiratory distress syndrome who retain maximal alveolar fluid clearance (AFC) have better clinical outcomes. The release of endogenous catecholamines associated with shock or the administration of β2-adrenergic receptor (β2AR) agonists enhances AFC via a 3'-5'-cyclic adenosine monophosphate-dependent mechanism. The authors have previously reported that transforming growth factor-β1 (TGF-β1) and interleukin-8 (IL-8), two major mediators of alveolar inflammation associated with the early phase of acute respiratory distress syndrome, inhibit AFC upregulation by β2AR agonists via a phosphoinositol-3-kinase (PI3K)-dependent mechanism. However, whether TGF-β1 and IL-8 cause an additive or synergistic inhibition of AFC is unclear. Thus, the central hypothesis of the study was to determine whether they synergistically inhibit the β2AR-stimulated AFC by activating two different isoforms of PI3K.

METHODS

The effects of TGF-β1 or IL-8 on β2AR agonist-stimulated net alveolar fluid transport were studied using short-circuit current studies. Molecular pathways of inhibition were confirmed by pharmacologic inhibitors and Western blotting of p-Akt, G-protein-coupled receptor kinase 2, protein kinase C-ζ, and phospho-β2AR. Finally, our observations were confirmed by an in vivo model of AFC.

RESULTS

Combined exposure to TGF-β1 and IL-8/cytokine-induced neutrophil chemoattractant-1 caused synergistic inhibition of β2AR agonist-stimulated vectorial Cl across alveolar epithelial type II cells (n = 12 in each group). This effect was explained by activation of different isoforms of PI3K by TGF-β1 and IL-8/cytokine-induced neutrophil chemoattractant-1 (n = 12 in each group). Furthermore, the inhibitory effect of TGF-β1 on 3'-5'-cyclic adenosine monophosphate-stimulated alveolar epithelial fluid transport required the presence of IL-8/cytokine-induced neutrophil chemoattractant-1 (n = 12 in each group). Inhibition of cytokine-induced neutrophil chemoattractant-1 prevented TGF-β1-mediated heterologous β2AR downregulation and restored physiologic β2AR agonist-stimulated AFC in rats (n = 6 in each group).

CONCLUSIONS

TGF-β1 and IL-8 have a synergistic inhibitory effect on β2AR-mediated stimulation of pulmonary edema removal by the alveolar epithelium. This result may, in part, explain why a large proportion of the patients with acute respiratory distress syndrome have impaired AFC.

The intracerebroventricular injection of rimonabant inhibits systemic lipopolysaccharide-induced lung inflammation

We investigated the role of intracerebroventricular (ICV) injection of rimonabant (500ng), a CB1 antagonist, on lipopolysaccharide ((LPS) 5mg/kg)-induced pulmonary inflammation in rats in an isolated perfused lung model. There were decreases in pulmonary capillary pressure (Ppc) and increases in the ((Wet-Dry)/Dry lung weight)/(Ppc) ratio in the ICV-vehicle/LPS group at 4h. There were decreases in TLR4 pathway markers, such as interleukin receptor-associated kinase-1, IκBα, Raf1 and phospho-SFK (Tyr416) at 30min and at 4h increases in IL-6, vascular cell adhesion molecule-1 and myeloperoxidase in lung homogenate. Intracerebroventricular rimonabant attenuated these LPS-induced responses, indicating that ICV rimonabant modulates LPS-initiated pulmonary inflammation.

Paxillin mediates stretch-induced Rho signaling and endothelial permeability via assembly of paxillin-p42/44MAPK-GEF-H1 complex

Suboptimal ventilator support or regional ventilation heterogeneity in inflamed lungs causes excessive tissue distension, which triggers stretch-induced pathological signaling and may lead to vascular leak and lung dysfunction. Focal adhesions (FAs) are cell-substrate adhesive complexes participating in cellular mechanotransduction and regulation of the Rho GTPase pathway. Stretch-induced Rho regulation remains poorly understood. We used human lung endothelial cells (ECs) exposed to pathological cyclic stretch (CS) at 18% distension to test the hypothesis that FA protein paxillin participates in CS-induced Rho activation by recruiting the Rho-specific guanine nucleotide exchange factor GEF-H1. CS induced phosphorylation of paxillin and activated p42/44-MAP kinase, Rho GTPase, and paxillin/GEF-H1/p42/44-MAPK association. CS caused nearly 2-fold increase in EC permeability, which was attenuated by paxillin knockdown. Expression of the paxillin-Y31/118F phosphorylation mutant decreased the CS-induced paxillin/GEF-H1 association (16.3 ± 4.1%), GEF-H1 activation (28.9 ± 9.2%), and EC permeability (28.7 ± 8.1%) but not CS-induced p42/44-MAPK activation. Inhibition of p42/44-MAPK suppressed CS-induced paxillin/GEF-H1 interactions (15.9 ± 7.9%), GEF-H1 activation (11.7 ± 4.3%), and disruption of EC monolayer. Expression of GEF-H1T678A lacking p42/44-MAPK phosphorylation site attenuated Rho activation (31.2±11.6%). We conclude that MAPK-dependent targeting of GEF-H1 to paxillin is involved in the regulation of CS-induced Rho signaling and EC permeability. This study proposes a novel concept of paxillin-GEF-H1-p42/44-MAPK module as a regulator of pathological mechanotransduction.-Gawlak, G., Tian, Y., O'Donnell, J. J., III, Tian, X., Birukova, A. A., Birukov, K. G. Paxillin mediates stretch-induced Rho signaling and endothelial permeability via assembly of paxillin-p42/44MAPK-GEF-H1 complex.

Resolvin D1 stimulates alveolar fluid clearance through alveolar epithelial sodium channel, Na,K-ATPase via ALX/cAMP/PI3K pathway in lipopolysaccharide-induced acute lung injury

Resolvin D1 (7S,8R,17S-trihydroxy-4Z,9E,11E,13Z,15E,19Z-docosahexaenoic acid) (RvD1), generated from ω-3 fatty docosahexaenoic acids, is believed to exert anti-inflammatory properties including inhibition of neutrophil activation and regulating inflammatory cytokines. In this study, we sought to investigate the effect of RvD1 in modulating alveolar fluid clearance (AFC) on LPS-induced acute lung injury. In vivo, RvD1 was injected i.v. (5 μg/kg) 8 h after LPS (20 mg/kg) administration, which markedly stimulated AFC in LPS-induced lung injury, with the outcome of decreased pulmonary edema. In addition, rat lung tissue protein was isolated after intervention and we found RvD1 improved epithelial sodium channel (ENaC) α, γ, Na,K-adenosine triphosphatase (ATPase) α1, β1 subunit protein expression and Na,K-ATPase activity. In primary rat alveolar type II epithelial cells stimulated with LPS, RvD1 not only upregulated ENaC α, γ and Na,K-ATPase α1 subunits protein expression, but also increased Na+ currents and Na,K-ATPase activity. Finally, protein kinase A and cGMP were not responsible for RvD1's function because a protein kinase A inhibitor (H89) and cGMP inhibitor (Rp-cGMP) did not reduce RvD1's effects. However, the RvD1 receptor (formyl-peptide receptor type 2 [FPR2], also called ALX [the lipoxin A4 receptor]) inhibitor (BOC-2), cAMP inhibitor (Rp-cAMP), and PI3K inhibitor (LY294002) not only blocked RvD1's effects on the expression of ENaC α in vitro, but also inhibited the AFC in vivo. In summary, RvD1 stimulates AFC through a mechanism partly dependent on alveolar epithelial ENaC and Na,K-ATPase activation via the ALX/cAMP/PI3K signaling pathway.

IL-8 inhibits cAMP-stimulated alveolar epithelial fluid transport via a GRK2/PI3K-dependent mechanism

Patients with acute lung injury (ALI) who retain maximal alveolar fluid clearance (AFC) have better clinical outcomes. Experimental and small clinical studies have shown that β2-adrenergic receptor (β2AR) agonists enhance AFC via a cAMP-dependent mechanism. However, two multicenter phase 3 clinical trials failed to show that β2AR agonists provide a survival advantage in patients with ALI. We hypothesized that IL-8, an important mediator of ALI, directly antagonizes the alveolar epithelial response to β2AR agonists. Short-circuit current and whole-cell patch-clamping experiments revealed that IL-8 or its rat analog CINC-1 decreases by 50% β2AR agonist-stimulated vectorial Cl(-) and net fluid transport across rat and human alveolar epithelial type II cells via a reduction in the cystic fibrosis transmembrane conductance regulator activity and biosynthesis. This reduction was mediated by heterologous β2AR desensitization and down-regulation (50%) via the G-protein-coupled receptor kinase 2 (GRK2)/PI3K signaling pathway. Inhibition of CINC-1 restored β2AR agonist-stimulated AFC in an experimental model of ALI in rats. Finally, consistent with the experimental results, high pulmonary edema fluid levels of IL-8 (>4000 pg/ml) were associated with impaired AFC in patients with ALI. These results demonstrate a novel role for IL-8 in inhibiting β2AR agonist-stimulated alveolar epithelial fluid transport via GRK2/PI3K-dependent mechanisms.-Roux, J., McNicholas, C. M., Carles, M., Goolaerts, A., Houseman, B. T., Dickinson, D. A., Iles, K. E., Ware, L. B., Matthay, M. A., Pittet, J.-F. IL-8 inhibits cAMP-stimulated alveolar epithelial fluid transport via a GRK2/PI3K-dependent mechanism.

δ ENaC: a novel divergent amiloride-inhibitable sodium channel

The fourth subunit of the epithelial sodium channel, termed delta subunit (δ ENaC), was cloned in human and monkey. Increasing evidence shows that this unique subunit and its splice variants exhibit biophysical and pharmacological properties that are divergent from those of α ENaC channels. The widespread distribution of epithelial sodium channels in both epithelial and nonepithelial tissues implies a range of physiological functions. The altered expression of SCNN1D is associated with numerous pathological conditions. Genetic studies link SCNN1D deficiency with rare genetic diseases with developmental and functional disorders in the brain, heart, and respiratory systems. Here, we review the progress of research on δ ENaC in genomics, biophysics, proteomics, physiology, pharmacology, and clinical medicine.

Stroke-induced activation of the α7 nicotinic receptor increases Pseudomonas aeruginosa lung injury

Infectious complications, predominantly pneumonia, are the most common cause of death in the postacute phase of stroke, although the mechanisms underlying the corresponding immunosuppression are not fully understood. We tested the hypothesis that activation of the α7 nicotinic acetylcholine receptor (α7nAChR) pathway is important in the stroke-induced increase in lung injury caused by Pseudomonas aeruginosa pneumonia in mice. Prior stroke increased lung vascular permeability caused by P. aeruginosa pneumonia and was associated with decreased lung neutrophil recruitment and bacterial clearance in mice. Pharmacologic inhibition (methyllycaconitine IC(50): 0.2-0.6 nM) or genetic deletion of the α7nAChR significantly (P<0.05) attenuates the effect of prior stroke on lung injury and mortality caused by P. aeruginosa pneumonia in mice. Finally, pretreatment with PNU-282987, a pharmacologic activator of the α7nAChR (EC(50): 0.2 μM), significantly (P<0.05) increased lung injury caused by P. aeruginosa pneumonia, significantly (P<0.05) decreased the release of KC, a major neutrophil chemokine, and significantly (P<0.05) decreased intracellular bacterial killing by a mouse alveolar macrophage cell line and primary mouse neutrophils. In summary, the α7 nicotinic cholinergic pathway plays an important role in mediating the systemic immunosuppression observed after stroke and directly contributes to more severe lung damage induced by P. aeruginosa.

Mesenchymal stem cells enhance survival and bacterial clearance in murine Escherichia coli pneumonia

RATIONALE

Bacterial pneumonia is the most common infectious cause of death worldwide and treatment is increasingly hampered by antibiotic resistance. Mesenchymal stem cells (MSCs) have been demonstrated to provide protection against acute inflammatory lung injury; however, their potential therapeutic role in the setting of bacterial pneumonia has not been well studied.

OBJECTIVE

This study focused on testing the therapeutic and mechanistic effects of MSCs in a mouse model of Gram-negative pneumonia.

METHODS AND RESULTS

Syngeneic MSCs from wild-type mice were isolated and administered via the intratracheal route to mice 4 h after the mice were infected with Escherichia coli. 3T3 fibroblasts and phosphate-buffered saline (PBS) were used as controls for all in vivo experiments. Survival, lung injury, bacterial counts and indices of inflammation were measured in each treatment group. Treatment with wild-type MSCs improved 48 h survival (MSC, 55%; 3T3, 8%; PBS, 0%; p<0.05 for MSC vs 3T3 and PBS groups) and lung injury compared with control mice. In addition, wild-type MSCs enhanced bacterial clearance from the alveolar space as early as 4 h after administration, an effect that was not observed with the other treatment groups. The antibacterial effect with MSCs was due, in part, to their upregulation of the antibacterial protein lipocalin 2.

CONCLUSIONS

Treatment with MSCs enhanced survival and bacterial clearance in a mouse model of Gram-negative pneumonia. The bacterial clearance effect was due, in part, to the upregulation of lipocalin 2 production by MSCs.

Relationship between inhaled β₂-agonists and ventilator-associated pneumonia: a cohort study

OBJECTIVE

To determine the impact of aerosolized bronchodilators on ventilator-associated pneumonia.

DESIGN

Prospective cohort study.

SETTING

A 30-bed medical and surgical intensive care unit.

METHODS

All intubated patients requiring mechanical ventilation for >48 hrs were eligible during a 13-month period. Nebulized β2-agonists were administered at the intensive care unit physician's discretion. Ventilator-associated pneumonia definition included clinical and quantitative microbiological criteria. Only first ventilator-associated pneumonia episodes were analyzed. Risk factors for ventilator-associated pneumonia were determined using univariate and multivariate analyses. The influence of inhaled β2-agonists on ventilator-associated pneumonia occurrence was also adjusted for confounding factors using Cox's proportional-hazards model.

RESULTS

Ventilator-associated pneumonia was diagnosed in 137 (31%) of the 439 enrolled patients. Ventilator-associated pneumonia was early-onset in 14 (10%) patients. The incidence rate of ventilator-associated pneumonia was 20 per 1,000 ventilator days. Ventilator-associated pneumonia was polymicrobial in 16 (11%) patients, and related to multidrug-resistant bacteria in 42 (28%) patients. Most cases of ventilator-associated pneumonia were caused by Gram-negative bacteria. Inhaled β2-agonists were significantly more frequently used in patients with ventilator-associated pneumonia compared with those without ventilator-associated pneumonia (49% vs. 34%, odds ratio [95% confidence interval] = 1.9 [1.2-2.8], p = .003). Multivariate analysis identified aerosolized β2-agonists (odds ratio [95% confidence interval] = 1.7 [1.1-2.6], p = .012), Simplified Acute Physiology Score II at intensive care unit admission (odds ratio [95% confidence interval] = 1.01 [1.001-1.02] per point, p = .031), and red blood cell transfusion (odds ratio [95% confidence interval] = 2 [1.3-3.1], p = .001) as independent risk factors for ventilator-associated pneumonia. Cox's proportional-hazards model also identified inhaled β2-agonists as a risk factor for ventilator-associated pneumonia (odds ratio [95% confidence interval] = 1.52 [1.06-2.19], p = .021).

CONCLUSION

Use of aerosolized bronchodilators in intensive care unit mechanically ventilated patients is an independent risk factor for ventilator-associated pneumonia.

An official American Thoracic Society workshop report: features and measurements of experimental acute lung injury in animals

Acute lung injury (ALI) is well defined in humans, but there is no agreement as to the main features of acute lung injury in animal models. A Committee was organized to determine the main features that characterize ALI in animal models and to identify the most relevant methods to assess these features. We used a Delphi approach in which a series of questionnaires were distributed to a panel of experts in experimental lung injury. The Committee concluded that the main features of experimental ALI include histological evidence of tissue injury, alteration of the alveolar capillary barrier, presence of an inflammatory response, and evidence of physiological dysfunction; they recommended that, to determine if ALI has occurred, at least three of these four main features of ALI should be present. The Committee also identified key "very relevant" and "somewhat relevant" measurements for each of the main features of ALI and recommended the use of least one "very relevant" measurement and preferably one or two additional separate measurements to determine if a main feature of ALI is present. Finally, the Committee emphasized that not all of the measurements listed can or should be performed in every study, and that measurements not included in the list are by no means "irrelevant." Our list of features and measurements of ALI is intended as a guide for investigators, and ultimately investigators should choose the particular measurements that best suit the experimental questions being addressed as well as take into consideration any unique aspects of the experimental design.

Antibacterial effect of human mesenchymal stem cells is mediated in part from secretion of the antimicrobial peptide LL-37

Recent in vivo studies indicate that mesenchymal stem cells (MSCs) may have beneficial effects in the treatment of sepsis induced by bacterial infection. Administration of MSCs in these studies improved survival and enhanced bacterial clearance. The primary objective of this study was to test the hypothesis that human MSCs possessed intrinsic antimicrobial properties. We studied the effect of human MSCs derived from bone marrow on the bacterial growth of Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. MSCs as well as their conditioned medium (CM) demonstrated marked inhibition of bacterial growth in comparison with control medium or normal human lung fibroblasts (NHLF). Analysis of expression of major antimicrobial peptides indicated that one of the factors responsible for the antimicrobial activity of MSC CM against Gram-negative bacteria was the human cathelicidin antimicrobial peptide, hCAP-18/LL-37. Both m-RNA and protein expression data showed that the expression of LL-37 in MSCs increased after bacterial challenge. Using an in vivo mouse model of E. coli pneumonia, intratracheal administration of MSCs reduced bacterial growth (in colony-forming unit) in the lung homogenates and in the bronchoalveolar lavage (BAL) fluid, and administration of MSCs simultaneously with a neutralizing antibody to LL-37 resulted in a decrease in bacterial clearance. In addition, the BAL itself from MSC-treated mice had a greater antimicrobial activity in comparison with the BAL of phosphate buffered saline (PBS)-treated mice. Human bone marrow-derived MSCs possess direct antimicrobial activity, which is mediated in part by the secretion of human cathelicidin hCAP-18/ LL-37.

The lectin-like domain of tumor necrosis factor improves lung function after rat lung transplantation--potential role for a reduction in reactive oxygen species generation

OBJECTIVE

To test the hypothesis that the lectin-like domain of tumor necrosis factor, mimicked by the TIP peptide, can improve lung function after unilateral orthotopic lung isotransplantation. Because of a lack of a specific treatment for ischemia reperfusion-mediated lung injury, accompanied by a disrupted barrier integrity and a dysfunctional alveolar liquid clearance, alternative therapies restoring these parameters after lung transplantation are required.

DESIGN

Prospective, randomized laboratory investigation.

SETTING

University-affiliated laboratory.

SUBJECTS

Adult female rats.

INTERVENTIONS

Tuberoinfundibular peptide, mimicking the lectin-like domain of tumor necrosis factor, mutant TIP peptide, N,N'-diacetylchitobiose/TIP peptide, and amiloride/TIP peptide were instilled intratracheally in the left lung immediately before the isotransplantation was performed. An additional group received an intravenous TIP peptide treatment, 1.5 mins before transplantation. Studies using isolated rat type II alveolar epithelial cell monolayers and ovine pulmonary endothelial cells were also performed.

MEASUREMENTS AND MAIN RESULTS

Intratracheal pretreatment of the transplantable left lung with the TIP peptide, but not with an inactive mutant TIP peptide, resulted in significantly improved oxygenation 24 hrs after transplantation. This treatment led to a significantly reduced neutrophil content in the lavage fluid. Both the effects on oxygenation and neutrophil infiltration were inhibited by the epithelial sodium channel blocker amiloride. The TIP peptide blunted reactive oxygen species production in pulmonary artery endothelial cells under hypoxia and reoxygenation and reduced reactive oxygen species content in the transplanted rat lungs in vivo. Ussing chamber experiments using monolayers of primary type II rat pneumocytes indicated that the primary site of action of the peptide was on the apical side of these cells.

CONCLUSIONS

These data demonstrate that the TIP peptide significantly improves lung function after lung transplantation in the rat, in part, by reducing neutrophil content and reactive oxygen species generation. These studies suggest that the TIP peptide is a potential therapeutic agent against the ischemia reperfusion injury associated with lung transplantation.

Transforming growth factor beta1 inhibits cystic fibrosis transmembrane conductance regulator-dependent cAMP-stimulated alveolar epithelial fluid transport via a phosphatidylinositol 3-kinase-dependent mechanism

Exogenous or endogenous beta(2)-adrenergic receptor agonists enhance alveolar epithelial fluid transport via a cAMP-dependent mechanism that protects the lungs from alveolar flooding in acute lung injury. However, impaired alveolar fluid clearance is present in most of the patients with acute lung injury and is associated with increased mortality, although the mechanisms responsible for this inhibition of the alveolar epithelial fluid transport are not completely understood. Here, we found that transforming growth factor beta1 (TGF-beta1), a critical mediator of acute lung injury, inhibits beta(2)-adrenergic receptor agonist-stimulated vectorial fluid and Cl(-) transport across primary rat and human alveolar epithelial type II cell monolayers. This inhibition is due to a reduction in the cystic fibrosis transmembrane conductance regulator activity and biosynthesis mediated by a phosphatidylinositol 3-kinase (PI3K)-dependent heterologous desensitization and down-regulation of the beta(2)-adrenergic receptors. Consistent with these in vitro results, inhibition of the PI3K pathway or pretreatment with soluble chimeric TGF-beta type II receptor restored beta(2)-adrenergic receptor agonist-stimulated alveolar epithelial fluid transport in an in vivo model of acute lung injury induced by hemorrhagic shock in rats. The results demonstrate a novel role for TGF-beta1 in impairing the beta- adrenergic agonist-stimulated alveolar fluid clearance in acute lung injury, an effect that could be corrected by using PI3K inhibitors that are safe to use in humans.

Receptor for advanced glycation end-products (RAGE) is an indicator of direct lung injury in models of experimental lung injury

Receptor for advanced glycation end-products (RAGE) is a marker of alveolar type I cells and is elevated in the pulmonary edema fluid of patients with acute lung injury (ALI). We tested the hypothesis that RAGE in the bronchoalveolar lavage (BAL) would be elevated in experimental models of direct ALI characterized by alveolar epithelial cell injury. We developed ELISA measurements for RAGE and studied ALI (direct and indirect) mouse models and collected BAL at specified endpoints to measure RAGE. We also tested whether levels of BAL RAGE correlated 1) with the severity of lung injury in acid and hyperoxia-induced ALI and 2) with the beneficial effect of a novel treatment, mesenchymal stem cells (MSC), in LPS-induced ALI. In ALI models of direct lung injury induced by intratracheal instillation of acid, LPS, or Escherichia coli, the BAL RAGE was 58-, 22-, and 13-fold elevated, respectively. In contrast, BAL RAGE was not detectable in indirect models of ALI induced by an intraperitoneal injection of thiourea or by an intravenous injection of MHC I monoclonal antibody that produces a mouse model of transfusion-related ALI. BAL RAGE did correlate with the severity of lung injury in acid and hyperoxia-induced ALI. In addition, with LPS-induced ALI, BAL RAGE was markedly reduced with MSC treatment. In summary, BAL RAGE is an indicator of ALI, and it may be useful in distinguishing direct from indirect models of ALI as well as assessing the response to specific therapies.

A2B adenosine receptor signaling attenuates acute lung injury by enhancing alveolar fluid clearance in mice

Although acute lung injury contributes significantly to critical illness, resolution often occurs spontaneously via activation of incompletely understood pathways. We recently found that mechanical ventilation of mice increases the level of pulmonary adenosine, and that mice deficient for extracellular adenosine generation show increased pulmonary edema and inflammation after ventilator-induced lung injury (VILI). Here, we profiled the response to VILI in mice with genetic deletions of each of the 4 adenosine receptors (ARs) and found that deletion of the A2BAR gene was specifically associated with reduced survival time and increased pulmonary albumin leakage after injury. In WT mice, treatment with an A2BAR-selective antagonist resulted in enhanced pulmonary inflammation, edema, and attenuated gas exchange, while an A2BAR agonist attenuated VILI. In bone marrow-chimeric A2BAR mice, although the pulmonary inflammatory response involved A2BAR signaling from bone marrow-derived cells, A2BARs located on the lung tissue attenuated VILI-induced albumin leakage and pulmonary edema. Furthermore, measurement of alveolar fluid clearance (AFC) demonstrated that A2BAR signaling enhanced amiloride-sensitive fluid transport and elevation of pulmonary cAMP levels following VILI, suggesting that A2BAR agonist treatment protects by drying out the lungs. Similar enhancement of pulmonary cAMP and AFC were also observed after beta-adrenergic stimulation, a pathway known to promote AFC. Taken together, these studies reveal a role for A2BAR signaling in attenuating VILI and implicate this receptor as a potential therapeutic target during acute lung injury.

Prior statin use is associated with improved outcomes in community-acquired pneumonia

BACKGROUND

Statins have potent anti-inflammatory effects in laboratory studies of pulmonary inflammation. We investigated whether statin users had improved outcome when admitted with community-acquired pneumonia.

METHODS

We carried out a prospective observational study of patients admitted to the hospital with community-acquired pneumonia between January 2005 and November 2007. The use of statins, angiotensin-converting enzyme inhibitors, beta-blockers, and aspirin were recorded. The outcomes of interest were 30-day mortality, need for mechanical ventilation or inotropic support, and the development of complicated pneumonia.

RESULTS

On multivariate logistic regression, statin use was associated with significantly lower 30-day mortality (adjusted odds ratio [AOR] 0.46, 95% confidence interval [CI], 0.25-0.85, P=.01) and development of complicated pneumonia (AOR 0.44, 95% CI, 0.25-0.79, P=.006). There was no effect on requirement of mechanical ventilation or inotropic support (AOR 0.93, 95% CI, 0.49-1.76, P=.8). Patients prescribed statins had more severe pneumonia (median Pneumonia Severity Index 4, interquartile range [IQR] 3-4) compared with patients not prescribed cardiovascular drugs (median Pneumonia Severity Index 3, IQR 2-4, P < .0001). Despite this, C-reactive protein levels on admission were significantly lower in patients prescribed statins (median 119 mg/L, IQR 46-215) compared with patients prescribed no cardiovascular drugs (182 mg/L, IQR 66-326, P < .0001). On multivariate logistic regression, statin use was independently protective against a C-reactive protein that failed to fall by 50% or more at day 4 (AOR 0.50, 95% CI 0.27-0.92, P=.02).

CONCLUSIONS

Statin use is associated with reduced markers of systemic inflammation and improved outcomes in patients admitted with community-acquired pneumonia.

Animal models of acute lung injury

Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury.

Animal models of human pneumonia

Pneumonia is a medical and public health priority, and advances against this disease will require improved knowledge of biological mechanisms. Human pneumonia is modeled with experimental infections of animals, most frequently mice. Mouse models are leading to important discoveries relevant to pneumonia, but their limitations must be carefully considered. Several approaches to establishing pneumonia in mice have been developed, and each has specific strengths and weaknesses. Similarly, procedures for characterizing microbial and host responses to infection have unique advantages and disadvantages. Mice are not small humans, and the applicability of results from murine models to human disease depends on understanding the similarities and differences between species. Additional considerations such as mouse strain, microbe strain, and prior mouse-microbe interactions also influence the design and interpretation of experiments. Results from studies of pneumonia in animals, combined with complementary basic and translational studies, are elucidating mechanisms responsible for susceptibility to and pathophysiology of lung infection.

Alveolar epithelial beta2-adrenergic receptors

beta(2)-adrenergic receptors are present throughout the lung, including the alveolar airspace, where they play an important role for regulation of the active Na(+) transport needed for clearance of excess fluid out of alveolar airspace. beta(2)-adrenergic receptor signaling is required for up-regulation of alveolar epithelial active ion transport in the setting of excess alveolar edema. The positive, protective effects of beta(2)-adrenergic receptor signaling on alveolar active Na(+) transport in normal and injured lungs provide substantial support for the use of beta-adrenergic agonists to accelerate alveolar fluid clearance in patients with cardiogenic and noncardiogenic pulmonary edema. In this review, we summarize the role of beta(2)-adrenergic receptors in the alveolar epithelium with emphasis on their role in the regulation of alveolar active Na(+) transport in normal and injured lungs.

Omega-3 polyunsaturated fatty acids improve host response in chronicPseudomonas aeruginosalung infection in mice

Pseudomonas aeruginosa is a gram-negative bacilli frequently encountered in human pathology. This pathogen is involved in a large number of nosocomial infections and chronic diseases. Herein we investigated the effects of polyunsaturated fatty acids (PUFA) in chronic Pseudomonas aeruginosa lung infection. C57BL/6 mice were fed for 5 wk with specifically designed diets with high contents in either omega-3 (ω-3) or ω-6 PUFA and compared to a control diet. P. aeruginosa included in agarose beads was then instilled intratracheally, and the animals were studied for 7 days. On the 4th day, the mice fed with the ω-3 diet had a higher lean body mass gain and a lower ω-6:ω-3 ratio of fatty acids extracted from the lung tissue compared with the other groups ( P < 0.05). The ω-3 group had the lowest mortality. Distal alveolar fluid clearance (DAFC) as well as the inflammatory response and the cellular recruitment were higher in the ω-3 group on the 4th day. The effect on DAFC was independent of α-epithelial Na+channels (α-ENaC), β-ENaC, and α1-Na-K-ATPase mRNA expressions, which were not altered by the different diets. In conclusion, a diet enriched in ω-3 PUFA can change lung membrane composition and improve survival in chronic pneumonia. This effect on survival is probably multifactorial involving the increased DAFC capacity as well as the optimization of the initial inflammatory response. This work suggests that a better control of the ω-6/ω-3 PUFA balance may represent an interesting target in the prevention and/or control of P. aeruginosa infection in patients.