Activity of pulmonary edema fluid interleukin-8 bound to alpha(2)-macroglobulin in patients with acute lung injury

Alpha-2-Macroglobulin in Inflammation, Immunity and Infections

Alpha-2-macroglobulin is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor. By presenting itself as an optimal substrate for endopeptidases of all catalytic types, alpha-2-macroglobulin lures active proteases into its molecular cage and subsequently ‘flags’ their complex for elimination. In addition to its role as a regulator of extracellular proteolysis, alpha-2-macroglobulin also has other functions such as switching proteolysis towards small substrates, facilitating cell migration and the binding of cytokines, growth factors and damaged extracellular proteins. These functions appear particularly important in the context of immune-cell function. In this review manuscript, we provide an overview of all functions of alpha-2-macroglobulin and place these in the context of inflammation, immunity and infections.

Liver-Dependent Lung Remodeling during Systemic Inflammation Shapes Responses to Secondary Infection

Systemic duress, such as that elicited by sepsis, burns, or trauma, predisposes patients to secondary pneumonia, demanding better understanding of host pathways influencing this deleterious connection. These pre-existing circumstances are capable of triggering the hepatic acute-phase response (APR), which we previously demonstrated is essential for limiting susceptibility to secondary lung infections. To identify potential mechanisms underlying protection afforded by the lung-liver axis, our studies aimed to evaluate liver-dependent lung reprogramming when a systemic inflammatory challenge precedes pneumonia. Wild-type mice and APR-deficient littermate mice with hepatocyte-specific deletion of STAT3 (hepSTAT3-/-), a transcription factor necessary for full APR initiation, were challenged i.p. with LPS to induce endotoxemia. After 18 h, pneumonia was induced by intratracheal Escherichia coli instillation. Endotoxemia elicited significant transcriptional alterations in the lungs of wild-type and hepSTAT3-/- mice, with nearly 2000 differentially expressed genes between genotypes. The gene signatures revealed exaggerated immune activity in the lungs of hepSTAT3-/- mice, which were compromised in their capacity to launch additional cytokine responses to secondary infection. Proteomics revealed substantial liver-dependent modifications in the airspaces of pneumonic mice, implicating a network of dispatched liver-derived mediators influencing lung homeostasis. These results indicate that after systemic inflammation, liver acute-phase changes dramatically remodel the lungs, resulting in a modified landscape for any stimuli encountered thereafter. Based on the established vulnerability of hepSTAT3-/- mice to secondary lung infections, we believe that intact liver function is critical for maintaining the immunological responsiveness of the lungs.

Development of a biomarker mortality risk model in acute respiratory distress syndrome

Background

There is a compelling unmet medical need for biomarker-based models to risk-stratify patients with acute respiratory distress syndrome. Effective stratification would optimize participant selection for clinical trial enrollment by focusing on those most likely to benefit from new interventions. Our objective was to develop a prognostic, biomarker-based model for predicting mortality in adult patients with acute respiratory distress syndrome.

Methods

This is a secondary analysis using a cohort of 252 mechanically ventilated subjects with the diagnosis of acute respiratory distress syndrome. Survival to day 7 with both day 0 (first day of presentation) and day 7 sample availability was required. Blood was collected for biomarker measurements at first presentation to the intensive care unit and on the seventh day. Biomarkers included cytokine-chemokines, dual-functioning cytozymes, and vascular injury markers. Logistic regression, latent class analysis, and classification and regression tree analysis were used to identify the plasma biomarkers most predictive of 28-day ARDS mortality.

Results

From eight biologically relevant biomarker candidates, six demonstrated an enhanced capacity to predict mortality at day 0. Latent-class analysis identified two biomarker-based phenotypes. Phenotype A exhibited significantly higher plasma levels of angiopoietin-2, macrophage migration inhibitory factor, interleukin-8, interleukin-1 receptor antagonist, interleukin-6, and extracellular nicotinamide phosphoribosyltransferase (eNAMPT) compared to phenotype B. Mortality at 28 days was significantly higher for phenotype A compared to phenotype B (32% vs 19%, p = 0.04).

Conclusions

An adult biomarker-based risk model reliably identifies ARDS subjects at risk of death within 28 days of hospitalization.

Short-term physiological hypoxia potentiates the therapeutic function of mesenchymal stem cells

Background

In the bone marrow, MSCs reside in a hypoxic milieu (1–5% O₂) that is thought to preserve their multipotent state. Typically, in vitro expansion of MSCs is performed under normoxia (~ 21% O₂), a process that has been shown to impair their function. Here, we evaluated the characteristics and function of MSCs cultured under hypoxia and hypothesized that, when compared to normoxia, dedicated hypoxia will augment the functional characteristics of MSCs.

Methods

Human and porcine bone marrow MSCs were obtained from fresh mononuclear cells. The first study evaluated MSC function following both long-term (10 days) and short-term (48 h) hypoxia (1% O₂) culture. In our second study, we evaluated the functional characteristics of MSC cultured under short-term 2% and 5% hypoxia. MSCs were evaluated for their metabolic activity, proliferation, viability, clonogenicity, gene expression, and secretory capacity.

Results

In long-term culture, common MSC surface marker expression (CD44 and CD105) dropped under hypoxia. Additionally, in long-term culture, MSCs proliferated significantly slower and provided lower yields under hypoxia. Conversely, in short-term culture, MSCs proliferated significantly faster under hypoxia. In both long-term and short-term cultures, MSC metabolic activity was significantly higher under hypoxia. Furthermore, MSCs cultured under hypoxia had upregulated expression of VEGF with concomitant downregulation of HMGB1 and the apoptotic genes BCL-2 and CASP3. Finally, in both hypoxia cultures, the pro-inflammatory cytokine, IL-8, was suppressed, while levels of the anti-inflammatories, IL-1ra and GM-CSF, were elevated in short-term hypoxia only.

Conclusions

In this study, we demonstrate that hypoxia augments the therapeutic characteristics of both porcine and human MSCs. Yet, short-term 2% hypoxia offers the greatest benefit overall, exemplified by the increase in proliferation, self-renewing capacity, and modulation of key genes and the inflammatory milieu as compared to normoxia. These data are important for generating robust MSCs with augmented function for clinical applications.

Leukotriene B4 indicates lung injury and on-going inflammatory changes after severe trauma in a porcine long-term model

BACKGROUND

Recognizing patients at risk for pulmonary complications (PC) is of high clinical relevance. Migration of polymorphonuclear leukocytes (PMN) to inflammatory sites plays an important role in PC, and is tightly regulated by specific chemokines including interleukin (IL)-8 and other mediators such as leukotriene (LT)B4. Previously, we have reported that LTB4 indicated early patients at risk for PC after trauma. Here, the relevance of LTB4 to indicating lung integrity in a newly established long-term porcine severe trauma model (polytrauma, PT) was explored.

METHODS

Twelve pigs (3 months old, 30 ± 5kg) underwent PT including standardized femur fracture, lung contusion, liver laceration, hemorrhagic shock, subsequent resuscitation and surgical fracture fixation. Six animals served as controls (sham). After 72h lung damage and inflammatory changes were assessed. LTB4 was determined in plasma before the experiment, immediately after trauma, and after 2, 4, 24 or 72h. Bronchoalveolar lavage (BAL)-fluid was collected prior and after the experiment.

RESULTS

Lung injury, local gene expression of IL-8, IL-1β, IL-10, IL-18 and PMN-infiltration into lungs increased significantly in PT compared with sham. Systemic LTB4 increased markedly in both groups 4h after trauma. Compared with declined plasma LTB4 levels in sham, LTB4 increased further in PT after 72h. Similar increase was observed in BAL-fluid after PT.

CONCLUSIONS

In a severe trauma model, sustained changes in terms of lung injury and inflammation are determined at day 3 post-trauma. Specifically, increased LTB4 in this porcine long-term model indicated a rapid inflammatory alteration both locally and systemically. The results support the concept of LTB4 as a biomarker for PC after severe trauma and lung contusion.

The mercurial nature of neutrophils: still an enigma in ARDS?

The acute respiratory distress syndrome (ARDS) is a life-threatening lung condition resulting from direct and indirect insults to the lung. It is characterized by disruption of the endothelial-epithelial barrier, alveolar damage, pulmonary edema, and respiratory failure. A key feature of ARDS is the accumulation of neutrophils in the lung microvasculature, interstitium, and alveolar space. Despite a clear association between neutrophil influx into the lung and disease severity, there is some debate as to whether neutrophils directly contribute to disease pathogenesis. The primary function of neutrophils is to provide immediate host defense against pathogenic microorganisms. Neutrophils release numerous antimicrobial factors such as reactive oxygen species, proteinases, and neutrophil extracellular traps. However, these factors are also toxic to host cells and can result in bystander tissue damage. The excessive accumulation of neutrophils in ARDS may therefore contribute to disease progression. Central to neutrophil recruitment is the release of chemokines, including the archetypal neutrophil chemoattractant IL-8, from resident pulmonary cells. However, the chemokine network in the inflamed lung is complex and may involve several other chemokines, including CXCL10, CCL2, and CCL7. This review will therefore focus on the experimental and clinical evidence supporting neutrophils as key players in ARDS and the chemokines involved in recruiting them into the lung.

Growth factors and cytokines in acute lung injury

Cytokines and growth factors play an integral role in the maintenance of immune homeostasis, the generation of protective immunity, and lung reparative processes. However, the dysregulated expression of cytokines and growth factors in response to infectious or noxious insults can initiate and perpetuate deleterious lung inflammation and fibroproliferation. In this article, we will comprehensively review the contribution of individual cytokines and growth factors and cytokine networks to key pathophysiological events in human and experimental acute lung injury (ALI), including inflammatory cell recruitment and activation, alveolar epithelial injury and repair, angiogenesis, and matrix deposition and remodeling. The application of cytokines/growth factors as prognostic indicators and therapeutic targets in human ALI is explored.

Novel aspects of urokinase function in the injured lung: role of α2-macroglobulin

The level of active urokinase (uPA) is decreased in lung fluids of patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) whereas α(2)-macroglobulin (α(2)-M), a plasma proteinase inhibitor, is a major component of these fluids. Since there have been reports describing the ability of α(2)-M to form complexes with uPA in vitro, we hypothesized that α(2)-M may interact with uPA in the lung to modulate its biological activity. Pulmonary edema fluids and lung tissues from patients with ALI/ARDS were evaluated for the presence of uPA associated with α(2)-M. Complexes between α(2)-M and uPA were detected in alveolar edema fluids as well as in lungs of patients with ALI/ARDS where they were located mainly in close proximity to epithelial cells. While uPA bound to α(2)-M retains its amidolytic activity towards low-molecular-weight substrates, it is not inhibited by its main physiological inhibitor, plasminogen activator inhibitor 1. We also investigated the functional consequences of formation of complexes between uPA and α(2)-M in vitro. We found that when α(2)-M:uPA complexes were added to cultures of human bronchial epithelial cells (BEAS-2B), activation of nuclear factor-κB as well as production of interleukin-6 and -8 was substantially suppressed compared with the addition of uPA alone. Our findings indicate for the first time that the function of uPA in patients with ALI/ARDS may be modulated by α(2)-M and that the effects may include the regulation of the fibrinolytic and signaling activities of uPA.

Role of lung contusions on posttraumatic inflammatory response and organ dysfunction in traumatized patients

BACKGROUND

Multiple trauma is often accompanied by lung contusion leading to secondary pulmonary inflammation and organ dysfunction. The particular role of lung contusions on the systemic inflammatory response remains unclear. Therefore, the aim of the present study was to compare the degree of lung contusion with markers of inflammation and multiple organ failure (MOF) in trauma patients.

METHODS

According to the Injury Severity Score (ISS), 45 patients were assigned to a low (< 25 points) and a high ISS group (> 25 points), respectively. Both groups were subdivided into minor and major lung injury groups as defined by computed tomography (CT) scan. Plasma levels of interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor (TNF) receptors, C-reactive protein (CRP), and polymorphonuclear (PMN) elastase were assessed, as well as the Murray lung score (MLS) and the MOF score.

RESULTS

Patients with low ISS present moderate activation of inflammation which is not influenced by the degree of lung contusion. In contrast, patients with a high ISS develop significant posttraumatic inflammation and MOF. Patients with high ISS and severe lung contusions present significantly higher MLS and MOF scores. Interestingly, patients of the high ISS group without severe lung contusions develop a similar degree of MLS and MOF only after 5 days following the traumatic insult. However, the initial plasma levels of IL-6 and IL-8 differ significantly in this group.

CONCLUSION

Our data show that severe lung contusions contributes to an immediate onset of posttraumatic inflammation in severely traumatized patients, resulting in MOF, while in severely injured patients without lung contusion, this development requires up to 5 days.

Alpha1-antitrypsin deficiency in 26-year-old subjects: lung, liver, and protease/protease inhibitor studies

BACKGROUND

Clinical and biochemical signs of lung and liver disease have been followed prospectively in a birth cohort of individuals with alpha1-antitrypsin (AAT) deficiency.

OBJECTIVE

At age 26 years, the focus was on clinical health, lung and liver function tests, and plasma markers of the protease/antiprotease balance. The effect of early childhood environment and symptoms was also studied.

METHODS

Eligible individuals were 26-year-old subjects with AAT deficiency (PiZ, n = 122; PiZ -, n = 2; PiSZ/S-, n = 53) and control subjects (PiMM, n = 44). Of the original AAT-deficient subjects, 119 completed the clinical examination and 134 answered the questionnaire.

RESULTS

The prevalence of respiratory symptoms did not differ between the PiZ and SZ groups. Sixteen percent of PiZ and 14% of PiSZ subjects had asthma. Four current smokers (67%) and 22% of ex-smokers/never-smokers reported recurrent wheezing (p = 0.03). No difference in FEV1 or FEV1/FVC ratio was found between the PiZ, SZ (5% being smokers), and MM individuals (all nonsmokers). A decreased FEV1/FVC ratio was found in PiZ subjects with neonatal cholestasis, compared to remaining PiZ subjects (p = 0.02). Recurrent wheezers at age 2 years with AAT deficiency had decreased FEV1/FVC ratio (p = 0.025) at age 26 years. None had clinical symptoms of liver disease. Six percent of PiZ and 9% of PiSZ subjects had a marginal increase of serum alanine aminotransferase; 7% of PiZ and 4% of PiSZ had abnormal gamma-glutamyl transferase test results. The PiZ and SZ individuals had decreased plasma albumin (p = 0.0002). Secretory leukocyte protease inhibitor (SLPI) was increased in PiZ and SZ subjects compared to PiMM subjects (p = 0.0001). Neutrophil lipocalin was decreased in PiZ subjects (p = 0.0004) and PiSZ subjects (p = 0.001) compared to PiMM individuals. The elastase/AAT complex concentration was lower in AAT-deficient subjects (p = 0.0001).

CONCLUSION

Twenty-six-year-old PiZ and SZ individuals (5% smokers) had normal lung function test results, and 4 to 9% had marginal deviations in liver test results. Analyses of SLPI and neutrophil lipocalin, a marker of neutrophil activity, indicate compensatory changes in the AAT-deficiency state.

Soluble alpha2-macroglobulin receptor is increased in endotracheal aspirates from infants and children after cardiopulmonary bypass

OBJECTIVE

Cytokine dysregulation contributes to the systemic inflammatory response after cardiopulmonary bypass. Clearance of cytokine binding proteins may be important in the resolution of inflammation. Our aim was to determine whether the cytokine binding protein alpha 2 -macroglobulin and its soluble receptor were upregulated in endotracheal aspirates from infants and children undergoing cardiopulmonary bypass.

METHODS

Seventy tracheal aspirates were collected before and after cardiopulmonary bypass from 35 infants and children undergoing surgical correction of congenital heart defects. alpha 2 -Macroglobulin and the soluble alpha 2 -macroglobulin receptor were identified by Western blot. With the use of multi-analyte cytokine profiling, pro-inflammatory and anti-inflammatory cytokines were quantified, normalized to total protein, and expressed as ratios. Paired t tests and Wilcoxon signed-rank tests were performed between prebypass and postbypass samples. Correlations were examined among alpha 2 -macroglobulin, soluble alpha 2 -macroglobulin receptor, cytokine ratios, and the clinical variables of cardiopulmonary bypass, aortic crossclamp, and circulatory arrest times.

RESULTS

alpha 2 -Macroglobulin increased by 50% (mean densitometry increase 82,683 +/- 184,594, P = .012), and soluble alpha 2 -macroglobulin receptor increased by 17% (mean densitometry increase 506,148 +/- 687,037, P = .0001) after cardiopulmonary bypass. The ratio of interleukin-8/interleukin-4 increased by 136% ( P = .0001), and interleukin-8/interleukin-10 increased by 102% ( P = .001). The increase in soluble alpha 2 -macroglobulin receptor was positively correlated with the ratios of interleukin-8/interleukin-4 and interleukin-8/interleukin-10. There were no statistically significant positive correlations between the increase in alpha 2 -macroglobulin or soluble alpha 2 -macroglobulin receptor and measured clinical variables.

CONCLUSIONS

We report for the first time the upregulation of alpha 2 -macroglobulin and soluble alpha 2 -macroglobulin receptor in tracheal aspirates after cardiopulmonary bypass in infants and children. Soluble alpha 2 -macroglobulin receptor correlates with increased alpha 2 -macroglobulin and a disproportionate increase in pro-inflammatory to anti-inflammatory cytokine ratios.

Chemokines in acute respiratory distress syndrome

A characteristic feature of all inflammatory disorders is the excessive recruitment of leukocytes to the site of inflammation. The loss of control in trafficking these cells contributes to inflammatory diseases. Leukocyte recruitment is a well-orchestrated process that includes several protein families including the large cytokine subfamily of chemotactic cytokines, the chemokines. Chemokines and their receptors are involved in the pathogenesis of several diseases. Acute lung injury that clinically manifests as acute respiratory distress syndrome (ARDS) is caused by an uncontrolled systemic inflammatory response resulting from clinical events including major surgery, trauma, multiple transfusions, severe burns, pancreatitis, and sepsis. Systemic inflammatory response syndrome involves activation of alveolar macrophages and sequestered neutrophils in the lung. The clinical hallmarks of ARDS are severe hypoxemia, diffuse bilateral pulmonary infiltrates, and normal intracardiac filling pressures. The magnitude and duration of the inflammatory process may ultimately determine the outcome in patients with ARDS. Recent evidence shows that activated leukocytes and chemokines play a key role in the pathogenesis of ARDS. The expanding number of antagonists of chemokine receptors for inflammatory disorders may hold promise for new medicines to combat ARDS.

Proteomics: current techniques and potential applications to lung disease

Proteomics aims to study the whole protein content of a biological sample in one set of experiments. Such an approach has the potential value to acquire an understanding of the complex responses of an organism to a stimulus. The large vascular and air space surface area of the lung expose it to a multitude of stimuli that can trigger a variety of responses by many different cell types. This complexity makes the lung a promising, but also challenging, target for proteomics. Important steps made in the last decade have increased the potential value of the results of proteomics studies for the clinical scientist. Advances in protein separation and staining techniques have improved protein identification to include the least abundant proteins. The evolution in mass spectrometry has led to the identification of a large part of the proteins of interest rather than just describing changes in patterns of protein spots. Protein profiling techniques allow the rapid comparison of complex samples and the direct investigation of tissue specimens. In addition, proteomics has been complemented by the analysis of posttranslational modifications and techniques for the quantitative comparison of different proteomes. These methodologies have made the application of proteomics on the study of specific diseases or biological processes under clinically relevant conditions possible. The quantity of data that is acquired with these new techniques places new challenges on data processing and analysis. This article provides a brief review of the most promising proteomics methods and some of their applications to pulmonary research.

Cytokine-mediated inflammation in acute lung injury

Clinical acute lung injury (ALI) is a major cause of acute respiratory failure in critically ill patients. There is considerable experimental and clinical evidence that pro- and anti-inflammatory cytokines play a major role in the pathogenesis of inflammatory-induced lung injury from sepsis, pneumonia, aspiration, and shock. A recent multi-center clinical trial found that a lung-protective ventilatory strategy reduces mortality by 22% in patients with ALI. Interestingly, this protective ventilatory strategy was associated with a marked reduction in the number of neutrophils and the concentration of pro-inflammatory cytokines released into the airspaces of the injured lung. Further research is needed to establish the contribution of cytokines to both the pathogenesis and resolution of ALI.

Orthologous gene-expression profiling in multi-species models: search for candidate genes

Microarray-driven gene-expression profiles are generally produced and analyzed for a single specific experimental model. We have assessed an analytical approach that simultaneously evaluates multi-species experimental models within a particular biological condition using orthologous genes as linkers for the various Affymetrix microarray platforms on multi-species models of ventilator-associated lung injury. The results suggest that this approach may be a useful tool in the evaluation of biological processes of interest and selection of process-related candidate genes.

Proinflammatory activity of anti-IL-8 autoantibody:IL-8 complexes in alveolar edema fluid from patients with acute lung injury

A significant fraction of IL-8 in lung fluids from patients with the acute lung injury (ALI) is associated with anti-IL-8 autoantibodies (anti-IL-8:IL-8 complexes), and lung fluid concentrations of these complexes correlate with development and outcome of ALI. In this study, we examined whether anti-IL-8:IL-8 complexes exhibit proinflammatory activity in vitro. These complexes were purified from pulmonary edema fluid samples obtained from patients with ALI. First, we found that IL-8 bound to the autoantibody retained its ability to trigger chemotaxis of neutrophils, whereas control antibody did not have significant chemotactic activity. Next, we examined the ability of anti-IL-8:IL-8 complexes to induce neutrophil activation, i.e., neutrophil respiratory burst and degranulation. Anti-IL-8:IL-8 complexes triggered superoxide and myeloperoxidase release from human neutrophils, and in contrast, the control antibody had no effect. We also demonstrated that IgG receptor, FcgammaRIIa, is the receptor involved in cellular activation mediated by these complexes. Blockade of FcgammaRIIa completely reverses activity of the complexes with the exception of chemotaxis. Both FcgammaRIIa and IL-8 receptors mediate chemotactic activity of anti-IL-8:IL-8 complexes, with FcgammaRIIa being, however, a predominant receptor. Furthermore, activity of the complexes is partially dependent on the activation of the mitogen-activated protein kinases, i.e., ERK and p38, important components of the FcgammaRIIa signaling cascade. Anti-IL-8:IL-8 complexes may therefore be involved in the pathogenesis of lung inflammation in clinical acute lung injury.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.