Keratinocyte growth factor reduces lung damage due to acid instillation in rats

Synthetic surfactant with a combined SP-B and SP-C analogue is efficient in rabbit models of adult and neonatal respiratory distress syndrome

Respiratory distress syndrome (RDS) in premature infants is caused by insufficient amounts of endogenous lung surfactant and is efficiently treated with replacement therapy using animal-derived surfactant preparations. On the other hand, adult/acute RDS (ARDS) occurs secondary to for example, sepsis, aspiration of gastric contents, and multitrauma and is caused by alveolar endothelial damage, leakage of plasma components into the airspaces and inhibition of surfactant activity. Instillation of surfactant preparations in ARDS has so far resulted in very limited treatment effects, partly due to inactivation of the delivered surfactants in the airspace. Here, we develop a combined surfactant protein B (SP-B) and SP-C peptide analogue (Combo) that can be efficiently expressed and purified from Escherichia coli without any solubility or purification tag. NMR spectroscopy shows that Combo peptide forms α-helices both in organic solvents and in lipid micelles, which coincide with the helical regions described for the isolated SP-B and SP-C parts. Artificial Combo surfactant composed of synthetic dipalmitoylphosphatidylcholine:palmitoyloleoylphosphatidylglycerol, 1:1, mixed with 3 weights % relative to total phospholipids of Combo peptide efficiently improves tidal volumes and lung gas volumes at end-expiration in a premature rabbit fetus model of RDS. Combo surfactant also improves oxygenation and respiratory parameters and lowers cytokine release in an acid instillation-induced ARDS adult rabbit model. Combo surfactant is markedly more resistant to inhibition by albumin and fibrinogen than a natural-derived surfactant in clinical use for the treatment of RDS. These features of Combo surfactant make it attractive for the development of novel therapies against human ARDS.

Pulmonary Fibrosis as a Result of Acute Lung Inflammation: Molecular Mechanisms, Relevant In Vivo Models, Prognostic and Therapeutic Approaches

Pulmonary fibrosis is a chronic progressive lung disease that steadily leads to lung architecture disruption and respiratory failure. The development of pulmonary fibrosis is mostly the result of previous acute lung inflammation, caused by a wide variety of etiological factors, not resolved over time and causing the deposition of fibrotic tissue in the lungs. Despite a long history of study and good coverage of the problem in the scientific literature, the effective therapeutic approaches for pulmonary fibrosis treatment are currently lacking. Thus, the study of the molecular mechanisms underlying the transition from acute lung inflammation to pulmonary fibrosis, and the search for new molecular markers and promising therapeutic targets to prevent pulmonary fibrosis development, remain highly relevant tasks. This review focuses on the etiology, pathogenesis, morphological characteristics and outcomes of acute lung inflammation as a precursor of pulmonary fibrosis; the pathomorphological changes in the lungs during fibrosis development; the known molecular mechanisms and key players of the signaling pathways mediating acute lung inflammation and pulmonary fibrosis, as well as the characteristics of the most common in vivo models of these processes. Moreover, the prognostic markers of acute lung injury severity and pulmonary fibrosis development as well as approved and potential therapeutic approaches suppressing the transition from acute lung inflammation to fibrosis are discussed.

Mesenchymal stem cell-based therapy as a new therapeutic approach for acute inflammation

Acute inflammatory diseases such as acute colitis, kidney injury, liver failure, lung injury, myocardial infarction, pancreatitis, septic shock, and spinal cord injury are significant causes of death worldwide. Despite advances in the understanding of its pathophysiology, there are many restrictions in the treatment of these diseases, and new therapeutic approaches are required. Mesenchymal stem cell-based therapy due to immunomodulatory and regenerative properties is a promising candidate for acute inflammatory disease management. Based on preclinical results, mesenchymal stem cells and their-derived secretome improved immunological and clinical parameters. Furthermore, many clinical trials of acute kidney, liver, lung, myocardial, and spinal cord injury have yielded promising results. In this review, we try to provide a comprehensive view of mesenchymal stem cell-based therapy in acute inflammatory diseases as a new treatment approach.

Exploiting the potential of lung stem cells to develop pro-regenerative therapies

Acute and chronic lung diseases are a leading cause of morbidity and mortality globally. Unfortunately, these diseases are increasing in frequency and we have limited treatment options for severe lung diseases. New therapies are needed that not only treat symptoms or slow disease progression, but also enable the regeneration of functional lung tissue. Both airways and alveoli contain populations of epithelial stem cells with the potential to self-renew and produce differentiated progeny. Understanding the mechanisms that determine the behaviour of these cells, and their interactions with their niches, will allow future generations of respiratory therapies that protect the lungs from disease onset, promote regeneration from endogenous stem cells or enable regeneration through the delivery of exogenous cells. This review summarises progress towards each of these goals, highlighting the challenges and opportunities of developing pro-regenerative (bio)pharmaceutical, gene and cell therapies for respiratory diseases.

Post-treatment with a heat shock protein 90 inhibitor prevents chronic lung injury and pulmonary fibrosis, following acute exposure of mice to HCl

Aim/Purpose: Exposure to high levels of hydrochloric acid (HCl) is associated with severe lung injury including both acute inflammation and chronic lung disease, which leads to the development of pulmonary fibrosis. Currently, there are no specific therapeutic agents for HCl-induced lung injury. Heat shock protein 90 (HSP90) has been implicated in the pathogenesis of pulmonary fibrosis. Thus, we have used a murine model of intra-tracheal acid instillation to investigate the antidotal effects of AUY-922, a small molecule HSP90 inhibitor, already in clinical trials for various types of cancer, against HCl-induced chronic lung injury and pulmonary fibrosis.Methods: HCl (0.1 N, 2 μl/g body weight) was instilled into male C57Bl/6J mice at day 0. After 24 h, mice began receiving 1 mg/kg AUY-922, 2x/week for 15 or 30 days.Results: AUY-922 suppressed the HCl-induced sustained inflammation, as reflected in the reduction of leukocyte and protein concentrations in bronchoalveolar lavage fluid, and inhibited the activation of pro-fibrotic biomarkers, ERK and HSP90. Furthermore, AUY-922 improved lung function, decreased the overexpression and accumulation of extracellular matrix proteins and dramatically reduced histologic evidence of fibrosis in the lungs of mice exposed to HCl.Conclusions: We conclude that AUY-922, and possibly other HSP90 inhibitors, successfully block the adverse effects associated with acute exposures to HCl and may represent an effective antidote against HCl-induced chronic lung injury and fibrosis.

Role of extracellular vesicles in cell-cell communication and inflammation following exposure to pulmonary toxicants

Extracellular vesicles (EVs) have emerged as key regulators of cell-cell communication during inflammatory responses to lung injury induced by diverse pulmonary toxicants including cigarette smoke, air pollutants, hyperoxia, acids, and endotoxin. Many lung cell types, including epithelial cells and endothelial cells, as well as infiltrating macrophages generate EVs. EVs appear to function by transporting cargo to recipient cells that, in most instances, promote their inflammatory activity. Biologically active cargo transported by EVs include miRNAs, cytokines/chemokines, damage-associated molecular patterns (DAMPs), tissue factor (TF)s, and caspases. Findings that EVs are taken up by target cells such as macrophages, and that this leads to increased proinflammatory functioning provide support for their role in the development of pathologies associated with toxicant exposure. Understanding the nature of EVs responding to toxic exposures and their cargo may lead to the development of novel therapeutic approaches to mitigating lung injury.

Acute exposure of mice to hydrochloric acid leads to the development of chronic lung injury and pulmonary fibrosis

Objective: Accidental exposure to hydrochloric acid (HCl) is associated with acute lung injury in humans, development of long-term chronic airway obstruction, and fibrosis. However, the mechanisms responsible for the progression to pulmonary fibrosis remain unclear. We utilized a mouse model of progressive lung injury from a single exposure to HCl to investigate the effects of HCl on the lower respiratory tract. Materials and methods: HCl (0.05-0.3 N) or saline was injected intratracheally into male C57Bl/6J mice. At 1, 4, 10 and 30 days post instillation, bronchoalveolar lavage fluid (BALF) and lung tissues were collected and examined for multiple outcomes. Results and discussion: We observed an early inflammatory response and a late mild inflammation present even at 30 d post HCl exposure. Mice treated with HCl exhibited higher total leukocyte and protein levels in the BALF compared to the vehicle group. This was characterized by increased number of neutrophils, monocytes, and lymphocytes as well as pro-inflammatory cytokines during the first 4 d of injury. The late inflammatory response exhibited a predominant presence of mononuclear cells, increased permeability to protein, and higher levels of the pro-fibrotic mediator TGFβ. Pro-fibrotic protein biomarkers, phosphorylated ERK, and HSP90, were also overexpressed at 10 and 30 d following HCl exposure. In vivo lung function measurements demonstrated lung dysfunction and chronic lung injury associated with increased lung hydroxyproline content and increased expression of extracellular matrix (ECM) proteins. The acute inflammation and severity of fibrosis increased in HCl-concentration dependent manner. Conclusions: Our findings suggest that the initial inflammatory response and pro-fibrotic biomarker upregulation may be linked to the progression of pulmonary fibrosis and airway dysfunction and may represent valuable therapeutic targets.

Transitional human alveolar type II epithelial cells suppress extracellular matrix and growth factor gene expression in lung fibroblasts

Epithelial-fibroblast interactions are thought to be very important in the adult lung in response to injury, but the specifics of these interactions are not well defined. We developed coculture systems to define the interactions of adult human alveolar epithelial cells with lung fibroblasts. Alveolar type II cells cultured on floating collagen gels reduced the expression of type 1 collagen (COL1A1) and α-smooth muscle actin (ACTA2) in fibroblasts. They also reduced fibroblast expression of hepatocyte growth factor (HGF), fibroblast growth factor 7 (FGF7, KGF), and FGF10. When type II cells were cultured at an air-liquid interface to maintain high levels of surfactant protein expression, this inhibitory activity was lost. When type II cells were cultured on collagen-coated tissue culture wells to reduce surfactant protein expression further and increase the expression of some type I cell markers, the epithelial cells suppressed transforming growth factor-β (TGF-β)-stimulated ACTA2 and connective tissue growth factor (CTGF) expression in lung fibroblasts. Our results suggest that transitional alveolar type II cells and likely type I cells but not fully differentiated type II cells inhibit matrix and growth factor expression in fibroblasts. These cells express markers of both type II cells and type I cells. This is probably a normal homeostatic mechanism to inhibit the fibrotic response in the resolution phase of wound healing. Defining how transitional type II cells convert activated fibroblasts into a quiescent state and inhibit the effects of TGF-β may provide another approach to limiting the development of fibrosis after alveolar injury.

ATRA reduces inflammation and improves alveolar epithelium regeneration in emphysematous rat lung

INTRODUCTION

Pulmonary emphysema characterized by alveolar wall destruction is resultant of persistent chronic inflammation. All-trans retinoic acid (ATRA) has been reported to reverse elastase-induced emphysema in rats. However, the underlying molecular mechanisms are so far unknown.

OBJECTIVE

To investigate the therapeutic potential effect of ATRA via the amelioration of the ERK/JAK-STAT pathways in the lungs of emphysematous rats.

METHODS

In silico analysis was done to find the binding efficiency of ATRA with receptor and ligands of ERK & JAK-STAT pathway. Emphysema was induced by porcine pancreatic elastase in Sprague-Dawley rats and ATRA was supplemented as therapy. Lungs were harvested for histopathological, genomics and proteomics analysis.

RESULTS AND DISCUSSION

In silico docking, analysis confirms that ATRA interferes with the normal binding of ligands (TNF-α, IL6ST) and receptors (TNFR1, IL6) of ERK/JAK-STAT pathways respectively. ATRA restored the histology, proteases/antiproteases balance, levels of inflammatory markers, antioxidants, expression of candidate genes of ERK and JAK-STAT pathways in the therapy group.

CONCLUSION

ATRA ameliorates ERK/JAK-STAT pathway in emphysema condition, resulting in alveolar epithelium regeneration. Hence, ATRA may prove to be a potential drug in the treatment of emphysema.

TGF beta inhibits HGF, FGF7, and FGF10 expression in normal and IPF lung fibroblasts

TGF beta is a multifunctional cytokine that is important in the pathogenesis of pulmonary fibrosis. The ability of TGF beta to stimulate smooth muscle actin and extracellular matrix gene expression in fibroblasts is well established. In this report, we evaluated the effect of TGF beta on the expression of HGF, FGF7 (KGF), and FGF10, important growth and survival factors for the alveolar epithelium. These growth factors are important for maintaining type II cells and for restoration of the epithelium after lung injury. Under conditions of normal serum supplementation or serum withdrawal TGF beta inhibited fibroblast expression of HGF, FGF7, and FGF10. We confirmed these observations with genome wide RNA sequencing of the response of control and IPF fibroblasts to TGF beta. In general, gene expression in IPF fibroblasts was similar to control fibroblasts. Reduced expression of HGF, FGF7, and FGF10 is another means whereby TGF beta impairs epithelial healing and promotes fibrosis after lung injury.

Causative treatment of acid aspiration induced acute lung injury - Recent trends from animal experiments and critical perspective

Aspiration of low-pH gastric fluid leads to an initial pneumonitis, which may become complicated by subsequent pneumonia or acute respiratory distress syndrome. Current treatment is at best supportive, but there is growing experimental evidence on the significant contribution of both neutrophils and platelets in the development of this inflammatory pulmonary reaction, a condition that can be attenuated by several medicinal products. This review aims to summarize novel findings in experimental models on pathomechanisms after an acid-aspiration event. Given the clinical relevance, specific emphasis is put on deduced potential experimental therapeutic approaches, which make use of the characteristic alteration of microcirculation in the injured lung.

Regeneration of the lung alveolus by an evolutionarily conserved epithelial progenitor

Functional tissue regeneration is required for the restoration of normal organ homeostasis after severe injury. Some organs, such as the intestine, harbour active stem cells throughout homeostasis and regeneration; more quiescent organs, such as the lung, often contain facultative progenitor cells that are recruited after injury to participate in regeneration. Here we show that a Wnt-responsive alveolar epithelial progenitor (AEP) lineage within the alveolar type 2 cell population acts as a major facultative progenitor cell in the distal lung. AEPs are a stable lineage during alveolar homeostasis but expand rapidly to regenerate a large proportion of the alveolar epithelium after acute lung injury. AEPs exhibit a distinct transcriptome, epigenome and functional phenotype and respond specifically to Wnt and Fgf signalling. In contrast to other proposed lung progenitor cells, human AEPs can be directly isolated by expression of the conserved cell surface marker TM4SF1, and act as functional human alveolar epithelial progenitor cells in 3D organoids. Our results identify the AEP lineage as an evolutionarily conserved alveolar progenitor that represents a new target for human lung regeneration strategies.

Treatments for Pulmonary Ricin Intoxication: Current Aspects and Future Prospects

Ricin, a plant-derived toxin originating from the seeds of Ricinus communis (castor beans), is one of the most lethal toxins known, particularly if inhaled. Ricin is considered a potential biological threat agent due to its high availability and ease of production. The clinical manifestation of pulmonary ricin intoxication in animal models is closely related to acute respiratory distress syndrome (ARDS), which involves pulmonary proinflammatory cytokine upregulation, massive neutrophil infiltration and severe edema. Currently, the only post-exposure measure that is effective against pulmonary ricinosis at clinically relevant time-points following intoxication in pre-clinical studies is passive immunization with anti-ricin neutralizing antibodies. The efficacy of this antitoxin treatment depends on antibody affinity and the time of treatment initiation within a limited therapeutic time window. Small-molecule compounds that interfere directly with the toxin or inhibit its intracellular trafficking may also be beneficial against ricinosis. Another approach relies on the co-administration of antitoxin antibodies with immunomodulatory drugs, thereby neutralizing the toxin while attenuating lung injury. Immunomodulators and other pharmacological-based treatment options should be tailored according to the particular pathogenesis pathways of pulmonary ricinosis. This review focuses on the current treatment options for pulmonary ricin intoxication using anti-ricin antibodies, disease-modifying countermeasures, anti-ricin small molecules and their various combinations.

Distinct Mesenchymal Lineages and Niches Promote Epithelial Self-Renewal and Myofibrogenesis in the Lung

The lung is an architecturally complex organ comprising a heterogeneous mixture of various epithelial and mesenchymal lineages. We use single-cell RNA sequencing and signaling lineage reporters to generate a spatial and transcriptional map of the lung mesenchyme. We find that each mesenchymal lineage has a distinct spatial address and transcriptional profile leading to unique niche regulatory functions. The mesenchymal alveolar niche cell is Wnt responsive, expresses Pdgfrα, and is critical for alveolar epithelial cell growth and self-renewal. In contrast, the Axin2+ myofibrogenic progenitor cell preferentially generates pathologically deleterious myofibroblasts after injury. Analysis of the secretome and receptome of the alveolar niche reveals functional pathways that mediate growth and self-renewal of alveolar type 2 progenitor cells, including IL-6/Stat3, Bmp, and Fgf signaling. These studies define the cellular and molecular framework of lung mesenchymal niches and reveal the functional importance of developmental pathways in promoting self-renewal versus a pathological response to tissue injury.

Mitogenic stimulation accelerates influenza-induced mortality by increasing susceptibility of alveolar type II cells to infection

Development of pneumonia is the most lethal consequence of influenza, increasing mortality more than 50-fold compared with uncomplicated infection. The spread of viral infection from conducting airways to the alveolar epithelium is therefore a pivotal event in influenza pathogenesis. We found that mitogenic stimulation with keratinocyte growth factor (KGF) markedly accelerated mortality after infectious challenge with influenza A virus (IAV). Coadministration of KGF with IAV markedly accelerated the spread of viral infection from the airways to alveoli compared with challenge with IAV alone, based on spatial and temporal analyses of viral nucleoprotein staining of lung tissue sections and dissociated lung cells. To better define the temporal relationship between KGF administration and susceptibility to IAV infection in vivo, we administered KGF 120, 48, 24, and 0 h before intrapulmonary IAV challenge and assessed the percentages of proliferating and IAV-infected, alveolar type II (AECII) cells in dispersed lung cell populations. Peak AECII infectivity coincided with the timing of KGF administration that also induced peak AECII proliferation. AECII from mice that were given intrapulmonary KGF before isolation and then infected with IAV ex vivo exhibited the same temporal pattern of proliferation and infectious susceptibility. KGF-induced increases in mortality, AECII proliferation, and enhanced IAV susceptibility were all reversed by pretreatment of the animals with the mTOR inhibitor rapamycin before mitogenic stimulation. Taken together, these data suggest mTOR signaling-dependent, mitogenic conditioning of AECII is a determinant of host susceptibility to infection with IAV.

Keratinocyte growth factor supports pulmonary innate immune defense through maintenance of alveolar antimicrobial protein levels and macrophage function

Keratinocyte growth factor (KGF) is an epithelial mitogen that has been reported to protect the lungs from a variety of toxic and infectious insults. In prior studies we found that recombinant human KGF accelerates clearance of bacteria from the murine lung by augmenting the function of alveolar macrophages (AM). In this study we tested the hypothesis that endogenous KGF plays a role in the maintenance of innate pulmonary defense against gram-negative bacterial infections. KGF-deficient mice exhibited delayed clearance of Escherichia coli from the lungs, attenuated phagocytosis by AM, and decreased antimicrobial activity in bronchoalveolar lavage (BAL) fluid, due in part to reductions in levels of surfactant protein A, surfactant protein D, and lysozyme. These immune deficits were accompanied by lower alveolar type II epithelial cell counts and reduced alveolar type II epithelial cell expression of collectin and lysozyme genes on a per cell basis. No significant between-group differences were detected in selected inflammatory cytokines or BAL inflammatory cell populations at baseline or after bacterial challenge in the wild-type and KGF-deficient mice. A single intranasal dose of recombinant human KGF reversed defects in bacterial clearance, AM function, and BAL fluid antimicrobial activity. We conclude that KGF supports alveolar innate immune defense through maintenance of alveolar antimicrobial protein levels and functions of AM. Together these data demonstrate a role for endogenous KGF in maintenance of normal pulmonary innate immune function.

Keratinocyte growth factor-2 inhibits bacterial infection with Pseudomonas aeruginosa pneumonia in a mouse model

To determine protective effects of concurrent administration of Keratinocyte growth factor-2 (KGF-2) with Pseudomonas aeruginosa (P. aeruginosa) inoculation on the induced pneumonia. KGF-2 (5 mg/kg) was concurrently administered into the left lobe of 55 mice with P. aeruginosa PAO1 (5 × 10(6) CFU, half-lethal dose); 55 mice in the control group were concurrently administered PBS with the PAO1. We detected and analyzed: body temperature; amount of P. aeruginosa in homogenates; count of total number of nucleated cells and of mononuclear macrophages; protein concentration in bronchoalveolar lavage fluid (BALF); lung wet-to-dry weight ratio; cytokines in BALF and blood; and lung morphology. To study survival rate, concurrent administration of KGF-2 (experimental group) versus PBS (control) with a lethal dose of PAO1 (1 × 10(7) CFU was performed, and survivorship was documented for 7 days post-inoculation. The bacterial CFU in lung homogenates was significantly decreased in the KGF-2 group compared to the control group. There were significantly more mononuclear macrophages in the BALF from the KGF-2 group than from the control group (p < 0.05). KGF-2 increased the surfactant protein and GM-CSF mRNA in lung at 6 h and 72 h after inoculation. Significant reduction of lung injury scores, protein concentrations, lung wet-to-dry weight ratio, and IL-6 and TNF-α levels was noted in the KGF-2 treated rats at 72 h after inoculation (p < 0.05). The 7-day survival rate of the KGF-2 group was significantly higher than that of the control group (p < 0.05). Concurrent administration of KGF-2 facilitates the clearance of P. aeruginosa from the lungs, attenuates P. aeruginosa-induced lung injury, and extends the 7-day survival rate in mice model with P. aeruginosa pneumonia.

Avoiding the prenatal programming effects of glucocorticoids: are there alternative treatments for the induction of antenatal lung maturation?

BACKGROUND

The long-term outcomes of antenatal glucocorticoids (GCs) vary between reports, and have generated controversy in terms of repeated and single-course events, causing irreversible effects on endocrine set points.

AIM

This study aimed to assess the effects of alternative therapeutic agents other than synthetic glucocorticoid GC administration for fetal lung maturation.

METHODS

A review of literature from PubMed, EMBASE, Cochrane Library, and Google Scholar was conducted to assess the use of alternative therapies to synthetic GCs using recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (PRISMA). End points included the rates of respiratory distress syndrome (RDS), mRNA expression for pneumocyte type II, concentration of surfactant proteins in alveolar lavage, morphological differences, histological proof of lung maturation, and angiogenesis or quantification of the surfactant pool.

RESULTS

In all 41 studies examined, we found that ambroxol showed positive effects on lung maturation, but it has yet to be analyzed with sufficient significance in humans. Interleukins and TNF-alpha produce accelerated lung maturation, but have only been evaluated in basic research/experimental studies. Growth factors promote structural and functional growth in all phases of lung maturation, but little is known about their reciprocal effects and exact mechanisms as therapeutics. Thyroid releasing hormone or vitamin A cause detrimental side effects or were less effective for lung maturation.

CONCLUSIONS

The efficacy and safety of these alternative agents are differentiated and none up to now can be recommended as an alternative to GCs.

Emerging therapies for the prevention of acute respiratory distress syndrome

The development of acute respiratory distress syndrome (ARDS) carries significant risk of morbidity and mortality. To date, pharmacological therapy has been largely ineffective for patients with ARDS. We present our personal review aimed at outlining current and future directions for the pharmacological prevention of ARDS. Several available risk-stratification or prediction score strategies for identification of patients at risk of ARDS have been reported. Although not ready for clinical everyday use, they are and will be instrumental in the ongoing and future trials of pharmacoprevention of ARDS.Several systemic medications established the potential role in ARDS prevention based on the preclinical studies and observational data. Due to potential for systemic adverse effects to neutralize any pharmacological benefits of systemic therapy, inhaled medications appear particularly attractive candidates for ARDS prevention. This is because of their direct delivery to the site of proposed action (lungs), while the pulmonary epithelial surface is still functional.We postulate that overall morbidity and mortality rates from ARDS in the future will be contingent upon decreasing the overall incidence of ARDS through effective identification of those at risk and early application of proven supportive care and pharmacological interventions.

Mesenchymal Stem Cell-derived Extracellular Vesicles: Toward Cell-free Therapeutic Applications

Mesenchymal stem (stromal) cells (MSCs) are multipotent cells with the ability to differentiate into several cell types, thus serving as a cell reservoir for regenerative medicine. Much of the current interest in therapeutic application of MSCs to various disease settings can be linked to their immunosuppressive and anti-inflammatory properties. One of the key mechanisms of MSC anti-inflammatory effects is the secretion of soluble factors with paracrine actions. Recently it has emerged that the paracrine functions of MSCs could, at least in part, be mediated by extracellular vesicles (EVs). EVs are predominantly released from the endosomal compartment and contain a cargo that includes miRNA, mRNA, and proteins from their cells of origin. Recent animal model-based studies suggest that EVs have significant potential as a novel alternative to whole cell therapies. Compared to their parent cells, EVs may have a superior safety profile and can be safely stored without losing function. In this article, we review current knowledge related to the potential use of MSC-derived EVs in various diseases and discuss the promising future for EVs as an alternative, cell-free therapy.

Keratinocyte growth factor administration attenuates murine pulmonary mycobacterium tuberculosis infection through granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent macrophage activation and phagolysosome fusion

Augmentation of innate immune defenses is an appealing adjunctive strategy for treatment of pulmonary Mycobacterium tuberculosis infections, especially those caused by drug-resistant strains. The effect of intranasal administration of keratinocyte growth factor (KGF), an epithelial mitogen and differentiation factor, on M. tuberculosis infection in mice was tested in prophylaxis, treatment, and rescue scenarios. Infection of C57BL6 mice with M. tuberculosis resulted in inoculum size-dependent weight loss and mortality. A single dose of KGF given 1 day prior to infection with 10(5) M. tuberculosis bacilli prevented weight loss and enhanced pulmonary mycobacterial clearance (compared with saline-pretreated mice) for up to 28 days. Similar effects were seen when KGF was delivered intranasally every third day for 15 days, but weight loss and bacillary growth resumed when KGF was withdrawn. For mice with a well established M. tuberculosis infection, KGF given every 3 days beginning on day 15 postinoculation was associated with reversal of weight loss and an increase in M. tuberculosis clearance. In in vitro co-culture experiments, M. tuberculosis-infected macrophages exposed to conditioned medium from KGF-treated alveolar type II cell (MLE-15) monolayers exhibited enhanced GM-CSF-dependent killing through mechanisms that included promotion of phagolysosome fusion and induction of nitric oxide. Alveolar macrophages from KGF-treated mice also exhibited enhanced GM-CSF-dependent phagolysosomal fusion. These results provide evidence that administration of KGF promotes M. tuberculosis clearance through GM-CSF-dependent mechanisms and enhances host defense against M. tuberculosis infection.

Preventing ARDS: progress, promise, and pitfalls

Advances in critical care practice have led to a substantial decline in the incidence of ARDS over the past several years. Low tidal volume ventilation, timely resuscitation and antimicrobial administration, restrictive transfusion practices, and primary prevention of aspiration and nosocomial pneumonia have likely contributed to this reduction. Despite decades of research, there is no proven pharmacologic treatment of ARDS, and mortality from ARDS remains high. Consequently, recent initiatives have broadened the scope of lung injury research to include targeted prevention of ARDS. Prediction scores have been developed to identify patients at risk for ARDS, and clinical trials testing aspirin and inhaled budesonide/formoterol for ARDS prevention are ongoing. Future trials aimed at preventing ARDS face several key challenges. ARDS has not been validated as an end point for pivotal clinical trials, and caution is needed when testing toxic therapies that may prevent ARDS yet potentially increase mortality.

Human mesenchymal stem cell microvesicles for treatment of Escherichia coli endotoxin-induced acute lung injury in mice

We previously found that human mesenchymal stem cells (MSC) or its conditioned medium restored lung protein permeability and reduced alveolar inflammation following Escherichia coli endotoxin-induced acute lung injury (ALI) in an ex vivo perfused human lung in part through the secretion of soluble factors such as keratinocyte growth factor (KGF). Recently, MSC were found to release microvesicles (MVs) that were biologically active because of the presence of mRNA or miRNA with reparative properties. MVs are circular fragments of membrane released from the endosomal compartment as exosomes or shed from the surface membranes. These studies were designed to determine if MVs released by human bone marrow derived MSCs would be effective in restoring lung protein permeability and reducing inflammation in E. coli endotoxin-induced ALI in C57BL/6 mice. The intratracheal instillation of MVs improved several indices of ALI at 48 hours. Compared to endotoxin-injured mice, MVs reduced extravascular lung water by 43% and reduced total protein levels in the bronchoalveolar lavage (BAL) fluid by 35%, demonstrating a reduction in pulmonary edema and lung protein permeability. MVs also reduced the influx of neutrophils and macrophage inflammatory protein-2 levels in the BAL fluid by 73% and 49%, respectively, demonstrating a reduction in inflammation. KGF siRNA-pretreatment of MSC partially eliminated the therapeutic effects of MVs released by MSCs, suggesting that KGF protein expression was important for the underlying mechanism. In summary, human MSC-derived MVs were therapeutically effective following E. coli endotoxin-induced ALI in mice in part through the expression of KGF mRNA in the injured alveolus.

Effect of recombinant human keratinocyte growth factor in inducing Ras-Raf-Erk pathway-mediated cell proliferation in emphysematous mice lung

CONTEXT

Pulmonary emphysema is resulted due to destruction of the structure of the alveoli. Recently, exogenous recombinant human Keratinocyte growth factor (rHuKGF) has been reported to induce the regeneration of gas exchange structures. However, the molecular mechanisms governing this process are so far unknown.

OBJECTIVE

The objective of this study was to investigate the effect of rHuKGF in the lungs of emphysema-challenged mice on Ras-Raf-Erk (Erk, extracellular signal-regulated kinase) mediated signaling pathway that regulates alveolar epithelial cell proliferation.

METHODS

Three experimental groups (i.e. emphysema, therapy and control group) were prepared. Lungs of mice were therapeutically treated at three occasions by oropharyngeal instillation of 10 mg rHuKGF per kg body weight after induction of emphysema by porcine pancreatic elastase (PPE). Subsequently, lung tissues from each mouse were collected for histopathology and molecular biology studies.

RESULTS AND DISCUSSION

Histopathology photomicrographs and Destructive Index analysis have shown that elastase induced airspace enlargement and loss of alveoli were recovered in therapy group. Moreover, proliferating cell nuclear antigen (PCNA) at mRNA and protein expression level was markedly increased in therapy group than emphysema group. Upon validation at mRNA level, expressions of FGF-7, FGF-R, Ras, c-Raf, Erk-1, Erk-2, c-Myc and were significantly increased, whereas Elk-1 was notably decreased in therapy group when compared with emphysema group and were well comparable with the control group.

CONCLUSION

Therapeutic supplementation of rHuKGF rectifies the deregulated Ras-Raf-Erk pathway in emphysema condition, resulting in alveolar epithelium regeneration. Hence, rHuKGF may prove to be a potential drug in the treatment of emphysema.

Recombinant Human Keratinocyte Growth Factor Induces Akt Mediated Cell Survival Progression in Emphysematous Mice

INTRODUCTION

Emphysema has been associated with decreased VEGF and VEGFR-2 expression and the presence of high numbers of apoptotic alveolar cells. Keratinocyte growth factor stimulates VEGF synthesis which in turn confers normal lung structure maintenance via the Akt pathway. In this study the potential role of rHuKGF in the improvement of deregulated Akt mediated cell survival pathway in emphysematous mice was investigated.

METHODS

Three experimental groups, i.e., emphysema, treatment and control groups, were prepared. Lungs of mice were treated on 3 occasions by oropharyngeal instillation of 10mg rHuKGF per kg body weight after induction of emphysema with porcine pancreatic elastase. Subsequently, lung tissues from mice were collected for histopathology and molecular biology studies.

RESULTS AND DISCUSSION

Histopathology photomicrographs and destructive index analysis have shown that elastase-induced airspace enlargement and loss of alveoli recovered in the treatment group. rHuKGF stimulates VEGF production which in turn induces the Akt mediated cell survival pathway in emphysematous lungs. mRNA expression of VEGF, VEGFR, PI3K and Akt was significantly increased while Pten, Caspase-9 and Bad was notably decreased in treatment group when compared with emphysema group, being comparable with the control group. Moreover, VEGF protein expression was in accordance with that found for mRNA.

CONCLUSION

Therapeutic rHuKGF supplementation improves the deregulated Akt pathway in emphysema, resulting in alveolar cell survival through activation of the endogenous VEGF-dependent cell survival pathway. Hence rHuKGF may prove to be a potential drug in the treatment of emphysema.

Keratinocyte growth factor-2 is protective in lipopolysaccharide-induced acute lung injury in rats

Keratinocyte growth factor-2 (KGF-2) plays a key role in lung development, but its role in acute lung injury has not been well characterized. Lipopolysaccharide instillation caused acute lung injury, which significantly elevated lung wet-to-dry weight ratio, protein and neutrophils in bronchoalveolar lavage fluid (BALF), inhibited surfactant protein A and C expression in lung tissue, and increased pathological injury. Pretreatment with KGF-2 improved the above lung injury parameters, partially restored surfactant protein A and C expression, and KGF-2 given 2-3 days before LPS challenge showed maximum lung injury improvement. Pretreatment with KGF-2 also markedly reduced the levels of TNF-α, MIP-2, IL-1β and IL-6 in BALF and the levels of IL-1β and IL-6 in lung tissue. Histological analysis showed there was increased proliferation of alveolar type II epithelial cells in lung parenchyma, which reached maximal 2 days after KGF-2 instillation. Intratracheal administration of KGF-2 attenuates lung injury induced by LPS, suggesting KGF-2 may be potent in the intervention of acute lung injury.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Clinical grade allogeneic human mesenchymal stem cells restore alveolar fluid clearance in human lungs rejected for transplantation

The lack of suitable donors for all solid-organ transplant programs is exacerbated in lung transplantation by the low utilization of potential donor lungs, due primarily to donor lung injury and dysfunction, including pulmonary edema. The current studies were designed to determine if intravenous clinical-grade human mesenchymal stem (stromal) cells (hMSCs) would be effective in restoring alveolar fluid clearance (AFC) in the human ex vivo lung perfusion model, using lungs that had been deemed unsuitable for transplantation and had been subjected to prolonged ischemic time. The human lungs were perfused with 5% albumin in a balanced electrolyte solution and oxygenated with continuous positive airway pressure. Baseline AFC was measured in the control lobe and if AFC was impaired (defined as <10%/h), the lungs received either hMSC (5 × 10(6) cells) added to the perfusate or perfusion only as a control. AFC was measured in a different lung lobe at 4 h. Intravenous hMSC restored AFC in the injured lungs to a normal level. In contrast, perfusion only did not increase AFC. This positive effect on AFC was reduced by intrabronchial administration of a neutralizing antibody to keratinocyte growth factor (KGF). Thus, intravenous allogeneic hMSCs are effective in restoring the capacity of the alveolar epithelium to remove alveolar fluid at a normal rate, suggesting that this therapy may be effective in enhancing the resolution of pulmonary edema in human lungs deemed clinically unsuitable for transplantation.

Keratinocyte growth factor gene delivery via mesenchymal stem cells protects against lipopolysaccharide-induced acute lung injury in mice

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with high morbidity and mortality, and have no specific therapy. Keratinocyte growth factor (KGF) is a critical factor for pulmonary epithelial repair and acts via the stimulation of epithelial cell proliferation. Mesenchymal stem cells (MSCs) have been proved as good therapeutic vectors. Thus, we hypothesized that MSC-based KGF gene therapy would have beneficial effects on lipopolysaccharide(LPS)-induced lung injury. After two hours of intratracheal LPS administration to induce lung injury, mice received saline, MSCs alone, empty vector-engineered MSCs (MSCs-vec) or KGF-engineered MSCs (MSCs-kgf) via the tail vein. The MSCs-kgf could be detected in the recipient lungs and the level of KGF expression significantly increased in the MSCs-kgf mice. The MSC-mediated administration of KGF not only improved pulmonary microvascular permeability but also mediated a down-regulation of proinflammatory responses (reducing IL-1β and TNF-α) and an up-regulation of anti-inflammatory responses (increasing cytokine IL-10). Furthermore, the total severity scores of lung injury were significantly reduced in the MSCs-kgf group compared with the other three groups. The underlying mechanism of the protective effect of KGF on ALI may be attributed to the promotion of type II lung epithelial cell proliferation and the enhancement of surfactant synthesis. These findings suggest that MSCs-based KGF gene therapy may be a promising strategy for ALI treatment.

Pulmonary surfactant synthesis after unilateral lung injury in mice

Aspiration pneumonitis can lead to alveolar surfactant dysfunction. We employed a murine model of unilateral aspiration to compare surfactant synthesis in the injured (I) and noninjured (NI) contralateral lung. Mice were instilled with hydrochloric acid in the right bronchus and, after 18 h, an intraperitoneal dose of deuterated water was administered as precursor of disaturated phosphatidylcholine (DSPC)-palmitate. Selected bronchoalveolar lavage fluid (BALF) was collected at scheduled time points and lungs were removed. We measured DSPC-palmitate synthesis in lung tissue and secretion in BALF by gas chromatography-isotope ratio mass spectrometry, together with total proteins and myeloperoxidase activity (MPO) by spectrophotometry. BALF total proteins and MPO were significantly increased in the I lungs compared with NI and naïve control lungs. The DSPC pool size was significantly lower in the BALF of the I lungs compared with naïve controls. DSPC synthesis was accelerated in the I and NI lungs. DSPC secretion of the I lungs was similar to their respective naïve controls, and it was markedly lower compared with their respective NI contralateral lungs. DSPC synthesis and secretion were faster, especially in the NI lungs, compared with naïve control lungs, as a possible compensatory mechanism due to a cross-talk between the lungs triggered by inflammation, hyperventilation, and/or undetermined type II cell reaction to the injury.

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.

Therapeutic effects of human mesenchymal stem cells in ex vivo human lungs injured with live bacteria

RATIONALE

Mesenchymal stem cells secrete paracrine factors that can regulate lung permeability and decrease inflammation, making it a potentially attractive therapy for acute lung injury. However, concerns exist whether mesenchymal stem cells' immunomodulatory properties may have detrimental effects if targeted toward infectious causes of lung injury.

OBJECTIVES

Therefore, we tested the effect of mesenchymal stem cells on lung fluid balance, acute inflammation, and bacterial clearance.

METHODS

We developed an Escherichia coli pneumonia model in our ex vivo perfused human lung to test the therapeutic effects of mesenchymal stem cells on bacterial-induced acute lung injury.

MEASUREMENTS AND MAIN RESULTS

Clinical-grade human mesenchymal stem cells restored alveolar fluid clearance to a normal level, decreased inflammation, and were associated with increased bacterial killing and reduced bacteremia, in part through increased alveolar macrophage phagocytosis and secretion of antimicrobial factors. Keratinocyte growth factor, a soluble factor secreted by mesenchymal stem cells, duplicated most of the antimicrobial effects. In subsequent in vitro studies, we discovered that human monocytes expressed the keratinocyte growth factor receptor, and that keratinocyte growth factor decreased apoptosis of human monocytes through AKT phosphorylation, an effect that increased bacterial clearance. Inhibition of keratinocyte growth factor by a neutralizing antibody reduced the antimicrobial effects of mesenchymal stem cells in the ex vivo perfused human lung and monocytes grown in vitro injured with E. coli bacteria.

CONCLUSIONS

In E. coli-injured human lungs, mesenchymal stem cells restored alveolar fluid clearance, reduced inflammation, and exerted antimicrobial activity, in part through keratinocyte growth factor secretion.

Therapeutic potential of growth factors in pulmonary emphysematous condition

Pulmonary emphysema is a major manifestation of chronic obstructive pulmonary disease (COPD), which is characterized by progressive destruction of alveolar parenchyma with persistent inflammation of the small airways. Such destruction in the distal respiratory tract is irreversible and irreparable. All-trans-retinoic acid was suggested as a novel therapy for regeneration of lost alveoli in emphysema. However, profound discrepancies were evident between studies. At present, no effective therapeutic options are available that allow for the regeneration of lost alveoli in emphysematous human lungs. Recently, some reports on rodent's models have suggested the beneficial effects of various growth factors toward alveolar maintenance and repair processes.

Potential clinical application of KGF-2 (FGF-10) for acute lung injury/acute respiratory distress syndrome

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is an acute life-threatening form of hypoxemic respiratory failure with a high mortality rate, and there is still a great need for more effective therapies for such a severe and lethal disease. Dysfunction of endothelial and epithelial barriers is one of the most important mechanisms in hypoxia-associated ALI/ARDS. The acceleration of the epithelial repair process in the injured lung may provide an effective therapeutic target. KGF-2, a potent alveolar epithelial cell mitogen, plays an important role in organ morphogenesis and epithelial differentiation, and modulates a variety of mechanisms recognized to be important in alveolar repair and resolution in ALI/ARDS. Preclinical and clinical studies have suggested that KGF-2 may be the candidate of novel therapies for alveolar epithelial damage during ALI/ARDS.

Concise review: Mesenchymal stem cells for acute lung injury: role of paracrine soluble factors

Morbidity and mortality have declined only modestly in patients with clinical acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), despite extensive research into the pathophysiology. Current treatment remains primarily supportive with lung-protective ventilation and a fluid conservative strategy. Pharmacologic therapies that reduce the severity of lung injury in preclinical models have not yet been translated to effective clinical treatment options. Consequently, further research in translational therapies is needed. Cell-based therapy with mesenchymal stem cells (MSCs) is one attractive new therapeutic approach. MSCs have the capacity to secrete multiple paracrine factors that can regulate endothelial and epithelial permeability, decrease inflammation, enhance tissue repair, and inhibit bacterial growth. This review will focus on recent studies, which support the potential therapeutic use of MSCs in ALI/ARDS, with an emphasis on the role of paracrine soluble factors.

Stem cells in sepsis and acute lung injury

INTRODUCTION

Critical illnesses continue to be major causes of morbidity and mortality worldwide. Recent investigations show that stem cells may be beneficial as prognostic biomarkers and novel therapeutic strategies in these syndromes. This article reviews the use of stem cells in sepsis and acute lung injury as prognostic biomarkers and also as a potential for exogenous cell-based therapy.

METHODS

A directed search of the medical literature was done using PubMed and OVID to evaluate topics related to pathophysiology of sepsis and acute lung injury, in addition to the characterization and utilization of stem cells in these diseases.

CONCLUSIONS

Stem cells have shown significant promise in the field of critical care medicine both for prognostication and treatment strategies. Although recent studies have been done to describe the mechanistic pathways of stem cells in critical illness, further investigation is necessary to fully delineate the mechanisms behind a stem cell's immunomodulatory characteristics and its ability to mobilize and engraft in tissues.

Keratinocyte growth factor augments pulmonary innate immunity through epithelium-driven, GM-CSF-dependent paracrine activation of alveolar macrophages

Keratinocyte growth factor (KGF) is an epithelial mitogen that has been reported to protect the lungs from a variety of insults. In this study, we tested the hypothesis that KGF augments pulmonary host defense. We found that a single dose of intrapulmonary KGF enhanced the clearance of Escherichia coli or Pseudomonas aeruginosa instilled into the lungs 24 h later. KGF augmented the recruitment, phagocytic activity, and oxidant responses of alveolar macrophages, including lipopolysaccharide-stimulated nitric oxide release and zymosan-induced superoxide production. Less robust alveolar macrophage recruitment and activation was observed in mice treated with intraperitoneal KGF. KGF treatment was associated with increased levels of MIP1γ, LIX, VCAM, IGFBP-6, and GM-CSF in the bronchoalveolar lavage fluid. Of these, only GM-CSF recapitulated in vitro the macrophage activation phenotype seen in the KGF-treated animals. The KGF-stimulated increase in GM-CSF levels in lung tissue and alveolar lining fluid arose from the epithelium, peaked within 1 h, and was associated with STAT5 phosphorylation in alveolar macrophages, consistent with epithelium-driven paracrine activation of macrophage signaling through the KGF receptor/GM-CSF/GM-CSF receptor/JAK-STAT axis. Enhanced bacterial clearance did not occur in response to KGF administration in GM-CSF(-/-) mice, or in mice treated with a neutralizing antibody to GM-CSF. We conclude that KGF enhances alveolar host defense through GM-CSF-stimulated macrophage activation. KGF administration may constitute a promising therapeutic strategy to augment innate immune defenses in refractory pulmonary infections.

Keratinocyte growth factor (KGF) gene therapy mediated by an attenuated form of Salmonella typhimurium ameliorates radiation induced pulmonary injury in rats

The aim of this study is to investigate the effect of KGF (Keratinocyte growth factor) gene therapy mediated by the attenuated Salmonella typhimurium Ty21a on radiation-induced pulmonary injury in rats model. Sprague-Dawley rats were divided into three groups: TPK group (treated with TPK strain, attenuated Salmonella typhimurium Ty21a-recombined human KGF gene); TP group (treated with TP strain, attenuated Salmonella typhimurium Ty21a-recombined blank plasmid); and Saline group (treated with saline). After intraperitoneal administration for 48 h, the thoraxes of the rats were exposed to X-ray (20 Gy), and the rats were administered again two weeks after radiation. On the 3rd, 5th, 7th, 14th and 28th day after radiation, the rats were sacrificed and lung tissues were harvested. Histological analysis was performed, MDA contents and SOD activity were detected, mRNA levels of KGF, TGF-β, SP-A and SP-C were measured by Real-time RT-PCR, and their concentrations in the BALF were quantified with ELISA. Administration of TPK strain improved the pathological changes of the lung on the 28th day. In the TPK group, KGF effectively expressed since the 3rd day, MDA contents decreased and SOD activity increased significantly, on the 7th day and 14th day respectively. SP-A and SP-C expression elevated, whereas TGF-β expression was inhibited in the TPK group. These results suggest that this novel gene therapy of KGF could ameliorate radiation-induced pulmonary injury in rats, and may be a promising therapy for the treatment of radiative pulmonary injury.

Stem cells in sepsis and acute lung injury

OBJECTIVE

Sepsis and acute lung injury continue to be major causes of morbidity and mortality worldwide despite advances in our understanding of pathophysiology and the discovery of new management strategies. Recent investigations show that stem cells may be beneficial as prognostic biomarkers and novel therapeutic strategies in these syndromes. This article reviews the potential use of endogenous adult tissue-derived stem cells in sepsis and acute lung injury as prognostic markers and also as exogenous cell-based therapy.

DATA SOURCES

A directed systematic search of the medical literature using PubMed and OVID, with particular emphasis on the time period after 2002, was done to evaluate topics related to 1) the epidemiology and pathophysiology of sepsis and acute lung injury; and 2) the definition, characterization, and potential use of stem cells in these diseases. DATA SYNTHESIS AND FINDINGS: When available, preferential consideration was given to prospective nonrandomized clinical and preclinical studies.

CONCLUSIONS

Stem cells have shown significant promise in the field of critical care both for 1) prognostic value and 2) treatment strategies. Although several recent studies have identified the potential benefit of stem cells in sepsis and acute lung injury, further investigations are needed to more completely understand stem cells and their potential prognostic and therapeutic value.

Keratinocyte growth factor enhances barrier function without altering claudin expression in primary alveolar epithelial cells

Keratinocyte growth factor (KGF) has efficacy in several experimental models of lung injury; however, the mechanisms underlying KGF's protective effect remain incompletely understood. This study was undertaken to determine whether KGF augments barrier function in primary rat alveolar epithelial cells grown in culture, specifically whether KGF alters tight junction function via claudin expression. KGF significantly increased alveolar epithelial barrier function in culture as assessed by transepithelial electrical resistance (TER) and paracellular permeability. Fluorescence-activated cell sorting of freshly isolated type 1 (AT1) and type 2 (AT2) cells followed by quantitative real-time RT-PCR revealed that more than 97% of claudin mRNA transcripts in these cells were for claudins-3, -4, and -18. Using cultured AT2 cells, we then examined the effect of KGF on the protein levels of the claudins with the highest mRNA levels: -3, -4, -5, -7, -12, -15, and -18. KGF did not alter the levels of any of the claudins tested, nor of zona occludens-1 (ZO-1) or occludin. Moreover, localization of claudins-3, -4, -18, and ZO-1 was unchanged. KGF did induce a marked increase in the apical perijunctional F-actin ring. Actin depolymerization with cytochalasin D blocked the KGF-mediated increase in TER without significantly changing TER in control cells. Together, these data support a novel mechanism by which KGF enhances alveolar barrier function, modulation of the actin cytoskeleton. In addition, these data demonstrate the complete claudin expression profile for AT1 and AT2 cells and indicate that claudins-3, -4, and -18 are the primary claudins expressed in these cell types.

Determinants of initiation and progression of idiopathic pulmonary fibrosis

IPF is a devastating disease with few therapeutic options. The precise aetiology of IPF remains elusive. However, our understanding of the pathologic processes involved in the initiation and progression of this disease is improving. Data on the mechanisms underlying IPF have been generated from epidemiologic investigations as well as cellular and molecular studies of human tissues. Although no perfect animal model of human IPF exists, pre-clinical animal studies have helped define pathways which are likely important in human disease. Epithelial injury, fibroblast activation and repetitive cycles of injury and abnormal repair are almost certainly key events. Factors which have been associated with initiation and/or progression of IPF include viral infections, abnormal cytokine, chemokine and growth factor production, oxidant stress, autoimmunity, inhalational of toxicants and gastro-oesophageal reflux disease. Furthermore, recent evidence identifies a role for a variety of genetic and epigenetic abnormalities ranging from mutations in surfactant protein C to abnormalities in telomere length and telomerase activity. The challenge remains to identify additional inciting agents and key dysregulated pathways that lead to disease progression so that we can develop targeted therapies to treat or prevent this serious disease.

Potential application of mesenchymal stem cells in acute lung injury

Despite extensive research into the pathogenesis of acute lung injury and the acute respiratory distress syndrome (ALI/ARDS), mortality remains high at approximately 40%. Current treatment is primarily supportive, with lung-protective ventilation and a fluid conservative strategy. Pharmacologic therapies that reduce the severity of lung injury in experimental studies have not yet been translated into effective clinical treatment options. Therefore, innovative therapies are needed. Recent studies have suggested that bone-marrow-derived multipotent mesenchymal stem cells (MSC) may have therapeutic applications in multiple clinical disorders including myocardial infarction, diabetes, sepsis, hepatic and acute renal failure. Recently, MSC have been studied in several in vivo models of lung disease. This review focuses on first describing the existing experimental literature that has tested the use of MSC in models of ALI/ARDS, and then the potential mechanisms underlying their therapeutic use with an emphasis on secreted paracrine soluble factors. The review concludes with a discussion of future research directions required for potential clinical trials.

Bronchoalveolar lavage fluid from preterm infants with chorioamnionitis inhibits alveolar epithelial repair

Background

Preterm infants are highly susceptible to lung injury. While both chorioamnionitis and antenatal steroids induce lung maturation, chorioamnionitis is also associated with adverse lung development. We investigated the ability of bronchoalveolar lavage fluid (BALF) from ventilated preterm infants to restore alveolar epithelial integrity after injury in vitro, depending on whether or not they were exposed to chorioamnionitis or antenatal steroids. For this purpose, a translational model for alveolar epithelial repair was developed and characterised.

Methods

BALF was added to mechanically wounded monolayers of A549 cells. Wound closure was quantified over time and compared between preterm infants (gestational age < 32 wks) exposed or not exposed to chorioamnionitis and antenatal steroids (≥ 1 dose). Furthermore, keratinocyte growth factor (KGF) and vascular endothelial growth factor (VEGF) were quantified in BALF, and their ability to induce alveolar epithelial repair was evaluated in the model.

Results

On day 0/1, BALF from infants exposed to antenatal steroids significantly increased epithelial repair (40.3 ± 35.5 vs. -6.3 ± 75.0% above control/mg protein), while chorioamnionitis decreased wound-healing capacity of BALF (-2.9 ± 87.1 vs. 40.2 ± 36.9% above control/mg protein). BALF from patients with chorioamnionitis contained less KGF (11 (0-27) vs. 0 (0-4) pg/ml) and less detectable VEGF (66 vs. 95%) on day 0. BALF levels of VEGF and KGF correlated with its ability to induce wound repair. Moreover, KGF stimulated epithelial repair dose-dependently, although the low levels in BALF suggest KGF is not a major modulator of BALF-induced wound repair. VEGF also stimulated alveolar epithelial repair, an effect that was blocked by addition of soluble VEGF receptor-1 (sVEGFr1/Flt-1). However, BALF-induced wound repair was not significantly affected by addition of sVEGFr1.

Conclusion

Antenatal steroids improve the ability of BALF derived from preterm infants to stimulate alveolar epithelial repair in vitro. Conversely, chorioamnionitis is associated with decreased wound-healing capacity of BALF. A definite role for KGF and VEGF in either process could not be established. Decreased ability to induce alveolar epithelial repair after injury may contribute to the association between chorioamnionitis and adverse lung development in mechanically ventilated preterm infants.

Allogeneic human mesenchymal stem cells for treatment of E. coli endotoxin-induced acute lung injury in the ex vivo perfused human lung

Recent studies have suggested that bone marrow-derived multipotent mesenchymal stem cells (MSCs) may have therapeutic applications in multiple clinical disorders including myocardial infarction, diabetes, sepsis, and hepatic and acute renal failure. Here, we tested the therapeutic capacity of human MSCs to restore alveolar epithelial fluid transport and lung fluid balance from acute lung injury (ALI) in an ex vivo perfused human lung preparation injured by E. coli endotoxin. Intra-bronchial instillation of endotoxin into the distal airspaces resulted in pulmonary edema with the loss of alveolar epithelial fluid transport measured as alveolar fluid clearance. Treatment with allogeneic human MSCs or its conditioned medium given 1 h following endotoxin-induced lung injury reduced extravascular lung water, improved lung endothelial barrier permeability and restored alveolar fluid clearance. Using siRNA knockdown of potential paracrine soluble factors, secretion of keratinocyte growth factor was essential for the beneficial effect of MSCs on alveolar epithelial fluid transport, in part by restoring amiloride-dependent sodium transport. In summary, treatment with allogeneic human MSCs or the conditioned medium restores normal fluid balance in an ex vivo perfused human lung injured by E. coli endotoxin.

Overexpression of fibroblast growth factor-10 during both inflammatory and fibrotic phases attenuates bleomycin-induced pulmonary fibrosis in mice

RATIONALE

Fibroblast growth factor-10 (FGF10) controls survival, proliferation, and differentiation of distal-alveolar epithelial progenitor cells during lung development.

OBJECTIVES

To test for the protective and regenerative effect of Fgf10 overexpression in a bleomycin-induced mouse model of pulmonary inflammation and fibrosis.

METHODS

In SP-C-rtTA; tet(O)Fgf10 double-transgenic mice, lung fibrosis was induced in 2-month-old transgenic mice by subcutaneous delivery of bleomycin (BLM), using an osmotic minipump for 1 week. Exogenous Fgf10 expression in the alveolar epithelium was induced for 7 days with doxycycline during the first, second, and third weeks after bleomycin pump implantation, and lungs were examined at 28 days.

MEASUREMENTS AND MAIN RESULTS

Fgf10 overexpression during Week 1 (inflammatory phase) resulted in increased survival and attenuated lung fibrosis score and collagen deposition. In these Fgf10-overexpressing mice, an increase in regulatory T cells and a reduction in both transforming growth factor-beta(1) and matrix metalloproteinase-2 activity were observed in bronchoalveolar lavage fluids whereas the number of surfactant protein C (SP-C)-positive, alveolar epithelial type II cells (AEC2) was markedly elevated. Analysis of SP-C and TUNEL (terminal deoxynucleotidyltransferase dUTP nick end labeling) double-positive cells and isolation of AEC2 from lungs overexpressing Fgf10 demonstrated increased AEC2 survival. Expression of Fgf10 during Weeks 2 and 3 (fibrotic phase) showed significant attenuation of the lung fibrosis score and collagen deposition.

CONCLUSIONS

In the bleomycin model of lung inflammation and fibrosis, Fgf10 overexpression during both the inflammatory and fibrotic phases results in a greatly reduced extent of lung fibrosis, suggesting that FGF10 may be useful as a novel approach to the treatment of pulmonary fibrosis.