Vascular endothelial growth factor mRNA increases in alveolar epithelial cells during recovery from oxygen injury

Biomarkers of lung alveolarization and microvascular maturation in response to intermittent hypoxia and/or early antioxidant/fish oil supplementation in neonatal rats

OBJECTIVE

Extremely preterm infants experience frequent intermittent hypoxia (IH) episodes during oxygen therapy which causes significant damage to the lungs and curtails important signaling pathways that regulate normal lung alveolarization and microvascular maturation. We tested the hypothesis that early supplementation with fish oil and/or antioxidants in rats exposed to neonatal IH improves expression of lung biomarkers of alveolarization and microvascular maturation, and reduces IH-induced lung injury.

STUDY DESIGN/METHODS

From birth (P0) to P14, rat pups were exposed to room air (RA) or neonatal IH during which they received daily oral supplementation with either: (1) olive oil (OO) (control); (2) Coenzyme Q10 (CoQ10) in OO; (3) fish oil; (4) glutathione nanoparticles (nGSH); or (5) fish oil +CoQ10. At P14 pups were placed in RA until P21 with no further treatment. RA controls were similarly treated. Lung growth and alveolarization, histopathology, apoptosis, oxidative stress and biomarkers of alveolarization and microvascular maturation were determined.

RESULTS

Neonatal IH was associated with reduced lung weights and severe histopathological outcomes. These effects were curtailed with fish oil and nGSH. nGSH was also protective against apoptosis, while CoQ10 prevented IH-induced ROS production. Of all treatments, nGSH and CoQ10 + fish oil-induced vascular endothelial growth factor165 and CD31 (Platelet endothelial cell adhesion molecule-1), which are associated with angiogenesis. CoQ10 + fish oil improved alveolarization in RA and IH despite evidence of hemorrhage.

CONCLUSIONS

The benefits of nGSH and CoQ10 + fish oil suggest an antioxidant effect which may be required to curtail IH-induced lung injury. Further clinical assessment of the effectiveness of nGSH is warranted.

The underappreciated role of resident epithelial cell populations in metastatic progression: contributions of the lung alveolar epithelium

Metastatic cancer is difficult to treat and is responsible for the majority of cancer-related deaths. After cancer cells initiate metastasis and successfully seed a distant site, resident cells in the tissue play a key role in determining how metastatic progression develops. The lung is the second most frequent site of metastatic spread, and the primary site of metastasis within the lung is alveoli. The most abundant cell type in the alveolar niche is the epithelium. This review will examine the potential contributions of the alveolar epithelium to metastatic progression. It will also provide insight into other ways in which alveolar epithelial cells, acting as immune sentinels within the lung, may influence metastatic progression through their various interactions with cells in the surrounding microenvironment.

PLCβ2 Promotes VEGF-Induced Vascular Permeability

BACKGROUND

Regulation of vascular permeability is critical to maintaining tissue metabolic homeostasis. VEGF (vascular endothelial growth factor) is a key stimulus of vascular permeability in acute and chronic diseases including ischemia reperfusion injury, sepsis, and cancer. Identification of novel regulators of vascular permeability would allow for the development of effective targeted therapeutics for patients with unmet medical need.

METHODS

In vitro and in vivo models of VEGFA-induced vascular permeability, pathological permeability, quantitation of intracellular calcium release and cell entry, and phosphatidylinositol 4,5-bisphosphate levels were evaluated with and without modulation of PLC (phospholipase C) β2.

RESULTS

Global knock-out of PLCβ2 in mice resulted in blockade of VEGFA-induced vascular permeability in vivo and transendothelial permeability in primary lung endothelial cells. Further work in an immortalized human microvascular cell line modulated with stable knockdown of PLCβ2 recapitulated the observations in the mouse model and primary cell assays. Additionally, loss of PLCβ2 limited both intracellular release and extracellular entry of calcium following VEGF stimulation as well as reduced basal and VEGFA-stimulated levels of phosphatidylinositol 4,5-bisphosphate compared to control cells. Finally, loss of PLCβ2 in both a hyperoxia-induced lung permeability model and a cardiac ischemia:reperfusion model resulted in improved animal outcomes when compared with wild-type controls.

CONCLUSIONS

The results implicate PLCβ2 as a key positive regulator of VEGF-induced vascular permeability through regulation of both calcium flux and phosphatidylinositol 4,5-bisphosphate levels at the cellular level. Targeting of PLCβ2 in a therapeutic setting may provide a novel approach to regulating vascular permeability in patients.

Molecular Biomarkers of Oxygen Therapy in Patients with Diabetic Foot Ulcers

Hyperbaric oxygen therapy (HBOT) and topical oxygen therapy (TOT) including continuous diffuse oxygen therapy (CDOT) are often utilized to enhance wound healing in patients with diabetic foot ulcerations. High pressure pure oxygen assists in the oxygenation of hypoxic wounds to increase perfusion. Although oxygen therapy provides wound healing benefits to some patients with diabetic foot ulcers, it is currently performed from clinical examination and imaging. Data suggest that oxygen therapy promotes wound healing via angiogenesis, the creation of new blood vessels. Molecular biomarkers relating to tissue inflammation, repair, and healing have been identified. Predictive biomarkers can be used to identify patients who will most likely benefit from this specialized treatment. In diabetic foot ulcerations, specifically, certain biomarkers have been linked to factors involving angiogenesis and inflammation, two crucial aspects of wound healing. In this review, the mechanism of how oxygen works in wound healing on a physiological basis, such as cell metabolism and growth factor signaling transduction is detailed. Additionally, observable clinical outcomes such as collagen formation, angiogenesis, respiratory burst and cell proliferation are described. The scientific evidence for the impact of oxygen on biomolecular pathways and its relationship to the outcomes in clinical research is discussed in this narrative review.

Role of oxygen in wound healing

Not only does oxygen play an essential role in each stage of the wound healing process. It also helps to increases host resistance to infection. Any impairment to the oxygen supply can therefore delay healing. This article explores the affects of oxygen on the wound cells and tissue, and explains how an adequate supply is required for granulation tissue formation and epithelialisation to occur

The Functional Implications of Endothelial Gap Junctions and Cellular Mechanics in Vascular Angiogenesis

Angiogenesis—the sprouting and growth of new blood vessels from the existing vasculature—is an important contributor to tumor development, since it facilitates the supply of oxygen and nutrients to cancer cells. Endothelial cells are critically affected during the angiogenic process as their proliferation, motility, and morphology are modulated by pro-angiogenic and environmental factors associated with tumor tissues and cancer cells. Recent in vivo and in vitro studies have revealed that the gap junctions of endothelial cells also participate in the promotion of angiogenesis. Pro-angiogenic factors modulate gap junction function and connexin expression in endothelial cells, whereas endothelial connexins are involved in angiogenic tube formation and in the cell migration of endothelial cells. Several mechanisms, including gap junction function-dependent or -independent pathways, have been proposed. In particular, connexins might have the potential to regulate cell mechanics such as cell morphology, cell migration, and cellular stiffness that are dynamically changed during the angiogenic processes. Here, we review the implication for endothelial gap junctions and cellular mechanics in vascular angiogenesis.

Tracheal aspirate VEGF and sphingolipid metabolites in the preterm infant with later development of bronchopulmonary dysplasia

OBJECTIVE

Vascular endothelial growth factor (VEGF) and sphingolipid metabolites, sphingosine 1-phosphate (S1P), and ceramides are important to lung development and repair. We hypothesized specific sphingolipid and VEGF alterations would be associated with BPD development and aimed to investigate the early tracheal aspirate (TA) VEGF and S1P relationship with later diagnosis of preterm infant bronchopulmonary dysplasia, BPD.

DESIGN

TA VEGF and lipidomics were measured in TA from Infants <32 weeks gestational age at birth with and without later BPD. BPD was defined using the NICHD severity BPD definition. Clinical demographics and medical course were identified with statistical analysis performed with JMP, Statistical Analysis Software.

RESULTS

The analysis included 25 infants (9 NoBPD and 16 BPD) with mean gestational age of 27.8 ± 2.5 SD weeks and 25.1 ± 1.9 SD weeks respectively, P < 0.01. Later development of BPD was associated with elevated mean TA VEGF 604.3 ± 150.2 SE pg/mL versus NoBPD 120 ± 34.3 SE pg/mL, elevated S1P, 11.5 ± 2.3 SE pmol/mL versus NoBPD 4.8 ± 0.6 SE pmol/mL, and elevated selected ceramides during the first week of life.

CONCLUSIONS

Airway VEGF and sphingolipid metabolites were distinctly elevated within the first days of postnatal life in preterm infants with later BPD progression. These biomarkers may be useful as indicators of lung injury development or as targets to decrease BPD risk.

TNF-α induction of IL-6 in alveolar type II epithelial cells: Contributions of JNK/c-Jun/AP-1 element, C/EBPδ/C/EBP binding site and IKK/NF-κB p65/κB site

Although participation of IL-6 in lung inflammation has been widely elucidated, the transcriptional regulation of its generation in alveolar type II cells stimulated by TNF-α remain unclear. Here, we find that TNF-α significantly induces IL-6 production, and TNF-α induction of IL-6 is mainly regulated at transcriptional level. Upon stimulated by TNF-α, Activator Protein-1 (AP-1)-mediated transcriptional activity is apparently increased in alveolar type II epithelial cells, which might be derived from elevated phosphorylation of JNK and subsequent activation of c-Jun. Either down-regulation of c-Jun or the AP-1 site mutation leads to significant reduction of IL-6 expression. In contrast, ectopic expression of c-Jun notably increases IL-6 generation. So, c-Jun, one of the AP-1 family members, plays a pivotal role in TNF-α-induced IL-6 generation. CCAAT/enhancer binding protein δ (C/EBPδ) expression is significantly amplified by TNF-α, which may contribute to the rise of C/EBP activity in alveolar type II cells. C/EBPδ shRNA treatment results in attenuation of IL-6 expression in the cells, which is consistent with data by introduction of mutations into the C/EBP site in the promoter. However, overexpression of C/EBPδ greatly increases the IL-6 promoter activity. In addition, data regarding another transactivator in the family-C/EBPβ show that it does not affect IL-6 production. We also find that the IKK/NF-κB p65 pathway is activated in TNF-α-treated alveolar type II epithelial cells, and plays an essential role in positive regulation of IL-6 expression in TNF-α-treated alveolar type II epithelial cells via knockdown or forced expression of NF-κB p65, or elimination of κB sites in the IL-6 promoter. Notably, IL-6 promoter-driven luciferase production in primary alveolar type II epithelial cells can also be increased by the ectopic expression of c-Jun, C/EBPδ, and NF-κB p65, respectively. Collectively, our data provide insights into molecular mechanism involved in IL-6 expression in alveolar type II epithelial cells on TNF-α treatment, which provides a theoretical basis for specific inhibition of IL-6 production at the transcriptional level.

VEGF (Vascular Endothelial Growth Factor) and Fibrotic Lung Disease

Interstitial lung disease (ILD) encompasses a group of heterogeneous diseases characterised by varying degrees of aberrant inflammation and fibrosis of the lung parenchyma. This may occur in isolation, such as in idiopathic pulmonary fibrosis (IPF) or as part of a wider disease process affecting multiple organs, such as in systemic sclerosis. Anti-Vascular Endothelial Growth Factor (anti-VEGF) therapy is one component of an existing broad-spectrum therapeutic option in IPF (nintedanib) and may become part of the emerging therapeutic strategy for other ILDs in the future. This article describes our current understanding of VEGF biology in normal lung homeostasis and how changes in its bioavailability may contribute the pathogenesis of ILD. The complexity of VEGF biology is particularly highlighted with an emphasis on the potential non-vascular, non-angiogenic roles for VEGF in the lung, in both health and disease.

Reactive Oxygen Species, Biomarkers of Microvascular Maturation and Alveolarization, and Antioxidants in Oxidative Lung Injury

The lungs of extremely low gestational age neonates (ELGANs) are deficient in pulmonary surfactant and are incapable of efficient gas exchange necessary for successful transition from a hypoxic intrauterine environment to ambient air. To improve gas exchange and survival, ELGANs often receive supplemental oxygen with mechanical ventilation which disrupts normal lung developmental processes, including microvascular maturation and alveolarization. Factors that regulate these developmental processes include vascular endothelial growth factor and matrix metalloproteinases, both of which are influenced by generation of oxygen byproducts, or reactive oxygen species (ROS). ELGANs are also deficient in antioxidants necessary to scavenge excessive ROS. Thus, the accumulation of ROS in the preterm lungs exposed to prolonged hyperoxia, results in inflammation and development of bronchopulmonary dysplasia (BPD), a form of chronic lung disease (CLD). Despite advances in neonatal care, BPD/CLD remains a major cause of neonatal morbidity and mortality. The underlying mechanisms are not completely understood, and the benefits of current therapeutic interventions are limited. The association between ROS and biomarkers of microvascular maturation and alveolarization, as well as antioxidant therapies in the setting of hyperoxia-induced neonatal lung injury are reviewed in this article.

Effects of intermittent hypoxia and hyperoxia on angiogenesis and lung development in newborn mice

BACKGROUND

Premature birth disrupts hypoxia driven microvascular development that directs alveolar and lung growth. Changes in oxygen exposure after birth can perturb the regulation of angiogenesis leading to bronchopulmonary dysplasia (BPD). We studied the effects of intermittent hypoxia or hyperoxia on HIF and angiogenic gene expression and lung development in newborn mice.

METHODS

Newborn litters were randomized within 12 h of birth to 12% O2 (4 h), 50% O2 (4 h) or 12% O2 (2 h)/50% O2 (2 h) followed by room air (RA) recovery for 20 h. Mice in RA were the control group. The mice were exposed to 6 such cycles (D1-D6) and sacrifice on D7. Whole lung mRNA was isolated and gene expression performed by qRT-PCR (HIF1α/2α/1β; PHD2, Ang1, Tie2, Vegf, VegfR1 & VegfR2) and analyzed by PCR array data analysis web portal. HIF-1α, prolyl hydroxylase-2 and VEGF protein were analyzed in whole lung by ELISA. Lung morphology was assessed by H&E sections and radial alveolar counts; cell proliferation by Ki67 immunostaining.

RESULTS

HIF-1α mRNA and VEGF protein were significantly downregulated in the 50% O2 group; VEGF mRNA and protein were significantly downregulated in the 12% O2-50% O2 group; Ang-1 and its receptor mRNA expression were downregulated in 12% O2 and 12% O2-50% O2 groups. 50% O2 (hyperoxia) and 12% O2-50% O2 (hypoxia-hyperoxia) groups demonstrated alveolar simplification by RAC and the same groups had decreased cell proliferation by Ki67 staining compared to RA and hypoxia (12% O2) groups.

CONCLUSIONS

Downregulation of HIF and angiogenic gene expression with associated changes in lung histology following intermittent hypoxia-hyperoxia is likely an important contributing factor in the development of BPD.

Thyroid Transcription Factor 1 Reprograms Angiogenic Activities of Secretome

Through both gain- and loss-of-TTF-1 expression strategies, we show that TTF-1 positively regulates vascular endothelial growth factor (VEGF) and that the VEGF promoter element contains multiple TTF-1-responsive sequences. The major signaling receptor for VEGF, i.e VEGFR2, also appears to be under a direct and positive regulation of TTF-1. The TTF-1-dependent upregulation of VEGF was moderately sensitive to rapamycin, implicating a partial involvement of mammalian target of rapamycin (mTOR). However, hypoxia did not further increase the secreted VEGF level of the TTF-1⁺ lung cancer cells. The TTF-1-induced VEGF upregulation occurs in both compartments (exosomes and exosome-depleted media (EDM)) of the conditioned media. Surprisingly, the EDM of TTF-1⁺ lung cancer cells (designated EDM-TTF-1⁺) displayed an anti-angiogenic activity in the endothelial cell tube formation assay. Mechanistic studies suggest that the increased granulocyte-macrophage colony-stimulating factor (GM-CSF) level in the EDM-TTF-1⁺ conferred the antiangiogenic activities. In human lung cancer, the expression of TTF-1 and GM-CSF exhibits a statistically significant and positive correlation. In summary, this study provides evidence that TTF-1 may reprogram lung cancer secreted proteome into an antiangiogenic state, offering a novel basis to account for the long-standing observation of favorable prognosis associated with TTF-1⁺ lung adenocarcinomas.

A topical aqueous oxygen emulsion stimulates granulation tissue formation in a porcine second-degree burn wound

BACKGROUND

Oxygen is an essential substance for wound healing. Limited studies have shown that topical oxygen can influence healing. This study evaluated the effects of a Topical Oxygen Emulsion (TOE) on burn wound healing.

METHODS

A porcine second-degree burn wound model was used in the study. Burn wounds were randomly assigned to TOE, vehicle control, and no-treatment (air) groups. Effects of TOE on the granulation tissue formation and angiogenesis were studied using hematoxylin and eosin histological analysis. Protein production and gene expression of types I and III collagen and vascular endothelial growth factor (VEGF) were determined using immunofluorescent staining and Reverse Transcription and Polymerase Chain Reaction (RT-PCR), respectively.

RESULTS

The TOE treated wounds exhibited better angiogenesis and granulation tissue formation by histology examination. The immunofluorescence staining and RT-PCR analysis demonstrated that protein production and mRNA expression of VEGF and collagen III were significantly higher in TOE treatment group than vehicle alone and air control groups, while there was no significant difference in the level of collagen I.

CONCLUSIONS

Our data demonstrate that TOE enhances burn wound healing via stimulating the expression of VEGF and type III collagen and strongly indicates the potential use of TOE in wounds.

Regulation of tissue morphogenesis by endothelial cell-derived signals

Endothelial cells (ECs) form an extensive network of blood vessels that has numerous essential functions in the vertebrate body. In addition to their well-established role as a versatile transport network, blood vessels can induce organ formation or direct growth and differentiation processes by providing signals in a paracrine (angiocrine) fashion. Tissue repair also requires the local restoration of vasculature. ECs are emerging as important signaling centers that coordinate regeneration and help to prevent deregulated, disease-promoting processes. Vascular cells are also part of stem cell niches and have key roles in hematopoiesis, bone formation, and neurogenesis. Here, we review these newly identified roles of ECs in the regulation of organ morphogenesis, maintenance, and regeneration.

Neonatal hyperoxia stimulates the expansion of alveolar epithelial type II cells

Supplemental oxygen used to treat infants born prematurely disrupts angiogenesis and is a risk factor for persistent pulmonary disease later in life. Although it is unclear how neonatal oxygen affects development of the respiratory epithelium, alveolar simplification and depletion of type II cells has been observed in adult mice exposed to hyperoxia between postnatal Days 0 and 4. Because hyperoxia inhibits cell proliferation, we hypothesized that it depleted the adult lung of type II cells by inhibiting their proliferation at birth. Newborn mice were exposed to room air (RA) or hyperoxia, and the oxygen-exposed mice were recovered in RA. Hyperoxia stimulated mRNA expressed by type II (Sftpc, Abca3) and type I (T1α, Aquaporin 5) cells and inhibited Pecam expressed by endothelial cells. 5-Bromo-2'-deoxyuridine labeling and fate mapping with enhanced green fluorescence protein controlled statically by the Sftpc promoter or conditionally by the Scgb1a1 promoter revealed increased Sftpc and Abca3 mRNA seen on Day 4 reflected an increase in expansion of type II cells shortly after birth. When mice were returned to RA, this expanded population of type II cells was slowly depleted until few were detected by 8 weeks. These findings reveal that hyperoxia stimulates alveolar epithelial cell expansion when it disrupts angiogenesis. The loss of type II cells during recovery in RA may contribute to persistent pulmonary diseases such as those reported in children born preterm who were exposed to supplemental oxygen.

Multiple wall in-folds sub-divide single segments during capillary regression in hyperoxic acute lung injury

The present study provides further insight into the structural processes that remodel pulmonary capillaries in the injured adult lung. Early in hyperoxia acute lung injury (HALI), many sub-dividing segments are present throughout the capillary network before segment occlusion and loss predominate and capillary density decreases later in the period. A second segment sub-division triggered in regenerating capillaries after air breathing (post-HALI) demonstrates a similar mechanism of organization at a time of contrasting change in the capillary density. As we have previously reported, the process of segment sub-division includes in-folding of the endothelial-epithelial surface (alveolar-capillary membrane) to form inter-luminal structures (ILSs) and loops, with loop separation increasing segment number. Unexpectedly, the findings support remodeling of the capillary density by wall in-folding in acute lung injury, demonstrating a similar mechanism in capillary regression as well as in regeneration in the adult lung.

Vascular endothelial growth factor in acute lung injury and acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is the most severe form of lung injury, characterised by alveolar oedema and vascular permeability, in part due to disruption of the alveolar capillary membrane integrity. Vascular endothelial growth factor (VEGF) was originally identified as a vascular permeability factor and has been implicated in the pathogenesis of acute lung injury/ARDS. This review describes our current knowledge of VEGF biology and summarises the literature investigating the potential role VEGF may play in normal lung maintenance and in the development of lung injury.

Cytoskeletal dynamics and lung fluid balance

This article examines the role of the endothelial cytoskeleton in the lung's ability to restrict fluid and protein to vascular space at normal vascular pressures and thereby to protect lung alveoli from lethal flooding. The barrier properties of microvascular endothelium are dependent on endothelial cell contact with other vessel-wall lining cells and with the underlying extracellular matrix (ECM). Focal adhesion complexes are essential for attachment of endothelium to ECM. In quiescent endothelial cells, the thick cortical actin rim helps determine cell shape and stabilize endothelial adherens junctions and focal adhesions through protein bridges to actin cytoskeleton. Permeability-increasing agonists signal activation of "small GTPases" of the Rho family to reorganize the actin cytoskeleton, leading to endothelial cell shape change, disassembly of cortical actin rim, and redistribution of actin into cytoplasmic stress fibers. In association with calcium- and Src-regulated myosin light chain kinase (MLCK), stress fibers become actinomyosin-mediated contractile units. Permeability-increasing agonists stimulate calcium entry and induce tyrosine phosphorylation of VE-cadherin (vascular endothelial cadherin) and β-catenins to weaken or pull apart endothelial adherens junctions. Some permeability agonists cause latent activation of the small GTPases, Cdc42 and Rac1, which facilitate endothelial barrier recovery and eliminate interendothelial gaps. Under the influence of Cdc42 and Rac1, filopodia and lamellipodia are generated by rearrangements of actin cytoskeleton. These motile evaginations extend endothelial cell borders across interendothelial gaps, and may initiate reannealing of endothelial junctions. Endogenous barrier protective substances, such as sphingosine-1-phosphate, play an important role in maintaining a restrictive endothelial barrier and counteracting the effects of permeability-increasing agonists.

Alveolar oxygen tension and angio-architecture of the distal adult lung

The present study demonstrates the fine structure of pulmonary capillaries first injured and then undergoing growth in response to a change in the ambient alveolar oxygen tension. Breathing a high fraction of inspired oxygen (FiO2 0.75) triggers restriction by endothelial cell injury and effacement leading to segment narrowing and shortening and segment loss as demonstrated by a fall in density. Subsequently, breathing a relatively low fraction (FiO2 0.21) triggers capillary assembly (angiogenesis), which reverses the changes. The data underscore the structural reprogramming (reduction and restoration) of pulmonary capillaries in response to significant shifts in oxygen tension.

Comparative molecular developmental aspects of the mammalian- and the avian lungs, and the insectan tracheal system by branching morphogenesis: recent advances and future directions

Gas exchangers fundamentally form by branching morphogenesis (BM), a mechanistically profoundly complex process which derives from coherent expression and regulation of multiple genes that direct cell-to-cell interactions, differentiation, and movements by signaling of various molecular morphogenetic cues at specific times and particular places in the developing organ. Coordinated expression of growth-instructing factors determines sizes and sites where bifurcation occurs, by how much a part elongates before it divides, and the angle at which branching occurs. BM is essentially induced by dualities of factors where through feedback- or feed forward loops agonists/antagonists are activated or repressed. The intricate transactions between the development orchestrating molecular factors determine the ultimate phenotype. From the primeval time when the transformation of unicellular organisms to multicellular ones occurred by systematic accretion of cells, BM has been perpetually conserved. Canonical signalling, transcriptional pathways, and other instructive molecular factors are commonly employed within and across species, tissues, and stages of development. While much still remain to be elucidated and some of what has been reported corroborated and reconciled with rest of existing data, notable progress has in recent times been made in understanding the mechanism of BM. By identifying and characterizing the morphogenetic drivers, and markers and their regulatory dynamics, the elemental underpinnings of BM have been more precisely explained. Broadening these insights will allow more effective diagnostic and therapeutic interventions of developmental abnormalities and pathologies in pre- and postnatal lungs. Conservation of the molecular factors which are involved in the development of the lung (and other branched organs) is a classic example of nature's astuteness in economically utilizing finite resources. Once purposefully formed, well-tested and tried ways and means are adopted, preserved, and widely used to engineer the most optimal phenotypes. The material and time costs of developing utterly new instruments and routines with every drastic biological change (e.g. adaptation and speciation) are circumvented. This should assure the best possible structures and therefore functions, ensuring survival and evolutionary success.

Mesenchymal stem cell transplantation increases expression of vascular endothelial growth factor in papain-induced emphysematous lungs and inhibits apoptosis of lung cells

BACKGROUND

Pulmonary emphysema is characterized by loss of alveolar structures. We have found that bone marrow (BM) mesenchymal stem cell (MSC) transplantation ameliorates papain-induced pulmonary emphysema. However, the underlying mechanism is not completely understood. It has been shown that blocking the vascular endothelial growth factor (VEGF) signaling pathway leads to apoptosis of lung cells and pulmonary emphysema, and MSC are capable of secreting VEGF. We hypothesized that MSC transplantation may have a protective effect on pulmonary emphysema by increasing VEGF-A expression and inhibiting apoptosis of lung cells.

METHODS

We examined the morphology and expression of VEGF-A in rat lung after papain treatment and MSC transplantation. We also used a co-culture system in which MSC and cells prepared from papain-treated lungs or control lungs were cultured together. The levels of VEGF-A in cells and culture medium were determined, and apoptosis of cultured lung cells was evaluated.

RESULTS

VEGF-A expression in rat lungs was decreased after papain treatment, which was partly rescued by MSC transplantation. MSC production of VEGF-A was increased when MSC were co-cultured with cells prepared from papain-treated lungs. Furthermore, the apoptosis of papain-treated lung cells was inhibited when co-cultured with MSC. The induction of MSC production of VEGF-A by papain-treated lung cells was inhibited by adding anti-tumor necrosis factor (TNF)-alpha antibody to the medium.

CONCLUSIONS

The protective effect of MSC transplantation on pulmonary emphysema may be partly mediated by increasing VEGF-A expression and inhibiting the apoptosis of lung cells. TNF-alpha released from papain-treated lung cells induces MSC to secret VEGF-A.

Vascular endothelial growth factor in bronchoalveolar lavage fluid in sulfur mustard exposed lung patients

OBJECTIVES

To determine the levels of vascular endothelial growth factor isoform consisting of 165 amino acids (VEGF165) in Bronchoalveolar Lavage Fluid from Mustard Exposed Patients.

METHODS

Bronchoscopy with Bronchoalveolar Lavage was performed on sulphur mustard exposed patients. A total of 39 patients with documented exposure to Sulfur Mustard during the Iran-Iraq war participated in this study, of which 38 patients were males and one patient was female.

RESULTS

The mean±SD age of patients was 41 ± 6.6 years. The mean time after exposure to sulfur mustard was 19 ±1.7 years. Eighteen patients had concomitant war injuries but they were not related to the respiratory system. While Twenty-two patients had a history of submassive persistent hemoptysis. There was no case with massive hemoptysis. Most of the patients had small airway obstruction (FEV1/FVC% = 78.14 ± 9.76 and FEV1% =82.79±18.23). Twenty-three patients had significant air trapping in the chest. High Resolution Computed Tomography was compatible with BOS. VEGF165 concentrations in BALF were 36.87 ± 34.68 pg/ml. When corrected to total protein of Bronchoalveolar Lavage Fluid (BALF) it was 0.76 ± 0.70 pg/mg. BALF of VEGF did not correlate with hemoptysis or air trapping in chest HRCT. Thus, there was also no correlation between level of VEGF165 in BALF and any of PFT indexes (FVC, FEV1, MMEF or PEF).

CONCLUSIONS

Although VEGF is one of the cytokines which has an important role in chronic pulmonary disorders, it seems that it has no essential role in the severity of Mustard Lung Disease.

Thioredoxin-interacting protein inhibits hypoxia-inducible factor transcriptional activity

Vascular endothelial growth factor (VEGF) is required for proper lung development and is transcriptionally regulated in alveolar epithelial cells by hypoxia-inducible factor (HIF). Previous findings in a newborn mouse model of bronchopulmonary dysplasia (BPD) suggest that thioredoxin-interacting protein (Txnip) is a novel regulator of VEGF expression. The present studies were designed to test the hypothesis that Txnip negatively regulates VEGF through effects on HIF-mediated gene expression. To test this hypothesis, we first examined the levels of VEGF and Txnip protein in the lungs of 1-day-old newborn mice and E19 embryos and detected a significant inverse correlation. To elucidate the mechanisms underlying this relationship, we studied the effects of Txnip overexpression on HIF-mediated transcription using murine lung epithelial (MLE-12) cells. Overexpression of Txnip inhibited HIF-mediated reporter activity in both hypoxia and room air. Suppression of HIF activity by Txnip seemed to be independent of the ability of Txnip to bind to thioredoxin. Thus, our studies support a model in which Txnip is a potentially critical regulator of HIF-mediated gene transcription in the murine lung. Alterations in Txnip expression could alter lung VEGF expression in prematurely born human infants and contribute to the development of BPD.

Evidence-based recommendations for the use of topical oxygen therapy in the treatment of lower extremity wounds

Topical oxygen therapy provides another tool in the armamentarium of clinicians treating refractory lower extremity wounds. Devices suitable for providing topical oxygen therapy in a clinical setting have recently become available. This article reviews the evidence to justify the use of this treatment modality, including in vitro, preclinical data, and clinical data. It also provides a protocol for how to administer topical oxygen therapy as well as guidance on patient selection and management to optimize outcomes. Randomized controlled trials are not yet reported and clearly necessary. The current body of evidence suggests that topical oxygen therapy may be considered as a second line of therapy for refractory wounds.

Vascular Endothelial Growth Factor (VEGF) isoform expression and activity in human and murine lung injury

BACKGROUND

The properties of vascular endothelial growth factor (VEGF) as a potent vascular permogen and mitogen have led to investigation of its potential role in lung injury. Alternate spliced VEGF transcript generates several isoforms with potentially differing functions. The purpose of this study was to determine VEGF isoform expression and source in normal and ARDS subjects and investigate the expression and regulation of VEGF isoforms by human alveolar type 2 (ATII) cells.

METHODS

VEGF protein expression was assessed immunohistochemically in archival normal and ARDS human lung tissue. VEGF isoform mRNA expression was assessed in human and murine lung tissue. Purified ATII cells were cultured with proinflammatory cytokines prior to RNA extraction/cell supernatant sampling/proliferation assay.

MEASUREMENTS AND MAIN RESULTS

VEGF was expressed on alveolar epithelium, vascular endothelium and alveolar macrophages in normal and ARDS human lung tissue. Increases in VEGF expression were detected in later ARDS in comparison to both normal subjects and early ARDS (p < 0.001). VEGF121, VEGF165 and VEGF189 isoform mRNA expression increased in later ARDS (p < 0.05). The ratio of soluble to cell-associated isoforms was lower in early ARDS than normal subjects and later ARDS and also in murine lung injury. ATII cells constitutionally produced VEGF165 and VEGF121 protein which was increased by LPS (p < 0.05). VEGF165 upregulated ATII cell proliferation (p < 0.001) that was inhibited by soluble VEGF receptor 1 (sflt) (p < 0.05).

CONCLUSION

These data demonstrate that changes in VEGF isoform expression occur in ARDS which may be related to their production by and mitogenic effect on ATII cells; with potentially significant clinical consequences.

Alterations of the thioredoxin system by hyperoxia: implications for alveolar development

Alterations in vascular endothelial growth factor (VEGF) contribute to alveolar simplification seen in animal models of bronchopulmonary dysplasia, and VEGF expression is redox regulated by thioredoxin (Trx)-1 in other diseases. The present studies tested the hypothesis that exposure to 85% O2 negatively impacts the Trx1 system and VEGF expression in the lungs of newborn mice. There was no effect of fraction of inspired oxygen on lung Trx1 or Trx reductase-1 protein levels; however, lung Trx1 protein was predominantly oxidized in the lungs of newborn mice exposed to 85% O2 by 24 hours of exposure. In room air (RA), lung Trx interacting protein (Txnip) levels decreased developmentally through Day 7 (1.0 +/- 0.06 [Day 1] vs. 0.49 +/- 0.10 [Day 3] vs. 0.29 +/- 0.03 [Day 7]; P < 0.01), whereas VEGF expression increased (1.25 +/- 0.16 [Day 1] vs. 4.35 +/- 1.51 [Day 3] vs. 13.23 +/- 0.37 [Day 7]; P < 0.01). Newborn mice exposed to 85% O2 had no developmental decrease in Txnip protein levels and a delayed increase in VEGF protein levels. Lung Txnip and VEGF protein levels were different than in corresponding RA controls at Day 3, before the detection of lung morphologic abnormalities in our model. Txnip and VEGF protein levels were inversely correlated in both the RA and hyperoxia-exposed groups (n = 18; R = -0.66; P = 0.003). In conclusion, oxidation of Trx1 and sustained Txnip expression in the lungs of newborn mice exposed to 85% oxygen is likely to severely attenuate normal Trx1 function. The inverse correlation of Txnip with VEGF expression suggests that decreased Trx1 function contributes to the observed lung developmental abnormalities.

A protocol for a lung neovascularization model in rodents

By providing insight into the cellular events of vascular injury and repair, experimental model systems seek to promote timely therapeutic strategies for human disease. The goal of many current studies of neovascularization is to identify cells critical to the process and their role in vascular channel assembly. We propose here a protocol to analyze, in an in vivo rodent model, vessel and capillary remodeling (reorganization and growth) in the injured lung. Sequential analyses of stages in the assembly of vascular structures, and of relevant cell types, provide further opportunities to study the molecular and cellular determinants of lung neovascularization.

Serum-free differentiation of murine embryonic stem cells into alveolar type II epithelial cells

Alveolar type II (AT2) epithelial cells have important functions including the production of surfactant and regeneration of lost alveolar type I epithelial cells. The ability of in vitro production of AT2 cells would offer new therapeutic options in treating pulmonary injuries and disorders including genetically based surfactant deficiencies. Aiming at the generation of AT2-like cells, the differentiation of murine embryonic stem cells (mESCs) toward mesendodermal progenitors (MEPs) was optimized using a "Brachyury-eGFP-knock in" mESC line. eGFP expression demonstrated generation of up to 65% MEPs at day 4 after formation of embryoid bodies (EBs) under serum-free conditions. Plated EBs were further differentiated into AT2-like cells for a total of 25 days in serum-free media resulting in the expression of endodermal marker genes (FoxA2, Sox17, TTR, TTF-1) and of markers for distal lung epithelium (surfactant proteins (SP-) A, B, C, and D, CCSP, aquaporin 5). Notably, expression of SP-C as the only known AT2 cell specific marker could be detected after serum-induction as well as under serum-free conditions. Cytoplasmic localization of SP-C was demonstrated by confocal microscopy. The presence of AT2-like cells was confirmed by electron microscopy providing evidence for polarized cells with apical microvilli and lamellar body-like structures. Our results demonstrate the differentiation of AT2-like cells from mESCs after serum-induction and under serum-free conditions. The established serum-free differentiation protocol will facilitate the identification of key differentiation factors leading to a more specific and effective generation of AT2-like cells from ESCs.

Vascular endothelial growth factor in epithelial lining fluid of patients with acute respiratory distress syndrome

BACKGROUND AND OBJECTIVE

Vascular endothelial growth factor (VEGF) is known to contribute to the development of pulmonary oedema, and has been suggested to have a protective role against lung injury. To determine the role of VEGF in acute lung injury (ALI) and ARDS, VEGF levels were measured in lung epithelial lining fluid (ELF) collected from patients with ALI/ARDS.

METHODS

Forty patients with ALI/ARDS underwent bronchoscopic microsampling to collect ELF on days 0 (onset of ALI/ARDS), 1, 3, 5, 7 and 10, unless the patient was extubated or had died. Twelve patients, who underwent bronchoscopy for examination of small, peripheral pulmonary nodules, served as controls.

RESULTS

The initial (day 0) levels of VEGF in ELF of the ALI/ARDS patients who survived and those who did not were 5.5 ng/mL (IQR: 2.3-19.7) and 1.7 ng/mL (IQR: 0.0-6.4), respectively. On days 0, 5, 7 and 10, the VEGF levels in ELF were significantly greater in survivors than in non-survivors (P < 0.05). VEGF levels on days 1 and 3 did not differ between survivors and non-survivors. There was no significant difference in ELF VEGF levels between control subjects and patients with ALI/ARDS at any time point. Lung injury score was inversely correlated with VEGF concentration in ELF (P < 0.001).

CONCLUSIONS

In patients with ALI/ARDS, elevated VEGF levels in ELF may predict a better outcome. Increased production of VEGF in the injured lung may contribute to resolution of inflammation in the lung.

Topical oxygen therapy induces vascular endothelial growth factor expression and improves closure of clinically presented chronic wounds

1. Chronic wounds, especially in diabetics, represent a serious threat to human health. 2. Correcting a compromised state of tissue oxygenation by the administration of supplemental O(2) is known to benefit wound healing. Beyond its role as a nutrient and antibiotic, O(2) supports wound healing by driving redox signaling. 3. Hyperbaric oxygen (HBO) therapy is widely used and approved by Center for Medicare and Medicaid Services to treat specific ulcerations. The current literature supports the notion that approaches to topically oxygenate wounds may be productive. 4. Here, we present the results of two simultaneous studies testing the effects of HBO and portable topical oxygen (TO) therapies. These two therapeutic approaches have several contrasting features. 5. In total, 1854 patients were screened in outpatient wound clinics for non-randomized enrolments into the HBO (n = 32; 31% diabetic) and TO (n = 25; 52% diabetic) studies. 6. Under the conditions of the present study, HBO treatment seemed to benefit some wounds while not benefiting others. Overall, HBO did not result in statistically significant improvements in wound size in the given population over the time monitored in the present study. 7. However, TO significantly improved wound size. Among the three O(2)-sensitive genes (VEGF, TGFbeta1 and COL1A1) studied in wound edge tissue biopsies, TO treatment was associated with higher VEGF165 expression in healing wounds. Expression of the other genes mentioned was not affected by TO. There was no significant change in the expression levels of any of genes studied in patients in the HBO study. This establishes a link between VEGF gene expression and healing outcome for TO therapy. 8. Taken together, the present study provides evidence demonstrating that TO treatment benefits wound healing in patients suffering from chronic wounds. Treatment with TO is associated with an induction of VEGF expression in wound edge tissue and an improvement in wound size.

Protective role of vascular endothelial growth factor in endotoxin-induced acute lung injury in mice

BACKGROUND

Vascular endothelial growth factor (VEGF), a substance that stimulates new blood vessel formation, is an important survival factor for endothelial cells. Although overexpressed VEGF in the lung induces pulmonary edema with increased lung vascular permeability, the role of VEGF in the development of acute lung injury remains to be determined.

METHODS

To evaluate the role of VEGF in the pathogenesis of acute lung injury, we first evaluated the effects of exogenous VEGF and VEGF blockade using monoclonal antibody on LPS-induced lung injury in mice. Using the lung specimens, we performed TUNEL staining to detect apoptotic cells and immunostaining to evaluate the expression of apoptosis-associated molecules, including caspase-3, Bax, apoptosis inducing factor (AIF), and cytochrome C. As a parameter of endothelial permeability, we measured the albumin transferred across human pulmonary artery endothelial cell (HPAEC) monolayers cultured on porous filters with various concentrations of VEGF. The effect of VEGF on apoptosis HPAECs was also examined by TUNEL staining and active caspase-3 immunoassay.

RESULTS

Exogenous VEGF significantly decreased LPS-induced extravascular albumin leakage and edema formation. Treatment with anti-VEGF antibody significantly enhanced lung edema formation and neutrophil emigration after intratracheal LPS administration, whereas extravascular albumin leakage was not significantly changed by VEGF blockade. In lung pathology, pretreatment with VEGF significantly decreased the numbers of TUNEL positive cells and those with positive immunostaining of the pro-apoptotic molecules examined. VEGF attenuated the increases in the permeability of the HPAEC monolayer and the apoptosis of HPAECs induced by TNF-alpha and LPS. In addition, VEGF significantly reduced the levels of TNF-alpha- and LPS-induced active caspase-3 in HPAEC lysates.

CONCLUSION

These results suggest that VEGF suppresses the apoptosis induced by inflammatory stimuli and functions as a protective factor against acute lung injury.

Genotypes and haplotypes of the VEGF gene are associated with higher mortality and lower VEGF plasma levels in patients with ARDS

BACKGROUND

Endothelial injury is an important prognostic factor in acute respiratory distress syndrome (ARDS). Vascular endothelial growth factor (VEGF) plays a critical role in endothelial destruction and angiogenesis. Genetic variations of the VEGF gene have been associated with VEGF production. A study was undertaken to investigate the impact of VEGF gene polymorphisms on the clinical outcomes of ARDS.

METHODS

Three VEGF polymorphisms (-460C/T, +405C/G and +936C/T) were determined in 1253 patients in an intensive care unit with risk factors for ARDS, 394 of whom developed ARDS. Patients were followed for assessment of 60 day survival. Plasma VEGF levels were measured in 71 patients with ARDS.

RESULTS

The +936TT (OR 4.29, 95% CI 1.12 to 16.40, p = 0.03) and +936CT+TT (OR 1.98, 95% CI 1.14 to 3.42, p = 0.01) genotypes were significantly associated with increased mortality from ARDS. Plasma VEGF levels in patients with ARDS with the +936CT+TT genotype were significantly lower than in subjects with the +936CC genotype (median 49 (IQR 16-98) pg/ml vs 112 (IQR 47-162) pg/ml, p = 0.02). At the haplotype level, haplotype TCT (-460T+405C+936T) was significantly associated with a higher rate of mortality (OR 2.89, 95% CI 1.30 to 6.43, p = 0.009) and haplotype CGT (-460C+405G+936T) was associated less strongly with increased mortality (OR 1.90, 95% CI 0.94 to 3.83, p = 0.07) in patients with ARDS. Lower plasma VEGF levels were correlated with the probability of haplotype CGT (coefficient = -0.26, p<0.05), but the same trend of correlation was not significant to haplotype TCT.

CONCLUSIONS

VEGF polymorphisms may contribute to the prognosis and inter-individual variations in circulating VEGF levels in patients with ARDS.

Bronchopulmonary dysplasia: where have all the vessels gone? Roles of angiogenic growth factors in chronic lung disease

Bronchopulmonary dysplasia and emphysema are significant global health problems at the extreme stages of life. Both are characterized by arrested alveolar development or loss of alveoli, respectively. Both lack effective treatment strategies. Knowledge about the genetic control of branching morphogenesis in mammals derives from investigations of the respiratory system in Drosophila, but mechanisms that regulate alveolar development remain poorly understood. Even less is known about regulation of the growth and development of the pulmonary vasculature. Understanding how alveoli and the underlying capillary network develop, and how these mechanisms are disrupted in disease states, are critical for developing effective therapies for lung diseases characterized by impaired alveolar structure. Recent observations have challenged old notions that the development of the blood vessels in the lung passively follows that of the airways. Rather, increasing evidence suggests that lung blood vessels actively promote alveolar growth during development and contribute to the maintenance of alveolar structures throughout postnatal life. Our working hypothesis is that disruption of angiogenesis impairs alveolarization, and that preservation of vascular growth and endothelial survival promotes growth and sustains the architecture of the distal airspace. Furthermore, the explosion of interest in stem cell biology suggests potential roles for endothelial progenitor cells in the pathogenesis or treatment of lung vascular disease. In this Pulmonary Perspective, we review recent data on the importance of the lung circulation, specifically examining the relationship between dysmorphic vascular growth and impaired alveolarization, and speculate on how these new insights may lead to novel therapeutic strategies for bronchopulmonary dysplasia.

Genetic basis of murine responses to hyperoxia-induced lung injury

To evaluate the effect of genetic background on oxygen (O2) toxicity, nine genetically diverse mouse strains (129/SvIm, A/J, BALB/cJ, BTBR+(T)/tf/tf, CAST/Ei, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ) were exposed to more than 99% O2 for 72 h. Immediately following the hyperoxic challenge, the mouse strains demonstrated distinct pathophysiologic responses. The BALB/cJ and CAST/Ei strains, which were the only strains to demonstrate mortality from the hyperoxic challenges, were also the only strains to display significant neutrophil infiltration into their lower respiratory tract. In addition, the O2-challenged BALB/cJ and CAST/Ei mice were among six strains (A/J, BALB/cJ, CAST/Ei, BTBR+(T)/tf/tf, DBA/2J, and C3H/HeJ) that had significantly increased interleukin 6 concentrations in the whole lung lavage fluid and were among all but one strain that had large increases in lung permeability compared with air-exposed controls. In contrast, the DBA/2J strain was the only strain not to have any significant alterations in lung permeability following hyperoxic challenge. The expression of the extracellular matrix proteins, including collagens I, III, and IV, fibronectin I, and tenascin C, also varied markedly among the mouse strains, as did the activities of total superoxide dismutase (SOD) and manganese-SOD (Mn-SOD or SOD2). These data suggest that the response to O2 depends, in part, on the genetic background and that some of the strains analyzed can be used to identify specific loci and genes underlying the response to O2.

Type II epithelial cells are critical target for hyperoxia-mediated impairment of postnatal lung development

Type II epithelial cells are essential for lung development and remodeling, as they are precursors for type I cells and can produce vascular mitogens. Although type II cell proliferation takes place after hyperoxia, it is unclear why alveolar remodeling occurs normally in adults whereas it is permanently disrupted in newborns. Using a line of transgenic mice whose type II cells could be identified by their expression of enhanced green fluorescent protein and endogenous expression of surfactant proteins, we investigated the age-dependent effects of hyperoxia on type II cell proliferation and alveolar repair. In adult mice, type II cell proliferation was low during room air and hyperoxia exposure but increased during recovery in room air and then declined to control levels by day 7. Eight weeks later, type II cell number and alveolar compliance were indistinguishable from those in room air controls. In newborn mice, type II cell proliferation markedly increased between birth and postnatal day 7 before declining by postnatal day 14. Exposure to hyperoxia between postnatal days 1 and 4 inhibited type II cell proliferation, which resumed during recovery and was aberrantly elevated on postnatal day 14. Eight weeks later, recovered mice had 70% fewer type II cells and 30% increased lung compliance compared with control animals. Recovered mice also had higher levels of T1alpha, a protein expressed by type I cells, with minimal changes detected in genes expressed by vascular cells. These data suggest that perinatal hyperoxia adversely affects alveolar development by disrupting the proper timing of type II cell proliferation and differentiation into type I cells.

Hyperbaric oxygen induces vascular endothelial growth factor and reduces liver injury in regenerating rat liver after partial hepatectomy

BACKGROUND/AIMS

The aim of this study was to investigate the effect and the mechanism of hyperbaric oxygen treatment on regenerating rat liver after partial hepatectomy (PH).

METHODS

Wistar rats underwent a 70% PH, followed by treatment with hyperbaric oxygen starting 8 h after PH. The regenerated liver weight and serum parameters were compared. Proliferation of both hepatocytes and sinusoidal endothelial cell (SEC) was also monitored by evaluating the proliferating cell nuclear antigen (PCNA) labeling index. Furthermore, the hepatic adenosine triphosphate levels and vascular endothelial growth factor (VEGF) protein expression were analyzed at different times.

RESULTS

Hyperbaric oxygen treatment significantly reduced the serum alanine aminotransferase levels at 24 h, total bilirubin and total bile acid levels at 48 and 72 h, respectively. No significant differences in the hepatic adenosine triphosphate levels, the restitution of liver weight, or PCNA positive hepatocytes were observed between the two groups. The PCNA positive SEC, in contrast, was significantly increased in the hyperbaric oxygen group at 48h, furthermore, the hyperbaric oxygen treatment significantly increased the expression of VEGF protein in the regenerating liver at 24 and 48 h.

CONCLUSIONS

Hyperbaric oxygen treatment can be considered as a therapeutic modality after massive PH.

Cytokines in tolerance to hyperoxia-induced injury in the developing and adult lung

Cytokines are peptides that are produced by virtually every nucleated cell type in the body, possess overlapping biological activities, exert different effects at different concentrations, can either synergize or antagonize the effects of other cytokines, are regulated in a complex manner, and function via cytokine cascades. Hyperoxia-induced acute lung injury (HALI) is characterized by an influx of inflammatory cells, increased pulmonary permeability, and endothelial and epithelial cell injury/death. Some of these effects are orchestrated by cytokines. There are significant differences in the response of the developing versus the adult lung to hyperoxia. We review here cytokines (and select growth factors) that are involved in tolerance toward HALI in animal models. Increased cytokine expression and release have a cascade effect in HALI. IL-1 precedes the increase in IL-6 and CINC-1/IL-8 and this seems to predate the influx of inflammatory cells. Inflammatory cells in the alveolar space amplify the lung damage. Other cytokines that are primarily involved in this inflammatory response include IFN-gamma, MCP-1, and MIP-2. Certain cytokines (and growth factors) seem to ameliorate HALI by affecting cell death pathways. These include GM-CSF, KGF, IL-11, IL-13, and VEGF. There are significant differences in the type and temporal sequence of cytokine expression and release in the adult and newborn lung in response to hyperoxia. The newborn lung is greatly resistant to hyperoxia compared to the adult. The delayed increase in lung IL-1 and IL-6 in the newborn could induce protective factors that would help in the resolution of hyperoxia-induced injury. Designing a therapeutic approach to counteract oxygen toxicity in the adult and immature lung first needs understanding of the unique responses in each scenario.

Vascular endothelial growth factor (VEGF) in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS): paradox or paradigm?

Acute respiratory distress syndrome (ARDS), the most severe form of acute lung injury (ALI), remains a devastating condition with a high mortality. It is characterised by alveolar injury and increased pulmonary vascular permeability. Vascular endothelial cell growth factor (VEGF) was identified by its properties to increase permeability and act as a cellular growth factor, hence its potential for a key role in the pathogenesis of ALI/ARDS. This review describes the basic biology of VEGF and its receptors as an essential prerequisite to discussing the available and sometimes paradoxical published data, before considering a paradigm for the role of VEGF in the human lung.