VEGF-A and -C but not -B mediate increased vascular permeability in preserved lung grafts

Altered hypoxia-induced cellular responses and inflammatory profile in lung fibroblasts from COPD patients compared to control subjects

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease characterized by chronic bronchitis, emphysema and vascular remodelling. The disease is associated with hypoxia, inflammation and oxidative stress. Lung fibroblasts are important cells in remodelling processes in COPD, as main producers of extracellular matrix proteins but also in synthesis of growth factors and inflammatory mediators.

METHODS

In this study we aimed to investigate if there are differences in how primary distal lung fibroblasts obtained from COPD patients and healthy subjects respond to hypoxia (1% O2) and pro-fibrotic stimuli with TGF-β1 (10 ng/mL). Genes and proteins associated with oxidative stress, endoplasmic reticulum stress, remodelling and inflammation were analysed with RT-qPCR and ELISA.

RESULTS

Hypoxia induced differences in expression of genes involved in oxidative stress (SOD3 and HIF-1α), ER stress (IRE1, PARK and ATF6), apoptosis (c-Jun and Bcl2) and remodelling (5HTR2B, Collagen7 and VEGFR2) in lung fibroblasts from COPD subjects compared to control subjects, where COPD fibroblasts were in general less responsive. The release of VEGF-C was increased after hypoxia, whereas TGF-β significantly reduced the VEGF response to hypoxia and the release of HGF. COPD fibroblasts had a higher release of IL-6, IL-8, MCP-1 and PGE2 compared to lung fibroblasts from control subjects. The release of inflammatory mediators was less affected by hypoxia, whereas TGFβ1 induced differences in inflammatory profile between fibroblasts from COPD and control subjects.

CONCLUSION

These results suggest that there is an alteration of gene regulation of various stress responses and remodelling associated mediator release that is related to COPD and hypoxia, where fibroblasts from COPD patients have a deficient response.

Primary Graft Dysfunction: The Role of Aging in Lung Ischemia-Reperfusion Injury

Transplant centers around the world have been using extended criteria donors to remedy the ongoing demand for lung transplantation. With a rapidly aging population, older donors are increasingly considered. Donor age, at the same time has been linked to higher rates of lung ischemia reperfusion injury (IRI). This process of acute, sterile inflammation occurring upon reperfusion is a key driver of primary graft dysfunction (PGD) leading to inferior short- and long-term survival. Understanding and improving the condition of older lungs is thus critical to optimize outcomes. Notably, ex vivo lung perfusion (EVLP) seems to have the potential of reconditioning ischemic lungs through ex-vivo perfusing and ventilation. Here, we aim to delineate mechanisms driving lung IRI and review both experimental and clinical data on the effects of aging in augmenting the consequences of IRI and PGD in lung transplantation.

Endothelin-Converting Enzyme 1 and Vascular Endothelial Growth Factor as Potential Biomarkers during Ex Vivo Lung Perfusion with Prolonged Hypothermic Lung-Sparing

Lung transplantation requires optimization of donor's organ use through ex vivo lung perfusion (EVLP) to avoid primary graft dysfunction. Biomarkers can aid in organ selection by providing early evidence of suboptimal lungs during EVLP and thus avoid high-risk transplantations. However, predictive biomarkers of pulmonary graft function such as endothelin-converting enzyme (ECE-1) and vascular endothelial growth factor (VEGF) have not been described under EVLP with standard prolonged hypothermic preservation, which are relevant in situations where lung procurement is difficult or far from the transplantation site. Therefore, this study is aimed at quantifying ECE-1 and VEGF, as well as determining their association with hemodynamic, gasometric, and mechanical ventilatory parameters in a swine model of EVLP with standard prolonged hypothermic preservation. Using a protocol with either immediate (I-) or delayed (D-) initiation of EVLP, ECE-1 levels over time were found to remain constant in both study groups (p > 0.05 RM-ANOVA), while the VEGF protein was higher after prolonged preservation, but it decreased throughout EVLP (p > 0.05 RM-ANOVA). Likewise, hemodynamic, gasometric, mechanical ventilatory, and histological parameters had a tendency to better results after 12 hours of hypothermic preservation in the delayed infusion group.

Minimizing Ischemia Reperfusion Injury in Xenotransplantation

The recent dramatic advances in preventing "initial xenograft dysfunction" in pig-to-non-human primate heart transplantation achieved by minimizing ischemia suggests that ischemia reperfusion injury (IRI) plays an important role in cardiac xenotransplantation. Here we review the molecular, cellular, and immune mechanisms that characterize IRI and associated "primary graft dysfunction" in allotransplantation and consider how they correspond with "xeno-associated" injury mechanisms. Based on this analysis, we describe potential genetic modifications as well as novel technical strategies that may minimize IRI for heart and other organ xenografts and which could facilitate safe and effective clinical xenotransplantation.

Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a form of acute lung injury after transplantation characterized by hypoxemia and the development of alveolar infiltrates on chest radiograph that occurs within 72 hours of reperfusion. PGD is among the most common early complications following lung transplantation and significantly contributes to increased short-term morbidity and mortality. In addition, severe PGD has been associated with higher 90-day and 1-year mortality rates compared with absent or less severe PGD and is a significant risk factor for the subsequent development of chronic lung allograft dysfunction. The International Society for Heart and Lung Transplantation released updated consensus guidelines in 2017, defining grade 3 PGD, the most severe form, by the presence of alveolar infiltrates and a ratio of PaO₂:FiO₂ less than 200. Multiple donor-related, recipient-related, and perioperative risk factors for PGD have been identified, many of which are potentially modifiable. Consistently identified risk factors include donor tobacco and alcohol use; increased recipient body mass index; recipient history of pulmonary hypertension, sarcoidosis, or pulmonary fibrosis; single lung transplantation; and use of cardiopulmonary bypass, among others. Several cellular pathways have been implicated in the pathogenesis of PGD, thus presenting several possible therapeutic targets for preventing and treating PGD. Notably, use of ex vivo lung perfusion (EVLP) has become more widespread and offers a potential platform to safely investigate novel PGD treatments while expanding the lung donor pool. Even in the presence of significantly prolonged ischemic times, EVLP has not been associated with an increased risk for PGD.

The Effects of Volatile Anesthetics on Lung Ischemia-Reperfusion Injury: Basic to Clinical Studies

Case reports from as early as the 1970s have shown that intravenous injection of even a small dose of volatile anesthetics result in fatal lung injury. Direct contact between volatile anesthetics and pulmonary vasculature triggers chemical damage in the vessel walls. A wide variety of factors are involved in lung ischemia-reperfusion injury (LIRI), such as pulmonary endothelial cells, alveolar epithelial cells, alveolar macrophages, neutrophils, mast cells, platelets, proinflammatory cytokines, and surfactant. With a constellation of factors involved, the assessment of the protective effect of volatile anesthetics in LIRI is difficult. Multiple animal studies have reported that with regards to LIRI, sevoflurane demonstrates an anti-inflammatory effect in immunocompetent cells and an anti-apoptotic effect on lung tissue. Scattered studies have dismissed a protective effect of desflurane against LIRI. While a single-center randomized controlled trial (RCT) found that volatile anesthetics including desflurane demonstrated a lung-protective effect in thoracic surgery, a multicenter RCT did not demonstrate a lung-protective effect of desflurane. LIRI is common in lung transplantation. One study, although limited due to its small sample size, found that the use of volatile anesthetics in organ procurement surgery involving "death by neurologic criteria" donors did not improve lung graft survival. Future studies on the protective effect of volatile anesthetics against LIRI must examine not only the mechanism of the protective effect but also differences in the effects of different types of volatile anesthetics, their optimal dosage, and the appropriateness of their use in the event of marked alveolar capillary barrier damage.

Novel function of VEGF-B as an antioxidant and therapeutic implications

Oxidative stress, due to insufficiency of antioxidants or over-production of oxidants, can lead to severe cell and tissue damage. Oxidative stress occurs constantly and has been shown to be involved in innumerable diseases, such as degenerative, cardiovascular, neurological, and metabolic disorders, cancer, and aging, thus highlighting the vital need of antioxidant defense mechanisms. Vascular endothelial growth factor B (VEGF-B) was discovered a long time ago, and is abundantly expressed in most types of cells and tissues. VEGF-B remained functionally mysterious for many years and later on has been shown to be minimally angiogenic. Recently, VEGF-B is reported to be a potent antioxidant by boosting the expression of key antioxidant enzymes. Thus, one major role of VEGF-B lies in safeguarding tissues and cells from oxidative stress-induced damage. VEGF-B may therefore have promising therapeutic utilities in treating oxidative stress-related diseases. In this review, we discuss the current knowledge on the newly discovered antioxidant function of VEGF-B and the related molecular mechanisms, particularly, in relationship to some oxidative stress-related diseases, such as retinitis pigmentosa, age-related macular degeneration, diabetic retinopathy, glaucoma, amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease.

Primary Graft Dysfunction After Lung Transplantation

Primary graft dysfunction is a form of acute injury after lung transplantation that is associated with significant short- and long-term morbidity and mortality. Multiple mechanisms contribute to the pathogenesis of primary graft dysfunction, including ischemia reperfusion injury, epithelial cell death, endothelial cell dysfunction, innate immune activation, oxidative stress, and release of inflammatory cytokines and chemokines. This article reviews the epidemiology, pathogenesis, risk factors, prevention, and treatment of primary graft dysfunction.

Hyperbaric Oxygen Inhibits Reperfusion-Induced Neutrophil Polarization and Adhesion Via Plasmin-Mediated VEGF Release

Background:

Ischemia-reperfusion (IR) injury is seen in many settings such as free flap salvage and limb replantation/revascularization. The consequences—partial/total flap loss, functional muscle loss, or amputation—can be devastating. Of the treatment options available for IR injury, hyperbaric oxygen (HBO) is the most beneficial. HBO inhibits neutrophil-endothelial adhesion through interference of CD18 neutrophil polarization in IR, a process mediated by nitric oxide. The purposes of this study were to examine the involvement of vascular endothelial growth factor (VEGF) in the beneficial HBO effect on CD18 polarization and neutrophil adhesion and investigate the effect of plasmin on VEGF expression in skeletal muscle following IR injury.

Methods:

A rat gracilis muscle model of IR injury was used to evaluate the effect of VEGF in IR, with and without HBO, on neutrophil CD18 polarization and adhesion in vivo and ex vivo. Furthermore, we investigated the effects that plasmin has on VEGF expression in gracilis muscle and pulmonary tissue by blocking its activation with alpha-2-antiplasmin.

Results:

HBO treatment following IR injury significantly decreased neutrophil polarization and adhesion ex vivo compared with the IR group. Anti-VEGF reversed the beneficial HBO effect after IR with polarization and adhesion. In vivo adhesion was also increased by anti-VEGF. HBO treatment of IR significantly increased the VEGF protein in both gracilis and pulmonary vasculature. Alpha-2-antiplasmin significantly reversed the HBO-induced increase of VEGF in gracilis muscle.

Conclusions:

These results suggest that HBO inhibits CD18 polarization and neutrophil adhesion in IR injury through a VEGF-mediated pathway involving the extracellular matrix plasminogen system.

The role of vascular endothelial growth factor-B in metabolic homoeostasis: current evidence

It has been shown that adipose tissue and skeletal muscles in lean individuals respond to meal-induced hyperinsulinemia by increase in perfusion, the effect not observed in patients with metabolic syndrome. In conditions of hyperglycaemia and hypertriglyceridemia, this insufficient vascularization leads to the liberation of reactive oxygen species (ROS), and disruption of nitric oxide (NO) synthesis and endothelial signalling responsible for the uptake of circulating fatty acids (FAs), whose accumulation in skeletal muscles and adipose tissue is widely associated with the impairment of insulin signalling. While the angiogenic role of VEGF-A and its increased circulating concentrations in obesity have been widely confirmed, the data related to the metabolic role of VEGF-B are diverse. However, recent discoveries indicate that this growth factor may be a promising therapeutic agent in patients with metabolic syndrome. Preclinical studies agree over two crucial metabolic effects of VEGF-B: (i) regulation of FAs uptake and (ii) regulation of tissue perfusion via activation of VEGF-A/vascular endothelial growth factor receptor (VEGFR) 2 (VEGFR2) pathway. While in some preclinical high-fat diet studies, VEGF-B overexpression reverted glucose intolerance and stimulated fat burning, in others it further promoted accumulation of lipids and lipotoxicity. Data from clinical studies point out the changes in circulating or tissue expression levels of VEGF-B in obese compared with lean patients. Potentially beneficial effects of VEGF-B, achieved through enhanced blood flow (increased availability of insulin and glucose uptake in target organs) and decreased FAs uptake (prevention of lipotoxicity and improved insulin signalling), and its safety for clinical use, remain to be clarified through future translational research.

Role of VEGF, Nitric Oxide, and Sympathetic Neurotransmitters in the Pathogenesis of Tendinopathy: A Review of the Current Evidences

Chronic tendinopathy is a painful common condition affecting athletes as well as the general population undergoing to tendon overuse. Although its huge prevalence, little is known about tendinopathy pathogenesis, and even cloudier is its treatment. Traditionally, tendinopathy has been defined as a lack of tendon ability to overcome stressing stimuli with appropriate adaptive changes. Histologic studies have demonstrated the absence of inflammatory infiltrates, as a consequence conventional antinflammatory drugs have shown little or no effectiveness in treating tendinopathies. New strategies should be therefore identified to address chronic tendon disorders. Angiofibroblastic changes have been highlighted as the main feature of tendinopathy, and vascular endothelial growth factor (VEGF) has been demonstrated as one of the key molecules involved in vascular hyperplasia. More recently, attention has been focused on new peptides such as Substance P, nitric oxide, and calcitonin gene-related peptide (CGRP). Those new findings support the idea of a nerve-mediated disregulation of tendon metabolism. Each of those molecules could be a target for new treatment options. This study aimed to systematically review the current available clinical and basic science in order to summarize the latest evidences on the pathophysiology and its effect on treatment of chronic tendinopathy, and to spread suggestions for future research on its treatment.

Primary graft dysfunction: lessons learned about the first 72 h after lung transplantation

PURPOSE OF REVIEW

In 2005, the International Society for Heart and Lung Transplantation published a standardized definition of primary graft dysfunction (PGD), facilitating new knowledge on this form of acute lung injury that occurs within 72 h of lung transplantation. PGD continues to be associated with significant morbidity and mortality. This article will summarize the current literature on the epidemiology of PGD, pathogenesis, risk factors, and preventive and treatment strategies.

RECENT FINDINGS

Since 2011, several manuscripts have been published that provide insight into the clinical risk factors and pathogenesis of PGD. In addition, several transplant centers have explored preventive and treatment strategies for PGD, including the use of extracorporeal strategies. More recently, results from several trials assessing the role of extracorporeal lung perfusion may allow for much-needed expansion of the donor pool, without raising PGD rates.

SUMMARY

This article will highlight the current state of the science regarding PGD, focusing on recent advances, and set a framework for future preventive and treatment strategies.

Physiological and pathological angiogenesis in the adult pulmonary circulation

Angiogenesis occurs during growth and physiological adaptation in many systemic organs, for example, exercise-induced skeletal and cardiac muscle hypertrophy, ovulation, and tissue repair. Disordered angiogenesis contributes to chronic inflammatory disease processes and to tumor growth and metastasis. Although it was previously thought that the adult pulmonary circulation was incapable of supporting new vessel growth, over that past 10 years new data have shown that angiogenesis within this circulation occurs both during physiological adaptive processes and as part of the pathogenic mechanisms of lung diseases. Here we review the expression of vascular growth factors in the adult lung, their essential role in pulmonary vascular homeostasis and the changes in their expression that occur in response to physiological challenges and in disease. We consider the evidence for adaptive neovascularization in the pulmonary circulation in response to alveolar hypoxia and during lung growth following pneumonectomy in the adult lung. In addition, we review the role of disordered angiogenesis in specific lung diseases including idiopathic pulmonary fibrosis, acute adult distress syndrome and both primary and metastatic tumors of the lung. Finally, we examine recent experimental data showing that therapeutic enhancement of pulmonary angiogenesis has the potential to treat lung diseases characterized by vessel loss.

Prednisolone as preservation additive prevents from ischemia reperfusion injury in a rat model of orthotopic lung transplantation

The lung is, more than other solid organs, susceptible for ischemia reperfusion injury after orthotopic transplantation. Corticosteroids are known to potently suppress pro-inflammatory processes when given in the post-operative setting or during rejection episodes. Whereas their use has been approved for these clinical indications, there is no study investigating its potential as a preservation additive in preventing vascular damage already in the phase of ischemia. To investigate these effects we performed orthotopic lung transplantations (LTX) in the rat. Prednisolone was either added to the perfusion solution for lung preservation or omitted and rats were followed for 48 hours after LTX. Prednisolone preconditioning significantly increased survival and diminished reperfusion edema. Hypoxia induced vasoactive cytokines such as VEGF were reduced. Markers of leukocyte invasiveness like matrix metalloprotease (MMP)-2, or common pro-inflammatory molecules like the CXCR4 receptor or the chemokine (C-C motif) ligand (CCL)-2 were downregulated by prednisolone. Neutrophil recruitment to the grafts was only increased in Perfadex treated lungs. Together with this, prednisolone treated animals displayed significantly reduced lung protein levels of neutrophil chemoattractants like CINC-1, CINC-2α/β and LIX and upregulated tissue inhibitor of matrix metalloproteinase (TIMP)-1. Interestingly, lung macrophage invasion was increased in both, Perfadex and prednisolone treated grafts, as measured by MMP-12 or RM4. Markers of anti-inflammatory macrophage transdifferentiation like MRC-1, IL-13, IL-4 and CD163, significantly correlated with prednisolone treatment. These observations lead to the conclusion that prednisolone as an additive to the perfusion solution protects from hypoxia triggered danger signals already in the phase of ischemia and thus reduces graft edema in the phase of reperfusion. Additionally, prednisolone preconditioning might also lead to macrophage polarization as a beneficial long-term effect.

Primary graft dysfunction

Primary graft dysfunction (PGD) is a syndrome encompassing a spectrum of mild to severe lung injury that occurs within the first 72 hours after lung transplantation. PGD is characterized by pulmonary edema with diffuse alveolar damage that manifests clinically as progressive hypoxemia with radiographic pulmonary infiltrates. In recent years, new knowledge has been generated on risks and mechanisms of PGD. Following ischemia and reperfusion, inflammatory and immunological injury-repair responses appear to be key controlling mechanisms. In addition, PGD has a significant impact on short- and long-term outcomes; therefore, the choice of donor organ is impacted by this potential adverse consequence. Improved methods of reducing PGD risk and efforts to safely expand the pool are being developed. Ex vivo lung perfusion is a strategy that may improve risk assessment and become a promising platform to implement treatment interventions to prevent PGD. This review details recent updates in the epidemiology, pathophysiology, molecular and genetic biomarkers, and state-of-the-art technical developments affecting PGD.

Overload and neovascularization of shoulder tendons in volleyball players

BACKGROUND

In overhead sports like volleyball, the onset of a rotator cuff tendinopathy due to functional overload is a common observation. An angiofibroblastic etiopathogenesis has been hypothesized, whereby a greater anaerobic metabolism occurs in critical zones of the tendon with a lower degree of vascularization; this would induce collagen and extracellular matrix degradation, that could then trigger a compensatory neovascularization response. We performed a clinical observational study of 80 elite volleyball players, monitoring the perfusion values of the supraspinatus tendons by oximetry.

RESULTS

No statistically significant differences were found between the oximetry data and age, sex or years of sports activity, nor when comparing the right and left arm or the dominant and non-dominant arm. A statistically significant difference was found for the dominant arm values in relation to the competitive role, higher values being obtained in outside hitters (62.7%) than middle hitters (53.7%) (p = 0.01), opposite hitters (55.5%) (p = 0.02) and libero players (54.4%) (p = 0.008), whereas there were no differences in setters (56.2%) (p > 0.05).

CONCLUSIONS

The different tendon vascularization values found in players with different roles in the team may be attributed to a response to the specific biomechanical demands posed by the different overhead throwing roles.

Deguelin attenuates reperfusion injury and improves outcome after orthotopic lung transplantation in the rat

The main goal of adequate organ preservation is to avoid further cellular metabolism during the phase of ischemia. However, modern preservation solutions do rarely achieve this target. In donor organs hypoxia and ischemia induce a broad spectrum of pathologic molecular mechanisms favoring primary graft dysfunction (PGD) after transplantation. Increased hypoxia-induced transcriptional activity leads to increased vascular permeability which in turn is the soil of a reperfusion edema and the enhancement of a pro-inflammatory response in the graft after reperfusion. We hypothesize that inhibition of the respiration chain in mitochondria and thus inhibition of the hypoxia induced mechanisms might reduce reperfusion edema and consecutively improve survival in vivo. In this study we demonstrate that the rotenoid Deguelin reduces the expression of hypoxia induced target genes, and especially VEGF-A, dose-dependently in hypoxic human lung derived cells. Furthermore, Deguelin significantly suppresses the mRNA expression of the HIF target genes VEGF-A, the pro-inflammatory CXCR4 and ICAM-1 in ischemic lungs vs. control lungs. After lung transplantation, the VEGF-A induced reperfusion-edema is significantly lower in Deguelin-treated animals than in controls. Deguelin-treated rats exhibit a significantly increased survival-rate after transplantation. Additionally, a downregulation of the pro-inflammatory molecules ICAM-1 and CXCR4 and an increase in the recruitment of immunomodulatory monocytes (CD163+ and CD68+) to the transplanted organ involving the IL4 pathway was observed. Therefore, we conclude that ischemic periods preceding reperfusion are mainly responsible for the increased vascular permeability via upregulation of VEGF. Together with this, the resulting endothelial dysfunction also enhances inflammation and consequently lung dysfunction. Deguelin significantly decreases a VEGF-A induced reperfusion edema, induces the recruitment of immunomodulatory monocytes and thus improves organ function and survival after lung transplantation by interfering with hypoxia induced signaling.

Complicated life, complicated VEGF-B

No other member of the VEGF (vascular endothelial growth factor) family has been as mysterious as VEGF-B. Notwithstanding its name, VEGF-B can hardly be regarded as a growth factor because growth occurs fairly normally in Vegf-b deficient mice. Moreover, VEGF-B is barely angiogenic under most conditions, although it was expected to be an angiogenic factor for a long time. Under certain conditions, VEGF-B has been shown to be involved in blood vessel growth. Under other conditions, however, VEGF-B can act to inhibit tumor growth and angiogenesis. Given these contradictory findings, the biological function of VEGF-B appears enigmatic. In this review, we summarize recent advances in VEGF-B biology and discuss its multifaceted roles, the underlying mechanisms, and the potential therapeutic implications.

Vascular protection by angiotensin receptor antagonism involves differential VEGF expression in both hemispheres after experimental stroke

We identified that the angiotensin receptor antagonist, candesartan, has profound neurovascular protective properties when administered after ischemic stroke and was associated with a proangiogenic state at least partly explained by vascular endothelial growth factor A (VEGFA). However, the spatial distribution of vascular endothelial growth factor (VEGF) isoforms and their receptors remained unknown. Protein analysis identified a significant increase in vascular endothelial grow factor B (VEGFB) in the cerebrospinal fluid (CSF) and the ischemic hemispheres (with increased VEGF receptor 1 activation) of treated animals (p<0.05) which was co-occurring with an increase in protein kinase B (Akt) phosphorylation (p<0.05). An increase in VEGFA protein in the contralesional hemisphere corresponded to a significant increase in vascular density at seven days (p<0.01) after stroke onset. Vascular restoration by candesartan after stroke maybe related to differential regional upregulation of VEGFB and VEGFA, promoting a “prosurvival state” in the ischemic hemisphere and angiogenesis in the contralesional side, respectively. These vascular changes in both hemispheres after effective treatment are likely to contribute to enhanced recovery after stroke.

Reduced local perfusion after shock wave treatment of rotator cuff tendinopathy

A marked neovascularity has been demonstrated in tendinopathies, due to the inflammatory-degenerative process. The aim of this study was to assess the effect of extracorporeal shock wave therapy (ESWT) on tissue perfusion in the treatment of tendinopathy. An observational clinical study was made of 30 patients undergoing ESWT for tendinopathy of the rotator cuff. A clinical improvement was obtained in 65.6% of patients at 2 and 6 months. This was associated with a statistically significant reduction in the oxygen tissue saturation, measured by oxymetry that was apparent already during treatment, as well as at subsequent follow-up visits. The reduced perfusion achieved with ESWT supports the hypothesis that this treatment can regulate the inflammatory process and offset increased vascularization, restoring physiologic tendon conditions.

The contribution of airway and lung tissue ischemia to primary graft dysfunction

PURPOSE OF REVIEW

Primary graft dysfunction (PGD) is the primary obstacle to short-term survival for post-lung transplant patients. PGD is a form of acute lung injury secondary to donor brain death and ischemia-reperfusion damage to the allograft affecting 10-25% of all lung transplant recipients. This article reviews the significant role of allograft ischemia in the phenotypic presentation of PGD and the evidence for activation and disruption of normal cellular pathways for the development and long-term sequelae.

RECENT FINDINGS

Pathways implicated in the pathogenesis of PGD resultant from tissue ischemia include abnormalities in coagulation and fibrinolysis, epithelial cell injury, endothelial cell dysfunction, chemotaxis, and alterations in cell adhesion. Blood and bronchoalveolar lavage fluid biomarkers from these pathways have been increasingly identified as useful for diagnosing and predicting the development of severe PGD.

SUMMARY

Future efforts at preventing and treating severe PGD should focus on techniques for altering the pathways involved in PGD pathogenesis. Ex-vivo lung perfusion and transduction with interleukin-10 are promising modalities for preventing PGD and expanding the available lung transplant donor pool.

Association of aorta intima permeability with myosin light chain kinase expression in hypercholesterolemic rabbits

The development of hypercholesterolemia is a multifactorial process in which elevated plasma cholesterol levels play a central role. This study analyzed the variability of the expression and activity of myosin light chain kinase (MLCK) and endothelial permeability in the artery wall of rabbits after feeding the animals with a normal or a high-cholesterol diet. Hypercholesterolemia was induced by a high-cholesterol diet for 4 weeks. Aortas were removed and analyzed for endothelial permeability and MLCK expression. Samples of the arterial media were analyzed for MLCK activity and expression. A selective MLCK inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML7) were used in hypercholesterolemia rabbit (1 mg/kg body weight). The aortas of high-cholesterol diet rabbits showed an increase in MLCK expression and activity (nearly threefold compare with control) as well as endothelial permeability. ML7 inhibit MLC phosphorylation and MLCK activity (nearly twofold compare with control) and endothelial permeability stimulated by cholesterol. These results indicate for the first time that hypercholesterolemia may be associated with MLCK expression and activity through which endothelial permeability is increased.

Lung ischemia-reperfusion injury: a molecular and clinical view on a complex pathophysiological process

Lung ischemia-reperfusion injury remains one of the major complications after cardiac bypass surgery and lung transplantation. Due to its dual blood supply system and the availability of oxygen from alveolar ventilation, the pathogenetic mechanisms of ischemia-reperfusion injury in the lungs are more complicated than in other organs, where loss of blood flow automatically leads to hypoxia. In this review, an extensive overview is given of the molecular and cellular mechanisms that are involved in the pathogenesis of lung ischemia-reperfusion injury and the possible therapeutic strategies to reduce or prevent it. In addition, the roles of neutrophils, alveolar macrophages, cytokines, and chemokines, as well as the alterations in the cell-death related pathways, are described in detail.

Lymph angiogenesis after lung transplantation and relation to acute organ rejection in humans

BACKGROUND

Acute rejection after kidney transplantation was found to be associated with increased recipient-derived lymph angiogenesis. However, the relation of lymph angiogenesis to acute rejection in lung transplantation has not yet been investigated.

METHODS

Transbronchial biopsies from 23 lung transplant recipients (47 + or - 15 years old, 15 male, 19 double lungs, 4 single lungs), taken at 14 and 90 days after transplantation were investigated. Immunohistostaining for PROX-1 (an lymphatic endothelial marker) and for vascular endothelial growth factor receptor (VEGFR) 1 and 2 (blood capillary markers) was performed. Biopsies with no sign of rejection (International Society for Heart and Lung Transplantation [ISHLT] grade A0, n = 27) were compared with biopsies with rejection grade A1/A2 (n = 19).

RESULTS

Biopsies with ISHLT rejection grade A1 or A2 showed a significantly higher density of PROX-1 marked lymphatics in comparison with biopsies of grade A0 at 14 days (p < 0.001) and at 90 days (p < 0.001) after transplantation, and in the collective comparison (all biopsies with ISHLT grade A1 or A2 versus all biopsies with grade A0, p < 0.001). For VEGFR-1 and VEGFR-2, no difference was found between ISHLT grade A1 or A2 compared with grade A0, neither at 14 or 90 days nor in the collective comparison.

CONCLUSIONS

Increased lymphatic angiogenesis after lung transplantation, demonstrated by increased density of the PROX-1 lymphatic endothelial marker, was associated with histologically evident acute organ rejection in humans. Although the exact role of lymphatic angiogenesis in acute organ rejection remains to be determined, further study of the interaction between the microvasculature and acute rejection seems warranted. Pending further investigation, analysis of PROX-1 density may develop into a new tool for rejection monitoring, supplementing conventional rejection grading.

Biomarkers of lung injury in primary graft dysfunction following lung transplantation

Primary graft dysfunction, a form of reperfusion pulmonary edema that occurs early after lung transplantation, shares key clinical and pathological features with acute lung injury and its more severe form, the acute respiratory distress syndrome. However, in contrast to acute lung injury/acute respiratory distress syndrome, in which biomarkers in plasma, urine and lung edema fluid have prognostic and pathogenetic value, the role of biomarkers in primary graft dysfunction has been less thoroughly explored. This review summarizes human and animal studies on biomarkers in primary graft dysfunction, including cytokines and markers of acute inflammation, VEGF, endothelial markers and adhesion molecules, markers of coagulation and fibrinolysis and markers of lung epithelial injury. Similarities to the literature in acute lung injury/acute respiratory distress syndrome are highlighted where appropriate, and future directions for research on the role of biomarkers in primary graft dysfunction are suggested.

VEGF-B: a survival, or an angiogenic factor?

Despite its early discovery and high sequence homology to the other VEGF family members, the biological function of VEGF-B remained debatable for a long time, and VEGF-B has received little attention from the field thus far. Recently, we and others have found that (1) VEGF-B is a potent survival factor for different types of cells by inhibiting apoptosis via suppressing the expression of BH3-only protein and other apoptotic/cell death-related genes. (2) VEGF-B has a negligible role in inducing blood vessel growth in most organs. Instead, it is critically required for blood vessel survival. VEGF-B targeting inhibited pathological angiogenesis by abolishing blood vessel survival in different animal models. (3) Using different types of neuro-injury and neurodegenerative disease models, VEGF-B treatment protected endangered neurons from apoptosis without inducing undesired blood vessel growth or permeability. Thus, VEGF-B is the first member of the VEGF family that has a potent survival/anti-apoptotic effect, while lacking a general angiogenic activity. Our work thus advocates that the major function of VEGF-B is to act as a "survival", rather than an "angiogenic" factor and implicates a therapeutic potential of VEGF-B in treating different types of vascular and neurodegenerative diseases.

VEGF-B is dispensable for blood vessel growth but critical for their survival, and VEGF-B targeting inhibits pathological angiogenesis

VEGF-B, a homolog of VEGF discovered a long time ago, has not been considered an important target in antiangiogenic therapy. Instead, it has received little attention from the field. In this study, using different animal models and multiple types of vascular cells, we revealed that although VEGF-B is dispensable for blood vessel growth, it is critical for their survival. Importantly, the survival effect of VEGF-B is not only on vascular endothelial cells, but also on pericytes, smooth muscle cells, and vascular stem/progenitor cells. In vivo, VEGF-B targeting inhibited both choroidal and retinal neovascularization. Mechanistically, we found that the vascular survival effect of VEGF-B is achieved by regulating the expression of many vascular prosurvival genes via both NP-1 and VEGFR-1. Our work thus indicates that the function of VEGF-B in the vascular system is to act as a "survival," rather than an "angiogenic" factor and that VEGF-B inhibition may offer new therapeutic opportunities to treat neovascular diseases.

VEGF expression in patellar tendinopathy: a preliminary study

Vascular function and angiogenesis are regulated by vascular endothelial growth factor-A (VEGF). The purpose of this preliminary study was to address the following questions: Is VEGF expression in the patellar tendon more prevalent in patients with patellar tendinopathy than in individuals with normal, pain-free patellar tendons? Which cell populations express VEGF in normal and tendinopathic tendon? Is there a difference in symptom duration between VEGF+ and VEGF- tendons? We collected patellar tendon tissue from 22 patients undergoing open débridement of the patellar tendon and from 10 patients undergoing intramedullary nailing of the tibia. VEGF expression was assessed immunohistochemically. Relevant inflammatory and repair cell types were immunolabeled. VEGF expression was absent from control tendons, but was present in a subset of patients with histopathological evidence of angiofibroblastic tendinosis. VEGF was expressed in the intimal layer of tendon vessels, but was absent in other cell types. Patients demonstrating VEGF expression in the patellar tendon had a shorter symptom duration (12 +/- 7.8 months) than patients with no detectable VEGF (32.8 +/- 23.5 months). VEGF may contribute to the vascular hyperplasia that is a cardinal feature of symptomatic tendinosis, particularly in cases with more recent onset.

VEGF-B inhibits apoptosis via VEGFR-1-mediated suppression of the expression of BH3-only protein genes in mice and rats

Despite its early discovery and high sequence homology to the other VEGF family members, the biological functions of VEGF-B remain poorly understood. We revealed here a novel function for VEGF-B as a potent inhibitor of apoptosis. Using gene expression profiling of mouse primary aortic smooth muscle cells, and confirming the results by real-time PCR using mouse and rat cell lines, we showed that VEGF-B inhibited the expression of genes encoding the proapoptotic BH3-only proteins and other apoptosis- and cell death-related proteins, including p53 and members of the caspase family, via activation of VEGFR-1. Consistent with this, VEGF-B treatment rescued neurons from apoptosis in the retina and brain in mouse models of ocular neurodegenerative disorders and stroke, respectively. Interestingly, VEGF-B treatment at the dose effective for neuronal survival did not cause retinal neovascularization, suggesting that VEGF-B is the first member of the VEGF family that has a potent antiapoptotic effect while lacking a general angiogenic activity. These findings indicate that VEGF-B may potentially offer a new therapeutic option for the treatment of neurodegenerative diseases.

Vascular endothelial growth factors in pulmonary edema: an update

Pulmonary edema is a life-threatening complication of critical illness. Identification of the underlying mechanisms of pulmonary edema is a prerequisite for the development of adequate treatment. The initial description of fluid transportation across capillaries (Starling's law) while of critical importance, did not provide full insight into the underlying pathophysiology of vascular leakage. Pulmonary edema can be differentiated into two distinct categories based on the Starling theory; the high-permeability type is attributed to inflammatory changes occurring in conditions such as the adult respiratory distress syndrome (ARDS) and the cardiogenic type is characterized by an imbalance in the Starling hydrostatic forces and occurs in acute or decompensated heart failure. However, it has long been recognized that there is significant overlap between the various types of pulmonary edema, raising important questions regarding the role of novel mechanisms that may contribute to the development of interstitial and alveolar leakage. Recently, several studies on VEGF, an angiogenic growth factor which affects endothelial permeability, have identified this molecule as a potential regulator of vascular leakage and repair in pulmonary edema. We review here the underlying the mechanisms by which VEGF may do this and will discuss the still unanswered questions regarding vascular pharmacology in the setting of pulmonary edema.

Peroxisome proliferator-activated receptors ligands and ischemia-reperfusion injury

Peroxisome proliferator-activated receptors (PPARs) belong to a subfamily of transcription nuclear factors. Three isoforms of PPARs have been identified: alpha, beta/delta and gamma, encoded by different genes and distributed in various tissues. They play important roles in metabolic processes like regulation of glucose and lipid redistribution. They also have anti-atherogenic, anti-inflammatory as well as antihypertensive functions. There is good evidence that ligands of PPARs reduce tissue injury associated with ischemia and reperfusion. The potential utility of PPAR ligands in ischemia and reperfusion will be discussed in this review.

Recipient vascular endothelial growth factor serum levels predict primary lung graft dysfunction

Primary graft dysfunction (PGD) is a severe complication in lung transplantation. Therapeutic strategies are limited and there exist no predictive markers for PGD. To investigate whether vascular endothelial growth factor (VEGF) that regulates vascular permeability could predict PGD, pretransplant VEGF serum concentrations were measured in 150 lung transplant patients and 12 controls by ELISA. PGD was scored from 0 to 3 using chest radiographs and PaO(2)/FiO(2) ratios according to the International Society for Heart and Lung Transplantation guidelines. The mean graft ischemia time was 5 h 47 min and the donors' PaO(2)/FiO(2) ratios were >300. PGD grades 0-3 occurred in 23%, 44%, 21%, and 11% of patients, respectively. Pre-operative VEGF serum concentrations were significantly higher in PGD grade 3 (p < 0.0001) versus grade 0-2 and controls. VEGF concentrations significantly predicted PGD grade 3 versus 0-2 in logistic regression analysis (p < 0.0001) and receiver operating analysis (AUC = 0.778). At a cut-off level of > or =650 pg/mL VEGF had 86% sensitivity and 62% specificity to identify PGD grade 3 versus 0-2. Pre-operative VEGF serum concentrations could identify lung transplant recipients with high PGD risk.

The Myc-dependent angiogenic switch in tumors is mediated by interleukin 1beta

Although induction of blood vessel growth is acknowledged as a pivotal requirement for the evolution of macroscopic tumors, the events that trigger onset of tumor angiogenesis remain largely obscure. The pervasive Myc oncoprotein is itself a potent inducer of angiogenesis in a wide range of tissues. We have used a reversibly switchable mouse transgenic model of Myc-dependent beta-cell carcinogenesis to delineate the kinetics and causal sequence of angiogenic processes following acute Myc activation. We show that onset of endothelial cell proliferation is induced shortly after Myc-induced cell cycle entry of beta cells. Endothelial cell proliferation is not indirectly induced by local tissue hypoxia but instead via a diffusible angiogenic signal produced by Myc-expressing beta cells. This signal triggers the release of pre-existing, sequestered VEGF from the islet extracellular matrix, that then homes to the endothelial compartment where it induces endothelial cell proliferation. Myc activation in beta cells rapidly induces expression and release of the proinflammatory cytokine interleukin 1beta (IL-1beta). We show that IL-1beta is the principal effector downstream of Myc responsible for triggering rapid onset of islet angiogenesis. Together, our data delineate a complete pathway in vivo by which the highly pleiotropic Myc oncoproteins elicits coexpansion of the vascular compartment during tumorigenic progression.

The two-event model of transfusion-related acute lung injury

The objective of this review is to present the two-event model of transfusion-related acute lung injury (TRALI), a life-threatening complication of transfusions that has been the most common cause of transfusion-related death over the past 2 yrs in the United States. The two-event model of TRALI, which is identical to the pathogenesis of the acute respiratory distress syndrome (ARDS), is reviewed and contrasted to antibody-mediated TRALI. Laboratory studies, both in vitro and in vivo, are discussed as well as human studies of TRALI. Methods to avoid patient exposure to blood components that may cause TRALI are also discussed.

Vascular endothelial growth factor antagonist modulates leukocyte trafficking and protects mouse livers against ischemia/reperfusion injury

Although hypoxia stimulates the expression of vascular endothelial growth factor (VEGF), little is known of the role or mechanism by which VEGF functions after ischemia and reperfusion (I/R) injury. In this report, we first evaluated the expression of VEGF in a mouse model of liver warm ischemia. We found that the expression of VEGF increased after ischemia but peaked between 2 and 6 hours after reperfusion. Mice were treated with a neutralizing anti-mouse VEGF antiserum (anti-VEGF) or control serum daily from day -1 (1 day before the initiation of ischemia). Treatment with anti-VEGF significantly reduced serum glutaminic pyruvic transaminase levels and reduced histological evidence of hepatocellular damage compared with controls. Anti-VEGF also markedly decreased T-cell, macrophage, and neutrophil accumulation within livers and reduced the frequency of intrahepatic apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells. Moreover, there was a reduction in the expression of pro-inflammatory cytokines (tumor necrosis factor-alpha and interferon-gamma), chemokines (interferon-inducible protein-10 and monocyte chemoattractant protein-1) and adhesion molecules (E-selectin) in parallel with enhanced expression of anti-apoptotic genes (Bcl-2/Bcl-xl and heme oxygenase-1) in anti-VEGF-treated animals. In conclusion, hypoxia-inducible VEGF expression by hepatocytes modulates leukocyte trafficking and leukocyte-induced injury in a mouse liver model of warm I/R injury, demonstrating the importance of endogenous VEGF production in the pathophysiology of hepatic I/R injury.

The biology of vascular endothelial growth factor-B (VEGF-B)

The formation of new blood vessels (angiogenesis) is critical for both embryonic development and a variety of normal postnatal physiological processes. Various pathological processes, most notably tumour growth and chronic inflammation, are also known to be dependent on the new vessel formation. Amongst the variety of factors that contribute to the regulation of this complex process, vascular endothelial growth factor (VEGF or VEGF-A) is arguably the most well characterised. The VEGF family of growth factors is now known to comprise of VEGF-A plus four additional members, including VEGF-B. In contrast to VEGF-A, surprisingly little is known about the precise biological role of VEGF-B. Unlike VEGF-A, which binds to the two receptor tyrosine kinases VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR), VEGF-B binds only to VEGFR-1 and the functional significance of VEGFR-1 signalling has remained problematic. More recently, however, evidence has emerged suggesting a key role for VEGFR-1 signalling in pathological angiogenesis and this has raised the possibility that, like VEGF-A, VEGFR-1 specific ligands such as VEGF-B may provide for novel therapeutic strategies and/or represent new therapeutic targets. Here we review current knowledge of the biology of VEGF-B. We note that although analysis to date, including expression profiling and the generation of gene targetted mice, has provided only limited insights, future studies using recently generated recombinant proteins and antagonist monoclonal antibodies should provide for a more comprehensive understanding.

Transcriptional responses of rat skeletal muscle following hypoxia-reoxygenation and near ischaemia-reperfusion

AIM

The effect of ischaemia/reperfusion or hypoxia/reoxygenation on gene expression has not been extensively studied. We hypothesized that in skeletal muscle, tissue hypoxia of similar magnitude but induced by different mechanisms would lead to different transcriptional responses.

METHODS

Muscle gene transcription was assessed using microarray analysis and reverse transcriptase polymerase chain reaction in 18 rats exposed to regional hind limb near ischaemia/reperfusion (n = 6), hypoxia/reoxygenation (n = 6) or sham operation (n = 6). Hypoxic burden was measured by the area under the PtO(2)-time curve.

RESULTS

PtO(2) was reduced in both the near ischaemia/reperfusion and hypoxia/reoxygenation groups. Although the hypoxic burden was similar, the genomic response was different for each condition. Near ischaemia/reperfusion had a greater effect on gene expression than hypoxia/reoxygenation. Using stringent criteria for changes in gene expression (i.e. more than or equal to twofold change vs. control) unique patterns of gene expression could be identified suggesting individualized transcriptional responses to each of these injuries. Several genes, including insulin-like growth factor 1 (IGF-1) and cyclin-dependent kinase inhibitor (p27(Kip1)) were induced by both injury types and these may have potential clinical application as markers of tissue damage. In contrast, no single gene was downregulated by both injury conditions.

CONCLUSIONS

The mechanism of skeletal muscle hypoxia has a profound effect on its subsequent transcriptional response. We identified several potential candidates as markers of skeletal muscle ischaemic damage.

Neuropilin-1 regulates vascular endothelial growth factor-mediated endothelial permeability

Neuropilin-1 (Npn-1) is a cell surface receptor that binds vascular endothelial growth factor (VEGF), a potent mediator of endothelial permeability, chemotaxis, and proliferation. In vitro, Npn-1 can complex with VEGF receptor-2 (VEGFR2) to enhance VEGFR2-mediated endothelial cell chemotaxis and proliferation. To determine the role of Npn-1/VEGFR2 complexes in VEGF-induced endothelial barrier dysfunction, endothelial cells were stably transfected with Npn1 or VEGFR2 alone (PAE/Npn and PAE/KDR, respectively), or VEGFR2 and Npn-1 (PAE/KDR/Npn-1). Permeability, estimated by measurement of transendothelial electrical resistance (TER), of PAE/Npn and PAE/KDR cell lines was not altered by VEGF165. In contrast, TER of PAE/KDR/Npn-1 cells decreased in dose-dependent fashion following VEGF165 (10 to 200 ng/mL). Activation of VEGFR2, and 2 downstream signaling intermediates (p38 and ERK1/2 MAPK) involved in VEGF-mediated permeability, also increased in PAE/KDR/Npn-1. Consistent with these data, inhibition of Npn-1, but not VEGFR2, attenuated VEGF165-mediated permeability of human pulmonary artery endothelial cells (HPAE), and VEGF121 (which cannot ligate Npn-1) did not alter TER of HPAE. Npn-1 inhibition also attenuated both VEGF165-mediated pulmonary vascular leak and activation of VEGFR2, p38, and ERK1/2 MAPK, in inducible lung-specific VEGF transgenic mice. These data support a critical role for Npn-1 in regulating endothelial barrier dysfunction in response to VEGF and suggest that activation of distinct receptor complexes may determine specificity of cellular response to VEGF.

Upregulated hypoxia-inducible factor-1 DNA binding activity to the vascular endothelial growth factor-A promoter mediates increased vascular permeability in donor lung grafts

BACKGROUND

Transplantation-induced hypoxia results in enhanced vascular permeability and tissue vascular endothelial growth factor (VEGF) and endothelin-1 (ET-1) overexpression in donor lung grafts. Promoter studies have uncovered a hypoxia-inducible factor (HIF)-1 binding site (HBS) in 5'-flanking region of VEGF gene that regulates the hypoxia-induced expression of VEGF; and ET-1 potently stimulates VEGF-A production. We hypothesized that HIF-1 regulates VEGF-mediated vascular permeability in lung grafts.

METHODS

We studied the mRNA and protein expression of HIF-1 and its protein-binding capacity to the HBS of the VEGF gene in biopsies of preserved donor and control lungs, using real-time reverse transcription-polymerase chain reaction, Western blotting, and electrophoretic mobility shift assay. Wet-to-dry lung weight ratio was measured in donor and control lungs.

RESULTS

While HIF-1 alpha mRNA expression was unchanged, HIF-1 beta was downregulated (p < 0.05) in donor versus control lungs. Protein expression of both, HIF-1 alpha and -beta was significantly upregulated in donor lung grafts. HIF-1 binding to the HBS of the VEGF promoter as well as tissue fluid content were increased in donor lung biopsies versus controls (p < 0.05).

CONCLUSIONS

These data indicate that upregulated HIF-1 DNA binding activity to the HBS of VEGF-A most likely contributes to elevated VEGF levels in preserved lung grafts. Unchanged HIF-1 alpha mRNA expression did not affect HIF-1 alpha protein levels. Endothelin-1 increases HIF-1 alpha accumulation and activates HIF-1 transcription complex in vitro. Therefore, ET-1-mediated increased HIF-1 alpha protein stability most likely leads to transcriptional activation of VEGF during lung graft preservation. Targeting HIF might be of benefit to counteract edema formation in preserved lung grafts.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.