Elevated plasma angiopoietin-2 levels and primary graft dysfunction after lung transplantation

Early serum biomarkers to characterise different phenotypes of primary graft dysfunction after lung transplantation: a systematic scoping review

Background

Lung transplantation (LUTX) is often complicated by primary graft dysfunction (PGD). Plasma biomarkers hold potential for PGD phenotyping and targeted therapy. This scoping review aims to collect the available literature in search of serum biomarkers for PGD phenotyping.

Methods

Following JBI and PRISMA guidelines, we conducted a systematic review searching MEDLINE, Web of Science, EMBASE and The Cochrane Library for papers reporting the association between serum biomarkers measured within 72 h of reperfusion and PGD, following International Society for Heart and Lung Transplantation (ISHLT) guidelines. We extracted study details, patient demographics, PGD definition and timing, biomarker concentration, and their performance in identifying PGD cases.

Results

Among the 1050 papers screened, 25 prospective observational studies were included, with only nine conducted in the last decade. These papers included 1793 unique adult patients (1195 double LUTX, median study size 100 (IQR 44-119)). Most (n=21) compared PGD grade 3 to less severe PGD, but only four adhered to 2016 PGD definitions. Enzyme-linked immunosorbent assays and the multiplex bead array technique were utilised in 23 and two papers, respectively. In total, 26 candidate biomarkers were identified, comprising 13 inflammatory, three endothelial activation, three epithelial injury, three cellular damage and two coagulation dysregulation markers. Only five biomarkers (sRAGE, ICAM-1, PAI-1, SP-D, FSTL-1) underwent area under the receiver operating characteristic curve analysis, yielding a median value of 0.58 (0.51-0.78) in 406 patients (276 double LUTX).

Conclusions

Several biomarkers exhibit promise for future studies aimed at PGD phenotyping after LUTX. To uncover the significant existing knowledge gaps, further international prospective studies incorporating updated diagnostic criteria, modern platforms and advanced statistical approaches are essential.

Development and validation of primary graft dysfunction predictive algorithm for lung transplant candidates

BACKGROUND

Primary graft dysfunction (PGD) is the leading cause of early morbidity and mortality after lung transplantation. Accurate prediction of PGD risk could inform donor approaches and perioperative care planning. We sought to develop a clinically useful, generalizable PGD prediction model to aid in transplant decision-making.

METHODS

We derived a predictive model in a prospective cohort study of subjects from 2012 to 2018, followed by a single-center external validation. We used regularized (lasso) logistic regression to evaluate the predictive ability of clinically available PGD predictors and developed a user interface for clinical application. Using decision curve analysis, we quantified the net benefit of the model across a range of PGD risk thresholds and assessed model calibration and discrimination.

RESULTS

The PGD predictive model included distance from donor hospital to recipient transplant center, recipient age, predicted total lung capacity, lung allocation score (LAS), body mass index, pulmonary artery mean pressure, sex, and indication for transplant; donor age, sex, mechanism of death, and donor smoking status; and interaction terms for LAS and donor distance. The interface allows for real-time assessment of PGD risk for any donor/recipient combination. The model offers decision-making net benefit in the PGD risk range of 10% to 75% in the derivation centers and 2% to 10% in the validation cohort, a range incorporating the incidence in that cohort.

CONCLUSION

We developed a clinically useful PGD predictive algorithm across a range of PGD risk thresholds to support transplant decision-making, posttransplant care, and enrich samples for PGD treatment trials.

Postreperfusion Pulmonary Artery Pressure Indicates Primary Graft Dysfunction After Lung Transplant

BACKGROUND

Primary graft dysfunction is a risk factor of early mortality after lung transplant. Models identifying patients at high risk for primary graft dysfunction are limited. We hypothesize high postreperfusion systolic pulmonary artery pressure is a clinical marker for primary graft dysfunction.

METHODS

This is a retrospective review of 158 consecutive lung transplants performed at a single academic center from January 2020 through July 2022. Only bilateral lung transplants were included and patients with pretransplant extracorporeal life support were excluded.

RESULTS

Primary graft dysfunction occurred in 42.3% (n = 30). Patients with primary graft dysfunction had higher postreperfusion systolic pulmonary artery pressure (41 ± 9.1 mm Hg) than those without (31.5 ± 8.8 mm Hg) (P < .001). Logistic regression showed postreperfusion systolic pulmonary artery pressure is a predictor for primary graft dysfunction (odds ratio 1.14, 95% CI 1.06-1.24, P < .001). Postreperfusion systolic pulmonary artery pressure of 37 mm Hg was optimal for predicting primary graft dysfunction by Youden index. The receiver operating characteristic curve of postreperfusion systolic pulmonary artery pressure at 37 mm Hg (sensitivity 0.77, specificity 0.78, area under the curve 0.81), was superior to the prereperfusion pressure curve at 36 mm Hg (sensitivity 0.77, specificity 0.39, area under the curve 0.57) (P < .01).

CONCLUSIONS

Elevated postreperfusion systolic pulmonary artery pressure after lung transplant is predictive of primary graft dysfunction. Postreperfusion systolic pulmonary artery pressure is more indicative of primary graft dysfunction than prereperfusion systolic pulmonary artery pressure. Using postreperfusion systolic pulmonary artery pressure as a positive signal of primary graft dysfunction allows earlier intervention, which could improve outcomes.

The Impact of Donor Smoking on Primary Graft Dysfunction and Mortality after Lung Transplantation

Rationale: Primary graft dysfunction (PGD) is the leading cause of early morbidity and mortality after lung transplantation. Prior studies implicated proxy-defined donor smoking as a risk factor for PGD and mortality. Objectives: We aimed to more accurately assess the impact of donor smoke exposure on PGD and mortality using quantitative smoke exposure biomarkers. Methods: We performed a multicenter prospective cohort study of lung transplant recipients enrolled in the Lung Transplant Outcomes Group cohort between 2012 and 2018. PGD was defined as grade 3 at 48 or 72 hours after lung reperfusion. Donor smoking was defined using accepted thresholds of urinary biomarkers of nicotine exposure (cotinine) and tobacco-specific nitrosamine (4-[methylnitrosamino]-1-[3-pyridyl]-1-butanol [NNAL]) in addition to clinical history. The donor smoking-PGD association was assessed using logistic regression, and survival analysis was performed using inverse probability of exposure weighting according to smoking category. Measurements and Main Results: Active donor smoking prevalence varied by definition, with 34-43% based on urinary cotinine, 28% by urinary NNAL, and 37% by clinical documentation. The standardized risk of PGD associated with active donor smoking was higher across all definitions, with an absolute risk increase of 11.5% (95% confidence interval [CI], 3.8% to 19.2%) by urinary cotinine, 5.7% (95% CI, -3.4% to 14.9%) by urinary NNAL, and 6.5% (95% CI, -2.8% to 15.8%) defined clinically. Donor smoking was not associated with differential post-lung transplant survival using any definition. Conclusions: Donor smoking associates with a modest increase in PGD risk but not with increased recipient mortality. Use of lungs from smokers is likely safe and may increase lung donor availability. Clinical trial registered with www.clinicaltrials.gov (NCT00552357).

Biometric Profiling to Quantify Lung Injury Through Ex Vivo Lung Perfusion Following Warm Ischemia

Standard physiologic assessment parameters of donor lung grafts may not accurately reflect lung injury or quality. A biometric profile of ischemic injury could be identified as a means to assess the quality of the donor allograft. We sought to identify a biometric profile of lung ischemic injury assessed during ex vivo lung perfusion (EVLP). A rat model of lung donation after circulatory death (DCD) warm ischemic injury with subsequent EVLP evaluation was utilized. We did not observe a significant correlation between the classical physiological assessment parameters and the duration of the ischemic. In the perfusate, solubilized lactate dehydrogenase (LDH) as well as hyaluronic acid (HA) significantly correlated with duration of ischemic injury and length of perfusion ( p < 0.05). Similarly, in perfusates, the endothelin-1 (ET-1) and Big ET-1 correlated ischemic injury ( p < 0.05) and demonstrated a measure of endothelial cell injury. In tissue protein expression, heme oxygenase-1 (HO-1), angiopoietin 1 (Ang-1), and angiopoietin 2 (Ang-2) levels were correlated with the duration of ischemic injury ( p < 0.05). Cleaved caspase-3 levels were significantly elevated at 90 and 120 minutes ( p < 0.05) demonstrating increased apoptosis. A biometric profile of solubilized and tissue protein markers correlated with cell injury is a critical tool to aid in the evaluation of lung transplantation, as accurate evaluation of lung quality is imperative and improved quality leads to better results. http://links.lww.com/ASAIO/B49.

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 Future of Lung Transplantation

The field of lung transplant has made significant advances over the last several decades. Despite these advances, morbidity and mortality remain high when compared with other solid organ transplants. As the field moves forward, the speed by which progress can be made will in part be determined by our ability to overcome several stumbling blocks, including donor shortage, proper selection of candidates, primary graft dysfunction, and chronic lung allograft dysfunction. The advances and developments surrounding these factors will have a significant impact on shaping the field within the coming years. In this review, we look at the current climate (ripe for expanding the donor pool), new technology (ex vivo lung perfusion and bioengineered lungs), cutting-edge innovation (novel biomarkers and new ways to treat infected donors), and evidence-based medicine to discuss current trends and predict future developments for what we hope is a bright future for the field of lung transplantation.

Cell-free hemoglobin promotes primary graft dysfunction through oxidative lung endothelial injury

Primary graft dysfunction (PGD) is acute lung injury within 72 hours of lung transplantation. We hypothesized that cell-free hemoglobin (CFH) contributes to PGD by increasing lung microvascular permeability and tested this in patients, ex vivo human lungs, and cultured human lung microvascular endothelial cells. In a nested case control study of 40 patients with severe PGD at 72 hours and 80 matched controls without PGD, elevated preoperative CFH was independently associated with increased PGD risk (odds ratio [OR] 2.75, 95%CI, 1.23-6.16, P = 0.014). The effect of CFH on PGD was magnified by reperfusion fraction of inspired oxygen (FiO2) ≥ 0.40 (OR 3.41, P = 0.031). Isolated perfused human lungs exposed to intravascular CFH (100 mg/dl) developed increased vascular permeability as measured by lung weight (CFH 14.4% vs. control 0.65%, P = 0.047) and extravasation of Evans blue-labeled albumin dye (EBD) into the airspace (P = 0.027). CFH (1 mg/dl) also increased paracellular permeability of human pulmonary microvascular endothelial cell monolayers (hPMVECs). Hyperoxia (FiO2 = 0.95) increased human lung and hPMVEC permeability compared with normoxia (FiO2 = 0.21). Treatment with acetaminophen (15 μg/ml), a specific hemoprotein reductant, prevented CFH-dependent permeability in human lungs (P = 0.046) and hPMVECs (P = 0.037). In summary, CFH may mediate PGD through oxidative effects on microvascular permeability, which are augmented by hyperoxia and abrogated by acetaminophen.

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.

Pathophysiology and classification of primary graft dysfunction after lung transplantation

The term primary graft dysfunction (PGD) incorporates a continuum of disease severity from moderate to severe acute lung injury (ALI) within 72 h of lung transplantation. It represents the most significant obstacle to achieving good early post-transplant outcomes, but is also associated with increased incidence of bronchiolitis obliterans syndrome (BOS) subsequently. PGD is characterised histologically by diffuse alveolar damage, but is graded on clinical grounds with a combination of PaO2/FiO2 (P/F) and the presence of radiographic infiltrates, with 0 being absence of disease and 3 being severe PGD. The aetiology is multifactorial but commonly results from severe ischaemia-reperfusion injury (IRI), with tissue-resident macrophages largely responsible for stimulating a secondary 'wave' of neutrophils and lymphocytes that produce severe and widespread tissue damage. Donor history, recipient health and operative factors may all potentially contribute to the likelihood of PGD development. Work that aims to minimise the incidence of PGD in ongoing, with techniques such as ex vivo perfusion of donor lungs showing promise both in research and in clinical studies. This review will summarise the current clinical status of PGD before going on to discuss its pathophysiology, current therapies available and future directions for clinical management of PGD.

Potential Roles for C1 Inhibitor in Transplantation

Complement is a major contributor to inflammation and graft injury. This system is especially important in ischemia-reperfusion injury/delayed graft function as well as in acute and chronic antibody-mediated rejection (AMR). The latter is increasingly recognized as a major cause of late graft loss, for which we have few effective therapies. C1 inhibitor (C1-INH) regulates several pathways which contribute to both acute and chronic graft injuries. However, C1-INH spares the alternative pathway and the membrane attack complex (C5–9) so innate antibacterial defenses remain intact. Plasma-derived C1-INH has been used to treat hereditary angioedema for more than 30 years with excellent safety. Studies with C1-INH in transplant recipients are limited, but have not revealed any unique toxicity or serious adverse events attributed to the protein. Extensive data from animal and ex vivo models suggest that C1-INH ameliorates ischemia-reperfusion injury. Initial clinical studies suggest this effect may allow transplantation of donor organs which are now discarded because the risk of primary graft dysfunction is considered too great. Although the incidence of severe early AMR is declining, accumulating evidence strongly suggests that complement is an important mediator of chronic AMR, a major cause of late graft loss. Thus, C1-INH may also be helpful in preserving function of established grafts. Early clinical studies in transplantation suggest significant beneficial effects of C1-INH with minimal toxicity. Recent results encourage continued investigation of this already-available therapeutic agent.

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

The monolayer of endothelial cells lining the vessel wall forms a semipermeable barrier (in all tissue except the relatively impermeable blood-brain and inner retinal barriers) that regulates tissue-fluid homeostasis, transport of nutrients, and migration of blood cells across the barrier. Permeability of the endothelial barrier is primarily regulated by a protein complex called adherens junctions. Adherens junctions are not static structures; they are continuously remodeled in response to mechanical and chemical cues in both physiological and pathological settings. Here, we discuss recent insights into the post-translational modifications of junctional proteins and signaling pathways regulating plasticity of adherens junctions and endothelial permeability. We also discuss in the context of what is already known and newly defined signaling pathways that mediate endothelial barrier leakiness (hyperpermeability) that are important in the pathogenesis of cardiovascular and lung diseases and vascular inflammation.

Protein biomarkers associated with primary graft dysfunction following lung transplantation

Severe primary graft dysfunction affects 15-20% of lung transplant recipients and carries a high mortality risk. In addition to known donor, recipient, and perioperative clinical risk factors, numerous biologic factors are thought to contribute to primary graft dysfunction. Our current understanding of the pathogenesis of lung injury and primary graft dysfunction emphasizes multiple pathways leading to lung endothelial and epithelial injury. Protein biomarkers specific to these pathways can be measured in the plasma, bronchoalveolar lavage fluid, and lung tissue. Clarification of the pathophysiology and timing of primary graft dysfunction could illuminate predictors of dysfunction, allowing for better risk stratification, earlier identification of susceptible recipients, and development of targeted therapies. Here, we review much of what has been learned about the association of protein biomarkers with primary graft dysfunction and evaluate this association at different measurement time points.

Endothelial permeability following coronary artery bypass grafting: an observational study on the possible role of angiopoietin imbalance

BACKGROUND

Unresolved inflammation resulting in capillary leakage with endothelial barrier dysfunction is a major contributor to postoperative morbidity and mortality after coronary artery bypass graft (CABG). Angiopoietins (ANGs) are vascular growth factors, also mediating inflammation and disruption of the endothelium, thus inducing capillary leakage. We hypothesized that changes in the relative serum levels of ANG1 and ANG2 influence endothelial barrier function and perioperative morbidity after CABG.

METHODS

After approval and informed consent, serum samples (n = 28) were collected pre CABG surgery, 1, 6, and 24 h after aortic de-clamping. ANG1, ANG2, soluble ANG receptor TIE2 (sTIE2), and IL-6 serum concentrations were analyzed by ELISA. Human pulmonary microvascular endothelial cells (HPMECs) were incubated with patient serum and FITC-dextran permeability was assessed. Furthermore, ANG2 secretion of HPMECs was analyzed after incubation with IL-6-containing patient serum.

RESULTS

CABG induced an early and sustained increase of ANG2/ANG1 ratio (5-fold after 24 h compared to pre-surgery). These changes correlated with elevated serum lactate levels, fluid balance, as well as the duration of mechanical ventilation. Permeability of HPMECs significantly increased after incubation with post-surgery serum showing a marked shift of ANG2/ANG1 balance (18-fold) compared to serum with a less pronounced increase (6-fold). Furthermore, CABG resulted in increased IL-6 serum content. Pre-incubation with serum containing high levels of IL-6 amplified the ANG2 secretion by HPMECs; however, this was not influenced by blocking IL-6.

CONCLUSIONS

CABG affects the balance between ANG1 and ANG2 towards a dominance of the barrier-disruptive ANG2. Our data suggest that this ANG2/ANG1 imbalance contributes to an increased postoperative endothelial permeability, likewise being reflected by the clinical course. The results strongly suggest a biological effect of altered angiopoietin balance during cardiac surgery on endothelial permeability.

MicroRNA-150 Suppression of Angiopoetin-2 Generation and Signaling Is Crucial for Resolving Vascular Injury

OBJECTIVE

Increased vascular permeability is a hallmark of sepsis and acute respiratory distress syndrome. Angiopoietin (Ang2) induces vascular leak, and excess Ang2 generation is associated with patient mortality from these diseases. However, mechanisms dampening Ang2 generation during injury remain unclear. Interestingly, microRNA (miR)-150 levels were decreased in septic patients. miR regulate signaling networks by silencing mRNAs containing complementary sequences. Thus, we hypothesized that miR-150 suppresses Ang2 generation and thereby resolves vascular injury.

APPROACH AND RESULTS

Wild-type or miR-150(-/-) mice or endothelial cells were exposed to lipopolysaccharide or sepsis, and Ang2 levels, adherens junction reannealing, endothelial barrier function, and mortality were determined. Although Ang2 transiently increased during lipopolysaccharide-induced injury in wild-type endothelial cells and lungs, miR-150 expression was elevated only during recovery from injury. Deletion of miR-150 caused a persistent increase in Ang2 levels and impaired adherens junctions reannealing after injury, resulting thereby in an irreversible increase in vascular permeability. Also, miR-150(-/-) mice died rapidly after sepsis. Rescuing miR-150 expression in endothelial cells prevented Ang2 generation, thereby restoring vascular barrier function in miR-150(-/-) mice. miR-150 terminated Ang2 generation by targeting the transcription factor, early growth response 2. Thus, early growth response 2 or Ang2 depletion in miR-150(-/-) endothelial cells restored junctional reannealing and reinstated barrier function. Importantly, upregulating miR-150 expression by injecting a chemically synthesized miR-150 mimic into wild-type mice vasculature decreased early growth response 2 and Ang2 levels and hence mortality from sepsis.

CONCLUSIONS

miR-150 is a novel suppressor of Ang2 generation with a key role in resolving vascular injury and reducing mortality resulting from sepsis.

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.

Role of innate immunity in primary graft dysfunction after lung transplantation

PURPOSE OF REVIEW

Primary graft dysfunction (PGD), a form of acute lung injury after lung transplantation, has a significant impact on clinical outcomes after lung transplantation. This potentially reversible graft impairment occurs after ischemia-reperfusion injury. This review describes the expanding body of literature evaluating the central role of innate immune activation, nonadaptive responses and dysregulation in the development of PGD after lung transplant.

RECENT FINDINGS

The innate immune system, highlighted by Toll-like receptor pathways and neutrophil migration and influx, plays an important role in the initiation and propagation of ischemia-reperfusion injury. Recent plasma biomarker and gene association studies have identified several genes and proteins composing innate immune pathways to be associated with PGDs. Long pentraxin-3 and Toll-like receptors, as well as inflammasomes and Toll-interacting protein, are associated with the development of PGD after lung transplantation.

SUMMARY

Innate immune pathways are involved in the development of PGD and may provide attractive targets for therapies. It may be possible to prevent or treat PGD, as well as to allow pre-transplant PGD risk stratification. To improve understanding of the mechanisms behind clinical risk factors for PGD will require further in-depth correlation of donor-specific and recipient-related triggers of nonadaptive immune responses.

Elevated levels of angiopoietin-2 as a biomarker for respiratory failure after cardiac surgery

OBJECTIVES

Angiopoietin-1 and angiopoietin-2 are important factors in regulating endothelial vascular permeability. This study evaluated perioperative changes in serum levels of angiopoietin-1 and -2 in patients undergoing cardiac surgery.

DESIGN

Measurement of serum levels of angiopoietin-1 and angiopoietin-2 in samples collected during a previously conducted prospective, multicenter, observational study.

SETTING

Three university hospitals.

PARTICIPANTS

Eighty-four adult patients undergoing cardiac surgery.

INTERVENTION

Serum levels of angiopoietins were measured at baseline, immediately after surgery, and the day after surgery (POD-1).

MEASUREMENTS AND MAIN RESULTS

Serum levels of angiopoietin-2 were elevated by POD-1 (median 3.3 ng/mL, interquartile range [IQR] 2.5-4.6 ng/mL) compared with baseline (median 1.6 ng/mL, IQR 1.3-2.1 ng/mL, p < 0.0001), and angiopoietin-1 levels were decreased immediately after surgery (baseline median 23.2 ng/mL, IQR 10.2-32.8 ng/mL; postoperative median 8.0 ng/mL, IQR 1.5-13.2 ng/mL, p<0.0001). Angiopoietin-2 levels on POD-1 in patients undergoing off-pump coronary artery bypass grafting were significantly lower than those in patients undergoing aortic surgery (p = 0.0009) and valve surgery (p = 0.008). Angiopoietin-2 levels on POD-1 had a predictive performance of the area under the curve (AUC) of the receiver operating characteristic curve 0.74 for mechanical ventilation>3 days. Angiopoietin-1 levels and the angiopoietin-2/angiopoietin-1 ratio showed lower predictive performance (AUC values 0.58 and 0.68, respectively).

CONCLUSIONS

Angiopoietin-2 serum levels were elevated after cardiac surgery. Elevated angiopoietin-2 had a good predictive performance for respiratory failure after cardiac surgery, perhaps reflecting the severity of lung dysfunction related to postoperative increases in vascular permeability.

Twist1 controls lung vascular permeability and endotoxin-induced pulmonary edema by altering Tie2 expression

Tight regulation of vascular permeability is necessary for normal development and deregulated vascular barrier function contributes to the pathogenesis of various diseases, including acute respiratory distress syndrome, cancer and inflammation. The angiopoietin (Ang)-Tie2 pathway is known to control vascular permeability. However, the mechanism by which the expression of Tie2 is regulated to control vascular permeability has not been fully elucidated. Here we show that transcription factor Twist1 modulates pulmonary vascular leakage by altering the expression of Tie2 in a context-dependent way. Twist1 knockdown in cultured human lung microvascular endothelial cells decreases Tie2 expression and phosphorylation and increases RhoA activity, which disrupts cell-cell junctional integrity and increases vascular permeability in vitro. In physiological conditions, where Ang1 is dominant, pulmonary vascular permeability is elevated in the Tie2-specific Twist1 knockout mice. However, depletion of Twist1 and resultant suppression of Tie2 expression prevent increase in vascular permeability in an endotoxin-induced lung injury model, where the balance of Angs shifts toward Ang2. These results suggest that Twist1-Tie2-Angs signaling is important for controlling vascular permeability and modulation of this mechanism may lead to the development of new therapeutic approaches for pulmonary edema and other diseases caused by abnormal vascular permeability.

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.

Dysregulation of the angiopoietin-Tie-2 axis in sepsis and ARDS

Dynamic changes in microvascular endothelial structure and function are pivotal in the acute inflammatory response, the body's rapid, coordinated effort to localize, sequester, and eliminate microbial invaders at their portal of entry. To achieve this, the endothelium becomes leaky and inflamed, providing innate immune cells and humoral effector molecules access to the site of infection. During sepsis this locally adaptive response becomes manifest throughout the body, leading to dangerous host consequences. Increased leakiness in the pulmonary circulation contributes to acute respiratory distress syndrome (ARDS), a complication of sepsis associated with 40% mortality. Understanding the molecular governance of vascular leak and inflammation has major diagnostic, prognostic, and potentially therapeutic implications for this common and pernicious disease. This review summarizes results from cell-based experiments, animal models, and observational human studies; together, these studies suggest that an endothelial receptor called Tie2 and its ligands, called angiopoietins, form a signaling axis key to the vascular dyshomeostasis that underlies sepsis.