Plasma angiopoietin-2 levels increase in children following cardiopulmonary bypass

Promising results of a clinical feasibility study: CIRBP as a potential biomarker in pediatric cardiac surgery

Objective

Cold-inducible RNA binding Protein (CIRBP) has been shown to be a potent inflammatory mediator and could serve as a novel biomarker for inflammation. Systemic inflammatory response syndrome (SIRS) and capillary leak syndrome (CLS) are frequent complications after pediatric cardiac surgery increasing morbidity, therefore early diagnosis and therapy is crucial. As CIRBP serum levels have not been analyzed in a pediatric population, we conducted a clinical feasibility establishing a customized magnetic bead panel analyzing CIRBP in pediatric patients undergoing cardiac surgery.

Methods

A prospective hypothesis generating observational clinical study was conducted at the German Heart Center Berlin during a period of 9 months starting in May 2020 (DRKS00020885, https://drks.de/search/de/trial/DRKS00020885). Serum samples were obtained before the cardiac operation, upon arrival at the pediatric intensive care unit, 6 and 24 h after the operation in patients up to 18 years of age with congenital heart disease (CHD). Customized multiplex magnetic bead-based immunoassay panels were developed to analyze CIRBP, Interleukin-1β (IL-1β), Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10), Monocyte chemotactic protein 1 (MCP-1), Syndecan-1 (SDC-1), Thrombomodulin (TM), Vascular endothelial growth factor (VEGF-A), Angiopoietin-2 (Ang-2), and Fibroblast growth factor 23 (FGF-23) in 25 µl serum using the Luminex MagPix® system.

Results

19 patients representing a broad range of CHD (10 male patients, median age 2 years, 9 female patients, median age 3 years) were included in the feasibility study. CIRBP was detectable in the whole patient cohort. Relative to individual baseline values, CIRBP concentrations increased 6 h after operation and returned to baseline levels over time. IL-6, IL-8, IL-10, and MCP-1 concentrations were significantly increased after operation and except for MCP-1 concentrations stayed upregulated over time. SDC-1, TM, Ang-2, as well as FGF-23 concentrations were also significantly increased, whereas VEGF-A concentration was significantly decreased after surgery.

Discussion

Using customized magnetic bead panels, we were able to detect CIRBP in a minimal serum volume (25 µl) in all enrolled patients. To our knowledge this is the first clinical study to assess CIRBP serum concentrations in a pediatric population.

The Role of Angiopoietin-2 on Plasma Leakage in the Critical Phase and Convalescence of Dengue Virus Infection in Children

Abstract Background: The worst complication of dengue haemorrhagic fever (DHF) that lead to death is hypovolemic shock due to plasma leakage from intravascular to extravascular space caused by endothelial dysfunction. This study is aimed to analyze the difference of Ang-2 level in dengue haemorrhagic fever patients related to plasma leakage between critical phase and convalescence.   Aim: One hundred and ten children with DHF confirmed serologically with positive IgM anti-dengue or IgM and IgG anti-dengue were recruited in this study. We examine the clinical manifestations, laboratory parameters (platelet count, AST and ALT levels), and molecular test (Ang-2). The molecular indicator was tested by Enzyme-Linked Immunosorbent Assay (ELISA). Data were collected between July – November 2019. This is an observational study with cross-sectional comparative design.   Results: In our study, we found correlation of clinical symptoms (abdominal pain, persistent vomit, and hepatomegaly) with the occurrence of plasma leakage in DHF patients. We also found that Ang-2 level is significantly higher in children with DHF during critical phase compared to convalescence (p< 0.01).   Conclusion: There is a significant difference of Ang-2 level in DHF patients during critical phase and convalescence.   Keywords: Dengue hemorrhagic fever, children, Ang-2, critical phase, convalescence

Changes in Plasma Angiopoietin Levels After Transcatheter Aortic Valve Replacement and Surgical Aortic Valve Replacement: A Prospective Cohort Study

OBJECTIVE

Angiopoietins (Angs) regulate endothelial permeability. Ang-1 and 2 (Ang-1 and Ang-2) are implied in endothelial stability through an antagonism effect. The objectives of the present study were to describe and compare changes in Ang levels after transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR).

DESIGN

A prospective, single-center study.

PARTICIPANTS

Adult patients with aortic stenosis scheduled for SAVR or TAVR.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Ang-1 and Ang-2 were measured using an enzyme-linked immunosorbent assay right before surgery (T0), at the end of surgery (T1), and at day one (T2). Sixty consecutive patients (SAVR group [n = 30] and TAVR group [n = 30]) were included between January and June 2017. Ang-1 decreased significantly after both TAVR (T0: 3,663 [2,602-4,262]; T1: 1,611 [981-2,409]; T2: 1,082 [652-1,589] ng/mL; p < 0.0001) and SAVR (T0: 1,603 [975-2,849]; T1: 783 [547-1,024]; T2: 828 [460-1,227] ng/mL; p = 0.0001). Ang-2 increased significantly after SAVR (T0: 2,472 [1,502-3,622]; T1: 2,997 [1,759-3,839]; T2: 5,421 [3,557-7,087] ng/mL; p < 0.0001) but did not change markedly after TAVR (T0: 3,343 [2,661-6,272]; T1: 3,788 [2,574-5,016]; T2: 3,446 [3,029-6,313] ng/mL; p = 0.066). Among patients with paravalvular leakage, the changes in the plasma Ang-2 level and the Ang-2/Ang-1 ratio were greater.

CONCLUSION

SAVR induces greater alterations of Ang homeostasis than TAVR, confirming a role for the use of cardiopulmonary bypass. Paravalvular leakage after TAVR is associated with Ang changes similar to those observed with SAVR.

Rise in Angiopoietin-2 Following Neonatal Cardiac Surgery Is Associated With Adverse Clinical Outcomes

OBJECTIVES

Neonatal cardiac surgery for congenital cardiac defects is associated with significant morbidity and mortality, and there is a need for early identification of patients at highest risk of adverse outcomes. Because vascular endothelial injury mediates damage across organ systems, we measured serum biomarkers of endothelial injury in neonates following cardiopulmonary bypass and examined their associations with short-term outcomes.

DESIGN

Prospective cohort study.

SETTING

Pediatric cardiac ICU.

PATIENTS

Thirty neonates less than 2 weeks old undergoing repair of congenital cardiac defects with cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Biomarkers of endothelial integrity, angiopoietin-1 and angiopoietin-2, were measured preoperatively and at 24 hours postoperatively. A composite adverse outcome was defined as any of the following: stroke, need for renal replacement therapy, extracorporeal membrane oxygenation support, cardiac arrest, or death. Associations of biomarkers with adverse outcomes were examined using Wilcoxon rank-sum test. There was an increase in angiopoietin-2 from preoperatively to 24 hours postoperatively (p < 0.0001) and a decrease in angiopoietin-1 from preoperatively to 24 hours postoperatively (p < 0.0001). Patients with greater rise in angiopoietin-2 from preoperatively to 24 hours postoperatively had greater risk of composite adverse outcome (p = 0.04). They had a trend toward higher Vasoactive-Inotropic Score (p = 0.06) and a higher prevalence of low cardiac output syndrome (p = 0.06). Twenty-four hour postoperative angiopoietin-2 level was associated with the composite adverse outcome (p = 0.03). The rise in angiopoietin-2 level from preoperatively to 24 hours postoperatively directly correlated with cardiopulmonary bypass duration (r = 0.47; p = 0.01).

CONCLUSIONS

In neonatal cardiac surgery, longer duration of cardiopulmonary bypass is directly associated with greater endothelial injury as measured by increased serum levels of angiopoietin-2. Angiopoietin-2 levels 24 hours postoperatively were significantly associated with a composite adverse outcome. Postoperative angiopoietin-2 level may serve as an early indicator of patients in need of closer monitoring and protective intervention. Further research into endothelial protective strategies is warranted.

Plasma and Urinary FGF-2 and VEGF-A Levels Identify Children at Risk for Severe Bleeding after Pediatric Cardiopulmonary Bypass: A Pilot Study

Severe bleeding after cardiothoracic surgery with cardiopulmonary bypass (CPB) is associated with increased morbidity and mortality in adults and children. Fibroblast Growth Factor-2 (FGF-2) and Vascular Endothelial Growth Factor-A (VEGF-A) induce hemorrhage in murine models with heparin exposure. We aim to determine if plasma and urine levels of FGF-2 and VEGF-A in the immediate perioperative period can identify children with severe bleeding after CPB. We performed a prospective, observational biomarker study in 64 children undergoing CPB for congenital heart disease repair from June 2015 - January 2017 in a tertiary pediatric referral center. Primary outcome was severe bleeding defined as ≥ 20% estimated blood volume loss within 24-hours. Independent variables included perioperative plasma and urinary FGF-2 and VEGF-A levels. Analyses included comparative (Wilcoxon rank sum, Fisher's exact, and Student's t tests) and discriminative (receiver operator characteristic [ROC] curve) analyses. Forty-eight (75%) children developed severe bleeding. Median plasma and urinary FGF-2 and VEGF-A levels were elevated in children with severe bleeding compared to without bleeding (preoperative: plasma FGF-2 = 16[10-35] vs. 9[2-13] pg/ml; urine FGF-2= 28[15-76] vs. 14.5[1.5-22] pg/mg; postoperative: plasma VEGF-A = 146[34-379] vs. 53 [0-134] pg/ml; urine VEGF-A = 132 [52-257] vs. 45[0.1-144] pg/mg; all p < 0.05). ROC curve analyses of combined plasma and urinary FGF-2 and VEGF-A levels discriminated severe postoperative bleeding (AUC: 0.73-0.77) with mean sensitivity and specificity above 80%. We conclude that the perioperative plasma and urinary levels of FGF-2 and VEGF-A discriminate risk of severe bleeding after pediatric CPB.

Angiopoietin Level Trajectories in Toddlers With Severe Sepsis and Septic Shock and Their Effect on Capillary Endothelium

OBJECTIVE

Angiopoietins are postulated diagnostic biomarkers in children and adults with severe sepsis and septic shock. The diagnostic value of angiopoietins in children less than 5 years old has not been established, nor has their effect on permeability in the capillary microvasculature. We aim to determine if levels of angiopoietin-1 or -2 (angpt-1, -2) are diagnostic for severe sepsis/shock in young children and whether they affect the permeability of cultured human dermal microvascular endothelial cells (HDMEC).

DESIGN

Prospective observational study of children < 5 years old. Patients were classified as non-systemic inflammatory response syndrome (SIRS), SIRS/sepsis and severe sepsis/septic shock.

SETTING

Tertiary care pediatric hospitals.

PATIENTS

Critically ill children.

INTERVENTIONS

None.

MEASUREMENTS

Plasma angpt-1 and -2 levels were measured with enzyme-linked immunoassays. Expression of angpt-2 in endothelial cells was assessed with quantitative polymerase chain reaction. Permeability changes in cultured HDMECs were assessed with transendothelial electrical resistance measurements.

RESULTS

Angpt-1 levels were significantly higher in younger children compared with levels found in previous study of older children across disease severity (all P < 0.001). Angpt-2 was significantly higher in this cohort with severe sepsis/septic shock compared with children without SIRS and SIRS/sepsis (all P < 0.003). Angpt-2/1 ratio was also elevated in children with severe sepsis/septic shock but an order of magnitude less than older children (P < 0.02, P = 0.002). Angpt-1 and -2 did not affect basal HDMEC permeability or modulate leak in isolation or in the presence of tumor necrosis factor (TNF).

CONCLUSIONS

Angpt-2 levels and the angpt-2/1 ratio are appropriate diagnostic biomarkers of severe sepsis/septic shock in children less than 5 years old. Neither angpt-1 nor -2 affects basal HDMEC permeability alone or modulates TNF induced capillary leak.

Endothelial-Dependent Vasomotor Dysfunction in Infants After Cardiopulmonary Bypass

OBJECTIVES

Cardiopulmonary bypass-induced endothelial dysfunction has been inferred by changes in pulmonary vascular resistance, alterations in circulating biomarkers, and postoperative capillary leak. Endothelial-dependent vasomotor dysfunction of the systemic vasculature has never been quantified in this setting. The objective of the present study was to quantify acute effects of cardiopulmonary bypass on endothelial vasomotor control and attempt to correlate these effects with postoperative cytokines, tissue edema, and clinical outcomes in infants.

DESIGN

Single-center prospective observational cohort pilot study.

SETTING

Pediatric cardiac ICU at a tertiary children's hospital.

PATIENTS

Children less than 1 year old requiring cardiopulmonary bypass for repair of a congenital heart lesion.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Laser Doppler perfusion monitoring was coupled with local iontophoresis of acetylcholine (endothelium-dependent vasodilator) or sodium nitroprusside (endothelium-independent vasodilator) to quantify endothelial-dependent vasomotor function in the cutaneous microcirculation. Measurements were obtained preoperatively, 2-4 hours, and 24 hours after separation from cardiopulmonary bypass. Fifteen patients completed all laser Doppler perfusion monitor (Perimed, Järfälla, Sweden) measurements. Comparing prebypass with 2-4 hours postbypass responses, there was a decrease in both peak perfusion (p = 0.0006) and area under the dose-response curve (p = 0.005) following acetylcholine, but no change in responses to sodium nitroprusside. Twenty-four hours after bypass responsiveness to acetylcholine improved, but typically remained depressed from baseline. Conserved endothelial function was associated with higher urine output during the first 48 postoperative hours (R = 0.43; p = 0.008).

CONCLUSIONS

Cutaneous endothelial dysfunction is present in infants immediately following cardiopulmonary bypass and recovers significantly in some patients within 24 hours postoperatively. Confirmation of an association between persistent endothelial-dependent vasomotor dysfunction and decreased urine output could have important clinical implications. Ongoing research will explore the pattern of endothelial-dependent vasomotor dysfunction after cardiopulmonary bypass and its relationship with biochemical markers of inflammation and clinical outcomes.

Microcirculatory perfusion disturbances following cardiac surgery with cardiopulmonary bypass are associated with in vitro endothelial hyperpermeability and increased angiopoietin-2 levels

Background

Endothelial hyperpermeability following cardiopulmonary bypass (CPB) contributes to microcirculatory perfusion disturbances and postoperative complications after cardiac surgery. We investigated the postoperative course of renal and pulmonary endothelial barrier function and the association with microcirculatory perfusion and angiopoietin-2 levels in patients after CPB.

Methods

Clinical data, sublingual microcirculatory data, and plasma samples were collected from patients undergoing coronary artery bypass graft surgery with CPB (n = 17) before and at several time points up to 72 h after CPB. Renal and pulmonary microvascular endothelial cells were incubated with patient plasma, and in vitro endothelial barrier function was assessed using electric cell–substrate impedance sensing. Plasma levels of angiopoietin-1,-2, and soluble Tie2 were measured, and the association with in vitro endothelial barrier function and in vivo microcirculatory perfusion was determined.

Results

A plasma-induced reduction of renal and pulmonary endothelial barrier function was observed in all samples taken within the first three postoperative days (P < 0.001 for all time points vs. pre-CPB). Angiopoietin-2 and soluble Tie2 levels increased within 72 h after CPB (5.7 ± 4.4 vs. 1.7 ± 0.4 ng/ml, P < 0.0001; 16.3 ± 4.7 vs. 11.9 ± 1.9 ng/ml, P = 0.018, vs. pre-CPB), whereas angiopoietin-1 remained stable. Interestingly, reduced in vitro renal and pulmonary endothelial barrier moderately correlated with reduced in vivo microcirculatory perfusion after CPB (r = 0.47, P = 0.005; r = 0.79, P < 0.001). In addition, increased angiopoietin-2 levels moderately correlated with reduced in vitro renal and pulmonary endothelial barrier (r = − 0.46, P < 0.001; r = − 0.40, P = 0.005) and reduced in vivo microcirculatory perfusion (r = − 0.43, P = 0.01; r = − 0.41, P = 0.03).

Conclusions

CPB is associated with an impairment of in vitro endothelial barrier function that continues in the first postoperative days and correlates with reduced postoperative microcirculatory perfusion and increased circulating angiopoietin-2 levels. These results suggest that angiopoietin-2 is a biomarker for postoperative endothelial hyperpermeability, which may contribute to delayed recovery of microcirculatory perfusion after CPB.

Trial registration

NTR4212.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2418-5) contains supplementary material, which is available to authorized users.

Evaluation of plasma angiopoietin-2 and vascular endothelial growth factor in healthy dogs and dogs with systemic inflammatory response syndrome or sepsis

Background

Angiopoietin‐2 (Ang‐2) and vascular endothelial growth factor (VEGF) are regulators of endothelial permeability.

Objective

Plasma concentrations of Ang‐2 and VEGF are increased in dogs with systemic inflammatory response syndrome (SIRS) and sepsis and are correlated with disease severity and outcome.

Animals

Healthy dogs (n = 18) and client‐owned dogs with SIRS (n = 34) or sepsis (n = 25).

Methods

Prospective observational study. Ang‐2 and VEGF concentrations in admission plasma samples were compared between healthy dogs and dogs with SIRS or sepsis, and between survivors and non‐survivors. Correlations with the acute patient physiologic and laboratory evaluation (APPLE_fast) disease severity score were examined.

Results

Median Ang‐2 was significantly higher in dogs with SIRS (19.3; interquartile range [IQR]: 8.6‐25.7 ng/mL) and sepsis (21.2; IQR: 10.3‐30.1 ng/mL) compared to healthy dogs (7.6; IQR: 6.7‐9.8 ng/mL). Ang‐2 was significantly higher in non‐survivors (24.1; IQR: 11.9‐50.0 ng/mL) than survivors (10.2; IQR: 7.2‐21.5 ng/mL) but did not correlate with the APPLE_fast score. Admission Ang‐2 predicted negative outcome in dogs with SIRS and sepsis with reasonable accuracy (area under the curve [AUC]: 0.75, confidence interval [CI]: 0.59‐0.85; sensitivity: 0.5, CI: 0.29‐0.71; specificity: 0.87, CI: 0.75‐0.95); differentiation between sepsis and SIRS was poor (AUC: 0.58). Plasma VEGF was significantly higher in dogs with sepsis (45; IQR: 14‐107.5 pg/mL) than in dogs with SIRS (3.3; IQR: 0‐35.6 pg/mL) or healthy dogs (0; IQR: 0 pg/mL; P = 0.008). VEGF was significantly (P = .0004) higher in non‐survivors (34.5; IQR: 0‐105.7 pg/mL) than in survivors (0; IQR: 0‐55.2 pg/mL). The ability of VEGF to predict a negative outcome was poor.

Conclusions and Clinical Importance

Ang‐2 may represent a useful additional prognostic marker in dogs with SIRS.

Sera From Children After Cardiopulmonary Bypass Reduces Permeability of Capillary Endothelial Cell Barriers

OBJECTIVES

Children undergoing cardiopulmonary bypass develop clinically impactful capillary leak of unclear etiology. A widely held hypothesis that exposure of circulating cells to the cardiopulmonary bypass circuit induces the release of inflammatory mediators that act to disrupt intercellular junctions of capillary endothelial cells inducing paracellular capillary leak either directly or through new gene expression.

DESIGN

Cohort study.

SETTING

Tertiary pediatric hospital.

PATIENTS

Twenty children undergoing surgery with cardiopulmonary bypass for congenital heart disease. Serum was collected before cardiopulmonary bypass, 2 hours after cardiopulmonary bypass, and 18 hours after cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We analyzed the effects of 10% patient sera on the "function, structure, and gene expression" of cultured human dermal and pulmonary microvascular endothelial cells. Changes in barrier "function" were measured using transendothelial electrical resistance. Associations between changes in transendothelial electrical resistance and subject characteristics were analyzed using linear mixed effects model with area under the resistance curve as outcome. Changes in junctional "structure" were assessed by analyzing the organization of the endothelial cell junctional proteins claudin-5 and VE-cadherin using immunofluorescence microscopy. Changes in inflammatory "gene expression" were measured using real-time quantitative reverse transcription-polymerase chain reaction. All serum samples induced a transient, 120-minute increase in transendothelial electrical resistance followed by persistent loss of barrier function. Unexpectedly, sera collected postcardiopulmonary bypass-induced significantly less loss of barrier function in both dermal and pulmonary capillary endothelial cell compared with precardiopulmonary bypass sera. Consistent with the transendothelial electrical resistance results, claudin-5 and vascular endothelial-cadherin junctional staining showed less disruption in cultures treated with postcardiopulmonary bypass sera. Expression of genes commonly associated with inflammation was largely unaffected by patient sera.

CONCLUSIONS

Contrary to the hypothesis, sera taken from children after cardiopulmonary bypass induces less capillary barrier disruption relative to sera taken from children before cardiopulmonary bypass, and none of the sera induced significant changes in expression of inflammatory genes.

Endothelial Cell Function and Dysfunction in Critically Ill Children

Endothelial cells (ECs) line the lumen of the entire vascular system and actively regulate blood flow; maintain blood fluidity; control water, solute, and macromolecular transfer between blood and tissue; and modulate circulating immune cell recruitment and activation. These vital functions, combined with the broad anatomic distribution of ECs, implicate them in all forms of critical illness. The present article discusses how ECs adapt and break down during the course of critical illness. We first review the biology of ECs, highlighting the vascular segmental differences and their specific roles in the maintenance of homeostasis. We then discuss how ECs acquire new functions to restore local and systemic homeostasis (activation) as well as how breakdowns in EC functions (dysfunction) contribute to local and systemic pathologic responses, with clinical correlations. Lastly, how these processes have been studied in critically ill children is discussed.

Systemic angiopoietin-1/2 dysregulation following cardiopulmonary bypass in adults

AIM

Vascular leakage following cardiopulmonary bypass contributes to morbidity. Angiopoietin-1 and -2 are biomarkers of endothelial dysfunction. Our aim was to characterize Ang-1 and -2 association with clinical characteristics and outcomes.

METHODS

Observational cohort study measuring Ang-1/-2 with a panel of cytokines in adults undergoing cardiopulmonary bypass.

RESULTS

Ang-2 levels increased immediately postop whereas Ang-1 levels decreased over time. No significant correlation was found with other inflammatory mediators. High correlation was found between the hospital length of stay and Ang-2 increase at 24 h (rho = 0.590; p < 0.0001). The predictors of Ang-2 increase were female gender, cross clamp time, transfusion of blood and absence of angiotensin-converting enzyme inhibitor as a pre-op medication.

CONCLUSION

Angiopoietins can detect vascular leakage early and could impact patient's management to decrease length of stay after cardiac surgery.

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.

Angiopoietin/Tie2 Dysbalance Is Associated with Acute Kidney Injury after Cardiac Surgery Assisted by Cardiopulmonary Bypass

INTRODUCTION

The pathophysiology of acute kidney injury (AKI) after cardiac surgery is not completely understood. Recent evidence suggests a pivotal role for the endothelium in AKI. In experimental models of AKI, the endothelial specific receptor Tie2 with its ligands Angiopoietin (Ang) 1 and Ang2 are deranged. This study investigates their status after cardiac surgery, and a possible relation between angiopoietins and AKI.

METHODS

From a cohort of 541 patients that underwent cardiac surgery, blood and urine was collected at 5 predefined time points. From this cohort we identified 21 patients who had at least 50% post-operative serum creatinine increase (AKI). We constructed a control group (n = 21) using propensity matching. Systemic levels of Ang1, Ang2, and sTie2 were measured in plasma and the AKI markers albumin, kidney injury molecule-1 (KIM-1) and N-acetyl-beta-D-glucosaminidase (NAG) were measured in the urine.

RESULTS

Ang2 plasma levels increased over time in AKI (from 4.2 to 11.6 ng/ml) and control patients (from 3.0 to 6.7 ng/ml). Ang2 levels increased 1.7-fold more in patients who developed AKI after cardiac surgery compared to matched control patients. Plasma levels of sTie2 decreased 1.6-fold and Ang1 decreased 3-fold over time in both groups, but were not different between AKI and controls (Ang1 P = 0.583 and sTie2 P = 0.679). Moreover, we found a positive correlation between plasma levels of Ang2 and urinary levels of NAG.

CONCLUSIONS

The endothelial Ang/Tie2 system is in dysbalance in patients that develop AKI after cardiac surgery compared to matched control patients.

Raised plasma Robo4 and cardiac surgery-associated acute kidney injury

OBJECTIVE

Endothelial dysfunction associated with systemic inflammation can contribute to organ injury/failure following cardiac surgery requiring cardiopulmonary bypass (CPB). Roundabout protein 4 (Robo4), an endothelial-expressed transmembrane receptor and regulator of cell activation, is an important inhibitor of endothelial hyper-permeability. We investigated the hypothesis that plasma levels of Robo4 are indicative of organ injury, in particular acute kidney injury (AKI), after cardiac surgery.

METHODS

Patients (n = 32) undergoing elective cardiac surgery with CPB were enrolled, prospectively. Plasma Robo4 concentrations were measured pre-, 2 and 24 h post-operatively, using a commercially available ELISA. Plasma and endothelial markers of inflammation [interleukin (IL) -6, -8, -10: von Willibrand factor (vWF) and angiopoeitin-2 (Ang-2)] and the AKI marker, neutrophil gelatinase-associated lipocalin (NGAL), were also measured by ELISA.

RESULTS

Plasma Robo4 increased significantly (p<0.001) from pre-operative levels of 2515 ± 904 pg/ml to 4473 ± 1915 pg/ml, 2 h after surgery; and returned to basal levels (2682 ± 979 pg/ml) by 24 h. Plasma cytokines, vWF and NGAL also increased 2 h post-operatively and remained elevated at 24 h. Ang-2 increased 24 h post-operatively, only. There was a positive, significant correlation (r = 0.385, p = 0.0298) between Robo-4 and IL-10, but not other cytokines, 2 h post-operatively. Whilst raised Robo4 did not correlate with indices of lung dysfunction or other biomarkers of endothelial activation; there was a positive, significant correlation between raised (2 h) plasma NGAL and Robo4 (r = 0.4322, p = 0.0135). When patients were classed as AKI or non-AKI either using NGAL cut-off of 150 ng/ml, or the AKI Network (AKIN) clinical classification; plasma Robo4 was significantly higher (p = 0.0073 and 0.003, respectively) in AKI vs. non-AKI patients (NGAL cut-off: 5350 ± 2191 ng/ml, n = 16 vs. 3595 ± 1068 pg/ml, n = 16; AKIN: 6546 pg/ml, IQR 5025-8079, n = 6; vs. 3727 pg/ml, IQR 1962-3727, n = 26) subjects.

CONCLUSION

Plasma Robo4 levels are increased, transiently, following cardiac surgery requiring CPB; and higher levels in patients with AKI suggest a link between endothelial dysregulation and onset of AKI.

The effect of modified ultrafiltration on angiopoietins in pediatric cardiothoracic operations

BACKGROUND

Cardiopulmonary bypass subjects patients' blood to hemodilution and nonphysiologic conditions, resulting in a systemic inflammatory response. Modified ultrafiltration (MUF) counteracts hemodilution and has also been postulated to improve outcomes by proinflammatory cytokine removal. The objective of this study was to investigate whether the benefits of MUF include the removal of proinflammatory mediators, such as angiopoietin-2 (angpt-2). We hypothesize that some of the clinical benefits of MUF are related to the preferential removal of angpt-2.

METHODS

We performed a prospective cohort study in children 18 years old or younger undergoing cardiopulmonary bypass. Serum samples were obtained from each patient preoperatively, after cardiopulmonary bypass, and on intensive care unit admission. A fluid sample from the MUF effluent was also analyzed. Angpt-1, angpt-2, interleukin-8, and interleukin-10 levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Thirty-one patients were enrolled. Angpt-1 levels significantly decreased across all time points (p<0.01). Angpt-2 concentrations were significantly elevated at intensive care unit admission when compared with both preoperative and post-cardiopulmonary bypass levels (p<0.01). The angpt-2:1 ratio significantly increased after cardiopulmonary bypass to intensive care unit admission (p<0.01). There was no significant difference between the angpt-2 or angpt-1 percentage of extraction within MUF effluent. Interleukin-8 and interleukin-10 significantly increased from preoperative to intensive care unit admission (both p<0.01).

CONCLUSIONS

The results of this study demonstrate that MUF removes both proinflammatory and antiinflammatory mediators equally. This study suggests that the clinical benefits of MUF cannot be attributed to the removal of larger quantities of proinflammatory mediators such as angpt-2 and interleukin-8.

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.

The temporal kinetics of circulating angiopoietin levels in children with sepsis

OBJECTIVE

Capillary integrity continues to challenge critical care physicians worldwide when treating children with sepsis. Vascular growth factors, specifically angiopoietin-1 and angiopoietin-2, play opposing roles in capillary stabilization in patients with sepsis. We aim to determine whether pediatric patients with severe sepsis/shock have persistently high angiopoietin-2/1 ratios when compared with nonseptic PICU patients over a 7-day period.

DESIGN

Prospective observational study. Patients were classified within 24 hours of admission into non-systemic inflammatory response syndrome, systemic inflammatory response syndrome/sepsis, or severe sepsis/shock. Plasma levels of angiopoietin-1 and angiopoietin-2 were measured via enzyme-linked immunosorbent assay. The angiopoietin-2/1 ratio was graphically plotted and determined whether patients fell into "constant" or "variable" patterns.

SETTING

Tertiary care center PICU.

PATIENTS

Critically ill pediatric patients with varying sepsis severity.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty-five patients were enrolled (nine non-systemic inflammatory response syndrome, 19 systemic inflammatory response syndrome/sepsis, and 17 severe sepsis/shock). Gender, age, weight, comorbidities, and PICU length of stay were not significantly different between the groups. Admission pediatric risk stratification scores and net fluid ins/outs were significantly elevated in the severe sepsis/shock group when compared (all p < 0.05). Admission angiopoietin-2 levels and angiopoietin-2/1 ratios were significantly different in the severe sepsis/shock group when all groups were compared (both p < 0.05). Additionally, the latter were significantly elevated in the severe sepsis/shock group at multiple time points (all p ≤ 0.05) with the peak occurring on day 2 of illness. In a separate analysis, 32% of systemic inflammatory response syndrome/sepsis and 82% of severe sepsis/shock had variable angiopoietin-2/1 ratio patterns compared with none in the control group (p < 0.001).

CONCLUSIONS

Pediatric patients with severe sepsis and septic shock possess significantly elevated angiopoietin-2/1 ratios during their first 3 days of illness, which peak at day 2 of illness. A subset of these patients demonstrated variable angiopoietin-2/1 ratio patterns.

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

INTRODUCTION

Primary graft dysfunction (PGD) is a significant contributor to early morbidity and mortality after lung transplantation. Increased vascular permeability in the allograft has been identified as a possible mechanism leading to PGD. Angiopoietin-2 serves as a partial antagonist to the Tie-2 receptor and induces increased endothelial permeability. We hypothesized that elevated Ang2 levels would be associated with development of PGD.

METHODS

We performed a case-control study, nested within the multi-center Lung Transplant Outcomes Group cohort. Plasma angiopoietin-2 levels were measured pre-transplant and 6 and 24 hours post-reperfusion. The primary outcome was development of grade 3 PGD in the first 72 hours. The association of angiopoietin-2 plasma levels and PGD was evaluated using generalized estimating equations (GEE).

RESULTS

There were 40 PGD subjects and 79 non-PGD subjects included for analysis. Twenty-four PGD subjects (40%) and 47 non-PGD subjects (59%) received a transplant for the diagnosis of idiopathic pulmonary fibrosis (IPF). Among all subjects, GEE modeling identified a significant change in angiopoietin-2 level over time in cases compared to controls (p = 0.03). The association between change in angiopoietin-2 level over the perioperative time period was most significant in patients with a pre-operative diagnosis of IPF (p = 0.02); there was no statistically significant correlation between angiopoietin-2 plasma levels and the development of PGD in the subset of patients transplanted for chronic obstructive pulmonary disease (COPD) (p = 0.9).

CONCLUSIONS

Angiopoietin-2 levels were significantly associated with the development of PGD after lung transplantation. Further studies examining the regulation of endothelial cell permeability in the pathogenesis of PGD are indicated.

Imbalance of angiopoietin-1 and angiopoetin-2 in severe dengue and relationship with thrombocytopenia, endothelial activation, and vascular stability

The pathogenesis of plasma leakage during dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) is largely unknown. Angiopoietins are key regulators of vascular integrity: Angiopoietin-1 is stored in platelets and maintains vascular integrity, and endothelium-derived angiopoietin-2 promotes vascular leakage. We determined angiopoietin-1 and angiopoietin-2 levels in a cohort of children in Indonesia with DHF/DSS and related them to plasma leakage markers. Patients with DHF/DSS had reduced angiopoietin-1 and increased angiopoietin-2 plasma levels on the day of admission when compared with levels at discharge and in healthy controls. There was an inverse correlation between angiopoietin-1 and markers of plasma leakage and a positive correlation between angiopoietin-2 and markers of plasma leakage. Angiopoietin-1 levels followed the same trend as the soluble platelet activation marker P-selectin and correlated with platelet counts. Dengue-associated thrombocytopenia and endothelial activation are associated with an imbalance in angiopoietin-2: angiopoietin-1 plasma levels. This imbalance may contribute to the transient plasma leakage in DHF/DSS.

Angiopoietin-2 is a potential mediator of endothelial barrier dysfunction following cardiopulmonary bypass

INTRODUCTION

Endothelial activation leading to vascular barrier dysfunction and organ failure is a well-recognized complication of cardiovascular surgery with cardiopulmonary bypass (CPB). The endothelial-specific angiopoietin-Tie2 ligand-receptor system has been identified as a non-redundant regulator of endothelial activation. Binding of angiopoietin-2 (Ang-2) to the Tie2 receptor antagonizes Tie2 signaling and renders the endothelial barrier responsive to pro-inflammatory cytokines. We aimed to study the time course and potential triggering factors of Ang-2 release after CPB, as well as the association of Ang-2 changes with surrogates of increased vascular permeability, organ dysfunction, and outcome.

METHODS

Serum levels of Ang-2 from 25 adult patients (140 screened) were measured before and at 0, 12, and 24h following CPB procedure by in-house immuno-luminometric assay (ILMA), and compared with indices of organ dysfunction, duration of mechanical ventilation (MV), length of stay (LOS) in the intensive care unit (ICU), and hospital mortality. The effect of Ang-2 was studied in vitro by incubating high Ang-2 patient serum with endothelial cells (EC).

RESULTS

Ang-2 levels steadily increased from 2.6 ± 2.4 ng/mL at 0 h up to 7.3 ± 4.6 ng/mL at 24h following CPB (P<0.001). The release of Ang-2 correlated with the duration of CPB, aortic cross-clamp time, and post-CPB lactate levels. Changes in Ang-2 during follow-up correlated with partial pressure of oxygen in arterial blood (PaO(2))/fraction of inspired oxygen (FiO(2)) ratio, alveolar-arterial oxygen tension difference (AaDO(2)), hemodynamics, fluid balance, and disease severity measures. Ang-2 levels at 12h predicted the duration of MV, ICU-LOS, and hospital mortality. High Ang-2 patient sera disrupted EC architecture in vitro, an effect reversed by treatment with the competitive Tie2 ligand angiopoietin-1 (Ang-1).

CONCLUSIONS

Collectively, our results suggest that Ang-2 is a putative mediator of endothelial barrier dysfunction after CPB. These findings suggest that targeting the Ang/Tie2 pathway may mitigate organ dysfunction and improve outcome in patients undergoing CPB.

The synthetic tie2 agonist peptide vasculotide protects against vascular leakage and reduces mortality in murine abdominal sepsis

INTRODUCTION

Angiopoietin-1 (Angpt1), the natural agonist ligand for the endothelial Tie2 receptor, is a non-redundant endothelial survival and vascular stabilization factor that reduces endothelial permeability and inhibits leukocyte-endothelium interactions. Here we evaluate the efficacy of a novel polyethylene glycol (PEG)-clustered Tie2 agonist peptide, Vasculotide (VT), to protect against vascular leakage and mortality in a murine model of polymicrobial abdominal sepsis.

METHODS

Polymicrobial abdominal sepsis in C57BL6 mice was induced by cecal-ligation-and-puncture (CLP). Mice were treated with different dosages of VT or equal volume of phosphate-buffered saline (PBS). Sham-operated animals served as time-matched controls.

RESULTS

Systemic administration of VT induced long-lasting Tie2 activation in vivo. VT protected against sepsis-induced endothelial barrier dysfunction, as evidenced by attenuation of vascular leakage and leukocyte transmigration into the peritoneal cavity. Histological analysis revealed that VT treatment ameliorated leukocyte infiltration in kidneys of septic mice, probably due to reduced endothelial adhesion molecule expression. VT-driven effects were associated with significantly improved organ function and reduced circulating cytokine levels. The endothelial-specific action of VT was supported by additional in vitro studies showing no effect of VT on either cytokine release from isolated peritoneal macrophages, or migratory capacity of isolated neutrophils. Finally, administration of VT pre-CLP (Hazard Ratio 0.39 [95% Confidence interval 0.19-0.81] P < 0.001) and post-CLP reduced mortality in septic mice (HR 0.22 [95% CI 0.06-0.83] P < 0.05).

CONCLUSIONS

We provide proof of principle in support of the efficacious use of PEGylated VT, a drug-like Tie2 receptor agonist, to counteract microvascular endothelial barrier dysfunction and reduce mortality in a clinically relevant murine sepsis model. Further studies are needed to pave the road for clinical application of this therapeutic concept.

Does low angiopoietin-1 predict adverse outcome in sepsis?

Endothelial injury has emerged as a crucial early event in the pathogenesis of microcirculatory dysfunction, capillary leakage and multiorgan dysfunction syndrome. The endothelial-specific angiopoietin (Ang)/Tie2 ligand-receptor system has been identified recently as a nonredundant regulator of endothelial responsiveness. Ang-1 is a Tie2 agonist and promotes endothelial stabilization and quiescence, whereas Ang-2 is a Tie2 antagonist and promotes endothelial activation, destabilization, and inflammation. While the mediator function of both Ang-1 and Ang-2 has been well established in preclinical research, only Ang-2 has been identified as a clinically useful biomarker in the critical care arena. In the previous issue of Critical Care, Mankhambo and colleagues report on angiogenic factors in Malawian children with severe bacterial infection. Among those children, diminished levels of the vessel-protective factor Ang-1 remained a significant predictor of outcome after multivariate adjustment. Whether low Ang-1 represents an important risk factor of adverse outcome in critically ill adults remains to be seen.

The interaction of soluble Tie2 with angiopoietins and pulmonary vascular permeability in septic and nonseptic critically ill patients

Circulating angiopoietin (Ang) 1 may inhibit and Ang-2 may enhance pulmonary vascular permeability in septic and nonseptic patients with or at risk for acute lung injury or acute respiratory distress syndrome. We hypothesized that the soluble form of the Ang-binding Tie2 receptor (sTie2), whose shedding may be induced by vascular endothelial growth factor (VEGF) levels, may bind circulating Angs and thereby inhibit their effects on pulmonary vascular permeability. In 24 septic and 40 nonseptic mechanically ventilated patients, sTie2, Ang-1, Ang-2, and VEGF plasma levels were measured together with the pulmonary leak index (PLI) for (67)Gallium-labeled transferrin as a measure of pulmonary vascular permeability. Soluble Tie2 and VEGF levels correlated (r = 0.53, P = 0.001). Soluble Tie2 was higher in septic than in nonseptic patients (7.43 [6.57 - 8.40] vs. 5.03 [4.57 - 5.54] ng/mL; P < 0.001). Soluble Tie2 was associated with the PLI (standardized regression coefficient [beta] = 0.26; P = 0.006) but lost its association with the PLI when the Angs were included in a multivariate model. Soluble Tie2 did not affect the association between Ang-1 or Ang-2 and the PLI (beta = -0.39, P < 0.001; beta = 0.52, P < 0.001, respectively), independently of underlying disease. Although limited to correlations and associations, the clinical data support in vivo shedding of sTie2 through VEGF signaling upon pulmonary vascular injury. However, this shedding may not prevent a direct role of Angs in pulmonary vascular permeability.

Angiopoietin-2 in patients requiring renal replacement therapy in the ICU: relation to acute kidney injury, multiple organ dysfunction syndrome and outcome

PURPOSE

Endothelial activation has emerged as an early event in the pathogenesis of microcirculatory dysfunction, capillary leakage and multi-organ dysfunction syndrome (MODS). Angiopoietin-2 (Ang-2), a circulating antagonistic ligand of the endothelial-specific Tie2 receptor, has been identified as a non-redundant gatekeeper of endothelial activation. On the basis of our previous report demonstrating release of Ang-2 in endotoxemia and sepsis, we aimed to study the utility of Ang-2 to serve as an outcome-specific biomarker in patients requiring renal replacement therapy (RRT) in the intensive care unit (ICU).

METHODS

We measured circulating Ang-2 by ELISA in 117 critically ill patients with AKI at inception of RRT in the ICU. Mortality, length of stay and renal recovery were prospectively assessed during a study period of 28 days after the inception of RRT.

RESULTS

Circulating Ang-2 levels were significantly higher in AKI patients with RIFLE category-Injury or -Failure, compared to patients with RIFLE category-Risk. Elevated levels of circulating Ang-2 correlated with impaired oxygenation, low mean arterial pressure, vasopressor dose and the sequential organ failure assessment (SOFA) score. Ang-2 concentrations were significantly higher in non-survivors than in survivors at day 0 and day 14 after initiation of RRT. Multivariate Cox regression and decision tree analyses confirmed a strong independent prognostic impact of elevated Ang-2 as a predictor of 28-day survival.

CONCLUSIONS

The results from this study indicate that circulating Ang-2 is as a strong and independent predictor of mortality in ICU patients with dialysis-dependent AKI.

Circulating angiopoietin-2 levels in the course of septic shock: relation with fluid balance, pulmonary dysfunction and mortality

PURPOSE

To investigate whether angiopoietin-2, von Willebrand factor (VWF) and angiopoietin-1 relate to surrogate indicators of vascular permeability, pulmonary dysfunction and intensive care unit (ICU) mortality throughout the course of septic shock.

METHODS

In 50 consecutive mechanically ventilated septic shock patients, plasma angiopoietin-2, VWF and angiopoietin-1 levels and fluid balance, partial pressure of oxygen/inspiratory oxygen fraction and the oxygenation index as indicators of vascular permeability and pulmonary dysfunction, respectively, were measured until day 28.

RESULTS

Angiopoietin-2 positively related to the fluid balance and pulmonary dysfunction, was higher in non-survivors than in survivors and independently predicted non-survival throughout the course of septic shock. VWF inversely related to the fluid balance and pulmonary dysfunction throughout the course of septic shock, was comparable between survivors and non-survivors and predicted non-survival on day 0 only. Angiopoietin-1 positively related to pulmonary dysfunction throughout the course, but did not differ between survivors and non-survivors.

CONCLUSIONS

In contrast to VWF, plasma angiopoietin-2 positively relates to fluid balance, pulmonary dysfunction and mortality throughout the course of septic shock, in line with a suggested mediator role of the protein.

Angiopoietin 2 is a partial agonist/antagonist of Tie2 signaling in the endothelium

Angiopoietin 2 (Ang2) was originally shown to be a competitive antagonist for Ang1 of the receptor tyrosine kinase Tie2 in endothelial cells (ECs). Since then, reports have conflicted on whether Ang2 is an agonist or antagonist of Tie2. Here we show that Ang2 functions as an agonist when Ang1 is absent but as a dose-dependent antagonist when Ang1 is present. Exogenous Ang2 activates Tie2 and the promigratory, prosurvival PI3K/Akt pathway in ECs but with less potency and lower affinity than exogenous Ang1. ECs produce Ang2 but not Ang1. This endogenous Ang2 maintains Tie2, phosphatidylinositol 3-kinase, and Akt activities, and it promotes EC survival, migration, and tube formation. However, when ECs are stimulated with Ang1 and Ang2, Ang2 dose-dependently inhibits Ang1-induced Tie2 phosphorylation, Akt activation, and EC survival. We conclude that Ang2 is both an agonist and an antagonist of Tie2. Although Ang2 is a weaker agonist than Ang1, endogenous Ang2 maintains a level of Tie2 activation that is critical to a spectrum of EC functions. These findings may reconcile disparate reports of Ang2's effect on Tie2, impact our understanding of endogenous receptor tyrosine kinase signal transduction mechanisms, and affect how Ang2 and Tie2 are targeted under conditions such as sepsis and cancer.

Excess circulating angiopoietin-2 levels in sepsis: harbinger of death in the intensive care unit?

The early recognition and management of sepsis remain the greatest challenges in the field of critical care medicine. Endothelial injury is one of the hallmarks of sepsis, leading to capillary leak, microcirculatory dysfunction, organ failure, and eventual death in many critically ill patients. The angiogenic growth factors, angiopoietin (angpt)-1 and angpt-2, act upon the Tie-2 receptor in opposing roles. Angpt-2 has been found in abundance in septic patients when compared with healthy controls. In the study by Kümpers and colleagues in the previous issue of Critical Care, angpt-2 levels correlated with markers of tissue hypoxia, disease severity, and mortality in septic adults. However, the temporal kinetics of the angiopoietins were not assessed. It remains to be seen whether angpt-2 levels will function solely as an early marker of sepsis or whether the manipulation of the angpt/Tie-2 system will become a rational therapeutic target for the management of sepsis.