Circulating angiopoietin 2 correlates with mortality in a surgical population with acute lung injury/adult respiratory distress syndrome

Abstract

There are few blood biomarkers predictive of mortality in adult respiratory distress syndrome (ARDS), and none that currently serve as therapeutic targets. Here, we ask whether a circulating protein angiopoietin 2 (Ang2) correlates with severity of lung injury and mortality in a surgical intensive care unit cohort with acute lung injury (ALI)/ARDS. Tie 2 is a tyrosine kinase receptor expressed on endothelial cells. One ligand, angiopoietin 1, phosphorylates Tie 2 and stabilizes adult vasculature. An alternate ligand, Ang2, serves as a context-dependent antagonist and disrupts barrier function. Previously, our laboratory detected high circulating Ang2 levels in septic patients and a correlation with low Pa(O2)/F(IO2). In this study, daily plasma was collected in 63 surgical intensive care unit patients. Eighteen patients met clinical criteria for ALI or ARDS. The median Ang2 at admission in patients who never developed ALI/ARDS was 3.7 ng/mL (interquartile range [IQR], 5.6; n = 45). The Ang2 on the day a patient met criteria for ALI/ARDS was 5.3 ng/mL (IQR, 6.7) for survivors (n = 11) and 19.8 ng/mL (IQR, 19.2) for nonsurvivors (n = 7; P= 0.004). To explore the mechanism of high Ang 2 leading to increased permeability, plasma from patients with ALI was applied to cultured lung endothelial cells and found to disrupt normal junctional architecture. This effect can be rescued with the Tie 2 agonist angiopoietin 1. A patient's convalescent (low Ang2) plasma did not disrupt junctional architecture. Although further studies with larger sample sizes will be needed to confirm these results, high Ang2 in critically ill patients with ALI/ARDS is associated with a poor outcome. These data, coupled with our cell culture experiments, suggest that antagonism of Ang2 may provide a future novel therapeutic target for ARDS.

Fig. 1

Box and whisker plot of median Ang2 levels in survivors versus nonsurvivors (P = 0.004 by Wilcoxson rank sum).

Fig. 2

A, Adult respiratory distress syndrome survivor. Plasma from patient on SICU day 2 with high Ang2 (17.2 ng/mL) is incubated with HMVEC-Ls, actin stress fibers form and endothelial gaps develop. Vascular endothelial–cadherin staining is markedly altered, suggesting a disruption of endothelial barrier integrity. As an internal control, HMVEC-Ls exposed to the patient’s convalescent plasma on day 9 (Ang2, 3.3 ng/mL) did not disrupt cell architecture and seems similar to Ang1 rescue experiments. When Ang1, the endogenous agonist to Ang2, is given at the same time as high Ang2 plasma, there is minimal actin stress fiber formation and intact circumferential VE-cadherin cell surface expression, suggesting barrier integrity. This appearance is similar to convalescent sera (B). B, Adult respiratory distress syndrome nonsurvivor. Plasma from patient with ARDS and high Ang2 (49.5 ng/mL) is incubated with HMVEC-Ls and leads to actin stress fibers, VE-cadherin disruption, and gap formation. Angiopoietin 1 rescue decreases stress fibers, restores VE-cadherin, and attenuates gap formation.