Elevated Angiopoietin-2 Level in Patients With Continuous-Flow Left Ventricular Assist Devices Leads to Altered Angiogenesis and Is Associated With Higher Nonsurgical Bleeding

Abstract

Background Non-surgical bleeding (NSB) is the most common adverse event in patients with continuous-flow left ventricular assist devices (LVADs) and is caused by arteriovenous malformations (AVMs). We hypothesized that deregulation of an angiogenic factor, Angiopoietin-2 (Ang-2), in LVAD patients leads to increased angiogenesis and higher NSB. Methods Ang-2 and thrombin levels were measured by ELISA and Western blotting, respectively, in blood samples from 101 patients with heart failure (HF), LVAD, or orthotopic heart transplant (OHT). Ang-2 expression in endothelial biopsy was quantified by immunofluorescence. Angiogenesis was determined by in vitro tube formation using serum from each patient with or without Ang-2-blocking antibody. Ang-2 gene expression was measured by RT-PCR in endothelial cells incubated with plasma from each patient with or without the thrombin receptor blocker Vorapaxar. Results Compared with HF or OHT patients, serum levels and endothelial expression of Ang-2 were higher in LVAD patients (p=0.001 and p<0.001, respectively). This corresponded with increased angiogenic potential of serum from patients with LVADs (p<0.001), which was normalized with Ang-2 blockade. Furthermore, plasma from LVAD patients contained higher amounts of thrombin (p=0.003) which was associated with activation of the contact coagulation system. Plasma from LVAD patients induced more Ang-2 gene expression in endothelial cells (p<0.001) which was reduced with thrombin receptor blockade (p=0.013). LVAD patients with Ang-2 levels above the mean (12.32 ng/mL) had more NSB events compared with patients with Ang-2 levels below the mean (p=0.003). Conclusions Our findings indicate that thrombin-induced Ang-2 expression in LVAD patients leads to increased angiogenesis in vitro and may be associated with higher NSB events. Ang-2 therefore may contribute to AVM formation and subsequent bleeding in LVAD patients.

Tumor necrosis factor-α levels and non-surgical bleeding in continuous-flow left ventricular assist devices

“…Inclusions, exclusions and timing of recruitment were reported previously 12 and are addressed in the Supplementary Material (available online at www.jhltonline.org/). The protocol was approved by the institutional review board of the University of Chicago and all participants provided written informed consent.…”

“…8,9 Ang-2 induces endothelial destabilization and altered vessel growth. 10,11 We have shown that Ang-1 is decreased in LVAD patients, 12 although the underlying mechanism is unknown. We have also shown that thrombin-dependent overexpression of Ang-2 in LVAD patients induces altered angiogenesis and is associated with NSB.…”

“…We have also shown that thrombin-dependent overexpression of Ang-2 in LVAD patients induces altered angiogenesis and is associated with NSB. 12 Because Ang-1 and Ang-2 are regulators of vascular growth, determining the mechanisms underlying the loss of Ang-1 and overexpression of Ang-2 in LVAD patients is critical to understanding LVAD-related angiodysplasia and NSB.…”

Long-Acting Octreotide Reduces the Recurrence of Gastrointestinal Bleeding in Patients With a Continuous-Flow Left Ventricular Assist Device

“…9 We demonstrated recently that thrombin-induced angiopoietin-2 expression in LVAD patients leads to increased angiogenesis in vitro which may contribute to AVM formation in vivo . 10 …”

Multicenter Evaluation of Octreotide as Secondary Prophylaxis in Patients With Left Ventricular Assist Devices and Gastrointestinal Bleeding

“…It is thought that the loss of pulsatility and potential hypoxia result in upregulation of angiogenic mediators, such as vascular endothelial growth factor and angiopoietin-2, may contribute to the development of angiodysplasia. [10][11][12] Consequently, appropriate primary and secondary bleeding prophylaxis is essential in improving long-term outcomes after LVAD implantation.…”