Plasma Levels of Soluble Tie2 and Vascular Endothelial Growth Factor Distinguish Critical Limb Ischemia From Intermittent Claudication in Patients With Peripheral Arterial Disease

OBJECTIVES: Our purpose was to determine whether factors that regulate angiogenesis are altered in peripheral arterial disease (PAD) and whether these factors are associated with the severity of PAD. BACKGROUND: Alterations in angiogenic growth factors occur in cardiovascular disease (CVD), but whether these factors are altered in PAD or correlate with disease severity is unknown. METHODS: Plasma was collected from patients with PAD (n = 46) and healthy control subjects (n = 23). Peripheral arterial disease patients included those with intermittent claudication (IC) (n = 23) and critical limb ischemia (CLI) (n = 23). Plasma angiopoietin-2 (Ang2), soluble Tie2 (sTie2), vascular endothelial growth factor (VEGF), soluble VEGF receptor 1 (sVEGFR-1), and placenta growth factor (PlGF) were measured by enzyme-linked immunoadsorbent assay. In vitro, endothelial cells (ECs) were treated with recombinant VEGF to investigate effects on sTie2 production. RESULTS: Plasma concentrations of sTie2 (p < 0.01), Ang2 (p < 0.001), and VEGF (p < 0.01), but not PlGF or sVEGFR-1, were significantly greater in PAD patients compared with control subjects. Plasma Ang2 was significantly increased in both IC and CLI compared with control subjects (p < 0.0001), but there was no difference between IC and CLI. Plasma VEGF and sTie2 were similar in control subjects and IC but were significantly increased in CLI (p < 0.001 vs. control or IC). Increased sTie2 and VEGF were independent of CVD risk factors or the ankle-brachial index, and VEGF treatment of ECs in vitro significantly increased sTie2 shedding. CONCLUSIONS: Levels of VEGF and sTie2 are significantly increased in CLI, and sTie2 production is induced by VEGF. These proteins may provide novel biomarkers for CLI, and sTie2 may be both a marker and a cause of CLI.