Measurement of the soluble angiopoietin receptor tie-2 in patients with coronary artery disease: development and application of an immunoassay

BACKGROUND: The angiopoietin family has emerged as a group of crucial growth factors to normal angiogenesis. They are essential to the development of the mature vessel wall and interact with the endothelium via endothelial cell-specific tyrosine kinase receptors, tie-1 and tie-2. The role of the tie-2 receptor has been extensively examined in neovascularization associated with malignancy, but little is known about the role it may play in atherosclerosis, a condition whose pathophysiology also involves angiogenesis. Soluble tie-2 has been detected in the plasma of healthy controls, but this has yet to be applied to patients in the clinical setting. MATERIALS AND METHODS: We developed an ELISA to detect plasma tie-2 levels and applied these to a clinical setting. The intra- and interassay coefficients of variation for the assay were 4.7% and 9.6%, respectively. We then measured levels of tie-2, vascular endothelial growth factor (VEGF), another factor associated with angiogenesis, and the soluble VEGF receptor Flt-1 (sFlt-1) in 75 patients with coronary artery disease [25 with acute myocardial infarction (AMI), 25 with acute coronary syndromes (ACS) and 25 with stable angina] and 25 healthy controls. RESULTS: Median [IQR, interquartile range] levels of tie-2 were significantly higher in the coronary artery disease patients (AMI 12 [10-17] ng mL-1, ACS 10 [9-14] ng mL-1, stable angina 9 [3-11] ng mL-1) when compared with the controls (7.5 [7-9] ng mL-1P = 0.004). As expected, levels of VEGF and sFlt were significantly different from those in the healthy controls (P = 0.011 and P <0.001, respectively). Significant correlations were found between levels of tie-2 and VEGF (Spearman r = 0.59, P <0.001), tie-2 and sFlt-1 (r = 0.45, P <0.001) and VEGF and sFlt-1 (r = 0.56, P <0.001) in the whole study group. CONCLUSION: We suggest that tie-2 may be potentially used as a marker of angiogenesis in atherosclerosis and may help elucidate the role of the angiopoietin/tie-2 system in atherogenesis.