Since atherosclerosis is characterized by endothelial damage, re-growth seems likely to be occurring in order to repair or replace injured cells. Angiogenic vascular endothelial growth factor (VEGF), a likely mediator of these events, acts on the endothelium via a specific receptor, Flt-1. We hypothesized that patients with different manifestations of atherosclerosis, and others with diabetes, would have altered plasma levels of VEGF and Flt-1 compared with healthy individuals. Accordingly, 70 patients with peripheral artery disease (PAD), 70 patients with coronary artery disease (CAD), and 70 age- and sex-matched healthy controls were recruited. We also recruited 14 patients with diabetes asymptomatic for atherosclerosis, 14 patients with diabetes and atherosclerosis, and 14 age- and sex-matched controls. VEGF and soluble Flt-1 (sFlt-1) were measured by ELISA. In the main study of PAD and CAD, VEGF was raised in both patient groups (P<0.05) compared with the controls, but was not different between the patient groups. sFlt-1 was lower in patients with PAD (P<0.05), but not in those with CAD, compared with the controls. VEGF was raised in the patients with diabetes plus atherosclerosis (P<0.05), but not in the group with diabetes alone; levels of sFlt-1 were unaltered in both diabetes groups. Our data point to changes in plasma levels of VEGF and its receptor sFlt-1 in diabetes and atherosclerosis that may have relevance for therapy and angiogenesis in these conditions.

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Vascular endothelial growth factor (VEGF) mediates endothelial cell mitogenesis and enhances vascular permeability. VEGF interacts with the endothelium via two membrane-spanning receptors, fms-like tyrosine kinase (Flt)-1 and kinase domain receptor. A soluble form of Flt-1 (sFlt-1) was isolated from endothelial cell media; however, its biological significance is still unknown, with limited data on plasma sFlt-1 levels in disease states. We have developed two new ELISAs for detecting free and VEGF-complexed sFlt-1, which were tested in accordance with standard validation and assessment methodologies employed in commercial settings. The intra-and inter-assay coefficients of variation are <5% and 10% respectively, and results are highly reproducible. Applying these ELISAs in a clinical setting, we measured levels of VEGF, free and complexed sFlt-1 in citrated plasma from 40 patients with cardiovascular disease and 40 healthy controls. Median (interquartile range) plasma levels of VEGF in patients were significantly greater than controls [403 pg/ml (158--925 pg/ml) versus 113 pg/ml (33--231 pg/ml), P< or =0.05]. Free sFlt-1 was significantly lower in patients compared with controls [8 ng/ml (2--22 ng/ml) versus 21 ng/ml (10--73 ng/ml), P< or =0.05]. There was no significant difference in the levels of complexed sFlt-1 between the two groups. Plasma levels of VEGF-complexed sFlt-1 are minimal, despite the presence of excess free sFlt-1. Thus unbound plasma VEGF detected by ELISA may represent the majority of circulating VEGF, and justifies the measurement of plasma VEGF as an indicator of circulating VEGF levels. Furthermore, these results suggest that circulating sFlt-1 may serve as a selective inhibitor of VEGF activity, and that this regulatory mechanism may be altered by pathological conditions.