Abstract 5805: Adenosine Down-Regulates Soluble Vascular Endothelial Growth Factor Receptor-1

Background: The cardioprotective nucleoside adenosine acts through 4 types of receptors: A1, A2a, A2b, A3. An emerging concept is that adenosine is a major factor driving angiogenesis, thus contributing to the repair of the ischemic heart. Angiogenesis is controlled by a plethora of vasculogenic factors, among which Vascular Endothelial Growth Factor (VEGF) and its receptor VEGFR1 (or Flt-1). A soluble form of VEGFR1 (sFlt-1) traps circulating VEGF, thereby preventing its binding to VEGF receptors. Both VEGF and sFlt-1 are induced by Hypoxia Inducible Factor 1 α . The aim of the present study was to characterize the effect of adenosine on the production sFlt-1. Methods: Primary blood monocytes obtained from healthy volunteers and patients with acute myocardial infarction (MI) were differentiated to macrophages in vitro. Treatments included: adenosine (10 μ M), CGS21680 (A2a receptor agonist, 0.1–10 μ M), SCH58261 (A2a receptor antagonist, 0.1–10 μ M), and/or LPS (100 ng/mL). ELISA, immuno-blotting and TransAM™ assay were used to measure expression levels and activation of sFlt-1 and HIF-1 α . In vitro formation of microtubules by human coronary artery endothelial cells (HCAEC) was used to evaluate angiogenesis. Results: LPS induced sFlt-1 production by macrophages from healthy volunteers and adenosine inhibited this induction (43% decrease, P=0.006, n=12). This inhibition was replicated by the A2a agonist and reversed by the A2a antagonist. The formation of a network of microtubules by HCAEC was enhanced in the presence of conditioned medium from adenosine-treated macrophages and impaired by exogenous sFlt-1. Adenosine inhibited the LPS-induced nuclear translocation of HIF-1 α , thereby preventing its activation. The effect of adenosine was replicated in macrophages isolated from acute MI patients. Conclusion: We show here for the first time that adenosine down-regulates the production of sFlt-1. This mechanism involves the adenosine A2a receptor and the transcriptional activator HIF-1 α . Our data suggest that this effect of adenosine may play a significant role in angiogenesis.