Inhibition Of Adenosine Kinase Induces Expression Of VEGF MRNA And Protein In Myocardial Myoblasts
We tested whether increased endogenous adenosine produced by the adenosine kinase inhibitor GP-515 (Metabasis Therapeutics) can induce vascular endothelial growth factor (VEGF) expression in cultured rat myocardial myoblasts (RMMs). RMMs were cultured for 18 h in the absence (control) and presence of GP-515, adenosine (Ado), adenosine deaminase (ADA), or GP-515 + ADA. GP-515 (0.2–200 μM) caused a dose-related increase in VEGF protein expression (1.99–2.84 ng/mg total cell protein); control VEGF was 1.84 ± 0.05 ng/mg. GP-515 at 2 and 20 μM also increased VEGF mRNA by 1.67- and 1.82-fold, respectively. ADA (10 U/ml) decreased baseline VEGF protein levels by 60% and completely blocked GP-515 induction of VEGF. Ado (20 μM) and GP-515 (20 μM) caused a 59 and 39% increase in VEGF protein expression and a 98 and 33% increase in human umbilical vein endothelial cell proliferation, respectively, after 24 h of exposure. GP-515 (20 μM) had no effect on VEGF protein expression during severe hypoxia (1% O2) but increased VEGF by an additional 27% during mild hypoxia (10% O2). These results indicate that raising endogenous levels of Ado through inhibition of adenosine kinase can increase the expression of VEGF and stimulate endothelial cell proliferation during normoxic and hypoxic conditions.