Inhibition of adenosine kinase induces expression of VEGF mRNA and proteinin myocardial myoblasts

We tested whether increased endogenous adenosine produced by the adenosine kinase inhibitor GP-515 (Metabasis Therapeutics) can induce vascular endoth elial growth factor (VEGF) expression in cultured rat myocardial myoblasts (RMMs). RMMs were cultured for 18 h in the absence (control) and presence o f GP-515, adenosine (Ado), adenosine deaminase (ADA), or GP-515 + ADA. GP-5 15 (0.2-200 muM) 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 muM also increased VEGF mRNA by 1.67- and 1.82-fold, re spectively. ADA (10 U/ml) decreased baseline VEGF protein levels by 60% and completely blocked GP-515 induction of VEGF. Ado (20 muM) and GP-515 (20 m uM) caused a 59 and 39% increase in VEGF protein expression and a 98 and 33 % increase in human umbilical vein endothelial cell proliferation, respecti vely, after 24 h of exposure. GP-515 (20 muM) had no effect on VEGF protein expression during severe hypoxia (1% O-2) but increased VEGF by an additio nal 27% during mild hypoxia (10% O-2). These results indicate that raising endogenous levels of Ado through inhibition of adenosine kinase can increas e the expression of VEGF and stimulate endothelial cell proliferation durin g normoxic and hypoxic conditions.