Adenosine modifies the balance between membrane and soluble forms of Flt-1.

VEGFR-1 (or Flt-1) exists under a sFlt-1 or a mFlt-1 form. sFlt-1 is antiangiogenic, and mFlt-1 is proangiogenic. The cardioprotective nucleoside Ado is proangiogenic, but its effects on Flt-1 are unknown and were tested in this study. In primary human macrophages from healthy volunteers, Ado inhibited sFlt-1 expression induced by LPS (-43%, P=0.006), HS, and IL-1beta but not hypoxia. This effect was also observed in macrophages from patients with acute MI (-33%, P<0.001). It was reproduced by the A(2A) Ado receptor agonist CGS21680 and abrogated by the A(2A) antagonist SCH58261. Conversely, Ado increased mFlt-1 expression, thus switching sFlt-1 from the soluble toward the membrane form. This switch was also present in macrophages from acute MI patients (P<0.001). Assessment of HIF-1alpha nuclear translocation and activation together with siRNA experiments suggested that the effect of Ado on Flt-1 involves HIF-1alpha. In conclusion, Ado down-regulates sFlt-1 and up-regulates mFlt-1 production, an effect that indicates that Ado may be used to stimulate angiogenesis in the heart.