Background— Peripheral artery disease (PAD) is a prevalent cardiovascular disorder that results in tissue ischemia which can progress to critical limb ischemia. Restoration of tissue perfusion in the setting of chronic ischemia through stimulation of arteriogenesis and angiogenesis remains a key therapeutic target for PAD. However, experimental therapeutics, including growth factor and gene therapy, have had little clinical success indicating the need for a better understanding of molecular pathways required for therapeutic angiogenesis. Methods and Results— Here we report that phosphodiesterase-5 inhibition by sildenafil significantly increases vascular perfusion, tissue blood flow, and vascular density during chronic ischemia of the mouse hind limb. Importantly, sildenafil therapy did not alter any of these parameters in nonischemic limbs. Sildenafil increased tissue cGMP levels independently of increases in nitric oxide production, and sildenafil therapy stimulated angiogenesis in ischemic limbs of eNOS −/− and iNOS −/− mice. Lastly, sildenafil-mediated angiogenic activity was blocked by inhibition of protein kinase G using the PKG antagonist DT-3. Conclusions— These data demonstrate that sildenafil therapy results in increased angiogenic activity through a PKG-dependent pathway that is independent of nitric oxide production or NOS activity and identify the angiogenic therapeutic potential of sildenafil for critical limb ischemia.

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Previous studies suggest that inflammatory cell adhesion molecules may modulate endothelial cell migration and angiogenesis through unknown mechanisms. Using a combination of in vitro and in vivo approaches, herein we reveal a novel redox sensitive mechanism by which ICAM-1 modulates endothelial GSH that controls VEGF-A induced eNOS activity, endothelial chemotaxis, and angiogenesis. In vivo disk angiogenesis assays showed attenuated VEGF-A mediated angiogenesis in ICAM-1 −/− mice. Moreover, VEGF-A dependent chemotaxis, eNOS phosphorylation, and nitric oxide (NO) production were impaired in ICAM-1 −/− MAEC compared to WT MAEC. Decreasing intracellular GSH in ICAM-1 −/− MAEC to levels observed in WT MAEC with 150 μM buthionine sulfoximine (BSO) restored VEGF-A responses. Conversely, GSH supplementation of WT MAEC with 5 mM glutathione ethyl ester (GEE) mimicked defects observed in ICAM-1 −/− cells. Deficient angiogenic responses in ICAM-1 −/− cells were associated with increased expression of the lipid phosphatase, PTEN, consistent with antagonism of signaling pathways leading to eNOS activation. PTEN expression was also sensitive to GSH status, decreasing or increasing in proportion to intracellular GSH concentrations. These data suggest a novel role for ICAM-1 in modulating VEGF-A induced angiogenesis and eNOS activity through regulation of PTEN expression via modulation of intracellular GSH status.