Sildenafil Increases Endothelial Progenitor Cell Function and Improves Ischemia-Induced Neovascularization in Hypercholesterolemic Apolipoprotein E–Deficient Mice

Abstract

Abstract-Hypercholesterolemia is associated with impaired neovascularization in response to ischemia. Potential mechanisms include defective NO bioactivity and a reduction in the number/function of endothelial progenitor cells (EPCs). Here we tested the hypothesis that sildenafil, a phosphodiesterase 5 inhibitor that increases NO-driven cGMP levels, could stimulate EPC function and improve ischemia-induced neovascularization in hypercholesterolemic conditions. Apolipoprotein E-deficient (ApoE Ϫ/Ϫ ) mice were treated (or not treated) with sildenafil (40 mg/kg per day in water), and hindlimb ischemia was surgically induced by femoral artery removal. Sildenafil treatment led to an improved blood flow recovery, an increased capillary density, and a reduction of oxidative stress levels in ischemic muscles at day 7 after surgery. Sildenafil therapy is associated with an increased activation of angiogenic transduction pathways, including Akt, p44/42 mitogen-activated protein kinase, and p38. In vitro, sildenafil increases cellular migration and tubule formation of mature endothelial cells (human umbilical vascular endothelial cells) in a cGMP-dependent manner. In vivo, ApoE Ϫ/Ϫ mice treated with sildenafil exhibit a significant increase in the number of bone marrow-derived EPCs. Moreover, the angiogenic activities of EPCs (migration and adhesion) are significantly improved in ApoE Ϫ/Ϫ mice treated with sildenafil. In summary, this study demonstrates that sildenafil treatment is associated with improved ischemia-induced neovascularization in hypercholesterolemic ApoE Ϫ/Ϫ mice. The mechanisms involve beneficial effects on angiogenic transduction pathways together with an increase in the number and the functional activity of EPCs. Sildenafil could constitute a novel therapeutic strategy to reduce tissue ischemia in atherosclerotic diseases. Key Words: sildenafil Ⅲ endothelial Ⅲ progenitor Ⅲ cells Ⅲ angiogenesis hypercholesterolemia T he ability of the organism to develop new blood vessels (neovascularization) constitutes an important adaptive response to vascular occlusive diseases. 1 Postnatal neovascularization necessitates the activation, migration, and proliferation of mature endothelial cells (angiogenesis). 2 In response to ischemia, hypoxia-inducible factor 1 (HIF-1) and vascular endothelial growth factor (VEGF) have been shown to be critical limiting factors for the induction of angiogenesis. 3,4 The importance of NO for endothelial cell migration and VEGF-induced angiogenesis was also demonstrated recently. 5,6 However, increasing evidence suggests that postnatal neovascularization relies not exclusively on the sprouting of preexisting vessels, but also the contribution of bone marrowderived circulating endothelial progenitor cells (EPCs). 7 In young patients and in animal models with young and healthy animals, the neovascularization process is very effective so that blood flow restoration after ischemia is almost complete. Neovascularization, however, is impaired in several clinical situations, which leads to i...

Sildenafil (Viagra®) Prevents Cox-1/ TXA2 Pathway-Mediated Vascular Hypercontractility in ApoE-/- Mice

“…In addition, we demonstrated an exacerbated vasoconstrictor response to sympathetic agonists in the same experimental model, with relative contribution of eicosanoids and ROS using nonselective cyclooxygenase (Cox-1/Cox-2) and NADPH oxidase inhibitors, respectively [18, 20]. In parallel, our laboratories [15, 18, 21-23] and others [24, 25] have published several data supporting the idea that chronic use of sildenafil, a phosphodiesterase 5 (PDE5) inhibitor, improves endothelial function in the apoE -/- mouse. However, the beneficial effects of this drug on the prostanoid vasoconstrictors and on inflammatory cytokines have not yet been evaluated in this suitable animal model of AT [26, 27].…”

Pinocembrin, a major flavonoid in propolis, improves the biological functions of EPCs derived from rat bone marrow through the PI3K-eNOS-NO signaling pathway

“…Therefore, the ability to restore the number and function of EPCs would provide novel therapies for the treatment of atherosclerotic and ischemic diseases. The number and function of EPCs has been shown to be increased by certain drugs such as aspirin, calcium antagonists, and PDE5 inhibitors (Chen et al 2006; Sugiura et al Dussault et al 2009). Although the effect of PIN on EPCs has not been studied previously, Du suggests that PIN induces the relaxation of rat aortic rings through endothelium-dependent and -independent pathways (Zhu et al 2007) and that it exerts an acute neurovascular protective effect against permanent focal cerebral ischemia (Guang and Du 2006).…”

Extrarenal Progenitor Cells Do Not Contribute to Renal Endothelial Repair

“…For BM transplantation, BM cells were isolated from tibiae and femurs by flushing with DMEM. Two hours after recipient's irradiation (7,6 Gray for 7 min), BM cells containing 2310 6 BM mononuclear cells in 0.2 ml Hanks' Balanced Salt solution were injected into the lateral tail vein of recipients. After BM transplantation, mice were housed under sterile conditions and received antibiotic treatment with ofloxacin 20 mg/ml in the drinking water for 4 weeks.…”

“…Following the landmark publication by Asahara and colleagues, 5 in which they provided the first evidence that circulating bone marrow (BM)-derived endothelial progenitor cells (EPCs) may participate in processes of vascular postnatal angiogenesis, a huge amount of literature appeared to support this view in various organ systems. [6][7][8][9] Based on these findings, the so far prevalent theory of endothelial self-renewal was questioned.…”