We have previously shown that ultrasound-mediated (UM) delivery of vascular endothelial growth factor (VEGF) plasmid-bearing microbubbles promotes therapeutic angiogenesis. While VEGF is important during the initiation of angiogenesis, it results in primarily immature vessels, which are prone to late regression. Angiopoietin (Ang)-1 is a potent growth factor that acts to stabilize the neovasculature, later in the angiogenic process. We hypothesized that temporal delivery of VEGF and Ang-1 plasmid DNA would result in a more sustained angiogenic response, as compared to VEGF alone, in the setting of severe chronic ischemia.
Methods
: Unilateral hindlimb ischemia was produced by iliac artery ligation in 30 rats. At day 14 post-ligation, microvascular blood velocity (β) and flow (MBF) in the proximal hindlimb muscles were assessed by contrast-enhanced ultrasound (CEU). UM-delivery of plasmid (500 μg cDNA)-bearing microbubbles (1×109), was then performed at pre-specified time points, with treatment groups including
VEGF alone at day 14;
VEGF at day 14 followed by Ang-1 at day 28; and
control rats receiving no therapy (n=10 per group). β and MBF were re-assessed at day 28 and 8 wks post-ligation.
Results
: Relative MBF (normalized to the contralateral normal leg) remained reduced at all time points after ligation in the control group. In VEGF-alone treated animals, MBF in the ischemic leg increased 2 wks after delivery (0.48 ± 0.19 to 0.82 ± 0.23, p < 0.001), but regressed over the next 4 wks (0.61 ± 0.14 at 8 wk, NS vs. 2 wks). In the VEGF/Ang-1 treated animals, MBF in the ischemic leg also increased 2 weeks after VEGF delivery (0.39 ± 0.19 to 0.69 ± 0.28, p < 0.01); however, vascular regression was prevented by late Ang1 delivery (0.83 ± 0.20 at 8 wks, p < 0.005 vs. 2 wks and p<0.01 vs VEGF alone at 8 wks). At week 8, relative β values were greater in VEGF/Ang-1 treated compared to VEGF-alone treated animals (0.87 ± 0.33 to 0.60 ± 0.23, p < 0.05).
Conclusions
: Compared to delivery of VEGF alone, delivery of Ang-1 plasmid DNA at 2 wks post-VEGF gene delivery results in sustained improvement in MBF, with prevention of late vascular regression. The greater microvascular blood velocity in VEGF/Ang-1 treated muscle may signify improved vascular functionality with late Ang-1 therapy.
Implications of Vascular Endothelial Growth Factor for Postischemic Neurovascular Remodeling