Abstract 564: Multi-Modality Imaging of Angiogenesis and Arteriogenesis of Swimming-Induced Nitric Oxide Protection Against Hindlimb Ischemia
Objectives: Exercise training can be beneficial in presence of peripheral arterial disease (PAD), although the mechanisms are not fully understood. Investigators have demonstrated the important role of endothelial-derived nitric oxide synthase (eNOS) in hindlimb ischemia (HLI), however, controversy remains regarding the role of eNOS in exercise training.
Methods: To evaluate effects of exercise and role of eNOS in PAD, we performed serial imaging of angiogenesis and arteriogenesis in wild-type (WT) and eNOS−/− mice (n = 72) assigned to 3 groups:
sedentary no HLI (SED);
daily swimming (SW) no HLI,
swimming with HLI (SW-HLI).
Angiogenesis was evaluated by in vivo microSPECT imaging of a 99mTc-labeled RGD-peptide (NC100692(NC), GE Healthcare) reflecting activated αv integrins, and muscle 201Tl perfusion during vasodilation with selective A2a agonist at days 7 and 14. Images were quantified using validated semi-automated approach, and absolute uptake expressed as % injected dose (%ID) and ischemic (I) to non-ischemic (NI) ratios computed. Ex vivo microCT imaging was performed on day 14 with 20% bismuth in 10% gelatin for quantitative evaluation of arteriogenesis.
Results: The microSPECT NC uptake at day 7 was increased with SW-WT compared to SED-WT (SW:1.67±0.27%ID; SED:0.79±0.18%ID, p<0.01) not eNOS−/−(SW:0.81±0.35%ID; SED:0.83±0.23%ID, p=ns). The I/NI ratio was increased with SW-HLI in both WT and eNOS−/− mice at day 7 (WT:1.48±0.17; eNOS−/−:4.57±0.45, p<0.05) and 14 (WT:1.36 ±0.34; eNOS−/−:3.84±1.19, p<0.01), although augmented in eNOS−/−. The I/NI ratio of 201Tl was less significantly reduced in WT mice (WT:0.46± 0.07; eNOS−/−:0.33±0.05, P= 0.025) 14 days after SW-HLI. MicroCT arteriography showed a significant increase of small arterioles (24 – 48 μm) in distal hindlimb in eNOS−/− HLI mice (p<0.05) consistent with NC uptake, but not in WT-HLI mice. However, there was no change in proximal arteriolar density with SW-HLI.
Conclusions: There was an exaggerated increase in distal HLI angiogenesis and arteriogenesis in eNOS−/− mice with exercise, in the absence of increases in proximal collateral formation or distal perfusion, suggesting reduced improvement in the absence of eNOS.