Fibroblast growth factor as therapy for critical limb ischemia: a case report

Assessment of skeletal muscle perfusion by contrast medium first-pass magnetic resonance imaging: technical feasibility and preliminary experience in healthy volunteers

PURPOSE

To probe the potential and pitfalls of contrast medium first-pass skeletal muscle perfusion imaging under reproducible stress conditions.

MATERIALS AND METHODS

Magnetic resonance (MR) signal dynamics in calf muscle and lower-leg arteries of 20 healthy volunteers were analyzed under postarterial occlusion reactive hyperemia and concurrent contrast medium first pass, using a saturation recovery spoiled gradient-echo type sequence without heartbeat synchronization. The signal vs. time curves were analyzed descriptively and by two-compartment deconvolution analysis.

RESULTS

Highly significant changes in calf muscle signal dynamics in the hyperemic leg vs. those in the contralateral leg at rest were found in phenomenological and deconvolution analysis. Although a distortion of the arterial signal derived input function by inflow effects was found to cause large variations of the deconvolution results, the magnitude of the observed effects suggested a potential for immediate visual detection of areas with reduced tissue perfusion.

CONCLUSION

The first-pass approach appeared promising for visual evaluation. However, a disentanglement of inflow and contrast medium-induced effects on arterial signal intensity was deemed a prerequisite for input function-based numerical assessment.

Electrical stimulation promotes angiogenesis in a rabbit hind-limb ischemia model

In previous investigations, it was shown that applying a modest regimen of electrical stimulation (ES), even in severely ischemic tissue, improves the healing process, accelerates neovascularization, and enhances angiogenesis in muscle tissue. Our objective in this current report was to further understand ES as a potential alternative treatment for severe muscle ischemia. Immediately after the left distal external iliac artery and the femoral artery were excised, ES (30 contractions per minute [cpm], 2 V, single impulses per burst) was applied to rabbit adductor muscle near the site of the excised femoralis artery for 24 hours daily over 1 month. Three other series served as controls: ES without arterial excision; arterial excision without ES or lead implantation; and arterial excision with lead implantation but no ES. Histologic study of capillary density was performed by angiography (employing a grid template) and by measuring the lower limb-calf blood pressure ratio. At the end of 30 days in the ES series, 10.5 +/-1.2 contrast-medium opacified arteries (COAs) crossed a specific grid section segment compared with 7.2 +/-1.5 in the control series without ES (p<0.05); 68.2 +/-9.3 COAs crossed a grid section compared with 43.2 +/-6.4 in controls (p<0.05); 27.3 +/-1.2 grids contained COAs compared with 29.3 +/-3.5 in controls (p<0.05); lower limb-calf blood pressure ratio was 0.81 +/-0.06 compared with 0.31 +/-0.07 in controls (p<0.05); and capillary density was 283.7 +/-24.5 mm2 compared with 91.4 +/-20.9 mm2 in controls (p<0.001). These preliminary results show that cautious ES enhances and accelerates muscle revascularization in severely ischemic tissue.

Direct fibrin injection to promote new collateral growth in hind limb ischemia in a rabbit model

Local stimulation of angiogenesis is a new approach for the treatment of critical limb ischemia. Our investigation tested intramuscular (i.m.) injection of a modified fibrin meshwork in a rabbit model.

METHODS

The left external iliac and femoral arteries were excised in 24 rabbits that were divided into four groups: control; i.m. saline injection; fibrin meshwork plus low dose (2.5 mg) fibrinogen i.m.; fibrin meshwork plus high-dose (5.0 mg) fibrinogen i.m. Angiography was performed before surgery, immediately after surgery, and one month postoperatively. Lower limb-calf blood pressure was measured immediately after surgery and at postoperative days 10, 20, and 30. On day 30, conventional indirect immunostaining was performed to determine the percentage of the area occupied by capillaries.

RESULTS

Immediately after surgery, in all four groups, the number of contract-opacified arteries (COA) crossing a specific segment of a grid decreased from 5.3 +/- 1.3 to 3.2 +/- 1.0 (p < 0.05); the number of grid intersections decreased from 30.2 +/- 6.5 to 19.3 +/- 4.8 (p < 0.05); and the total number of grids with COA decreased from 18.3 +/- 3.8 to 12.2 +/- 2.5 (p < 0.05). One month after surgery, in the control group, these parameters were 6.2 +/- 1.1, 33.2 +/- 5.7 and 20.3 +/- 1.5, respectively; in the saline-treated group, these parameters were 6.1 +/- 0.8, 28.3 +/- 6.9 and 19.8 +/- 1.1, respectively (p > 0.05 versus control and versus baseline data). When fibrin containing 5.0 mg fibrinogen was used, these parameters increased to 8.5 +/- 0.9, 48.3 +/- 5.1, and 27.1 +/- 0.9, respectively (p < 0.001 versus immediately after surgery and p < 0.05 versus control). In all four series, no Doppler flow signal was detected from the posterior tibial artery by day 10. By day 30, the lower limb-calf blood pressure ratio had improved in all four series, but was significantly improved in only the two groups treated with fibrin sealant (0.3 +/- 0.05 control; 0.3 +/- 0.08 saline; 0.6 +/- 0.06 fibrinogen 2.5; 0.7 +/- 0.05 fibrinogen 5.0).

CONCLUSION

Intramuscular injection of a fibrin meshwork considerably increased angiogenesis in the severely ischemic hind limb and may be strongly recommended for clinical use in patients with limb-threatening ischemia.

Clinical applications of cardiovascular angiogenesis

Angiogenesis is fundamental to both normal physiologic (wound healing) and pathologic (cancer) processes. Manipulation of divergent angiogenic signals promises effective therapy of atherosclerotic cardiovascular disease. Positive proangiogenic strategies promise collateral circulation to ischemic territories, while negative antiangiogenic strategies starve the fibromuscular proliferation within the atherosclerotic lesion. Indeed, recent phase 1 trials suggest that delivering DNA or recombinant protein to the site of vascular occlusion may stimulate physiologically significant collateral circulation in chronically ischemic myocardium. While symptomatic and functional improvement has been documented, toxicity profiles and effects on long-term patient survival are still unclear. The purposes of this article are as follows: (1) to review the pathophysiologic basis for pro- and antiangiogenic strategies in the treatment of cardiovascular disease, (2) to examine the clinical trials of proangiogenic gene or recombinant protein delivery into ischemic beds, and conversely, (3) to explore antiangiogenic strategies in the prevention and treatment of intimal neovascularization and smooth muscle proliferation within the vessel wall.

Gene therapy for therapeutic angiogenesis in critically ischaemic lower limb - on the way to the clinic

Currently, no effective pharmacological treatment is available for vascularisation defects in lower limbs. Many patients presenting with persistent pain and ischaemic ulcers are not suitable candidates for surgical or endovascular approaches. Further refinement of the available methods will undoubtedly lead to a more active approach towards treatment of peripheral arterial occlusive disease (PAOD). Recently, therapeutic angiogenesis, in the form of recombinant growth factor administration or gene therapy, has emerged as a novel tool to treat these patients. However, improved gene transfer methods and better understanding of blood vessel formation are required to bring therapeutic angiogenesis to clinical practice. Here we review the clinical problem (PAOD), mechanisms of blood vessel formation (angiogenesis, vasculogenesis and arteriogenesis), experimental evidence and clinical trials for therapeutic angiogenesis in critically ischaemic lower limbs. Also, angiogenic growth factors, including vascular endothelial growth factors (VEGFs) and fibroblast growth factors (FGFs), delivery methods, and vectors for gene transfer in skeletal muscle, are discussed. In addition to vascular growth, gene transfer of growth factors may enhance regeneration, survival, and innervation of ischaemic skeletal muscle. Nitric oxide (NO) appears to be a key mediator in vascular homeostasis and growth, and a reduction in its production by age, hypercholesterolemia or diabetes leads to the impairment of ischaemic disorders.