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.

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.

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).

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.