Granulocyte-macrophage colony-stimulating factor stimulates arteriogenesis in a pig model of peripheral artery disease using clinically applicable infusion pumps

BACKGROUND

A growing number of patients suffer from peripheral artery disease (PAD). Current therapies are often limited by the extent of vascular pathology and the occurrence of restenosis after angioplasty. The stimulatory effect of growth factor administration on collateral vessel formation (arteriogenesis) has evolved as a potential new treatment for this patient group. Granulocyte-macrophage colony-stimulating factor (GM-CSF) was shown to stimulate arteriogenesis in small-animal models and in a pilot study in patients with coronary artery disease. Although a recent clinical study demonstrated disappointing results after subcutaneous GM-CSF application in patients with PAD, we hypothesized that intra-arterial cytokine application using implantable infusion pumps might well stimulate arteriogenesis in a large-species model of peripheral vascular disease. We also aimed to compare continuous and intermittent infusion regimens and to validate experimental and clinically available measurements of collateral artery growth.

METHODS

Twenty-four pigs underwent unilateral occlusion of the right femoral artery and received either GM-CSF continuously, GM-CSF intermittently, or phosphate-buffered saline (PBS). After 1 week, collateral conductance was determined under maximal vasodilatation with adenosine and by using a pump-driven extracorporal shunt system.

RESULTS

Conductance showed a significant stimulatory effect of GM-CSF on arteriogenesis (collateral conductance [mL/min/mm Hg]: PBS, 37.7 +/- 5.4; GM-CSF continuous, 69.2 +/- 12.5; GM-CSF intermittent, 71.5 +/- 11.1). Flow measurements under reactive hyperemia were consistent with these results (flow occluded/non-occluded hind limb: PBS, 40.5% +/- 9.1%; GM-CSF continuous, 48.9% +/- 3.9%; GM-CSF intermittent, 48.7% +/- 4.4%). Measurements of ankle/brachial indices were not sensitive enough to detect the differences in collateral growth between the three groups.

CONCLUSION

These results demonstrate the proarteriogenic properties of GM-CSF in larger animal species, revealing comparable efficacy of continuous and intermittent intra-arterial infusion. Furthermore, we provide evidence that implantable pumps offer a possible means for the intra-arterial application of growth factors. Intra-arterial application of GM-CSF might be a future treatment option for vascular occlusive disease. Finally, we show that in the peripheral circulation, pressure measurements alone have a low sensitivity to determine the effects of proarteriogenic therapy compared with flow or combined flow-pressure measurements.

Leukocyte subpopulations and arteriogenesis: Specific role of monocytes, lymphocytes and granulocytes

OBJECTIVE

Circulating leukocytes play a crucial role during arteriogenesis. However, known pro-arteriogenic compounds (MCP-1, GM-CSF) acting via monocytic pathways also exert positive effects on granulocytes and lymphocytes. The role of these two cell types in arteriogenesis remains yet to be clarified, which was the aim of the current study.

METHODS

Ninety New Zealand White Rabbits received either phosphate buffered saline (PBS), monocyte chemoattractant protein-1 (MCP-1), interleukin-8 (IL-8), neutrophil activating protein-2 (NAP-2) or lymphotactin (Ltn) via osmotic minipumps after unilateral femoral artery ligation. In vitro stimulation and in vivo assessment of chemoattraction confirmed cell-specific action of the compounds in rabbits. Arteriogenesis was evaluated by angiography and collateral conductance measurements using fluorescent microspheres. Quantitative immunohistology was used to quantify transmigrated leukocyte subtypes after infusion of the factors.

RESULTS

MCP-1 infusion attracts monocytes and granulocytes, whereas IL-8 attracts all three cell types albeit monocytes to a significantly lower degree than MCP-1. NAP-2 and lymphotactin selectively attract granulocytes, respectively, lymphocytes. Of the tested cytokines, only MCP-1 stimulates arteriogenesis, as assessed by collateral conductance measurements ((ml/(min 100 mmHg)): PBS, 50.70+/-5.15; MCP-1, 216.30+/-12.30; IL-8, 58.91+/-5.56; NAP-2, 66.83+/-8.72; Ltn, 52.80+/-5.37) and angiographic findings.

CONCLUSION

This study for the first time provides evidence that not granulocytes or T-lymphocytes but monocytes are the key mediators of arteriogenesis.

Anti-tumor necrosis factor-{alpha} therapies attenuate adaptive arteriogenesis in the rabbit

The specific antagonists of tumor necrosis factor-alpha (TNF-alpha), infliximab and etanercept, are established therapeutic agents for inflammatory diseases such as rheumatoid arthritis and Crohn's disease. Although the importance of TNF-alpha in chronic inflammatory diseases is well established, little is known about its implications in the cardiovascular system. Because proliferation of arteriolar connections toward functional collateral arteries (arteriogenesis) is an inflammatory-like process, we tested in vivo the hypothesis that infliximab and etanercept have antiarteriogenic actions. Sixty-three New Zealand White rabbits underwent femoral artery occlusion and received infliximab, etanercept, or vehicle according to clinical dosage regimes. After 1 wk, collateral conductance, assessed with fluorescent microspheres, revealed significant inhibition of arteriogenesis (collateral conductance): 52.4 (SD 8.1), 35.2 (SD 7.7), and 33.3 (SD 10.1) ml x min(-1) x 100 mmHg(-1) with PBS, infliximab, and etanercept, respectively (P < 0.001). High-resolution angiography showed no significant differences in number of collateral arteries, but immunohistochemical analysis demonstrated a decrease in mean collateral diameter, proliferation of vascular smooth muscle cells, and reduction of leukocyte accumulation around collateral arteries in treated groups. Infliximab and etanercept bound to infiltrating leukocytes, which are important mediators of arteriogenesis. Infliximab induced monocyte apoptosis, and neither substance affected monocyte expression of the adhesion molecule Mac-1. We demonstrated that TNF-alpha serves as a pivotal modulator of arteriogenesis, which is attenuated by treatment with TNF-alpha inhibitors. Reduction of collateral conductance is most likely due to inhibition of perivascular leukocyte infiltration and subsequent lower vascular smooth muscle cell proliferation. This is the first report showing a negative influence of TNF-alpha inhibitors on collateral artery growth.

Differential effects of MCP-1 and leptin on collateral flow and arteriogenesis

OBJECTIVE

Strategies to therapeutically stimulate collateral artery growth in experimental models have been studied intensively in the last decades. However, the experimental methods to detect collateral artery growth are discussed controversially and vary significantly. We compared different methods in a model of arteriogenesis in the rabbit hind limb and determined the effects on collateral flow of a known pro-arteriogenic factor, monocyte chemoattractant protein-1 (MCP-1), and a cytokine not previously evaluated for its arteriogenic efficacy, the adipocytokine leptin.

METHODS AND RESULTS

Forty-two New Zealand White rabbits received either MCP-1, leptin or PBS after ligation of the right femoral artery. The pro-arteriogenic effect of MCP-1 was confirmed by flow measurements during reactive hyperemia, as demonstrated by increased flow ratio (PBS 0.56+/-0.07 vs. MCP-1 0.77+/-0.06, no unit, p<0.0001), ankle-brachial index and microsphere-based conductance measurements (PBS 50.8+/-2.1 vs. MCP-1 225.8+/-8.8 ml/min/100 mm Hg, p<0.001). Biological activity of leptin on rabbit monocytes was shown by a dose dependent increase in Mac-1 expression. In-vivo administration of leptin also led to an increase in hyperemic flow and flow ratio (leptin 0.69+/-0.03, p<0.05 vs. PBS), but not to an increase in collateral conductance (leptin 54.7+/-4.1 ml/min/100 mm Hg, p=ns vs. PBS) or proliferation of vascular smooth muscle cells (Ki-67 staining: PBS 24.7+/-3.9%, leptin 22.7%+/-0.8% (p=ns), MCP-1 32.0+/-1.9% (p<0.01)). Ki-67 mRNA measured by real-time polymerase chain reaction increased (8.8+/-3.1-fold, p<0.01) during natural arteriogenesis, and was further enhanced (25.5+/-8.1-fold, p<0.005) after stimulation with MCP-1.

CONCLUSION

MCP-1 and leptin increase collateral flow in the rabbit hind limb model. In contrast to MCP-1, leptin does not enhance direct markers of vascular proliferation such as collateral conductance under maximal vasodilation and proliferation indices. The observed increase in hyperemic collateral flow thus most probably can be attributed to the well-documented vasodilatory effects of leptin. These data stress the necessity of the use of proliferation markers and microsphere-based conductance measurements under maximal vasodilation in order to separate effects of substances on vascular proliferation from effects on vasodilation.

Liquid 2-P-HEMA for endovascular tumor therapy: in vivo feasibility study

BACKGROUND

To evaluate a new liquid polymer developed for selective arterial tumor embolization.

MATERIAL/METHODS

In six rabbits we embolized the renal artery with pure 2-P-HEMA. Three rabbits were killed immediately after embolization, one after 12 h, and two animals underwent follow-up angiography after two weeks. In a second part of the study we embolized the left renal artery in three mini-swine with pure 2-P-HEMA. The kidneys were examined post mortem by soft-tissue radiography and kidney-tissue section microscopy.

RESULTS

Complete occlusion of small distal arteries, most of the arterioles together with the precapillary vascular bed, was achieved in all animals. The speed of injection influenced the grade of distal occlusion; repeated injections through the same microcatheter were possible. The relatively fast injection speed of 0.3 ml/min led to an optimal distribution of the liquid embolic. There was no reperfusion in the two follow-up angiographies two weeks after embolization. Histopathologically, there was no angionecrosis and subintimal bleeding. No marked inflammatory reaction in the vessel wall or perivascular tissue was observed in the embolized arteries.

CONCLUSIONS

This study suggests that liquid 2-P-HEMA may be feasible for the treatment of tumors.