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.