Monocyte Chemoattractant Protein 1-Induced Monocyte Infiltration Produces Angiogenesis but Not Arteriogenesis in Chronically Infarcted Myocardium

Background: Monocyte chemoattractant protein 1 (MCP-1) stimulates the invasion of monocytes into ischemic tissue with concomitant adhesion to endothelial cells. Monocyte stimulation has been shown to be involved in the induction of arteriogenesis, which is the development of functional arterioles resulting in improvement of perfusion. However, angiogenesis (newly developed capillaries contribute to improved tissue perfusion) in several models has not resulted in any improvement in blood flow.

Objective: The effects of MCP-1 on potential angiogenesis and arteriogenesis as well as changes in left ventricular function were tested in a chronic infarct model in rat hearts.

Methods: Anesthetized rats were subjected to open-chest ligation of the left coronary artery with subsequent myocardial infarction. After 6 weeks, animals were randomized to receive either MCP-1 (3 µL in 0.15 mL NaCl, group 1, n = 9) or saline (0.15 mL, group 2, n = 9), which was injected into the myocardium at the border zones of the infarcts. For assessment of left ventricular dimensions and global cardiac function, transthoracic two-dimensional echocardiography was performed at baseline, 6 weeks after myocardial infarction, and 4 weeks after MCP-1 or saline injection, by use of a 12-MHz pediatric transducer. For light microscopic analysis, myocardial tissue was stained with Elastica-van-Giesson and von Willebrand factor for blood vessels and endothelial cells, respectively. In a subset of animals, hearts were excised 24 hours after MCP-1 administration (n = 4) or saline administration (n = 4) for assessment of monocyte infiltration by immunohistologic staining of the CD31 antigen.

Results: Left ventricular dimensions and ejection fraction changed after coronary occlusion (from 60.4% ± 2.85% to 24.8% ± 5.01% ejection fraction in group 1, and from 58.4% ±2.06% to 26.3% ± 4.3% ejection fraction in group 2 at 6 weeks, P < .005) without any further change 4 weeks after treatment (ejection fraction in group 1, 26.3% ± 2.7%, ejection fraction in group 2, 25.0% ± 5.18%). The MCP-1 group resulted in 390.6 ± 10.36 endothelial cells compared with 285.2 ± 13.56 in group 2 (P < .005) at the injection site. Monocyte infiltration was observed at the MCP-1 injection site with an increase in capillary growth (angiogenesis). However, there was no difference in the number of arteriolar structures between animals treated with MCP-1 and saline animals (group 1, 19.0 ± 1.52 vs group 2,16.4 ± 0.68, P > .05).

Conclusion: A single intramyocardial injection of MCP-1 into the infarct border zone resulted in neo-angiogenesis and monocyte infiltration but not arteriogenesis in the rat heart. There was no functional change of chronically infarcted myocardium in the present model.