Abstract 183: Carbon Monoxide Induces Macrophage VEGF Production and Promotes Angiogenic Behavior in Endothelial Cells

Abstract

Introduction: Carbon monoxide (CO) has potent anti-inflammatory and pro-healing properties. We have previously shown that CO enhances endothelial cell (EC) angiogenic behavior in vitro. More striking, however, is that conditioned medium (CM) from macrophages isolated from CO treated rats can promote angiogenesis indirectly. We sought to examine the mechanism of this indirect angiogenic effect of CO. Methods: Peritoneal macrophages were collected from rats after inhaled CO treatment (250 PPM for 1 hr) or air treatment. Macrophages were cultured overnight and CM was collected to treat human umbilical vein ECs (HUVECs). VEGF and eNOS expression was assessed by Western blot. Results: CM from macrophages isolated from CO treated rats (CO) showed a 3-fold increase in VEGF vs Air CM (Ratio CO/Air=2.96, Range 1.6-4.2) (Figure). VEGF levels were similar between the macrophages from CO or air treated rats (CO/Air=0.89). HUVECs treated with CO or Air CM also showed no difference in VEGF levels (CO/Air=1.07). However, eNOS expression was significantly increased in HUVECs treated with CO CM vs. Air CM (CO/Air=26.4, Range 20-32; p=0.004). HUVECs cultured in a CO chamber or a standard incubator exhibited no change in eNOS expression (CO/Air, 1.38 p=0.11). Conclusion: In vivo CO promotes macrophage secretion of VEGF. These cells can promote angiogenic behavior in ECs through this VEGF and other secreted products. These macrophage products upregulate eNOS but not VEGF expression in HUVECs. The effect of the CO CM on eNOS expression in HUVECs could not be reproduced by direct CO treatment of the cells. Future studies will further characterize the phenotypic change of the macrophages induced by inhaled CO that favors angiogenesis and healing.