α1-acid glycoprotein disrupts capillary-like tube formation of human lung microvascular endothelia

Purpose: The acute phase protein, \u3b11-acid glycoprotein, is expressed in the lung, and influences endothelial cell function. We asked whether it might regulate angiogenesis in human lung microvascular endothelia. Materials and Methods: \u3b11-acid glycoprotein was isolated from human serum by HPLC ion exchange chromatography. Its effects on endothelial cell functions including capillary-like tube formation on Matrigel, migration in a wounding assay, chemotaxis in a modified Boyden chamber, adhesion, and transendothelial flux of the permeability tracer, 14C-albumin, were tested. Results: \u3b11-acid glycoprotein dose-dependently inhibited capillary-like tube formation without loss of cell viability. At 650.50 mg/mL, it inhibited tube formation >70%, and at 0.75 mg/mL, >97%. \u3b11-acid glycoprotein dose- and time-dependently restrained EC migration into a wound as early as 2 hours, and in washout studies, did so reversibly. It was inhibitory against vascular endothelial growth factor-A and fibroblast growth factor-2-driven migration but failed to inhibit chemotactic responsiveness. When \u3b11-acid glycoprotein was added to preformed tubes, it provoked their almost immediate disassembly. As early as 15 minutes, it induced tube network collapse without endothelial cell-cell disruption. It exerted a biphasic effect on cell adhesion to the Matrigel substrate. At lower concentrations (0.05-0.25 mg/mL), it increased cell adhesion, whereas at higher concentrations ( 650.75 mg/mL) decreased adhesion. In contrast, it had no effect on transendothelial 14C-albumin flux. Conclusion: \u3b11-acid glycoprotein, at concentrations found under physiological conditions, rapidly inhibits endothelial cell capillary-like tube formation that may be explained through diminished cell adhesion to the underlying matrix and/or reversibly decreased cell migration