Grateloupia longifolia polysaccharide inhibits angiogenesis by downregulating tissue factor expression in HMEC-1 endothelial cells

1 The antiangiogenic and antitumor properties of Grateloupia longifolia polysaccharide (GLP), a new type of polysaccharide isolated from the marine alga, were investigated with several in vitro and in vivo models. Possible mechanisms underlying its antiangiogenic activity were also assessed. 2 GLP dose-dependently inhibited proliferation of human microvascular endothelial cells (HMEC-1) and human umbilical vein endothelial cells (HUVEC), with IC50 values of 0.86 and 0.64 mg ml(-1), respectively. In tube formation and cell migration assays using HMEC-1 cells, noncytotoxic doses of GLP significantly inhibited formation of intact tube networks and reduced the number of migratory cells. Inhibition by GLP was VEGF-independent. 3 In the chick chorioallantoic membrane (CAM) assay, GLP (2.5 mu g egg(-1)) reduced new vessel formation compared with the vehicle control. GLP (0.1 mg plug(-1)) also reduced the vessel density in Matrigel plugs implanted in mice. 4 The levels of pan and phosphorylated recptors for VEGF, VEGFR-1 (flt-1) and VEGFR-2 (KDR) were not significantly altered by 5 mg ml(-1) GLP treatment of HMEC-1, although tissue factor (TF) showed significant decreases at both mRNA and protein levels following GLP treatment. 5 In mice bearing sarcoma-180 cells, intravenous administration of GLP (200 mg kg(-1)) decreased tumor weight by 52% without obvious toxicity. Vascular density in sections of the tumor was reduced by 64% after GLP treatment. 6 Collectively, these results indicate that GLP has antitumor properties, associated at least, in part, with the antiangiogenesis induced by downregulation of TF.