The acute phase protein orosomucoid (ORM), also known as alpha1-acid glycoprotein (AGP), is found to be increased in infection, inflammation and cancer. Recently, we demonstrated that ORM is produced by endothelial cells and detectable in urine samples of patients with bladder cancer. However, it was not clarified yet whether ORM plays a role in new vessel formation. To this aim we performed overexpression and gene silencing for ORM in human microvascular endothelial cells (HDMECs). ORM purified from human plasma was used individually or in combination with VEGF-A in endothelial tube formation, migration and proliferation assay. The in vivo effect of ORM in angiogenesis was studied using the chicken chorionallantois membrane (CAM) with subsequent counting of blood vessels on histological sections from the stimulated areas of CAM tissue. Our data show that ORM alone enhances migration but not proliferation of HDMECs. ORM alone does not induce endothelial tubes in vitro but simultaneous application of ORM with VEGF-A increases the number and the network of VEGF-A-induced endothelial tubes. Remarkably, ORM alone induces new vessel formation in vivo using CAM assay and supports the VEGF-A-induced new vessel formation in this assay. Taken together, our results let assume that ORM has pro-angiogenic properties and supports the angiogenic effect of VEGF-A. Thus, ORM seems to be involved in the regulation of angiogenesis.
