Research Article Pro-angiogenic properties of orosomucoid (ORM) Ster Irmak a , Leticia Oliveira-Ferrer b , Bernhard B. Singer a , Süleyman Ergün a, ⁎ , Derya Tilki c a Institute of Anatomy, University Hospital Essen, Hufelandstr. 55, D-45147 Essen, Germany b Department of Oncology/Hematology, University Hospital Hamburg-Eppendorf, Hamburg, Germany c Department of Urology, University Hospital Groβhadern, Munich, Germany ARTICLEINFORMATION ABSTRACT Article Chronology: Received 14 April 2009 Revised version received 28 July 2009 Accepted 29 July 2009 Available online 3 August 2009 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. © 2009 Elsevier Inc. All rights reserved. Keywords: Angiogenesis Endothelial cells Tube assay Migration assay Human Introduction Orosomucoid (ORM), also known as alpha1-acid glycoprotein (AGP), was first described in 1950 by Schmid [1]. It belongs to a group of acute phase proteins (APPs) and along with many other functions plays a role in the modulation of immune response to stress [2,3]. The high serum concentration of ORM (0.5–1.4 mg/ml) in healthy humans is known to rise two- to fivefold in response to different conditions such as acute infection, inflammation and lymphoproliferative disorders and various types of cancers [3]. The structure of ORM is composed of a polypeptide chain carry- ing about 45% carbohydrate residues including a large amount of fucosylic and sialic acids. Thus, its proposed immunomodulatory activities have been attributed to its glycosylation pattern. It has been postulated that the strongly fucosylated and sialylated ORM glycoforms have the ability to bind to E-selectin and to inhibit complement activation [4]. ORM is synthesized in liver and various extrahepatic cell types e.g. granulocytes and endothelial cells [5]. IL-1, IL-6 and glucocorticoids are the major modulators of ORM gene expression in liver cells [6–8]. An induced expression of sialyl Lewis X (sLeX) on ORM during acute inflammation has been reported, leading to the speculation that it might influence the E- or P-selectin- mediated influx of sLeX-expressing leukocytes into inflamed areas. It has been suggested that an increased level of sLeX- expressing ORM might have a feedback inhibitory effect on the EXPERIMENTAL CELL RESEARCH 315 (2009) 3201 – 3209 ⁎ Corresponding author. Fax: +49 201 7235916. E-mail address: sueleyman.erguen@uk-essen.de (S. Ergün). 0014-4827/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.yexcr.2009.07.024 available at www.sciencedirect.com www.elsevier.com/locate/yexcr