Ageing poses one of the largest risk factors for the development of cardiovascular disease (CVD). The increased propensity towards vascular pathology with advancing age maybe explained, in part, by a reduction in the ability of circulating endothelial progenitor cells (EPCs) to contribute to vascular repair and regeneration. Among all current putative EPC populations, outgrowth endothelial cells (OECs) display the most features consistent with a human postnatal vasculogenic cell. Cell-surface heparan sulfate (HS) proteoglycans, by virtue of specific sulfated domains within the glycosaminoglycan chain, are able to bind and modulate the activities of a variety of proteins important for EPC mobilisation, homing and function at sites requiring neovascularization. This study aimed to determine if human OEC function is impaired with age, and to ascertain whether this is accompanied by changes in the fine structure of OEC HS.Using in vitro cell culture methods, OECs were isolated from healthy subjects across an age range and cell phenotype was verified by the demonstration of numerous endothelial, but not hematopoietic, cell characteristics. The functional capacity of peripheral blood derived OECs from young and old subjects, and comparative cord blood derived OECs, was assessed in terms of their susceptibility to apoptosis, proliferative, migratory and tube-forming capabilities. In vitro scratch and transwell migration assays revealed that the migratory capacity of peripheral blood derived OECs isolated from old subjects was impaired in comparison to those from young subjects and cord blood derived OECs. Structural analysis of HS by high performance liquid chromatography (HPLC) demonstrated a significant reduction in the relative percentage of the trisulfated disaccharide, 2-O-sulfated-uronic acid, N, 6-O-sulfated-glucosamine (UA[2S]-GlcNS[6S]), within OEC HS with age (r = -0.847, p=<0.01). Moreover, a decline in the migratory response of OECs towards a gradient of VEGF significantly correlated with the percentage expression of this disaccharide (r = 0.840, p<0.01). Disruption of cell surface HS by pre-treatment with heparinase I and III was found to significantly reduce the VEGF-induced migratory response of peripheral blood derived OECs isolated from young subjects to levels similar to that observed for OECs from older individuals. Understanding the role of HS in regulating the directional migration of EPCs to sites requiring neovascularization and developing approaches to facilitate EPC migration may aid in the design of more successful strategies to optimise the regenerative capacity of these cells in the ageing vasculature.

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There is convincing evidence in vivo that the vascular homing of endothelial progenitor cells (EPCs) contributes to rapid endothelial regeneration, which could prevent thrombosis and restenosis of cardiovascular devices. To enhance the EPC homing on cardiovascular devices, immobilization of an EPC capture agent (e.g. an anti-CD34 antibody) on the surface of cardiovascular devices is critical. We describe a way of immobilizing anti-CD34 Ab on 316L Stainless Steel (316L SS). For this, surface modification of 316L SS was performed via self-polymerization of dopamine (DA) and covalent grafting of staphylococcal protein A (SPA). On this coating the anti-CD34 Abs were oriented immobilized through their Fc constant region with SPA. In this process, the results of quartz crystal microbalance, X-ray photoelectron spectroscopy and water contact angle studies indicate that DA, SPA and anti-CD34 Ab were successfully immobilized onto the surface step by step. In vitro blood-compatibility tests confirmed that the modified surface induced less pro-coagulant fibrinogen denaturation, less platelet adhesion and lower activation of the adherent platelets. The affinity of EPCs for the modified surface has been demonstrated under flow conditions. This study provides potential applications for cardiovascular implant materials.