Macrophage Polarization Mediated by Chitooligosaccharide (COS) and Associated Osteogenic and Angiogenic Activities

The host response to implanted biomaterials can influence the functionality of the materials and modulate the tissue repair and remolding. Macrophages, key cells in the host response to biomaterials, can be polarized into different phenotypes, which are important in regenerative medicine. The objective of this study was to evaluate the effect of chitooligosaccharide (COS) on the modulation of macrophage (RAW 264.7) polarization and the associated osteogenic and angiogenic activities. The results demonstrate that COS can shift the macrophage response to an alternatively activated reparative response, which can then upregulate the expression of anti-inflammatory cytokines. COS can also create an immune-modulated microenvironment, with osteogenesis- and angiogenesis-related proteins and a biological process that further influences the osteogenic/angiogenic differentiation and promotion of bone mesenchymal stem cells (BMSCs) and vascular activation of human umbilical vein endothelial cells (HUVECs). In this work, at a low concentration of 4 μg/mL [COS(4)] and suitable polymerization degree of 5 (chitopentaose hydrochloride, COS5) of COS, the associated effect on an alternatively activated reparative response and upregulation of anti-inflammatory cytokine expression was better than that of COS at other concentrations or polymerization degrees. The supernatant from a culture of RAW 264.7 stimulated by COS(4) and COS5 [conditioned medium S-COS(4) and S-COS5] contained more osteogenesis- and angiogenesis-related proteins like DKK-1, OPN, osteoactivin, vascular endothelial growth factor (VEGF) R1, epidermal growth factor (EGF), and insulin-like growth factor binding protein-5 (IGFBP-5) for regulation of osteogenesis/angiogenesis. Specifically, the alkaline phosphatase (ALP) activity and typical osteogenesis-related proteins of BMSCs were significantly influenced by the conditioned media of COS-stimulated macrophages [S-COS(4) and S-COS5]. Furthermore, the conditioned media affected HUVEC proliferation and migration for vascularization. Our results suggest that COS at a low concentration and suitable polymerization degrees has a beneficial effect on immunity modulation (an alternatively activated reparative response) and can modulate osteogenesis/angiogenesis processes for tissue regeneration without using any inductive agent.