Enhancement\nof the Cytokine Adsorption Capacity of\nOctacalcium Phosphate by Interaction-Controlled Glycosaminoglycan\nModification to Promote Osteoblastic Differentiation

This study was designed to investigate how the strength\nof the\ninteraction between octacalcium phosphate (OCP) and modified chondroitin-A\nsulfate (CS-A), a glycosaminoglycan, regulates the adsorption–desorption\nof cytokines and subsequently affects the osteoblastic differentiation\nof mesenchymal stem cells (MSCs) in vitro. The utilization of cytokines\nproduced by cells, such as macrophages, stimulated by the hydrolysis\nof OCP, is expected to enhance the bone regeneration capacity of the\nOCP. CS-Na was used to modify CS-A on the OCP immobilized with the\namino group through electrostatic interactions. On the other hand, <i>N</i>-hydroxysuccinimide (NHS)-esterified CS-A was used to form\nthe covalent bond between CS-A and the amino group on the surface\nof OCP. X-ray diffraction and Raman spectroscopy indicated that the\nCS-A-modified OCP maintained its structure, regardless of the modification\nprocess. The remaining ratio of the modified CS-A in the buffer suggests\nthat increasing the immobilized density of the amino group and the\nmodification using NHS ester may enhance interaction strength between\nOCP and CS-A. The adsorption amount and retention rate of recombinant\nhuman bone morphological protein-2 (rhBMP-2, an endogenous cytokine\nmodel) increased onto CS-A-modified OCP under physiological conditions\nwhen the interaction strength between OCP and the protein was stronger.\nThe higher interaction strength between the OCP and CS-A could be\nassociated with the enhanced adsorption affinity for the lower-molecular-weight\nbasic protein. The alkaline phosphatase activity of MSCs increased\ndepending on the remaining rate of rhBMP-2 adsorption on the CS-A-modified-OCP.\nFourier transform infrared spectroscopy and chemical analysis indicated\nthat the hydrolysis of the OCP progressed regardless of CS-A modification\nafter MSC incubation. The present study suggests that stronger interactions\nbetween the OCP and glycosaminoglycans could contribute to the capture\nand retention of endogenous cytokines on the surface to further promote\nosteoblastic differentiation under the chemical environment induced\nby the hydrolysis of the OCP.