Effect of calcium phosphate phases affecting the crosstalk between osteoblasts and osteoclasts in vitro

Abstract

Previous studies have reported that octacalcium phosphate (OCP) enhances osteoblast differentiation and osteoclast formation during the hydrolysis process to hydroxyapatite (HA). However, the crystal phases that affect the crosstalk between osteoclasts and osteoblasts are unknown, which should determine the bone substitute material's property of OCP. The present study was designed to investigate whether the chemical composition and crystal structure of calcium phosphates affect osteoclast formation and the osteoclast–osteoblast crosstalk. Biodegradable β‐tricalcium phosphate (β‐TCP) was used as the control material. Osteoclasts were cultured on HA/OCP or HA/TCP disks and their cellular responses were assessed. Both OCP and β‐TCP had a similar ability to create multinucleated osteoclasts. However, OCP promoted the expression of complement component 3a (C3a), a positive coupling factor, in osteoclasts, whereas β‐TCP enhanced that of EphrinB2 (EfnB2) and collagen triple helix repeat containing 1 (Cthrc1). During osteoclast culture, phosphate ions were released from the crystals, and OCP‐HA conversion was advanced in HA/OCP mixtures and OCP. X‐ray diffraction analysis revealed no remarkable changes in the crystal structures of HA/TCP mixtures and β‐TCP before and after osteoclast culture. These results indicate that the distinct chemical environment induced by the calcium phosphate phases affects the crosstalk between osteoclasts and osteoblasts. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1001–1013, 2019.

Octacalcium phosphate bone substitute materials: Comparison between properties of biomaterials and other calcium phosphate materials

“…This also supports the hydrolysis of OCP in SBF 33) . Such analysis also demonstrated that the hydrolysis of OCP for the conversion into HA had been induced in a cell culture medium supersaturated with respect to OCP and HA 30) . On the other hand, the transformation of OCP into HA in vivo has been confirmed by ultrastructural observation and crystallographic analysis 7,9) .…”

“…This is because OCP incorporates Ca 2+ and releases Pi ions during the hydrolysis reaction 8) . The decrement or increment of these ions in the medium depends on the amount of OCP incubated 28,30,100) . Furthermore, the pH locally decreased at the area adjacent to the OCP surface of its granules in a Tris-HCl buffer containing F − , although the buffering effect occurs to maintain the pH under the physiological condition 101) .…”

“…Furthermore, the pH locally decreased at the area adjacent to the OCP surface of its granules in a Tris-HCl buffer containing F − , although the buffering effect occurs to maintain the pH under the physiological condition 101) . When β-TCP is incubated, the concentrations of Ca 2+ and pH increase, whereas the concentration of the Pi ions decreases in the medium 30) . Such behavioral change in the ion concentration could be attributed to HA formation on the β-TCP surface 102) .…”

“…In order to investigate the role of different kinds of Ca-Ps with varying chemical compositions on osteoclast formation and osteoclast-osteoblast crosstalk, mouse bone marrow macrophages were cultured on disks composed of OCP, HA, β-TCP, and mixtures of these compounds 30) . Large tartrate-resistant acid phosphatase (TRAP)positive cells, indicating multinucleated osteoclasts, were observed more frequently in the cultures with OCP or β-TCP disks compared to HA disks.…”

“…A review paper classified OCP as an osteoconductive and biodegradable material like HA and β-tricalcium phosphate (β-TCP), respectively 27) . However, a series of studies, including this first experiment, further revealed that OCP is capable of stimulating bone formation through osteoblast differentiation and osteoclast formation 6,7,15,16,25,[28][29][30] , which might have properties between osteoconductivity and osteoinductivity. HA and β-TCP have been widely used clinically in oral and orthopedic surgeries 27,31,32) .…”