Abstract
Introduction
As a result of recent biological analyses, the medaka (Oryzias latipes) has gained much attention as an animal model of human disease. In this study, we examined the effects of irradiation on osteoclastogenesis in pharyngeal bones. We also investigated immunochemically the expression of the osteoclast differentiation factors receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG).
Material and Method
We irradiated entire medaka with 15, 30, or 45 Gy of carbon ions or gamma rays. Histochemical assays were performed to determine the effects of irradiation on sections of pharyngeal bone to analyze the histochemical localization of tartrate-resistant acid phosphatase (TRAP) activity, the main marker of osteoclasts and their immediate precursors. Immunostaining assay with RANKL and OPG antibodies was performed.
Result
Early on, both irradiated groups showed high TRAP activity, whereas 5 days after irradiation, no statistical differences were observed between groups that were irradiated at the same dose. Seven days after irradiation, TRAP activity in the gamma ray–irradiated group was stronger than that in the control and carbon ion–irradiated groups. The localization of RANKL was strong in the supporting pharyngeal bone adjacent to the teeth of the gamma ray–irradiated medaka. Expression of OPG was activated in the same parts of the pharyngeal bone in carbon ion–irradiated medaka.
Conclusion
The TRAP activity of osteoclasts increased with gamma ray irradiation; it was lower with carbon ion irradiation than with gamma ray irradiation, although it was slightly increased with carbon ion irradiation than with no irradiation. This suggests that gamma ray irradiation stimulates osteoclast activity, increasing the resorption of pharyngeal bone. Carbon ion irradiation has a different effect on osteoclast activity and might suppress maturation via OPG expression. These observations suggest that carbon ion irradiation induces differential modulation of osteoclast growth factor expression.
