Inhibitory effects of autologous γ-irradiated cell conditioned medium on osteoblasts in vitro

Skeletal complications from radiation therapy have been reported in patients with breast, brain and pelvic cancer, and types of blood cancer. However, it remains to be elucidated whether localized radiotherapy may result in systemic adverse effects on the unirradiated skeleton through an abscopal mechanism. The present study investigated the abscopal effect of radiation on osteoblasts mediated by autologous γ-irradiated cell conditioned medium. Osteoblasts obtained from calvarial bones were incubated with irradiated cell conditioned medium (ICCM) and changes in cell viability, alkaline phosphatase (ALP) activity, mineralization ability, cell apoptosis and the gene expression levels of ALP, osteocalcin (BGP), osteoprotegerin (OPG), receptor activator of nuclear factor-κB ligand (RANKL) and caspase 3 were observed. Notably, ICCM regulated osteoblast function, inhibiting viability and differentiation, resulting in apoptosis or cell death. ICCM at 10 or 20%, from osteoblasts irradiated with 10 Gy γ-rays, significantly inhibited the proliferation of osteoblastic cells (P<0.001). In addition, an increase in apoptosis was noted in the osteoblasts incubated with ICCM at 40% with increasing doses of radiation, accompanied by an upregulation in the mRNA expression of caspase 3. In addition, ICCM at 20% inhibited the ALP activity in the 5 and 10 Gy groups and osteoblast mineralization, particularly at 10 Gy ICCM. Additionally, the mRNA expression levels of ALP, BGP, OPG and RANKL of the cells treated with ICCM at 20% were downregulated significantly compared with those treated with medium from unirradiated cells. The present study provided novel evidence to elucidate radiation-therapy-associated side effects on the skeleton.