Bystander Effects in Osteoblasts and Osteoclasts: Comparison Between X- and Proton-Irradiation

This study investigated radiation-induced bystander responses (RIBR) in osteoblasts and osteoclasts and compared x-rays with protons regarding RIBR effects.

MC3T3-E1 subclone 4 (preosteoblasts), differentiated MC3T3-E1 (osteoblasts), and differentiated RAW264.7 (osteoclasts) were irradiated with x-rays (225 kVp) and protons with a linear energy transfer of -2.3 keV/µm. A trans-well insert coculture system, allowing the transfer of soluble factors without contact between irradiated and nonirradiated cells, was used to study medium-mediated RIBR. The range of intended dose was 0.5 to 2 Gy for both x-ray and proton-irradiation. The RIBRs of nonirradiated cells were evaluated based on the expression of 53BP1 at 1 h postirradiation and micronuclei assay at 72 h or later.

RIBR was evident in bystander cells regardless of the irradiated/nonirradiated cell combination. The percentage of 53BP1-positive cells was 3.2% to 4.2% in controls and 8.6% to 11.7% in bystander cells (P < .05). Similarly, binucleated cells with micronuclei were 3.7% to 6.0% in controls versus 13.1% to 15.4% in bystanders (P < .05). No differences in RIBR were observed based on radiation type or dose.

This study provides preliminary evidence that RIBR occurs in osteoblasts and osteoclasts, irrespective of cell combination, dose, or radiation type, suggesting that both x-rays and protons may induce comparable bystander effects in bone-related cells.