Effects of ionizing radiation on osteoblastic cells: In vitro insights into the etiopathogenesis of osteoradionecrosis

Objective: This in vitro study aimed to analyze the effects of ionizing radiation on immortalized human osteoblast-like cells (SaOS-2) and further assess their cellular response in co-culture with fibroblasts. These analyses, conducted in both monoculture and co-culture, are based on two theoretical models of osteoradionecrosis - the theory of hypoxia and cellular necrosis and the theory of the radiation-induced fibroatrophic process.

Design: SaOS-2 cells were exposed to ionizing radiation and evaluated for cell viability, nitric oxide (NO) production, cellular morphology, wound healing, and gene expression related to the PI3K-AKT-mTOR pathway. SaOS-2 cells were co-cultured with human gingival fibroblasts using transwell membranes and subjected to the same irradiation. Subsequent evaluations included cell viability, NO levels, and gene expression analysis.

Results: After 24 hours, a 16 Grays dose reduced cell viability by 40 % (p < 0.0001) and increased NO production by 14 % (p < 0.05). Additionally, the nuclear area was enlarged by 18 % (p < 0.01), and the nucleus-to-cytoplasm ratio in non-stimulated cells was around 33 %, but after radiation, this ratio increased to nearly 100 %. Also, there was a delay in wound closure of 6.6 % (p < 0.0001) post-irradiation and a trend toward down-regulation of genes related to the PI3K-AKT-mTOR pathway (p > 0.05). Under co-culture conditions, the dose of 16 Grays did not affect cell viability but increased NO production by 14 % (p < 0.001) and tended to up-regulate markers of the PI3K-AKT-mTOR pathway (p > 0.05).

Conclusions: The findings of this study demonstrate that an irradiation dose of 16 Grays induces a reduction in cell viability, an increase in NO production, and various other metabolic and morphologic effects on osteoblastic cells while emphasizing the impact of intercellular interaction in the etiopathogenesis.