Hyperbaric oxygen inhibits growth but not differentiation of normal and irradiated osteoblasts

Hyperbaric oxygen (HBO) therapy is used in the treatment of osteoradionecrosis. Although HBO is thought to improve radiation-induced hypocellularity and bone tissue hypoxia, the precise effects of HBO on bone cells such as osteoblasts have not been described. In this study, our goal was to assess the effect of HBO on irradiated and nonirradiated primary osteoblast cultures and assess for changes in growth, apoptosis, cell cycle profile, differentiation, and gene expression. We found that daily HBO treatments caused a 24% decrease in cell growth after 9 days in culture. Hyperbaric oxygen negatively affects growth by inducing osteoblast apoptosis and cell cycle arrest. Hyperbaric oxygen leads to G1/S cell cycle arrest in unirradiated osteoblasts where as it causes G2/M arrest in cells that were previously irradiated with either 7 or 12 Gy of ionizing radiation. Although radiation was shown to have a dose-dependent inhibitory effect on early osteoblast differentiation as measured by alkaline phosphatase activity, HBO did not have a significant effect on osteoblast differentiation. Microarray analysis revealed that exposure to HBO leads to a differential expression of a variety of gene families including stress response pathways. In summary, although successive daily HBO treatments resulted in growth delay, osteoblast function as measured by the ability to produce alkaline phosphatase was not significantly affected. These data suggest that HBO does not have any positive effects on either normal or radiation-damaged osteoblasts in vitro.