Cellular responses of rat periodontal ligament cells under hypoxia and re-oxygenation conditions in vitro

Background and Objective: The aim of this study was to investigate the responses of periodontal ligament cells under hypoxia and re-oxygenation conditions in vitro. Material and Methods: Periodontal ligament fibroblasts were isolated from rat incisors. In the hypoxia group, cells were incubated in 2% O-2 for 1-3 d. In the re-oxygenation group, cells were first incubated under the same conditions as the hypoxia group for 24 h and then were returned to normoxic conditions and cultured for 1-2 additional days. Results: Proliferation ratios increased in all groups in a time-dependent manner. Proliferation ratios in both the hypoxia and re-oxygenation groups were significantly higher than in the control group on days 2 and 3. Alkaline phosphatase activity was significantly higher in the hypoxia group than in the control and the re-oxygenation groups. The expression of bone sialoprotein mRNA was significantly higher in the hypoxia group than in the control group on days 1 and 2. The expression of vascular endothelial growth factor mRNA was significantly higher in the hypoxia group than in the control group on days 1 and 2. In the re-oxygenation group, the level of expression of bone sialoprotein mRNA and vascular endothelial growth factor mRNA were similar to those of the control group. The expression of heat shock protein 70 mRNA in the hypoxia group was similar to that in the control group, whereas in the re-oxygenation group it was statistically higher than in the other groups. Conclusion: These results suggest that periodontal ligament cells maintain their osteogenic ability in hypoxia and re-oxygenation conditions in vitro.