Effects of Extracellular pH on Dental Pulp Cells In Vitro

• The objective of this work was to investigate the effects of extracellular pH conditions on dental pulp cell (DPC) proliferation and migration in vitro.
• DPCs conditioned from a pH of 3.5 to 5.5 induced cell death and from a pH of 6.5 to 7.5 induced growth arrest or cell death within 120 hours. DPSs conditioned at a pH of 9.5 proliferated mildly.
• The DPC migratory activity was not affected by extracellular pH levels as long as the cells were alive.
• An acidic extracellular pH condition reduced proliferating cell nuclear antigen (PCNA)-positive cell numbers.
• In teeth with a small abscess in the coronal pulp chamber and asymptomatic irreversible pulpitis, a PCNA-negative pulp cell layer was observed in close proximity to the infectious lesion.
• These results suggested an acidic extracellular pH condition was associated with growth arrest or cell death on DPCs and reduced PCNA-positive cell numbers.

IntroductionThe proliferation and migration of dental pulp stem cells (DPSCs), a population comprised of dental pulp cells (DPCs), are important processes for pulp tissue repair. Dental pulp is exposed to changes in extracellular pH under various conditions, such as acidosis and exposure to caries-associated bacteria or a pulp capping agent. The objective of this study was to investigate the effects of extracellular pH on DPC proliferation and migration in vitro.MethodsTo evaluate the proliferation potency of DPCs in various extracellular pH conditions, 2 × 104 cells were seeded into 35-mm dishes. The following day, we changed to NaHCO3-free medium, which was adjusted to different extracellular pH levels.ResultsAfter 120 hours, DPCs cultured in media from a pH of 3.5 to 5.5 showed cell death, those cultured in conditions from a pH of 6.5 to 7.5 showed growth arrest or cell death, and those grown at a pH of 9.5 showed mild proliferation. The migratory activity of living DPCs was not affected by extracellular pH. For histologic analysis, human teeth possessing a small abscess in the coronal pulp chamber were sliced for histologic analysis. Proliferating cell nuclear antigen (PCNA) immunolocalization was used as an index of cell proliferation for the sections and cultured cells. Acidic extracellular pH conditions resulted in reduced numbers of PCNA-positive DPCs in the dishes. As for pulp tissue affected by a small abscess, a PCNA-negative pulp cell layer was observed in close proximity to the infectious lesion.ConclusionsTogether, these results suggest that an acidic extracellular pH condition is associated with DPC growth arrest or cell death.