OR29 - Effect of Rapamycin on Human Periodontal Ligament Stem Cells That Have Been Exposed to Sodium Hypochlorite

Objectives: Disinfection is crucial for successful regenerative endodontics. However, currently available materials may be cytotoxic to stem cells. This study investigated the effect of rapamycin on the viability and osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) exposed to sodium hypochlorite (NaOCl).

Methods: After determining the minimum inhibitory concentration of NaOCl and optimal rapamycin concentration, the viability of hPDLSCs was assessed using the MTT assay following exposure to NaOCl, rapamycin, or both. Osteogenic differentiation was evaluated through cell mineralization assays performed by alizarin red S staining, alkaline phosphatase activity, and expression of osteogenic markers (Runt-related transcription factor 2, osteocalcin, and osteoprotegerin) via real-time quantitative polymerase chain reaction (RT-qPCR). Autophagy-related genes (PI3K, Akt, mTOR) were also analyzed. Statistical significance was set at α=0.05, with all experiments repeated three times and samples measured in triplicates.

Results: Stem cells treated with rapamycin exhibited the highest viability in the presence of NaOCl. This trend was consistent across all osteogenic differentiation assays, with rapamycin-treated hPDLSCs showing increased calcium nodule deposition, alkaline phosphatase activity, and osteogenic gene expression. The hPDLSCs in this group were unaffected by exposure to NaOCl. Rapamycin significantly inhibited mTOR expression, with no differences observed in PI3K and Akt gene expression.

Conclusion: Rapamycin counteracts the cytotoxic effect of NaOCl by enhancing the viability and osteogenic differentiation potential of hPDLSCs. Rapamycin appears to accomplish these processes via autophagy activation by inhibiting mTOR gene expression. The incorporation of rapamycin in regenerative endodontic therapy may encourage a higher success rate.