Photodynamic Therapy: A Promising Strategy for Alveolar Bone Regeneration

Introduction: Alveolar bone loss can result from multiple dental conditions or systemic pathologies, with functional and aesthetic consequences. The treatment of such defects remains a major clinical challenge, largely due to the limited regenerative capacity of alveolar bone. Photodynamic therapy (PDT) represents a promising approach to bone regeneration by modulating cellular activity through photochemical processes. Thus, the main objective of this study was to investigate the effects of Porphyrin 1a (meso-tetraphenylporphyrin with Pt (II)) on the function of bone cells and on the osteogenic differentiation of rat bone marrow stem cells (BM-MSCs). Additionally, this study intended to optimise the therapeutic protocol regarding the photosensitiser concentration and light exposure regimens.

Materials and Methods: The effect of the photosensitiser on the SaOS-2 cell line was assessed by testing 3 and 5 J irradiation regimens and a range of concentrations from 1 to 100 nM. The protein content (SRB assay), cell cycle (flow cytometry), Ki-67 expression (RT-PCR), and formation of mineralised deposits (Alizarin Red staining) were evaluated 24 and 72 hours after treatment. Additionally, the subcellular localisation of Porphyrin 1a was determined using confocal microscopy on BM-MSCs, and the impact of PDT on the proliferation and formation of mineralised deposits was evaluated in these cells 72 hours after treatment.

Results: Porphyrin 1a promoted a significant increase in protein content of SaOS-2 cells and BM-MSCs after irradiation at 5 J. After PDT, the cell populations were mainly in the G₀/G₁ phase of the cell cycle. Furthermore, increased Ki-67 expression and more mineralised deposits were observed in SaOS‑2 cells. Additionally, it was demonstrated that Porphyrin 1a colocalises with the nucleus, mitochondria, plasma membrane, and endoplasmic reticulum of BM-MSCs.

Conclusions: Overall, PDT promoted cellular proliferation, with the most pronounced effects observed under 5 J and at low photosensitiser concentrations. Additional studies are required to elucidate the specific cellular mechanisms behind PDT-induced proliferation and differentiation.