A Comparative Study on the Influence of Zirconia and Titanium Nanoparticles on the Functionality of Osteocytes In Vitro.

Abstract

The aim of this study was to compare the influence of zirconia dioxide nanoparticles (ZrO 2 -NPs) and titanium dioxide nanoparticles (TiO 2 -NPs) on the functionality of osteocytes in vitro. MLO-Y4 osteocytic cells were treated with varying concentrations of ZrO 2 -NPs or TiO 2 -NPs for viability studies. Apoptosis assays following treatment with 100 and 500 µg/mL of ZrO 2 -NPs or TiO 2 -NPs for 72 h were performed. Sclerostin (SOST) levels were assessed at 24 and 72 h, while receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) were measured at 72 h by ELISA and real-time PCR analysis. Viability assays revealed a dose-dependent cytotoxicity for both types of nanoparticles, with TiO 2 -NPs reducing cell viability at 100 µg/mL within 24 h, while ZrO 2 -NPs promoted proliferation at lower concentrations but showed similar cytotoxicity at higher doses. Apoptosis and necrosis assays revealed a dose-dependent cytotoxic response, with TiO 2 -NPs inducing significant cell death at 100 µg/mL, while ZrO 2 NPs showed minimal effects at the same concentration; at 500 µg/mL, both nanoparticles markedly increased apoptosis, with TiO 2 -NPs eliciting higher apoptosis. SOST gene expression and SOST release were significantly enhanced following exposure to both ZrO 2 -NPs and TiO 2 -NPs, with TiO 2 -NPs inducing significantly higher levels. TiO 2 -NPs upregulated RANKL while downregulating OPG both at the gene and protein levels. Although ZrO 2 -NPs exhibited a similar trend, their impact on SOST expression, RANKL, and OPG release was notably lower, suggesting a potentially less disruptive impact on bone remodeling. The findings offer valuable insights into the osteocyte-mediated effects of implant-related nanoparticles. ZrO 2 -NPs are a less disruptive alternative to TiO 2 -NPs for bone implants, offering insights into osteocyte-mediated remodeling and guiding biomaterial selection for implant longevity.