Angiogenesis is a process associated with the migration and proliferation of endothelial cells (EC) to form new blood vessels. It is involved in various physiological and pathophysiological conditions and is controlled by a wide range of proangiogenic and antiangiogenic molecules. The plasminogen activator–plasmin system plays a major role in the extracellular matrix remodeling process necessary for angiogenesis. Urokinase/tissue-type plasminogen activators (uPA/tPA) convert plasminogen into the active enzyme plasmin, which in turn activates matrix metalloproteinases and degrades the extracellular matrix releasing growth factors and proangiogenic molecules such as the vascular endothelial growth factor (VEGF-A). The plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of uPA and tPA, thereby an inhibitor of pericellular proteolysis and intravascular fibrinolysis, respectively. Paradoxically, PAI-1, which is expressed by EC during angiogenesis, is elevated in several cancers and is found to promote angiogenesis by regulating plasmin-mediated proteolysis and by promoting cellular migration through vitronectin. The urokinase-type plasminogen activator receptor (uPAR) also induces EC cellular migration during angiogenesis via interacting with signaling partners. Understanding the molecular functions of the plasminogen activator plasmin system and targeting angiogenesis via blocking serine proteases or their interactions with other molecules is one of the major therapeutic strategies scientists have been attracted to in controlling tumor growth and other pathological conditions characterized by neovascularization.

Introduction and Aim: 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. Methods: 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. Results: 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. Conclusion: 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.