PCNA and osteoporosis: Thus, the main purpose of our study was to assess the prospective roles of nanoparticles of zinc-doped hydroxyapatite (ZnHA-NPs) to prevent or treat osteoporosis in comparison to E2 administration through the evaluation of serum bone turnover markers and oxidative/inflammatory responses, femoral expression of RANKL-OPG, vascular endothelial growth factor (VEGF), and proliferating cell nuclear antigen (PCNA).