Investigation of the biological activity of hydroxyapatite on vascular endothelial cells.

Objective: This study aims to explore the impact of nano-hydroxyapatite (na-HA) and micron-hydroxyapatite (mi-HA) on human umbilical vein endothelial cells (HUVEC) using in vitro experiments, assessing their influence on cellular biological activity. These findings offer crucial experimental data for informing the development of more vascularized tissue-engineered bone constructs. Methods: We employed the Cell Counting Kit-8 (CCK-8) assay to assess the impact of various concentrations of both HA extracts on HUVEC metabolic activity post 48, 72, and 96 h of treatment. Transwell experiments were conducted to evaluate the influence of HA extract on HUVEC migratory capabilities. The cell proliferation activity was assessed using the 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay, elucidating the impact of varying concentrations of both HA extracts on cell proliferation. Lumen formation experiments were conducted to assess the capacity of HA-treated HUVECs to form lumen-like structures. The Enzyme-Linked Immunosorbent Assay (ELISA) was employed to measure the impact of HA extract on vascular endothelial growth factor (VEGF) secretion by HUVECs. Western blotting (WB) was utilized to analyze alterations in the expression levels of PI3K/Akt signaling pathway-related proteins following HA extract treatment of cells. Results: At extract concentrations of 100 g/L and 12.5 g/L, both the mi-HA and na-HA groups demonstrated suppression of cell metabolic activity, migration, and proliferation. Conversely, at 25 g/L, increased cell metabolic activity and proliferative activity were observed. Lumen formation experiments demonstrated that both HA extracts at 100 g/L concentration facilitated lumen formation, with the na-HA group at 25 g/L concentration displaying a more pronounced impact on lumen formation. The ELISA results indicated a notable reduction in VEGF secretion within the mi-HA group at a concentration of 100 g/L. WB experiments revealed that within the na-HA group, treatment of HUVECs with 25 g/L and 12.5 g/L extract concentrations led to upregulation of PI3K and Akt protein expression, while at 100 g/L concentration, Akt protein expression decreased. In the mi-HA group, intracellular expression of both PI3K and Akt proteins exhibited reduction. Conclusion: Hydroxyapatite extract at both high and low concentrations impacts the biological activity of vascular endothelial cells, with the potential mechanism of action involving the PI3K/Akt signaling pathway.