Tanshinone I Represses Ferroptosis to Protect Against Steroid-Induced Osteonecrosis of the Femoral Head by Activating the Nrf2/SLC7A11 Axis.

We sought to explore how Tanshinone I (TsI) mediates ferroptosis in femur tissue in a rat model of steroid-induced osteonecrosis of the femoral head (SIONFH). Rats were given lipopolysaccharide and methylprednisolone to develop a rat model of SIONFH and treated with 5 mg/kg or 10 mg/kg TsI or in combination with ferroptosis inhibitor Fer-1. After different treatments, bone parameters (BMD, BV/TV, Tb.N, Tb.Th, and Tb.Sp), the levels of osteoblast markers (RUNX2, BGLAP, and Osteopontin proteins), and ferroptosis markers (SLC7A11, GPX4, and ACSL4) in femur tissues were detected; Additionally, ferroptosis indicators Fe²⁺, MDA, and GSH in femur tissues were detected by corresponding commercial kits. Additionally, this research conducted experiments including TUNEL staining for the cell death rate in femur tissue and immunofluorescence for reactive oxygen species (ROS) detection. The levels of GPX4 (ferroptosis resistance marker), Nrf2, and SLC7A11 through PCR, Western blot, and immunohistochemistry experiments. Furthermore, lentivirus was delivered into SIONFH rats to knock Nrf2 or SLC7A11 down to investigates whether TsI mediated Nrf2/SLC7A11. BMD, BV/TV, Tb.N, and Tb.Th decreased while Tb.SP increased in SIONFH rats, with increased pathological damage to femoral tissue, reductions in expression of osteoblast markers, and increased positive TUNEL signal and cell death rate. Meanwhile, enhanced ferroptosis evidenced by relevant markers was noted in femur tissues. Low- and high-dose TsI treatment attenuated ferroptosis in femoral tissue, improved bone parameters and pathological lesions in SIONFH rats, with the high-dose group demonstrating more pronounced therapeutic effects. Similarly, Fer-1 treatment exerted a comparable protective effect to that of TsI. Mechanistically, low-dose or high-dose TsI treatment up-regulated Nrf2 and SLC7A11 levels, while down-regulation of Nrf2 or SLC7A11 partly compromised the aforementioned impacts of TsI. TsI may alleviate the pathological lesions of SIONFH rats by activating the Nrf2 signaling pathway, thereby promoting SLC7A11 expression and inhibiting ferroptosis in femoral tissue. TsI holds significant potential for therapeutic applications in the treatment of SIONFH.