Objective:To investigate whether the necroptosis pathway receptor interacting protein 1-receptor interacting protein 3-mixed lineage kinase domain-like protein (RIP1-RIP3-MLKL) is involved in fluoride-induced osteoblastic death.Methods:Human osteosarcoma cell line (Saos-2 cells) were cultured in vitro and divided into NC group, sodium fluoride (NaF) groups (5.0, 10.0, 20.0 and 40.0 mg/L NaF), necroptosis inhibitor Necrostatin-1 (Nec-1) group (50.0 μmol/L Nec-1) and NaF + Nec-1 groups (5.0, 10.0, 20.0 and 40.0 mg/L NaF + 50.0 μmol/L Nec-1). After cultured for 24 and 48 h, respectively, cell proliferation was determined via the CCK-8 method, and the activity of lactate dehydrogenase (LDH) was determined by chemical colorimetry. To further analyze the influence of NaF on RIP1-RIP3-MLKL pathway, Saos-2 cells were divided into NCⅡgroup and NaFⅡgroups (2.5, 5.0, 10.0, 20.0 and 40.0 mg/L NaF). After cultured for 24 and 48 h, respectively, the protein expression levels of RIP1, RIP3 and MLKL were determined by Western blotting. Results:The cell proliferation rates (%: 100.00 ± 0.59, 104.90 ± 0.44, 104.16 ± 0.41, 82.45 ± 1.91, 64.59 ± 1.83, 103.56 ± 0.41, 107.18 ± 0.87, 105.35 ± 1.28, 89.63 ± 1.20, 77.51 ± 1.30; 100.00 ± 0.33, 107.92 ± 0.44, 101.78 ± 1.06, 75.45 ± 0.39, 57.94 ± 1.17, 106.74 ± 0.21, 111.85 ± 0.21, 107.82 ± 0.68, 82.34 ± 0.56, 70.19 ± 0.99) among all groups were significantly different at both 24 and 48 h ( F = 77.13, 2 313.43, P < 0.05). Except the cell proliferation rate of the 10.0 mg/L NaF + Nec-1 group that was not significantly different with that of the 10.0 mg/L NaF group at 24 h ( P > 0.05), the cell proliferation rates of other NaF + Nec-1 groups were significantly higher than those of corresponding NaF groups at both 24 and 48 h ( P < 0.05). The proliferation rate was negatively correlated with fluoride concentration ( r24 h = - 0.976, r48 h = - 0.969, P < 0.001). The LDH activity in all concentrations of NaF groups was significantly higher than that in NC group and corresponding NaF + Nec-1 groups at both 24 and 48 h ( P < 0.05). The LDH activity was positively correlated with fluoride concentration ( r24 h = 0.985, r48 h = 0.988, P < 0.001). The protein expression levels of RIP1, RIP3 and MLKL of 5.0 mg/L NaFⅡ group at 24 h, RIP3 of 5.0 mg/L NaFⅡ group at 48 h, and RIP1, RIP3 and MLKL of 10.0, 20.0 and 40.0 mg/L NaFⅡ groups at both 24 and 48 h were higher than that in NCⅡ group ( P < 0.05). The protein expression levels of RIP1, RIP3 and MLKL were positively correlated with fluoride concentration ( r24 h-RIP1 = 0.881, r48 h-RIP1 = 0.952, r24 h-RIP3 = 0.867, r48 h-RIP3 = 0.938, r24 h-MLKL = 0.758, r48 h-MLKL = 0.907, P < 0.001). Conclusion:Fluoride can directly cause necroptosis of osteoblasts through the RIP1-RIP3-MLKL pathway, and the severity of cell damage is closely related to fluoride concentration, Nec-1 has partially reversed the effects of fluoride.