ABSTRACT
<p><b>OBJECTIVE</b>To explore the toxic effect of fluoride on the human thyroid cells (Nthy-ori 3-1) and its mechanism.</p><p><b>METHODS</b>Nthy-ori 3-1 cells were exposed to 0.0, 0.1, 1.0, 3.0 mmol/L of sodium fluoride (NaF) in vitro. After 24 hours incubation, 3 (4,5-Dimethylthiazol-z-yl)-3, 5-diphenyltetrazolium bromide (MTT) assay and lactate dehydrogenase (LDH) assay were used to measure cell viability and the LDH leakage rate. Reactive oxygen species (ROS) level, constituent ratio of the cell cycle, and apoptosis rate were measured by flow cytometry.</p><p><b>RESULTS</b>Comparing to viability of control group (set as 100.00%), the cell viability of the 1.0, 3.0 mmol/L fluoride-treated groups (76.64 +/- 9.13)%, (64.04 +/- 6.32)% were significantly decreased (all P values <0.01). LDH leakage rate and ROS level of the 3.0 mmol/L fluoride-treated group ((48.66 +/-7.15)%, (29993.50 +/- 1786. 86) FI) were significantly increased (all P values <0.01) compared to control group ((35.24 +/- 3.02)%, (13021.33 +/- 1067.55) FI). The G0/G1 phase cells of the 1.0 mmol/L fluoride-treated group ((40.76 +/- 5.65)%) were lower than control group (60.09 +/- 1.76)% (P < 0.01), yet the percentage of cells in S phase ((54.05 +/- 4.59)%) were higher than the control group (32.59 +/- 2.43) % (P < 0.01). Comparing to control group ((9.64 +/- 3.44)%), the percentage of apoptosis cells increased in the 3.0 mmol/L fluoride-treated group ((20.09 +/- 3.22)%) (P < 0.01).</p><p><b>CONCLUSION</b>To Nthy-ori 3-1 cells, fluoride under experimental concentrations decreases cell viability, improve the LDH leakage rate, and ROS level. It blocks the cells in S phase and induce cell apoptosis.</p>