Abstract:
Objective To investigate the role of oxidative stress in high iodide and/or high fluoride induced thyroid damage.
Methods Models of thyroid cells were exposed to 50 mmol/L KI (high iodide), 1 mmol/L NaF (high fluoride), and 50 mmol/L KI+1 mmol/L NaF (high iodide and high fluoride); models of Wistar rats were exposed to water containing 1.685 mg/L KIO3 (high iodide), 20 mg/L NaF (high fluoride), and 1.685 mg/L KIO3+20 mg/L NaF (high iodide and high fluoride); and an epidemiological survey was carried out. Cell viabilities and reactive oxygen species (ROS) levels, rat urinary iodide and fluoride levels, blood malondialdehyde (MDA) and superoxide dismutase (SOD) levels, as well as human blood ROS, triiodothyronine (T3), thyroxine (T4), and thyrotropin (TSH) levels were detected by methyl thiazolyl tetrazolium (MTT) assay, flow cytometry, spectrophotometry, electrode, colorimetry, and radioimmunoassay.
Results The cell viability of the control group was (100.00±0.00)%, and the cell viabilities of the high iodide, high fluoride, and combined groups were reduced to (73.54±8.37)%, (84.54±7.55)%, and (72.62±7.15)% (P < 0.05), respectively. Morphological changes were observed in the cells of the high iodide groups and/or high fluoride groups. The fluorescence intensity of ROS in the control group was 1 409.50±208.46, and the high fluoride groups and the combined groups induced intracellular ROS fluorescence intensity to 2 304.15±390.47 and 2 669.24±646.80 respectively (P < 0.05). The high iodide and the combined treatments increased the levels of urinary iodide in rats (P < 0.05). The high fluoride and the combined groups increased the levels of urinary fluoride in rats (P < 0.05). Morphological changes in rat thyroid follicles were observed in the high iodide and/or high fluoride treated groups. The MDA and SOD levels in the male control rat group were (3.00±0.33) μmol/mL and (300.92±36.02)×103 U/L, and those in the high fluoride group were (4.27±0.82) μmol/mL (P < 0.05) and (226.33±41.21)×103 U/L (P < 0.05) respectively. The children's T4 was elevated in the combined group (P < 0.05); the serum ROS levels were elevated in the high fluoride and the combined groups from (72.83±13.70)×103 IU/L in the control group to (76.65±125.45)×103 IU/mL and (89.95±63.85)×103 IU/mL respectively (P < 0.05).
Conclusion High iodide and/or high fluoride could cause thyroid damage and there is no evidence indicating oxidative stress induced by high iodide, but oxidative stress is involved in the process of thyroid damage induced by high fluoride and the combination of high iodide and high fluoride.
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