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DNA DAMAGE IN THYROID GLAND CELLS OF RATS EXPOSED TO LONG-TERM INTAKE OF HIGH FLUORIDE AND LOW IODINE

Thirty-two one-month-old Wistar albino rats were divided randomly into four equal groups of eight (female:male = 3:1). To assess damage to DNA in their thyroid gland cells, the first group (1) of rats served as the untreated control, the second group (2) was administered a high concentration of fluoride (HiF, 100 mg NaF/ L [45 mg F–/L] in their drinking water), the third group (3) was placed on a low iodine intake (LI, 0.0855 mg I/kg diet), and the fourth group (4) was exposed to the high fluoride and low iodine treatment combined (HiF+LI). At 20 months of age, the rats were sacrificed for experimental purpose and their thyroid gland cells were removed for single cell gel electrophoresis (SCGE = comet assay). In comparison with DNA damage in the thyroid gland cells of the control group 1 (10.74 ± 12.59%), such DNA damage in the LI, HiF, and HiF+LI groups 2, 3, and 4, was 83.50 ± 10.20%, 83.03 ± 12.11%, and 89.32 ± 8.21%, respectively. Moreover, the proportion of grade III thyroid gland cell damage increased by 32.26% in group 2, 47.83% in group 3, and 69.23% in group 4, as compared to the control group 1. These findings indicate that excessive long-term intake of fluoride, with or without adequate I intake, is a significant risk factor for the development of thyroid dysfunction.