Effects of fluoride on rat thyroid morphology, thyroid peroxidase activity and the expression of thyroid peroxidase protein

Abstract

Objective To observe the effect of long-term fluoride excess on rat thyroid morphology,thyroid peroxidase(TPO) activity and the expression of TPO protein,and to explore its possible mechanism of action.Methods Forty male SD rats were randomly divided into four groups by weight:control group,low-fluoride group,moderate-fluoride group and high-fluoride group(n =10),and they were fed with ordinary tap water containing fluorine 0.40,15.00,30.00,60.00 mg/L,respectively,and ate ordinary food prepared feed.After fed for 180 days,rats were anesthetized,and thyroid was taken.The morphology of thyroid was observed under light microscope.TPO activity was measured with improved guaiacol method.The expression of TPO protein was evaluated by Western blotting.Results The thyroid histopathology results show:in control group,the thyroid follicular epithelial cells were columnar or cuboidal,with the follicular cavity filled with pink gum; in low-fluoride group,the thyroid follicular epithelial cell presented active hyperplasia; in moderate-fluoride group,the size of follicular increased,and follicular cavity was filled with dark,sticky colloid follicular; follicular increases,follicular cavity filled with dark,sticky colloid follicular; in high-fluoride group,the follicular epithelial cells showed apparent flat shape and excessive concentration of follicular colloid,a small amount of follicular lumen even showed the phenomenon of fusion,forming a giant follicular or cystic cavity.Among the four groups of control group,low-fluoride group,moderate-fluoride group and high-fluoride group,with increased fluoride,TPO activity [ ( 1.572 ± 0.046), ( 1.414 ± 0.086), (1.322 ± 0.049), (0.960 ± 0.083)U/L] decreased,and the differences were statistically significant between the two groups(all P ＜ 0.05).With increased fluoride,the expression of TPO protein (0.335 ± 0.011,0.156 ± 0.027,0.084 ± 0.020,0.045 ± 0.002) decreased,and the differences were statistically significant between the two groups(all P ＜ 0.05).Conclusioons Long-term intake of excessive fluoride can inhibit the thyroid TPO activity and the expressions of TPO as well as thyroid hormone synthesis,and leads to histological changes in rat thyroid. Key words: Fluoride poisoning; Rats; Thyroid gland; Thyroid peroxidase