Effect of fluoride on the expression of rat thyroid peroxidase mRNA

Abstract

Objective To study the effect of long-term fluoride excess on the activity of thyroid peroxidase (TPO) and the expression of TPO mRNA in rat thyroid,and explore the underlying mechanism.Methods Forty male SD rats were randomly divided into four groups based on their body mass(n =10 in each group):control group,low-fluoride group,moderate-fluoride group and high-fluoride group,and rats were fed on water containing 0.40(tap water),15.00,30.00 and 60.00 mg/L NaF,respectively,eating ordinary food formulated feed.All rats were sacrificed 180 days afterwards.Serum FT3 and FT4,TPO activity and mRNA expression level were determined by radio-immunoassay,modificd guaiacol method and semi-quantitative RT-PCR,respectively.Results Although serum FT3 levels in low-fluoride [(3.62 ± 0.47)pmol/L],moderate-fluoride [(3.57 ± 0.55)pmoi/L]and high-fluoride [(3.30 ± 0.68)pmol/L]treated groups were decreased compared with the control[(3.64 ± 0.45)pmol/L],the difference was not statistically significant (P ＞ 0.05).Serum T4 levels of the high-fluoride group [(8.64 ± 1.72)pmol/L]were significantly lower compared with other groups[(13.08 ± 1.69),(12.68 ± 1.32),(12.05 ± 1.43)pmol/L,all P ＜ 0.05].TPO activity in control,low-fluoride,moderate-fluoride and high-fluoride-treated groups[(1.572 ± 0.064),(1.414 ± 0.086),(1.322 ± 0.049),(0.960 ± 0.083)U/L]was decreased with the dose of fluoride increasing,the difference was statistically significant between any two groups(all P ＜ 0.05).The TPO activity was negatively correlated with the dose of fluoride(r =-0.955,P ＜ 0.05).With increased fluoride,the expression of TPO mRNA (0.936 ± 0.160,0.368 ± 0.095,0.115 ± 0.018,0.016 ± 0.008) decreased,the difference was statistically significant between any two groups (all P ＜ 0.05).Conclusion Chronic fluoride excess inhibits the activity and the expression of TPO as well as thyroid hormone synthesis. Key words: Fluorosis,dental; Rats; Thyroid gland; Thyroid peroxidase