Study On The Mechanism Of Thyroid Gland Injuried By Fluoride

Fluoride is a essential trace element to the body,which maintained normal life activities of the body if we intake properly,but it is the systemic poisonous substance, its negative influence to endocrine glands has changed to be a topic of general interest in the field of fluoride research in recent years worldwide. There have been some researches showed that fluoride could induce thyroid goiter, but some scholars hold opposing views. Fluorosis models of SD rat were aministered 0,50mg/L,100mg/L,200mg/L of sodium fluoride in drinking water,respectively. The total feeding experiment lasted 156days; primarily cultured SD rat thyroid cells were treated with different concentrations of sodium fluoride at 0,10μmol/L,100μmol/L,1000μmol/L,FRTL (fisher rat thyroid cell line, rat thyroid cell line) cells were treated with 0,1.25mg/L,2.5mg/L,5.0mg/L, 10.0mg/L,20.0 mg/L of sodium fluoride respectively.The effects of fluoride on thyroid hormone metabolism gene expression,protein expression and distribution and the cytokine gene expression and secretion were performed by electron microscopy, molecular biology and immunology.The experiments of fluorisis in vitro and can remove the impact of hypothalamus- pituitary-thyroid axis and clarify the molecular mechanism of thyroid injury, and further elucidate theoretical basis of thyroid damage.The animal models of SD rat fluorosis was successfully established and the fluorisis samples of thyroid cell in vitro was prepared.Using the methods followed as Scanning Electron Microscope(SEM),RIA(radioimmunoassay)and so on.A series of indexes reflecting the hormone secreting function of thyroid were determined separately, the result showed that fluoride could disturb the synthesis and secretion of thyroid hormone T₃ and T₄, what directly interfering with the growth and metabolism of the whole body.The high level fluoride(200mg/L) cause angiogenesis hyperplasia and large nodules in rat thyroid gland and the effects of fluoride on thyroid cell membrane injury;using followed as HE staining and SEM detected the fluoride on thyroid injury,the results showed that fluoride can cause goiter and a sequence of injuries.Related enzyme and growth factor were determined by RTPCR,immunocytochemistry and immunofluorescent histochemical.The results were as follows: the indexes such as TG,NIS,TPO,TSHR,VEGF which closely correlated with thyroid function were abnormal. Fluoride disturbed the free radical metabolism, changed the expression of enzyme and growth factor like iNOS and VEGF, the capillary vessels proliferated, free radical metabolism and lipid peroxides accumulated, then damaged the structure and function of thyroid follicles, disturbed the colloid catabolism, inhibited the transference and organic proceeding of thyroid iodine, restrained the activity of thyroid enzyme system like TPO and TSHR-cAMP, destroy every series of synthesis and secretion of thyroid hormone,which block TSH stimulation of thyroid cells and TSHR-cAMP can not play a normal role in thyroid cells,further caused the abnormality of thyroid hormone metaboism.To investigate the effects of fluoride on cytokine gene expression and secretion of FRTL cell, IL-6 mRNA, IL-8 mRNA, IFN-γmRNA, TNF-a mRNA and cell supernatant VEGF and NO of FRTL cells treated with fluoride for 72h were collected and RT-PCR, ELISA were performed,NF-kB p65 protein level was determined by western blot.The results showed that fluoride stimulate the over expression of cytokines, which further inhibited the thyroid hormone metabolism related gene expression in thyroid cells; On the other hand, fluoride stimulated over expression of cytokines and NF-κB p65, further cause FRTL cell own ability decline to resist fluoride.Fluoride can affect the growth and development of thyroid cell and damage the structure and morphology, sodium fluoride affects the morphologyic characteristics of thyroid cells in a dose-response manner and long-term intake of excessive fluoride caused nodular thyroid enlargement occurred; Fluoride stimulate iNOS (inducible nitric oxide synthase) ,the expression of cytokines and NF-kB p65, these cytokines by inhibiting the metabolism of thyroid hormone-related gene expression ,further cause thyroid cell function decline; It can be concluded that fluoride can cause dysfunction of thyroid in uptaking and using iodine, synthesizing, storing and secreting thyroid hormones, which finally can induce structural and functional abnormalities in thyroid gland.