The Effect Of Selenium On Autoimmune Thyroid Disease With Adequate And Low Iodine

ObjectiveIn this study through establishing the experimental autoimmune thyroiditis (EAT) model, to observe the effect of selenium on disease prevention and treatment when iodine is adequacy and deficiency, moreover,discuss the mechanism,then to provide the scientific basis for the selenium to prevent and control diseases.Methodes1. The determination of iodine, selenium content in feedstuff:The methods of arsenic cerium catalysis spectrophotometric and2,3-diaminonaphthalene by fluorometry were carried on,and the precision and accuracy were examined,the amount of sodium selenite was add to the feedstuff according to the determined results.2. The effect of selenium on autoimmune thyroid disease with adequate and low iodine:Thyroglobulin (TG) and complete Freund’s adjuvant (CFA) mixed to reproduct experimental autoimmune thyroiditis model. Carried on the pathological examination to the thyroid tissues, and observed the lymphocyte infiltration and thyroid epithelial cell structure changes. At the same time,RIA determination of thyroid autoantibodies (TGAb,TMAb). Detection Kits for use to examine GSH-Px and SOD activities in liver tissue, the method of RIA to determine the type I and II deiodinase activities in liver tissue.Immunohistochemical staining was used to observe apoptosis Fas and FasL.Results 1. The content of iodine,selenium in the feedstuff:The content of iodine was in the range of0-0.90mg/kg,the content of selenium was in0.01～0.30mg/kg for low selenium, low iodine and normal feedstuff. The parallel samples of the relative standard deviation were all lower than10%;the recovery of three kinds of feedstuff were85～105%.2. The effect of selenium on autoimmune thyroid disease with adequate and low iodine:(1)The changes for thyroid absolute and relative weight:Compared with Control group (Control), the thyroid absolute and relative weight of Model group were increased (P<0.05). The volume of thyroid in three groups which were fed with low iodine feedstuff (I-Se++M, I-Se+M, I-Se-+M groups) were significantly enlarged compared with the Control and Model group,the absolute or relative weights was increased (P<0.05).(2)The effect of different selenium levels on antioxidant system:①The changes of GSH-Px activity in rat liver tissue:GSH-Px activity in Model group was decreased than Control group but the difference was not statistically significant (P>0.05). Among three groups when iodine was adequacy under conditions of different selenium level(Se++M, Se+M, Se-+M), the GSH-Px activity of Se++M group was highest (P<0.05), Se-+M group was significantly decreased (P<0.05); Among three groups when iodine was deficiency under conditions of different selenium level(I-Se++M, I-Se+M, I-Se-+M), the GSH-Px activity of I-Se++M group was higher than I-Se+M group (P<0.05), I-Se-+M group compared with the previous two groups significantly reduced (P<0.05).②The changes of SOD activity:I-Se++M, TSe+M, I-Se-+M groups compared with Control, Model, Se++M, Se+M, Se-+M groups,the SOD activity had a significant difference(P<0.05).(3) The effect of different selenium levels on deiodinase:①The changes of type Ⅰ deiodinase enzyme activity in rat liver tissue:Model group compared with Control group had no change(P>0.05). When the iodine is adequacy, type Ⅰ deiodinase enzyme activity of Se++M group is higher than Control group and Model group (P<0.05).The deiodinase enzyme activity of Se-+M group is lower than Se++M group and Se+M group(P<0.05), Se++M group is higher than Se+M, Se-+M groups(P<0.05); when iodine is deficiency, although we can see the group for deficient selenium is lower than the group supplied with selenium, but no significant difference (P>0.05).②Type Ⅱ deiodinase activity changes in rat brain tissue：Model group compared with the Control group is relatively lower,However,the difference was not statistically significant (P>0.05). When iodine is adequacy, type Ⅱ deiodinase activity in Se-+M group compared with Se++M, Se+M group had the decreasing trend, but no significant difference (P>0.05). When iodine is deficiency, I-Se-+M group compared with I-Se++M, I-Se+M had a tendency to increase,but differences were not statistically significant (P>0.05).(4) The changes of thyroid autoantibodies (TG antibody and TM antibody):Model group compared with Control group were significantly increased (P<0.05),and TG antibody increased by719%, TM antibody increased by929%. When iodine is adequacy and deficiency, the groups compared with Control group increased (P<0.05), but compared Model group did not change (P>0.05). In addition, there were positive correlation between TG and TM(P<0.05).(5) Histopathologic examination of the thyroid:Compared to the normal thyroid tissue, the rat thyroid tissue of Model group injuried, including follicular epithelial necrosis and the large number of lymphocyte infiltration. The glands in other groups had suffered varying degrees of damage.(6)Fas and Fas ligand expression in thyroid tissue:Compared with Control group,the other groups were significantly increased (P <0.05). When iodine is adequacy, visibility Fas expression in Se++M group compared with Model group decreased; When iodine is deficiency, I-Se-+M group relatively increased(P<0.05); FasL expressionin in I-Se-+M group had a significant increase(P<0.05). Conclusions1. Using thyroglobulin (TG) and complete Freund’s adjuvant (CFA)to reproduct EAT model was successful, and found lymphocyte infiltration and increased autoantibody obviously in the thyroid tissue.2. When iodine is adequacy, supplement of selenium could increase the activity of deiodinase,catalysed T4conversion for T3,made activity of GSH-Px raised,decreased the level of peroxide,regulated the metabolism of the thyroid gland hormone.Moreover,selenium could repress the expression of Fas and restrain the apoptosis in the mediate of Fas.3. When iodine is deficiency, supplement of selenium could increase the activity of GSH-Px,decrease the expression of Fas,and to affect the disease.Low iodine and low selenium could aggravate the injury.