Effect Of Excessive Iodine On Immunotoxicity In Mice With Selenium Intervention

Autoimmune thyroid disease (AITD) is a kind of organ-specific autoimmune disease of thyroid. Iodine is the major raw material for thyroid hormone synthesis, and is also an important modulatory factor for the function of thyroid. With the elimination of iodine deficiency disease with iodine supplement, many people pay close attention to the relationship between excessive iodine and AITD. Data of epidemiology suggest that the morbility of AITD is significantly high in the region where the concentration of iodine in the water is high. Although iodine deficiency exists in our country, there are about 92 counties (600 million people )with excessive iodine in drinking water. It results in a major public health problem for the people lived in these areas. Therefore, it is important to study the harm of excessive iodine to the human immune system and understand the related mechanism of AITD and to prevent the harm of excessive iodine intake with valid measurment. Up to now, no research has been reported on this aspect. In addition, it is known that selenium plays an important role in regulating the immune system in the synthesis and metabolism of thyroid hormone and in the antioxidation. It has no studies reported that selenium can prevent the damage of overdosing of iodine to the immune system. The purpose of our reserch is to study the immune toxicity induced by excessive iodine intake in mice and intervention with selenium by hybridization in situ, flow cytometry assay, ELISA, immunohistochemistry. The results are reported as follows: Part oneThe study of immune system toxcity induced by excessive iodine intake in mice Objective To investigate the effects of excessive iodine on specific immunity and nonspecific immunity in mice. To study the relationship between excessive iodine and immune system.Method 160 female BALB/C mice were divided into 4 groups randomly according to body weight, 40 for each group ,10 of each group was considered as one batch for test .Mice in 4 groups were orally administrated with tap water 0,1500, 3000, 6000μgI/L respectively for 30 days. Body weight, spleen index , thymusgland index, lymphproliferation response, CD4⁺/CD8⁺, Th1/Th2, 50% haemolysis value, antibody formation cell, phagocyte function, the activity of natural-killer cells(NK) were observed.Result On 6000μgI/L, spleen index, thymusgland index, 50% haemolysis value, antibody formation cell, CD4⁺/CD8⁺, were significantly lower than those in control group. Lymphproliferation response, Th1/Th2, the activity of natural-killer cells(NK) were significantly higher than those in control group. There were no significance differences about phagocyte function, thymusgland index among all dosagesConclusion Iodine, as an exogenous chemical material, is related to immune reaction. The dosage 6000μgI/L can induce disorders of immune function in mice. It may play a central role in the development of autoimmune disease.Part TwoStudy on AITD in mice induced by excessive iodineObjective To investigate relationship between excessive iodine intake and AITD.To observe the changes of T₃, T₄, TSH, TSHRAb, thyroid IgG and to exame pathological change of thyroid.Methods 120 weanling BALB/C mice were assigned into 6 groups and given taper water or drinking water including different doses of iodine. The iodine concentrations were 0μgI/L, 1500μgI/L, 3000μgl/L, 6000μgI/L, 12000μgI/L and 24000μgI/L respectively. Three months later, serum was used for thyroid hormone level, TSH and TSHRAb determination and thyroid was used for thyroid IgG detection and histological examination.Results In excessive iodine intake groups, mice showed diffused colloid goiter. Serum TT₄, TSH levels were significantly higher, and TT₃ level lower than control group when iodine level reached or exceeded 3000μg/L with a dose-dependent manner. Serum TT₄, TSH levels were negatively correlated with iodine intake, serum TT₃ level was positively correlated with iodine intake. In addition, we found thyroid IgG antibody and serum TSHRAb in excessive iodine group above 6000μgI/L were significantly higher than normal control group. Moreover, TSHRAb increased in a concerntration -dependent maner.Conclusion Excessive iodine intake could successfully induce AITD. The threshold level of iodine induced immunotoxicity in this study is 6000μgI/L . Humoral immunity predominates in this kind of autoimmune reaction.Part three Study of mechanism on AITD induced by excessive iodine intake in miceObjective Toinvestigate enzymatic activity of antioxidase and deiodinase in serum and thyroid, Se content in liver, iodine content in urine in mice after fed excessive iodine one month and three months. To investigate the DC antigen presentation function , splenic corpuscle and TSHR's mRNA expression level in mice after fed excessive iodine three months. To explore the mechanism about AITD induced by excessive iodine.Methods 120 weanling BALB/C mice were assigned into 6 groups and given taper water(control group) or drinking water with 1500μg/L, 3000μg/L, 6000μg/L, 12000μg/L and 24000μg/L iodine respectively. One month and three months later, serum of mice was used for SOD, MDA, GPX determination and thyroid used for pathology examination and hybridization in situ analysis. Meanwhile the content of Se in liver, iodine content in urine and enzymatic activity of 5'deiodinase in liver were determined respectively. Three months later, DC from mice spleen were primary cultured, then CD11c, CD86, CD80 and MHC II were detected.Results (1) Urine iodine in mice fed excessive iodine was significantly higer than control (P<0.01) after one month and three months and urine iodine levels increased in a concentration-dependent manner (P<0.01) . Intaking excessive iodine could reduce the level of the liver selenium. At the end of three months, the levels of selenium in the liver was significantly lower than the control group above the 3000μg/L group (P<0.05, P<0.01 respectively), and in a concentration-dependent manner. (2) GSH-Px activity of serum at end of one month in all groups showed no difference from normal control , but the level of excessive group was significantly decreased compared with normal control at end of three months (p<0.01) and in a concentration-dependent manner (r =-0.566 p<0.01) . SOD activity of serum at end of one month was significant different from nomal control above 3000μg/L (p<0.05) but SOD activity of serum at end of three months was significant different from nomal control above 1500μg/L group (p<0.05) , SOD activity of serum both at end of one month, and at end of three months reduced in a concentration-dependent manner. Meanwhile, MDA of serum increased when iodine dose increased. MDA of serum at end of one month was significantly higher above 6000μg/L group compared with normal control group (p<0.05) , but MDA of serum in three months was significantly higher from 3000μg/L group compared with normal control group (p<0.05), and they were all in a concentration-dependent manner.(3) Excessive iodine intake can decrease 1-ID enzyme activity, liver 1-ID enzyme activity was significantly decreased at end of three months above 3000μg/L group compared with normal control and was in a concentration-dependent manner (4) Excessive iodine intake can increase TSHR's mRNA expression level, it significantly increased compared with normal control group at end of three months above 3000μg/L group, and was in a concentration-dependent manner. (5) Excessive iodine intake can increased DC surface marker CD80, CD86, CD11c, MHC-II expression level, and was in a concentration-dependent manner. (6) Excessive iodine intake can significantly enlarge splenic corpuscle compared with normal control group.Conclusion (1) Excessive iodine could reduce the capability of antioxidation of mice, and the organism was intend to oxidative damage. (2) Excessive iodine could reduce the level of the selenium. The liver selenium could reduce the activity of selenoenzyme which is important to the thyroid hormone secretion. (3) Excessive iodine could increase DC. antigen- presentation ,and increrase the risk of developing AITD. It could activate B cells through signal transmission, then generate autoantibody. (3)Excessive iodine upregulated the TSH receptor mRNA levels, this is results of TSHRAb competing TSH receptor with TSH, which enhance autoimmune response. (4)1500μg/L and 3000μg/L iodine resulted in mice oxidative damage, and the autoimmunologic recognition reaction appeared after the concentration of the iodine reached 6000μg/L. (5) The toxicity of the excessive iodine had cumulative effect.Part FourIntervention of selenium on the immunity toxicity induced by excessive iodine intakeObjective To investigate the intervention of selenium on the immunity toxicity induced by excessive iodine intake. To observe the mechanism of selenium against immunotoxicity induced by excessive iodine.Methods 280 weanling BALB/C mice were assigned into 4 groups(A,B,C,D) and given taper water or drinking water including iodine and selenium. A group was normal control; B group was fed 0.3mg/L Se; C group was fed 6000μg/L iodine; D group was fed 6000μg/L iodine +0.3mg/L Se. The treatment of mice and the parameter assayed are same as previous parts.Results (1) Selenium could reverse the immune function disorder induced by excessive iodine. After selenium intervention, the spleen index increased compared with the control group, and the OD value degraded from 3.33±0.14 to 2.04±0.29. Selenium intervention could upregulate CD4⁺/ CD8⁺, downregulate IFN-γ/IL-4 expression and inhibit the excursion of Th₁/Th₂. There were no significant difference in HC₅₀, antibody formation cell and NK cytoactive compared with control group. (2) Selenium intervention could reduce the development of AITD effectively. The thyroid follicle had shrink tendency and the endothelial cells were to be normal morph after selenium intervention. After adding selenium, the level of serum TT₄ and TSH decreased and TT₃ increased. The levels of the TT₃, TSH and TT₄ were significantly different in the selenium intervention groups compared with the high iodine groups (p<0.05 and p<0.01, respectively). These results demonstrated that selenium was effective in preventing thyroid hormone parasecretion induced by excessive iodine. Selenium intervention could degrade the level of thyroid IgG antibody and the concentration of serum TSHRAb in mice. It also could inhibit that TSH and TSHRAb, so the level of TSHR mRNA was no significant different compared with the control group. (3) Intaking excessive iodine could reduce the level of the liver selenium, but selenium intervention could increase it. There were significant difference between the high iodine group and the control group, and selenium intervention group was significantly different from the control group. (4) Selenium intervention could elevate the capability of the antioxidation in mice, serum GSH-P_X, and serum SOD and serum MDA were significantly different in 6000μg/L iodine from the control group (p<0.01). Selenium intervention could enhance the activity of the GSH-P_X and the level of the SOD, and decrease the level of the MDA. The level of the GSH-P_X was significantly different in selenium intervention group from the control group (p<0.05). The level of the SOD and MDA were evidently significantly different compared with the excessive iodine group (p<0.01). (5) Selenium intervention could increase the activity of the liver type 1 deiodinase effectively in mice,and the difference between the selenium intervention group and the high iodine group was significant (p<0.05). (6) Selenium intervention could inhibit the increasing expression of the costimulatory molecules CD80 and CD86, cell surface antigen histocompatibility complex MHC-II, and specific express marker of DC CD11c. It demonstrated that selenium intervention was an effective measurement for inhibition of autoregonization reaction induced by excessive iodine intake. (7) Selenium intervention could effectively control the change of spleen structure caused by excessive iodine. Spleen pathology of the selenium intervention group was similar to the control group. Conclusion Selenium could obviously improve the selenium nutritional state of the animals fed by excessive iodine, and reverse the disorder of the immune function, decrease the risk of developing AITD caused by excessive iodine. Our experiment proved that 0.3mg/L is the optimal selenium dosage which could inhibit the immunotoxicity caused by 6000μg/L iodine.