Effect Of Sodium Selenite On Apoptosis Of Experimental Autoimmune Thyroiditis

Objective To investigate the effect of sodium selenite on the apoptosis in thyroid tissues of rats with autoimmune thyroiditis and its protective mechanism.Methods Wistar rats were divided into three groups:normal control,experimental autoimmune throiditis(EAT) group and selenium prophylaxis EAT group.EAT model was established by high-dose iodine intake and pig thyroglobulin injection.Rats in selenium curatio-EAT group were given a certain amount of sodium selenite(0.2mg/kg) by intragastric administration.At the end of our experiment,we observed the histio-strcture,apoptosis of thyroid cells using TUNEL,levels of bax,bcl-2,Fas,FasL mRNA using real-time RT-PCR in tissue bomogenate of thyroid and the levels of IFN-γ,IL-4,IL-10 and autoantibodies in the serum.The expression and distribution of Bcl-2,Bax and Caspase-3 were also detected using immunohistochemical method and analyzed by Sample PCI pathological image system.Results(1) At the end of experiment,the levels of TgAb in normal control,EAT group and selenium curatio-EAT group were(6.94±1.13)%,(36.24±3.64)%,(17.23±2.90)%respectively,the levels of TmAb were(5.96±1.40)%,(27.12±5.06)%,(15.98±2.45)%respectively.In selenium curatio-EAT group,the levels of autoantibodies became much lower than EAT group(P＜0.05).(2) Compared with EAT group, lymphocytes in thyroid were fewer and follicles were better and the number of apoptotic thyroid cells were fewer in selenium curatio-EAT group(P＜0.05).(3) Compared with EAT group,the lymphocytes in thyroid and the strongly positive Caspase-3 staining were fewer in selenium prophylaxis EAT group.The strong-dyeing area of Bcl-2 located far from the infiltration region,and the strong-dyeing area of Bax located in the vicinity of the infiltration region(P＜0.05).The expression of Caspase-3 and Bax has a positive correlation(r = 0.89,P＜0.01),and the expression of Caspase-3 and Bcl-2 has a negative correlation(r=-0.85,P＜0.01).(4) Compared with EAT group,the level of Bcl-2 mRNA in selenium prophylaxis EAT group was higher,the level ofbax mRNA was lower and the ratios of Bcl-2/Bax was higher(P＜0.05).The level of Fas mRNA and FasL mRNA was lower(P＜0.05).(5) Compared with EAT group,the levels of IL-4,IL-10 in selenium prophylaxis EAT group were higher,and the level of IFN-γwas lower.Conclusion Sodium selenite can inhibit the apoptosis of thyroid cells and the immune damage in thyroid tissue.Its effects may be operated through increasing the Bcl-2/Bax ratio,reducing the expression of Caspase-3,as well as the maintenance of Th1/Th2 cytokine balance.