Effect Of Excess Iodine On Neuron Development In Cerebrum Of Filial Mice And Intervention Of Selenium

The goal of eliminating iodine deficiency disease (IDD) has been achieved since Universal Salt Iodization (USD policy has been widely carried out in many nations including China. On the other hand, reports are increasingly appearing about the side effects caused by excess iodine intake. Iodine-induced goiter has been reported in many nations and areas resulted from ingestion of excess iodine in foods, in drinking water and in medications, or resulted from excess iodine supplementation in iodated foods. Previous studies reveal that excess iodine intake may result in diffused colloid goiter. However, it is not well documented if iodine excess also has an effect on brain development as iodine deficiency. Another microelement selenium is essential to thyroid hormone metabolism and thyroid function by the selenocysteine-containing glutathione peroxidase (GSH-Px) system and deiodinase system. Se influences nervous system development by thyroid hormone. Several studies have been carried out to establish the effects of combined selenium and iodine deficiency on brain development. However, few researches were carried out to study the intervention of selenium on dysfunction induced by excess iodine. It is necessary to study the possible intervention of Se on brain development defect induced by excess iodine. In this study, on the basis of excess iodine animal model successfully established in Balb/c mice, first, we observed the effects of excess iodine on thyroid hormone and deiodinase, and intervention by different doses of selenium in maternal mice. Second, we observed the effects of excess iodine on thyroid hormone metabolism in pregnant mice and intervention by different doses of Se. Third, we observed the effects of excess iodine on thyroid hormone metabolism of filial mice and intervention of Se. Fourth, we observed the pathological change by histomorphometry and ultrastructure of cerebrum and hippocampus. At last, we detected the expression level of NSE, SYP, RC3, α-tubulin, TRα1, TRβ1 and G0α in cerebrum of filial mice with excess iodine intake and intervention of selenium by real-time quantitative PCR, immunohistochemistry and western-blot, and try to study the molecular mechanism of the effect of excess iodine on neuron development and intervention of selenium from the three aspects of neuron development, thyroid hormone receptor and signal transmission. The results were summarized as follow:Part oneEstablishment of excess iodine model in maternal mice and intervention of selenium on effects of excess iodineObjective To establish excess iodine model of maternal mice and observed the effects of excess iodine on thyroid hormone metabolism and intervention by different doses of selenium in maternal mice and establish the optimal dose range of selenium.Methods 240 weanling Balb/c mice were divided into 8 groups randomly. Normal control group(NC) was given taper water; excess iodine(EI) control group was given drinking water containing 3000μg/L iodine; C～H groups were selenium supplementation groups and given drinking water containing 0.1, 0.2, 0.3, 0.4, 0.5, 0.75mg/L selenium, respectively, besides 3000μg/L iodine. After four months, such indices were determined as urinary iodine and selenium, hepatic selenium, thyroid hormones in serum, type I iothyronine deiodinase (D1) activity and mRNA in liver, kidney and thyroid gland Thyroid was used for histological examination.Result 3000μg/L iodine could induced diffused colloid goiter. Median of urinary iodine, and serum T₄ level was significantly higher in excess iodine than in normal control, and median of urinary selenium, hepatic selenium level and T₃ level decreased significantly in excess iodine group than in normal control (P<0.05). Activity and mRNA level of D1 in liver and kidney was decreased significantly in excess iodine group compared with normal group (P<0.05). Supplementing Se alleviated goiter, enhanced hepatic selenium level and T₃ level and activity and mRNA level of D1, lowered serum T₄ level significantly (P<0.05). Under the conditions of this study, the optimal dose range of selenium intervention was 0.2 0.4mg/L.Conclusion Excess iodine model of Balb/c was established successfully and 3000 μ g/L iodine intake can lead to goiter and abnormal thyroid hormone metabolism. Supplementing Se improved thyroid hormone metabolism. It is proposed that the optimal dose range of selenium was 0.2～0.4mg/L and supplementing selenium improves thyroid hormone metabolism in maternal mice with excess iodine. The results lay a foundation for exploring the intervention of selenium on neuron development of cerebrum in filial mice with excess iodine.Part twoEffects of excess iodine on thyroid hormone metabolism in pregnant mice and intervention by different doses of SeleniumObjective To observe the effects of excess iodine on thyroid hormone metabolism and intervention of selenium, and explore the optimal dose range of selenium.Methods 240 weanling Balb/c mice were divided into 8 groups randomly. Normal control group(A) was given taper water; excessive iodine(B) control group was given drinking water containing 3000μg/L iodine; C^H groups were selenium supplementation groups (SS) and given drinking water containing 0.1, 0.2, 0.3, 0.4, 0.5, 0.75mg/L selenium, respectively, besides 3000μg/L iodine. Four months later, urinary iodine concentration of female mice was determined. Then the mice were mated (female: male = 2:1) and the morning of appearance of a vaginal plug was taken as 0.5 day (0.5d) of pregnancy. On the 19.5d of pregnancy, pregnant mice were killed and the uteri were cut open to take out placenta immediately. Meanwhile, serum of pregnant mice was used for thyroid hormone level determination. Liver, kidney and placenta of 12.5d and 19.5d pregnant mice were used to determine the selenium level, and the activity and mRNA level of deiodinase.Results â‘ Excess iodine lowered significantly hepatic selenium level, and selenium nutritional status in pregnant mice was improved by supplementing selenium (P<0.05). Compared with EI group, selenium level in liver and placenta increased in 0.2mg/L～0.75mg/L or 0.3mg/L～0.75mg/L SS groups, respectively. â‘¡Excess iodine reduced placenta weight (P<0.05). Placenta weight was significant higher in 0.3mg/L SS group than that in EI group (P<0.05). â‘¢Excess iodine enhanced significantly serum T₄ level and lowered serum T₃ level, and selenium supplementation decreased serum T₄ and increased T₃ from 0.1 to 0.5mg/L selenium dose (P<0.05). No change was found in 0.75mg/L SS group. â‘£Excess iodine reduced significantly activity of D1 in liver and kidney, and mRNA level of hepatic D1. A dose-dependant increase of D1 activity in liver and kidney was observed in SS groups from 0.2 to 0.5mg/L selenium dose (P<0.05). Compared with EI group, D1 mRNA expression in liver markedly increased in 0.2 ～ 0.5mg/L SS groups, and in kidney increased significantly in 0.3～0.75mg/L SS group (P<0.05). ⑤Excess iodine reduced significantly D2 activity in placenta and uterus, and enhanced D3 activity in uterus on pregnant day 19.5 (P<0.05). Selenium supplementation enhanced D2 activity in placenta and uterus at a certain range of doses (P<0.05), but had no effect on the D3 activity in placenta. D3 activity in 19.5d uterus decreased obviously in 0.2～0.75mg/L SS groups.Conclusion Excess iodine influences on deiodinase in liver, kidney, placenta and uterus, and thyroid hormone metabolism in pregnant mice. Excess iodine finally may influence on thyroid hormone metabolism in fetus. Selenium supplementation resulted in an elevation of selenium level in mice with excess iodine intake and had a favorable intervention on the embryo toxicity induced by excessive iodine intake. Supplementing selenium influences on maternal-fetal thyroid hormone level by regulating activity of deiodinase. Under the conditions of this study, the optimal dose range of selenium was 0.2～0.4mg/L. It is initiated that supplementing seleniumalleviates the influences of excess iodine on filial mice during pregnancy.Part ThreeEffects of excess iodine on thyroid hormone metabolism in filial miceand intervention by different doses of seleniumObjective To observe the thyroid hormone metabolism in filial mice with excess iodine and intervention of selenium by different dosesMethods 240 weanling Balb/c mice were divided into 8 groups. Normal control group(NC) was given taper water; excessive iodine(EI) control group was given drinking water containing 3000μg/L iodine; C～H groups were selenium supplementation groups (SS) and given drinking water containing 0.1, 0.2, 0.3, 0.4, 0.5, 0.75mg/L selenium, respectively, besides 3000μg/L iodine. Four months later, urinary iodine concentration of female mice was determined. Then the mice were mated (female: male=2:1) and the morning of appearance of a vaginal plug was taken as 0.5 day (0.5d) of pregnancy. Thyroid hormones, and activity and mRNA of deiodinase in serum, cerebrum, liver, kidney and BAT of filial mice were measured on postnatal day 0, 14 and 28. Thyroid gland of filial mice was used for histological examination on postnatal day 14.Results Excess iodine induced diffused colloid goiter of filial mice on postnatal day 14 and supplementing selenium by different doses alleviated the goiter, but 0.75mg/L selenium has little effects. Hepatic selenium level fell in filial mice in EI group, but no significant difference compared with normal control. Excess iodine lowered significantly T₄ level in serum, T₄ and T₃ level in cerebrum, activity and mRNA level of D3, activity of D1 in liver and kidney, meanwhile, enhanced significantly activity and mRNA level of D2 in cerebrum and BAT on postnatal day 0 and 14 (P<0.05). Supplementing Selenium antagonized the influences induced by excess iodine. No significant difference was found in all indices between all groups on postnatal day 28.Conclusion Excess iodine and high T₄ in serum may pass through placenta to fetus and results in diffused colloid goiter and abnormal synthesis and release of thyroid hormone and hypothyroidism in filial mice. Although excess iodine brought about relative selenium deficiency in maternal mice, not significant selenium deficiency in filial mice. It is proposed that supplementing selenium can antagonize abnormal histo-morphalogy and function induced by excess iodine in filial mice through influencing on thyroid hormone metabolism in maternal mice. The optimaldose range of selenium was 0.2～0.4mg/L.Part FourThe effects of excess iodine on histo-morphalogy and ultrastructure of neuron in cerebrum of filial mice and intervention of seleniumObjective To observe the pathological change of cerebrum and ultrastructure of neuron in filial mice with excess iodine intake and selenium intervention.Method Animal treatment and mating was the same as the part three. The pathological change of cerebrum and ultrastructure of neuron in hippocampus were observed by HE and electron microscope.Results In EI group, the cells in the cerebrum are packed closer together and smaller, thus leading to a decrease in the overall size of the brain, staining thicker in nuclear, heterochromatin obviously increased and the degree of cell differentiation is lower in filial mice on postnatal day 14 compared with NC. Under electron microscope, nucleus and the ratio of nuclear/cytoplasm is bigger, cytoplasm surrounding nucleus reduces, nuclear membrane is thinner, microtubule and microfilament of axon and dendrites reduces, the number of cellular organelle reduces in EI group. The results demonstrate that excess iodine results in a delay of brain development. Supplementing selenium alleviates the effects of excess iodine. Conclusion The new ideas are brought forth that excess iodine leads to abnormality in histo-morphalogy and ultrastructure of cerebrum and delay in brain development, and supplementing selenium improves the brain development. The study on morphyology and ultrastructure of cerebrum lays a foundation of selenium intervening intelligence under the condition of excess iodine intake. Part Five Molecular mechanism of effects of excess iodine on neurondevelopment in filial mice and intervention of seleniumObjective To study the molecular mechanism of the effects of excess iodine on neuron development in filial mice and intervention of selenium by real-time quantitative PCR, immunohistochemistry and western-blot from the three aspects of neuron development, thyroid hormone receptor and signal transmission.Methods 120 weanling Balb/c mice were divided into 4 groups. Normal control group(NC) was given taper water; excess iodine(EI) control group was given drinking water containing 3000μg/L iodine; selenium(Se+) was given drinking water containing 0.2mg/L selenium; selenium supplementation group (EI+Se+) was given drinking water containing 0.2 mg/L selenium, respectively, besides 3000μg/L iodine. Four months later, urinary iodine concentration of female mice was determined. Then the mice were mated (female: male=2:1) and the morning of appearance of a vaginal plug was taken as 0.5 day (0.5d) of pregnancy. Cerebrum of filial mice on postnatal day 0,14 and 28 was taken out for measurement.Results Excess iodine down-regulated the expression of NSE, SYP, RC3 in cerebrum of filial mice on postnatal day 0 and 14, and α—tubulin on postnatal day 0 (P<0.05), delayed the developmental downregulation of α—tubulin, and up-regulated the expression of TRα1,TRβ1 and Goα on postnatal day 0 and 14 (P<0.05). No significant difference was found in the expression level of NSE, SYP, α—tubulin, RC3, TRα1, TRβ1and G0α between four groups on postnatal day 28. Supplementing selenium antagonized the effects induced by excess iodine.Conclusion Excess iodine influences development and mature of neuron, dendrites and synapse in cerebrum of filial mice and supplementing selenium antagonized the effects induced by excess iodine from molecular mechanism. The new ideas are brought forth that selenium intervened on development of neuron of cerebrum in filial mice by intervening on thyroid hormone metabolism in maternal and filial mice with excess iodine.