| ObjectivesAfter successfully establishing animal models of iodine excess, including potassium iodide andpotassium iodate, and iodine deficiency in Wistar rats and cultured FRTL cells, we explored theeffects of iodine on structure and functions of thyroid, the anti-oxidative capability of thyroid,liver, brain and blood in vivo. We also explored the content of H2O2, the calcium current of cellmembrane, intracellular free calcium concentration and the anti-oxidative ability of thyrocytes invitro.MethodsWistar rats, weaning one month and weighing 120-140g, were randomly divided into six groupsaccording to their sex and body weight, i. e.,①low iodine(LI);②normal iodine (NI);③fivefold high iodine(5HI);④ten fold high iodine;⑤fifty-fold high iodine(50HI);⑥one hundred foldhigh iodine(100HI). By controlling foodstuff and drinking water (adding different amounts ofpotassium iodide and potassium iodate), all groups got prospective iodine intake respectively,that is, 0.6μg/d, 6.15μg/d, 30.75μg/d, 61.5μg/d, 307.5μg/d and 615μg/d. After 3 months, 6months and 12 months, rats were sacrificed. The following parameters were measured, i. e.,thyroid absolute and relative weight, thyroid hormones in serum, and thyroid morphology, theGPx mRNA and SOD mRNA of thyroid by RT-PCR. We also tested the glutathione peroxidase(GPx) activity, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content ofthyroid, liver, brain and blood by biological chemistry method. At the same time, FRTL cellswere passaged and cultured. Incubations were performed for 6, 12, 24, 48, 72 and 144 hoursrespectively with different dosage of potassium iodide ranging from 10-6mol/L to 10-2mol/L. Weobserved the number and the morphology of cells. Using RT-PCR and Western blot, we observedthe effects of iodine on specific genes expression in FRTL cells, and NIS protein at high iodinestatues. The following parameters also were measured, i. e. the content of H2O2, intracellular freecalcium concentration, the calcium current of cell membrane by electrophysiological method, theanti-oxidative ability of FRTL cells and culture medium.Results1. After long-term administration (3, 6 and 12 months), thyroid hormones contents in serum ofLI group were significantly lower than those of NI group; rats in LI group demonstrated a typicalgoiter of iodine deficiency; the follicles were small and the number increased obviously. Thyroid hormones content in serum of 50HI and 100HI groups showed a decreasing tendency; thefollicles in HI group showed polymorphic changes, and colloid in follicles increased; but thethyroid absolute and relative weight did not change significantly. For the more, cell membranedamage and lipid were observed in these two groups.2. After given low iodine diet for 3, 6 and 12 months, the activity of GPx and SOD in thyroidwere both increased; the activity of GPx in liver and blood declined, but SOD increased; theactivity of GPx in brain was lower than that in NI group; the activity of SOD in brain increasedin 3 months, but decreased in 6 and 12 months. The content of MDA of thyroid, liver and brainin LI group were higher than those of NI group, but no difference was found in blood.3. After administration by different dosage of KI for 3, 6 and 12 moths, the results were:(1) In thyroid: There was no difference in the SOD and GPx activity and MDA content amongNI, 5HI and 10HI groups. The MDA content in 50HI group was lower than that in NI group afteradministration for 12 months, but no difference was found between them after treatment for 6months. Compared with NI group, the GPx activity, SOD activity and MDA content in 100HIgroup increased after intake with high iodide for 6 months, however, decreased afteradministration for 12 months.(2) In liver: The GPx activity and SOD activity of 100HI group was lower than that of NI groupafter administration for 12 months, but no difference between these two groups after treated for 3and 6 months, No difference was found in the GPx activity and SOD activity of NI group andthose of 5HI, 10HI and 50HI groups. There was no difference in MDA content between NI groupand 4 high iodide groups.(3) In blood: The GPx activity in 100HI group was lower than that in NI group afteradministration for 3 months, but no difference between these two groups after treatment for 6and 12 months, no difference was found in the GPx activity of NI group and those of 5HI, 10HIand 50HI groups. There was no difference in SOD activity and MDA content among NI groupand 4 high iodide groups.(4) in brian: There was no difference in the GPx activity, SOD activity and MDA content amongNI group, and 4 high iodine groups.4. After administration by different dosage of KIO3 for 3, 6 and 12 moths, the results were:(1) In thyroid: There was no difference in the SOD and GPx activity among NI, 5HI and 10HIgroups. The GPx activity in 50HI and 100HI groups were lower than that in NI group afteradministration for 12 months, but no difference between these three groups after treatment for 3and 6 months. The SOD activity in 50HI and 100HI groups were lower than that in NI groupafter administration for 6 and 12 months, but no difference was found between them aftertreatment for 3 months. There was no difference in MDA content among NI group and 4 highiodine groups.(2) In liver: The SOD activity of 10HI group was higher than that of NI group after administration for 6 and 12 months, but no difference was found after administration for 3month. The SOD activity of 50HI and 100HI groups were higher than that of NI group afteradministration for 3, 6 and 12 months. There were no difference in GPx activity and MDAcontent between NI group and 4 high iodide groups.(3) In blood: The GPx activity in 100HI group was lower than that in NI group afteradministration for 3 months, but no difference between these two groups after treatment for 6and 12 months. No difference was found in the GPx activity of NI group and those of 5HI, 10HIand 50HI groups. The SOD activity in 50HI and 100HI groups were higher than that in NI groupafter administration for 12 months. There was no difference in MDA content among NI groupand 4 high iodide groups.(4) In brian: There was no difference in the SOD and GPx activity and MDA content among NI,5HI and 10HI groups. The GPx activity and MDA content in 50HI and 100HI groups werehigher than those in NI group after administration for 3 months, but no difference was foundamong them after treatment for 6 and 12 months. There was no difference in the SOD activityamong NI, 50HI and 100HI groups.5. GPx mRNA (12 months) and SOD mRNA (3, 6 and 12 months) of thyroid in HI group wereboth higher than those in NI group. After administration for 12 months, the SOD mRNA of 50HIgroup, the GPx mRNA and SOD mRNA of 100HI group were higher than those of NI group.6. The more dosage of KI was given to FRTL cells, the fewer cells were survived, and the moreH2O2 were detected in these cells. Furthermore, if we extended the incubated period, thesetendencies were more obviously. When FRTL cells had been cultured in iodide with differentconcentration for 24 hours and 48 hours, NIS mRNA, TPO mRNA, and TG mRNA expressionshad no difference between high iodine groups and control group. However, high iodidedecreased the levels of NIS protein in FRTL cells. After given by different dosage of KI, rangingfrom 10-6mol/L to 10-2mol/L, the calcium current and intracellular free calcium concentrationwere increasing; after administration for 48h and 72h, there were no difference in GPx mRNAand SOD mRNA among control, 10-4mol/L KI, 10-3mol/L KI and 10-2mol/L KI groups, however,the SOD activity and MDA content of cells and culture medium were both on inclined with thedosage of KI.Conclusion1. Low iodine intake would damage the anti-oxidative capability of thyroid, liver, blood andbrain in normal rats.2. Treated with high KI(100HI) would induce the decrease of the activity of anti-oxidativeenzymes in thyroid, liver, blood and brain, but no oxidative damage was found in these tissues.3. Treated with high KIO3 (50HI and 100HI) would induce the decrease of the activity ofanti-oxidative enzymes in thyroid, liver, blood and brain, but no oxidative damage was found inthese tissues. 4. There was no significant difference in oxidative damage effect between KIO3 and KI at thesame iodine supplying level, but the anti-oxidative enzyme activity in KIO3 groups was lowerthan that in KI groups.5. High dosage of KI, ranging 10-4mol/L to 10-2mol/L, would have a damage effect on FRTLcells.6. High dosage of KI, ranging 10-5mol/L to 10-2mol/L, would make FRTL cells' H2O2 content,cell membrane calcium current and intracellular free calcium concentration increase, that washigh dosage of KI would induce FRTL cells' oxidative stress effect.7. After incubated by High dosage of KI, ranging 10-4mol/L to 10-2mol/L, FRTL cells and culturemedium's anti-oxidative ability would decreased, furthermore, high iodine had a strong oxidativeinjury effect on cells.8. In a word, low iodine intake would induce oxidative damage on rats, but the anti-oxidativesystem of rats had a certain tolerance to high KI and KIO3 intake; after administration by10-6mol/L KI, there was no obvious effect on FRTL cells, but when given by 10-5mol/L KI wouldinduce oxidative stress, furthermore, when given by 10-4mol/L KI and 10-3mol/L KI wouldinduce oxidative damage on cells, furthermore, after incubate with 10-2mol/L KI would make astrong oxidative injury effect on FRTL cells. |
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