Effects Of Iodine Excess On Islet Beta Cells And The Mechanism

Objective: To explore the new risk factors of diabetes and the influence of excessive iodine on glucose metabolism,this study evaluated the effects of excessive iodine exposure on islet ?-cell and explored its mechanism from the perspective of endoplasmic reticulum stress pathway.Methods: Animal Experiment Female BALB/c mice were fed at the temperature ranging 22? to 28?,and 12 hours in a light and dark cycle environment.Mice were randomly divided into a control group and four excessive iodine(EI)groups,10 mice in each group.The control group was fed with tap water(5 ?g/L iodine),EI groups with different iodine(Potassium iodate)concentrations of 300 ?g/L,600 ?g/L,1200 ?g/L and 2400 ?g/L in drinking water.After mice had been fed for 6 months,urinary samples were collected and urinary iodine concentration was detected,glucose tolerance test was performed.After the sacrifice,the pancreas of each mouse was separated and the blood was collected.The pathological changes of the pancreas were observed by microscope and the fasting blood glucose level and insulin level were measured.The HOMR-IR index was calculated to evaluate the degree of insulin resistance.Cell Experiment Beta-TC-6 cells were cultured in Dulbecco's minimal essential medium(DMEM)containing with or without excessive iodine(Sodium iodide)in vitro under the condition of 37?,5%CO2,saturation humidity.When cells lied in logarithm growth,they were divided into control group and EI groups.The concentrations of iodine in the medium were 0.01 mmol/L,0.1 mmol/L,1 mmol/L,10 mmol/L and 100 mmol/L,respectively.After 24 hours of exposure to excessive iodine,the MTT assay was used to measure the cells viabilities.GSIS: Beta-TC-6 cells were exposed to excessive iodine(0.01 mmol/L,1 mmol/L and 100 mmol/L)for 24 hours,then were stimulated with Krebs–Ringer bicarbonate buffer containing 5.6 mmol/L glucose or without glucose for 1 hour at 37? in incubator,then the supernatant was collected for insulin concentration determination by using ELISA kit.Western blot was used to detect the expression of endoplasmic reticulum stress signaling proteins and Bcl-2 family proteins.Results:1.Excessive iodine in drinking water for six months caused mice persistent excessive iodine status.The median of urinary iodine concentration in each EI group was followed by 658.84 ?g/L,994.90 ?g/L,2132.85 ?g/L and 3249.00 ?g/L,respectively,indicating that all the EI group mice were under the excessive iodine intake status.2.Excessive iodine in drinking water for six months caused mice pancreas pathological morphological changes.Compared with the control group,the islet of mice in 1200 ?g/L and 2400 ?g/L EI group were more irregular,islet cells volume reduced.The islets were infiltrated with inflammatory cells,and even obvious bleeding and necrosis were observed in 2400 ?g/L EI group.3.Excessive iodine for six months impaired mice glucose tolerance.At the time of 15 min after glucose loading,the blood glucose level in control group and EI groups showed a rising trend,but there was no significant difference of the blood glucose level between the control group and the EI groups(P>0.05).After 15 min of glucose load,the blood glucose level in the control group and EI groups showed a downward trend,the descending speed in EI groups was slower than that in control group,and the blood glucose level was higher in EI group than that of control group at the same time points,especially at the time of 60 min,90 min and 120 min,the blood glucose level in 600 ?g/L,1200 ?g/L and 2400 ?g/L EI group was significantly higher than those in the control group(P<0.01).4.Excessive iodine in drinking water for six months caused the elevation of fasting blood glucose and insulin level in mice.Compared with the control group,the fasting blood glucose level in 600 ?g/L,1200 ?g/L and 2400 ?g/L EI group was significantly higher(P <0.05),and the serum insulin level was significantly higher than that in the control group(P <0.01),HOMA-IR index increased significantly(P <0.01).5.Effect of excessive iodine on beta-TC-6 cells viabilitiesIn 0.01 mmol/L and 0.1 mmol/L EI group,beta-TC-6 cells viabilities slightly increased,but there was no significant difference when compared with the control group.The rate of cells viabilities decreased gradually from 1 mmol/L to 100 mmol/L EI group by a dose-dependent manner and was significantly lower than the control group(P<0.05).6.Effect of excessive iodine on insulin secretion of beta-TC-6 cellsCompared with the control group,the basal insulin secretion of beta-TC-6 cells in 0.1 mmol/L EI group was not significantly changed(P>0.05),but the basal insulin secretion of 1 mmol/L EI group was significantly increased(P<0.05).The basal insulin secretion of 100 mmol/L EI group was significantly decreased(P<0.01).In GSIS experiment,compared with the control group(5.6 mmol/L glucose + 0 mmol/L EI group),the insulin secretion of glucose-stimulated in 0.01 mmol/L EI group was significantly increased(P<0.05),but it decreased(P<0.05)in 1 mmol/L and 100 mmol/L EI group were significantly.7.Effect of iodine excess on endoplasmic reticulum stress proteins expression.Compared with the control group,from 1 mmol/L to 10 mmol/L EI group,the expression of GRP78 and IRE1? were increased significantly when compared with control group(P<0.05),the expression of GRP78,IRE1? and Bcl-2 in 0.01 mmol/L and 0.1 mmol/L EI group had no significant difference.The expression of Bcl-2 decreased while the expression of Bax increased significantly when compared with control group(P<0.05).Excessive iodine stimulation did not affect the protein expression of P-PERK,ATF6?,P-EIF2? and EIF2?.8.Effect of iodine excess on apoptosis-related proteins expressionThe protein expression of Bcl-2 in 1 mmol/L and 10 mmol/L EI group was significantly lower than the control group(P<0.05),while the expression of Bax protein was significantly higher than that of the control group(P<0.01),and the ratio of Bcl-2/Bax was significantly lower than that of the control group(P<0.05).Conclusion:1.Long-term excessive iodine exposure can cause mice islet ? cells inflammatory cell infiltration,vacuolization,and even necrosis and other pathological damage;2.Long-term excessive iodine exposure can cause mice higher fasting blood glucose level,insulin level and HOMR-IR index,leading to insulin resistance;3.Excessive iodine exposure can reduce the survival rate of islet ? cells,damage the insulin secretion function;4.The damage of islet ? cells function by excessive iodine may be mediated by the endoplasmic reticulum stress,activation of IRE1?-mediated unfolded protein signaling pathway,mediated by Bcl-2 protein family-induced apoptosis.