Mechanism Of Iodine Nutrition During Pregnancy On Brain Development Of Offspring

Objective:Iodine is an essential element that is required to produce thyroid hormone(TH).According to the guidelines of the WHO/United Nations Children's Fund(UNICEF)for adults(>12 years),the suggested iodine intake is 150 ?g/ day;however,this increases to 250 ?g/day during pregnancy.Iodine supplementation information in pregnant women is collected in most European countries;of these European countries,two-thirds have reported low iodine intake during pregnancy.It is common knowledge that the America has been an iodine-sufficient country.However,recently,mild iodine deficiency(ID)has been more prevalent among pregnant women.Although China is an iodine-adequate country,almost 50 percent of pregnant women are iodine deficient.Randomized trials involving pregnant women from areas with severe ID have verified the effect of severe maternal ID on children's cognitive growth.Recently,an observational study performed in the UK(n=1040)found that children born to mothers with mild-to-moderate ID were at risk of damage to their reading skillsand non-verbal IQ.Similarly,Hynes et al evaluated 228 Australian mother–child pairs and showed an association between maternal mild ID(UIC<150 ?g/L)and standardized academic test scores,such as spelling errors,in children.However,in iodine-sufficient countries,for example,the Netherlands,mild maternal ID did not influence offspring's cognitive development.Several reports have shown a powerful relationship between impaired neuro-intellectual consequences in children and either maternal SCH,IH or TPOAbs.However,other trials have failed to verify these associations[1].A randomized control trial evaluated the effects of LT4 treatment during pregnancy in women with mild thyroid dysfunction(SCH and IH)on children's cognitive development.Controlled Antenatal Thyroid Screening Study(CATS)study suggested the inefficiency of maternal LT4 treatment on children's cognitive development in the areas which were ID.Taken together,the evidence suggests that gestational iodine status and LT4 treatment in women with mild thyroid dysfunction(such as SCH,IH,positive TPOAbs)may be critical for determining cognitive development in children.To evaluate this hypothesis,we conducted a prospective pilot study to observe the influence of iodine levels on LT4 efficiency for the cognitive development of offspring of mothers with mild thyroid dysfunction during early pregnancy.Methods:This pilot,prospective,observational study divided into two groups,each comprising 60 mother-child pairs,according to maternal iodine status(urinary iodine concentration(UIC)<150 ?g/L and UIC?150 ?g/L).The two groups were then labeled as followings: Control,hypothyroxinemia(IH)+LT4,subclinical hypothyroidism(SCH)+LT4,positive thyroid peroxidase antibodies(TPOAbs)+LT4.Finally,the study included eight groups,each comprising 15 mother–child pairs.Child neurodevelopment was assessed at age 12 to 30 months by the Bayley Scales of Infant Development-II.Age-adjusted scores from the Mental Development Index(MDI)and Psychomotor Development Index(PDI)were used as the primary outcomes.Results:The results refer to eight groups including 120 mother–child pairs(15 pairs in each group).No differences in demographic parameters that might influence the children's development outcomes were observed among the eight study groups(Table 1).Before LT4 treatment,f T4 levels in the IH group were lower,and TSH levels in the SCH group were higher than those in the control group.The TSH and f T4 values were not significantly different in the positive-TPOAb group compared to the control group.The changes in maternal thyroid function parameters during pregnancy are shown in Table 2.We found that after LT4 treatment,TSH and f T4 returned to normal levels during the subsequent trimesters of pregnancy.Furthermore,for the TPOAb+LT4 group,LT4 therapy did not efficiently improve TPOAbs during subsequent trimesters of pregnancy.Table 3 shows the M±SD,median,and range of the MDI and PDI in each group.We found that children from the iodine deficiency group(UIC<150 ?g/L)displayed lower MDI scores than children from the iodine-sufficient group(UIC?150 ?g/L)(P=0.000).There was no significant difference between the two groups in the PDI scores(P=0.405).Under similar thyroid function conditions,we also investigated the influence of iodine on the cognition of the offspring.We found that iodine status during pregnancy can affect children's MDI scores.The MDI scores of children were lower in the iodine deficiency group than in the iodine-sufficient group,regardless of whether maternal thyroid function was normal or not during the first trimester.However,we failed to find any differences in the PDI scores between these groups(P>0.05).The results are shown in Figure 1.Interestingly,we found that under different maternal iodine statuses among mothers with SCH and IH,there was a significant difference in the effect of LT4 on the children's MDI scores.Under ID status,LT4 treatment for SCH or IH patients did not improve their children's MDI scores compared to offspring born to euthyroid women(P=0.000 and P=0.037).However,under conditions of normal iodine status,LT4 treatment for SCH or IH patients could improve their children's MDI scores compared to offspring born to euthyroid women(P=0.233,P=0.305).Furthermore,we failed to find any differences in the PDI scores among these groups.There was a significant difference in the MDI scores between the control group and the TPOAb+LT4 group under conditions of ID(P=0.008;P=0.000).Additionally,we found that maternal TPOAbs could affect the PDI scores of their offspring under conditions of maternal ID.Under conditions of ID,LT4 treatment could not improve the PDI scores of offspring in maternal euthyroid TPOAb-positive patients compared to euthyroid TPOAb-negative women(P=0.019).However,under conditions of a non-deficient iodine status,no significant difference was found in the PDI scores between the two groups(P=0.187).All these results suggest that maternal ID might affect the efficacy of LT4 treatment for improving the MDI scores of offspring born to SCH and IH women.Only if the maternal iodine status was restored to normal(UIC?150 ?g/L)were the beneficial effects of LT4 treatment(<12 weeks)on the MDI scores of the offspring MDI apparent.TPOAb,which is independent of iodine status,might be another important factor affecting the MDI scores of offspring.Linear regression models were used to assess the probable dependency of cognitive development on explanatory variables and confounders(Table 4).These analyses demonstrated a significant positive relationship of maternal UIC with the MDI(B = 0.0325 [CI 0.0097-0.0553];P= 0.006).Moreover,a statistically negative association of maternal TPOAb with the MDI was found(B =-0.030[CI-0.052-0.008];P=0.008).Interestingly,there was also a negative correlation between TPOAb positivity and the PDI(B =-0.037[CI-0.061-0.014];P=0.002).Other factors were not potential confounders in the linear regression analysis.Objective: Iodine is an essential element that is required for thegrowth of most organs,particularly the brain.As most countries have implemented a universal salt iodization(USI)guideline,the public health focus has shifted to a mild or moderate iodine deficiency(ID),which is still prevalent in many areas.Meanwhile,some cities in China because of drinking high iodine water,people are in adequate or excess iodine status.There has been a controversy about the relationship between maternal abnormal iodine status and fetal mental development.Little is known about the mechanism.Our aim was to inspect the effects of abnormal iodine levels on the mental function of pups and investigate the role of Wnt/?-catenin signalling,which is crucial for the development of the hippocampus.Method:By feeding dam rats with a diet deficient in iodine and providing deionized water supplemented with potassium iodide,three developmental rat models were created: a marginal ID group,a normal iodine status group(N group),and a group that received 6 times the normal iodine intake(6HI group).An inductively coupled plasma mass spectrometry(ICP-MS)and enzyme-linked immunosorbent assay(ELISA),respectively,were used to examine urinary iodine levels and TSH,f T4,TT4 to identify the success of the animal model.Morris water maze wasused to analyse the mental function of the pups on postnatal day 21(P21),P40.Meanwhile,we also employed brain slices for LTP measurements to analyse thesynaptic plasticity in hippocampal CA1 of pups on P10,P21,P40.Western blotting,real-time quantitative RT-PCR,and immunofluorescence were utilized to measure the expression/protein levels of Wnt/ ?-catenin pathway genes and PSD-95 gene in hippocampus of pups on P10,P21,P40.Results:Before pregnancy,there were no differences in urine iodine concentrations(UIC)and thyroid function of dams among three groups(P>0.05).UIC and TT4 values were correlated with iodine intake on E17(P<0.05).The outcomes of LTP measurements in pups were influenced by maternal marginal ID and 6HI compared to the pups from N group at P10 points.The results of morris water maze and LTP measurements in pups were affected by maternal marginal ID and 6HI compared to the pups from N group at P21 points(P<0.05).However,at P40 points,the consequences of morris water maze and LTP measurements were not significant differences among three groups(P>0.05).Consistent with the functional experiments,pups from marginal ID and 6HI suppressed the the expression/protein levels of Wnt/ ?-catenin pathway genesand PSD-95 gene in the hippocampus compared to the pups from N group at P10,and P21 points(P<0.05).Meanwhile,on P40,we failed to observe significant difference in the expression/protein levels of Wnt/ ?-catenin pathway genes and PSD-95 gene among these groups(P30.05).Immunofluorescence staining was utilized to co-localize ?-catenin and PSD-95 in the hippocampal CA1 region.Pups from the marginal ID and 6HI groups also displayed reduced numbers of immune-positive cells as well as decreased labelling brightness for the similar patterns of ?-catenin and PSD-95 staining in the hippocampus compared to the N group on P10,and P21.However,the difference was disappeared in pups among these groups at P40 points.Conclusion:Maternal abnormal iodine levels induced impairments in the cognitive development of pups that may be due to the suppression of the Wnt/?-catenin signalling pathway.However,this effect might be limited,and appeared to be self-healing when the pups grew to adulthood.Objective: It is well known that severe iodine deficiency(ID)during pregnancy causes dysfunction of the cerebellum.Little is known about the effect of maternal marginal ID or high iodine diet during pregnancy on the motor function of pups.Our aim was to study the effects of abnormal maternal iodine status on the motor function of pups and investigate the role of Wnt/ ?-catenin signalling pathway,which is crucial for the development of cerebellum.Methods: By feeding dam rats with a diet deficient in iodine and providing deionized water supplemented with potassium iodide,three developmental rat models were created: a marginal ID group,a normal iodine status group(N group),and a group that received 6 times the normal iodine intake(6HI group).TSH,f T4,TT4 were detected by enzyme-linked immunosorbent assay(ELISA)and iodine status were examined by inductively coupled plasma mass spectrometry(ICP-MS)to identify the success of the animal model.Mid-air body righting,beam balance test,and rotarod test were used to analyse the motor function of the pups.Western blotting,real-time quantitative RT-PCR,and immunofluorescence were utilized to measure the expression of Wnt/ ?-catenin signalling in cerebellum of pups on postnatal day 0(P0),P10,P21.Results: Before pregnancy,no differences were found in urine iodine concentrations(UIC)and thyroid function of dams among three groups(P>0.05).UIC and TT4 were correlated with iodine intake on E17(P<0.05).Three functional experiments suggested motor function of pups was affected by maternal marginal ID and 6HI compared to the pups from N group(P<0.05),which due to significantly alter expression/protein levels of Wnt/ ?-catenin pathway genes in the cerebellum on P0,P10,P21.Pups from marginal ID and 6HI decreased the positive regulatory genes(Wnt 1,?-catenin,Dvl),nuclear transcription factor(TCF)and increased the negative regulatory gene(DKK)in the cerebellum compared to the pups from N group on P0,P10,and P21,respectively(P<0.05).Western blot revealed that maternal marginal ID and 6HI significantly reduced the levels of Wnt/?-catenin pathway proteins(Wnt 1,TCF,and Dvl)and increased the levels of an agonist of Wnt/ ?-catenin pathway(DKK)in the cerebellum compared to the N group on P0,P10,and P21(P<0.05).Interestingly,we found that maternal marginal ID and 6HI significantly reduced the ratio of P-GSK-3?/GSK-3?,thus the ratio of P-?-catenin/?-catenin significantly enhanced in the cerebellum compared to the N group on P0,P10,and P21(P<0.05).The pups from mild ID and 6HI groups also displayed reduced numbers of immunopositive cells as well as decreased labelling brightness for ?-catenin in the cerebellum compared to the pups from normal group on P0,P10,and P21,respectively.Conclusions: Our study was the first research using rats model to verify the cerebellar function impairment of pups affected by marginal ID and high iodine diet during pregnancy,which may be ascribed to the down-regulation of Wnt/ ?-cateninsignalling.