Association Of Prenatal Rare Earth Elements Exposure With Newborn Mitochondrial DNA Copy Number And Development Of Infants Aged 0 To 24 Months

Rare earth elements(REE)refer to a series of elements with similar properties in the periodic table,which are non-essential elements for human body,including yttrium(Y),scandium(Sc)and fifteen lanthanide elements [lanthanum(La),cerium(Ce),ytterbium(Yb),europium(Eu),dysprosium(Dy),gadolinium(Gd),holmium(Ho),thulium(Tm),erbium(Er),neodymium(Nd),praseodymium(Pr),lutecium(Lu),samarium(Sm),promethium(Pm),terbium(Tb)].In recent years,REE have been widely utilized in industry,medicine,agriculture,and high technology,and there was an explosive increase in the demand of REE.The increasing exploitation and application led to emissions of REE into the environment which resulted in the risk of human exposure.REE-associated health impacts have attracted public concern in recent years,but most of studies on the influence of REE exposure focused on general population.There are limited studies on the influence of prenatal REE exposure on the health of newborn and infant so far.Therefore,we used data from a birth cohort in Wuhan,to analyze the urinary REE levels of pregnant women during three trimesters and the influencing factors of urinary REE levels,and to explore the associations of maternal REE exposure during three trimesters with newborn mitochondrial DNA copy number and to identify a potential critical window for sensitivity of newborn mitochondrial DNA copy number to REE exposure,and to explore the associations of maternal REE exposure during three trimesters with the growth and development of infants aged 0 to 24 months and the probable influence of newborn mitochondrial DNA copy number on this association.Part I.Exposure levels and the influencing factors of urinary rare earth elements during pregnancyObjective: Most of studies on the exposure levels of REE focused on occupational population or population from REE mining area.There are few studies on the body load of REE in general population and special population.The aim of the study was to determine the urinary REE levels of pregnant women during first,second,and third trimester and evaluate the reproducibility of urinary REE concentrations across three trimesters,and to explore the influencing factors of urinary REE levels.Methods: The participants of the study were recruited from a prospective birth cohort study in Wuhan Children's Hospital(Wuhan Maternal and Child Healthcare Hospital).A total of 597 mother-newborn pairs were included in the present study.Information on demographic characteristics,lifestyle habits and clinical delivery were obtained from structured questionnaires and medical records.We collected urine samples of pregnant women during three trimesters(first trimester,second trimester,and third trimester).Inductively coupled plasma mass spectrometry(ICP-MS)was used to measure urinary REE concentrations(Ce,Yb,La,Pr,Nd,Eu,Gd,Dy,Ho,Er,Tm,Sm,and Lu).The creatinine-corrected urinary REE levels were assessed by median(25th–75th).The differences of urinary REE levels in three trimesters were assessed by Kruskal-Wallis test.The intraclass correlation coefficient(ICC)was used to evaluate the reproducibility of urinary REE concentrations across three trimesters.The ICC values of < 0.40,0.40–0.75,and > 0.75 were defined as weak,moderate,and strong reproducibility,respectively.The influencing factors of urinary REE levels were evaluated using multivariate linear regression models.Results: The detection rate of REE in urine samples collected during three trimesters was above 80%(except for Sm and Lu).The median of creatinine-corrected urinary REE concentrations in the first,second,and third trimesters were from 0.008 ?g/g crea to 0.072 ?g/g crea,0.012 ?g/g crea to 0.122 ?g/g crea,and 0.016 ?g/g crea to 0.135 ?g/g crea,respectively.There was significant difference between the urinary REE levels during three trimesters(P < 0.05).The ICCs for creatinine-corrected urinary REE concentrations across three trimesters were from 0.12 to 0.31.Passive smoking was positively associated with urinary REE(Yb,Eu,Gd,Ho,and Tm)levels during the first trimester [?(95% CI): Yb,0.11(0.01,0.21);Eu,0.13(0.02,0.23);Gd,0.10(0.00,0.20);Ho,0.14(0.01,0.27);Tm,0.16(0.02,0.30)].Conclusions: All 13 REE were detected during pregnancy.The detection rate of REE in urine samples collected during three trimesters was above 80%,except for Sm and Lu.The reproducibility of urinary REE levels was weak during three trimesters.There was significant difference between the urinary REE levels during three trimesters and the urinary REE levels in the third trimester were highest.The levels of urinary REE were influenced by several factors,such as passive smoking during pregnancy.Part II.Association of prenatal rare earth elements exposure with newborn mitochondrial DNA copy numberObjective: Prior studies have suggested environmental pollutants exposure during pregnancy might influence newborn mitochondrial DNA copy number.However,there was no studies on the influence of prenatal REE exposure on newborn mitochondrial DNA copy number so far.The aim of the study was to explore the associations of prenatal REE exposure during three trimesters with newborn mitochondrial DNA copy number.Methods: A total of 587 mother-newborn pairs were included in the present study after excluding participants with no DNA for cord blood or ineligible DNA quality(n = 10)based on the study population in the Part I.We collected urine samples of pregnant women and cord blood samples of newborns.The measurement of urinary REE concentrations are the same as the Part I.The quantitative real-time polymerase chain reaction(q PCR)method was adopted to measure the relative cord blood mitochondrial DNA copy number.Multiple informant models were employed to evaluate the associations between urinary REE concentrations of all three trimesters and newborn mitochondrial DNA copy number.Weighted quantile sum(WQS)regression models were used to estimate the association of REE co-exposure with newborn mitochondrial DNA copy number.Results: After adjusting potential confounders,one unit increase(?g/g creatinine)in log-transformed urinary REE(Gd,Dy,Er,and Pr)levels during the third trimester were respectively related to 17.29%(95% CI: 1.32%,35.79%),17.75%(95% CI: 2.58%,35.17%),16.75%(95% CI: 2.20%,33.36%)and 16.84%(95% CI: 1.70%,34.24%)increase in newborn mitochondrial DNA copy number,the associations of other urinary REE(Ce,Yb,La,Eu,Ho,Nd,and Tm)levels during the third trimester with newborn mitochondrial DNA copy number were not statistically significant.Compared with the lowest quartile,urinary REE(Eu,Gd,Dy,Er,and Pr)levels in the highest quartile were respectively related to 30.62%(95% CI: 3.96%,64.4%),26.47%(95% CI: 1.48%,57.70%),28.82%(95% CI: 3.40%,60.66%),34.28%(95% CI: 7.16%,68.08%)and 33.66%(95% CI: 7.30%,66.83%)increase in newborn mitochondrial DNA copy number during the third trimester.In the stratified analysis,the positive associations between prenatal REE exposure during the third trimester and newborn mitochondrial DNA copy number were more evident among male infants.Furthermore,the co-exposure of urinary REE was significantly associated with increased newborn mitochondrial DNA copy number during the third trimester.Conclusions: Prenatal REE exposure during the third trimester was associated with the increased newborn mitochondrial DNA copy number,and the third trimester might be a potential critical window for sensitivity of newborn mitochondrial DNA copy number to REE exposure.Our results suggest that REE exposure during pregnancy may have adverse effect on newborn mitochondrial function.Part III.Association of prenatal rare earth elements exposure with the growth and development of infants aged 0 to 24 months and the potential effect of newborn mitochondrial DNA copy numberObjective: The fetus period is a critical stage of growth and development in early life.Adverse intrauterine environment may have an important impact on health after birth and until adulthood.The aim of the study was to investigate the associations of maternal urinary REE levels in three trimesters with the growth and development of infants aged 0 to 24 months,and to investigate the probable influence of newborn mitochondrial DNA copy number on this association.Methods: The population recruitment and the measurement of urinary REE concentrations are the same as the part II.We collected growth data of infants at birth,6,12,18,and 24 months.According to the WHO standards,the physical development of children was evaluated using Z-Score,and we respectively calculated weight-for-age Z-score(WAZ),length/height-for-age Z-score(HAZ),and BMI-for-age Z-score(BMIZ).Linear mixed models were used to analyze the associations of urinary REE levels in three trimesters with the growth of infants aged 0 to 24 months.Latent category growth models were used to establish the growth trajectory,and multivariate logistic regression models were used to evaluate the associations between urinary REE levels in three trimesters and different growth trajectories of infants.The mediation analysis was used to analyze the potential role of newborn mitochondrial DNA copy number in the association between prenatal REE exposure and the growth of infants.Results: After adjustment for potential confounders,with one unit increase(?g/g creatinine)in log-transformed urinary REE(Ce,Yb,Gd,Dy,Ho,Er,and Nd)levels during the first trimester,the BMIZ in male infants respectively decreased 0.15(95% CI:-0.27,-0.03),0.14(95% CI:-0.27,-0.02),0.16(95% CI:-0.29,-0.04),0.14(95% CI:-0.26,-0.02),0.11(95% CI:-0.20,-0.01),0.13(95% CI:-0.24,-0.01)and 0.15(95% CI:-0.28,-0.02).There was three different growth trajectories for the WAZ,HAZ,and BMIZ of infants(slow growth,moderate growth,and rapid growth).The log-transformed urinary REE(Ce,La,and Eu)levels during the second trimester were associated with the increased risk of slow growth trajectory of BMIZ,and the ORs(95% CIs)were 1.75(95% CI: 1.12,2.72),1.82(95% CI: 1.17,2.84)and 1.60(95% CI: 1.03,2.49).The log-transformed urinary REE(Gd and Nd)levels during the third trimester were related to the increased risk of slow growth trajectory of WAZ,and the ORs(95% CIs)were 1.72(95% CI: 1.05,2.80)and 1.64(95% CI: 1.00,2.69).The mediation analysis found that newborn mitochondrial DNA copy number was not a mediating variable for the association between prenatal REE exposure and the growth of infants.In the stratified analysis by newborn mitochondrial DNA copy number,the negative associations of urinary REE levels during the first trimester with WAZ and BMIZ were more evident among the high mitochondrial DNA copy number group.Conclusions: Prenatal REE exposure had adverse effect on the growth and development of infants aged 0 to 24 months,and the effect may be related to newborn mitochondrial DNA copy number although the newborn mitochondrial DNA copy number was not a mediating variable.The specific mechanism needs to be further explored.