Effects Of Prenatal Exposure To Ambient Fine Particulate Matter On Birth Outcomes And Infants’ Neurodevelopment And Related Mechanism

Section one.The effects of prenatal exposure to ambient fine particulate matter on birth outcomesBackground and Objectives:Prenatal exposure to ambient levels of air pollution has been reported to adversely affect birth outcomes,yet few studies have investigated refined susceptible windows for adverse birth outcomes.The study aimed at estimating associations between maternal exposure to ambient fine particulate matter(PM2.5)and birth outcomes,including birth weight,low birth weight(LBW)and preterm birth(PTB),and identify specific susceptible windows.Methods:A total of 3,692 singleton live births were enrolled between 2013 and 2016 in Shanghai Birth Cohort,China.Based on mothers’ residential addresses,weekly mean concentrations of PM2.5 over gestation were estimated based on an incorporated evaluating approach combining satellite-based estimates and ground-level measurements.Pregnancy was clinically classified as whole pregnancy and three trimesters(the first,second,and third trimester).Then associations between trimester-average exposure levels and birth outcomes were evaluated.Meanwhile,distributed lag non-liner models(DLNMs)were fitted flexibly by incorporating with multiple liner models and Cox proportional hazard models to evaluate weekly-exposure-lag-response associations between average PM2.5 level and birth weight,LBW and PTB,and to identify refined critical windows.Results:In this study,trimester-specific associations were found for all birth outcomes during the third trimester.DLNM results suggested that gestational exposure to PM2.5 was in association with adverse birth outcomes in infants,and critical windows were identified as 31st-34th gestational weeks for reduced birth weight,38th-42nd weeks for LBW and 27th-30th weeks for PTB,respectively.Sex-specific associations were observed in stratified analyses,only among girls.Conclusions:Ambient PM2.5 exposure exhibited adverse impacts on multiple outcomes including reduced birth weight,LBW and PTB in the late pregnancy.And sex-specific effects were noticed.The study provides further evidence supporting harmful effects of maternal PM2.5 exposure on birth outcomes and identifying refined critical windows.Section two.The effects of prenatal fine particulate matter exposure on infants’ neurodevelopmentBackground:Fine particulate matter(PM2.5)is a newly suspected neurotoxicant,but there is limited human evidence focusing on prenatal PM2.5 exposure and child neurodevelopment,not to mention exploring critical windows and sex differences.Methods:A total of 3,692 mother-infant pairs were recruited in a prospective birth cohort(Shanghai Birth Cohort)in China between 2013 and 2016.2,599 participants were included in the analysis with a follow-up for infants at 12 month to test neurodevelopment based on the Ages&Stages Questionnaires(ASQ:communication,fine and gross motor,problem solving,personal-social domain).Individual prenatal exposure to PM2.5 was measured through a high-resolution satellite-cooperated approach based on self-reported residence.Associations between trimester-average exposure levels and neurodevelopment outcomes were evaluated.Meanwhile,distributed lag non-liner model(DLNM)was incorporated with multiple liner regression model,to estimate the potentially delayed and non-liner effects of weekly PM2.5 exposure on neurodevelopment,and identify sensitive windows.Effect modification by sex as well as breastfeeding was evaluated.Results:Among 2,599 infants,infants’ neurodevelopment at 12 month was negatively associated with weekly prenatal exposure during early(1st-9th weeks for problem solving domain)and late pregnancy(34th-42nd weeks for communication,36th-42nd weeks for gross and fine motor domain,28-37 weeks for problem solving domain and 32nd-39th weeks for person-social domain).Consistent effects was found for trimester-average exposure.Sex-differences were observed in stratified analyses,especially among boys.Conclusions:This study provide some of the first evidence that prenatal PM2.5 exposures are associated with poorer neurodevelopment in Chinese infants,and effects differed by sex.Given that critical windows and sex-specific associations were rarely explored before,more studies are needed to confirm our findings.Section three.Fine particulate matter exposure induced zebrafish embryonic toxicity and larval’s neurotoxicity and related mechanismObjectives:This study was aimed to evaluate the embryonic toxicity and neurotoxicity of PM2.5 in a zebrafish(Danio rerio)model,and explore underlying mechanism.Methods:Healthy zebrafish embryos were chosen at 4 h post fertilization(hpf)and exposed to PM2.5(25,50,100 μg/mL)for 4-120 hpf.Embryonic toxicity indicators were observed,including survival,malformation and hatching rate,autonomic movement at 24 hpf and heart rate at 48 hpf during embryonic periods,respectively.Neurotoxicity assessment were detected through spontaneous movement and locomotor ability under light-dark stimulus of larval zebrafish at 120 hpf.Thyroid hormones and expression levels of hypothalamus-pituitary-thyroid(HPT)axis related genes were examined after neurotoxicity assessment.Results:Exposure to PM2.5 affected embryonic development.The autonomic movement at 24 hpf of zebrafish embryos that exposed to 50,100 μg/mL PM2.5 decreased compared with the control group(P<0.05).The heart rate of all exposure groups decreased at 48 hpf(P<0.05).We found no effects of exposure on the survival,malformation and hatching rate of zebrafish.The locomotor behavior results showed that,the total distance and average speed of larval zebrafish at 120 hpf decreased for all treated groups(P<0.01).During 3 light-dark stimulus periods,the reduced locomotion of larval exposed to 50 μg/mL PM2.5 were found under 3rd dark stimulation(P<0.05),larval exposed to 100 μg/mL showed decreased total distance of movement under the 1st and 3rd dark period,and all treated groups exhibited reduced locomotion under 3 light stimulation periods(P<0.05).Thyroid hormones of larval at 120 hpf were detected.25,50 μg/mL groups showed decreased T3 and T4,while exposure at 100 μg/mL showed increased T3 and T4.FT3 of larval exposure decreased at exposure concentration of 50 μg/mL and increased at concentration of 100 μg/mL.FT4 of zebrafish that exposed to 50,100 μg/mL were PM2.5 significantly reduced,and increased in 25 μg/mL group(P<0.01).Compared with the control group,the expression level of tg decreased significantly of larval that exposed to 25μg/mL PM2.5.Exposure to 50 μg/mL increased the expression level of tpo(P<0.05)The decreased expression ofpax8 were found for all treated groups(P<0.01)。Conclusion:The study demonstrated PM2.5-induced embryonic toxicity and neurotoxocity in zebrafish model,and PM2.5 exposure disturbed thyroid hormones levels as well as expression of HPT axis-related genes,indicating that the thyroid disturbing pathway could be the potential toxicity mechanism.