| BackgroundOrganochlorine pesticide dichlorodiphenyltrichloroethane was widely used as an insecticide in agricultural production,and its chemical stability and undecomposed characteristics caused serious environmental pollution.DDTs were banned worldwide in the 1970s and 1980s,but many African and Latin American countries still use DDTs to control malaria epidemics.Although our country stopped producing DDTs and other pesticides in 1983,there were also some DDTs reserves to prevent malaria.In China,DDTs have been used as antifouling paint for ship hull,which has become the main source of DDTs in China.Xiamen is located in China's southeastern coast,with the rapid development of economy,Xiamen' surrounding seas were affected by Jiulong river estuary and Minnan terrigenous pollution,residents' health was threatened by the terrestrial pollution.Coastal residents were detected high concentrations of organochlorine pesticides in their body in recent years because they have special dietary structure characteristics,especially like seafood which has biological amplification of the organochlorine pesticide.After exposure to organochlorine pesticides,the risk of leukemia,breast cancer,central nervous system(CNS)tumor and Wilm's tumor of man increased.Compared to the adults,the fetus is more sensitive to environmental pollution,because the body development of detoxification mechanisms such as immature and enzyme system is not perfect.DDTs can be transferred from the mother to the fetus,thus the fetus suffered to the risk of exposure to organochlorine pesticides in the womb.This early exposure may make epigenetic change in fetal genes through DNA methylation,it would have a major impact in the disease risk of children after the birth of life(such as a variety of cancer).In order to confirm the causal relationship,our team had studied how prenatal organochlorine pesticide DDTs exposure influence on the fetus genome-wide methylation in the early stage.We found prenatal organochlorine pesticide DDTs exposure indeed caused the gene methylation differences.Now we choose two methylation differences sites of the breast cancer susceptibility gene 1 for further verification.We want to know whether prenatal organochlorine pesticide DDTs exposure have influence on breast cancer susceptibility gene 1(BRCA1)of the fetus.Thus we could to more powerful speculate the relationship between prenatal exposure to DDTs and disease in later life of the fetus,understand the first cause of the disease,promote the understanding of offspring disease risk and causes.ObjectivesTo understand the level of organochlorine pesticide DDTs exposure in the pregnant women and the fetus in Xiamen,as well as the influence factors of DDTs in fetal umbilical cord serum.Analysis the situation of BRCA1 gene methylation level and gene expression level in different DDTs exposure groups and the association of prenatal organochlorine pesticide DDTs exposure and fetal BRCA1 gene methylation and expression level.Thus we would provide new clues for mechanism research where organochlorine pesticides increased the risk of breast cancer.Methods1.On the basis of previous studies,126 fetuses were selected as the verification sample to analyze the exposure level and possible influencing factors of 6 DDTs homologs in the umbilical cord serum.2.Select two gene methylation differences site on the BRCA1 as the verification site.Pyrosequencing technology and TaqMan reverse transcription quantitative real-time polymerase chain reaction(RT-qPCR)were used to test the DNA methylation and gene expression level of the identified CpGs in BRCA1,respectively.Correlation and logistic regression were used to analyze the association between organochlorine pesticide-DDTs exposure and DNA methylation and gene expression level in the identified CpGs of BRCA1.Results1.The detection rates of 6 kinds of DDTs homologue p,p'-the DDT,o,p'-the DDT,p,p'-the DDD,o,p'-the DDD,p,p'-DDE,o,p'-DDE in fetal umbilical cord serum were 64.3%,10.3%,50.0%,34.9%,86.5%,47.6%,respectively.p,p'-DDE has the highest detection rate,and the median concentration of p,p'-DDE was 0.30 p,g/ml.2.The influence factors of fetal umbilical cord DDTs exposure levels in serum were analyzed,and the results showed that having seafood occasionally,having seafood often compared with the frequency of seafood consumption barely,pregnant women,whose peripheral blood have higher DDTs concentration.The values of OR(95%CI)were 2.26(1.03?4.92),10.37(2.67?40.32),respectively.3.The average levels of methylation in site 1 and site 2 were 0.35 and 0.36,respectively.The average level of BRCA1 gene expression was 1.19.The levels of methylation in site 1 and site 2 presented a positive correlation(r=0.66,P<0.001),a negative correlation with the levels of BRCA1 gene expression was found,and the correlation coefficients were r=-0.44(<P<0.05)r=-0.3 8(P<0.05),respectively.4.In subsequent validation studies,we found that the level of DNA methylation of cg25067160 increased with increased exposure to o,p'-DDT(OR(95%CI):2.867(1.360?6.041)),the level of DNA methylation of cg25067162 increased with increased exposure to p,p'-DDE(OR(95%CI):3.025(1.464?6.247)),and the level of gene expression in the identified CpGs of BRCA1 decreased with increased exposure to o,p'-DDD(OR(95%CI):0.216(0.102?0.458)).Conclusions1.The presence of organochlorine pesticides DDTs can still be detected in pregnant women in Xiamen area,and DDTs can enter the fetus through the placental barrier.2.High frequency of seafood intake may be a risk factor affecting the exposure level of DDTs in the fetus.3.As the concentration of DDT increased,the methylation level of site 1 and site 2 increased,and the gene expression level decreased,which suggested us DDTs exposure levels may affect fetal early BRCA1 gene methylation and its expression level,increasing the risk of disease in later life of fetus.4.Organochlorine pesticide DDTs may increase the risk of breast cancer by changing the methylation status of the promoter region of the BRCA1 gene. |
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