Exposure To Disinfection By-products And CYP2E1 And HOGG1 Polymorphisms: Effect On Birth Weight

Chlorination is applied to kill pathogenic microorganisms in drinking water and has been widely used over the world to reduce the incidence of waterborne diseases. However, chlorination disinfection by-products (CDBPs) are formed when disinfectants used in water treatment plants react with natural organic matter present in the source water. Several of the halogenated by-products have been evaluated in animal studies and showed evidences of their potential to induce adverse reproductive health outcomes, such as reductions in birth weight and live birth, and congenital malformations of the cardiovascular and neurological systems. In epidemiological studies, the relationship between CDBPs exposure and reproductive health outcomes such as low birth weight, pregnancy loss, still birth and birth defects remains unclear, mainly owing to limitations in the exposure assessment in most studies. How to make CDBP exposure measurement more accurate has become a major problem when conducting CDBPs health effects studies.ObjectivesWe conducted this study to investigate the relationship between CDBPs exposure and reduced birth weight. Two means of exposure assessment, external and internal exposure measurement, were adopted_in our study. Several of CDBPs levels in the pregnant women living_in a same area were monitored at three locations in the middle of each month to collect the data for external exposure assessment and we also examined the trichloracetic acid (TCAA) levels in the first morning urine obtained from the pregnant women, and these levels were used as biomarker of CDBPs internal exposure. Besides, our study is the first one to use urinary TCAA as biomarker for CDBPs exposure in epidemiological studies. The molecular mechanism by which CDBPs may influence human reproductive health is not well understood and in order to investigate the mechanisms, we analyzed the association between CYP2E1G1259C and hOGG1Ser326Cys genotype in newborns and CDBPs'health effects.MethodsPregnant women and newborns in our study were recruited form one hospital in Wuhan during the period from Jan.2008 to May 2009. Their basic information such as maternal age, education, disease history, gestational duration, and newborn's birth weight were obtained from the hospital birth records.In our first part, the pregnant women were recruited from one area where the water supply was from a single water plant. Water samples were collected from 3 locations:point 1 (about lkm from the plant), point 2 (about 4 km from the plant), and point 3 (about 8 km from the plant). During the period from Jan 2008 to May 2009, water samples were monthly collected from the these 3 points at fixed intervals, and the parameters including four halomethanes (chloroform, chlorodibromomethane, bromodicloromethane and bromoform) and two chloro-haloacetic acids (trichloracetic acid and dichloroacetic acid) were obtained from these samples. Both time and distance had taken into account when we collected this data. We selected 1385 pregnant women who were living in this area during their pregnancy and their trimester-specific CDBPs exposure assessment was based on this environmental data. Then we analyzed the relationship between CDBPs exposure during the pregnancy and their newborns'birth weight among these 1385 women.A number of 398 pregnant women were participated in our second part study and we had examined the urinary trichloracetic acid levels in their first morning urine, and this was used as internal exposure biomarker. This exposure assessment is more accurate than that used in the previous epidemiological studies. The association between maternal urinary trichloracetic acid levels and fetal birth weight was investigated in this part. In addition, we conducted a questionnaire survey to collect the vital information such as maternal water-use behaviors, family incomes, and reproductive disease history to control the birth weight confounders and we also investigate the effects of multi-route exposure to CDBPs.In the third part, we collected the cord blood of 158 newborns for DNA isolation. Taqman technique was adopted to genotype the CYP2E1 (G-1259C) and hOGGl (Ser326Cys) polymorphisms and maternal urinary trichloracetic acid levels were used for CDBPs exposure assessment. With these results, we conducted the gene-environment interaction analysis and try to find out the molecular mechanism of CDBPs.ResultsOur drinking water monitor lasted for 17 months and the CDBPs levels from month to month and from one point to another. Among the 51 water samples, the concentration ranges are:3.15～85.75 mg/L for chloroform,0.77～12.44 mg/L for chlorodibromoethane, LOD (limit of detection)-4.21 mg/L for bromodicloromethane, LOD～18.15 mg/L for bromoform,6.05-28.76 mg/L for dichloroacetic acid and 1.93～25.51mg/L for trichloracetic acid. The levels of CDBPs met the national standards for drinking water quality_except for the chloroform in one sample in July 2008. Based on this environmental data, we estimated maternal exposure levels and we found that high exposure to chloroform and bromo-trihalomethanes during the last trimester may result in increased risk in reduced birth weight (OR=1.82,95CI: 1.10～3.02; OR=1.51,95CI:1.05～2.17, respectively). Besides, exposure to high level of dichloroacetic acid during the first two trimesters could also lead to reduction of birth weight, with an OR of 1.60 (95CI:1.02～2.47).The urinary trichloroacetic acid levels among 398 women ranges from 0.9～123.3μg/gCr. Our results showed that high level of urinary trichloroacetic acid in the late pregnancy may be associated with reduced birth weight (β=-0.15,95%CI: 0.31～-0.01, P=0.04). In addition, we also observed that there was a positive correlation between urinary trichloroacetic acid levels and water consumption(β=0.23, 95%CI:0.38-14.06, P=0.04).In our gene-environment interaction study,158 newborns were genotyped for the CYP2E1 G1259C and hOGG1 Ser326Cys polymorphisms and the distribution of the polymorphism is:CC=7 (4.4%), CG=56 (35.4%), GG=95 (60.2%) forCYP2E1 and Cys/Cys=23(14.6%), Ser/Cys=74(46.8%), Ser/Ser=61(38.6%) for hOGGl. Compared with the newborns with heterozygous and wild type homozygous, the mean birth weight of newborns with the CC genotype for CYP2E1 or Cys/Cys genotype for hOGG1 were lower than others. However, when we divided newborns into two groups, wild type homozygous and other genotypes, we did not find any differences in birth weight between high and normal exposure groups, which indicated that these two polymorphisms may not relate to CDBPs effects on birth weight. But the sample size in our study is a bit small and our results need to be confirmed in large scale studies.ConclusionIn conclusion, our results showed evidences that exposure to CDBPs during pregnancy may relate to reduced birth weight. Many scientists consider the last trimester as an important period for fetal growth, and our study found that high exposure to chloroform and bromo-trihalomethanes may lead to reductions in birth weight. In addition, exposure to high levels of dichloroacetic acid during the first two trimesters may also result in reduced birth weight, which indicated that fetal growth during the first and second trimester may be more sensitive to dichloroacetic acid. Meanwhile, by using urinary trichlroacetic acid as the internal biomarker, we observed that high exposure to CDBPs can lead to reductions in birth weight. In our third part, we did not found the gene-environment interaction effects of CYP2E1 (G-1259C) andhOGG1 (Ser326Cys) polymorphism and the molecular mechanism of CDBPs still need to be studies in the future.The new ideas(1) We conducted a 17 months study to monitor several CDBPs concentrations distribution systems and during our study both the time and geographic variations were taken into account.(2) Our study is the first one to use urinary trichloroacetic acid as the biomarker for CDBPs exposure in epidemiological studies.(3) The molecular mechanism through which CDBPs may influence human reproductive health is still unclear. We studied the polymorphism of phaseⅠmetabolism enzymes (CYP2E1) and DNA repair enzymes (hOGGl) to investigate the molecular mechanism of CDBPs.