Grantee Research Project Results

Final Report: Genetic Susceptibility to the Effects of Aromatic Solvents on Reproductive Health

EPA Grant Number: R825818
Title: Genetic Susceptibility to the Effects of Aromatic Solvents on Reproductive Health
Investigators: Xu, Xiping , Ryan, Louise , Chen, Dafang , Christiani, David , Wang, Lihua , Smith, Thomas
Institution: Harvard University
EPA Project Officer: Aja, Hayley
Project Period: February 1, 1998 through January 31, 2001
Project Amount: $792,308
RFA: Issues in Human Health Risk Assessment (1997) RFA Text |  Recipients Lists
Research Category: Human Health

Objective:

The objective of the research is to assess the impact of gene-aromatic solvent interaction on adverse reproductive outcomes, including menstrual disturbance, infertility, spontaneous abortion, preterm delivery, and low birthweight. Specifically, using resources from a large, well-characterized cohort study, we will prospectively investigate whether the risk of adverse reproductive outcomes associated with aromatic solvent exposure is elevated in individuals with relevant variants of one of the following nine genes: GSTM1, GSTT1, CYP1A1, CYP2D6, CYP2E1, NAT2, NQO1, ALDH2, and EPHX.

Summary/Accomplishments (Outputs/Outcomes):

We have focused on benzene exposure and two susceptibility genes CYP1A1 and GSTT1 (known to be responsible for the metabolism and detoxification of organic solvents) in relation to gestational age. The analysis included 542 female petrochemical workers (302 nonexposed and 240 benzene exposed) who gave live singleton births at a staff hospital. Benzene exposure was significantly associated with shortened gestation even at a level at least 5 times lower than that of the Occupational Safety and Health Administration (OSHA) limit. However, the association was significantly modified by maternal genotype. Among nonexposed, genetic susceptibility alone did not confer significant adverse effect. This study provides evidence of gene-environment interactions and supports further assessment of the role of genetic susceptibility in the evaluation of reproductive toxins.

Another project was a nested case-control study to investigate the association of the cytochromes P450 2D6 (CYP2D6) and Glutathione S-transferase Mu (GSTM1) with dysmenorrhea. The analysis included 129 cases (70 occasional and 59 recurrent dysmenorrhea) and 306 controls who did not smoke or drink, with adjustment for major covariates. CYP2D6 and GSTM1 were each associated with slightly increased risk of dysmenorrhea. When analysis was performed separately among the subgroups (occasional versus recurrent) of dysmenorrhea, neither polymorphism was associated with occasional dysmenorrhea but both were associated with increased risk of recurrent dysmenorrhea. When the combined genotypes of CYP2D6 (AA versus Aa/aa) and GSTM1 (present versus absent) were examined, the data showed a clear gradient of the association among the four groups, with the highest risk of recurrent dysmenorrhea observed among women with both CYP2D6 Aa/aa and GSTM1 absent genotypes. The study revealed an independent and interactive association of CYP2D6 and GSTM1 polymorphisms with the risk of recurrent dysmenorrhea providing evidence of a genetic susceptibility to recurrent dsymenorrhea.

To examine the genetic influence on preterm delivery, we have devised a study to evaluate the major candidate genes of preterm delivery and to test gene-environment interactions. Our study includes 500 existent preterm trios including 500 preterm babies and their parents and 500 maternal age matched term controls collected in China. We will perform the transmission/disequilibrium test (TDT) on candidate genes thought to be important in each of the four biological pathways of PTD: (1) decidual chorioamniotic inflammation: interleukin1 (IL-1), IL-6, and tumor necrosis factor (TNF); (2) maternal and fetal stress: corticotropin-releasing hormone (CRH); (3) uteroplacenta vasculopathy: methylenetereahydrofolate reductase (MTHFR); and (4) susceptibility to environmental toxins: GSTM1, GSTT1, GYP1A1, CYP2D6, CYP2E1, NAT2, NQO1, ALDH2, and EPHX. We also will perform more standard case-control analyses on the 500 preterm cases and 500 term controls to examine gene-environment interactions. The major environmental, nutritional, and social factors as well as clinical variables known or suspected to be associated with PTD will be used to test for gene-environment interactions. This study integrates epidemiologic and clinical data as well as genetic markers along major pathogenic pathways of PTD. The findings from this study should improve our understanding on genetic influence on PTD and potential gene-environment interactions.

In another project, investigators assessed whether the association between maternal cigarette smoking and infant birthweight is modified by two maternal genes: CYP1A1 and GSTT1 that encode cytochrome P-450 and glutathione-transferase metabolic enzymes, respectively. A total of 740 mothers (173 smokers and 567 nonsmokers) who delivered singleton live births were studied. Smoking and other epidemiologic data were obtained by questionnaire interview. CYP1A1 and GSTT1 genotypes were determined for all mothers. Without consideration of genotype, continuous maternal smoking was associated with a 360 g (se = 91) reduction in birthweight. When stratified by CYP1A1 genotype, the estimated reduction in birthweight associated with continuous maternal smoking was 215 g (se = 119) for the AA group, but was 565 g (se = 147) for the Aa/aa group. When stratified by GSTT1 genotype, the estimated reduction in birthweight was 266 g (se = 107) for the present group, but was 659 g (se = 187) for the absent group. When both CYP1A1 and GSTT1 were considered, the greatest reduction in birthweight was found among smoking mothers with CYP1A1 Aa/aaBGSTT1 absent genotypes (1278 g, se = 235). Among non-smoking mothers, genotype alone did not confer an adverse effect. A similar pattern was found for the risk of low birthweight and preterm delivery. We found that CYP1A1 and GSTT1 genotypes can influence maternal susceptibility to the adverse effect of cigarette smoking on birthweight and gestation.

We conducted a nested case-control study to examine the association of microsomal epoxide hydrolase polymorphism with spontaneous abortion. The analysis included 127 cases and 107 controls from a rural community in China. The prevalence of the homozygous wild-type (AA), the heterozygous variant (Aa), and the homozygous variant (aa) in exon 3 of epoxide hydrolase was 13.4 percent, 34.6 percent, and 52.0 percent in cases and 27.1 percent, 30.8 percent, and 42.1 percent in controls, respectively. In contrast, the variant genotypes in exon 4 of epoxide hydrolase were less frequent in cases than controls. Using women with genotype AA as reference, the adjusted odds ratio of SA was 2.69 (95% CI: 1.33-5.42) for those with genotype Aa or aa in exon 3, but was 0.45 (95% CI: 0.22-0.94) for those with genotype Aa or aa in exon 4, suggesting that the two variants have opposite association with spontaneous abortion. The findings persisted after adjustment for age, education, parity, smoking, alcohol use, occupation, and pesticide exposure, as well as in subgroup analysis. Moreover, for the variant genotypes Aa or aa in exon 3, the odds ratio was twice as great in those cases with 3 or more SA than in those with fewer. These data suggest a genetic susceptibility among women who had spontaneous abortions?in particular, among those who had had three or more. The functional significance of the known polymorphism in this gene could have important clinical implications.

The association between birthweight and exposure to benzene, work stress, and other occupational and environmental hazards was investigated. In a large petrochemical industry, 792 pregnant workers were enrolled and followed up through delivery between May 1996 and December 1998. Exposure to benzene and other solvents was assessed by an industrial hygienist based on each woman=s job title and workplace information. Other occupational and environmental exposures and personal information, including perceived work stress, exposure to noise, physical exertion at work, and passive smoking, were obtained by an interview questionnaire. Univariate and multivariate regression models were used to examine the individual and combined associations of occupational and environmental exposures with birthweight, with adjustment for major confounders including gestational age. In the univariate model, birthweight was negatively associated with exposure to benzene [-58 g (95% confidence interval (95% CI), -115 to -2)] and with work stress [-84 g (95% CI, -158 to -10)]. In the multivariate model, there was a significant interaction between exposure to benzene and work stress relative to reduced birthweight, after adjustment for other environmental and occupational exposures and personal variables. Adjusted mean birthweight was 3445 g (95% CI 3401 to 3489) among those with neither exposure, 3430 g for those with exposure to benzene only, 3426 g for those with work stress only, and 3262 g (95% CI 3156 to 3369) for those with both exposures. In other words, there was a 183 g (95% CI 65 to 301) reduction in birthweight among those with both exposure to benzene and work stress compared with those with neither exposure. Other work or environmental factors could not explain these findings. Low-level exposure to benzene and work stress interact to reduce birthweight in this population.

Few published studies have examined the role of genetic factors and gene-environment interactions in relation to preterm delivery. We assessed maternal and fetal CYP1A1 HincII genotypes and benzene exposure in relation to gestational age among 502 mother-infant pairs (277 unexposed and 225 exposed) in Beijing, China. We used two complementary analytical approaches: Transmission Disequilibrium Test when only one parent is available (1-TDT) and mixed effects model, with adjustment for maternal age, passive smoking, prepregnancy weight and height, and infant gender. We also extended 1-TDT to use the log-linear analysis to test gene-environment interaction. The 1-TDT did not detect an excess transmission of CYP1A1 alleles among mothers with reduced (<40 weeks) gestational age (p = 0.83 and 0.16, for benzene exposed and unexposed, respectively) compared to mothers without, and the log-linear analysis did not detect an interaction between the CYP1A1 gene and the benzene exposure. Using the mixed effects model, we found that the fetal AA-maternal AA genotype combination was associated with a significant reduction in gestational age in the benzene-exposed group (b = -0.280.14, p<0.05). A linear regression-based test of gene-benzene interaction also was highly significant (b = -0.660.22, p<0.005). In conclusion, consistent with our earlier report, our data suggest that CYP1A1 genotype alone is not associated with gestational age. However, CYP1A1 gene polymorphisms significantly modified the association between benzene exposure and gestational age (i.e., there is a gene-benzene interaction). Our study underscores the importance of further assessing the role of both maternal and fetal genetic susceptibility in the evaluation of reproductive toxins.

Journal Articles on this Report : 6 Displayed | Download in RIS Format

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Other project views:	All 6 publications	6 publications in selected types	All 6 journal articles

Publications

Type	Citation	Project	Document Sources
Journal Article	Chen D, Cho SI, Chen CZ, Wang XO, Damokosh AI, Ryan L, Smith TJ, Christiani DC, Xu XP. Exposure to benzene, occupational stress, and reduced birth weight. Occupational and Environmental Medicine 2000;57(10):661-667.	R825818 (Final)	Full-text from PubMed Abstract from PubMed
Journal Article	Wang XB, Chen DF, Niu TH, Wang ZX, Wang LH, Ryan L, Smith T, Christiani DC, Zuckerman B, Xu XP. Genetic susceptibility to benzene and shortened gestation: evidence of gene-environment interaction. American Journal of Epidemiology 2000;152(8):693-700.	R825818 (1999) R825818 (Final)	Abstract from PubMed Full-text: Oxford - Full Text HTML Exit
Journal Article	Wang XB, Zuckerman B, Kaufman G, Wise P, Hill M, Niu TH, Ryan L, Wu D, Xu XP. Molecular epidemiology of preterm delivery: methodology and challenges. Paediatric and Perinatal Epidemiology 2001;15(Suppl 2):63-77	R825818 (2000) R825818 (Final)	not available
Journal Article	Wang X, Zuckerman B, Pearson C, Kaufman G, Chen C, Wang G, Niu T, Wise P, Bauchner H, Xu X. Maternal cigarette smoking, metabolic gene polymorphism, and infant birth weight. JAMA-Journal of the American Medical Association 2002, Volume: 287, Number: 2 (JAN 9), Page: 195-202.	R825818 (2000) R825818 (Final)	not available
Journal Article	Wang X, Wang M, Niu T, Chen CZ, Xu X. Microsomal epoxide hydrolase (EPHX) polymorphism and risk of spontaneous abortion. Epidemiology 1998;9(5):540-544.	R825818 (1999) R825818 (Final)	Abstract: JSTOR - Abstract HTML Exit
Journal Article	Wu D, Wang X, Chen D, Niu T, Ni J, Liu X, Xu X. Metabolic gene polymorphisms and risk of dysmenorrhea. Epidemiology 2000;11(6):648-653.	R825818 (Final)	not available

Supplemental Keywords:

candidate genes, gene polymorphisms, preterm delivery, gestational age, transmission/disequilibrium test, TDT, aromatic solvents, case-control study, maternal cigarette smoking, genetic susceptibility, gene-environment interaction, birthweight, gestational age, nested case-control study, genetic susceptibility, spontaneous abortion, Chinese population., Health, Scientific Discipline, Air, Geographic Area, Toxics, International, Risk Assessments, Chemistry, HAPS, Environmental Chemistry, 33/50, air toxics, Genetics, Benzene (including benzene from gasoline), toxic environmental contaminants, benzene, human exposure, genetic analysis, Toluene, genetic susceptibility, developmental effects, aromatic solvents, China, reproductive health, biomarker, blood samples, Styrene

Progress and Final Reports:

Original Abstract

1998

1999 Progress Report