Associations among genetic susceptibility, DNA damage, and pregnancy outcomes of expectant mothers exposed to environmental tobacco smoke
Introduction
Recent studies have linked maternal tobacco smoking and environmental tobacco smoke (ETS) exposure to increased risk for intrauterine growth retardation (IUGR), low-birth-weight (LBW), and preterm delivery (Martin and Bracken, 1986, Windham et al., 2000, Mochizuki et al., 1984, Castles et al., 1999, Cnattingius et al., 1993). ETS exposure levels among non-smokers are correlated with nicotine concentrations in the air, exposure duration, and individual respiration rates (Scherer and Richter, 1997). However, the risk may not be the same for all expectant mothers exposed to ETS. Unspecified factors, such as individual differences in susceptibility to tobacco exposure of expectant mothers might affect the relationship between prenatal smoking or ETS exposure and neonatal birth weight (Wang et al., 2002, Hong et al., 2003).
Polymorphic gene studies of tobacco smoke carcinogens have found variability between individuals (Wang et al., 2002, Hong et al., 2003, Katho et al., 1996, Falck et al., 1999, Millidan et al., 1998). Susceptible polymorphic genes, such as isoenzyme of cytochrome P450 (CYP1A1), glutathione S-transferase (GST), and N-acetyltransferases (NAT), were associated with the metabolism of polycyclic aromatic hydrocarbons (PAHs) and aromatic amines in tobacco, as well as its enzymic activity (Wang et al., 2002, Hong et al., 2003, Katho et al., 1996, Falck et al., 1999, Millidan et al., 1998). The CYP1A1 metabolizes PAH compounds into genotoxic products, which bind covalently to DNA and proteins (Gottieb and Manchester, 1986, Manchester et al., 1992). The GST enzymes catalyze the reaction between glutathion and substrates, such as reactive intermediates of PAH, thus preventing genotoxic compounds binding to DNA and proteins. Individuals without the GST gene are susceptible to carcinogenic PAH (Katho et al., 1996). In determining the effects of the GSTM1 and GSTT1 polymorphisms on the relationship between maternal exposure to ETS and neonatal birth weight, analytical data show that the adverse effects of maternal exposure to ETS on infant birth weight can be modified by the maternal genotypes (Hong et al., 2003). A previous investigation identified an interaction between benzene exposure and metabolic genes during pregnancy (Wang et al., 2000), suggesting that increased risk of LBW in association with the exposure was modified by maternal metabolic gene polymorphisms (i.e., CYP1A1, GSTT1) (Wang et al., 2002).
The comet assay is a rapid and sensitive technique that permits the detection and estimation of DNA damage at the single cell level. This assay is effective in detecting DNA damage induced by tobacco smoke toxicants in peripheral blood cells. Previous studies identified increased DNA damage among smokers compared with that of non-smokers (Frenzilli et al., 1997, Mohankumar et al., 2002, Ellahuene et al., 2004), and found no correlation between DNA damage and the number of cigarettes smoked or smoking frequency (Frenzilli et al., 1997, Mohankumar et al., 2002). However, the effects of genotoxicity (determined by comet assay) on biomarkers of exposure in ETS-exposed pregnant women are not well documented. This is the first study of using comet assay to assess the DNA damage for association between prenatal smoking or ETS exposure and adverse pregnancy outcomes, and to analyze the correlations between genotoxicity and susceptible polymorphism genes (i.e., CYP1A1, GSTT1, GSTM1, and NAT2), and the interactions between these genes.
Section snippets
Subjects and study site
A letter explaining the study risk, benefit and limitation was delivered to invite all eligible pregnant women who received prenatal care between August 2003 and October 2004 at three central Taiwan hospitals for their participation in this study. Three hundred fourteen pregnant women agreed to participate with consents during their first trimester of gestation. Of which, 215 subjects remained during their second trimester, resulting in a follow-up rate of 68.5%. Additionally, 371 new subjects
Statistical analysis
All analyses were performed using SAS statistical software for Windows version 8.2 (SAS institute, Cary, NC). Chi-square tests were employed to compare the basic characteristics between the smoker, ETS-exposed non-smoker and non-smoker groups. Distributions of self-reported exposure and neonatal birth outcomes were compared among the three groups using the non-parametric Kruskal–Wallis test. Using a dichotomous score variable, the differences in DNA damage between mean values were tested for
Results
Table 1 presents the distribution of basic characteristics of pregnant women according to the smokers, ETS-exposed subjects and non-smokers. Chi-square tests identified significant differences between the three groups for age, occupation, education level, and monthly household income. Smokers were significantly more likely to be young, not college educated (74.6%), housewives (47.7%) and unemployed (10.8%), and had household monthly incomes less than US$1,250 (48.4%) and previous miscarriages
Discussion
Socioeconomic status was estimated by combining education level, occupational characteristics, and income. In this study, education was negatively associated with smoking or exposure to ETS. This finding is consistent with the strong inverse association of education with smoking prevalence rates obtained in previous studies (Giovino et al., 1995, Misra and Nguyen, 1999, Jaakkola and Samet, 1999). Persons of low and medium education level, social, and economic backgrounds typically encounter
Acknowledgment
This study was supported by the grants of the Bureau of Health Promotion, Department of Health (BHP-92-Anti-Tobacco-F204), and China Medical University (CMC90-EM-02, CMC91-EM-02, CMU92-EM-03, CMU92-PH-04, CMU93-EM-04). The authors thank the Taichung Hospital for the assistance of data and specimen collections. In addition, special thanks to Tsui-Wen Chang, MPH, Shih-Ching Yu, MPH, Hsien-Tsai Chiu, MPH, and Yang-Chen Cheng, BA for their assistance.
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