Global DNA hypomethylation is associated with in utero exposure to cotinine and perfluorinated alkyl compounds

Abstract

Environmental exposures in-utero may alter the epigenome, thus impacting chromosomal stability and gene expression. We hypothesized that in utero exposures to maternal smoking and perfluoroalkyl compounds (PFCs) are associated with global DNA hypomethylation in umbilical cord serum. Our objective was to determine if global DNA methylation could be used as a biomarker of in utero exposures to maternal smoking and PFCs. Using an ELISA-based method, global DNA methylation was quantified in umbilical cord serum from 30 newborns with high (>10 ng/ml, mean 123.8 ng/ml), low (range 1-10 ng/ml, mean 1.6 ng/ml) and very low (<1 ng/ml, mean 0.06 ng/ml) cord serum cotinine levels. Y chromosome analysis was performed to rule out maternal DNA cross-contamination. Cord serum global DNA methylation showed an inverse dose response to serum cotinine levels (p<0.001). Global DNA methylation levels in cord blood were the lowest among newborns with smoking mothers (mean=15.04%; 95% CI, 8.4, 21.7) when compared to babies of mothers who were second-hand smokers (21.1%; 95% CI, 16.6, 25.5) and non-smokers (mean=29.2%; 95% CI, 20.1, 38.1). Global DNA methylation was inversely correlated with serum PFOA (r= -0.72, p <0.01) but not PFOS levels. Serum Y chromosome analyses did not detect maternal DNA cross-contamination. This study supports the use of global DNA methylation status as a biomarker of in utero exposure to cigarette smoke and PFCs.

Acknowledgements

This research was supported in part by the NCI 5U01CA13-8. It also received support from the Maryland Cigarette Restitution Program Research Grant given to the Johns Hopkins Medical Institutions and by funding from the NIOSH Education and Research Center for Occupational Safety and Health at the Johns Hopkins Bloomberg School of Public Health (#T42CCT310419). R.U.H. was supported in part by grant 1R01ES015445 of the National Institute of Environmental Health Sciences (NIEHS). The authors wish to thank Jose Rodriguez-Orengo for assisting with genetic analyses, John Bernert and the CDC Tobacco Exposure Biomarkers laboratory for performing the cotinine analyses and Antonia Calafat and the CDC Organic Analytical Toxicology laboratory for performing analyses of PFCs, as well as reviewing the draft manuscript. We also thank Larry Needham for helpful comments and administrative support of this study. Many thanks to Julie Herbstman and Jochen Heidler for data and umbilical cord sample collection and Ruth Quinn for study coordination.

Figures and Tables

Figure 1 Global DNA methylation index in cord blood serum DNA of 11 newborns exposed in utero to tobacco smoke constituents from maternal smoking, 11 newborns whose mothers were passive smokers and eight newborns whose mothers were nonsmokers. (Box plots).

Figure 2 (A) Linear relationship between the natural log of cotinine in cord blood serum and the global DNA methylation index in 30 newborns with high (11), low (11) and very low (8) cotinine serum levels. (B) Linear relationship between the natural log of PFOA in cord blood serum and the global DNA methylation index in 30 newborns. (C) Linear relationship between the natural log of PFOS in cord blood serum and the global DNA methylation index in 30 newborns.

Table 1 Characteristics of infants selected for epigenetics study compared with all eligible infants, Baltimore THREE study

Table 2 Results of linear models (pearson's correlations and slope beta values) for cotinine, PFOA and PFOS concentrations (log-transformed) and other selected study variables on %5-mC (n = 30), Baltimore THREE study

Table 3 Quantification of serum Y chromosome human DNA (ng/ul) and serum total human DNA (ng/ul) obtained from umbilical cord blood of seven male infants, Baltimore THREE study