Sodium bisulfite pyrosequencing revealed that developmental exposure to environmental contaminant mixtures does not affect DNA methylation of DNA repeats in Sprague-Dawley rats

ABSTRACT

Hypomethylation of DNA repeats has been linked to diseases and cancer predisposition. Human studies suggest that higher blood concentrations of environmental contaminants (EC) correlate with levels of hypomethylation of DNA repeats in blood. The objective of this study was to examine the effect of in utero and/or lactational exposure to EC on the methylation of DNA repeats (LINE-1 and identifier element) in Sprague-Dawley rat pups at birth, at postnatal day (PND) 21, and in adulthood (PND78–86). From gestation day 0 to PND20, dams were exposed to a mixture “M” of polychlorinated biphenyls (PCB), pesticides, and methylmercury (MeHg), at 0.5 or 1 mg/kg/d (0.5M and M). At birth, some control (C) and M litters were cross-fostered to create the following in utero/postnatal exposure groups: C/C, M/C, C/M, M/M. Additional dams received 1.8 ng/kg/d of a mixture of aryl-hydrocarbon receptor (AhR) agonists (non-ortho-PCB, PC-dibenzodioxins, and PC-dibenzofurans) without or with 0.5M (0.5MAhR). Measurements of EC residue levels confirmed differences in their accumulation across treatments, age, and tissues. Although induction of hepatic detoxification enzyme activities (cytochrome P-450) demonstrated biological effects of treatments, the assessment of methylation in DNA repeats by sodium bisulfite pyrosequencing of liver, spleen, and thymus samples revealed no marked treatment-related effects but significant tissue- and age-related methylation differences. Further studies are required to determine whether absence of significant observable treatment effects on methylation of DNA repeats in the rat relate to tissue, strain, or species differences.

Funding

The authors are grateful to Dr. Guillaume Pelletier, Dr. Dalibor Breznan, and Dr. Bill Casley for carefully reviewing this article, to Ron Strathern for chemical analyses, and to Ming-Yan Yang and the personnel from the Animal Resources Division for their valued assistance. Funded by Health Canada, the Chemical Management Plan, and the Northern Contaminants Program, Indian and Northern Affairs Canada.

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Funding

The authors are grateful to Dr. Guillaume Pelletier, Dr. Dalibor Breznan, and Dr. Bill Casley for carefully reviewing this article, to Ron Strathern for chemical analyses, and to Ming-Yan Yang and the personnel from the Animal Resources Division for their valued assistance. Funded by Health Canada, the Chemical Management Plan, and the Northern Contaminants Program, Indian and Northern Affairs Canada.