Association of Environmental Exposure to Chromium with Differential DNA Methylation: An Epigenome-Wide Study

To identified the differential methylation of genes and regions to elucidate the mechanisms of toxicity related to environmental chromium exposure. Fasting whole blood samples were collected by clinicians in ethylenediaminetetraacetic acid (EDTA) anticoagulant tubes, and stored them at −80 °C. A DNeasy Blood and Tissue Kit (Qiagen) was used to isolate DNA from whole blood. The purity and concentration of DNA were estimated using Nanodrop 2000 (ThermoScietific). Approximately 500 ng of genomic DNA from each sample was used for sodium bisulfite conversion with the EZ DNA methylation Gold Kit (Zymo Research, USA) in accordance with the manufacturer’s standard protocol. Genome-wide DNA methylation was performed using the Illumina Infinium HumanMethylation850K (EPIC) BeadChip (Illumina Inc, USA) in accordance with the manufacturer’s instructions. To reveal epigenome-wide DNA methylation patterns in response to Cr exposure, a cross-sectional study was conducted in Taihe district, Jinzhou City, Liaoning Province of northeast China, which experienced severe Cr pollution in the 1960s. Because of the large-scale production of ferroalloys, large amounts of wastewater, ore residue, and gas containing Cr(VI) were discharged into the environment surrounding Taihe district. Although the local government has taken restorative measures, the local environment experienced severe Cr(VI) pollution, and relatively high levels of Cr remain. Participants are included in the present study, who have lived in local areas for more than 40 years without occupational Cr exposure and the history of cancers. Finally, the Cr exposure group comprised 10 individuals from Cr-exposed regions along a contaminated river less than 10 km from the ferroalloy factory, and the unexposed group comprised 10 individuals from unexposed regions at least 50 km from that factory. Both groups had similar lifestyles, cultural backgrounds, and socioeconomic status. All participants signed informed consent forms.