Introduction: Engineered nanoparticles (ENPs) are one of the most widely used types of nanomaterials. Recently, ENPs have been shown to cause cellular damage by inducing ROS (reactive oxygen species) both directly and indirectly, leading to the changes in DNA methylation levels, which is an important epigenetic mechanism. In this study, we investigated the effect of ENP-induced ROS on DNA methylation. Materials and methods: Human embryonic kidney and human keratinocyte (HaCaT) cells were exposed to three different types of ENPs: gold nanoparticles, silicon nanoparticles (SiNPs), and chitosan nanoparticles (CSNPs). We then evaluated the cytotoxicity of the ENPs by measuring cell viability, morphology, cell apoptosis, cell proliferation, cell cycle distribution and ROS levels. Global DNA methylation levels was measured using 5-methylcytosine immunocytochemical staining and HPLC analysis. DNA methylation levels of the transposable elements, long interspersed element-1 (LINE-1) and Alu, were also measured using combined bisulfite restriction analysis technique. DNA methylation levels of the TEs LINE-1 and Alu were also measured using combined bisulfite restriction analysis technique. Results: We found that HaCaT cells that were exposed to SiNPs exhibited increased ROS levels, whereas HaCaT cells that were exposed to SiNPs and CSNPs experienced global and Alu hypomethylation, with no change in LINE-1 being observed in either cell line. The demethylation of Alu in HaCaT cells following exposure to SiNPs and CSNPs was prevented when the cells were pretreated with an antioxidant. Conclusion: The global DNA methylation that is observed in cells exposed to ENPs is associated with methylation of the Alu elements. However, the change in DNA methylation levels following ENP exposure is specific to particular ENP and cell types and independent of ROS, being induced indirectly through disruption of the oxidative defense process.
Keywords: Alu; DNA methylation; LINE-1; epigenetic; nanotoxicity.