Persistent DNA methylation changes in zebrafish following graphene quantum dots exposure in surface chemistry-dependent manner.

Modified nano-graphene quantum dots (M-GQDs) are widely used in bioimaging, drug delivery, and chemical engineering. Because M-GQDs could induce reactive oxygen species and DNA damage, we hypothesized that M-GQDs modulate DNA methylation. To test this hypothesis, zebrafish were exposed to reduced, hydroxylated, or aminated GQDs (graphene quantum dots) at different concentrations for 7 days; global DNA methylation in liver, gill, and intestine was then studied. M-GQDs induced global DNA hypermethylation in various tissues in a dose-dependent manner. The global DNA methylation of reduced and aminated GQDs exposure showed a significant increase in intestines even at low concentrations (2 mg/L), suggesting that intestines are the main target for these two M-GQDs. The effects of global DNA methylation were evaluated 14 days after exposure had ceased. DNA methylation in the livers of exposure groups was significantly higher than in control zebrafish. Global DNA methylation increased in livers of zebrafish even after exposure to aminated GQDs (2 mg/L) had ceased, indicating a more complex mechanism of DNA methylation deregulation. The present results showed that chemical groups in the surface of GQDs are a critical factor for modulating DNA methylation.