Global DNA Adenine Methylation in Caenorhabditis elegans after Multigenerational Exposure to Silver Nanoparticles and Silver Nitrate.

Multigenerational and transgenerational reproductive toxicity in a model nematode Caenorhabditis elegans has been shown previously after exposure to silver nanoparticles (Ag-NPs) and silver ions (AgNO 3 ). However, there is a limited understanding on the transfer mechanism of the increased reproductive sensitivity to subsequent generations. This study examines changes in DNA methylation at epigenetic mark N6-methyl-2'-deoxyadenosine (6mdA) after multigenerational exposure of C. elegans to pristine and transformed-via-sulfidation Ag-NPs and AgNO 3 . Levels of 6mdA were measured as 6mdA/dA ratios prior to C. elegans exposure (F 0 ) after two generations of exposure (F 2 ) and two generations of rescue (F 4 ) using high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS). Although both AgNO 3 and Ag-NPs induced multigenerational reproductive toxicity, only AgNO 3 exposure caused a significant increase in global 6mdA levels after exposures (F 2 ). However, after two generations of rescue (F 4 ), the 6mdA levels in AgNO 3 treatment returned to F 0 levels, suggesting other epigenetic modifications may be also involved. No significant changes in global DNA methylation levels were observed after exposure to pristine and sulfidized sAg-NPs. This study demonstrates the involvement of an epigenetic mark in AgNO 3 reproductive toxicity and suggests that AgNO 3 and Ag-NPs may have different toxicity mechanisms.