Silver, Gold, and Iron Oxide Nanoparticles Alter miRNA Expression but Do Not Affect DNA Methylation in HepG2 Cells

Abstract

The increasing use of nanoparticles (NPs) in various applications entails the need for reliable assessment of their potential toxicity for humans. Originally, studies concerning the toxicity of NPs focused on cytotoxic and genotoxic effects, but more recently, attention has been paid to epigenetic changes induced by nanoparticles. In the present research, we analysed the DNA methylation status of genes related to inflammation and apoptosis as well as the expression of miRNAs related to these processes in response to silver (AgNPs), gold (AuNPs), and superparamagnetic iron oxide nanoparticles (SPIONs) at low cytotoxic doses in HepG2 cells. There were no significant differences between treated and control cells in the DNA methylation status. We identified nine miRNAs, the expression of which was significantly altered by treatment with nanoparticles. The highest number of changes was induced by AgNPs (six miRNAs), followed by AuNPs (four miRNAs) and SPIONs (two miRNAs). Among others, AgNPs suppressed miR-34a expression, which is of particular interest since it may be responsible for the previously observed AgNPs-mediated HepG2 cells sensitisation to tumour necrosis factor (TNF). Most of the miRNAs affected by NP treatment in the present study have been previously shown to inhibit cell proliferation and tumourigenesis. However, based on the observed changes in miRNA expression we cannot draw definite conclusions regarding the pro- or anti-tumour nature of the NPs under study. Further research is needed to fully elucidate the relation between observed changes in miRNA expression and the effect of NPs observed at the cellular level. The results of the present study support the idea of including epigenetic testing during the toxicological assessment of the biological interaction of nanomaterials.

Epigenetic Effects of Nanomaterials and Nanoparticles

“…Sooklert et al [ 23 ] found reduced global DNA methylation 72 h after exposure of human kidney embryonic HEK293 cells to 100 µg/mL of gold nanoparticles (Au-NPs). Similar findings of DNA demethylating activity of AuNPs were reported by Patil et al [ 30 ]; however, no changes to the extent of global DNA methylation were found in Au-NPs-treated SK-BR-3 human breast cancer cells [ 31 ], HepG2 human liver cancer cells [ 32 ], or MRC5 human fetal fibroblasts [ 33 ]. Likewise, no changes in the DNA methylation status of the down-regulated PROS1 gene were found in Au-NPs-treated MRC5 cells [ 33 ].…”

“…Blanco et al [ 35 ] reported increased global cytosine DNA methylation in response to the exposure of human lung adenocarcinoma A549 cells to 200 µg/mL Ag-NPs for 72 h, while no changes were found in cells exposed to the lower concentrations of Ag-NPs ranging from 10 to 100 µg/mL. Brzóska et al [ 32 ] reported similar findings with no effect of Ag-NPs on human liver cancer HepG2 cells, and Gliga et al [ 36 ] demonstrated a minimal effect on DNA methylation in human BEAS-2B cells exposed to 1 µg/mL Ag-NPs for 6 weeks.…”

DNA Methylation Profiles in a Group of Workers Occupationally Exposed to Nanoparticles

“…A detailed DNA methylation profile of DNA methyltransferase genes in breast cancer cell line MCF-7 after treatment with maghemite nanoparticles revealed epigenetic changes, even though the overall percentage of DNA methylation was not affected [8], which in contrast to altered global methylation by the same nanomaterial but in human submandibular gland cells, which was analyzed in a later study [9]. No significant differences in the DNA methylation status of inflammatory and apoptosis response genes of human liver cancer cells (HepG2) was found after silver, gold and superparamagnetic iron nanoparticle (SPION) exposure [10].…”

The Promises and Challenges of Toxico-Epigenomics: Environmental Chemicals and Their Impacts on the Epigenome

“…Following the frequent inclusion of epigenetics as a parameter in environmental epidemiology studies, numerous reports have been made in recent years associating alterations in DNA methylation with various environmental factors, including biological agents, dietary habits, and air pollution (Ambatipudi et al 2016;Barouki et al 2018;de FC Lichtenfels et al 2018;Degli Esposti et al 2017;Fasanelli et al 2019;Feil and Fraga 2012;Hattori and Ushijima 2016;Herceg et al 2018;Martin and Fry 2018;Perrier et al 2019;Woo et al 2018). Similarly, many reports indicate that microRNA (miRNA) profiles are responsive to various environmental exposures, including air pollution ; Espín-Pérez et al (2018), both epidemiological studies], nanoparticles [Brzóska et al (2019), utilizing human liver cells], endocrine disruptors, such as bisphenol A (BPA) [Chou et al (2017), using human endometrial cells, and Martínez-Ibarra et al (2019), using human blood samples], and dichlorodiphenyltrichloroethane (DDT) [Krauskopf et al (2017), using human blood]. Long noncoding RNAs (lncRNAs), although still a relatively new area of research, have been reported to be associated with levels of phthalates in first trimester urine of pregnant women (LaRocca et al 2014), benzene in seven exposed individuals (Bai et al 2014b), and occupational exposure to cadmium (Zhou et al 2015) and to be responsive to developmental exposure to BPA in mice (Kumamoto and Oshio 2013) and to certain heavy metals in in vitro (Tani et al 2014;Zhou et al 2015) and in vivo experimental systems (Zhou et al 2015).…”