Epigenetic modulation upon exposure of lung fibroblasts to TiO₂ and ZnO nanoparticles: alterations in DNA methylation

Abstract

Titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles (NPs) are promising candidates for numerous applications in consumer products. This will lead to increased human exposure, thus posing a threat to human health. Both these types of NPs have been studied for their cell toxicity, immunotoxicity, and genotoxicity. However, effects of these NPs on epigenetic modulations have not been studied. Epigenetics is an important link in the genotype and phenotype modulation and misregulation can often lead to lifestyle diseases. In this study, we have evaluated the DNA methylation-based epigenetic changes upon exposure to various concentrations of NPs. The investigation was designed to evaluate global DNA methylation, estimating the corresponding methyltransferase activity and expression of Dnmt gene using lung fibroblast (MRC5) cell line as lungs are the primary route of entry and target of occupational exposure to TiO₂ and ZnO NPs. Enzyme-linked immunosorbent assay-based immunochemical assay revealed dose-related decrease in global DNA methylation and DNA methyltransferase activity. We also found direct correlation between the concentration of NPs, global methylation levels, and expression levels of Dnmt1, 3A, and 3B genes upon exposure. This is the first study to investigate effect of exposure to TiO₂ and ZnO on DNA methylation levels in MRC5 cells. Epigenetic processes are known to play an important role in reprogramming and adaptation ability of an organism and can have long-term consequences. We suggest that changes in DNA methylation can serve as good biomarkers for early exposure to NPs since they occur at concentrations well below the sublethal levels. Our results demonstrate a clear epigenetic alteration in response to metal oxide NPs and that this effect was dose-dependent.

Keywords:

• nanotoxicity
• epigenetics
• global DNA methylation
• 5-mC
• DNA methyltransferase
• Dnmt

Acknowledgments

This research was funded by the UGC Dr DS Kothari Postdoctoral fellowship. WNG and DDD acknowledge the departmental (Biotechnology and Zoology) research grant and UPE Phase II Biotherapeutics grant.

Author contributions

NAP carried out all experiments and analyzed the data sets. WNG and DDD conceived the experiments, supervised, and provided major intellectual inputs. NAP, WNG, and DDD contributed in revising the article critically for important intellectual content. All authors have approved the final article. All authors contributed toward data analysis, drafting and revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.