Time-Dependent Toxic and Genotoxic Effects of Zinc Oxide Nanoparticles after Long-Term and Repetitive Exposure to Human Mesenchymal Stem Cells.

Pascal Ickrath,Thomas Gehrke,Rudolf Hagen,Norbert Kleinsasser,Agmal Scherzad,Martin Wagner,Stephan Hackenberg,Katrin Radeloff,Marc Burghartz

doi:10.3390/ijerph14121590

Abstract

Zinc oxide nanoparticles (ZnO-NP) are widely spread in consumer products. Data about the toxicological characteristics of ZnO-NP is still under controversial discussion. The human skin is the most important organ concerning ZnO-NP exposure. Intact skin was demonstrated to be a sufficient barrier against NPs; however, defect skin may allow NP contact to proliferating cells. Within these cells, stem cells are the most important toxicological target for NPs. The aim of this study was to evaluate the genotoxic and cytotoxic effects of ZnO-NP at low-dose concentrations after long-term and repetitive exposure to human mesenchymal stem cells (hMSC). Cytotoxic effects of ZnO-NP were measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Furthermore, genotoxicity was evaluated by the comet assay. For long-term observation over 6 weeks, transmission electron microscopy (TEM) was applied. The results of the study indicated cytotoxic effects of ZnO-NP beginning at high concentrations of 50 μg/mL and genotoxic effects in hMSC exposed to 1 and 10 μg/mL ZnO-NP. Repetitive exposure enhanced cyto- but not genotoxicity. Intracellular NP accumulation was observed up to 6 weeks. The results suggest cytotoxic and genotoxic potential of ZnO-NP. Even low doses of ZnO-NP may induce toxic effects as a result of repetitive exposure and long-term cellular accumulation. This data should be considered before using ZnO-NP on damaged skin.

Highlights

A quantity of 10 mg of Zinc oxide nanoparticles (ZnO-NP) was suspended in 870 μL distilled aqua and sonicated (Bandelin, Sonopuls HD 60, Berlin, Germany) for 120 s at 4.2 × 105 kJ/m3 using a continuous mode to create a high grade of dispersion
zinc oxide (ZnO)-NPexposure exposure was Results are are expressed in %inviability in in relation control.The indicated a significant expressed
A recent study showed an accumulation of ZnO-NP after topical application within hair follicles of the skin, leading to apoptosis and DNA damage of hair follicle stem cells (HFSCs) [32]. Consistent with these findings, the long-term observations of ZnO-NP in human mesenchymal stem cells (hMSC) by transmission electron microscopy (TEM) in the present study showed an intracellular accumulation and penetration of the nucleus, which may favor an ongoing cytotoxic and genotoxic effect even after six weeks

Summary

Introduction

Due to their specific physical and chemical characteristics, they are increasingly gaining importance for biological and biomedical applications [1,2,3]. Among the wide range of metal oxide NP, titanium dioxide (TiO2 ) and zinc oxide (ZnO) belong to the most commonly used materials, especially in manufacturing paints and in the cosmetic industry [4]. Previous studies have shown different genotoxic and cytotoxic risk potential of ZnO-NP in several cell lines as well as in primary cells. Some authors declared ZnO-NP to be without any toxic effects [5], there are numerous studies demonstrating genotoxic and cytotoxic effects of ZnO-NP, even at

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