NanoGenotoxicology: present and the future

Mutagenesis, 2017, 32, 1–4 doi:10.1093/mutage/gew066 Commentary Commentary NanoGenotoxicology: present and the future Shareen H. Doak1 and Maria Dusinska2,* 1 In Vitro Toxicology Group, Institute of Life Science and Centre for NanoHealth, Swansea Univeristy Medical School, Swansea University, Singleton Park, Swansea SA2 8PP, Wales, UK and 2Health Effects Group, Department of Environmental Chemistry, NILU- Norwegian Institute for Air Research, N-2027 Kjeller, Norway *To whom correspondence should be addressed. Tel: +47 63898157; Fax: +47 63898050; Email: Received 18 November 2016; Editorial decision 22 November 2016; Accepted 23 November 2016. Abstract This Mutagenesis special issue is on the topic of nanogenotoxicology. It unites a collection of reports that provide insight into: (i) the properties of engineered nanomaterials (ENMs) that contribute to genotoxicity, (ii) the genotoxic mechanisms associated with DNA damage observed in both in vitro and in vivo tests and (iii) the future test systems that will provide more accurate prediction of ENM genotoxicity to support regulatory hazard assessment frameworks. The contributions within therefore provide collective oversight of our current understanding, coupled to future perspectives aimed at overcoming technical hurdles and describing novel analytical methods to further advance the field. Commentary The nanotechnology industrial sector is delivering significant scientific, economic and societal benefits. The industry is therefore expanding, leading to increased human exposure to engineered nanomaterials (ENMs) through direct application (e.g. in cosmetics products, nanomedicine, food additives) and indirectly, due to their increasing abundance in the workplace and environment. Despite this growth, there remain limitations in our knowledge on the human health and environmental impacts of ENM exposure that affect the public’s trust in this new technology. Over recent years, there has been increasing momentum in nanosafety research, boosting our understanding of key factors that govern ENM toxicity and, importantly, the DNA damaging capacity of ENMs. Understanding genotoxicity is vital as substances that damage DNA commonly lead to carcinogenesis. Accumulation of DNA damage in somatic cells is also related to degenerative conditions such as immune dysfunction, while in germ cells DNA damage is associated with malformation or heritable damage in subsequent generations. It is therefore imperative that we reach a detailed understanding of the factors that orchestrate genotoxicity, in addition to determining the modes of action (MoA) and types of DNA damage induced by ENMs in order to support future hazard and risk assessment. An additional complication, however, is that it has become increasingly evident that our current safety testing regimes may require adaptation to predict ENM genotoxicity more accurately. There is also a lack of standardised safety testing protocols suitable for ENMs. Thus, improved test systems are required with a particular focus on in vitro assays to reduce the necessity for animal testing. This special issue therefore unites key elements of strategic research that provide insight into: (i) the properties of ENMs that contribute to genotoxicity, (ii) the genotoxic mechanisms contributing to DNA damage observed within both in vitro and in vivo tests and (iii) the future test systems that will provide more accurate prediction of ENM genotoxicity to support regulatory hazard assessment frameworks. Of the 20 publications in this special issue dedicated to the genotoxicity of ENMs, eight focus on in vivo studies (1–8), nine are in vitro studies (9–17) and three are reviews highlighting future perspectives (18–20). Mechanisms of ENM genotoxicity and their adverse outcome pathways (AOP) have been investigated in recent European and national research projects. Several results from European Commission 7th Framework Programme for Research and Technological Development (FP7) projects such as ENPRA (9), SUNPAP (3), NANoREG (2,10,11) and NanoMILE (14) are included in this issue sharing identical reference ENMs with the same intrinsic properties. Nanotechnology has applications in a very wide range of industrial sectors. Titanium dioxide (TiO2) is the most highly used ENM worldwide, occurring in paints, plastics, papers, inks, foods, pharmaceuticals, toothpaste and cosmetics. There has therefore been extensive research assessing its genotoxicity and MoA; indeed TiO2 is the most frequently investigated ENM in this issue. Three manuscripts describe studies with TiO2 exposure in rats and mice (4–6), and six papers report in vitro effects of TiO2 in several cell lines (9–14). Silver ENMs were evaluated in four in vitro studies (9,10,13,17), © The Author 2016. Published by Oxford University Press on behalf of The UK Environmental Mutagen Society. All rights reserved. For permissions, please e-mail: . 1 2 while carbon-based ENMs (fullerenes, single and multiwall carbon nanotubes) were assessed both in vivo (7,8) and in vitro (9,15,16). Other materials considered in the special issue include silica (1), barium sulfate (BaSO4) (2), cerium oxide (CeO2) (2,10), zinc oxide (ZnO) (9,10), iron oxide (17) and cellulose (3). In these studies, a range of DNA damage endpoints were considered including DNA strand breaks (SBs) measured with the comet assay (with the option of detecting oxidised purines using formamidopyrimidine DNA glycosylase, Fpg), DNA repair, gene mutations in vivo and in vitro, chromosomal damage measured by the micronucleus (MN) assay and cell transformation. Furthermore, novel approaches are presented in several papers including epigenetics (8,16), toxicogenomics approaches (1,4,6,8,14,16), high-throughput assays and miniaturisation (10,11,19). Data generated by the in vivo studies provide insight into both the level of genotoxicity induced in several species by ENMs and their underlying MoA. Pfuhler et al. (1) investigated the genotoxicity of silica ENMs by examining DNA damage and transcriptional regulation in the liver after intravenous administration; an increase in DNA base oxidation was consistent with a MoA involving reactive oxygen species (ROS). Histopathology showed liver damage and neutrophil involvement, while changes in expression of key genes indicated that inflammation and oxidative stress were the primary response, with DNA damage resulting as a secondary effect. The authors also suggested that the concept of a threshold might be applicable in the risk assessment of these materials. In contrast to silica, Cordelli et al. (2) reported that inhalation of CeO2 and BaSO4 ENMs by rats for up to 6 months caused no genotoxicity in a range of blood-based tests (comet assay, flow cytometric Pig-a gene mutation assay and MN assay). It remains to be seen whether the full 2-year exposure to these two ENMs will result in lung tumour formation. Of the in vivo studies conducted in mice, the ass (...truncated)