Academic journal article Environmental Health Perspectives

Effects of Laser Printer-Emitted Engineered Nanoparticles on Cytotoxicity, Chemokine Expression, Reactive Oxygen Species, DNA Methylation, and DNA Damage: A Comprehensive in Vitro Analysis in Human Small Airway Epithelial Cells, Macrophages, and Lymphoblasts

Academic journal article Environmental Health Perspectives

Effects of Laser Printer-Emitted Engineered Nanoparticles on Cytotoxicity, Chemokine Expression, Reactive Oxygen Species, DNA Methylation, and DNA Damage: A Comprehensive in Vitro Analysis in Human Small Airway Epithelial Cells, Macrophages, and Lymphoblasts

Article excerpt

Introduction

The recent incorporation of engineered nanomaterials (ENMs) into toner formulations has potential health implications based on consumer exposure to released particulate matter (PM) from laser-based printing equipment. Laser printers are widely used in office and home environments, and there has been an exponential increase of market sales in recent years (IDC 2014). Recent studies have shown that emissions from this growing technology comprise a variety of pollutants including PM, semi-volatile organic compounds (sVOCs), and other gaseous pollutants (He et al. 2007; Morawska et al. 2009; Wang et al. 2012).

Recently, our group developed a laboratory-based printer exposure generation system (PEGS) that allows generation and sampling of airborne printer-emitted particles (PEPs) for subsequent physicochemical, morphological, and toxicological analysis (Pirela et al. 2014). This platform was used to evaluate emission profiles from 11 laser printers that are currently on the market. The study showed that the particle concentration of PEPs varied across printers/manufacturers, with printers emitting as much as 1.3 million particles/[cm.sup.3] with diameters < 200 nm (Pirela et al. 2014). The detailed assessment of both toners and PEPs confirmed the presence of nanoscale materials in the airborne state and revealed the complex chemistry of these materials, which included elemental/ organic carbon and inorganic compounds (e.g., metals, metal oxides). These findings confirmed that toners are nanoenabled products (NEPs) (Pirela et al. 2015).

Both in vitro and in vivo toxicological assays may help characterize the effects of laser printer emissions and toners on the respiratory system. However, the results obtained to date are contradictory. Notably, the toxicity of PEPs remains poorly characterized primarily because most studies have used toner powders rather than PEPs. For example, Gminski et al. (2011) reported that toner powders exhibited genotoxic potential on epithelial lung cells. Similar in vitro assays using an air/liquid interphase system showed significant cyto- and genotoxicity (Tang et al. 2012). In contrast, cell magnetometry analysis of alveolar macrophages exposed to toner powder revealed no effects (Furukawa et al. 2002). An even smaller number of in vivo toxicological studies have evaluated the effects of exposure to PEPs. Bai et al. (2010) reported that mice exposed to printer toner particles showed significant pulmonary inflammation, damage to the epithelial-capillary barrier, and enhanced cell permeability. Comparable inflammatory and fibrotic responses were also observed in rats exposed to toner powders (Morimoto et al. 2013).

Concerns continue to be raised with regard to the possible epigenetic effects associated with PEP inhalation exposure. In general, the ability of ENMs to affect the cellular epigenome remains largely unexplored. One important epigenetic mechanism, DNA methylation, can regulate the proper expression of genetic information in a sex-, tissue-, and cell type-dependent manner (Jones 2012). Additionally, DNA methylation plays a central role in regulating the expression of transposable elements (TEs) that comprise a large part of the eukaryotic genome (Smith et al. 2012). TEs are essential regulators of the stability and proper function of the genome, including the expression of genetic information and chromatin structure. Numerous studies indicate that exposure to various environmental stressors, including PM, may compromise the methylome and TEs (Baccarelli et al. 2009; Madrigano et al. 2011). An in vitro study by Gong et al. (2010) concluded that short-term exposure of human keratinocytes to nanomaterials might result in alterations of both global DNA methylation patterns and the DNA methylation machinery. However, the epigenetic effects of ENMs contained in PEPs remain largely unknown, and, to our knowledge, the use of in vitro systems to characterize epigenetic effects resulting from exposure to PEPs has not yet been done. …

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