| Use of silver nanoparticles (AgNPs) is ubiquitous, due to their unique antimicrobial properties. AgNPs are commonly employed in pharmaceuticals, medical imaging, medical devices, fuel cells, water purification, food preservation, cosmetics, clothing (adult and infant), food storage containers, baby bottles, mattresses, pillows, toothpaste, toilet paper, yoga mats, air conditioners, computers (keyboards), carpet, wallpaper, and many more consumer products. As nanoparticle use increases, so does the potential for human exposure both in the occupational setting, as well as, in the general public, which consumes AgNP goods.;Since bulk silver has been used for centuries, AgNPs have been deemed safe by default. However, nano-sized particles have significantly different properties than larger sized analogous particles and due to their unique physicochemical properties (e.g. small size, large surface area, increased redox activity, and surface hydrophobicity) these particles have an increased potential to initiate toxic effects in mammalian organisms, as well as, in the environment.;Toxicity and safety testing of AgNPs is gravely lacking. Recent in vitro studies suggest that AgNPs post a threat to human health, however in vivo studies are needed to fully delineate and either support or refute recent questions and hypotheses raised by in vitro work. Further, there are critical gaps in our understanding of environmental epigenetics, in particular, concerning the existence of epigenetic alterations occurring from exposure to environmental toxicants, as well as, the time points at which these changes occur. Legitimate concerns exist, regarding the potential adverse health effects from AgNP exposure, and therefore, research that addresses specific critical questions concerning the toxicity and hazards of these technologies is vital to the advancement of the field and the protection of public health.;This study examined the hypothesis that: inhaled AgNPs cause lung and extrapulmonary organ dysfunction via molecular aberrations in gene expression, which are likely mediated by alterations in gene promoter methylation. These molecular aberrations are likely occurring in oxidative stress and inflammatory pathways, and further impact mitochondrial function and membrane integrity. Male FVB/NJ mice were exposed to AgNPs generated using a Palas spark generator, via nose only inhalation, at either a single 4 hr exposure of 1 mg/m3, or at an exposure of 0.25 mg/m3 for 30 days. At 24hr, 48hr, and 7d post-exposure, animals were euthanized and blood, lavage and tissue were collected, and fresh mitochondria was isolated from lung and liver tissue within one hour of sacrifice. Lavage was analyzed for total cell counts, differential cell analysis, and protein levels. Fifty-four samples, isolated from lung and liver tissue, were used in Affymetrix Mouse Gene 2.0 ST Array Analysis. Microarrays were analyzed using Agilent GeneSpring and results verified by real-time RT-PCR. DNA isolated from lung and liver tissue was used in the analysis of gene-specific promoter methylation using Epitect Methyl II arrays. Inner mitochondrial membrane integrity was quantified using JC-1 staining and fluorescence microscopy. Outer mitochondrial membrane integrity was examined by measuring cytochrome c oxidase activity in the presence and absence of n-dodecyl beta-D-maltoside. Highly significant alterations in gene expression were observed in response to both acute and subchronic AgNP exposure, in both lung and liver tissues, in a time dependent manner. In addition, AgNP exposure resulted in significant decreases in both inner and outer mitochondrial membrane integrity. These experiments suggest that exposure to inhaled AgNPs results in gene expression alterations, which may be regulated by alterations in promoter methylation, in a time dependent manner. Further, cellular uptake of inhaled AgNPs, in lung and extra-pulmonary organs results in detrimental effects on mitochondrial membrane integrity. |
