Christina M. Powers

Silver Nanoparticles Compromise Neurodevelopment in PC12 Cells: Critical Contributions of Silver Ion, Particle Size, Coating, and Composition

Background Silver exposures are rising because of the increased use of silver nanoparticles (AgNPs) in consumer products. The monovalent silver ion (Ag+) impairs neurodevelopment in PC12 cells and zebrafish. Objectives and methods We compared the effects of AgNPs with Ag+ in PC12 cells for neurodevelopmental end points including cell replication, oxidative stress, cell viability, and differentiation. First, we compared citrate-coated AgNPs (AgNP-Cs) with Ag+, and then we assessed the roles of particle size, coating, and composition by comparing AgNP-C with two different sizes of polyvinylpyrrolidone-coated AgNPs (AgNP-PVPs) or silica nanoparticles. Results In undifferentiated cells, AgNP-C impaired DNA synthesis, but to a lesser extent than an equivalent nominal concentration of Ag+, whereas AgNP-C and Ag+ were equally effective against protein synthesis; there was little or no oxidative stress or loss of viability due to AgNP-C. In contrast, in differentiating cells, AgNP-C evoked robust oxidative stress and impaired differentiation into the acetylcholine phenotype. Although the effects of AgNP-PVP showed similarities to those of AgNP-C, we also found significant differences in potencies and differentiation outcomes that depended both on particle size and coating. None of the effects reflected simple physical attributes of nanoparticles, separate from composition or coating, as equivalent concentrations of silica nanoparticles had no detectable effects. Conclusions AgNP exposure impairs neurodevelopment in PC12 cells. Further, AgNP effects are distinct from those of Ag+ alone and depend on size and coating, indicating that AgNP effects are not due simply to the release of Ag+ into the surrounding environment.

Silver Nanoparticles Alter Zebrafish Development and Larval Behavior: Distinct Roles for Particle Size, Coating and Composition

Silver nanoparticles (AgNPs) act as antibacterials by releasing monovalent silver (Ag(+)) and are increasingly used in consumer products, thus elevating exposures in human and wildlife populations. In vitro models indicate that AgNPs are likely to be developmental neurotoxicants with actions distinct from those of Ag(+). We exposed developing zebrafish (Danio rerio) to Ag(+) or AgNPs on days 0-5 post-fertilization and evaluated hatching, morphology, survival and swim bladder inflation. Larval swimming behavior and responses to different lighting conditions were assessed 24h after the termination of exposure. Comparisons were made with AgNPs of different sizes and coatings: 10nm citrate-coated AgNP (AgNP-C), and 10 or 50nm polyvinylpyrrolidone-coated AgNPs (AgNP-PVP). Ag(+) and AgNP-C delayed hatching to a similar extent but Ag(+) was more effective in slowing swim bladder inflation, and elicited greater dysmorphology and mortality. In behavioral assessments, Ag(+) exposed fish were hyperresponsive to light changes, whereas AgNP-C exposed fish showed normal responses. Neither of the AgNP-PVPs affected survival or morphology but both evoked significant changes in swimming responses to light in ways that were distinct from Ag(+) and each other. The smaller AgNP-PVP caused overall hypoactivity whereas the larger caused hyperactivity. AgNPs are less potent than Ag(+) with respect to dysmorphology and loss of viability, but nevertheless produce neurobehavioral effects that highly depend on particle coating and size, rather than just reflecting the release of Ag(+). Different AgNP formulations are thus likely to produce distinct patterns of developmental neurotoxicity.

Silver Impairs Neurodevelopment: Studies in PC12 Cells

Background Exposure to silver is increasing because of silver nanoparticles in consumer products. Objectives and methods Many biological effects of silver entail actions of Ag+ (monovalent silver ions), so we used neuronotypic PC12 cells to evaluate the potential for silver to act as a developmental neurotoxicant, using chlorpyrifos (CPF), a pesticide known to evoke developmental neurotoxicity, as a positive control for comparison. Results In undifferentiated cells, a 1-hr exposure to 10 μM Ag+ inhibited DNA synthesis more potently than did 50 μM CPF; it also impaired protein synthesis but to a lesser extent than its effect on DNA synthesis, indicating a preferential effect on cell replication. Longer exposures led to oxidative stress, loss of viability, and reduced numbers of cells. With the onset of cell differentiation, exposure to 10 μM Ag+ evoked even greater inhibition of DNA synthesis and more oxidative stress, selectively impaired neurite formation without suppressing overall cell growth, and preferentially suppressed development into the acetylcholine phenotype in favor of the dopamine phenotype. Lowering the exposure to 1 μM Ag+ reduced the net effect on undifferentiated cells. However, in differentiating cells, the lower concentration produced an entirely different pattern, enhancing cell numbers by suppressing ongoing cell death and impairing differentiation in parallel for both neurotransmitter phenotypes. Conclusions Our results show that silver has the potential to evoke developmental neurotoxicity even more potently than known neurotoxicants, such as CPF, and that the spectrum of effects is likely to be substantially different at lower exposures that do not show signs of outright toxicity.

Silver exposure in developing zebrafish (Danio rerio): persistent effects on larval behavior and survival.

The increased use of silver nanoparticles in consumer and medical products has led to elevated human and environmental exposures. Silver nanoparticles act as antibacterial/antifungal agents by releasing Ag(+) and recent studies show that Ag(+) impairs neural cell replication and differentiation in culture, suggesting that in vivo exposures could compromise neurodevelopment. To determine whether Ag(+) impairs development in vivo, we examined the effects of exposure on survival, morphological, and behavioral parameters in zebrafish embryos and larvae. We exposed zebrafish from 0 to 5days post-fertilization to concentrations of Ag(+) ranging from 10nM to 100microM in order to assess effects on survival and early embryonic development. We then tested whether concentrations below the threshold for dysmorphology altered larval behavior and subsequent survival. Ag(+) concentrations >or=3microM significantly reduced embryonic survival, whereas 1microM delayed hatching with no effect on survival. Reducing the concentration to as low as 0.1microM delayed the inflation of the swim bladder without causing gross dysmorphology or affecting hatching. At this concentration, swimming activity was impaired, an effect that persisted past the point where swim bladder inflation became normal; in contrast, general motor function was unaffected. The early behavioral impairment was then predictive of subsequent decreases in survival. Ag(+) is a developmental toxicant at concentrations only slightly above allowable levels. At low concentrations, Ag(+) acts as a neurobehavioral toxicant even in the absence of dysmorphology.

Silver exposure in developing zebrafish produces persistent synaptic and behavioral changes

Environmental silver exposures are increasing due to the use of silver nanoparticles, which exert antimicrobial actions by releasing Ag+, a suspected developmental neurotoxicant. We evaluated the long-term neurochemical and behavioral effects of embryonic Ag+ exposure in zebrafish at concentrations that had no overt effects on morphological development. Exposure to 0.03, 0.1 or 0.3 μM Ag+ during the first five days post-fertilization caused elevations in both dopamine and serotonin turnover in the adult zebrafish brain without affecting basal neurotransmitter levels. Consistent with these synaptic effects, Ag+-exposed fish showed a faster acquisition of avoidance behavior in a three-chamber test apparatus, without any change in response latency or overall swimming ability. Our results indicate that Ag+ is a developmental neurotoxicant that causes persistent neurobehavioral effects, reinforcing health concerns about Ag+ released from silver nanoparticles.

Comprehensive Environmental Assessment: A Meta-Assessment Approach

With growing calls for changes in the field of risk assessment, improved systematic approaches for addressing environmental issues with greater transparency and stakeholder engagement are needed to ensure sustainable trade-offs. Here we describe the comprehensive environmental assessment (CEA) approach as a holistic way to manage complex information and to structure input from diverse stakeholder perspectives to support environmental decision-making for the near- and long-term. We further note how CEA builds upon and incorporates other available tools and approaches, describe its current application at the U.S. Environmental Protection Agency, and point out how it could be extended in evaluating a major issue such as the sustainability of biofuels.

Improving the risk assessment of lipophilic persistent environmental chemicals in breast milk

Abstract Lipophilic persistent environmental chemicals (LPECs) have the potential to accumulate within a womans body lipids over the course of many years prior to pregnancy, to partition into human milk, and to transfer to infants upon breastfeeding. As a result of this accumulation and partitioning, a breastfeeding infants intake of these LPECs may be much greater than his/her mothers average daily exposure. Because the developmental period sets the stage for lifelong health, it is important to be able to accurately assess chemical exposures in early life. In many cases, current human health risk assessment methods do not account for differences between maternal and infant exposures to LPECs or for lifestage-specific effects of exposure to these chemicals. Because of their persistence and accumulation in body lipids and partitioning into breast milk, LPECs present unique challenges for each component of the human health risk assessment process, including hazard identification, dose–response assessment, and exposure assessment. Specific biological modeling approaches are available to support both dose–response and exposure assessment for lactational exposures to LPECs. Yet, lack of data limits the application of these approaches. The goal of this review is to outline the available approaches and to identify key issues that, if addressed, could improve efforts to apply these approaches to risk assessment of lactational exposure to these chemicals.

The Nanomaterial Data Curation Initiative: A collaborative approach to assessing, evaluating, and advancing the state of the field

Summary The Nanomaterial Data Curation Initiative (NDCI), a project of the National Cancer Informatics Program Nanotechnology Working Group (NCIP NanoWG), explores the critical aspect of data curation within the development of informatics approaches to understanding nanomaterial behavior. Data repositories and tools for integrating and interrogating complex nanomaterial datasets are gaining widespread interest, with multiple projects now appearing in the US and the EU. Even in these early stages of development, a single common aspect shared across all nanoinformatics resources is that data must be curated into them. Through exploration of sub-topics related to all activities necessary to enable, execute, and improve the curation process, the NDCI will provide a substantive analysis of nanomaterial data curation itself, as well as a platform for multiple other important discussions to advance the field of nanoinformatics. This article outlines the NDCI project and lays the foundation for a series of papers on nanomaterial data curation. The NDCI purpose is to: 1) present and evaluate the current state of nanomaterial data curation across the field on multiple specific data curation topics, 2) propose ways to leverage and advance progress for both individual efforts and the nanomaterial data community as a whole, and 3) provide opportunities for similar publication series on the details of the interactive needs and workflows of data customers, data creators, and data analysts. Initial responses from stakeholder liaisons throughout the nanoinformatics community reveal a shared view that it will be critical to focus on integration of datasets with specific orientation toward the purposes for which the individual resources were created, as well as the purpose for integrating multiple resources. Early acknowledgement and undertaking of complex topics such as uncertainty, reproducibility, and interoperability is proposed as an important path to addressing key challenges within the nanomaterial community, such as reducing collateral negative impacts and decreasing the time from development to market for this new class of technologies.

A systematic evaluation of the potential effects of trichloroethylene exposure on cardiac development.

The 2011 EPA trichloroethylene (TCE) IRIS assessment, used developmental cardiac defects from a controversial drinking water study in rats (Johnson et al. [51]), along with several other studies/endpoints to derive reference values. An updated literature search of TCE-related developmental cardiac defects was conducted. Study quality, strengths, and limitations were assessed. A putative adverse outcome pathway (AOP) construct was developed to explore key events for the most commonly observed cardiac dysmorphologies, particularly those involved with epithelial-mesenchymal transition (EMT) of endothelial origin (EndMT); several candidate pathways were identified. A hypothesis-driven weight-of-evidence analysis of epidemiological, toxicological, in vitro, in ovo, and mechanistic/AOP data concluded that TCE has the potential to cause cardiac defects in humans when exposure occurs at sufficient doses during a sensitive window of fetal development. The study by Johnson et al. [51] was reaffirmed as suitable for hazard characterization and reference value derivation, though acknowledging study limitations and uncertainties.

A web-based tool to engage stakeholders in informing research planning for future decisions on emerging materials.

Prioritizing and assessing risks associated with chemicals, industrial materials, or emerging technologies is a complex problem that benefits from the involvement of multiple stakeholder groups. For example, in the case of engineered nanomaterials (ENMs), scientific uncertainties exist that hamper environmental, health, and safety (EHS) assessments. Therefore, alternative approaches to standard EHS assessment methods have gained increased attention. The objective of this paper is to describe the application of a web-based, interactive decision support tool developed by the U.S. Environmental Protection Agency (U.S. EPA) in a pilot study on ENMs. The piloted tool implements U.S. EPAs comprehensive environmental assessment (CEA) approach to prioritize research gaps. When pursued, such research priorities can result in data that subsequently improve the scientific robustness of risk assessments and inform future risk management decisions. Pilot results suggest that the tool was useful in facilitating multi-stakeholder prioritization of research gaps. Results also provide potential improvements for subsequent applications. The outcomes of future CEAWeb applications with larger stakeholder groups may inform the development of funding opportunities for emerging materials across the scientific community (e.g., National Science Foundation Science to Achieve Results [STAR] grants, National Institutes of Health Requests for Proposals).