Polymyxin B complexation enhances the antimicrobial potential of graphene oxide.

Introduction: The antibacterial activity of graphene oxide (GO) has been widely explored and tested against various pathogenic bacterial strains. Although antimicrobial activity of GO against planktonic bacterial cells was demonstrated, its bacteriostatic and bactericidal effect alone is not sufficient to damage sedentary and well protected bacterial cells inside biofilms. Thus, to be utilized as an effective antibacterial agent, it is necessary to improve the antibacterial activity of GO either by integration with other nanomaterials or by attachment of antimicrobial agents. In this study, antimicrobial peptide polymyxin B (PMB) was adsorbed onto the surface of pristine GO and GO functionalized with triethylene glycol. Methods: The antibacterial effects of the resulting materials were examined by evaluating minimum inhibitory concentration, minimum bactericidal concentration, time kill assay, live/dead viability staining and scanning electron microscopy. Results and discussion: PMB adsorption significantly enhanced the bacteriostatic and bactericidal activity of GO against both planktonic cells and bacterial cells in biofilms. Furthermore, the coatings of PMB-adsorbed GO applied to catheter tubes strongly mitigated biofilm formation, by preventing bacterial adhesion and killing the bacterial cells that managed to attach. The presented results suggest that antibacterial peptide absorption can significantly enhance the antibacterial activity of GO and the resulting material can be effectively used not only against planktonic bacteria but also against infectious biofilms.

Synergistic effects of Rapamycin and Fluorouracil to treat a gastric tumor in a PTEN conditional deletion mouse model.

The tumor suppressor gene phosphatase and tensin homolog (PTEN) in PI3K/Akt/mTOR pathway is essential in inhibiting tumor growth and metastasis. However, whether the mutation of PTEN gene could induce tumorigenesis and impact the treatment of gastric cancer is still unclear. The purpose of the study was to investigate the combined treatment of gastric tumorigenesis using Rapamycin and Fluorouracil (5-Fu) through interfering with the Akt/mTOR pathway in a mouse model with PTEN conditional deletion. Three groups of mice were exposed for 5 days to Rapamycin and 5-Fu separately and together. The gene expression of the Akt/mTOR pathway, the protein expression of caspase-3 and p-Akt, p-S6K and p-4EBP1, and the pathological changes in stomachs were analyzed. Our study demonstrates that the conditional PTEN deletion in the cells of glandular stomach induces hyperplastic gastric tumors in mice. The combined Rapamycin administration with 5-Fu resulted in better outcomes than their separate administration for the treatment of gastric cancer by inhibiting the mTOR signal pathway. Our study indicates that Rapamycin has a synergistic interaction with chemotherapeutic 5-Fu, and demonstrates a potential therapeutic combination treatment on glandular stomach tumor with PTEN functional absence or aberrantly activated Akt/mTOR pathway. It provides important insights into the inhibition of the Akt/mTOR pathway in gastric cancer clinical therapy.

Transformation and Cytotoxicity of Surface-Modified Silver Nanoparticles Undergoing Long-Term Aging.

Silver nanoparticles (AgNPs) are constituents of many consumer products, but the future of their production depends on ensuring safety. The stability of AgNPs in various physiological solutions and aging in storage may affect the accuracy of predicted nanoparticle toxicity. The goal of this study was to simulate the transformation of AgNPs in different media representatives to the life cycle in the environment and to identify their toxicity to Hepa1c1c7 cells in a long-term aging process. AgNPs coated with citrate, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and branched polyethyleneimine (BPEI) were studied. Our results show that the exposure media had a significant impact on the transformation of AgNPs. Citrate-coated AgNPs showed significant aggregation in phosphate-buffered saline. The aging of AgNPs in optimal storage showed that the charge-stabilized particles (citrate) were more unstable, with significant aggregation and shape changes, than sterically stabilized particles (PEG AgNPs, PVP AgNPs). The BPEI AgNPs showed the highest dissolution of AgNPs, which induced significantly increased toxicity to Hepa1c1c7 cells. Overall, our findings showed that storage and media of AgNPs influenced the transformation of AgNPs and that the resulting changes in the AgNPs' physicochemical properties influenced their toxicity. Our study contributes to the understanding of AgNPs' transformations under realistic exposure scenarios and increasing the predictability of risk assessments.

2,3,7,8-Tetrachloodibenzo-p-dioxin affects the differentiation of CD4 helper T cell.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins, is a persistent and ubiquitous environmental contaminant. Although the immunotoxic effects of TCDD have been reported, the mechanisms underlying these effects are still unclear. In this study, we have determined the toxic effects of TCDD on thymocytes and splenic T cells with in vitro cell culture systems. Magnetically isolated mouse splenic Th cells, Treg cells and the mixed spleen lymphocytes (SLC) were cultured and treated with TCDD and the differentiation of CD4 Th cells was determined by flow cytometery. Our results showed that different concentrations of TCDD caused immunotoxic effects through different toxicological mechanisms in both the purified mouse splenic Th cells and the mixed SLC. The low dose exposure to TCDD triggered regulatory effects in the immune system, while the high dose TCDD exposure resulted in severe immune toxicity. Notably, a decline of Treg subset was observed, suggesting an imbalanced immune regulation by TCDD treatment, as well as a possible decrease of TCDD's indirect effects on bystander immune cells. Our CD4 Th subset co-culture experiments showed that TCDD-induced pathobiology depended on immune cell balance, suggesting that cytokine-induced microenvironments further modulated toxic effects associated with TCDD exposure.

Biomolecule-corona formation confers resistance of bacteria to nanoparticle-induced killing: Implications for the design of improved nanoantibiotics.

Multidrug-resistant bacterial infections are a global health threat. Nanoparticles are thus investigated as novel antibacterial agents for clinical practice, including wound dressings and implants. We report that nanoparticles' bactericidal activity strongly depends on their physical binding to pathogens, including multidrug-resistant primary clinical isolates, such as Staphylococcus aureus, Klebsiella pneumoniae or Enterococcus faecalis. Using controllable nanoparticle models, we found that nanoparticle-pathogen complex formation was enhanced by small nanoparticle size rather than material or charge, and was prevented by 'stealth' modifications. Nanoparticles seem to preferentially bind to Gram-positive pathogens, such as Listeria monocytogenes, S. aureus or Streptococcus pyrogenes, correlating with enhanced antibacterial activity. Bacterial resistance to metal-based nanoparticles was mediated by biomolecule coronas acquired in pathophysiological environments, such as wounds, the lung, or the blood system. Biomolecule corona formation reduced nanoparticles' binding to pathogens, but did not impact nanoparticle dissolution. Our results provide a mechanistic explanation why nano-sized antibiotics may show reduced activity in clinically relevant environments, and may inspire future nanoantibiotic designs with improved and potentially pathogen-specific activity.

Probabilistic risk assessment of emerging materials: case study of titanium dioxide nanoparticles.

The development and use of emerging technologies such as nanomaterials can provide both benefits and risks to society. Emerging materials may promise to bring many technological advantages but may not be well characterized in terms of their production volumes, magnitude of emissions, behaviour in the environment and effects on living organisms. This uncertainty can present challenges to scientists developing these materials and persons responsible for defining and measuring their adverse impacts. Human health risk assessment is a method of identifying the intrinsic hazard of and quantifying the dose-response relationship and exposure to a chemical, to finally determine the estimation of risk. Commonly applied deterministic approaches may not sufficiently estimate and communicate the likelihood of risks from emerging technologies whose uncertainty is large. Probabilistic approaches allow for parameters in the risk assessment process to be defined by distributions instead of single deterministic values whose uncertainty could undermine the value of the assessment. A probabilistic approach was applied to the dose-response and exposure assessment of a case study involving the production of nanoparticles of titanium dioxide in seven different exposure scenarios. Only one exposure scenario showed a statistically significant level of risk. In the latter case, this involved dumping high volumes of nano-TiO2 powders into an open vessel with no personal protection equipment. The probabilistic approach not only provided the likelihood of but also the major contributing factors to the estimated risk (e.g. emission potential).

Bioaccumulation and effects of sediment-associated gold- and graphene oxide nanoparticles on Tubifex tubifex.

With the development of nanotechnology, gold (Au) and graphene oxide (GO) nanoparticles have been widely used in various fields, resulting in an increased release of these particles into the environment. The released nanoparticles may eventually accumulate in sediment, causing possible ecotoxicological effects to benthic invertebrates. However, the impact of Au-NPs and GO-NPs on the cosmopolitan oligochaete, Tubifex tubifex, in sediment exposure is not known. Mortality, behavioral impact (GO-NP and Au-NP) and uptake (only Au-NP) of sediment-associated Au-NPs (4.9±0.14nm) and GO-NPs (116±0.05nm) to T. tubifex were assessed in a number of 5-day exposure experiments. The results showed that the applied Au-NP concentrations (10 and 60µg Au/g dry weight sediment) had no adverse effect on T. tubifex survival, while Au bioaccumulation increased with exposure concentration. In the case of GO-NPs, no mortality of T. tubifex was observed at a concentration range of 20 and 180µg GO/g dry weight sediment, whereas burrowing activity was significantly reduced at 20 and 180µg GO/g dry weight sediment. Our results suggest that Au-NPs at 60µg Au/g or GO-NPs at 20 and 180µg GO/g were detected by T. tubifex as toxicants during short-term exposures.

Multi-criteria decision analysis applied to harmful algal bloom management: A case study.

Harmful algal blooms (HABs) have received greater attention in recent years due to an increase in the frequency of outbreaks and a growing potential for blooms to exact considerable economic losses and negatively impact ecosystem health. Human activity has been shown to intensify HAB outbreaks through increased eutrophication, elevated local air and water temperatures, disturbance of the thermal stratification of lakes, and modification of local hydrology. With the advent of new remediation technologies and a better understanding of the ecological factors affecting HABs, mitigating the adverse effects of HABs has become more feasible than ever before but still requires balancing mitigation efficiency, environmental impacts, costs, and stakeholder needs. In the present paper, we discuss potential HAB management solutions and propose using a Multi-Criteria Decision Analysis (MCDA) framework to analyze the perspectives and priorities of various stakeholders as they pertain to 4 major considerations for HAB mitigation: human health, environmental impact, social impact, and technical feasibility. A hypothetical case study of an HAB-affected lake is used to demonstrate how stakeholders may prioritize HAB management alternatives within the MCDA framework. Integr Environ Assess Manag 2017;13:631-639. © 2016 SETAC.

Probabilistic approach for assessing infants' health risks due to ingestion of nanoscale silver released from consumer products.

Silver nanoparticles (n-Ag) are widely used in consumer products and many medical applications because of their unique antibacterial properties. Their use is raising concern about potential human exposures and health effects. Therefore, it is informative to assess the potential human health risks of n-Ag in order to ensure that nanotechnology-based consumer products are deployed in a safe and sustainable way. Even though toxicity studies clearly show the potential hazard of n-Ag, there have been few attempts to integrate hazard and exposure assessments to evaluate risks. The underlying reason for this is the difficulty in characterizing exposure and the lack of toxicity studies essential for human health risk assessment (HHRA). Such data gaps introduce significant uncertainty into the risk assessment process. This study uses probabilistic methods to assess the relative uncertainty and potential risks of n-Ag exposure to infants. In this paper, we estimate the risks for infants potentially exposed to n-Ag through drinking juice or milk from sippy cups or licking baby blankets containing n-Ag. We explicitly evaluate uncertainty and variability contained in available dose-response and exposure data in order to make the risk characterization process transparent. Our results showed that individual margin of exposures for oral exposure to sippy cups and baby blankets containing n-Ag exhibited minimal risk.

Predicting toxic potencies of metal oxide nanoparticles by means of nano-QSARs.

BACKGROUND: The enormous physicochemical and structural diversity of metal oxide nanoparticles (MeONPs) poses significant challenges to the testing of their biological uptake, biodistribution, and effects that can be used to develop understanding of key nano-bio modes of action. This has generated considerable uncertainties in the assessment of their human health and environmental risks and has raised concerns about the adequacy of their regulation. In order to surpass the extremely resource intensive case-by-case testing, intelligent strategies combining testing methods and non-testing predictive modeling should be developed. METHODS: The quantitative structure-activity relationship (QSARs) in silico tools can be instrumental in understanding properties that affect the potencies of MeONPs and in predicting toxic responses and thresholds of effects. RESULTS: The present study proposes a predictive nano-QSAR model for predicting the cytotoxicity of MeONPs. The model was applied to test the relationships between 26 physicochemical properties of 51 MeONPs and their cytotoxic effects in Escherichia coli. The two parameters, enthalpy of formation of a gaseous cation (▵Hme+) and polarization force (Z/r), were elucidated to make a significant contribution for the toxic effect of these MeONPs. The study also proposed the mechanisms of toxic potency in E. coli through the model, which indicated that the MeONPs as well as their released metal ions could collectively induce DNA damage and cell apoptosis. SIGNIFICANCE: These findings may provide an alternative method for prioritizing current and future MeONPs for potential in vivo testing, virtual prescreening and for designing environmentally benign nanomaterials.

Demonstrating approaches to chemically modify the surface of Ag nanoparticles in order to influence their cytotoxicity and biodistribution after single dose acute intravenous administration.

With the advance in material science and the need to diversify market applications, silver nanoparticles (AgNPs) are modified by different surface coatings. However, how these surface modifications influence the effects of AgNPs on human health is still largely unknown. We have evaluated the uptake, toxicity and pharmacokinetics of AgNPs coated with citrate, polyethylene glycol, polyvinyl pyrolidone and branched polyethyleneimine (Citrate AgNPs, PEG AgNPs, PVP AgNPs and BPEI AgNPs, respectively). Our results demonstrated that the toxicity of AgNPs depends on the intracellular localization that was highly dependent on the surface charge. BPEI AgNPs (ζ potential = +46.5 mV) induced the highest cytotoxicity and DNA fragmentation in Hepa1c1c7. In addition, it showed the highest damage to the nucleus of liver cells in the exposed mice, which is associated with a high accumulation in liver tissues. The PEG AgNPs (ζ potential = -16.2 mV) showed the cytotoxicity, a long blood circulation, as well as bioaccumulation in spleen (34.33 µg/g), which suggest better biocompatibility compared to the other chemically modified AgNPs. Moreover, the adsorption ability with bovine serum albumin revealed that the PEG surface of AgNPs has an optimal biological inertia and can effectively resist opsonization or non-specific binding to protein in mice. The overall results indicated that the biodistribution of AgNPs was significantly dependent on surface chemistry: BPEI AgNPs > Citrate AgNPs = PVP AgNPs > PEG AgNPs. This toxicological data could be useful in supporting the development of safe AgNPs for consumer products and drug delivery applications.

Bioaccumulation, toxicokinetics, and effects of copper from sediment spiked with aqueous Cu, nano-CuO, or micro-CuO in the deposit-feeding snail, Potamopyrgus antipodarum.

The present study examined the relative importance of copper (aqueous Cu and CuO particles of different sizes) added to sediment to determine the bioaccumulation, toxicokinetics, and effects in the deposit feeder Potamopyrgus antipodarum. In experiment 1, the bioaccumulation of Cu (240 µg Cu/g dry wt of sediment) added as aqueous Cu (CuCl2 ), nano- (6 nm, 100 nm), or micro- (<5 µm) CuO particles in adult snails was measured. In experiment 2, a more comprehensive analysis of the toxicokinetics of Cu (aqueous Cu, 6 nm, or 100 nm) was conducted. In experiment 3, the effects of Cu form (aqueous Cu and 6 nm CuO) on juvenile growth and survival at 0, 30, 60, 120, and 240 µg Cu/g dry weight sediment were assessed. Snails took up less of the 5-µm CuO particles than nano-CuO or aqueous Cu. A substantial fraction of Cu taken up was associated with shell, and this was rapidly lost when snails were transferred to clean sediment. Net uptake rates from sediment amended with 6 nm CuO and aqueous Cu were significantly higher (∼40-50%) than from sediment amended with 100 nm CuO. During 2 wk of depuration, there were no significant differences in depuration rates (kd ) among forms (aqueous Cu: kd = -0.12 wk(-1) ; 6 nm CuO: kd = -0.22 wk(-1) ; 100 nm CuO: kd = -0.2 wk(-1) ). Average juvenile growth was reduced by 0.11 mm (41%) at measured exposure concentrations of 127.2 µg Cu/g dry weight sediment for aqueous Cu and 71.9 µg Cu/g dry weight sediment for 6 nm CuO compared with control; however, differences between forms were not statistically significant. Juvenile snails in the highest exposure concentrations (aqueous Cu and 6-nm CuO groups pooled) reduced their growth by 0.18 mm on average (67%) compared with the control group. Although we observed minor differences in toxicity among Cu forms, effects on juvenile snail growth occurred at bulk sediment concentrations lower than those in the Canadian interim sediment quality guidelines. Characterization of the CuO particles showed that particle size distributions of commercially prepared particles deviated substantially from the manufacturers' specifications and highlighted the importance of fully characterizing particles when using them in toxicity tests.

Effects of sediment-associated copper to the deposit-feeding snail, Potamopyrgus antipodarum: a comparison of Cu added in aqueous form or as nano- and micro-CuO particles.

Increasing use of engineered nanoparticles (NPs) is likely to result in release of these particles to the aquatic environment where the NPs may eventually accumulate in sediment. However, little is known about the potential ecotoxicity of sediment-associated engineered NPs. We here consider the case of metal oxide NPs using CuO to understand if the effects of NPs differ from micron-sized particles of CuO and aqueous Cu (CuCl2). To address this issue, we compared effects of copper added to the sediment as aqueous Cu, nano- (6 nm) and micro- (<5 µm) CuO particles on the deposit-feeding snail, Potamopyrgus antipodarum. Effects were assessed as mortality, specific growth rate, feeding rate, reproduction, and bioaccumulation after 8 weeks of exposure to nominal concentrations of 0, 30, 60, 120 and 240 µg Cu/g dry weight sediment. The results demonstrate that copper added to sediment as nano-CuO had greater effects on growth, feeding rate, and reproduction of P. antipodarum than copper added as micro-CuO or aqueous Cu. P. antipodarum accumulated more copper in the nano-CuO treatment than in aqueous Cu or micro-CuO treatments, indicating that consideration of metal form may be important when assessing risks of metals to the aquatic environment.