Hormetic dose-responses in nanotechnology studies

Toxicity evaluation of silver nanoparticles synthesized from naringin flavonoid on human promyelocytic leukemic cells and human blood cells

Increasing applications of silver nanoparticles (AgNPs) in multiple products like cosmetics, medicines, drugs, paints, and other new materials have raised concern for their toxic effects on living beings and the surrounding environment. In the present study, cytotoxicity and genotoxicity of AgNPs synthesized using plant flavonoid (Naringin) as a reducing agent were investigated on human promyelocytic leukemic (HL-60) cells and human blood as an in vitro model. The LC50 of AgNPs was found to be 4.85 µM. Dose-dependent increase in cell death and caspase activity was observed in the presence of AgNPs. The comet assay showed a 60%-70% (p < .05) increase in tail DNA at 0.48 and 0.96 µM AgNPs. CBMN in PBMCs also confirmed the genotoxic potential of AgNPs-induced DNA damage. AgNPs resulted in 1.5-1.54 fold (p < .05) increase in the level of ROS in HL-60 cells after 12 h of exposure. AgNP showed toxicity in human cells through ROS generation and cellular damage through membrane dysfunction, caspase activation, apoptosis, and DNA damage.

The challenges of defining hormesis in epidemiological studies: The case of radiation hormesis

In the current radiation protection system, preventive measures and occupational exposure limits for controlling occupational exposure to ionizing radiation are based on the linear no-threshold extrapolation model. However, currently an increasing body of evidence indicates that this paradigm predicts very poorly biological responses in the low-dose exposure region. In addition, several in vitro and in vivo studies demonstrated the presence of hormetic dose response curves correlated to ionizing radiation low exposure. In this regard, it is noteworthy that also the findings of different epidemiological studies, conducted in different categories of occupationally exposed workers (e.g., healthcare, nuclear industrial and aircrew workers), observed lower rates of mortality and/or morbidity from cancer and/or other diseases in exposed workers than in unexposed ones or in the general population, then suggesting the possible occurrence of hormesis. Nevertheless, these results should be considered with caution since the identification of hormetic response in epidemiological studies is rather challenging because of a number of major limitations. In this regard, some of the most remarkable shortcomings found in epidemiological studies performed in workers exposed to ionizing radiation are represented by lack or inadequate definition of exposure doses, use of surrogates of exposure, narrow dose ranges, lack of proper control groups and poor evaluation of confounding factors. Therefore, considering the valuable role and contribution that epidemiological studies might provide to the complex risk assessment and management process, there is a clear and urgent need to overcome the aforementioned limits in order to achieve an adequate, useful and more real-life risk assessment that should also include the key concept of hormesis. Thus, in the present conceptual article we also discuss and provide possible approaches to improve the capacity of epidemiological studies to identify/define the hormetic response and consequently improve the complex process of risk assessment of ionizing radiation at low exposure doses.

Exposure to Oxidized Multi-Walled CNTs Can Lead to Oxidative Stress in the Asian Freshwater Clam Corbicula fluminea (Müller, 1774)

The increasing attention that carbon-based nanomaterials have attracted due to their distinctive properties makes them one of the most widely used nanomaterials for industrial purposes. However, their toxicity and environmental effects must be carefully studied, particularly regarding aquatic biota. The implications of these carbon-based nanomaterials on aquatic ecosystems, due to their potential entry or accidental release during manufacturing and treatment processes, need to be studied because their impacts upon living organisms are not fully understood. In this research work, the toxicity of oxidized multi-walled carbon nanotubes (Ox-MWCNTs) was measured using the freshwater bivalve (Corbicula fluminea) after exposure to different concentrations (0, 0.1, 0.2, and 0.5 mg·L-1 Ox-MWCNTs) for 14 days. The oxidized multi-walled carbon nanotubes were analyzed (pH, Raman microscopy, high-resolution electron microscopy, and dynamic light scattering), showing their properties and behavior (size, aggregation state, and structure) in water media. The antioxidant defenses in the organism's digestive gland and gills were evaluated through measuring oxidative stress enzymes (glutathione-S-transferase, catalase, and superoxide dismutase), lipid peroxidation, and total ubiquitin. The results showed a concentration-dependent response of antioxidant enzymes (CAT and GST) in both tissues (gills and digestive glands) for all exposure periods in bivalves exposed to the different concentrations of oxidized multi-walled carbon nanotubes. Lipid peroxidation (MDA content) showed a variable response with the increase in oxidized multi-walled carbon nanotubes in the gills after 7 and 14 exposure days. Overall, after 14 days, there was an increase in total Ub compared to controls. Overall, the oxidative stress observed after the exposure of Corbicula fluminea to oxidized multi-walled carbon nanotubes indicates that the discharge of these nanomaterials into aquatic ecosystems can affect the biota as well as potentially accumulate in the trophic chain, and may even put human health at risk if they ingest contaminated animals.

Low-dose chemical stimulation and pest resistance threaten global crop production

Pesticide resistance increases and threatens crop production sustainability. Chemical contamination contributes to the development of pest resistance to pesticides, in part by causing stimulatory effects on pests at low sub-toxic doses and facilitating the spread of resistance genes. This article discusses hormesis and low-dose biological stimulation and their relevance to crop pest resistance. It highlights that a holistic approach is needed to tackle pest resistance to pesticides and reduce imbalance in accessing food and improving food security in accordance with the UN's Sustainable Development Goals. Among others, the effects of sub-toxic doses of pesticides should be considered when assessing the impact of synthetic and natural pesticides, while the promotion of alternative agronomical practices is needed to decrease the use of agrochemicals. Potential alternative solutions include camo-cropping, exogenous application of phytochemicals that are pest-suppressing or -repelling and/or attractive to carnivorous arthropods and other pest natural enemies, and nano-technological innovations. Moreover, to facilitate tackling of pesticide resistance in poorer countries, less technology-demanding and low-cost practices are needed. These include mixed cropping systems, diversification of cultures, use of 'push-pull cropping', incorporation of flower strips into cultivations, modification of microenvironment, and application of beneficial microorganisms and insects. However, there are still numerous open questions, and more research is needed to address the ecological and environmental effects of many of these potential solutions, with special reference to trophic webs.

The Effect of Silver Nanoparticle Addition on Micropropagation of Apricot Cultivars (Prunus armeniaca L.) in Semisolid and Liquid Media

Silver nanoparticles (AgNPs) are novel compounds used as antimicrobial and antiviral agents. In addition, AgNPs have been used to improve the growth of different plants, as well as the in vitro multiplication of plant material. In this work the effect of AgNPs on in vitro growth of 'Canino' and 'Mirlo Rojo' cultivars, as well as the leaf ion composition, are studied. Different concentrations of AgNPs (0, 25, 50, 75 and 100 mg L^-1) were added to two culture systems: semisolid medium with agar (SSM) in jars and liquid medium in temporary immersion system (TIS). Proliferation (number of shoots), shoot length, productivity (number of shoot × average length), leaf surface, fresh and dry weight were measured. Additionally, the silver and other ion accumulation in the leaves were evaluated by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. The productivity of 'Canino' and 'Mirlo Rojo' decreased when increasing the concentration of AgNPs in the semisolid medium. However, the use of AgNPs in the TIS improved the proliferation and productivity of 'Canino' and Mirlo Rojo', increasing biomass production, and the concentration of nutrients in the plants, although these effects are genotype-dependent. TISs are the best system for introducing silver into shoots, the optimum concentration being 50 mg L^-1 for 'Canino' and 75 mg L^-1 for 'Mirlo Rojo'. Principal component analysis, considering all the analyzed ions along the treatments, separates samples in two clear groups related to the culture system used. The use of bioreactors with a liquid medium has improved the productivity of 'Canino' and 'Mirlo Rojo' in the proliferation stage, avoiding hyperhydration and other disorders. The amount of metallic silver that penetrates apricot plant tissues depends on the culture system, cultivar and concentration of AgNPs added to the culture medium. Silver ion accumulation measured in the shoots grown in the TIS was higher than in shoots micropropagated in a semisolid medium, where it is barely detectable. Furthermore, AgNPs had a beneficial effect on plants grown in TIS. However, AgNPs had a detrimental effect when added to a semisolid medium.

Protective Effect of Indomethacin-loaded Polymeric Nanoparticles Against Oxidative Stress-Induced Cytotoxicity in Human Breast Adenocarcinoma Cell Model

Introduction: Anti-inflammatory drugs are being utilized to treat cancer because of its inflammatory microenvironment. Objective: The objective of this study is to investigate the antioxidant potential of indomethacin and its genotoxicity, since free or loaded in polymeric nanocapsules using MCF-7 (human breast cancer) cells as an in vitro model. Method: Development of indomethacin-loaded polyepsiloncaprolactone (PCL) nanocapsules by interfacial deposition method. It is characterized by pH determination by potentiometer, mean diameter and polydispersity index by dynamic light scattering; zeta potential by electrophoretic mobility; encapsulation efficacy by high performance liquid chromatography method; corona effect formation; 2ʹ,7ʹ-dichlorofluorescin diacetate (DCFH-DA) method by spectrofluorimetric assay; nitric oxide (NO) determination by spectrophotometric and genotoxicity assay by plasmid DNA cleavage method. Results: The results showed a mild acidic pH (4.78 ± 0.10), sizes around 200 nm and PDI<0.2 with a zeta potential around -20 mV and encapsulation efficiency of 99% (1 mg mL-1), showing a dose-dependent corona formation profile in 24h incubation. Conclusion: DCFH-DA assay showed no production of reactive oxygen species (ROS) while NO determination showed that Ind-OH-NC from 26.7 to 100 μM increased reactive nitrogen species (RNS), demonstrating antioxidant potential against MCF-7 cells. No sample at the concentrations evaluated induced DNA cleavage, being considered a safe treatment.

Hormetic dose responses induced by antibiotics in bacteria: A phantom menace to be thoroughly evaluated to address the environmental risk and tackle the antibiotic resistance phenomenon

The environmental contamination of antibiotics caused by their over or inappropriate use is a major issue for environmental and human health since it can adversely impact the ecosystems and promote the antimicrobial resistance. Indeed, considering that in the environmental matrices these drugs are present at low levels, the possibility that bacteria exhibit a hormetic response to increase their resilience when exposed to antibiotic subinhibitory concentrations might represent a serious threat. Information reported in this review showed that exposure to different types of antibiotics, either administered individually or in mixtures, is capable of exerting hormetic effects on bacteria at environmentally relevant concentrations. These responses have been reported regardless of the type of bacterium or antibiotic, thus suggesting that hormesis would be a generalized adaptive mechanism implemented by bacteria to strengthen their resistance to antibiotics. Hormetic effects included growth, bioluminescence and motility of bacteria, their ability to produce biofilm, but also the frequency of mutation and plasmid conjugative transfer. The evaluation of quantitative features of antibiotic-induced hormesis showed that these responses have both maximum stimulation and dose width characteristics similar to those already reported in the literature for other stressors. Notably, mixtures comprising individual antibiotic inducing stimulatory responses might have distinct combined effects based on antagonistic, synergistic or additive interactions between components. Regarding the molecular mechanisms of action underlying the aforementioned effects, we put forward the hypothesis that the adoption of adaptive/defensive responses would be driven by the ability of antibiotic low doses to modulate the transcriptional activity of bacteria. Overall, our findings suggest that hormesis plays a pivotal role in affecting the bacterial behavior in order to acquire a survival advantage. Therefore, a proactive and effective risk assessment should necessarily take due account of the hormesis concept to adequately evaluate the risks to ecosystems and human health posed by antibiotic environmental contamination.

Rice Seedling Growth Promotion by Biochar Varies With Genotypes and Application Dosages

While biochar use in agriculture is widely advocated, how the effect of biochar on plant growth varies with biochar forms and crop genotypes is poorly addressed. The role of dissolvable organic matter (DOM) in plant growth has been increasingly addressed for crop production with biochar. In this study, a hydroponic culture of rice seedling growth of two cultivars was treated with bulk mass (DOM-containing), water extract (DOM only), and extracted residue (DOM-free) of maize residue biochar, at a volumetric dosage of 0.01, 0.05, and 0.1%, respectively. On seedling root growth of the two cultivars, bulk biochar exerted a generally negative effect, while the biochar extract had a consistently positive effect across the application dosages. Differently, the extracted biochar showed a contrasting effect between genotypes. In another hydroponic culture with Wuyunjing 7 treated with biochar extract at sequential dosages, seedling growth was promoted by 95% at 0.01% dosage but by 26% at 0.1% dosage, explained with the great promotion of secondary roots rather than of primary roots. Such effects were likely explained by low molecular weight organic acids and nanoparticles contained in the biochar DOM. This study highlights the importance of biochar DOM and crop genotype when evaluating the effect of biochar on plants. The use of low dosage of biochar DOM could help farmers to adopt biochar technology as a solution for agricultural sustainability.

Boron Oxide Nanoparticles Exhibit Minor, Species-Specific Acute Toxicity to North-Temperate and Amazonian Freshwater Fishes

Boron oxide nanoparticles (nB₂O₃) are manufactured for structural, propellant, and clinical applications and also form spontaneously through the degradation of bulk boron compounds. Bulk boron is not toxic to vertebrates but the distinctive properties of its nanostructured equivalent may alter its biocompatibility. Few studies have addressed this possibility, thus our goal was to gain an initial understanding of the potential acute toxicity of nB₂O₃ to freshwater fish and we used a variety of model systems to achieve this. Bioactivity was investigated in rainbow trout (Oncorhynchus mykiss) hepatocytes and at the whole animal level in three other North and South American fish species using indicators of aerobic metabolism, behavior, oxidative stress, neurotoxicity, and ionoregulation. nB₂O₃ reduced O. mykiss hepatocyte oxygen consumption (ṀO₂) by 35% at high doses but whole animal ṀO₂ was not affected in any species. Spontaneous activity was assessed using ṀO₂ frequency distribution plots from live fish. nB₂O₃ increased the frequency of high ṀO₂ events in the Amazonian fish Paracheirodon axelrodi, suggesting exposure enhanced spontaneous aerobic activity. ṀO₂ frequency distributions were not affected in the other species examined. Liver lactate accumulation and significant changes in cardiac acetylcholinesterase and gill Na⁺/K⁺-ATPase activity were noted in the north-temperate Fundulus diaphanus exposed to nB₂O₃, but not in the Amazonian Apistogramma agassizii or P. axelrodi. nB₂O₃ did not induce oxidative stress in any of the species studied. Overall, nB₂O₃ exhibited modest, species-specific bioactivity but only at doses exceeding predicted environmental relevance. Chronic, low dose exposure studies are required for confirmation, but our data suggest that, like bulk boron, nB₂O₃ is relatively non-toxic to aquatic vertebrates and thus represents a promising formulation for further development.

In vivo evaluation of Nano-palladium toxicity on larval stages and adult of zebrafish (Danio rerio)

The existence and usage of nano-sized palladium (nano-Pd) as catalytic promoters among industries and researchers have been laid a way to explore the release of nano-Pd particles into the aquatic environment, bio-accumulating in living organisms. However, the data on fate and toxicity in response to nano-Pd on aquatic organisms are very limited. Herein, we report the concentration-specific toxicity of nano-Pd in zebrafish (Danio rerio). Nano-Pd was synthesized and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Dynamic Light Scattering (DLS) and Zeta potential. To determine the in vivo toxicity of nano-Pd, the 96 hpf larvae and the adult zebrafish were treated with two (22 and 0.4 ng/L) environmental relevant concentrations. High doses of nano-Pd influenced the hatching rate, embryo survival, heartbeat and teratological anomalies in the 96 hpf larvae. Reactive oxygen species (ROS) and apoptosis were also influenced by nano-Pd exposure while the acetylcholinesterase (AChE) activity was declined in a dose dependent manner. In long-term exposure (42 days), the adult fish showed erratic movements in swimming pattern inhibiting the AChE activity in both the concentrations of brain and liver. The antioxidant enzyme activity such as superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione reductase (GR) and lipid peroxidation (LPO), showed a significant change (P < 0.05) indicating that oxidative stress was induced by nano-Pd. Similarly, nano-Pd also induced histopathological lesions in gill, liver and brain providing an insight of fate and toxicity of nano-Pd in the aquatic environment. Our study contributes a significant mechanism to understand the toxicity concern of nano-Pd in the aquatic environment.

Mechanisms for the stimulatory effects of a five-component mixture of antibiotics in Microcystis aeruginosa at transcriptomic and proteomic levels

Antibiotic contaminants could promote the formation of harmful cyanobacterial blooms through hormetic stimulation, but the mechanisms underlying these stimulatory effects remain unclear. This study investigated the biochemical, transcriptomic, and proteomic responses of a dominant bloom-forming cyanobacterium, Microcystis aeruginosa, to a five-component mixture of frequently detected antibiotics at current contamination levels. The growth rate of M. aeruginosa presented a U-shaped dose-response to 50-500 ng L^-1 of mixed antibiotics. Alterations in the transcriptome of M. aeruginosa suggested the excitation of both photosynthesis and carbon metabolism, increasing energy generation in response to oxidative stress induced by low-dose antibiotics, and thus contributing to the significant (p < 0.05) increase in growth rate, F_v/F_m, and cell density. Comparison between transcriptomic and proteomic responses further confirmed the action mode of the mixed antibiotics. Proteins and their corresponding genes related to ROS scavenging, photosynthesis, carbon fixation, electron transport, oxidative phosphorylation, and biosynthesis, showed consistent expression tendencies in response to 200 ng L^-1 of mixed antibiotics, which were credible action targets of mixed antibiotics in M. aeruginosa. Mixed antibiotics stimulated microcystin synthesis by upregulating a microcystin synthetase and its encoding gene (mcyC), which could increase the hazard of M. aeruginosa in aquatic environments.

Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends

Nanotechnology is a tool that in the last decade has demonstrated multiple applications in several sectors, including agroindustry. There has been an advance in the development of nanoparticulated systems to be used as fertilizers, pesticides, herbicides, sensors, and quality stimulants, among other applications. The nanoencapsulation process not only protects the active ingredient but also can affect the diffusion, interaction, and activity. It is important to evaluate the negative aspects of the use of nanoparticles (NPs) in agriculture. Given the high impact of the nanoparticulated systems in the agro-industrial field, this review aims to address the effects of various nanomaterials on the morphology, metabolomics, and genetic modification of several crops.

Hormesis Effects of Nano- and Micro-sized Copper Oxide

The concerns about the possible risk of manufactured nanoparticles (NPs) have been raised recently. Nano- and micro-sized copper oxide (CO and CONP) are widely used in many industries. In this regard, in-vitro studies have demonstrated that CONP is a toxic compound in different cell lines. Despite their unique properties, NPs possess unexpected toxicity profiling relative to the bulk materials. This study was designed to examine and compare the toxic effects of CO and CONPs in-vivo and in isolated rat mitochondria. Male Wistar albino rats received 50 to 1000 mg/kg CO or CONP by gavage and several toxicological endpoints including biochemical indices and oxidative stress markers. Then, the pathological parameters in the multiple organs such as liver, brain, spleen, kidney, and intestine were assessed. Mitochondria were isolated from the rat liver and several mitochondrial indices were measured. The results of this study demonstrated that CO and CONP exhibited biphasic dose-response effects. CONPs showed higher toxicity compared with the bulk material. There were no significant changes in the results of CONP and CO in isolated rat liver mitochondria. The present studies provided more information regarding the hormetic effects of CO and CONPs in-vivo and in isolated rat mitochondria.

The two faces of nanomaterials: A quantification of hormesis in algae and plants

The rapid progress in nanotechnology has dramatically promoted the application of engineered nanomaterials in numerous sectors. The wide application of nanomaterials and the potential accumulation in the environment sparked interest in studying the effects of nanomaterials on algae and plants. Hormesis is a dose response phenomenon characterized by a biphasic dose response with a low dose stimulation and a high dose inhibition. This paper quantifies for the first time nanomaterial-induced hormesis in algae and plants. Five hundred hormetic concentration-response relationships were mined from the published literature. The median maximum stimulatory response (MAX) was 123%, and commonly below 200%, of control response. It was also lower in algae than in plants, and occurred commonly at concentrations <100 mg L^-1. The no-observed-adverse-effect-level (NOAEL) to MAX ratio was 2.4 for algae and 1.7 for plants, and the two distributions differed significantly. Ag nanoparticles induced higher MAX than TiO₂ and ZnO nanoparticles. The MAX varied upon nanomaterial application methods, growth stage of application (seed versus vegetative), type of endpoint and time window. While nanomaterial size did not affect significantly the MAX, sizes ≤50 nm appeared to have lower NOAEL:MAX ratio than sizes ≥100 nm, suggesting higher risks from incorrect application. The mechanisms underlying nanomaterial-induced hormetic concentration responses are discussed. This paper provides a strong foundation for enhancing research protocols of studies on nanomaterial effects on algae and plants as well as for incorporating hormesis into the risk assessment practices.

Magnitude of the mixture hormetic response of soil alkaline phosphatase can be predicted based on single conditions of Cd and Pb

In soil ecosystems, it is very challenging to predict mixture hormesis effects. In the present study, soil alkaline phosphatase (ALP) was selected to investigate and predict its potential hormetic responses under Cd and Pb stresses. Typical reverse U-shaped dose-response relationships between ALP activities and the single and combined Cd and Pb were observed, showing a hormetic response of soil itself. The maximum stimulatory magnitudes ranged in 8.0 - 8.6% under 0.004 - 0.2 mg/kg Cd and 80 - 400 mg/kg Pb, respectively. An enhanced stimulation of 15.7% occurred under the binary mixtures of 0.6 mg/kg Cd and 200 mg/kg Pb. In addition, a dosage-independent binary linear regression model was proposed based on an assumption of a linear relationship between the single and combined hormetic responses under Cd and Pb. Our model can well predict ALP's responses in the presence of the two metals' mixtures (p < 0.1). Our findings provided new understandings to hormesis in soil.

Multivariate modeling of engineered nanomaterial features associated with developmental toxicity

Despite the increasing prevalence of engineered nanomaterials (ENMs) in consumer products, their toxicity profiles remain to be elucidated. ENM physicochemical characteristics (PCC) are known to influence ENM behavior, however the mechanisms of these effects have not been quantified. Further confounding the question of how the PCC influence behavior is the inclusion of structural and molecular descriptors in modeling schema that minimize the effects of PCC on the toxicological endpoints. In this work, we analyze ENM physico-chemical measurements that have not previously been studied within a developmental toxicity framework using an embryonic zebrafish model. In testing a panel of diverse ENMs to build a consensus model, we found nonlinear relationships between any singular PCC and bioactivity. By using a machine learning (ML) method to characterize the information content of combinatorial PCC sets, we found that concentration, surface area, shape, and polydispersity can accurately capture the developmental toxicity profile of ENMs with consideration to whole-organism effects.

Growth inhibition in Raphidocelis subcapita - Evidence of nanospecific toxicity of silver nanoparticles

Silver, known for its antibacterial properties and for its toxicity to aquatic organisms, is one of the most frequently used nanomaterials and silver nanoparticles can be found in a range of consumer products as well as medical applications. The present study investigated the toxicity of three different silver nanomaterials (Mesosilver (M-Ag), NM300K and NM302) and AgNO₃, in the algae Raphidocelis subcapitata. Exposures in the low μg L^-1 range were combined with characterization of exposure media to determine whether differences in toxicity could be linked to changes in Ag speciation and/or any nanospecific mechanisms. All tested Ag compounds, except the NM302, reduced growth in the following order AgNO₃ ≥ M-Ag > NM300K > NM302 with 50% effect concentrations of 7.09 (3.83-10.52), 9.7 (range not calculated) and 24.18 (15.66-98.16) μg L^-1, for AgNO₃, Mesosilver and NM300K, respectively. Characterization of exposure media showed that both concentration and time influenced the speciation and stability of Ag in algal test media, regardless of Ag source, and also affected the toxicity to R. subcapitata. In both AgNO₃ and Mesosilver exposure the toxicity was correlated with the presence of dissolved Ag species (<10 kDa), however levels of dissolved Ag were too low to account for the observed Mesosilver effects, indicating a nanospecific contribution. Nanospecific toxicity was also observed for NM300K after 24 h of exposure, however the algal population recovered over time, probably due to changes in exposure caused by aggregation of the nanoparticles.

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects-An updated review

The present review covers developments in studies of nanomaterials (NMs) in the environment since our much cited review in 2008. We discuss novel insights into fate and behavior, metrology, transformations, bioavailability, toxicity mechanisms, and environmental impacts, with a focus on terrestrial and aquatic systems. Overall, the findings were that: 1) despite substantial developments, critical gaps remain, in large part due to the lack of analytical, modeling, and field capabilities, and also due to the breadth and complexity of the area; 2) a key knowledge gap is the lack of data on environmental concentrations and dosimetry generally; 3) substantial evidence shows that there are nanospecific effects (different from the effects of both ions and larger particles) on the environment in terms of fate, bioavailability, and toxicity, but this is not consistent for all NMs, species, and relevant processes; 4) a paradigm is emerging that NMs are less toxic than equivalent dissolved materials but more toxic than the corresponding bulk materials; and 5) translation of incompletely understood science into regulation and policy continues to be challenging. There is a developing consensus that NMs may pose a relatively low environmental risk, but because of uncertainty and lack of data in many areas, definitive conclusions cannot be drawn. In addition, this emerging consensus will likely change rapidly with qualitative changes in the technology and increased future discharges. Environ Toxicol Chem 2018;37:2029-2063. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Nanoparticle Exposure and Hormetic Dose-Responses: An Update

The concept of hormesis, as an adaptive response of biological systems to moderate environmental challenges, has raised considerable nano-toxicological interests in view of the rapid pace of production and application of even more innovative nanomaterials and the expected increasing likelihood of environmental and human exposure to low-dose concentrations. Therefore, the aim of this review is to provide an update of the current knowledge concerning the biphasic dose-responses induced by nanoparticle exposure. The evidence presented confirmed and extended our previous findings, showing that hormesis is a generalized adaptive response which may be further generalized to nanoscale xenobiotic challenges. Nanoparticle physico-chemical properties emerged as possible features affecting biphasic relationships, although the molecular mechanisms underlining such influences remain to be fully understood, especially in experimental settings resembling long-term and low-dose realistic environmental exposure scenarios. Further investigation is necessary to achieve helpful information for a suitable assessment of nanomaterial risks at the low-dose range for both the ecosystem function and the human health.

Hormetic effects of Cd on alkaline phosphatase in soils across particle-size fractions in a typical coastal wetland

Hormetic responses in soil ecosystem are increasingly reported recently. Soil enzymes are involved in almost all biochemical reactions, but insufficient investigations were conducted to define its hormetic responses. The objective of this study is to investigate the hormetic responses across soil particle-size fractions with cadmium (Cd) as a stressor and alkaline phosphatase (ALP) as a potential endpoint. Soils were treated by adding CdCl₂·2.5H₂O solution with 0, 0.003, 0.03, 0.3, 3.0 and 30.0mg·kg^-1 of Cd, respectively. A low-power ultrasonic method was used to separate the bulk soil into 0.1-2, 2-63, 63-200 and 200-2000μm fractions. In 2-63μm, ALP activity at doses of 0.3-3.0mg·kg^-1 of Cd was significantly higher than that of CK (0.0mg·kg^-1 of Cd), showing a typical U-shaped dose-response with the amplitude of 72.3-118.6%. Similarly, ALP activity at 0.003-0.3mg·kg^-1 of Cd was 36.4-66.1% higher than that of CK in 63-200μm. However, no similar phenomenon was observed in 0.1-2 and 200-2000μm fractions. This suggested that low doses of Cd induced the hormetic responses of soil ALP, particularly in 2-63 and 63-200μm. In addition, analysis of the microbial community structure and diversity indicates that, at genus level, the relative abundance (RA) of Gillisia at 0.03-0.3mg·kg^-1 of Cd was significantly higher than that of CK with the amplitude of 3.7-37.5% in 2-63μm. The similar responses were observed that the RA of Pontibacter at 0.003-0.03mg·kg^-1 of Cd was 4.0-85.4% higher than that of CK in 63-200μm. This showed that Gillisia and Pontibacter possibly contribute to the hormetic responses of soil ALP when low contents of Cd presented in soils. This study will provide a good insight into the hormetic phenomenon at soil ecosystem scales.

Hormetic Response by Silver Nanoparticles on In Vitro Multiplication of Sugarcane (Saccharum spp. Cv. Mex 69-290) Using a Temporary Immersion System

Background:

Hormesis is considered a dose–response phenomenon characterized by growth stimulation at low doses and inhibition at high doses. The hormetic response by silver nanoparticles (AgNPs) on in vitro multiplication of sugarcane was evaluated using a temporary immersion system.

Methods:

Sugarcane shoots were used as explants cultured in Murashige and Skoog medium with AgNPs at concentrations of 0, 25, 50, 100, and 200 mg/L. Shoot multiplication rate and length were used to determine hormetic response. Total content of phenolic compounds of sugarcane, mineral nutrition, and reactive oxygen species (ROS) was determined.

Results:

Results were presented as a dose–response curve. Stimulation phase growth was observed at 50 mg/L AgNPs, whereas inhibition phase was detected at 200 mg/L AgNPs. Mineral nutrient analysis showed changes in macronutrient and micronutrient contents due to the effect of AgNPs. Moreover, AgNPs induced ROS production and increased total phenolic content, with a dose-dependent effect.

Conclusion:

Results suggested that the production of ROS and mineral nutrition are key mechanisms of AgNP-induced hormesis and that phenolic accumulation was obtained as a response of the plant to stress produced by high doses of AgNPs. Therefore, small doses of AgNPs in the culture medium could be an efficient strategy for commercial micropropagation.

Phytotoxicity of soluble graphitic nanofibers to model plant species

Carbon nanomaterials are considered promising for applications in energy storage, catalysis, and electronics. This has motivated study of their potential environmental toxicity. Recently, a novel nanomaterial consisting of graphene oxide wrapped around a carbon nanotube (CNT) core was synthesized. The resulting soluble graphitic nanofibers were found to have superior catalytic properties, which could result in their use in fuel cells. Before this material undergoes widespread use, its environmental toxicity must be determined because of its aqueous solubility. The authors used the plant species Lolium multiflorum, Solanum lycopersicum, and Lactuca sativa to study the toxicity of the soluble graphitic nanofibers, as well as multiwalled carbon nanotubes (MWCNTs) and graphene oxide, all synthesized in-house. Soluble graphitic nanofiber-exposed plant roots and shoots showed decreased growth, with roots showing more toxicity than shoots. Decreased pH of nanomaterial solutions corresponded to insignificantly decreased root growth, suggesting that another mechanism of toxicity must exist. Agglomeration and adsorption of soluble graphitic nanofibers onto the roots likely caused the remaining toxicity because a gray layer could be seen around the surface of the root. Multiwalled carbon nanotubes showed little toxicity over the concentration range tested, whereas graphene oxide showed a unique pattern of high toxicity at both the lowest and highest concentrations tested. Overall, soluble graphitic nanofibers showed moderate toxicity between that of the more toxic graphene oxide and the relatively nontoxic MWCNTs. Environ Toxicol Chem 2016;35:2941-2947. © 2016 SETAC.

Cyto-genotoxicity and oxidative stress induced by zinc oxide nanoparticle in human lymphocyte cells in vitro and Swiss albino male mice in vivo

ZnO-np has immense potential and application in cosmetic and health care sectors. Hence it was imperative to assess the toxicity/safety of these nanoparticles. In this study, we have evaluated the effects of ZnO-np in human peripheral blood mononuclear cells (PBMCs) in vitro and in Swiss albino male mice in vivo for cyto-genotoxicity and oxidative damage. In vitro results showed that ZnO-nps were weakly genotoxic, induced significant decrease in mitochondrial membrane potential and was capable of ROS generation, leading to apoptosis. In bone marrow cells in vivo, reduction of mitochondrial membrane potential (MMP), increased oxidative stress and G0/G1 cell cycle arrest was observed along with chromosome aberrations and micronuclei formation. In liver cells DNA damage and induction of oxidative stress with concurrent decrease in inhibition of antioxidant enzymes were noted. These in vitro and in vivo results demonstrated that ZnO-np induced genotoxic response and ROS production leading to apoptotic cell death and established a good co-relation between the two biological systems. More importantly, the results stress on the need of multiple endpoint assay-approaches, with an in vitro-in vivo study design to assess nanoparticle toxicology.

Effects of ZnO nanoparticles in plants: Cytotoxicity, genotoxicity, deregulation of antioxidant defenses, and cell-cycle arrest

Cytotoxicity, genotoxicity, and biochemical effects were evaluated in the plants Allium cepa, Nicotiana tabacum, and Vicia faba following exposure to ZnO nanoparticles (np; diameter, ∼85nm). In the root meristems of Allium cepa cells, we observed loss of membrane integrity, increased chromosome aberrations, micronucleus formation, DNA strand breaks, and cell-cycle arrest at the G2/M checkpoint. In Vicia faba and Nicotiana tabacum, we observed increased intracellular ROS production, lipid peroxidation, and activities of some antioxidant enzymes. TEM images revealed gross morphological alterations and internalization of the np. Our findings provide evidence of ZnO np toxicity, characterized by deregulation of components of ROS-antioxidant machinery, leading to DNA damage, cell-cycle arrest, and cell death. These plants, especially Allium cepa, are reliable systems for assessment of np toxicology.

Exposure to Palladium Nanoparticles Affects Serum Levels of Cytokines in Female Wistar Rats

Background

Information currently available on the impact of palladium on the immune system mainly derives from studies assessing the biological effects of palladium salts. However, in the last years, there has been a notable increase in occupational and environmental levels of fine and ultrafine palladium particles released from automobile catalytic converters, which may play a role in palladium sensitization. In this context, the evaluation of the possible effects exerted by palladium nanoparticles (Pd-NPs) on the immune system is essential to comprehensively assess palladium immunotoxic potential.

Aim

Therefore, the aim of this study was to investigate the effects of Pd-NPs on the immune system of female Wistar rats exposed to this xenobiotic for 14 days, by assessing possible quantitative changes in a number of cytokines: IL-1α, IL-2, IL-4, IL-6, IL-10, IL-12, GM-CSF, INF-γ and TNF-α.

Methods

Twenty rats were randomly divided into four exposure groups and one of control. Animals were given a single tail vein injection of vehicle (control group) and different concentrations of Pd-NPs (0.012, 0.12, 1.2 and 12 μg/kg). A multiplex biometric enzyme linked immunosorbent assay was used to evaluate cytokine serum levels.

Results

The mean serum concentrations of all cytokines decreased after the administration of 0.012 μg/kg of Pd-NPs, whereas exceeded the control levels at higher exposure doses. The highest concentration of Pd-NPs (12 μg/kg) induced a significant increase of IL-1α, IL-4, IL-6, IL-10, IL-12, GM-CSF and INF-γ compared to controls.

Discussion and Conclusions

These results demonstrated that Pd-NP exposure can affect the immune response of rats inducing a stimulatory action that becomes significant at the highest administered dose. Our findings did not show an imbalance between cytokines produced by CD4⁺ T helper (Th) cells 1 and 2, thus suggesting a generalized stimulation of the immune system with a simultaneous activation and polarization of the naïve T cells towards Th1 and Th2 phenotype.

Oxidative stress by inorganic nanoparticles

Metallic and metallic oxide nanoparticles (NPs) have been increasingly used for various bio-applications owing to their unique physiochemical properties in terms of conductivity, optical sensitivity, and reactivity. With the extensive usage of NPs, increased human exposure may cause oxidative stress and lead to undesirable health consequences. To date, various endogenous and exogenous sources of oxidants contributing to oxidative stress have been widely reported. Oxidative stress is generally defined as an imbalance between the production of oxidants and the activity of antioxidants, but it is often misrepresented as a single type of cellular stress. At the biological level, NPs can initiate oxidative stress directly or indirectly through various mechanisms, leading to profound effects ranging from the molecular to the disease level. Such effects of oxidative stress have been implicated owing to their small size and high biopersistence. On the other hand, cellular antioxidants help to counteract oxidative stress and protect the cells from further damage. While oxidative stress is commonly known to exert negative biological effects, measured and intentional use of NPs to induce oxidative stress may provide desirable effects to either stimulate cell growth or promote cell death. Hence, NP-induced oxidative stress can be viewed from a wide paradigm. Because oxidative stress is comprised of a wide array of factors, it is also important to use appropriate assays and methods to detect different pro-oxidant and antioxidant species at molecular and disease levels. WIREs Nanomed Nanobiotechnol 2016, 8:414-438. doi: 10.1002/wnan.1374 For further resources related to this article, please visit the WIREs website.

Reducing Environmental Toxicity of Silver Nanoparticles through Shape Control

The use of antibacterial silver nanomaterials in consumer products ranging from textiles to toys has given rise to concerns over their environmental toxicity. These materials, primarily nanoparticles, have been shown to be toxic to a wide range of organisms; thus methods and materials that reduce their environmental toxicity while retaining their useful antibacterial properties can potentially solve this problem. Here we demonstrate that silver nanocubes display a lower toxicity toward the model plant species Lolium multiflorum while showing similar toxicity toward other environmentally relevant and model organisms (Danio rerio and Caenorhabditis elegans) and bacterial species (Esherichia coli, Bacillus cereus, and Pseudomonas aeruginosa) compared to quasi-spherical silver nanoparticles and silver nanowires. More specifically, in the L. multiflorum experiments, the roots of silver nanocube treated plants were 5.3% shorter than the control, while silver nanoparticle treated plant roots were 39.6% shorter than the control. The findings here could assist in the future development of new antibacterial products that cause less environmental toxicity after their intended use.

Excessive secretion of IL-8 by skeletal muscle in type 2 diabetes impairs tube growth: potential role of PI3K and the Tie2 receptor

Reduced capillary density is a feature of skeletal muscle (SkM) in type 2 diabetes (T2D), which is associated with multiple metabolic and functional abnormalities. SkM has been identified as a secretory tissue, releasing myokines that regulate multiple processes, including vascularization. We sought to determine how myokines secreted from T2D myotubes might influence SkM angiogenesis. Conditioned media (CM) were generated by myotubes from T2D and nondiabetic (ND) subjects. Primary human endothelial cells (HUVEC) and SkM explants were exposed to CM or recombinant myokines, and tube number or capillary outgrowth was determined as well as measurement of protein expression and phosphorylation. CM from ND myotubes stimulated tube formation of HUVEC to a greater extent than T2D myotubes (T2D-CM = 100%, ND-CM = 288 ± 90% after 48 h, P < 0.05). The effects of T2D myotube CM were mediated by IL-8, not IL-15 or GROα, and were due not to cell damage but rather through regulating tube production and maintenance (response to T2D-IL-8 = 100%, response to ND-IL-8 = 263 ± 46% after 48 h, P < 0.05). A similar effect was seen in SkM explants with exposure to IL-8. The dose-dependent effect of IL-8 on tube formation was also observable in the PI3K and FAK signaling pathways and mediated at least in part by PI3K, leading to regulation of Tie2 expression. These results suggest that elevated levels of IL-8 secreted from T2D myotubes create a muscle microenvironment that supports reduced capillarization in T2D. Impaired vascularization of SkM limits the availability of substrates, including glucose and contributes to the T2D phenotype.

Effects of carbon nanotubes on atrazine biodegradation by Arthrobacter sp

The environmental risks of engineered nanoparticles have attracted attention. However, little is known regarding the effects of carbon nanotubes (CNTs) on the biodegradation and persistence of organic contaminants in water. We investigated the impacts of pristine and oxidized multiwalled CNTs on the atrazine biodegradation rate and efficiency using Arthrobacter sp. At a concentration of 25mg/L, the CNTs enhanced the biodegradation rate by up to 20%; however, at a concentration of 100mg/L, the CNTs decreased the biodegradation rate by up to 50%. The stimulation effects resulted from enhanced bacterial growth and the overexpression of degradation genes. The inhibitory effects resulted from the toxicity of the CNTs at high concentrations. The differences between the two CNTs at tested concentrations were not significant. The biodegradation efficiency was not impacted by adsorption, and the pre-adsorbed atrazine on the CNTs was fully biodegraded when the CNT concentration was ≤25mg/L. This finding was consistent with the lack of observable desorption hysteresis for atrazine on the tested CNTs. Our results indicate that CNTs can enhance or inhibit biodegradation through a balance of two effects: the toxic effects on microbial activity and the effects of the changing bioavailability that result from adsorption and desorption.