Bioactivity of nanosilver in Caenorhabditis elegans: Effects of size, coat, and shape

Application of 3Rs in Caenorhabditis elegans Research for the Identification of Health-Promoting Natural Products

The average age of the population is increasing worldwide, which has a profound impact on our society. This leads to an increasing demand for medicines and requires the development of new strategies to promote health during the additional years. In the search for resources and therapeutics for improved health during an extended life span, attention has to be paid to environmental exposure and ecosystem burdens that inevitably emerge with the extended consumption of medicines and drug development, even in the preclinical stage. The hereby introduced sustainable strategy for drug discovery is built on 3Rs, "R: obustness, R: eliability, and saving R: esources", inspired by both the 3Rs used in animal experiments and environmental protection, and centers on the usefulness and the variety of the small model organism Caenorhabditis elegans for detecting health-promoting natural products. A workflow encompassing a multilevel screening approach is presented to maximize the amount of information on health-promoting samples, while considering the 3Rs. A detailed, methodology- and praxis-oriented compilation and discussion of proposed C. elegans health span assays and more disease-specific assays are presented to offer guidance for scientists intending to work with C. elegans, thus facilitating the initial steps towards the integration of C. elegans assays in their laboratories.

The worm Adult Activity Test (wAAT): A de novo mathematical model for detecting acute chemical effects in Caenorhabditis elegans

We have adapted a semiautomated method for tracking Caenorhabditis elegans spontaneous locomotor activity into a quantifiable assay by developing a sophisticated method for analyzing the time course of measured activity. The 16-h worm Adult Activity Test (wAAT) can be used to measure C. elegans activity levels for efficient screening for pharmacological and toxicity-induced effects. As with any apical endpoint assay, the wAAT is mode of action agnostic, allowing for detection of effects from a broad spectrum of response pathways. With caffeine as a model mild stimulant, the wAAT showed transient hyperactivity followed by reversion to baseline. Mercury chloride (HgCl2 ) produced an early dose-response hyperactivity phase followed by pronounced hypoactivity, a behavior pattern we have termed a toxicant "escape response." Methylmercury chloride (meHgCl) produced a similar pattern to HgCl2 , but at much lower concentrations, a weaker hyperactivity response, and more pronounced hypoactivity. Sodium arsenite (NaAsO2 ) and dimethylarsinic acid (DMA) induced hypoactivity at high concentrations. Acute toxicity, as measured by hypoactivity in C. elegans adults, was ranked: meHgCl > HgCl2  > NaAsO2  = DMA. Caffeine was not toxic with the wAAT at tested concentrations. Methods for conducting the wAAT are described, along with instructions for preparing C. elegans Habitation Medium, a liquid nutrient medium that allows for developmental timing equivalent to that found with C. elegans grown on agar with OP50 Escherichia coli feeder cultures. A de novo mathematical parametric model for adult C. elegans activity and the application of this model in ranking exposure toxicity are presented.

Grape juice reduces the effects of amyloid β aggregation phenotype and extends the longevity in Caenorhabditis elegans

OBJECTIVES

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence of aggregated amyloid-β (Aβ) peptides. Several natural compounds have been proposed against this disease and grape products are among these. However, little is known about grape juice potential. Transgenic Caenorhabditis elegans (C. elegans) strains that express human Aβ have been used as an in vivo model for AD.

METHODS

In this study, we have exposed CL2006 worms to nine different juices obtained from different cultivars.

RESULTS

Cora, Bordo, Isabel, Isabel Precoce, BRS-Magna, BRS-Rubea and BRS-Violeta juices improved the behavioral phenotype (paralysis) that is caused by Aβ aggregation in the transgenic animals at the concentrations tested and no toxic effects were found. Some juices were also able to increase the worm's lifespan. We could not attribute lifespan increase and paralysis reduction with any specific compound found in the phytochemical analysis.

DISCUSSION

Our data indicate that the rich constitution of the juices is responsible for attenuating the phenotype caused by Aβ aggregation in C. elegans.

Silver-Silica nanoparticles induced dose-dependent modulation of histopathological, immunohistochemical, ultrastructural, proinflammatory, and immune status of broiler chickens

Silver nanoparticles (AgNPs) are a powerful disinfectant, but little information is available on their potential use as a growth promoter and the safety margin of this. In this study, 480 1-day-old Cobb chicks were assigned to one control and three treated groups. The treated groups were supplemented with silver-doped silica nanoparticles (SiO₂@AgNPs) at three dietary levels (8, 16, and 20 mg/kg diet) for 35 days. The results revealed no significant changes in the growth performance and oxidative parameters, and in most of the hematological and biochemical parameters among the control and treated groups. In contrast, dose-dependent adverse effects were exerted on the histopathological structure and immunohistochemical expression of CD45 in liver, kidneys, and lymphoid organs (spleen, bursa, and thymus). In addition, the relative weight of lymphoid organs and the serum levels of immunoglobulins M and G were significantly diminished. Moreover, the gene expression of proinflammatory cytokines (IL-β1 and TNF-α) and the ultrastructural morphology in breast muscle showed significant dose-dependent alterations. It could be concluded that the dietary supplementation of SiO₂@AgNPs at a level of 8 mg/kg diet or more has dose-dependent proinflammatory and immunosuppressive effects on broiler chickens.

Physiological and transcriptomic effects of hexafluoropropylene oxide dimer acid in Caenorhabditis elegans during development

Per- and polyfluoroalkyl substances (PFAS) are chemicals resistant to degradation. While such a feature is desirable in consumer and industrial products, some PFAS, including perfluorooctanoic acid (PFOA), are toxic and bioaccumulate. Hexafluoropropylene oxide dimer acid (HFPO-DA), an emerging PFAS developed to replace PFOA, has not been extensively studied. To evaluate the potential toxicity of HFPO-DA with a cost- and time-efficient approach, we exposed C. elegans larvae for 48 h to 4 × 10^-9-4 g/L HFPO-DA in liquid media and measured developmental, behavioral, locomotor, and transcriptional effects at various exposure levels. Worms exposed to 1.5-4 g/L HFPO-DA were developmentally delayed, and progeny production was significantly delayed (p < 0.05) in worms exposed to 2-4 g/L HFPO-DA. Statistically significant differential gene expression was identified in all fourteen HFPO-DA exposure groups ranging from 1.25 × 10^-5 to 4 g/L, except for 6.25 × 10^-5 g/L. Among 10298 analyzed genes, 2624 differentially expressed genes (DEGs) were identified in the developmentally delayed 4 g/L group only, and 78 genes were differentially expressed in at least one of the thirteen groups testing 1.25 × 10^-5-2 g/L HFPO-DA exposures. Genes encoding for detoxification enzymes including cytochrome P450 and UDP glucuronosyltransferases were upregulated in 0.25-4 g/L acute exposure groups. DEGs were also identified in lower exposure level groups, though they did not share biological functions except for six ribosomal protein-coding genes. While our transcriptional data is inconclusive to infer mechanisms of toxicity, the significant gene expression differences at 1.25 × 10^-5 g/L, the lowest concentration tested for transcriptional changes, calls for further targeted analyses of low-dose HFPO-DA exposure effects.

Combining secondary ion mass spectrometry image depth profiling and single particle inductively coupled plasma mass spectrometry to investigate the uptake and biodistribution of gold nanoparticles in Caenorhabditis elegans

Analytical techniques capable of determining the spatial distribution and quantity (mass and/or particle number) of engineered nanomaterials in organisms are essential for characterizing nano-bio interactions and for nanomaterial risk assessments. Here, we combine the use of dynamic secondary ion mass spectrometry (dynamic SIMS) and single particle inductively coupled mass spectrometry (spICP-MS) techniques to determine the biodistribution and quantity of gold nanoparticles (AuNPs) ingested by Caenorhabditis elegans. We report the application of SIMS in image depth profiling mode for visualizing, identifying, and characterizing the biodistribution of AuNPs ingested by nematodes in both the lateral and z (depth) dimensions. In parallel, conventional- and sp-ICP-MS quantified the mean number of AuNPs within the nematode, ranging from 2 to 36 NPs depending on the size of AuNP. The complementary data from both SIMS image depth profiling and spICP-MS provides a complete view of the uptake, translocation, and size distribution of ingested NPs within Caenorhabditis elegans.

Impact of multigenerational exposure to AgNO3 or NM300K Ag NPs on antioxidant defense and oxidative stress in Caenorhabditis elegans

Adaptation of the nematode Caenorhabditis elegans towards NM300K silver nanoparticles (Ag NPs) has previously been demonstrated. In the current study, the sensitivity to a range of secondary stressors (CeO2 NP, Ce3+, Cu2+, Cd2+, and Paraquat) following the multigenerational exposure to silver nanoparticles (Ag NPs NM300K) or AgNO3 was investigated. This revealed improved tolerance to the ROS inducer Paraquat with higher fecundity after pre-exposure to Ag NP, indicating an involvement of reactive oxygen species (ROS) metabolism in the adaptive response to NM300K. The potential contribution of the antioxidant defenses related to adaptive responses was investigated across six generations of exposure using the sod-1::GFP reporter (GA508), and the Grx1-roGFP2 (GRX) biosensor strains. Results showed an increase in sod-1 expression by the F3 generation, accompanied by a reduction of GSSG/GSH ratios, from both AgNO3 and Ag NP exposures. Continuous exposure to AgNO3 and Ag NP until the F6 generation resulted in a decreased sod-1 expression, with a concomitant increase in GSSG/GSH ratios. The results thus show that despite an initial enhancement, the continuous exposure to Ag caused a severe impairment of the antioxidant defense capacity in C. elegans.

Dietary supplementation of silver-silica nanoparticles promotes histological, immunological, ultrastructural, and performance parameters of broiler chickens

Silver nanoparticles (AgNPs) have been used as a promising alternative to antibiotics in poultry feed. In this study, silver-doped silica nanoparticles (SiO₂@AgNPs) were prepared in powder form, using starch, via the chemical reduction method and sol-gel technique followed by full characterization. SiO₂@AgNPs were added to the poultry diet at three doses (2, 4, and 8 mg/kg diet). The safety of the oral dietary supplementation was estimated through the evaluation of the growth performance and hematological, biochemical, and oxidative parameters of birds. Moreover, the immunohistochemical examination of all body organs was also performed. Results of this study showed that SiO₂@AgNPs have no negative effects on the growth performance and hematological, biochemical, and oxidative parameters of birds. Moreover, the immunohistochemical examination revealed the minimum inflammatory reactions and lymphoid depletion under a dose level of 8 mg/kg. In conclusion, SiO₂@AgNPs could be considered as a promising and safe nano-growth promoter in broilers when added to poultry diet under a dose level of 4 mg/kg diet.

Detoxification mechanisms of nickel sulfate in nematode Caenorhabditis elegans

Nickel is the most prevailing metal allergen with the highest sensitization rate among the "TOP 25" contact allergens and can affect about 15% of the human population. It is an essential trace metal in plants, animals, and humans. However, the environmental levels of nickel are considerably higher than what is needed for human life. Exposure to high levels of nickel can lead to skin allergies, lung fibrosis, and carcinogenesis. Few existing studies have closely examined the toxicity of nickel, let alone investigated the effective detoxification pathways. Here, we developed a high-throughput screening platform to comprehensively evaluate the nickel toxicity in wild-type C. elegans and explore the underlying detoxification mechanisms in transgenic nematodes. We demonstrated that nickel exerted multiple toxic effects on growth, brood size, feeding, and locomotion in C. elegans. Of which, brood size is the most sensitive endpoint. Nickel was found to first bind to phytochelatin (PC) after entering the worms' body and this PC-Ni complex was further transported by the ABC transporter, CeHMT-1, into the coelomocytes for further detoxification. Our study also demonstrated that the high-throughput screening platform is a promising system for evaluation and investigation of the ecological risks of heavy metals.

The Potential of Silver Nanoparticles for Antiviral and Antibacterial Applications: A Mechanism of Action

Rapid development of nanotechnology has been in high demand, especially for silver nanoparticles (AgNPs) since they have been proven to be useful in various fields such as medicine, textiles, and household appliances. AgNPs are very important because of their unique physicochemical and antimicrobial properties, with a myriad of activities that are applicable in various fields, including wound care management. This review aimed to elucidate the underlying mechanisms of AgNPs that are responsible for their antiviral properties and their antibacterial activity towards the microorganisms. AgNPs can be synthesized through three different methods-physical, chemical, and biological synthesis-as indicated in this review. The applications and limitations of the AgNPs such as their cytotoxicity towards humans and the environment, will be discussed. Based on the literature search obtained, the properties of AgNPs scrutinizing the antibacterial or antiviral effect shown different interaction towards bacteria which dependent on the synthesis processes followed by the morphological structure of AgNPs.

Antibacterial activity of AgNPs–TiO2 nanotubes: influence of different nanoparticle stabilizers

Enhanced antibacterial properties of nanomaterials such as TiO₂ nanotubes (TNTs) and silver nanoparticles (AgNPs) have attracted much attention in biomedicine and industry. The antibacterial properties of nanoparticles depend, among others, on the functionalization layer of the nanoparticles. However, the more complex information about the influence of different functionalization layers on antibacterial properties of nanoparticle decorated surfaces is still missing. Here we show the array of ∼50 nm diameter TNTs decorated with ∼50 nm AgNPs having different functionalization layers such as polyvinylpyrrolidone, branched polyethyleneimine, citrate, lipoic acid, and polyethylene glycol. To assess the antibacterial properties, the viability of Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) has been assessed. Our results showed that the functional layer of nanoparticles plays an important role in antibacterial properties and the synergistic effect such nanoparticles and TiO₂ nanotubes have had different effects on adhesion and viability of G⁻ and G⁺ bacteria. These findings could help researchers to optimally design any surfaces to be used as an antibacterial including the implantable titanium biomaterials.

Synergictic antibacterial effect of AgNPs–TiO₂ nanotubes is influenced by different nanoparticle stabilizers.

Exposure to nickel oxide nanoparticles insinuates physiological, ultrastructural and oxidative damage: A life cycle study on Eisenia fetida

Although, health and environmental hazards of Ni are ironclad; however, that of Nickle oxide nanoparticles (NiO-NPs) are still obscure. Therefore, impact of NiO-NPs exposure (0, 5, 50, 200, 500 and 1000 mg kg^-1 soil) on the earthworm (Eisenia fetida) survival (at 28th day), reproduction (at 56th day), histopathology, ultrastructures, antioxidant enzymes and oxidative DNA damage was appraised in full life cycle study. Lower concentrations of NiO-NPs (5, 50 and 200) did not influence the survival, reproduction and growth rate of adult worms significantly. However, reproduction reduced by 40-50% with 500 and 1000 mg kg^-1 exposure, which also induced oxidative stress leading to DNA damage in earthworms. Ultrastructural observation and histology of earthworms exposed to higher NiO-NPs concentrations revealed abnormalities in epithelium layer, microvilli and mitochondria with underlying pathologies of epidermis and muscles, as well as adverse effects on the gut barrier. To the best of our knowledge, this is the first study unveiling the adverse effects of NiO-NPs on a soil invertebrate (Eisenia fetida). Our findings clue towards looking extensively into the risks of NiO-NPs on soil organisms bearing agricultural and environmental significance.

High-throughput COPAS assay for screening of developmental and reproductive toxicity of nanoparticles using the nematode Caenorhabditis elegans

With the rapid advancement and numerous applications of engineered nanomaterials (ENMs) in science and technology, their effects on animal health, environment and safety should be considered carefully. However, quick assessment of their effects on developmental and reproductive health and an understanding of how they cause such adverse toxic effects remain challenging, because of the fast-growing number of ENMs and the limitations of the different toxicity assays currently in use as well as lack of suitable animal model systems. In this study, we performed a high-throughput complex object parametric analyzer and sorter (COPAS) assay for assessing the developmental and reproductive toxicity of ENMs using Caenorhabditis elegans and provide descriptions of the data and their subsequent analysis. The results showed significant reproductive and developmental toxicity potential of different ENMs. We assessed the usefulness of this method in terms of error-free data, user-friendliness and results being consistent with those of visual, molecular and cellular studies. Moreover, the COPAS Biosort system could be used on a larger scale to screen thousands of chemicals, drugs, pharmaceuticals and ENMs. This study also indicates that the COPAS-based high-throughput screening system is highly reliable for the assessment of toxicity and health risks of NMs.

Size-dependent cytotoxicity of silver nanoparticles to Azotobacter vinelandii: Growth inhibition, cell injury, oxidative stress and internalization

The influence of nanomaterials on the ecological environment is becoming an increasingly hot research field, and many researchers are exploring the mechanisms of nanomaterial toxicity on microorganisms. Herein, we studied the effect of two different sizes of nanosilver (10 nm and 50 nm) on the soil nitrogen fixation by the model bacteria Azotobacter vinelandii. Smaller size AgNPs correlated with higher toxicity, which was evident from reduced cell numbers. Flow cytometry analysis further confirmed this finding, which was carried out with the same concentration of 10 mg/L for 12 h, the apoptotic rates were20.23% and 3.14% for 10 nm and 50 nm AgNPs, respectively. Structural damage to cells were obvious under scanning electron microscopy. Nitrogenase activity and gene expression assays revealed that AgNPs could inhibit the nitrogen fixation of A. vinelandii. The presence of AgNPs caused intracellular reactive oxygen species (ROS) production and electron spin resonance further demonstrated that AgNPs generated hydroxyl radicals, and that AgNPs could cause oxidative damage to bacteria. A combination of Ag content distribution assays and transmission electron microscopy indicated that AgNPs were internalized in A. vinelandii cells. Overall, this study suggested that the toxicity of AgNPs was size and concentration dependent, and the mechanism of antibacterial effects was determined to involve damage to cell membranes and production of reactive oxygen species leading to enzyme inactivation, gene down-regulation and death by apoptosis.

Nanoparticle tracking analysis versus dynamic light scattering: Case study on the effect of Ca2+ and alginate on the aggregation of cerium oxide nanoparticles

The effect of Ca²⁺ and alginate on the stability of CeO₂ nanoparticles (NPs) was investigated using dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA); the two methods were then compared. DLS showed rapid aggregation of CeO₂ NPs in 8 mM Ca²⁺ solution; however, NTA showed that some primary aggregates (200-400 nm) still remained-a result that was obscured in DLS measurements. Aggregation of alginate molecules was also studied using DLS and NTA, where NTA particle concentration and video provided additional information on the alginate aggregation progress. Finally, DLS showed that in the presence of alginate, the aggregation rate and size of CeO₂ NPs increased. NTA intensity measurements provided insight into a heteroaggregation and bridging mechanism. NTA particle concentration and video also showed CeO₂ NPs were linked by alginate gel in high Ca²⁺ concentration (>4 mM). the DLS and NTA had different advantages in measuring particle size. DLS could better study the initial aggregation stage and large aggregates, while NTA could better detect small aggregates. NTA also measured particle number concentration, individual intensity, and particle motion video, which provided additional insight. Combining these two methods could help us to better understand the behavior and fate of NPs in water.

Synthesis and Comparative Biological Properties of Ag-PEG Nanoparticles with Tunable Morphologies from Janus to Multi-Core Shell Structure

Silver nanoparticles synthesized with polymers as coating agents is an effective method to overcome their poor stability and aggregation in solution. Silver-polyethylene glycol (Ag-PEG) nanoparticles were synthesized with the thiol-functionalized polyethylene glycol (SH-PEA) as the coating, reducing and stabilizing agent. The UV irradiation time, polymer and silver nitrate concentration for the synthesis were investigated. The concentration of silver nitrate had significant effect on the morphology of Ag-PEG nanoparticles. When increasing the concentration of silver nitrate, SEM and TEM images showed that Ag-PEG nanoparticles changed from Janus to multi-core shell structure. Meanwhile, pure silver particles in the two hybrid nanoparticles presented spherical shape and had the similar size of 15 nm. The antibacterial activities and cytotoxicity of the two structural Ag-PEG nanoparticles were investigated to understand colloid morphology effect on the properties of AgNPs. The results of antibacterial activities showed that the two structural Ag-PEG nanoparticles exhibited strong antibacterial activities against Staphylococcus aureus, Escherichia coli and Bacillus subtilis. The Janus nanoparticles had larger minimal inhibitory concentration (MIC) and minimum bacterial concentration (MBC) values than the multi-core shell counterparts. The results of cytotoxicity showed the Janus Ag-PEG nanoparticles had lower toxicity than the multi-core shell nanoparticles.

The C. elegans model in toxicity testing

Caenorhabditis elegans is a small nematode that can be maintained at low cost and handled using standard in vitro techniques. Unlike toxicity testing using cell cultures, C. elegans toxicity assays provide data from a whole animal with intact and metabolically active digestive, reproductive, endocrine, sensory and neuromuscular systems. Toxicity ranking screens in C. elegans have repeatedly been shown to be as predictive of rat LD50 ranking as mouse LD50 ranking. Additionally, many instances of conservation of mode of toxic action have been noted between C. elegans and mammals. These consistent correlations make the case for inclusion of C. elegans assays in early safety testing and as one component in tiered or integrated toxicity testing strategies, but do not indicate that nematodes alone can replace data from mammals for hazard evaluation. As with cell cultures, good C. elegans culture practice (GCeCP) is essential for reliable results. This article reviews C. elegans use in various toxicity assays, the C. elegans model's strengths and limitations for use in predictive toxicology, and GCeCP. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Journal of Applied Toxicology published by John Wiley & Sons Ltd.

Caenorhabditis elegans, a Biological Model for Research in Toxicology

Caenorhabditis elegans is a nematode of microscopic size which, due to its biological characteristics, has been used since the 1970s as a model for research in molecular biology, medicine, pharmacology, and toxicology. It was the first animal whose genome was completely sequenced and has played a key role in the understanding of apoptosis and RNA interference. The transparency of its body, short lifespan, ability to self-fertilize and ease of culture are advantages that make it ideal as a model in toxicology. Due to the fact that some of its biochemical pathways are similar to those of humans, it has been employed in research in several fields. C. elegans' use as a biological model in environmental toxicological assessments allows the determination of multiple endpoints. Some of these utilize the effects on the biological functions of the nematode and others use molecular markers. Endpoints such as lethality, growth, reproduction, and locomotion are the most studied, and usually employ the wild type Bristol N2 strain. Other endpoints use reporter genes, such as green fluorescence protein, driven by regulatory sequences from other genes related to different mechanisms of toxicity, such as heat shock, oxidative stress, CYP system, and metallothioneins among others, allowing the study of gene expression in a manner both rapid and easy. These transgenic strains of C. elegans represent a powerful tool to assess toxicity pathways for mixtures and environmental samples, and their numbers are growing in diversity and selectivity. However, other molecular biology techniques, including DNA microarrays and MicroRNAs have been explored to assess the effects of different toxicants and samples. C. elegans has allowed the assessment of neurotoxic effects for heavy metals and pesticides, among those more frequently studied, as the nematode has a very well defined nervous system. More recently, nanoparticles are emergent pollutants whose toxicity can be explored using this nematode. Overall, almost every type of known toxicant has been tested with this animal model. In the near future, the available knowledge on the life cycle of C. elegans should allow more studies on reproduction and transgenerational toxicity for newly developed chemicals and materials, facilitating their introduction in the market. The great diversity of endpoints and possibilities of this animal makes it an easy first-choice for rapid toxicity screening or to detail signaling pathways involved in mechanisms of toxicity.