The Effect of the Chorion on Size-Dependent Acute Toxicity and Underlying Mechanisms of Amine-Modified Silver Nanoparticles in Zebrafish Embryos

Assessing developmental and transcriptional effects of PM2.5 on zebrafish embryos

Investigating fine particulate matter (PM2.5) toxicity is crucial for health risk assessment and pollution control. This study explores the developmental toxicity of two PM2.5 sources: standard reference material 2786 (NIST, USA) and PM2.5 from Chakri Naruebodindra Medical Institute (CNMI, Thailand) located in the Bangkok Metropolitan area. Zebrafish embryos exposed to these samples exhibited embryonic mortality, with 50% lethal concentration (LC50) values of 1476 µg/mL for standard PM2.5 and 512 µg/mL for CNMI PM2.5. Morphological analysis revealed malformations, including pericardial and yolk sac edema, and blood clotting in both groups. Gene expression analysis highlighted source-specific effects. Standard PM2.5 downregulated sod1 and cat while upregulating gstp2. Inflammatory genes tnf-α and il-1b were upregulated, and nfkbi-αa was downregulated. Apoptosis-related genes bax, bcl-2, and casp3a were downregulated. CNMI PM2.5 consistently downregulated all examined genes. These findings underscore PM2.5 source variability's significance in biological system impact assessment, providing insights into pollutant-gene expression interactions. The study emphasizes the need for source-specific risk assessment and interventions to address PM2.5 exposure's health impacts effectively.

Ecotoxicity and trophic transfer of metallic nanomaterials in aquatic ecosystems

Metallic nanomaterials (MNMs) possess unique properties that have led to their widespread application in fields such as electronics and medicine. However, concerns about their interactions with environmental factors and potential toxicity to aquatic life have emerged. There is growing evidence suggesting MNMs can have detrimental effects on aquatic ecosystems, and are potential for bioaccumulation and biomagnification in the food chain, posing risks to higher trophic levels and potentially humans. While many studies have focused on the general ecotoxicity of MNMs, fewer have delved into their trophic transfer within aquatic food chains. This review highlights the ecotoxicological effects of MNMs on aquatic systems via waterborne exposure or dietary exposure, emphasizing their accumulation and transformation across the food web. Biomagnification factor (BMF), the ratio of the contaminant concentration in predator to that in prey, was used to evaluate the biomagnification due to the complex nature of aquatic food chains. However, most current studies have BMF values of less than 1 indicating no biomagnification. Factors influencing MNM toxicity in aquatic environments include nanomaterial properties, ion variations, light, dissolved oxygen, and pH. The multifaceted interactions of these variables with MNM toxicity remain to be fully elucidated. We conclude with recommendations for future research directions to mitigate the adverse effects of MNMs in aquatic ecosystems and advocate for a cautious approach to the production and application of MNMs.

Hues of risk: investigating genotoxicity and environmental impacts of azo textile dyes

The textile industry, with its extensive use of dyes and chemicals, stands out as a significant source of water pollution. Exposure to certain textile dyes, such as azo dyes and their breakdown products like aromatic amines, has been associated with health concerns like skin sensitization, allergic reactions, and even cancer in humans. Annually, the worldwide production of synthetic dyes approximates 7 × 107 tons, of which the textile industry accounts for over 10,000 tons. Inefficient dyeing procedures result in the discharge of 15-50% of azo dyes, which do not adequately bind to fibers, into wastewater. This review delves into the genotoxic impact of azo dyes, prevalent in the textile industry, on aquatic ecosystems and human health. Examining different families of textile dye which contain azo group in their structure such as Sudan I and Sudan III Sudan IV, Basic Red 51, Basic Violet 14, Disperse Yellow 7, Congo Red, Acid Red 26, and Acid Blue 113 reveals their carcinogenic potential, which may affect both industrial workers and aquatic life. Genotoxic and carcinogenic characteristics, chromosomal abnormalities, induced physiological and neurobehavioral changes, and disruptions to spermatogenesis are evident, underscoring the harmful effects of these dyes. The review calls for comprehensive investigations into the toxic profile of azo dyes, providing essential insights to safeguard the aquatic ecosystem and human well-being. The importance of effective effluent treatment systems is underscored to mitigate adverse impacts on agricultural lands, water resources, and the environment, particularly in regions heavily reliant on wastewater irrigation for food production.

Developmental impacts and toxicological hallmarks of silver nanoparticles across diverse biological models

Silver nanoparticles (AgNPs), revered for their antimicrobial prowess, have become ubiquitous in a range of products, from biomedical equipment to food packaging. However, amidst their rising popularity, concerns loom over their possible detrimental effects on fetal development and subsequent adult life. This review delves into the developmental toxicity of AgNPs across diverse models, from aquatic species like zebrafish and catfish to mammalian rodents and in vitro embryonic stem cells. Our focus encompasses the fate of AgNPs in different contexts, elucidating associated hazardous results such as embryotoxicity and adverse pregnancy outcomes. Furthermore, we scrutinize the enduring adverse impacts on offspring, spanning impaired neurobehavior function, reproductive disorders, cardiopulmonary lesions, and hepatotoxicity. Key hallmarks of developmental harm are identified, encompassing redox imbalances, inflammatory cascades, DNA damage, and mitochondrial stress. Notably, we explore potential explanations, linking immunoregulatory dysfunction and disrupted epigenetic modifications to AgNPs-induced developmental failures. Despite substantial progress, our understanding of the developmental risks posed by AgNPs remains incomplete, underscoring the urgency of further research in this critical area.

Enhanced neurotoxic effect of PCB-153 when co-exposed with polystyrene nanoplastics in zebrafish larvae

Nanoplastics (NPs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs) are ubiquitous aquatic pollutants. The coexistence of these pollutants in the environment emphasises the need to study their combined toxicity. NPs can cross biological membranes and act as vectors for other pollutants, whereas PCBs are known for their ability to bioaccumulate and biomagnify. The present work aimed to study the combined toxicity of polystyrene NPs and PCB-153 using physiological (development, heart rate, respiration), behavioural (swimming behaviour) and molecular (transcriptome) endpoints in zebrafish larvae. The results show that exposure to NPs, PCB and their mixture significantly affected the development and respiration in zebrafish larvae. Larvae co-exposed to NPs and PCB exhibited significant hyperlocomotion, whereas no such effect was observed after exposure to NPs or PCB alone. The transcriptomic results revealed that NPs exposure significantly affected several pathways associated with DNA compaction and nucleosome assembly, whereas PCB exposure significantly affected critical neurogenic pathways. In contrast, co-exposure to NPs and PCB generated multi-faceted toxicity and suppressed neurobehavioural, immune-related and detoxification pathways. The study highlights the complex interplay between NPs and PCBs, and documents how the two toxicants in combination give a stronger effect than the single toxicants alone. Understanding the mixture toxicity of these two pollutants is important to assess the environmental risks and developing effective management strategies, ultimately safeguarding ecosystems and human health.

Implications of biotic factors for toxicity testing in laboratory studies

There is an emerging call from scientists globally to advance the environmental relevance of laboratory studies, particularly within the field of ecotoxicology. To answer this call, we must carefully examine and elucidate the shortcomings of standardized toxicity testing methods that are used in the derivation of toxicity values and regulatory criteria. As a consequence of rapidly accelerating climate change, the inclusion of abiotic co-stressors are increasingly being incorporated into toxicity studies, with the goal of improving the representativeness of laboratory-derived toxicity values used in ecological risk assessments. However, much less attention has been paid to the influence of biotic factors that may just as meaningfully impact our capacity to evaluate and predict risks within impacted ecosystems. Therefore, the overarching goal is to highlight key biotic factors that should be taken into consideration during the experimental design and model selection phase. SYNOPSIS: Scientists are increasingly finding that lab reared results in toxicology might not be reflective of the external wild environment, we highlight in this review some key considerations when working between the lab and field.

Toxic effects of environmental-relevant exposure to polyethylene terephthalate (PET) micro and nanoparticles in zebrafish early development

Polyethylene terephthalate (PET) is a commonly used thermoplastic in industry due to its excellent malleability and thermal stability, making it extensively employed in packaging manufacturing. Inadequate disposal of PET packaging in the environment and natural physical-chemical processes leads to the formation of smaller particles known as PET micro and nanoplastics (MNPs). The reduced dimensions enhance particle bioavailability and, subsequently, their reactivity. This study involved chemical degradation of PET using trifluoroacetic acid to assess the impact of exposure to varying concentrations of PET MNPs (0.5, 1, 5, 10, and 20 mg/L) on morphological, functional, behavioral, and biochemical parameters during the early developmental stages of zebrafish (Danio rerio). Characterization of the degraded PET revealed the generated microplastics (MPs) ranged in size from 1305 to 2032 μm, and that the generated nanoplastics (NPs) ranged from 68.06 to 955 nm. These particles were then used for animal exposure. After a six-day exposure period, our findings indicate that PET MNPs can diminish spontaneous tail coiling (STC), elevate the heart rate, accumulate on the chorion surface, and reduce interocular distance. These results suggest that PET exposure induces primary toxic effects on zebrafish embryo-larval stage of development.

Using Electroporation to Improve and Accelerate Zebrafish Embryo Toxicity Testing

Zebrafish have emerged as a useful model for biomedical research and have been used in environmental toxicology studies. However, the presence of the chorion during the embryo stage limits cellular exposure to toxic elements and creates the possibility of a false-negative or reduced sensitivity in fish embryo toxicity testing (FET). This paper presents the use of electroporation as a technique to improve the delivery of toxic elements inside the chorion, increasing the exposure level of the toxins at an early embryo stage (<3 h post-fertilization). A custom-made electroporation device with the required electrical circuitry has been developed to position embryos between electrodes that provide electrical pulses to expedite the entry of molecules inside the chorion. The optimized parameters facilitate material entering into the chorion without affecting the survival rate of the embryos. The effectiveness of the electroporation system is demonstrated using Trypan blue dye and gold nanoparticles (AuNPs, 20-40 nm). Our results demonstrate the feasibility of controlling the concentration of dye and nanoparticles delivered inside the chorion by optimizing the electrical parameters, including pulse width, pulse number, and amplitude. Next, we tested silver nanoparticles (AgNPs, 10 nm), a commonly used toxin that can lower mortality, affect heart rate, and cause phenotypic defects. We found that electroporation of AgNPs reduces the exposure time required for toxicity testing from 4 days to hours. Electroporation for FET can provide rapid entry of potential toxins into zebrafish embryos, reducing the time required for toxicity testing and drug delivery experiments.

Evaluating the In Vivo Virulence of Environmental Pseudomonas aeruginosa Using Microinjection Model of Zebrafish (Danio rerio)

(1) Background: Microinjection of zebrafish (Danio rerio) embryos offers a promising model for studying the virulence and potential environmental risks associated with Pseudomonas aeruginosa. (2) Methods: This work aimed to develop a P. aeruginosa infection model using two parallel exposition pathways on zebrafish larvae with microinjection into the yolk and the perivitelline space to simultaneously detect the invasive and cytotoxic features of the examined strains. The microinjection infection model was validated with 15 environmental and clinical strains of P. aeruginosa of various origins, antibiotic resistance profiles, genotypes and phenotypes: both exposition pathways were optimized with a series of bacterial dilutions, different drop sizes (injection volumes) and incubation periods. Besides mortality, sublethal symptoms of the treated embryos were detected and analyzed. (3) Results: According to the statistical evaluation of our results, the optimal parameters (dilution, drop size and incubation period) were determined. (4) Conclusions: The tested zebrafish embryo microinjection infection model is now ready for use to determine the in vivo virulence and ecological risk of environmental P. aeruginosa.

Transgenic expression in zebrafish embryos with an intact chorion by electroporation and microinjection

Electroporation is regularly used to deliver agents into cells, including transgenic materials, but it is not used for mutating zebrafish embryos due to the lack of suitable systems, information on appropriate operating parameters, and the challenges posed by the protective chorion. Here, a novel method for gene delivery in zebrafish embryos was developed by combining microinjection into the space between the chorion and the embryo followed by electroporation. This method eliminates the need for chorion removal and injecting into the space between the chorion and embryo eliminates the need for finding and identifying key cell locations before performing an injection, making the process much simpler and more automatable. We also developed a microfluidic electroporation system and optimized electric pulse parameters for transgenesis of embryos. The study provided a novel method for gene delivery in zebrafish embryos that can be potentially implemented in a high throughput transgenesis or mutagenesis system.

Influence of exposure scenario on the sensitivity to caffeine

The chorion acts as a protective barrier, restricting some chemical absorption into the embryo and the surrounding fluids. In this sense, larvae may only have direct contact with some chemicals after dechorionation. This study aimed to evaluate the effects of caffeine (CAF) (0, 13, 20, 44, 67, and 100 mg.L-1) under different exposure scenarios (embryos with chorion or embryos/larvae already hatched) and rank the stage sensitivity. Thus, three scenarios were investigated: from 2 to 120 hours post fertilization (hpf) (5 days of exposure- 5dE), from 72 to 120 hpf (2dE), and from 96 to 120 hpf (1dE). Heart rate (48 hpf) and energy reserves (120 hpf) were measured in the 5dE scenario, and behavior and acetylcholinesterase (AChE) activity were evaluated at 120 hpf in all scenarios (5dE, 2dE, and 1dE). At 120 hpf, some of the fish was transferred to clean medium for a 10 days depuration period (10dPE). Behavior and AChE activity were assessed after this period. In the 5dE scenario, CAF increased heartbeat (13, 20, and 30 mg.L-1) and reduced carbohydrates (67, and 100 mg.L-1), while inhibiting AChE activity (100 mg.L-1) in the 5dE, 2dE, and 1dE scenarios. CAF reduced the total distance moved in the 5dE (67, and 100 mg.L-1), 2dE (20, 30, 44, 67, and 100 mg.L-1), and 1dE fish (67, and 100 mg.L-1) and increased erratic movements. Based on the lowest observed effect concentration (LOEC) for total distance moved (20 mg.L-1) and higher inhibition of AChE activity (100 mg.L-1) (65%), 2dE fish appear to be more sensitive to CAF. After 10dPE, a recovery in behavior was detected in all scenarios (5dE, 2dE, and 1dE). AChE activity remained inhibited in the 2dE scenario while increasing in the 1dE scenario. This study demonstrated that the presence of the chorion is an important factor for the analysis of CAF toxicity. After the loss of the chorion, organisms show greater sensitivity to CAF and can be used to evaluate the toxicity of various substances, including nanomaterials or chemicals with low capacity to cross the chorion. Therefore, the use of hatched embryos in toxicity tests is suggested, as they allow a shorter and less expensive exposure scenario that provides similar outcome as the conventional scenario.

Comparison of toxicity of silver nanomaterials and silver nitrate on developing zebrafish embryos: Bioavailability, osmoregulatory and oxidative stress

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish (Danio rerio) embryos were exposed to lethal concentrations of silver nitrate (AgNO₃) or silver (Ag) ENMs (primary size 42.5 ± 10.2 nm). The 96 h-LC₅₀ for AgNO₃ was 32.8 ± 0.72 μg Ag L^-1 (mean ± 95% CI) compared to 6.5 ± 0.4 mg L^-1 of the whole material for Ag ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC₅₀ for hatching success was 30.5 ± 1.4 μg Ag L^-1 and 6.04 ± 0.4 mg L^-1 for AgNO₃ and Ag ENMs, respectively. Further sub-lethal exposures were performed with the estimated LC₁₀ concentrations for both AgNO₃ or Ag ENMs over 96 h where about 3.7% of the total Ag as AgNO₃ was internalised, as measured by Ag accumulation in the dechorionated embryos. However, for the ENMs exposures, nearly all (99.8%) of the total Ag was associated with chorion; indicating the chorion as an effective barrier to protect the embryo in the short term. Calcium (Ca²⁺) and sodium (Na⁺) depletion was induced in embryos by both forms of Ag, but hyponatremia was more pronounced in the nano form. Total glutathione (tGSH) levels declined in embryos exposed to both Ag forms, but a superior depletion occurred with the nano form. Nevertheless, oxidative stress was mild as superoxide dismutase (SOD) activity stayed uniform and the sodium pump (Na⁺/K⁺-ATPase) activity had no appreciable inhibition compared to the control. In conclusion, AgNO₃ was more toxic to the early life stage zebrafish than the Ag ENMs, still differences were found in the exposure and toxic mechanisms of both Ag forms.

Zn-Al layered double hydroxides induce embryo malformations and impair locomotion behavior in Danio rerio

Layered double hydroxides (LDHs) are stimuli-responsive anionic nanoclays. The vast possibilities of using LDHs can lead to their existence in the ecosystem, raising a question of potential ecological concern. However, little is known about the effect of these nanomaterials on freshwater organisms. The present study aimed to assess the ecotoxicological effects of Zinc-Aluminium LDH-nitrate (ZnAl LDH-NO₃) in zebrafish (Danio rerio) early life stages. The endpoints measured were mortality, malformations and hatching rate after exposure of D. rerio embryos and larvae to ZnAl LDH-NO₃ following the OECD 236 guideline. The behavioral, biochemical (markers of oxidative stress and neurotoxicity), and molecular (at DNA level) alterations were also assessed using sub-lethal concentrations. No observable acute effects were detected up to 415.2 mg LDH/L while the 96 h-LC₅₀ was estimated as 559.9 mg/L. Tested LDH caused malformations in D. rerio embryos, such as pericardial edema, incomplete yolk sac absorption and tail deformities (96 h-EC₅₀ = 172.4 mg/L). During the dark periods, the locomotor behavior in zebrafish larvae was affected upon ZnAl LDH-NO₃ exposure. However, no significant biochemical and molecular changes were recorded. The present findings suggest that ZnAl LDH-NO₃ can be regarded as a non-toxic nanomaterial towards D. rerio (E/LC₅₀ > > 100 mg/L) although impairment of the locomotion behavior on zebrafish embryos can be expected at concentrations below 100 mg/L.

Differences in toxicity and accumulation of metal from copper oxide nanomaterials compared to copper sulphate in zebrafish embryos: Delayed hatching, the chorion barrier and physiological effects

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish embryos were exposed to lethal concentrations of copper sulphate (CuSO₄) or copper oxide (CuO) ENMs (primary size ∼15 nm), and then the sub-lethal effects investigated at the LC₁₀ concentrations over 96 h. The 96 h-LC₅₀ (mean ± 95% CI) for CuSO₄ was 303 ± 14 µg Cu L^-1 compared to 53 ± 9.9 mg L^-1 of the whole material for CuO ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC₅₀ for hatching success was 76 ± 11 µg Cu L^-1 and 0.34 ± 0.78 mg L^-1 for CuSO₄ and CuO ENMs respectively. Failure to hatch was associated with bubbles and foam-looking perivitelline fluid (CuSO₄), or particulate material smothering the chorion (CuO ENMs). In the sub-lethal exposures, about 42% of the total Cu as CuSO₄ was internalised, as measured by Cu accumulation in the de-chorionated embryos, but for the ENMs exposures, nearly all (94%) of the total Cu was associated with chorion; indicating the chorion as an effective barrier to protect the embryo from the ENMs in the short term. Both forms of Cu exposure caused sodium (Na⁺) and calcium (Ca²⁺), but not magnesium (Mg²⁺), depletion from the embryos; and CuSO₄ caused some inhibition of the sodium pump (Na⁺/K⁺-ATPase) activity. Both forms of Cu exposure caused some loss of total glutathione (tGSH) in the embryos, but without induction of superoxide dismutase (SOD) activity. In conclusion, CuSO₄ was much more toxic than CuO ENMs to early life stage zebrafish, but there are subtle differences in the exposure and toxic mechanisms for each substance.

Development a high-throughput zebrafish embryo acute toxicity testing method based on OECD TG 236

The Organization for Economic Co-operation and Development (OECD）Test Guideline (TG) 236 for zebrafish embryo acute toxicity testing was adopted for chemical toxicity assessment in 2013. Due to the increasing demand for prediction and evaluation of the acute toxicity using zebrafish embryos, we developed a method based on OECD 236 test guideline with the aim to improve the testing efficiency. We used 4-128 cell stage zebrafish embryos and performed an exposure assay in a 96-well microtiter plate, observing the lethality endpoints of embryos at 48-h postexposure. A total of 32 chemicals (two batches) were used in the comparison study. Our results indicated that the logarithmic LC₅₀ (half lethal concentration) obtained by the modified method exhibited good correlation with that obtained by the OECD 236 testing method, and the R² of the linear regression analysis was 0.9717 (0.9621 and 0.9936 for the two batches, respectively). Additionally, the intra- and inter-laboratory coefficient of variation (CVs) for the LC₅₀ from the testing chemicals (17 chemicals in second batch) was less than 30%, except for CuSO₄. Therefore, the developed method was less time-consuming and demonstrated a higher throughput for toxicity testing compared to the prior method. We argue the developed method could be used as an additional choice for high-throughput zebrafish embryo acute toxicity test.

On the In Vitro and In Vivo Hazard Assessment of a Novel Nanomaterial to Reduce the Use of Zinc Oxide in the Rubber Vulcanization Process

Zinc oxide (ZnO) is the most efficient curing activator employed in the industrial rubber production. However, ZnO and Zn(II) ions are largely recognized as an environmental hazard being toxic to aquatic organisms, especially considering Zn(II) release during tire lifecycle. In this context, aiming at reducing the amount of microcrystalline ZnO, a novel activator was recently synthetized, constituted by ZnO nanoparticles (NPs) anchored to silica NPs (ZnO-NP@SiO₂-NP). The objective of this work is to define the possible hazards deriving from the use of ZnO-NP@SiO₂-NP compared to ZnO and SiO₂ NPs traditionally used in the tire industry. The safety of the novel activators was assessed by in vitro testing, using human lung epithelial (A549) and immune (THP-1) cells, and by the in vivo model zebrafish (Danio rerio). The novel manufactured nanomaterial was characterized morphologically and structurally, and its effects evaluated in vitro by the measurement of the cell viability and the release of inflammatory mediators, while in vivo by the Fish Embryo Acute Toxicity (FET) test. Resulting data demonstrated that ZnO-NP@SiO₂-NP, despite presenting some subtoxic events, exhibits the lack of acute effects both in vitro and in vivo, supporting the safe-by-design development of this novel material for the rubber industry.

Effects of plastic particles on aquatic invertebrates and fish - A review

This review summarises the current knowledge on the effects of microplastics and their additives on organisms living in the aquatic environment, particularly invertebrates and fish. To date, microplastics have been recognised to affect not only the behaviour of aquatic animals but also their proper development, causing variations in fertility, oxidative stress, inflammations and immunotoxicity, neurotoxicity, and changes in metabolic pathways and gene expression. The ability of microplastics to bind other xenobiotics and cause combined toxicity along side the effect of other agents is also discussed as well. Microplastics are highly recalcitrant materials in both freshwater and marine environments and should be considered extremely toxic to aquatic ecosystems. They are severely problematic from ecological, economic and toxicological standpoints.

Morphological characteristics of zebrafish's yolk sac for malformation based on orthogonal-polarization-gating optical coherence tomography

In this study, an automatic algorithm combining an ellipsoid approximation and U-net has been presented for the characterization of a zebrafish's yolk sac. The polarization-difference-balanced-detection image of zebrafish was obtained based on orthogonal-polarization-gating optical coherence tomography and used to segment the yolk sac region. And ellipsoid can approximate the shape of the three-dimensional yolk sac, and the multiple parameters of volume and the three principal axes (k, l and m) can be used to quantify the yolk sac. In addition, the multiple parameters of two principal axes (l and m) and volume can distinguish the malformation from the normal controlled group. Finally, the volume malformation of the yolk sac calculated by the proposed algorithm ranges from 16.55% to 46.05%. Thus, the degree of malformation can be applied for toxicity analysis. And this method provides a potential application for an accurate judgment index for biotoxicological testing.

Understanding Ecotoxicological Responses of Fish Embryos and Gill Cells to Cationic Polymers

Cationic polymers are considered by the scientific and regulatory communities as a group of greater interest amongst the polymers in commerce. As a category, relatively little hazard information is available in the public literature. Very few examples exist of published, high-quality polymer characterization and quantification of exposure. In the present study we describe a series of fish embryo toxicity (FET) and fish gill cytotoxicity assays used to establish a baseline understanding of several representative polyquaternium categories (PQ-6, PQ-10, PQ-16) in animal alternative models, accompanied by high-quality analytical characterization. Materials were chosen to encompass a range of molecular weights and charge densities to determine the influence of test material characteristics on toxicity. Both chorionated and dechorionated FET assays were generally similar to published acute fish toxicity data. Toxicity was correlated with cationic polymer charge density, and not with molecular weight, and was a combination of physical effects and likely toxicity at the site of action. Toxicity could be ameliorated by humic acid in a dose-dependent manner. Fish gill cytotoxicity results were orders of magnitude less sensitive than FET test responses. Environ Toxicol Chem 2022;41:2259-2272. © 2022 SETAC.

Gut-derived metabolites influence neurodevelopmental gene expression and Wnt signaling events in a germ-free zebrafish model

BACKGROUND

Small molecule metabolites produced by the microbiome are known to be neuroactive and are capable of directly impacting the brain and central nervous system, yet there is little data on the contribution of these metabolites to the earliest stages of neural development and neural gene expression. Here, we explore the impact of deriving zebrafish embryos in the absence of microbes on early neural development as well as investigate whether any potential changes can be rescued with treatment of metabolites derived from the zebrafish gut microbiota.

RESULTS

Overall, we did not observe any gross morphological changes between treatments but did observe a significant decrease in neural gene expression in embryos raised germ-free, which was rescued with the addition of zebrafish metabolites. Specifically, we identified 354 genes significantly downregulated in germ-free embryos compared to conventionally raised embryos via RNA-Seq analysis. Of these, 42 were rescued with a single treatment of zebrafish gut-derived metabolites to germ-free embryos. Gene ontology analysis revealed that these genes are involved in prominent neurodevelopmental pathways including transcriptional regulation and Wnt signaling. Consistent with the ontology analysis, we found alterations in the development of Wnt dependent events which was rescued in the germ-free embryos treated with metabolites.

CONCLUSIONS

These findings demonstrate that gut-derived metabolites are in part responsible for regulating critical signaling pathways in the brain, especially during neural development. Video abstract.

Toxic Effects and Mechanisms of Silver and Zinc Oxide Nanoparticles on Zebrafish Embryos in Aquatic Ecosystems

The global application of engineered nanomaterials and nanoparticles (ENPs) in commercial products, industry, and medical fields has raised some concerns about their safety. These nanoparticles may gain access into rivers and marine environments through industrial or household wastewater discharge and thereby affect the ecosystem. In this study, we investigated the effects of silver nanoparticles (AgNPs) and zinc oxide nanoparticles (ZnONPs) on zebrafish embryos in aquatic environments. We aimed to characterize the AgNP and ZnONP aggregates in natural waters, such as lakes, reservoirs, and rivers, and to determine whether they are toxic to developing zebrafish embryos. Different toxic effects and mechanisms were investigated by measuring the survival rate, hatching rate, body length, reactive oxidative stress (ROS) level, apoptosis, and autophagy. Spiking AgNPs or ZnONPs into natural water samples led to significant acute toxicity to zebrafish embryos, whereas the level of acute toxicity was relatively low when compared to Milli-Q (MQ) water, indicating the interaction and transformation of AgNPs or ZnONPs with complex components in a water environment that led to reduced toxicity. ZnONPs, but not AgNPs, triggered a significant delay of embryo hatching. Zebrafish embryos exposed to filtered natural water spiked with AgNPs or ZnONPs exhibited increased ROS levels, apoptosis, and lysosomal activity, an indicator of autophagy. Since autophagy is considered as an early indicator of ENP interactions with cells and has been recognized as an important mechanism of ENP-induced toxicity, developing a transgenic zebrafish system to detect ENP-induced autophagy may be an ideal strategy for predicting possible ecotoxicity that can be applied in the future for the risk assessment of ENPs.

Investigating Chaperone like Activity of Green Silver Nanoparticles: Possible Implications in Drug Development

Protein aggregation and amyloidogenesis have been associated with several neurodegenerative disorders like Alzheimer’s, Parkinson’s etc. Unfortunately, there are still no proper drugs and no effective treatment available. Due to the unique properties of noble metallic nanoparticles, they have been used in diverse fields of biomedicine like drug designing, drug delivery, tumour targeting, bio-sensing, tissue engineering etc. Small-sized silver nanoparticles have been reported to have anti-biotic, anti-cancer and anti-viral activities apart from their cytotoxic effects. The current study was carried out in a carefully designed in-vitro to observe the anti-amyloidogenic and inhibitory effects of biologically synthesized green silver nanoparticles (B-AgNPs) on human serum albumin (HSA) aggregation taken as a model protein. We have used different biophysical assays like thioflavin T (ThT), 8-Anilino-1-naphthalene-sulphonic acid (ANS), Far-UV CD etc. to analyze protein aggregation and aggregation inhibition in vitro. It has been observed that the synthesized fluorescent B-AgNPs showed inhibitory effects on protein aggregation in a concentration-dependent manner reaching a plateau, after which the effect of aggregation inhibition was significantly declined. We also observed meaningful chaperone-like aggregation-inhibition activities of as-synthesized florescent B-AgNPs in astrocytes.

Influence of nanosilver in hybrid carriers on morphological and biochemical blood pa-rameters of laying hens

The search for an alternative to antibiotics in poultry has led to a study of the effectiveness of using nanosilver preparations in the production of table eggs. The experiment determined the effect of the drug nanosilver in carriers based on polymer/inorganic hybrids (AgNPs/SPH) on morphological and biochemical parameters of the blood of laying hens. For this, 45 Hy-Line W36 hens were used at the age of 38 weeks, which were randomly divided into three groups. The AgNPs/SPH solution was administered 3 times a month with an interval of 10 days at concentrations of 0.0, 1.0, and 2.0 mg/L (0.0, 0.2 and 0.4 mg per hen per day). The introduction of AgNPs/SPH in doses of 0.2 and 0.4 mg per hen per day three times a month did not have a significant effect on the morphological parameters of the blood. A single dose of 0.2 mg AgNPs/SPH solution per hen per day increased the level of total protein, glucose, cholesterol, as well as the activity of alanine aminotransferase and alkaline phosphatase in the blood serum and decreased albumin, creatinine and gamma-glutamyl transpeptidase activity. Feeding laying hens a solution of nanosilver in a larger dose had a less pronounced effect on these indicators. Two-fold administration of AgNPs/SPH solution at a dose of 0.2 mg per laying hen per day increased only gamma-glutamyl transpeptidase activity in the blood serum, but decreased the level of total activity of protein, albumin, phosphorus, and alkaline phosphatase. At the same time, the drug nanosilver in double dose per day caused an increase in albumin content and alkaline phosphatase activity in the serum of hens. Triple feeding of laying hens with a solution of nanosilver at a dose of 0.2 mg per hen per day did not affect most of the biochemical parameters of serum, but in the double dose increased the content of total protein against the background of lowered cholesterol and gamma-glutamyl transpeptidase activity. With the increase in the frequency of feeding laying hens solutions of nanosilver in carriers based on polymer / inorganic hybrids, the level of severity of their impact on the metabolic profile of serum decreased. The results of research can be the basis for determining the optimal interval of application of nanosilver drugs in poultry, depending on the method of their synthesis and stabilization.

Lentinan Impairs the Early Development of Zebrafish Embryos, Possibly by Disrupting Glucose and Lipid Metabolism

LNT is the major biologically active substance extracted from Lentinus edodes (L. edodes). Although functional and pharmacological studies have demonstrated that LNT has multiple benefits for animals and humans, the safety assessment is far from sufficient. To evaluate the potential safety risk, larval zebrafish were continuously exposed to varying concentrations of LNT for 120 h. The 96 h LC50 of LNT was determined to be 1228 μg/mL, and morphological defects including short body length, reduced eye and swim bladder sizes and yolk sac edema were observed. In addition, LNT exposure significantly reduced the blood flow velocity and locomotor activity of larval zebrafish. The biochemical parameters were also affected, showing reduced glucose, triglyceride and cholesterol levels in zebrafish larvae after being exposed to LNT. Correspondingly, the genes involved in glucose and lipid metabolism were disrupted. In conclusion, the present study demonstrates the adverse potential of high concentrations of LNT on the development of zebrafish larvae in the early life stage.

Chemical composition and particle size influence the toxicity of nanoscale plastic debris and their co-occurring benzo(α)pyrene in the model aquatic organisms Daphnia magna and Danio rerio

Little is known about how particle chemical composition and size might influence the toxicity of nanoscale plastic debris (NPD) and their co-occurring chemicals. Herein, we investigate the toxicity of 3 × 10¹⁰ particles/L polyethylene (PE, 50 nm), polypropylene (PP, 50 nm), polystyrene (PS, 200 and 600 nm), and polyvinyl chloride (PVC, 200 nm) NPD and their co-occurring benzo(a)pyrene (BaP) to Daphnia magna and Danio rerio. During the 21 days of exposure to PE 50 nm and PS 200 nm, the number of broods produced by D. magna decreased compared to other treatments. Exposure to BaP alone did not produce any effects on the reproduction of the daphnids, however, the mixture of BaP with PS (200 or 600 nm) or with PE (50 nm) reduced the number of broods. Exposure of D. rerio embryos to PE 50 nm, PS 200 nm, and PS 600 nm led to a delay in the hatching. The presence of PS 200 nm and PVC 200 nm eliminated the effects of BaP on the hatching rate of zebrafish. Our findings suggest that data generated for the toxicity of one type of NPD, e.g. PVC or PS may not be extrapolated to other types of NPD.

Zebrafish, an In Vivo Platform to Screen Drugs and Proteins for Biomedical Use

The nearly simultaneous convergence of human genetics and advanced molecular technologies has led to an improved understanding of human diseases. At the same time, the demand for drug screening and gene function identification has also increased, albeit time- and labor-intensive. However, bridging the gap between in vitro evidence from cell lines and in vivo evidence, the lower vertebrate zebrafish possesses many advantages over higher vertebrates, such as low maintenance, high fecundity, light-induced spawning, transparent embryos, short generation interval, rapid embryonic development, fully sequenced genome, and some phenotypes similar to human diseases. Such merits have popularized the zebrafish as a model system for biomedical and pharmaceutical studies, including drug screening. Here, we reviewed the various ways in which zebrafish serve as an in vivo platform to perform drug and protein screening in the fields of rare human diseases, social behavior and cancer studies. Since zebrafish mutations faithfully phenocopy many human disorders, many compounds identified from zebrafish screening systems have advanced to early clinical trials, such as those for Adenoid cystic carcinoma, Dravet syndrome and Diamond-Blackfan anemia. We also reviewed and described how zebrafish are used to carry out environmental pollutant detection and assessment of nanoparticle biosafety and QT prolongation.

Modulation of Innate Immune Toxicity by Silver Nanoparticle Exposure and the Preventive Effects of Pterostilbene

Silver nanoparticles pose a potential risk to ecosystems and living organisms due to their widespread use in various fields and subsequent gradual release into the environment. Only a few studies have investigated the effects of silver nanoparticles (AgNPs) toxicity on immunological functions. Furthermore, these toxic effects have not been fully explored. Recent studies have indicated that zebrafish are considered a good alternative model for testing toxicity and for evaluating immunological toxicity. Therefore, the purpose of this study was to investigate the toxicity effects of AgNPs on innate immunity using a zebrafish model and to investigate whether the natural compound pterostilbene (PTE) could provide protection against AgNPs-induced immunotoxicity. Wild type and neutrophil- and macrophage-transgenic zebrafish lines were used in the experiments. The results indicated that the exposure to AgNPs induced toxic effects including death, malformation and the innate immune toxicity of zebrafish. In addition, AgNPs affect the number and function of neutrophils and macrophages. The expression of immune-related cytokines and chemokines was also affected. Notably, the addition of PTE could activate immune cells and promote their accumulation in injured areas in zebrafish, thereby reducing the damage caused by AgNPs. In conclusion, AgNPs may induce innate immune toxicity and PTE could ameliorate this toxicity.

Fatty acid alteration in liver, brain, muscle, and oocyte of zebrafish (Danio rerio) exposed to silver nanoparticles and mitigating influence of quercetin-supplemented diet

No to less effort has been made to assess the toxicity of silver nanoparticles (AgNPs) to lipid composition in biological systems and also to discover a mitigating agent against their oxidative stress. Hence, this research evaluated the antioxidant capability of quercetin (Qu) against silver nanoparticles (AgNPs) toxicity towards the lipid contents of ovarian, nervous, and hepatic systems as well as skeletal muscles. To this end, zebrafish (n = 180) were assigned into four experimental dietary groups: negative and positive controls, without Qu supplementation; Qu-200, 200 mg Qu per kg diet; and Qu-400, 400 mg Qu per kg diet. At the end of the feeding trial (40 days), the experimental groups, except the negative control, were exposed to sublethal concentration of AgNPs (0.15 mg L^-1) for 96 h. As to the liver tissue of the positive and Qu-200 treatments, total polyunsaturated fatty acids (∑PUFA) decreased 3 times, as well as total high unsaturated fatty acids (∑HUFA) reduced about 30% and 50%, respectively. However, the brain ∑HUFA, predominated by DHA, enhanced in Qu-400 treatment. Interestingly, ∑MUFA, ∑PUFA, and ∑HUFA increased in the muscle of all treated groups, especially Qu-200 and Qu-400. The oocyte ∑MUFA content increased in the positive and Qu-200 treatments, whereas ∑HUFA reduced about 25%, 25%, and 20%, respectively, in the positive, Qu-200, and Qu-400 groups. Generally, the findings suggest that unsaturated acyl chains, particularly HUFAs, in the liver tissue and oocyte cell are highly susceptible to peroxidation or degeneration by AgNPs. More broadly, in the context of ecotoxicological risk assessment, the alteration in HUFAs and PUFAs of the liver and oocyte could impact on maternal and offspring health and consequently alter long-term population dynamics of aquatic animals.

Novel phenylpyrimidine derivatives containing a hydrazone moiety protect rice seedlings from injury by metolachlor

One strategy for solving the phytotoxicity of herbicides is to apply herbicide safeners that can efficiently alleviate the injuries of agricultural crops caused by herbicides. When metolachlor, a chloroacetamide herbicide, is applied with paddy rice, for example, the mechanisms associated with metolachlor and its residue negatively impact on the growth and yields of rice. To identify novel high-activity herbicide safener candidates for metolachlor, a series of (E)-4-(2-substituted hydrazinyl)-6-chloro-2-phenyl pyrimidines were synthesized and their structures were confirmed using IR (infrared radiation), ¹H NMR, ¹³C NMR, and HRMS (high resolution mass spectrometry). The herbicide safener activities were then evaluated via primary tests. Compounds 3i and 3t were found to have the best herbicide activity on plant height. These compounds were then further screened for their activities at lower concentrations and showed better or similar activities compared to the positive control fenclorim, a commercial herbicide safener. The compounds 3i and 3t significantly enhanced glutathione S-transferase (GST) activity related with the herbicide safener activity in both shoots and roots tissues. Moreover, a qPCR (Real-time quantitative polymerase chain reaction) analysis found that the 3i and 3t treatments enhanced the expressions of OsGSTU3, OsGsTU39, and OsGSTF5. Finally, the results of an acute toxicity assessment with zebrafish (Danio rerio) embryos using treatments 3i and 3t indicated they are relatively safe to aquatic organisms.

New Lead Discovery of Herbicide Safener for Metolachlor Based on a Scaffold-Hopping Strategy

The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of the existing herbicides in the field. Sanshools, which are well known as spices, are N-alkyl substituted compounds extracted from the Zanthoxylum species and have several essential physiological and pharmacological functions. Sanshools display excellent safener activity for the herbicide metolachlor in rice seedlings. However, the high cost of sanshools extraction and difficulties in the synthesis of their complicated chemical structures limit their utilization in agricultural fields. Thus, the present study designed and synthesized various N-alkyl amide derivatives via the scaffold-hopping strategy to solve the challenge of complicated structures and find novel potential safeners for the herbicide metolachlor. In total, 33 N-alkyl amide derivatives (2a–k, 3a–k, and 4a–k) were synthesized using amines and saturated and unsaturated fatty acids as starting materials through acylation and condensation. The identity of all the target compounds was well confirmed by ¹H-NMR, ¹³C-NMR, and high-resolution mass spectrometry (HRMS). The primary evaluation of safener activities for the compounds by the agar method indicated that most of the target compounds could protect rice seedlings from injury caused by metolachlor. Notably, compounds 2k and 4k displayed excellent herbicide safener activities on plant height and demonstrated relatively similar activities to the commercialized compound dichlormid. Moreover, we showed that compounds 2k and 4k had higher glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO) activities in rice seedlings, compared to the metolachlor treatment. In particular, 2k and 4k are safer for aquatic organisms than dichlormid. Results from the current work exhibit that compounds 2k and 4k have excellent crop safener activities toward rice and can, thus, be promising candidates for further structural optimization in rice protection.

Toxicity Studies on Graphene-Based Nanomaterials in Aquatic Organisms: Current Understanding

Graphene and its oxide are nanomaterials considered currently to be very promising because of their great potential applications in various industries. The exceptional physiochemical properties of graphene, particularly thermal conductivity, electron mobility, high surface area, and mechanical strength, promise development of novel or enhanced technologies in industries. The diverse applications of graphene and graphene oxide (GO) include energy storage, sensors, generators, light processing, electronics, and targeted drug delivery. However, the extensive use and exposure to graphene and GO might pose a great threat to living organisms and ultimately to human health. The toxicity data of graphene and GO is still insufficient to point out its side effects to different living organisms. Their accumulation in the aquatic environment might create complex problems in aquatic food chains and aquatic habitats leading to debilitating health effects in humans. The potential toxic effects of graphene and GO are not fully understood. However, they have been reported to cause agglomeration, long-term persistence, and toxic effects penetrating cell membrane and interacting with cellular components. In this review paper, we have primarily focused on the toxic effects of graphene and GO caused on aquatic invertebrates and fish (cell line and organisms). Here, we aim to point out the current understanding and knowledge gaps of graphene and GO toxicity.

The Recent Progress in Nanotoxicology and Nanosafety from the Point of View of Both Toxicology and Ecotoxicology

This editorial aims to summarize the 14 scientific papers contributed to the Special Issue “Nanotoxicology and nanosafety 2.0 from the point of view of both toxicology and ecotoxicology”.