Morphometric characteristics and time to hatch as efficacious indicators for potential nanotoxicity assay in zebrafish

Exploring Alternatives for Marine Toxicity Testing: Initial Evaluation of Fish Embryo and Mysid Tests

Current regulations require that toxicity assessments be performed using standardized toxicity testing methods, often using fish. Recent legislation in both the European Union and United States has mandated that toxicity testing alternatives implement the 3Rs of animal research (replacement, reduction, and refinement) whenever possible. There have been advances in the development of alternatives for freshwater assessments, but there is a lack of analogous developments for marine assessments. One potential alternative testing method is the fish embryo toxicity (FET) test, which uses fish embryos rather than older fish. In the present study, FET methods were applied to two marine model organisms, the sheepshead minnow and the inland silverside. Another potential alternative is the mysid shrimp survival and growth test, which uses an invertebrate model. The primary objective of the present study was to compare the sensitivity of these three potential alternative testing methods to two standardized fish-based tests using 3,4-dichloroaniline (DCA), a common reference toxicant. A secondary objective was to characterize the ontogeny of sheepshead minnows and inland silversides. This provided a temporal and visual guide that can be used to identify appropriately staged embryos for inclusion in FET tests and delineate key developmental events (e.g., somite development, eyespot formation, etc.). Comparison of the testing strategies for assessing DCA indicated that: (1) the standardized fish tests possessed comparable sensitivity to each other; (2) the mysid shrimp tests possessed comparable sensitivity to the standardized fish tests; (3) the sheepshead minnow and inland silverside FET tests were the least sensitive testing strategies employed; and (4) inclusion of sublethal endpoints (i.e., hatchability and pericardial edema) in the marine FETs increased their sensitivity. Environ Toxicol Chem 2024;43:1285-1299. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Toxic effects and comparison of common amino antioxidants (AAOs) in the environment on zebrafish: A comprehensive analysis based on cells, embryos, and adult fish

The ubiquity of amino antioxidants (AAOs) in the environment has attracted increasing attention, given their potential toxicity. This investigation represents a pioneering effort, systematically scrutinizing the toxicological effects of four distinct AAOs across the developmental spectrum of zebrafish, encompassing embryonic, larvae, and adult stages. The results indicate that four types of AAO exhibit varying degrees of cell proliferation toxicity. Although environmentally relevant concentrations of AAOs exhibit a comparatively circumscribed impact on zebrafish embryo development, heightened concentrations (300 μg/L) of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD) distinctly evoke developmental toxicity. Behavioral analysis results indicate that at concentrations of 20 and 300 μg/L, the majority of AAOs significantly reduced the swimming speed and activity of larvae. Moreover, each AAO triggers the generation of reactive oxygen species (ROS) in larvae, instigating diverse levels of oxidative stress. The study delineates parallel toxicological patterns in zebrafish exposed to 300 μg/L of 6PPD and IPPD, thereby establishing a comparable toxicity profile. The comprehensive toxicity effects among the four AAOs is as follows: IPPD >6PPD > N-Phenyl-1-naphthylamine (PANA) > diphenylamine (DPA). These findings not only enrich our comprehension of the potential hazards associated with AAOs but also provide data support for structure-based toxicity prediction models.

A copper-platinum nanoplatform for synergistic photothermal and chemodynamic tumor therapy via ROS outburst and GSH exhaustion

A multifunctional nanoplatform is obtained by modifying copper hexacyanoferrate (Cu-HCF) nanozyme with hyaluronic acid (HA) and further loading platinum (Pt) nanoparticles. This Cu-HCF-HA@Pt platform shows peroxidase-like and glutathione oxidase-like dual-enzyme catalytic activities and photothermal properties, enabling synergistic chemodynamic and photothermal tumor therapy. HA binds to the CD44 receptor, which is highly expressed on the exterior surface of tumor cells, endowing the nanoplatform with tumor specificity. Cu-HCF-HA@Pt catalyzes the decomposition of H2O2 to produce abundant hydroxyl radicals within tumor cells, increasing intracellular oxidative stress levels and inducing tumor cell apoptosis. Meanwhile, Cu-HCF-HA@Pt catalyzes the conversion of intracellular reduced glutathione (GSH) to oxidized glutathione, resulting in GSH exhaustion. The conversion of CuII to CuI in Cu-HCF via a Fenton-like reaction can improve the peroxidase-like property of Cu-HCF-HA@Pt. After the probe is targeted to the tumor site, irradiation by an 808 nm near-infrared laser causes local heating and brings about photothermal tumor apoptosis when reaching 45 °C. The prepared Cu-HCF-HA@Pt combines nanozyme-catalyzed therapy with photothermal therapy to induce apoptosis in tumor cells.

Toxicological effects of hydroxychloroquine sulfate and chloroquine diphosphate substances on the early-life stages of fish in the COVID-19 pandemic context

Hydroxychloroquine sulfate (HCQ) and chloroquine diphosphate (CQ) have been used at increased rates to treat COVID-19 but can constitute a potential environmental risk. The objective was to evaluate the toxicity of sublethal concentrations of HCQ and CQ in zebrafish embryos/larvae. The 50% lethal concentrations (LC50) of HCQ and CQ at 96 h post-fertilization (hpf) were calculated by testing various concentrations on 2,160 embryos. The LC50 obtained were 560 and 800 µM for HCQ and CQ, respectively. Next, the embryotoxicity assay was performed, where 1,200 embryos were subjected to sublethal concentrations of HCQ and CQ. The hatching and heart rates were recorded. After euthanasia, photomicrographs of all larvae were taken to measure the total length, pericardial and yolk sac areas. The embryos exposed to sublethal concentrations of HCQ and CQ showed delayed hatching at 72 hpf, as well as an increase in the heart rate, larger pericardial and yolk sac areas, and body malformations at 96 hpf. The findings show that HCQ and CQ are toxic to fish in the early development phases. Understanding the mechanisms of toxicity will help extrapolate the effects of 4-aminoquinoline derivatives when they reach the aquatic environment in the context of the COVID-19 pandemic.

Progress on the toxicity of quantum dots to model organism-zebrafish

In vivo toxicological studies are currently necessary to analyze the probable dangers of quantum dots (QDs) to the environment and human safety, due to the fast expansion of QDs in a range of applications. Because of its high fecundity, cost-effectiveness, well-defined developmental phases, and optical transparency, zebrafish has long been considered the "gold standard" for biosafety assessment of chemical substances and pollutants. In this review, the advantages of using zebrafish in QD toxicity assessment were explored. Then, the target organ toxicities such as developmental toxicity, immunotoxicity, cardiovascular toxicity, neurotoxicity, and hepatotoxicity were summarized. The hazardous effects of different QDs, including cadmium-containing QDs like CdTe, CdSe, and CdSe/ZnS, as well as cadmium-free QDs like graphene QDs (GQDs), graphene oxide QDs (GOQDs), and others, were emphasized and described in detail, as well as the underlying mechanisms of QDs generating these effects. Furthermore, general physicochemical parameters determining QD-induced toxicity in zebrafish were introduced, such as chemical composition and surface coating/modification. The limitations and special concerns of using zebrafish in QD toxicity studies were also mentioned. Finally, we predicted that the utilization of high-throughput screening assays and omics, such as transcriptome sequencing, proteomics, and metabolomics will be popular topic in nanotoxicology.

An Endeavor to Find Starter Feed Alternatives and Techniques for Zebrafish First-Feeding Larvae: The Effects on Viability, Morphometric Traits, Digestive Enzymes, and Expression of Growth-Related Genes

Low and variable growth and survival rates (SR) of 6-10 days postfertilization zebrafish larvae are a problem. This problem seems to be linked to starter feed characteristics. This study is an attempt to find alternatives to address these requests. For this, larvae were fed fresh and lyophilized microalgae (Chlorella, Scenedesmus, and Haematococcus), egg yolk (YOLK), lyophilized Artemia nauplii (LAN), and a combination of them. The lowest SR was observed in algae-fed larvae. All died on day 11 showing an emaciated appearance, similar to starved larvae. The highest SR was observed in YOLK- and LAN-fed larvae, which also showed an elongated anterior part of the body. Negative correlations of SR with vegfaa (vascular endothelial growth factor) and morphometric traits with igf2a (insulin-like growth factor) were also found and supported by changes at the molecular level. The presence of algae in the digestive tract of the larvae and the observation of fecal droppings indicate that the algae have an appropriate size and are palatable. The increase in the digestive enzyme activity shows the larval effort to digest the algae. The fact that the algae-fed larvae died even before the larvae were kept in starvation indicates the dramatic amount of energy that the larvae spent in microalgae digestion. Although both YOLK- and LAN-fed larvae had the highest SR, LAN group started to feed on Artemia nauplii sooner. This can be linked to the delayed growth in YOLK-fed larvae and an accelerated growth in the case of LAN-fed group. LAN is an expensive feed with negative effects on water quality, whereas YOLK is a cheap and nutritionally balanced feed with fine granular texture that contributes to a larval SR similar to LAN without affecting water quality. In conclusion, microalgae cannot be considered a suitable starter food for zebrafish, whereas LAN and YOLK can be considered good starter feeds.

Effect of acute exposure of saxitoxin on development of zebrafish embryos (Danio rerio)

As a type of cyanobacterial toxins, saxitoxin (STX) is receiving great interest due to its increasing presence in waterbodies. However, the underlying mechanism of STX-induced adverse effect is poorly understood. Here, we examined the developmental toxicity and molecular mechanism induced by STX using zebrafish embryos as an animal model. The embryonic toxicity induced by STX was demonstrated by inhibition of embryo hatching, increase in mortality rate, abnormal heart rate, abnormalities in embryo morphology as well as defects in angiogenesis and common cardinal vein remodeling. STX induced embryonic DNA damage and cell apoptosis, which would be alleviated by antioxidant N-acetyl-L-cysteine. Additionally, STX significantly increased reactive oxygen species level, catalase activity and malondialdehyde content and decreased the activity of superoxide dismutase and glutathione content. STX also promoted the expression of vascular development-related genes DLL4 and VEGFC, and inhibited VEGFA expression. Furthermore, STX altered the transcriptional regulation of apoptosis-related genes (BAX, BCL-2, P53 and CASPASE 3). Taken together, STX induced adverse effect on development of zebrafish embryos, which might be associated with oxidative stress-induced apoptosis.