Studies on immunotoxicity induced by emamectin benzoate in zebrafish embryos based on metabolomics

Investigation of the mechanisms of liver injury induced by emamectin benzoate exposure at environmental concentrations in zebrafish: A multi-omics approach to explore the role of the gut-liver axis

Emamectin benzoate (EMB) is a lipophilic pesticide that enters aquatic systems and adversely affects non-target organisms. This study investigated the long-term effects of EMB on zebrafish, exposing them to concentrations of 0, 0.1, 1, and 10 μg/L from the 4-hour post-fertilization (hpf) embryo stage to the 120-day post-fertilisation (dpf) adult stage. We found that exposure to 1 μg/L EMB induced liver damage, manifested as impaired liver function (elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT)), histopathological damage (lipid accumulation), as well as inflammatory and oxidative damage, with a dose - dependent effect. Non-targeted metabolomic analysis revealed an increase in lipid molecules in the liver, affecting the pathways related to glycerophospholipid metabolism. In addition, EMB exposure resulted in damage to the intestinal barrier and inflammatory responses in zebrafish. 16S rRNA sequencing demonstrated that EMB exposure resulted in notable alterations in the gut microbiota composition. Notably, the abundance of Plesiomonas and Cetobacterium increased in the EMB exposure group and exhibited a positive correlation with the majority of liver lipid metabolites. In contrast, reductions in Muribaculaceae and Alloprevotella were negatively correlated. The results of this study indicate that long-term exposure to EMB disrupts the gut microbiota, leading to the dysregulation of hepatic phospholipid metabolism. These findings provide new insights into the health risks associated with EMB and highlight its potential threats to higher organisms, including mammals.

Transcriptome Sequencing Reveals Effects of Artificial Feed Domestication on Intestinal Performance and Gene Expression of Carnivorous Mandarin Fish (Siniperca chuatsi) and Related Mechanisms

Mandarin fish (Siniperca chuatsi) is a voracious carnivorous species, usually consuming only live bait fish, but dietary acclimation enables it to accept artificial feed. However, the effects of dietary acclimation on intestinal performance and gene expression in mandarin fish and related mechanisms remain largely unknown. Therefore, this study investigated the effects of artificial feed on intestinal physicochemical and biochemical performance and gene expression in mandarin fish. Mandarin fish were sampled on day 10 after feeding with live dace (LD), at day 40 after subsequent feeding with dead dace plus artificial feed (DD + AF) from day 11 to day 40, and at day 90 after continuous feeding with artificial feed (AF) alone from day 41 to day 90 for transcriptome sequencing. The biochemical analysis results indicated that artificial feed significantly increased the activity of antioxidant enzymes glutathione peroxidase and superoxide dismutase in the intestine, liver, and stomach. Histological analysis demonstrated intestinal damage in mandarin fish fed with artificial feed. The GO and KEGG enrichment analyses indicated that the DEGs in AF vs. DD + AF were significantly enriched in the pentose phosphate pathway, and the DEGs in AF vs. LD were mainly significantly enriched in glycolysis/gluconeogenesis and PPAR signaling pathways. Nineteen feed acclimation-related key genes such as gene pfkfb4a and scd were identified in the intestine and found to exhibit upregulated expressions. These results revealed that artificial feed domestication enhanced the antioxidant capacity of the mandarin fish intestine and reduced hepatic lipid deposition by upregulating the related gene expression of mandarin fish and that the regulation of carbon metabolisms, including sugar, lipid, and steroid metabolisms, might be fundamental mechanisms for mandarin fish to acclimatize to dietary changes. These findings provide novel insights into the feed acclimation mechanism of mandarin fish, holding implications for promoting large-scale artificial feed aquaculture of mandarin fish and improving economic efficiency.

Emamectin benzoate exposure induced carp kidney injury by triggering mitochondrial oxidative stress to accelerate ferroptosis and autophagy

Emamectin benzoate (EMB), commonly used as an insecticide in fishery production, inevitably leaves residual chemicals in aquatic environments. High-level EMB exposure can cause severe damage to multiple systems of marine animals, potentially through mechanisms involving severe mitochondrial damage and oxidative stress. However, it is not clear yet how EMB exposure at a certain level can cause damage to fish kidney tissue. In this study, we exposed carps to an aquatic environment containing 2.4 μg/L of EMB and cultured carp kidney cells in vitro, established a cell model exposed to EMB. Our findings revealed that EMB exposure resulted in severe kidney tissue damage in carp and compromised the viability of grass carp kidney cells (CIK cells). By RNA-seq analysis, EMB exposure led to significant differences in mitochondrial homeostasis, response to ROS, ferroptosis, and autophagy signals in carp kidney tissue. Mechanistically, EMB exposure induced mitochondrial oxidative stress by promoting the generation of mitochondrial superoxide and reducing the activity of antioxidant enzymes. Additionally, EMB exposure triggered loss of mitochondrial membrane potential, an imbalance in mitochondrial fusion/division homeostasis, and dysfunction in oxidative phosphorylation, ultimately impairing ATP synthesis. Notably, EMB exposure also accelerated excessive autophagy and ferroptosis of cells by contributing to the formation of lipid peroxides and autophagosomes, and the deposition of Fe2+. However, N-acetyl-L-cysteine (NAC) treatment alleviated the damage and death of CIK cells by inhibiting oxidative stress. Overall, our study demonstrated that EMB exposure induced mitochondrial oxidative stress, impaired mitochondrial homeostasis, and function, promoted autophagy and ferroptosis of kidney cells, and ultimately led to kidney tissue damage in carp. Our research enhanced the toxicological understanding on EMB exposure and provides a model reference for comparative medicine.

Design, Synthesis, and Bioactivity of Trifluoroethylthio-Substituted Phenylpyrazole Derivatives

As the first marketed phenylpyrazole insecticide, fipronil exhibited remarkable broad-spectrum insecticidal activity. However, it poses a significant threat to aquatic organisms and bees due to its high toxicity. Herein, 35 phenylpyrazole derivatives containing a trifluoroethylthio group on the 4 position of the pyrazole ring were designed and synthesized. The predicted physicochemical properties of all of the compounds were within a reasonable range. The biological assay results revealed that compound 7 showed 69.7% lethality against Aedes albopictus (A. albopictus) at the concentration of 0.125 mg/L. Compounds 7, 7g, 8d, and 10j showed superior insecticidal activity for the control of Plutella xylostella (P. xylostella). Notably, compound 7 showed similar insecticidal activity against Aphis craccivora (A. craccivora) compared with fipronil. Potential surface calculation and molecular docking suggested that different lipophilicity and binding models to the Musca domestica (M. domestica) gamma-aminobutyric acid receptors may be responsible for the decreased activity of the tested derivatives. Toxicity tests indicated that compound 8d (LC50 = 14.28 mg/L) induced obviously 14-fold lower toxicity than fipronil (LC50 = 1.05 mg/L) on embryonic-juvenile zebrafish development.

The uses of zebrafish (Danio rerio) as an in vivo model for toxicological studies: A review based on bibliometrics

An in vivo model is necessary for toxicology. This review analyzed the uses of zebrafish (Danio rerio) in toxicology based on bibliometrics. Totally 56,816 publications about zebrafish from 2002 to 2023 were found in Web of Science Core Collection, with Toxicology as the top 6 among all disciplines. Accordingly, the bibliometric map reveals that "toxicity" has become a hot keyword. It further reveals that the most common exposure types include acute, chronic, and combined exposure. The toxicological effects include behavioral, intestinal, cardiovascular, hepatic, endocrine toxicity, neurotoxicity, immunotoxicity, genotoxicity, and reproductive and transgenerational toxicity. The mechanisms include oxidative stress, inflammation, autophagy, and dysbiosis of gut microbiota. The toxicants commonly evaluated by using zebrafish model include nanomaterials, arsenic, metals, bisphenol, and dioxin. Overall, zebrafish provide a unique and well-accepted model to investigate the toxicological effects and mechanisms. We also discussed the possible ways to address some of the limitations of zebrafish model, such as the combination of human organoids to avoid species differences.