The effects of fipronil exposure on oxidative stress, non-specific immunity, autophagy, and apoptosis in the common carp

Investigating Immunotoxicity in Black Carp (Mylopharyngodon piceus) Fingerlings Exposed to Niclosamide

Niclosamide (NIC) is a potent salicylanilide molluscicide/helminthicide commonly utilized for parasite and mollusc control in aquatic environments. Due to its persistent presence in water bodies, there is growing concern regarding its impact on aquatic organisms, yet this remains inadequately elucidated. Consequently, this study aims to assess the hepatotoxic effects and detoxification capacity of black carp (Mylopharyngodon piceus) in a semi-static system, employing various parameters for analysis. NIC was applied to juvenile black carp at three different concentrations (0, 10 and 50 μg/L) for 28 days in an environmentally realistic manner. Exposure to 50 μg/L NIC resulted in an increase in hepatic lysozyme (LYZ), alkaline phosphatase (ALP), and complement 4 (C4) levels while simultaneously causing a decrease in peroxidase (POD) activity. Additionally, NIC exposure exhibited a dose-dependent effect on elevating serum levels of LYZ, ALP, complement 3 (C3), C4, and immunoglobulin T (IgT). Notably, the mRNA levels of immune-related genes tnfα, il8, and il6, as well as nramp and leap2, were upregulated in fish exposed to NIC. RNA-Seq analysis identified 219 differentially expressed genes (DEGs) in M. piceus after NIC exposure, with 94 upregulated and 125 downregulated genes. KEGG and GO analyses showed enrichment in drug metabolism pathways and activities related to oxidoreductase, lip oprotein particles, and cholesterol transport at 50 μg/L NIC. Additionally, numerous genes associated with lipid metabolism, oxidative stress, and innate immunity were upregulated in NIC-exposed M. piceus. Taken together, these findings indicate that NIC has the potential to cause hepatotoxicity and immunotoxicity in M. piceus. This research offers important insights for further understanding the impact of molluscicide/helminthicide aquatic toxicity in ecosystems.

Alteration of haematological and biochemical biomarkers after sub-lethal chronic malathion (Elathion®) intoxication in freshwater fish, Labeo rohita (Hamilton, 1822)

The present investigation aimed to evaluate the long-term effects of malathion (Elathion®) at two sub-lethal concentrations (0.36 and 1.84 mgL-1) for 45 days after the determination of 96 h-LC50 value (18.35 mgL-1) in a commercially important aquaculture species, Labeo rohita by assaying multiple biomarker approaches. Total erythrocyte count (TEC), and haemoglobulin count (Hb) were found to be decreased while total leucocyte counts (TLC) were increased (p < 0.05) in malathion-intoxicated fish. Malathion exposure significantly reduced (p < 0.05) serum protein levels while significantly increased (p < 0.05) blood glucose levels. RNA activity in muscle was reduced (p < 0.05) while DNA activity increased (p < 0.05) in malathion-intoxicated fish. Acid phosphatase (ACP) activities in the brain; lacate dehydrogenase (LDH) activities in brain and liver were increased (p < 0.05), while alkaline phosphatase (ALP) activities in the brain; succinate dehydrogenase (SDH) activities in the brain, liver and kidney; acetylcholine esterase (AChE) activity in the brain; and ATPase activities in the brain, liver and kidney were reduced (p < 0.05) in comparison to control. Thus, the alteration in studied biomarkers was in a concentation-time dependent manner; however, it was more pronounced at the higher concentration at 45 days of exposure. The alteration in biomarker activity is probably a defensive mechanism/ adaptive response of fish to overcome the stress induced by malathion, which is a novel insight and possible impact on L.rohita. Our findings suggest malathion-induced stress, therefore, the use of malathion needs to be regulated to safeguard aquatic animals including fish and human health.

Immunoassays and Emerging Analytical Techniques of Fipronil and its Metabolites for Food Safety: A Review

Fipronil, classified as a phenylpyrazole insecticide, is utilized to control agricultural, public health, and veterinary pests. Notably, its unique ecological fate involves degradation to toxic metabolites, which poses the risk of contamination in water and foodstuffs and potential human exposure through the food chain. In response to these concerns, there is a pressing need to develop analytical methodologies for detecting fipronil and its metabolites. This review provides a concise overview of the mode of action, metabolism, and toxicology of fipronil. Additionally, various detection strategies, encompassing antibody-based immunoassays and emerging analytical techniques, such as fluorescence assays based on aptamer/molecularly imprinted polymer/fluorescent probes, electrochemical sensors, and Raman spectroscopy, are thoroughly reviewed and discussed. The focus extends to detecting fipronil and its metabolites in crops, fruits, vegetables, animal-derived foods, water, and bodily fluids. This comprehensive exploration contributes valuable insights into the field, aiming to foster the development and innovation of more sensitive, rapid, and applicable analytical methods.

Niclosamide exposure disrupts antioxidant defense, histology, and the liver and gut transcriptome of Chinese soft-shelled turtle (Pelodiscus sinensis)

Niclosamide (NIC) is the only commercially available molluscicide for controlling schistosomiasis, and its negative effects on aquatic animals had been frequently reported in recent years. However, the toxicity mechanism of NIC on the Chinese soft-shelled turtle (Pelodiscus sinensis) have not yet been investigated. Therefore, juvenile turtles were exposed to 0 (control group), 10 (low NIC, L), and 50 (high NIC, H) μg/L NIC for 120 h and our results demonstrated that NIC exposure induced severe pathological changes in the liver of P. sinensis. And the typical symptom included edema, nuclear migration and deformation, and vacuolization. Compared with the liver, the NIC exposure did not cause significant damage in the gut tissue. In addition, the DHE staining demonstrated that the ROS production of liver and gut increased with the increase in concentration of NIC. The activities of antioxidant enzymes including superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) was inhibited with increased malondialdehyde (MDA) content, indicating that the antioxidant defense was significantly perturbed. Further, the transcriptome sequencing and was applied to evaluate the underlying toxicity mechanisms of NIC exposure in liver and gut of P. sinensis. Pathway enrichment showed that the disorder of lipid metabolism and innate immune regulation, including Toll-like receptors (TLRs), tumor necrosis factor (TNF), lectins, and complement and coagulation cascades, were toxicological properties of NIC on P. sinensis. Overall, the current study provides valuable information to understand the toxic effect of NIC on Chinese soft-shelled turtle.

Abamectin causes toxicity to the carp respiratory system by triggering oxidative stress, inflammation, and apoptosis and inhibiting autophagy

Abamectin is a commonly used pesticide in agriculture and fisheries and poses a risk to aquatic species. However, the mechanism of its toxic effects on fish remains to be discovered. In this study, we explored the effects of abamectin exposure at different concentrations on the respiratory system of carp. Carp were divided into three groups, namely the control group, low-dose abamectin treatment group, and high-dose abamectin treatment group. Gill tissue was collected after abamectin exposure for histopathological, biochemical, tunnel, mRNA, and protein expression analysis. Histopathological analysis indicated that abamectin damaged the gill structure. Biochemical analysis showed that abamectin triggered oxidative stress with lowered antioxidant enzyme activities and increased MDA content. Moreover, abamectin led to enhanced INOS levels and pro-inflammatory transcription, activating inflammation. Tunnel results demonstrated that exposure to abamectin induced gill cell apoptosis through an exogenous pathway. In addition, exposure to abamectin activated the PI3K/AKT/mTOR pathway, leading to inhibition of autophagy. Overall, abamectin caused respiratory system toxicity in carp via triggering oxidative stress, inflammation, and apoptosis and inhibiting autophagy. The study suggests that abamectin has a profound toxicity mechanism in the respiratory system of carp, contributing to a better understanding of pesticide risk assessment in aquatic systems.

Comprehensive analysis of immune parameters, mRNA and miRNA profiles, and immune genes expression in the gill of rainbow trout infected with infectious hematopoietic necrosis virus (IHNV)

Rainbow trout (Oncorhynchus mykiss) is a species of cold-water fish with important economic values, widely cultivated worldwide. However, the outbreak of infectious hematopoietic necrosis virus (IHNV) caused the large-scale death of rainbow trout and seriously restricted the development of the trout farming industry. In this study, the changes of immune parameters in different periods (6-, 12-, 24-, 48-, 72-, 96-, 120-, and 144 h post-infection (hpi)), transcriptome profiles of 48 hpi (T48G) compared to control (C48G), and key immune-related genes expression patterns were measured in rainbow trout gill following IHNV challenge through biochemical methods, RNA sequencing (RNA-seq), and quantitative real-time polymerase chain reaction (qRT-PCR). The results showed that alkaline phosphatase (AKP), acid phosphatase (ACP), total superoxide dismutase (T-SOD), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activities, as well as lysozyme (LZM) and malonaldehyde (MDA) content decreased and then increased during infection, and remained at a high level after 48 hpi (P < 0.05), whereas catalase (CAT) activity showed a significant peak at 48 hpi (P < 0.05). The mRNA and miRNA analysis identified 4343 differentially expressed genes (DEGs) and 11 differentially expressed miRNAs (DEMs), and numerous immune-related DEGs involved in the Toll-like receptor signaling pathway, apoptosis, DNA replication, p53 signaling, RIG-I-like receptor signaling pathway, and NOD-like receptor signaling pathway and expression were significantly up-regulated in T48Gm group, including tlr3, tlr7, tlr8, traf3, ifih1, trim25, dhx58, ddh58, hsp90a.1, nlrc3, nlrc5, socs3, irf3, irf7, casp7, mx1, and vig2. The integrated analysis identified several important miRNAs (ola-miR-27d-3p_R+5, gmo-miR-124-3-5p, ssa-miR-301a-5p_L+2, and ssa-miR-146d-3p) that targeted key immune-related DEGs. Expression analysis showed that tlr3, tlr7, traf3, ifih1, dhx58, hap90a.1, irf3, irf7, and mx1 genes increased and then decreased during infection, and peaked at 72 hpi (P < 0.05). However, trim25 expression peaked at 96 hpi (P < 0.05). This study contributes to understanding immune response of rainbow trout against IHNV infection, and provides new insights into the immune regulation mechanisms and disease resistance breeding studies.

Koumine induces apoptosis in Cyprinus carpio liver cells by regulating JAK-STAT and p53 signaling pathways

Koumine is an alkaloid with significant anti-anxiety, anticancer cell proliferation, and analgesic activities, and our previous studies have shown that koumine can be used as an immunostimulant in aquaculture, but the molecular mechanism of its effect remains unclear. We fed a basal diet with 0, 0.2, 2, and 20 mg/kg koumine to C. carpio for 10 weeks, and comprehensive studies of the histological and biochemical parameters and transcriptomes of the four groups were performed. Histological results indicated that the number of apoptotic cells in the liver increased with increasing koumine concentration. Compared with those of the control group, the malondialdehyde, superoxide dismutase, catalase, acid phosphatase, alkaline phosphatase, and lactate dehydrogenase levels of the treatment group increased to varying degrees. In total, 100.11 GB of clean data, 4774 DEGs, and 138 differentially expressed genes were obtained from the transcriptome data. Differentially expressed genes were classified into 187 signalling pathways, and the circadian rhythm signalling pathway, the JAK-STAT signalling pathway, the p53 signalling pathway and the PPAR signalling pathway were the top enriched pathways. The qRT-PCR results confirmed that the key genes ifnar1, socs3l, epoa, ghra, cMyc, mcl-1, shisa4, and gtse1 involved in balancing cell proliferation and apoptosis were enriched in these pathways. We discovered that the JAK-STAT and p53 pathways are important targets of koumine. Such information contributes to a better understanding of the potential mechanism by which koumine regulates hepatic immunity as well as to lays the theoretical foundation for its application.

Difenoconazole causes cardiotoxicity in common carp (Cyprinus carpio): Involvement of oxidative stress, inflammation, apoptosis and autophagy

Difenoconazole, a commonly used broad-spectrum triazole fungicide, is widely applied to fish culture in paddy fields. Due to its high chemical stability, low biodegradability, and easy transfer, difenoconazole persists in aquatic systems, raising public awareness of environmental threats. Difenoconazole causes cardiotoxicity in carp, however, the potential mechanisms of difenoconazole-induced cardiotoxicity remain unclear. Here, common carp were exposed to difenoconazole, and cardiotoxicity was evaluated by measuring the creatine kinase (CK) and the lactate dehydrogenase (LDH) in the serum. Cardiac pathological injury was determined by HE staining. The content and expression of oxidative stress indicators were detected using biochemical kits and qPCR analysis. Changes in inflammation-related cytokines were examined by qPCR. Apoptosis levels were assessed by TUNEL assay and qPCR. The occurrence of autophagy was measured by western blotting detection of autophagy flux LC3II/LC3I, and autophagy regulatory pathways were detected using qPCR. The results showed that difenoconazole exposure induced cardiotoxicity accompanied by obviously elevated LDH and CK levels and caused myocardial fibers to swell and inflammatory cells to increase. Elevated peroxide MDA and reduced transcriptional and activity levels of the antioxidant enzymes CAT, SOD and GSH-Px were dependent on the Nrf2/Keap-1 pathway. Moreover, the proinflammatory cytokines IL-1β, IL-6, and TNF-α were upregulated, iNOS activity was enhanced, whereas the anti-inflammatory cytokines TGF-β1 and IL-10 were downregulated after exposure to difenoconazole. Moreover, apoptosis was observed in the TUNEL assay and mediated through the p53/Bcl-2/Bax-Caspase-9 mitochondrial pathway. Furthermore, difenoconazole increased the autophagy markers LC3II, ATG5 and p62 and regulated them through the PI3K/AKT/mTOR pathway. Altogether, this study demonstrated that difenoconazole exposure caused common carp cardiotoxicity, which is regulated by oxidative stress, inflammation, apoptosis and autophagy, providing central data for toxicological risk assessment of difenoconazole in the ecological environment.

Global Metabolomics of Fireflies (Coleoptera: Lampyridae) Explore Metabolic Adaptation to Fresh Water in Insects

Aquatic insects are well-adapted to freshwater environments, but metabolic mechanisms of such adaptations, particularly to primary environmental factors (e.g., hypoxia, water pressure, dark light, and abundant microbes), are poorly known. Most firefly species (Coleoptera: Lampyridae) are terrestrial, but the larvae of a few species are aquatic. We generated 24 global metabolomic profiles of larvae and adults of Aquatica leii (freshwater) and Lychnuris praetexta (terrestrial) to identify freshwater adaptation-related metabolites (AARMs). We identified 110 differentially abundant metabolites (DAMs) in A. leii (adults vs. aquatic larvae) and 183 DAMs in L. praetexta (adults vs. terrestrial larvae). Furthermore, 100 DAMs specific to aquatic A. leii larvae were screened as AARMs via interspecific comparisons (A. leii vs. L. praetexta), which were primarily involved in antioxidant activity, immune response, energy production and metabolism, and chitin biosynthesis. They were assigned to six categories/superclasses (e.g., lipids and lipid-like molecules, organic acids and derivatives, and organoheterocyclic compound). Finally, ten metabolic pathways shared between KEGG terms specific to aquatic fireflies and enriched by AARMs were screened as aquatic adaptation-related pathways (AARPs). These AARPs were primarily involved in energy metabolism, xenobiotic biodegradation, protection of oxidative/immune damage, oxidative stress response, and sense function (e.g., glycine, serine and threonine metabolism, drug metabolism-cytochrome P450, and taste transduction), and certain aspects of morphology (e.g., steroid hormone biosynthesis). These results provide evidence suggesting that abundance changes in metabolomes contribute to freshwater adaptation of fireflies. The metabolites identified here may be vital targets for future work to determine the mechanism of freshwater adaptation in insects.

Integrated analysis of immune parameters, miRNA-mRNA interaction, and immune genes expression in the liver of rainbow trout following infectious hematopoietic necrosis virus infection

Rainbow trout (Oncorhynchus mykiss) is an important economical cold-water fish worldwide. However, infection with infectious hematopoietic necrosis virus (IHNV) has severely restricted the development of aquaculture and caused huge economic losses. Currently, little is known about the immune defense mechanisms of rainbow trout against IHNV. In this study, we detected the changes of immune parameters over different post-infection periods (6-, 12-, 24-, 48-, 72-, 96-, 120-, and 144 hours post-infection (hpi)), mRNA and miRNA expression profiles under 48 hpi (T48L) compared to control (C48L), and key immune-related genes expression patterns in rainbow trout liver following IHNV challenge through biochemical methods, RNA-seq, and qRT-PCR, and the function of miR-330-y was verified by overexpression and silencing in vitro and in vivo. The results revealed that alkaline phosphatase (AKP), alanine aminotransferase (ALT), catalase (CAT), and total superoxide dismutase (T-SOD) activities, and lysozyme (LZM) content showed significant peaks at 48 hpi, whereas malondialdehyde (MDA) content and aspartate aminotransferase (AST) activity decreased continuously during infection, and acid phosphatase (ACP) activity varied slightly. From RNA-seq, a total of 6844 genes and 86 miRNAs were differentially expressed, and numerous immune-related differentially expressed genes (DEGs) involved in RIG-I-like receptor signaling pathway, Toll-like receptor signaling pathway, NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, and antigen processing and presentation were significantly upregulated in T48Lm group, including IFIH1, DHX58, MAVS, TRAF3, IRF3, IRF7, MX1, TLR3, TLR8, MYD88, NOD1, NOD2, IL-8, CXCR1, CD209, CD83, and TAP1. Integrated analysis identified seven miRNAs (miR-425-x, miR-185-x, miR-338-x, miR-330-y, miR-361-x, miR-505-y, and miR-191-x) that target at least three key immune-related DEGs. Expression analysis showed that IFIH1, DHX58, IRF3, IRF7, MX1, TLR3, TLR8, and MYD88 showed a marked increase after 24 hpi during infection. Further research confirmed TAP1 as one of the targets of miR-330-y, overexpression of miR-330-y with mimics or agomir significantly reduced the expression levels of TAP1, IRF3, and IFN, and the opposite effects were obtained by inhibitor. These results facilitate in-depth understanding of the immune mechanisms in rainbow trout against IHNV.

Chronic exposure to deltamethrin disrupts intestinal health and intestinal microbiota in juvenile crucian carp

The indiscriminate use of deltamethrin in agriculture and aquaculture can lead to residues increased in many regions, which poses negative impacts on intestinal health of aquatic organisms. Although the potential toxicity of deltamethrin have recently attracted attention, the comprehensive studies on intestinal injuries after chronic deltamethrin exposure remain poorly understood. Herein, in a 28-day chronic toxicity test, crucian carp expose to different concentrations of deltamethrin (0, 0.3, and 0.6 μg/L) were used as the research object. We found that the morphology changes and increased goblet cells in intestinal tissue, and the extent of tissue injury increased along with the increasing exposure dose of deltamethrin. Additionally, the genes expression of antioxidant activity (Cu/Zn superoxide dismutase (Cu-Zn SOD), glutathione peroxidase 1 (GPX1), and catalase (CAT)), inflammatory response (tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), and interleukin 1 beta (IL-1β)), and tight junctions (Claudin 12 (CLDN12), and tight junction protein 1 (ZO-1)) dramatically increased. Meanwhile, the apoptosis and autophagy process were triggered through caspase-9 cascade and autophagy related 5 (ATG5)- autophagy related 12 (ATG12) conjugate. Besides, chronic deltamethrin exposure increased the amount of Proteobacteria and Verrucomicrobiota, while decreased Fusobacteriota abundance, resulting in intestinal microbiota function disorders. In summary, our results highlight that chronic exposure to deltamethrin cause serious intestinal toxicity and results in physiological changes and intestinal flora disturbances.

Direct analysis of metabolites in the liver tissue of zebrafish exposed to fiproles by internal extractive electrospray ionization mass spectrometry

Exploring the metabolic disturbance of fipronil and its derivatives in aquatic organisms may provide a more comprehensive understanding of the impact of fipronil on the ecological environment. In this work, internal extractive electrospray ionization mass spectrometry (iEESI-MS) was used to directly analyze metabolites in the liver tissue of zebrafish exposed to fipronil and its three derivatives. Partial least squares-discriminant analysis (PLS-DA) revealed that 32 signals were considered as differential signals in zebrafish after the exposure treatment of fipronil and its derivatives, including phosphatidylcholines (PCs), lysophosphatidylcholines (LPCs), phosphatidylethanolamines (PEs), fatty acids and so on. The pathway analysis result showed that both fipronil and its derivatives have a significant impact on the glycerophospholipid metabolism of zebrafish. Besides, the intensities of PC signals in the liver samples of each group showed such a trend: mixed fiprole exposed group > fipronil sulfone exposed group ≈ fipronil sulfide exposed group > fipronil exposed group > fipronil desulfinyl exposed group > control group, indicating that mixed exposure of fipronil and its derivatives exhibited more significant metabolic disturbance in zebrafish. Taken together, iEESI-MS is applied to environmental toxicology and investigating the metabolic disturbance induced by fipronil and its derivatives in aquatic organisms, providing a new analytical method for this field.