Mixture toxicity of thiophanate-methyl and fenvalerate to embryonic zebrafish (Danio rerio) and its underlying mechanism

Synergistic risk in the gut and liver: Insights into the toxic mechanisms and molecular interactions of combined exposure to triazophos and fenvalerate in zebrafish

The simultaneous or sequential application of pesticides such as triazophos (TRI) and fenvalerate (FEN) in agriculture results in their residues co-existing in the environments. However, the impact of co-exposure to TRI and FEN on the gut-liver axis, along with the underlying mechanisms, remains unclear. Our results showed that exposure to FEN (96 h-LC50 value of 0.096 mg a.i. L-1) was more toxic to adult zebrafish compared to TRI (96 h-LC50 value of 6.75 mg a.i. L-1). Furthermore, the study aimed to reveal the toxic potencies of individual and combined exposure to TRI and FEN on the liver-gut axis in zebrafish (Danio rerio). Our results also indicated that pesticide exposure decreased tight junction molecule expression and increased intestinal inflammatory molecule expression in D. rerio, with co-exposure demonstrating enhanced toxicity. Co-exposure altered gut flora structure and species abundance. RNA-Seq sequencing revealed changes in liver gene expressions, particularly enrichment of P53 signaling. Molecular docking demonstrated FEN's stronger binding to P53 and Caspase3, correlating with its higher toxicity. Liver pathology confirmed exacerbated liver damage by individual and co-exposures, with co-exposure inducing more severe liver injury. qPCR results showed increased pro-apoptotic gene expression and decreased anti-apoptotic gene expression, with co-exposure exhibiting an interactive effect. Overall, this study identifies specific targets and pathways influenced by these pesticides, revealing toxicity mechanisms involving the gut-liver axis, which is crucial for environmental risk assessment of pesticide mixtures.

Biocontrol Methods for the Management of Sclerotinia sclerotiorum in Legumes: A Review

Sclerotinia sclerotiorum is an economically damaging fungal pathogen that causes Sclerotinia stem rot in legumes, producing enormous yield losses. This pathogen is difficult to control due to its wide host spectrum and ability to produce sclerotia, which are resistant bodies that can remain active for long periods under harsh environmental conditions. Here, the biocontrol methods for the management of S. sclerotiorum in legumes are reviewed. Bacillus strains, which synthesized lipopeptides and volatile organic compounds, showed high efficacies in soybean plants, whereas the highest efficacies for the control of the pathogen in alfalfa and common bean were observed when using Coniothyrium minitans and Streptomyces spp., respectively. The biocontrol efficacies in fields were under 65%, highlighting the lack of strategies to achieve a complete control. Overall, although most studies involved extensive screenings using different biocontrol agent concentrations and application conditions, there is a lack of knowledge regarding the specific antifungal mechanisms, which limits the optimization of the reported methods.

Behavioral Effects of the Mixture and the Single Compounds Carbendazim, Fipronil, and Sulfentrazone on Zebrafish (Danio rerio) Larvae

Pesticides are often detected in freshwater, but their impact on the aquatic environment is commonly studied based on single compounds, underestimating the potential additive effects of these mixtures. Even at low concentrations, pesticides can negatively affect organisms, altering important behaviors that can have repercussions at the population level. This study used a multi-behavioral approach to evaluate the effects of zebrafish larvae exposure to carbendazim (C), fipronil (F), and sulfentrazone (S), individually and mixed. Five behavioral tests, thigmotaxis, touch sensitivity, optomotor response, bouncing ball test, and larval exploratory behavior, were performed to assess potential effects on anxiety, fear, and spatial and social interaction. Significant changes were observed in the performance of larvae exposed to all compounds and their mixtures. Among the single pesticides, exposure to S produced the most behavioral alterations, followed by F and C, respectively. A synergistic effect between the compounds was observed in the C + F group, which showed more behavioral effects than the groups exposed to pesticides individually. The use of behavioral tests to evaluate pesticide mixtures is important to standardize methods and associate behavioral changes with ecologically relevant events, thus creating a more realistic scenario for investigating the potential environmental impacts of these compounds.

Biochemical and gene expression alterations due to individual exposure of atrazine, dichlorvos, and imidacloprid and their combination in zebrafish

In environmental toxicology, combined toxicity has emerged as an important concern. Atrazine (ATZ), dichlorvos (DIC), and imidacloprid (IMD) are the major pesticides, extensively used to control insect, flies, mosquitoes, and weed. Here, we investigate whether the exposure to three different types of pesticides individually and in combination for 24 h alters antioxidant enzyme responses in zebrafish (Danio rerio). Oxidative stress parameters (biochemical and mRNA expression), acetylcholinesterase (AChE) activity, and Metallothionein-II (MT-II) mRNA expression levels were measured. Present work includes toxicological assessment of individual and combined (CMD) exposure of ATZ (185.4 µM), DIC (181 µM), IMD (97.8 µ), and CMD (ATZ 92.7 µM + DIC 90.5 µM + IMD 48.9 µM), in the liver, kidney, and brain of adult zebrafish. Lipid peroxidation (LPO), glutathione (GSH) content, AChE, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activity along with mRNA expression of SOD, CAT, GPx, and MT-II were evaluated. Briefly, LPO, GSH content, the activity of AChE, and all antioxidant enzymes enhanced significantly in individual exposure, which was further altered in the CMD group. The mRNA expression of SOD, CAT, GPx, and MT-II in the liver and kidney showed significant down-regulation in all exposed groups. In the brain, significant upregulation in mRNA expression of SOD, CAT, GPx, and MT-II was observed in DIC and IMD groups, while ATZ and CMD showed significant downregulation except for GPx. Findings postulate that the CMD group exhibits synergistic toxic manifestation. The present study provides the baseline data on the combined toxic effects of pesticides and suggests regulating the use of pesticides.

Interacted toxic mechanisms of ochratoxin A and tricyclazole on the zebrafish (Danio rerio)

Despite the current efforts to identify the mixtures of chemical pollutants, they are often "binned" into their corresponding pollutant groups. Limited studies have investigated complex mixtures of chemical pollutants co-occurring across different groups. The combined toxic impacts of several substances become a critical consideration in toxicology because chemical combinations can exert a greater deleterious effect than the single components in the mixture. In the current work, we assessed the joint impacts of ochratoxin A and tricyclazole on the zebrafish (Danio rerio) embryos and explored their underlying signaling pathways. Ochratoxin A displayed higher toxicity than tricyclazole, with a 10-day LC₅₀ of 0.16 mg L^-1, whereas that for tricyclazole was 1.94 mg L^-1. The combination of ochratoxin A and tricyclazole exhibited a synergistic impact on D. rerio. The activities of detoxification enzymes GST and CYP450, as well as apoptosis-associated enzyme caspase 3, were distinctly changed in most individual and mixture exposures comparing to the untreated group. Upon both individual and mixture exposures, more dramatic variations were detected in the expressions of nine genes, such as the apoptosis genes cas3 and bax, antioxidant gene mn-sod, immunosuppression gene il-1β, and the endocrine system genes trα, dio1, trβ, ugtlab, and crh, compared with the untreated group. These findings suggested that the simultaneous exposure to low doses of mycotoxins and pesticides in food commodities was more toxic than predicted from the individual chemicals. Considering the frequent co-occurrence of mycotoxins and pesticides in the diet, this synergy should be considered in future assessments.

Impacts of co-exposure to zearalenone and trifloxystrobin on the enzymatic activity and gene expression in zebrafish

Although humans and animals are usually exposed to combinations of toxic substances, little is known about the interactive toxicity of mycotoxins and farm chemicals. Therefore, we can not precisely evaluate the health risks of combined exposure. In the present work, using different approaches, we examined the toxic impacts of zearalenone and trifloxystrobin on zebrafish (Danio rerio). Our findings showed that the lethal toxicity of zearalenone to embryonic fish with a 10-day LC₅₀ of 0.59 mg L^-1 was lower than trifloxystrobin (0.037 mg L^-1). Besides, the mixture of zearalenone and trifloxystrobin triggered acute synergetic toxicity to embryonic fish. Moreover, the contents of CAT, CYP450, and VTG were distinctly altered in most single and combined exposures. Transcriptional levels of 23 genes involved in the oxidative response, apoptosis, immune, and endocrine systems were determined. Our results implied that eight genes (cas9, apaf-1, bcl-2, il-8, trb, vtg1, erβ1, and tg) displayed greater changes when exposed to the mixture of zearalenone and trifloxystrobin compared with the corresponding individual chemicals. Our findings indicated that performing the risk assessment based on the combined impact rather than the individual dosage response of these chemicals was more accurate. Nevertheless, further investigations are still necessary to reveal the modes of action of mycotoxin and pesticide combinations and alleviate their effects on human health.

Combined toxicity of acetamiprid and cadmium to larval zebrafish (Danio rerio) based on metabolomic analysis

Emerging contaminants, such as neonicotinoid pesticide acetamiprid (Ace), are frequently detected in the water environment, which can interact with existing heavy metal cadmium (Cd) to produce unpredicted influence. Limited studies have evaluated the effects of multiple pollutant exposures on aquatic animals. Here, we characterized the joint toxicity of Ace and Cd exposure to zebrafish (Danio rerio). The results revealed that Cd and its combined exposure with Ace had an inhibitory effect on the growth of larval zebrafish and induced morphological defects. Combined exposure to high doses of Ace and Cd could significantly reduce the levels of TG, glucose, and pyruvate in larval zebrafish. Untargeted metabolomics revealed that Cd treatment (285) produced more differentially expressed metabolites (DEMs) than Ace treatment (115), and combined treatment produced the most DEMs (294). The KEGG pathway enrichment analysis showed that they could disrupt riboflavin metabolism, amino acid metabolism, and glycolipid metabolism in the larvae of D. rerio. ELISA showed that VB2, FMN, and FAD levels were significantly increased. In addition, gene expression analysis exhibited that the mRNA levels of essential genes related to glycolipid metabolism were substantially affected, such as PK, PEPckc, PPAR-α, and FABP6. Furthermore, targeted amino acid metabolomics confirmed that both single exposure to Cd and combined exposure to Ace and Cd altered the levels of amino acids in larvae, including ALA, ARG, MET, PRO, TYR, VAL, GLY, ORN, and PHE. Taken together, exposure to Ace and Cd, alone or in combination, exerted harmful effects on the individual development, riboflavin metabolism, glycolipid metabolism, and amino acid metabolism disorder of D. rerio. These findings highlighted that more attention should be paid to the compound toxicity of chemical mixtures to aquatic organisms.

Thiophanate-methyl induces notochord toxicity by activating the PI3K-mTOR pathway in zebrafish (Danio rerio) embryos

Thiophanate-methyl (TM), a typical pesticide widely used worldwide, was detected in rivers, soil, fruits, and vegetables. Thus, it is urgent to identify the potential harm of TM residual to non-target organisms and its molecular mechanisms. We used zebrafish (Danio rerio) in this study to evaluate TM toxicity. TM exposure induced developmental toxicity, including inhibited hatchability, reduced heart rates, restrained spontaneous locomotion, and decreased body length. Furthermore, we observed obvious toxicity in the notochord and detected increased expression levels of notochord-related genes (shha, col2a, and tbxta) by in situ hybridization in zebrafish larvae. In addition, calcein staining, alkaline phosphatase (ALP) activity analysis, and anatomic analysis indicated that TM induced notochord toxicity. We used rescue experiments to verify whether the PI3K-mTOR pathway involved in the notochord development was the cause of notochord abnormalities. Rapamycin and LY294002 (an inhibitor of PI3K) relieve notochord toxicity caused by TM, including morphological abnormalities. In summary, TM might induce notochord toxicity by activating the PI3K-mTOR pathway in zebrafish.

Transgenerational effects of co-exposure to cadmium and carbofuran on zebrafish based on biochemical and transcriptomic analyses

The combined toxicity of heavy metals and pesticides to aquatic organisms is still largely unexplored. In this study, we investigated the combined impacts of cadmium (Cd) and carbofuran (CAR) on female zebrafish (F0 generation) and their following F1 generation. Results showed that mixtures of Cd and CAR induced acute synergistic effects on both zebrafish adults of the F0 generation and embryos of the F1 generation. Combined exposure to Cd and CAR could obviously alter the hepatic VTG level of females, and the individual exposures increased the relative mRNA levels of vtg1 and vtg2. Through maternal transmission, co-exposure of Cd and CAR caused toxicity to 4-day-old larvae of the F1 generation, evidenced by the significant changes in T4 and VTG levels, CYP450 activity, and the relative transcriptional levels of genes related to the hormone, oxidative stress, and apoptosis. These effects were also reflected by the global gene expression pattern to 7-day-old larvae of F1 generation using the transcriptomic analysis, and they could also affect energy metabolism. Our results provided a more comprehensive insight into the transgenerational toxic impacts of heavy metal and pesticide mixtures. These findings highlighted that it was highly necessary to consider transgenerational exposures in the ecological risk assessment of chemical mixtures.

Immunotoxicological effects of insecticides in exposed fishes

Biologically active compounds used in agriculture that develop near aquatic environments easily spill into rivers or lakes. As a result, insecticides, herbicides and fungicides are observed worldwide in aquatic environments and accumulated in aquatic organism. Many insecticides, including organochlorine and organophosphate, have long been banned long ago because of their high persistence and non-target toxicity. However, previous studies have shown that persistent pesticides remain in aquatic organisms. The immune system is the first defense mechanism against exposure to persistent organic pollutants or pesticides that have been released into the aquatic environment. Many insecticides have been reported to cause immunotoxicity, which is represented by alteration of phagocytic and lysozyme activity. Recent studies show that immunotoxicity by insecticides exerts a more complex mechanism in fish. Insecticides induce immunotoxic effects, such as the release of inflammatory cytokines from head kidney macrophages and inhibition of immune cell proliferation in fish, which can lead to death in severe cases. Even currently used pesticides, such as pyrethroid, with low bioaccumulation have been shown to induce immunotoxicological effects in fish when exposed continuously. Therefore, this review describes the types and bioaccumulation of insecticides that cause immunotoxicity and detailed immunotoxicological mechanisms in fish tissues.

Combined toxicity of endocrine-disrupting chemicals: A review

The combined toxicological assessment provides a realistic approach for hazard evaluation of chemical cocktails that co-existed in the environment. This review provides a holistic insight into the studies highlighting the mixture toxicity of the endocrine-disrupting chemicals (EDCs), especially focusing on the screening of biochemical pathways and other toxicogenetic endpoints. Reviewed literature showed that numerous multiplexed toxicogenomic techniques were applied to determine reproductive effects in vertebrates, but limited studies were found in non-mammalian species after mixture chemical exposure. Further, we found that the experimental design and concentration selection are the two important parameters in mixture toxicity studies that should be time- and cost-effective, highly precise, and environmentally relevant. A summary of EDC mixtures affecting the thyroid axis, estrogen axis, androgen axis, growth stress, and immune system via in vivo bioassays was also presented. It is interesting to mention that majority of estrogenic effects of the mixtures were sex-dependent, particularly observed in male fish as compared to female fish. Further, the androgen axis was perturbed with serious malformations in male rat testis (epididymal or gubernacular lesions, and deciduous spermatids). Also, transgenerational epigenetic effects were promoted in the F₃ and F₄ generations in the form of DNA methylation epimutations in sperm, increasing polycystic ovaries and reducing the offspring. Similarly, increased oxidative stress, high antioxidant enzymatic activities, disturbed estrous cycle, and decreased steroidogenesis were the commonly found effects after acute or chronic exposure to EDC mixtures. Importantly, the concentration addition (CA) and independent action (IA) models became more prevalent and suitable predictive models to unveil the prominence of synergistic estrogenic and anti-androgenic effects of chemical mixtures. More importantly, this review encompasses the research challenges and gaps in the existing knowledge and specific future research perspectives on combined toxicity.

Proteomic analysis of hemocyte reveals the immune regulatory mechanisms after the injection of corticosteroid-releasing hormone in mud crab Scylla Paramamosain

Corticosteroid-releasing hormone (CRH) is a crucial neuroendocrine-immune factor regulating the immune response of Scylla paramamosain. To understand the regulatory mechanisms of CRH in S. paramamosain, the hemolymph of S. paramamosain with injection of CRH (1.5 ng/crab) at 24 h were chosen to perform proteomic analysis in this study. Furthermore, quantitative real-time PCR (RT-PCR) method was used to validate the accuracy of proteomic data at 24 h after CRH injection. The proteomic data showed that 255 DEPs were identified, in which 231 and 24 were up- or down-regulated, respectively. Besides, the results of enriched pathways showed that the DEPs were involved in signaling pathways, cellular immunity, humoral immunity and the response of immune related processes. These results revealed that CRH promoted the activation of signal transduction, regulated immune systems and antioxidation, and enhanced the immune related processes (such as protein synthesis, protein transport, carbohydrate mobilization and energy redistribution). These findings will benefit to foster the understanding on the effects of glucocorticoids on neuroendocrine-immune (NEI) networks of crustacean, and supply a substantial material and foundation for further researching of the NEI response. SIGNIFICANCE: Corticotrophin-releasing hormone (CRH) is a 41-amino acid neuropeptide and has been preliminarily studied in aquatic animals. CRH can regulate many important physiological activities comprising protein synthesis, energy metabolism, growth, breeding and behavior in fish, which play an important roles in neuroendocrine-immune (NEI) regulatory network of fish. The neuroendocrine system of crustacean has a primary research, that inspired by fish NEI network. Despite the research on the neuroendocrine system in crustacean has rapidly increased in recent years, our understanding of the regulation between neuroendocrine system and immune system in crustacean is still limited. The research on the strategy of NEI network in crustaceans becomes a significant issue. In the present study, the isobaric tags for relative and absolute quantification (iTRAQ) technology approach were applied to examine the NEI network of Scylla Paramamosain. control group and treatment group (CRH: 1.5 ng/crab) were settled for the iTRAQ experiment, and sampled at 24 h after CRH injection. The study aimed to gain knowledge on the immune response in Scylla Paramamosain after CRH injection and identify related differentially expressed proteins (DEPs) of the crab. The results of this study provide a preliminary resource for analysis the immune mechanism for crustaceans. In general, our work represents the first report of the utilization of the iTRAQ proteomics method for the study of NEI regulatory network in Scylla Paramamosain after CRH injection. We identified a number of DEPs involved in diverse pathways including immune signaling pathways, cellular immunity, humoral immunity, immune related process. These results demonstrated a very complex network involving immune and multiple related metabolic pathways in hemocytes of Scylla Paramamosain and will be of great value in understanding the crab neuroendocrine-immune immune mechanism.