Malformations and mortality in zebrafish early stages associated with elevated caspase activity after 24 h exposure to MS-222

Chemical Composition, In Vitro Antitumor Effect, and Toxicity in Zebrafish of the Essential Oil from Conyza bonariensis (L.) Cronquist (Asteraceae)

The essential oil from Conyza bonariensis (Asteraceae) aerial parts (CBEO) was extracted by hydrodistillation in a Clevenger-type apparatus and was characterized by gas chromatography-mass spectrometry. The antitumor potential was evaluated against human tumor cell lines (melanoma, cervical, colorectal, and leukemias), as well as non-tumor keratinocyte lines using the MTT assay. The effect of CBEO on the production of Reactive Oxygen Species (ROS) was evaluated by DCFH-DA assay, and a protection assay using the antioxidant N-acetyl-L-cysteine (NAC) was also performed. Moreover, the CBEO toxicity in the zebrafish model was assessed. The majority of the CBEO compound was (Z)-2-lachnophyllum ester (57.24%). The CBEO exhibited selectivity towards SK-MEL-28 melanoma cells (half maximal inhibitory concentration, IC50 = 18.65 ± 1.16 µg/mL), and induced a significant increase in ROS production. In addition, the CBEO's cytotoxicity against SK-MEL-28 cells was reduced after pretreatment with NAC. Furthermore, after 96 h of exposure, 1.5 µg/mL CBEO induced death of all zebrafish embryos. Non-lethal effects were observed after exposure to 0.50-1.25 µg/mL CBEO. Additionally, significant alterations in the activity of enzymes associated with oxidative stress in zebrafish larvae were observed. These results provide evidence that CBEO has a significant in vitro antimelanoma effect by increasing ROS production and moderate embryotoxicity in zebrafish.

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.

Mixture toxicity of pyraclostrobine and metiram to the zebrafish (Danio rerio) and its potential mechanism

The interplay between pesticides plays a critical role in ecotoxicology since these chemicals rarely emerge as single substances but rather in mixtures with other chemicals. In the present work, we purposed to clarify the combined toxic impacts of pyraclostrobine (PYR) and metiram (MET) on the zebrafish by using numerous indicators. Results exhibited that the 4-day LC₅₀ value of MET to fish embryos was 0.0025 mg a.i. L^-1, which was lower compared with PYR (0.019 mg a.i. L^-1). Combinations of PYR and MET presented a synergetic impact on fish embryos. Contents of POD, CYP450, and VTG were drastically increased in the plurality of the single and joint treatments relative to the baseline value. Three genes, including vtg1, crh, and il-8, related to the endocrine and immune systems, were also surprisingly up-regulated when fish were challenged by the individual and mixture pesticides compared with the baseline value. These results afforded valuable information on the latent toxicity mechanisms of co-exposure for PYR and MET in the early growth stage of fish. Moreover, our data also revealed that frequent application of these two pesticides might exert a potentially ecotoxicological hazard on aquatic ecosystems. Collectively, the present study provided valuable guidance for the risk evaluation of chemical combinations.

Mixture effects of imidacloprid and difenconazole on enzymatic activity and gene expression in small yellow croakers (Larimichthys polyactis)

Agrochemicals usually exist as mixtures in aqueous ecosystems and have harmful impacts on the natural environment. Nonetheless, the combined effects and underlying mechanisms of agrochemicals on aqueous organisms remain poorly understood. In the present study, the interactive effects of imidacloprid (IMI) and difenconazole (DIF) on the embryos of small yellow croakers (Larimichthys polyactis) were assessed using various toxicological assays, including acute toxicity, enzymatic activity, and gene expression changes. The results showed that DIF (72-h LC₅₀ value of 0.20 mg L^-1) had higher toxicity than IMI (72-h LC₅₀ value of 12.5 mgL^-1). Simultaneously, combinations of IMI and DIF exerted synergistic acute effects on the embryos of L. polyactis. In addition, the SOD, CAT, GST, and CarE activities were noticeably altered in most single and mixed exposures, relative to the untreated control. The expression of four genes (cyp19a1b, ngln2, klf2a, and socs3a) related to the immune system, endocrine system, and neurodevelopment was also surprisingly altered when the embryos of L. polyactis were subjected to individual and combined exposures relative to the untreated control. Changes in enzymatic activity and gene expression might provide early warning indices for the identification of agrochemical co-exposure. The results of this study provide valuable insights into the comprehensive toxicity of agrochemical mixtures to L. polyactis. Further studies on the long-term effects of agrochemical mixtures on marine fish should be conducted to formulate definitive conclusions concerning hazards.

Joint toxic effects of phoxim and lambda-cyhalothrin on the small yellow croaker (Larimichthys polyactis)

Although pesticides commonly exist as combinations in real-life situations of the aquatic ecosystem, the impact of the toxicity of their mixtures has remained largely unclear. In this study, we investigated the combined effects of two neurotoxic pesticides, including one organophosphate insecticide phoxim (PHO) and one pyrethroid insecticide lambda-cyhalothrin (LCY), on the embryos of the small yellow croaker (Larimichthys polyactis), and their potential pathways. LCY exhibited higher toxicity relative to PHO, with a 72-h LC₅₀ value of 0.0074 mg a.i. L^-1, while the corresponding value for PHO was 0.12 mg a.i. L^-1. The mixture of PHO and LCY exerted a synergistic effect on the embryos of L. polyactis. The activities of antioxidant enzyme CAT and apoptotic enzyme caspase 3 were substantially changed in most single and combined exposure groups relative to the baseline value. Under both single and combined exposures, more significant changes were found in the mRNA expression of five genes, including the immunosuppression gene ngln2, the apoptosis gene P53, the endocrine system gene cyp19a1b, as well as neurodevelopment genes of ap and acp2, relative to the baseline value. Furthermore, the non-target metabolomic analysis demonstrated that hundreds of differential metabolites, including two bile acids (taurodeoxycholic acid and tauroursodeoxycholic acid), were significantly increased in the exposure groups. The bile acids were closely associated with the gut microbiota, and 16S rRNA sequencing results demonstrated dysfunction of the gut microbiota after exposure, especially in the combined exposure group. Our findings indicated that there might be a potential risk connected to the co-occurrence of these two pesticides in aquatic vertebrates. Consequently, future ecological risk assessments should incorporate synergistic mixtures because the current risk assessments do not consider them.

Mixture toxicity of cadmium and acetamiprid to the early life stages of zebrafish (Danio rerio)

Aquatic organisms are often exposed to contaminants that occur in the natural environment. Nevertheless, the toxic effects of chemical combinations on aquatic animals and their underlying toxic mechanisms for dealing with such exposures are still not fully understood. In this study, we investigated the combined effects of cadmium (Cd) and acetamiprid (ACE) on zebrafish (Danio rerio) using various endpoints. Cd exhibited a 96-h LC₅₀ value of 4.77 mg a.i. L^-1 against zebrafish embryos, which was lower than that of ACE (152.6 mg a.i. L^-1). In contrast, the 96-h LC₅₀ value of the mixture of Cd and ACE was 157.4 mg a.i. L^-1. The mixture of Cd and ACE had a synergetic effect on the organisms. The activities of T-SOD, POD, and CarE were significantly changed in most exposures compared with the control group. In addition, five genes (TRα, crh, Tnf, IL, and P53) involved in oxidative stress, cellular apoptosis, the immune system, and the endocrine system exhibited more remarkable changes when exposed to chemical mixtures relative to their individual counterparts, demonstrating variations in the cellular and mRNA expression levels induced by the mixture exposure of ACE and Cd during the embryonic development of zebrafish. Therefore, these results indicated that the combined pollution of ACE and Cd could be a potentially hazardous factor, and further investigation is necessary for the safety evaluation and application of ACE. Moreover, further investigation on the combined toxicities of various chemicals must be performed to determine the chemical mixtures with synergistic responses.

Cysteamine affects skeletal development and impairs motor behavior in zebrafish

Cysteamine is a kind of feed additive commonly used in agricultural production. It is also the only targeted agent for the treatment of cystinosis, and there are some side effects in clinical applications. However, the potential skeletal toxicity remains to be further elucidated. In this study, a zebrafish model was for the first time utilized to synthetically appraise the skeletal developmental defects induced by cysteamine. The embryos were treated with 0.35, 0.70, and 1.05 mM cysteamine from 6 h post fertilization (hpf) to 72 hpf. Substantial skeletal alterations were manifested as shortened body length, chondropenia, and abnormal somite development. The results of spontaneous tail coiling at 24 hpf and locomotion at 120 hpf revealed that cysteamine decreased behavioral abilities. Moreover, the level of oxidative stress in the skeleton ascended after cysteamine exposure. Transcriptional examination showed that cysteamine upregulated the expression of osteoclast-related genes but did not affect osteoblast-related genes expression. Additionally, cysteamine exposure caused the downregulation of the Notch signaling and activating of Notch signaling partially attenuated skeletal defects. Collectively, our study suggests that cysteamine leads to skeletal developmental defects and reduces locomotion activity. This hazard may be associated with cysteamine-mediated inhibition of the Notch signaling and disorganization of notochordal cells due to oxidative stress and apoptosis.

Behavioural impairment and oxidative stress by acute exposure of zebrafish to a commercial formulation of tebuconazole

Tebuconazole is a systemic follicular fungicide known to cause diverse problems in non-target organisms namely associated to the pure active ingredient. As such, the objective of this work was to evaluate developmental changes induced by a tebuconazole commercial formulation to a non-target animal model. Zebrafish embryos at ± 2 h post-fertilization were exposed to tebuconazole wettable powder concentrations (0.05, 0.5 and 5 mg L^-1) for 96 h with developmental toxicity assessed throughout the exposure period and biochemical parameters evaluated at the end of the exposure. Behavioural assessment (spatial exploration and response to stimuli) was conducted 24 h after the end of the exposure. While no developmental and physiological alterations were observed, exposure to tebuconazole resulted in an increased generation of reactive oxidative species at the 0.05 and 0.5 mg L^-1 concentrations and a decreased GPx activity at the 0.5 mg L^-1 concentration suggesting a potential protection mechanism. There was also a change in the avoidance-escape behaviour supporting an anxiolytic effect suggesting possible alterations in the central nervous system development demanding further studies.

Inflammatory, Oxidative Stress, and Apoptosis Effects in Zebrafish Larvae after Rapid Exposure to a Commercial Glyphosate Formulation

Glyphosate-based herbicides (GBH) are the most used herbicides in the world, carrying potentially adverse consequences to the environment and non-target species due to their massive and inadequate use. This study aimed to evaluate the effects of acute exposure to a commercial formulation of glyphosate, Roundup^® Flex (RF), at environmentally relevant and higher concentrations in zebrafish larvae through the assessment of the inflammatory, oxidative stress and cell death response. Transgenic Tg(mpxGFP)i114 and wild-type (WT) zebrafish larvae (72 h post-fertilisation) were exposed to 1, 5, and 10 µg mL^-1 of RF (based on the active ingredient concentration) for 4 h 30 min. A concentration of 2.5 µg mL^-1 CuSO₄ was used as a positive control. Copper sulphate exposure showed effectiveness in enhancing the inflammatory profile by increasing the number of neutrophils, nitric oxide (NO) levels, reactive oxygen species (ROS), and cell death. None of the RF concentrations tested showed changes in the number of neutrophils and NO. However, the concentration of 10 µg a.i. mL^-1 was able to induce an increase in ROS levels and cell death. The activity of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)), the biotransformation activity, the levels of reduced (GSH) and oxidised (GSSG) glutathione, lipid peroxidation (LPO), lactate dehydrogenase (LDH), and acetylcholinesterase (AChE) were similar among groups. Overall, the evidence may suggest toxicological effects are dependent on the concentration of RF, although at concentrations that are not routinely detected in the environment. Additional studies are needed to better understand the underlying molecular mechanisms of this formulation.