Toxicological assessment of the anti-salmon lice drug diflubenzuron on Atlantic cod Gadus morhua

Lufenuron treatment temporarily represses gene expression and affects the SUMO pathway in liver of Atlantic salmon

Lufenuron is a benzoylurea insecticide currently in use to combat sea lice infestation in salmon aquaculture in Chile. With pending approval in Norway, the aim of this work was to study the uptake and toxicity of lufenuron in liver tissue of Atlantic salmon. Juvenile salmon weighing 40 g were given a standard 7-day oral dose, and bioaccumulation and transcriptional responses in the liver were examined 1 day after the end-of-treatment (day 8) and after 1 week of elimination (day 14). Bioaccumulation levels of lufenuron were 29 ± 3 mg/kg at day 8 and 14 ± 1 mg/kg at day 14, indicating relatively rapid clearance. However, residues of lufenuron were still present in the liver after 513 days of depuration. The exposure gave a transient inhibition of transcription in the liver at day 8 (2437 significant DEGs, p-adj < .05), followed by a weaker compensatory response at day 14 (169 significant DEGs). Pathways associated with RNA metabolism such as the sumoylation pathway were most strongly affected at day 8, while the apelin pathway was most profoundly affected at day 14. In conclusion, this study shows that lufenuron easily bioaccumulates and that a standard 7-day oral dose induces a transient inhibition of transcription in liver of salmon.

Bioaccumulation and elimination, acute toxicity analysis and risk assessment of diflubenzuron in common carp (Cyprinus carpio)

Diflubenzuron has been applied in agriculture and aquaculture, and its residues in ecological environment and food chain could result in chronic exposure and long-term toxicity effects for human health. However, limited information is available regarding diflubenzuron levels in fish and associated risk assessment. This study performed the analysis for dynamic bioaccumulation and elimination distribution of diflubenzuron in carp tissues. The results indicated that diflubenzuron was absorbed and enriched by fish body along with higher enrichment in lipid-rich tissues of fish. The peak concentration in carp muscle reached 6-fold of diflubenzuron concentration in aquaculture water. The median lethal concentration (LC₅₀) of diflubenzuron at 96 h was 12.29 mg/L, presented low toxicity to carp. Risk assessment results showed that the chronic risk from dietary exposure to diflubenzuron through carp consumption for Chinese residents of children and adolescents, adults and elderly people were acceptable, while posed a certain risk for young children. This study provided the reference for pollution control, risk assessment and scientific management of diflubenzuron.

Transaminase profile and hepatic histopathological traits in Piaractus mesopotamicus exposed to insecticide Diflubenzuron

Diflubenzuron (DFB) is a widely used insecticide to control ectoparasites in fish farming. Although therapeutic concentrations (i.e., 50 to 100 mg/L) are safe as they fail to induce mortality, they can promote tissue changes. In Brazil, Pacu (Piaractus mesopotamicus) is a native species used for commercial production, and it remains crucial to determine underlying mechanisms to mitigate the potential effects of pathogens on productivity. The aim of this study was to analyze the transaminase profile and histopathological changes in the liver of P. mesopotamicus exposed to a DFB bath. Hence, the fish were exposed to an immersion bath containing a 70 mg/L nominal concentration of Difluchem 240 SC® (24% (m/m) DFB) for 30 (n = 10), 60 (n = 10), and 120 min (n = 10), every 24 h for 3 days. Following exposure, plasma transaminases and liver histology were analyzed. In DFB-exposed fish, levels of aspartate transaminase (AST) and alanine transaminase (ALT) were elevated when compared with the control at 30 and 60 min. Furthermore, liver morphology was altered based on exposure times. Compared with controls, the degree of reversible damage (degree of tissue change (DTC)) demonstrated high scores for all exposure times, with no difference between individual groups. Irreversible changes were increased in the 60 and 120-min baths. These findings highlight the impact of the therapeutic DFB concentration (i.e., 70 mg/L), revealing that 60-min and 120-min bathing induces irreversible and progressive hepatic changes.

Effects of diallyl trisulfide, an active substance from garlic essential oil, on structural chemistry of chitin in Sitotroga cerealella (Lepidoptera: Gelechiidae)

The environmental pollution, evolution of resistance, and risks to human and aquatic animal health associated with pesticide application have attracted much attention globally. Herein, we tested the capacity of diallyl trisulfide (DAT) from garlic essential oil to control the destructive stored-product pest, Sitotroga cerealella. The effects of DAT on the total content of cuticular chitin and structure of adults S. cerealella were evaluated. This study was the first to investigate changes in chitin structure in adults due to exposure to DAT through Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and differential scanning calorimetry. The results of these analyses revealed that the cuticular chitin content of pests decreased after DAT treatment. DAT treatment also reduced thermal stability and crystallinity of chitin. These findings indicate that DAT is a potent biopesticide that is active against the moth, and establishes the basis for its use as an IPM and alternative to chitin synthesis inhibitors.

Larvicidal activity of substituted chalcones against Aedes aegypti (Diptera: Culicidae) and non-target organisms

BACKGROUND

The expansion of Aedes aegypti (Diptera: Culicidae) population has increased the number of cases of arboviruses, in part due to the inefficiency and toxicity of the chemical control methods available to control this vector. We synthesized 19 chalcone derivatives and examined their activity against Ae. aegypti larvae in order to select larvicidal compounds that are non-toxic to other organisms.

RESULTS

Seven chalcone derivatives (3a, 3e, 3f, 6a, 6c, 6d, and 6f) had lethal concentrations of substituted chalcones capable of killing 50% (LC₅₀ ) values lower than 100 mg mL^-1 at 24 h post-treatment, which is the dose that the World Health Organization recommends for the selection of promising larvicides. The type of substituent added to (E)-1,3-diphenylprop-2-en-1-one (3a) markedly affected the larvicidal activity. Addition of chlorine, bromine and methoxy groups to the aromatic rings reduced the larvicidal activity, while replacement of the B-ring (phenyl) by a furan ring significantly increased the larvicidal activity. The furan-chalcone (E)-3-(4-bromophenyl)-1-(furan-2-yl)prop-2-en-1-one (6c) killed Ae. aegypti larvae (LC₅₀ = 6.66 mg mL^-1 ; LC₉₀ = 9.97 mg mL^-1 ) more effectively than the non-substituted chalcone (3a) (LC₅₀ = 14.43 mg mL^-1 ; LC₉₀ = 20.96 mg mL^-1 ), and was not toxic to the insect Galleria mellonella, to the protozoan Tetrahymena pyriformis, and to the algae Chorella vulgaris.

CONCLUSIONS

The substitution pattern of chalcones influenced their larvicidal activity. In the set of compounds tested, (E)-3-(4-bromophenyl)-1-(furan-2-yl)prop-2-en-1-one (6c) was the most effective larvicide against Ae. aegypti, with no clear signs of toxicity to other animal models. Its mechanism of action and effectiveness under field conditions remain to be determined.

The effects of teflubenzuron on mortality, physiology and accumulation in Capitella sp

The chitin synthesis inhibitor teflubenzuron (TFB) is a feed antiparasitic agents used to impede molting of the salmon lice, an ecto-parasite that severely affects the salmon industry. Low absorption of oral administered TFB may cause elevated concentrations in the feces discharged from the salmon into the benthic environment. The polychaete Capitella sp. are often dominant in such habitats and consume organic waste deposited on the sediment. In the present study, Capitella sp. were exposed to doses of TFB in salmon feed of 1, 2 and 4 g TFB kg^-1 (0 g TFB kg^-1 in control group) over an experimental period of 32 days. Cumulative mortality was 12%-15% in both treatment groups with 1 and 2 g TFB kg^-1 and reached 27% in the group with 4 g TFB kg^-1. Only the highest dose (4 g TFB kg^-1) negatively affected feed intake, growth and respiration of the polychaetes while food conversion efficiency was not affected. At the end of the experiment, the concentrations of TFB in the Capitella sp. were high, in the range of 9.24-10.32 μg g^-1 for the three treatment groups. It was suggested that a maximum level of absorption rate was reached, also for the lowest dose. High concentrations of TFB in the Capitella sp. might pose a risk to crustaceans that forage for polychaetes in the vicinity of fish farms. We conclude that the effects of TFB on Capitella sp. may therefore primarily be to the predators rather than the Capitella sp.

Metabolism of triflumuron in the human liver: Contribution of cytochrome P450 isoforms and esterases

Triflumuron (TFM) is a benzoylurea insecticide commonly used in Tunisian agriculture and around the world to control crop pests and flies as a promising alternative to conventional insecticides for its arthropod specificity and low toxicity. From the evidence available in animal models, it can be expected that the metabolism of TFM is catalyzed by cytochrome P450 (CYP) and esterases. However, no data are available on human metabolism of TFM with regards to phase I metabolism and CYP isoform specificity. Hence, this manuscript describes experimental investigations to underpin in vitro phase I TFM metabolism in human samples for the first time. TFM biotransformation by recombinant human CYPs was characterized, then human liver microsomes (HLM) and chemical specific inhibitors have been used to identify the relative contribution of CYPs and esterases. Our results showed that all CYP isoforms were able to metabolize TFM with different affinity and efficiency. The relative contribution based both on the kinetic parameters and the CYP hepatic content was 3A4 > >2C9 > 2C8 > 2A6 > 1A2 > 2B6 > 2D6 > 2C19 > 2C18 > 1A1 at low TFM concentration, whilst at high TFM concentration it was 1A2 > >2C9 = 3A4 = 2A6 > 2C19 > 2B6 = 2C8 > 2D6 > 1A1 > 2C18. Experiments with HLMs confirmed the involvement of the most relevant CYPs in the presence of specific chemical inhibitors with a catalytic efficiency (Cliapp) lower by an order of magnitude compared with recombinant enzymes. Esterases were also relevant to the overall TFM kinetics and metabolism, with catalytic efficiency higher than that of CYPs. It is foreseen that such isoform-specific information in humans will further support in silico models for the refinement of the human risk assessment of single pesticides or mixtures.

Preparation of a magnetic graphene/polydopamine nanocomposite for magnetic dispersive solid-phase extraction of benzoylurea insecticides in environmental water samples

A magnetic graphene/polydopamine (MG/PDA) nanocomposite has been prepared and used as sorbent for magnetic dispersive solid-phase extraction (MDSPE) of four benzoylurea insecticides in environmental water samples. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometry, powder X-ray diffraction, fourier transform infrared spectroscopy, surface area and porosity analysis and thermogravimetric analysis. To investigate the adsorption performance of MG/PDA for target analytes, various parameters affecting the MG/PDA-based MDSPE procedure were optimized. Under the optimal conditions, the established method exhibits good linearity (R2 ≥ 0.9988) in the concentration range 2.5-500 µg L-1. A low limit of detection (0.75 µg L-1, signal/noise = 3:1), a low limit of quantification (2.50 µg L-1, signal/noise = 10:1), and good precision (intraday relative standard deviation ≤3.6%, interday relative standard deviation ≤4.5%) are also achieved. Finally, the simple, fast, and sensitive sample preparation technique was successfully used to determine benzoylurea insecticides in environmental water samples.

Metabolism of Diflubenzuron in Lizard ( Eremias argus) and Comparative Toxicity of Diflubenzuron and Its Metabolite

The metabolic process of diflubenzuron in rat or fish has been well studied, but little is known about its elimination pathway in lizard. The current study predicted the metabolic route of diflubenzuron in lizard feces and compared the toxicity of diflubenzuron and 4-chloroaniline on lizard thyroid system. The amido bond cleavage was the major route for diflubenzuron elimination in lizard feces. 4-Chloroaniline as the most toxic diflubenzuron metabolite was also abundant in feces. According to liver slices, 4-chloroaniline exposure induced significant changes of nuclear shape, while diflubenzuron exposure caused significant hepatocytes clustering. On the basis of thyroid hormone and thyroid-related gene levels, triiodothyronine (T3) level in lizard liver was regulated by thyroid hormone receptors, while thyroxine (T4) concentration was modulated by dio2 and udp genes after diflubenzuron or 4-chloroaniline exposure. These results showed that both diflubenzuron and 4-chloroaniline could disrupt lizard thyroid system, which could provide evidence for lizard population decline.

Chitin synthesis inhibitors promote liver cancer cell metastasis via interfering with hypoxia-inducible factor 1α

Chitin synthesis inhibitors (CSIs), as alternatives to conventional insecticides, have been in worldwide demand in recent years. However, little attention has been paid to the potential ecological safety and health risks of CSIs, especially their abilities to interfere with nonsexual hormone receptors such as hypoxia-inducible factor 1α (HIF-1α). In this work, we conducted a systematic study regarding the influence of CSIs on HIF-1α-related liver cancer cell metastasis. The dual-luciferase reporter gene assay revealed that two of fourteen CSIs exhibited dose-response HIF-1α agonistic activities at noncytotoxic concentrations with relative luciferase activity (RLA) values of 25.6% for diflubenzuron (DFB) and 20.9% for triflumuron (TFM). Following this result, in vitro bioassays demonstrated that both DFB and TFM stimulated HepG2 cell migration and invasion. This action was associated with the varied expression levels of genes involved in epithelial-to-mesenchymal transition (EMT) activation and extracellular matrix (ECM) degradation, such as the upregulation of fibronectin (FN1) and matrix metalloproteinase-2 (MMP-2) and the suppression of E-cadherin (E-cad) and tissue inhibitor of metalloproteinases-2 (TIMP-2). Moreover, changes in these EMT and ECM phenotype markers were dramatically blocked by a HIF-1α inhibitor (KC7F2), which further verified the involvement of HIF-1α in CSI-induced HepG2 cell metastasis. For the first time, our findings reveal that CSIs play crucial roles in promoting the metastasis of human liver cancer cells and that HIF-1α is potentially responsible for these changes.

Oral and dermal diflubenzuron exposure causes a hypothalamic-pituitary-thyroid (HPT) axis disturbance in the Mongolian racerunner (Eremias argus)

Diflubenzuron (DFB) is a potential endocrine-disrupting chemical. However, its thyroid endocrine effect on reptiles has not been reported. In this study, immature lizards (Eremias argus) were exposed to 20 mg kg^-1 DFB once a week for 42 days through oral or dermal routes. Their body weight, plasma thyroid hormone levels, thyroid gland histology and the transcription of hypothalamic-pituitary-thyroid (HPT) axis-related genes in different tissues were assessed to explore the effects of DFB on the HPT axis of lizards. The body weight decreased significantly only after the dermal exposure to DFB. Triiodothyronine (T3) to thyroxine (T4) ratio in the male plasma also significantly increased after the dermal exposure. After oral exposure, the activity of thyroid gland was positively related to the thyroid hormone levels. Furthermore, the alterations in thyroid hormone levels affected the HPT axis-related gene expression, which was tissue dependent and sexually selected. The thyroid hormone receptor genes (trα and trβ) in the brain and thyroid were more sensitive to oral exposure. However, only the dermal treatment affected the trα, trβ and type 2 deiodinase (dio2) genes in the male liver. These results suggest that DFB exposure caused sex-specific changes in the thyroid function of lizards, and the dermal treatment may be an important route for the risk assessment of reptiles.

Impact of teflubenzuron on the rockpool shrimp (Palaemon elegans)

Concerns have been raised over the environmental impacts of antiparasitic drugs used to delouse farmed salmon. Released into the marine environment, some of these drugs can have negative impact on non-targeted crustaceans in the vicinity of farming facilities. In this study, we examined the molecular effect of the insecticide teflubenzuron on a shrimp species inhabiting the littoral zone, the rockpool shrimp (Palaemon elegans). Rockpool shrimp was exposed for 98days to a dose representing 2% of a regular teflubenzuron medication applied to Atlantic salmon. Accumulation of teflubenzuron was studied in whole body samples, except abdominal segments 5 and 6, which were used for gene expression analysis. Insight into sublethal mode of action was sought by examining the transcriptional responses of 38 genes encoding proteins linked to molting and exoskeleton change, stress and detoxification. The accumulated levels of teflubenzuron in exposed animals varied between 1.7 and 33.0ng/g. Significant transcriptional effects of exposure were seen for markers linked to molting and exoskeleton change (chh, ctbs, gap65), stress and apoptosis (hsp40, hsp70, casp3), as well for detoxification (cyp6a18). In conclusion, this study shows that teflubenzuron can bioaccumulate in shrimps living in the littoral zone and at sublethal concentrations affects molecular mechanisms in non-hepatopancreatic tissue.

The tissue distribution, metabolism and hepatotoxicity of benzoylurea pesticides in male Eremias argus after a single oral administration

Benzoylurea pesticides (BPUs) are widely used to control the locust, but the toxicokinetics and hepatotoxicity of BPUs in lizards have not been investigated. In this study, the tissue distribution, metabolism and liver toxicity of diflubenzuron and flufenoxuron were assessed in the Eremias argus following a single oral exposure. Diflubenzuron preferred to accumulate in the fat and brain (>1.0 mg kg^-1) and was rapidly eliminate in other tissues. In the liver, 4-chloroaniline was one of diflubenzuron metabolites, although with a concentration less than 0.05% of the accumulated diflubenzuron. No significant difference was observed in the liver histopathology between the control and diflubenzuron exposure group. The expressions of Cyp1a and Ahr gene which control the cell apoptosis were also equal to the control level. After flufenoxuron exposure, biomodal phenomenon was observed in the liver, skin, brain, gonad, kidney, heart and blood circulation was an important route for the flufenoxuron penetration. The concentrations of flufenoxuron in all tissues were greater than 1.0 mg kg^-1 at 168 h. The excretion of flufenoxuron in the faeces was 1.5 fold higher than diflubenzuron. The hepatocytes in the flufenoxuron treated group showed vacuolation of cytoplasm and decreased nucleus. In addition, the Cyp1a and Ahr genes were significantly up-regulated in the flufenoxuron exposure group. These results suggested that the higher hepatotoxicity of flufenoxuron may be attributed to the higher residual level in the lizard tissues and the Cyp1a and Ahr genes can serve as biomarkers to assess the liver toxicity.

Transcriptional responses to teflubenzuron exposure in European lobster (Homarus gammarus)

Increasing use of pharmaceutical drugs to delouse farmed salmon raises environmental concerns. This study describes an experiment carried out to elucidate the molecular mechanisms of the antiparasitic drug teflubenzuron on a non-target species, the European lobster. Juvenile lobsters (10.3±0.9 mm carapace length) were fed two environmentally relevant doses of teflubenzuron, corresponding to 5 and 20% of a standard salmon medication (10 mg/kg day), termed low and high dose in this study. After 114 days of dietary exposure, whole-animal accumulation of teflubenzuron was determined. One claw from each animal was collected for transcriptional analysis. Overall, exposed animals showed low cumulative mortality. Six animals, two from the low dose treatment and four from the high dose, showed exoskeletal abnormalities (claw deformities or stiff walking legs). Residual levels of teflubenzuron in juvenile lobster were 2.7-fold higher in the high dose (282 ng/g) compared to the low dose treatment (103 ng/g). The transcriptional examination showed significant effects of teflubenzuron on 21 out of 39 studied genes. At the transcriptional level, environmentally relevant levels of the anti-salmon lice drug impacted genes linked to drug detoxification (cyp3a, cyp6a2, cyp302a, sult1b1, abcc4), cellular stress (hsp70, hsp90, chh), oxidative stress (cat, gpx3) and DNA damage (p53), as well as molting and exoskeleton regulation (chi3l1, ecr, jhl1, chs1, ctbs, gap65, jhel-ces1) in claw tissue (muscle and exoskeleton). In conclusion, teflubenzuron at sub-lethal levels can affect many molecular mechanisms in European lobster claws.

Distribution and persistence of the anti sea-lice drug teflubenzuron in wild fauna and sediments around a salmon farm, following a standard treatment

The salmon louse (Lepeoptheirus salmonis) is a challenge in the farming of Atlantic salmon (Salmo salar). To treat an infestation, different insecticides are used like the orally administered chitin synthetase inhibitor teflubenzuron. The concentrations and distribution of teflubenzuron were measured in water, organic particles, marine sediment and biota caught in the vicinity of a fish farm following a standard medication. Low concentrations were found in water samples whereas the organic waste from the farm, collected by sediment traps had concentrations higher than the medicated feed. Most of the organic waste was distributed to the bottom close to the farm but organic particles containing teflubenzuron were collected 1100 m from the farm. The sediment under the farm consisted of 5 to 10% organic material and therefore the concentration of teflubenzuron was much lower than in the organic waste. Teflubenzuron was persistent in the sediment with a stipulated halflife of 170 days. Sediment consuming polychaetes had high but decreasing concentrations of teflubenzuron throughout the experimental period, reflecting the decrease of teflubenzuron in the sediment. During medication most wild fauna contained teflubenzuron residues and where polychaetes and saith had highest concentrations. Eight months later only polychaetes and some crustaceans contained drug residues. What dosages that induce mortality in various crustaceans following short or long-term exposure is not known but the results indicate that the concentrations in defined individuals of king crab, shrimp, squat lobster and Norway lobster were high enough shortly after medication to induce mortality if moulting was imminent. Considering food safety, saith and the brown meat of crustaceans contained at first sampling concentrations of teflubenzuron higher than the MRL-value set for Atlantic salmon. The concentrations were, however, moderate and the amount of saith fillet or brown meat of crustaceans to be consumed in order to exceed ADI is relatively large.

Transcriptional responses in Atlantic salmon (Salmo salar) exposed to deltamethrin, alone or in combination with azamethiphos

Recently, Atlantic salmon (Salmo salar) fish farmers have applied a combination of deltamethrin and azamethiphos in high-concentration and short-duration immersion treatment to improve protection against sea-lice (Lepeophtheirus sp.). In this work we aimed to study the effects of deltamethrin, alone or in combination with azamethiphos, on the transcription of stress and detoxification marker genes. Atlantic salmon kept at 12°C (one group was also kept at 4-5°C) were treated with deltamethrin alone or in combination with azamethiphos for a total of 40min, and gill and liver tissue harvested for transcriptional analysis 2 and 24h post treatment. No lethality was observed during the experiment. The result showed that deltamethrin, alone or in combination with azamethiphos, affected the transcriptional levels of several oxidative stress markers, including MnSOD (SOD2) and HSP70 (HSPA8) in the liver, and GPX1, CAT, MnSOD, HSP70 and GSTP1 in the gills. Significant responses for CASP3B, BCLX, IGFBP1B and ATP1A1 (Na-K-ATPase a1b) by some of the treatments suggest that the pharmaceutical drugs may affect apoptosis, growth and ion regulation mechanisms. In fish kept at 4-5°C, different effects were observed, suggesting a temperature-dependent response. In conclusion, the observed responses indicate that short-term exposure to deltamethrin has a profound effect on transcription of the evaluated markers in gills and liver of fish. Co-treatment with azamethiphos appears to have small mitigating effects on the transcriptional response caused by deltamethrin exposure alone.