Early life exposure of zebrafish (Danio rerio) to synthetic pyrethroids and their metabolites: a comparison of phenotypic and behavioral indicators and gene expression involved in the HPT axis and innate immune system

Mechanistic insights into the parental co-exposure of T-2 toxin and epoxiconazole on the F1 generation of zebrafish (Danio rerio)

Mycotoxins and pesticides frequently coexist in agricultural commodities on a global scale. The potential transgenerational consequences induced by these substances pose a significant threat to human health. However, there is a lack of data concerning the effects of co-contamination by these chemicals in the F1 generation following parental exposure. This investigation delved into the mixture effects of T-2 toxin (T-2) and epoxiconazole (EPO) on the offspring of zebrafish (Danio rerio). The findings revealed that exposure across generations to a combination of T-2 and EPO resulted in toxicity in the larvae of the F1 generation. This was demonstrated by a significant increase in the levels or activities of malondialdehyde (MDA), thyroxine (T4), Caspase3, and cas9, along with a decrease in the levels of cyp19a, ERα, and ERβ. These outcomes suggested that cross-generational exposure to T-2 and EPO in D. rerio disrupted oxidative balance, induced cell apoptosis, and affected the endocrine system. Moreover, these effects were magnified when the F1 generation was continuously exposed to these compounds. Notably, these adverse effects could persist in subsequent generations without additional exposure. This study underscored the potential dangers associated with the simultaneous presence of T-2 and EPO on the development of fish offspring and the resulting environmental hazards to aquatic ecosystems. These findings emphasized the significant health risks posed by cross-generational exposure and highlighted the need for additional legislative measures to address these concerns.

Association between pesticide exposure and thyroid function: analysis of Chinese and NHANES databases

Background

Pesticides are widely used in agricultural activities. Although pesticide use is known to cause damage to the human body, its relationship with thyroid function remains unclear. Therefore, this study aimed to investigate the association between pesticide exposure and thyroid function.

Methods

The Chinese database used included 60 patients with pyrethroid poisoning and 60 participants who underwent health checkups between June 2022 and June 2023. The NHANES database included 1,315 adults enrolled from 2007 to 2012. The assessed pesticide and their metabolites included 2,4-dichlorophenoxyacetic acid (2,4-D), 4-fluoro-3-phenoxybenzoic acid (4F3PB), para-nitrophenol (PN), 3-phenoxybenzoic acid (3P), and trans-dichlorovinyl-dimethylcyclopropane carboxylic acid (TDDC). The evaluated indicators of thyroid function were measured by the blood from the included population. The relationship between pesticide exposure and thyroid function indexes was investigated using linear regression, Bayesian kernel machine regression (BKMR), restricted cubic spline (RCS), and weighted quantile sum (WQS) models.

Results

The Chinese data showed that pesticide exposure was negatively correlated with the thyroid function indicators FT4, TT4, TgAb, and TPOAb (all p < 0.05). The BKMR model analysis of the NHANES data showed that the metabolic mixture of multiple pesticides was negatively associated with FT4, TSH, and Tg, similar to the Chinese database findings. Additionally, linear regression analysis demonstrated positive correlations between 2,4-D and FT3 (p = 0.041) and 4F3PB and FT4 (p = 0.003), whereas negative associations were observed between 4F3PB and Tg (p = 0.001), 4F3PB and TgAb (p = 0.006), 3P and TgAB (p = 0.006), 3P and TPOAb (p = 0.03), PN and TSH (p = 0.003), PN and TT4 (p = 0.031), and TDDC and TPOAb (p < 0.001). RCS curves highlighted that most pesticide metabolites were negatively correlated with thyroid function indicators. Finally, WQS model analysis revealed significant differences in the weights of different pesticide metabolites on the thyroid function indexes.

Conclusion

There is a significant negative correlation between pesticide metabolites and thyroid function indicators, and the influence weights of different pesticide metabolites on thyroid function indicators are significantly different. More research is needed to further validate the association between different pesticide metabolites and thyroid disease.

Cypermethrin: An Emerging Pollutant and Its Adverse Effect on Fish Health and some Preventive Approach-A Review

Pesticides are substance that are used to manage pests, such as aquatic weeds, plant diseases and insects. It has been shown that these substances are highly hazardous to fish as well as other organisms that are part of the food chain. The presence of cypermethrin in food and groundwater has raised environmental concerns, there is a need to develop economical, rapid, and reliable techniques that can be used for field applications Many studies have shown that Cypermethrin (CYP) can cause toxic effect in various animals including fishes. But the molecular mechanism behind the toxicity mediated Cypermethrin (CYP) at genome levels and proteome levels is still need to be studied. However, there is a gap in emerging and undeveloped nations to begin to use these methods and several other recently developed approaches to inhibit the negative consequences and enhance health which may be profitable. The toxicological information currently available might be used to gain a clear understanding of the possibilities of these synthetic pyrethroid insecticides causing various health hazards to environmental and provides insight for future research evaluating the toxic effects of pyrethroid insecticides. This present review article is concerned with the toxicological effects of pesticides and a brief overview of sources, classification of pesticides with an emphasis on the effects of Cypermethrin (CYP) on fish as well mode of toxicity and the mechanism of action (CYP) and toxicity signs in several fish species have been illustrated. The primary controls and appropriate preventive measures that must be adopted are also discussed.

Enantioselective Toxicity of Tetramethrin to Different Developmental Stages of Zebrafish (Danio rerio)

Chiral pesticides exhibit enantioselective differences in processes such as biological absorption, metabolism, and toxic effects. Organisms have different physiological characteristics at different developmental stages. Therefore, conducting enantiomeric toxicity studies at different developmental stages of organisms can help deepen the understanding of the ecological effects of chiral pesticides. This study focused on trans-tetramethrin (Tet) and investigated the enantioselectivity in bioconcentration, developmental toxicity, estrogenic effects, and immunotoxicity of Tet's racemate ((±)-Tet) and its two enantiomers ((+)-Tet and (-)-Tet) in three developmental stages of zebrafish: embryos, yolk sac larvae, and juveniles. The results showed that Tet exhibited different enantioselectivity in lethal, bioconcentration, and teratogenic effects on zebrafish at different developmental stages. The LC50 value was (+)-Tet > (±)-Tet > (-)-Tet, with embryos being the most sensitive, followed by juveniles and yolk sac larvae. The enantioselective bioconcentration was (±)-Tet > (+)-Tet > (-)-Tet, and the bioconcentration effect was greater in embryos than that in yolk sac larvae and juveniles. Developmental toxicity indicated that (+)-Tet and (±)-Tet had higher teratogenic effects on yolk sac larvae than on embryos. Tet exhibited different enantioselective effects on the expression of zebrafish estrogen-related genes and innate immune-related genes at different developmental stages. These results will contribute to a more comprehensive assessment of the aquatic toxicity and environmental risks of chiral pesticides.

Adverse effects of fenpropathrin on the intestine of common carp (Cyprinus carpio L.) and the mechanism involved

Fenpropathrin (FEN), a pyrethroid pesticide, is frequently detected in natural water bodies, unavoidable pose adverse effects to aquatic organisms. However, the harmful effects and potential mechanisms of FEN on aquatic species are poorly understood. In this study, common carp were treatment with FEN at 0.45 and 1.35 μg/L for 14 d, and the toxic effects and underlying mechanisms of FEN on the intestine of carp were revealed. RNA-seq results showed that FEN exposure cause a wide range of transcriptional alterations in the intestine and the differentially expressed genes were mainly enrichment in the pathways related to immune and metabolism. Specifically, FEN exposure induced pathological damage and altered submicroscopic structure of the intestine, elevated the levels of Bacteroides fragilis enterotoxin, altered the contents of claudin-1, occludin, and zonula occluden-1 (ZO-1), and causing injury to the intestinal barrier. In addition, inflammation-related index TNF-α in the serum and IL-6 in the intestinal tissues were generally increased after FEN exposure. Moreover, FEN exposure promoted an increase in reactive oxygen species (ROS), altered the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), upregulated the contents of malondialdehyde (MDA) in the intestines. The apoptosis-related parameter cytochrome c, caspase-9, and caspase-3 were significantly altered, indicating that inflammation reaction, oxidative stress, and apoptosis may be involved in the toxic mechanism of FEN on carp. Moreover, FEN treatment also altered the intestinal flora community significantly, which may affect the intestinal normal physiological function and thus affect the growth of fish. Overall, the present study help to clarify the intestinal reaction mechanisms after FEN treatment, and provide a basis for the risk assessment of FEN.

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.

Maternal exposure to chiral triazole fungicide tebuconazole induces enantioselective thyroid disruption in zebrafish offspring

Pesticides could induce long-term impacts on aquatic ecosystem via transgenerational toxicity. However, for many chiral pesticides, the potential enantioselectivity of transgenerational toxicity has yet to be fully understood. In this study, we used zebrafish as models to evaluate the maternal transfer risk of tebuconazole (TEB), which is a chiral triazole fungicide currently used worldwide and has been frequently detected in surface waters. After 28-day food exposure (20 and 400 ng/g) to the two enantiomers of TEB (S- and R-TEB) in adult female zebrafish (F0), increased malformation rate and decreased swimming speed were found in F1 larvae, with R-TEB showing higher impacts than S-enantiomer. Additionally, enantioselective effects on the secretion of thyroid hormones (THs) and expression of TH-related key genes along the hypothalamic-pituitary-thyroid (HPT) axis were found in both F0 and F1 after maternal exposure. Both the two enantiomers significantly disrupted the triiodothyronine (T3) and thyroxine (T4) contents in F0 with different degrees, whereas in F1, significant effects were only found in R-TEB groups with decreasing of both T3 and T4 contents. Most of the HPT axis related genes in F0 were upregulated by TEB and more sensitive to R-TEB than to S-TEB. In contrast, most of the genes in F1 were downregulated by both R- and S-TEB, especially the genes that are primarily responsible for thyroid development and growth (Nkx2-1), TH synthesis (NIS and TSHꞵ) and metabolism (Deio1). Findings from this study highlight the key role of enantioselectivity in the ecological risk assessment of chiral pesticides through maternal transfer.

Biodegradation of the pyrethroid cypermethrin by bacterial consortia collected from orange crops

Pyrethroids, such as cypermethrin (CYP), are widely employed in agriculture, promoting environmental pollution and the need for efficient decontamination methods. In this study, bacteria from orange crops were explored for CYP biodegradation. Among 40 tested bacterial strains, 20 grew in the presence of CYP and 19 performed statistically significant CYP biodegradation in 5 days (20.5%-97.8%). In addition, 3-phenoxybenzoic acid, the main metabolite from CYP, was quantified ranging from 1.1 mg.L^-1 to 32.1 mg.L^-1. The five most efficient strains, and consortia composed of 5, 10 and 20 bacteria biodegraded the CYP formulation as sole carbon source in phosphate buffer and in minimum mineral medium. Under optimized conditions determined employing Response Surface Methodology, Bacillus sp. CSA-1 and the consortium composed of 10 strains biodegraded 71.0% and 71.6% CYP in 24 h, respectively. Moreover, metabolite identification enabled the proposal of an extended biodegradation pathway with 29 identified compounds, including different new amide and amine derivatives that expanded the knowledge about the fate of this compound in the environment. Experiments of bioaugmentation in soil using Bacillus sp. CSA-1 and the consortium of 10 bacterial strains resulted in faster CYP biodegradation than natural attenuation, showing that the selection of efficient strains for composing a consortium is an interesting approach for bioremediation of pyrethroids.

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.

Imazalil and its metabolite imazalil-M caused developmental toxicity in zebrafish (Danio rerio) embryos via cell apoptosis mediated by metabolic disorders

Imazalil (IMZ) is a highly effective fungicide employed in crop production. It has been consistently detected in aquatic environments. The main environmental metabolite of IMZ is imazalil-M (IMZ-M). Limited studies have focused on the toxicity of IMZ and IMZ-M in aquatic organisms. This study systematically evaluated the developmental toxicity of IMZ and IMZ-M on zebrafish (Danio rerio) embryos and explored the potential mechanisms involved. The results showed that IMZ and IMZ-M caused developmental toxicity, characterized by decreased heart rate, hatching inhibition, and pericardial cyst in zebrafish embryos. Subsequently, acridine orange (AO) staining revealed cell apoptosis in the area around the heart regions of zebrafish larvae. Besides, the expression levels of apoptosis-related genes also varied significantly. Furthermore, ¹H NMR-based metabolomics analysis showed that IMZ and IMZ-M exposure could induce metabolic profiles disorder in zebrafish larvae. Importantly, zebrafish exposure to IMZ and IMZ-M significantly affected the metabolism of branched - chain amino acids, energy, and ketone bodies, which are related to cell apoptosis. Overall, the toxicity of IMZ and IMZ-M in zebrafish embryos and larvae was characterized, suggesting a theoretical basis for the potential environmental risks of IMZ and its metabolite IMZ-M on non-target organisms.

Combined lethal toxicity, biochemical responses, and gene expression variations induced by tebuconazole, bifenthrin and their mixture in zebrafish (Danio rerio)

Pesticides commonly occur as mixtures in an aqueous environment, causing deleterious effects on human health and the environment. However, the mechanism underlying the combined effects on aqueous organisms remains largely unknown, especially at low concentrations. In the current study, we inspected the interactive toxicity of tebuconazole (TEB), a triazole fungicide, and bifenthrin (BIF), a pyrethroid insecticide, to zebrafish (Danio rerio) using various toxicological assays. Our data revealed that the 96 h-LC50 (lethal concentration 50) values of BIF to fish at different life periods (embryonic, larval, juvenile, and adult periods) ranged from 0.013 (0.011-0.016) to 0.41 (0.35-0.48) mg a.i. L-1, which were lower than that of TEB ranging from 1.1 (0.88-1.3) to 4.8 (4.1-5.7) mg a.i. L-1. Combination of TEB and BIF induced synergetic acute toxicity to embryonic fish. Activities of T-SOD, POD, and GST were distinctly altered in most individual and joint administrations. Expressions of 16 genes associated with oxidative stress, cellular apoptosis, immune system, and endocrine system at the mRNA level were evaluated, and the information revealed that embryonic zebrafish were impacted by both individual compounds and their combinations. Six genes (cas9, P53, gr, TRα, IL-8, and cxcl-clc) exhibited greater changes when exposed to pesticide mixtures. Therefore, the joint effects induced by the pesticides at low concentrations should be considered in the risk assessment of mixtures and regulated as priorities for mixture risk management in the aqueous ecosystem. More research is needed to identify the threshold concentrations of the realistic pesticide mixtures above which synergistic interactions occur.

Lambda-cyhalothrin and its common metabolite differentially modulate thyroid disruption effects in Chinese lizards (Eremias argus)

Although the thyroid effects of pyrethroids on non-target organisms have been well studied, research on the toxic effects of pyrethorid metabolites is still limited. In this study, a type of representative Chinese lizards was used as the model and exposed to environmentally relevant concentrations of lambda-cyhalothrin (LCT) and 3-phenoxybenzoic acid (PBA) through cultivation on 3 and 15 μg/g soil to evaluate and compare their disruption effects on lizard hypothalamus-pituitary-thyroid (HPT) axis. The alterations occurred in lizards were examined through histopathology analyses, hormone level and gene expression measurements, the molecular binding interactions were analyzed in silico as well. The results showed that LCT exposure increased the plasma triiodothyronine (T3), thyroxine (T4) levels and the follicular epithelium heights of thyroid glands, whereas PBA induced no or much less degree of alterations. The ugt and dio2 gene expression in lizard liver was significantly up-regulated by LCT, but PBA caused less or opposite effects. The in silico homology simulation illustrated that LCT binds to TRα in the similar way of T3, while PBA binds to TRβ in the same manner of T3. The results demonstrated that both LCT and its metabolite-PBA could disrupt lizard HPT axis but through distinct mechanisms. The information would facilitate the comprehensive environmental safety assessment of pyrethroids.

Developmental toxicity of 3-phenoxybenzoic acid (3-PBA) and endosulfan sulfate derived from insecticidal active ingredients: Abnormal heart formation by 3-PBA in zebrafish embryos

Pyrethroid and organochlorine insecticides are enormously used to control agricultural and indoor insect pests. The metabolites of pyrethroid and endosulfan were used to evaluate environmental toxicities using a representative animal model, zebrafish (Danio rerio) embryos in this study. The LC50 values in 3-phenoxy benzoic acid (3-PBA) and endosulfan sulfate (ES) were 1461 μg/L and 1459 μg/L, respectively. At the concentration of 2000 μg/L, spine curvature was observed in the ES-treated embryos. ES showed seizure-like events with an EC50 value of 354 μg/L. At the concentration of 1000 μg/L, the pericardial edema was observed in 3-PBA-treated embryos. The inhibition of heart development and the reduction of beating rates were observed in Tg(cmlc2:EGFP) embryos after the exposure to 3-PBA. Down-regulation of the vmhc gene coding ventricular myosin during heart development was significantly found in 3-PBA-treated embryos at 48 hpf, but recovered afterward. It indicates that ventricular malformation occurred at the initial stage of 3-PBA exposure. Considered together, both 3-PBA and ES need public concerns with periodic monitoring of these metabolites in households and agricultural areas to prevent humans and environmental organisms from their unexpected attacks.

The possible hormetic effects of fluorene-9-bisphenol on regulating hypothalamic-pituitary-thyroid axis in zebrafish

Fluorene-9-bisphenol (BHPF) is a bisphenol A substitute, which has been introduced for the production of so-called 'bisphenol A (BPA)-free' plastics. However, it has been reported that BHPF can enter living organisms through using commercial plastic bottles and cause adverse effects. To date, the majority of the toxicologic study of BHPF focused on investigating its doses above the toxicological threshold. Here, we studied the effects of BHPF on development, locomotion, neuron differentiation of the central nervous system (CNS), and the expression of genes in the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish exposed to different doses of BHPF ranging from 1/5 of LD1 to LD50 (300, 500, 750, 1500, 3000, and 4500 nM). As a result, the possible hormetic effects of BHPF on regulating the HPT axis were revealed, in which low-dose BHPF positively affected the HPT axis while this regulation was inhibited as the dose increased. Underlying mechanism investigation suggested that BHPF disrupted myelination through affecting HPT axis including related genes expression and TH levels, thus causing neurotoxic characteristics. Collectively, this study provides the full understanding of the environmental impact of BHPF and its toxicity on living organisms, highlighting a substantial and generalized ongoing dose-response relationship with great implications for the usage and risk assessment of BHPF.

An Overview on the Potential Hazards of Pyrethroid Insecticides in Fish, with Special Emphasis on Cypermethrin Toxicity

Simple Summary

Pyrethroid insecticides are extensively used in controlling agricultural insects and treatment of ectoparasitic infestation in farm animals. However, the unhygienic disposable and seepage of pyrethroids from the agricultural runoff will lead to contamination of the aquatic ecosystems, which will, in turn, induce harmful toxic effects in the exposed living aquatic organisms, including fish. Cypermethrin (CYP) is a commonly and widely used type II pyrethroid insecticide with known dangerous toxic effects on the exposed organisms. Serious hazardous effects of these toxicants have been reported in several fish species leading to high mortalities and economic losses of the exposed fish.

Abstract

Pesticides are chemicals used to control pests, such as aquatic weeds, insects, aquatic snails, and plant diseases. They are extensively used in forestry, agriculture, veterinary practices, and of great public health importance. Pesticides can be categorized according to their use into three major types (namely insecticides, herbicides, and fungicides). Water contamination by pesticides is known to induce harmful impacts on the production, reproduction, and survivability of living aquatic organisms, such as algae, aquatic plants, and fish (shellfish and finfish species). The literature and information present in this review article facilitate evaluating the toxic effects from exposure to various fish species to different concentrations of pesticides. Moreover, a brief overview of sources, classification, mechanisms of action, and toxicity signs of pyrethroid insecticides in several fish species will be illustrated with special emphasis on Cypermethrin toxicity.

PKCα mediated by the PI3K/Akt-FOXA1 cascade facilitates cypermethrin-induced hyperthyroidism

Cypermethrin (CYP), a broad-spectrum pyrethroid insecticide is extensively used. CYP is also considered as a potential endocrine disruptor with the thyroid-disturbing property. Protein kinase C alpha (PKCα) is a pleiotropic signal transduction molecule that functions crucially in thyroid hormone (TH) homeostasis and thyroid functions. To explore underlying roles of PKCα in CYP-mediated disturbance of TH homeostasis, Sprague-Dawley rats and rat thyroid cells were used in this study. Results showed that β-CYP stimulated TH biosynthesis, as shown by the increase in plasma levels of TT4, FT4, TT3, FT3, and TSH. After β-CYP treatment, expressions of PKCα, three miRNAs (miR-17-5p, miR-330-3p, and miR-331-3p), thyroid transcription factor TTF-1, and thyroid-specific proteins (TSHr, TPO, and Tg) were significantly increased, while expressions of PI3K p110α, p-Akt, FOXA1, and thyroid transcription factors (TTF-2 and Pax8) were decreased. Further studies found that β-CYP induced PKCα translation by the miR-330-3p-targeted PI3K/Akt-FOXA1 cascade and then PKCα positively regulated TTF-1 to promote TPO and Tg expressions, which in turn facilitated TH biosynthesis. Likewise, PKCα positively modulated TSHr expressions to strengthen the TSH/TSHr signal in the HPT axis, thereby synergistically contributing to TH biosynthesis. Moreover, β-CYP also disturbed TH biotransformation and biotransport by inducing DIO1 and inhibiting DIO3 in thyroids and TTR expressions in livers. Taken together, β-CYP has the thyroid-disturbing effect and could promote TH biosynthesis, and PKCα plays vital roles in β-CYP-caused hyperthyroidism.

Exposure to permethrin or chlorpyrifos causes differential dose- and time-dependent behavioral effects at early larval stages of an endangered teleost species

Pyrethroid and organophosphate pesticides are two of the most commonly used classes of insecticide worldwide. At sublethal concentrations, permethrin (a pyrethroid) and chlorpyrifos (an organophosphate) impact behavior in model fish species. We investigated behavioral effects of environmentally relevant concentrations of permethrin or chlorpyrifos on early larval delta smelt Hypomesus transpacificus, a Critically Endangered teleost species endemic to the San Francisco Bay Delta, California, USA. Using a photomotor behavioral assay of oscillating light and dark periods, we measured distance moved, turn angle, meander, angular velocity, rotations, thigmotaxis (time spent in the border versus center), and swim speed duration and frequency. The lowest concentrations of permethrin used in the tests (0.05 and 0.5 μg l⁻¹) caused significant increases in distance moved at 72 and 96 h, respectively. At 48, 72, and 96 h of exposure, 5 μg l⁻¹ of permethrin caused a hyperactive state in which the larvae significantly decreased thigmotaxis, quickly turning in short bouts of activity, characterized by significant increases in rotations and freezing events. Larvae exposed to 0.05 μg l⁻¹ chlorpyrifos significantly increased thigmotaxis at 72 and 96 h. In response to 5 μg l⁻¹ chlorpyrifos, larvae significantly increased velocity at 72 h exposure, and significantly increased freezing events at 96 h. Behavioral data on larval delta smelt exposed to contaminants present in their limited habitat have the potential to aid evaluations of the suitability of spawning and rearing habitats for this endangered species, thus improving conservation management strategies focused on this sensitive life stage.

Waterborne uranium causes toxic effect and thyroid disruption in zebrafish larvae

Uranium is a radioactive element that is widely present in aquatic environment. However, limited knowledge is available about the effect of uranium on thyroid system, which plays a key role in the development of animals. In this study, zebrafish embryos were exposed to different environmentally relevant concentrations of uranium (2, 20 and 100 μg/L) for 120 h. The bioaccumulation, developmental toxicities, changes of thyroid hormones (THs) and key genes related to the hypothalamic-pituitary-thyroid (HPT) axis in larvae were analyzed after exposure. Results showed that uranium could bioaccumulate in zebrafish larvae, with the bioconcentration factors ranging from 49.6 to 523. Consequently, significant developmental toxicities and changes in locomotor activities were observed with a concentration-dependent manner. The levels of triiodothyronine (T3) levels in larvae were substantially decreased, whereas those of thyroxine (T4) were increased in fish bodies. The levels of THs were regulated by the negative feedback loops through HPT axis related genes, most of which (NIS, Deio1, Deio2, TRα, TSHβ and UGT1ab) were significantly depressed after exposure to uranium. Our results suggest the potential toxicities and thyroid disruption of uranium on zebrafish, which would provide baseline data set for better understanding the impact of waterborne uranium on aquatic organisms and the associated mechanisms. This study also highlights the key role of thyroid disruption in the ecological risk assessment of uranium pollution.

Biochemical responses of a freshwater fish Cirrhinus mrigala exposed to tris(2-chloroethyl) phosphate (TCEP)

Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs).

Construction and characterization of a class-specific single-chain variable fragment against pyrethroid metabolites

Pyrethroids are insecticides that are widely used in rural and urban areas worldwide. After entering the environment, pyrethroids are rapidly metabolized or degraded by various biological or abiotic methods. In this study, a single-chain variable fragment (scFv) which could simultaneously detect three pyrethroid metabolites was constructed based on a hybridoma raised against 3-phenoxybenzoic acid (3-PBA). By molecular docking, it showed that there were hydrogen bonds, hydrophobic interactions, CH-π interaction, and cation-π interaction between 3-PBA and its scFv. All the contact residues contributing to hydrogen bonds are located in VH-CDR2 or its neighboring region, and two of them were mutants of the closest germline sequence. Based on competitive ELISA, the half maximal inhibitory concentration (IC₅₀) of the scFv for 3-PBA, 3-phenoxybenzaldehyde (PBAld), and 3-phenoxybenzyl alcohol (PBAlc) were calculated to be 0.55, 0.59, and 0.63 μgmL^-1, respectively. The scFv also showed 23.91%, 13.41%, 1.15%, 1.00%, and 0.56% cross-reactivity with phenothrin, deltamethrin, fenvalerate, beta-cypermethrin, and fenpropathrin. The broad specificity of the scFv may be due to its hapten design. The scFv could be employed in class-specific immunoassays for pyrethroid metabolites with phenoxybenzyl (PB) group. It is also potentially used for characterizing degradation of pyrethroids or detecting PBAlc (PBAld) alone, and the detection results should be confirmed by other selective methods. KEY POINTS: • A scFv which can simultaneously detect 3-PBA, PBAlc, and PBAld was constructed. • Antibody informatics and binding mode of the scFv were obtained. • The reason for its broad specificity was discussed. • It could be used to monitor single or multi-pyrethroid metabolites with PB group.

An epigenome-wide association study of ambient pyrethroid pesticide exposures in California's central valley

BACKGROUND

Pyrethroid pesticide use is increasing worldwide, although the full extent of associated health effects is unknown. An epigenome-wide association study (EWAS) with exploratory pathway analysis may help identify potential pyrethroid-related health effects.

METHODS

We performed an exploratory EWAS of chronic ambient pyrethroid exposure using control participants' blood in the Parkinson's Environment and Genes Study in the Central Valley of California (N = 237). We estimated associations of living and working near agricultural pyrethroid pesticide applications in the past 5 years (binary) with site-specific differential methylation, and used a false discovery rate (FDR) cut off of 0.05 for significance. We controlled for age, sex, education, cell count, and an ancestral marker for Hispanic ethnicity. We normalized methylation values for Type I/II probe bias using Beta-Mixture Quantile (BMIQ) normalization, filtered out cross-reactive probes, and evaluated for remaining bias with Surrogate Variable Analysis (SVA). We also evaluated the effects of controlling for cell count and normalizing for Type I/II probe bias by comparing changes in effect estimates and p-values for the top hits across BMIQ and GenomeStudio normalization methods, and controlling for cell count. To facilitate broader interpretation, we annotated genes to the CpG sites and performed gene set overrepresentation analysis, using genes annotated to CpG sites that were associated with pyrethroids at a raw p < 0.05, and controlling for background representation of CpG sites on the chip. We did this for both a biological process context (Gene Ontology terms) using missMethyl, and a disease set context using WebGestalt. For these gene set overrepresentation analyses we also used an FDR cut off of 0.05 for significance of gene sets.

RESULTS

After controlling for cell count and applying BMIQ normalization, 4 CpG sites were differentially methylated in relation to pyrethroid exposures. When using GenomeStudio's Illumina normalization, 415 CpG sites were differentially methylated, including all four identified with the BMIQ method. In the gene set overrepresentation analyses, we identified 6 GO terms using BMIQ normalization, and 76 using Illumina normalization, including the 6 identified by BMIQ. For disease sets, we identified signals for Alzheimer's disease, leukemia and several other cancers, diabetes, birth defects, and other diseases, for both normalization methods. We identified minimal changes in effect estimates after controlling for cell count, and controlling for cell count generally weakened p-values. BMIQ normalization, however, resulted in different beta coefficients and weakened p-values.

CONCLUSIONS

Chronic ambient pyrethroid exposure is associated with differential methylation at CpG sites that annotate to a wide variety of disease states and biological mechanisms that align with prior research. However, this EWAS also implicates several novel diseases for future investigation, and highlights the relative importance of different background normalization methods in identifying associations.

Core-satellite surface imprinting polymer-based pipette tip solid-phase extraction for the colorimetric determination of pyrethroid metabolite

A core-satellite-structured surface molecularly imprinted polymer has been synthesized for the enrichment of 3-phenoxybenzaldehyde by pipette tip solid-phase extraction (SPE). In a typical sol-gel process, two silane reagents as functional monomers and 3-phenoxybenzoic acid as the dummy template, the surface imprinting layer was coated on the core-satellite silica microsphere, which formed the core-satellite-structured molecularly imprinted polymer (CSMIP). Compared to the silica-based core-shell ones, this CS-MIP exhibits a stunning surface area (142 m² g^-1) in micrometer size and also overcomes the aggregation trends of core-shell structure in nanoscale. Taking potassium permanganate solution as oxidizer and indicator, the adsorbed 3-phenoxybenzaldehyde can be a quantitatively determined through redox reaction after elution. The value of maximum adsorption capacity and imprinting factor of CS-MIP were calculated to be 87.5 μg mg^-1 and 2.13, respectively. These CS-MIPs were packed into commercial pipette tip as the sorbent to concentrate 3-phenoxybenzaldehyde. Under the optimum condition, a liner relationship was achieved in the range 0.200 to 1.00 μg mL^-1 and the limit of detection was 81 ng mL^-1. Moreover, this customized SPE device exhibits good adsorption capability after six sequential adsorption-desorption cycles, and the high recovery range of 92.2~99.7% of spiked tap water assay demonstrated its potential application for real sample analysis. Graphical abstract Schematic presentation of core-satellite molecularly imprinted polymer preparation strategy and customized pipette tip solid-phase extraction device.

Testing for thyroid hormone disruptors, a review of non-mammalian in vivo models

Thyroid hormones (THs) play critical roles in profound changes in many vertebrates, notably in mammalian neurodevelopment, although the precise molecular mechanisms of these fundamental biological processes are still being unravelled. Environmental and health concerns prompted the development of chemical safety testing and, in the context of endocrine disruption, identification of thyroid hormone axis disrupting chemicals (THADCs) remains particularly challenging. As various molecules are known to interfere with different levels of TH signalling, screening tests for THADCs may not rely solely on in vitro ligand/receptor binding to TH receptors. Therefore, alternatives to mammalian in vivo assays featuring TH-related endpoints that are more sensitive than circulatory THs and more rapid than thyroid histopathology are needed to fulfil the ambition of higher throughput screening of the myriad of environmental chemicals. After a detailed introduction of the context, we have listed current assays and parameters to assess thyroid disruption following a literature search of recent publications referring to non-mammalian models. Potential THADCs were mostly investigated in zebrafish and the frog Xenopus laevis, an amphibian model extensively used to study TH signalling.

Pesticides With Potential Thyroid Hormone-Disrupting Effects: A Review of Recent Data

Plant Protection Products, more commonly referred to as pesticides and biocides, are used to control a wide range of yield-reducing pests including insects, fungi, nematodes, and weeds. Concern has been raised that some pesticides may act as endocrine disrupting chemicals (EDCs) with the potential to interfere with the hormone systems of non-target invertebrates and vertebrates, including humans. EDCs act at low doses and particularly vulnerable periods of exposure include pre- and perinatal development. Of critical concern is the number of pesticides with the potential to interfere with the developing nervous system and brain, notably with thyroid hormone signaling. Across vertebrates, thyroid hormone orchestrates metamorphosis, brain development, and metabolism. Pesticide action on thyroid homeostasis can involve interference with TH production and its control, displacement from distributor proteins and liver metabolism. Here we focused on thyroid endpoints for each of the different classes of pesticides reviewing epidemiological and experimental studies carried out both in in vivo and in vitro. We conclude first, that many pesticides were placed on the market with insufficient testing, other than acute or chronic toxicity, and second, that thyroid-specific endpoints for neurodevelopmental effects and mixture assessment are largely absent from regulatory directives.

Long-term exposure to the non-steroidal anti-inflammatory drug (NSAID) naproxen causes thyroid disruption in zebrafish at environmentally relevant concentrations

The presence of trace levels of pharmaceuticals is an emerging issue impacting the aquatic ecosystem. Naproxen (NPX) is a nonsteroidal anti-inflammatory drug (NSAID) that has been frequently detected in aquatic environments worldwide. Recently, concerns regarding endocrine disruption by NSAIDs have increased; however, their effects on the thyroid system have yet to be understood. In this study, zebrafish were utilized to evaluate the thyroid-disrupting effects of NPX. After a 60-day exposure to various concentrations of NPX (0.1, 1, 10 and 100 μg/L), the body length and weight of the zebrafish were significantly decreased. The decrease of cytochrome P450 gene expression and enzyme activity might inhibit the metabolism of NPX, which might result in the significant bioconcentration in zebrafish. Thyroid hormone (TH) analysis showed that both triiodothyronine (T3) and thyroxine (T4) levels were substantially decreased. Gene transcription expressions along the hypothalamic-pituitary-thyroid (HPT) axis were also markedly affected. Significant downregulation of dio1, dio2, nis, nkx2.1, pax8, tg, tpo, trβ and ttr levels, along with the stimulation of the tshβ gene, were also observed in exposed fish compared to controls. Western blot analysis indicated that expression of the TTR protein was significantly decreased, which coincides with the results of the gene expression analysis. Collectively, our observations show that NPX increases the risk of bioconcentration and thyroid disruption in zebrafish. Given the continued increasing consumption and emission of pharmaceuticals, thyroid disruption should be considered when assessing the aquatic risk of long-term exposure to environmentally relevant concentrations of pharmaceuticals.

Influence of Nanomolar Deltamethrin on the Hallmarks of Primary Cultured Cortical Neuronal Network and the Role of Ryanodine Receptors

BACKGROUND

The pyrethroid deltamethrin (DM) is broadly used for insect control. Although DM hyperexcites neuronal networks by delaying inactivation of axonal voltage-dependent [Formula: see text] channels, this mechanism is unlikely to mediate neurotoxicity at lower exposure levels during critical perinatal periods in mammals.

OBJECTIVES

We aimed to identify mechanisms by which acute and subchronic DM altered axonal and dendritic growth, patterns of synchronous [Formula: see text] oscillations (SCOs), and electrical spike activity (ESA) functions critical to neuronal network formation.

METHODS

Measurements of SCOs using [Formula: see text] imaging, ESA using microelectrode array (MEA) technology, and dendritic complexity using Sholl analysis were performed in primary murine cortical neurons from wild-type (WT) and/or ryanodine receptor 1 ([Formula: see text]) mice between 5 and 14 d in vitro (DIV). [Formula: see text] binding analysis and a single-channel voltage clamp were utilized to measure engagement of RyRs as a direct target of DM.

RESULTS

Neuronal networks responded to DM ([Formula: see text]) as early as 5 DIV, reducing SCO amplitude and depressing ESA and burst frequencies by 60-70%. DM ([Formula: see text]) enhanced axonal growth in a nonmonotonic manner. [Formula: see text] enhanced dendritic complexity. DM stabilized channel open states of RyR1, RyR2, and cortical preparations expressing all three isoforms. DM ([Formula: see text]) altered gating kinetics of RyR1 channels, increasing mean open time, decreasing mean closed time, and thereby enhancing overall open probability. SCO patterns from cortical networks expressing [Formula: see text] were more responsive to DM than WT. [Formula: see text] neurons showed inherently longer axonal lengths than WT neurons and maintained less length-promoting responses to nanomolar DM.

CONCLUSIONS

Our findings suggested that RyRs were sensitive molecular targets of DM with functional consequences likely relevant for mediating abnormal neuronal network connectivity in vitro. https://doi.org/10.1289/EHP4583.

Maternal exposure to fipronil results in sulfone metabolite enrichment and transgenerational toxicity in zebrafish offspring: Indication for an overlooked risk in maternal transfer?

Ecotoxicological studies show the association between pesticide pollution and transgenerational toxicity in aquatic organisms. However, a less considered risk is that many pesticides can be metabolized and transferred to offspring as new toxicants. In this study, we used zebrafish to evaluate the maternal transfer risk of fipronil (FIP), which is a great threat to aquatic organisms with toxic metabolite formation. After 28-day exposure to environmentally relevant concentrations (1.0, 5.0 and 10.0 μg/L) of FIP in adult female zebrafish (F0), the toxicants off-loading and transgenerational toxicity in offspring were studied. High burdens of FIP and its sulfone metabolite were found in both F0 and the embryos (F1), resulting in increased CYP450 activity. The residual levels of the metabolite were higher than those of the parent compound. Chiral analysis further showed a preferential accumulation of S-enantiomer of FIP in both F0 and F1. Maternal exposure to FIP increased the malformation rate and decreased the swim speed in larvae. Additionally, after exposure, the levels of thyroid hormones (THs), including triiodothyronine (T3) and thyroxine (T4), decreased in both generations, particularly in the F1. Gene transcription expression along the hypothalamic-pituitary-thyroid (HPT) axis was also significantly affected. Maternal exposure to FIP increased sulfone metabolite enrichment and cause multiple toxic effects in F1. Findings from this study highlight the key role of biologically active product formation in the maternal transfer of pollutants and associated risk assessment.

Enantioselective thyroid disruption in zebrafish embryo-larvae via exposure to environmental concentrations of the chloroacetamide herbicide acetochlor

Acetochlor (ACT) is a chiral chloroacetamide pesticide that has been heavily used around the world, resulting in its residues being frequently found in surface waters. It has been reported that ACT is an endocrine disrupting chemical (EDC) with strong thyroid hormone-disrupting activity in aquatic organisms. However, the enantioselectivity underlying thyroid disruption has yet to be understood. In this study, using a zebrafish embryo-larvae model, the enantioselective thyroid disruption of ACT was investigated at a series of environmentally relevant concentrations (1, 2, 10 and 50 μg/L). Our results showed that both racemic ACT and its enantiomers significantly increased the malformation rates of embryos at 72 h postfertilization (hpf). Decreased thyroxine (T₄) contents and increased triiodothyronine (T₃) contents were found in larvae at 120 hpf, with (+)-S-ACT exhibiting a greater effect than (-)-R-enantiomer. Similarly, (+)-S-ACT also showed a stronger effect on the mRNA expressions of thyroid hormone receptors (TRα and TRβ), deiodinase2 (Dio2) and thyroid-stimulating hormone-β (TSHβ) genes. The observed enantioselectivity in TR expressions was consistent with that of in silico binding analysis, which suggested that (+)-S-enantiomer binds more potently to the TRs than (-)-R-enantiomer. In general, ACT enantiomers showed different influences on the secretion of THs, expression of TH-related key genes and binding affinity to TRs. Considering the different toxicity of different enantiomers, our study highlights the importance of enantioselectivity in understanding of thyroid disruption effects of chiral pesticides.

Pyrethroid pesticide metabolite, 3-PBA, in soils: method development and application to real agricultural soils

3-Phenoxybenzoic acid (3-PBA) is a shared metabolite of several synthetic pyrethroid pesticides (SPs) resulting from environmental degradation of parent compounds and thus occurs frequently as a residue in samples. Hence, the importance of 3-PBA evaluation after pyrethroid application. There is a gap of analytical methods to determine 3-PBA in soil samples. Therefore, an analytical method that combines the solid-phase extraction (SPE) and gas chromatography-mass spectrometry (GC/MS) detection has been developed for the determination of 3-PBA in soil samples. The analytical method was validated in terms of linearity, sensitivity, intra- and inter-day batch precisions, recoveries, and quantification limits. An SPE method using a Strata X cartridge allows obtaining limits of detection and quantification equal to 4.0 and 13.3 ng g^-1, respectively. Under optimized conditions, the method average recovery levels ranged from 70.3 to 93.5% with a relative standard deviation below 3.4%. Method intra- and inter-day precision was under 5.0 and 4.8%, respectively. The developed method was applied to 11 agricultural soil samples in the north of Portugal. The developed methodology allowed for the determination of the pyrethroid metabolite, 3-PBA, in agricultural soil samples at levels of few ng g^-1. Graphical abstract ᅟ.