Combined endocrine disruptive toxicity of malathion and cypermethrin to gene transcription and hormones of the HPG axis of male zebrafish (Danio rerio)

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.

Reproductive endocrine disruption effect and mechanism in male zebrafish after life cycle exposure to environmental relevant triclosan

Triclosan (TCS) is a wide-spectrum antibacterial agent that is found in various water environments. It has been reported to have estrogenic effects. However, the impact of TCS exposure on the reproductive system of zebrafish (Danio rerio) throughout their life cycle is not well understood. In this study, zebrafish fertilized eggs were exposed to 0, 10, and 50 μg/L TCS for 120 days. The study investigated the effects of TCS exposure on brain and testis coefficients, the expression of genes related to the hypothalamus-pituitary-gonadal (HPG) axis, hormone levels, vitellogenin (VTG) content, histopathological sections, and performed RNA sequencing of male zebrafish. The results revealed that life cycle TCS exposure had significant effects on zebrafish reproductive parameters. It increased the testis coefficient, while decreasing the brain coefficient. TCS exposure also led to a decrease in mature spermatozoa and altered the expression of genes related to the HPG axis. Furthermore, TCS disrupted the balance of sex hormone levels and increased VTG content of male zebrafish. Transcriptome sequencing analysis indicated that TCS affected reproductive endocrine related pathways, including PPAR signaling pathway, cell cycle, GnRH signaling pathway, steroid biosynthesis, cytokine-cytokine receptor interaction, and steroid hormone biosynthesis. Protein-protein interaction (PPI) network analysis confirmed the enrichment of hub genes in these pathways, including bub1bb, ccnb1, cdc20, cdk1, mcm2, mcm5, mcm6, plk1, and ttk in the brain, as well as fabp1b.1, fabp2, fabp6, ccr7, cxcl11.8, hsd11b2, and hsd3b1 in the testis. This study sheds light on the reproductive endocrine-disrupting mechanisms of life cycle exposure to TCS.

Effect of chronic deltamethrin exposure on brain transcriptome and metabolome of juvenile crucian carp

Deltamethrin (Del), a widely administered pyrethroid insecticide, has been established as a common contaminant of the freshwater environment and detected in many freshwater ecosystems. In this study, we investigated the changes in brain transcriptome and metabolome of crucian carp after exposure to 0.6 μg/L Del for 28 days. Elevated MDA levels and inhibition of SOD activity indicate damage to the antioxidant system. Moreover, a total of 70 differential metabolites (DMs) were identified using the liquid chromatography-mass spectrometry, including 32 upregulated and 38 downregulated DMs in the Del-exposed group. The DMs associated with chronic Del exposure were enriched in steroid hormone biosynthesis, fatty acid metabolism, and glycerophospholipid metabolism for prostaglandin G2, 5-oxoeicosatetraenoic acid, progesterone, androsterone, etiocholanolone, and hydrocortisone. Transcriptomics analysis revealed that chronic Del exposure caused lipid metabolism disorder, endocrine disruption, and proinflammatory immune response by upregulating the pla2g4, cox2, log5, ptgis, lcn, and cbr expression. Importantly, the integrative analysis of transcriptomics and metabolomics indicated that the arachidonic acid metabolism pathway and steroid hormone biosynthesis were decisive processes in the brain tissue of crucian carp after Del exposure. Furthermore, Del exposure perturbed the tight junction, HIF-1 signaling pathway, and thyroid hormone signaling pathway. Overall, transcriptome and metabolome data of our study offer a new insight to assess the risk of chronic Del exposure in fish brains.

Pesticides exposure and compromised fitness in wild birds: Focusing on the reproductive endocrine disruption

Exposure of pesticides to wildlife species, especially on the aspect of endocrine disruption is of great concern. Wildlife species are more at risk to harmful exposures to the pesticides in their natural habitat through diet and several other means. Species at a higher tropic level in the food chain are more susceptible to the deleterious effects due to sequential biomagnifications of the pesticides/metabolites. Pesticides directly affect fitness of the species in the wild causing reproductive endocrine disruption impairing the hormones of the gonads and thyroid glands as reproduction is under the influence of cross regulations of these hormones. This review presents a comprehensive compilation of important literatures on the impact of the current use pesticides in disruption of both the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-thyroid axes particularly in birds addressing impacts on the reproductive impairments and overall fitness. In addition to the epidemiological studies, laboratory investigations those provide supportive evidences of the probable mechanisms of disruption in the wild also have been incorporated in this review. To accurately predict the endocrine-disruption of the pesticides as well as to delineate the risk associated with potential cumulative effects, studies are to be more focused on the environmentally realistic exposure dose, mixture pesticide exposures and transgenerational effects. In addition, strategic screening/appropriate methodologies have to be developed to reveal the endocrine disruption potential of the contemporary use pesticides. Demand for adequate quantitative structure-activity relationships and insilico molecular docking studies for timely validation have been highlighted.

Phthalates (PAEs) and reproductive toxicity: Hypothalamic-pituitary-gonadal (HPG) axis aspects

Phthalates (PAEs) are widely used for their excellent ability to improve plastic products. As an essential endocrine axis that regulates the reproductive system, whether dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis is involved in reproductive toxicity mediated by environmental endocrine disruptors PAEs has become a hot topic of widespread concern. This study systematically reviewed the adverse effects of multiple PAEs on the HPG axis in different models and objectively discussed the possible underlying mechanisms. The abnormal release of gonadotropin-releasing hormone and gonadotropin, dysfunction of sex hormone receptors and steroid hormone synthesis, and general damage, including cell proliferation, oxidative stress, apoptosis, and autophagy have been confirmed to be involved in this process. Although it is widely established that PAEs induce HPG axis dysfunction, the specific mechanisms involved remain unclear. From a systematic review of relevant publications, it appears that the abnormal expression of peroxisome proliferator-activated, aryl hydrocarbon, and insulin receptors mediated by PAEs is key upstream event that induces these adverse outcomes; however, this inference needs to be further verified. Overall, this study aimed to provide reliable potential biomarkers for future environmental risk assessment and epidemiological investigation of PAEs.

Synergistic effects on oxidative stress, apoptosis and necrosis resulting from combined toxicity of three commonly used pesticides on HepG2 cells

The widespread use of pesticides performs a vital role in safeguarding crop yields and quality, providing the opportunity for multiple pesticides to co-exist, which poses a significant potential risk to human health. To assess the toxic effects caused by exposures to individual pesticides (chlorpyrifos, carbofuran and acetamiprid), binary combinations and ternary combinations, individual and combined exposure models were developed using HepG2 cells and the types of combined effects of pesticide mixtures were assessed using concentration addition (CA), independent action (IA) and combination index (CI) models, respectively, and the expression of biomarkers related to oxidative stress, apoptosis and cell necrosis was further examined. Our results showed that both individual pesticides and mixtures exerted toxic effects on HepG2 cells. The CI model indicated that the toxic effects of pesticide mixtures exhibited synergistic effects. The results of the lactate dehydrogenase (LDH) release and apoptosis assay revealed that the pesticide mixture increased the release of LDH and apoptosis levels. Moreover, our results also showed that individual pesticides and mixtures disrupted redox homeostasis and that pesticide mixtures produced more intense oxidative stress effects. In conclusion, we have illustrated the enhanced combined toxicity of pesticide mixtures by in-vitro experiments, which provides a theoretical basis and scientific basis for further toxicological studies.

Broad-spectrum portable magnetic relaxation switching immunosensor with gold-functionalized magnetic nanoprobes for the sensitive detection of multiple pyrethroids

At present, the most available pyrethroid (PYR) detection methods still suffer from a narrow detection spectrum, low sensitivity, and less portability. Herein, a novel magnetic relaxation switching (MRS) sensor was elaboratively designed to detect multiple PYRs, combining a novel broad-spectrum antibody CL-CN/1D2 and synthesized immune gold-functionalized magnetic nanoparticles, with the inherent response of the sensor. A series of antibodies and the immune gold-functionalized magnetic nanoparticles were designed and synthesized. The broad-spectrum antibody CL-CN/1D2 and high-performance gold-functionalized magnetic nanoprobe were further selected. The target analytes were effectively captured by the gold-functionalized magnetic nanoparticles in 20% (v/v) ethanol, resulting in the number increase of the signaling probes in the supernatant after magnetic separation. This sensor can detect multiple PYRs with a detection limit of 2.72 μg/L for cypermethrin, 3.58 μg/L for β-cypermethrin, 4.07 μg/L for cyfluthrin, 3.66 μg/L for λ-cyhalothrin, 4.42 μg/L for β-cyhalothrin, 3.51 μg/L for fenpropathrin, 4.41 μg/L for fenvalerate, and 4.12 μg/L for deltamethrin in lake water and milk within 35 min. This study not only achieves broad-spectrum PYRs detection at a trace amount but also provides an effective and universal strategy for enhancing the sensitivity and stability of the portable MRS sensor when detecting hydrophobic analytes in the environment.

Malathion exposure during juvenile and peripubertal periods downregulate androgen receptor and 17-ß-HSD testicular gene expression and compromised sperm quality in rats

Malathion is an insecticide that is used to control arboviruses and agricultural pests. Adolescents that are exposed to this insecticide are the most vulnerable as they are in the critical period of postnatal sexual development. This study aimed to evaluate whether malathion damage can affect sperm function and its respective mechanisms when adolescents are exposed during postnatal sexual development. Twenty-four male Wistar rats (PND 25) were divided into three experimental groups and treated daily for 40 d: control group (saline 0.9%), 10 mg/kg (M10 group), or 50 mg/kg (M50 group) of malathion. At PND 65, the rats were anesthetized and euthanized. Testicles were collected for the evaluation of gene expression. Sperm cells from the epididymis were used for evaluation of the oxidative profile or spermatic function. Data showed that a lower dose of malathion downregulated the gene expression of androgen receptors and testosterone converter enzyme 17-β-HSD in the testis. The acrosomal integrity of sperm cells was compromised in the M50 group, but not the M10 group. The mitochondrial activity was not impaired by exposure. Finally, although no alterations in malondialdehyde and glutathione levels were observed, malathion, at both doses, increased antioxidant enzyme catalase activity and, at a higher dose, superoxide dismutase activity. The present study showed that low doses of malathion considered to be inoffensive are capable of impairing sperm quality and function through the downregulation of testicular genic expression of AR enzyme 17-β-HSD and can damage the spermatic antioxidant profile during critical periods of development.

Bioaccumulation, metabolism and toxicological effects of chiral insecticide malathion and its metabolites in zebrafish (Danio rerio)

The bioaccumulation, metabolism, tissue-specific distribution and toxicity of the widely used organophosphorous pesticide malathion to zebrafish were investigated on an enantiomeric level for evaluating the environmental risks. The metabolites were also monitored and evaluated. Malathion was metabolized by zebrafish very fast with the half-life of 0.12 d and showed a middle accumulation capacity in zebrafish with bioaccumulation factor (BCF) of 12.9 after a 15-d exposure. Brain could enrich higher concentration of malathion than other tissues. The metabolites malaoxon, malathion/malaoxon monocarboxylic acid (DMA), malathion/malaoxon dicarboxylic acid (DCA), dimethylthiophosphate (DMTP) and dimethyldithiophosphate (DMDTP) were found, in which DMTP and DCA were in higher level, indicating the metabolism was mainly induced by carboxylesterase degradation. The accumulation of malathion and malaoxon was stereoselective in zebrafish tissues, exhibiting S-enantiomer preferentially enriched. The acute toxicity test showed rac-malathion was low toxic to zebrafish, which was 1.2 and 1.6 folds more toxic than S-malathion and R-malathion respectively. Malaoxon was highly toxic to zebrafish and approximately 32 times more toxic than malathion. The toxicity of other metabolites was lower than malathion. Malathion could cause an apparent developmental toxicity to zebrafish embryo, including bradycardia, hatchability reduction and deformity, and abnormal movement patterns in zebrafish larva. Chronic toxicity indicated that malathion and malaoxon induced oxidative damage and neurotoxicity in the liver, brain and gill of zebrafish, and malaoxon exhibited a relatively high injury to the zebrafish brain. The results can provide information for the comprehensive assessment of the potential risk of malathion to aquatic organisms and highlight the necessity of consideration of stereoselectivity and metabolites when systemically evaluating pesticides.

A transcriptomic-based analysis predicts the neuroendocrine disrupting effect on adult male and female zebrafish (Danio rerio) following long-term exposure to tetrabromobisphenol A bis(2-hydroxyethyl) ether

Endocrine-disrupting chemicals (EDCs) are now ubiquitously distributed in the environment. Tetrabromobisphenol A bis(2-hydroxyethyl) ether (TBBPA-DHEE) pollution in environment media poses a significant threat to humans and aquatic organisms as a result of its potential neurotoxicity and endocrine-disrupting effect. The endocrine-disrupting effects of TBBPA-DHEE on aquatic organisms, however, have received limited attention. In this study, the neurotoxicity and reproductive endocrine-disruptive effect of TBBPA-DHEE was evaluated by observing the neurobehavioral changes, vitellogenin (VTG), testosterone, 17β-estradiol and gene expression levels in adult male and female zebrafish exposed to TBBPA-DHEE (0.05, 0.2 and 0.3 mg/L) for 100 days. Furthermore, transcriptomic analysis was conducted to unravel other potential neuroendocrine-disrupting mechanism. Our result showed TBBPA-DHEE significantly (p < 0.05) altered the locomotor behavior and motor coordination abilities in both sexes. Steroid hormone and VTG levels were also altered indicating the neuroendocrine-disrupting effect of TBBPA-DHEE on the hypothalamic-pituitary-gonadal-axis. A total of 1568 genes were upregulated and 542 genes downregulated in males, whereas, 1265 upregulated and 535 downregulated genes were observed in females. The KEGG enrichment analysis showed that cell cycle and p55 signaling pathways were significantly enriched due to TBBPA-DHEE exposure. These pathways and its component genes are potential target of EDCs. The significant upregulation of genes in these pathways could partly explain the neuroendocrine disrupting effect of TBBPA-DHEE. The observed toxic effects of TBBPA-DHEE observed in this study is confirmation of the endocrine-disrupting toxicity of this chemical which would be valuable in biosafety evaluation and biomonitoring of TBBPA-DHEE for public health purposes.

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.

The protective effects of quercetin on the physiological responses in malathion-exposed common carp, Cyprinus carpio

This study aimed to evaluate the protective effects of quercetin on the biochemical parameters, immunity, and growth performance in malathion-exposed common carp, Cyprinus carpio. The methods six experimental groups, including the control group, fish exposed to concentrations of 1.04 and 2.08 mg/l malathion, fish supplemented with quercetin (200 mg/kg diet), and fish treated with quercetin + malathion for 21 days, were considered for the experiment. After the feeding period, in results the activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST) were significantly decreased in the hepatocyte, while malondialdehyde (MDA) content increased in response to malathion. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities and glucose, cortisol, and urea levels significantly increased after exposure to malathion. Exposure of fish to malathion-induced decreases in protease, lysozyme, and alternative complement (ACH50) activities and total immunoglobulin (total Ig) in the mucosa. Changes in other parameters were different depending on malathion concentrations. The supplementation of fish with quercetin had no ameliorating effect on the malathion-related alternations of mucosal lysozyme and protease activities. However, quercetin ameliorated the depressing effects of malathion on biochemical and immunological parameters. Changes in the growth performance and hematological parameters indicated the toxic effect of malathion. In conclusion, quercetin could efficiently reduce the toxic effects of malathion on the biochemical, immune, and hematological parameters of the common carp.

The masculinization steroid milieu caused by fluorene-9-bisphenol disrupts sex-typical courtship behavior in female zebrafish (Danio rerio)

In vertebrates, the behavior of congenital sex differences between males and females is highly dependent on steroid signals and hormonal milieu. The presence of endocrine disrupting chemicals (EDCs) in the environment generally plays a similar role to sex hormones, so its interference with aquatic organism population stability can not be ignored and is worth studying. Fluorene-9-bisphenol (BHPF) has been clarified as an endocrine disruptor on organisms by several studies but its mechanism in perturbation of courtship behavior of female zebrafish is not clear. Here, we proposed an automated multi-zebrafish tracking method quantifying the courtship process and reported that zebrafish females exposed to BHPF, are not receptive to males but rather court females, and lose normal ovarian function with an altered sex steroid milieu. Our results showed that BHPF damaged 17β-estradiol synthesis by down-regulation of sox3 and cyp19a1a, linking apoptosis with ovary development and female fecundity. The down-regulated expression of estrogen signaling through an estrogen receptor, esr2b, caused the induction of masculinization of female courtship behavior and sexual preference in zebrafish females after BHPF treatment. This process might be mediated by inhibiting the transcription of a neuropeptide B (npb) in the brain. Our study reveals that the estrogen signaling pathway may play an important role in classical courtship behavior and sexual preference of zebrafish. This study provided evidence that anti-estrogenic chemical exposure caused adverse effects on the regulation of the brain-gonad-estrogen axis of aquatic organisms, which should be of concern and highlighted the importance of controlling environmental contamination.

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.

Acute toxicity and teratogenicity of carbaryl (carbamates), tebufenpyrad (pyrazoles), cypermethrin and permethrin (pyrethroids) on the European sea bass (Dicentrarchus labrax L, 1758) early life stages

The toxicity of carbaryl, tebufenpyrad, cypermethrin and permethrin was evaluated in European sea bass Dicentrarchus labrax during the embryonic and larval development using six different concentrations per chemical. The order of the toxicity effectiveness was carbaryl > tebufenpyrad > cypermethrin > permethrin. The larvae were more sensitive to all tested chemicals than embryos. The LC50 of carbaryl, tebufenpyrad, cypermethrin and permethrin was determined as 13.88, 43.96, 92 and 142 ppm and 9.27, 25.67, 48.4 and 72.7 ppm in embryo and larvae, respectively. Furthermore, the tested pesticides exhibited teratogenic effects on D. labrax embryo-larval stages. The observed malformations were coagulation, no spherical egg, unhatched egg, pericardial oedemata, yolk oedemata, lordosis, kyphosis, scoliosis, no eye, cranial deformation and body atrophy. Malformations were induced with 0.5 ppm carbaryl, 10 ppm tebufenpyrad and 50 ppm cypermethrin and permethrin; the highest rates of malformation were noted with 16 ppm carbaryl, 160 ppm tebufenpyrad, 400 ppm cypermethrin and 400 ppm permethrin as 34.5%, 28%, 17.5% and 16%, respectively. A positive correlation between the incidence of malformation and the increase of pesticide concentration was established.

Identification of 2,2',4,5,5'-Pentachlorobiphenyl (PCB101) metabolites and their transmission characteristics in silver crucian carp (Carassius auratus gibelio)

Polychlorinated biphenyls (PCBs) have been attracting global concern due to their persistence and toxicity. However, the study on the metabolites of PCBs in freshwater fish is limited. In this study, the metabolites of 2,2',4,5,5'-Pentachlorobiphenyl (PCB101) in silver crucian carp (Carassius auratus gibelio) were identified for the first time. After intraperitoneal injection of PCB101 (2 mg/kg), the results showed that it could be metabolized to at least three types of metabolites, including hydroxylated (OH-), methoxylated (MeO-) and methyl sulfonated (MeSO₂-) PCB101. The OH- metabolites identified in most tissues were 3-OH-PCB101and 4-OH-PCB101, such as liver, gallbladder, blood and muscle. MeSO₂- metabolites identified in gallbladder, blood and brain were 3-MeSO₂-PCB101 and 4-MeSO₂-PCB101. Meanwhile, the MeO- metabolite identified in liver, gallbladder, blood and spleen of silver crucian carp was 4-MeO-PCB101. The investigation of the types and structures of PCB101 and its metabolites, as well as the tissue distribution and accumulation characteristics in silver crucian carp are beneficial to understand the transformation and metabolic mechanisms of PCBs in aquatic organisms. It is of great significance to identify potential pollution hazards of precursor compounds and their metabolites on aquatic products and ensure the quality and safety of aquatic products.

Sex-specific responses of the reproductive system of zebrafish (Danio rerio) to electrolysis

Adult zebrafish (Danio rerio) were electrolyzed at different current densities to explore the effects of electrolysis on their reproductive system, especially on embryo production, and to uncover the molecular mechanism of changes in sex hormone and vitellogenin (VTG) levels. The results showed that embryo reproduction of zebrafish was reduced at a current density of 0.64 A/m² after 28 days of exposure. In addition, the 17β-estradiol concentration significantly decreased and the testosterone concentration increased in female zebrafish above 0.53 A/m². However, opposite trends were observed in male zebrafish. The VTG concentration was reduced considerably in the livers of female zebrafish in the 0.64 A/m² electrolysis group (p < 0.05). In addition, the mRNA expression of hormone-regulating genes was significantly altered in female and male zebrafish when the current density was greater than 0.53 A/m², and their change trends were sex-dependent. The genes expression levels of vtg1 and esr1 were downregulated in female zebrafish. However, the gene expression of esr1 and cyp19a was upregulated in male zebrafish. These changes were related to disruption in the hormone balance and VTG levels of adult zebrafish. Thus, electrolysis could cause masculinization of female zebrafish and feminization of male zebrafish. Nonetheless, there were few influences on the hormone levels and reproduction rate of adult zebrafish at the threshold of 0.26 A/m². Thus, the current density of electrolysis needs to be controlled within a specific range to reduce its harmful effects on the reproductive system of aquatic animals.

Role of endocrine disruption in toxicity of 6-benzylaminopurine (6-BA) to early-life stages of Zebrafish

6-benzylaminopurine (6-BA), classified as a "plant hormone", is an important ingredient in production of "toxic bean sprouts". Although there is no direct evidence of adverse effects, its hazardous effects have received some attention and aroused furious debate between proponents and environmental regulators. In this study, potential adverse effects of 6-BA were investigated by exposing zebrafish in vivo to 0.2 - 25 mg 6-BA/L. Results indicated that, when exposure was limited to early-life stage (4-36 hpf), 20 mg 6-BA/L caused early hatching, abnormal spontaneous movement, and precocious hyperactivity in zebrafish embryos/larvae. While under a continuous exposure regime, 6-BA at 0.2 mg/L was able to cause hyperactive locomotion and transcription of genes related to neurogenesis (gnrh3 and nestin) and endocrine systems (cyp19a and fshb) in 5 dpf larvae. Quantification by use of LC/MS indicated bioaccumulation of 6-BA in zebrafish increased when exposed to 0.2 or 20 mg 6-BA/L. These results suggested that 6-BA could accumulate in aquatic organisms and disrupt neuro-endocrine systems. Accordingly, exposure to 0.2 mg 6-BA/L increased production of estradiol (E2) and consequently E2/T ratio in zebrafish larvae, which directly indicated 6-BA is estrogenic. In silico simulations demonstrated potential for binding of 6-BA to estrogen receptor alpha (ERa) and cytochrome P450 aromatase (CYP19A). Therefore, induction of estrogenic effects, via potential interactions with hormone receptors or disturbance of downstream transcription signaling, was possible mechanism underlying the toxicity of 6-BA. Taken together, these findings demonstrate endocrine disrupting properties of 6-BA, which suggest concerns about risks posed to endocrine systems.

Oxidative stress is involved in the activation of NF-κB signal pathway and immune inflammatory response in grass carp gill induced by cypermethrin and/or sulfamethoxazole

At present, the concentration of environmental pollutants, such as pesticides and antibiotics exposed in environment, especially in aquatic environment is increasing. Research on environmental pollutants has exploded in the last few years. However, studies on the combined effects of pesticides and antibiotics on fish are rare, especially the toxic damage to gill tissue is vague. In this paper, cypermethrin (CMN) and sulfamethoxazole (SMZ) were analyzed and found that there was a strong correlation between the pathways affected by the first 30 genes regulated by CMN and SMZ, respectively. Therefore, the toxic effects of CMN (0.651 μg L^-1) and/or SMZ (0.3 μg L^-1) on grass carp gill were studied in this paper. Histopathology, quantitative real-time PCR, and other methods were used to detect the tissue morphology, oxidative stress level, inflammation, and apoptosis-related indicators of the fish gills after exposure of 42 days. It was found that compared with the single exposure (CMN/SMZ) group, the combined exposure (MIX) group had a more pronounced oxidative stress index imbalance. At the same time, nuclear factor-κB (NF-κB) signal pathway was activated and immuno-inflammatory reaction appeared in MIX group. The expression of tumor necrosis factor (TNF-α) in the rising range is 2.94 times that of the C group, while the expression of interleukin 8 (IL-8) is as high as 32.67 times. This study reveals the harm of CMN and SMZ to fish, and provides a reference and basis for the rational use of pesticides and antibiotics.

Tissue distribution and endocrine disruption effects of chronic exposure to pharmaceuticals and personal care products mixture at environmentally relevant concentrations in zebrafish

Pharmaceuticals and personal care products (PPCPs) as emerging contaminants are ubiquitously present in the aquatic environment. Using in vivo and in silico techniques, this study aims to elucidate tissue distribution and endocrine disruption effects of chronic exposure (120 days) to PPCP mixture at environmentally relevant concentrations (ERCs) in adult zebrafish. Results from UHPLC-MS/MS analyses showed elevated distribution of PPCPs in zebrafish tissues in the order of liver > gonad > brain. Upregulation of steroid hormone receptors, both gonadotropin, and steroidogenic genes perturb the HPG axis pathway in females, while male fish exhibited significantly downregulated expressions of vtg, cyp17, and 17βhsd genes with inhibited fecundity. The Spearman correlation indicated a significant positive relationship between PPCPs bioaccumulation and mRNA levels of HPG axis genes. In silico molecular docking (MD) revealed specific amino acid residues of PPCPs binding with zebrafish estrogen receptors. Furthermore, the strongest binding energies of sulfamethoxazole, carbamazepine, and triclosan were discovered in erα and erβ estrogen receptors, confirming PPCPs' xenoestrogenic behavior. To summarize, chronic exposure to ERCs resulted in a high accumulation of PPCPs in the liver and gonad tissues of adult zebrafish, as well as associated perturbed genetic responses. As a result, strict environmental regulations for the disposal of PPCPs should be ensured to protect ecological and public health.

Effects of common environmental endocrine-disrupting chemicals on zebrafish behavior

Environmental endocrine-disrupting chemicals (EDCs), a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Therefor, this review focused on the use of the zebrafish as a model to explore the effect of different EDCs on behavior, as well as the molecular mechanisms that drive these effects. Furthermore, our study summarizes the current knowledge on the neuromodulatory effects of different EDCs in zebrafish. This study also reviews the current state of zebrafish behavior research, in addition to the potential mechanisms of single and mixed pollutant-driven behavioral dysregulation at the molecular level, as well as the applications of zebrafish behavior experiments for neuroscience research. This review broadens our understanding of the influence of EDCs on zebrafish behavior and provides guidance for future research.

Combined toxicity of endocrine-disrupting chemicals: A review

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