Sex-specific effects of fluoride and lead exposures on histology, antioxidant physiology, and immune system in the liver of zebrafish (Danio rerio)

Co-exposure to cadmium and triazophos induces variations at enzymatic and transcriptional levels in Opsariichthys bidens

Heavy metals and pesticides are significant pollutants in aquatic environments, often leading to combined pollution and exerting toxic effects on aquatic organisms. With the rapid growth of modern industry and agriculture, heavy metal cadmium (Cd) and pesticide triazophos (TRI) are frequently detected together in various water bodies, particularly in agricultural watersheds. However, the combined toxic mechanisms of these pollutants on fish remain poorly understood. This experiment involved a 21-day co-exposure of Cd and TRI to the hook snout carp Opsariichthys bidens to investigate the toxic effects on liver tissues at both enzymatic and transcriptional levels. Biochemical analysis revealed that both individual and combined exposures significantly increased the content or activity of caspase-3 (CASP-3) and malondialdehyde (MDA). Moreover, the impact on these parameters was greater in the combined exposure groups compared to the corresponding individual exposure groups. These findings suggested that both individual and combined exposures could induce mitochondrial dysfunction and lipid peroxidation damage, with combined exposure exacerbating the toxicological effects of each individual pollutant. Furthermore, at the molecular level, both individual and combined exposures upregulated the expression levels of cu-sod, cat, and erβ, while downregulating the expression of il-1. Similar to the patterns observed in the biochemical parameters, the combined exposure group exhibited a greater impact on the expression of these genes compared to the individual exposure groups. These results indicated that exposure to Cd, TRI, and their combination induced oxidative stress, endocrine disruption, and immunosuppression in fish livers, with more severe effects observed in the combined exposure group. Overall, the interaction between Cd and TRI appeared to be synergistic, shedding light on the toxic mechanisms by which fish livers responded to these pollutants. These findings contributed to the understanding of mixture risk assessment of pollutants and were valuable for the conservation of aquatic resources.

Combined Effects of Fluoride and Dietary Seleno-L-Methionine at Environmentally Relevant Concentrations on Female Zebrafish (Danio rerio) Liver: Histopathological Damages, Oxidative Stress and Inflammation

Fluoride, a global environmental pollutant, is ubiquitous in aquatic environments and coexists with selenium, which can cause complex effects on exposed organisms. However, data on the interaction of fluoride and selenium remain scarce. In this study, female zebrafish (Danio rerio) were exposed to fluoride (80 mg/L sodium fluoride) and/or dietary selenomethionine (Se-Met) for 30, 60 and 90 days, the effects on the liver of zebrafish were investigated. The results indicated that an increase in fluoride burden, inhibited growth and impaired liver morphology were recorded after fluoride exposure. Furthermore, fluoride alone caused oxidative stress and inflammation in the liver, as reflected by the increase in ROS and MDA contents, the reduction of anti-oxidative enzymes, the altered immune related enzymes (ACP, AKP, LZM and MPO) and the expression of IL-6, IL-1β, TNF-α, IL-10 and TGF-β. In contrast, co-exposure to fluoride and Se-Met decreased fluoride burden and restored growth. Furthermore, dietary Se-Met alleviated oxidative stress, inflammation and impaired morphology in liver trigger by fluoride. However, dietary Se-Met alone increased the activities of SOD and CAT. These results demonstrate that the protective effect of dietary Se-Met against chronic fluoride toxicity at a certain level.

Vitamin E alleviates pyraclostrobin-induced toxicity in zebrafish (Danio rerio) and its potential mechanisms

Strobilurin fungicides (SFs) are commonly used in agriculture worldwide and frequently detected in aquatic environments. High toxicity of SFs to aquatic organisms has caused great concerns. To explore whether vitamin E (VE) can relieve the toxicity caused by pyraclostrobin (PY), zebrafish were exposed to PY with or without VE supplementation. When co-exposure with VE (20 μM), the 96 h-LC50 values of PY to zebrafish embryos, adult, and the 24 h-LC50 value of PY to larvae increased from 43.94, 58.36 and 38.16 μg/L to 64.72, 108.62 and 72.78 μg/L, respectively, indicating that VE significantly decreased the toxicity of PY to zebrafish at different life stages. In addition, VE alleviated the deformity symptoms (pericardial edema and brain damage), reduced speed and movement distance, and decreased heart rate caused by 40 μg/L PY in zebrafish larvae. Co-exposure of PY with VE significantly reduced PY-caused larval oxidative stress and immunotoxicity via increasing the activities of superoxide dismutase, catalase and level of glutathione, as well as reducing the malondialdehyde production and the expression levels of Nrf2, Ucp2, IL-8, IFN and CXCL-C1C. Meanwhile, the expression levels of gria4a and cacng4b genes, which were inhibited by PY, were significantly up-regulated after co-exposure of PY with VE. Moreover, co-exposure with VE significantly reversed the increased mitochondrial DNA copies and reduced ATP content caused by PY in larvae, but had no effect on the expression of cox4i1l and activity of complex III that reduced by PY, suggesting VE can partially improve PY-induced mitochondrial dysfunction. In conclusion, the potential mechanisms of VE alleviating PY-induced toxicity may be ascribed to decreasing the oxidative stress level, restoring the functions of heart and nervous system, and improving the immunity and mitochondrial function in zebrafish.

Arsenic and chromium induced hepatotoxicity in zebrafish (Danio rerio) at environmentally relevant concentrations: Mixture effects and involvement of Nrf2-Keap1-ARE pathway

Arsenic (As) and chromium (Cr), two well-known cytotoxic and carcinogenic metals are reported to coexist in industrial effluents and groundwater. Their individual toxicities have been thoroughly studied but the combined effects, especially the mechanism of toxicity and cellular stress response remain unclear. Considering co-exposure as a more realistic scenario, current study compared the individual and mixture effects of As and Cr in the liver of zebrafish (Danio rerio). Fish were exposed to environmentally relevant concentrations of As and Cr for 15, 30 and 60 days. ROS generation, biochemical stress parameters like lipid peroxidation, reduced glutathione content, catalase activity and histological alterations were studied. Results showed increase in ROS production, MDA content and GSH level; and vicissitude in catalase activity as well as altered histoarchitecture, indicating oxidative stress conditions after individual and combined exposure of As and Cr which were additive in nature. This study also included the expression of Nrf2, the key regulator of antioxidant stress responses and its nuclear translocation. Related antioxidant and xenobiotic metabolizing enzyme genes like keap1, nqo1, ho1, mnsod and cyp1a were also studied. Overall results indicated increased nrf2, nqo1, ho1, mnsod expression at all time points and increased cyp1a expression after 60 days exposure. Emphasizing on the Nrf2-Keap1 pathway, this study exhibited additive or sometimes synergistic effects of As and Cr in zebrafish liver.

Neurotoxicity of Combined Exposure to the Heavy Metals (Pb and As) in Zebrafish (Danio rerio)

Lead (Pb) and arsenic (As) are commonly occurring heavy metals in the environment and produce detrimental impacts on the central nervous system. Although they have both been indicated to exhibit neurotoxic properties, it is not known if they have joint effects, and their mechanisms of action are likewise unknown. In this study, zebrafish were exposed to different concentrations of Pb (40 μg/L, 4 mg/L), As (32 μg/L, 3.2 mg/L) and their combinations (40 μg/L + 32 μg/L, 4 mg/L + 3.2 mg/L) for 30 days. The histopathological analyses showed significant brain damage characterized by glial scar formation and ventricular enlargement in all exposed groups. In addition, either Pb or As staining inhibited the swimming speed of zebrafish, which was enhanced by their high concentrations in a mixture. To elucidate the underlying mechanisms, we examined changes in acetylcholinesterase (AChE) activity, neurotransmitter (dopamine, 5-hydroxytryptamine) levels, HPI axis-related hormone (cortisol and epinephrine) contents and neurodevelopment-related gene expression in zebrafish brain. The observations suggest that combined exposure to Pb and As can cause abnormalities in swimming behavior and ultimately exacerbate neurotoxicity in zebrafish by interfering with the cholinergic system, dopamine and 5-hydroxytryptamine signaling, HPI axis function as well as neuronal development. This study provides an important theoretical basis for the mixed exposure of heavy metals and their toxicity to aquatic organisms.

Experimental exploration of estrogenic effects of norethindrone and 17α-ethinylestradiol on zebrafish (Danio rerio) gonads

Synthetic progestins and xenoestrogens found in aquatic habitats are currently gaining attention on global scale. The current study aimed to investigate the time-and dose-dependent effects of synthetic progestin Norethindrone (NET; 100, 500 and 1000 ng/L) and estrogen 17α-ethinylestradiol (EE2; 100 ng/L) individually as well as in binary mixture (1000 ng/L NET + 100 ng/L EE2) on reproductive histology and transcriptional expression profile of genes in adult zebrafish. For this, 20 female (3.15 ± 0.18 cm & 0.33 ± 0.06 g) and 20 male zebrafish in each group (2.93 ± 0.13 cm & 0.29 ± 0.04 g) were exposed to drugs dissolved in water for 30 days in 12 L rectangular tanks. We found that both NET and EE2 exposure reduced the gonadosomatic index in females, while only EE2 exposure caused significant reduction in males (p ≤ 0.05). Interestingly, NET delayed oocyte maturation in females and accelerated spermatogenesis in males, while EE2 consistently suppressed sperm maturation throughout the experiment. Further, qRT-PCR results revealed differential expression pattern of the study genes (er-α, er-β1, er-β2, pgr, vegfaa and p53) in male and female zebrafish. Co-exposure indicated potential inconsistencies in steroidal function in mixtures rather than single exposures. Our findings imply that changes in gonadal histology after NET and EE2 exposure may result from unique regulation of steroid hormone receptors. Additionally, significantly reduced p53 levels (p ≤ 0.05) following co-exposure in both sexes may suggest an elevated risk of neoplastic transformations. Further research with mammalian models will help to explore the mechanisms behind differing effects of alone and co-exposures.

Combined Effects of Fluoride and Dietary Seleno-L-methionine at Environmentally Relevant Concentrations on Female Zebrafish (Danio rerio) Liver: Histopathological Damages, Oxidative Stress and Inflammation

Fluoride, a global environmental pollutant, is ubiquitous in aquatic environments and coexists with selenium, which can cause complex effects on exposed organisms. However, data on the interaction of fluoride and selenium remain scarce. In this study, female zebrafish (Danio rerio) were exposed to fluoride (80 mg/L sodium fluoride) and/or dietary selenomethionine for 30, 60 and 90 days, the effects on the liver of zebrafish were investigated. The results indicated that an increase in fluoride burden, inhibited growth and impaired liver morphology were recorded after fluoride exposure. Furthermore, fluoride alone caused oxidative stress and inflammation in the liver, as reflected by the increase in ROS and MDA contents, the reduction of anti-oxidative enzymes, the altered immune related enzymes (ACP, AKP, LZM and MPO) and the expression of IL-6, IL-1β, TNF-α, IL-10 and TGF-β. In contrast, co-exposure to fluoride and Se-Met decreased fluoride burden and restored growth. Furthermore, dietary Se-Met alleviated oxidative stress, inflammation and impaired morphology in liver trigger by fluoride. However, dietary Se-Met alone increased the activities of SOD and CAT. These results demonstrate that the protective effect of dietary Se-Met against chronic fluoride toxicity at a certain level.

Bixafen causes hepatotoxicity and pancreas toxicity in zebrafish (Danio rerio)

Bixafen (BIX), a widely used succinate dehydrogenase inhibitor (SDHI) in agricultural disease control, has garnered significant attention due to its known hazardous effects on aquatic organisms. In this study, we exposed zebrafish embryos to 0.1, 0.2, and 0.3 μM BIX, to explore the impact of BIX on liver and pancreas. The results showed that BIX caused deformities and dysfunction in zebrafish embryos, including spinal curvature, pericardial edema, heart rate decrease, and hatching delay. Moreover, BIX significantly affected the development of the liver and pancreas in zebrafish and downregulated zebrafish fabp10a gene expression. Overall, this study presents strong evidence for BIX's potential toxicity to zebrafish liver and pancreas. The results may provide new insights into the evaluation of BIX'S impact on aquatic organisms.

Multiomics Analysis Revealed the Molecular Mechanism of miRNAs in Fluoride-Induced Hepatic Glucose and Lipid Metabolism Disorders

Fluoride-induced liver injury seriously endangers human and animal health and animal food safety, but the underlying mechanism remains unclear. This study aims to explore the mechanism of miRNAs in fluoride-induced hepatic glycolipid metabolism disorders. C57 male mice were used to establish the fluorosis model (22.62 mg/L F^-, 12 weeks). The results indicated that fluoride increased fluoride levels, impaired the structure and function, and disrupted the glycolipid metabolism in the liver. Furthermore, the sequencing results showed that fluoride exposure resulted in the differential expression of 35 miRNAs and 480 mRNAs, of which 23 miRNAs were related to glycolipid metabolism. miRNA-mRNA network analyses and RT-PCR revealed that miRNAs mediated fluoride-induced disturbances in the hepatic glycolipid metabolism. Its possible mechanism was to regulate the insulin pathway, PPAR pathway, and FOXO pathway, which in turn affected the bile secretion, the metabolic processes of glucose, the decomposition of lipids, and the synthesis of unsaturated fatty acids in the liver. This study provides a theoretical basis for miRNAs as diagnostic indicators and target drugs for the treatment of fluoride-induced liver injury.

Sex-specific effects of fluoride and lead on thyroid endocrine function in zebrafish (Danio rerio)

Fluoride (F) and lead (Pb) are widespread pollutants in the environment. F and Pb affect the thyroid endocrine system, but the mechanism of action between F and Pb is still unclear. In this study, in order to evaluate the effects of F or/and Pb on histopathological changes, antioxidant indices, the levels of thyroid hormones (THs), and the expression of endocrine-related genes in zebrafish thyroid. One thousand and two hundred zebrafish (female:male = 1:1) were randomly divided into four groups: control group (C group), 80 mg/L F group (F group), 60 mg/L Pb group (Pb group), and 80 mg/L F + 60 mg/L Pb group (F + Pb group) for 45 d and 90 d. Histopathological sections showed a loss of glia and follicular epithelial hyperplasia in the thyroid gland after exposure to F and Pb. Oxidative stress in the thyroid was induced after F and Pb exposure. And each oxidation index was increased after F + Pb exposure. Combined F and Pb exposure aggravated the downregulation of thyroid hormones T3 and T4 compared to exposure alone. Furthermore, F and Pb exposure altered the expression of thyroid endocrine-related genes in a time-dependent manner. These results indicate that F and Pb can affect the endocrine system of thyroid by changing the tissue structure, antioxidant capacity, thyroid hormone secretion and the levels of endocrine-related genes in thyroid. F and Pb can also produce toxic effects on thyroid, but the degree of poisoning is different in different indicators, mainly for the additive effect between them. Additionally, males are more sensitive than females to F or Pb toxicity. However, the specific molecular mechanism of the effects of F and Pb on thyroid endocrine system needs to be further studied.

Fluoride Intake Through Dental Care Products: A Systematic Review

Fluoride (F) is added to many dental care products as well as in drinking water to prevent dental decay. However, recent data associating exposure to F with some developmental defects with consequences in many organs raise concerns about its daily use for dental care. This systematic review aimed to evaluate the contribution of dental care products with regard to overall F intake through drinking water and diet with measurements of F excretion in urine used as a suitable biomarker. According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using keywords related to chronic exposure to F in the human population with measurements of F levels in body fluids, 1,273 papers published between 1995 and 2021 were screened, and 28 papers were finally included for data extraction concerning daily F intake. The contribution of dental care products, essentially by toothbrushing with kinds of toothpaste containing F, was 38% in the mean regardless of the F concentrations in drinking water. There was no correlation between F intake through toothpaste and age, nor with F levels in water ranging from 0.3 to 1.5 mg/L. There was no correlation between F intake and urinary F excretion levels despite an increase in its content in urine within hours following exposure to dental care products (toothpastes, varnishes, or other dental care products). The consequences of exposure to F on health are discussed in the recent context of its suspected toxicity reported in the literature. The conclusions of the review aim to provide objective messages to patients and dental professionals worried about the use of F-containing materials or products to prevent initial caries or hypomineralized enamel lesions, especially for young children.