Waterborne fluoride exposure changed the structure and the expressions of steroidogenic-related genes in gonads of adult zebrafish (Danio rerio)

Fluoride-induced testicular and ovarian toxicity: evidence from animal studies

Fluoride (F), as a natural element found in a wide range of sources such as water and certain foods, has been proven to be beneficial in preventing dental caries, but concerns have been raised regarding its potential deleterious effects on overall health. Sodium fluoride (NaF), another form of F, has the ability to accumulate in reproductive organs and interfere with hormonal regulation and oxidative stress pathways, contributing to reproductive toxicity. While the exact mechanisms of F-induced reproductive toxicity are not fully understood, this review aims to elucidate the mechanisms involved in testicular and ovarian injury. In males, F exposure at different doses has been associated with reduced testis weight, reduced sperm quality in terms of count, motility, and viability, as well as abnormal sperm morphology and disruption of seminiferous tubules by altering hormone levels (especially testosterone), impairing spermatogenesis, and inducing oxidative stress and zinc deficiency. Similarly, administration of F can impact female reproductive health by affecting ovarian function, hormone levels, oocyte quality, and the regularity of the estrous cycle. However, the impact of F exposure on LH, FSH, and GnRH levels is controversial between males and females. In both males and females, F exerts its adverse effects by triggering apoptosis, autophagy, inflammation, mitochondrial dysfunction, reduction in ATP synthesis, and modulation of important genes involved in steroidogenesis. Furthermore, genetic susceptibility and individual variations in F metabolism may contribute to different responses to fluoride exposure.

Embryonal exposure to 4-methylbenzylidene camphor induces reproduction impairment in adult zebrafish (Danio rerio)

This study investigated how early exposure to xenobiotics can lead to disease in adulthood, which is challenging for toxicologists. We employed a 'cradle to grave' approach using zebrafish (Danio rerio) embryos exposed to 4-methylbenzylidene camphor (4-MBC), a commonly used organic UV filter. Molecular docking and simulation studies confirmed the predictive toxicity and stable interaction of 4-MBC with androgen and estrogen receptors, with binding energies of -9.28 and -9.01 kcal/mol, respectively. Exposure to 4-MBC at 5, 50, and 500 μg/L concentrations resulted in significantly altered transcriptional and translational responses of ar, esr1, and vtg1 genes in embryos at 120 h post-fertilization (hpf). The exposure induced a non-monotonic dose-response pattern (NMDR), a characteristic feature of endocrine-disrupting chemicals. Additionally, a significant decrease in fertilization was observed in adults. Although fecundity was not affected in inter- and intra-breeding performances, developmental deformities were observed in F1 progenies with impaired survival at 10 days post-fertilization. The findings of this study show that embryonic exposure to 4-MBC is likely to induce reproductive and transgenerational toxicity in D. rerio and exhibit endocrine disruption in aquatic non-target organisms. This work is the first to elucidate the low-level long-term effects of 4-MBC from the embryonic stage to adulthood.

Gender-Specific Toxic Effects of S-Metolachlor and Its Metabolite on Hibernating Lizards: Implications for Reproductive Health and Ecosystem Vulnerability

Reptiles rely on hibernation to survive harsh winters, but climate change and pesticide use in agriculture jeopardize their survival, making the ecosystem vulnerable. S-metolachlor (SM), a commonly found herbicide in soil, and its metabolite metolachlor oxanilic acid (MO) induce oxidative stress and disrupt reproductive hormones. In this study, lizards were exposed to SM- and MO-contaminated soil for 45 days during hibernation. Weight loss and deaths occurred at the beginning of hibernation in all groups. Furthermore, the exposure group experienced severe oxidative stress and damage in the liver, kidney, heart, gonad, and brain. The testosterone levels significantly decreased in male lizards in both the SM and MO groups, whereas estradiol levels increased significantly in female lizards in the SM group. Gender-specific expression of steroidogenic-related genes in the brains and gonads of lizards was observed. Histological analysis revealed toxic effects induced by both SM and MO in vital organs during hibernation. Moreover, MO induced more severe reproductive toxicity in male lizards during hibernation. Therefore, this study suggests gender-specific toxic effects were observed in hibernating lizards exposed to SM and MO, underscoring the importance of vigilant monitoring of pesticide application in agriculture and assessing the potential harm of its metabolites.

Sodium Fluoride Exposure Induces Developmental Toxicity and Cardiotoxicity in Zebrafish Embryos

Fluorosis is a worldwide public health problem, in which the heart is an important target organ. However, studies on its toxicological mechanism in embryonic development are limited. This study assessed the toxicity of sodium fluoride (NaF) toward zebrafish embryos. We determined the mortality, hatching rate, phenotypic malformation, heart function, and morphology of zebrafish embryos after exposure to NaF. Subsequently, the molecular mechanism was revealed using high-throughput RNA sequencing analysis. The expression levels of key genes for heart development were detected using quantitative real-time reverse transcription PCR. The 50% lethal concentration (LC50) value of NaF toward zebrafish embryos at 96 h post-fertilization was 335.75 mg/L. When the concentration of NaF was higher than 200 mg/L, severe deformities, such as pericardial edema, yolk sac edema, spine curvature, shortened body length, reduced head area, and eye area, were observed. The heart rate of the embryos exposed to NaF decreased in a dose-dependent fashion. The distance between the sinus venosus and bulbus arteriosus was significantly increased in the NaF-exposed group compared with that in the control group. The stroke volume and cardiac output decreased significantly in the NaF groups. Compared with the control group, the expression levels of Gata4, Tbx5a, Hand2, Tnnt2c, Nppa, and Myh6 were significantly increased in the NaF-treated group. Through transcriptome sequencing, 1354 differentially expressed genes (DEGs) were detected in the NaF (200 mg/L) treated groups, including 1253 upregulated genes and 101 downregulated genes. Gene ontology functional analysis and Kyoto Encyclopedia of Genes and Genomes pathway analyses of the DEGs showed that cardiac-related pathways, such as actin cytoskeleton regulation, Jak-Stat, PI3k-Akt, and Ras, were activated in the NaF-exposed group. This study revealed the underlying mechanism of fluoride-induced cardiac morphological and functional abnormalities and provides clues for the clinical prevention and treatment of fluorosis.

Effects of whole life-cycle exposure to carbaryl on reproduction of female marine medaka (Oryzias melastigma) and their offspring

Carbaryl is widely used as a highly effective insecticide which harms the marine environment. This study aimed to assess the reproductive toxicity of chronic carbaryl exposure on female marine medaka and their female offspring. After a 180-day exposure from embryonic period to adulthood, females exhibited reduced attraction to males, decreased ovulation, increased gonadosomatic index and a higher proportion of mature and atretic follicles. These reproductive toxic effects of carbaryl may stem from changes in hormone levels and transcription levels of key genes along the HPG axis. Furthermore, maternal carbaryl exposure had detrimental effects on the offspring. F1 females showed the reproductive disorders similar to those observed in F0 females. The significant changes in the transcription levels of DNA methyltransferase and demethylase genes in the F0 and F1 generations of ovaries indicate changes in their DNA methylation levels. The changes in DNA methylation levels in F1 female marine medaka may lead to changes in the expression of certain reproductive key genes, such as an increase in the transcription level of cyp19a, which may be the reason for F1 reproductive toxicity. These findings indicate that maternal exposure may induce severe generational toxicity through alterations in DNA methylation levels. This study assesses the negative impacts of whole life-cycle carbaryl exposure on the reproductive and developmental processes of female marine medaka and its female offspring, while offering data to support the evaluation of the ecological risk posed by carbaryl in marine ecosystems.

Effects of water fluoridation on early embryonic development of zebrafish

Fluoride has strong electronegativity and exposes diversely in nature. Water fluoridation is the most pervasive form of occurrence, representing a significant threat to human health. In this study, we investigate the morphometric and physiological alterations triggered by fluoride stimulation during the embryogenesis of zebrafish and reveal its putative effects of stage- and/or dose-dependent. Fluoride exhibits potent biological activity and can be extensively absorbed by the yolk sac, exerting significant effects on the development of multiple organs. This is primarily manifested as restricted nutrient utilization and elevated levels of lipid peroxidation, further leading to the accumulation of superoxide in the yolk sac, liver, and intestines. Moreover, pericardial edema exerts pressure on the brain and eye development, resulting in spinal curvature and reduced body length. Besides, acute fluoride exposure with varying concentrations has led to diverse teratogenic outcomes. A low dose of water fluoridation tends to induce abnormal development of the embryonic yolk sac, while vascular malformation is widely observed in all fluoride-treated groups. The effect of fluoride exposure on blood circulation is universally present, even in zebrafish larvae that do not exhibit obvious deformities. Their swimming behavior is also affected by water fluoridation, resulting in reduced activity and delayed reactions. In conclusion, this study provides valuable insights into the monitoring of environmental quality related to water fluoridation and disease prevention.

Deriving seawater quality criteria of tris(2-chloroethyl) phosphate for ecological risk assessment in China seas through species sensitivity distributions

Tris(2-chloroethyl) phosphate (TCEP), one of the widely used organophosphorus flame retardants (OPFRs), has been frequently detected in the marine environment in the seas off China. The existing freshwater biotoxicity data are not suited to derivation of the seawater quality criteria of TCEP and evaluating the associated ecological risks. This study aimed at deriving water quality criteria (WQC) of TCEP for marine organisms based on species sensitivity distribution (SSD) approach using the acute toxicity data generated from multispecies bioassays and chronic toxicity data by converting acute data with the acute-to-chronic ratios (ACRs); the derived WQC were then used to evaluate the ecological risk for TCEP in China Seas. According to median effective concentration (EC50) and median lethal concentration (LC50), TCEP had a moderate or low toxicity to eight marine species selected, among which mysid Neomysis awatschensis (96h-LC50 of 39.65 mg/L) and green alga Platymonas subcordiformis (96-h EC50 of 395.42 mg/L) were the most sensitive and the most tolerant, respectively. The acute and chronic hazardous concentrations of TCEP for 5% of marine species (HC5) were estimated to be 29.55 and 2.68 mg/L, respectively. The short-term and long-term WQC were derived to be 9.85 and 0.89 mg/L, respectively. The risk quotient (RQ) values indicated that TECP at current levels poses a negligible risk to marine ecosystems in China. These results will provide valuable reference for the government to establish a seawater quality standard for TCEP.

A Short Review of the Toxicity of Dentifrices-Zebrafish Model as a Useful Tool in Ecotoxicological Studies

This review aims to summarize the literature data regarding the effects of different toothpaste compounds in the zebrafish model. Danio rerio provides an insight into the mechanisms of the ecotoxicity of chemicals as well as an assessment of their fate in the environment to determine long-term environmental impact. The regular use of adequate toothpaste with safe active ingredients possessing anti-bacterial, anti-inflammatory, anti-oxidant, and regenerative properties is one of the most effective strategies for oral healthcare. In addition to water, a typical toothpaste consists of a variety of components, among which three are of predominant importance, i.e., abrasive substances, fluoride, and detergents. These ingredients provide healthy teeth, but their environmental impact on living organisms are often not well-known. Each of them can influence a higher level of organization: subcellular, cellular, tissue, organ, individual, and population. Therefore, it is very important that the properties of a chemical are detected before it is released into the environment to minimize damage. An important part of a chemical risk assessment is the estimation of the ecotoxicity of a compound. The zebrafish model has unique advantages in environmental ecotoxicity research and has been used to study vertebrate developmental biology. Among others, the advantages of this model include its external, visually accessible development, which allows for providing many experimental manipulations. The zebrafish has a significant genetic similarity with other vertebrates. Nevertheless, translating findings from zebrafish studies to human risk assessment requires careful consideration of these differences.

Chronic diflubenzuron exposure causes reproductive toxic effects in female marine medaka (Oryzias melastigma)

Diflubenzuron, an insecticide commonly used in marine fish farming, has been detected in various marine environments. However, its potential impact on marine fish remains largely unknown. This study investigated the reproductive toxicity of chronic diflubenzuron exposure in female marine medaka (Oryzias melastigma). Marine medaka were exposed continuously to environmentally relevant concentrations of diflubenzuron (0.1, 1, and 10 μg/L) or a solvent control from the fertilized egg to adulthood. In exposed female marine medaka, the gonadosomatic index (GSI) and the number of laid eggs were significantly reduced. Moreover, diflubenzuron-exposed female marine medaka showed altered ovarian histopathology, with an increased relative proportion of immature oocytes and atretic follicles and a decreased relative proportion of mature oocytes. Maternal exposure to diflubenzuron also inhibited the development of the F1 generation, significantly reducing the hatching rate of F1 embryos and significantly increasing the malformation rate of F1 larvae. Furthermore, changes in hormone levels and expression of genes along the hypothalamus-pituitary-gonad-liver (HPGL) axis were observed, which may be the fundamental reason for all the reproductive toxic effects mentioned above. These results provide new insights into the impact of diflubenzuron on the female marine medaka reproductive system and underscore the importance of investigating the potential environmental risks of diflubenzuron in the marine environment.

Exposure to Fluoride From in Utero to Puberty Alters Gonadal Structure and Steroid Hormone Expression in Offspring Rats

The reproductive toxicity of fluoride has been proven by a large number of studies. While the underlying mechanism of reproductive toxicity during pregnancy is still unclear. Hence, in this study, we investigated the effects of fluoride exposure on ovarian and testicular steroid hormone synthesis in young and adult rat offspring. We established a model of fluoride-exposed rat pups from in utero to puberty to explore the mechanisms of fluoride impacts on reproductive toxicity in the offspring. The results showed that NaF exposure did not affect the 3 weeks of age offspring. Whereas the body weight in both sexes significantly decreased, and the ovarian and testicular tissue structures were damaged at 11 weeks of age. In females, the total number of secondary follicles and mature follicles were significantly reduced after NaF exposure. Moreover, estradiol (E2) and follicle-stimulating hormone (FSH) levels in the females were significantly reduced in the 100 mg/L NaF exposure group. In males, the sperm viability and testosterone (T) were significantly decreased in the NaF exposure groups. Additionally, during steroidogenesis in ovaries and testes, fluoride remarkably decreased the expression levels of genes and proteins, including acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17a-hydroxylase (CYP17A1), and cholesterol side-chain cleavage enzyme (CYP11A1), while the mRNA levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) decreased only in the testes. These results indicated that fluoride exposure disrupted the steroid hormone balance by changing several important steroidogenic-related genes associated with the development of the gonads, and damage the normal structure of the gonads in rat offspring.

Alleviating effects of selenium on fluoride-induced testosterone synthesis disorder and reproduction toxicity in rats

Fluoride (F) exists widely in food, water and other natural resources, and can cause damage to the reproductive system of human and animals. Studies have shown that selenium (Se) is a necessary trace element to maintain the normal male reproductive system. However, it is not clear whether it can alleviate the damage of reproductive system induced by F. Hence, sodium fluoride (NaF) was administered singly in drinking water at 100 mg L^-1 alone and co-administered by drinking with sodium selenite (Na₂SeO₃) at 0.5, 1.0, 2.0 mg L^-1 for 10 consecutive weeks. The results demonstrated that the sperm deformity rate were increased significantly by F, however, it was improved significantly after the addition of 2.0 mg L^-1 Na₂SeO₃. The contents of glutathione peroxidase 4 (GPX-4), selenoprotein P (SePP), pregnenolone (PREG), androstenedione (ASD), and testosterone (T) were reduced obviously in the F group, however, it was increased significantly after adding 0.5, 1.0 and 2.0 mg L^-1 Na₂SeO₃. F decreased noticeably the mRNA and protein expression levels of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side chain lyase (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase (P450c17) and 17β-hydroxysteroid dehydrogenase (17β-HSD), which was increased obviously after the addition of 1.0 and 2.0 mg L^-1 Na₂SeO₃. In summary, 2.0 mg L^-1 Na₂SeO₃ can alleviate testosterone synthesis disorder induced by F via reducing oxidative stress, increasing the level of selenoprotein in testis and regulating the content of related hormones and enzyme activity during testosterone synthesis pathway.

Interactive effects of fluoride and seleno-l-methionine at environmental related concentrations on zebrafish (Danio rerio) liver via the gut-liver axis

Fluoride (F) is a ubiquitous aquatic environmental pollutant and co-exists with other pollutants to form combined pollution. Selenium (Se) is beneficial at low levels yet toxic at high levels and can interact with some metals. However, the interactive effects of F and Se on the liver in fish remains enigmatic. In this study, zebrafish (Danio rerio) were exposed to F (80 mg/L) and dietary seleno-l-methionine (Se-Met, 0.25, 0.5 and 1.0 μg/g dry weight) alone or in combination for 90 d. The results indicated that co-treatment to F and Se-Met attenuated the histopathological damage, oxidative stress, and inflammatory in the liver, compared with the F treatment alone. Meanwhile, dietary Se-Met treatment improved F-induced intestinal barrier dysfunction, increased the transcripts of tight junction proteins (ZO-1, Claudin-1 and Occludin), and restored the homeostasis of intestinal microbiota. Moreover, dietary Se-Met ameliorated F-induced intestinal and liver inflammation by inhibiting lipopolysaccharide (LPS) levels and transcripts of TLR4 and p65 in the intestine and liver. This study manifested that Se-Met alleviates F-induced liver and intestinal injury when both co-occur at specific concentrations, and that the gut-liver axis pathway may serve as a mechanistic base for these alleviative effects.

Long term exposure to tris (2-chloroethyl) phosphate (TCEP) causes alterations in reproductive hormones, vitellogenin, antioxidant enzymes, and histology of gonads in zebrafish (Danio rerio): In vivo and computational analysis

In aquatic milieus, tris (2-chloroethyl) phosphate (TCEP) was detected as an emerging environmental contaminant. In this study, in vivo experiment and in-silico docking was integrated systematically to explore the toxic mechanisms of TCEP using zebrafish (Danio rerio). Fish (mean weight of 0.24 ± 0.02 g) were exposed to 100 and 1500 μg L^-1 concentrations of TCEP for 28 days under the static renewal method. During chronic exposure, plasma steroid hormones such as testosterone (T) and 17β estradiol (E2), plasma vitellogenin (Vtg) and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and lipid peroxidation (LPO) in gonads were significantly (P < 0.05) altered in TCEP exposed group (1500 μg L^-1) compared to the control group. However, the alterations of these parameters were not significant on the 14th day (except Vtg and GR in testis) in 100 μg L^-1 of TCEP exposed groups. There were no significant differences (p > 0.05) in the growth parameters comparing TCEP exposed groups with the control group. The gonads of fish exposed to TCEP showed significant histopathological changes when compared to the control groups. A docking study observed that TCEP possessed binding affinity with the estrogen receptor (ERβ) and androgen receptor (AR). These data indicate that TCEP at tested concentrations adversely affects the aquatic organisms.

Fluoride exposure changed the expression of microRNAs in gills of male zebrafish (Danio rerio)

Fluoride has been found to cause detrimental effects on fish gills. Despite essential roles in various metabolism activities, whether and how miRNAs participate in the course of toxicity caused by fluoride in gills is still unclear. In this study, male zebrafish were exposed to 0, 20, 40 mg/L fluoride for 60 days to study the underlying osmotic regulatory mechanism by determining the influences of fluoride on the miRNAs and regulated genes in gills. mRNAs were isolated from the gills and the expression profiles were analyzed by using Illumina Hiseq 2500 platforms. Expressions of 7 differentially miRNAs and some related-genes in gills were validated by qRT-PCR. The results showed that miRNAs expressions were notably altered by fluoride. A total of 584 and 327 miRNAs were remarkably changed after 20 and 40 mg/L fluoride exposure, of which 322 were increased and 262 were decreased in 20 mg/L fluoride group, whereas 219 were elevated and 108 were reduced in 40 mg/L fluoride group. The differentially expressive miRNAs confirmed by qRT-PCR were consistent with micro-assay data. Cluster of Orthologous Groups of proteins (COG) function classification showed that the target genes of differentially expressive miRNAs are mainly related to signal transduction mechanisms, replication, transcription, inorganic ion transport and metabolism, repair and recombination, and energy formation and transformation. In addition, fluoride disturbed the expressions of target genes involved in the osmoregulation of the gill in the fluoride-exposed zebrafish, such as the increased expressions of OSTF1 and the decreased expressions of Na⁺-K⁺-ATPase, CFTR, and AQP-3, which provides a possibility that miRNAs regulation induced by fluoride has an effects on osmotic regulation, providing new hints to the osmotic regulatory mechanism of the toxicity caused by fluoride in zebrafish, and distinguishes new biomarkers of miRNAs for fluoride toxicity.

Fluoride impairs ovary development by affecting oogenesis and inducing oxidative stress and apoptosis in female zebrafish (Danio rerio)

Previous studies have shown that waterborne fluoride exposure has adverse effects on the reproductive system of zebrafish. However, the underlying toxic mechanisms were still not clear. In the present study, female zebrafish were exposed to different concentrations of 0.787 (Control), 18.599, 36.832 mg/L of fluoride for 30 d and 60 d, and the effects of different doses of fluoride on ovary development, reproductive hormones, oogenesis, ROS content, antioxidant levels, and the expression of apoptosis-related genes and proteins in the ovaries of female zebrafish were analyzed. The results showed that ovarian weight and GSI were significantly decreased, FSH, LH and VTG levels were significantly reduced, the transcriptional profiles of oogenesis-related genes (tgfβ1, bmp15, gdf9, mprα, mprβ, ptg2β) were remarkably altered, ROS levels was notably increased, the SOD, CAT, GPx activities and GSH content as well as their mRNA expressions were significantly decreased, MDA content was remarkably increased, the expressions of apoptosis-related genes and proteins (caspase3, caspase8, caspase9, Fas-L, Cytochrome C, Bax and Bcl-2) were significantly changed, the ratio of Bax/Bcl-2 protein levels were notably increased. Taken together, this study demonstrated that fluoride exposure significantly affected ovarian development, decreased the reproductive hormones, affected oogenesis, induced oxidative stress, caused apoptosis through both extrinsic and intrinsic pathways in ovary of zebrafish. Indicating that oogenesis, oxidative stress, and apoptosis were responsible for the impairment of ovarian development.

Reproductive toxicity and estrogen activity in Japanese medaka (Oryzias latipes) exposed to environmentally relevant concentrations of octocrylene

The growing use of octocrylene (OC) in sunscreens has posed a great threat to aquatic organisms. In the present study, to assess its reproductive toxicity and mechanism, paired Japanese medaka (Oryzias latipes) (F0) were exposed to OC at nominal concentrations of 5, 50, and 500 μg/L for 28 d. Significant increases were observed in the gonadosomatic index (GSI) and hepatosomatic index (HSI) of F0 medaka at 500 μg/L OC (p < 0.05) without significant differences in fecundity. The fertility was significantly decreased at all treatments (p < 0.05). Significant increases in the percent of mature oocytes were observed at 5 and 500 μg/L OC, in which contrary to the percent of spermatozoa (p < 0.05). The plasma sex hormones and vitellogenin levels significantly increased in males at all treatments and in females at 50 and 500 μg/L OC (p < 0.05). In addition, the levels of fshβ and lhβ in the brains and the levels of fshr, lhr and cyp17α in the gonads were significantly upregulated in males at all treatments (p < 0.05), in line with those of ar, erα, erβ and cyp19β in the brains of male and female. The upregulation of vtg in male and female livers was observed only at 500 μg/L OC and upregulation of star and hsd3β was observed in testis at all treatments (p < 0.05). Continued exposure to OC significantly induced increases in the time to hatching, morphological abnormality rates, and cumulative death rates of F1 embryos, inconsistent with body length of F1 larvae (p < 0.05). Therefore, the responses of the exposed fish at the biochemical and molecular levels indicated reproductive toxicity and estrogenic activity of OC, providing insights into the mechanism of OC.

Associations of fluoride exposure with sex steroid hormones among U.S. children and adolescents, NHANES 2013-2016

Fluoride mediated disruption of sex steroid hormones has been demonstrated in animals. However, evidence from humans was limited and contradictory, especially for children and adolescents. Based on data of the National Health and Nutrition Survey (NHANES) 2013-2016, a total of 3392 subjects aged 6-19 years were analyzed in this cross-sectional study. Both plasma and water fluoride levels were quantified electrometrically using the ion-specific electrode. Sex steroid hormones of total testosterone, estradiol and sex hormone-binding globulin (SHBG) were tested in serum. Percent changes and 95% confidence intervals (CIs) in sex steroid hormones associated with tertiles of fluoride levels (setting the first as reference) were estimated using adjusted linear regression models by stratification of gender and age. Compared with subjects at the first tertile of plasma fluoride, percent changes (95% CIs) in testosterone were -8.08% (-17.36%, 2.25%) and -21.65% (-30.44%, -11.75%) for the second and third tertiles, respectively (P _trend <0.001). Male adolescents at the third tertile of plasma fluoride had decreased levels of testosterone (percent change = -21.09%, 95% CIs = -36.61% to -1.77%). Similar inverse associations were also found when investigating the relationships between plasma fluoride and estradiol. Besides, the data indicated decreased levels of SHBG associated with water and plasma fluoride among the male adolescents (percent change of the third tertile = -9.39%, 95% CIs = -17.25% to -0.78%) and female children (percent change of the second tertile = -10.78%, 95% CIs = -17.55% to -3.45%), respectively. The data indicated gender- and age-specific inverse associations of fluoride in plasma and water with sex steroid hormones of total testosterone, estradiol and SHBG in U.S. children and adolescents. Prospective cohort studies are warranted to confirm the causality.

Gonadal disruption after single dose exposure of prothioconazole and prothioconazole-desthio in male lizards (Eremias argus)

Prothioconazole (PTC) is a widely used triazole fungicide with low toxicity, and its desulfurization metabolite, prothioconazole-desthio (PTC-d), is reported to have higher reproductive toxicity to mammals. However, little is known about the reproductive toxicity, much less endocrine disrupting effect, of these two chemicals on reptiles. In this study, we investigated the effects of single dose of PTC/PTC-d (100 mg kg^-1 body weight) exposure on the pathomorphism of testes and epididymides, serum sex steroid hormones (testosterone and 17β-estradiol) and transcription of steroidogenic-related genes (STARD, cyp11A, cyp17, cyp19A, 17β-HSD, 3β-HSD, AR and ER-α) in gonads of male lizards (Eremias argus). Although structural disorder existed in PTC-d exposure group, severe gonadal disruption, especially suppression of spermatogenesis was only observed in testis after PTC treatment, which consequently led to the lack of spermatozoa in epididymal ducts. Consistent with this result, T/E₂ value in PTC exposure was elevated to a significant higher level compared with control and continually increased over time, while T/E₂ value in the PTC-d exposure group slightly increased only at 12 h. These results demonstrated a more serious disruption of PTC on male lizard gonads than PTC-d. In addition, the expression of cyp17 gene was inhibited at 6 h, however, was induced at 12 h, and exhibited negative correlations with STARD, cyp11A and 3β-HSD after PTC exposure at each timepoint. In PTC-d group, the expression of STARD and 3β-HSD were significantly down-regulated, in contrast, cyp11A and cyp17 were up-regulated, and each gene showed consistent changes over time. For 17β-HSD, no significance was observed in both treated groups. This study was the first to compare the gonadal disruption of PTC and PTC-d in male lizards and elucidated that these two chemicals influenced the physiological function of male gonads through differential transcriptional modulation.

Bioaccumulation and biochemical effects of ethylhexyl methoxy cinnamate and its main transformation products in zebrafish

The purpose of this study was to investigate the bioaccumulation and biochemical responses exposed to one of the main organic ultraviolet (UV) pollutants in the environment, ethylhexyl methoxy cinnamate (EHMC), and its main transformation product, either alone or in combination in zebrafish (Danio rerio). Four-month-old zebrafish were exposed to EHMC (34.4, 344 nmol/L) solution for 14 days, the species and contents of EHMC transformation products in zebrafish were determined and 3,5-dichloro-2-hydroxyacetophenone (3,5DCl₂HAcP) was the one with the highest concentration in transformation products. Then, zebrafish were exposed to EHMC, 3,5DCl₂HAcP alone and mixed solution for 21 days. At 7, 14 and 21 d, the related indexes of antioxidant defense system were determined. Results showed that both EHMC and 3,5DCl₂HAcP can lead to the increase of malondialdehyde (MDA) and glutathione (GSH) contents, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) activities in visceral mass compared with the corresponding control group, thus produced oxidative stress effect in organism and 3,5DCl₂HAcP even showed stronger oxidative stress than EHMC. The effects of the two lower concentration co-exposure groups were similar and more significant to that of single exposure groups, while excessive oxidative stress occurred at the highest co-exposure group indicated by the decrease of GSH content, SOD, CAT, GR activities and the continued increase of MDA content. At 21 d, estradiol (E₂), vitellogenin (Vtg) and testosterone (T) contents, estrogen receptor (Esr), progesterone receptor (Pgr), androgen receptor (Ar), Vtg1, P450 aromatase (Cyp19a1) and 17β-hydroxysteroid dehydrogenase (Hsd17b3) expression were all significantly increased when exposed to 3,5DCl₂HAcP alone, showing complex estrogen and androgen effects. When exposed to EHMC alone, E₂ and Vtg contents, Esr, Pgr, Vtg1, Cyp19a1 and Hsd17b1 gene expression levels decreased significantly, and T content and Ar and Hsd17b3 expression increased significantly, indicated that EHMC can produce anti-estrogen and androgen effect. Last, the decrease of estrogen effect and increase of androgen effect in co-exposure group suggested that 3,5DCl₂HAcP might weaken the estrogen effect and promote the androgen effect of EHMC.

Recovery of reproductive function of female zebrafish from the toxic effects of microcystin-LR exposure

Fish has a strong resistance to microcystins (MCs), cyclic heptapeptide cyanotoxins, known as endocrine disrupting chemicals (EDCs) which are released during cyanobacterial blooms and many laboratory and field studies have found the hepatic recovery of fish from the MCs exposure. The aim of the present study was to investigate the recovery mechanisms of reproductive function of adult zebrafish (Danio rerio) from microcystin-LR (MC-LR) exposure. Therefore, adult female zebrafish were exposed to 0, 1 or 50 μg/L of MC-LR for 21days and transferred to MC free water for another 21 days to investigate the recovery. After MC-LR exposure, marked histological lesions in the gonads, decreased the percentage of mature oocytes, decreased number of spawned eggs, decreased fertilization and hatching rates were observed. MC-LR exposure increased the concentration of 17β-estradiol (E2), testosterone (T) and vitellogenin (VTG) in female zebrafish. Some gene transcriptions of the hypothalamic-pituitary-gonad (HPG) axis significantly changed. The protein levels of 17βhsd and cyp19a remarkably increased in the MC-LR exposure groups. However, our laboratory observation also indicates that zebrafish transferred from microcystin exposure to toxin-free water and reared for 21 days exhibited a nearly complete recovery of reproductive functions, including histological structure, increased the percentage of matured oocytes and spawned eggs, stable hormone levels, well-balanced transcriptional and translational levels. These results indicate that after MC-LR exposure, the reproductive impairments in zebrafish are also reversible likewise hepatic recovery seen by different studies in fish. Future studies should be conducted to explore a better understanding of the recovery mechanisms of fish from microcystins exposure.

The PFOS disturbed immunomodulatory functions via nuclear Factor-κB signaling in liver of zebrafish (Danio rerio)

Excessive perfluorooctane sulfonate (PFOS) in natural water ecosystem has the potential to detrimentally affect immune system, but little is known of such effects or underlying mechanisms in fish. In the present study, we evaluated the effects of PFOS on growth performance, organizational microstructure, activities of immune-related enzymes and expressions of immune-related genes in male zebrafish (Danio rerio) exposed to different concentrations of 0, 0.02, 0.04 and 0.08 mg/L of PFOS for 7, 14, and 21 days or cotreatment with PFOS and PDTC to investigate the effects of PFOS on immune system and the potential toxic mechanisms caused by PFOS. The results indicated that PFOS accumulated in livers after exposure, and remarkably elevations were found in three exposure groups compared with the control group at three stages. The growth of the adult zebrafish in the experiments was significantly inhibited, the microstructures of liver were serious damaged. The ROS levels were remarkably increased. The activities of ACP, AKP, and lysozyme were obviously decreased, while the activities of MPO and NF-κB were significantly increased. The expressions of immune-related mRNA were significantly affected. After co-treatment with PFOS and PDTC, the growth inhibition, the morphological damage, the ROS induction, and the expressions of immune-related mRNA were reversed. Taken together, the results indicated that PFOS can significantly inhibit the growth, disturb the immune system by changing the normal structure of liver, the activities of immune-related enzymes, and a series of gene transcriptions involved in immune regulation in liver of male zebrafish. PFOS-induced pro-inflammatory effect of hepatocytes was observed, and the involvement of NF-κB signaling pathway was participated in its action mechanism. These findings provide further evidence that PFOS interferes with the immune regulation of liver of male zebrafish under in vivo conditions.

Accumulation and toxicity of thiamethoxam and its metabolite clothianidin to the gonads of Eremias argus

The endocrine disrupting effect of pesticides is considered to be an important factor in the decline of reptile populations. The large-scale application of neonicotinoids in the environment poses a potential threat to small farmland lizards Eremias argus. In this study, we evaluated the disruption effects of thiamethoxam and its metabolite clothianidin on the endocrine disruption of Eremias argus during 28 d exposure. Thiamethoxam and clothianidin could accumulate in the testis and ovary. Adequate blood exchange was the main cause of thiamethoxam and clothianidin accumulation in the gonads. The production of clothianidin aggravated the effect of endocrine disruption to lizards. Thiamethoxam/clothianidin exhibited two distinct ways of interfering with the endocrine disruption of the male and female lizards. Thiamethoxam/clothianidin significantly up-regulated the expression of cyp17 and cyp19 genes in the testis, which ultimately led to a significant decrease in testosterone levels and a significant increase in the 17-estradiol concentrations in plasma. The expression of the estrogen receptor gene in the liver was also significantly increased in male lizards. The significant declines in testosterone and prostaglandin D2 levels in the plasma indicated that thiamethoxam and clothianidin could cause androgen deficiency in male lizards. Meanwhile, in female lizards, thiamethoxam/clothianidin increased the expression of hsd17β gene in the ovary, causing an increase in testosterone levels in the plasma and an up-regulation of androgen receptor expression in the liver. The effects of thiamethoxam and clothianidin on male lizards were more pronounced. This study verified the possible endocrine disrupting effects of neonicotinoids and provided a new perspective for the study of global recession of reptiles.

Copper caused reproductive endocrine disruption in zebrafish (Danio rerio)

Cu in surface waters has been demonstrated to affect aquatic animals at ecologically relevant concentrations. However, its effects on reproductive endocrine system and the underlying toxicological mechanisms are largely unknown. In this study, zebrafish (Danio rerio) were exposed to 0, 10, 20, 40 μg/L of Cu for 30 days. Growth, gonad histopathology, the hormone levels and the transcriptional profiles of genes in the hypothalamic-pituitary-gonadal (HPG) axis in both sexes were examined. The results indicated that body weight was significantly reduced, the gonadal development was affected, and the levels of E₂, T and 11-KT were remarkably disturbed in Cu-exposed fish. Moreover, the expression profiles of steroidogenesis-related genes in gonad (3βhsd, 17βhsd, cyp11a1, cyp17, cyp19a, lhr, fshr, hmgra and star) and in brains (ar, cyp19b, erα, er2β, lhβ, fshβ, gnrh2, gnrh3, gnrhr1, gnrh2 and gnrh4) displayed alterations after exposure to Cu. These results demonstrated that Cu could suppress the growth of zebrafish and significantly affect the reproductive biology in both sexes by damaging the structure of the gonads, altering the steroid hormone levels and the expressions of endocrine-related genes in HPG of zebrafish. This study suggests that Cu adversely affects the reproductive endocrine system in zebrafish and could pose a potential threat to fish populations inhabiting Cu-contaminated waters.

Comparative Transcriptomics Reveals the Role of the Toll-Like Receptor Signaling Pathway in Fluoride-Induced Cardiotoxicity

Many studies have shown that fluorosis due to long-term fluoride intake has damaging effects on the heart. However, the mechanisms underlying cardiac fluorosis have not been illuminated in detail. We performed high-throughput transcriptome sequencing (RNA-Seq) on rat cardiac tissue to explore the molecular effects of NaF exposure. In total, 372 and 254 differentially expressed genes (DEGs) were identified between a group given 30 mg/L NaF and control and between a group given 90 mg/L NaF and control, respectively. The transcript levels of most of these genes were significantly down-regulated and many were distributed in the Toll-like receptor signaling pathway. Transcriptome analysis revealed that herpes simplex infection, ECM-receptor interaction, influenza A, cytokine-cytokine receptor interaction, apoptosis, and Toll-like receptor signaling pathway were significantly affected. IL-6 and IL-10 may play a crucial role in the cardiac damage caused by NaF as external stimuli according to protein-protein interaction (PPI) network analysis. The results of qRT-PCR and Western blotting showed a marked decreased mRNA and protein levels of IL-1, IL-6, and IL-10 in the low concentration fluoride (LF) and high concentration fluoride (HF) groups, which was in agreement with RNA-Seq results. This is the first study to investigate NaF-induced cardiotoxicity at a transcriptome level.

Parental transfer of ethylhexyl methoxy cinnamate and induced biochemical responses in zebrafish

Ethylhexyl methoxy cinnamate (EHMC) is one of the major organic ultraviolet (UV) filter pollutants in the environment. The purpose of this study was to investigate the parental transfer of EHMC and induced biochemical responses in zebrafish (Danio rerio). Zebrafish embryos were exposed to EHMC solution (1, 10, and 100 μg/L) for 4 months until sexual maturation. Then male and female parents were paired to lay eggs. F1 generations were divided into 2 categories: with and without continued EHMC exposure. EHMC was detected in both F0 parents and F1 eggs, indicating that EHMC can accumulate in zebrafish and transfer to offspring through reproduction. The hatching rate decreased and malformation rate increased significantly among parents and progeny embryos in the high concentration exposure group. For 40 dpf (days post-fertilisation) F0 generations, estradiol hormone and vitellogenin (Vtg) contents, the expression levels of Vtg1, P450 aromatase (Cyp19a and Cyp19b), 17β-hydroxysteroid dehydrogenase (Hsd17b1, Hsd17b3), estrogen receptor-alpha and progesterone receptor in all concentration groups decreased significantly, while androgen receptor increased significantly in 10 and 100 μg/L exposure groups compared with the corresponding control group, showing anti-estrogen and androgen effects. For 120 dpf F0 generations, acetylcholinesterase activity was significantly decreased and glutathione and malondialdehyde levels, superoxide dismutase, catalase and glutathione reductase activities were significantly increased in all treatment groups compared with the corresponding control group. In addition, F1 offspring with or without continued exposure to EHMC suffered similar or stronger oxidative stress compared with their parents. DNA breakage and apoptosis also occurred in 120 dpf parental liver cells in all treatment groups as a result of oxidative damage. Results suggested that EHMC have transfer effects between parents and offspring, which may cause negative effects on growth and development of zebrafish and induce biochemical responses in both parents and offspring.

Effects of sodium fluoride on the reproductive development of Bombyx mori

Bombyx mori was used as a model to evaluate the reproductive toxicity of NaF in insects. Significant reduction in cocoon quality, survival rate, fecundity, and hatchability were observed upon NaF treatment groups. Fluoride determination indicated that F^- has a cumulative effect on the gonad of silkworm. High-performance liquid chromatography revealed that the testosterone content of males was decreased in NaF-treated groups, and enzyme-linked immunosorbent assay showed that the estradiol content was decreased in NaF-treated females. Ultrastructural observation of testicles of silkworm larvae revealed mitochondrial turgescence, endoplasmic reticulum destruction, the appearance of vacuoles and lysosomes, and apoptosis and necrosis of cells in NaF-treated groups. Altered tail length and tail DNA content in Comet assays further confirmed DNA damage in NaF-treated larvae. We demonstrated reproductive toxicity of fluoride toward silkworm at physiological and biochemical levels, and the results provide a theoretical basis for revealing the reproductive toxicity of fluoride in terrestrial insects.

Mycotoxin zearalenone induced gonadal impairment and altered gene expression in the hypothalamic-pituitary-gonadal axis of adult female zebrafish (Danio rerio)

In the present study, we aimed to assess the adverse effects of zearalenone (ZEA) at environmentally relevant concentrations (0.5, 1, 5 and 10 μg l^-1 ) on hypothalamic-pituitary-gonadal axis associated reproductive function using zebrafish model. ZEA was exposed to female zebrafish for 21 days to assess growth indices such as condition factor, hepatosomatic index, gonadosomatic index and caspase 3 activity. Further, expression of estrogen receptor (ER) α and CYP19a1b genes in the brain, ERα and vitellogenin (Vtg) genes in the liver and follicle-stimulating hormone receptor, luteinizing hormone receptor, ERα, steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase (HSD), 17-βHSD and CYP19a1 genes in the ovary were also investigated. Our results showed that there were no significant changes in the condition factor and hepatosomatic index, whereas a significant (P < .05) reduction in the gonadosomatic index, increase in caspase 3 activities and Vtg expression was observed at higher concentration. However, no significant changes were observed at lower treatment levels. Further, we also observed significant (P < .05) upregulation in ERα, Vtg, luteinizing hormone receptor, steroidogenic acute regulatory protein, 3β-HSD, 17β-HSD, CYP19a1 and CYP19a1b genes in treatment groups with higher levels of ZEA. Moreover, in histopathological examination, we observed oocyte atresia and oocyte membrane detachment in ovaries at the highest concentration. In conclusion, the present study revealed the negative impact of ZEA on zebrafish reproductive system by involvement of the hypothalamic-pituitary-gonadal axis-associated reproductive function.

Fluoride-Induced Autophagy via the Regulation of Phosphorylation of Mammalian Targets of Rapamycin in Mice Leydig Cells

Fluoride is known to impair testicular function and decrease testosterone levels, yet the underlying mechanisms remain inconclusive. The objective of this study is to investigate the roles of autophagy in fluoride-induced male reproductive toxicity using both in vivo and in vitro Leydig cell models. Using transmission electron microscopy and monodansylcadaverine staining, we observed increasing numbers of autophagosomes in testicular tissue, especially in Leydig cells of fluoride-exposed mice. Further study revealed that fluoride increased the levels of mRNA and protein expression of autophagy markers LC3, Beclin1, and Atg 5 in primary Leydig cells. Furthermore, fluoride inhibited the phosphorylation of mammalian targets of rapamycin and 4EBP1, which in turn resulted in a decrease in the levels of AKT and PI3K mRNA expression, as well as an elevation of the level of AMPK expression in both testes and primary Leydig cells. Additionally, fluoride exposure significantly changed the mRNA expression of the PDK1, TSC, and Atg13 regulator genes in primary Leydig cells but not in testicular cells. Taken together, our findings highlight the roles of autophagy in fluoride-induced testicular and Leydig cell damage and contribute to the elucidation of the underlying mechanisms of fluoride-induced male reproductive toxicity.

Fluoride induces apoptosis in H9c2 cardiomyocytes via the mitochondrial pathway

Numerous studies have shown that chronic excessive fluoride intake can adversely affect different organ systems. In particular, the cardiovascular system is susceptible to disruption by a high concentration of fluoride. The objectives of this study were to explore the mechanism of apoptosis by detecting the toxic effects of different concentrations of sodium fluoride (NaF) in H9c2 cells exposed for up to 96 h. NaF not only inhibited H9c2 cell proliferation but also induced apoptosis and morphological damage. With increasing NaF concentrations, early apoptosis of H9c2 cells was increased while the mitochondrial membrane potential was decreased. Compared with the control group, the mRNA levels of caspase-3, caspase-9, and cytochrome c all increased with increasing concentrations of NaF. In summary, these data suggest that apoptosis is involved in NaF-induced H9c2 cell toxicity and that activation of the mitochondrial pathway may occur.

Disruption of sex-hormone levels and steroidogenic-related gene expression on Mongolia Racerunner (Eremias argus) after exposure to triadimefon and its enantiomers

Triadimefon (TF) is a widely used chiral fungicide with one chiral centre and two enantiomers (TF₁ and TF₂). However, little is reported about the ecological toxicity of reptiles on an enantioselective level. TF is a potential endocrine disruptor that may interfere with sex steroid hormones, such as testosterone (T) and 17beta-estradiol (E₂). In our study, the lizards Mongolia Racerunner (Eremias argus) were orally exposed to TF and its enantiomers for 21 days. Plasma sex steroid hormones and steroidogenic-related genes, including 17-beta-hydroxysteroid (hsd17β), cytochrome P450 enzymes (cyp19 and cyp17), and steroid hormone receptors (erα and Ar) were evaluated. After exposure, the plasma testosterone level in the 100 mg/kg^bw group was elevated, while the oestradiol level was reduced. This phenomenon may be caused by the transformation of cyp19, which may inhibit the conversion of testosterone to oestradiol and affect sexual behaviour. In addition, the two enantiomers have different effects on hormone levels, which testified to the previously reported biotoxic dissimilarity between TF₁ and TF₂ in organisms. Furthermore, the cyp19 mRNA level in liver and gonad of the TF₂ and TF group (100 mg/kg^bw) were significantly down-regulated, while the cyp17 and hsd17β mRNA levels were up-regulated. The expression of erα and Ar mRNA levels were up-regulated in males but not in females, which may indicate that TF has sex differences on these two genes. As seen from the above results, TF and its enantiomers may have endocrine-disrupting effects on lizards (E. argus) by acting sensitively on sex steroid hormones and steroidogenic-related genes.

Fluoride exposure changed the structure and the expressions of Y chromosome related genes in testes of mice

It is known that during spermatogenesis, pluripotent germ cells differentiate to become efficient delivery vehicles to the oocyte of paternal DNA, and the process is easily damaged by external poison. In this study, the effects of fluoride on the body weight, fluoride content in femur, testosterone levels in serum and testis, sperm quality, and the expressions of Y chromosome microdeletion genes and protein levels were examined in testes of Kunming male mice treated with different concentrations of 0, 25, 50, 100 mg/L of NaF in drinking water for 11 weeks, respectively. The results showed that compared with the control group, fluoride contents in three treatment groups were significantly increased and the structure of testes was seriously injured. The testosterone contents and the sperm count were decreased. Sperm malformation ratio was distinctly elevated. The expressions of Sly and HSF2 mRNA were markedly reduced in 100 mg/L NaF group and Ssty2 mRNA expression was dramatically decreased in 50 and 100 mg/L NaF groups. Meanwhile, the protein levels of Ssty2 and Sly were significantly reduced in 50 and 100 mg/L NaF groups and HSF2 protein levels were significantly decreased in 100 mg/L NaF group. These studies indicated that fluoride had toxic effects on male reproductive system by reducing the testosterone and sperm count, and increasing the sperm malformation ratio, supported by the damage of testicular structure, as a consequence of depressed HSF2 level, which resulted in the down-regulation of Ssty2 and Sly mRNA and protein.

Chronic fluoride exposure-induced testicular toxicity is associated with inflammatory response in mice

Previous studies have indicated that fluoride (F) can affect testicular toxicity in humans and rodents. However, the mechanism underlying F-induced testicular toxicity is not well understood. This study was conducted to evaluate the sperm quality, testicular histomorphology and inflammatory response in mice followed F exposure. Healthy male mice were randomly divided into four groups with sodium fluoride (NaF) at 0, 25, 50, 100 mg/L in the drinking water for 180 days. At the end of the exposure, significantly increased percentage of spermatozoa abnormality was found in mice exposed to 50 and 100 mg/L NaF. Disorganized spermatogenic cells, vacuoles in seminiferous tubules and loss and shedding of sperm cells were also observed in the NaF treated group. In addition, chronic F exposure increased testicular interleukin-17(IL-17), interleukin-17 receptor C (IL-17RC), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in transcriptional levels, as well as IL-17 and TNF-α levels in translational levels. Interestingly, we observed that F treated group elevated testicular inducible nitric oxide synthase (iNOS) mRNA level and nitric oxide (NO) concentration. Taken together, these results indicated that testicular inflammatory response could contribute to chronic F exposure induced testicular toxicity in mice.