Changes in Histopathology, Enzyme Activities, and the Expression of Relevant Genes in Zebrafish (Danio rerio) Following Long-Term Exposure to Environmental Levels of Thallium

Effects of Acute and Subchronic Waterborne Thallium Exposure on Ionoregulatory Enzyme Activity and Oxidative Stress in Rainbow Trout (Oncorhynchus mykiss)

The mechanisms of acute (96-hour) and subchronic (28-day) toxicity of the waterborne trace metal thallium (Tl) to rainbow trout (Oncorhynchus mykiss) were investigated. Specifically, effects on branchial and renal ionoregulatory enzymes (sodium/potassium adenosine triphosphatase [ATPase; NKA] and proton ATPase) and hepatic oxidative stress endpoints (protein carbonylation, glutathione content, and activities of catalase and glutathione peroxidase) were examined. Fish (19-55 g) were acutely exposed to 0 (control), 0.9 (regulatory limit), 2004 (half the acute median lethal concentration), or 4200 (acute median lethal concentration) µg Tl L-1 or subchronically exposed to 0, 0.9, or 141 (an elevated environmental concentration) µg Tl L-1 . The only effect following acute exposure was a stimulation of renal H+ -ATPase activity at the highest Tl exposure concentration. Similarly, the only significant effect of subchronic Tl exposure was an inhibition of branchial NKA activity at 141 µg Tl L-1 , an effect that may reflect the interaction of Tl with potassium ion handling. Despite significant literature evidence for effects of Tl on oxidative stress, there were no effects of Tl on any such endpoint in rainbow trout, regardless of exposure duration or exposure concentration. Elevated basal levels of antioxidant defenses may explain this finding. These data suggest that ionoregulatory perturbance is a more likely mechanism of Tl toxicity than oxidative stress in rainbow trout but is an endpoint of relevance only at elevated environmental Tl concentrations. Environ Toxicol Chem 2024;43:87-96. © 2023 SETAC.

Thallium exposure interfered with heart development in embryonic zebrafish (Danio rerio): From phenotype to genotype

Thallium (Tl) is a rare trace metal element but increasingly detected in wastewater produced by coal-burning, smelting, and more recently, high-tech manufacturing industries. However, the adverse effects of Tl, especially cardiotoxicity, on aquatic biota remain unclear. In this study, zebrafish model was used to elucidate the effects and mechanisms of Tl(I) cardiotoxicity in developing embryos. Exposure of embryonic zebrafish to low-dose Tl(I) (25-100 μg/L) decreased heart rate and blood flow activity, and subsequently impaired swim bladder inflation and locomotive behavior of larvae. Following high-level Tl(I) administration (200-800 μg/L), embryonic zebrafish exhibited pericardial edema, incorrect heart looping, and thinner myocardial layer. Based on RNA-sequencing, Tl(I) altered pathways responsible for protein folding and transmembrane transport, as well as negative regulation of heart rate and cardiac jelly development. The gene expression of nppa, nppb, ucp1, and ucp3, biomarkers of cardiac damage, were significantly upregulated by Tl(I). Our findings demonstrate that Tl(I) at environmentally relevant concentrations interfered with cardiac development with respect to anatomy, function, and transcriptomic alterations. The cardiotoxic mechanisms of Tl(I) provide valuable information in the assessment of Tl-related ecological risk in freshwater environment.

Associations between trace level thallium and multiple health effects in rural areas: Chinese Exposure and Response Mapping Program (CERMP)

Thallium (Tl) is a cumulative high toxicant in the environment, but few studies have investigated the comprehensive health effects underlying chronic Tl exposure at trace levels. This study aims to evaluate the liver, kidney, lung and other potential health effects associated with chronic Tl exposure at trace levels in rural areas of China. Urinary Tl concentrations of 2883 adults from rural areas of 12 provinces in China were measured and 2363 participants were involved in the final analysis. Indicators of liver and kidney functions in the serum, as well as the lung function indicators, were determined in the participants. General linear regression and restricted cubic spline regression were combined to study the associations between urinary Tl and health indicators or outcomes. In this study, the detected rate of Tl in the urine of the participants was 97.28 %. When the urinary Tl concentration was ranged at the fourth quintile, the risk of having liver function disorder was 70 % higher [Odds ratio (OR) = 1.70 (95 % confidence intervals (CI): 1.30, 2.22)] in all the participants, whereas the farmers were more likely to have the disorder [OR = 2.08 (95 % CI: 1.49, 2.92)] than the non-farmers [OR = 1.20 (95 % CI: 0.77, 1.88)]. Nonlinear associations between most of the liver health indicators and urinary Tl were identified, of which serum bilirubin was strongly associated with the elevation of urinary Tl when its concentration was >0.40 μg/g creatinine. Besides, urinary Tl was negatively associated with lung health indicators. Our study proposes the safety re-assessment of the current exposure level of Tl in the environment, especially in rural areas of China.

Integrated physiological, biochemical, and transcriptomic analysis of thallium toxicity in zebrafish (Danio rerio) larvae

Although several studies have evaluated the effects of Thallium (Tl) in adult species of fish, the developmental toxicity of Tl has not been previously explored. In this study, zebrafish embryos (<4 h post fertilization (hpf)) were exposed to Tl at concentrations from 0.8 to 400 μg L^-1 for 7 d. The results showed that the decreased hatching rate and increased malformation rate were observed in the larvae. The swimming velocity of larvae from 200 and 400 μg L^-1 treatments was respectively reduced by ~26 % and 15 %. Histopathological analysis of liver indicated the number of cells of karyolysis (143 % and 202 %) and pyknosis (170 % and 131 %) were respectively increased in 200 and 400 μg L^-1 Tl treatments. Meanwhile, the Tl body burden and metallothionein (MT) levels in the larvae were increased with elevated Tl concentrations. The level of malondialdehyde (MDA) was increased by ~20 to 51 % in all Tl treatments and total antioxidant capacity (TAC) was decreased by ~12 % at 200 μg L^-1. The activities of Na⁺/K⁺-ATPase and protease were inhibited in 200 and 400 μg L^-1 Tl treatments. Moreover, the transcripts of genes (Nrf2, HO-1, TNF-α, IL-1β, IL-8, IL-10, TGF) were significantly altered. In addition, a total of 930 differentially expressed genes (DEGs) and 1549 DEGs were found in the 200 and 400 μg L^-1 treatments with 458 overlapped DEGs by transcriptomic analysis. The protein digestion and absorption, ECM-receptor interaction, and complement and coagulation cascades pathways were shown to be the most significantly enriched pathways. This study helps better understand the molecular mechanisms of Tl toxicity in fish.

Abamectin promotes behavior changes and liver injury in zebrafish

The indiscriminate use of pesticides is a worldwide concern due to the environment contamination since it can cause deleterious effects to non-target organisms including the fishes. The effects of abamectin, a pesticide from the avermectin family, were evaluated in adult zebrafish (Danio rerio) after exposure to a commercial formula commonly used in Brazil. The animals were submitted to acute (96 h) and to a short-term chronic exposure (15 days) of distinct concentrations of abamectin. LC50 was determined and a histological study followed by an immunohistochemistry analysis for P-gp and HSP70 identification were performed on livers of the animals submitted to the acute and chronic treatment, respectively. Moreover, behavior patterns were observed daily in both trials. A LC50 value of 105.68 μg/L was determined. The histological analysis revealed a morphological alteration of the hepatocytes, glycogen accumulation, degeneration, and disorganization of the cytoplasm, and a pyknotic, irregular, and laterally located nuclei. The immunohistochemistry for HSP70 and P-gp showed strong staining in the hepatocytes of the control groups and progressive decrease as the concentration of abamectin increased. Changes were observed in body posture, movement around the aquarium, opercular activity, body color and search for food in the groups treated with abamectin. The results presented suggest that abamectin can affect the behavioral pattern of the animals, promote morphological changes, and decrease the expression of HSP70 and P-gp in zebrafish liver.

Immunosuppressive Effects of Thallium Toxicity in Nile Tilapia Fingerlings: Elucidating the Rescue Role of Astragalus membranaceus Polysaccharides

This study evaluated the immunotoxic effects of thallium (Tl) in Nile tilapia fingerlings and the recovery role of dietary Astragalus membranaceus polysaccharides (ASs). An 8-week experiment was designed where 180 fishes were randomly and equally assigned in triplicates into the six groups: the control group (CNT) was reared in unpolluted water and fed a commercial diet, two groups were fed a well-balanced commercial diet plus 1.5 and 3.0 g AS/kg diet (AS0.15 and AS0.30), respectively, the fourth group was exposed to a sublethal dose of Tl (41.9 μg l^-1) [equal to 1/10 of 96-h lethal concentration 50 (LC50)], and the last two groups were fed 0.15 and 0.3% AS, respectively, and concurrently exposed to Tl (41.9 μg l^-1) (AS0.15+Tl and AS0.30+Tl). Fish hematobiochemical parameters, serum immunity [nitric oxide, total immunoglobulin M (IgM) levels, and lysozyme activity], transcription of hepatic interferon-γ (IFN-γ), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α), and resistance to Aeromonas hydrophila (A. hydrophila) were assessed. Hematobiochemical parameters and serum immune indices were significantly decreased in the fish group exposed to sublethal Tl concentration compared to the CNT group. Furthermore, Tl exposure significantly induced overexpression of IL-1β, TNF-α, and IFN-γ genes (4.22-, 5.45-, and 4.57-fold higher, respectively) compared to CNT values. Tl exposure also increased the cumulative mortality (%) in Nile tilapia challenged with A. hydrophila. Remarkably, the groups fed AS0.15+Tl and AS0.30+Tl significantly ameliorated all the aforementioned parameters, but did not reach CNT values. Our findings suggest the possible immunomodulating roles of dietary AS in recovering the immunotoxic effects of Tl in Nile tilapia. We can conclude that dietary AS would be useful for maintaining the immunity of Nile tilapia fingerlings.

Astragalus membranaceus polysaccharides modulate growth, hemato-biochemical indices, hepatic antioxidants, and expression of HSP70 and apoptosis-related genes in Oreochromis niloticus exposed to sub-lethal thallium toxicity

A 60-day experiment was performed to assess the efficacy of dietary Astragalus membranaceus polysaccharides (ASP) in attenuation of sub-lethal thallium (Tl) toxicity in Nile tilapia. Six experimental groups (in triplicates) were designed where a fish group was raised in clean water and fed basal diet and served as control (CONT), two groups were fed the basal diet supplemented with 0.15% and 0.30% ASP (ASPL and ASPH), Tl-intoxicated group exposed to 1/10 of 96-h LC50 (= 41.9 μg/L), and two other groups were fed 0.15% and 0.30% ASP and concomitantly exposed to 41.9 μg Tl/L (ASPL-Tl and ASPH-Tl). At the end of the experiment, fish behavioral responses, clinical signs, survivability, growth, whole-body composition, intestinal digestive enzymes, serum biochemical parameters, hepatic antioxidative biomarkers, and transcription of stress and apoptosis genes were assessed. Results showed that the whole-body composition, intestinal α-amylase and protease enzymes, serum AST and blood urea levels, and hepatic GSH were not significantly different among groups (P > 0.05). The Tl-intoxicated fish group was off food, had darkened skin, showed restlessness and hyperexcitability, and high mortalities. FBW, WG, SGR and FI were significantly decreased alongside increase FCR in the Tl-exposed group. Tl exposure caused significant increases (P < 0.05) in intestinal lipase enzyme and serum indices such as ALT, creatinine, total cholesterol, triglycerides, glucose, and cortisol levels. Moreover, a significant decreases in hepatic CAT and SOD enzyme activities and significant increases in hepatic MDA contents were also noticed (P < 0.05). Furthermore, Tl exposure induced significant upregulation of hepatic HSP70 and apoptosis-related genes (p53 and caspase 3). Interestingly, dietary supplementation with ASP in ASPL-Tl and ASPH-Tl groups modulated the parameters mentioned above but still not reached the CONT values. Altogether, this study suggests that ASP could be beneficial in the modulation of sub-lethal Tl toxicity effects in Nile tilapia. Additionally, we can conclude that using natural feed supplements such as ASP in aquafeed might be necessary for maintaining the overall health performances of Nile tilapia.

Thallium in aquatic environments and the factors controlling Tl behavior

Although thallium (Tl) usually exists in a very low level in the natural environment, it is highly toxic. With the development of mining and metallurgical industry and the wide application of Tl in the field of high technologies, Tl poses an increasing threat to the ecological environment and human health. This paper summarizes the research results of the toxicity of Tl as well as the distribution, occurrence forms, migration, and transformation mechanism of Tl in rivers, lakes, mining areas, estuaries, coastal waters, and oceans. It also discusses the influence mechanisms of pH, redox potential, suspended particulate matters, photochemical reaction, natural minerals, cation/anion, organic matters, and microorganisms on the environmental behavior of Tl. This paper points out the shortcomings of Tl research methods in water environment, and looks forward to the future development directions: First, the technology for separating Tl(III) and Tl(I) is still immature, especially it is difficult to effectively separate Tl(III) and Tl(I) in seawater. Second, the development of many advanced in situ detection technologies will bring great convenience to the studies of the dynamic mechanisms of Tl migration and transformation in the environments. Third, adsorption is the most effective mechanism to remove Tl from water, in which modified metal oxides or macrocyclic organic compounds have high application potential.

A case-control study of thallium exposure with the risk of premature ovarian insufficiency in women

Thallium exposure has been associated with female reproductive health, but little is known about its potential association with premature ovarian insufficiency (POI). In this study, a total of 169 patients with POI and 209 healthy women were recruited from Zhejiang province, China. Urinary thallium concentrations were significantly positively associated with the risk of POI [adjusted odds ratio (OR) = 1.63, 95% CI: 1.25-2.13, p < 0.001], geometric mean values of which were significantly higher in POI cases (0.213 μg/L, 0.302 μg/g for creatinine adjustment) than those of controls (0.153 μg/L, 0.233 μg/g for creatinine adjustment). Furthermore, the serum levels of follicle-stimulating hormone and luteinizing hormone were positively associated with urinary thallium concentrations, whereas anti-Mullerian hormone and estradiol were negatively correlated with thallium. To the best of our knowledge, this is the first study to provide evidence that thallium exposure at currently environmental levels is the potential risk factor for POI in women.

In vivo evaluation of Nano-palladium toxicity on larval stages and adult of zebrafish (Danio rerio)

The existence and usage of nano-sized palladium (nano-Pd) as catalytic promoters among industries and researchers have been laid a way to explore the release of nano-Pd particles into the aquatic environment, bio-accumulating in living organisms. However, the data on fate and toxicity in response to nano-Pd on aquatic organisms are very limited. Herein, we report the concentration-specific toxicity of nano-Pd in zebrafish (Danio rerio). Nano-Pd was synthesized and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Dynamic Light Scattering (DLS) and Zeta potential. To determine the in vivo toxicity of nano-Pd, the 96 hpf larvae and the adult zebrafish were treated with two (22 and 0.4 ng/L) environmental relevant concentrations. High doses of nano-Pd influenced the hatching rate, embryo survival, heartbeat and teratological anomalies in the 96 hpf larvae. Reactive oxygen species (ROS) and apoptosis were also influenced by nano-Pd exposure while the acetylcholinesterase (AChE) activity was declined in a dose dependent manner. In long-term exposure (42 days), the adult fish showed erratic movements in swimming pattern inhibiting the AChE activity in both the concentrations of brain and liver. The antioxidant enzyme activity such as superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione reductase (GR) and lipid peroxidation (LPO), showed a significant change (P < 0.05) indicating that oxidative stress was induced by nano-Pd. Similarly, nano-Pd also induced histopathological lesions in gill, liver and brain providing an insight of fate and toxicity of nano-Pd in the aquatic environment. Our study contributes a significant mechanism to understand the toxicity concern of nano-Pd in the aquatic environment.

Different responses in metallothionein gene expression and antioxidative enzyme activity lead to more ROS accumulation in rice exposed to Tl(III) than to Tl(I)

This is the first study to investigate the reduction mechanism of Tl (III) to Tl(I) in the presence of plants, especially rice. Smaller plant density could effectively reduce the content of organic acids in the hydroponic system to keep the stability of Tl(III). As the plant density was reduced from 40 seedlings to 10 seedlings in 100 mL Tl(III) solution, the content of oxalate was declined to one-third of the original, and the ratio of Tl(III)/total Tl was increased from 39.6% to 81.0% in the first 2 h treatment. Then the differences in antioxidant capacity of rice exposed to the two Tl species were studied. The contents of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and superoxide anion (O₂˙^-) of rice roots exposed to Tl(III) were all higher than those to Tl(I). Meanwhile, the catalase (CAT) activity was significantly depressed and peroxidase (POD) was increased by Tl(III), whereas superoxide dismutase (SOD) showed a rise in both Tl(I) and Tl(III) with no significant difference between them. The expression of metallothionein gene OsMT1a to Tl(I) was upregulated to 255.5 times of Tl(III) though OsMT2c was downregulated to 0.39 times of Tl(III). Overall, the different responses in metallothionein gene expression and antioxidative enzyme activation might result in more ROS accumulation to rice roots by Tl(III) treatment than those by Tl(I).

Norethindrone alters mating behaviors, ovary histology, hormone production and transcriptional expression of steroidogenic genes in zebrafish (Danio rerio)

The impact of progestins (i.e. synthetic forms of progesterone) on aquatic organisms has drawn increasing attention due to their widespread occurrence in the aquatic environments and potential effects on the endocrine system of fish. In this study, the effects of norethindrone (NET, a progestin) on the reproductive behavior, sex hormone production and transcriptional expressions were evaluated by exposing female zebrafish to NET at 0, 3.1, 36.2 and 398.6 ng L^-1 for 60 days. Results showed that NET impaired the mating behaviors of female at 36.2 and 398.6 ng L^-1 exhibited by males and increased the frequency of atretic follicular cells in the ovary exposed to NET at 398.6 ng L^-1. As for sex hormones, plasma testosterone concentration in zebrafish increased, while estradiol concentration decreased. Up-regulation of genes (Npr, Mpra, Mprβ, Fshβ, Lβ, Tshb, Nis and Dio2) was detected in the brain of fish exposed to NET at 398.6 ng L^-1. The transcriptional levels of genes (Esr1, Vtg1, Ar, Cyp19a, Cyp11b and Ptgs2) were generally inhibited in the ovary of zebrafish by NET at 398.6 ng L^-1. Moreover, the transcripts of genes (Vtg1, Esr1, Ar and Pgr) in the liver were reduced by NET at 36.2 and 398.6 ng L^-1. Our findings suggest that NET can potentially diminish the of fish populations not only by damaging their reproductive organs, but also by altering their mating behavior through the changes in the expressions of genes responsible for the production of sex hormones.

Gene expression changes and toxicity of selected rare earth elements in rainbow trout juveniles

Rare earth elements (REEs) are increasingly used in electronics industry and other areas of our economy and questions were raised about their impacts to the environment. The purpose of this study was to examine the lethal and sublethal toxicity of REEs in juvenile rainbow (Oncorhynchus mykiss) trout. The fish were exposed to increasing concentrations (0.064, 0.32, 1.6, 8 and 40 mg/L) of the following 7 REEs for 96 h at 15 °C: cerium (CeCl₃), erbium (ErCl₃), gadolinium (GdCl₃), lanthanum (LaCl₃), neodymium (NdCl₃), samarium (SmCl₃) and yttrium (YCl₃). The mortality were determined and in the surviving fish, 10 target gene transcripts were measured in the liver to track changes in oxidative stress, DNA repair, tissue growth/proliferation, protein chaperoning, xenobiotic biotransformation and ammonia metabolism. The data revealed that Y, Sm, Er and Gd formed a distinct group based on toxicity (mortality) and gene expression changes. Electronegativity was significantly correlated (r = -0.8, p < 0.01) with the lethal concentration (LC50). Gene expression changes occurred at concentration circa 120 times lower than the LC50 and the following transcripts in protein chaperoning (heat shock proteins), DNA repair (growth arrest DNA Damage) and CYP1A1 gene expression involved in the metabolism of coplanar aromatic hydrocarbons were involved. In conclusion, the study revealed that the more electronegative REEs were the most toxic to trout juveniles and produced sublethal effects at concentrations 2 orders of magnitude lower than the lethal concentrations. The toxicity of REEs depends on the elements were toxicity involves specific pathways at the gene expression level.

Effect of thallium exposure and its interaction with smoking on lung function decline: A prospective cohort study

BACKGROUND

Thallium (Tl) is a cumulative high toxicant in the environment, but few longitudinal studies have investigated the respiratory impairment of Tl exposure.

OBJECTIVES

This study aimed to evaluate the effect of Tl and its interaction with smoking on lung function decline, and explore the potential mechanisms.

METHODS

The baseline and follow-up lung functions were measured from a prospective cohort study of 1243 workers, who were followed from 2010 to 2014. Their baseline urinary levels of Tl were determined. We also measured the plasma C-reactive protein (CRP) and urinary 8-iso-prostaglandin-F2α (8-iso-PGF2α) in a randomly selected subcohort of 474 subjects.

RESULTS

The results showed that a 2-fold increase in urinary Tl was associated with 29.81 mL (95%CI: 3.83-55.80) increased decline in forced expiratory volume in 1 s (FEV₁). The effect was more pronounced among heavy-smokers (≥15 pack-years) [β(95%CI) = 56.42 mL (9.66-103.19)]. In particular, compared to never-smokers with low Tl, heavy-smokers with high Tl had a separate 158.44 mL (95%CI: 54.88-262.00) and 4.58% (95%CI: 1.40-7.76) increased declines in FEV₁ and percentage of predicted (ppFEV₁), respectively. There was a significant interaction between Tl and smoking intensity on ppFEV₁ decline (P_int = 0.034). More importantly, the increasing level of urinary Tl was correlated with elevated CRP and 8-iso-PGF2α.

CONCLUSION

Our prospective cohort study identified that exposure to high Tl had a deleterious effect on lung function, and this effect may be enhanced by tobacco smoking. Increased inflammation may partly contribute to the joint effects of Tl and smoking on impaired lung function, but the biological mechanisms need further explorations.

Prenatal thallium exposure and poor growth in early childhood: A prospective birth cohort study

BACKGROUND

Thallium (Tl) exposure remains a public health problem with potential impacts on humans. Studies have suggested that prenatal exposure to thallium may be associated with fetal growth, but no studies are known have explored its association with early childhood anthropometry.

OBJECTIVE

To investigate the effects of prenatal Tl exposures on early child growth and development aged 0-2 years in a prospective birth cohort study.

METHODS

3080 pregnant women and their children participated in the study, which were recruited from a birth cohort in China. Serum samples collected in the first and second trimester of pregnant subjects and umbilical cord blood of infants were analyzed for Tl exposure assessment. Infant length or standing height and weight were obtained from medical records and 2 years planned visits. We used length/height and weight to calculate z-scores for weight-for-age (WAZ), height-for-age (HAZ), weight-for-height (WHZ), and body mass index-for-age (zBMI) based on World Health Organization standards. Linear mixed model was used to investigate the association between serum concentrations of Tl and the children's anthropometric characteristics (WAZ, HAZ, WHZ, and zBMI), and stratification analysis by sex was also examined.

RESULTS

The median (P₂₅-P₇₅) of Tl levels in the first trimester, second trimester and umbilical cord serum were 61.7 (50.7-77.0), 60.1 (50.9-74.8) and 38.4 (33.6-43.9) ng/L, respectively. Paired Mann-Whitney tests found Tl concentrations in umbilical cord serum were significantly less than that in maternal serum during the first and second trimesters (all p < 0.01). Using adjusted linear mixed model, no significant relationships were observed between maternal Tl exposure and child growth parameters. However, the umbilical cord serum Tl levels may contributed to decreased WAZ (β = -0.382, 95% confidence interval (CI): -0.670, -0.095) and HAZ (β = -0.427, 95% CI: -0.702, -0.152). When stratified by sex, the umbilical cord serum Tl levels were negatively related to WAZ (β = -0.450, 95% CI: -0.853, -0.048) and HAZ (β = -0.775, 95% CI: -1.160, -0.391) for girls. Among boys, overall Tl exposures were not significantly associated with early children anthropometric outcomes.

CONCLUSIONS

In the present study, our results suggested that prenatal Tl exposures may have a sex specific effect on child anthropometric measurements in the first 2 years of life. Umbilical cord serum Tl levels tended to be reduced child's stature and weight in young girls.

The progestin norethindrone affects sex differentiation and alters transcriptional profiles of genes along the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes in juvenile zebrafish Dario renio

Natural and synthetic progestins may pose a threat to wild fish populations living in receiving waters. In this study, the effects of norethindrone (NET) on the sex differentiation of zebrafish (Dario renio) and the mechanisms underlying these effects were investigated. Juvenile zebrafish (20 days post fertilization, pdf) were exposed to environmentally relevant concentrations (5, 50, 500, and 1000 ng L^-1) for 45 d. Sex ratio of the NET-exposed populations, the histology of the gonads and the transcriptional profile of the regulatory genes involved in sex differentiation and steroidogenesis were examined. The results showed that a significantly higher ratio of male/female was induced in the zebrafish populations exposed to NET at concentrations higher than 32.3 ng L^-1. Exposure to NET caused acceleration of sexual mature in males and a delay in ovary maturation in female zebrafish. Among the genes regulating sexual differentiation, transcripts of Dmrt1 showed a dose-dependent increase while transcripts of Figa and Fox12 showed a dose-dependent decrease in response to exposure to NET. For genes regulating the steroidogenesis, the expressions of Cyp11a1, Cyp17, Cyp19a1a, and Cyp11b were significantly down-regulated by exposure to NET, while Hsd17b3 expression was significantly up-regulated by exposure to NET at 421.3 and 892.9 ng L^-1. For the receptor genes in the gonads, the transcriptional expression of Pgr, Ar, and Mr was significantly up-regulated at 421.3 and 892.9 ng L^-1 of NET. For genes involved in the hypothalamic-pituitary axis, the transcriptional expression of Gnrh3 and Pomc was significantly up-regulated by exposure to NET with the exception for Gnrh3 at 4.2 ng L^-1. The results demonstrated that exposure to NET at the juvenile stage could affect gonad differentiation and sex ratio, which might be accounted for by the alterations of the transcriptional expressions of genes along the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axes.