In vivo and in vitro effects of prochloraz and nonylphenol ethoxylates on trout spermatogenesis

The journey of prochloraz pesticide in Citrus sinensis: Residual distribution, impact on transcriptomic profiling and reduction by plasma-activated water

Prochloraz (PTIC) is a hazardous fungicide used worldwide on agricultural produce despite concerns about potential impacts on human health and environmental pollution. The residue of PTIC and its metabolite 2,4,6-trichlorophenol (2,4,6-TCP) in fresh produce has largely not been clarified. Herein, we address this research gap by examining residues of PTIC and 2,4,6-TCP in fruit of Citrus sinensis through a typical storage period. PTIC residue in the exocarp and mesocarp peaked on days 7 and 14, respectively, while 2,4,6-TCP residue gradually increased throughout storage period. Based upon gas chromatography-mass spectrometry and RNA-sequencing analysis, we reported the potential impact of residual PTIC on endogenous terpene production, and identified 11 DEGs encoding enzymes involved in terpene biosynthesis in Citrus sinensis. Additionally, we investigated both the reduction efficacy (max: 58.93%) of plasma-activated water in citrus exocarp and the minimal impact on quality attributes of citrus mesocarp. The present study not only sheds light on the residual distribution of PTIC and its impact on endogenous metabolism in Citrus sinensis, but also further provides theoretical basis for potential approaches for efficiently reducing or eliminating pesticide residues.

Studies of Endocrine Disruptors: Nonylphenol and Isomers in Biological Models

Certain emerging pollutants are among the most widely used chemicals globally, causing widespread concern in relation to their use in products devoted to cleaniness and asepsis. Nonylphenol ethoxylate (NPEOn) is one such contaminant, along with its degradation product, nonylphenol, an active ingredient presents in nonionic surfactants used as herbicides, cosmetics, paints, plastics, disinfectants, and detergents. These chemicals and their metabolites are commonly found in environmental matrices. Nonylphenol and NPEOn, used, are particularly concerning, given their role as endocrine disruptors chemical and possible neurotoxic effects recorded in several biological models, primarily aquatic organisms. Limiting and detecting these compounds remain of paramount importance. The objective of the present review was to evaluate the toxic effects of nonylphenol and NPEOn in different biological models. Environ Toxicol Chem 2023;00:1-12. © 2023 SETAC.

Alkylphenols cause cytotoxicity and genotoxicity induced by oxidative stress in RTG-2 cell line

Alkylphenols ethoxylates are industrial surfactants, and the release in the environmental matrices produces degraded products, of which nonylphenol (NP) and octylphenol (OP) were the most common. They can be classified as endocrine disruptors since the estrogenic potential is widely recognized, but some others toxic aspects are in discussion. This study aimed to evaluate the toxicity of NP, OP, and mixtures of both through cellular, biochemical and genetic biomarkers in fish gonadal cell line RTG-2 exposed to nominal concentrations of 0.05; 0.5; 5; 50, and 100 μg mL^-1 of each chemical and their mixtures of 0.05, 0.5; 5 μg mL^-1 concentrations. After 24 h, the cells were collected for cytotoxic (neutral red - NR; crystal violet - CV, resazurin assay - RA and lactate-dehydrogenase - LDH), antioxidant system (glutathione-s-transferase - GST; superoxide-dismutase - SOD; glutathione-peroxidase - GPx and malondialdehyde - MDA) and genotoxic assays (alkaline comet assay and Fpg-modified alkaline comet assay). The chemicals and their mixtures were cytotoxic at 50 and 100 μg mL^-1, in general aspect, but LDH showed cytotoxicity since 0.05 μg mL^-1. The GST and SOD showed an activity increase trend in most tested groups, while GPx decreased at 5 μg mL^-1 of the mixture. The MDA increase in all groups resulted in lipid peroxidation. The reactive oxygen species caused DNA damage for all groups. The tested chemicals and concentrations have been found in the freshwater systems. They can induce cell toxicity in several parameters that could impair the gonadal tissues considering the RTG-2 responses.

Addition of Phenylmethylsulfonyl Fluoride Increases the Working Lifetime of the Trout Liver S9 Substrate Depletion Assay, Resulting in Improved Detection of Low Intrinsic Clearance Rates

The activity of a trout liver S9 substrate depletion assay has been shown to decline over time, presumably due to proteolytic degradation of biotransformation enzymes. To address this problem, assay performance was evaluated following the addition of phenylmethylsulfonyl fluoride (PMSF) or a general-purpose protease inhibitor cocktail to liver homogenization buffers and/or S9 reaction mixtures. Addition of PMSF to liver homogenization buffers and/or S9 reaction mixtures had little or no effect on clearance of phenanthrene, a model cytochrome P450 substrate, in short-term (25 or 30 min) depletion experiments but resulted in significant improvements in retention of this initial activity over time. The protease inhibitor cocktail strongly inhibited initial activity when added to homogenization buffers or reaction mixtures. Taking into consideration potential effects on liver carboxylesterases, the treatment approach determined to be optimal was addition of 10 µM PMSF to the S9 reaction mixture. Addition of 10 µM PMSF to the mixture resulted in significantly higher rates of phenanthrene clearance in 2-h incubations relative to those obtained in the absence of PMSF and a 6-fold increase in the working lifetime of the preparation. The results of a statistical power analysis suggest that by increasing the working lifetime of the assay, addition of PMSF to the reaction mixture could result in substantially improved detection of low in vitro clearance rates when compared to current practice. These findings demonstrate the value of adding PMSF to the trout S9 preparation and may have broad implications for use of this assay to support chemical bioaccumulation assessments for fish. Environ Toxicol Chem 2021;40:148-161. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Biotransformation of Polycyclic Aromatic Hydrocarbons by Trout Liver S9 Fractions: Evaluation of Competitive Inhibition Using a Substrate Depletion Approach

Environmental contaminants frequently occur as part of a chemical mixture, potentially resulting in competitive inhibition among multiple substrates metabolized by the same enzyme. Trout liver S9 fractions were used to evaluate the biotransformation of 3 polycyclic aromatic hydrocarbons (PAHs): phenanthrene, pyrene, and benzo[a]pyrene, tested as binary mixtures. Initial rates of biotransformation were determined using a substrate-depletion approach. The resulting data were then fitted by simultaneous nonlinear regression to a competitive inhibition model. In each case, the PAH possessing the lower Michaelis-Menten affinity constant (K_M ) competitively inhibited biotransformation of the other compound. Inhibition constants determined for the lower-K_M compound were generally close to previously determined K_M values, consistent with the suggestion that phase I biotransformation of PAHs is largely catalyzed by one or a small number of cytochrome P450 enzymes. The use of a substrate-depletion approach to perform enzyme-inhibition studies imposes practical limitations on experimental design and complicates the interpretation of derived kinetic constants. Nevertheless, the resulting information may have utility for chemical hazard assessments as well as the design and interpretation of controlled laboratory studies. Depletion experiments informed by measured chemical concentrations in tissues may also provide a means of determining whether enzyme inhibition occurs under relevant environmental conditions. Environ Toxicol Chem 2019;38:2729-2739. Published 2019 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America.

A comparison of endocrine disruption potential of nonylphenol ethoxylate, vanillin ethoxylate, 4-n-nonylphenol and vanillin in vitro

The widely used surfactant nonylphenol ethoxylate (NPEO) and its raw material 4-n-nonylphenol (4-n-NP), as well as its degradation products, are recognized as endocrine disrupting chemicals. The USA Environmental Protection Agency (EPA) released an assessment that looked for safe alternatives to NPEO. Vanillin ethoxylate (VAEO) is a novel substitute for NPEO and is quite similar to NPEO in structure; there is a risk that it has similar endocrine disrupting effects to NPEO. However, their effects on various nuclear hormone receptors have not been thoroughly examined. In this study, the effects of NPEO, VAEO, 4-n-NP and Vanillin on the estrogen receptor α (ERα), androgen receptor (AR), thyroid hormone receptor (TR), retinoic X receptor β (RXRβ) and estrogen-related receptor γ (ERRγ) were determined and compared using a battery of recombined yeast strains expressing β-galactosidase. The results showed that NPEO and 4-n-NP acted as significant antagonists of ER, AR, TR and ERRγ. In addition, 4-n-NP also had antagonistic activity toward RXRβ. Moreover, VAEO was shown to be a very weak antagonist of TR and ERRγ, and Vanillin had no interaction with any nuclear receptors. For the first time, it was found that NPEO had AR, TR and ERRγ antagonistic effects and that 4-n-NP was an antagonist of RXRβ. The in vitro data indicated that NPEO, 4-n-NP and VAEO have the potential to act as endocrine disruptors involving more than one nuclear hormone receptor, but VAEO has much lower endocrine disrupting potential than NPEO. Thus, it is critical to find safe substitutes for NPEO and a substitute of NPEO with structural analogues should be carried out with caution. Furthermore, to look for preferable alternatives for NPEO, more in vivo and in vitro studies of the alternatives concerning endocrine disruption are needed, especially in vitro studies need to involve various target points, not only focus on their effects on ER but also take other nuclear hormone receptor pathways into consideration.

Measurement of kinetic parameters for biotransformation of polycyclic aromatic hydrocarbons by trout liver S9 fractions: Implications for bioaccumulation assessment

In vitro substrate depletion methods developed by the pharmaceutical industry are being used with increasing frequency to support chemical bioaccumulation assessments for fish. However, the application of these methods to high log K _ow chemicals poses special challenges. Biotransformation of three polycyclic aromatic hydrocarbons (PAHs) was measured using trout liver S9 fractions. Measured activity declined with incubation time and was reduced by acetone (used as a spiking solvent) at concentrations greater than 0.5%. Addition of alamethicin, a pore-forming peptide used to support UDP-glucuronosyltransferase activity, also reduced activity in a concentration-dependent manner. The substrate concentration dependence of activity was evaluated to estimate K _M and V _max values for each compound. Derived kinetic constants suggested that all three PAHs are transformed by the same reaction pathway and indicated an inverse correlation between K _M and chemical log K _ow. Binding effects on activity were evaluated by measuring unbound chemical concentrations across a range of S9 protein levels. Reaction rates were proportional to the unbound concentration except when these concentrations approached saturating levels, providing a direct demonstration of the free chemical hypothesis. These findings suggest that previous in vitro work with high log K _ow compounds was conducted at inappropriately high substrate concentrations resulting in underestimation of true in vivo activity. Preliminary calculations also indicate that PAH metabolism in fish may approach saturation during standardized in vivo testing efforts, potentially resulting in concentration-dependent accumulation and/or steady-state levels of accumulation greater than those which occur in a natural setting.

Allometric scaling of hepatic biotransformation in rainbow trout

Biotransformation may substantially impact the toxicity and accumulation of xenobiotic chemicals in fish. However, this activity can vary substantially within and among species. In this study, liver S9 fractions from rainbow trout (4-400 g) were used to evaluate relationships between fish body mass and the activities of phase I and phase II metabolic enzymes. An analysis of log-transformed data, expressed per gram of liver (g liver-1), showed that total cytochrome P450 (CYP) concentration, UDP-glucuronosyltransferase (UGT) activity, and glutathione S-transferase (GST) activity exhibited small but significant inverse relationships with fish body weight. In contrast, in vitro intrinsic clearance rates (CLIN VITRO,INT) for three polycyclic aromatic hydrocarbons (PAHs) increased with increasing body weight. Weight normalized liver mass also decreased inversely with body weight, suggesting a need to express hepatic metabolism data per gram of body weight (g BW-1) in order to reflect the metabolic capabilities of the whole animal. When the data were recalculated in this manner, negative allometric relationships for CYP concentration, UGT activity, and GST activity became more pronounced, while CLIN VITRO,INT rates for the three PAHs showed no significant differences across fish sizes. Ethoxyresorufin O-deethylase (EROD) activity normalized to tissue weight (g liver-1) or body weight (g BW-1) exhibited a non-monotonic pattern with respect to body weight. The results of this study may have important implications for chemical modeling efforts with fish.

Reliability of In Vitro Methods Used to Measure Intrinsic Clearance of Hydrophobic Organic Chemicals by Rainbow Trout: Results of an International Ring Trial

In vitro assays are widely employed to obtain intrinsic clearance estimates used in toxicokinetic modeling efforts. However, the reliability of these methods is seldom reported. Here we describe the results of an international ring trial designed to evaluate two in vitro assays used to measure intrinsic clearance in rainbow trout. An important application of these assays is to predict the effect of biotransformation on chemical bioaccumulation. Six laboratories performed substrate depletion experiments with cyclohexyl salicylate, fenthion, 4-n-nonylphenol, deltamethrin, methoxychlor, and pyrene using cryopreserved hepatocytes and liver S9 fractions from trout. Variability within and among laboratories was characterized as the percent coefficient of variation (CV) in measured in vitro intrinsic clearance rates (CLIN VITRO, INT; ml/h/mg protein or 106 cells) for each chemical and test system. Mean intralaboratory CVs for each test chemical averaged 18.9% for hepatocytes and 14.1% for S9 fractions, whereas interlaboratory CVs (all chemicals and all tests) averaged 30.1% for hepatocytes and 22.4% for S9 fractions. When CLIN VITRO, INT values were extrapolated to in vivo intrinsic clearance estimates (CLIN VIVO, INT; l/d/kg fish), both assays yielded similar levels of activity (<4-fold difference for all chemicals). Hepatic clearance rates (CLH; l/d/kg fish) calculated using data from both assays exhibited even better agreement. These findings show that both assays are highly reliable and suggest that either may be used to inform chemical bioaccumulation assessments for fish. This study highlights several issues related to the demonstration of assay reliability and may provide a template for evaluating other in vitro biotransformation assays.

Toxicokinetic models and related tools in environmental risk assessment of chemicals

Environmental risk assessment of chemicals for the protection of ecosystems integrity is a key regulatory and scientific research field which is undergoing constant development in modelling approaches and harmonisation with human risk assessment. This review focuses on state-of-the-art toxicokinetic tools and models that have been applied to terrestrial and aquatic species relevant to environmental risk assessment of chemicals. Both empirical and mechanistic toxicokinetic models are discussed using the results of extensive literature searches together with tools and software for their calibration and an overview of applications in environmental risk assessment. These include simple tools such as one-compartment models, multi-compartment models to physiologically-based toxicokinetic (PBTK) models, mostly available for aquatic species such as fish species and a number of chemical classes including plant protection products, metals, persistent organic pollutants, nanoparticles. Data gaps and further research needs are highlighted.

Comparison of trout hepatocytes and liver S9 fractions as in vitro models for predicting hepatic clearance in fish

Isolated hepatocytes and liver S9 fractions have been used to collect in vitro biotransformation data for fish as a means of improving modeled estimates of chemical bioaccumulation. To date, however, there have been few direct comparisons of these 2 methods. In the present study, cryopreserved trout hepatocytes were used to measure in vitro intrinsic clearance rates for 6 polycyclic aromatic hydrocarbons (PAHs). These rates were extrapolated to estimates of in vivo intrinsic clearance and used as inputs to a well stirred liver model to predict hepatic clearance. Predicted rates of hepatic clearance were then evaluated by comparison with measured rates determined previously using isolated perfused livers. Hepatic clearance rates predicted using hepatocytes were in good agreement with measured values (<2.1-fold difference for 5 of 6 compounds) under 2 competing binding assumptions. These findings, which may be attributed in part to high rates of PAH metabolism, are similar to those obtained previously using data from liver S9 fractions. For 1 compound (benzo[a]pyrene), the in vivo intrinsic clearance rate calculated using S9 data was 10-fold higher than that determined using hepatocytes, possibly due to a diffusion limitation on cellular uptake. Generally, however, there was good agreement between calculated in vivo intrinsic clearance rates obtained using either in vitro test system. These results suggest that both systems can be used to improve bioaccumulation assessments for fish, particularly when vitro rates of activity are relatively high, although additional work is needed to determine if the chemical domain of applicability for each system differs. Environ Toxicol Chem 2017;36:463-471. Published 2016 SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

In vitro effects of nonylphenol on motility, mitochondrial, acrosomal and chromatin integrity of ram and boar spermatozoa

The objective of this study was to determine the effects of nonylphenol (NP) on viability of ram and boar sperm in vitro. Ram or boar spermatozoa were exposed to 1, 10, 100, 250 and 500 μg NP ml(-1) for 1, 2, 3 or 4 h. Computer-assisted sperm motility analysis (CASA) system was used to evaluate sperm motility characteristics. Flow cytometry was used to determine mitochondrial membrane potential (MMP) and chromatin integrity, while epifluorescent microscopy was used to determine sperm acrosomal status. Exposure of both species spermatozoa to 250 and 500 μg NP ml(-1) was detrimental to progressive motility (P < 0.05), and its adverse effect was significant at lower (100 μg NP ml(-1) ) concentration (P < 0.05). The percentages of ram and boar spermatozoa with high MMP declined drastically after exposures to ≥250 μg ml(-1) NP (P < 0.05). Unlike chromatin integrity, which did not appear to be altered by NP exposure, there were dose-dependent NP effects (P < 0.05) on acrosomal integrity of both species at as low as 1 μg ml(-1) NP for boar spermatozoa and 10 μg ml(-1) NP for ram spermatozoa. These data show adverse effects of NP on ram and boar spermatozoa and thus its potential harmful effects on male reproduction as NP is found in fruits, vegetables, human milk, fish and livestock products.

Effects on development, growth responses and thyroid-hormone systems in eyed-eggs and yolk-sac larvae of Atlantic salmon (Salmo salar) continuously exposed to 3,3',4,4'-tetrachlorobiphenyl (PCB-77)

Thyroid hormones (triiodothyronine, T3; and thyroxine, T4) play significant roles in development, metamorphosis, metabolism, homeostasis, cellular proliferation, and differentiation, for which the effects are mediated through thyroid hormone receptors (TRα and TRβ). Similarly, the insulin-like growth factor (IGF) is involved in growth and development through regulation of somatic growth. This study was designed to examine the effects of the dioxin-like 3,3',4,4'-tetrachlorobiphenyl (PCB-77) on responses related to growth and thyroid hormone system in eyed eggs and yolk-sac larvae of Atlantic salmon. Salmon eggs were continuously exposed to two waterborne concentrations of PCB-77 (1 or 10 ng/L) over a period of 50 d covering hatching and through yolk-sac absorption stages. Sampling was performed regularly throughout the exposure period and at different time intervals. Gene expression patterns were performed on whole-body homogenate at age 500, 548, 632, 674, and 716 dd (dd: day degrees) using quantitative polymerase chain reaction (PCR). Total T3 (TT3) and total T4 (TT4) were measured using radioimmunoassay (RIA). Data showed that 10 ng PCB-77 increased dioiodinase 2 (Dio2) at 500 dd and both PCB-77 concentrations decreased dio2 expression at 548 dd. PCB-77 elevated cellular TT3 at 500 dd and was lowered at 548 dd only at 10 ng. Otherwise, time-related reduction was not affected by PCB-77 exposure as observed for the rest of the exposure period. For TT4, 1 ng PCB-77 produced a rise at 500 dd, and an apparent concentration decrease at 548 dd, before a total inhibition at 632 dd. The IGF-1 and IGF-1R were variably affected by PCB-77. For IGF-2, PCB-77 produced a concentration-dependent increase at 548 dd, and thereafter an elevation (1 ng) and fall (10 ng) at 632 dd. TRβ mRNA demonstrated PCB-77 related increases during the exposure period, and this effect returned to control levels at 716 dd. For TRα, a rise was noted only after exposure to 10 ng PCB-77 at 500 dd. Overall, the present study demonstrates some possible growth and developmental consequences following exposure to PCB-77 during early life stages of Atlantic salmon.

A rapid screening test for endocrine disrupting chemicals using primary cell culture of the marine medaka

While endocrine disrupting chemicals (EDCs) pose a significant threat to wildlife worldwide, their diverse chemical structures present a major challenge to their detection, particularly since they are present at very low concentrations in the environment. We here report the development of an in vitro system for rapid screening of EDCs, using primary cell cultures (pituitary, ovarian follicular and testicular cells) of the marine medaka (Oryzias melastigma). Pituitary, testis and ovary cell cultures were developed and challenged by environmentally relevant concentrations of three well known EDCs (viz. estradiol, 2,2',4,4'-tetrabromodiphenyl ether, and 4-n-nonylphenol) as well as hypoxia (which has been shown to be a potent endocrine disruptor). In general, the mRNA expression levels of gonadotropins, their receptors and steroidogenic enzymes exhibited dose response relationships to the four endocrine disruptors in different tissues. The sensitivity and responses were also comparable to in vivo responses of whole fish and in vitro responses of the H295R human adrenocortical cell line. Our results suggest that the use of marine medaka primary cultured cells can serve as a cost effective tool for rapid screening of EDCs in the marine environment, and at the same time, sheds light on the underlying mechanisms of EDCs by deciphering their specific target sites along the hypothalamus-pituitary-gonad axis of vertebrates.

The maturity index as a tool to facilitate the interpretation of changes in vitellogenin production and sex ratio in the Fish Sexual Development Test

In July 2011, the Fish Sexual Development Test (FSDT) has officially been adopted as OECD test guideline 234 for the detection of endocrine disrupting chemicals (EDCs). Sex ratio and vitellogenin (VTG) induction are the mandatory endocrine endpoints within this test, whereas gonad staging is only included as an option. In the present study, five FSDTs with zebrafish (Danio rerio) were conducted with EDCs with different modes of action (17α-ethinylestradiol, dihydrotestosterone, 17β-trenbolone, prochloraz and 4-tert-pentylphenol). Results document that not only sex ratio and VTG production of the exposed fish were massively affected, but also gonad maturation. As a novel approach for the quantification of gonad maturation in zebrafish, the maturity index was developed to allow not only an improved assessment of dose-dependent EDC-related effects on gonad maturation, but also statistical analysis of histological data. VTG induction and maturity index showed an excellent correlation for all five EDCs tested. Most importantly, the maturity index often helped to find appropriate interpretations for results that seemed contradictory at first sight. Results show that histological analyses and their predictive power for population fitness are currently underestimated and should become a standard component in the evaluation of potential EDCs.

Reproductive biomarkers to identify endocrine disruption in Clarias gariepinus exposed to 4-nonylphenol

The present study investigated the hormones concentrations and gonads alterations of Clarias gariepinus caused by sublethel concentrations of 4-nonylphenol (0, 0.05, 0.08 and 0.1 mg/l). The changes in the activities of the hormones after exposure to these sublethel doses of 4-nonylpenol referred to endocrine disruption in Clarias gariepinus in association with histopathological changes in reproductive tissues. The levels of thyroid stimulating hormone (TSH), triiodothyronine (T3), total thyroxine (T4), follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone concentrations significantly decreased (P<0.05) in the treated fish in comparison with control. 17-β-estradiol increased significantly (P<0.05) with 4-nonylphenol concentrations increase. Reduction in the gonadosomatic index was evident with increase of sublethal doses of 4-nonylphenol. The histopathological changes of NP-treated were recorded in gonads of Clarias gariepinus reflecting their sensitivity to NP-estrogenic like effects.

Mode of sexual differentiation and its influence on the relative sensitivity of the fathead minnow and zebrafish in the fish sexual development test

Exogenous treatment of fish with natural sex hormones and their mimics has been shown to influence gonadal differentiation resulting in biased phenotypic sex-ratios. This has lead to the development of the Fish Sexual Development Test (FSDT) as a method for the detection of endocrine active chemicals. Proposed test organisms include the medaka, zebrafish (ZF) and stickleback, although the guideline also allows for inclusion of species such as the fathead minnow (FHM), provided the test duration allows for sufficient sexual differentiation. However, although the processes underlying sexual differentiation are known to differ for each of these species, it is not known how, or if, these differences would influence the results of the FSDT. In the experiments reported here, responses of the ZF and FHM to prochloraz, a sterol biosynthesis inhibitor and androgen antagonist, were characterized and compared. Exposure to 320 μg/L of prochloraz, from embryo until 60 (ZF) or 95-125 (FHM) days post hatch inhibited somatic growth of both species, but while a negative impact on ZF larval survival was observed (LOEC 32 μg/L) there was no evidence for an effect on FHM larval survival. Prochloraz influenced sexual differentiation in both species by decreasing the proportion of females (LOEC 100 μg/L (ZF), 320 μg/L (FHM)) and delaying completion of sexual differentiation; manifest as an increased incidence of ovotestis in the ZF (LOEC 100 μg/L) and as an increased number of fish with undifferentiated gonads in the FHM (LOEC 320 μg/L). However, while exposure to 320 μg/L prochloraz delayed maturation of the differentiated FHM testis, there was no such effect in the ZF. These results demonstrate that the different strategy of sexual differentiation in the ZF and FHM influences the profile of responses of their gonads to the masculinising effects of prochloraz, but does not affect their overall sensitivity.

Myostatin-deficient medaka exhibit a double-muscling phenotype with hyperplasia and hypertrophy, which occur sequentially during post-hatch development

Myostatin (MSTN) functions as a negative regulator of skeletal muscle mass. In mammals, MSTN-deficient animals result in an increase of skeletal muscle mass with both hyperplasia and hypertrophy. A MSTN gene is highly conserved within the fish species, allowing speculation that MSTN-deficient fish could exhibit a double-muscled phenotype. Some strategies for blocking or knocking down MSTN in adult fish have been already performed; however, these fish show either only hyperplastic or hypertrophic growth in muscle fiber. Therefore, the role of MSTN in fish myogenesis during post-hatch growth remains unclear. To address this question, we have made MSTN-deficient medaka (mstnC315Y) by using the targeting induced local lesions in a genome method. mstnC315Y can reproduce and have the same survival period as WT medaka. Growth rates of WT and mstnC315Y were measured at juvenile (1-2wk post-hatching), post-juvenile (3-7wk post-hatching) and adult (8-16wk post-hatching) stages. In addition, effects of MSTN on skeletal muscle differentiation were investigated at histological and molecular levels at each developmental stage. As a result, mstnC315Y show a significant increase in body weight from the post-juvenile to adult stage. Hyper-morphogenesis of skeletal muscle in mstnC315Y was accomplished due to hyperplastic growth from post-juvenile to early adult stage, followed by hypertrophic growth in the adult stage. Myf-5 and MyoD were up-regulated in mstnC315Y at the hyperplastic growth phase, while myogenin was highly expressed in mstnC315Y at the hypertrophic growth phase. These indicated that MSTN in medaka plays a dual role for muscle fiber development. In conclusion, MSTN in medaka regulates the number and size of muscle fiber in a temporally-controlled manner during posthatch growth.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Development of an enzyme-linked immunosorbent assay for quantifying vitellogenin in Pacific salmon and assessment of field exposure to environmental estrogens

A competitive enzyme-linked immunosorbent assay was developed to quantitate vitellogenin (VTG) in plasma and serum of coho (Oncorhynchus kisutch) and chinook (O. tshawytscha) salmon. The working range of the assay was 9 to 313 ng/ml (80-20% binding), with 50% binding at 54 ng/ml. The intra-assay and interassay variations at approximately 50% binding were 8.1% (n = 9) and 9.0% (n = 9), respectively. Dilution curves of plasma or serum from coho and chinook females and estrogen-treated males were parallel to the purified coho VTG standard curve. Male plasma samples could be assayed at a minimum dilution of 1:40 (chinook) or 1:75 (coho) without assay interference because of high sample concentration, whereas minimum acceptable dilutions of male serum samples were 1:200 (chinook) or 1:600 (coho). Identification of proper techniques for preserving VTG integrity in plasma and serum samples showed that VTG from both species was robust; both sample types required no protease inhibitor despite subjection to two freeze-thaw cycles. To test its applicability, this assay was used to measure VTG in out-migrating juvenile chinook that were collected from urban and nonurban areas in Puget Sound, Washington, USA. Results showed a small but significant plasma VTG elevation at two urban sites, suggesting that these juveniles may be exposed to environmental estrogens at an early life stage. Also, wild fish tended to have higher plasma VTG levels than hatchery fish collected in the field. Elevation of mean VTG levels was similar to that previously reported in male English sole from the same area, where both males and females exhibited alterations in timing of spawning.

Prochloraz-induced oocyte maturation in rainbow trout (Oncorhynchus mykiss), a molecular and functional analysis

In the present study, we aimed at characterizing the effect of prochloraz, an imidazole fungicide, on the oocyte meiotic maturation process in a freshwater teleost species, the rainbow trout (Oncorhynchus mykiss). Full-grown post-vitellogenic ovarian follicles were incubated in vitro with prochloraz, Luteinizing Hormone (LH), or a combination of prochloraz and LH. The occurrence of oocyte maturation was assessed by monitoring germinal vesicle breakdown (GVBD) after 62-h in vitro incubation. Experiments were repeated in presence of actinomycin D, cycloheximide, or trilostane. The effect of prochloraz on the production of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP), the natural maturation-inducing steroid, was quantified by radioimmunoassay. In addition, the effect of prochloraz on ovarian expression of 12 genes was monitored by real-time PCR. Prochloraz (10(-5)M) administered alone was able to induce 100% GVBD in the most responsive females. The occurrence of GVBD observed after prochloraz stimulation of follicles originating from various females was similar and highly correlated with the occurrence of GVBD observed after stimulation with low LH concentration. In addition, oocyte maturation induced by LH or prochloraz was totally inhibited by actinomycin D, cycloheximide, and trilostane. Similarly to LH, prochloraz was able to trigger 17,20βP production by the ovarian follicle. Finally, prochloraz induced the overexpression of genes participating in 17,20βP production, intercellular communication, and paracrine control of preovulatory follicular differentiation such as igf, igf2, connexin 43, and 20β hydroxysteroid dehydrogenase (hsbd20). Together, our results demonstrate that prochloraz administered alone is able to trigger oocyte maturation through the induction of specific genes, some of them being also triggered by LH. Finally, our results clearly indicate that the effects of prochloraz and LH on oocyte maturation are synergistic.

Effects of nonylphenol on motility and subcellular elements of epididymal rat sperm

Nonylphenol (NP) is an important environmental toxicant and potential endocrine disrupting chemical. The objective of these studies was to determine the effects of NP on epididymal rat sperm in vitro. Epididymal sperm samples from Sprague-Dawley rats were incubated in 1, 10, 100, 250, and 500 microg/ml NP for 1, 2, 3, or 4h. Computer-assisted sperm analysis was used to determine motility. Epifluorescent microscopy was used to determine acrosomal status and flow cytometry was used to determine mitochondrial membrane potential (MMP) and chromatin integrity. Exposure of epididymal rat sperm to 250 or 500 microg/ml NP was highly detrimental to motility (P<0.05), with complete loss of motility observed after exposure to 500 microg/ml NP (P<0.05). The acrosomal integrity of sperm was significantly reduced with the lowest concentration (1 microg/ml) of NP, and higher concentrations resulted in a dose-dependent induction of the acrosomal reaction (P<0.05). Similarly, the percentage of sperm with high MMP declined dramatically after exposure to 100, 250, and 500 microg/ml NP (P<0.05). Duration of NP exposure did not have any effect on motility or MMP and NP did not appear to have detrimental effects on chromatin integrity (P>0.05). These results indicate that major mechanism of action of NP on rat sperm is by adversely affecting their acrosomal integrity. However, NP-induced impaired sperm motility, decreased mitochondrial membrane potential also likely to play an important role in destruction of sperm function.

Degradation dynamics and dissipation kinetics of an imidazole fungicide (Prochloraz) in aqueous medium of varying pH

Laboratory degradation studies were performed in water at pH 4.0, 7.0 and 9.2 using Prochloraz (450 EC) formulation at the concentration of 1.0 (T₁) and 2.0 (T₂) µg/mL. Water samples collected on 0 (2 h), 3, 7, 15, 30, 45, 60 and 90 days after treatments were processed for residue analysis of Prochloraz by HPLC-UV detector. In 60 days, dissipation was 89.1–90.5% at pH 4.0, 84.1–88.2% at pH 7.0, and 92.4–93.8% at pH 9.2 in both treatments. The results indicate that at pH 7.0 the degradation of Prochloraz was much slower as compared to other two. Between pH 4.0 and 9.2 the degradation of compound is little faster at pH 9.2. The half-life periods observed were 18.35 and 19.17 days at pH 4.0, 22.6 and 25.1 days at pH 7.0 and 15.8 and 16.6 days at pH 9.2 at T₁ and T₂ doses respectively.

Effects of the fungicide prochloraz on the sexual development of zebrafish (Danio rerio)

Some chemicals have the potential to adversely affect sexual development through multiple endocrine actions. Prochloraz is an imidazole fungicide that displays diverse mechanisms of action, including inhibition of aromatase activity, inhibition of androgen synthesis, and antagonism of the androgen receptor. The objective of this study was to assess the effects of prochloraz on the sexual development of zebrafish (Danio rerio) in the Fish Sexual Development Test (FSDT) proposed as an OECD test guideline for detection of endocrine disruptors. Zebrafish were exposed to prochloraz (0, 16, 64 or 202 microg/L) for 60 days from 24 h post fertilization. Fish exposed to 202 microg/L prochloraz showed an increased proportion of males. Furthermore, the incidence of intersex and the stages of the gonads were altered in the treated fish compared to the control fish. A significant vitellogenin decrease was observed in both female and male zebrafish at an exposure concentration of 202 microg/L prochloraz. However, in the male fish, significantly increased vitellogenin concentrations were observed in the groups exposed to 16 or 64 microg/L prochloraz. This study serves as a part of the validation of the FSDT and indicates that the FSDT is suitable in detecting compounds with multiple endocrine actions. This is of importance in the assessment of the potential risk of existing and new chemicals.

Correlations of nonylphenol-ethoxylates and nonylphenol with biomarkers of reproductive function in carp (Cyprinus carpio) from the Cuyahoga River

Various chemical and biological measures were determined in carp (Cyprinus carpio) sampled from seven sites along the Cuyahoga River, Ohio; from the relatively pristine headwaters to the lower portion heavily polluted from various industrial, urban and wastewater treatment plants (WWTP). Levels of nonylphenol (NP), nonylphenol ethoxylates (NPEs; NP1EO, NP2EO) and total NPEs (NP plus the NPEs) in fish increased in a downstream direction, with maximal values observed below the discharge of the Akron WWTP. In female fish there were no significant differences between sites in GSI or levels of vitellogenin (VTG) and 17beta-estradiol (E2). However, differences were observed between sites using measures of 11-ketotestosterone (11-KT) and the ratio E2/11-KT. In male fish the highest levels of VTG were observed downstream of the Akron WWTP and a significant correlation (r=85%) between levels of NP and VTG was demonstrated. No site differences were observed in the measures of GSI, E2, 11-KT or the E2/11-KT ratio in male fish. These data suggest that endocrine active chemicals, such as, NP and NPEs are impacting fish downstream of the Akron WWTP; however, further work is warranted to separate linkages to other possible chemical factors in the water.

A Survey on the Expression of IGF-I in the Early Developing Bony Fish with Special Emphasis on the Tilapia,Oreochromis niloticus

The present study investigates the expression of IGF-I in the early developing tilapia (Oreochromis niloticus). IGF-I was detected very early in ontogeny (4-5 days postfertilization, DPF), first in liver and in organs involved in growth and metabolism, thus suggesting a high physiological impact of IGF-I in growth, metabolism, and organogenesis.

In vivo metabolism and organ distribution of a branched 14C-nonylphenol isomer in pond snails, Lymnaea stagnalis L

The branched isomers of p-nonylphenol (NP) are perceived to be more resistant to biodegradation in aquatic environments as well as to have more estrogen-like toxicity than the straight chain isomers. By use of GC-MS, some of them have been identified and found to exist in higher concentrations in the isomeric compound mixture than the straight chain isomers. The investigations of the distribution and metabolism of these branched isomers in aquatic organisms are therefore considered to be important in understanding the mechanisms of toxicity of NP. A single tertiary isomer of NP, 4(3'-,6'-dimethyl-3'-heptyl)-phenol, was synthesized in the laboratory and used in in vivo studies of its organ distribution and metabolism in Lymnaea stagnalis L., following a constant exposure of the organisms to 14C-NP isomer in water over a period of 8 days at an average exposure concentration of 105 ppb (range: 93-116 ppb). The results obtained clearly showed the distribution and bioconcentration of the isomer residues in various internal organs of Lymnaea after uptake in water and food. Analysis of the extracts of the organ tissues and faeces by HPLC and GC-MS after digestion with Pankreatin/beta-glucuronidase and nitric acid, respectively, showed that the isomer was metabolized by conjugation to glucuronic acid and hydroxylation to a catechol. The findings from these studies and their implications in the biotransformation and estrogenicity of NP in Lymnaea stagnalis L. are further discussed in detail in this paper.

Effects of nonylphenol on estrogen receptor conformation, transcriptional activity and sexual reversion in rainbow trout (Oncorhynchus mykiss)

Estrogenic potency of 4-n-nonylphenol diethoxylate, 4-n-nonylphenol (NP) and metabolites were tested using two bioassays: rainbow trout hepatocyte culture and recombinant yeast stably expressing rainbow trout estrogen receptor (rtER) and containing estrogen-dependent reporter genes. Since NP was the only compound active in both systems, its interaction with rtER was studied in more detail. Qualitative and quantitative differences were observed in the presence of 17beta-estradiol (E2) or NP when estrogen-dependent promoters containing one to three estrogen-responsive elements were used in yeast. Moreover, limited proteolysis of rtER after E2 or NP binding presented different patterns after SDS-PAGE analysis suggesting that NP induces a differential conformation of rtER compare to E2. This finding may have important implications with respect to the biological activity of NP. Thus, the effects of NP on the activation of an E2-dependent gene and on sexual differentiation were assessed on all-male trout embryos exposed to NP for 1 h per day for 10 days. Although in situ hybridization demonstrated that E2, and to a lesser extend NP, were able to increase rtER mRNA level in the liver of embryos, no indication of total or partial sexual reversion was observed (even in E2 treated fishes) when the gonads were examined 8 months after hatching.

Prochloraz and nonylphenol diethoxylate inhibit an mdr1-like activity in vitro, but do not alter hepatic levels of P-glycoprotein in trout exposed in vivo

P-glycoproteins (P-gps) encoded by multidrug resistance 1 (mdr1) genes are ATP-dependent transporters located in the cytoplasmic membrane which mediate the efflux of a broad spectrum of hydrophobic compounds from the cell. The tissue distribution of P-gps suggests their role in the organismal defense against xenobiotics by effecting xenobiotic excretion and reducing xenobiotic uptake. In the present work, the interaction of P-gp(s) in the liver and in primary cultured hepatocytes of rainbow trout with two model pollutants was studied - the imidazole fungicide prochloraz and the alkylphenolic surfactant nonylphenol diethoxylate (NP2EO). Using a monoclonal antibody (mAB C219) directed against a conserved P-gp epitope, an immunoreactive protein of 160 kDa was detected in immunoblots of liver extracts from control trout. In sections of control trout livers, immunohistochemistry with the mAB C219 resulted in specific staining of bile canaliculi. In juvenile trout exposed for 7 days to sublethal concentrations of prochloraz (0.027 microM; 0.27 microM) or NP2EO (0.32 microM; 1.30 microM), no changes in levels of hepatic P-gp(s) were found in immunoblot and immunochemical investigations. The efflux of the fluorescent mdr 1 substrate rhodamine 123 (Rh123) from cultured isolated trout hepatocytes was partly inhibited by verapamil and vinblastine, compounds known to interfere with mdr 1-dependent transport. This demonstrates the presence of a mdr1-like mechanism in trout liver which is probably involved in the biliary excretion of hydrophobic xenobiotics. Non-cytotoxic concentrations of prochloraz and NP2EO were tested for effects on the efflux of Rh123 from trout hepatocytes. Prochloraz was a potent inhibitor of the mdr1-like mechanism, being effective at 0.3 microM and above. NP2EO inhibited Rh123 efflux only at the highest concentration tested (31.6 microM). The accumulation and elimination of 14C-prochloraz by cultured trout hepatocytes was not affected by mdr 1-type substrates (Rh123, vinblastine) and a mdr 1 inhibitor (verapamil). This shows that prochloraz is, despite its inhibitory potency, not a substrate of the mdr1-like mechanism in trout liver. The inhibition by prochloraz and NP2EO of the md r1-like mechanism in trout hepatocytes suggests that water pollutants can interfere with P-gp-function in fish and thus may impair the organismal defense against xenobiotics.

In vitro effect of various xenobiotics on trout gill cell volume regulation after hypotonic shock

Their functions and localisation can expose gill cells to volume changes. To maintain their vital functions, these gill cells must regulate their own volume after cellular swelling or shrinkage. Recently, we showed that rainbow trout pavement gill cells in primary culture have the capacity to regulate their own volume after cellular swelling induced by hypotonic shock. This so-called regulatory volume decrease (RVD) is associated with intracellular calcium increase, which occurs as a transient peak followed by a plateau when maintained a hypotonic condition. Return to an isotonic medium restores baseline [Ca2+]i level. In this study, the effect of different xenobiotics on cellular swelling induced RVD and its calcium signal was investigated in trout pavement gill cells in primary culture. These cells were exposed to different pollutants after confluent epithelium was obtained. After 36 h in xenobiotics exposure in vitro, cellular volume and intracellular calcium concentration were measured. Nonylphenol poly- and di-ethoxylate were lethal at concentrations of 10 and 100 microM, respectively. With 10 microM of the diethoxylate form, cells did not die but, unlike non-treated cells, burst during hypotonic shock (2/3rd strength Ringer solution). With 1 microM nonylphenol polyethoxylate (NPnEO), RVD and [Ca2+]i were reduced. Copper (10 and 100 microM) had no significant effect on gill cell volume regulation. However, the heavy metal modified calcium response to hypotonic shock by inhibiting return to baseline level under isotonic conditions. 10 microM prochloraz and 2,4-dichloroaniline had no effect on cell morphology, volume and [Ca2+]i concentration. With 100 microM, however, prochloraz was lethal and dichloroaniline increased baseline [Ca2+]i. These results indicate that the effects observed on gill cells are consistent with the known toxic properties of the molecules tested, thus confirming the validity of primary culture to investigate the toxic effects of xenobiotics on fish gill epithelium.

Metabolic fate of 2,4-dichloroaniline, prochloraz and nonylphenol diethoxylate in rainbow trout: a comparative in vivo/in vitro approach

The metabolism and distribution of 2,4-dichloroaniline (2,4-DCA), prochloraz and 4-n-nonylphenol diethoxylate (NP2EO) were investigated in vivo and in vitro in rainbow trout (Oncorhynchus mykiss). Each compound was administered p.o. (10 mg/kg wet weight) and urine was collected during 48 h (2,4-DCA, prochloraz) or 72 h (NP2EO). Fish were sacrificed, the gall bladder was excised and radioactivity was measured in tissues, viscera and carcasses. Metabolic profiles were performed by radio-HPLC and when possible metabolites were identified by LC/MS. For comparison, the biotransformation of these xenobiotics was also investigated in freshly isolated hepatocytes. The metabolic pathways of 2,4-DCA have been identified leading to the glucuronide conjugate (in vivo) and to the glucuronide conjugate and the hydroxylamine metabolite (in vitro). This difference highlights the usefulness of the hepatocyte system in metabolic studies, since the formation of the hydroxylamine reactive metabolite cannot be demonstrated in vivo. For prochloraz, we observed that residue levels are significantly higher in males than in females for gill, fat, brain and carcasses, however, the reasons for this difference remain unclear. Although, the presence of glucuronide conjugates was detected in vivo and in vitro, the chemical structure of isolated metabolites has to be determined. However, the comparison of the in vivo versus in vitro metabolic profiles indicates that several peaks, probably corresponding to intermediate metabolites, were present only in hepatocyte incubations. Biotransformation of NP2EO occurred in vivo and in vitro in rainbow trout, but did not result in the formation of 4-n-NP. The major metabolite present in bile corresponded to the NP2EO-glucuronide but this metabolite was not found in vitro. It is concluded that hepatocytes may produce a different metabolic pattern than in the whole fish, but may also give evidence of a metabolic pathway difficult to apprehend in vivo.