Mitochondrial metabolism of 17alpha-hydroxyprogesterone in male sea bass (Dicentrarchus labrax): a potential target for endocrine disruptors

A comprehensive review on environmental toxicity of azole compounds to fish

BACKGROUND

Azoles are considered as one of the most efficient fungicides for the treatment of humans, animals, and plant fungal pathogens. They are of significant clinical importance as antifungal drugs and are widely used in personal care products, ultraviolet stabilizers, and in aircraft for its anti-corrosive properties. The prevalence of azole compounds in the natural environment and its accumulation in fish raises questions about its impact on aquatic organisms.

OBJECTIVES

The objective of this paper is to review the scientific studies on the effects of azole compounds in fish and to discuss future opportunities for the risk evaluation.

METHODS

A systematic literature search was conducted on Web of Science, PubMed, and ScienceDirect to locate peer-reviewed scientific articles on occurrence, environmental fate, and toxicological impact of azole fungicides on fish.

RESULTS

Studies included in this review provide ample evidence that azole compounds are not only commonly detected in the natural environment but also cause several detrimental effects on fish. Future studies with environmentally relevant concentrations of azole alone or in combination with other commonly occurring contaminants in a multigenerational study could provide a better understanding.

CONCLUSION

Based on current knowledge and studies reporting adverse biological effects of azole on fish, considerable attention is required for better management and effective ecological risk assessment of these emerging contaminants.

Azoles additively inhibit cytochrome P450 1 (EROD) and 19 (aromatase) in rainbow trout (Oncorhynchus mykiss)

Antifungal azoles are widely used in medicine, agriculture, and material protection and several antifungal azoles have been found in environmental samples. Although these compounds were designed to inhibit fungal enzymes such as lanosterol-14-demethylase (cytochrome P450 (CYP) 51), it is well established that the inhibitory actions of azoles are not specific for fungal CYP isozymes. We refined a gill filament assay to determine the inhibition of CYP1, measured as reduced 7-ethoxyresorufin-O-deethylase (EROD) activity, in rainbow trout (Oncorhynchus mykiss) gill tissue ex vivo. The advantage of this method is that both induction and inhibition of EROD are performed ex vivo. Among thirteen azoles studied, the five that caused the strongest inhibition of gill EROD activity at a concentration of 5 μM were selected for concentration-response assessment. These compounds (bifonazole, clotrimazole, imazalil, miconazole, and prochloraz) showed IC₅₀ values ranging from 0.1 to 1.5 μM. CYP19 (aromatase) inhibition was measured using microsomes from rainbow trout brains. Concentration-response curves for CYP19 inhibition were determined for letrozole, bifonazole, clotrimazole, imazalil, miconazole and prochloraz, which gave IC₅₀ values ranging from 0.02 to 3.3 μM. It was further found that mixtures of the five most potent azoles reduced both CYP1 and 19 catalytic activity in an additive fashion (IC₅₀ = 0.7 μM and 0.6 μM, in the respective assay). Bifonazole (IC₅₀ = 0.1 μM) is not previously known to inhibit CYP1 activity. The additive inhibition of CYP1 and CYP19 catalytic activity is an important finding of the present study. We conclude that this additive action of azoles could mediate adverse impacts on CYP regulated physiological functions in environmentally exposed fish.

Effects of azocyclotin on gene transcription and steroid metabolome of hypothalamic-pituitary-gonad axis, and their consequences on reproduction in zebrafish (Danio rerio)

The widely used organotins have the potential to disrupt the endocrine system, but little is known of underlying mechanisms of azocyclotin toxicity in fish. The objective of the present study was to investigate the impact of azocyclotin on reproduction in zebrafish. Adult zebrafish were exposed to 0.09 and 0.45μg/L azocyclotin for 21days, and effects on steroid hormones and mRNA expression of the genes belonging to the hypothalamic-pituitary-gonad (HPG) axis were investigated. Mass spectrometry methodology was developed to profile steroids within the metabolome of the gonads. They were disrupted as a result of azocyclotin exposure. Alterations in the expression of key genes associated with reproductive endocrine pathways in the pituitary (lhβ), gonad (cyp19a1a, cyp17a1 and 17β-hsd3), and liver (vtg1, vtg2, cyp1a1, comt, ugt1a and gstp1) were correlated with significant reductions in estrogen in both sexes and increased testosterone in females. Azocyclotin-induced down-regulation of cyp19a1a in males suggested a reduction in the rate of estrogen biosynthesis, while up-regulation of hepatic cyp1a1 and comt in both sexes suggested an increase in estrogen biotransformation and clearance. Azocyclotin also induced change in the expression of 17β-hsd3, suggesting increased bioavailability of 11-ketotestosterone (11-KT) in the blood. Furthermore, the down-regulation of lhβ expression in the brains of azocyclotin-exposed fish was associated with inhibition of oocyte maturation in females and retarded spermatogenesis in males. As a histological finding, retarded development of the ovaries was found to be an important cause for decreased fecundity, with down-regulation of vtg suspected to be a likely underlying mechanism. Additionally, relatively high concentrations of azocyclotin in the gonads may have directly caused toxicity, thereby impairing gametogenesis and reproduction. Embryonic or larval abnormalities occurred in the F1 generation along with accumulated burdens of azocyclotin in F1 eggs, following parental exposure. Overall, our results indicate that exposure to azocyclotin can impair reproduction in fish, and induce toxicity related abnormalities in non-exposed offspring.

Steroids in teleost fishes: A functional point of view

Steroid hormones are involved in the regulation of a variety of processes like embryonic development, sex differentiation, metabolism, immune responses, circadian rhythms, stress response, and reproduction in vertebrates. Teleost fishes and humans show a remarkable conservation in many developmental and physiological aspects, including the endocrine system in general and the steroid hormone related processes in particular. This review provides an overview of the current knowledge about steroid hormone biosynthesis and the steroid hormone receptors in teleost fishes and compares the findings to the human system. The impact of the duplicated genome in teleost fishes on steroid hormone biosynthesis and perception is addressed. Additionally, important processes in fish physiology regulated by steroid hormones, which are most dissimilar to humans, are described. We also give a short overview on the influence of anthropogenic endocrine disrupting compounds on steroid hormone signaling and the resulting adverse physiological effects for teleost fishes. By this approach, we show that the steroidogenesis, hormone receptors, and function of the steroid hormones are reasonably well understood when summarizing the available data of all teleost species analyzed to date. However, on the level of a single species or a certain fish-specific aspect of physiology, further research is needed.

Effects of pharmaceuticals present in aquatic environment on Phase I metabolism in fish

The fate of pharmaceuticals in aquatic environments is an issue of concern. Current evidence indicates that the risks to fish greatly depend on the nature and concentrations of the pharmaceuticals and might be species-specific. Assessment of risks associated with the presence of pharmaceuticals in water is hindered by an incomplete understanding of the metabolism of these pharmaceuticals in aquatic species. In mammals and fish, pharmaceuticals are primarily metabolized by cytochrome P450 enzymes (CYP450). Thus, CYP450 activity is a crucial factor determining the detoxification abilities of organisms. Massive numbers of toxicological studies have investigated the interactions of human pharmaceuticals with detoxification systems in various fish species. In this paper, we review the effects of pharmaceuticals found in aquatic environments on fish hepatic CYP450. Moreover, we discuss the roles of nuclear receptors in cellular regulation and the effects of various groups of chemicals on fish, presented in the recent literature.

Determination of 17α-hydroxylase-C17,20-lyase (P45017α) enzyme activities and their inhibition by selected steroidal picolyl and picolinylidene compounds

17α-hydroxylase-C17,20-lyase (P45017α) is a key regulator enzyme of the steroid hormone biosynthesis in both the adrenals and the testes. Inhibition of this enzyme can block androgen synthesis in an early step, and may thereby be useful in the treatment of several androgen-dependent diseases. We developed radio-substrate in vitro incubation methods for the determination of the distinct 17α-hydroxylase and C17,20-lyase activities of the enzyme using rat testicular homogenate as enzyme source. With this method we have studied the inhibiting activity of selected steroidal picolyl and picolinylidene compounds. Tests revealed a substantial inhibitory action of the 17-picolinyliden-androst-4-en-3-one compound.

The in vitro interference of synthetic progestogens with carp steroidogenic enzymes

Synthetic progestogens represent a class of pharmaceuticals widely used in oral contraceptives and in hormone replacement therapies. They reach the aquatic environment through wastewater effluents; however, environmental concentrations and effects on non-target organisms are poorly known. Given the important role of progestogens regulating fish spawning processes, this study aimed at assessing the in vitro interference of four currently used progestogens-drospirenone (DRO), levonorgestrel (LNG), norethindrone (NOR) and cyproterone acetate (CPA) - with key enzymatic activities involved in the synthesis of active steroids in carp (Cyprinus carpio). The enzymatic pathways investigated were (a) CYP17 (C17,20-lyase) and CYP11β involved in the synthesis of androgens, (b) CYP19 that catalyses the aromatization of androgens to estrogens, and (c) 20β-hydroxysteroid dehydrogenase (20β-HSD) responsible for the synthesis of maturation-inducing hormones. All tested progestogens significantly inhibited the synthesis of androgens: DRO (IC50: 3.8 μM) was the strongest inhibitor of CYP17 followed by CPA (IC50s: 183 μM). Moreover, NOR (IC50: 0.4 μM), DRO (IC50: 1.8 μM) and CPA (IC50s: 87 μM) inhibited CYP11β. An inhibition by NOR of ovarian CYP19 activity, and by DRO and CPA of 20β-HSD was also observed, but at rather high concentrations (500 μM). Overall, this study highlights the potential of synthetic progestogens, and particularly DRO and NOR, to interfere with the biosynthesis of androgens in carp gonads.

Characterization of the environmental quality of sediments from two estuarine systems based on different in-vitro bioassays

This study characterizes the environmental quality of sediments from the Arade and Guadiana estuaries using different in-vitro bioassays: a) fish hepatoma cell line (PLHC-1) to determine cytotoxicity and presence of CYP1A and oxidative stress inducing agents; b) gonad subcellular fractions from sea bass (Dicentrarchus labrax) to detect compounds that are likely to act as endocrine disrupters by interfering with the synthesis of androgens (CYP17, CYP11β) and estrogens (CYP19). Approximately 60% of extracts from the Arade estuary were cytotoxic when tested at 60 mg eQsed/mL, while only one sample from Guadiana showed cytotoxicity. Sediments from Arade collected close to harbours and waste water effluents were enriched with CYP1A inducing agents, while those from the upper Guadiana induced oxidative stress in PLHC-1 cells. On the other hand, several extracts from both estuaries were able to significantly inhibit CYP17, CYP11β and CYP19 activities in gonad subcellular fractions of sea bass, which indicates the presence of endocrine disrupters, particularly in several sites from the Arade estuary. Overall, the study highlights the usefulness of in-vitro bioassays to identify those sediments that could pose risk to aquatic organisms and that require further action to improve their environmental quality.

Metabolism of the polycyclic musk galaxolide and its interference with endogenous and xenobiotic metabolizing enzymes in the European sea bass (Dicentrarchus labrax)

This study investigates the metabolism and mode of action of galaxolide (HHCB) in the European sea bass -Dicentrarchus labrax- following a single intraperitoneal injection of 50 mg HHCB/kg body weight. In addition, a group of fish was injected with 50 mg/kg of ketoconazole (KCZ), a fungicide that is known to interfere with different Cyp isoenzymes. HHCB was actively metabolised by sea bass and acted as a weak inhibitor of the synthesis of oxyandrogens in gonads of male fish. Both, HHCB and a hydroxylated metabolite were detected in bile. The fungicide ketoconazole was a strong inhibitor of Cyp11β and Cyp3a-catalyzed activities. The work contributes to the better understanding of the impact of synthetic musks on fish and proposes the determination of HHCB and/or its hydroxylated metabolite in bile as a tool to assess environmental exposure in wild fish.

Hydroxylated PAHs alter the synthesis of androgens and estrogens in subcellular fractions of carp gonads

Four different polycyclic aromatic hydrocarbons (naphthalene, phenanthrene, pyrene, chrysene) and their hydroxylated metabolites (1-hydroxynaphthalene, 9-hydroxy-phenanthrene, 1-hydroxypyrene, 1-hydroxychrysene) were investigated for their ability to alter the synthesis of steroids by testes and ovaries of the carp Cyprinus carpio. Parental compounds had no significant effect on C17,20-lyase (CYP17), CYP11β and 11β-HSD catalyzed activities, all of them involved in the synthesis of active androgens in carp testes. Conversely, hydroxylated metabolites significantly inhibited C17,20-lyase and CYP11β activities; the strongest inhibitor was 9-hydroxyphenanthrene with IC50s of 10.8 and 31.3 μM for CYP17 and CYP11β, respectively. As for the biosynthesis of estrogens, only 9-hydroxyphenanthrene had a significant inhibitory effect on ovarian CYP19 activity (IC50: 4.3 μM). The study highlights the potential of hydroxylated-polycyclic aromatic hydrocarbons, and particularly 9-hydroxyphenanthrene, to disrupt the synthesis of androgens and estrogens in carp gonads.

Ibuprofen reduces zebrafish PGE(2) levels but steroid hormone levels and reproductive parameters are not affected

Prostaglandins are important regulators of reproductive function in fish. Analgesics like aspirin and ibuprofen are prostaglandin inhibitors and have been detected in freshwater systems at ng/L-μg/L levels. We investigated whether ibuprofen would affect prostaglandin and sex steroid hormone levels in adult zebrafish (Danio rerio) and if expression levels of genes involved in steroidogenesis and prostaglandin synthesis were affected. Zebrafish were exposed to moderate concentrations of ibuprofen (21, 201 or 506 μg/L) for 7 days in a semi-static test system. Ibuprofen concentrations were close to nominal levels and decreased by a maximum of 12-13% over 24 h. Prostaglandin E(2) (PGE(2)) levels in whole body homogenates of males and ovaries of females decreased in a monotonic dose-response relationship whereas male 11-ketotestosterone levels and ovarian 17β-estradiol levels remained unchanged. Ibuprofen did not have an influence on vitellogenin levels, female gonadosomatic index or cumulative egg production and no dose-response relationship in ovarian and testicular expression levels of the investigated genes was observed. This study shows that ibuprofen reduces PGE(2) levels in male and female zebrafish but has no consistent effects on other investigated reproductive parameters.

Alternatives to in vivo tests to detect endocrine disrupting chemicals (EDCs) in fish and amphibians--screening for estrogen, androgen and thyroid hormone disruption

Endocrine disruption is considered a highly relevant hazard for environmental risk assessment of chemicals, plant protection products, biocides and pharmaceuticals. Therefore, screening tests with a focus on interference with estrogen, androgen, and thyroid hormone pathways in fish and amphibians have been developed. However, they use a large number of animals and short-term alternatives to animal tests would be advantageous. Therefore, the status of alternative assays for endocrine disruption in fish and frogs was assessed by a detailed literature analysis. The aim was to (i) determine the strengths and limitations of alternative assays and (ii) present conclusions regarding chemical specificity, sensitivity, and correlation with in vivo data. Data from 1995 to present were collected related to the detection/testing of estrogen-, androgen-, and thyroid-active chemicals in the following test systems: cell lines, primary cells, fish/frog embryos, yeast and cell-free systems. The review shows that the majority of alternative assays measure effects directly mediated by receptor binding or resulting from interference with hormone synthesis. Other mechanisms were rarely analysed. A database was established and used for a quantitative and comparative analysis. For example, a high correlation was observed between cell-free ligand binding and cell-based reporter cell assays, between fish and frog estrogenic data and between fish embryo tests and in vivo reproductive effects. It was concluded that there is a need for a more systematic study of the predictive capacity of alternative tests and ways to reduce inter- and intra-assay variability.

The social status of the male Nile tilapia (Oreochromis niloticus) influences testis structure and gene expression

Dominant and territorial behaviour are known social phenomena in cichlids and social stress influences reproduction and growth. The gonadotropic hormones trigger spermatogenesis and subordinate males have typically lower levels of gonadotropins than dominant males. In this study, we compared testis morphology and gene expression of dominant and subordinate Nile tilapia males (d- and s-males) in socially stable communities. The d-males had the highest gonadosomatic index but they were not the largest animals in the majority of studied cases. Long-term d-males showed large groups of Leydig cells and hyperplasia of the tunica albuginea due to numerous cytochrome-P450-11β-hydroxylase (Cyp11b) expressing myoid cells. Increased Cyp11b expression in d-males was reflected by elevated 11-ketotestosterone plasma values. However, immunofluorescence microscopy and expression analysis of selected genes revealed that most s-males conserved their capability for spermatogenesis and are, therefore, ready for reproduction when the social environment changes. Moreover, in s-males gene expression analysis by quantitative RT-PCR showed increased transcript levels for germ line-specific genes (vasa,sox2anddmc1) and Sertoli-specific genes (amh,amhrIIanddmrt1) whereas gene expression of key factors for steroid production (sf1andcyp11b) were reduced. The Nile tilapia is a promising model to study social cues and gonadotropic signals on testis development in vertebrates.

Can pharmaceuticals interfere with the synthesis of active androgens in male fish? An in vitro study

The in vitro interference of fibrate (gemfibrozil, clofibrate, clofibric acid), anti-inflammatory (ibuprofen, diclofenac), and anti-depressive (fluoxetine, fluvoxamine) drugs with key enzymatic activities-C17,20-lyase and CYP11β-involved in the synthesis of active androgens in gonads of male carp have been investigated. Among the tested compounds, fluvoxamine and fluoxetine were the strongest inhibitors of C17,20-lyase and CYP11β enzymes, with IC50s in the range of 321-335 μM and 244-550 μM, respectively. To our knowledge this is the first report on the interaction of pharmaceutical compounds with enzymatic systems involved in the synthesis of oxy-androgens. As oxy-androgens are known to influence spermatogenesis and stimulate reproductive behavior and secondary sexual characteristics in male fish, this work highlights the need for further investigating these endpoints when designing specific in vivo studies to assess the endocrine disruptive effect of pharmaceuticals in fish.

The interference of nitro- and polycyclic musks with endogenous and xenobiotic metabolizing enzymes in carp: an in vitro study

Synthetic musks are widely used as perfuming agents in products, such as cosmetics, detergents, and soaps. The increased detection of these substances in the aquatic environment and their high bioconcentration potential raises concerns about potential effects on aquatic species. This work aimed at assessing the interactions of the most widely used musks: nitromusks (musk xylene, musk ketone) and polycyclic musks (celestolide, galaxolide, and tonalide) with fish enzymatic systems involved in both xenobiotic and endogenous metabolism. Therefore, CYP catalyzed pathways were investigated in carp liver microsomes (CYP1A, CYP3A), ovarian microsomes (CYP19) and testicular mitochondria (CYP17 and CYP11beta) using standard substrates. Phase II activities (UDP-glucuronosyltransferases and sulfotransferases) were determined in carp liver microsomes and cytosol, respectively. Polycyclic musks (galaxolide and tonalide) were stronger inhibitors of CYP3A- (IC(50): 68-74 microM), CYP17- (IC(50): 213-225 microM), CYP11beta- and CYP19-catalyzed activities than nitromusks, while the latter showed higher ability to interfere with CYP1A (IC(50): 35-37 microM). The sulfation of estradiol was also significantly inhibited by tonalide and galoxolide (IC(50): 140-294 microM). Overall, polycyclic musks showed the highest potential to interfere with those activities involved in the synthesis and metabolism of steroids while nitromusks mainly interfered with xenobiotic metabolism (CYP1A-catalyzed reactions). The obtained data suggest that CYP isoforms are potentially sensitive targets of synthetic musk substances in fish.