Characterisation of genes transcriptionally upregulated in the liver of sand goby (Pomatoschistus minutus) by 17α-ethinyloestradiol: identification of distinct vitellogenin and zona radiata protein transcripts

Genome-wide DNA methylation of the liver reveals delayed effects of early-life exposure to 17-α-ethinylestradiol in the self-fertilizing mangrove rivulus

Organisms exposed to endocrine disruptors in early life can show altered phenotype later in adulthood. Although the mechanisms underlying these long-term effects remain poorly understood, an increasing body of evidence points towards the potential role of epigenetic processes. In the present study, we exposed hatchlings of an isogenic lineage of the self-fertilizing fish mangrove rivulus for 28 days to 4 and 120 ng/L of 17-α-ethinylestradiol. After a recovery period of 140 days, reduced representation bisulphite sequencing (RRBS) was performed on the liver in order to assess the hepatic genome-wide methylation landscape. Across all treatment comparisons, a total of 146 differentially methylated fragments (DMFs) were reported, mostly for the group exposed to 4 ng/L, suggesting a non-monotonic effect of EE2 exposure. Gene ontology analysis revealed networks involved in lipid metabolism, cellular processes, connective tissue function, molecular transport and inflammation. The highest effect was reported for nipped-B-like protein B (NIPBL) promoter region after exposure to 4 ng/L EE2 (+ 21.9%), suggesting that NIPBL could be an important regulator for long-term effects of EE2. Our results also suggest a significant role of DNA methylation in intergenic regions and potentially in transposable elements. These results support the ability of early exposure to endocrine disruptors of inducing epigenetic alterations during adulthood, providing plausible mechanistic explanations for long-term phenotypic alteration. Additionally, this work demonstrates the usefulness of isogenic lineages of the self-fertilizing mangrove rivulus to better understand the biological significance of long-term alterations of DNA methylation by diminishing the confounding factor of genetic variability.

Early-life exposure to the endocrine disruptor 17-α-ethinylestradiol induces delayed effects in adult brain, liver and ovotestis proteomes of a self-fertilizing fish

Early-life represents a critically sensitive window to endocrine disrupting chemicals, potentially leading to long-term repercussions on the phenotype later in life. The mechanisms underlying this phenomenon, referred to as the Developmental Origins of Health and Disease (DOHaD), are still poorly understood. To gain molecular understanding of these effects, we exposed mangrove rivulus (Kryptolebias marmoratus) for 28 days post hatching (dph) to 4 and 120 ng/L 17-α-ethinylestradiol, a model xenoestrogen. After 28 days, fish were raised for 140 days in clean water and we performed quantitative label-free proteomics on brain, liver and ovotestis of 168 dph adults. A total of 820, 888 and 420 proteins were robustly identified in the brain, liver and ovotestis, respectively. Effects of 17-α-ethinylestradiol were tissue and dose-dependent: a total of 31, 51 and 18 proteins were differentially abundant at 4 ng/L in the brain, liver and ovotestis, respectively, compared to 20, 25 and 39 proteins at 120 ng/L. Our results suggest that estrogen-responsive pathways, such as lipid metabolism, inflammation, and the innate immune system were affected months after the exposure. In addition, the potential perturbation of S-adenosylmethionine metabolism encourages future studies to investigate the role of DNA methylation in mediating the long-term effects of early-life exposures. SIGNIFICANCE: The Developmental Origins of Health and Disease (DOHaD) states that early life stages of humans and animals are sensitive to environmental stressors and can develop health issues later in life, even if the stress has ceased. Molecular mechanisms supporting DOHaD are still unclear. The mangrove rivulus is a new fish model species naturally reproducing by self-fertilization, making it possible to use isogenic lineages in which all individuals are highly homozygous. This species therefore permits to strongly reduce the confounding factor of genetic variability in order to investigate the effects of environmental stress on the phenotype. After characterizing the molecular phenotype of brain, liver and ovotestis, we obtained true proteomic reaction norms of these three organs in adults after early life stages have been exposed to the common endocrine disruptor 17-α-ethinylestradiol (EE2). Our study demonstrates long-term effects of early-life endocrine disruption at the proteomic level in diverse estrogen-responsive pathways 5 months after the exposure. The lowest tested and environmentally relevant concentration of 4 ng/L had the highest impact on the proteome in brain and liver, highlighting the potency of endocrine disruptors at low concentrations.

Response of gene expression in zebrafish exposed to pharmaceutical mixtures: Implications for environmental risk

Complex mixtures of pharmaceutical chemicals in surface waters indicate potential for mixture effects in aquatic organisms. The objective of the present study was to evaluate whether effects on target gene expression and enzymatic activity of individual substances at environmentally relevant concentrations were additive when mixed. Expression of zebrafish cytochrome P4501A (cyp1a) and vitellogenin (vtg) genes as well as activity of ethoxyresorufin-O-deethylase (EROD) were analyzed after exposure (96h) to caffeine-Caf, ibuprofen-Ibu, and carbamazepine-Cbz (0.05 and 5µM), tamoxifen-Tmx (0.003 and 0.3µM), and after exposure to pharmaceutical mixtures (low mix: 0.05µM of Caf, Ibu, Cbz and 0.003µM of Tmx, and high mix: 5µM of Caf, Ibu, Cbz and 0.3µM of Tmx). Pharmaceuticals tested individually caused significant down regulation of both cyp1a and vtg, but EROD activity was not affected. Exposure to low mix did not cause a significant change in gene expression; however, the high mix caused significant up-regulation of cyp1a but did not affect vtg expression. Up-regulation of cyp1a was consistent with induction of EROD activity in larvae exposed to high mix. The complex mixture induced different responses than those observed by the individual substances. Additive toxicity was not supported, and results indicate the need to evaluate complex mixtures rather than models based on individual effects, since in environment drugs are not found in isolation and the effects of their mixtures is poorly understood.

Genomic organization and transcriptional modulation in response to endocrine disrupting chemicals of three vitellogenin genes in the self-fertilizing fish Kryptolebias marmoratus

Vitellogenin (Vtg) is the precursor of egg yolk proteins, and its expression has been used as a reliable biomarker for estrogenic contamination in the aquatic environment. To examine the biomarker potential of the self-fertilizing killifish Kryptolebias marmoratus Vtgs (Km-Vtgs), full genomic DNAs of Km-Vtgs-Aa, Km-Vtgs-Ab, and Km-Vtgs-C were cloned, sequenced, and characterized. Three Vtg genes in K. marmoratus are tandemly placed in a 550 kb section of the same chromosome. In silico analysis of promoter regions revealed that both the Km-Vtgs-Aa and Km-Vtgs-Ab genes had an estrogen response element (ERE), but the Km-Vtgs-C gene did not. However, all three Km-Vtgs genes had several ERE-half sites in their promoter regions. Phylogenetic analysis demonstrated that the three deduced amino acid residues were highly conserved with conventional Vtgs protein, forming distinctive clades within teleost Vtgs. Liver tissue showed the highest expression of Km-Vtg transcripts in all tested tissues (brain/pituitary, eye, gonad, intestine, skin, and muscle) in response to endocrine disrupting chemical (EDC)-exposed conditions. Km-Vtg transcripts were significantly increased in response to 17β-estradiol (E2), tamoxifen (TMX), 4-n-nonylphenol (NP), bisphenol A (BPA), and octylphenol (OP) over 24hr exposure. The Km-Vtg-A gene was highly expressed compared to the control in response to NP and OP. EDC-induced modulatory patterns of Km-Vtg gene expression were different depending on tissue, gender, and isoforms.

Regulamentação do estrogênio sintético 17α-etinilestradiol em matrizes aquáticas na Europa, Estados Unidos e Brasil

O estrogênio sintético 17α-etinilestradiol, principal componente utilizado em formulações de contraceptivos orais, tem sido apontado como um dos principais compostos responsáveis por provocar efeitos adversos no sistema endócrino de várias espécies. O objetivo deste estudo foi analisar o estado da arte dos dispositivos legais e normativos referentes ao controle desse estrogênio sintético nas águas da Europa e dos Estados Unidos, e traçar um paralelo com a realidade brasileira. No geral, os países têm buscado ampliar a regulamentação e monitoramento de alguns micropoluentes emergentes que antes não eram objeto de atenção por parte dos dispositivos legais. A Europa está mais avançada no que tange à qualidade dos corpos hídricos, enquanto que nos Estados Unidos esta substância é alvo de regulamentação apenas para a água destinada ao consumo humano. No Brasil, ainda não há nenhum dispositivo legal ou normativo que aborde esse estrogênio, o que pode ser associado a uma baixa maturidade do sistema brasileiro quanto ao controle de poluentes hídricos.

Relationship between biomarkers and endocrine-disrupting compounds in wild Girardnichthys viviparus from two lakes with different degrees of pollution

Despite great efforts worldwide to evaluate the effects of endocrine-disrupting compounds (EDCs) in fish, there is little information available about the interactions of EDCs with the disruption of the sexual endocrine axis in fish species with matrotrophic viviparity and intraluminal gestation. To understand these interactions, six sampling campaigns were performed within a period of 1 year in two lakes with different degrees of pollution. A battery of biomarkers of the oestrogenic response was assessed in the liver [vitellogenin, CYP 1A1, epoxide hydrolase activity, and metallothioneins (MT)] and MT in the head of Girardinichthys viviparus. Linear correlation analysis and canonical correspondence analysis were performed to explore the relationship between the oestrogenic response with EDCs and with metals. The biomarker responses were assessed using the water content of EDCs (oestrone, 17-β-oestradiol, oestriol, 17-α-ethinyl oestradiol, total phenols, bisphenol A, nonyl phenol, octyl phenol), as well as the PAHs indene[1,2,3-c,d]pyrene, naphthalene, pyrene, benzo[a]anthracene, benzo[k]fluoranthene and benzo[a]pyrene) and metals (Cu, Fe, Mn, Pb and Zn). Greater disruption of the sexual endocrine axis occurred in fish of both sexes inhabiting the polluted lake whose effects were apparently influenced by CYP 1A1 activity and by 17-α-ethinyl oestradiol. In addition, non-estrogenic mechanisms in the hypothalamus and pituitary glands in male fish were observed, elicited by endogenous levels and the water concentration of Pb. In contrast, in females from the less polluted lake, VTG induction was related to exogenous oestrogens. The disruption of the hypothalamic-pituitary-gonadal axis is a complex process influenced by both endogenous and exogenous factors and contributes to male feminisation by exposure to EDCs.

A developmental hepatotoxicity study of dietary bisphenol A in Sparus aurata juveniles

Previous studies in rats have indicated that a diet enriched with Bisphenol A adversely effects metabolism and reproductive success. In rats exposed to BPA by maternal gavage, alteration in the developmental programming, higher obesity rates and reproductive anomalies were induced. Starting with this evidence, the aim of this study was to provide important insights on the effects induced by a BPA enriched diet, on the reproductive physiology and metabolism of juvenile fish, simulating the scenario occurring when wild fish fed on prey contaminated with environmental BPA. Seabream was chosen as model, as it is one of the primary commercial species valued by consumers and these results could provide important findings on adverse effects that could be passed on to humans by eating contaminated fish. A novel method for measuring BPA in the food and water by affinity chromatography was developed. Analysis of signals involved in reproduction uncovered altered levels of vtg and Zp, clearly indicating the estrogenic effect of BPA. Similarly, BPA up-regulated catd and era gene expression. A noteworthy outcome from this study was the full length cloning of two vtg encoding proteins, namely vtgA and vtgB, which are differently modulated by BPA. Cyp1a1 and EROD activity were significantly downregulated, confirming the ability of estrogenic compounds to inhibit the detoxification process. GST activity was unaffected by BPA contamination, while CAT activity was down regulated. These results collectively confirm the estrogenic effect of BPA and provide additional characterization of novel vtg genes in Sparus aurata.

Occurrence of 17α-ethynylestradiol (EE2) in the environment and effect on exposed biota: a review

17α-ethynylestradiol (EE2) is a synthetic hormone, which is a derivative of the natural hormone, estradiol (E2). EE2 is an orally bio-active estrogen, and is one of the most commonly used medications for humans as well as livestock and aquaculture activity. EE2 has become a widespread problem in the environment due to its high resistance to the process of degradation and its tendency to (i) absorb organic matter, (ii) accumulate in sediment and (iii) concentrate in biota. Numerous studies have reported the ability of EE2 to alter sex determination, delay sexual maturity, and decrease the secondary sexual characteristics of exposed organisms even at a low concentration (ng/L) by mimicking its natural analogue, 17β-estradiol (E2). Thus, the aim of this review is to provide an overview of the science regarding EE2, the concentration levels in the environment (water, sediment and biota) and summarize the effects of this compound on exposed biota at various concentrations, stage life, sex, and species. The challenges in respect of EE2 include the extension of the limited database on the EE2 pollution profile in the environment, its fate and transport mechanism, as well as the exposure level of EE2 for better prediction and definition revision of EE2 toxicity end points, notably for the purpose of environmental risk assessment.

Effects of 17α-ethinyl estradiol exposure on estrogen receptors α and β and vitellogenins A, B and C mRNA expression in the liver of sand goby (Pomatoschistus minutus)

This study aims to characterize the estrogen receptor (er) in sand goby (Pomatoschistus minutus) and determine the temporal effects of 17α-ethinyl estradiol (EE2) on erα and vitellogenin (vtg) gene expression in males. Two partial cDNA sequences (erα and erβ1) are presented showing conserved structural features with ers of other species. Transcript levels for both ers were low in control fish but EE2 exposure (11 ng/L, for 29 days) increased both to a pattern similar to vitellogenic females. The relative expression of three vtg genes (vtga, vtgb and vtgc) along with erα was determined in control and male fish exposed to EE2 (11 ng/L) at multiple time-points over 29 days. All four transcripts were significantly induced due to exposure and expression rose during the time course with distinct temporal patterns and vtga reached a substantially higher level at the end of the time course coinciding with rapid elevation in erα expression.