Publications by authors named "Nadine Le Belle"

7 Publications

  • Page 1 of 1

Detection of the anti-androgenic effect of endocrine disrupting environmental contaminants using in vivo and in vitro assays in the three-spined stickleback.

Aquat Toxicol 2009 May 21;92(4):228-39. Epub 2009 Feb 21.

University of Bergen, Institute of Biology, HIB, Thormohlensgt. 55, 5020 Bergen, Norway.

We have previously developed a novel in vitro assay that utilises cultures of primed female stickleback kidney cells for the screening of potential androgenic and anti-androgenic environmental contaminants. Stickleback kidney cells are natural targets for steroid hormones and are able to produce a protein, spiggin, in response to androgenic stimulation. We undertook a combined in vivo/in vitro study where we used the magnitude of spiggin production as an endpoint to test the anti-androgenic properties of the pharmaceutical androgen antagonist flutamide and three environmental contaminants: the organophosphate insecticide fenitrothion, the urea-based herbicide linuron and the fungicide vinclozolin. In vitro, kidney cells were exposed to a range of concentrations [from 10(-14) M (2.5 pg/L) up to 10(-6) M (280 microg/L)] of the test compounds alone for determining agonist activities, or together with 10(-8) M (3 microg/L) dihydrotestosterone (DHT) for determining antagonist activities. An in vivo flow-through aquarium-based study was carried out in parallel. Female sticklebacks were exposed to a range of concentrations of the same chemicals alone or in combination with DHT (5 microg/L) for 21 days. All of the compounds significantly inhibited DHT-induced spiggin production in a concentration-dependent manner in both the in vitro (FN > or = FL > or = LN > VZ) and in vivo (FN > FL > or = VZ > LN) assays. Fenitrothion and flutamide inhibited spiggin production in vitro at a concentration as low as 10(-12) M (P < 0.05), while linuron and vinclozolin inhibited DHT-induced spiggin production at concentrations of 10(-10) M (P < 0.05) and 10(-6) M (P < 0.001) respectively. Similarly, fenitrothion and flutamide were the most potent chemicals in vivo and significantly reduced DHT-induced spiggin production at a concentration of 10 microg/L and 25 microg/L respectively (P < 0.01). Both linuron and vinclozolin induced a significant decrease in DHT-induced spiggin production at a concentration of 100 microg/L when tested in vivo. In addition, kidney cell primary culture was used to test the (anti-)androgenic effects of the major environmental contaminants: oestradiol (E2), nonylphenol (NP) and bisphenol A (BPA) for the first time in teleosts. We observed that these compounds were able to significantly inhibit spiggin production at high doses (E2: 270 microg/L; NP: 2.2 microg/L; BPA: 2.3 microg/L). When tested in the absence of DHT, none of the compounds showed a significant agonistic activity in either in vivo or in vitro assays. Overall, our data further demonstrate that kidney cell primary culture is a reliable and a sensitive screening tool for the detection of (anti-)androgenic compounds. In addition, our study represents the first attempt to develop a combined in vivo/in vitro screening strategy for assessing the effects of (anti-)androgenic endocrine disrupters.
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http://dx.doi.org/10.1016/j.aquatox.2009.02.006DOI Listing
May 2009

Development of real-time RT-PCR assays for eel gonadotropins and their application to the comparison of in vivo and in vitro effects of sex steroids.

Gen Comp Endocrinol 2007 Aug-Sep;153(1-3):333-43. Epub 2007 Mar 2.

USM 0401, UMR 5178 CNRS/MNHN/Université Pierre et Marie Curie, Biologie des Organismes Marins et Ecosystèmes, Département des Milieux et Peuplements Aquatiques, Muséum National d'Histoire Naturelle, 75231 Paris Cedex 05, France.

Gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are key factors in the brain-pituitary-gonad axis and understanding their regulation remains essential for future management of eel reproduction. In this regard, we developed quantitative real-time RT-PCR (qrtRT-PCR) assays for the expression of European eel LHbeta, FSHbeta and GPalpha subunits, using the Light Cycler system. The qrtRT-PCR was adapted to permit detection of the three gonadotropin subunit mRNAs in individual pituitaries and in dispersed pituitary cells. The validated assays were applied to investigate the effects of sex steroids (estrogens and androgens) on gonadotropin subunit expression, in vivo in steroid-injected eels, and in vitro by steroid treatments of primary cultures of eel pituitary cells. In vivo, a stimulation of LHbeta mRNA was observed after estradiol (E2) treatments, while testosterone (T) or the non-aromatizable androgen dihydrotestosterone (DHT) had no effect. Concerning FSHbeta expression, slight but non-significant decreases were observed after both E2 and androgen treatments. Different results were obtained in vitro: E2 induced an increase in FSHbeta mRNA levels but had no effect on LHbeta expression. In contrast, androgens (T and DHT) stimulated LHbeta expression while no significant variation was observed on FSHbeta mRNA levels following androgen treatment. Concerning the GPalpha mRNA, no significant effect of sexual steroids was observed in vivo or in vitro. This demonstrated specific direct actions of steroids on gonadotropin subunit expression. The differences observed between in vivo and in vitro experiments may be explained by the involvement of cerebral control, including GnRH and dopamine neurons, and their specific regulation by sex steroids. The data indicate that sex steroid feedbacks on gonadotropins are exerted via multiple pathways, indirectly at the brain level and directly on pituitary gonadotrope cells.
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http://dx.doi.org/10.1016/j.ygcen.2007.02.027DOI Listing
October 2007

Development of a stickleback kidney cell culture assay for the screening of androgenic and anti-androgenic endocrine disrupters.

Aquat Toxicol 2006 Aug 14;79(2):158-66. Epub 2006 Jul 14.

Department of Biology, University of Bergen, Institute of Biology, HIB, Thormohlensgt. 55, 5020 Bergen, Norway.

Issues raised by the presence in the environment of chemicals able to mimic or antagonize the action of androgenic hormones are of growing concern. Here we report the development of a novel in vitro test for the screening of (anti-)androgenic chemicals, based on primary cultures of stickleback kidney cells that produce a protein, the spiggin, in response to androgenic stimulation. Cell spiggin content was measured by ELISA. Comparison between cell cultures from quiescent males, photoperiodically stimulated males, control females and dihydrotestosterone (DHT)-primed females led to the selection of cell cultures from DHT-primed females for the development of a standardized protocol. 48h of treatment with androgens proved to be sufficient to induce concentration-dependent increase in spiggin cell content with a high sensitivity. DHT induced a significant spiggin increase at 10(-12)M, while testosterone (T) and the teleost specific androgen 11-ketotestosterone (11-KT) had a significant effect at 10(-10)M. Maximal responses were obtained with 10(-8)M DHT and 10(-6)M T and 11-KT. This indicates a higher sensitivity to DHT than to T and 11-KT, in agreement with previous data on stickleback kidney androgen receptor affinity. No effect was observed with other steroids or thyroid hormone, indicating the androgen specificity of the test. The anabolic steroid 17beta-Trenbolone (TB) was able to stimulate spiggin synthesis in a concentration-dependent manner with a significant effect at a concentration as low as 10(-10)M, and a maximal effect at 10(-6)M. The synthetic human androgen receptor antagonist, flutamide had no effect alone, but concentration-dependently inhibited the stimulatory effect of 10(-8)M 11-KT with a complete inhibition at 10(-6)M flutamide. This cell culture system provides an innovative tool for the rapid and sensitive screening of androgenic and anti-androgenic properties of environmental contaminants.
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http://dx.doi.org/10.1016/j.aquatox.2006.06.005DOI Listing
August 2006

Androgen-dependent stimulation of brain dopaminergic systems in the female European eel (Anguilla anguilla).

Endocrinology 2006 Jun 16;147(6):2964-73. Epub 2006 Mar 16.

Unité Scientifique de Muséum 0401, Centre National de la Recherche Scientifique/MNHN/UPMC Biologie des Organismes Marins et Ecosystèmes Département des Milieux et Peuplements Aquatiques, Muséum National d'Histoire Naturelle, 75231 Paris, France.

Dopamine (DA), a neurotransmitter present in all vertebrates, is involved in processes such as motor function, learning and behavior, sensory activities, and neuroendocrine control of pituitary hormone release. In the female eel, we analyzed how gonadal steroids regulate brain expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of DA. TH mRNA levels were assayed by quantitative real-time RT-PCR. TH-positive nuclei were also localized by in situ hybridization (ISH) and immunohistochemistry, and the location of TH nuclei that project to the pituitary was determined using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindicarbocyanine perchlorate retrograde tracing. Chronic in vivo treatment with testosterone increased TH mRNA specifically in the periglomerular area of the olfactory bulbs and in the nucleus preopticus anteroventralis (NPOav). NPOav was labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindicarbocyanine perchlorate, showing that this nucleus is hypophysiotropic in the eel. The nonaromatizable 5alpha-dihydrotestosterone gave identical results in both areas, whereas 17beta-estradiol had no stimulatory effect, showing that the observed stimulatory effects of testosterone were androgen dependent. In teleosts, DA neurons originating from the NPOav directly inhibit gonadotropic function, and our results indicate an androgen-dependent, positive feedback on this neuroendocrine control in the eel. In mammals, DA interneurons in the olfactory bulbs are involved in the enhancement of olfactory sensitivity and discrimination. Our results in the European eel suggest an androgen-dependent stimulation of olfactory processing, a sensory function believed to be important in eel navigation during its reproductive migration toward the oceanic spawning grounds. To our knowledge, this is the first evidence from any vertebrate of an androgen-dependent effect on DAergic activity in the olfactory bulbs, providing a new basis for understanding the regulation by gonadal steroids of central DAergic systems in vertebrates.
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http://dx.doi.org/10.1210/en.2005-1477DOI Listing
June 2006

Differential regulation of luteinizing hormone and follicle-stimulating hormone expression during ovarian development and under sexual steroid feedback in the European eel.

Neuroendocrinology 2005 16;81(2):107-19. Epub 2005 Jun 16.

Department of Aquaculture, Swedish University of Agricultural Sciences, Umea, Sweden.

Pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are, in teleosts as in mammals, under the control of hypothalamic factors and steroid feedbacks. In teleosts, feedback regulations largely vary depending on species and physiological stage. In the present study the regulation of FSH and LH expression was investigated in the European eel, a fish of biological and phylogenetical interest as a representative of an early group of teleosts. The eel FSHbeta subunit was cloned, sequenced and together with earlier isolated eel LHbeta and glycoprotein hormone alpha (GPalpha) subunits used to study the differential regulation of LH and FSH. In situ hybridization indicated that FSHbeta and LHbeta are expressed by separate cells of the proximal pars distalis of the adenohypophysis, differently from the situation in mammals. The profiles of LHbeta and FSHbeta subunit expression were compared during experimental ovarian maturation, using dot-blot assays. Expression levels for LHbeta and GPalpha increased throughout ovarian development with a positive correlation between these two subunits. Conversely, FSHbeta mRNA levels decreased. To understand the role of sex steroids in these opposite variations, immature eels were treated with estradiol (E2)and testosterone (T), both steroids being produced in eel ovaries during gonadal development. E2 treatment induced increases in both LHbeta and GPalpha mRNA levels, without any significant effect on FSHbeta. In contrast, T treatment induced a decrease in FSHbeta mRNA levels, without any significant effect on the other subunits. These data demonstrate that steroids exert a differential feedback on eel gonadotropin expression, with an E2-specific positive feedback on LH and a T-specific negative feedback on FSH, leading to an opposite regulation of LH and FSH during ovarian development.
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http://dx.doi.org/10.1159/000086404DOI Listing
August 2005

Dopamine inhibits luteinizing hormone synthesis and release in the juvenile European eel: a neuroendocrine lock for the onset of puberty.

Biol Reprod 2004 Nov 30;71(5):1491-500. Epub 2004 Jun 30.

USM 0401, UMR 5178 CNRS/MNHN/UPMC Biologie des Organismes Marins et Ecosystèmes, DMPA, Muséum National d'Histoire Naturelle, 7 rue Cuvier, 75231 Paris Cedex 05, France.

In various adult teleost fishes, LH ovulatory peak is under a dual neurohormonal control that is stimulatory by GnRH and inhibitory by dopamine (DA). We investigated whether DA could also be involved in the inhibitory control of LH at earlier steps of gametogenesis by studying the model of the European eel, Anguilla anguilla, which remains at a prepubertal stage until the oceanic reproductive migration. According to a protocol previously developed in the striped bass, eels received sustained treatments with GnRH agonist (GnRHa), DA-receptor antagonist (pimozide), and testosterone (T) either alone or in combination. Only the triple treatment with T, GnRHa, and pimozide could trigger dramatic increases in LH synthesis and release as well as in plasma vitellogenin levels and a stimulation of ovarian vitellogenesis. Thus, in the prepubertal eel, removal of DA inhibition is required for triggering GnRH-stimulated LH synthesis and release as well as ovarian development. To locate the anatomical support for DA inhibition, the distribution of tyrosine hydroxylase (TH) in the brain and pituitary was studied by immunocytochemistry. Numerous TH-immunoreactive cell bodies were observed in the preoptic anteroventral nucleus, with a dense tract of immunoreactive fibers reaching the pituitary proximal pars distalis, where the gonadotrophs are located. This pathway corresponds to that mediating the inhibition of LH and ovulation in adult teleosts. To our knowledge, this is the first demonstration of a pivotal role for DA in the control of LH and puberty in a juvenile teleost. These data support the view that DA inhibition on LH secretion is an ancient evolutionary component in the neuroendocrine regulation of reproduction that may have been partially maintained throughout vertebrate evolution.
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http://dx.doi.org/10.1095/biolreprod.104.030627DOI Listing
November 2004

[An antagonist to GnRH in the control of reproduction in teleost fish: dopaminergic inhibition. Ancestral origin and differential conservation within vertebrates?].

J Soc Biol 2004 ;198(1):61-7

DEPSN , UPR CNRS 2197, Institut de Neurobiologie Alfred Fessard, CNRS, 91198 Gif-sur-Yvette, France.

In mammals, the neurohormonal control of the pituitary gonadotropes is provided by the gonadoliberin GnRH. Several studies on teleost fish indicate that a single positive control by GnRH is not a general rule among vertebrates. Peter and colleagues presented the first evidence of an inhibitory neurohormonal factor, "GRIF" (gonadotropin-release inhibiting factor). They induced a preovulatory LH surge by injuring particular brain areas in the goldfish. Subsequent in vivo and in vitro studies identified dopamine as GRIF, and neuroanatomical investigations have demonstrated that dopaminergic neurones in the anterior preoptic area projecting to the pituitary represent the anatomical substrate for GRIF activity. An inhibitory role of dopamine on the control of LH and ovulation/spermiation has been evidenced in many adult teleosts, including its implications for aquaculture. However, dopamine does not play an inhibitory role in all adult teleosts. As regards the early stages of gametogenesis and especially the control of puberty, a role for dopamine has been suggested or rejected depending on species. The European eel has a unique life cycle with a long prepubertal stage, which has made it a useful model to demonstrate the key-role of dopamine in the control of puberty. Data from tetrapods suggest that the role of dopamine as a GRIF is not restricted to the teleosts, but that it may have an ancient evolutionary origin, and has been differentially conserved throughout vertebrate evolution.
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July 2004