Elsevier

Environmental Research

Volume 134, October 2014, Pages 158-168
Environmental Research

Perfluorooctane sulfonate effects on the reproductive axis in adult male rats

https://doi.org/10.1016/j.envres.2014.07.006Get rights and content

Highlights

  • PFOS exposure disrupts male reproductive axis activity at different levels.

  • PFOS modifies noradrenaline concentration, gene expression and the release of GnRH.

  • PFOS alters the gene expression and the secretion of gonadotropin hormones.

  • Testosterone secretion is inhibited by the exposure to PFOS.

  • The reproductive alterations exerted by PFOS could be due to structural changes.

Abstract

Perfluorooctane sulfonate (PFOS) is a neurotoxic agent and it can disrupt the endocrine system activity. This work was undertaken to evaluate the possible effects of PFOS exposure on the hypothalamic–pituitary–testicular axis (HPT) in adult male rats, and to evaluate the possible morphological alterations induced by PFOS in the endocrine tissues of this axis. Adult male rats were orally treated with 0.5; 1.0; 3.0 and 6.0 mg of PFOS/kg/day for 28 days. After PFOS exposure, hypothalamic noradrenaline concentration increased in the anterior hypothalamus and in the median eminence, not changing in the mediobasal hypothalamus. PFOS treated rats presented a decrease of the gonadotropin releasing hormone (GnRH) gene expression, increasing the mRNA levels of the luteinizing hormone (LH) in rats treated with all doses administered except with the dose of 6 mg/kg/day. PFOS also induced a raise of the follicle stimulating hormone (FSH) gene expression in the animals exposed to 0.5 and 1.0 mg of PFOS/kg/day. After PFOS exposure, hypothalamic GnRH concentration was modified, LH and testosterone release was inhibited and FSH secretion was stimulated. Moreover, PFOS induced several histopathological alterations in the hypothalamus, pituitary gland and testis. The results obtained in the present study suggest in general terms that PFOS can inhibit the physiological activity of the reproductive axis in adult male rats, which could be explained, at least in part, by the structural alterations showed in the animals exposed to this chemical: very dense chromatin, condensed ribosomes and a loss of the morphology in the hypothalamus; a degeneration of the gonadotrophic cells, as well as a loss and degeneration of the spermatozoids and a very marked edema in the testis.

Introduction

Perfluorooctane sulfonate (PFOS) is a fluorinated organic compound declared as a Persistent Organic Pollutant (Stockholm Convention, 2009), having extreme thermal, biological, and chemical stability as well as hydrophobic and lipophobic characteristics. This chemical is extremely persistent in the environment, it is neither hydrolyzed, nor photolyzed or degraded by any of the environmental conditions tested (Organisation for Economic Co-operation and Development (OECD), 2002). Perhaps for this reason, and according to the European Directive 2013/39/EU, this chemical is a priority hazardous substance (European Comission, 2013). This fact has been reported by several authors, who showed that this chemical is present in many environmental compartments (Gómez et al., 2011, Corsolini et al., 2012, Kwadijk et al., 2013). In addition, it is the final product of the degradation of more than 50 fluorinated organic compounds. Therefore, it has shifted among biological populations via biological concentration and magnification, leading to excessive accumulation among the higher trophic level of the food chain (such as predator and human beings) (Houde et al., 2006, Tittlemier et al., 2007). The diet is the main exposure route of perfluoralkyl acids in humans only exposed to background levels (Domingo et al., 2012, Vestergren et al., 2013). Previous studies have shown that fish and seafood accounted for >50% of PFOS exposures in nonoccupationally exposed populations in Canada (Fromme et al., 2007), Spain (Ericson et al., 2008), and Poland (Falandysz et al., 2006), since after cooking, amounts of PFOS largely remain unchanged (Bhavsar et al., 2014). Analyses of PFOS and perfluorooctanoic acid have been carried out in river water samples and in the different stages of drinking water treatment plants (DWTP) which have recently improved its conventional treatment process by adding ultrafiltration and reverse osmosis in a parallel treatment line (Flores et al., 2013). Conventional and advanced treatments carried in several pilot plants and in DWTP have shown that neither preoxidation, sand filtration, nor ozonation, removed both perfluorinated compounds (Flores et al., 2013).

PFOS has been extensively used in industry, being the 3M company the principal producer (United States Environmental Protection Agency (US-EPA, 2000). This compound is widely used as surfactant, in lubricants, polymers, fire fighting foams, in the photographic industry, as component of adhesives and paper coatings, in cosmetics, pesticides and food packaging, as well as in semiconductor production or in hydraulic fluids in the aviation industry. PFOS is a surface-active substance and it is used as water and fat repellent in textiles, carpets, etc. (US-EPA (United States Environmental Protection Agency), 2000, Beach et al., 2006). Furthermore, studies focused on people not occupationally exposed to PFOS in the United States, Colombia, Brazil, Belgium, Italy, Poland, India, Malaysia and Korea, showed that this xenobiotic is the most predominant perfluoroalkyl compound of those tested in blood, with a maximum value of 30 ng/ml (in United States and Poland) and a minimum of 3 ng/ml (in India) (Kannan et al., 2004).

PFOS is accumulated in different tissues like liver and kidney, brain and in several endocrine glands like pituitary, adrenal gland and gonads (Austin et al., 2003). The hypothalamus is the one of the brain regions where the major concentration of PFOS is detected, being three times higher than in other organs and physiological systems studied, fact shown in rats (Austin et al., 2003).

It is well known that PFOS is a neurotoxic agent (Johansson et al., 2008, Mariussen, 2012, Pereiro, 2012, Lee et al., 2012, Long et al., 2013). In addition and according to previous studies, PFOS can disrupt the neuroneuroendocrine system activity, fact evidenced in mammals (Austin et al., 2003, Chang et al., 2009, Ribes et al., 2010, Zhao et al., 2011, Pereiro, 2012; Pereiro et al. 2013) as well as in fish (Fang et al., 2012, Du et al., 2013). It can affect the hypothalamic–pituitary–testicular (HPT) and the hypothalamic–pituitary–adrenal axes function (Austin et al., 2003, Ribes et al., 2010, Zheng et al., 2011, Pereiroet al., 2014), having similar endocrine effects than other endocrine disruptors (Harvey and Everett, 2006, Lafuente, 2013). More concretely, this chemical seems to alter the estrous cycle (Austin et al., 2003) and to exert estrogenic activity (Fang et al., 2012) by modifying the gene expression of hypothalamic estrogens receptors in adult male rats (Lafuente et al., 2013) and acting as an estrogen receptor agonist (Fang et al., 2012, Du et al., 2013) as well as interfering with steroidogenesis in mice (Wan et al., 2011) and zebrafish (Du et al., 2013).

On the other hand, the regulation of the HPT axis activity has been well established (Matsumoto and Bremner, 1987, Schlatt and Ehmcke, 2014). Noradrenaline stimulates gonadotrophin-releasing hormone (GnRH) release (Herbison, 1997, Han and Herbison, 2008) in hypothalamus, which stimulates luteinizing hormones (LH) and follicle stimulating hormone (FSH) secretion by the pituitary gland (Schlatt and Ehmcke, 2014). At the testicular level, LH stimulates testosterone synthesis in Leydig cells and FSH regulates the spermatogenesis in the Sertoli cells (Schlatt and Ehmcke, 2014). Based on these regulatory mechanisms, many xenobiotics can alter the reproductive axis activity in the male by modifying the noradrenaline concentration and/or the gene expression and secretion of GnRH at the hypothalamic level, by altering the gene expression of LH and FSH and/or the release of these hormones in the pituitary gland, as well as acting on the testis by changing testosterone secretion. Therefore, PFOS might modify the reproductive axis activity in different ways: 1) possible alterations observed in testicular function could be due to several actions of the chemical in the hypothalamus and/or in the pituitary gland; 2) PFOS effects on gonadotropin hormones could be explained by the action of this xenobiotic on different hypothalamic neuromodulators and/or on testosterone secretion, and finally; 3) PFOS could induce several hypothalamic alterations by modifying gonadotropin hormones secretion at the pituitary level and/or changing testosterone release by the Leydig cells. Taking into account these physiological relationships, PFOS effects on the male reproductive axis should be evaluated in in vivo experimental models with intact HPT axis function, in order to study several neuroendocrine markers at the same time in the same animal.

In view of the facts above mentioned, the present study was undertaken to evaluate the possible effects of PFOS exposure on HPT axis in adult male rats, by (1) analyzing noradrenaline concentration in the anterior and mediobasal hypothalamus and in the median eminence; (2) quantifying the gene expression and concentration of GnRH, LH, FSH and serum testosterone levels, and finally; (3) evaluating the possible morphological alterations induced by PFOS in the reproductive axis through light and electron microscopy. The hormones and the neuromodulators of this neuroendocrine axis, evaluated in the present study are shown in Fig. 1.

Section snippets

Chemical

Perfluorooctanesulfonic acid has been used as potassium salt. It was purchased from Sigma-Aldrich (Madrid, Spain) and it was dissolved in 2.5% Tween 20, which was obtained from VWR International (Radnor, Pensilvania, USA).

Animals and experimental design

Adult male Sprague-Dawley rats were obtained from the animal facilities of the University of Santiago (Santiago de Compostela, Spain), which were 60 day-old and their weigh was 305±16.4 g at the beginning of the experiment. All animals were remained under constant environmental

Results

Stress or behavioral alterations were not observed in PFOS exposed rats. Furthermore, the relative weight of the hypothalamus, pituitary gland and testes did not change after the treatment with this chemical. In addition, PFOS-treated animals do not present any clinical sign such as variations of body weight, changes on food and water consumption or diarrhea, throughout the experiment.

Discussion

In general terms, the obtained results suggest an inhibition of the reproductive axis activity induced by oral exposure of PFOS at the doses of 0.5; 1.0; 3.0 and 6.0 mg/kg/day in adult male rats, reflected on GnRH gene expression and on LH and testosterone secretion. These effects could be related to several histological alterations observed in the hypothalamus, pituitary gland and the testis.

PFOS can trigger the “opening” of tight junction in brain endothelial cells, thus reaching the brain and

Acknowledgments

This work was supported by grants from the Ministry of Science and Innovation, Spain (AGL2009-09061) and from the Xunta de Galicia (INCITE09 383 314PR). The authors would like to thank Ms Ana Ramos Moro for the revision of the English texts.

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