Postnatal exposure to a glyphosate-based herbicide modifies mammary gland growth and development in Wistar male rats
Introduction
Glyphosate (N-phosphonomethyl glycine) is an active ingredient in many commercially available broad-spectrum herbicides. Over the past decades, glyphosate-based herbicide (GBH) use has diversified and expanded significantly. Benbrook (2016) reported that the application of these herbicides increased ∼ 100-fold worldwide from 1974 to 2014. In Argentina, increasing use of these chemicals has been associated with agricultural expansion due to the ongoing adoption of glyphosate tolerant genetically modified soybeans (CASAFE, 2012). In recent years, glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), have been detected in surface water, sediments and soil that surround horticultural production areas of different regions of Argentina (Aparicio et al., 2013; Bonansea et al., 2017; Lupi et al., 2015; Mac Loughlin et al., 2017; Primost et al., 2017; Ronco et al., 2016). These pesticide residues have also been detected in foodstuff (EFSA, 2017) and human urine (Connolly et al., 2017; Goen et al., 2017; Mills et al., 2017; Parvez et al., 2018) and serum samples (Kongtip et al., 2017). In addition, it has been demonstrated in rats that exposure to a mixture containing glyphosate is able to induce hepatoxicity (Docea et al., 2018) and that low doses of GBH provokes kidney and especially liver oxidative damage and non-alcoholic fatty liver disease (Mesnage et al., 2015a, 2017b). These findings suggest that there is a risk of environmental exposure to GBH and raise concern of its possible effects on the environment and human health.
Several studies have reported the adverse effects of GBH exposure on both female and male reproductive systems at low and environmentally relevant doses (Cai et al., 2017; Guerrero Schimpf et al., 2017; Ingaramo et al., 2016, 2017; Nardi et al., 2017; Varayoud et al., 2017). In male rats, glyphosate exposure modifies testicular function and morphology, decreases testosterone serum levels, increases aromatase expression level, and alters sperm production, suggesting that GBH could act as an endocrine disruptor in vivo (Cassault-Meyer et al., 2014; Dallegrave et al., 2007; Owagboriaye et al., 2017; Romano et al., 2010). In addition, glyphosate was shown to reduce aromatase enzyme activity in human placental cells (Richard et al., 2005) and induce human breast cancer cell proliferation by directly activating the estrogen receptor alpha (ESR1) in vitro (Thongprakaisang et al., 2013). In contrast, Mesnage et al. (2017a) showed that glyphosate activates ESR1 through a ligand-independent mechanism in hormone-dependent human cancer cells. Therefore, the estrogenic potential effect of glyphosate remains under investigation. In general, new epidemiological and toxicological studies as well as human biomonitoring are urgently needed to determinate whether GBH could be considered an endocrine disruptor and to improve safety standard (Myers et al., 2016; Vandenberg et al., 2017).
Given the effects on male reproductive organs and the suggested estrogenic properties of this compound, male mammary gland development could also be affected. The male mammary gland of rats has been used by several researchers as a useful model to study the effects of potential endocrine disruptors that may affect the risk of breast cancer in humans (Filgo et al., 2016; Mandrup et al., 2015, 2016). Recently, we showed that prenatal exposure to the endocrine disruptor bisphenol A induces a growth delay and decreases the expression of androgen receptor (AR) in the pre-pubertal male rat mammary gland (Kass et al., 2015) and that early postnatal exposure to endosulfan induces premalignant lesions in the mammary gland of post-pubertal male rats (Altamirano et al., 2017). There is evidence that chronic exposure to GBH increases mammary tumor incidence in adults rats (Seralini et al., 2014). However, to date, the effects of postnatal GBH exposure on the male mammary gland in vivo remain mostly unknown. Therefore, the aim of the present study was to evaluate whether early postnatal exposure to GBH affects mammary gland growth and development in pre- and post-pubertal male rats.
Section snippets
Animals
Sexually mature female rats (90 days old) of a Wistar-derived strain bred at the Department of Human Physiology (Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral (UNL), Santa Fe, Argentina) were used. The animals were maintained in a controlled environment (22 ± 2 °C; 14 h of light) and had free access to pellet laboratory chow (16-014007 Rat-Mouse diet, Nutrición Animal, Santa Fe, Argentina). All the experimental protocols were approved by the Ethical Committee of
Results
No signs of acute or chronic toxicity were observed in the litters, and no differences were found in the weight gain between treated and control pups during the treatment (PND1-PND7). At PND21, the pup body weight was similar between the experimental groups (Control: 34.39 ± 0.96 g vs GBH: 35.85 ± 0.78 g), whereas in post-pubertal (PND60) male rats exposed to GBH, a significant increase in the body weight was observed (Control: 218.10 ± 3.82 g vs GBH: 230.70 ± 2.98 g; p < 0.05).
Discussion
In recent years, the effects of endocrine-disrupting chemicals on the development of the male mammary gland of rodents has received increased attention due to its sensitive response to estrogenic and/or androgenic compounds (Altamirano et al., 2017; Filgo et al., 2016; Kass et al., 2015; Kolla et al., 2017; Mandrup et al., 2015; Vandenberg et al., 2013). In the current study, postnatal subacute exposure of male rats to GBH during a critical period of development resulted in alterations in the
Declaration of interest
The authors declare that there are no conflicts of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding
This work was supported by grants from the Universidad Nacional del Litoral (CAI + D program 2016 50420150100088L) and the Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT PICT 2014 Nª1348). These funding sources were not involved in the study design, the collection, analysis or interpretation of the data, the writing of the report, or the decision to submit the article for publication.
Acknowledgments
We would like to thank Dr. Pablo M. Beldomenico (Laboratorio de Ecología de Enfermedades, Instituto de Ciencias Veterinarias del Litoral (ICiVet-Litoral), UNL-CONICET) for advice on statistics and Juan Grant and Laura Bergero (ISAL; UNL-CONICET) for technical assistance and animal care. G.A.A. and A.L.G. are fellows and L.K., P·I., V.L.B. and E.H.L. are Career Investigators of CONICET.
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